CN111834649A

CN111834649A - Rechargeable sodium-water gas fuel cell unit

Info

Publication number: CN111834649A
Application number: CN201910327042.9A
Authority: CN
Inventors: 黄子强; 黄逸青
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-04-23
Filing date: 2019-04-23
Publication date: 2020-10-27

Abstract

The rechargeable sodium-water vapor fuel cell unit adopts fluid sodium containing liquid metal sodium as a cathode, water vapor or oxygenated water vapor as an oxidant, and solves the problem of unsmooth discharge of alkali liquor in the conventional sodium fuel cell and the problem of discharge of oxygen bubbles during charging by using a multi-pipeline array structure. The sodium fuel cell with the final structure can realize continuous power generation with high power density and can be charged under reasonable current. The invention takes a sodium ion conductive diaphragm as a selective sodium ion permeation medium, takes a carbon-free gas cathode as a selective leakage medium of hydroxide ions, and takes a reserved space between the diaphragm and the cathode as a space for mixing positive ions and negative ions (namely a mixing space) to complete the basic structure of the battery. The alkali discharge pipe array formed by the multi-pipeline array exchanges electrochemical reaction products in the mixing chamber, so that the reaction of the battery can be continuously and efficiently carried out, and the characteristics of continuity and high power density are further obtained.

Description

Rechargeable sodium-water gas fuel cell unit

Technical Field

The invention discloses a rechargeable sodium-water gas fuel cell unit (hereinafter referred to as a sodium water rechargeable battery), relating to the field of fuel cells, in particular to the field of rechargeable fuel cells using metal sodium.

Background

Fossil energy and atomic energy are major sources of human energy and are always facing depletion problems. Compared with fossil energy, solar energy has the advantages of inexhaustibility. Solar energy includes wind energy, light energy, tidal energy. For the long-distance transmission of energy, the energy is generally converted into electric energy, and the generated electricity is often called wind power and photoelectric power. The photovoltaic power and the wind power fluctuate due to the restriction of natural conditions, such as fluctuation of solar energy and wind energy power generation caused by overcast and rainy days, no wind in sunny days and the like, and the photovoltaic power generation is almost zero especially under the condition that a large amount of electricity is needed at night. This relates to the technology of storage of electrical energy, and in particular to the technology of high capacity, high power batteries. On the other hand, electric vehicles also involve the above-mentioned battery technology. In addition to high capacity and high power, the requirements of batteries for electric vehicles include high power density. In the two use scenes, the battery is required to be low in cost, environment-friendly, disassembled and recycled and the like, so that the living environment of human is protected, and sustainable development is realized.

The lithium batteries used in large quantities at present work in a rocking chair mode. In the anode, graphite is needed to store lithium in the form of ions, so that the problems of short circuit, lithium death and the like caused by lithium dendrites are avoided, but the effective content of lithium is greatly reduced; at the cathode, oxygen is stored in the form of a salt of a valence-change compound, so that the amount of oxygen participating in the electrochemical reaction can be effectively utilized is low. The graphite and the valence-variable compound have no mass change and do not store electric energy in the charging and discharging processes of the battery, and are auxiliary materials of the battery. The auxiliary material is at least ten times as large as the element directly participating in the electrochemical reaction among all the materials of the battery as a whole. The energy density of the battery can be increased only by reducing the weight proportion of the material serving as an auxiliary.

An example of the ability to scale down auxiliary materials appears to be a "vanadium flow battery". Electrochemical energy is stored in valence-variable vanadium ions in the aqueous solution, and only the proton exchange membrane of the cell body does not participate in electrochemical reaction except for structural materials such as a housing, a container and the like, so that the weight ratio of auxiliary materials except water as the solution is minimized. However, the energy density of vanadium fluid batteries is not high because most of the vanadium ion solution is water, which does not participate in the electrochemical reaction. In addition, vanadium ions are extremely toxic, and vanadium resources on earth are few and much less than lithium.

Yet another practical example is a hydrogen fuel cell. Hydrogen is stored in a high-pressure storage tank as an anode material and reacts with oxygen in a fuel cell in an electrochemical way, the main auxiliary material of the cell is only a proton exchange membrane with a platinum catalyst, and the rest materials are only the structural materials of a shell and the cell. Hydrogen and oxygen flow into the anode and cathode of the fuel cell, respectively, and liquid water is obtained as a result of the reaction and is easily discharged to the outside of the fuel cell. This can be analogized to the case of a "vanadium flow battery". The difference is that the reaction product is water, which does not have to be stored, and the hydrogen fuel cell energy density should be reasonably high. However, this is not the case. Hydrogen gas requires compression to be stored. At present, in the best technical case, a 26-liter high-pressure tank is required for storing 5 kg of hydrogen, the internal pressure of the high-pressure tank reaches 600 atmospheres, and the weight of the tank itself reaches 100 kg. Considering the weight of the hydrogen storage tank, the hydrogen storage system has a hydrogen weight ratio of only 5%, which greatly reduces the overall energy density of the hydrogen fuel cell. In addition, the explosive nature of the high pressure tank, the possibility of hydrogen gas leaking at critical locations such as joints and valves, and the flammable and explosive nature of the hydrogen gas itself, limit the use of hydrogen fuel cells. If a vehicle leaks air chronically in the underground garage, the whole garage and the whole building are very dangerous. Moreover, the hydrogen fuel cell voltage is low (only 0.6-0.8 v), and the capacity is further reduced by times. Yet another disadvantage is that none of the existing hydrogen fuel cells can be charged.

The use of oxygen in air can avoid the storage problem of oxygen, i.e., the normal sodium (or lithium) -air cell model, if the hydrogen in a hydrogen fuel cell is replaced with an alkali metal to avoid the problem of the need for a high pressure tank for storage of the anode material. However, the melting point of the alkali metal oxide is too high, reaching above 800 degrees, and cannot form a flow at a reasonable temperature to be discharged outside the battery.

