Molten fluid device with non-brittle solid electrolyte

Abstract

A battery comprising a fluid anode and a fluid cathode separated by a solid electrolyte when at least the electrodes and electrolyte are at operating temperature. The solid electrolyte comprises ions of the anode material forming the fluid anode and has a lower flexibility than solid beta-alumina electrolyte (BASE) ceramics. In one example, the fluid anode comprises lithium (Li), the fluid cathode comprises sulfur (S), and the solid electrolyte comprises lithium iodide (LiI). [Selection diagram] [Figure 1]

Description

Priority claims

[0001] This application claims the benefit of priority to U.S. patent application Ser. No. 15 / 982,475, entitled "Molt Fluid Device with Non-Brittle Solid Electrolyte," filed May 17, 2018, Attorney Docket No. VBC002, which is incorporated herein by reference in its entirety. STATEMENT REGARDING GOVERNMENT-SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Contract No. DE-AC02-06CH11357 awarded by the Department of Energy. The government has certain rights in this invention.

[0003] The present invention relates generally to thermal batteries, and more particularly to methods, devices and systems including molten fluid electrodes and non-brittle solid electrolytes.

[0004] Generally, a battery contains a positive electrode (cathode), a negative electrode (anode), and an electrolyte. Typically, a battery contains current collectors within its electrodes that conduct electrical current to the battery's terminals. Attempts have been made to use fluids as electrodes, where the electrode material is heated and one or both electrodes are maintained in a fluid state. These batteries are often called thermal or high-temperature batteries. For example, the devices are often called liquid-metal batteries and rechargeable liquid-metal batteries. Unfortunately, decades of research and development have not produced a safe and reliable thermal battery utilizing electrochemical combinations with high gravimetric energy densities (kWh / kg), such as sodium-sulfur or lithium-sulfur. [Brief explanation of the drawings]

[0005] It should be understood that the drawings are for illustrative purposes only and do not limit the scope of the appended claims. Further, elements in the drawings are not necessarily to scale, and in the drawings, like reference numerals indicate corresponding parts from different perspectives.

[0006] [Figure 1]1 is a block diagram of an example of a battery including a reaction chamber with fluid electrodes separated by a non-brittle solid electrolyte.

[0007] [Figure 2] 1 is a block diagram of an example of a battery including a reaction chamber with fluid electrodes separated by a solid lithium iodide (LiI) electrolyte.

[0008] [Figure 3] 1 is a flow chart of an example method of operating a fluid electrode battery with a non-brittle solid electrolyte. Detailed Description of the Invention

[0009] Thermal batteries have several advantages over other types of batteries. Their relatively low cost, high energy density, and high power density make them very attractive for some applications. Unfortunately, these devices have safety concerns and have not been widely adopted. Due to their high-energy chemistry, thermal batteries pose a risk of fire and explosion. Conventional thermal batteries are designed to contain two pools of fluid (i.e., molten) materials separated by a third material. If this third material fails and the molten materials mix and react, a huge amount of thermal energy is released in a short period of time. This condition often results in a dangerous fire or explosion. While there has been a demand for safe thermal batteries since the emergence of thermal batteries during World War II, this severe limitation still persists today. Decades of attempts have failed to provide a suitable solution to this problem. For example, some attempts include the use of gravity flow batteries. In these designs, one of the molten active materials is contained in a large reservoir physically located above a smaller reaction chamber, the walls of which are made of a solid electrolyte. On the other side of the solid electrolyte is a large reservoir of another molten active material. If the solid electrolyte were to fail and the two molten active materials were allowed to mix, a solid product formed by the chemical reaction occurring upon their mixing would be expected to restrict the flow of active material from the large reservoir physically located above the other large reservoir of molten active material. However, attempts to design this gravity flow battery failed because the solid product intended to block flow from the upper reservoir did not form into agglomerates capable of blocking flow at the operating temperatures of a thermal battery. Therefore, the design merely delayed the mixing of the two molten active materials, but was insufficient to prevent a thermal runaway event. Other attempts have included chemically modifying the molten active material to a metal halide so that failure of the solid electrolyte would not cause a thermal runaway event. Unfortunately, this technique comes at the cost of reducing the specific energy density (kWh / kg) and volumetric energy density (kWh / l), making thermal batteries a less viable solution for many applications.

