RU2031491C1 - Method of thermal control over high-temperature storage battery - Google Patents

Abstract

FIELD: electric batteries. SUBSTANCE: thermal control is conducted thanks to use of heat of phase transformation "melting-crystallization" of substance which is placed in space of battery and is kept in two-phase state during operational mode providing from relationship between masses of melted and crystallized phase within range of 10-15:1. Prior to storage or charging battery is enclosed in constant-temperature cabinet decreasing heat release to environment and providing for gradual crystallization of melt of substance in space of battery. Release of crystallization heat is used to prolong storage time of battery without additional. EFFECT: prolonged storage time of battery. 2 cl, 1 dwg

Description

The invention relates to chemical sources of current and can be used for high temperature control of batteries, for example, sodium-sulfur systems (operating temperature of 300 ... 350 ° ^C), nickel chloride-sodium (250 ... 370 ° ^C), lithium iron sulfide (400 ... 480 ^{° C),} and others.

 For batteries used in transport installations (electric cars, electric forklifts), as well as in systems with an unstable primary energy source (wind, sun, etc.), it is necessary to maintain the temperature in a range close to the working one even when the battery is disconnected from the load for several hours for example at night. At the same time, maintaining the molten state of the electrodes and sufficient electrical conductivity of the solid electrolyte from beta-alumina allows increasing the battery life and improving the operational characteristics of the plants. The use of additional heating for this purpose (electricity or burning fuel) is not always possible, especially in certain places, on road conditions and in open parking lots, and the use of high-performance screen-vacuum or fiber-ampoule thermal insulation significantly complicates the design of batteries and makes their manufacture more expensive. When using less effective thermal insulation, its volume can occupy up to 50 ... 80% of the battery volume, which is unacceptable for most transport installations.

 A known method of temperature control of a sulfur-sodium battery, in which the temperature of the internal thermally insulated volume of the battery is measured, where high-temperature batteries are located and when the temperature drops below an acceptable level, it is heated using an electric heater or heat pipe with a catalytic chamber for burning hydrocarbon fuel. When the temperature rises above the permissible level, the heat sources are turned off and air is passed through the named volume using a fan, providing its circulation. When the battery is disconnected from the load and gradually cooled, it is periodically heated using a heat pipe, since the electric heater is also disconnected [1].

 The disadvantage of this method is the need for periodic use of an external heating source - a catalytic combustion chamber with a heat pipe, when the battery is in the off state, which requires the consumption of hydrocarbon fuel, complicates and increases the cost of battery operation, especially as part of a transport installation.

A known method of thermoregulation of a high-temperature sulfur-sodium battery, in which a heating or cooling liquid is passed through an internal insulated volume with batteries placed in it, the flow control of which is carried out using a temperature-controlled valve. At temperatures above or below a given, for example at ^about 370 and 300 ^{° C,} the valve opens and passes respectively cold or hot liquid. To reduce heat loss from the battery, screen-vacuum thermal insulation is used [2].

 The disadvantages of this method are the difficulty of selecting a liquid that does not boil in the specified temperature range; in the hardware complexity of the system for pumping fluid, its heating and cooling. In addition, with this method, as well as with the previous one, it is necessary to periodically turn on an external heat source - an electric heater to heat the battery during storage.

 There is a method of thermoregulation of a high-temperature sulfur-sodium battery mounted on an electric vehicle, in which external air is used to cool the batteries, blowing it in between the batteries. To do this, pre-establish the relationship between the temperature inside the battery and the consumed load, and simultaneously with the air supply, the output power of the battery is changed taking into account the corresponding change in internal heat generation in its heat-insulated volume. Continuously record the operating temperature of the battery and, when reached, turn on air cooling. If the temperature continues to increase, then reduce the load of the battery until the temperature starts to decrease, and when it reaches its lower value, the load is increased, if necessary, turning off the air cooling [3].

 The disadvantages of this method are that in battery storage mode to maintain the temperature of the batteries, they must be periodically heated. In addition, the need for frequent changes in the amount of consumed load reduces the efficiency of the battery and the electric vehicle as a whole.

