Method for preparing flat ultrathin lithium foil negative electrode based on ultrasonic rolling

Abstract

The invention provides a method for preparing a flat ultrathin lithium foil negative electrode based on ultrasonic rolling, and belongs to the technical field of lithium battery negative electrodes, and the method comprises the following steps: carrying out primary ultrasonic rolling treatment on a lithium strip to form a lithium foil with the thickness of not more than 20 microns; compounding the lithium foil and a current collector through a cold pressing method to form a lithium foil negative electrode A; performing secondary ultrasonic rolling treatment on the lithium foil negative electrode A to obtain a lithium foil negative electrode B; the lithium foil negative electrode B is immersed in acetone for ultrasonic vibration aging treatment, and a lithium foil negative electrode C is obtained; and immersing the lithium foil negative electrode C in acetone for cleaning, and carrying out vacuum drying to obtain the flat ultrathin lithium foil negative electrode. A two-stage ultrasonic rolling technology of first high-amplitude impact and second low-amplitude impact is introduced, the technology utilizes an energy converter to efficiently convert alternating voltage into high-frequency mechanical vibration, the double advantages of ultrasonic impact and static pressure rolling are ingeniously fused, and the defects that in the prior art, the relative error of effective thickness is large, the surface roughness is high, and the machining precision is high are overcome. And therefore, the technical defects of poor film forming effect and poor battery cycle performance are overcome.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery anode technology, and specifically relates to a method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling. Background Technology

[0002] With the continuous development of lithium-ion battery technology, the requirements for electrode materials are becoming increasingly stringent. Lithium metal, due to its high energy density, has become an ideal anode material. However, lithium metal anodes are prone to lithium dendrite growth during charge and discharge, leading to short circuits and safety hazards. Lithium foil, as an anode material for lithium-ion batteries, can significantly improve the battery's energy density and cycle stability. Especially in lithium metal batteries (LMBs), ultrathin lithium foil paired with common lithium transition metal oxide cathodes can achieve battery designs with high energy density and long cycle life. Therefore, the fabrication of ultrathin, self-supporting lithium metal anodes has become crucial for solving this problem.

[0003] Current technologies primarily rely on traditional stretching and compression processes, as well as electrodeposition methods, to manufacture lithium foil. However, lithium foil produced using only stretching and compression processes typically exceeds 50 micrometers in thickness, making further thinning difficult. Furthermore, during processing, the high residual stress and inherent thickness unevenness make the lithium foil prone to breakage, significantly reducing the yield. On the other hand, lithium foil prepared by electrodeposition exhibits high surface roughness and numerous defects, which negatively impacts the integrity of the subsequently formed solid electrolyte interphase (SEI) film. Summary of the Invention

[0004] Therefore, the present invention aims to provide a method for preparing a flat ultrathin lithium foil anode based on ultrasonic rolling, in order to solve at least one of the technical problems in the background art.

[0005] This invention is implemented as follows: This invention provides a method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling, comprising the following steps: The lithium strip is subjected to first-stage ultrasonic rolling to form a lithium foil with a thickness of no more than 20μm; The lithium foil is combined with a current collector by a cold pressing method to form a lithium foil negative electrode A; The lithium foil anode A is subjected to a secondary ultrasonic rolling process to obtain the lithium foil anode B. The lithium foil anode B is immersed in acetone for ultrasonic vibration aging treatment to obtain the lithium foil anode C; The lithium foil anode C is immersed in acetone for cleaning and then vacuum dried to obtain a flat, ultra-thin lithium foil anode.

[0006] Furthermore, the conditions for the first-stage ultrasonic rolling process include: an ultrasonic rolling frequency of 10KHz~20KHz, an amplitude of 4μm~6μm, a static pressure of 2N~10N, a feed rate of 0.5m / min~1.5m / min, a step size of 0.15mm, and 1~3 rolling cycles.