US3703415 shows a sodium-water battery, which uses a solid electrolyte film with an open circuit voltage of 2.65 v, because ceramic is used as the sodium ion conductive membrane, the resistance at room temperature is too high, the current density is only a few milliamperes, and if a mixture of polymer and sodium salt is used as the sodium ion conductive membrane, the sodium salt in the film is easily dissolved in water, so that the mechanical strength is reduced, and the film is broken to cause direct contact reaction between sodium and water, which is unsafe.

Chinese patent CN108365238A discloses a liquid metal fuel cell, which has a structure of liquid metal-solid conductive membrane-gas cathode-humidified oxygen or air. Because the solid electrolyte sodium ion conductive diaphragm is directly bonded with the gas cathode, the product generated by the electrochemical reaction of the liquid metal and the wet oxygen, namely the waste material, can not be discharged smoothly, so that the battery can not work normally. Although the inventors claim that the waste material can be discharged through the micro-gaps in the gas cathode, while wet oxygen enters through the nano-gaps in the gas cathode. However, it is practically impossible to achieve a relatively countercurrent flow of a mixture of gas and liquid in the same medium. Now, the following is explained: the gas cathode is the one that achieves the largest catalytic surface, where both solid particles and gaps between particles are very small, typically on the order of nanometers to micrometers in size. The resulting micro-channels for the discharge of waste liquid are both curved and of very non-uniform diameter. In other words, in the zigzag-shaped microchannel for discharging the waste liquid, the dimensions of the different positions are also between nanometer and micrometer. According to the inventor, the waste liquid flows out of the battery through the larger holes, and the wet oxygen enters the battery through the smaller holes, so that the waste liquid is bound to block the position with smaller radius in the micro-channel, and the wet oxygen channel is not smooth. Furthermore, whether the wet oxygen pressure is increased or decreased, the difference between the pressure applied to the waste liquid and the wet oxygen pressure is close to zero. Therefore, the waste liquid can flow out of the battery while the wet oxygen flows into the battery. In summary, this invention is not practical because the waste liquid cannot be discharged and the wet oxygen as the oxidizing agent cannot enter the battery. Moreover, the metal fuel cell with the structure also belongs to a disposable battery, and cannot be charged.

Although the fuel cell has a high energy storage density, the conventional fuel cell cannot be charged, so that the process of adding fuel is complicated and dangerous, and the application of the fuel cell to an electric vehicle is limited.

The present invention selects sodium as an energy storage medium to manufacture a rechargeable fuel cell. The liquid sodium is used as the fuel of the battery, and the following advantages of sodium are taken: a. the safety is good. Since sodium has a boiling point of approximately 1000 degrees, sodium burns only on the surface during combustion, and does not explode because explosive gas is not easily formed. Hydrogen or gasoline (gasoline has a boiling point of about 80 degrees) is mixed with air upon combustion, and then causes explosion. b. Sodium is relatively easy to store in a can filled with inert gas, nitrogen gas or silicone oil, and even if there is residual oxygen in the can, oxidation is caused only on the surface of sodium, and the oxidation process is stopped after the oxygen is exhausted. c. The charging of the battery is not required to be a continuous process, so that the charging process is simple and safe, and the used electric power can be electric power generated in a night electricity utilization valley time period and a photoelectric wind power generation time period, and can also be conventional commercial power, industrial electricity, hydroelectric power, coal power and atomic power.

Disclosure of Invention

The invention mainly solves the problem that the alkali liquor in the sodium fuel cell is not smoothly discharged at present and also solves the problem that the sodium fuel cell can only generate electricity and can not be charged.

The structure of the sodium water rechargeable battery of the present invention is as follows.

The invention relates to a sodium water rechargeable battery, which is composed of a fuel unit, a sodium ion conductive diaphragm, a gas cathode, an oxidant unit, an alkali discharge pipe array and an alkali liquor collecting room. The negative electrode of the cell is drawn from the fuel cell and the positive electrode of the cell is drawn from the gas cathode. The fuel unit comprises a fuel chamber and fluid sodium filled in the fuel chamber, and the oxidant unit comprises an oxidant chamber and a gas oxidant filled in the oxidant chamber.

The invention relates to a sodium ion conductive membrane, which is a membrane made of ion conductive material and is characterized in that the mobility of sodium ions in the membrane is far larger (more than 10 times) than that of electrons and other ions (such as hydrogen ions and hydroxide ions). A typical sodium ion conducting membrane is a Beta alumina ceramic sheet.

The "fluid sodium" referred to in the present invention is sodium or a mixture of sodium in the following three forms or a mixture of the three forms: 1. liquid formed by placing simple substance sodium in an environment higher than a melting point (97 ℃); 2. an alloy material or intermetallic compound of sodium and other materials, such as potassium, mercury, tin, etc., which is melted at a temperature higher than the eutectic point to form a liquid; 3. flowable composite materials containing sodium (e.g., sodium microspheres, sodium alloy microspheres, liquid paraffin containing sodium microspheres, aluminized sodium microspheres, and the like). The liquid sodium acts as the cathode consuming material of the cell, i.e. the fuel of the sodium water rechargeable cell of the invention, in the sodium water rechargeable cell of the invention.

The "alkali liquor" referred to in the present invention is a product of electrochemical reaction of sodium and water molecules or a mixture of sodium and oxygen water molecules, and contains sodium hydroxide in a high-temperature molten state, and may also contain gas, and may also contain a mixture formed by mixing sodium hydroxide with other compounds in order to lower the melting point of the alkali liquor. Examples of lye are: sodium hydroxide in a molten state, a eutectic mixture of potassium hydroxide and sodium hydroxide, a eutectic mixture of ammonium hydroxide and sodium hydroxide, and a liquid formed by blending sodium hydroxide and an ionic liquid. Due to the operational characteristics of the rechargeable cells of the sodium brine of the present invention, and the impurities present in the raw materials, the lye may contain gases such as moisture, hydrogen, oxygen, nitrogen. Furthermore, since air and water contain small amounts of carbon dioxide and other gases, the lye may also contain small amounts of solid substances, such as sodium carbonate. After all the possibilities mentioned above are considered, the lye in the present invention is a liquid, possibly also a liquid containing sodium hydroxide and a flowing body of gases and solids.

