Electrolytic cell and method for the production of aluminum-lithium alloys by solid cathode molten salt electrolysis

Abstract

This invention belongs to the field of molten salt electrolysis technology, specifically relating to an electrolytic cell and method for preparing aluminum-lithium alloys by solid-state cathode molten salt electrolysis. The electrolytic cell includes a tank shell, a cover plate, a heat insulation layer, a bottom insulating layer, a cathode liner, an auxiliary heating device, a gas recovery device, an integrally cast irregularly shaped solid aluminum cathode, and an anode. This method uses LiCl as the lithium source and low-temperature chloride molten salts such as NaCl-KCl-LiCl as the electrolyte, electrolyzing at 360–550°C, allowing the deposited metallic lithium to alloy in situ on the surface of the solid aluminum cathode. The cathode has a finned structure to capture floating lithium for further alloying, preventing burn-off. The electrolysis temperature is significantly lower than traditional processes, the lithium content is controllable and the composition is uniform, the lithium yield is high, and the anode chlorine gas is collected and recovered for reuse. This invention has advantages such as low-temperature energy saving, safety and stability, excellent product quality, and environmental friendliness, and is suitable for the large-scale preparation of high-quality aluminum-lithium alloys.

Description

Technical Field

[0001] This invention belongs to the field of molten salt electrolysis technology, specifically relating to an electrolytic cell and method for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis. Background Technology

[0002] Aluminum-lithium alloys, due to their low density, high specific strength, high specific stiffness, and excellent fatigue and corrosion resistance, have become key lightweight materials for structural weight reduction in aerospace and defense industries. Studies show that adding 1% lithium to aluminum alloys can reduce their density by approximately 3% and increase their elastic modulus by approximately 6%. The relentless pursuit of extreme lightweighting in next-generation aircraft, rocket fuel tanks, and satellite structural components makes the demand for high-quality aluminum-lithium alloys increasingly urgent.

[0003] However, lithium is the lightest metallic element in nature and is extremely chemically reactive. Traditional smelting methods, which directly mix and melt pure aluminum and pure lithium, suffer from lithium loss and component segregation, leading to decreased alloy quality and reduced production efficiency. To overcome these inherent defects, aluminum-lithium alloys can also be produced using molten salt electrolysis. This route typically uses a chloride molten salt system as the electrolyte, LiCl as the lithium source, and liquid aluminum as the cathode for electrolytic deposition, allowing lithium to be deposited at the cathode while simultaneously alloying with aluminum in situ. Given that traditional processes require maintaining sufficient fluidity of the molten salt at high operating temperatures and ensuring stable co-deposition of lithium on the liquid aluminum cathode, the electrolysis temperature generally needs to be maintained above 700°C. Furthermore, during electrolysis, if the deposited metallic lithium fails to alloy with the aluminum cathode in time, its density is much lower than that of the molten salt, making it highly susceptible to floating to the electrolyte surface in liquid metal form, where it comes into contact with air or anolyte gas, resulting in severe loss. This not only directly reduces current efficiency and the actual lithium yield, but the floating lithium metal may also form an electronic conductive channel between the anode and cathode, causing local short circuits and seriously threatening the stability and safety of the electrolysis process. These numerous drawbacks have become key bottlenecks restricting the economic viability and large-scale industrial application of this technology. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an electrolytic cell and method for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis. The method is carried out in a temperature range of 360~550℃, using LiCl as raw material, graphite as anode, and integrally cast irregularly shaped solid aluminum as consumable cathode for electrolysis.

[0005] The technical solution of this invention is:

[0006] This invention discloses an electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, comprising: a cell shell, a cover plate, a heat insulation layer, a bottom insulating layer, a cathode liner, an auxiliary heating device, a gas recovery device, an integrally cast solid aluminum cathode, an anode, and an anode guide rod;

[0007] The tank shell forms the outermost layer of the electrolytic cell, and the heat insulation layer is tightly attached to its inner wall; the top of the tank shell is equipped with the cover plate, which has an anode cover plate opening, a cathode cover plate opening and a gas collection device opening.

[0008] The cathode liner includes a cathode side liner and a cathode bottom liner. The cathode bottom liner is connected to the bottom insulation layer and sealed to form a complete cathode liner structure. The cathode side liner is attached to the side wall of the insulation layer, and the bottom insulation layer is located above the bottom of the insulation layer.

