CN114597331A

CN114597331A - Ultrathin lithium film complex and preparation method thereof

Info

Publication number: CN114597331A
Application number: CN202011397225.7A
Authority: CN
Inventors: 孙兆勇; 陈强; 郇庆娜; 孔德钰; 刘承浩
Original assignee: China Energy Lithium Co ltd
Current assignee: China Energy Lithium Co ltd
Priority date: 2020-12-03
Filing date: 2020-12-03
Publication date: 2022-06-07

Abstract

The invention provides an ultrathin lithium film complex and a preparation method thereof. The composite has: a bearing layer, a stress control layer on at least one surface of the bearing layer and an ultrathin lithium film compounded with the bearing layer via the stress control layer, wherein the ultrathin lithium film is a uniform film with through holes with the aperture of 5-200 microns, has a uniform thickness of 0.5-20 microns and a thickness tolerance within +/-0.5 microns, and the bonding force between the ultrathin lithium film and the bearing layer is 0.5-15 N.m^‑1。

Description

Ultrathin lithium film complex and preparation method thereof

Technical Field

The invention relates to the technical field of energy storage, in particular to an ultrathin lithium film complex applicable to a secondary battery and a preparation method thereof.

Background

The lithium battery is widely applied to the fields of aerospace, computers, mobile communication equipment, robots, electric automobiles and the like due to the advantages of high energy density, long cycle life and wide applicable temperature range. With the development of society and the progress of science and technology, the requirements on the energy density and the cycle life of a lithium battery are higher and higher, but the lithium ion battery which only uses graphite as a negative electrode at present cannot meet the social expectation, so that the development of a novel positive and negative electrode material with higher specific capacity is needed. For the negative electrode material, the pre-lithiation work can effectively improve the specific energy of the battery and prolong the service life of the battery. Lithium metal has a high specific capacity (3860mAh/g, 10 times that of graphite negative electrodes) and the lowest redox potential (-3.04V VS standard hydrogen potential). The method has the advantages that the lithium metal is adopted to carry out pre-lithiation treatment on the traditional graphite cathode, so that on one hand, the first coulomb efficiency of the battery can be improved, the specific energy of the battery is increased, and on the other hand, the cycle life of the battery can be effectively prolonged, so that the lithium ion battery has a wider application field.

Although prelithiation (lithium compensation) has this advantage, it places higher demands on the anode prelithiation to precisely control its amount in the cell. The anode material adopted by the existing lithium ion battery is lithium-containing material (such as lithium cobaltate, lithium iron phosphate, ternary material and the like), the lithium contained in the anode can meet the charge and discharge requirements of the lithium ion battery, and the lithium supplemented in the cathode only needs to provide a small amount of lithium to make up the lithium loss in the circulation process, so that the energy density of the battery can be improved and the cycle life of the battery can be prolonged. Since the amount of lithium pre-intercalation in the negative electrode is very small, the thickness of the lithium film for lithium replenishment is usually only 0.5 to 15 μm. In the chinese patent application CN201610102992.8 of new energy in ningde time, lithium powder is scattered on the surface of a pole piece during the lithium supplement process, and pre-lithiation is performed after rolling, so that the amount of lithium is small. However, the lithium supplement method cannot realize the precise control of the lithium supplement amount, and has the disadvantages of complex process, high cost and difficult control of safety. In view of this, a technology capable of controlling the amount of lithium supplement and achieving a high energy density of a battery is required.