[0007] Furthermore, the secondary ultrasonic rolling treatment conditions include: a frequency of 15KHz~25KHz, an amplitude of 1μm, a static pressure of 0.5N~2N, a feed rate of 0.1m / min~0.5m / min, a step size of 0.1mm, and one rolling cycle.

[0008] Furthermore, during the primary and secondary ultrasonic rolling processes, acetone is continuously released into the rolling ball.

[0009] Furthermore, the pressure applied during the cold pressing is in the range of 20MPa to 50MPa, and the pressure is maintained for 1min to 3min.

[0010] Furthermore, the temperature for ultrasonic vibration aging is controlled between 0℃ and 10℃, and the vibration time lasts between 5 min and 15 min. The vibration parameters are set to a frequency of 10 kHz and an amplitude precisely controlled between 1 μm and 2 μm.

[0011] Furthermore, the cleaning process employs ultrasonic cleaning for 5 to 10 minutes.

[0012] Furthermore, the vacuum drying temperature is 50℃~70℃.

[0013] Furthermore, the current collector is made of copper foil.

[0014] Furthermore, during the first-stage ultrasonic rolling process and the second-stage ultrasonic rolling process, the lithium strip and lithium foil negative electrode A are respectively placed on a steel substrate, wherein the steel substrate is selected from 304 stainless steel, 316 stainless steel, carbon steel or 20 alloy.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces a two-stage ultrasonic rolling technology with high amplitude followed by low amplitude impact. This technology utilizes an energy converter to efficiently convert AC voltage into high-frequency mechanical vibration, cleverly combining the dual advantages of ultrasonic impact and hydrostatic rolling. It overcomes the technical defects of existing technologies, such as large relative error in effective thickness and high surface roughness, which lead to poor battery cycle performance.

[0016] 2. This invention first allows the aluminum foil surface to undergo plastic deformation under high amplitude conditions to achieve thickness reduction, unlike the simple pressing and stretching process which is limited by the uneven initial lithium foil thickness and is prone to high processing defect rate; then, under low amplitude, the surface defects are effectively eliminated through the "valley filling" effect, significantly reducing surface roughness, unlike lithium foil prepared by deposition method which has high surface roughness and many defects.

[0017] 3. The present invention utilizes the ultrasonically rolled lithium foil negative electrode to form an SEI film in the subsequent electrolyte, which exhibits lower impedance and is beneficial to lithium ion transport.

[0018] 4. The present invention introduces vibration aging treatment, which effectively eliminates residual stress introduced during processing and significantly enhances the overall stability of the negative electrode material. Attached Figure Description

[0019] Figure 1 The AC impedance test results are for the negative electrodes prepared in Example 2 and Comparative Example 3 of this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] The method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling includes steps one through four.