[0010] Research into thermal batteries has been hindered by their high risk. For example, in 1993, a major automobile manufacturer developed an electric vehicle fleet using thermal sodium-sulfur batteries. During testing, two vehicles caught fire while charging. The fires led the manufacturer to terminate its thermal sodium-sulfur battery program. Furthermore, despite the significant benefits that safe thermal batteries offer to the electric vehicle and other industries, the U.S. Department of Energy ended support for research into thermal batteries. If the risk of fire could be reduced, the relatively low weight and low cost of thermal batteries would make these devices the clear choice for electric vehicle applications.

[0011] Thermal batteries offer several advantages over other batteries. For example, they exhibit high gravimetric energy density (kWh / kg), high volumetric energy density, high gravimetric power density, and high volumetric power density at low cost. However, conventional thermal batteries with fluid electrodes have significant safety limitations. Electrolyte separators used in conventional thermal batteries include liquid electrolytes, such as molten salts, and brittle solid electrolytes, such as ceramics and glass. Liquid electrolytes are limited in several aspects. For example, during operation, these batteries generate chemical species of the electrode material, which reduces the electrolyte and performance. Ultimately, these by-products in the electrolyte lead to the battery's shutdown. On the other hand, ceramic and glass electrolytes are prone to failure due to their fragile structure. As mentioned above, serious fires and explosions can occur when the solid electrolyte separator breaks and the molten electrode materials come into contact with each other.

[0012] Despite decades of research and development, no thermal battery with fluid electrodes containing a non-brittle, crack-resistant solid electrolyte has yet been proposed. Glass or ceramic solid electrolytes have been the only solid electrolytes proposed for use in thermal batteries with fluid electrodes. These materials have melting points significantly higher than those of the electrodes. As a result, one or both electrode materials can enter the gas phase at temperatures close to the melting point of the glass or ceramic electrolyte.

[0013] The technology described herein maximizes the safety of thermal batteries by separating the fluid electrodes with a relatively non-brittle solid electrolyte. Within the battery's operating temperature range, the electrolyte material has a relatively soft, less brittle solid structure than ceramics and glasses, making it significantly less susceptible to cracking and fracture than conventional thermal batteries. The electrolyte includes cations and anions of the negative electrode material. In the examples herein, the anions are selected to be relatively large and chemically stable with respect to the materials in the reaction chamber. Thus, in embodiments, the anions are stable with respect to the negative electrode material, the positive electrode material, and any species generated from the materials. In the specific examples described below, the negative electrode includes lithium, and the solid electrolyte contains lithium cations (Li + ) and iodide anion (I - ) is LiI. In some circumstances, the electrolyte may contain other elements and additives. Even if the additives have a brittle structure, the overall structure of the solid electrolyte according to the technology described herein is not brittle and is less susceptible to cracking than ceramic and glass electrolytes. By operating the battery at lower temperatures, near the melting point of the LiI electrolyte, the electrolyte becomes softer and less susceptible to cracking and fracture. Applying such technology to electrolyte materials with significantly higher melting points significantly increases the complexity and cost of the battery. This implementation must take into account the increased corrosion of electrode materials in the gas phase and at these high temperatures. Therefore, the example of a lithium-sulfur thermal battery with a solid lithium iodide electrolyte provides a safer and less expensive thermal battery with high energy density for use in various applications, including electric vehicles.

[0014] In the examples described below, the positive and negative electrodes are in a fluid state when the battery is at a temperature within its operating temperature range. However, in some embodiments, one electrode may be in a solid state when the battery temperature is within the operating temperature range. In other words, within the operating temperature range, only the positive or negative electrode is in a fluid state, while the other is solid. Also, in some situations, the operating temperature range may include temperatures at which both electrodes are fluid and temperatures at which only one electrode is fluid. When a material is in a fluid state, it is a fluid; when a material is in a non-fluid state, it is a non-fluid. In the examples described herein, the electrode material transitions from a non-fluid state to a fluid state upon heating. This can be referred to as a molten electrode material and a molten fluid electrode material.