Disclosure of Invention

The inventor finds that: when the ultra-thin lithium film is compounded on the support layer by a rolling process, the ultra-thin lithium film is not easily firmly attached to the surface of the support layer due to a large difference between the surface properties of the support layer (e.g., a plastic material) and the metallic lithium, and if a large pressure (stress) is applied for firm attachment, breakage of the ultra-thin lithium film or incomplete surface shape (breakage or uneven holes) is easily caused. For this reason, the inventors have made intensive studies and have unexpectedly found that: through forming specific stress control layer on the surface of bearer layer, not only can alleviate the surface property difference of bearer layer and metal lithium for ultra-thin lithium membrane is changeed and is adhered to the bearer layer, and the stress influence when can reducing rolling moreover makes ultra-thin lithium membrane keep better surface morphology. In addition, the adhesion force of the ultrathin lithium film and the bearing layer can be controlled through the stress control layer to be in a proper level, so that the ultrathin lithium film can be ensured to be compounded on the bearing layer, and can be easily transferred to other substrates such as a lithium battery cathode from the bearing layer. The inventors have also surprisingly found that: for the lithium film used for the negative electrode pre-lithiation, if the lithium film is provided with through holes, the electrolyte can easily enter the contact interface of the lithium film and the negative electrode diaphragm due to the existence of the holes, so that the pre-lithiation speed is improved, and gas generated during the pre-lithiation can be released from the through holes, so that the lithium film is prevented from being separated from the negative electrode diaphragm. Therefore, the lithium film having the through-holes can achieve a better pre-lithiation effect than the complete lithium film. Thus, ultra-thin lithium films with through-holes (0.5-20 microns, even 1-5 microns thick) can be produced by rolling in a roll-to-roll manner. Due to the existence of the through holes, the accumulation of internal stress in the lithium film in the rolling process is relieved to a certain extent, so that the lithium film is not easy to deform, and a thinner lithium film (for example, 1-5 microns) with uniform thickness can be prepared. Based on these findings, the present invention has been completed.

Accordingly, an aspect of the present invention is directed to an ultra-thin lithium film composite having: a carrier layer; a stress control layer on at least one surface of the carrier layer; and an ultra-thin lithium film composited with the bearing layer via the stress control layer, wherein the ultra-thin lithium film is a uniform film having through holes with a pore diameter of 5-200 micrometers, has a uniform thickness of 0.5-20 micrometers, and has a thickness tolerance within ± 0.5 μm; the ultra-thin lithium film and the carrier layerThe bonding force between the two is 0.5 to 15 N.m^-1。

In the present invention, the ultra-thin lithium film is a uniform film, which means that the ultra-thin lithium film has a complete film shape (no significant wrinkles and deformation, with neat edges) and has a uniform thickness. Preferably, the ultra-thin lithium film has through-holes uniformly distributed throughout the lithium film.

Alternatively, the ultra-thin lithium film of the present invention is continuous or intermittent in the length direction; or continuously or intermittently in the width direction.

Optionally, the intermittent lithium film in the length direction comprises a blank area with controllable length and a metal lithium layer area, the length of the metal lithium layer area ranges from 1 mm to 2000mm, and the length of the blank area ranges from 1 mm to 200mm, preferably from 1 mm to 100 mm.

Alternatively, the lithium film is intermittently formed in the width direction, the width of the lithium film portion is 1 to 200mm, and the interval between the lithium film portions is 0.5 to 10 mm.

Optionally, the lithium film surface of the ultrathin lithium film complex body is bright and is silver white, the lithium content is 99.90-99.95%, and the lithium element content of the lithium film main body (inside) can be 99.95% -99.99%. The lithium film has a thickness in the range of 0.5 to 15 microns, preferably 1 to 10 microns, more preferably 5 microns or less, and a thickness tolerance of + -0.5 μm, preferably + -0.1 μm.

Alternatively, the ultra-thin lithium film has uniformly distributed through-holes having a pore size of 5 to 200 micrometers, preferably 10 to 50 micrometers.

Optionally, the ultrathin lithium film has a porosity of 0.1% to 20%, preferably 0.1% to 10%, more preferably 0.5% to 5%.

Alternatively, the through-holes of the ultra-thin lithium film are in the shape of circular holes or circular-like holes, and the pitch of the holes is 5 to 1000 micrometers, preferably 5 to 200 micrometers, and more preferably 5 to 50 micrometers.