Closest to the proposed method of thermoregulation of a high-temperature battery in technical essence is a method in which between batteries located in the internal heat-insulated volume of the battery, an additional volume is placed with heat-storage substance, which is distributed in separate ampoules between the batteries. The substance is selected with a melting temperature in the range of the maximum allowable battery operating temperature under load and, when it is exceeded, the heat of the phase transition of the melting-crystallization substance is used to thermally stabilize the battery and provide a reserve of time for turning on the cooling system (gas or liquid). Subsequent cooling to a temperature below the maximum allowable melt crystallizes, which is accompanied by the release of heat in ampoules and its distribution in the internal volume of the battery. As heat-accumulating substances, compositions based on potassium, sodium, magnesium, lithium chlorides with a melting point in the range of 350 ... 400 ^o C can be used [4].

 The disadvantage of this method is that the heat of a highly efficient phase transition is used to thermally stabilize the battery only when the batteries overheat. In all other modes, and especially when the battery is off (for several hours), the phase transition heat is not used, which also requires the use of electric heaters or other heat sources. As a result, the efficiency of the battery thermal control process decreases and the process of its implementation is complicated.

 The aim of the invention is to increase the efficiency and simplify the process of thermal control of the battery.

 This is achieved by the fact that with the method of thermoregulation of a high-temperature storage battery, including the use of the heat of the melting-crystallization phase transition when the internal heat-insulated volume of the battery is thermally stabilized, a volume with a heat-storage substance having a melting temperature in the range of the optimum operating temperature of the battery under load is placed in the said volume, the value is controlled heat transfer from the battery and support the substance in a two-phase state in the operating mode, and By the storage mode of the battery with the load off or by the mode of its charge, thermostat the battery volume and use the heat of crystallization of the substance in the indicated modes.

 Moreover, to control the amount of heat loss, a volumetric change in the heat-accumulating substance is used during its melting and crystallization, the value of which is set from the ratio of the volumes of the molten and crystallized phases and is supported by a controlled change in heat transfer conditions, for example, by blowing the battery or changing the thickness of its heat insulation in local areas from the front crystallized phase.

 In addition, the mass ratio of the molten and crystallized phases is maintained in the range (10-15): 1.

 The use of a heat-accumulating substance having a melting point in the range of the optimum operating temperature of the battery makes it quite simple, for example, by controlling the convective heat exchange with the external environment, by changing the thickness of the thermal insulation of the battery, to maintain the substance in a two-phase state. At the same time, a part of its volume located in close proximity to the heat-generating accumulators will be in the form of a melt, and a part located near the heat-insulated and less heated wall of the battery case will be in a crystallized state.

 In the event of overheating of the batteries and an increase in heat generation inside the battery, the melt front will gradually move toward the wall of the housing and until the entire volume of the substance is completely melted, the temperature inside the housing will remain at the optimal level. The time during which the substance melts can be used to alert the emergency cooling system or load shedding system, to localize emergency batteries or sections, etc.

 The signal for the operation of these systems, used to control the amount of heat loss from the battery, can be an increase in the volume of the heat-accumulating substance during its melting, which can reach 20 ... 30%, i.e., a signal about the danger of overheating of the battery is generated before this process develops. on the scale of the battery when it is in the range of optimal operating temperature despite the increase in its internal heat generation.

 If the battery worked in normal mode without overheating and it must be disconnected from the load for several hours, then before that it is thermostated, providing the minimum achievable heat loss to the environment. Thermostating can consist, for example, in that the forced (air or liquid) cooling of the battery is stopped, the thickness of the insulation is increased with the help of an additional cover or layer, etc. Slowing down the cooling rate of the battery allows you to slow down the speed of movement of the crystallization front in the direction from the wall of the battery to the batteries. Until the full crystallization of the melt, the temperature in the volume of the battery will remain at the optimal level. As the calculated and experimental estimates show, the optimal mass ratio of the molten and crystallized phases is (10-15): 1. The mass of the crystallized phase is selected from the condition in order to provide a margin of time for the resorption of the local overheating region during the destruction of individual batteries, emergency shutdown of the load, as well as the activation of the emergency cooling system. The mass of the molten phase should be sufficient to maintain the required temperature level for several hours of storage of the battery with the load off (7. ..10 h) without additional heating. In this case, the heat loss from the battery to the environment will be compensated by heat release during the gradual crystallization of the melt.

