WO2012114954A1 - 溶融塩電池の充放電制御装置及び溶融塩電池の充電方法 - Google Patents
溶融塩電池の充放電制御装置及び溶融塩電池の充電方法 Download PDFInfo
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- WO2012114954A1 WO2012114954A1 PCT/JP2012/053494 JP2012053494W WO2012114954A1 WO 2012114954 A1 WO2012114954 A1 WO 2012114954A1 JP 2012053494 W JP2012053494 W JP 2012053494W WO 2012114954 A1 WO2012114954 A1 WO 2012114954A1
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- molten salt
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
- H01M10/399—Cells with molten salts
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
- H01M10/443—Methods for charging or discharging in response to temperature
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
- H01M10/486—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for measuring temperature
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/381—Alkaline or alkaline earth metals elements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0048—Molten electrolytes used at high temperature
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a charge / discharge control device for controlling charge / discharge of a molten salt battery and a method for charging the molten salt battery.
- This molten salt battery uses a molten salt as an electrolyte, and is charged and discharged by melting the molten salt. For this reason, the conventional molten salt battery is used within a temperature range of 57 ° C. or higher, which is the melting point of the molten salt, and 190 ° C. or lower, which is the temperature at which the molten salt is thermally divided (for example, non-patent). Reference 1).
- the molten salt battery has a characteristic that the internal resistance increases as the temperature decreases. For this reason, when the molten salt battery is charged at a low temperature, a voltage drop (IR drop) occurs due to the internal resistance, which causes a problem of increased energy loss. In addition, when the molten salt battery is discharged at a low temperature, the voltage drops when a large current is passed, so that a necessary voltage cannot be obtained.
- IR drop voltage drop
- the present invention has been made in view of the above-described ⁇ Problem 1>, and provides a charge / discharge control device for a molten salt battery that can suppress energy loss during charging at low temperatures and can secure a necessary voltage during discharge. It is intended to provide.
- ⁇ Problem 2> Regarding ⁇ Background Art 2>, in a secondary battery using alkali ions such as lithium and sodium as conductive ions, it is possible to realize high capacity density by storing the alkali ions in the negative electrode in the state of alkali metal during charging.
- alkali ions such as lithium and sodium as conductive ions
- One of the methods in lithium secondary batteries, so-called dendritic growth in which lithium metal grows in a dendritic manner during charging occurs, causing short circuit between the positive and negative electrodes and low charge / discharge efficiency, and storage in a metal state cannot be realized.
- the present invention has been made in view of the above ⁇ Problem 2>, and an object of the present invention is to provide a method for charging a molten salt battery capable of suppressing deterioration in charge / discharge cycle characteristics.
- the charge / discharge control apparatus for a molten salt battery of the present invention is a charge / discharge control apparatus for controlling charge / discharge of a molten salt battery containing a molten salt as an electrolyte.
- a temperature measurement unit for measuring the temperature of the molten salt battery and when the measurement temperature of the temperature measurement unit is equal to or lower than a predetermined temperature higher than the melting point of the molten salt, the current value of charge / discharge is reduced as the measurement temperature decreases.
- the current value at the time of charging can be reduced, so that the voltage drop due to the internal resistance of the molten salt battery can be reduced. Therefore, energy loss when charged at a low temperature can be suppressed. Moreover, since the current value at the time of discharge can be reduced when the temperature of the molten salt battery is lowered, a voltage drop at the time of discharge can be prevented. Therefore, a necessary voltage can be secured when discharged at a low temperature.
- the controller controls the charge / discharge current value so as to have a predetermined current value according to the temperature of the molten salt battery. In this case, the control of the current value by the control unit is facilitated, and charging / discharging of the molten salt battery can be suitably controlled.
- control unit stops supplying current for charging / discharging when the temperature measured by the temperature measuring unit is lower than the melting point of the molten salt. In this case, it is possible to prevent the molten salt battery 2 from being charged and discharged in a state having no electrical conductivity below the melting point.
