CN116979065B - Preparation method and application of copper current collector with step-shaped structure for inducing lithium metal to grow inwards - Google Patents

Abstract

A preparation method and application of a copper current collector with a "step" structure that induces the inward growth of lithium metal. The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a preparation method and application of a copper current collector with a "step" structure that induces the inward growth of lithium metal. The present invention is to solve the problems in existing structural modification methods, that most template materials cannot be reused and the template synthesis is too complicated, which is not conducive to large-scale commercialization and environmental friendliness. In addition, the prepared current collector cannot effectively alleviate the volume expansion phenomenon during the growth of lithium metal. Method: Through laser etching technology, a low-power multiple bombardment processing method is adopted. While preparing a distributed micro-pit array, a layered nanostructure is introduced on the inner wall of the micro-pit to increase the structural hierarchy and roughness, thereby inducing lithium metal to deposit on the inner wall of the micropore. The present invention is used for lithium-sulfur batteries and lithium-air battery systems based on lithium metal negative electrodes.

Description

Preparation method and application of a copper current collector with a "step" structure that induces lithium metal to grow inward

Technical Field

The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a preparation method and application of a copper current collector having a "step" structure for inducing inward growth of lithium metal.

Background Art

In lithium metal-based batteries, the current collector is not only the connection between the negative electrode active material and the external circuit, but also the substrate for lithium electroplating. Therefore, it has a great influence on the nucleation and growth of lithium, as well as the battery capacity and stability. However, commercially available copper foils are usually defective, containing many cracks and pits on the micron to nanometer scale. Compared with other surface locations, these defective sites have a lower nucleation potential and can serve as sites for rapid nucleation and growth of lithium, thereby causing uneven deposition of lithium metal and inducing lithium dendrite growth. In addition, the planar copper foil has a low specific surface area, and the lithium metal negative electrode as a host-free structure will cause a large volume expansion, resulting in frequent rupture and regeneration of the SEI layer, resulting in a reduction in active materials and a decrease in battery capacity. Through the structural design of the negative electrode and the current collector, lithium metal is composited with various three-dimensional structures. On the one hand, the current density can be reduced to effectively inhibit the growth of lithium dendrites, and on the other hand, it can provide accommodation space and reduce the volume expansion during the cycle. By changing the structure and size of the current collector, it can better meet the use requirements and safety specifications. Studies have shown that reducing the effective current density on the surface of the current collector can effectively delay the formation of lithium dendrites and slow down the growth of lithium dendrites. In order to reduce the current density, microstructured current collectors including grids and foams have been reported. For example, copper current collectors such as grid structures can stably accommodate lithium agglomerates formed during the deposition/deposition process, thereby inhibiting the formation of dead lithium. These methods can delay the short circuit induced by lithium dendrites and improve the coulombic efficiency. However, the preparation process of microstructured current collectors such as grids and foams is cumbersome and energy-intensive, which is not conducive to large-scale production. Moreover, under extreme conditions, micrometer-scale structures are not enough to reduce the effective current density. In order to reduce the effective current density, nanoscale structures are more effective due to their significant specific surface area. Researchers introduced nanostructures such as copper nanowires, nanorods, and nanopillars on the current collector to further reduce the current density. Even under extremely high current conditions, the large relative surface area can inhibit the formation of dendrites and show a lower overpotential. However, the electric field may inadvertently concentrate and shrink the pores between nanostructures, reduce the diffusion of lithium ions, and hinder the uniform nucleation of lithium. In addition, the structural stability of nanoscale structures is lower than that of micrometer structures, making it more difficult to withstand the infinite volume change of lithium metal anodes. In view of the different characteristics between the microstructure and nanostructure of lithium metal negative electrode, the preparation of structural layered copper current collector with coexistence of micro and nano retains the advantages of each. The existing structural layered copper current collector process is relatively complicated and it is impossible to prepare the layered structure in one step. The micro and nano structures need to be introduced step by step.