The sodium water rechargeable battery of the present invention has the following features:

a gap is reserved between the gas cathode and the sodium ion conductive diaphragm to serve as a mixing chamber, and the inner space of the mixing chamber is filled with alkali liquor; the alkali discharge pipe array is composed of a plurality of alkali discharge pipes, and the alkali discharge pipes are pipelines which penetrate through the gas cathode and the oxidant unit and are filled with alkali liquor.

The mixing chamber is a space formed by adding a mixing chamber frame to a gap reserved between a gas cathode and a sodium ion conductive diaphragm, and the space is filled with alkali liquor. The alkali liquor is used as electrolyte to play the role of ion transmission and ion mixing. In the structure of the invention, the sodium ion conductive diaphragm is a solid electrolyte, and the alkali liquor in the mixing chamber is a liquid electrolyte, so the invention uses a solid and liquid double-layer electrolyte structure. Sodium ions diffused from the sodium ion conductive membrane into the mixing chamber and hydroxide ions diffused from the gas cathode are transmitted, diffused and mixed in the mixing chamber due to electrostatic force and ion diffusion movement to form sodium hydroxide, and then the sodium hydroxide is mixed with gas generated by electrochemical reaction and foreign impurities to form alkali liquor. The alkali liquor in the mixing room of the sodium water rechargeable battery needs to be discharged outwards due to continuous generation during power generation, and the alkali liquor in the mixing room needs to be replenished due to continuous consumption during charging.

The central positions of the cross sections of the alkali discharge pipes forming the alkali discharge pipe array are preferably uniformly distributed. For example, the array may be a matrix, a concentric circle array, a triangular array, a hexagonal array, or a random uniform array.

The alkali discharge pipe is used for exchanging alkali liquor between the inner part of the mixing chamber and the outer part of the mixing chamber. The pipe orifice of the alkali discharge pipe communicated with the mixing chamber (which is referred to as the inlet of the alkali discharge pipe in the invention) is immersed in the alkali liquor in the mixing chamber, and the pipe orifice of the other end of the alkali discharge pipe (which is referred to as the outlet of the alkali discharge pipe in the invention) is communicated with the alkali liquor collecting chamber. During power generation, alkali liquor enters the alkali discharge pipe from the mixing chamber through the inlet of the alkali discharge pipe and is discharged to the alkali liquor collecting chamber through the outlet of the alkali discharge pipe; during charging, the alkali liquor in the alkali liquor collecting chamber is sequentially input into the mixing chamber through the alkali discharge pipe outlet, the alkali discharge pipe and the alkali discharge pipe inlet. The purpose of arranging the alkali discharge pipe array formed by the plurality of alkali discharge pipes is to enable alkali liquor to enter and exit the mixing chamber more easily, thereby providing larger current density per unit area. Under the condition that the length of the alkali discharge pipe is far smaller than the diameter, the shape of the alkali discharge pipe pipeline is represented as a through hole.

The alkali liquor collecting room is a collecting space of alkali liquor discharged from the outlet of the alkali discharge pipe array in a power generation mode and is used for collecting and concentrating the alkali liquor discharged from the outlet of the alkali discharge pipe array. An alkali liquor discharge port is formed at the periphery of the alkali liquor collecting chamber and used for discharging alkali liquor. And a bubble-free alkali liquor injection opening is also formed in the alkali liquor collecting room and is used for injecting bubble-free alkali liquor to dilute the concentration of gas in the alkali liquor. Examples of the foamless alkali solution are a eutectic of potassium hydroxide and sodium hydroxide, an ionic liquid containing sodium hydroxide, and the foamless alkali solution may also be molten sodium hydroxide. In the power generation mode, the alkali liquor enters the alkali liquor collecting chamber from the outlet of the alkali discharge pipe, and is discharged to an external device (such as a gas separator and an alkali liquor collector) from an alkali liquor discharge port after being collected. In the charging mode, the non-foaming alkali liquor is input into the alkali liquor collecting chamber through the non-foaming alkali liquor injection port, one part of the alkali liquor flows through the outlet of the alkali discharge pipe, oxygen generated by charging in the alkali discharge pipe is taken out in a liquid vortex mode, then the oxygen is discharged from an alkali liquor discharge port on the alkali liquor collecting chamber, and the other part of the alkali liquor is injected into the mixing chamber through the alkali discharge pipe. No matter in the charging state or in the power generation state, when alkali liquor flows through the alkali liquor collecting chamber rapidly, the alkali liquor generates vortex near the outlet of the alkali discharge pipe, so that air bubbles in the alkali discharge pipe can be discharged to the alkali liquor collecting chamber rapidly and then discharged to an external device from an alkali liquor discharge port. The alkali discharge pipe is preferably made into a funnel shape, namely, the alkali discharge pipe can generate vortex at the pipe opening of the alkali liquid collecting room more easily, and bubbles can be taken away with high efficiency.

Further, the sodium ion conductive separator is preferably made of a thin sheet of an inorganic non-metallic material. The diaphragm made of inorganic non-metal material has higher strength, so that the sodium water rechargeable battery has better reliability. Examples of inorganic non-metallic materials are: ceramic materials, glass materials, inorganic single crystal materials, and the like. The thickness of the thin sheet is as thin as possible on the premise of ensuring the strength of the sodium ion conductive diaphragm and the requirement that sodium element can be effectively dissociated into sodium ions. The sodium ion conductive diaphragm made of inorganic non-metallic materials has the advantages of high temperature resistance, alkali corrosion resistance and high strength. One example of the sodium ion conductive membrane made of an inorganic nonmetallic material is a sodium ion conductive membrane made of a Beta alumina ceramic sheet. The main components of the Beta alumina ceramic material are alumina and sodium oxide, and metal oxides such as magnesium, calcium and the like can be added to obtain better ionic conductivity and aging performance. It will be appreciated by those skilled in the art that other types of inorganic non-metallic materials may be used as the sodium ion conductive membrane instead of the Beta alumina made sheet, in addition to the Beta alumina ceramic made sheet as the sodium ion conductive membrane.

