Lithium composite and method for producing the same

Abstract

The present invention provides a lithium composite and a method for producing the same, which is tape-shaped and includes a structural layer, a stress-balancing layer located on at least one surface of the structural layer and having a patterned metallic lithium and / or lithium alloy and a thickness of 0.1 to 1 μm, and a lithium membrane having a width of 185 to 1500 mm, a uniform thickness of 0.5 to 30 μm, and a thickness tolerance of 20% or less, the lithium membrane being combined with the structural layer via the stress-balancing layer to form the lithium composite.

Description

[Technical Field]

[0001] The present invention relates to the field of energy storage technology, and more particularly to an ultra-thin and ultra-wide lithium composite usable in secondary batteries and a method for manufacturing the same. [Background technology]

[0002] Lithium batteries, with their advantages of high energy density, long cycle life, and wide operating temperature range, are widely used in fields such as aerospace, computers, mobile communications devices, robotics, and electric vehicles. With the development of society and advances in science and technology, demands for higher energy density and cycle life for lithium batteries are increasing. However, conventional lithium-ion batteries, which use only graphite as the anode, no longer meet these expectations. Therefore, the development of new cathode and anode materials with higher specific capacity is necessary. For the anode material, metallic lithium is ideal. Lithium metal has a high specific capacity (3860 mAh / g, 10 times that of graphite anodes) and the lowest redox potential (-3.04 V vs. standard hydrogen potential). The use of metallic lithium as the anode significantly improves the specific energy of the battery, enabling lithium-ion batteries to be used in a wider range of applications.

[0003] Currently, commercially available lithium-ion batteries use lithium-containing cathode materials (e.g., lithium cobalt oxide, lithium iron phosphate, ternary materials, etc.). The lithium contained in the cathode already meets the charge / discharge requirements of lithium-ion batteries. The anode only needs to provide a small amount of lithium to compensate for lithium loss during cycling and guide the deposition of lithium ions on the cathode, significantly improving the battery's energy density. The amount of lithium required in the anode is very small; typically, lithium membranes for batteries only require a thickness of 0.5 microns to 30 microns. Furthermore, to be compatible with conventional lithium-ion batteries, the width requirements for metallic lithium anodes are high. This is particularly true for current blade batteries, where the width requirements for the anode are extremely high. Conventional metallic lithium anodes cannot be made both ultrathin and ultrawide. Given this, a technology is needed to enable ultrathin and ultrawide metallic lithium anodes. Summary of the Invention

[0004] The inventors unexpectedly discovered that for a lithium composite comprising an ultrathin (thickness of 30 microns or less) metallic lithium film and a structural layer, by properly balancing the stress between the ultrathin lithium film and the structural layer, it is possible to produce an ultrathin and ultrawide metallic lithium composite (wherein the lithium film has a thickness of 30 microns or less and a width of 150 mm or more, e.g., 185 mm or more). By constructing a patterned metallic lithium and / or lithium alloy stress-balancing layer on the structural layer, stress accumulation within the lithium film during the rolling process is alleviated to some extent, making the lithium film less likely to deform during the combining process, and making it possible to produce a lithium composite with a wider, thinner, and more uniform lithium film (e.g., 1-5 microns). Based on these findings, the present invention was completed.

[0005] Accordingly, one aspect of the present invention provides a lithium composite, the lithium composite being in the form of a tape, comprising a structural layer and a stress-balancing layer located on at least one surface of the structural layer, the stress-balancing layer comprising patterned metallic lithium and / or a lithium alloy, the stress-balancing layer having a thickness of 0.1 to 1 μm; a lithium membrane having a width of 185 to 1500 mm, a uniform thickness of 0.5 to 30 microns, and a thickness tolerance of within 20% of the thickness; Equipped with The lithium film is combined with the structural layer via the stress balancing layer to form the lithium composite.

[0006] The lithium composite of the present invention is a composite strip comprising an ultrathin and ultrawide lithium film, which may be continuous or discontinuous, with or without through-holes, supported by a structural layer (copper foil substrate), and whose width and thickness are adjustable (stress balancing layer and pressure control).