- the method for charging a molten salt battery of the present invention includes a molten salt as an electrolyte, and a method for charging a molten salt battery in which metallic sodium is deposited on the negative electrode during charging.
- the molten salt battery is charged at a predetermined temperature of 80 ° C. or higher and lower than 98 ° C.
- the molten salt battery is charged at a predetermined temperature of 80 ° C. or higher and lower than 98 ° C., it is possible to suppress the sodium metal deposited on the negative electrode of the molten salt battery from growing due to dendrite and falling off. It is possible to suppress the deterioration of the charge / discharge cycle characteristics. That is, the inventors of the present application, as a result of intensive research, found that the metal sodium deposited on the negative electrode grows and dendrites and the temperature at the time of charging the molten salt battery is the most dominant factor. The knowledge that the drop of metal sodium is suppressed by keeping the temperature during charging within a predetermined range was obtained, and the present invention was completed based on this knowledge.
- the negative electrode preferably contains metallic sodium as a negative electrode active material.
- metallic sodium as a negative electrode active material.
- the molten salt battery controls a current value during charging according to the predetermined temperature.
- the current value during charging according to the predetermined temperature it is possible to balance the deposition rate of sodium metal and the dendrite growth affected by the hardness of the sodium metal at the predetermined temperature. Therefore, it is possible to effectively suppress dendrite growth of metallic sodium during precipitation from the negative electrode of the molten salt battery. Thereby, it can suppress further that the cycle characteristic of charging / discharging falls.
- FIG. 3 is a graph showing the relationship between the internal resistance and temperature of a molten salt battery in Chapter 1 and Chapter 2.
- 5 is a table showing current densities determined in advance according to the temperature of the molten salt battery in Chapter 1 and Chapter 2.
- It is a schematic block diagram of the molten salt battery in which the charging method which concerns on one embodiment of this invention in Chapter 2 is used.
- It is a graph which shows the cycle evaluation result of charging / discharging of the molten salt battery in Chapter 2.
- It is a schematic block diagram of the molten salt battery in which the charging method which concerns on other embodiment in Chapter 2 is used.
- FIG. 1 is a schematic configuration diagram of a charge / discharge control device for a molten salt battery according to an embodiment of the present invention in Chapter 1.
- the charge / discharge control device 1 performs charge / discharge of a molten salt battery 2 used as a power source of the electric motor, for example, in a hybrid vehicle (HEV) that is driven by appropriately switching between an engine and an electric motor (not shown). It is something to control.
- HEV hybrid vehicle
- FIG. 2 is a schematic configuration diagram of the molten salt battery 2.
- the molten salt battery 2 is configured by housing a positive electrode 22, a negative electrode 23, and a separate 24 interposed between the two electrodes 22, 23 inside a box-shaped battery container 21 (see FIG. 1). Has been.
- the positive electrode 22 includes a positive electrode current collector 22a and a positive electrode active material layer 22b disposed inside the positive electrode current collector 22a.
- the positive electrode current collector 22a is made of, for example, an aluminum alloy porous body, and the positive electrode active material layer 22b contains, for example, sodium chromite (NaCrO 2 ) as the positive electrode active material.
- the negative electrode 23 has a negative electrode current collector 23a and a negative electrode active material layer 23b disposed inside the negative electrode current collector 23a.
- the negative electrode current collector 23a is made of, for example, an aluminum foil, and the negative electrode active material layer 23b contains, for example, tin (Sn) as the negative electrode active material.
- the separator 24 is made of a fluororesin porous film that is resistant to molten salt at a temperature at which the molten salt battery 2 operates, and is immersed in a molten salt (not shown) filled in the battery container 21. Yes.
- a heater not shown
- FIG. 3 is a graph showing the relationship between the temperature of the molten salt battery 2 and the internal resistance.
- the molten salt battery 2 has a characteristic that the internal resistance becomes extremely large when the temperature is about 70 ° C. or less.
- the internal resistance value shown in this graph is calculated by the following formula (1) based on the temperature when the distance between the electrodes of the molten salt battery 2 (the thickness of the separator 24) is 200 ⁇ m.
