Extrusion die and method for producing lithium-based composites based on an extrusion die

Abstract

The application discloses an extrusion die and a method for preparing a lithium-based composite material based on the extrusion die, the extrusion die comprising a die cavity, an upper press head and a lower press head, the die cavity being composed of an upper cavity, a lower cavity and a central passage communicating the upper cavity and the lower cavity, the upper press head being slidingly arranged in the upper cavity, the lower press head being slidingly arranged in the lower cavity, and the central passage being composed of an upper flared section, an equal-diameter section and a lower flared section connected in sequence; the method for preparing the lithium-based composite material based on the extrusion die comprises the following steps: loading a mixture composed of metallic lithium and micro-nano materials into the upper cavity, extruding downward by the upper press head, making the mixture pass through the central passage from the upper cavity to the lower cavity, extruding upward by the lower press head, making the mixture pass through the central passage from the lower cavity to the upper cavity, continuing the extrusion from top to bottom and the extrusion from bottom to top as a cycle, and repeatedly extruding, so as to obtain the lithium-based composite material.

Description

Technical Field

[0001] This invention relates to an extrusion die and a method for preparing lithium-based composite materials based on the extrusion die, belonging to the field of lithium-based composite material preparation technology. Background Technology

[0002] Metal matrix composites are composite materials formed by artificially combining a metal matrix with dissimilar materials. Typically, this involves mixing powders and then sintering, hot pressing, or extruding. To prevent chemical reactions between the materials or to achieve nanoscale composites, low-temperature extrusion, low-temperature high-energy ball milling, and rapid sintering techniques are used. Low-temperature superposition and pressing, stir welding, and other techniques can also be employed.

[0003] Currently, the most mature systems for low-temperature mechanical composites are aluminum-based and magnesium-based composites. From the perspective of material performance combinations and processing difficulty, the development trend towards highly active and highly ductile metal-based composites should focus on the preparation technologies of calcium, sodium, lithium, and soft rare-earth metal-based composites.

[0004] Lithium-ion batteries are among the most active emerging products in recent decades. While carbon electrodes have solved the safety issues of lithium metal anodes, they have significantly reduced the volumetric and gravimetric capacity of the batteries. Reusing lithium metal as the anode is currently a highly active research area. New lithium-based batteries, lithium-sulfur batteries, and lithium solid-state batteries must also use lithium metal as the anode material to fully utilize their high-capacity characteristics. To improve the safety and stability of lithium metal anodes, current research methods mainly include improving electrolyte formulations to enhance the suppression of lithium dendrites while maintaining high rate capability; introducing conductive frameworks into lithium metal to increase the effective discharge area; and alloying lithium to alter the kinetics of lithium dendrite nucleation. The manufacture of these lithium alloys and composite materials mostly employs high-temperature melting processes. Recent research shows that the SEI film at the lithium-electrolyte interface in lithium metal batteries is composed of organic and inorganic substances generated from the reaction of various components in the electrolyte with lithium. Nano-organic polymers and inorganic compounds added to the electrolyte will appear in the SEI film to regulate lithium dendrite growth. Because of the extremely high reactivity of lithium metal, the use of high-temperature melting methods to prepare lithium alloy materials is severely limited. However, if lithium metal can be mixed with nano-additives at low temperatures, the possibilities for addition can be greatly increased. During the charge-discharge process, the lithium metal anode can control the SEI film from the lithium metal side. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an extrusion die and a method for preparing lithium-based composite materials based on the extrusion die. This invention utilizes the significant shear strain present in the extruded material during cold extrusion to achieve micro- to nano-scale micro-mixing. In a confined space and under compressive stress, the material is protected from external oxidation, and the specially designed flow field ensures uniform and efficient macro-mixing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses an extrusion die, comprising a die cavity, an upper pressure head, and a lower pressure head. The die cavity consists of an upper chamber, a lower chamber, and a central channel connecting the upper and lower chambers. The upper pressure head is slidably disposed in the upper chamber, and the lower pressure head is slidably disposed in the lower chamber. The central channel consists of an upper flared section, a constant diameter section, and a lower flared section connected in sequence. The diameter of the upper flared section gradually increases towards the upper pressure head, and the diameter of the lower flared section gradually increases towards the lower pressure head.