[0007] In the present invention, the lithium film is a uniform film, that is, the lithium film has a perfect film shape (no obvious wrinkles or deformations, and has clean boundaries) and has a uniform thickness.

[0008] In the present invention, the lithium film may be continuous or discontinuous in the longitudinal or width direction.

[0009] Optionally, the intermittent lithium film in the longitudinal direction has a metallic lithium layer area length ranging from 1 to 2000 mm and a blank area length ranging from 1 to 200 mm.

[0010] Optionally, the widthwise discontinuous lithium film has a width of the metallic lithium layer area of ​​1 to 200 mm and a spacing between the metallic lithium layers of 0.5 to 10 mm.

[0011] Optionally, the surface of the lithium film of the lithium composite may be shiny and metallic silver-white, the lithium content may be 99.90 to 99.95%, and the lithium element content of the lithium film body (inside) may be 99.95 to 99.99%. The thickness of the lithium film may be in the range of 0.5 to 30 microns, preferably 1 to 20 microns, more preferably 10 microns or less, and most preferably 1 to 5 microns, and the thickness tolerance may be within 20% of the thickness, preferably within 15%.

[0012] Optionally, the lithium film is lithium and / or various alloys of lithium, including alloys of lithium with one or more of silicon, magnesium, aluminum, indium, boron, tin, gallium, yttrium, silver, copper, lead, bismuth, sodium, carbon, germanium, titanium, chromium, cobalt, tungsten, iron, niobium, nickel, gold, barium, cadmium, cesium, calcium, manganese, nitrogen, platinum, sulfur, thallium, strontium, tellurium, zinc, antimony, zirconium, where the content of lithium in the lithium alloy may be 70% or more, or even 90% or more.

[0013] Optionally, the stress-balancing layer comprises a patterned lithium metal and / or lithium alloy, the patterned lithium metal and / or lithium alloy being in a striped pattern or array formed of elongated or linear lithium metal and / or lithium alloy, the elongated or linear lithium metal and / or lithium alloy having a width of 0.5-5 mm and a spacing distance of 1-3 mm between the stripes, and the array comprising an equilateral polygonal array having sides ≥ 3 and a side length of 2-15 mm.

[0014] Optionally, the ratio of the area of ​​the equilateral polygonal lithium metal and / or lithium alloy to the area of ​​the gap in the stress balancing layer is 1.2 to 20, preferably 2 to 6, and optionally the ratio of the width of the striped lithium and / or lithium alloy to the spacing distance is 1 / 4 to 3, preferably 1 / 3 to 1.5.

[0015] Optionally, the structural layer material is the metallic material copper or a single or multi-layer composite copper-organic material, wherein the organic material is at least one of polyethylene terephthalate, polypropylene, polyvinyl chloride, and polyimide.

[0016] Optionally, the structural layer has a thickness of 3.5 to 20 microns, preferably 3.5 to 10 microns, and more preferably 3.5 to 6 microns.

[0017] Optionally, the interface between the structural layer and the metallic lithium is stress balanced, preferably by vapor deposition of metallic lithium onto the interface between the structural layer and the metallic lithium.

[0018] Another aspect of the present invention provides a method for producing the above-mentioned lithium composite, the method comprising the steps of: forming a pattern of metallic lithium and / or a lithium alloy on a structural layer by pressure compounding, spraying, dip-transfer coating, extrusion coating, scraper coating, curtain coating, screen printing, vapor deposition, or vapor deposition to obtain a stress-balancing layer; and rolling a metallic lithium strip having a thickness of 5 to 2000 μm as a raw material, to compound the metallic lithium strip on the stress-balancing layer, thereby obtaining the lithium composite.

[0019] Optionally, the method for manufacturing the lithium composite employs a roll-to-roll continuous manufacturing process.

[0020] Optionally, the thickness of the metallic lithium strip is 10 to 100 μm, preferably 10 to 50 μm.

[0021] Optionally, the rolling includes cold rolling, hot rolling or combined rolling, and the temperature range of the hot rolling is controlled to be 60-120°C, and in combined rolling, preferably hot rolling is followed by cold rolling.

[0022] Optionally, the pressure range of the rolling is 0.1 to 150 MPa, preferably 80 to 120 MPa.

