A high specific energy thermal battery single cell

Abstract

The present invention discloses a high specific energy thermal battery single cell, which is composed of a heating layer, a first molten salt buffer current collector layer, a second molten salt composite positive electrode layer, a third molten salt separator layer, a negative electrode layer and a negative electrode current collector layer. The single cell has a directional pressure relief composite positive electrode layer, a dual heterogeneous thermal buffer material, and a triple heterogeneous functional ring. The first molten salt contains heavy metal element ions Ni that preferentially accept electrons 2+ , and the molar ratio of element F to Br is about 22:47, and the molar ratio n of Cl element is determined by the molar ratio m of cation Ni element, and its value n = 31c + m×2, where m = 1-10. The no-load single cell voltage of the battery is 2-2.6V, and it has strong load capacity in the later stage.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal batteries for chemical power sources, and particularly relates to a high specific energy thermal battery single cell. Background Art

[0002] As a space power source, a thermal battery is an electrochemical system formed by heating molten salt to a molten state using its own heating system. Thermal batteries have the characteristics of high output power, long storage life, and short activation time. Since the current positive electrode materials of thermal batteries are mainly sulfides (Masset Patrick, Guidotti Ronald A. Thermal activated (“thermal”) battery technology: Part IIIb. Sulfur and oxide-based cathode materials [J]. Journal of Power Sources, 2008, 178(1): 456 - 466), sulfides will decompose to produce sulfur vapor at high temperatures, resulting in loss of positive electrode capacity or exothermic side reactions, and in severe cases, it will cause the battery to thermal runaway. Therefore, using molten salt for thermal buffering can effectively reduce the decomposition of sulfides and extend the working time of the battery. In addition, with the development of remote equipment, there is a requirement for thermal batteries with a small initial discharge current and a large terminal current for a long time at the later stage of the load. The positive electrode material is required to provide a relatively high voltage at the initial stage, be no-load in the middle stage, and have high ionic conductivity and electronic conductivity at the later stage. Therefore, positive electrode materials with high conductivity and high thermal shock resistance have become one of the important development directions of thermal batteries.

[0003] In current research, thermal battery single cells are mainly composed of a series-parallel connection of "heating + positive electrode + separator + negative electrode + current collector" single cells. For example, CN202010436675.6 reports a high specific power thermal battery single cell, which is composed of a Cu - CuO - V2O5 positive electrode material + boron nitride fiber composite separator + LiB alloy + Al - Ni heating sheet. CN201811243436.8 proposes a single cell strategy of introducing a small amount of lithium silicon alloy between the lithium boron alloy negative electrode and the separator to construct a dual negative electrode to achieve high capacity output. CN201811610439.0 reports a thermal battery single cell with a hole in the middle. CN201621040160.X reports a single cell with a current limiting ring to prevent the separator and the negative electrode from flowing.

[0004] In existing thermal battery single cells, the classic single cell structure mode can solve most technical problems of medium and short time thermal battery applications. However, with the development of remote equipment, the classic single cell has the following problems:

[0005] 1. The decomposition temperature of the cathode material is low, and the initial thermal shock during activation will cause capacity loss. Generally, sulfides are used as the cathode material, especially pyrite-type iron cobalt nickel disulfide, with a decomposition temperature of 550-650°C. Under the initial high-temperature shock of 1000°C, sulfur vapor will be decomposed, resulting in a more serious thermal effect and exacerbating the material decomposition.

[0006] 2. The internal resistance of sulfides is large in the later stage of discharge, and the large-current load capacity is poor. Since the discharge products of sulfides are transition metal sulfides, such as Z-phase Li3Fe2S4 and Co3S4, the by-products have a large internal resistance and poor electronic conductivity, unable to support the large-current output in the later stage.

[0007] 3. The monomer voltage of sulfides is low. The monomer voltage of pyrite-type sulfides is 2V, while that of tungsten molybdenum sulfides is about 1.5V, which is not conducive to the design and application of high-power batteries, especially the safe output of batteries under high heat.