[0009] The anode guide rod passes through the anode cover plate opening and is connected to the anode via a threaded or phosphorus iron casting connection; after the connection is completed, the anode cover plate opening is sealed and insulated.

[0010] The gas recovery device is installed at the inlet of the gas collection device;

[0011] The electrolytic cell contains molten electrolyte with a height of 50-90cm. An auxiliary heating device is provided on the side 30-60cm away from the cover plate to precisely control the electrolysis temperature.

[0012] Furthermore, in the aforementioned solid cathode molten salt electrolytic preparation of aluminum-lithium alloy, the electrolytic cell is cylindrical in shape; the cell shell is made of steel plate with a thickness of 5-8 mm; the insulation layer is constructed from one or more of mullite bricks, clay bricks, and alumina bricks, with a thickness of 15-30 cm; the cover plate is a composite structure, with an upper layer of steel plate and a lower layer of insulation material, wherein the insulation material is one of alumina, mullite, or calcium silicate, and the total thickness of the cover plate is 8-15 cm.

[0013] Furthermore, in the aforementioned electrolytic cell for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis, the cathode liner is made of carbonaceous material, the bottom liner of the cathode has a height of 30-80cm and a thickness of 5-8cm, and the carbonaceous material is petroleum coke, graphite, or calcined anthracite; the bottom insulating layer is made of one of corundum, silicon carbide, silicon nitride, or boron nitride, with a thickness of 5-8cm and a height of 10-30cm.

[0014] Furthermore, in the aforementioned electrolytic cell for preparing aluminum-lithium alloys by solid-state cathode molten salt electrolysis, the solid aluminum cathode is an irregularly shaped cathode integrally cast from pure aluminum, comprising a cathode substrate and fins disposed on the top of the cathode substrate; the cathode substrate is a quarter-circular arc-shaped plate structure with a radial thickness of 5-20 cm; the fins have a thickness of 5-10 cm, and the width of the fins along the radial direction of the cathode substrate is greater than the radial thickness of the cathode substrate, and extends 5-20 cm beyond the corresponding side of the cathode substrate on the inner side; the fins are immersed in the molten salt to a depth of 2-3 cm; the circumferential end faces of the cathode substrate are respectively provided with mutually cooperating concave-convex fitting structures, four solid aluminum cathodes of the same shape are disposed, and are sequentially spliced ​​together by the concave-convex fitting structures to form an annular cathode.

[0015] Furthermore, in the aforementioned electrolytic cell for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis, the cover plate is only opened when replacing the anode and cathode or when feeding is performed, and remains closed at other times; after the anode guide rod is connected to the anode, the opening of the anode guide rod is sealed and insulated.

[0016] This invention also discloses a method for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis, using the above-mentioned electrolytic cell, comprising the following steps:

[0017] S1. After the electrolytic cell is built, it is first heated to above 500°C by gas.

[0018] S2. Heat the electrolyte outside the electrolytic cell to the electrolysis temperature until it melts, and then pour it into the electrolytic cell;

[0019] S3. Splice and install the four irregularly shaped solid aluminum cathodes onto the electrolytic cell, seal the electrolytic cell, and turn on the power to carry out electrolysis.

[0020] S4. During the electrolysis process, LiCl raw material is added to the molten electrolyte in molten or solid form every 1 hour according to the current intensity of the electrolytic cell, and the consumable cathode is replaced every 10 to 48 hours.

[0021] S5. As electrolysis continues, the lithium content in the aluminum alloy gradually increases. Once the predetermined target content is reached, the cover is opened to remove the solid aluminum cathode for subsequent melting and casting.

[0022] Furthermore, in the above-mentioned method for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis, the electrolyte is a low-temperature chloride molten salt system with a primary crystallization temperature of 350~500℃. The mass or molar percentage of each substance in the electrolyte is: NaCl: 10~60%, KCl: 10~60%, LiCl: 10~70%, AlCl3: 0~15%, and LiF may be added. During the electrolysis process, the electrolysis temperature is controlled at 360~550℃, and the cathode current density is controlled at 0.5~1.0A / cm².

