RU2046461C1 - Process of filling with sodium of internal volume of leak-tight electrolyte tubes with current taps for sulphur-sodium cell - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: process of filling with sodium of internal volume of leak-tight electrolyte tubes made of bets-alumina is conducted by their immersion into sodium melt and by formation of difference of potentials of corresponding sign between sodium and current lead by connection to D.C. power supply source. When conductance of electrolyte reaches minimal permissible value sign of potentials is changed, conductance is restored and sign of potentials is changed again repeating this cycle till tubes are filled with excessive quantity of sodium as compared with working quantity. After this passing of excessive quantity of sodium with reversed sign of potentials is ensured and D.C. power supply source is disconnected. In process of filling of tubes with sodium the latter is agitated by action of ultrasonic oscillations. EFFECT: enhanced efficiency of filling. 2 cl, 1 dwg, 1 tbl

Description

 The invention relates to chemical current sources and can be used when refueling sodium sulfide batteries with liquid sodium.

There is a method of filling with liquid sodium the interelectrode volume of a solid electrolyte of a sodium disodium battery, in which the battery cover is preliminarily provided with a refueling tube with a temporary seal, the air is pumped out of the interelectrode volume, it is filled with gaseous argon, and vacuum again. Then, the filling tube is inserted inside the pouring tube of smaller diameter and poured therethrough liquid sodium at a temperature of ¹⁵⁰ ° C in a volume vnutrielektrodny then evacuated, the primer tube is partially withdrawn from the filling tube and the latter was then sealed with clamping and welding. To exclude thermal shock due to contact of the electrolyte tube from beta-alumina with molten sodium, the battery is preheated and slowly cooled after refueling [1]
The disadvantage of this method is the need for a number of operations in a vacuum and in an inert environment, which significantly complicates its hardware design. In addition, preliminary cleaning of sodium from various impurities is required, which increases the cost of refueling technology and the manufacture of the battery as a whole.

A known method of filling with liquid sodium the interelectrode volume of a solid electrolyte of a sodium disodium battery, including the operations of sequentially moving the electrolyte containers of the flasks through the inlet heating chamber, the refueling chamber with liquid sodium, where, after refueling with sodium, the current collector is inserted into the flask and welded to the flask lid, sealing it, and the output chamber where refilled flasks slowly cool. All operations are carried out in an inert gas of argon, providing overlapping (locking) of the chambers from each other and from the external environment by shutters driven by pneumatic cylinders. Process control is carried out from a single control unit [2]
The disadvantages of this method, as well as the previous one, are the complexity of its implementation due to the need to carry out operations in an inert gas environment, as well as the need to use pre-purified sodium and the use of special means of monitoring process parameters.

Closest to the claimed method of filling with sodium the interelectrode volume of the sodium chloride battery is a method in which tubes sealed with a ceramic-metal assembly made of solid electrolyte based on beta-alumina and having an interelectrode volume for filling with liquid sodium are placed in a bath with molten sodium or its compounds create negative charges in the interelectrode volume of each tube, and positive charges in the melt and form a voltage between them at a given polarity direct current, under which sodium electrochemically fills their interelectrode volume through the walls of the tubes [3]
The disadvantage of this method is the deposition of impurities from a sodium melt and especially from its mixtures containing chlorides, iodides, hydroxides, sulfates and carbonates, on the outer surface of electrolyte tubes. As a result, the conductivity of each electrolyte tube by sodium ions not only decreases, but also differs from each other even in the batch of tubes. During subsequent operation as part of the battery, individual batteries can have significantly different parameters and thereby cause a decrease in battery performance.

 The aim of the invention is to improve product quality by reducing the degree of contamination of electrolyte tubes.

 The goal is achieved by the fact that in the known method of filling sodium into the interelectrode volume of a sodium disodium battery, in which a tube sealed with a ceramic-metal assembly made of a solid electrolyte based on beta-alumina and having an interelectrode volume is placed in a molten sodium or its compounds, it is created in the interelectrode volume the pipes are negative, and in the sodium melt positive charges are obtained at a given polarity between them a DC voltage, in the electrolyte circuit I measure voltage and current, they determine the conductivity of the electrolyte and, when it reaches the minimum acceptable value, they change the polarity in the circuit, restore the conductivity of the electrolyte and again change the polarity in the circuit to the original one, repeat this cycle until the interelectrode volume is filled with excess sodium relative to the initial working amount, after which ensure the passage of excess sodium into the melt with reverse polarity in the circuit and turn off the voltage.

 In addition, the sodium melt is mixed, for example, by exposure to ultrasonic vibrations.