Optionally, the material of the carrier layer is a polymer: such as polyimide, nylon, cellulose, high strength thin film polyolefins (polyethylene, polypropylene, polystyrene); polyesters (polyethylene terephthalate, polybutylene terephthalate, polyarylates); inorganic oxide(s): such as alumina; inorganic conductor: such as graphite, carbon nanotubes, graphene; a metal current collector: such as copper, aluminum; the bearing layer can be a single layer or a composite of multiple layers.

Optionally, the thickness of the carrier layer is 1-500 microns, preferably 5-100 microns, more preferably 10-50 microns.

Alternatively, the stress control layer is formed of a stress adjusting material, or is formed by surface-treating the carrier layer with a stress adjusting material.

Alternatively, the stress control layer is formed by spraying, dipping, transfer coating, extrusion coating, doctor blade coating, curtain coating, screen printing or vapor deposition of a stress modulating material on the carrier layer.

Optionally, the stress control layer has a thickness of 50-200 nm.

Optionally, the stress adjusting material comprises one or more of vinyl dimethyl polysiloxane, hydrogen-containing silicone oil, punching shear oil, liquid paraffin, methyl silicone oil, emulsified methyl silicone oil, hydrogen-containing methyl silicone oil, silicone grease and polyethylene wax.

Alternatively, the stress adjusting material may be used alone, or may be dissolved in a solvent to prepare a solution.

Optionally, the solvent for the stress adjusting material solution comprises: one or more of toluene, n-butanol, polyvinyl alcohol, butanone and n-hexane.

Optionally, the adhesion between the support layer and the ultrathin lithium film is 1-10 Nm^-1Preferably 1 to 5 N.m^-1. The binding force between the bearing layer and the ultrathin lithium film can ensure that the ultrathin lithium film is stably compounded on the bearing layer, and can be easily transferred from the bearing layer to other substrates such as a lithium battery cathode.

Another aspect of the present invention is to provide a method for preparing the above ultra-thin lithium film composite, which is characterized in that a roll-to-roll continuous production method is adopted, a lithium metal strip with a thickness of 10 to 250 μm is used as a raw material, and the lithium metal strip is rolled by a rolling manner and is composited on a stress control layer of a bearing layer with the stress control layer, so as to obtain the ultra-thin lithium film composite.

Alternatively, the thickness of the lithium metal strip is 10-100 μm, preferably 10-50 μm.

Optionally, the rolling comprises cold rolling, hot rolling and combined rolling, wherein the hot rolling is controlled at the temperature of 60-120 ℃, and the combined rolling is preferably hot rolling and then cold rolling.

Alternatively, the rolling pressure is in the range of 0.1 to 150MPa, preferably 80 to 120 MPa.

Optionally, the adhesion of the ultra-thin lithium film and the carrier layer is controlled by controlling the stress control layer such that the adhesion is 0.5-15N/m.

Optionally, the roll surface has a release material comprising: polyethylene, polyoxymethylene, silicone polymers, ceramics.

Optionally, the winding is performed by using a roller with the maximum tension range of 0.1-10N, wherein the supporting roller is self-powered.

By providing the stress control layer and controlling the rolling process, the present invention obtains a complex body loaded with a uniform ultra-thin lithium film having through-holes in a simple process, the ultra-thin lithium film having through-holes of the complex body can be easily transferred to a negative electrode of a lithium battery, and has an improved pre-lithiation effect, achieving a high energy density of the battery.

Drawings

Fig. 1 is a schematic view of a process for producing a continuous ultra-thin lithium film composite by pressure recombination according to the present invention.

Fig. 2 is a schematic view of a width-direction intermittent ultrathin lithium film composite.

Fig. 3 is a schematic view of a longitudinally intermittent ultrathin lithium film composite.

Fig. 4 shows a schematic process diagram for producing a batch ultra-thin lithium film composite.

Fig. 5 shows a 5 μm thick ultra-thin lithium film composite product prepared in example 1 of the present application.