[0015] FIG. 1 is a block diagram of an example battery device 100. It includes a reaction chamber 102 having fluid electrodes 104 and 106 separated by a solid electrolyte 108. FIG. 1 illustrates the general principles of this embodiment but does not necessarily depict the specific shapes, relative dimensions and distances, or other structural details of the components shown. In some situations, structures of two or more blocks can be implemented in a single component or structure. Also, functions described as being implemented in a single block in FIG. 1 may be implemented in another structure.

[0016] As discussed herein, a material is in a fluid state when it has sufficient liquefied permanence to allow it to flow from one region to another. In other words, the viscosity of a fluid material is such that the material can be induced, pumped, or flowed from one region to another. However, a fluid material may have some components that are at least partially solid, while other components are in the liquid phase. Consequently, a fluid material need not necessarily be entirely in the liquid phase. As discussed herein, a material is in a non-fluid state when it is sufficiently solidified to prevent it from flowing. In other words, the viscosity of a material in a non-fluid state is such that the material cannot be induced, pumped, or flowed from one region to another. However, a non-fluid material may have some components that are in the liquid phase while other components are in the solid phase. As referred to herein, a solid electrolyte is any material, mixture, compound, or combination with other materials that forms an electrolyte structure in the solid phase. While the solid electrolyte is in the solid phase within the operating temperature range, the electrolyte material may soften if the temperature approaches its melting point. Therefore, when the solid electrolyte 108 is operated near its melting point and subjected to stress, it can absorb at least some of the energy before fracture and undergoes greater plastic deformation than glasses and ceramics. In other words, the solid electrolyte 108 is softer and exhibits a higher creep rate at the battery's operating temperatures compared to glasses and ceramics.

[0017] The battery 100 includes at least a reaction chamber 102 having an anode region 110 and a cathode region 112 separated from the anode region 110 by a solid electrolyte 108. The anode region 110 includes an anode material 114, and the cathode region 112 includes a cathode material 116. The battery 100 also includes a heating system 118 for sufficiently heating the positive and negative electrode materials within the reaction chamber 102 during operation. The electrode materials 114 and 116 are heated to maintain a fluid state during operation of the battery 100, while the solid electrolyte 108 is maintained in a solid state. This ensures that the operating temperature of the reaction chamber is below the melting point of the solid electrolyte 108. In the example of FIG. 1 , the heating system 118 is an electric heating system including one or more heating elements that facilitate heating the reaction chamber 102 and maintaining the electrode materials 114 and 116 in a fluid state. In some situations, other types of heating systems 118 may be used. The heating system heats the reaction chamber such that the anode material 114 and cathode material 116 are in a fluid state while the solid electrolyte 108 is maintained in a solid state.

[0018] The solid electrolyte 108 includes anions selected such that at least the cations and anions of the anode material 114 are chemically stable with respect to the materials in the reaction chamber 102. Some example anode materials 114 include lithium, sodium, potassium, rubidium, and cesium. Some example anions include chloride, bromide, and iodide anions. Other materials may be used in some situations.

[0019] The fluid anode material 114 in the anode region 110 forms the fluid anode 104 of the battery 100. The fluid cathode material 116 in the cathode region 112 forms the fluid cathode 106 of the battery 100. The fluid electrodes 104 and 106 and electrode materials may include one or more elements. For example, the cathode region 112 may include some reaction products resulting from reactions within the battery 100. A first current collector 120 is disposed within the fluid anode 104, and a second current collector 122 is disposed within the fluid cathode 106. With the current collectors 120 and 122 appropriately positioned within the electrodes 104 and 106, respectively, electrical energy can be harnessed from the electrochemical reactions occurring within the battery between the fluid anode 104 and the fluid cathode 106 via the solid electrolyte 108. Thus, the operation of the reaction chamber 102 in the example of FIG. 1 is similar to that of a conventional thermal battery. However, a notable advantage over conventional thermal batteries is the inclusion of a solid electrolyte, which is much more resistant to cracking and fracture compared to conventional solid electrolytes used in thermal batteries. While solid electrolytes have been proposed, none of the prior art considers the use of solid electrolytes other than ceramic or glass. As discussed above, such brittle electrolyte materials are susceptible to cracking and failure with dangerous consequences.