Further, in order to ensure uniform and stable thickness of the gap between the gas cathode and the sodium ion conductive membrane, i.e., in order to ensure uniform and stable thickness of the mixing chamber, a spacer is disposed (e.g., … … is manufactured and placed) in the mixing chamber between the gas cathode and the sodium ion conductive membrane. The term "spacer" as used herein refers to an element or combination of elements located between the gas cathode and the sodium ion conductive membrane for maintaining the spacing between the gas cathode and the sodium ion conductive membrane. Three examples of spacers are as follows: A. a plurality of uniformly distributed solid particles in the mixing chamber; B. a mesh or sieve-like spacer disposed in the mixing chamber; C. a structure in which the gas cathode faces the surface of the mixing chamber and is formed into a concavo-convex shape (e.g., a wavy shape) by machining (e.g., milling, molding, calcining, etc.); D. the surface of the sodium ion conductive membrane facing the mixing chamber is formed into a concavo-convex shape (e.g., a wavy shape) by machining (e.g., milling, molding, calcining, etc.). The spacer may also be a combination of the above four examples. It is preferable to attach the gas cathode, the spacer, and the sodium ion conductive separator together and assemble them in the sodium water rechargeable battery of the present invention, so that the thickness of the mixing chamber is uniform and stable.

Further, the gaseous oxidant is gaseous water. The "gaseous water" referred to herein is a gaseous phase of water at any pressure above the boiling point of water at that pressure. Gaseous water functions as the anode material, i.e., the oxidant, of the cell in the sodium rechargeable cell of the present invention. The gaseous water is provided by an external device other than the sodium water rechargeable cell of the present invention. The gaseous water is adopted as the gas oxidant, so that the gaseous water is easier to store than oxygen, is clean and free of impurities compared with air, and can avoid solid phase substances (such as carbon dioxide impurities in the air to generate high-melting-point sodium carbonate) in the alkali liquor; furthermore, the gaseous water is easy to be dissociated into ions compared with oxygen, the manufacturing difficulty of the gas cathode surface catalyst is reduced, and the service life is longer. The use of gaseous water as the gaseous oxidant has the disadvantage that hydrogen is generated in the vicinity of the gas cathode, which reduces the efficiency of the power generation.

Further, the gaseous oxidant may also be gaseous water containing oxygen, which is referred to herein simply as "oxygen water gas". The oxygen-water gas is a mixed gas of gaseous water and oxygen or air. The role of oxygen water gas in the sodium water rechargeable battery of the present invention is as the positive electrode material of the battery, i.e., the oxidant. The oxygen water gas is used as the gas oxidant of the sodium water rechargeable battery, and compared with gaseous water, the oxygen water gas can reduce the discharge of hydrogen and improve the power generation efficiency of the sodium water rechargeable battery. The cost is that oxygen moisture accelerates the corrosion of the carbon-free gas cathode, and the oxygen content also increases the possibility of runaway of the sodium rechargeable battery of the invention. Therefore, the use of oxygen gas as the gas oxidizing agent for the sodium water rechargeable battery of the present invention is more suitable for a stationary sodium water rechargeable battery. Oxygen and water vapor are supplied from an external device other than the sodium water rechargeable battery of the present invention.

Further, an inlet for gaseous water or oxygen and water is made in the bulkhead of the oxidant chamber. So that gaseous water or oxygen water can flow into the oxidant compartment of the present invention.

Further, a sweep gas discharge port is also formed in the wall of the oxidizer tank to discharge the sweep gas in the oxidizer tank. The sweep gas herein includes gaseous species not utilized in the sodium rechargeable battery of the present invention, such as gaseous water, hydrogen, nitrogen, oxygen, and the like.

Further, a fluid sodium port is made in the bulkhead of the fuel tank. So that in the power generation state, external fluid sodium flows into the fuel tank; in the charged state, the fluid sodium is output from the fuel tank to the outside.

Further, a residual sodium discharge port is also manufactured in the bulkhead of the fuel tank. So as to output the residual liquid of the fluid sodium from the fuel tank to the outside. Raffinate of fluid sodium refers to fluid sodium that has been used to have a lower elemental sodium content.

Further, the gas cathode is preferably a carbon-free gas cathode. The term "carbon-free gas cathode" as used herein refers to a gas cathode to which no elemental carbon material is added, such as a gas cathode based on a foamed conductive material with or without a catalyst coating. The carbon-free gas cathode is made of a material in which water vapor or oxygen water vapor is dissociated into hydroxide ions, and is also a selective leakage medium of hydroxide.

The reason why the carbon-free gas cathode is used as the gas cathode of the sodium water rechargeable battery of the present invention is that elemental carbon is easily corroded by gaseous water and oxygen at high temperature. A specific example of a carbon-free gas cathode is the following element containing a large number of open micro-and nano-scale pores, made in a sintered or bonded manner: metal powder sheet, carbide powder sheet, and mixed powder sheet of carbide and metal. Carbon-free gas cathodes allow the presence of carbon compounds, such as binders, organofluorine compounds, organosilicon compounds, carbonates, and the like. The positive electrode can be directly led out from the carbon-free gas cathode, can be led out from a metal net which is in contact with the carbon-free gas cathode, and can also be respectively led out from the gas cathode and the metal net which is insulated from the carbon-free gas cathode. As an example of a method for manufacturing a carbon-free gas cathode mainly made of a foamed metal with a gas-permeable and anti-leakage layer, reference may be made to the manufacturing method described in the specification of CN 106611858A. If the sodium water rechargeable battery of the present invention uses gaseous water as the oxidizing agent, the catalyst layer referred to in CN106611858A is not absolutely necessary because gaseous water is easily ionized. Further, in case that the pressure of the gaseous water or oxygen water is higher than the pressure of the alkali liquor, the permeable waterproof layer called CN106611858A can be discarded.

The principle of the power generation of the sodium water rechargeable battery of the present invention will be described below.