- ⁇ (T) A ⁇ / SQRT (T) ⁇ exp ( ⁇ B ⁇ / (T ⁇ T 0 )) (1)
- ⁇ is the internal resistance value
- T is the temperature of the molten salt battery 2
- a ⁇ and B ⁇ are coefficients determined by the type of molten salt
- T 0 is the temperature at which the movement of ions stops
- SQRT is a mathematical expression in parentheses. Represents an operator for calculating the square root of the value obtained in.
- a ⁇ 1.92 ⁇ 10 2
- B ⁇ 0.837 ⁇ 10 3
- T 0 245K.
- a charge / discharge control device 1 controls charge / discharge in consideration of the above characteristics of the molten salt battery 2, a constant current power source 11 that supplies current to the molten salt battery 2 during charging, and a molten salt
- a temperature sensor (temperature measurement unit) 12 that measures the temperature of the battery 2 and a control unit 13 that controls the current value of charge / discharge based on the measured temperature of the temperature sensor 12 are provided.
- the control unit 13 When the measured temperature of the temperature sensor 12 is 70 ° C. or lower, the control unit 13 performs control so that the charge / discharge current value decreases as the measured temperature decreases.
- the current value is set so as to have a predetermined current density (current value) according to the temperature of the molten salt battery 2.
- the current density shown in FIG. 4 is calculated by the following formula (2) so that the IR value at each temperature is the same with respect to 50 mA / cm 2 when the temperature of the molten salt battery 2 is 90 ° C. is there.
- I T I 90 ⁇ R 90 / R T (2)
- I T is the current density
- R T is the internal resistance value
- R 90 is the temperature of the molten salt battery 2. Is the internal resistance value at 90 ° C.
- the control unit 13 controls the charge / discharge current value so that the current density predetermined by the table of FIG. 4 is obtained according to the measured temperature when the measured temperature of the temperature sensor 12 is 70 ° C. or lower. To do. For example, when the measurement temperature of the temperature sensor 12 is 60 ° C., the charge / discharge current value is controlled so that the current density corresponding to 60 ° C. is 4 mA / cm 2 from the table of FIG. And the control part 13 stops the electric current supply of charging / discharging, when the measurement temperature of the temperature sensor 12 will be less than 57 degreeC which is melting
- the control unit 13 controls the measured temperature when the measured temperature is 70 ° C. or lower.
- the temperature of the molten salt battery 2 reaches a current density corresponding to 110 ° C. It is prepared. Therefore, the predetermined temperature at which the control unit 13 starts control can be appropriately adjusted in the range of 70 ° C. to 110 ° C. according to actual charge / discharge control.
- the current value during charging can be reduced when the temperature of the molten salt battery 2 is lowered.
- the voltage drop can be reduced. Therefore, energy loss when charged at a low temperature can be suppressed.
- a molten salt battery that is not sufficiently heated in a garage or the like can be charged before driving. It can be used suitably for these electric vehicles.
- the current value at the time of discharge can be reduced when the temperature of the molten salt battery 2 is lowered, a voltage drop at the time of discharge can be prevented. Therefore, a necessary voltage can be secured when discharged at a low temperature.
- control part 13 is controlling the electric current value of charging / discharging so that it may become a predetermined current density according to the temperature of the molten salt battery 2, control of the electric current value by the control part 13 becomes easy, Charge / discharge of the molten salt battery 2 can be suitably controlled.
- the control unit 13 stops supplying the charge / discharge current, so that the molten salt battery 2 is charged in a non-conductive state below the melting point. It is possible to prevent discharge.
- control unit 13 controls the current value when the measurement temperature is 70 ° C. or lower. However, if the temperature is higher than the melting point of the molten salt and the internal resistance increases.
- the current value may be controlled when the temperature is lower than an arbitrary measurement temperature other than 70 ° C.
- the current density determined in advance according to the temperature of the molten salt battery 2 is calculated by the above equation (2), but other calculation equations may be used.