[0008] 4. The internal stress in the battery stack is large, causing the diaphragm to overflow and the battery to short-circuit. When the thermal battery is activated, the instantaneous high temperature causes the molten salt to melt. Coupled with the thermal expansion and contraction effect, when the height or thickness of the battery is determined, the pressure of the battery stack surges, and the electrolyte in the diaphragm overflows, causing adjacent monomer batteries to overlap and resulting in battery short-circuit. Summary of the Invention

[0009] In view of the characteristics of high heat, easy decomposition of the positive electrode, low monomer voltage of the sulfide positive electrode, large resistance of discharge by-products, poor large-current load capacity, large internal stress and poor safety of high-calorie thermal batteries for long-time end large-current load, the present invention develops a high specific energy thermal battery single cell.

[0010] Firstly, the present invention introduces the heavy metal element nickel into the first molten salt system to increase the melting point of the molten salt, reduce the thermal shock effect of the heating material on the cathode material in the initial activation stage, form the first thermal buffer, and combine with the second molten salt with different chemical components in the composite cathode layer to form the second thermal buffer to prevent the decomposition of the cathode active material. Secondly, the first molten salt in the single cell contains heavy metal element ions Ni 2+ , which can appropriately increase the monomer voltage during the initial small-current or no-load operation, and generate highly conductive metallic nickel by using weak electrochemical action or self-discharge effect, providing a highly active electronic conductive agent for the later electrochemical process of the battery to achieve large-current load output in the later stage. Finally, a triple heterogeneous functional ring is set to prevent the lateral movement of the molten salt or melt, form stress in the axial direction, and by constructing a regular or irregularly oriented pressure relief depression structure with a depth not exceeding the cathode layer on the surface of the composite cathode layer, the first and second molten salts can quickly fill the depression structure after activation, reducing the safety problems and quality reliability problems caused by volume expansion.

[0011] Specifically, the object of the present invention is achieved by the following technical solutions:

[0012] The present invention relates to a high specific energy thermal battery single cell, which is successively composed of a heating layer, a first molten salt buffer current collecting layer, a second molten salt composite positive electrode layer, a third molten salt separator layer, a negative electrode layer and a negative electrode current collecting layer. The first molten salt contains heavy metal element ions Ni that preferentially accept electrons 2+ as well as elements F, Cl, and Br. Since in the activated state of the thermal battery, the first molten salt contains heavy metal Ni 2+ ions, these ions will preferentially accept electrons in the single cell, thereby forming a single cell voltage greater than 2V, thus forming a regulation of the voltage. And Ni 2+ ions accepting electrons will be transformed into highly conductive metallic nickel, that is, the electrochemical product is metallic nickel, which can provide an electron conductive agent for reducing the resistance on the positive electrode side, enabling the battery to carry a larger current in the later stage of discharge.

[0013] As an embodiment, the molar ratio of element F to Br is about 22:47, and the molar ratio n of Cl element is determined by the molar ratio m of cation Ni element, and its value n = 31c + m×2, which is a ratio with a lower melting point, and the value of m is 1 to 10, preferably 1 to 5. When the nickel element ratio m < 1, the difference from the properties of conventional molten salts is small, and it will affect the large current load capacity of the battery in the later stage. When the ratio of nickel element m > 10, solid substances such as NiF2, NiCl2, and NiBr2 will be formed, increasing the melting point and viscosity of the ionic conductive agent. When the nickel element ratio is too large, a muddy melt will be formed, which is not suitable for use as the first molten salt.

[0014] The no-load single cell voltage of the battery is 2 - 2.6V. The single cell has a directional pressure relief composite positive electrode layer, a dual heterogeneous thermal buffer material, and a triple heterogeneous functional ring; among them,

[0015] As an embodiment, the directional pressure relief composite positive electrode layer is mainly provided with regular or irregular directional pressure relief concave structures on the surface of the composite positive electrode layer with a depth not exceeding the positive electrode layer. The concave structures include concave reticular textures, concave holes, concave rings, concave grooves, etc. When the battery is activated, the first and second molten salts will quickly fill the concave structures in the molten state, offsetting or reducing the volume expansion caused by material phase change or temperature change, and improving safety and quality reliability.

