Preparation method and application of ultrathin lithium foil based on distributed lithium injection

Abstract

The invention discloses a preparation method and application of an ultrathin lithium foil based on distributed lithium injection. The lithium foil is compounded by injecting molten metal lithium into a thermal expansion multilayer carbon film in a multi-site manner. The materials of the carbon film comprise graphene, carbon nanotubes and the like, and a large number of oxygen-containing functional groups are introduced into the carbon materials to improve the lithium affinity and promote the diffusion of molten lithium to the interlayer of the carbon film, so that the composite ultrathin lithium foil with highly controllable lithium distribution and total amount is formed. And the pre-lithiation effect on the electrode material can be achieved by rolling the pre-lithiation film onto the surface of the negative electrode of the lithium ion battery, so that the initial coulombic efficiency of the lithium ion battery is effectively improved. The capacity corresponding to the lithium foil can be regulated and controlled by changing the thickness and components of the carbon film, and the distribution of lithium can be regulated and controlled by changing injection sites, so that accurate pre-lithiation is realized. Therefore, the composite ultrathin lithium foil can further improve the performance of the lithium ion battery so as to meet the requirements of intermittent large-scale energy storage and new energy automobiles on high-performance batteries.

Description

Technical Field

[0001] The invention relates to the technical field of battery manufacturing, and more specifically, to a preparation method and application of ultra-thin lithium foil based on distributed lithium injection. Background Art

[0002] Lithium secondary batteries, mainly lithium-ion batteries, are widely used in the field of energy storage due to their high energy density, low loss, and flexible operation. Despite this, lithium-ion batteries face the inherent problem of low first coulombic efficiency, that is, the first discharge capacity is less than the charging capacity. This is mainly due to the reduction and decomposition of the organic electrolyte on the surface of the negative electrode to form a solid electrolyte interface (SEI) film with a complex composition structure, which permanently consumes a part of the lithium ions and causes irreversible capacity loss. In order to solve this problem, measures can be taken to pre-lithiate the negative electrode, that is, to introduce additional lithium sources to contribute lithium ions to form an SEI film, thereby improving the first coulombic efficiency, and then improving the overall capacity and energy density of the battery to meet the growing energy storage needs in daily life. It is worth noting that the degree of pre-lithiation of lithium-ion batteries needs to be strictly controlled. Insufficient pre-lithiation will cause the negative electrode to still expose reaction sites, and the first coulombic efficiency cannot be fully improved; while excessive pre-lithiation may cause too much lithium source to be deposited on the surface of the negative electrode into lithium dendrites or dead lithium, puncturing the diaphragm to cause battery short circuit, causing safety problems. Therefore, precise control of the pre-lithiation process is particularly important.

[0003] There are many ways to pre-lithiate, such as electrochemical method, chemical method, lithium powder method, direct contact method of lithium metal, etc. Among them, the direct contact method of lithium metal has high application potential due to its advantages such as high efficiency, convenience, and integration into the original battery assembly process. It is achieved by rolling an extremely thin lithium foil onto the surface of the negative electrode. In the electrolyte environment, the negative electrode active material will spontaneously insert lithium due to the potential difference with the negative electrode material. However, since the SEI film formed during the first charge of the lithium-ion battery has a complex and non-uniform composition structure, its formation depends on the components of the electrode and the electrolyte, and is affected by multiple factors such as temperature and battery test conditions. This non-uniform interface structure results in different amounts of lithium replenishment required at different sites. Therefore, using pure lithium foil with uniform thickness cannot completely and accurately pre-lithiate. In addition, if the pure lithium foil fails to contact the electrode evenly due to factors such as rough electrode surface or loose fitting, the lithium replenishment layer closest to the negative electrode material may be consumed, resulting in the formation of dead lithium, which greatly reduces the efficiency of lithium replenishment, and may also form dendrites, causing safety hazards. Chinese patent CN115642228A discloses a method for preparing a pre-lithiation negative electrode, in which the negative electrode and ultra-thin lithium foil or lithium alloy foil are pressure-compounded to obtain a lithium-supplementing negative electrode, which is then soaked in an electrolyte, cleaned and dried, thereby solving the problem of heat generation during the pre-lithiation process. Since uniform lithium foil or lithium alloy foil is still used, there is still a problem of inaccurate pre-lithiation. Chinese patent CN117981099A discloses a method for pre-lithiation of anode materials, in which the anode material is contacted with the substrate surface of the substrate material in an electrochemical cell, and the substrate surface contains patterned lithium, thereby forming a pre-lithiation anode material. This patterned lithium can cope with different lithium replenishment needs on the electrode surface to a certain extent, but the phenomenon of poor contact between the electrode and lithium and residual dead lithium may still occur. Therefore, there is an urgent need for a composite lithium foil with a conductive network and controllable lithium distribution for interface engineering regulation of lithium-ion batteries.