- the charge / discharge control device 1 of the present invention in Chapter 1 can be applied to an electric vehicle such as an electric vehicle (EV) or a train in addition to the hybrid vehicle.
- EV electric vehicle
- a train in addition to the hybrid vehicle.
- FIG. 5 is a schematic configuration diagram of a molten salt battery.
- the molten salt battery 1 is configured by accommodating a positive electrode 12, a negative electrode 13, and a separator 14 interposed between the two electrodes 12, 13 in a box-shaped battery container 11 (see FIG. 7). Has been.
- the positive electrode 12 includes a positive electrode current collector 12a and a positive electrode active material layer 12b disposed inside the positive electrode current collector 12a.
- the positive electrode current collector 12a is made of, for example, an aluminum alloy porous body, and the positive electrode active material layer 12b contains, for example, sodium chromite (NaCrO 2 ) as the positive electrode active material.
- the negative electrode 13 has a negative electrode current collector 13a and a negative electrode active material layer 13b disposed inside the negative electrode current collector 13a.
- the negative electrode current collector 13a is made of, for example, an aluminum foil having a thickness of 20 ⁇ m.
- the negative electrode active material layer 13b includes, for example, metal sodium (Na) having a thickness of 100 ⁇ m to several mm as a negative electrode active material, and is fixed to the negative electrode current collector 13a by rolling or dipping.
- the separator 14 is composed of a porous fluororesin membrane that is resistant to molten salt at the temperature at which the molten salt battery 1 is used, and is used as a molten salt (not shown) that is an electrolyte filled in the battery container 11. Soaked.
- the molten salt battery 1 configured as described above is heated by heating means (not shown) such as a heater to melt the molten salt, whereby the molten salt battery 1 can be charged and discharged. More specifically, the molten salt battery 1 is charged and discharged by the heating means up to a predetermined temperature (90 ° C. in the present embodiment) of 80 ° C. or higher and 120 ° C. or lower, more preferably 80 ° C. or higher and lower than 98 ° C. This is done by heating 1.
- a predetermined temperature 90 ° C. in the present embodiment
- 6A and 6B are graphs showing the charge / discharge cycle evaluation results. This evaluation was performed using a 10 cm square positive electrode and a 10.5 cm square negative electrode having masked edges and back surface.
- FIG. 6A when the molten salt battery 1 is charged and discharged at 75 ° C., which is close to the melting point (57 ° C.) of the molten salt, the capacity retention rate rapidly decreases as the number of cycles increases. On the other hand, when the molten salt battery 1 is charged and discharged at the predetermined temperature of 90 ° C., the capacity retention rate is maintained at almost 100% even if the number of cycles is increased. 6B, when the molten salt battery 1 is charged and discharged at 80 ° C.
- the capacity retention rate is slightly lower than when charging and discharging at 90 ° C. as the number of cycles increases. It was lower than the case of charging / discharging at 75 ° C. shown in (a), and a certain effect could be obtained in suppressing the decrease in capacity maintenance rate.
- FIG. 3 is a graph showing the relationship between the temperature of the molten salt battery 1 and the internal resistance.
- the molten salt battery 1 has a characteristic that the internal resistance becomes extremely large as the temperature decreases.
- the internal resistance value shown in this graph is calculated by the following formula (1) based on the temperature when the distance between the electrodes of the molten salt battery 1 (the thickness of the separator 14) is 200 ⁇ m.
- ⁇ (T) A ⁇ / SQRT (T) ⁇ exp ( ⁇ B ⁇ / (T ⁇ T 0 )) (1)
- ⁇ is the internal resistance value
- T is the temperature of the molten salt battery 1
- a ⁇ and B ⁇ are coefficients determined by the type of the molten salt
- T 0 is the temperature at which the movement of ions stops
- SQRT is a mathematical expression in parentheses. Represents an operator for calculating the square root of the value obtained in.
- a ⁇ 1.92 ⁇ 10 2
- B ⁇ 0.837 ⁇ 10 3
- T 0 245K.