[0008] In a preferred embodiment, the bottom end of the upper pressure head is provided with a first cone adapted to the upper flared section, and the top end of the lower pressure head is provided with a second cone adapted to the lower flared section.

[0009] In actual operation, the inner surface of the mold cavity is polished to a high gloss level.

[0010] In a preferred embodiment, there is a gap of 0.04-0.3mm between the upper pressure head, the lower pressure head and the mold cavity.

[0011] In a preferred embodiment, the taper of the first frustum and the second frustum is 10-45 degrees.

[0012] In a preferred embodiment, the axes of the upper chamber, lower chamber, and central channel coincide.

[0013] This invention discloses a method for preparing lithium-based composite materials based on the above-mentioned extrusion die. A mixture composed of metallic lithium and micro / nano materials is loaded into the upper chamber and extruded downward by an upper pressure head, causing the mixture to move from the upper chamber through the central channel to the lower chamber, completing one top-down extrusion. Then, the mixture is extruded upward by a lower pressure head, causing it to move from the lower chamber through the central channel to the upper chamber, completing one bottom-up extrusion. This cycle of top-down and bottom-up extrusion is repeated to obtain the lithium-based composite material.

[0014] In a preferred embodiment, the micro / nano material is selected from at least one of inorganic compounds, alloy materials, and polymer materials;

[0015] The micro / nano materials used in this invention can be any organic, inorganic non-metallic, or metallic substances that do not react violently with lithium metal and can modulate the structure or morphology of the electrochemical interface. The micro / nano materials selected for this invention do not react with lithium metal to produce gas, and thermodynamic and kinetic evaluations have shown that any exothermic reactions that may occur will not cause the lithium metal to melt.

[0016] In a further preferred embodiment, the nanomaterial is selected from at least one of siloxane micro / nano powder and cellulose filter paper.

[0017] In a preferred embodiment, the micro / nano materials are first subjected to dehydration and degassing treatment.

[0018] In a preferred embodiment, lithium metal and micro / nano materials are premixed uniformly in dry air with a dew point below -40°C or in an argon glove box, and then evenly stacked in the upper chamber.

[0019] In a preferred embodiment, the mass fraction of the micro / nano materials in the mixture is 0.1-30%, preferably 5-20%.

[0020] In a preferred embodiment, mineral oil is applied to the inner side surface of the extrusion die cavity before extrusion.

[0021] In the preferred embodiment, the temperature of the mold cavity is controlled at 40-80℃ during the extrusion process.

[0022] In a preferred embodiment, the extrusion speed is 1-8 mm / s, preferably 1-3 mm / s.

[0023] In a preferred embodiment, the extrusion pressure is 0-200 MPa.

[0024] This invention controls the degree of dispersion between materials and the crushing force on the dispersed phase by controlling the extrusion speed and temperature within the aforementioned range during the extrusion process, thereby obtaining a lithium-based composite material with micron- to nanometer-scale mechanical mixing. However, if the speed is too high, the temperature will increase significantly, causing severe softening of the metallic lithium, greatly reducing the shear pressure within the cavity, and preventing the dispersed phase from being broken up and dispersed.

[0025] In a preferred embodiment, the number of compressions is 50-500 times. More preferably, it is 300-500 times.

[0026] In this invention, a downward extrusion is counted as one instance, and a downward extrusion is also counted as one instance.

[0027] In a preferred embodiment, after extrusion, the material blank is removed in dry air at a dew point below -40°C or in an argon glove box, and the sharp corners of the material blank are rounded (to remove the dead zone where the dispersed phase is prone to aggregation), thus obtaining the lithium-based composite material.

[0028] In a further preferred embodiment, the radius of the fillet is R = 2 mm.

[0029] In practice, the resulting lithium-based composite material can be further processed by forging and rolling according to application requirements.