Summary of the invention

The present invention aims to solve the problems in existing structural modification methods, that most template materials cannot be reused and the template synthesis is too complicated, which is not conducive to large-scale commercialization and environmental friendliness. In addition, since the prepared current collector cannot effectively alleviate the volume expansion phenomenon during the growth of lithium metal, a preparation method and application of a copper current collector with a "step" structure to induce lithium metal to grow inward is provided.

The preparation method of a copper current collector having a "step" structure for inducing lithium metal to grow inwardly is carried out according to the following steps:

1. Select copper foil as raw material, clean the surface of copper foil, remove the natural oxide layer on the surface, and obtain the copper foil to be treated;

2. The surface of the copper foil to be processed is processed by a laser microprocessing system using a line-by-line laser scanning process to obtain the processed copper foil;

3. Polish the processed copper foil to remove the raised oxide layer at the edge of the micro-pits, and obtain a copper current collector with a "step" structure to induce lithium metal to grow inward.

Beneficial effects of the present invention:

1. The preparation process of the present invention is simple. Through laser etching technology and a low-power multiple bombardment processing method, while preparing a distributed micro-pit array, a layered nanostructure is introduced into the inner wall of the micro-pit to increase the structural level and roughness, thereby inducing lithium metal to deposit on the inner wall of the micropore. It has strong designability. According to different application conditions and performance requirements, the array density, scanning times, scanning power and other parameters can be adjusted to obtain a micro-pit structure with a "step" inner wall that is uniformly distributed, consistent in pore size and controllable in depth.

2. The deposition and precipitation process of metallic lithium has good electrochemical stability. Under different deposition surface capacities, compared with bare copper, the copper current collector with controllable pit structure has higher Coulomb efficiency and good electrochemical stability. During the cycle, lithium metal is deposited preferentially on the inner wall of the micro-pit, which can effectively alleviate volume expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope magnified image of a copper current collector having a "step" structure inducing lithium metal to grow inwardly in Example 1;

FIG2 is a micro-area Raman spectrum of a copper current collector having a "step" structure inducing lithium metal to grow inward in Example 1;

FIG3 is a scanning electron microscope magnified image of a copper current collector having a "step" structure inducing lithium metal to grow inward after lithium metal is deposited in Example 1;

FIG4 is a coulombic efficiency curve of a pure copper foil of a comparative example subjected to a charge and discharge test at a deposition current of 0.5 mA/cm ^-2 and a deposition surface capacity of 0.5 mAh/cm ^-2 ;

FIG5 is a coulombic efficiency curve of the copper current collector with a "step" structure inducing lithium metal to grow inward in the first experimental example for charge and discharge test at a deposition current of 0.5 mA/cm ^-2 and a deposition surface capacity of 0.5 mAh/cm ^-2 ;

FIG6 is a coulombic efficiency curve of the copper current collector with a "step" structure inducing lithium metal to grow inward in the second experimental example for charge and discharge test at a deposition current of 0.5 mA/cm ^-2 and a deposition surface capacity of 0.5 mAh/cm ^-2 ;

FIG7 is a charge-discharge test of pure copper foil of comparative example, and the capacity-voltage curve of the first ten cycles under the conditions of deposition current of 0.5 mA/cm ^-2 and deposition surface capacity of 0.5 mAh/cm ^-2 ;

FIG8 is a charge-discharge test using a copper current collector with a "step" structure to induce lithium metal to grow inward in Experimental Example 1, and the capacity-voltage curves of the first ten cycles under the conditions of a deposition current of 0.5 mA/cm ^-2 and a deposition surface capacity of 0.5 mAh/cm ^-2 ;

FIG9 shows the coulombic efficiency of pure copper foil of a comparative example with a lithium loading of 8 mAh/cm ^-2 in a full battery;

FIG. 10 shows the coulombic efficiency of the copper current collector in the full battery with a “step” structure inducing lithium metal inward growth in Experimental Example 1 with a lithium loading of 8 mAh/cm ^-2 .