- FIG. 7 is a schematic configuration diagram of a charge / discharge control device for a molten salt battery.
- the charge / discharge control device 2 controls the charge / discharge of the molten salt battery 1, and measures the temperature of the molten salt battery 1 and the constant current power supply 21 that supplies current to the molten salt battery 1 during charging.
- a temperature sensor (temperature measuring unit) 22 that controls the current value of charging / discharging based on the measured temperature of the temperature sensor 22.
- the control unit 23 controls the charge / discharge current value to decrease as the measurement temperature decreases.
- the current value is set to have a current density (current value) that is predetermined according to the temperature of the molten salt battery 1.
- the current density shown in FIG. 4 is calculated by the following formula (2) so that the IR value at each temperature is the same with respect to 50 mA / cm 2 when the temperature of the molten salt battery 1 is 90 ° C. is there.
- I T I 90 ⁇ R 90 / R T (2)
- I T is the current density
- R T is the internal resistance value
- R 90 is the temperature of the molten salt battery 1. Is the internal resistance value at 90 ° C.
- the control unit 23 has a current density predetermined by the table of FIG. 4 according to the measured temperature.
- the current value of charging / discharging is controlled.
- the measurement temperature of the temperature sensor 22 is 85 ° C.
- the charge / discharge current value is controlled so that the current density corresponding to 85 ° C. is 35 mA / cm 2 from the table of FIG.
- the control part 23 will stop the electric current supply of charging / discharging, if the measurement temperature of the temperature sensor 22 will be less than 57 degreeC which is melting
- the control unit 23 controls the current value when the measurement temperature is 110 ° C. or lower. However, if the temperature is higher than the melting point of the molten salt and the internal resistance is increased, the control unit 23 has a temperature other than 110 ° C. You may make it control an electric current value when it is below arbitrary measurement temperature. Further, the current density determined in advance according to the temperature of the molten salt battery 1 is calculated by the above equation (2), but other calculation equations may be used.
- the current value at the time of charging can be reduced, so that the voltage drop due to the internal resistance of the molten salt battery 1 can be reduced. it can. Therefore, energy loss when charged at a low temperature can be suppressed.
- the current value at the time of discharge can be reduced when the temperature of the molten salt battery 1 is lowered, a voltage drop at the time of discharge can be prevented. Therefore, a necessary voltage can be secured when discharged at a low temperature.
- control part 23 is controlling the electric current value of charging / discharging so that it may become a predetermined current density according to the temperature of the molten salt battery 1, control of the electric current value by the control part 23 becomes easy, Charge / discharge of the molten salt battery 1 can be suitably controlled.
- the control part 23 controls the current value according to the predetermined temperature, the influence of the precipitation rate of sodium metal during charging and the hardness of the sodium metal at the predetermined temperature You can balance the dendrite growth you receive. Thereby, it can suppress effectively that sodium metal dendrite grows in the negative electrode 13 of the molten salt battery 1, and can further suppress that the cycling characteristics of charging / discharging fall.
- FIG. 8 is a schematic configuration diagram of a molten salt battery according to another embodiment in Chapter 2.
- the form of FIG. 8 is different from the form of FIG. 5 in that the negative electrode 13 of the molten salt battery 1 is composed only of the negative electrode current collector 13a.
- the negative electrode current collector 13a is constituted by, for example, a zincate treatment for forming a thin layer made of zinc on the surface of an aluminum foil.
- this molten salt battery 1 In the molten salt battery 1 of the present embodiment, during charging, metallic sodium (Na) is transferred from the sodium chromite (NaCrO 2 ) contained in the positive electrode active material layer 12b on the positive electrode 12 side to the negative electrode current collector 13a.
- the metal sodium plays a role as a negative electrode active material. Therefore, this molten salt battery 1 has a molten salt up to a predetermined temperature of 80 ° C. or higher and lower than 98 ° C., similarly to the above-described embodiment, in order to suppress the metal sodium deposited on the negative electrode 13 from growing due to dendrite. Charging / discharging is performed by heating the battery 1.
