WO2020258842A1 - Ultra-thin lithium film preform and preparation method therefor - Google Patents

Abstract

The present invention provides an ultra-thin lithium film preform and a preparation method therefor. The preform is provided with: a load bearing layer, and an ultra-thin lithium film located on at least one surface of the load bearing layer and composited together with the load bearing layer. The ultra-thin lithium film is a uniform thin film provided with through holes having a diameter of 5-200 microns, and has a uniform thickness of 0.5-15 microns and a thickness tolerance within ±0.5µm.

Description

Ultra-thin lithium film preform and preparation method thereof Technical field

The invention relates to the technical field of energy storage, and in particular to an ultra-thin lithium film preform that can be used for secondary batteries and a preparation method thereof.

Background technique

Lithium batteries are widely used in aerospace, computers, mobile communication equipment, robots and electric vehicles due to their advantages of high energy density, long cycle life and wide applicable temperature range. With the development of society and the advancement of science and technology, the energy density and cycle life of lithium batteries are becoming higher and higher. At present, lithium-ion batteries that use graphite as the negative electrode cannot meet the expectations of society. Therefore, it is necessary to develop new types with higher ratios. Capacity of positive and negative materials. For the negative electrode material, the pre-lithiation work can effectively increase the specific energy of the battery and increase the battery life. Lithium metal has a high specific capacity (3860mAh/g, 10 times that of graphite anode) and the lowest redox potential (-3.04V vs standard hydrogen potential). Using metal lithium to pre-lithiate the traditional graphite negative electrode, on the one hand, it can improve the first coulombic efficiency of the battery and increase the specific energy of the battery. On the other hand, it can effectively extend the cycle life of the battery, which makes lithium-ion batteries have a broader application. field.

Although the pre-lithiation (replenishment of lithium) has such advantages, it is necessary to precisely control its amount in the battery, which puts forward higher requirements for the pre-lithiation of the negative electrode. At present, the current cathode materials used in 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 lithium-ion batteries, while the negative electrode supplements lithium. Only a small amount of lithium needs to be provided to make up for the lithium loss during the cycle, which can improve the energy density and cycle life of the battery. Since the amount of lithium pre-inserted in the negative electrode is very small, usually the thickness of the lithium foil used for replenishing lithium only needs to be 0.5 to 10 microns. In the Chinese patent application CN201610102992.8 of Ningde Times New Energy, lithium powder is sprinkled on the surface of the pole piece during the process of replenishing lithium, and pre-lithiation is performed after rolling, and the amount of lithium is small. However, the method for supplementing lithium cannot yet achieve precise control of the amount of supplementing lithium, and the process is complicated, the cost is high, and more importantly, the safety is difficult to control. In view of this, a technology that can control the amount of replenishment of lithium and achieve high energy density of the battery is required.

Summary of the invention

The inventor unexpectedly discovered that for the lithium film used for the prelithiation of the negative electrode, if the lithium film has through holes, the presence of the holes can not only make the electrolyte easier to enter the contact interface between the lithium film and the negative electrode film, and improve the The lithiation speed, and the gas generated during the pre-lithiation can be released from the through hole to avoid the separation of the lithium film from the negative electrode film. Therefore, a lithium film with through holes can achieve a better prelithiation effect than a complete lithium film. In addition, the inventor also discovered that ultra-thin lithium films (0.5-15 microns thick, or even 1-5 microns thick) with through holes can be produced in a roll-to-roll manner by rolling, and by controlling the rolling pressure and rolling sequence The adhesion of the ultra-thin lithium film with through holes and the supporting layer can be controlled to make it at an appropriate level, which can ensure that the ultra-thin lithium film can be composited on the supporting layer and can be easily transferred from the supporting layer To other substrates such as lithium battery negative electrodes. Due to the existence of the through holes, the internal stress accumulation of the lithium film during the rolling process is relieved to a certain extent, so that the lithium film is not easily deformed, so that a thinner lithium film with uniform thickness (for example, 1-5 microns) can be prepared. Based on these findings, the present invention has been completed.

Therefore, one aspect of the present invention aims to provide an ultra-thin lithium film preform having: a supporting layer; and located on at least one surface of the supporting layer and interacting with the supporting layer. An ultra-thin lithium film laminated together, the ultra-thin lithium film is a uniform thin film with a through hole with a pore diameter of 5-50 microns, a uniform thickness of 0.5-15 microns, and a thickness tolerance within ±0.5 μm.