DETAILED DESCRIPTION

Specific implementation method 1: A preparation method of a copper current collector having a "step" structure inducing lithium metal to grow inwardly is carried out in the following steps:

1. Select copper foil as raw material, clean the surface of copper foil, remove the natural oxide layer on the surface, and obtain the copper foil to be treated;

2. The surface of the copper foil to be processed is processed by a laser microprocessing system using a line-by-line laser scanning process to obtain the processed copper foil;

3. Polish the processed copper foil to remove the raised oxide layer at the edge of the micro-pits, and obtain a copper current collector with a "step" structure to induce lithium metal to grow inward.

This embodiment controls the scanning power and scanning times of the laser etching instrument, and bombards the foil surface with low power multiple times to obtain a pit-like structure with lithium-philic sites and a layered structure (different from the instantaneous breakdown of copper foil by high-power laser, the pit-like structure obtained by low-power multiple bombardment has a rougher surface, which is more conducive to the nucleation and growth of lithium metal on its surface), thereby increasing the active specific surface area of the inner wall of the pit. A one-step process for preparing a layered copper current collector is realized, and the obtained controllable pit-like structure is evenly distributed, the inner surface is tightly fitted, and a multi-layer oxide film with a nanostructure is formed.

This embodiment uses laser etching technology and selects appropriate parameters to process the surface of the copper foil to construct a micron-level evenly distributed pit-shaped structure array to promote uniform electric field distribution on the surface of the current collector. When the high-energy laser beam instantly releases energy on the surface of the copper foil, large pieces of metallic copper are decomposed into nanoparticles in situ to form a thin and dense oxide layer. After multiple bombardments, a typical stepped nano-layered structure is formed inside the pit-shaped structure, providing a large amount of accommodation volume and nucleation sites for subsequent lithium metal deposition.

Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the surface of the copper foil is cleaned by alcohol and acetone solution in step 1. The other steps and parameters are the same as those in specific implementation method 1.

Specific implementation method 3: This implementation method is different from specific implementation method 1 in that the thickness of the copper foil in step 1 is 10-100 μm. Other steps and parameters are the same as those in specific implementation method 1.

Specific implementation method 4: This implementation method is different from specific implementation method 3 in that the diameter of the copper foil to be processed in step 1 is 12-16 mm. The other steps and parameters are the same as those in specific implementation method 3.

Specific implementation example 5: This implementation example is different from specific implementation example 1 in that the laser microprocessing system in step 2 is a femtosecond laser microprocessing system. The other steps and parameters are the same as those in specific implementation example 1.

Specific implementation example 6: This implementation example is different from specific implementation example 1 in that the atmosphere of the laser scanning process in step 2 is an ambient atmosphere or an argon atmosphere. The other steps and parameters are the same as those in specific implementation example 1.

Specific embodiment 7: This embodiment differs from specific embodiment 1 in that the parameters of the laser scanning process described in step 2 are as follows: the micropit radius is 20 μm to 200 μm, the micropit array spacing is 50 μm to 500 μm, the number of scans is 1 to 10 times, and the scanning power is 5 to 10 W. Other steps and parameters are the same as those in specific embodiment 1.

Specific embodiment eight: This embodiment differs from specific embodiment seven in that the parameters of the laser scanning process in step two are as follows: the micropit radius is 25 μm, the micropit array spacing is 100 μm, the number of scans is 5, and the scanning power is 10 W. Other steps and parameters are the same as those in specific embodiment seven.

Specific embodiment 9: This embodiment is different from specific embodiment 1 in that the polishing process in step 3 is performed by a polishing plate. The other steps and parameters are the same as those in specific embodiment 1.

Specific embodiment ten: The application of the copper current collector with a "step" structure inducing lithium metal to grow inward in this embodiment is to use the copper current collector with a "step" structure inducing lithium metal to grow inward in lithium-sulfur batteries and lithium-air battery systems based on lithium metal negative electrodes.