[0020] Battery device 100 can be implemented using different materials and electrochemical combinations. In the example described below with reference to FIG. 2, the anode includes lithium (Li) and the cathode includes sulfur (S). In another example, a sodium-sulfur (NaS) battery includes a fluid anode including sodium (Na) and a fluid cathode including sulfur (S). Other materials may also be used for the electrodes. Furthermore, in some circumstances, the electrode material may contain a mixture or compound including multiple elements. For example, in some liquid metal batteries, the fluid cathode may be a molten mixture of sulfur and phosphorus.

[0021] The operating temperatures or temperature ranges of the anode and cathode regions can be selected based on several factors, including, for example, the melting point of the anode material, the melting point of the cathode material, the boiling point of the anode material, the boiling point of the cathode material, the eutectic point of the cathode material and the generated chemical species, and the melting point of the solid electrolyte. In the embodiments described herein, the heating system 118 maintains the anode region 110 and the cathode region 112 of the reaction chamber 102 at the same temperature to avoid temperature variations across the solid electrolyte 108. In some circumstances, the two regions of the reaction chamber may be maintained at different temperatures.

[0022] One advantage of the embodiments described herein is that they have a flexible electrolyte material at the battery's operating temperatures, minimizing cracking and fracture. As is well known, materials generally become soft at temperatures near their melting point under stress, increasing their flexibility and creep rate. By including an electrolyte with a melting point not significantly higher than the battery's operating temperature range, the electrolyte remains in solid form while exhibiting good sealing properties and high flexibility. Thus, the electrolyte functions well as a separator, separating and sealing the two fluid electrodes from each other while minimizing the chance of failure due to mechanical vibration or force. This offers significant advantages over conventional electrolyte materials used in thermal batteries with fluid electrodes. Glass electrolytes have melting points of approximately 1,700°C, while BASE ceramics have melting points near 2,000°C. These melting points are significantly higher than the boiling points of electrode materials that exhibit high power and energy density in thermal batteries. As mentioned above, for example, lithium-sulfur thermal batteries exhibit high energy and power density. The boiling point of sulfur is 444.6°C, significantly lower than the melting points of glass and BASE ceramics. Operating a lithium-sulfur battery at temperatures near the melting point of conventional electrolytes leaves the sulfur in the gas phase, complicating the design. However, as illustrated in the examples below, by using electrolyte materials with lower melting points, greater flexibility, and better sealing properties than conventional thermal battery electrolyte materials, the benefits of a thermal lithium-sulfur battery can be realized while minimizing the risk of electrolyte failure.

[0023] FIG. 2 is a block diagram of an example battery 200. It includes a fluidic lithium (Li) anode 202 and a fluidic sulfur (S) cathode 204 separated by a solid lithium iodide (LiI) electrolyte 206. Thus, battery 200 can be referred to as a lithium-sulfur (LiS) battery. This is an example of battery 100 in which the fluidic anode 202 includes lithium, the fluidic cathode 204 includes sulfur, and the solid electrolyte 206 includes lithium iodide (LiI). The diagram in FIG. 2 illustrates the general principles of this example but does not necessarily represent the specific shapes, relative dimensions and distances, or other structural details of the components shown. In some situations, the structure of two or more blocks can be implemented in a single component or structure. Additionally, the functionality described as being implemented in a single block in FIG. 2 may be implemented in another structure.