 When the crystallization time is not less than the storage time of the battery, it will be at a constant temperature close to the optimal operating range and, therefore, can be brought into working condition at any time on this period of time.

 The placement of the volume with heat-accumulating substance in the battery is carried out taking into account its design features. For example, if there are cooled gaps between the individual batteries, the crystallized part of the substance can be contained in ampoules placed in these gaps, and the molten part is contained in the cavity of the common heat-insulated base of the battery assembly. When the batteries are tightly packed, the heat-accumulating substance can be placed in the cavity of the screens fixed inside on the walls of the battery case.

 Ampoules, capsules, screens and similar elements with a heat-accumulating substance can also be placed in the battery with the possibility of their removal and replacement.

 The drawing shows the design of the battery in relation to the option with the placement of heat-accumulating substances inside the base of the battery assembly, section.

 The battery contains battery sections 1, connected by an electric circuit 2 and placed inside the housing 3, equipped with thermal insulation 4. The sections are mounted on the surface of the box-shaped container 5 filled with heat-accumulating substance, one (large) part of which is in the molten state 6, and the other (smaller) - in a crystallized state 7. In the upper part of the pallet, a compensation tube 8 is formed, which is brought out in one of the spaces between sections 1, into which an electric level gauge 9 is inserted.

 At the base of the battery, the thermal insulation is made with two movable layers 10, 11. Depending on the design of the battery, the heat storage substance can be divided into parts that are also placed between the individual sections and the batteries or in the inner walls of the housing; the pallet 5 can be made with the possibility of replacement without depressurization of the battery case, etc. The essence of the method with similar design variants of the battery remains unchanged.

 When the battery is warmed up and brought to the operating mode with the load connected, the heat release in the battery sections 1 increases and the substance gradually melts in the pan 5 with an increase in its volume and an increase in the melt level in the tube 8. When the battery reaches the rated mode, the level gauge 9 fixes the specified melt level in the tube 8. The signal from the level gauge is used to regulate the gap between the heat-insulating layers 10 and 11, which move apart or shift in the direction of the arrows 12 or 13, thereby setting m teplosbrosa value of the battery through the gap between the ends of layers 10 and 11, ensuring the maintenance of a predetermined level of the melt in the tube 8.

 The regulation of heat dissipation from the battery, in addition, can be carried out, for example, by additional blowing the battery housing with air. Other well-known level gauge circuits, for example, float or membrane types, can also be used.

 With an unplanned increase in heat dissipation in sections 1, when the efficiency of the heat removal system is insufficient, a gradual melting of the crystallized mass 7 begins, accompanied by an increase in the volume of the liquid phase 6 and an increase in its level in the tube 8. This process occurs at a constant temperature inside the battery case 3, which differs little from the temperature rated mode. Changing the electrical signal from the level gauge 9 serves to take preparatory measures to disconnect the load and / or additional cooling of the battery. The melting process is extended over time and prevents a sharp increase in temperature inside the battery. This allows the use of several emergency systems built on different physical principles and duplicating each other. As a result of a gradual decrease in temperature in the battery volume, a gradual crystallization of the melt begins at almost its constant value. The melt level in the tube 8 decreases and when the nominal value is reached, the level gauge generates a corresponding signal for the operation of the system for working regulation of heat release. The battery is in normal operating condition.

 When the battery is in storage mode, it is provided with temperature control, minimizing heat loss from the case. To do this, shift the insulation layers 10 and 11 in the direction of the arrows 13, stop blowing air into the case, put on an additional heat-insulating cover and disconnect the external electrical load from the battery. As a result, the crystallization process of melt 6 is sharply slowed down and thermal stabilization of the internal volume of the body is carried out at a constant temperature level. This process is accompanied by a gradual decrease in the level of the melt in the tube 8 and when the specified minimum value is reached, the level gauge 9 generates a signal to turn on the load or to force the battery to heat.