 In the proposed method, in contrast to the prototype, the melt-electrolyte system is subjected to active electrical (polarity reversal in the circuit) and physico-mechanical (ultrasound) effects. Moreover, in the process of filling electrolyte tubes with liquid sodium, the conductivity of each tube is constantly measured, which allows the rejection of the tubes directly when refueling and thereby reduce the cost of subsequent continuous monitoring. In this case, the change in polarity in the melt-electrolyte circuit is also carried out individually for each tube, preventing irreversible contamination of its surface by precipitates of impurities from the sodium melt.

 As a result of the reverse passage of a certain amount of pure sodium from the tube through its wall into the melt, the outer surface of the tube is cleaned of sediment and the required level of electrolyte conductivity is restored. Since the internal volume of the tube exceeds its working volume, filled with sodium, for guaranteed cleaning of the surface of the tube it is filled almost completely, after which an excess amount of sodium is transferred back into the melt. If the bathtub is filled with previously well-purified sodium and the amount of precipitation on the surface of the tube is small, then the reverse-pass cleaning operation can be carried out only at the end of refueling. When using various sodium compounds, the number of forward and reverse transmission cycles can increase. However, this does not require the use of any additional operations associated with moving the tubes, changing the composition of the medium (vacuum or inert gas), etc., which allows the use of fairly simple equipment to implement the proposed method.

 The mixing of the sodium melt or its compounds with the help of ultrasound energy is aimed at intensifying the process of cleaning the surface of electrolyte tubes from precipitation. In addition, the degassing of the melt in the bath occurs, which prevents possible clogging of the surface of the tubes with bubbles of gases dissolved in the melt, and also improves the wettability of the tubes by the melt and speeds up the process of filling them.

 The drawing shows a device for implementing the method.

 The device comprises a container 1, equipped with electric heaters 2 and a cover 3, in which openings 4 are made, which serve to accommodate electrolyte tubes, and also there are pressurized nodes for voltage supply, for inputs of an ultrasonic generator and a level gauge. In the bottom of the tank made fitting 5 for supplying and draining liquid sodium.

 The device operates as follows.

 The preheated container 1 is filled with sodium melt 6 (or its compounds) by feeding it through the nozzle 5 from a special melting furnace. To prevent contact of the sodium melt with the surrounding air, the bath mirror is protected with a layer of 7 paraffin. A cover 3 is mounted on the container, the corresponding pressurized nodes of which are inserted into the probe 8 of the level gauge, and the vibrator 9 of the ultrasonic generator. Through the openings 4 of the lid, electrolyte tubes 10 are inserted into the bathtub, sealed with standard ceramic-metal assemblies 11. Inside the tubes 10 there is a metal wick 12 connected to the metal cover 13 of the tube connected to the negative pole of an adjustable direct current source, in the circuit of which there is an ammeter 14, voltmeter 15 and time relay 16.

 Before filling the inner cavity of the tubes 10 with liquid sodium 6, a positive charge is applied to the container body and the time relay 16 is turned on, ground (close the circuit) and increase the current from zero by steps determined by steady-state current values during the lifting process. Upon termination of the non-stationary mode, the selected filling current is established, the circuit parameters (voltage and current) are continuously measured and the conductivity of each electrolyte tube 10 is determined. If the conductivity value drops to the minimum acceptable value, then the polarity in the electrolyte circuit is reversed and held for a while the electrolyte conductivity will not be restored to a predetermined value. After this, the polarity in the circuit is changed to the initial one and the filling of the tube 10 with sodium continues. Cycles of polarity reversal are automatically controlled, and the last of them ends with reverse polarity, when an excess of sodium is passed back into the melt 6 through the wall of the tube 10, before which it occupies a volume in the upper expanded part of the electrolyte tube (in the region of the ceramic-metal unit 11).

 Simultaneously with the electric current, the sodium melt 6 is affected by ultrasonic vibrations using a vibrator 9 immersed in the container 1. The sodium level in the container is controlled by a level gauge 8, the signal from which is used to supply additional sodium to the container through the nozzle 5.

 After completion of the filling process, the tube 10 is disconnected from the electric circuit, removed from the melt and slowly cooled to room temperature.

PRI me R. 300 g of paraffin was placed in a grounded container 1 with a diameter of 140 mm and a height of 240 mm. Capacity 1 was covered with a lid 3 and four flasks 10 made of solid β-alumina electrolyte were inserted into openings 4. Flask (tube) was vnutrielektrolitny volume of 91 cm ³ with dimensions: internal diameter 27 mm, height 160 mm, wall thickness 1 mm, the ionic conductivity of Na ⁺ at a temperature of 250 ^C. 0.2 ohm ^-1 cm ^-1. The metal cap 13 of the flask was connected to the negative of the stabilized current source B5-21, and the plus of the current source B5-21 through ammeter H340 14, the 2RVM time relay was grounded. The ammeter was calibrated using a copper coulometer included in the indicated circuit. The potential of the cover 13 was recorded using a H339 type recording voltmeter. With ohmic heater formed as a Nichrome spiral in ceramic beads, wound on the outer surface of the container 1 and the thermally insulated felt of alumina warmed tank 1, valve 5, the wax and the flasks of the solid electrolyte to a temperature of ¹⁵⁰ ° C with a rate of 5 degrees per per minute, held for 0.5 hour, open valve 5 and fed to the molten sodium in a special furnace at 150 ^{° C} in the container 1 until the short-circuit level gauge 8, after which valve 5 closed and the sodium flow is suspended. Raising the temperature of the container 1 and contents therein to a temperature of 250 ° ^C. The time switch includes a contactor and stepwise increased current in the circuit at 2 amps at 0.5 h to a desired value, for example 10 A.