Compared with battery systems using traditional graphite negative electrodes, the copper current collector with a "step" structure to induce the inward growth of lithium metal as described in this embodiment has higher energy density and lower electrode potential, and can be better applied to the future development of large-scale energy storage and the electric vehicle industry.

The following examples are used to verify the beneficial effects of the present invention:

Comparative Example: Untreated commercial pure copper foil with a thickness of 50 μm.

Example 1: First, the copper foil is cleaned with alcohol and acetone solution to remove the natural oxide layer on the surface. The thickness of the copper foil is 50μm. The cleaned copper foil is placed directly under the laser microprocessing system, and the processing begins after focusing. The radius of the micropit is 25μm, the spacing of the micropit array is 100μm, the number of scans is 5 times, the scanning power is 10W, and the laser processing atmosphere is the ambient atmosphere. After laser processing, the surface of the copper foil has micropits that are not penetrated, have a step-type oxide layer structure on the inner wall, and are evenly distributed in the array. The radius of the micropit is about 25μm, as shown in Figure 1. After multiple bombardments of low-power lasers, a significant step-type layered structure appears inside the micropits. After laser bombardment, large pieces of metal copper form a stacked, thin and dense oxide layer on the inner wall of the pit, which increases the structural size and roughness of the collector surface. The micropit structure is subjected to micro-area Raman spectroscopy analysis. As shown in Figure 2, the characteristic peak of Cu ₂ O appears, indicating that the main component of the oxide layer on the inner wall is Cu ₂ O. Lithium metal was deposited on the surface of the prepared current collector by assembling a lithium copper half-cell, with the prepared current collector on the positive electrode side and lithium foil on the negative electrode side. The applied current was 0.5 mA/cm ^-2 and the duration was 10 min. As shown in Figure 3, lithium metal grew evenly along the inner wall of the pit-like structure, and the metal grain deposition morphology was consistent with the stacking mode of the oxide layer, and grew in a step-like manner inside the pit-like structure. The grains were small and evenly distributed, which delayed the volume expansion phenomenon during the battery cycle.

The stability of the current collector was tested by assembling a lithium copper half-cell. The positive electrode side was the prepared current collector, the negative electrode side was lithium foil, the charging current was 0.5 mA/cm ^-2 , the cut-off voltage was set to 1V, the discharge current was 0.5 mA/cm ^-2 , and the discharge duration was 60 min. As shown in Figures 4 and 5, the coulombic efficiency of the lithium copper half-cell was significantly improved compared with that of the comparative example. As shown in Figures 7 and 8, in the first ten cycles of the cycle capacity-voltage curve, compared with the comparative example, the capacity-voltage curve of the assembled lithium copper half-cell in Experimental Example 1 tended to stabilize faster and had a lower polarization voltage. It shows that the current collector prepared by this method can effectively reduce the consumption of active materials during the cycle. At the same time, since most of the lithium metal is deposited on the inner wall of the micro-pit, the formation of lithium dendrites is delayed, and the risk of puncture of the diaphragm is greatly reduced, and more cycles can be stably cycled. In order to better illustrate the advantages of the current collector prepared by this method, a certain amount of lithium metal is first deposited on the surface of the prepared current collector by assembling a lithium-copper half-cell to prepare a composite negative electrode with a lithium metal loading of 8 mA/cm ^-2 . The current collector is then taken out and assembled into a full battery with a commercial NCM622 positive electrode material, and a charge and discharge test is performed with a test current of 1C. As shown in Figures 9 and 10, compared with the comparative example, the treated current collector has a better capacity retention rate and a higher coulombic efficiency, indicating that it has good electrochemical stability and effectively reduces the loss of active substances during the cycle.