[0016] As an embodiment, the dual heterogeneous thermal buffer material reduces the thermal shock impact of the heating material on the positive electrode material in the initial stage of activation through the first molten salt, forming the first layer of thermal buffer, and combining with the second molten salt with different chemical components in the composite positive electrode layer to form the second layer of thermal buffer to prevent the decomposition of the positive electrode active substance;

[0017] As an embodiment, the single cell is provided with a triple heterogeneous functional ring, and the first molten salt is provided with a flexible shaping ring. The flexible shaping ring is made of a flexible material, such as a loose flexible asbestos ring, a loose porous aerogel ring, a loose flexible inorganic fiber ring, etc. It is characterized by chemical inertness, loose and soft texture, and can ensure the integrated molding of the first molten salt by powder pressing. If a flexible shaping ring is not used, it is difficult to mold the first molten salt buffer sheet by powder pressing or the molding rate is low, and the possibility of application in practice is small.

[0018] Since the second molten salt is combined with the positive electrode, there is no need to set a ring.

[0019] The third molten salt is provided with a conventional anti-overflow ring. Generally, a conventional asbestos ring is used to mainly prevent the electrolyte in the diaphragm from flowing at high temperatures.

[0020] The negative electrode is provided with a rigid fixing ring. The material is generally an inorganic material with a dense texture and high hardness, such as mica, aluminum silicate, alumina, asbestos, etc. The rigid fixing ring is mainly used to maintain the negative electrode in a concentric structure, keep a gap between the negative electrode and the ring, prevent the volume expansion of metallic lithium under high temperature and high pressure, and maintain good structural stability to prevent the deformation of the quasi-liquid diaphragm layer and negative electrode layer in the stack.

[0021] As an embodiment, in the single cell, the weight of the heating layer is 30% - 100%, preferably 50% - 80%, of the sum of the masses of the second molten salt composite positive electrode layer, the second molten salt diaphragm layer, and the negative electrode layer. The heating layer uses a Fe-KClO4 heating material. If the dosage is less than 30%, the molten salt may not melt or just melt, with low ionic conductivity and too high internal resistance. If the dosage is greater than 100%, it is easy to cause the decomposition of the positive electrode, the flow of the diaphragm, and the reduction of the stability of the negative electrode, and it is easy to lead to thermal runaway and battery short circuit.

[0022] As an embodiment, the first molten salt buffer current collector (thermal buffer assisted positive electrode current collector) layer is 0.1 - 0.5 mm, the second molten salt composite positive electrode layer is 0.3 - 2 mm, the third molten salt diaphragm layer is 0.3 - 1 mm, and the negative electrode layer is 0.1 - 1 mm. The thickness of each electrode layer is determined according to the capacity design. Each electrode layer can discharge normally regardless of its thickness. If the thickness is too thick, it is easy to cause low heat transfer efficiency, large initial internal resistance, or the need to use too high heat design, reducing the utilization rate of the positive electrode material. If the thickness is too thin, the capacity is low, which is suitable for pulse batteries or short-time power batteries.

[0023] As an embodiment, the first molten salt thermal buffer assisted positive electrode current collector layer is an integrated structure or a layered structure composed of the first molten salt and a highly conductive current collector, and the first molten salt is in direct contact with the positive electrode. The first molten salt can adhere to the highly conductive current collector unilaterally or bilaterally. When adhering unilaterally, it must be in direct contact with the positive electrode to facilitate the utilization of the electrochemical product metallic nickel.

[0024] As an embodiment, the highly conductive current collector is any one or a combination of at least two of gold, silver, copper, nickel, stainless steel, graphite, carbon cloth, and carbon fiber. The structure of the highly conductive current collector is any one or a combination of at least two of sheet, mesh, foam, and other three-dimensional porous structures.

[0025] As an embodiment, the second molten salt composite cathode layer is formed by uniformly mixing 10% - 40% by mass of the second molten salt and 90% - 60% of the cathode active material containing additives or by high-temperature melting. The second molten salt includes molten salt systems composed of LiCl-KCl, LiF-LiCl-LiBr, LiF-LiBr-KBr, LiCl-LiBr-KBr, etc. and other combinations of alkali metal halides.

[0026] As an embodiment, the active material sulfide is the component that provides capacity in the cathode material and is the main substance for the electrochemical reaction. The active material sulfide in the second molten salt composite cathode layer includes any one or a combination of at least two of FeS2, CoS2, NiS2, Fe x Co y S2(x + y = 1), Fe x Co y Ni z S2(x + y + z = 1), WS2, MoS2, and high-entropy disulfides containing iron, cobalt, nickel, chromium, and manganese.