[0004] Therefore, new solutions need to be proposed to solve this problem. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing a composite ultra-thin lithium foil, which is obtained by multi-site injection of molten lithium into a thermally expandable multilayer carbon film. The specific steps are as follows: The above technical purpose of the present invention is achieved by the following technical solution: a method for preparing a composite ultra-thin lithium foil comprises the following steps: S1, dispersing hydroxylated carbon tubes, polyacrylonitrile, polyethylene glycol, etc. in high-purity water, and then mixing with aqueous graphene oxide to form a uniform slurry, coating the slurry on a substrate, contacting a heating plate in an inert gas environment after drying to rapidly reduce and expand the slurry, and then coating the slurry on both sides with a protective film or metal foil, and rolling the slurry through a roller mill to form a relatively flat thermal expansion multilayer carbon film with controllable porosity; S2, using a high temperature resistant tube with a diameter of 0.1-10 mm to absorb molten metal lithium droplets and continuously contact the thermal expansion multilayer carbon film obtained in step S1 at preset positions, so that a portion of molten lithium remains at each position and is cooled and fixed, and then the carbon film is heated to allow lithium to continuously diffuse into the interior of the carbon film under the action of capillary force, thereby preparing a composite ultra-thin lithium foil with highly controllable lithium loading and distribution.

[0006] Furthermore, the multilayer carbon film is composed of a mixture of graphene and other carbon materials or polymers, including one or more of hydroxylated carbon tubes, polyacrylonitrile, and polyethylene glycol; Furthermore, the solid content of the slurry described in step S1 is 0.5-5%, and the graphene accounts for no less than 50% of the solid matter, and the coating thickness of the slurry is 0.2-2 mm; the material of the substrate is one of glass, polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, polyethylene terephthalate, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium.

[0007] Furthermore, the temperature of the heating plate in step S1 is 200-500°C.

[0008] Furthermore, the thickness of the thermally expandable multilayer carbon film after rolling in step S1 is 5-50 μm.

[0009] Furthermore, the material of the protective film used during rolling in step S1 is a mixture of one or more of polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, and polyethylene terephthalate, and the material of the metal foil is a mixture of one or more of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium.

[0010] Furthermore, the high temperature resistant tube described in step S2 is made of one or more of metals (titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, osmium) and polymers (high temperature nylon, polyphenylene sulfide, polyaryletherketone, polyimide, polyetheretherketone), and the terminal pore diameter is 0.1~10 mm.

[0011] Furthermore, the lithium contact sites described in step S2 have a density of 1 to 10 cm -2 The pattern is one or more combinations of matrix, circle, ellipse, triangle, hexagon, etc., and the distribution type is uniform, gradient or radial.

[0012] Furthermore, the molten lithium diffusion waiting time in step S2 is 3 to 30 minutes.

[0013] A composite ultra-thin lithium foil is used in a lithium battery. The composite ultra-thin lithium foil is laminated with a negative electrode material by an electric roller, and then assembled with a positive electrode, a separator and an electrolyte. The composite ultra-thin lithium foil is used in a lithium-ion battery, a lithium-sulfur battery and a lithium-air battery.