The ultra-thin lithium film preform of the present invention is a continuous, through-hole, supporting layer (film base material) supported, adjustable width and thickness (controlling lithium film size and pressure) composite strip.

In the present invention, the ultra-thin lithium film is a uniform film means that the ultra-thin lithium film has a complete film shape (without obvious wrinkles and deformation, with neat edges) and a uniform thickness. Preferably, the ultra-thin lithium film has through holes uniformly distributed throughout the lithium film.

Optionally, the lithium film surface of the ultra-thin lithium film preform is bright, metallic silver-white, and the lithium content is 99.90-99.95%. The lithium element content of the main body (inside) of the lithium film may be 99.95%-99.99%. The thickness of the lithium film ranges from 0.5 to 15 microns, preferably 1 to 10 microns, more preferably less than 5 microns, and the thickness tolerance is ±0.5 μm, preferably ±0.1 μm.

Optionally, the ultra-thin lithium film has uniformly distributed through holes with a pore diameter of 5 to 200 microns.

Optionally, the through-hole diameter of the ultra-thin lithium film may be 10-50 microns.

Optionally, the porosity of the ultra-thin lithium film is 1%-75%, preferably 5%-60%, more preferably 10%-50%.

Optionally, the shape of the through hole of the ultra-thin lithium film is a round hole or a round hole, and the hole spacing is 5 to 1000 microns, preferably 5 to 200 microns, more preferably 5 to 50 microns.

Optionally, the supporting layer material is a polymer: such as nylon, cellulose, high-strength filmed polyolefin (polyethylene, polypropylene, polystyrene); inorganic oxide: such as aluminum oxide; inorganic conductor: For example, graphite, carbon nanotubes, graphene; metal current collectors: such as copper, aluminum; the supporting layer may be a single layer or a multilayer composite.

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

Optionally, the contact surface between the supporting layer and the metal lithium is subjected to bonding treatment, preferably, the contact surface between the supporting layer and the metal lithium is coated with a paraffin wax n-hexane solution.

Another aspect of the present invention aims to provide a method for preparing the above-mentioned ultra-thin lithium film preform, characterized in that a roll-to-roll continuous production method is adopted, and a metal lithium strip with a thickness of 10 to 250 μm is used as a raw material. In the rolling method, the metal lithium strip is rolled and compounded on the supporting layer to obtain the ultra-thin lithium film preform.

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

Optionally, the rolling includes cold rolling, hot rolling and composite rolling, wherein the control temperature of the hot rolling ranges from 60 to 120°C, and the composite rolling is preferably hot rolling and then cold rolling.

Optionally, the rolling pressure range is 0.1-150Mpa, preferably 80-120Mpa.

Optionally, the adhesive force of the ultra-thin lithium film and the supporting layer is controlled by adjusting the rolling pressure, so that the adhesive force is 15 to 110 N/m.

Optionally, the surface of the roller has an anti-sticking material, and the anti-sticking material includes: polyethylene, polyoxymethylene, organic silicon polymer, and ceramics.

Optionally, a roll with a maximum tension range of 0.1-10N is used for rewinding, and the supporting roll itself is powered.

By controlling the rolling process, the present invention uses a simple process to obtain a preform loaded with a uniform ultra-thin lithium film with through holes. The ultra-thin lithium film with through holes of the preform can be easily transferred to the negative electrode of the lithium battery On the other hand, it has an improved pre-lithiation effect to achieve a high energy density of the battery.

Description of the drawings

Fig. 1 is a schematic diagram of a process for producing ultra-thin lithium film preforms by pressure composite production according to the present invention.

Figure 2 shows the 5 micron thick ultra-thin lithium film preform product prepared in Example 1 of the present application.

3 is a schematic diagram of the through holes of the ultra-thin lithium film preform prepared in Example 1.

Figure 4 shows the 5 micron thick ultra-thin lithium composite tape product prepared in Comparative Example 1 (adhesion is not controlled).