The sodium water rechargeable battery of the present invention, when heated above the melting point of sodium hydroxide, produces the following processes at the anode and cathode, respectively.

a. In the anode area, sodium atoms are ionized at the interface of fluid sodium and the sodium ion conductive membrane, the sodium atoms emit electrons through the negative electrode to form sodium ions, and the sodium ions are diffused into the mixing chamber through the sodium ion conductive membrane. The chemical reaction formula is as follows:

Na→Na⁺+e^-

b. in the cathode area, under the condition that gaseous water is used as a gas oxidant, the gaseous water is dissociated into hydroxyl ions and hydrogen ions in a carbon-free gas cathode, the hydroxyl ions enter a mixing chamber, and sodium hydroxide generated by mixing with sodium ions enters an alkali discharge pipe array from an inlet of the alkali discharge pipe; the electrons obtained by the hydrogen ions on the carbon-free gas cathode through the positive electrode are reduced to generate hydrogen, and the generated hydrogen also enters the alkali discharge pipe array from the inlet of the alkali discharge pipe. And discharging the alkali liquor containing hydrogen from an outlet of the alkali discharge pipe to the alkali liquor collecting room. The chemical reaction formula of the cathode region is:

H₂O+e^-→OH^-+H₂

c. in the cathode area, under the condition of using oxygen water gas as a gas oxidant, the oxygen water gas obtains electrons from the positive electrode through the gas cathode and is reduced and dissociated into hydroxide radicals to enter the mixing chamber, and alkali liquor generated by mixing with sodium ions enters the alkali discharge pipe array from the inlet of the alkali discharge pipe. Further, the alkali liquor is discharged from the outlet of the alkali discharge pipe to the alkali liquor collecting room. The chemical reaction formula of the cathode region is:

2H₂O+O₂+e^-→4OH^-(oxygen-enriched water gas contains sufficient oxygen)

If the oxygen content in the oxygen-containing water gas is insufficient, hydrogen components will be present in the alkali solution.

The electrical energy generated by the sodium water rechargeable battery is respectively extracted from the positive electrode and the negative electrode.

The positive and negative ions generated by the anode and the cathode are mixed in the mixing chamber to generate the alkali liquor mainly containing sodium hydroxide. Depending on the composition of the gaseous oxidizing agent, different substances are produced in the following four cases. The description is as follows:

a. in the case of using gaseous water as the gaseous oxidizing agent, sodium hydroxide and hydrogen gas are mainly formed in the alkaline solution.

b. Under the condition of using oxygen water gas and strictly proportioning the water content and the oxygen content in the oxygen water gas according to a chemical reaction formula, only the sodium hydroxide component exists in the alkali liquor.

c. If the oxygen-containing water is formed by mixing gaseous water and air, and the content of the water and the oxygen are strictly proportioned according to the chemical reaction formula, the alkali liquor mainly contains sodium hydroxide, and possibly has nitrogen components. Since carbon dioxide and other gases contained in the air leak through the gas cathode, there are small amounts of sodium carbonate particles and other components in the lye.

d. If the water content in the gaseous water and the oxygen water is excessive, the water will leak through the gas cathode, and the alkali solution may have water components.

The principle of charging the sodium water rechargeable battery of the present invention is explained below.

The electrochemical process of charging is an electrolytic process. In this case, a reduction reaction occurs in a cathode region corresponding to a negative electrode of the power supply, and an oxidation reaction occurs in an anode region corresponding to a positive electrode of the power supply.

The sodium water rechargeable battery of the present invention has cathode connected to the negative electrode of an external power source, anode connected to the positive electrode of the external power source, voltage over 2.65V and heating to over the melting point of sodium hydroxide, and the following steps are performed separately for the cathode and the anode.

a. In the cathode region, sodium ions in the mixing chamber move to the fuel chamber through the sodium ion conductive diaphragm under the drive of an electric field, electrons are obtained at the interface of the sodium ion conductive diaphragm and fluid sodium in the fuel chamber and are reduced into sodium, and the metal sodium is output to an external device through a fuel inlet and outlet formed in the fuel chamber. The chemical reaction formula is as follows:

Na⁺+e^-→Na

b. in the anode area, near the interface between the carbon-free gas anode and the alkali liquor and near the interface between the alkali discharge pipe array and the alkali liquor, the hydroxyl in the alkali liquor loses electrons and is oxidized, and the generated oxygen and water are carried to the alkali liquor confluence channel by the alkali liquor through the alkali discharge pipe array and are discharged outside through an alkali liquor discharge port. The chemical reaction formula is as follows:

OH^--e^-→O₂+H₂O

the normal operating environment and conditions necessary for the present invention are described below.

In order to ensure the continuous operation of the sodium water rechargeable battery, the fluidity of the alkaline solution must be ensured. The sodium rechargeable battery should therefore operate above the melting point of the lye (the melting point of pure sodium hydroxide is about 319 degrees celsius, but in the presence of moisture, or in the presence of other co-melting compounds such as potassium hydroxide, or in the presence of a foamless lye such as an ionic liquid, the melting point of the lye will be significantly below 319 degrees). When the melting point of the alkali liquor is above, water, hydrogen, oxygen and nitrogen are in gas states. Thus, the lye generally takes on the appearance of a liquid containing bubbles in the continuous normal operation of a sodium-water rechargeable battery.

After the rechargeable sodium water battery is cooled to a temperature lower than the melting temperature of the alkali liquor, the alkali liquor loses fluidity, and the external output current of the rechargeable sodium water battery is reduced. Further, after the temperature is lower than the melting temperature of the fluid sodium, the element sodium is difficult to ionize at the interface of the sodium ion conductive diaphragm, and the current is gradually reduced until the electric energy is basically stopped to generate.

The advantages of the present invention are explained below.

The alkali discharging pipe array penetrating through the gas cathode and the oxidant unit is adopted, so that alkali liquor in the mixing chamber can be smoothly discharged under the condition of not increasing the thickness of the mixing chamber, and a novel fuel cell with low internal resistance, continuity and high power generation can be obtained; in the charging mode, the alkali liquor collecting chamber supplies alkali liquor to the mixing chamber through the alkali discharge pipe array and discharges oxygen generated in the charging process, so that the charging process is continuous and efficient.