[0023] Optionally, the contact stress between the ultrathin and ultrawide lithium film and the structural layer is controlled by controlling the stress balancing layer.

[0024] Optionally, the rolling roller has an anti-adhesion material on its surface, and the anti-adhesion material includes polyethylene, polyformaldehyde, silicone polymer, or ceramics.

[0025] Optionally, winding is performed using rollers with a maximum tension range of 0.1-10N, and the support rollers are themselves powered.

[0026] By controlling the rolling process, the present invention can obtain an ultra-thin and ultra-wide lithium membrane composite in a simple process. This composite has high specific energy, and when applied to the anode of a lithium battery, it has the effect of improving the energy density, thereby achieving a high energy density of the battery. Because the metallic lithium anode has a high gram-specific capacity, it can be applied to high-energy batteries, and the battery energy density can exceed 450 wh / kg.

[0027] As commercially available batteries become larger in size, the width of the lithium metal anode required also becomes wider. Ultra-wide, ultra-thin lithium membranes fit the development trend of currently available batteries. The present invention allows for the simple mass production of ultra-wide, ultra-thin lithium metal composites. Ultra-thin lithium metal anodes are suitable for current high-gram capacity cathodes and do not cause the problems of excess lithium and dendrites.

[0028] The bonding of metallic lithium to a current collector has been a major challenge in the industry, as perfect bonding is extremely difficult, resulting in poor current collection and poor battery rate characteristics. The ultra-thin and ultra-wide metallic lithium composite of the present invention effectively solves these problems, and by introducing a patterned stress balancing layer, the metallic lithium and the structural layer can be tightly bonded together. Furthermore, when the patterned layer is metallic lithium, no other impurity elements are introduced into the final product. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram of a process for producing a continuous ultrathin and ultrawide lithium composite by pressure compounding according to the present invention. [Figure 2]Figure 2 is a schematic diagram of an ultrathin and ultrawide lithium composite that is discontinuous in the width direction. [Figure 3] Figure 3 is a schematic diagram of an ultrathin and ultrawide lithium composite that is discontinuous in the longitudinal direction. [Figure 4] Figure 4 is a schematic diagram of the intermittent ultrathin and ultrawide lithium composite manufacturing apparatus. [Figure 5] FIG. 5 shows a schematic diagram of the patterning (stripes) in the stress-balancing layer of the present application. [Figure 6] FIG. 6 shows a schematic diagram of patterning (triangles) in another stress-balancing layer of the present application. [Figure 7] FIG. 7 shows a schematic diagram of patterning (squares, checkerboard) in yet another stress-balancing layer of the present application. [Figure 8] FIG. 8 shows a diagram of the 5 micron thick ultra-thin and ultra-wide lithium composite product produced in Example 1 of the present application. [Figure 9] FIG. 9 shows a diagram of a 5 micron thick discontinuous ultra-thin and ultra-wide lithium composite product produced in Example 2 of the present application. [Figure 10] FIG. 10 shows a diagram of the 5 micron thick ultra-thin and ultra-wide lithium composite product produced in Comparative Example 2 of the present application. [Figure 11] FIG. 11 shows the electrochemical performance diagram of the 5 micron-thick ultra-thin and ultra-wide lithium composite product prepared in Example 1 of the present application. [Explanation of symbols]

[0030] P structure layer L metallic lithium layer PL (continuous) lithium foil PNL Intermittent Lithium Foil H Lithium layer or alloying layer DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more apparent, the present invention will be described in more detail below with reference to the drawings and examples. It will be understood that the specific examples described in this specification are merely for the purpose of interpreting the present invention and are not intended to limit the present invention. In addition, the technical features of each embodiment of the present invention described below may be combined with each other as long as they are not inconsistent with each other.