- metallic sodium falls from the negative electrode 13 of the molten salt battery 1 by charging the molten salt battery 1 at a predetermined temperature of 80 ° C. or higher and lower than 98 ° C. Therefore, it is possible to suppress deterioration of the charge / discharge cycle characteristics.
- the molten salt battery of the above embodiment metallic sodium is used as the negative electrode active material, but hard carbon or tin (Sn) may be used as the negative electrode active material.
- Sn hard carbon or tin
- the charging method of the above-described embodiment it is possible to suppress the sodium metal deposited on the edge portion of the negative electrode active material layer during charging from growing due to dendrite and dropping off.
- the charging method of the said embodiment although the molten salt battery is charged / discharged at 90 degreeC, what is necessary is just to make it charge / discharge at arbitrary temperatures 80 degreeC or more and less than 98 degreeC.
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Abstract
Description
近年、二次電池は、ハイブリッド車両や電気自動車用等の電動車両の駆動用電源としてのニーズが高まっている。この目的に対応した二次電池として、高エネルギー密度で大容量の溶融塩電池が着目されている。この溶融塩電池は、溶融塩を電解質として用いており、この溶融塩を所定温度で融解することにより、充放電することができるようになっている(例えば、特許文献1参照)。
近年、高エネルギー密度で大容量の二次電池として、リチウム二次電池や溶融塩電池が着目されている。この溶融塩電池は、溶融塩を電解質として用いており、この溶融塩を融解することにより、充放電するようになっている。このため、従来の溶融塩電池は、溶融塩の融点である57℃以上であって、かつ溶融塩が熱分割する温度である190℃以下の温度範囲内で使用されている(例えば、非特許文献1参照)。
<背景技術1>に関して、前記溶融塩電池は、その温度が低下すると、内部抵抗が大きくなるという特性を有している。このため、溶融塩電池を低温下で充電した場合、前記内部抵抗によって電圧降下(IRドロップ)が生じるため、エネルギーロスが大きくなるという問題が生じる。また、溶融塩電池を低温下で放電した場合には、大電流を流すと電圧が降下するため、必要な電圧を得ることができないという問題が生じる。
<背景技術2>に関して、リチウムやナトリウム等のアルカリイオンを伝導イオンとする二次電池では、充電時において、アルカリイオンをアルカリ金属の状態として負極に貯蔵することが、高容量密度化を実現できる方法の一つとなっている。
しかし、リチウム二次電池では、充電時にリチウム金属が樹枝状成長するいわゆるデンドライト成長を起こして、正負極間の短絡や低充放電効率の原因となり、金属状態での貯蔵は実現できていない。
また、溶融塩電池の温度が低くなると放電時の電流値も小さくすることができるため、放電時の電圧降下を防止することとができる。したがって、低温下で放電したときに必要な電圧を確保することができる。
この場合、制御部による電流値の制御が容易となり、溶融塩電池の充放電を好適に制御することができる。
この場合、溶融塩電池2が前記融点未満の導電性のない状態で充放電されるのを防止することができる。