In addition, the invention uses gaseous water as the oxidant to avoid the problem that high melting point sodium oxide or sodium peroxide generated by using oxygen as the oxidant blocks the gas cathode; the carbon-free gas cathode is adopted to replace a common gas cathode, so that the problem that the common gas cathode is corroded by water and oxygen at the working temperature of the fuel cell is solved.

Drawings

FIG. 1 is a schematic diagram showing the structure of a sodium water rechargeable battery according to a first embodiment of the present invention.

FIG. 2 is a schematic structural view of a second embodiment of the sodium water rechargeable battery of the present invention.

The fuel cell system comprises a fuel unit 1, a fuel cabin 1a, a fluid sodium 1b, a fluid sodium inlet and outlet 1c, a fluid sodium flow 1d, a residual sodium discharge port 1e, residual sodium 1f, a sodium ion conductive membrane 2, a mixing chamber 3, an alkali liquor 3a, a mixing chamber frame 3b, a carbon-free gas cathode 4, an oxidant unit 5, an oxidant cabin 5a, a gaseous water or oxygen water 5b, a gaseous water or oxygen water 5c, a gaseous water or oxygen water inlet 5d, an external gaseous water or oxygen water 5e, a waste gas discharge port 5f, waste gas 6, an alkali discharge pipe 6a, an alkali discharge pipe inlet 6b, an alkali discharge pipe outlet 6, an alkali liquor collection chamber 7a, a foamless alkali liquor 7b, an alkali liquor 7c, an alkali liquor discharge port 7d, an alkali liquor discharged by an oxidant, a cabin cover plate 7e, a negative electrode 8, a positive electrode 9 and a spacer 10.

Detailed Description

The following describes in detail an embodiment of the sodium water rechargeable battery according to the present invention with reference to the accompanying drawings.

The first embodiment is as follows:

the first embodiment of the present invention will be described below with reference to fig. 1.

The sodium water rechargeable battery is composed of a fuel unit 1, a sodium ion conductive diaphragm 2, a carbon-free gas cathode 4, an oxidant unit 5 and an alkali discharge pipe array 6 x. The negative electrode 8 of the cell is led out from the fuel cell 1 and the positive electrode 9 of the cell is led out from the carbon-free gas cathode 4. Wherein, the fuel unit 1 comprises a fuel tank 1a, and fluid sodium 1b filled in the fuel tank 1 a; the oxidant unit 5 comprises an oxidant chamber 5a and gaseous water or oxygen water gas 5b filled in the oxidant chamber 5 a; a gap is reserved between the carbon-free gas cathode 4 and the sodium ion conductive diaphragm 2 to be used as a mixing chamber 3; the mixing space 3 is filled with lye 3 a.

In the first embodiment of the sodium-water rechargeable battery according to the present invention, the thickness of the mixing chamber 3 is determined by the thickness of the mixing chamber frame 3 b.

The first embodiment of the present invention is described below with reference to fig. 1a, 1b, and 1 c:

FIG. 1a is a front cross-sectional view of the present invention. FIG. 1B is a section A-A of FIG. 1a, and FIG. 1c is a section B-B of FIG. 1 a. As can be seen from fig. 1a, 1b and 1c, the alkali discharge pipe array 6x refers to a collection of alkali discharge pipes 6 passing through the carbon-free gas cathode 4 and the oxidizer unit 5, and conversely, the collection of alkali discharge pipes 6 is referred to as an alkali discharge pipe array 6x in the present invention. A pipe orifice 6a at one end of the alkali discharge pipe 6 is communicated with the mixing chamber 3, the alkali discharge pipe 6 penetrates through the carbon-free gas cathode 4 and the oxidant unit 5, and a pipe orifice 6b at the other end of the alkali discharge pipe 6 is communicated with the alkali liquor collecting chamber 7. The orifice 6a is smaller than the orifice 6b, so that the alkali discharge pipe 6 has a funnel shape. In this embodiment, the alkali exhaust pipe 6 is made of an electrically conductive material (e.g., metal, non-metallic inorganic material including silicon carbide) and is integrated with the carbon-free gas cathode 4.

The first embodiment of the present invention is described below with reference to fig. 1a and 1 d:

fig. 1d is a front view of the oxidant deck plate 7 e. The oxidant cabin cover plate 7e is used for separating the oxidant cabin 5a from the alkali liquor collecting room 7, the space on the left side of the oxidant cabin cover plate 7e is the oxidant cabin 5a, and the space on the right side of the oxidant cabin cover plate 7e is the alkali liquor collecting room 7. The oxidant compartment cover 7e is used for isolating the gaseous water 5b in the oxidant compartment 5a from the lye 3a in the lye collection compartment 7.

The operation of an embodiment of the present invention in the power generation mode is described below with reference to fig. 1:

the invention is heated to above the melting point of the lye 3a in any known manner, for example to 350 ℃. Since the melting point of the fluid sodium 1b is lower than that of the lye, the process fluid sodium 1b heated up is first in a liquid state. The negative electrode 8 and the positive electrode 9 communicate with the negative electrode and the positive electrode of the load, respectively.

When viewed from the fuel unit 1 side, a fluid sodium flow 1d supplied from an external fuel supply system enters the fuel tank 1a through the fluid sodium inlet/outlet 1c to become fluid sodium 1 b. Sodium atoms in the fluid sodium 1b are ionized on the interface of the sodium ion conductive membrane 2 to become sodium ions, and electrons released by the sodium atoms do work outwards through a negative electrode 8 which is electrically connected with the fluid sodium 1 b. The ionized sodium ions enter the sodium ion conductive diaphragm 2, are diffused into the alkali liquor in the mixing chamber 3, and then enter the alkali discharge pipe 6 through the alkali discharge pipe inlet 6 a.