[0030] Principles and advantages

[0031] This invention employs a specially designed extrusion die to achieve the mixing of metallic lithium and micro / nano additives at low temperatures through extrusion. The preparation method involves first loading the mixture to be extruded into the upper chamber (Cavity A) in a dry and clean environment. The conical extrusion cavity in the upper chamber (Cavity A) is designed to uniformly extrude materials with different properties into the equal-diameter section (Cavity B) with a central channel and a small diameter. This ensures sufficient tensile and shear strain during the transition from a large to a small diameter, resulting in microscopic mixing. The material is then extruded through the small-diameter orifice into the large-diameter orifice into the lower chamber (Cavity C), achieving macroscopic mixing. The resistance between the pressure head and the membrane wall in the lower chamber (Cavity C) ensures that the material remains dense after filling. Due to the large-small-large die cavity design, the material undergoes two processes—one shrinking and one enlarging—in a single extrusion stroke, rather than the single diameter change process typically seen in extrusion. After top-down extrusion, bottom-up extrusion is performed again. Depending on the application requirements, this process is repeated 50-500 times, completing the micro / nano-level low-temperature mechanical mixing process. Because active lithium metal reacts with air to form Li₂O, causing wear on the die, a certain gap is required between the extrusion mandrel and the die cavity. During extrusion, the sliding surface of the extrusion die must be able to slide, and the extruded metal surface must be protected with an oil film. This ensures the extruded material can complete hundreds of extrusions. Controlling the extrusion speed and temperature during extrusion controls the degree of material dispersion and the crushing force on the dispersed phase. After mixing, demolding and removing the material from the edges and corners yields a micron- to nanometer-scale mechanically mixed lithium-based composite material. Attached Figure Description

[0032] Figure 1 A schematic diagram of an extrusion die.

[0033] Figure 2 The surface of the composite lithium metal material obtained by extruding and mixing 10% by mass of siloxane powder with pure lithium is shown in the scanning electron microscope (SEM) image and the corresponding energy dispersive spectroscopy (EDS) image.

[0034] Figure 3 To extrude a hybrid siloxane / lithium composite anode with pure lithium at 1 mA / cm 2 -1 mAh / cm 2 Cyclic diagram of a symmetrical battery under test conditions.

[0035] Figure 4 0.5 mA / cm 2 Lithium stripping down to 5mAh / cm2 Electrode surface morphology: among which Figure 4 (a) is a pure lithium anode. Figure 4 (b) is an extruded mixed filter paper / lithium anode.

[0036] Figure 5 0.5 mA / cm 2 5mAh / cm 2 Then at 0.5mA / cm 2 Deposition 5mAh / cm 2 The surface morphology of the electrode after the process: Figure 5 (a) is a secondary electron image of the surface of a pure lithium anode. Figure 5 (b) is a secondary electron image of the extruded mixed filter paper / lithium hybrid anode. Figure 5 (c) is a backscatter photograph of the extruded mixed filter paper / lithium hybrid anode.

[0037] Figure 6 Cycling performance of lithium-symmetric batteries with extruded hybrid filter paper / lithium anode and pure lithium anode: (Li foil: pure lithium anode, LZLi: extruded hybrid filter paper / lithium anode; left figure shows long-term cycling, right figure shows the first cycle at 0.5 mA / cm²) 2 (Pre-exposed loop diagram after skeleton exposure). Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] As attached Figure 1 An extrusion die includes a die cavity, an upper pressure head, and a lower pressure head. The die cavity consists of an upper chamber (cavity A), a lower chamber (cavity C), and a central channel connecting the upper and lower chambers. The upper pressure head is slidably disposed in the upper chamber, and the lower pressure head is slidably disposed in the lower chamber. The central channel consists of an upper flared section, a constant diameter section (cavity B), and a lower flared section connected in sequence. The diameter of the upper flared section gradually increases towards the upper pressure head, and the diameter of the lower flared section gradually increases towards the lower pressure head.

[0040] As a further improvement to the above technical solution, the bottom end of the upper pressure head is provided with a first cone adapted to the upper flared section, and the top end of the lower pressure head is provided with a second cone adapted to the lower flared section.

[0041] In actual operation, the inner surface of the mold cavity is polished to a high gloss level.

[0042] As a further improvement to the above technical solution, there is a gap of 0.04-0.3mm between the upper pressure head, the lower pressure head and the mold cavity.

[0043] As a further improvement to the above technical solution, the taper of the first and second truncated cones is 10-45 degrees.