Fig. 6 shows a 10 μm thick ultra-thin lithium film composite product prepared in example 2 of the present application.

FIG. 7 shows a 5 micron batch ultra thin lithium film composite product made in example 3 of the present application.

Fig. 8 shows the negative electrode product after pre-lithiation of graphite of example 4 of the present application.

Fig. 9 shows the negative electrode product after the silicon carbon pre-lithiation of example 5 of the present application.

Fig. 10 shows a negative electrode product after pre-lithiation of graphite with an ultra-thin lithium film composite of comparative example 1 without the use of a stress control layer.

For short:

p substrate L lithium metal layer PL (continuous) lithium foil PNL intermittent lithium foil

Detailed Description

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

Fig. 1 shows a schematic view of a process for producing a continuous ultra-thin lithium film composite by pressure lamination according to the present invention. As shown in fig. 1, a metal lithium strip and a carrier strip (a stress control layer is provided on one side of the carrier strip) are used as raw materials, and are unreeled by an unreeling device, wherein the unreeling device at least comprises a metal lithium strip unreeling roller 11 and two unreeling support rollers 12 for supporting the unreeled metal lithium strip and the carrier strip respectively; the raw material lithium belt and the supporting belt material (the stress control layer of the supporting belt material faces the raw material lithium belt) pass through the unreeling support roller 12 and then enter the rolling mill 20; the rolling mill 20 at least comprises a pair of rollers 21 and a release coating 22 on the rollers 21, and the rolling pressure of the rolling mill 20 and the roll gap between the rollers 21 can be finely adjusted; the material of the anti-sticking layer 22 on the roller 21 can be one or more selected from polyethylene, polyformaldehyde, organic silicon polymer, ceramic and the like. And compounding the loading strip material and the lithium material together through pressure compounding to form the ultrathin lithium film composite product. A winding device is arranged at the outlet side of the rolling mill 20, and the winding device at least comprises a supporting roller 31, a tension control roller 32 and a winding roller 33; the supporting roller 31 is provided with power and can pull the ultrathin lithium film composite body to advance by utilizing micro pulling force; the tension control roller 32 can move up and down or swing, and can control the tension of the composite body and the winding speed of the winding roller 33 according to the height or the swing angle of the tension control roller 32.

Fig. 2 is a schematic view of an intermittent lithium film in a width direction, and fig. 3 is a schematic view of an intermittent lithium film in a length direction.

Fig. 4 is a schematic diagram of a production apparatus for producing an intermittent lithium film, which includes an unwinding device 100, a scraping device 200, and a winding device 300, and further includes a control device (not shown) for controlling a winding speed and an operating time interval of the scraping device. The unwinding device 100 comprises an unwinding shaft 101, a magnetic powder brake 102, an unwinding support roller 104, an unwinding deviation-correcting detection sensor 105 and an unwinding deviation-correcting device 103; the scraping device 200 comprises a scraper 201, a scraper drive 202, a scraper backing plate 203 and support rollers (204, 205); the winding device 300 comprises a winding shaft 301, a winding motor 302, a winding deviation correcting device 303, a winding support roller 304 and a winding deviation correcting detection sensor 305; in addition, a length measuring sensor 401 is optionally provided.

An unwinding shaft 101 on the unwinding device 100 is used for unwinding the lithium foil PL, and a magnetic powder brake 102 connected with the unwinding shaft 101 can control the magnitude of unwinding tension; the unwinding support roller 104 is used for supporting the lithium foil PL to enter the scraping device 200 at a constant inclination angle and facilitating the unwinding deviation-correcting detection sensor 105 to accurately perform deviation-correcting detection on the lithium foil PL. The supporting rollers 204/205 on the scraping device 200 respectively ensure that the inclination angles of the strip entering and exiting the device are constant and are not influenced by other process links; the scraper backing plate 203 is used for supporting the lithium foil PL and keeping the flat state of the lithium foil PL; the scraper driving device 202 is used for driving the scraper 201 to realize rapid movement in the up-down direction. The winding device 300 comprises a winding shaft 301 and a winding motor 302; the winding shaft 301 is used for winding the intermittent lithium foil PNL, and the winding shaft 301 is driven by a winding motor 302.