Experimental Example 2: First, the copper foil was cleaned with alcohol and acetone solution to remove the natural oxide layer on the surface. The thickness of the copper foil was 50μm. The cleaned copper foil was placed directly under the laser microprocessing system, and processing began after focusing. The micropit radius was 25μm, the micropit array spacing was 500μm, the number of scans was 5 times, the scanning power was 10W, and the laser processing atmosphere was the ambient atmosphere. The stability of the current collector was charged and discharged by assembling a lithium-copper half-cell. The positive side was the prepared current collector, the negative side was lithium foil, the charging current was 0.5mA/cm ^-2 , and the cut-off voltage was set to 1V. The discharge current was 0.5mA/cm ^-2 , and the discharge duration was 60min. As shown in Figure 6, the coulombic efficiency of the lithium-copper half-cell was significantly improved compared to the comparative example.

Experimental Example 3: First, the copper foil was cleaned with alcohol and acetone solution to remove the natural oxide layer on the surface. The thickness of the copper foil was 100μm. The cleaned copper foil was placed directly under the laser microprocessing system and started processing after focusing. The micropit radius was 50μm, the micropit array spacing was 500μm, the number of scans was 5, and the scanning power was 10W.

Claims (9)

1. The preparation method of the copper current collector with the step-shaped structure for inducing the lithium metal to grow inwards is characterized by comprising the following steps of:

1. selecting copper foil as a raw material, cleaning the surface of the copper foil, and removing a natural oxide layer on the surface to obtain the copper foil to be treated;

2. The surface of the copper foil to be treated is treated by a laser micro-treatment system through a progressive laser scanning process, so that a processed copper foil is obtained; parameter setting of the laser scanning process: the radius of the micro pits is 20-200 mu m, the distance between micro pit arrays is 50-500 mu m, the scanning times are 5 times, and the scanning power is 5-10W; micro pits which do not penetrate through the surface of the copper foil after laser processing, have a step-type oxide layer structure on the inner wall and are uniformly distributed in an array are formed on the surface of the copper foil; the inner wall of the micro pit is introduced with a layered nano structure; lithium metal uniformly grows along the inner wall of the pit-shaped structure of the micro pit, and grows in a step-type manner in the pit-shaped structure;

3. And polishing the processed copper foil to remove the raised oxide layer at the edge of the micro-pit, thereby obtaining the copper current collector with the step-shaped structure for inducing the lithium metal to grow inwards.

2. The method for preparing a copper current collector with a step-shaped structure for inducing lithium metal ingrowth according to claim 1, wherein the step one is characterized in that the surface of the copper foil is cleaned by alcohol and acetone solution.

3. The method for preparing a copper current collector with a step-shaped structure for inducing lithium metal ingrowth according to claim 1, wherein the thickness of the copper foil in the first step is 10-100 μm.

4. The method for preparing the copper current collector with the step-shaped structure for inducing the lithium metal to grow inwards, which is disclosed in claim 1, is characterized in that the diameter of the copper foil to be treated in the step one is 12-16 mm.

5. The method for preparing a copper current collector with a step-shaped structure for inducing lithium metal ingrowth according to claim 1, wherein the laser micro-processing system in the second step is a femtosecond laser micro-processing system.

6. The method for preparing a copper current collector with a step-shaped structure for inducing lithium metal ingrowth according to claim 1, wherein the atmosphere of the laser scanning process in the second step is an ambient atmosphere.

7. The method for preparing a copper current collector with a step-shaped structure for inducing lithium metal ingrowth according to claim 1, wherein the parameter setting of the laser scanning process in the second step is as follows: the radius of the micro-pits is 25 μm, the pitch of the micro-pit array is 100 μm, the scanning times are 5 times, and the scanning power is 10W.

8. The method for preparing a copper current collector with a step-type structure for inducing lithium metal ingrowth according to claim 1, wherein the polishing process in the third step is performed by a polishing plate.

9. Use of a copper current collector with "step" structure induced lithium metal in-growth prepared according to the method of claim 1, characterized in that a copper current collector with "step" structure induced lithium metal in-growth is used for lithium sulfur batteries and lithium air battery systems based on lithium metal negative electrodes.