When viewed from the side of the oxidizer unit 5, the externally supplied gaseous water 5d enters the oxidizer tank 5a through the gaseous water inlet 5c to become gaseous water 5b, the gaseous water 5b is ionized into hydrogen ions and hydroxyl ions in the carbon-free gas cathode 4, and the hydroxyl ions enter the mixing chamber 3 and enter the alkali discharge pipe 6 through the alkali discharge pipe inlet 6a to be mixed into sodium hydroxide together with the sodium ions coming from the side of the fuel unit 1. The hydrogen ions in the alkali discharge pipe 6 get electrons from a positive electrode 9 electrically connected with the carbon-free gas cathode 4 and the alkali discharge pipe 6 in the alkali discharge pipe 6 to become hydrogen, and part of the hydrogen gas formed in the mixing chamber 3 also enters the alkali discharge pipe 6 through an alkali discharge pipe inlet 6 a. The lye 3a in the lye discharge pipe 6 then has both a sodium hydroxide component and a hydrogen component. The sodium hydroxide and the hydrogen in the alkali discharge pipe 6 enter the alkali liquid collecting room 7 through an alkali discharge pipe outlet 6b on the outer side of the oxidant cabin cover plate 7 e.

An unfoamed alkali liquid 7b (for example, molten sodium hydroxide, an ionic liquid containing sodium hydroxide) is injected into the alkali liquid collecting space 7 from the unfoamed alkali liquid injection port 7a, the unfoamed alkali liquid 7b forms a vortex near the alkali discharge pipe outlet 6b when the alkali liquid collecting space 7 flows through, and a gas part contained in the alkali liquid 3a in the alkali discharge pipe 6 is discharged to an external device from the alkali liquid discharge port 7c together with a liquid part in the alkali liquid. Examples of external devices are: a gas-liquid separator and an alkali liquor collector.

If the present invention is used as a simple fuel cell, the impurity content of the fluid sodium 1b in the fuel tank 1a may gradually increase after a long power generation process, and eventually become residual sodium 1f deposited on the bottom of the fuel tank. The residual sodium discharge port 1e is used to discharge residual sodium 1f to a device or container other than the present invention in this case to clean the fuel tank 1 a.

A sentence summarizes the above process: after the rechargeable sodium battery in the embodiment is heated to 350 ℃, fluid sodium, gaseous water and foamless alkali liquor are respectively input into corresponding inlets of the rechargeable sodium battery, residual sodium, alkali liquor and waste gas are respectively discharged from corresponding outlets after electrochemical reaction, and positive and negative electrodes output current externally.

The gaseous water in the power generation mode can be directly replaced by oxygen water, and the working process is basically the same except that no hydrogen is generated.

The operation of the sodium water rechargeable battery of the present embodiment in the charge mode is described below.

The present invention is first heated to above the melting point of the lye by any known method, for example to 350 ℃. Because the melting point of the fluid sodium is lower than that of the alkali liquor, the fluid sodium 1b is in a liquid state in the heating process. The negative electrode 8 and the positive electrode 9 are respectively communicated with a negative power supply terminal and a positive power supply terminal of an external power supply to regulate the voltage of the external power supply to be more than 2.65. Preferably, to increase the charge rate, the voltage is preferably adjusted higher by a little, for example 3.5 volts.

In the charging mode, the non-foaming alkali liquor 7b is injected into the alkali liquor collecting chamber 7 from the non-foaming alkali liquor injection opening 7a, when the non-foaming alkali liquor 7b flows through the alkali liquor collecting chamber 7, a part of alkali liquor forms vortex near the alkali discharge pipe outlet 6b, and gas parts (gas sources and components are described in detail below) contained in the alkali liquor 3a in the alkali discharge pipe 6 are taken out and discharged into an external device from an alkali liquor discharge opening 7 c. The other part of the alkali liquor 3a sequentially enters the alkali discharging pipe 6 from the alkali discharging pipe outlet 6b, then enters the alkali discharging pipe inlet 6a and finally enters the mixing chamber 3.

The negative electrode 8 is electrically connected to the fluid sodium 1b, as seen from the fuel cell 1 side. Sodium ions in the alkali liquor 3a entering the mixing room 3 from the inlet 6a of the alkali discharge pipe diffuse to the interface of the fluid sodium 1b and the sodium ion conductive membrane 2, and electrons obtained through an electric path from the negative electrode 8 to the fluid sodium 1b become sodium elements and are dissolved in the fluid sodium 1 b. The above process continues. The volume of the fluid sodium 1b in the fuel compartment 1a then continues to increase with time. The added fluid sodium 1b overflows from the fluid sodium inlet/outlet 1c to form a fluid sodium stream 1d which is output outwards, and the fluid sodium 1b in the fluid sodium stream 1d is stored in an external device by any known method. In the charge mode, the residual sodium discharge port 1e is in a closed state.

The gaseous water inlet 5c is in a closed state as viewed from the oxidant unit 5 side. The hydroxide ions of the foamless alkali liquor which enters the alkali discharge pipe 6 from the alkali liquor collecting pipe 7 through the alkali discharge pipe outlet 6b and does not enter the mixing chamber yet are decomposed into oxygen and water in the alkali discharge pipe 6 after losing electrons from the positive electrode 9 electrically communicated with the carbon-free gas cathode 4, and the formed oxygen and water gas enter the alkali liquor collecting chamber 7 through the alkali discharge pipe outlet 6b along with the vortex formed in the process. Therefore, when the non-foaming alkali liquor 7b injected from the non-foaming alkali liquor injection opening 7a flows through the alkali discharge pipe outlet 6b, the components of oxygen and water are increased, and the alkali liquor collecting room 7 becomes the alkali liquor 3a containing gas. The lye 3a in the lye collection compartment 7 is discharged to the external device through the lye discharge opening 7 c.

As shown in FIG. 1, the space on the left side of the oxidant cover plate 7e is the oxidant compartment 5a, and the space on the right side of the oxidant cover plate 7e is the lye collecting room 7. The oxidant compartment cover 7e is used for isolating the gaseous water 5b in the oxidant compartment 5a from the lye 3a in the lye collection compartment 7.

A sentence summarizes the above process: after the temperature is raised to 350 ℃, and the positive and negative electrodes are respectively connected with corresponding external power supplies, the non-foaming alkali liquor 7b is injected into the sodium water rechargeable battery from the non-foaming alkali liquor injection port 7a, the gaseous water inlet 5c and the waste gas discharge port 5e are closed, the residual sodium discharge port 1e is closed, and the fluid sodium 1b is output to an external device (for example, a sodium storage tank) from the fluid sodium inlet and outlet 1 c. The waste gas-containing alkali liquor 3a is discharged to an external device from the alkali liquor discharge port 7 c. The positive and negative electrodes for the sodium water rechargeable battery of the present invention obtain energy from an external power source.

