Lithium complex and preparation method therefor

Abstract

Provided are a lithium complex and a preparation method therefor. The lithium complex is in a band shape, and comprises a structural layer; a stress equalization layer on at least one surface of the structural layer, the stress equalization layer having patterned metal lithium and / or lithium alloy having a thickness of 0.1-1 μm; and a lithium film, the lithium film having a width of 185-1500 mm, a uniform thickness of 0.5-30 microns, and a thickness tolerance within 20% of its thickness, wherein the lithium film is combined with the structural layer via the stress equalization layer to form the lithium complex.

Description

Lithium complex and preparation method thereof Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to an ultra-thin and ultra-wide lithium complex that can be used in secondary batteries and a preparation method thereof. Background Art

[0002] Lithium batteries, due to their high energy density, long cycle life, and wide operating temperature range, are widely used in aerospace, computers, mobile communications, robotics, and electric vehicles. With the development of society and advancements in technology, the demand for lithium batteries' energy density and cycle life is increasing. However, current lithium-ion batteries using only graphite as the negative electrode are unable to meet these expectations, necessitating the development of new positive and negative electrode materials with higher specific capacities. Lithium metal is an ideal negative electrode material. Lithium metal has a high specific capacity (3860 mAh / g, 10 times that of graphite) and the lowest redox potential (-3.04 V vs. standard hydrogen potential). Using lithium metal as the negative electrode significantly increases the battery's specific energy, expanding the application of lithium-ion batteries.

[0003] The positive electrode materials currently used in existing commercial lithium-ion batteries are all lithium-containing materials (such as lithium cobalt oxide, lithium iron phosphate, ternary materials, etc.). The lithium contained in the positive electrode can meet the charging and discharging needs of the lithium-ion battery, and the negative electrode only needs to provide a small amount of lithium to make up for the lithium loss during the cycle and guide the deposition of lithium ions in the positive electrode, which can greatly improve the energy density of the battery. Since the amount of lithium required for the negative electrode is very small, the thickness of the lithium film used in the battery is usually only 0.5 microns to 30 microns. In addition, in order to adapt to the current lithium-ion batteries, the width size of the metal lithium negative electrode also has high requirements, especially the current blade batteries, which have very high requirements on the width of the negative electrode. The current metal lithium negative electrode cannot be both ultra-thin and ultra-wide. In view of this, a technology that can achieve ultra-thin and ultra-wide metal lithium is needed.

[0004] Summary of the Invention

[0005] The inventors unexpectedly discovered that for lithium composites comprising an ultrathin (less than 30 microns thick) lithium metal film and a structural layer, by properly balancing the stress between the ultrathin lithium film and the structural layer, an ultrathin and ultra-wide lithium metal composite (wherein the lithium film has a thickness of less than 30 microns and a width of greater than 150 mm, for example, greater than 185 mm) can be produced. By constructing a patterned stress-balancing layer of lithium metal and / or lithium alloy on the structural layer, the accumulation of internal stress in the lithium film during rolling is alleviated to a certain extent, making the lithium film less susceptible to deformation during the composite process. This allows the production of lithium composites containing wider, thinner, and uniformly thick lithium films (e.g., 1-5 microns). Based on these findings, the present invention was completed.

[0006] Therefore, one aspect of the present invention provides a lithium composite, which is in the form of a ribbon and comprises: a structural layer; 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 and having a thickness of 0.1 to 1 μm; and a lithium film having a width of 185 to 1500 mm and a uniform thickness of 0.5 to 30 μm with a thickness tolerance within 20%, wherein the lithium film is composited with the structural layer via the stress-balancing layer to form the lithium composite.

[0007] The lithium composite of the present invention is a composite strip comprising an ultra-thin and ultra-wide lithium film, wherein the ultra-thin and ultra-wide lithium film is a lithium film which is continuous or intermittent, has or does not have through holes, is supported by a structural layer (copper foil substrate), and has adjustable width and thickness (to control the stress balance layer and pressure).

[0008] In the present invention, the lithium film is a uniform film, that is, the lithium film has a complete film shape (without obvious wrinkles and deformation, and with neat edges) and has a uniform thickness.

[0009] In the present invention, the lithium film may be continuous or intermittent in the length direction or the width direction.

[0010] Optionally, in the length direction of the intermittent lithium membrane, the length of the metal lithium layer region ranges from 1 to 2000 mm, and the length of the blank region ranges from 1 to 200 mm.

[0011] Optionally, in the intermittent lithium membrane in the width direction, the width of the metal lithium layer region is 1 to 200 mm, and the spacing between the metal lithium layers is 0.5 to 10 mm.