[0044] As a further improvement to the above technical solution, the axes of the upper chamber, lower chamber, and central channel coincide.

[0045] An example of obtaining lithium-based composite materials by extrusion using the above-mentioned mold is as follows:

[0046] Example 1

[0047] First, the mold is baked at 120℃ to remove moisture. A layer of sealing lubricating oil film is applied to the side surface of the extrusion head using a felt cloth containing mineral oil. Take 1.8 grams of battery-grade lithium metal sheet and 0.2 grams of siloxane micro / nano powder. Place the lithium sheet and siloxane powder in the extrusion chamber within an argon-filled glove box, attach the extrusion head, seal it with a plastic bag, and remove it. Place it under the press, set the maximum pressure to 50,000 N, and press slowly initially to ensure sufficient venting and internal compaction. Then, inject mineral oil onto the sliding surface of the mold. Afterward, adjust the pressure and extrude at a speed of 2 mm / s. Repeat this process 400 times to complete the mixing process.

[0048] After the mixing process is completed, clean the mold surface, move it into the drying room, loosen the mold, take out the cylindrical alloy billet obtained by extrusion and mixing in the extrusion chamber, clean the billet surface, and set it aside for use.

[0049] Figure 2 The surface electron scanning electron microscope image and corresponding energy dispersive spectroscopy image of the composite lithium metal material obtained by extruding and mixing 10% by mass of siloxane powder with pure lithium show that the extrusion mixing process of this patent can uniformly mix siloxane powder in the lithium metal matrix.

[0050] Figure 3 To extrude a hybrid siloxane / lithium composite anode with pure lithium at 1 mA / cm 2 -1 mAh / cm 2 Cyclic diagram of a symmetrical battery under test conditions (the electrolyte is an ether electrolyte containing 2 wt% LiNO3, SOLi is an extruded mixed siloxane / lithium composite anode, and Li foil is a pure lithium foil);

[0051] Depend on Figure 3It can be seen that the polarization of the pure lithium-ion anode continues to increase after 300 hours. This is because, during cycling, the continued growth of lithium dendrites in the pure lithium-ion anode leads to electrolyte consumption and the continued generation of dead lithium, resulting in a further increase in polarization. In contrast, the SOLi anode can cycle stably up to 1200 hours without a significant increase in polarization. Furthermore, throughout the entire cycling cycle, the polarization of the SOLi anode is consistently lower than that of the pure lithium anode. The polarization of SOLi stabilizes at around 14 mV, while that of pure lithium stabilizes at around 23 mV. This indicates that the composite anode obtained by extruding and mixing siloxane and pure lithium can effectively suppress lithium dendrite growth and reduce battery polarization.

[0052] Example 2

[0053] First, the mold is baked at 120℃ to remove moisture. A layer of oil film containing mineral oil is applied to the side surface of the extrusion cavity. 1.6 grams of battery-grade lithium metal sheet is taken, and 0.4 grams of cellulose filter paper is punched out using a mold of the same size as the lithium sheet. The lithium sheet and filter paper are stacked alternately in the extrusion cavity in an argon-filled glove box. The extrusion head is attached, and the mixture is sealed in a plastic bag and removed. The mixture is placed under a press and pressed at a maximum pressure of 50,000 N. The initial press is performed slowly to ensure sufficient venting and internal compaction. Mineral oil is then injected onto the sliding surface of the mold. The pressure is then adjusted to an extrusion speed of 2 mm / s. This process is repeated 200 times to complete the mixing process.

[0054] After the mixing process is completed, clean the mold surface, move it into the drying room, loosen the mold, take out the cylindrical alloy billet obtained by extrusion and mixing in the extrusion chamber, clean the billet surface, and set it aside for use.

[0055] Figure 4 0.5 mA / cm 2 Lithium stripping down to 5mAh / cm 2 Electrode surface morphology: among which Figure 4 (a) is a pure lithium anode. Figure 4 (b) is an extruded mixed filter paper / lithium anode.

[0056] Figure 5 0.5 mA / cm 2 5mAh / cm 2 Then at 0.5mA / cm 2 Deposition 5mAh / cm 2 The surface morphology of the electrode after the process: Figure 5 (a) is a secondary electron image of the surface of a pure lithium anode. Figure 5 (b) is a secondary electron image of the extruded mixed filter paper / lithium hybrid anode. Figure 5 (c) is a backscatter photograph of the extruded mixed filter paper / lithium hybrid anode.