[0022] Step 1: Take a 0.1mm thick high-purity lithium strip (purity > 99.9%) and place it on a steel material with excellent hardness to prepare for the first-stage ultrasonic rolling treatment (the steel material can be 304 stainless steel, 316 stainless steel, carbon steel or 20 alloy), reducing the lithium foil thickness to below 20μm; use a 14mm diameter WC / Co material rolling ball; during the rolling process, continuously release acetone into the rolling ball to effectively cool it and prevent the lithium foil from sticking to the rolling ball; The parameters for first-level ultrasonic rolling are set as follows: frequency 10KHz~20KHz, amplitude 4μm~6μm, static pressure 2N~10N, feed speed 0.5m / min~1.5m / min, step size 0.15mm, and rolling times 1~3 times. Step 2: The lithium foil that has undergone first-stage ultrasonic rolling is cut into specific sizes as required. Then, it is tightly bonded with a current collector copper foil of the same size at room temperature using cold pressing technology. The pressure applied during cold pressing is 20MPa~50MPa and the pressure is maintained for 1min~3min, thereby producing lithium foil anode A. Step 3: Place the lithium foil anode A on a hard steel material and perform two-stage ultrasonic rolling (the steel material can be 304 stainless steel, 316 stainless steel, carbon steel or 20 alloy) to further reduce the surface roughness. The frequency is 15KHz~25KHz, the amplitude is 1μm, the static pressure is 0.5N~2N, the feed speed is 0.1m / min~0.5m / min, the step size is 0.1mm, and the rolling is done once. Acetone is continuously used for cooling during the rolling process to prevent adhesion. Finally, the lithium foil anode B is obtained. Step 4: Install the lithium foil negative electrode B on an ultrasonic vibration aging device and completely immerse it in acetone for vibration aging treatment; during the treatment, the temperature is controlled at 0℃~10℃, and the vibration time lasts for 5min~15min; the vibration parameters are set to a frequency of 10KHz and the amplitude is precisely controlled between 1μm~2μm to ensure that the internal micro-plastic deformation is effectively excited without damaging the negative electrode; after the treatment is completed, turn off the device and remove the negative electrode to obtain the lithium foil negative electrode C. Step 5: Place the lithium foil anode C taken out in Step 4 into a beaker containing acetone and perform ultrasonic cleaning for 5 to 10 minutes to thoroughly remove any tiny dirt and metal particles that may remain from the previous steps. After cleaning, transfer the lithium foil anode to a vacuum drying oven, set the temperature to 50°C to 70°C, and evacuate to a suitable environment. After drying, a flat, ultra-thin lithium foil anode will be obtained.

[0023] This invention innovatively introduces ultrasonic rolling technology, which utilizes an energy converter to efficiently convert AC voltage into high-frequency mechanical vibration, cleverly combining the advantages of ultrasonic impact and hydrostatic rolling. The first stage of ultrasonic rolling involves plastic deformation of the aluminum foil surface under high amplitude conditions, achieving thickness reduction, unlike simple pulling processes which are prone to high defect rates due to uneven initial lithium foil thickness. The second stage of ultrasonic rolling, under low amplitude, effectively eliminates surface defects and significantly reduces surface roughness through a "valley-shaving and peak-filling" effect, unlike lithium foil prepared by deposition methods which has high surface roughness and numerous defects. Furthermore, the SEI film formed in the subsequent electrolyte by the ultrasonically rolled lithium foil anode exhibits lower impedance, facilitating lithium-ion transport. In addition, this invention also effectively eliminates residual stress introduced during the processing of the lithium foil and current collector through vibration aging treatment, significantly enhancing the overall stability of the anode material.

[0024] Example 1 The method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling includes the following steps: S1. A 0.1 mm thick high-purity lithium strip is placed on a 304 stainless steel substrate for first-stage ultrasonic rolling. A 14 mm diameter WC / Co rolling ball is used. The ultrasonic rolling parameters are set as follows: frequency 10 kHz, amplitude 4 μm, static pressure 2 N, feed speed 0.5 m / min, step size 0.15 mm, and rolling times 3. During the rolling process, acetone is continuously released into the tool ball head to effectively cool it and prevent the lithium foil from sticking to the ball head, resulting in a lithium foil with a thickness of 18.6 μm. S2. The lithium foil that has undergone first-stage ultrasonic rolling is cut into specific sizes as required, and then it is tightly bonded with a current collector copper foil of the same size at room temperature using cold pressing technology. The pressure applied during cold pressing is 20MPa and the pressure is maintained for 3 minutes, thereby producing the lithium foil negative electrode A. S3. The lithium foil anode A is placed on a hard steel material and subjected to a two-stage ultrasonic rolling process to further reduce the surface roughness. The ultrasonic rolling frequency is 15KHz, the amplitude is 1μm, the static pressure is 0.5N, the feed rate is 0.1m / min, the step size is 0.1mm, and the rolling passes are 1. Similarly, acetone is continuously used for cooling and to prevent adhesion during the rolling process, and finally the lithium foil anode B is obtained. S4. Install the lithium foil negative electrode B onto an ultrasonic vibration aging device and completely immerse it in acetone for vibration aging treatment. During the treatment, the temperature is controlled at 0℃ and the vibration time lasts for 5 minutes; the ultrasonic vibration parameters are set to a frequency of 10KHz and an amplitude of 1μm. After the treatment is completed, turn off the device and remove the electrode to obtain the lithium foil negative electrode C. S5. Place the removed lithium foil anode C in a beaker containing acetone and perform ultrasonic cleaning for 5 minutes to thoroughly remove any tiny dirt and metal particles that may remain from the previous steps. After cleaning, transfer the lithium foil anode to a vacuum drying oven, set the temperature to 50°C, and evacuate to a suitable environment. After drying, a flat, ultra-thin lithium foil anode will be obtained.