[0012] Optionally, the lithium film of the lithium complex has a shiny, metallic silver-white surface, a lithium content of 99.90% to 99.95%, and a lithium content of 99.95% to 99.99% within the main body (interior) of the lithium film. The lithium film has a thickness ranging from 0.5 to 30 microns, preferably 1 to 20 microns, more preferably less than 10 microns, and most preferably 1 to 5 microns; the thickness tolerance is within 20% of the thickness, preferably within 15%.

[0013] 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, and zirconium; the lithium content in the lithium alloy can be more than 70%, or even more than 90%.

[0014] Optionally, the stress-balancing layer has patterned metallic lithium and / or lithium alloy, and the patterned metallic lithium and / or lithium alloy is in the form of a striped pattern or array formed by strip-shaped or linear metallic lithium and / or lithium alloy, and the width of the strip-shaped or linear metallic lithium and / or lithium alloy is 0.5 to 5 mm, wherein the spacing distance of the striped pattern is 1 to 3 mm, and the array includes an equilateral polygonal array with ≥3 sides and a side length of 2 to 15 mm.

[0015] Optionally, the ratio of the area of ​​the equal-sided polygonal metal lithium and / or lithium alloy to the void area in the stress equalization layer is 1.2 to 20, preferably 2 to 6; or the ratio of the width of the striped lithium and / or lithium alloy to the intermittent distance is 1 / 4 to 3, preferably 1 / 3 to 1.5.

[0016] Optionally, the structural layer material is metallic copper, or a single-layer or multi-layer copper-organic material composite, wherein the organic material is at least one of polyethylene terephthalate, polypropylene, polyvinyl chloride and polyimide.

[0017] Optionally, the thickness of the structural layer is 3.5-20 microns, preferably 3.5-10 microns, more preferably 3.5-6 microns.

[0018] Optionally, the contact surface between the structural layer and the metallic lithium is subjected to stress equalization treatment. Preferably, metallic lithium is evaporated on the contact surface between the structural layer and the metallic lithium.

[0019] Another aspect of the present invention provides a method for preparing the above-mentioned lithium complex, comprising: patterning metallic lithium and / or lithium alloy on a structural layer by pressure lamination, spraying, dip-transfer coating, extrusion coating, blade coating, curtain coating, screen printing, evaporation or vapor deposition to obtain a stress-balancing layer; and using a metallic lithium strip having a thickness of 5 to 2000 μm as a raw material, rolling the metallic lithium strip and laminating it on the stress-balancing layer by rolling to obtain the lithium complex.

[0020] Optionally, the method for preparing the lithium composite adopts a roll-to-roll continuous production method.

[0021] Optionally, the thickness of the metal lithium strip is 10-100 μm, preferably 10-50 μm.

[0022] Optionally, the rolling includes cold rolling, hot rolling and composite rolling, wherein the hot rolling is controlled at a temperature range of 60 to 120° C., and the composite rolling is preferably hot rolling first and then cold rolling.

[0023] Optionally, the rolling pressure ranges from 0.1 to 150 MPa, preferably from 80 to 120 MPa.

[0024] Optionally, the contact stress between the ultra-thin and ultra-wide lithium film and the structural layer is controlled by controlling the stress-balancing layer.

[0025] Optionally, the surface of the roller has an anti-sticking material, and the anti-sticking material includes: polyethylene, polyoxymethylene, silicone polymer, and ceramic.

[0026] Optionally, a roller with a maximum tension range of 0.1 to 10 N is used for winding, wherein the supporting roller is itself powered.

[0027] By controlling the rolling process, the present invention achieves a simple process to create an ultra-thin, ultra-wide lithium film composite. This composite possesses high specific energy and, when applied to lithium battery anodes, improves energy density, achieving high energy density. The high gram-specific capacity of metallic lithium anodes makes them suitable for high-energy batteries, potentially exceeding 450 Wh / kg.

[0028] As commercial batteries grow in size, the required lithium metal anode widths are also increasing. Ultra-wide, ultra-thin lithium membranes are well-suited to current commercial battery trends. This invention enables simple, mass-produced ultra-wide, ultra-thin lithium metal composites. These ultra-thin lithium metal anodes can be used with existing high-gram-capacity cathodes without causing lithium overload and dendrite problems.