[0014] Furthermore, the negative electrode material is selected from graphite negative electrode, soft carbon negative electrode, hard carbon negative electrode, silicon-carbon negative electrode, graphite-silicon oxide negative electrode, nano-silicon negative electrode, silicon oxide negative electrode, and tin-based negative electrode.

[0015] In summary, the present invention has the following beneficial effects: 1) To address the problem of different amounts of lithium replenishment required in different areas of the negative electrode of a lithium-ion battery during pre-lithiation, the injection site of molten lithium in the thermally expandable multilayer carbon film can be changed to achieve regulation. The diffusion of molten lithium into the carbon film after heating has a certain concentration gradient, which makes the regulation of lithium distribution more flexible. Through quantitative adjustment, the differentiated needs of lithium replenishment at the micron or even nano level can be met.

[0016] 2) The thermally expandable carbon film is composed of a layered three-dimensional conductive network structure of graphene and carbon nanotubes, or other high-temperature carbonized polymers. When residual lithium appears locally, a loop can be formed between the conductive network and other nearby lithium-deficient sites to replenish lithium, thereby homogenizing the lithium replenishment demand at the nanoscale and achieving high-precision pre-lithiation.

[0017] 3) Graphene and other carbon materials promote the uniform deposition of lithium and effectively inhibit the formation of lithium dendrites by precisely controlling the surface electric field, thereby significantly improving the cycle stability of the battery.

[0018] 4) Each preparation stage covered by the present invention can rely on industrial-grade equipment to achieve efficient and smooth operation, and in the entire preparation process and its application, there is no need to introduce organic solvents, and the tedious steps of battery pre-assembly are also omitted. This innovative design ensures the efficiency, safety and environmental friendliness of the production process, and lays a solid foundation for large-scale production, thereby accurately meeting the urgent needs of the commercial battery market. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a photo of the composite ultra-thin lithium foil prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the thermally expandable multilayer carbon film prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the composite ultra-thin lithium foil prepared in Example 1 of the present invention; Figure 4 This is a Raman graph of the graphene / carbon nanotube composite ultra-thin lithium foil prepared in Example 1 of the present invention; Figure 5The first charge and discharge curves of the button batteries assembled in Example 1, Example 3 and Comparative Example 2 of the present invention are shown. DETAILED DESCRIPTION

[0020] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0021] Step 1: Take 150 mg of hydroxylated carbon nanotubes, put them into 10 ml of high-purity water, disperse them in a homogenizer for 15 min, and then take 35 ml of the solution with a concentration of 10 mg ml -1 The aqueous phase graphene oxide was mixed into a uniform slurry, coated on the substrate by a coater with a thickness of 0.5 mm, and then dried at room temperature for 3 days.

[0022] Step 2: peel the dried film from step 1 from the substrate, transfer it to a glove box filled with inert gas, and then contact it with a heating plate to quickly restore and expand it. Then, coat it with a protective film or metal foil on both sides and pass it through a roller mill at a speed of 20 mm s -1 The film was rolled into a relatively flat thermally expandable multilayer carbon film with controllable porosity.

[0023] Step 3: Use a stainless steel tube with a diameter of 1 mm to absorb molten metal lithium, so that the end droplets are continuously in contact with the thermal expansion multilayer carbon film obtained in step 2 according to the preset matrix-shaped sites, so that a portion of molten lithium remains at each site and is cooled and fixed. Then, the carbon film is heated to allow lithium to continuously diffuse into the carbon film under the action of capillary force, thereby preparing a composite ultra-thin lithium foil with highly controllable lithium loading and distribution.

[0024] The appearance of the obtained composite ultra-thin lithium foil is as follows Figure 1 As shown, it is a black film with silver spots. The thickness is about 20 μm as measured by a thickness gauge. SEM characterization shows that when molten lithium is not injected, the smooth graphene sheets are anchored to each other through carbon nanotubes and have large pores ( Figure 2 ); After the injection of molten lithium, the surface of the graphene sheet becomes obviously rough, indicating that it is fully wrapped by the lithium grains ( Figure 3 ). At the same time, no additional agglomeration of metallic lithium was found, indicating that it has excellent binding properties with graphene, ensuring that dead lithium will not be formed during the pre-lithiation process. There are obvious D and G peaks in the Raman spectrum, indicating that graphene and other carbon materials are not completely reduced, and the functional groups on their surfaces can more firmly bind to lithium ( Figure 4 ).