[0027] As an embodiment, the third molten salt separator layer is composed of 30% - 70% of alkali metal halide molten salts such as LiCl-KCl, LiF-LiCl-LiBr, etc. and 70% - 30% of magnesium oxide, aluminum oxide, silicon dioxide, and combined inert oxides.

[0028] As an embodiment, the negative electrode layer is any one or a combination of at least two of LiSi alloy, LiB alloy, LiC alloy, metallic lithium, and its modified materials as the main phase.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The thermal battery single cell prepared by the present invention can regulate the designed voltage with a small current or no-load operation at the initial stage, so that the single cell voltage of the battery exceeds 2V;

[0031] 2) The thermal battery single cell prepared by the present invention reduces the thermal shock impact of the heating material on the cathode material at the initial stage of activation, prevents the decomposition of the cathode active material, and improves the output capacity of the battery;

[0032] 3) The thermal battery single cell prepared by the present invention can generate highly conductive metallic nickel by means of weak electrochemical action or self-discharge effect, providing a highly active electron conductive agent for the later electrochemical process of the battery and realizing high-load output of the large battery in the later stage.

[0033] 4) The thermal battery single cell prepared by the present invention can mitigate the thermal shock and internal stress of the battery stack, forming a thermal buffer and a stress buffer, and improving the safety and reliability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features, objects, and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0035] Figure 1 Schematic structural diagram of the high specific energy thermal battery single cell for Example 1;

[0036] Figure 2 Schematic structural diagram of the composite positive electrode layer with a sunken reticular texture for directional pressure relief in Example 1;

[0037] Figure 3 Discharge curve of the sulfide positive electrode material of the thermal battery for Example 1;

[0038] Figure 4 Schematic diagram of the effect comparison when the composite positive electrode layer in the battery of Example 1 is replaced with a composite positive electrode layer without a sunken reticular texture;

[0039] Figure 5 Test curve of the no-load safety of the thermal battery pack under a high heat state; where 1 is the battery of Example 2 and 2 is a conventional battery;

[0040] Figure 6 Schematic structural diagram of the single cell for Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention will be described in detail below with reference to the embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several adjustments and improvements can be made without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0042] Example 1

[0043] A high specific energy thermal battery single cell ( Figure 1) It is composed of a heating layer, a first molten salt buffer current collector layer, a second molten salt composite positive electrode layer, a third molten salt separator layer, a negative electrode layer, and a negative electrode current collector layer in sequence. The single battery has a directional pressure relief composite positive electrode layer, a dual heterogeneous thermal buffer material, and a triple heterogeneous functional ring. Among them, the first molten salt contains heavy metal element ions Ni that preferentially accept electrons 2+ , the molar ratio of Ni element to Li element is 5:100, and the molar ratio of elements (F:Cl:Br) is 22:41:47. The directional pressure relief composite positive electrode layer is provided with a concave mesh texture ( Figure 2 ). The texture manufacturing method is to introduce a nickel mesh with a size smaller than the electrode plate into the positive electrode layer, and after forming the electrode plate by powder pressing, remove the nickel mesh in the surface layer of the positive electrode to form a concave mesh texture. The molten salt layer of the single battery is provided with a triple functional ring of different materials. The first molten salt is provided with a flexible shaping ring, and the material is flexible, loose and porous asbestos softened by anhydrous ethanol. The third molten salt is provided with a conventional anti-overflow ring, and the material is a mechanically cut asbestos ring. The negative electrode layer is provided with a rigid fixing ring, and a dense mica ring or asbestos ring treated at high temperature is used. In the single battery, the weight of the heating layer is 70% of the sum of the masses of the second molten salt composite positive electrode layer, the second molten salt separator layer, and the negative electrode layer. Among them, the first molten salt thermal buffer auxiliary positive electrode current collector layer is 0.3 mm, the second molten salt composite positive electrode layer is 1 mm, the third molten salt separator layer is 0.5 mm, and the negative electrode layer is 0.4 mm.

[0044] Specifically, the heating layer is a mixture of Fe powder and KClO4 powder with a mass ratio of 84:16. After weighing and powder mixing the Fe powder and KClO4 powder, they can be physically mixed evenly by mechanical or manual sieving. The heating layer is prepared into a circular electrode sheet with a diameter of φ52 by powder cold pressing, the forming pressure is about 9 Mpa, and the pressure is maintained for 10 s.