[0057] From the appendix Figure 4 and attached Figure 5 As shown, through an extrusion mixing process, the cellulose filter paper phase is broken down and uniformly distributed within the lithium matrix. After lithium stripping, stripping pits appear at the uniformly distributed filter paper areas on the negative electrode surface, while pure lithium shows localized stripping, such as... Figure 4 In (a), the yellow circle indicates the unpeeled portion, resulting in an uneven peeling morphology. During subsequent deposition processes, such as... Figure 5 As shown in (a), Li preferentially deposits in the pits left during the previous stripping. Therefore, a large area of ​​the pure lithium anode has no lithium deposition. In the case of filter paper, the deposition area is larger and more uniform, and the lithium is deposited on the filter paper until it is completely covered. Under BSE backscattering, the white phase is the filter paper. Figure 5 The filter paper phases shown sporadically in (c) are all distributed at the edges of the lithium deposition sites, and most of the filter paper has been covered by deposited lithium.

[0058] Figure 6 Cycling performance of lithium-ion symmetric batteries with extruded hybrid filter paper / lithium anode and pure lithium anode: (Li foil: pure lithium anode, LZLi: extruded hybrid filter paper / lithium anode; left figure shows long-term cycling, right figure shows the first cycle at 0.5 mA / cm²) 2 (Pre-exposed loop diagram after skeleton exposure).

[0059] From the appendix Figure 6 As shown, under harsh cyclic conditions (2.5 mA / cm²), 2 -5 mAh / cm 2 Under these conditions, the extruded hybrid filter paper / lithium anode exhibits more stable cycling performance and less polarization.

Claims

1. A method for preparing lithium-based composite materials based on an extrusion die, characterized in that: The extrusion die includes a die cavity, an upper pressure head, and a lower pressure head. The die cavity consists of an upper chamber, a lower chamber, and a central channel connecting the upper and lower chambers. The upper pressure head is slidably disposed in the upper chamber, and the lower pressure head is slidably disposed in the lower chamber. The central channel consists of an upper flared section, a constant diameter section, and a lower flared section connected in sequence. The diameter of the upper flared section gradually increases towards the upper pressure head, and the diameter of the lower flared section gradually increases towards the lower pressure head. The bottom end of the upper pressure head is provided with a first cone-shaped truncated section adapted to the upper flared section, and the top end of the lower pressure head is provided with a second cone-shaped truncated section adapted to the lower flared section. There is a gap of 0.04-0.3mm between the upper pressure head, the lower pressure head and the mold cavity; The taper of the first frustum and the second frustum is 10-45 degrees; A mixture of lithium metal sheets and micro / nano materials is loaded into the upper chamber and extruded downwards by an upper pressure head, causing the mixture to move from the upper chamber through the central channel to the lower chamber, completing one top-down extrusion. Then, the mixture is extruded upwards by a lower pressure head, causing it to move from the lower chamber through the central channel to the upper chamber, completing one bottom-up extrusion. This cycle of top-down and bottom-up extrusion is repeated to obtain the lithium-based composite material. The micro / nano materials are siloxane micro / nano powders or cellulose filter paper. Before extrusion, mineral oil is applied to the inner surface of the extrusion die cavity. During the extrusion process, the temperature of the die cavity is controlled at 40-80℃; The extrusion speed is 1-8 mm / s. The number of compressions is 50-500.

2. The method for preparing lithium-based composite materials based on an extrusion die according to claim 1, characterized in that: The axes of the upper chamber, lower chamber, and central channel coincide.

3. The method for preparing lithium-based composite materials based on an extrusion die according to claim 1, characterized in that: The micro-nano materials are first subjected to dehydration and degassing treatment; The mass fraction of the micro / nano materials in the mixture is 0.1-30%.

4. The method for preparing lithium-based composite materials based on an extrusion die according to claim 1, characterized in that: After extrusion, the material blank is removed in dry air at a dew point below -40°C or in an argon glove box, and the sharp corners of the material blank are rounded to obtain the lithium-based composite material.

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