[0025] Example 2 The method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling includes the following steps: S1. A 0.1 mm thick high-purity lithium strip is placed on a 316 stainless steel substrate for primary ultrasonic rolling treatment. A 14 mm diameter WC / Co rolling ball is used. The ultrasonic rolling parameters are set as follows: frequency 15 kHz, amplitude 5 μm, static pressure 5 N, feed rate 1.0 m / min, step size 0.15 mm, and rolling cycles 2. During the rolling process, acetone is continuously released into the tool ball head to effectively cool it and prevent the lithium foil from sticking to the ball head, resulting in a lithium foil with a thickness of 16.7 μm. S2. The lithium foil, after undergoing primary ultrasonic rolling, is cut into specific sizes as required. Then, using cold pressing technology, it is tightly bonded to a current collector copper foil of the same size at room temperature. The pressure applied during cold pressing is 35 MPa, and the pressure is maintained for 2 minutes, thereby producing the lithium foil negative electrode A. S3. The primary lithium foil anode is placed on a hard steel surface and subjected to a secondary ultrasonic rolling process to further reduce surface roughness. The amplitude is 20 kHz, the amplitude is 1 μm, the static pressure is 1.2 N, the feed rate is 0.3 m / min, the step size is 0.1 mm, and the rolling is performed once. Similarly, acetone is continuously used for cooling and to prevent adhesion during the rolling process, ultimately obtaining lithium foil anode B. S4. Install the lithium foil negative electrode B onto an ultrasonic vibration aging device and completely immerse it in acetone for vibration aging treatment. During the treatment, the temperature is controlled at 5℃, and the vibration time lasts for 8 minutes; the vibration parameters are set as follows: frequency 10KHz, amplitude 1.5μm. After the treatment is completed, turn off the device and remove the electrode to obtain the lithium foil negative electrode C. S5. Place the removed lithium foil anode C in a beaker containing acetone and perform ultrasonic cleaning for 8 minutes to thoroughly remove any remaining micro-dirt and metal particles from the previous steps. After cleaning, transfer the lithium foil anode to a vacuum drying oven, set the temperature to 60°C, and evacuate to a suitable environment. After drying, a flat, ultra-thin lithium foil anode will be obtained.