すなわち、本願発明者は、鋭意研究を重ねた結果、負極で析出する金属ナトリウムがデンドライト成長して脱落する現象は、溶融塩電池の充電時の温度が最も支配的な要素であることを見い出し、その充電時の温度を所定範囲内にすることにより金属ナトリウムの脱落が抑制されるという知見を得、かかる知見に基づいて本願発明を完成させた。
この場合、溶融塩電池の負極の一部である金属ナトリウムがデンドライト成長し脱落するのを抑制することができるため、充放電のサイクル特性が低下するのを抑制することができる。
この場合、前記所定温度に応じて充電時の電流値を制御することにより、ナトリウム金属の析出速度と、当該所定温度におけるナトリウム金属の硬さの影響を受けるデンドライト成長とのバランスをとることができるため、溶融塩電池の負極から析出において金属ナトリウムがデンドライト成長するのを効果的に抑制することができる。これにより、充放電のサイクル特性が低下するのをさらに抑制することができる。
以下、第1章における本発明の実施の形態を図面に基づいて説明する。
図1は、第1章における本発明の一実施の形態に係る溶融塩電池の充放電制御装置の概略構成図である。
図1において、充放電制御装置1は、例えば、図示しないエンジンと電動モータとを適宜切り替えて駆動するハイブリッド車両(HEV)において、前記電動モータの電力源として用いられる溶融塩電池2の充放電を制御するものである。
以上の構成により、溶融塩電池2をヒータ(図示省略)により80℃~100℃に加熱することにより、溶融塩が融解して充電及び放電が可能となる。
なお、このグラフに示す内部抵抗値は、溶融塩電池2の極間距離(セパレータ24の厚み)が200μmときの温度に基づいて、下記式(1)により算出したものである。
σ(T)=Aσ/SQRT(T)×exp(-Bσ/(T-T0)) ・・・(1)
ここで、σは内部抵抗値、Tは溶融塩電池2の温度、Aσ及びBσは溶融塩の種類によって定まる係数、T0はイオンの移動が止まる温度であり、SQRTはかっこ内の数式で求めた値の平方根を計算するための演算子を表す。本実施形態の溶融塩電池2の場合、Aσ=1.92×102、Bσ=0.837×103、T0=245Kとなる。
IT=I90×R90/RT ・・・(2)
ここで、ITは電流密度、I90は溶融塩電池2の温度が90℃のときの電流密度(=50mA/cm2)、RTは内部抵抗値、R90は溶融塩電池2の温度が90℃のときの内部抵抗値である。
さらに、溶融塩電池2の温度が低くなると放電時の電流値も小さくすることができるため、放電時の電圧降下を防止することとができる。したがって、低温下で放電したときに必要な電圧を確保することができる。
さらに、第1章における本発明の充放電制御装置1は、ハイブリッド車両以外に、電気自動車(EV)や電車等の電動車両にも適用することができる。
1 充放電制御装置
2 溶融塩電池
12 温度センサ(温度測定部)
13 制御部
次に、第2章における本発明の実施の形態を図面に基づいて説明する。
図5は、溶融塩電池の概略構成図である。図5において、溶融塩電池1は、ボックス状の電池容器11(図7参照)の内部に、正極12と、負極13と、これら両極12,13間に介在するセパレータ14とを収容して構成されている。
図6(a)において、溶融塩電池1を溶融塩の融点(57℃)に近い75℃で充放電した場合、サイクル数が増加すると容量維持率が急激に低下している。これに対して、溶融塩電池1を前記所定温度である90℃で充放電した場合、サイクル数が増加しても容量維持率がほぼ100%に維持されている。
また、図6(b)において、溶融塩電池1を80℃及び85℃で充放電した場合、サイクル数が増加すると容量維持率は90℃で充放電する場合よりも若干低くなるが、図6(a)に示す75℃で充放電する場合よりも緩やかに低下しており、容量維持率の低下抑制に一定の効果を得ることができた。
なお、このグラフに示す内部抵抗値は、溶融塩電池1の極間距離(セパレータ14の厚み)が200μmときの温度に基づいて、下記式(1)により算出したものである。
σ(T)=Aσ/SQRT(T)×exp(-Bσ/(T-T0)) ・・・(1)
ここで、σは内部抵抗値、Tは溶融塩電池1の温度、Aσ及びBσは溶融塩の種類によって定まる係数、T0はイオンの移動が止まる温度であり、SQRTはかっこ内の数式で求めた値の平方根を計算するための演算子を表す。本実施形態の溶融塩電池1の場合、Aσ=1.92×102、Bσ=0.837×103、T0=245Kとなる。