The specific using method and the flow are as follows: mounting and fixing the substrate-supported lithium foil PL on the unwinding shaft 101; the lithium foil PL is sequentially passed through the unwinding support roller 104, the unwinding deviation detecting sensor 105, the

support rollers

204 and 205 of the scraping device, the winding deviation detecting sensor 305, and the winding support roller 304, and then wound onto the winding shaft 301 and fixed. Starting the device, so that the winding motor 302 on the winding device 300 operates to drive the winding shaft 301 to rotate, and thus the lithium foil PL passes through the scraping device 200 from the unwinding device 100 end to be wound; in the process of winding by the winding device 300, the intermittent up-and-down movement of the scraper 201 is realized by controlling the scraper driving device 202 in the scraping device 200, so that part of the metal lithium layer on the lithium foil PL is scraped to form an intermittent lithium foil PNL, and the width direction or the length direction of the gap lithium film is produced by controlling the width and the number of the scrapers.

Hereinafter, the present invention will be described more specifically by examples using the above-mentioned process equipment. The following examples are typical examples of the product structure parameters, the reaction participants and the process conditions, but through the experiments of the present inventors, the other structure parameters, the reaction participants and other process conditions listed above are also applicable and all the claimed technical effects can be achieved.

Example 1:

the method comprises the steps of adopting a metal lithium strip with 99.95% of lithium content and 20 microns of thickness and a polyethylene film with 50 microns of thickness (the surface of the polyethylene film is provided with a stress control layer formed by spraying a butanone solution containing hydrogen silicone oil on a contact surface of a bearing layer and metal lithium), assisting an unreeling and reeling device, and adopting a cold rolling mode to control the pressure to be 100Mpa so as to obtain an ultrathin lithium film composite product with the thickness of 5 microns (the thickness tolerance is +/-0.5 microns).

Fig. 5 is a photograph of the ultra-thin lithium film composite product (illuminating from the side of the support layer, i.e., from the inside of the composite to the outside, with greater illumination intensity from the back side to show the through-holes, with the center highlight being the direct point of the light source). As can be seen from fig. 5, the ultra-thin lithium film has a relatively complete film shape with pin-hole-shaped (through-film) through holes distributed relatively uniformly, the size of the holes is 5-50 microns, and the hole pitch is 5-100 microns.

Example 2:

the method comprises the steps of adopting a metal lithium strip with 99.95% of lithium content and 20 microns of thickness and a copper foil with 10 microns of thickness (the surface of the copper foil is provided with a stress control layer formed by spraying a bearing layer and a contact surface of metal lithium with a paraffin-containing n-butane solution), assisting an unreeling and reeling device and a scraping device, and obtaining a length-direction intermittent ultrathin lithium film composite product with 10 microns of thickness (the thickness tolerance is +/-0.5 micron) by adopting a hot rolling mode at the temperature of 80 ℃ and the pressure of 120MPa (as shown in figure 6).

Example 3:

the method comprises the steps of adopting a metal lithium strip with the lithium content of 99.95% and the thickness of 20 microns and a polyethylene film with the thickness of 50 microns (the surface of the polyethylene film is provided with a stress control layer formed by spraying a contact surface of a bearing layer and metal lithium with punching shear oil), assisting an unreeling device, a reeling device and a scraping device, and obtaining a width-direction intermittent ultrathin lithium film composite product with the thickness of 5 microns (the thickness tolerance is +/-0.5 micron) by adopting a hot rolling mode, controlling the temperature at 80 ℃ and the pressure at 120Mpa (see figure 7).