[0025] The coating substrate described in step S1 is made of one of glass, polymer (polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, polyethylene terephthalate), and metal (titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium).

[0026] Furthermore, the temperature of the heating plate in step S2 is 200-500°C, and the material of the protective film used during rolling is a mixture of one or more of polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polyoxypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, and polyethylene terephthalate. The material of the metal foil is a mixture of one or more of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium.

[0027] The lithium contact sites described in step S3 have a density of 1 to 10 cm -2 The pattern is one or more combinations of matrix, circle, ellipse, triangle, hexagon, etc. The distribution type is uniform, gradual or radial. The waiting time for molten lithium diffusion is 3 to 30 minutes.

[0028] The main components of the obtained composite ultra-thin lithium foil are graphene, carbon nanotubes and metallic lithium. The carbon nanotubes are hydroxylated, and the graphene has a high degree of oxidation, which can react with lithium to improve its lithium affinity. The molten lithium can be evenly diffused into the multilayer carbon film to form a network structure. The composite ultra-thin lithium foil can regulate the total amount and distribution of lithium sources by changing the thickness of the carbon film, the density, pattern and distribution of lithium injection sites, and is coated on the surface of the negative electrode to accurately pre-lithiate the negative electrode, thereby improving the first coulomb efficiency of the lithium secondary battery.

[0029] The composite ultra-thin lithium foil obtained in Example 1 is used in lithium-ion batteries. The specific steps are as follows: Step 1, preparation of electrode: Silicon, PAALi, and graphene were mixed in a mass ratio of 9:1:10, and the film was scraped with a coating machine to a thickness of 1 mm. After the film was dried, it was foamed with hydrazine hydrate at a mass fraction of 10% for 10 min, and then rinsed with water and ethanol in a volume ratio of 1:1 for 3 times, each time for 30 min. After drying, it was heated for reduction and incubated in a tube furnace at 1 °C for 1 min. -1 Heat to 200℃, then 2℃ min -1 The temperature was raised to 1000 °C and kept for 1 h to obtain an electrode without pre-lithiation.

[0030] Step 2, pre-lithiation of the electrode: The electrode obtained in step 1 is laminated with the composite ultra-thin lithium foil obtained in Example 1, and rolled by an electric roller under the protection of a high-strength polytetrafluoroethylene film, and rolled 5 times at a rolling rate of 10 mm s-1 to fully combine the two.

[0031] Step 3, battery assembly: Assemble the above-mentioned pre-lithiated electrode, PP / PE / PP composite separator, and lithium sheet into a button battery. The electrolyte is 1 M lithium hexafluorophosphate in ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, and a solution of 1% by mass fraction of vinylene carbonate and 10% by mass fraction of fluoroethylene carbonate is added.

[0032] Figure 5 The first charge and discharge process of the battery that has been pre-lithiated with a composite ultra-thin lithium foil and that has not been pre-lithiated is demonstrated. Compared with the silicon negative electrode battery that has not been pre-lithiated, the first coulombic efficiency of the pre-lithiated battery has increased from 92.1% to 98.7%, and the effect of pre-lithiation will also change through the regulation of the lithium injection site. Based on a stable battery system, after quantitative analysis of the amount of lithium replenishment at different sites, the composite ultra-thin lithium foil corresponding to the lithium distribution is designed, which can achieve precise pre-lithiation with an initial coulombic efficiency of 100%.

[0033] Comparative Example 1 Assembly of the same battery without pre-lithiation treatment.