Detailed ways

In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Figure 1 shows a schematic diagram of a process for producing ultra-thin lithium film preforms by pressure composite production according to the present invention. As shown in Figure 1, the lithium metal strip and the carrier strip are used as raw materials, and the unwinding is carried out through the unwinding device. The unwinding device at least includes the lithium metal strip unwinding roller 11 and the supporting unwinding roller 11 respectively. The two unwinding support rolls 12 of the metal lithium belt and the supporting strip; the raw material lithium belt and the supporting strip enter the rolling mill 20 after passing the unwinding supporting roll 12; the rolling mill 20 includes at least a pair of rolls 21 and rolls 21 The adhesive coating 22, the rolling pressure of the rolling mill 20 and the roll gap between the rollers 21 can be fine-tuned; the material of the anti-adhesive coating 22 on the roller 21 can be selected from polyethylene, polyoxymethylene, and silicone polymer One or more of them; after pressure compounding, the carrier strip and the lithium material are compounded together to form an ultra-thin lithium film preform product; the exit side of the rolling mill 20 is provided with a winding device. The winding device includes at least a support roller 31, a tension control roller 32 and a winding roller 33; wherein the support roller 31 is powered and can use a small pulling force to pull the ultra-thin lithium film preform forward; the tension control roller 32 can move up and down or Swing 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 the swing angle of the tension control roller 32.

Hereinafter, using the above-mentioned process equipment, the present invention will be explained more specifically through examples. The various product structure parameters, various reaction participants, and process conditions used in the following examples are all typical examples. However, the inventors of the present case have verified a large number of experiments and other different structure parameters listed above , Other types of reaction participants and other process conditions are also applicable, and can also achieve the claimed technical effect of the invention.

Example 1:

The use of lithium metal strip with a lithium content of 99.95% and a thickness of 20 microns and a polyethylene film with a thickness of 50 microns (the surface of the polyethylene film has a coating formed by a paraffin-coated n-hexane solution) to assist in unwinding and winding The coiling device adopts a cold rolling method and controls a pressure of 100Mpa to obtain an ultra-thin lithium film preform product with a thickness of 5 microns (thickness tolerance of ±0.5 microns).

Figure 2 is a photo of a preform product with an ultra-thin lithium film of 5 microns thick. Figure 3 is a schematic diagram of the through hole of the ultra-thin lithium film preform (the light source is irradiated from the side of the carrier layer, that is, from the inside of the preform to the outside. The highlight in the middle is the direct point of the light source, and the light intensity is large and the light is illuminated from the back To show the through holes more clearly). As can be seen from Figure 3, the ultra-thin lithium film has a relatively complete film shape, with relatively uniformly distributed pinhole-like (through-the-film) through holes, the size of the holes is 5-50 microns, and the hole spacing is 5～ 100 microns.

Example 2:

The use of lithium metal strip with a lithium content of 99.95% and a thickness of 20 microns and a polyethylene film with a thickness of 50 microns (the surface of the polyethylene film has a coating formed by a paraffin-coated n-hexane solution) to assist in unwinding and winding The coiling device adopts the hot rolling method, the temperature is 80℃, and the control pressure is 120Mpa to obtain the ultra-thin lithium film preform product with a thickness of 5 microns (thickness tolerance of ±0.5 microns).

Example 3:

The use of lithium metal strip with a lithium content of 99.95% and a thickness of 20 microns and a polyethylene film with a thickness of 50 microns (the surface of the polyethylene film has a coating formed by a paraffin-coated n-hexane solution) to assist in unwinding and winding The coiling device first adopts hot rolling, temperature 80℃, pressure 120Mpa, and then cold rolling at ambient temperature, controlled pressure 100Mpa, to obtain ultra-thin lithium film preform products with a thickness of 5 microns (thickness tolerance of ±0.5 microns).

Example 4:

The use of lithium metal strip with a lithium content of 99.95% and a thickness of 20 microns and a polyethylene film with a thickness of 50 microns (the surface of the polyethylene film has a coating formed by a paraffin-coated n-hexane solution) to assist in unwinding and winding The coiling device adopts a cold rolling method with a pressure of 85Mpa to obtain an ultra-thin lithium preform product with a thickness of 10 microns (thickness tolerance of ±0.5 microns).

Comparative example 1:

Using lithium metal strip with a lithium content of 99.95% and a thickness of 20 microns and a polyethylene film with a thickness of 50 microns (without pretreatment of the film), auxiliary unwinding and rewinding devices, cold rolling method, controlled pressure 100Mpa, It is impossible to continuously obtain ultra-thin lithium film preform products with a thickness of 5 microns (thickness tolerance of ±0.5 microns), and the metal lithium foil prepared by this method has wrinkles and deformations and cannot be used, as shown in Figure 4.

