Fiber-carbon reinforced ultrathin lithium foil, and preparation method and application thereof

Abstract

The present application relates to the technical field of ultrathin lithium metal negative electrode, and particularly relates to a fiber carbon reinforced ultrathin lithium foil, a preparation method and application thereof. The thickness of the ultrathin lithium foil is <= 20 mu m, and the fiber carbon material loaded with zinc oxide is used as raw material to prepare the ultrathin lithium foil. The preparation method of the fiber carbon material loaded with zinc oxide is as follows: natural fibers are soaked in a zinc salt solution, and after sufficient stirring, the fibers are taken out and dried, and then high-temperature carbonization is carried out under anaerobic conditions. The carbon powder obtained by adding the biochar material loaded with zinc oxide to the ultrathin lithium foil greatly improves the mechanical strength and ductility of the lithium metal, so that the lithium metal is not easy to break and damage during rolling, and can be rolled to an ultrathin thickness of <= 20 mu m. The lithium battery negative electrode prepared from the ultrathin lithium foil has good electrochemical performance such as cycle performance and coulomb efficiency, and the preparation method is simple, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of ultrathin lithium metal anode technology, specifically to a fiber carbon-reinforced ultrathin lithium foil, its preparation method, and its application. Background Technology

[0002] Among numerous energy storage technologies, lithium-ion batteries have attracted significant attention due to their safety, portability, and high energy density. Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles, and the military and aerospace industries. Using metallic lithium as the negative electrode material, lithium-ion batteries possess high theoretical capacity and low redox potential; however, the high reactivity of metallic lithium can lead to problems such as dendrite growth and interfacial side reactions. To improve the safety, reduce cost, and increase cycle stability of lithium metal batteries, this can be achieved by thinning the lithium foil and reducing the excess lithium usage. This method not only reduces the risk of lithium dendrite growth and the possibility of short circuits but also improves lithium utilization efficiency, reduces the consumption of active lithium, thereby extending battery life and increasing coulombic efficiency.

[0003] Ultrathin lithium foil generally refers to lithium foil with a thickness of less than 50μm. Compared to traditional lithium foil, ultrathin lithium foil exhibits higher energy density and better safety. Ultrathin lithium foil possesses a larger specific surface area and uniform thickness, which improves the interfacial contact between the metal and the electrolyte, promoting the uniform distribution and transport of lithium ions, thereby reducing localized oversaturation. Furthermore, since the formation of lithium dendrites is usually related to the non-uniformity of lithium ion deposition on the surface, the design of ultrathin lithium foil helps improve the uniformity of the deposition process, reducing localized current density and thus lowering the dendrite growth rate. Therefore, both battery safety and cycle stability are improved.

[0004] However, the industrial production of ultrathin lithium foil faces severe challenges, primarily due to potential wrinkles and damage during production, as well as the complexity of the process. When the thickness approaches 50μm, it nears the thickness limit of lithium foil, at which point the yield rate of traditional mechanical rolling methods drops sharply. This is because metallic lithium undergoes dramatic stretching and sticking during rolling; further thinning leads to uneven thickness, easy breakage, and sticking to the rolls. Even if ultrathin rolling is successfully achieved, high uniformity and high strength are difficult to maintain, and its rough surface and internal defects often do not meet the requirements of high-end batteries.

[0005] Therefore, there is an urgent need for an ultrathin lithium foil that is simple to prepare, low in cost, and uniform and dense. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fiber carbon-reinforced ultrathin lithium foil that achieves at least the effects of uniform density, simple process, and low cost.

[0007] The objective of this invention is achieved through the following technical solution: A fiber-carbon reinforced ultrathin lithium foil with a thickness of ≤20μm is prepared from fibrous carbon material loaded with zinc oxide.

[0008] In some embodiments, the method for preparing the zinc oxide-loaded fibrous carbon material is as follows: natural fibers are soaked in a zinc salt solution, stirred thoroughly, dried, and then carbonized at high temperature under anaerobic conditions to obtain the final product.

[0009] In some examples, the zinc salt includes zinc acetate, zinc nitrate, or zinc sulfate.

[0010] In some examples, the natural fibers include cotton, bamboo, or hemp fibers.

[0011] In some examples, the molar concentration of zinc ions in the zinc salt solution is 0.6 mol / L.

[0012] Preferably, the weight ratio of the natural fiber to the zinc in the zinc salt is 1:3~5.

[0013] In some examples, the high-temperature carbonization temperature is 800~900°C.