[0023] Furthermore, in the above-mentioned method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, during electrolysis, the fins of the solid aluminum cathode are immersed in the molten salt to a depth of 2-3 cm; the electrochemically generated metallic lithium first precipitates on the solid aluminum cathode and then reacts with aluminum in situ to form an aluminum-lithium alloy; when some of the metallic lithium that fails to alloy in time floats to the surface, it contacts the aluminum on the surface of the fins and alloys, thus generating an aluminum-lithium alloy in situ.

[0024] Furthermore, in the above-mentioned method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, an oxidation reaction occurs on the anode surface during electrolysis, producing chlorine gas. The generated chlorine gas is collected and temporarily stored by a gas collection device for subsequent harmless treatment or resource utilization.

[0025] Advantages and beneficial effects of the present invention:

[0026] 1. This invention employs low-melting-point chloride molten salt systems with initial crystallization temperatures of 350–500℃, such as NaCl-KCl-LiCl, LiCl-KCl, and LiCl-KCl-AlCl3, combined with a solid aluminum cathode structure, to stably control the electrolysis temperature within the range of 360–550℃, significantly lower than the traditional liquid aluminum cathode molten salt electrolysis method (typically >700℃). Low-temperature operation not only significantly reduces energy consumption but also mitigates the corrosion of the electrolytic cell lining caused by high temperatures, extending equipment lifespan and reducing operating and maintenance costs.

[0027] 2. This invention employs a one-piece cast irregularly shaped solid aluminum cathode, with its finned structure immersed in molten salt only 2-3 cm. Electrolyzed metallic lithium is deposited in situ on the cathode surface and rapidly alloys with aluminum. Even if a small amount of lithium that is not alloyed in time floats to the surface, it will be captured by the aluminum on the fin surface and re-alloyed, fundamentally preventing liquid lithium from floating to the molten salt surface and burning upon contact with air or anode gas. This design significantly reduces unnecessary lithium loss, substantially improves the actual lithium yield, and eliminates the risk of short circuits caused by free lithium, ensuring a safe and stable electrolysis process and significantly improving current efficiency.

[0028] 3. This invention uses solid aluminum as a consumable cathode, and lithium is electrochemically infiltrated layer by layer into the aluminum matrix, with the alloying process proceeding uniformly within the cathode. By adjusting the electrolysis time, cathode current density, and electrolyte composition, the final lithium content in the alloy can be precisely controlled (in the examples, the lithium content reaches 7.56%–8.64%). Compared to the component segregation that easily occurs in traditional melting and alloying methods, the aluminum-lithium alloy obtained by this invention has a uniform composition and good batch stability, meeting the stringent requirements for material consistency in high-end applications.

[0029] 4. During the electrolysis process of this invention, the chlorine gas precipitated by the graphite anode is collected and temporarily stored by a gas collection device. It can be treated harmlessly or used as a chemical raw material for resource utilization, avoiding direct emission and pollution to the environment, and meeting the requirements of green manufacturing and clean production.

[0030] 5. The tank of this invention adopts a sealed cover design, maintaining a tight seal except for changing the anode and cathode and adding materials, effectively isolating air interference. The cathode uses four irregularly shaped pieces that can be quickly assembled through a concave-convex fit, making replacement convenient and allowing for online alternating replacement without affecting continuous electrolysis. The auxiliary heating device provides precise temperature control, further ensuring the stability of the process window. The overall structure is easy to scale up industrially, possessing good economic viability and promising prospects for widespread application. Attached Figure Description

[0031] Figure 1 This is a front view of the electrolytic cell structure of the present invention;

[0032] Figure 2 This is a top view of the electrolytic cell structure of the present invention;

[0033] Figure 3 This is a top view of the internal structure of the electrolytic cell of the present invention;

[0034] Figure 4 This is the 3D structure of the aluminum cathode of the present invention;

[0035] Among them, 1-solid aluminum cathode, 2-anode, 3-anode cover plate opening, 4-anode guide rod, 5-gas collection device opening, 6-cathode cover plate opening, 7-cathode side lining, 8-cover plate, 9-tank shell, 10-insulation layer, 11-molten electrolyte, 12-cathode bottom lining, 13-partial insulation layer, 14-auxiliary heating device. Detailed Implementation

[0036] like Figure 1-4 As shown, in a specific embodiment of the present invention, an electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis is provided, comprising: a cell shell 9, a cover plate 8, a heat insulation layer 10, a bottom insulation layer 13, a cathode liner, an auxiliary heating device 14, a gas recovery device, an integrally cast solid aluminum cathode 1, an anode 2, and an anode guide rod 4.