 The mass of the melt is selected from the calculation so that during storage of the battery with the load off, its full crystallization does not occur, up to the volume in the tube 8. For example, with a maximum storage time of 7 hours, the mass of the melt is selected from the calculation of its full crystallization in 7.5 hours, i.e., with a margin for unforeseen circumstances that could delay the inclusion of the battery. This condition is easily fulfilled for stationary power plants that do not have strict restrictions on weight and size characteristics. However, for transport installations there is a sufficiently large reserve to accommodate the required amount of heat-accumulating substance or to substantially approach its optimal loading.

 Thus, the functioning of the battery is carried out in the operating mode and during its storage at almost the same temperature level, ensuring the maintenance of optimal conditions for the batteries.

PRI me R. Thermal control of the sodium-sulfur battery was carried out, having 56 batteries with a capacity of 50 Ah each, combined in two sections 1 with 28 batteries each. The battery energy consumption is 5 kW 5 h. The sections are located inside the housing 2, which has the following overall dimensions: length 580 mm, width 520 mm, height 300 mm. A layer of powder-fiber thermal insulation 4 batteries (material type TZMK-10) is placed in a sealed cavity formed between the inner and outer walls of the housing and evacuated to 10 ^-2 mm RT.article. The coefficient of effective thermal conductivity of such thermal insulation is 0.01 W / m ˙K. Optimum temperature within the battery 350 to the operating mode ^C. The minimum permissible temperature of the storage battery with the load switched off ^about 300 C. The maximum temperature permitted in the case of accidental heating battery 400 ^C. The battery intended for use as a power source for an electric traction motor. Heat losses through its body are estimated at 180 watts. Battery storage time with disconnected load can reach 8 hours (time for which the temperature inside the battery can be reduced from 350 to 300 ° ^C). Container-pallet 5, made of stainless steel type 12X18H10T, 1 mm thick, has a length of 540 mm, a width of 480 mm, a height of 30 mm and occupies ≈10% of the battery volume. The pallet is equipped with a tube 8 with an inner diameter of 7 mm and a height of 200 mm, through the cover of which a probe of an electric level gauge is inserted, which has a coating of corrosion-resistant material. The tray is filled with a heat storage mixture consisting of (wt.%): Lithium carbonate 3.2-3.4, potassium chloride 46.8-47.0, lithium fluoride 2.1-2.4, lithium chloride - the rest. The mixture is melted at temperatures of 340-343 ^{° C,} a melting heat of 375 J / g, its loading in the sump 5 is 15 kg.

 When assembling the battery, the tray 5 is filled with the powdery mass of the mixture, taking into account its porosity and 20% volume expansion during melting, the probe 8 of the pre-calibrated level gauge 9 is installed in the tube 8, vacuum and seal the entire system.

Upon exiting the cold battery to the operation mode its temperature is gradually increased, continuously removing the signal from the transmitter 9 and when it reaches its predetermined value corresponding to a temperature of 350 ^{° C,} establish a gap between sloya- 10 and insulation 11, wherein inside the battery due teplosbrosa through the gap 350 is set temperature ± 2 ^{° C,} and on the bottom pallet 336 ± 2 ^{° C,} which provides much of the molten sump, and in its bottom part - the crystallized mass in amounts corresponding to the calculated range, i.e. ≈90% and 10%, respectively.

 Maintaining this ratio during further battery operation is carried out by automatically adjusting the gap width in accordance with changes in the signal from the level gauge.