[0032] FIG. 1 shows a schematic diagram of a process for producing a continuous ultrathin and ultrawide lithium composite by the pressure compounding method of the present invention. As shown in FIG. 1, metallic lithium strip and a structural layer strip (pre-patterned) having a stress-balancing layer are used as raw materials. They are unwound by an unwinding device, which includes at least a metallic lithium strip unwinding roller 11 and two unwinding support rollers 12 for supporting the unwound metallic lithium strip and structural layer strip, respectively. After passing through the unwinding support roller 12, the raw lithium strip and structural layer strip enter a rolling mill 20, which includes at least one pair of rolling rollers 21 and an anti-adhesion coating layer 22 on the rolling rollers 21. The rolling pressure of the rolling mill 20 and the roller gap between the rolling rollers 21 are finely adjustable. The material of the anti-adhesion coating layer 22 on the rolling roller 21 may be one or more selected from the group consisting of polyethylene, polyformaldehyde, silicone polymer, ceramics, etc. The structural layer strip and the lithium strip are combined by pressure combining to form an ultra-thin, ultra-wide lithium composite product. A winding device is provided at the exit side of the rolling mill 20, and the winding device includes at least a support roller 31, a tension control roller 32, and a winding roller 33. Among them, the support roller 31 has a power and can draw the ultra-thin, ultra-wide lithium composite forward with a small pulling force. The tension control roller 32 can move up and down or swing, and can not only control the tension of the preform but also control the winding speed of the winding roller 33 according to the height or swing angle of the tension control roller 32.

[0033] Figure 2 is a schematic diagram of a discontinuous lithium film in the width direction, and Figure 3 is a schematic diagram of a discontinuous lithium film in the length direction.

[0034] 4 shows an apparatus for manufacturing an intermittent lithium foil. The apparatus includes an unwinding device 100, a scraping device 200, and a winding device 300, and further includes a control device (not shown) for controlling the winding speed and the operation interval of the scraping device. Among these, the unwinding device 100 includes an unwinding shaft 101, a magnetic powder brake 102, an unwinding support roller 104, an unwinding deviation correction detection sensor 105, and an unwinding deviation correction device 103. The scraping device 200 includes a scraper 201, a scraper driving device 202, a scraper pad 203, and support rollers (204, 205). The winding device 300 includes a winding shaft 301, a winding motor 302, a winding deviation correction device 303, a winding support roller 304, and a winding deviation correction detection sensor 305. Furthermore, a length measuring sensor 401 may be provided.

[0035] The unwinding shaft 101 on the unwinding device 100 is used to unwind the lithium foil PL, and a magnetic powder brake 102 connected to the unwinding shaft 101 can control the magnitude of the unwinding tension. The unwinding support roller 104 supports the lithium foil PL so that it enters the scraping device 200 at a constant inclination angle and the unwinding deviation correction detection sensor 105 accurately detects the deviation of the lithium foil PL. The support rollers 204 / 205 on the scraping device 200 ensure that the inclination angle of the strip entering the device is constant, regardless of the influence of other process steps. The scraper pad 203 supports the lithium foil PL and keeps it flat. The scraper drive device 202 drives the scraper 201 to move rapidly up and down. The winding device 300 includes a winding shaft 301 and a winding motor 302. The winding shaft 301 is used for intermittently winding the lithium foil PNL, and the winding shaft 301 is driven by a winding motor 302 .

[0036] The specific method and process flow are as follows: Battery-grade lithium foil PL with a substrate support is attached and fixed to unwinding shaft 101. The lithium foil PL passes sequentially through unwinding support roller 104, unwinding deviation correction detection sensor 105, scraper support rollers 204 and 205, winding deviation correction detection sensor 305, and winding support roller 304, and is then wound onto winding shaft 301 and fixed. The device is started, and winding motor 302 on winding device 300 is operated to rotate winding shaft 301, causing the lithium foil PL to pass through scraper 200 from the unwinding device 100 side and be wound. During the winding process by the winding device 300, the scraper drive device 202 in the scraping device 200 is controlled to move the scraper 201 up and down intermittently, scraping off part of the metallic lithium layer on the lithium foil PL to form an intermittent lithium foil PNL, and the width and number of the scrapers are controlled to produce an intermittent lithium film in the width direction.