[0037] The tank shell 9 forms the outermost layer of the electrolytic cell, and the heat insulation layer 10 is tightly attached to its inner wall; the top of the tank shell 9 is equipped with the cover plate 8, and the cover plate 8 has an anode cover plate opening 3, a cathode cover plate opening 6 and a gas collection device opening 5.

[0038] The cathode liner includes a cathode side liner 7 and a cathode bottom liner 12. The cathode bottom liner is connected to the bottom insulation layer 13 and sealed to form a complete cathode liner structure. The cathode side liner 7 is attached to the side wall of the insulation layer 10, and the bottom insulation layer 13 is located above the bottom of the insulation layer 10.

[0039] The anode guide rod 4 passes through the anode cover plate opening 3 and is connected to the anode 2 by means of thread or phosphor iron casting; after the connection is completed, the anode cover plate opening 3 is sealed and insulated.

[0040] The gas recovery device is located at the inlet 5 of the gas collection device;

[0041] The electrolytic cell contains molten electrolyte 11 with a height of 50-90cm. An auxiliary heating device 14 is provided on the side at a distance of 30-60cm from the cover plate 8 to precisely control the electrolysis temperature.

[0042] The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis described above is cylindrical in shape; the cell shell 9 is made of steel plate with a thickness of 5-8 mm; the insulation layer 10 is constructed of one or more of mullite bricks, clay bricks, and alumina bricks with a thickness of 15-30 cm; the cover plate 8 is a composite structure with a steel plate as the upper layer and an insulation material as the lower layer, wherein the insulation material is one of alumina, mullite, or calcium silicate, and the total thickness of the cover plate is 8-15 cm.

[0043] The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis described above has a cathode liner made of carbonaceous material. The bottom liner 12 of the cathode has a height of 30-80 cm and a thickness of 5-8 cm. The carbonaceous material is petroleum coke, graphite, or calcined anthracite. The bottom insulating layer 13 is made of one of corundum, silicon carbide, silicon nitride, or boron nitride, with a thickness of 5-8 cm and a height of 10-30 cm.

[0044] The above-mentioned electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, wherein the solid aluminum cathode 1 is made of pure aluminum material and integrally formed by casting process, wherein the pure aluminum is primary aluminum obtained by electrolysis; the solid aluminum cathode 1 has an irregular structure and is provided with fins, the fin thickness being 5~10cm; a total of four cathodes are set in a single electrolytic cell, each cathode having the same shape and being spliced ​​and connected by a concave-convex mating structure. The solid aluminum cathode 1 is an irregularly shaped cathode integrally cast from pure aluminum, comprising a cathode substrate and fins disposed on the top of the cathode substrate; the cathode substrate is a quarter-circular arc-shaped plate structure with a radial thickness of 5-20 cm; the fins have a thickness of 5-10 cm, and the width of the fins along the radial direction of the cathode substrate is greater than the radial thickness of the cathode substrate, and extends 5-20 cm beyond the corresponding side of the cathode substrate on the inner side; the fins are immersed in molten salt to a depth of 2-3 cm; the two circumferential end faces of the cathode substrate are respectively provided with mutually cooperating concave-convex fitting structures, and four solid aluminum cathodes of the same shape are disposed thereon, and are sequentially spliced ​​together by the concave-convex fitting structures to form an annular cathode.

[0045] In the above-mentioned electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, the cover plate 8 is only opened when changing the anode and cathode or when adding materials, and is kept closed at other times; after the anode guide rod 4 is connected to the anode 2, the opening of the anode guide rod is sealed and insulated.

[0046] The following detailed description is provided in conjunction with specific embodiments.

[0047] Example 1

[0048] An electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis includes: a cell shell 9, a cover plate 8, a heat insulation layer 10, a bottom insulation layer 13, a cathode liner, an auxiliary heating device 14, a gas recovery device, an integrally cast solid aluminum cathode 1, an anode 2, and an anode guide rod 4.