250 Ом^-1 250 Ом^-1, что соответствовало исходной удельной проводимости твердого электролита
σ_уд=

0,22 Ом^-1см^-1 где l толщина стенки колбы 0,1 см;
R общее сопротивление колбы, 4˙ 10^-3 Ом;
S общая площадь колбы, равная 114 см².When the circuit of the long level gauge 8, set 5 lower than the short one, was opened, valve 5 was opened and a new portion of sodium was introduced into the tank 1 until the short level gauge 8 was closed. At each current level, the voltage change in the circuit was recorded using a self-recording voltmeter type H339 to a steady state. At a selected current of 10 A of the electrochemical filling process (determined by the critical current density, for the applied solid electrolyte and design, the limiting current of 100 A, j ≈ 1 A / cm ² ), the initial steady-state voltage value of 0.04 V (40 mV) was recorded, and the initial conductivity was determined flasks σ =

250 Ohm ^-1 250 Ohm ^-1 , which corresponded to the original conductivity of the solid electrolyte
σ _beats =

0.22 Ohm ^-1 cm ^-1 where l is the flask wall thickness of 0.1 cm;
R the total resistance of the bulb, 4˙ 10 ^-3 Ohm;
S a total flask area of 114 cm ² .

 The filling process was continued until the voltage on the flask increased from the initial value of 0.04 to 0.4 V, which took 2 hours for the technical sodium used (GOST 3273-75), total impurities ≈0.3%).

In this case, the conductivity of the flask decreased to 25 Ohm ^-1 due to impurities present in sodium.

The polarity of the source B5-21 was changed and the vibrator 9 was turned on, after 5-10 minutes the initial conductivity of 250 Ohm ^{-1 was} restored, the polarity of the source B5-21 was again changed, and the process of filling the interelectrolyte volume was repeated.

 When cycling in this way, the amount of electricity was constantly counted by the ammeter and occasionally to calibrate the ammeter and the process of charge transfer by sodium ions on a copper coulometer. With a charging capacity (taken as an example of a solid electrolyte flask) equal to 65 A ˙ h, the filling process was carried out according to the scheme shown in the table.

 The total amount of electricity transferred by sodium ions to the interelectrolyte volume, in this case, was 65 Ah.

 In the case of severe Na contamination with impurities (sodium, mechanically purified from safety lubricant, without vacuum degassing), an additional 10A charge cycle was carried out for 1 h and the same cycle with a change in the direction of the current when the vibrator 9 was turned on.

Upon completion of the filling process the temperature of the container 1 was lowered to 150 ^{° C,} the flask was removed from the openings 4 of the cover 3 and naturally cooled in a box filled with argon. When sodium flasks are filled with solid β-alumina electrolyte in a vacuum or in a neutral gas medium, paraffin protective materials can be omitted.

When the flask was removed from the container 1, a monolayer paraffin film was preserved on the surface of the solid electrolyte, which can play a positive role in protecting the electrolyte from environmental moisture, practically without affecting the properties of the sodium-sulfur battery in their application. If desired, the monolayer film is easily removed degassing flasks at 350 ^C. in a vacuum chamber.

 Using the proposed method in comparison with the prototype allows to reduce the contamination of electrolyte flasks with impurities contained in sodium, and to intensify the process of filling them. The rejection of the flasks directly in the process of filling reduces the cost of subsequent control of the received products and increases the operational reliability of multi-cell batteries.

Claims (2)

 1. METHOD FOR FILLING SODIUM WITH INTERNAL VOLUME OF SEALED ELECTROLYTE TUBES WITH SURFACE TREATMENT FOR SODIUM SODIUM BATTERY, made on the basis of beta-alumina, by immersing them in the sodium melt and creating a voltage difference between them from the drain to the current source that when the minimum permissible value of the electrolyte conductivity is reached, the sign of the potentials is changed, the electrolyte conductivity is restored, and the sign changes again to the potentials, repeating this cycle until the filling tubes excess amount of sodium with respect to the working, after which provides removal of excess amounts of sodium potentials with opposite sign on and off the constant current source.  2. The method according to claim 1, characterized in that the sodium melt is mixed, for example, by exposure to ultrasonic vibrations.

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