[0026] Example 3 The method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling includes the following steps: S1. A 0.1 mm thick high-purity lithium strip is placed on a carbon steel substrate to prepare for a first-stage ultrasonic rolling process to obtain lithium foil. A WC / Co rolling ball with a diameter of 14 mm is used. The ultrasonic rolling parameters are set as follows: frequency 20 kHz, amplitude 6 μm, static pressure 10 N, feed speed 1.5 m / min, step size 0.15 mm, and rolling times 1. During the rolling process, acetone is continuously released into the tool ball head to effectively cool it and prevent the lithium foil from sticking to the ball head, resulting in a lithium foil with a thickness of 15.4 μm. S2. The lithium foil that has undergone first-stage ultrasonic rolling is cut into specific sizes as required. Then, it is tightly bonded with a current collector copper foil of the same size at room temperature using cold pressing technology. The pressure applied during cold pressing is 50 MPa and the pressure is maintained for 1 minute to obtain lithium foil anode A. S3. The lithium foil anode A is placed on a hard steel material and subjected to a two-stage ultrasonic rolling process to further reduce the surface roughness. The amplitude is 25KHz, the amplitude is 1μm, the static pressure is 2N, the feed rate is 0.5m / min, the step size is 0.1mm, and the rolling is performed once. Similarly, acetone is continuously used for cooling and to prevent adhesion during the rolling process, and finally the lithium foil anode B is obtained. S4. Install the lithium foil negative electrode B on an ultrasonic vibration aging device and immerse it completely in acetone for vibration aging treatment. During the treatment, the temperature is controlled at 10℃ and the vibration time lasts for 15 minutes. The vibration parameters are set as follows: frequency 10KHz and amplitude 2μm. After the treatment is completed, turn off the device and take it out to obtain the lithium foil negative electrode C. S5. Place the removed lithium foil anode C in a beaker containing acetone and perform ultrasonic cleaning for 10 minutes to thoroughly remove any tiny dirt and metal particles that may remain from the previous steps. After cleaning, transfer the lithium foil anode to a vacuum drying oven, set the temperature to 70°C, and evacuate to a suitable environment. After drying, a flat, ultra-thin lithium foil anode will be obtained.

[0027] Comparative Example 1 Comparative Example 1 describes a method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling. The only difference between this method and Example 2 is that the secondary ultrasonic rolling process with low frequency S3 was not performed. The other steps are the same as in Example 2.

[0028] Comparative Example 2 Comparative Example 2 is a method for preparing flat ultrathin lithium foil anodes based on ultrasonic rolling. The only difference between this method and Example 2 is that the S4 ultrasonic vibration aging step is not performed. The other steps are the same as in Example 2.

[0029] Comparative Example 3 The method for preparing ultrathin lithium foil anodes in Comparative Example 3 differs from that in Example 2 only in that the ultrasonic rolling strengthening treatments in S1 and S3 were not performed. Instead, lithium strips and copper sheets of the same size were directly cold-pressed. The steps of cold pressing, ultrasonic vibration aging, degreasing and cleaning, and drying were the same as in Example 2.

[0030] Comparative Example 4 Comparative Example 4 is a method for preparing a flat ultrathin lithium foil anode based on ultrasonic rolling. The only difference between this method and Example 2 is that the high-frequency first-stage ultrasonic rolling process of S1 was not performed. Instead, lithium strips and copper sheets of the same size were directly cold-pressed. The other steps are the same as in Example 2.

[0031] To conduct electrochemical tests, the negative electrodes prepared in each example and comparative example were punched to obtain electrode sheets with a diameter of 15 mm. These circular electrode sheets were used as the negative electrodes, and LiFePO4 electrode sheets as the positive electrodes. Celgard 2400 was used as the separator, and 1 M LiPF6 EC:DMC (1:1 Vol%) was used as the electrolyte. A coin cell was assembled according to the following sequence: positive electrode shell → positive electrode sheet → separator → lithium sheet → gasket, spring sheet → negative electrode shell. Electrochemical tests were then performed on a Land electrochemical analyzer, initially at 1 mA / cm². 2 Lithium deposition and dissolution stability was continuously tested under current density. The fluctuation range of the theoretical potential is shown in Table 1.

[0032] Table 1

[0033] As shown in Table 1, the theoretical potential fluctuation of the negative electrode prepared in Examples 1 to 3 of this invention is relatively small. When the test time exceeds 500 hours, the fluctuation amplitude does not exceed 0.9V. The lower the fluctuation amplitude of the theoretical potential, the more stable the battery structure and the longer the battery life.

[0034] The theoretical potential fluctuations of the negative electrodes prepared in Comparative Examples 1 to 4 were not significantly different from those in Example 2 in the short term. However, as time went on, the fluctuations of the theoretical potentials of the negative electrodes in Comparative Examples 1 to 4 increased significantly, far exceeding those in Example 2.