Example 4-graphite lithium supplement test:

firstly, preparing a graphite electrode, dispersing graphite powder (fibrate-rich), acetylene black AB (fibrate-rich), sodium carboxymethylcellulose CMC (Shanghai Haiyi), styrene butadiene rubber SBR (Shanghai Haiyi), 94:3:1:2 in deionized water, controlling the solid content to be 35%, the viscosity to be 2000-friendly 3000cp, stirring for 6 hours, coating the single surface of a coating machine on a 10 mu m copper film, and drying to obtain the 50 mu m graphite pole piece. Then, the ultra-thin 10 μ M lithium composite product obtained in example 3 was processed with a stress control layer (control adhesion 2N/M), the lithium film was applied to the graphite electrode surface under a pressure of 15MPa (see FIG. 8), the support layer was peeled off, and the lithium film was punched into a 15.6cm diameter sheet, which was combined with a lithium film to form a half cell using 1M LiPF6, EC/DMC/EMC (1/1/1) (fir electrolyte) as an electrolyte. Compared with a half cell without pre-lithiation, in the half cell in which the graphite negative electrode is pre-lithiated by using the ultrathin lithium composite, the first efficiency of the graphite negative electrode is improved from 92% to 100%, and the first effect is greatly improved.

Example 5 silicon carbon lithium test

Firstly, preparing a silicon-carbon electrode, dispersing silicon-carbon powder (fibrate-rich carbon), acetylene black AB (fibrate-rich carbon), sodium carboxymethylcellulose CMC (Shanghai Haiyi), styrene butadiene rubber SBR (Shanghai Haiyi) 94:4:1:2 in deionized water, controlling the solid content to be 38%, the viscosity to be 2000-3000cp, stirring for 6 hours, coating the single surface of a coating machine on a 10 mu m copper film, and drying to obtain the 50 mu m silicon-carbon electrode piece. Then, the 5 μ M ultra-thin lithium composite product obtained in example 1 was subjected to stress control layer treatment (control of adhesion 3N/M), a lithium film was transferred to the surface of a silicon carbon electrode by applying pressure of 15MPa (see fig. 9), a support layer was peeled off, a 15.6cm diameter pole piece was punched out, and a half cell was formed with the lithium film using 1M LiPF6, EC/DMC/EMC (1/1/1) (cedar electrolyte). Compared with a half cell without pre-lithiation, in the half cell in which the silicon-carbon negative electrode is pre-lithiated by using the ultrathin lithium complex, the first efficiency of the silicon-carbon negative electrode is improved from 76% to 95%, and the first effect is greatly improved.

Comparative example 1:

the method is characterized in that a metal lithium strip with the lithium content of 99.95% and the thickness of 20 microns and a polyethylene film with the thickness of 50 microns (stress treatment is not performed on the film) are adopted, an unreeling and reeling device is assisted, the pressure is controlled to be 100Mpa in a cold rolling mode, and an obtained ultrathin lithium film complex product with the thickness of 5 microns (thickness tolerance is +/-0.5 microns) cannot be smoothly transferred onto a pole piece, so that the pole piece is damaged and an active substance falls off in the process of separating a bearing layer, as shown in figure 10.

And (3) performance testing:

adopting an American AR-1000 universal adhesion tester, and testing the temperature: 25. + -. 5 ℃ speed: 15cm/min, test angle: 120 degrees, bond on ultra-thin lithium membrane through the 3M sticky tape, fixed bearing layer separates through the pulling force, the pulling force when testing the separation. The ultra-thin lithium metal composites produced in examples 1-5 and comparative example 1 were tested for adhesion and the results are shown in table 1.

Adhesion test Table 1

Serial number	Name of product	State of lithium film	Adhesive force (N/m)
				1	Example 1	(Continuous)	2
2	Example 2	Intermittent type	10
				3	Example 3	Intermittent type	3
4	Example 4	Intermittent type	3
				5	Example 5	(Continuous)	2
6	Comparative example	(Continuous)	20

As can be seen from table 1: through the stress control layer, the adhesive force can be effectively controlled, so that the adhesive force between the pole piece and the lithium film is greater than the adhesive force between the lithium film and the bearing layer, and the lithium film product is effectively transferred to the negative electrode of the battery.