[0037] Figure 5 shows a schematic diagram of a stripe-patterned stress-balancing layer of the present application, Figure 6 shows a schematic diagram of a triangle-patterned stress-balancing layer of the present application, and Figure 7 shows a schematic diagram of a square-patterned stress-balancing layer (checkerboard pattern) of the present application. [Example]

[0038] The present invention will be described in more detail below by way of examples using the above process equipment. The structural parameters of various products, various reactants and process conditions used in the following examples are all typical examples, but the inventors have conducted extensive testing and verified that other structural parameters, other types of reactants and other process conditions than those listed above can also be applied, and the technical effects claimed by the present invention can also be achieved.

[0039] Example 1: A metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm was used, along with an 8-micron-thick copper foil (a 0.4-micron-thick strip of metallic lithium was deposited on the surface of the copper foil as a stress-balancing layer, with a lithium width (specifically, 3 mm) to spacing ratio of 1.5). Using an unwinding and rewinding device, the pressure was controlled at 80 MPa by cold rolling to obtain an ultra-thin, ultra-wide lithium composite product with a metallic lithium thickness of 5 microns (with a thickness tolerance of ±0.5 microns). Figure 8 shows the ultra-thin, ultra-wide lithium composite product. As can be seen from Figure 8, the ultra-thin, ultra-wide lithium film has a perfect film shape.

[0040] Example 2 A metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm was used, along with an 8-micron-thick copper foil (a square grid-shaped lithium-magnesium alloy was deposited on the surface of the copper foil as a stress-balancing layer (thickness: 0.1 μm), with a lithium width (width: 0.5 mm), a side length of 3 mm, and an area ratio of 2.25). Hot rolling was performed using an unwinding, winding, and scraping device at a temperature of 80°C under a pressure of 100 MPa to obtain an ultra-thin and ultra-wide lithium composite product (e.g., Figure 9) with a lithium layer thickness of 5 microns (thickness tolerance: ±0.5 microns).

[0041] Example 3 A metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 800 mm was used, along with a copper foil with a thickness of 8 microns (triangular metallic lithium was vapor-deposited on the surface of the copper foil as a stress-balancing layer (thickness: 0.2 microns), with a lithium width (specifically, width: 1 mm) and side length: 3 mm, with the ratio of the area of ​​the triangle to the area of ​​the gap within the triangle being 2). Using an unwinding and winding device, the pressure was controlled to 120 MPa by cold rolling to obtain an ultra-thin and ultra-wide lithium composite product with a metallic lithium thickness of 1 micron (thickness tolerance: ±0.5 microns).

[0042] Comparative Example 1 Using a metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns and a width of 185 mm, and copper foil with a thickness of 8 microns (the surface of the copper foil was not treated), an unwinding and rewinding device was used to cold roll the strip, controlling the pressure at 100 MPa, but an ultra-thin and ultra-wide lithium composite product with a metallic lithium thickness of 5 microns (thickness tolerance of ±0.5 microns) could not be obtained (lithium and copper cannot be composited).

[0043] Comparative Example 2 Using a metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm, and copper foil with a thickness of 8 microns (a stripe of metallic lithium was vapor-deposited on the surface of the copper foil as a stress-balancing layer (thickness: 0.5 microns), the lithium was 0.5 mm wide, the spacing distance was 2.5 mm, and the ratio of the two was controlled to 0.2), a thin and wide lithium composite product (e.g., Figure 10) with a uniform and continuous metallic lithium thickness of 5 microns (thickness tolerance: ±0.5 microns) was obtained by cold rolling using an unwinding and winding device and controlling the pressure at 100 MPa.

[0044] Comparative Example 3 Using a metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm, and copper foil with a thickness of 8 microns (a continuous, non-patterned lithium film of 0.5 microns was vapor-deposited on the surface of the copper foil), the pressure was controlled to 100 MPa by cold rolling using an unwinding and rewinding device, and an ultra-thin and ultra-wide lithium composite product (with no wrinkles or gathers) was obtained, with a uniform, continuous metallic lithium thickness of 5 microns (with a thickness tolerance of ±0.5 microns).