[0035] In addition, AC impedance tests were performed on Example 2 and Comparative Example 3, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the AC impedance spectrum of the negative electrode after ultrasonic rolling strengthening in Example 2 has a similar curve pattern to that of the untreated negative electrode in Comparative Example 3. However, it has a smaller radius capacitive arc in the high frequency region and a Warburg impedance closer to 45° in the low frequency region, which means that the lithium ion transport process is less hindered during charging and discharging, and can be deposited more smoothly and uniformly.

[0036] Ten locations were randomly selected from the negative electrodes prepared in each embodiment and comparative example to test the thickness of the lithium foil. The maximum and minimum values ​​were removed to calculate the average thickness (the lithium foil thickness is the negative electrode test thickness minus the copper sheet thickness), and the average error was calculated, as shown in Table 2.

[0037] Table 2

[0038] As can be seen from the data in Table 2, and as can be seen from the data in Table 1, the average thickness and relative error of the negative electrodes prepared in Examples 1 to 3 of the present invention are all small, with the average thickness not exceeding 14 μm and the relative error not exceeding 0.6%.

[0039] Comparative Examples 1 and 4 both used a single ultrasonic rolling process, and it can be seen that the average thickness of the resulting negative electrode was much higher than that of Example 2. Comparative Example 2 used a two-stage ultrasonic rolling process and omitted the ultrasonic aging treatment; it can be seen that its average thickness and relative error were not significantly different from those of Example 2. Comparative Example 3 completely omitted the ultrasonic rolling treatment step, and it can be seen that its average thickness and relative error increased significantly compared to Example 2.

[0040] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing flat, ultrathin lithium foil anodes based on ultrasonic rolling, characterized in that, The method includes the following steps: The lithium strip is subjected to first-stage ultrasonic rolling to form a lithium foil with a thickness of no more than 20μm; The lithium foil is combined with a current collector by a cold pressing method to form a lithium foil negative electrode A; The lithium foil anode A is subjected to a secondary ultrasonic rolling process to obtain the lithium foil anode B. The lithium foil anode B is immersed in acetone for ultrasonic vibration aging treatment to obtain the lithium foil anode C; The lithium foil anode C is immersed in acetone for cleaning and then vacuum dried to obtain a flat, ultra-thin lithium foil anode.

2. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The conditions for the first-stage ultrasonic rolling process include: an ultrasonic rolling frequency of 10KHz~20KHz, an amplitude of 4μm~6μm, a static pressure of 2N~10N, a feed rate of 0.5m / min~1.5m / min, a step size of 0.15mm, and 1~3 rolling cycles.

3. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The secondary ultrasonic rolling process conditions include: frequency of 15KHz~25KHz, amplitude of 1μm, static pressure of 0.5N~2N, feed rate of 0.1m / min~0.5m / min, step size of 0.1mm, and rolling times of 1.

4. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to any one of claims 1 to 3, characterized in that, During the first-stage and second-stage ultrasonic rolling processes, acetone is continuously released into the rolling ball.

5. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The pressure applied during cold pressing is in the range of 20MPa to 50MPa, and the pressure is maintained for 1min to 3min.

6. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The temperature for ultrasonic vibration aging is controlled at 0℃~10℃, and the vibration time lasts for 5min~15min; the vibration parameters are set to a frequency of 10KHz and an amplitude precisely controlled between 1μm~2μm.

7. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The cleaning process uses ultrasonic cleaning and takes 5 to 10 minutes.

8. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The vacuum drying temperature is 50℃~70℃.

9. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, The current collector is made of copper foil.

10. The method for preparing a flat, ultrathin lithium foil anode based on ultrasonic rolling according to claim 1, characterized in that, During the first-stage and second-stage ultrasonic rolling processes, the lithium strip and lithium foil negative electrode A are placed on a steel substrate, which is selected from 304 stainless steel, 316 stainless steel, carbon steel, or 20 alloy.

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