[0024] In addition to considering melting point, flexibility, and cost, the selection of electrolyte materials for LiS thermal batteries also requires consideration of ionic transport properties and the charge transport properties of lithium, sulfur, and Li2S. m The present inventors have conducted experiments to evaluate the chemical stability of lithium iodide against lithium, sulfur, and Li2S at high temperatures. m It was found to be chemically stable to species.

[0025] The operation of the LiS battery 200 follows that described with reference to the battery 100 of FIG. 1. The heating system 118 maintains the reaction chamber 102 at a suitable temperature to promote the desired reaction between sulfur and lithium via the lithium iodide electrolyte 206. In the example of FIG. 2, the temperatures of the anode region 114 and cathode region 112 are maintained at 400 degrees Celsius (°C). As mentioned above, the operating temperature can be based on several factors, including the properties of the electrode materials and the solid electrolyte. In the example of FIG. 2, some properties that may be considered are the melting point of lithium iodide (469°C), the boiling point of sulfur (444.6°C), and the temperature of the lithium polysulfide product (Li n S m) eutectic melting point (365°C). A temperature range above the eutectic melting point of the lithium polysulfide product but below the melting point of LiI provides a temperature range of 365°C to 469°C that can be used in some situations. Maintaining a temperature below the boiling point of sulfur is useful, providing a range of 365°C to 444°C that can be used in other situations. However, suitable temperature ranges include temperatures of 375°C to 425°C. In still other situations, a wider temperature range of 115.21°C to 469°C can be used. In the examples herein, the temperatures of the anode region 114 and the cathode region 112 are maintained at approximately the same temperature. Another advantage is that such a scheme avoids temperature variations across the solid LiI electrolyte 206. However, in some situations, temperatures may differ between the electrode regions. Other temperature ranges and schemes can be used as long as the electrode material is a fluid and the electrolyte is a solid. As a result, the temperature of the positive electrode region 112 should be above the melting point of sulfur (115.21° C.), and the temperature of the negative electrode region 114 should be above the melting point of lithium (180.5° C.).

[0026] During operation of the battery 200, the reaction may form other compounds or products. For example, in addition to the positive electrode region containing sulfur, this region may also contain di-lithium polysulfide species (LiS m , n is 2 or more) and lithium di-sulfide (LiS). Typically, the reaction across the electrolyte is m (m is an integer greater than or equal to 1), resulting in several different chemical species such as: Any number of chemical species can result, including, for example, the products LiS, LiS, LiS, and LiS, as well as several other situations.

[0027] In some circumstances, additional materials may be added to the positive electrode material and / or the negative electrode material. For example, phosphorus may be included in the positive electrode material. This results in a fluid phosphorus-sulfur positive electrode. Another example of the fluid electrode battery device 100 is a lithium phosphorus-sulfur (LiPS) battery. Thus, in one example, the positive electrode material includes sulfur. In another example, the positive electrode material includes sulfur and phosphorus. Examples of suitable temperature ranges for the reservoir and reaction chamber for a LiPS battery include those described above with reference to the LiS battery 200 of FIG. 2.

[0028] Thus, in the example described with reference to FIG. 2, the fire hazard of a lithium thermal battery was minimized by using a solid lithium iodide (LiI) electrolyte. LiI has a melting point below that of lithium, a melting point of sulfur, and a melting point below that of lithium polysulfide products (Li n S m ) while providing suitable electrochemical properties for use as an electrolyte in lithium thermal batteries, such as LiS batteries. The LiI electrolyte also provides a eutectic melting point well above the eutectic melting point of lithium and sulfur, as well as LiS. m Within the operating temperature range, the LiI electrolyte remains solid, but because its operating temperature is much closer to its melting point, it exhibits more plastic deformation than glass or ceramics like BASE.