[0045] Example 4 - Electrochemical Measurements: First, the 5 micron ultrathin lithium composite product obtained in Example 1 was punched into an electrode sheet with a diameter of 15.6 cm, and a commercially available NCM811 electrode sheet (manufactured by Hefei Kejing Co., Ltd.) was used to form a full cell, and 1M LiPF6, EC / DMC / EMC (1 / 1 / 1) (electrolyte manufactured by Shanshan Co., Ltd.) was used as the electrolyte, and cycle measurements were performed at a charge / discharge rate of 0.2 C. As a result, it was found that the ultrathin lithium composite product manufactured by the inventors had excellent cycle performance and could be stably cycled for 200 cycles (for example, FIG. 11).

[0046] Performance measurement Using an American AR-1000 general-purpose adhesive strength measuring device, the measurement temperature was 25±5°C, the speed was 15cm / min, and the measurement angle was 120°. The adhesive strength of the ultrathin and ultrawide metal-lithium composites prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured, and the results are shown in Table 1.

[0047] [Table 1]

[0048] As can be seen from Table 1, the stress balancing layer effectively controls the stress between the metallic lithium and the structural layer, enabling the efficient mass production of ultra-wide and ultra-thin lithium composites. In addition, the adhesion between the lithium membrane layer and the structural layer is strong, making them suitable for use as a battery anode and providing a long cycle life.

[0049] It should be understood that the above description is merely a preferred embodiment of the present invention and does not limit the present invention, and all modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium complex comprising: It is in tape form, a structural layer; a stress-balancing layer located on at least one surface of the structural layer, the stress-balancing layer having a thickness of 0.1 to 1 μm and comprising patterned metallic lithium and / or lithium alloy; a lithium membrane having a width of 185 to 1500 mm and a uniform thickness of 0.5 to 30 microns with a thickness tolerance of within 20% of the thickness; Equipped with the lithium film is combined with the structural layer via the stress balancing layer to form the lithium composite; the patterned lithium metal and / or lithium alloy in the stress-balancing layer is a striped pattern or array formed of elongated or linear lithium metal and / or lithium alloy strips, the elongated or linear lithium metal and / or lithium alloy strips have a width of 0.5 to 5 mm, and the spacing between the stripes is 1 to 3 mm; the array comprises an equilateral polygonal array having sides greater than or equal to 3 and a side length of 2 to 15 mm; and the ratio of the area of ​​the lithium metal and / or lithium alloy strips to the area of ​​the gaps in the equilateral polygonal array in the stress-balancing layer is 1.2 to 20, or optionally, the ratio of the width of the lithium metal and / or lithium alloy strips to the spacing is 1 / 4 to 3.

2. 2. The lithium composite according to claim 1, wherein the lithium film is continuous or discontinuous in the longitudinal direction, and the length of the metallic lithium layer area of ​​the discontinuous lithium film is in the range of 1 to 2000 mm, and the length of the blank area is in the range of 1 to 200 mm.

3. 2. The lithium composite according to claim 1, wherein the lithium film is continuous or discontinuous in the width direction, and the discontinuous portions of the discontinuous lithium film have intervals of 0.5 to 10 mm.

4. the lithium alloy is an alloy of lithium and one or more of silicon, silver, carbon, magnesium, aluminum, indium, boron, tin, and gallium; 2. The lithium composite of claim 1, wherein the structural layer comprises metallic copper or a single-layer or multi-layer composite of copper and organic material, the organic material being at least one of polyethylene terephthalate, polypropylene, polyvinyl chloride, and polyimide, and the structural layer has a thickness of 3.5 microns to 20 microns.

5. A method for producing the lithium composite according to any one of claims 1 to 4, comprising the steps of: forming a patterned lithium metal and / or lithium alloy on the structural layer by pressure compounding, spraying, dipping, transfer coating, extrusion coating, scraper coating, curtain coating, screen printing, evaporation or vapor deposition to obtain a stress-balancing layer; a step of rolling a metallic lithium strip having a thickness of 5 to 2000 μm into a composite on a stress balancing layer to obtain the lithium composite; A method comprising:

6. 6. The method according to claim 5, wherein the rolling pressure ranges from 0.1 to 150 MPa.

7. The method according to claim 5, wherein the rolling includes cold rolling, hot rolling, combined rolling or differential speed rolling, and the hot rolling temperature range is controlled to 60 to 120°C.

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