[0045] The first molten salt buffer (auxiliary positive electrode) current collector layer is an integrated structure composed of the first molten salt and a highly conductive current collector. The side of the current collector layer containing the first molten salt is in direct contact with the positive electrode, and the highly conductive current collector is a stainless steel current collector. During preparation, the first molten salt powder is placed in a φ52 circular mold, flattened, a flexible shaping ring with a diameter of φ52 and a ring width of 2 mm is placed horizontally, a pressing block is placed, and powder cold pressing is carried out on a hydraulic press. The forming pressure is 9 Mpa, and the pressure is maintained for 10 s. After forming, a φ52 first molten salt buffer sheet is obtained. The edge of the φ52 stainless steel current collector sheet is coated with water glass (sodium silicate aqueous solution) with the ring diameter of the flexible ring, and then the molten salt buffer sheet with the ring side is pasted on the stainless steel current collector sheet to obtain the first molten salt current collector layer. The preparation method of the first molten salt powder is as follows:

[0046] S1. Pretreatment: The raw materials containing NiCl2, LiF, LiCl, and LiBr are vacuum-dried at 180 °C for 12 h, transferred into a dry atmosphere with a water oxygen value lower than 1 ppm, and weighed according to the cation-anion ratio for standby. Among them, the halogen molar ratio (F:Cl:Br) is approximately 22:41:47, and the metal molar ratio (Ni:Li) is 5:100.

[0047] S2. Melting roasting: The weighed raw materials of LiF, LiCl, and LiBr are loaded into the bottom of the crucible, then NiCl2 is transferred into the crucible and covered on top of the lithium-containing raw materials, and then transferred into a high-temperature furnace for melting roasting at 550 °C for 4 h to form a uniform melt.

[0048] S3. Ultra-rapid cooling: Pour liquid nitrogen into a stainless-steel basin with a depth of 20 cm to form a liquid-phase gas pool of 10 cm, and then disperse the high-temperature melt through a grid of about 0.5 cm 2 and quickly drip it into the liquid-phase gas pool in a dropwise manner.

[0049] S4. Post-treatment: The molten salt crystal particles obtained after liquid-phase cooling are crushed in the cold state and sieved through 100 meshes to obtain the first molten salt powder.

[0050] The second molten salt composite cathode layer is composed of 18% by mass of the second molten salt, 80% of the cathode active material FeS2, 1% of carbon nanotubes, and the additive Li2O. The preparation method is to weigh the second molten salt, iron disulfide FeS2, and lithium oxide Li2O in proportion, mix them evenly, sinter at 350 °C for 5 h, cool and crush, then pass through a 100-mesh sieve, and then add 1% of carbon nanotubes and mix evenly to obtain the second molten salt composite cathode. Among them, the second molten salt is a eutectic salt of LiCl and KCl with a mass ratio of 45:55. The preparation method is to weigh LiCl and KCl in proportion, mix them evenly, melt at 400 °C for 5 h, cool and crush, and then pass through a 100-mesh sieve to obtain the second molten salt.

[0051] The third molten salt separator layer is composed of 50% of the all-lithium electrolyte (LiF-LiCl-LiBr molten salt) and 50% of magnesium oxide. The all-lithium electrolyte is formed by melting LiF, LiCl, and LiBr with a mass ratio of 9.6:22:68.4 at 450 °C for 10 h. The eutectic mixture is cooled, crushed, and sieved through a 100-mesh sieve. The crushed all-lithium electrolyte and magnesium oxide are proportioned by mass at 1:1, physically mixed, sintered at 350 - 500 °C for 10 h, cooled, crushed, and sieved through a 100-mesh sieve to obtain the third molten salt separator material.

[0052] The second molten salt composite cathode and the third molten salt separator are successively placed in a circular mold and pressed under cold pressing of powder at 9 Mpa for 10 s to prepare a double-layer composite sheet with a diameter of φ52. The layer containing the second molten salt composite cathode is the second molten salt composite cathode layer, and the layer containing the third molten salt separator is the third molten salt separator layer.

[0053] The negative electrode layer is a commercial LiB alloy sheet with a total lithium content of about 60%, a thickness of 0.4 mm, and a diameter of φ48.