[0049] The tank shell 9 forms the outermost layer of the electrolytic cell, and the heat insulation layer 10 is tightly attached to its inner wall; the top of the tank shell 9 is equipped with the cover plate 8, and the cover plate 8 has an anode cover plate opening 3, a cathode cover plate opening 6 and a gas collection device opening 5.

[0050] The anode guide rod 4 passes through the anode cover plate opening 3 and is connected to the anode 2 by means of thread or phosphor iron casting; after the connection is completed, the anode cover plate opening 3 is sealed and insulated.

[0051] The gas recovery device is located at the inlet 5 of the gas collection device;

[0052] The electrolytic cell contains molten electrolyte 11 with a height of 60cm. An auxiliary heating device 14 is provided on the side at a distance of 40cm from the bottom of the cover plate 8 for precise control of the electrolysis temperature.

[0053] The electrolytic cell is cylindrical in shape; the cell shell 9 is made of steel plate with a thickness of 8mm; the insulation layer 10 is constructed of one or more of mullite bricks, clay bricks, and alumina bricks, with a thickness of 20cm; the cover plate 8 is a composite structure with a steel plate on the upper layer and an insulation material on the lower layer, wherein the insulation material is calcium silicate, and the total thickness of the cover plate is 8cm.

[0054] The cathode liner includes a cathode side liner 7 and a cathode bottom liner 12. The cathode bottom liner is connected to the bottom insulation layer 13 and sealed to form a complete cathode liner structure. The cathode side liner 7 is attached to the side wall of the insulation layer 10, and the bottom insulation layer 13 is located above the bottom of the insulation layer 10.

[0055] The cathode liner is made of carbonaceous material. The bottom liner 12 of the cathode is 30cm high and 5cm thick. The carbonaceous material is calcined anthracite. The bottom insulating layer 13 is made of corundum, with a thickness of 5cm and a height of 10cm.

[0056] The solid aluminum cathode 1 is integrally formed from pure aluminum through a casting process. The pure aluminum is primary aluminum obtained by electrolysis. The solid aluminum cathode 1 has an irregular structure, including a cathode substrate and fins disposed on the top of the cathode substrate. The cathode substrate is a quarter-circular arc-shaped plate structure with a radial thickness of 10 cm. The fins are 5 cm thick, and the width of the fins along the radial direction of the cathode substrate is greater than the radial thickness of the cathode substrate, and extends 5 cm beyond the corresponding side of the cathode substrate on the inner side. The fins are immersed in molten salt to a depth of 2 cm. The two circumferential end faces of the cathode substrate are respectively provided with mutually cooperating concave and convex structures, and four solid aluminum cathodes 1 of the same shape are disposed and sequentially spliced ​​together by the concave and convex structures to form a ring cathode.

[0057] In the above-mentioned electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, the cover plate 8 is only opened when changing the anode and cathode or when adding materials, and is kept closed at other times; after the anode guide rod 4 is connected to the anode 2, the opening of the anode guide rod is sealed and insulated.

[0058] Example 2

[0059] This embodiment provides a method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, using the electrolytic cell described in Example 1. The electrolyte system is prepared with 59LiCl-41KCl (mol%), and the initial crystallization temperature of this system is approximately 380℃. The specific steps include:

[0060] After the electrolytic cell is constructed, it is first heated to 500℃ using gas. Then, the electrolyte is heated to the electrolysis temperature of 400℃ outside the cell and melted before being poured into the cell. Four irregularly shaped cathodes are then assembled and installed on the cell. The cell is sealed, and electrolysis is initiated by applying electricity. LiCl raw material is added to the molten electrolyte in molten or solid form every hour. During electrolysis, the electrolysis temperature is controlled at 400℃, and the current density inside the anode lining is 0.7 A / cm². 2 The electrolysis time was 10 hours, and after the cathode was removed, the mass percentage of lithium was measured to be 7.56%.