When the battery is put into storage mode with the load off, the layers 10 and 11 tightly shift, thereby ensuring thermostating of the battery. As a result of slow heat removal from the battery, the crystallization front of phase 7 gradually spreads up the height of the tray 5, which is accompanied by the release of the previously stored heat of fusion of the mixture inside the thermostatically controlled volume of the battery. Crystallization ≈90% of the melt occurs in 7 hours, which meets the requirements of battery operation. In this case, the temperature inside the battery during the time of crystallization of the melt does not decrease below 340-343 ^о С and, therefore, there is an additional reserve of time (2.5 h) until the temperature drops to 300 ^о С. or violations of thermal insulation, for example, due to loss of vacuum, when, with an accelerated decrease in the level of the melt in the tube 8, the signal from the level gauge gives a command to turn on a special battery heating system. The battery storage time without a heat storage tray is ≈3 hours, while its temperature drops to 300 ^about C.

If, at the maximum intensification of heat loss through the maximum gap between layers 10 and 11, the melt level in tube 8 continues to grow and exceeds a predetermined upper value, the signal from the level gauge (duplicating the thermocouple readings) gives a command to urgently disconnect the battery from the load and turn on the emergency battery cooling system. However, even after complete melting of the whole mixture in the sump when the melting proceeded without increasing battery temperature above 350 ^{° C,} has a time margin before reaching the maximum temperature of 400 ^{° C,} as further absorption of heat will occur due to the heat capacity battery. Thus, in the event of an emergency overheating of the battery, there are two safety barriers due to the heat of fusion and heat capacity. This ensures that there is sufficient time to take appropriate emergency safety measures.

In battery mode when its temperature may go down to 300 ^{° C} and lower its temperature control is performed as in the storage mode, i.e. layers 10 and 11 are tightly shifted, the battery is thermostated and the heat of crystallization of melt 6 is used during the charge time.

In case the battery temperature is still starts to decrease below 300 ^{° C,} the signal from the transmitter issues a command to auxiliary heating batteries, e.g., from embedded between the sections 1, electric heaters (not shown). Additional heating can also be carried out from an external heat source through the gap between the layers 10 and 11.

For the sodium-sulfur battery in question, a composition containing, wt%: cadmium chloride 18.36 and cadmium iodide 81.64 can also be used as a heat storage mixture. The melting point of a mixture of 350 ± 2 ^{° C,} heat of fusion 350 J / g.

 Thus, the proposed method provides an increase in the efficiency of the thermoregulation process in all operating modes of the battery, including its storage and emergency overheating or cooling. The method proceeds in a self-regulating mode and does not require any pumping devices and special adjusting elements such as valves.

The proposed method can also be effectively used in the operation of high-temperature batteries based on other electrochemical systems. For example, for the battery based on the system sodium-nickel chloride with an optimum working temperature ^of 350 C can be used, said composition containing cadmium chloride and iodide. Battery based on lithium-iron sulfide system with a working temperature ^of 475 C can be used alkali LiOH, having a melting point of 471 ^C and a specific melting heat of 1080 J / g. If such a battery operating temperature set at 400 ^{° C,} the mixture comprising, by weight can be used for it. %: 22 sodium chloride, barium nitric acid 78, having a melting point of 400 ± 2 ^{° C} and a specific heat of fusion of 360 J / g.

 Using the proposed method allows to expand the operational capabilities of high-temperature batteries designed for stationary and transport installations, to stabilize their temperature. Particularly effective is the use of the method for thermoregulation of batteries during storage with the load off.

Claims (2)

 1. METHOD OF THERMAL REGULATION OF A HIGH-TEMPERATURE BATTERY BATTERY, including the use of the heat of the phase transition melting - crystallization of the heat-accumulating substance during thermal stabilization of the internal heat-insulated volume of the battery, according to which the volume with the heat-storage substance is placed in the battery volume, having a working temperature under the optimum temperature in the range that regulate the amount of heat loss from the battery and support the substance in the phase state is in the operating mode, and before the battery storage mode with the load off or its charge mode, the battery volume is thermostated and the heat of crystallization of the substance is used in the mentioned modes.  2. The method according to claim 1, characterized in that for controlling the amount of heat loss, a volumetric change in the heat-accumulating substance is used during its melting and crystallization, the value of which is set from the ratio of the volumes of the molten and crystallized phases and is supported by a controlled change in the conditions of heat transfer from the front of the crystallized phase.

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