[0014] In some embodiments, the method for preparing the fiber-reinforced carbon ultrathin lithium foil includes the following steps: S1: Grind the zinc oxide-loaded fibrous carbon material into carbon powder; S2: In an oxygen-free environment, the carbon powder is evenly sprinkled on the surface of the lithium foil, and then folded and rolled several times to obtain a composite lithium strip, which is gray-black. S3: In an oxygen-free environment, the composite lithium strip is melted and then cooled to obtain a composite metal. The composite metal is then rolled at room temperature to obtain the ultrathin lithium anode.

[0015] The composite metal has a composition of Li / Li x C / Li y Zn.

[0016] In some examples, the folding and rolling is performed five times or more.

[0017] In some examples, in step S1, the particle size of the toner is...

[0018] In some examples, in step S2, the weight ratio of the toner to the lithium foil is 1:4 to 20.

[0019] In some embodiments, the fiber-reinforced carbon ultrathin lithium foil is used to prepare a lithium battery anode.

[0020] In some examples, the lithium battery negative electrode has a sandwich structure.

[0021] It is worth noting that this invention completes both biomass carbonization and ZnO nanoparticle growth in a one-step process, resulting in a simple and straightforward operation. The one-step method ensures that ZnO nanoparticles grow firmly on the carbonized fibers, thus making it easier to control the size and uniform growth of the ZnO nanoparticles.

[0022] This invention uses cotton fiber as a biomass raw material to produce fibrous carbon materials. Even after grinding into powder, the short fibrous carbon skeleton maintains its morphology and exhibits random orientation. When mixed with lithium, it forms an isotropic composite structure, which helps reduce local current density and suppress dendrite formation. The fibrous carbon skeleton possesses excellent mechanical properties and flexibility. When combined with anode materials, it improves creep resistance, preventing damage to lithium metal during repeated rolling processes. This makes it possible to prepare ultra-thin lithium anodes, significantly increasing the energy density of the anode material. Simultaneously, the addition of fibrous carbon powder provides excellent wettability and mixing uniformity, enabling more uniform and thorough physical mixing with lithium (whether molten lithium or lithium powder). This avoids potential "unfilled" or "poorly contacted" dead zones present in a complete carbon skeleton, making it easier to scale up production.

[0023] The presence of ZnO particles provides lithium-affinity sites. ZnO has good lithium affinity and can significantly reduce the nucleation overpotential of lithium metal. This makes lithium ions preferentially nucleate and deposit on these ZnO sites, rather than randomly and disorderly stacking, thus effectively suppressing the formation of lithium dendrites that lead to battery short circuits and failures.

[0024] During the first cycle of the battery or during contact with molten lithium, the ZnO in the bio-cellulose carbon-reinforced ultrathin lithium foil reacts with lithium to form a lithium-zinc (Li-Zn) alloy phase and lithium oxide (Li₂O). This in-situ generated alloy layer exhibits excellent lithiophilicity and high ionic conductivity, further promoting the uniform and rapid transport of subsequent lithium ions, while also optimizing the composition of the SEI film for a virtuous cycle. The presence of biomass carbon powder causes the fibrous carbon skeleton to interweave, forming a continuous, highly conductive network. This significantly enhances the overall electronic conductivity of the electrode, compensating for the poor conductivity of ZnO itself and ensuring uniform current distribution. Simultaneously, the biomass carbon powder provides a buffer space for volume expansion, preventing electrode structure collapse, while increasing the specific surface area, reducing local current density, effectively delaying dendrite initiation, and improving deposition uniformity. The carbon powder also acts as a stabilizing carrier for ZnO, preventing the active material from detaching from the current collector during cycling and ensuring the stability of the electrical contact.

[0025] The beneficial effects of this invention are: 1. The ultrathin lithium foil of the present invention is made by grinding carbon powder with zinc oxide-doped biochar material, which greatly improves the mechanical strength and ductility of lithium metal, making it less prone to breakage and damage during rolling. It can be rolled to an ultrathin thickness of ≤20μm. The presence of ZnO particles provides lithium-affinity sites. ZnO has good lithium affinity and can significantly reduce the nucleation overpotential of lithium metal. During the melting alloying process, the zinc oxide (ZnO) in the carbon powder reacts with lithium to form LiyZn alloy nanophase, which acts as "super-lithiophilic" sites, causing lithium ions to preferentially nucleate and deposit on these ZnO sites, thereby effectively suppressing the formation of lithium dendrites that lead to battery short circuits and failures.

[0026] 2. The ultrathin lithium foil of this invention is suitable for preparing lithium battery anode materials. During the first battery cycle or contact with molten lithium, it forms an SEI film with high mechanical strength, good ionic conductivity, and stable chemical properties. This results in low and stable interfacial impedance, minimal battery polarization, and a stable voltage plateau. Consequently, it significantly reduces electrolyte consumption and irreversible loss of active lithium, improving battery cycle performance, coulombic efficiency, and other electrochemical properties.