Example two:

the second embodiment of the present invention will be described below with reference to fig. 2.

The sodium water rechargeable battery is composed of a fuel unit 1, a sodium ion conductive diaphragm 2, a carbon-free gas cathode 4, an oxidant unit 5 and an alkali discharge pipe array 6 x. The negative electrode 8 of the cell is led out from the fuel cell 1 and the positive electrode 9 of the cell is led out from the carbon-free gas cathode 4. Wherein, the fuel unit 1 comprises a fuel tank 1a, and fluid sodium 1b filled in the fuel tank 1 a; the oxidant unit 5 comprises an oxidant chamber 5a and gaseous water or oxygen water gas 5b filled in the oxidant chamber 5 a; a spacer 10 is sandwiched between the carbon-free gas cathode 4 and the sodium ion conductive separator 2, and the gap formed serves as a mixing chamber 3; the mixing space 3 is filled with lye 3 a.

Since the spacer 10 is sandwiched between the carbon-free gas cathode 4 and the sodium ion conductive separator 2, the thickness of the mixing compartment 3 of the sodium water-rechargeable battery of the present invention is determined by the thickness of the spacer 10, as shown in fig. 2. The material used for the spacers 10 must ensure that the size and chemical properties of the spacers remain stable during 350 deg. lye immersion.

The second embodiment of the present invention is described below with reference to fig. 1a, 1b, and 1 c:

FIG. 1a is a front cross-sectional view of the present invention. FIG. 1B is a section A-A of FIG. 1a, and FIG. 1c is a section B-B of FIG. 1 a. As can be seen from fig. 1a, 1b and 1c, the alkali discharge pipe array 6x refers to a collection of alkali discharge pipes 6 passing through the carbon-free gas cathode 4 and the oxidizer unit 5, and conversely, the collection of alkali discharge pipes 6 is referred to as an alkali discharge pipe array 6x in the present invention. A pipe orifice 6a at one end of the alkali discharge pipe 6 is communicated with the mixing chamber 3, the alkali discharge pipe 6 penetrates through the carbon-free gas cathode 4 and the oxidant unit 5, and a pipe orifice 6b at the other end of the alkali discharge pipe 6 is communicated with the alkali liquor collecting chamber 7. The orifice 6a is smaller than the orifice 6b, and the alkali discharge pipe 6 is funnel-shaped. In this embodiment, the soda discharge pipe 6 is made of an inorganic conductive material (e.g., metal, silicon carbide) and is integrated with the carbon-free gas cathode 4.

The second embodiment of the present invention is described below with reference to fig. 1a and 1 d:

fig. 1d is a front view of the oxidant deck plate 7 e. The oxidant compartment cover 7e is located between the oxidant compartment 5a and the lye collection compartment 7. The space on the left side of the oxidant cabin cover plate 7e is an oxidant cabin 5a, and the space on the right side of the oxidant cabin cover plate 7e is an alkali liquor collecting room 7. The oxidant compartment cover 7e is used for isolating the gaseous water 5b in the oxidant compartment 5a from the lye 3a in the lye collection compartment 7.

The difference between the second embodiment of the present invention and the first embodiment is only the determination of the thickness of the spacer 3, the first embodiment uses a frame to determine the thickness of the spacer 3, and the second embodiment uses the spacer 10 to determine the thickness of the spacer 3. In comparison, the spacers 10 are used to determine that the thickness of the compartments 3 is more uniform. It is understood that the operation in the power generation mode and the operation in the charging mode are the same as in the first embodiment, and thus, the description thereof is omitted.

The flat plate structure is a pipe-shaped structure with infinite diameter, and although the principle of the present invention is explained by using the flat plate structure, any ordinary technician having high mathematical basis can change the present invention into the pipe-shaped structure according to the transformation relationship from the flat coordinate to the cylindrical coordinate.

Claims

1. A structure of a rechargeable sodium-water gas fuel cell unit comprises a fuel unit, a sodium ion conductive diaphragm, a gas cathode, an oxidant unit, an alkali discharge pipe array and an alkali liquor collecting chamber; the negative electrode of the cell is drawn from the fuel cell and the positive electrode of the cell is drawn from the gas cathode; the fuel unit comprises a fuel chamber and fluid sodium filled in the fuel chamber, and the oxidant unit comprises an oxidant chamber and a gas oxidant filled in the oxidant chamber; the method is characterized in that:

(1) a gap is reserved between the gas cathode and the sodium ion conductive diaphragm to serve as a mixing chamber, and the inner space of the mixing chamber is filled with alkali liquor;

(2) the alkali discharge pipe array is composed of a plurality of alkali discharge pipes, and the alkali discharge pipes are pipelines which penetrate through the gas cathode and the oxidant unit and are filled with alkali liquor.

2. The rechargeable sodium-water gas fuel cell unit according to claim 1, wherein a spacer is provided between the gas cathode and the sodium ion conducting membrane.

3. The rechargeable sodium-water gas fuel cell unit according to claim 1, wherein the gas cathode is a carbon-free gas cathode.

4. The rechargeable sodium-water gas fuel cell unit according to claim 1, wherein the gaseous oxidant is gaseous water or oxygen water gas.

5. Rechargeable sodium-water gas fuel cell unit according to claims 1, 4, characterised in that an inlet for gaseous water or oxygen water gas is made in the bulkhead of the oxidant compartment.

6. The rechargeable sodium-water gas fuel cell unit according to claims 1, 4 and 5, wherein a residual gas vent is also made in the bulkhead of the oxidant compartment.

7. The rechargeable sodium-water gas fuel cell unit according to claim 1, wherein a fluid sodium access port is made in a bulkhead of the fuel compartment.

8. The rechargeable sodium-water gas fuel cell unit according to claims 1 and 7, wherein a residual sodium drain is also made in the bulkhead of the fuel compartment.