[0054] The negative electrode current collector layer uses a circular stainless steel sheet with a diameter of φ52 and a thickness of 0.1 mm. A dense mica ring treated at high temperature is bonded to the current collector layer. The outer diameter of the ring is φ52, and the width of the ring is 2 mm.

[0055] The no-load single-cell voltages of the first molten salt buffer current collector layer single-cell battery and the conventional battery (heating + cathode + separator + anode + current collector, i.e., the heating layer + the second molten salt composite cathode layer + the third molten salt separator layer + the anode layer + the negative electrode current collector layer above) are 2.31 V and 2.05 V respectively. The former has a strong pulse load capacity, and the conventional battery cannot carry a large current. The discharge curve is shown in Figure 3 as shown.

[0056] Comparative Example 1

[0057] As a control for Example 1, the composite cathode layer in the battery is replaced with a composite cathode layer without a concave mesh texture. Due to the influence of thermal shock and molten salt phase change after activation, the internal stress increases, and the battery stack composed of single-cell batteries in series and parallel expands in volume, and the total height increases by 1 - 5 mm. The battery fasteners are deformed, and the battery bulges, presenting a safety hazard. The comparison effect diagram is shown in Figure 4 as shown.

[0058] Example 2

[0059] As a control, the heat design of the single cell in Example 1 was adjusted. Under the condition that the weight of the heating layer was 90% of the sum of the masses of the second molten salt composite positive electrode layer, the second molten salt separator layer, and the negative electrode layer, a single cell with a first molten salt buffer current collector layer and a composite positive electrode layer with a concave reticular texture was formed into a battery pack in a 16-series connection. After activation, an open-circuit test was carried out. Since the heat shock of the heating layer to the positive electrode material was reduced by the first molten salt buffer layer, the decomposition of the positive electrode was reduced, preventing thermal runaway. And because the composite positive electrode layer with a concave reticular texture reduced the internal stress of the battery stack, preventing the overflow of the third molten salt and the molten lithium in the negative electrode, the open-circuit curve of the battery pack was stable, the open-circuit voltage was 37.3 V, and the average single-cell voltage was 2.33 V. While for a conventional battery without the first molten salt buffer current collector layer and without the composite positive electrode layer with a concave reticular texture (heating + positive electrode + separator + negative electrode + current collector, that is, the same heating layer + the second molten salt composite positive electrode layer without a concave reticular texture + the third molten salt separator layer + the negative electrode layer + the negative electrode current collector layer), under a high heat design, the open-circuit voltage of the battery pack was 32.9 V, the average single-cell voltage was 2.05 V, and the battery short-circuited at about 600 s (as Figure 5 ).

[0060] Example 3

[0061] A high specific energy thermal battery single cell ( Figure 6 ) is composed of a heating layer, a first molten salt thermal buffer current collector layer, a second molten salt composite positive electrode layer, a third molten salt separator layer, a negative electrode layer, and a negative electrode current collector layer in sequence. The single cell has a directional pressure relief composite positive electrode layer, a dual heterogeneous thermal buffer material, and a triple heterogeneous functional ring. Among them, the first molten salt contains heavy metal element ions Ni that preferentially accept electrons 2+ , and the molar ratio of Ni element to Li element is 4.5:100, and the molar ratio of elements (F:Cl:Br) is 22:40:47. The directional pressure relief composite positive electrode layer is provided with concave holes, and the manufacturing method is to set protrusions on the bottom of the pressing mold, and form concave holes in the positive electrode layer by powder pressing the pole piece. Different material functional rings are set in the molten salt layer of the single cell. The first molten salt is provided with a flexible shaping ring, the material of which is a flexible porous aerogel softened by ethanol, the second molten salt is provided with a conventional anti-overflow ring, the material of which is asbestos cut mechanically, and the third molten salt is provided with a rigid fixing ring, which is a dense mica ring treated by electric cutting at high temperature. In the single cell, the weight of the heating layer is 72% of the sum of the masses of the second molten salt composite positive electrode layer, the second molten salt separator layer, and the negative electrode layer. Among them, the first molten salt thermal buffer auxiliary positive electrode current collector layer is 0.3 mm, the second molten salt composite positive electrode layer is 0.8 mm, the third molten salt separator layer is 0.3 mm, and the negative electrode layer is 0.3 mm.