[0029] Thus, in some circumstances, the selection of materials and operating temperature ranges for use in thermal batteries is based at least in part on the melting point of the electrolyte material. A useful ratio for the temperature of a material is the corresponding temperature T H The equivalent temperature is the ratio of the absolute temperature of a material to its absolute melting point temperature. The equivalent temperature is very useful because materials behave similarly when heated. For example, when the temperature of a material is much lower than its melting point temperature, the material is typically hard and its creep rate under stress is negligible. However, as the temperature of the material approaches its melting point, the material softens and its creep rate under stress increases. As an example, the equivalent temperatures of BASE and sodium borate glass solid electrolytes in a sodium-sulfur battery operating at 350°C are 0.27 T, respectively.MP and 0.32T MP At these comparable temperatures, BASE and sodium borate glasses are rigid and exhibit negligible creep rates under stress. By selecting a material combination where at least one electrode is fluid and the electrolyte material has an operating temperature that is relatively close to, but below, its melting point, the solid electrolyte is less brittle and more effectively separates and seals the electrode materials from one another. In most situations, the low end of the operating temperature range is at least 35% above the absolute melting point of the solid electrolyte (i.e., the T H is 0.35T MP As the minimum value of the operating temperature range increases, the electrolyte tends to become more flexible and less brittle. Thus, the minimum value may be greater than 50%, 60%, 70%, or 80% of the absolute melting point of the electrolyte (i.e., T H = 0.5T MP , 0.6T MP , 0.7T MP , 0.8T MP In many situations, the maximum operating temperature range may be limited by the boiling point of one of the electrode materials. To avoid the electrodes entering the gas phase, the maximum operating temperature range should be at least lower than the boiling point of the lower of the positive and negative electrode materials. In some situations, the maximum may be less than 98% of the absolute boiling point of the lowest electrode material. In still other situations, the maximum may be less than 95% of the absolute boiling point of the lowest electrode material.

[0030] Applying these relationships to lithium-sulfur batteries, the appropriate operating temperature range follows the one described above. For example, the temperature range of 390°C to 410°C when operating a LiS battery using a solid LiI electrolyte is 89% of the absolute melting point of lithium iodide (i.e., T H = 0.89T MP ) to 95% of the absolute boiling point of sulfur.

[0031] FIG. 3 is a flow chart of an example method of operating a fluid electrode battery. The steps of FIG. 3 may be performed in a different order than shown, and multiple steps may be combined into a single step. Additional steps may be performed, and some steps may be omitted. For example, in many situations, steps 302, 304, and 306 are performed simultaneously. While the method may be performed in any device having suitable structure, components, and materials, the embodiment described with reference to FIG. 3 is performed in a thermal battery, such as battery 100 described with reference to FIG. 1 or battery 200 described with reference to FIG. 2.

[0032] In step 302, the anode material in the negative region of the reaction chamber is heated to bring the anode material into a fluid state. By appropriately heating the negative region of the reaction chamber, a fluid anode is formed from the heated anode material.

[0033] In step 304, the cathode material in the positive region of the reaction chamber is heated to bring the cathode material into a fluid state. By appropriately heating the positive region of the reaction chamber, a fluid cathode is formed from the heated cathode material.

[0034] In step 306, the electrolyte is maintained in a solid state. The reaction chamber is heated to adequately heat the electrode material without melting the electrolyte. Solid electrolytes are in a solid state but are less brittle than glasses and ceramics. Therefore, solid electrolytes exhibit more plastic deformation than glasses and ceramics within the operating temperature range of a thermal battery because the operating temperature is very close to the melting point of the solid electrolyte.

[0035] It should be understood that, depending on the embodiment, certain acts or events of any of the methods described herein may be performed in a different order, added, combined, or entirely excluded (e.g., not all of the described acts or events are required to implement a method). Also, in some examples, acts or events may be performed simultaneously, rather than sequentially or reversely. Furthermore, while certain aspects of the present disclosure are described for clarity as being performed by a single module or component, it should be understood that the functionality described in this disclosure may be performed by any suitable combination of components.

[0036] Clearly, other embodiments and modifications of this invention will occur to those skilled in the art in light of these teachings. The foregoing description is illustrative and not limiting. The present invention is to be limited only by the appended claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. Therefore, the scope of the present invention should be determined not with reference to the above description, but instead with reference to the appended claims and all equivalents thereto.