It should be understood that the above-mentioned embodiments are merely preferred embodiments of the present invention, and not intended to limit the present invention, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An ultrathin lithium film composite, characterized in that the composite has:

a carrier layer;

a stress control layer on at least one surface of the carrier layer; and

an ultra-thin lithium film composited with the carrier layer via the stress control layer,

wherein,

the ultrathin lithium film is a uniform film with through holes with the aperture of 5-200 microns, has a uniform thickness of 0.5-20 microns and has a thickness tolerance within +/-0.5 microns;

the bonding force between the ultrathin lithium film and the bearing layer is 0.5-15 N.m^-1。

2. The ultra-thin lithium film composite of claim 1, wherein: the ultra-thin lithium film is continuous or intermittent in the length direction; or the ultra-thin lithium film may be continuous or intermittent in the width direction.

3. The ultra-thin lithium film composite of claim 2, wherein:

the ultrathin lithium film intermittent in the length direction comprises a blank area with controllable length and a metal lithium layer area, wherein the length range of the metal lithium layer area is 1-2000mm, and the length range of the blank area is 1-200 mm;

the ultra-thin lithium film intermittent in the width direction has ultra-thin lithium film portions having a width in the range of 1-200mm, and intermittent portions between the lithium films have a width of 0.5-10 mm.

4. The ultra-thin lithium film composite of claim 1, wherein: the ultra-thin lithium film satisfies at least one of the following conditions:

porosity ranging from 0.1% to 20%, preferably from 0.1% to 10%, more preferably from 0.5% to 5%;

the through hole is in the shape of a round hole or a round-like hole;

the via pitch is 5 to 1000 microns, preferably 5 to 200 microns, more preferably 5 to 50 microns;

the thickness of the ultrathin lithium film is 1-10 microns.

5. The ultra-thin lithium film composite of claim 1, wherein: the stress regulating material for forming the stress control layer includes: one or more of vinyl dimethyl polysiloxane, hydrogen-containing silicone oil, punching and shearing oil, liquid paraffin, methyl silicone oil, emulsified methyl silicone oil, hydrogen-containing methyl silicone oil, silicone grease and polyethylene wax.

6. The ultra-thin lithium film composite of claim 5, wherein: the stress adjusting material is coated on at least one surface of the bearing layer in the form of solution, and the solvent comprises: one or more of toluene, n-butanol, polyvinyl alcohol, butanone and n-hexane.

7. The ultra-thin lithium film composite of claim 1, wherein: the bearing layer is made of a polymer: polyimide, nylon, cellulose, high-strength thin-film polyolefin (polyethylene, polypropylene, polystyrene), polyester (polyethylene terephthalate, polybutylene terephthalate, polyarylate); inorganic oxide(s): aluminum oxide; inorganic conductor: graphite, carbon nanotubes, graphene; a metal current collector: copper and aluminum; the bearing layer is a single-layer or multi-layer composite.

8. A method of preparing the ultra-thin lithium film composite of any one of claims 1-7, wherein: the method is a roll-to-roll continuous production method, and the ultrathin lithium film complex is obtained by rolling and compounding a metal lithium strip with the thickness of 10-250 mu m on a stress control layer of a bearing layer with the stress control layer in a rolling mode by taking the metal lithium strip as a raw material.

9. The method of claim 8, wherein: the rolling pressure is in the range of 0.1 to 150MPa, preferably 80 to 120 MPa.

10. The method of claim 8, wherein: the rolling is cold rolling, hot rolling or composite rolling, wherein the hot rolling is controlled within the temperature range of 60-120 ℃, and the composite rolling is preferably performed by hot rolling and then rolling.