[0061] Example 3

[0062] This embodiment provides a method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, using the electrolytic cell described in Example 1. The electrolyte system is prepared with 56.05LiCl-38.95KCl-5AlCl3 (mol%), and the initial crystallization temperature of this system is approximately 360℃. The specific steps include:

[0063] After the electrolytic cell is constructed, it is first heated to 500℃ using gas. Then, the electrolyte is heated to the electrolysis temperature of 370℃ outside the cell and melted before being poured into the cell. Four irregularly shaped cathodes are then assembled and installed on the cell. The cell is sealed, and electrolysis is initiated by applying electricity. LiCl raw material is added to the molten electrolyte in molten or solid form every hour. During electrolysis, the electrolysis temperature is controlled at 370℃, and the current density inside the anode lining is 0.7 A / cm². 2 The electrolysis time was 48 hours, and the cathode was replaced every 12 hours. After the cathode was removed, the mass percentage of lithium was measured to be 8.64%.

[0064] Example 4

[0065] This embodiment provides a method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, using the electrolytic cell described in Example 1. The electrolyte system is prepared with 56.05LiCl-38.95KCl-LiF (mol%), and the initial crystallization temperature of this system is approximately 400℃. The specific steps include:

[0066] After the electrolytic cell is constructed, it is first heated to 500℃ using gas. Then, the electrolyte is heated to the electrolysis temperature of 420℃ outside the cell and melted before being poured into the cell. Four irregularly shaped cathodes are then assembled and installed on the cell. The cell is sealed, and electrolysis is initiated by applying electricity. LiCl raw material is added to the molten electrolyte in molten or solid form every hour. During electrolysis, the electrolysis temperature is controlled at 420℃, and the current density inside the anode lining is 0.7 A / cm². 2 The electrolysis time was 40 hours, and the cathode was replaced every 10 hours. After the cathode was removed, the mass percentage of lithium was measured to be 8.45%.

[0067] Example 5

[0068] This embodiment provides a method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, using the electrolytic cell described in Example 1. The electrolyte system is prepared with 56LiCl-36KCl-8NaCl (mol%), and the initial crystallization temperature of this system is approximately 370℃. The specific steps include:

[0069] After the electrolytic cell is constructed, it is first heated to 500℃ using gas. Then, the electrolyte is heated to the electrolysis temperature of 380℃ outside the cell and melted before being poured into the cell. Four irregularly shaped cathodes are then assembled and installed on the cell. The cell is sealed, and electrolysis is initiated by applying electricity. LiCl raw material is added to the molten electrolyte in molten or solid form every hour. During electrolysis, the electrolysis temperature is controlled at 380℃, and the current density inside the anode lining is 0.7 A / cm². 2 The electrolysis time was 20 hours, and the cathode was replaced every 10 hours. After the cathode was removed, the mass percentage of lithium was measured to be 8.12%.

Claims

1. An electrolytic cell for preparing aluminum-lithium alloys by solid cathode molten salt electrolysis, characterized in that, include: Tank shell (9), cover plate (8), insulation layer (10), bottom insulation layer (13), cathode liner, auxiliary heating device (14), gas recovery device, integrally cast solid aluminum cathode (1), anode (2) and anode guide rod (4); The solid aluminum cathode (1) is an irregularly shaped cathode integrally cast from pure aluminum material, including a cathode substrate and fins disposed on the top of the cathode substrate; the cathode substrate is a quarter-circular arc-shaped plate structure with a radial thickness of 5-20 cm; the fins have a thickness of 5-10 cm, and the width of the fins along the radial direction of the cathode substrate is greater than the radial thickness of the cathode substrate, and extends 5-20 cm beyond the corresponding side of the cathode substrate on the inner side; the fins are immersed in molten salt to a depth of 2-3 cm; the cathode substrate has interlocking concave-convex structures on both circumferential end faces, and four solid aluminum cathodes (1) of the same shape are disposed, and are sequentially spliced ​​together through the concave-convex structures to form an annular cathode; The tank shell (9) forms the outermost layer of the electrolytic cell, and the inner wall is tightly fitted with the heat insulation layer (10); the top of the tank shell (9) is fitted with the cover plate (8), and the cover plate (8) has an anode cover plate opening (3), a cathode cover plate opening (6) and a gas collection device opening (5). The cathode liner includes a cathode side liner (7) and a cathode bottom liner (12). The cathode bottom liner is connected to the bottom insulation layer (13) and sealed to form a complete cathode liner structure. The cathode side liner (7) is attached to the side wall of the insulation layer (10), and the bottom insulation layer (13) is located above the bottom of the insulation layer (10). The anode guide rod (4) passes through the anode cover plate opening (3) and is connected to the anode (2) by means of thread or phosphorus iron casting; after the connection is completed, the anode cover plate opening (3) is sealed and insulated. The gas recovery device is located at the inlet (5) of the gas collection device; The electrolytic cell contains molten electrolyte (11) with a height of 50-90cm. An auxiliary heating device (14) is provided on the side at a distance of 30-60cm from the cover plate (8) to precisely control the electrolysis temperature.