[0029] The bonding of lithium metal to the current collector has always been a challenge in the industry. Perfect adhesion is difficult, resulting in poor current collection and poor battery rate performance. The ultra-thin, ultra-wide lithium metal composite of the present invention effectively addresses this issue. By introducing a patterned stress-balancing layer, the lithium metal is tightly bonded to the structural layer. Furthermore, when the patterned layer is lithium metal, no other impurities are introduced into the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic diagram of a process for producing continuous ultra-thin and ultra-wide lithium composites by pressure compounding according to the present invention.

[0031] FIG2 is a schematic diagram of an intermittent ultra-thin and ultra-wide lithium composite in the width direction.

[0032] FIG3 is a schematic diagram of an intermittent ultra-thin and ultra-wide lithium complex in the longitudinal direction.

[0033] Figure 4 is a schematic diagram of an intermittent ultra-thin and ultra-wide lithium composite production device

[0034] FIG. 5 shows a schematic diagram of a patterned (striped) stress-balancing layer according to the present application.

[0035] FIG. 6 shows a schematic diagram of another stress-balancing layer patterning (triangle shape) of the present application.

[0036] FIG. 7 shows a schematic diagram of another stress-balancing layer patterning (quadrilateral, chessboard shape) of the present application.

[0037] FIG8 shows a product image of a 5-micron-thick ultra-thin and ultra-wide lithium composite prepared in Example 1 of the present application.

[0038] FIG9 shows a product image of an ultra-thin and ultra-wide lithium composite with an intermittent thickness of 5 μm prepared in Example 2 of the present application.

[0039] FIG10 shows a product image of a 5-micron-thick ultra-thin and ultra-wide lithium composite prepared in Comparative Example 2 of the present application.

[0040] FIG11 shows the electrochemical performance of the 5-micron-thick ultra-thin and ultra-wide lithium composite product prepared in Example 1 of the present application.

[0041] In the above figures: P structural layer L metal lithium layer PL (continuous) lithium foil PNL intermittent lithium foil H lithium layer or alloy layer DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0043] FIG1 shows a schematic diagram of a process for producing continuous ultra-thin and ultra-wide lithium composites by pressure lamination according to the present invention. As shown in FIG1 , a lithium metal strip and a structural layer strip having a stress-balancing layer (pre-patterned) are used as raw materials and unwound by an unwinding device. The unwinding device comprises at least a lithium metal strip unwinding roller 11 and two unwinding support rollers 12 for supporting the unwound lithium metal strip and structural layer strip, respectively. After passing through the unwinding support rollers 12, the raw lithium strip and structural layer strip enter a rolling mill 20. The rolling mill 20 comprises at least a pair of rollers 21 and an anti-stick coating 22 on the rollers 21. The rolling pressure of the rolling mill 20 and the roller gap between the rollers 21 can be fine-tuned. The material of the anti-stick coating 22 on the rollers 21 can be selected. The structure layer strip and the lithium strip are compounded together by pressure lamination to form an ultra-thin and ultra-wide lithium composite product. A winding device is provided on the outlet 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. The support roller 31 is powered and can use a small pulling force to pull the ultra-thin and ultra-wide lithium composite forward. The tension control roller 32 can move up and down or swing, which 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.

[0044] Figure 2 is a schematic diagram of an intermittent lithium membrane in the width direction. Figure 3 is a schematic diagram of an intermittent lithium membrane in the length direction.

[0045] FIG4 is a production device for producing intermittent lithium foil, which includes an unwinding device 100, a scraping device 200, and a rewinding device 300, and also includes a control device (not shown) for controlling the rewinding speed and the working time interval of the scraping device. The unwinding device 100 includes an unwinding shaft 101, a magnetic powder brake 102, an unwinding support roller 104, an unwinding correction detection sensor 105, and an unwinding correction device 103; the scraping device 200 includes a scraper 201, a scraper drive device 202, a scraper pad 203, and support rollers (204, 205); the rewinding device 300 includes a rewinding shaft 301, a rewinding motor 302, a rewinding correction device 303, a rewinding support roller 304, and a rewinding correction detection sensor 305; in addition, a length measuring sensor 401 is optionally provided.

[0046] The unwinding device 100 unwinds the lithium foil (PL) using the unwinding shaft 101. A magnetic powder brake 102 connected to the unwinding shaft 101 controls the unwinding tension. The unwinding support roller 104 supports the lithium foil (PL) at a constant angle as it enters the scraping device 200 and facilitates accurate deflection detection by the unwinding deflection detection sensor 105. The support rollers 204 and 205 on the scraping device 200 ensure a constant angle of inclination for the strip entering and exiting the device, unaffected by other process steps. The scraper pad 203 supports the lithium foil (PL) and maintains its flatness. The scraper drive 202 drives the scraper 201 for rapid vertical movement. The rewinding device 300 includes a rewinding shaft 301 and a rewinding motor 302. The rewinding shaft 301 is used for intermittent rewinding of the lithium foil (PNL) and is driven by the rewinding motor 302.