[0062] The heating layer is made of a mixture of Fe powder and KClO4 powder in a ratio of 84:16. After weighing and powder blending of the Fe powder and KClO4 powder, they can be physically mixed evenly by mechanical or manual sieving. The heating layer is prepared into a circular electrode sheet with a diameter of φ42.5 by powder cold pressing, and the forming pressure is about 6 Mpa.

[0063] The first molten salt thermal buffer auxiliary positive current collector layer is an integrated structure composed of the first molten salt and a highly conductive current collector. The side of the current collector layer containing the first molten salt is in direct contact with the positive electrode. The highly conductive current collector is a stainless steel current collector, and a copper mesh current collector is embedded in the molten salt. During preparation, a copper mesh with a diameter of φ35 is placed in a circular mold with a diameter of φ42, the first molten salt powder is poured in and leveled, a flexible shaping ring with a diameter of φ42 and a ring width of 2 mm is horizontally placed, a pressing block is placed, and powder cold pressing is carried out on a hydraulic press. The forming pressure is 6 Mpa, and the pressure is maintained for 5 s. After forming, a first molten salt buffer sheet with a diameter of φ42 is obtained. The edge of a φ42 stainless steel current collector sheet is coated with water glass (sodium silicate aqueous solution) with the ring diameter of the flexible ring, and then the molten salt buffer sheet on the side with the ring is pasted on the stainless steel current collector sheet to obtain the first molten salt current collector layer. The preparation method of the first molten salt powder is as follows:

[0064] S1. Pretreatment: The raw materials containing Li2NiCl4, LiF, LiCl, and LiBr are vacuum dried at 200 °C for 8 h, transferred into a dry atmosphere with a water oxygen value lower than 1 ppm, and weighed and reserved according to the cation-anion ratio. The molar ratio of halogens (F:Cl:Br) is about 22:37:47, and the molar ratio of metals (Ni:Li) is 3:100.

[0065] S2. Melting and roasting: The weighed raw materials of LiF, LiCl, and LiBr are loaded at the bottom of the crucible, and then Li2NiCl4 is transferred into the crucible and covered on the upper part of the lithium-containing raw materials. It is transferred into a high-temperature furnace and roasted at 600 °C for 8 h to form a uniform melt.

[0066] S3. Ultra-rapid cooling: Liquid nitrogen is poured into a stainless steel basin with a depth of 15 cm to form a liquid-phase gas pool with a depth of 10 cm, and then the high-temperature melt is dispersed through a grid with a diameter of about 1 cm 2 and quickly dropped into the liquid-phase gas pool in a drip-by-drip manner.

[0067] S4. Post-treatment: The molten salt crystal particles obtained after liquid-phase cooling are crushed in the cold state and sieved through 200 meshes to obtain the first molten salt powder.

[0068] The second molten salt composite cathode layer is formed by high-temperature melting of 18% by mass of the second molten salt, 77% of the cathode active material cobalt disulfide CoS2, and 5% of the electronic conductive additive graphite. The second molten salt includes LiCl-LiBr-KBr. The preparation method is to weigh the second molten salt, cobalt disulfide CoS2, and the electronic conductive additive graphite in proportion, mix them evenly, sinter at a high temperature of 350 °C for 5 h, cool, crush, and pass through a 100-mesh sieve to obtain the second molten salt composite cathode. Among them, the second molten salt is a eutectic salt of LiCl, LiBr, and KBr with a mass ratio of 12.05:36.54:51.41. The preparation method is to weigh LiCl, LiBr, and KBr in proportion, mix them evenly, melt at a high temperature of 400 °C for 5 h, cool, crush, and pass through a 100-mesh sieve to obtain the second molten salt.

[0069] The third molten salt separator layer is composed of 55% of the LiF-LiCl-LiBr molten salt and 45% of magnesium oxide. The all-lithium electrolyte is formed by melting LiF, LiCl, and LiBr with a mass ratio of 9.6:22:68.4 at a high temperature of 450 °C for 10 h. The eutectic is cooled, crushed, and passed through a 100-mesh sieve. The crushed all-lithium electrolyte and magnesium oxide are proportioned by mass at 1:1, physically mixed, sintered at a high temperature of 350 - 500 °C for 10 h, cooled, crushed, and passed through a 100-mesh sieve to obtain the third molten salt separator material.