図7において、充放電制御装置2は、溶融塩電池1の充放電を制御するものであり、充電時に溶融塩電池1に電流を供給する定電流電源21と、溶融塩電池1の温度を測定する温度センサ(温度測定部)22と、この温度センサ22の測定温度に基づいて充放電の電流値を制御する制御部23とを備えている。
IT=I90×R90/RT ・・・(2)
ここで、ITは電流密度、I90は溶融塩電池1の温度が90℃のときの電流密度(=50mA/cm2)、RTは内部抵抗値、R90は溶融塩電池1の温度が90℃のときの内部抵抗値である。
また、溶融塩電池1の温度に応じて予め定められた電流密度は、前記式(2)により算出されているが、他の算出式を用いてもよい。
また、溶融塩電池1の温度が低くなると放電時の電流値も小さくすることができるため、放電時の電圧降下を防止することとができる。したがって、低温下で放電したときに必要な電圧を確保することができる。
さらに、制御部23は、溶融塩電池1の温度に応じて予め定められた電流密度となるように充放電の電流値を制御しているため、制御部23による電流値の制御が容易となり、溶融塩電池1の充放電を好適に制御することができる。
また、溶融塩電池1を所定温度で充電する際に、当該所定温度に応じた電流値に制御することにより、充電時のナトリウム金属の析出速度と、当該所定温度におけるナトリウム金属の硬さの影響を受けるデンドライト成長とのバランスをとることができる。これにより、溶融塩電池1の負極13において金属ナトリウムがデンドライト成長するのを効果的に抑制することができ、充放電のサイクル特性が低下するのをさらに抑制することができる。
図8の形態が図5の形態と異なる点は、溶融塩電池1の負極13が、負極集電体13aのみからなる点である。この負極集電体13aは、例えばアルミニウム箔の表面に亜鉛からなる薄い層を形成するためにジンケート処理が施されたもので構成されている。
また、上記実施形態の充電方法では、溶融塩電池を90℃で充放電させているが、80℃以上98℃未満の任意の温度で充放電させればよい。
1 溶融塩電池
13 負極
13b 負極活物質層
Claims (6)
- 溶融塩を電解質として含む溶融塩電池の充放電を制御する充放電制御装置であって、
前記溶融塩電池の温度を測定する温度測定部と、
前記温度測定部の測定温度が前記溶融塩の融点よりも高い所定温度以下のとき、当該測定温度が低くなるほど充放電の電流値を小さくするように制御する制御部と、を備えていることを特徴とする溶融塩電池の充放電制御装置。 - 前記制御部は、前記溶融塩電池の温度に応じて予め定められた電流値となるように、充放電の電流値を制御する請求項1に記載の溶融塩電池の充放電制御装置。
- 前記制御部は、前記温度測定部の測定温度が前記溶融塩の融点未満のとき、充放電の電流供給を停止させる請求項1又は2に記載の溶融塩電池の充放電制御装置。
- 溶融塩を電解質として含み、充電時において負極に金属ナトリウムが析出する溶融塩電池の充電方法であって、
前記溶融塩電池を80℃以上98℃未満の所定温度で充電することを特徴とする溶融塩電池の充電方法。 - 前記負極が、負極活物質として金属ナトリウムを含んでいる請求項4に記載の溶融塩電池の充電方法。
- 前記所定温度に応じて充電時の電流値を制御する請求項4又は5に記載の溶融塩電池の充電方法。
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JPS6039324A (ja) * | 1983-08-13 | 1985-03-01 | 松下電工株式会社 | 充電器 |
JPH07320776A (ja) * | 1994-05-27 | 1995-12-08 | Yuasa Corp | ナトリウム−硫黄電池 |
JP2009067644A (ja) * | 2007-09-14 | 2009-04-02 | Kyoto Univ | 溶融塩組成物及びその利用 |
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JPS6039324A (ja) * | 1983-08-13 | 1985-03-01 | 松下電工株式会社 | 充電器 |
JPH07320776A (ja) * | 1994-05-27 | 1995-12-08 | Yuasa Corp | ナトリウム−硫黄電池 |
JP2009067644A (ja) * | 2007-09-14 | 2009-04-02 | Kyoto Univ | 溶融塩組成物及びその利用 |
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