[0047] The specific method and process are as follows: a battery-grade lithium foil PL with a substrate support is mounted on the unwinding shaft 101 and fixed; the lithium foil PL is sequentially passed through the unwinding support roller 104, the unwinding correction detection sensor 105, the support rollers 204 and 205 of the scraping device, the winding correction detection sensor 305, and the winding support roller 304, and then wound onto the winding shaft 301 and fixed. The equipment is turned on, and the winding motor 302 on the winding device 300 is operated, driving the winding shaft 301 to rotate, thereby winding the lithium foil PL from the unwinding device 100 end through the scraping device 200. During the winding process of the winding device 300, the scraper driving device 202 in the scraping device 200 is controlled to cause the scraper 201 to intermittently move up and down, thereby scraping off part of the metallic lithium layer on the lithium foil PL, forming an intermittent lithium foil PNL. By controlling the width and number of scrapers, a gap lithium film in the width direction is produced.

[0048] Figure 5 shows a schematic diagram of a striped patterned stress-balancing layer of the present invention. Figure 6 shows a schematic diagram of a triangular patterned stress-balancing layer of the present invention. Figure 7 shows a schematic diagram of a quadrilateral patterned stress-balancing layer (checkerboard shape) of the present invention.

[0049] The present invention is further described below through examples using the aforementioned process equipment. The various product structural parameters, reaction participants, and process conditions employed in the following examples are typical examples. However, extensive testing by the inventors has confirmed that other structural parameters, other types of reaction participants, and other process conditions listed above are also applicable and can achieve the claimed technical effects of the present invention.

[0050] Example 1:

[0051] Using a lithium metal strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm, and an 8-micron-thick copper foil (the copper foil surface is vapor-deposited with stripes of lithium metal to form a stress-balancing layer (thickness 0.4 μm), with a lithium width (specifically 3 mm) and an intermittent distance ratio of 1.5), auxiliary unwinding and rewinding devices are used, cold-rolling is performed, and a pressure of 80 MPa is controlled to produce an ultra-thin, ultra-wide lithium composite product with a lithium metal thickness of 5 microns (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 complete film shape.

[0052] Example 2:

[0053] A metal lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm and a copper foil with a thickness of 8 microns (the surface of the copper foil is evaporated with a quadrilateral checkerboard-shaped metal lithium-magnesium alloy as a stress balance layer (thickness 0.1 μm), lithium width (width 0.5 mm) and side length 3 mm, with a controlled area ratio of 2.25), auxiliary unwinding and winding devices and a scraping device are used. Hot rolling is adopted at a temperature of 80°C and a controlled pressure of 100 MPa to obtain an intermittent ultra-thin and ultra-wide lithium composite product in the longitudinal direction with a lithium layer thickness of 5 microns (thickness tolerance of ±0.5 microns) (as shown in Figure 9).

[0054] Example 3:

[0055] A metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 800 mm and a copper foil with a thickness of 8 microns are used (triangular metallic lithium is evaporated on the surface of the copper foil to serve as a stress balancing layer (thickness 0.2 microns), the lithium width (specifically 1 mm) has a side length of 3 mm, and the ratio of the area of ​​the triangle to the area of ​​the gap within the triangle is 2), auxiliary unwinding and winding devices are used, cold rolling is adopted, and the pressure is controlled at 120 MPa to obtain an ultra-thin and ultra-wide lithium composite product with a metallic lithium thickness of 1 micron (thickness tolerance of ±0.5 microns).

[0056] Comparative Example 1:

[0057] Using 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 copper foil surface is not treated), auxiliary unwinding and winding devices, cold rolling, and a controlled pressure of 100 MPa, it is impossible to obtain an ultra-thin and ultra-wide lithium composite product with a metallic lithium thickness of 5 microns (thickness tolerance of ±0.5 microns) (lithium and copper cannot be composited together).

[0058] Comparative Example 2:

[0059] Using a metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm and a copper foil with a thickness of 8 microns (striped metallic lithium is evaporated on the surface of the copper foil to serve as a stress balancing layer (thickness 0.5 microns), the lithium width is 0.5 mm and the interval distance is 2.5 mm, and the ratio of the two is controlled to be 0.2), auxiliary unwinding and winding devices, a cold rolling method, and a controlled pressure of 100 MPa, it is impossible to obtain a uniform and continuous ultra-thin and ultra-wide lithium composite product with a metallic lithium thickness of 5 microns (thickness tolerance of ±0.5 microns) (as shown in Figure 10).