[0070] The second molten salt composite cathode and the third molten salt separator are successively placed in a circular mold, and a φ42 double-layer composite sheet is prepared by powder cold pressing at 6 Mpa. The layer containing the second molten salt composite cathode is the second molten salt composite cathode layer, and the layer containing the third molten salt separator is the third molten salt separator layer.

[0071] The negative electrode layer is a LiB alloy sheet with a total lithium content of about 60%, a thickness of 0.3 mm, and a diameter of φ38.

[0072] The negative electrode current collector layer uses a φ42 circular stainless steel sheet with a thickness of 0.1 mm. A dense mica ring treated at high temperature is bonded to the current collector layer. The outer diameter of the ring is φ42, and the width of the ring is 2 mm.

[0073] The no-load single-cell voltage of the battery is 2.30 V.

[0074] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A high specific energy thermal battery single cell, characterized in that, The single cell is successively composed of a heating layer, a first molten salt buffer current collector layer, a second molten salt composite positive electrode layer, a third molten salt separator layer, a negative electrode layer, and a negative electrode current collector layer; the first molten salt contains heavy metal element ions Ni that preferentially accept electrons 2+ as well as elements F, Cl, and Br, and the molar ratio of element F to Br is 22:47, and the molar ratio n of Cl element is determined by the molar ratio m of cation Ni element, and its value n = 31c + m×2, where m = 1 to 10.

2. The single cell according to claim 1, characterized in that, The surface of the composite positive electrode layer has a concave structure with regular or irregularly oriented pressure relief, and the depth of the concave structure does not exceed that of the positive electrode layer; the concave structure includes at least one of concave reticular texture, concave holes, concave rings, and concave grooves.

3. The single cell according to claim 1, wherein The single cell is provided with a triple heterogeneous functional ring. The first molten salt buffer current collector layer is provided with a flexible shaping ring, the third molten salt separator layer is provided with a conventional anti-overflow ring, and the negative electrode layer is provided with a rigid fixing ring.

4. The single cell according to claim 1, characterized in that, The weight of the heating layer is 30% - 100% of the sum of the masses of the second molten salt composite positive electrode layer, the third molten salt separator layer, and the negative electrode layer; the first molten salt buffer current collector layer is 0.1 - 0.5 mm, the second molten salt composite positive electrode layer is 0.3 - 2 mm, the third molten salt separator layer is 0.3 - 1 mm, and the negative electrode layer is 0.1 - 1 mm.

5. The single cell according to claim 1, characterized in that, The first molten salt buffer current collector layer is an integrated structure or a layered structure composed of a first molten salt and a highly conductive current collector, and the first molten salt is in direct contact with the positive electrode.

6. The single cell according to claim 5, wherein The highly conductive current collector is any one or a combination of at least two of gold, silver, copper, nickel, stainless steel, graphite, carbon cloth, and carbon fiber; the structure of the highly conductive current collector is any one or a combination of at least two of sheet, net, and foam.

7. The single cell according to claim 1, characterized in that, The second molten salt composite positive electrode layer is uniformly mixed or melted at high temperature by 10% - 40% by mass of the second molten salt and 90% - 60% by mass of the positive electrode active material containing additives; the second molten salt is a molten salt system composed of a combination of alkali metal halides, including at least one of LiCl-KCl, LiF-LiCl-LiBr, LiF-LiBr-KBr, and LiCl-LiBr-KBr.

8. The single cell according to claim 1, wherein The cathode active materials in the second molten salt composite cathode layer include FeS2, CoS2, NiS2, Fe x Co y S2 (x + y = 1), Fe x Co y Ni z S2 (x + y + z = 1), WS2, MoS2, or a combination of any one or at least two of iron-cobalt-nickel-chromium-manganese high-entropy disulfides.

9. The single cell according to claim 1, characterized in that The third molten salt separator layer is composed of 30% - 70% of an alkali metal halide molten salt and 70% - 30% of a combination of one or at least two of magnesium oxide, aluminum oxide, and silicon dioxide; the alkali metal halide molten salt includes LiCl-KCl and LiF-LiCl-LiBr.

10. The single cell according to claim 1, characterized in that, The main phase of the negative electrode layer is any one or a combination of at least two of LiSi alloy, LiB alloy, and LiC alloy.

Images