Claims

1. a fluid anode comprising an anode material, the fluid anode being fluid at least within the operating temperature range of the device, the anode material being selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and combinations thereof; a fluidic cathode that is fluid at least within the operating temperature range of the device; and a solid electrolyte disposed between the fluid anode and the fluid cathode, the solid electrolyte comprising cations of the anode material and anions selected from the group consisting of chlorine, bromine, iodine, and combinations thereof, the solid electrolyte being in a solid state at least within an operating temperature range of the device, the operating temperature range of the device being at least 35% above the absolute melting point of the solid electrolyte; 1. An apparatus comprising:

2. 2. The device of claim 1, wherein the operating temperature range is comprised between 35% of the absolute melting point of the solid electrolyte and 95% of the absolute melting point.

3. 3. The device of claim 2, wherein the operating temperature range is comprised between 50% of the absolute melting point of the solid electrolyte and 95% of the absolute melting point.

4. 4. The device of claim 3, wherein the operating temperature range is comprised between 70% of the absolute melting point of the solid electrolyte and 95% of the absolute melting point.

5. 5. The device of claim 4, wherein the operating temperature range is comprised between 80% of the absolute melting point of the solid electrolyte and 95% of the absolute melting point.

6. 6. The device of claim 5, wherein the operating temperature range is comprised between 89% of the absolute melting point of the solid electrolyte and 95% of the absolute melting point.

7. 2. The device of claim 1, wherein the upper temperature limit of the operating temperature range is lower than the lowest boiling point among the positive electrode boiling point of the fluid positive electrode and the negative electrode boiling point of the fluid negative electrode.

8. 8. The device of claim 7, wherein the upper temperature limit of the operating temperature range is less than 98% of the lowest absolute boiling point among the positive electrode absolute boiling point of the fluid positive electrode and the negative electrode absolute boiling point of the fluid negative electrode.

9. A fluid anode comprising lithium, wherein at least a portion of the fluid anode is a fluid at least within the operating temperature of the device. a fluid cathode comprising sulfur, at least a portion of which is fluid within at least the operating temperature range of the device; and a solid electrolyte disposed between the fluid anode and the fluid cathode, the solid electrolyte comprising cations and anions selected from the group consisting of chlorine, bromine, iodine, and combinations thereof, the solid electrolyte being in a solid state at least within the operating temperature of the device.

1. An apparatus comprising:

10. 10. The device of claim 9, wherein the operating temperature range of the device is comprised between 365°C and 469°C.

11. The device of claim 10, wherein the operating temperature range of the device is comprised between 375°C and 425°C.

12. The device of claim 10, wherein the operating temperature range of the device is comprised between 390°C and 410°C.

13. 10. The device of claim 9, further comprising a heating system arranged and configured to heat the fluid anode, the fluid cathode, and the solid electrolyte to an operating temperature of the device.

14. A fluid anode comprising an anode material, at least a portion of which is fluid at least within the operating temperature range of the device, the anode material being selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and combinations thereof. a fluid cathode, at least a portion of which is fluid within at least the operating temperature range of the device; and an electrolyte disposed between the fluid anode and the fluid cathode, at least a portion of the electrolyte being in a solid state at least within the operating temperature range of the device, the electrolyte comprising cations of the anode material and anions selected from the group consisting of chlorine, bromine, iodine, and combinations thereof; 1. An apparatus comprising:

15. The device of claim 14, wherein the operating temperature range of the device is within the range between 35% of the absolute melting point of the electrolyte and 95% of that absolute melting point.

16. The device of claim 15, wherein the operating temperature range of the device is between 50% of the absolute melting point of the electrolyte and 95% of that absolute melting point.

17. The device of claim 16, wherein the operating temperature range of the device is between 70% of the absolute melting point of the electrolyte and 95% of that absolute melting point.

18. The device of claim 15, wherein the electrolyte comprises lithium iodide (LiI).

19. The device of claim 14, wherein the negative electrode material comprises lithium (Li).

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