[0027] 3. The method for preparing ultrathin lithium foil of the present invention is simple, has low raw material cost, and extremely high product qualification rate, making it suitable for large-scale industrial production. Attached Figure Description

[0028] Figure 1 This is a SEM image of the toner in Example 1 of the present invention.

[0029] Figure 2 This is a test diagram of the long-cycle performance of the ultrathin lithium anode in Experiment Example 1 of this invention.

[0030] Figure 3 This is a test diagram of the long-cycle performance of the ultrathin lithium anode in Experimental Example 2 of the present invention.

[0031] Figure 4 The image shows the coulombic efficiency test results of the ultrathin lithium anode in Examples 1-3 of Experiment 3 of this invention.

[0032] Figure 5 The coulombic efficiency test graphs for the ultrathin lithium anode in Example 1 and the comparative example of Experiment 4 of this invention are shown. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0034] Example 1 This embodiment is used to prepare a fiber-carbon reinforced ultrathin lithium foil and an ultrathin lithium anode with a sandwich structure. The specific method is as follows: 1) Take 0.5g of degreased cotton and wash it 2-3 times with deionized water and anhydrous ethanol in sequence, and finally wash it with deionized water to remove residual ethanol. Dry the washed degreased cotton in a vacuum oven at 60℃ for 6-10 hours to obtain dried degreased cotton.

[0035] 2) Accurately weigh 5.5g of zinc acetate using an electronic balance, pour it into 50mL of deionized water, and magnetically stir for 20-30 minutes at room temperature. Then add dry, defatted cotton and continue magnetically stirring for 2-3 hours at room temperature. Transfer the mixture (including the solution and the impregnated defatted cotton) to a constant temperature drying oven and dry at 60°C for 6-12 hours. Place the dried mixture in a tube furnace or muffle furnace, and purge with high-purity argon gas at a flow rate of 50-100ml / min. Purge for at least 30 minutes, raise the temperature at a rate of 5°C / min to 800°C, hold at that temperature for 2-3 hours, and then cool the furnace to obtain zinc oxide-doped fibrous carbon material.

[0036] 3) The fibrous carbon material was ground using a nano-grinding mill (grinding method: carbon powder was mixed with anhydrous ethanol (solid content 45%), zirconia balls were added (ball-to-material ratio 4:1), and the mixture was ground at 350 rpm for 12 hours. After grinding, the mixture was sieved through a 400-mesh and a 2400-mesh screen to remove the zirconia balls and large particles that were not ground), resulting in carbon powder with a particle size <100 nm, which appeared as a uniform black powder (SEM image as shown). Figure 1 (As shown). Take a lithium foil as a substrate, evenly sprinkle powder on its surface, and then composite it by folding and rolling (the weight ratio of powder to lithium metal is 1:9). Repeat the folding and rolling process five times to obtain a composite lithium strip.

[0037] 4) Place the composite lithium strip in a nickel crucible, then place it on a heating stage inside a glove box. Slowly heat the mixture to 270°C until it is completely melted, and hold it at that temperature for 30 minutes. Then turn off the heating stage and allow the melt to cool naturally inside the glove box until it completely solidifies, obtaining a "Li / LixC / LiyZn" composite metal ingot. Place this composite metal ingot in a roller mill and repeatedly roll it at room temperature until a uniform and dense ultrathin lithium anode with a thickness of 15 μm is obtained.

[0038] Example 2 This embodiment is used to prepare a fiber-carbon reinforced ultrathin lithium foil and an ultrathin lithium anode with a sandwich structure. The difference from the previous embodiment is that in step 3), the weight ratio of powder to lithium metal is 1:19, and some parameters are different. The specific method is as follows: 1) Take 0.5g of degreased cotton and wash it 2-3 times with deionized water and anhydrous ethanol in sequence, and finally wash it with deionized water to remove residual ethanol. Dry the washed degreased cotton in a vacuum oven at 60℃ for 6-10 hours to obtain dried degreased cotton.

[0039] 2) Accurately weigh 5.5g of zinc acetate using an electronic balance, pour it into 50mL of deionized water, and magnetically stir for 20-30 minutes at room temperature. Then add dry, defatted cotton and continue magnetically stirring for 2-3 hours at room temperature. Transfer the mixture (including the solution and the impregnated defatted cotton) to a constant temperature drying oven and dry at 60°C for 6-12 hours. Place the dried mixture in a tube furnace or muffle furnace, and purge with high-purity argon gas at a flow rate of 50-100ml / min. Purge for at least 30 minutes, raise the temperature at a rate of 5°C / min to 800°C, hold at that temperature for 2-3 hours, and then cool the furnace to obtain zinc oxide-doped fibrous carbon material.