[0060] Comparative Example 3:

[0061] Using a metallic lithium strip with a lithium content of 99.95%, a thickness of 5 microns, and a width of 185 mm and a copper foil with a thickness of 8 microns (a 0.5-micron continuous non-patterned lithium film is evaporated on the surface of the copper foil), auxiliary unwinding and winding devices, and a cold rolling method with a controlled pressure of 100 MPa, it is impossible to obtain an ultra-thin and ultra-wide lithium composite product (wrinkled and wrinkled) with a uniform and continuous metallic lithium thickness of 5 microns (thickness tolerance of ±0.5 microns).

[0062] Example 4 - Electrochemical Testing:

[0063] First, the 5-micron ultra-thin lithium composite product obtained in Example 1 was punched into a 15.6-cm diameter electrode. This electrode was then assembled into a full cell with purchased NCM811 electrode sheets (Hefei Kejing). Cycling tests were conducted using 1M LiPF6 and an EC / DMC / EMC (1 / 1 / 1) electrolyte (Shanshan electrolyte) at 0.2C charge and discharge. The results showed that the ultra-thin lithium composite product exhibited excellent cycling performance, capable of stable cycling for 200 cycles (see Figure 11).

[0064] Performance testing:

[0065] The adhesion of the ultra-thin and ultra-wide lithium metal composites produced in Examples 1-3 and Comparative Examples 1-3 was tested using an American AR-1000 universal adhesion tester at a test temperature of 25±5°C, a speed of 15 cm / min, and a test angle of 120°. The results are shown in Table 1.

[0066] Table 1. Adhesion test

[0067] It can be seen from Table 1 that the stress equalization layer can effectively control the stress between the metallic lithium and the structural layer, so that ultra-wide and ultra-thin lithium composites can be effectively and batch-produced. In addition, the bonding force between the lithium film layer and the structural layer is relatively large, and it can be used as a battery negative electrode to obtain a longer cycle life.

[0068] It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium complex, characterized in that: The lithium complex is in the shape of a ribbon and has: Structural layer; A stress balancing layer located on at least one surface of the structural layer, the stress balancing layer having patterned metallic lithium and / or lithium alloy and having a thickness of 0.1 to 1 μm; and The lithium film has a width of 185 to 1500 mm, a uniform thickness of 0.5 to 30 microns, and a thickness tolerance within 20% of the thickness. wherein the lithium film is compounded with the structural layer via the stress balance layer to form the lithium composite, The patterned metal lithium and / or lithium alloy in the stress equalization layer is in the form of a stripe pattern or array formed by stripe or line-shaped metal lithium and / or lithium alloy, the width of the stripe or line-shaped metal lithium and / or lithium alloy is 0.5-5 mm, the spacing distance of the stripe pattern is 1-3 mm, the array includes an equilateral polygon array with ≥3 sides and a side length of 2-15 mm, and the ratio of the area of ​​the equilateral polygonal metal lithium and / or lithium alloy to the gap area in the stress equalization layer is 1.2-20; or, the ratio of the width of the stripe-shaped lithium and / or lithium alloy to the intermittent distance is 1 / 4-3.

2. The lithium composite according to claim 1, characterized in that: The lithium film is continuous or intermittent in the length direction; the length of the metal lithium layer area of ​​the intermittent lithium film ranges from 1 to 2000 mm, and the length of the blank area ranges from 1 to 200 mm.

3. The lithium composite according to claim 1, characterized in that: The lithium film is continuous or intermittent in the width direction, wherein the intermittent parts of the intermittent lithium film have a spacing of 0.5-10 mm.

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

5. A method for preparing the lithium complex according to any one of claims 1 to 4, characterized in that: The method comprises: The stress equalization layer is obtained by patterning metallic lithium and / or lithium alloy on the structural layer by pressure lamination, spray coating, dip coating, transfer coating, extrusion coating, blade coating, curtain coating, screen printing, evaporation or vapor deposition; The lithium composite is obtained by using a metal lithium strip with a thickness of 5 to 2000 μm as a raw material, rolling the metal lithium strip and compounding it on a stress balance layer by a rolling method.

6. The method according to claim 5, characterized in that: The rolling pressure range is 0.1~150Mpa.

7. The method according to claim 5, characterized in that: The rolling includes cold rolling, hot rolling, composite rolling or asynchronous rolling, wherein the hot rolling is controlled at a temperature range of 60 to 120°C.

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