Performance Testing:

Adopt American AR-10 universal adhesion tester, test temperature: 25±5℃, speed: 15cm/min, test angle: 120°. The adhesion of the ultra-thin lithium metal preforms produced in Examples 1 to 4 and Comparative Example 1 was tested, and the results are shown in Table 1.

Adhesion Test Table 1

Serial number	product name	Rolling method	Adhesion (N/m)
1	Example 1	Cold rolled	twenty two
2	Example 2	Hot rolled	82
3	Example 3	Hot rolled + cold rolled	103
4	Example 4	Cold rolled	17
5	Comparative example	Cold rolled	6

It can be seen from Table 1 that hot rolling can effectively increase the adhesion between the lithium film and the supporting layer and make the lithium preform more stable.

Example 5-Lithium Supplement Test

First, prepare the graphite electrode, the graphite powder (Better): Acetylene black AB (Better): Sodium carboxymethyl cellulose CMC (Shanghai Haiyi): SBR (Shanghai Haiyi) = 94:3: 1:2, dispersed in deionized water, controlled solid content of 35%, viscosity 2000-3000cp, stirring time 6h, single-sided coating on 10μm copper foil using a coater, and drying to prepare 50μm graphite pole piece. Then, using the 5 micron ultra-thin lithium preform product obtained in Example 2, the lithium film was bonded and transferred to the surface of the graphite electrode through a bonding treatment (control pressure 20MPa), and the supporting layer was peeled off and punched into a diameter of 15.6 cm The pole piece, and lithium foil form a half-cell, using 1M LiPF6, EC/DMC/EMC (1/1/1) (Shanshan electrolyte) as the electrolyte. Compared with the half-cell without pre-lithiation, in the half-cell that uses ultra-thin lithium preforms to pre-lithiate the graphite negative electrode, the first efficiency of the graphite negative electrode is increased from 92% to 99%, and the first efficiency is greatly improved .

It should be understood that the above descriptions are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in this invention. Within the scope of protection of the invention.

Claims (10)

1. An ultra-thin lithium film preform, characterized in that the preform has:

   Supporting layer; and

   An ultra-thin lithium membrane located on at least one surface of the supporting layer and composited with the supporting layer, the ultra-thin lithium membrane is a uniform thin film with through holes with a pore diameter of 5 to 200 microns, with a diameter of 0.5 -15 microns uniform thickness, thickness tolerance within ±0.5μm.
2. The ultra-thin lithium film preform according to claim 1, wherein the porosity of the ultra-thin lithium film is 1%-75%, preferably 5%-60%, more preferably 10%-50%.
3. The ultra-thin lithium film preform according to claim 1, wherein the shape of the through hole is a round hole or a round hole, and the hole spacing is 5 to 1000 microns, preferably 5 to 200 microns, more preferably 5 to 50 microns .
4. The ultra-thin lithium film preform according to claim 1, wherein the thickness of the ultra-thin lithium film is 1-10 microns.
5. The ultra-thin lithium film preform according to claim 1, wherein the contact surface between the supporting layer and the metal lithium is bonded.
6. The ultra-thin lithium film preform according to claim 1, wherein the supporting layer material is a polymer: such as nylon, cellulose, high-strength thin-film polyolefin (polyethylene, polypropylene, polystyrene) Ethylene); inorganic oxides: such as aluminum oxide; inorganic conductors: such as graphite, carbon nanotubes, graphene; metal current collectors: such as copper, aluminum; the supporting layer is a single layer or a multilayer composite.
7. A method for preparing the ultra-thin lithium film preform according to any one of claims 1 to 6, characterized in that: the method is a roll-to-roll continuous production method, using a metal lithium belt with a thickness of 10 to 250 μm As the raw material, the metal lithium strip is rolled and compounded on the supporting layer by a rolling method to obtain the ultra-thin lithium film preform.
8. The method according to claim 7, characterized in that the rolling pressure range is 0.1-150Mpa, preferably 80-120Mpa.
9. The method according to claim 7, characterized in that the rolling is cold rolling, hot rolling or composite rolling, wherein the control temperature range of hot rolling is 60-120°C, and the composite rolling is preferably hot rolling followed by cold rolling.
10. The method according to any one of claims 7-9, characterized in that the adhesive force of the ultra-thin lithium film and the supporting layer is controlled by adjusting the rolling pressure, so that the adhesive force is 15-110N/ m.

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