[0034] (1) Preparation of electrode: Silicon, PAALi and graphene were mixed in a mass ratio of 9:1:10, and the film was scraped with a coating machine to a thickness of 1 mm. After the film was dried, it was foamed with hydrazine hydrate at a mass fraction of 10% for 10 min, and then rinsed with water and ethanol in a volume ratio of 1:1 for 3 times, each time for 30 min. After drying, it was heated for reduction and incubated in a tube furnace at 1 °C min -1 Heat to 200℃, then 2℃ min -1 The temperature was raised to 1000 °C and kept for 1 h to obtain an electrode without pre-lithiation.

[0035] (2) The above-mentioned non-pre-lithiated electrode, PP / PE / PP composite separator, and lithium sheet were assembled into a button cell. The electrolyte was 1M lithium hexafluorophosphate in ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, and a solution of 1% by mass of vinylene carbonate and 10% by mass of fluoroethylene carbonate was added.

[0036] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a composite ultra-thin lithium foil, characterized in that: The method is prepared by multi-site injection of molten lithium into a thermally expandable multilayer carbon film, comprising the following steps: S1, disperse hydroxylated carbon tubes, polyacrylonitrile, polyethylene glycol, etc. in high-purity water, mix with aqueous graphene oxide to form a uniform slurry, and coat it on the substrate. The dried film contacts a heating plate in an inert gas environment to quickly reduce and expand, and then double-sidedly coated with a protective film or metal foil, and rolled into a relatively flat thermal expansion multilayer carbon film with controllable porosity through a double-roller machine: S2, using a high temperature resistant tube with a diameter of 0.1-10 mm to absorb molten metal lithium droplets and continuously contact the thermal expansion multilayer carbon film obtained in step S1 at preset positions, so that a portion of molten lithium remains at each position and is cooled and fixed, and then the carbon film is heated to allow lithium to continuously diffuse into the carbon film under the action of capillary force, thereby preparing a composite ultra-thin lithium foil with highly controllable lithium loading and distribution; The multilayer carbon film is composed of graphene and other carbon materials or polymers, including a mixture of one or more of hydroxylated carbon tubes, polyacrylonitrile and polyethylene glycol.

2. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The solid content of the slurry in step S1 is 0.5-5%, and the graphene accounts for no less than 50% of the solid matter, and the coating thickness of the slurry is 0.2-2 mm; The material of the substrate is one of glass, polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, polyethylene terephthalate, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium.

3. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The temperature of the heating plate in step S1 is 200-500°C.

4. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The thickness of the thermally expandable multilayer carbon film after rolling described in step S1 is 5-50 μm.

5. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The material of the protective film used during rolling in step S1 is a mixture of one or more of polypropylene, polyacrylonitrile, polyethylene, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polycaprolactone, and polyethylene terephthalate; the material of the metal foil is a mixture of one or more of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, and osmium.

6. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The high temperature resistant tube described in step S2 is made of one or more of metals (titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, osmium) and polymers (high temperature nylon, polyphenylene sulfide, polyaryletherketone, polyimide, polyetheretherketone), and the terminal pore diameter is 0.1~10mm.

7. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The lithium contact sites described in step S2 have a density of 1 to 10 cm -2 The pattern is one or more combinations of matrix, circle, ellipse, triangle, hexagon, etc., and the distribution type is uniform, gradient or radial.

8. The method for preparing a composite ultra-thin lithium foil according to claim 1, characterized in that: The waiting time for the molten lithium diffusion described in step S2 is 3 to 30 minutes.

9. Application of a composite ultra-thin lithium foil in a lithium battery, characterized in that: The composite ultra-thin lithium foil is laminated with the negative electrode material through an electric roller machine, and then assembled with the positive electrode, separator and electrolyte. It is used in lithium-ion batteries, lithium-sulfur batteries and lithium-air batteries.

10. The use according to claim 9, characterized in that: The negative electrode material is selected from graphite negative electrode, soft carbon negative electrode, hard carbon negative electrode, silicon-carbon negative electrode, graphite-silicon oxide negative electrode, nano-silicon negative electrode, silicon oxide negative electrode, and tin-based negative electrode.

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