[0040] 3) The fibrous carbon material was ground using a nano-grinding machine to obtain carbon powder with a particle size of <100nm, which was a uniform black powder. A lithium foil was taken as a substrate, and the powder was evenly sprinkled on its surface. Then, the composite was formed by folding and rolling (the weight ratio of powder to lithium metal was 1:19). The folding and rolling were repeated five times to obtain a composite lithium strip.

[0041] 4) Place the composite lithium strip in a nickel crucible, then place it on a heating stage inside a glove box. Slowly heat the mixture to 270°C until it is completely melted, and hold it at that temperature for 30 minutes. Then turn off the heating stage and allow the melt to cool naturally inside the glove box until it completely solidifies, obtaining a "Li / LixC / LiyZn" composite metal ingot. Place this composite metal ingot in a roller mill and repeatedly roll it at room temperature until a uniform and dense ultrathin lithium anode with a thickness of 15 μm is obtained.

[0042] Example 3 This embodiment is used to prepare a fiber-reinforced carbon ultrathin lithium foil and an ultrathin lithium anode with a sandwich structure. The difference from the previous embodiment is that in step 3), the weight ratio of powder to lithium metal is 1:4, and some parameters are different. The specific method is as follows: 1) Take 0.5g of degreased cotton and wash it 2-3 times with deionized water and anhydrous ethanol in sequence, and finally wash it with deionized water to remove residual ethanol. Dry the washed degreased cotton in a vacuum oven at 60℃ for 6-10 hours to obtain dried degreased cotton.

[0043] 2) Accurately weigh 5.5g of zinc acetate using an electronic balance, pour it into 50mL of deionized water, and magnetically stir for 20-30 minutes at room temperature. Then add dry, defatted cotton and continue magnetically stirring for 2-3 hours at room temperature. Transfer the mixture (including the solution and the impregnated defatted cotton) to a constant temperature drying oven and dry at 60°C for 6-12 hours. Place the dried mixture in a tube furnace or muffle furnace, and purge with high-purity argon gas at a flow rate of 50-100ml / min. Purge for at least 30 minutes, raise the temperature at a rate of 5°C / min to 800°C, hold at that temperature for 2-3 hours, and then cool the furnace to obtain zinc oxide-doped fibrous carbon material.

[0044] 3) The fibrous carbon material was ground using a nano-grinding machine to obtain carbon powder with a particle size of <100nm, which was a uniform black powder. A lithium foil was taken as a substrate, and the powder was evenly sprinkled on its surface. Then, the composite was formed by folding and rolling (the weight ratio of powder to lithium metal was 1:10). The folding and rolling were repeated five times to obtain a composite lithium strip.

[0045] 4) Place the composite lithium strip in a nickel crucible, then place it on a heating stage inside a glove box. Slowly heat the mixture to 270°C until it is completely melted, and hold it at that temperature for 30 minutes. Then turn off the heating stage and allow the melt to cool naturally inside the glove box until it completely solidifies, obtaining a "Li / LixC / LiyZn" composite metal ingot. Place this composite metal ingot in a roller mill and repeatedly roll it at room temperature until a uniform and dense ultrathin lithium anode with a thickness of 15 μm is obtained.

[0046] Comparative Example This embodiment is used to prepare a bio-carbon-reinforced lithium foil. The method is the same as in Example 1, except that dried degreased cotton is not used as the biomass raw material, and fibrous carbon powder is replaced with granular nano-carbon powder (purchased from Guangzhou Metal Metallurgy Co., Ltd., 50nm specification). The specific steps are as follows: 1) Take a lithium foil as a substrate, evenly spread granular nano-carbon powder on its surface, and then composite it by folding and rolling (the weight ratio of powder to lithium metal is 1:9). Repeat the folding and rolling process five times to obtain a composite lithium strip.

[0047] 2) Place the composite lithium strip in a nickel crucible, then place it on a heating stage inside a glove box. Slowly heat the crucible to 270°C until it is completely melted, and hold it at that temperature for 30 minutes. Then turn off the heating stage and allow the molten metal to cool naturally inside the glove box until it completely solidifies, obtaining a composite metal ingot. Place this composite metal ingot in a roller mill and repeatedly roll it at room temperature until a uniform and dense ultrathin lithium anode with a thickness of 15 μm is obtained.