2. The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 1, characterized in that: The electrolytic cell is cylindrical in shape; the cell shell (9) is made of steel plate with a thickness of 5-8 mm; the insulation layer (10) is made of one or more of mullite bricks, clay bricks, and alumina bricks with a thickness of 15-30 cm; the cover plate (8) is a composite structure with a steel plate on the upper layer and an insulation material on the lower layer. The insulation material is one of alumina, mullite, or calcium silicate, and the total thickness of the cover plate is 8-15 cm.

3. The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 1, characterized in that: The cathode liner is made of carbonaceous material. The bottom liner (12) of the cathode has a height of 30~80cm and a thickness of 5~8cm. The carbonaceous material is petroleum coke, graphite or calcined anthracite. The bottom insulating layer (13) is made of corundum, silicon carbide, silicon nitride or boron nitride, with a thickness of 5~8cm and a height of 10~30cm.

4. The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 1, characterized in that: The solid aluminum cathode (1) is integrally formed by casting process using pure aluminum material. The pure aluminum is primary aluminum obtained by electrolysis. The solid aluminum cathode (1) has an irregular structure with fins. The fin thickness is 5~10cm. A total of four cathodes are set in a single electrolytic cell. Each cathode has the same shape and is spliced ​​and connected by a concave-convex mating structure.

5. The electrolytic cell for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 4, characterized in that: The cover plate (8) is only opened when the anode and cathode are replaced or when the material is added, and is kept closed at other times. After the anode guide rod (4) is connected to the anode (2), the opening of the anode guide rod is sealed and insulated.

6. A method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis, characterized in that, The electrolytic cell according to any one of claims 1 to 5 comprises the following steps: S1. After the electrolytic cell is built, it is first heated to above 500°C by gas. S2. Heat the electrolyte outside the electrolytic cell to the electrolysis temperature until it melts, and then pour it into the electrolytic cell; S3. Splice and install four irregularly shaped solid aluminum cathodes (1) onto the electrolytic cell, seal the electrolytic cell, and turn on the power to carry out electrolysis; S4. During the electrolysis process, LiCl raw material is added to the electrolyte in molten or solid form every 1 hour according to the current intensity of the electrolytic cell, and the consumable cathode is replaced every 10 to 48 hours. S5. As electrolysis continues, the lithium content in the aluminum alloy gradually increases. Once the predetermined target content is reached, the cover plate (8) is opened to remove the solid aluminum cathode (1) for subsequent melting and casting.

7. The method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 6, characterized in that: The molten salt electrolyte is a low-temperature chloride molten salt system with an initial crystallization temperature of 350~500℃. The mass or molar percentage of each substance in the electrolyte is: NaCl: 10~60%, KCl: 10~60%, LiCl: 10~70%, AlCl3: 0~15%, and LiF may be added. During electrolysis, the electrolysis temperature is controlled at 360~550℃, and the cathode current density is controlled at 0.5~1.0A / cm².

8. The method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 6, characterized in that: During electrolysis, the fins of the solid aluminum cathode (1) are immersed in the molten salt to a depth of 2-3 cm. Electrochemically generated metallic lithium is first deposited on the solid aluminum cathode (1) and then reacts with aluminum to form an aluminum-lithium alloy in situ. When some metallic lithium that fails to alloy in time floats to the surface, it comes into contact with the aluminum on the surface of the fin and alloys, forming an aluminum-lithium alloy in situ.

9. The method for preparing aluminum-lithium alloy by solid cathode molten salt electrolysis according to claim 6, characterized in that: During the electrolysis process, an oxidation reaction occurs on the surface of the anode (2) and chlorine gas is produced. The generated chlorine gas is collected and temporarily stored by a gas collection device for subsequent harmless treatment or resource utilization.

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