[0048] Experimental Example 1 This experimental example is used to test the electrochemical performance of an ultrathin lithium anode. The specific method is as follows: The ultrathin lithium anode of Example 1 was cut into electrode sheets with a diameter of 14 mm using a cutting machine; The electrolyte was 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), in which 1,3-dioxolane (DOL): ethylene glycol dimethyl ether (DME) was used as solvent in a volume ratio of 1:1, and 2wt% LiNO3 was used as additive. A 2032-type button cell was assembled using Cellgard 2325 as the separator in a glove box (high-purity argon atmosphere, where the O2 and H2O contents are both less than 0.01 ppm). Symmetrical cells were assembled and tested at 0.5 mA / cm². 2 Current density and 1mAh / cm 2 The electrochemical performance of this lithium anode was tested at its areal capacity, and the results are as follows: Figure 2 As shown in the figure. It can be seen that the symmetric cell prepared using the method of this invention achieves a current of 0.5 mA / cm². 2 Current density and 1mAh / cm 2 At its surface capacity, it can stably cycle for more than 950 hours, which is much greater than the 650 hours of pure lithium.

[0049] Experiment Example 2 This experimental example is used to test the cycle performance of ultrathin lithium anodes. The specific method is as follows: The symmetrical battery was prepared using the same method as in Example 1, except that the ultrathin lithium anode material from Example 2 was used as the electrode sheet. At 3 mA / cm² 2 Current density, 1mAh / cm 2 The cycling performance of this lithium metal anode was tested at its areal capacity, and the results are as follows: Figure 3 As shown, the symmetric battery prepared using this method can cycle stably for more than 350 hours, which is greater than the 250 hours for pure lithium.

[0050] Experimental Example 3 This experimental example is used to test the coulombic efficiency of ultrathin lithium anodes. The specific method is as follows: Using the ultrathin lithium anode electrode material from Examples 1-3, symmetrical cells were fabricated using the same method as in Experiment 1, at 0.5 mA / cm². 2 Current density, 1mAh / cm 2 The coulombic efficiency of this lithium metal anode was tested at the areal capacity, and the results are as follows: Figure 4 As shown, the symmetric battery prepared using this method can be stably cycled for 100 cycles with a coulombic efficiency retention of 100%, and the effect is optimal when the weight ratio of fibrous carbon powder to lithium metal is 1:9.

[0051] Experiment Example 4 This experimental example compares the coulombic efficiency of the lithium foil anode when granular carbon powder is used instead of fibrous bio-carbon powder. The specific method is as follows: Using the ultrathin lithium anodes from Example 1 and the comparative example as electrode materials, symmetrical cells were fabricated using the same method as in Example 1. The coulombic efficiency of the lithium metal anode was tested at a current density of 0.5 mA / cm² and an areal capacity of 1 mAh / cm². The results are as follows. Figure 5 As shown, the symmetric cell prepared using particulate carbon powder can stably cycle 100 times with a coulombic efficiency retention of 100%, while the cell prepared using particulate carbon powder fails after about 35 cycles.

[0052] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A fiber-reinforced carbon ultrathin lithium foil, characterized in that: It is prepared from fibrous carbon material loaded with zinc oxide; The method for preparing the zinc oxide-loaded fibrous carbon material is as follows: natural fibers are soaked in a zinc salt solution, stirred thoroughly, dried, and then carbonized at high temperature under anaerobic conditions to obtain the final product. The natural fibers include cotton fibers, bamboo fibers, or hemp fibers; The preparation method of the fiber carbon-reinforced ultrathin lithium foil includes the following steps: S1: Grind the zinc oxide-loaded fibrous carbon material into carbon powder; S2: In an oxygen-free environment, the carbon powder is evenly sprinkled on the surface of the lithium foil, and then folded and rolled several times to obtain a composite lithium strip; S3: Melt the composite lithium strip in an oxygen-free environment, then cool it to obtain a composite metal. Roll the composite metal at room temperature to obtain the fiber carbon-reinforced ultrathin lithium foil. In step S2, the weight ratio of the carbon powder to the lithium foil is 1:9; The thickness of the ultrathin lithium foil is ≤20μm; The high-temperature carbonization temperature is 800~900℃.

2. The fiber-reinforced carbon ultrathin lithium foil according to claim 1, characterized in that: The molar concentration of zinc ions in the zinc salt solution is 0.6 mol / L.

3. The fiber-reinforced carbon ultrathin lithium foil according to claim 1, characterized in that: In step S1, the particle size of the carbon powder is less than 100 nm.

4. The application of the fiber-reinforced carbon ultrathin lithium foil as described in any one of claims 1-3, characterized in that: Used to prepare lithium battery anodes.

Images