Method for manufacturing porous copper foil for lithium battery

Abstract

The present application relates to the technical field of copper foil preparation for lithium battery, and particularly relates to a method for preparing porous copper foil for lithium battery, which comprises the following steps: determining whether the stability of pore forming process is qualified based on the uniformity index of bubble coverage area of the surface of copper foil matrix in the pore forming process and the comparison result of the uniformity index with a preset uniformity index; determining whether the forming quality of micropore is qualified based on the energy distribution ratio determined by the forward electrical conversion efficiency in the forward pulse duration and the reverse copper dissolution efficiency in the reverse pulse duration, or based on the nucleation site instability rate of the pore forming distribution area; under the condition that the forming quality of micropore is unqualified, adjusting the duty cycle of reverse pulse based on the fluctuation amplitude of electrolytic cell voltage; periodically detecting the pore forming quality of porous copper foil, and optimizing the preset uniformity index based on the peak valley distribution skewness of pore wall roughness of pore forming. The present application improves the pore forming quality of porous copper foil.

Description

Technical Field

[0001] This invention relates to the field of copper foil preparation technology for lithium batteries, and in particular to a method for preparing porous copper foil for lithium batteries. Background Technology

[0002] With the increasing demands for energy density, cycle life, and safety performance of lithium batteries from new energy vehicles and large-scale energy storage systems, the structural innovation of negative electrode current collectors, as a core component affecting the overall performance of batteries, has become a hot topic in industry research and development. Traditional dense copper foils, due to their small specific surface area, result in excessively high local current density during lithium deposition, easily leading to problems such as lithium dendrite growth, "dead lithium" formation, and active material shedding, severely restricting the cycle stability and safety of batteries. In contrast, porous copper foils, with their three-dimensional framework structure, can significantly increase the specific surface area to reduce local current density, while providing a buffer space for lithium deposition, effectively suppressing lithium dendrites and increasing the active material loading, making them an ideal current collector choice for high-energy-density batteries. Currently, the main methods for preparing porous copper foils include laser drilling, chemical etching, and hydrogen bubble template electrodeposition. Among them, the hydrogen bubble template method has attracted much attention because it does not require additional removal of solid templates and is a green and efficient process. However, existing technologies generally suffer from defects such as uneven micropore distribution, difficulty in precisely controlling pore size, excessive dendrite growth leading to structural collapse, and large pore wall roughness.

[0003] Chinese Patent Application Publication No. CN116072884A discloses a porous copper foil for lithium batteries, its preparation method, and its application. The porous copper foil comprises a non-porous copper foil substrate and a porous copper foil layer covering the surface of the non-porous copper foil substrate. The porous copper foil layer has a porosity of 20-30% and contains copper and additive metal elements. The preparation method of the porous copper foil includes: covering the surface of the non-porous copper foil substrate with an alloy copper foil layer, and then performing a dealloying treatment on the alloy copper foil layer. Compared with traditional lithium battery copper foil of the same size, the porous copper foil provided by this invention, due to its specific structure, can reduce its volume fraction in the battery, reduce its weight by 20%, and increase its specific surface area, enabling it to tightly fill more active materials, thereby increasing the battery capacity density and meeting the current requirements for lightweight lithium-ion batteries.

[0004] The existing technology also has the following problems: In the process of preparing porous copper foil for lithium batteries using hydrogen bubble templates combined with pulsed reverse electrodeposition, the insufficient spatiotemporal uniformity of the bubble coverage area and the imbalance of energy distribution between forward hydrogen evolution and reverse copper dissolution can easily lead to violent dynamic fluctuations of hydrogen bubble nucleation sites and disordered cathode interface reaction state. This can cause uneven micropore distribution and skewed distribution of pore wall roughness peaks and valleys, resulting in large pore size distortion, pore wall collapse and low micropore penetration rate, ultimately leading to poor pore quality of porous copper foil. Summary of the Invention

[0005] To address this, the present invention provides a method for preparing porous copper foil for lithium batteries, which overcomes the problems in the prior art where hydrogen bubble templates are combined with pulsed reverse electrodeposition to prepare porous copper foil for lithium batteries. These problems arise from insufficient spatiotemporal uniformity of bubble coverage area and imbalance in energy distribution between forward hydrogen evolution and reverse copper dissolution. This leads to severe dynamic fluctuations in hydrogen bubble nucleation sites and disordered cathode interface reaction states, resulting in uneven micropore distribution and skewed peak-valley distribution of pore wall roughness. Consequently, large pore size distortion, pore wall collapse, and low micropore penetration rate occur, ultimately leading to poor pore quality of the porous copper foil.

[0006] To achieve the above objectives, the present invention provides a method for preparing porous copper foil for lithium batteries, comprising: Based on the comparison between the uniformity index of the bubble coverage area on the copper foil substrate surface during the hole-forming process and the preset uniformity index, it is determined whether the stability of the hole-forming process is qualified. The quality of micropore formation is determined by the energy distribution ratio based on the forward electrical conversion efficiency during the forward pulse duration and the reverse copper dissolution efficiency during the reverse pulse duration, or by the instability rate of nucleation sites in the pore distribution region. Under the condition that the forming quality of micropores is unqualified, the duty cycle of the reverse pulse is adjusted based on the fluctuation amplitude of the electrolytic cell voltage. The hole formation quality of the porous copper foil is periodically tested, and the preset uniformity index is optimized based on the skewness of the peak and valley distribution of the hole wall roughness.

[0007] Furthermore, the uniformity index is determined based on the time-series curve of the bubble coverage area of ​​a single detection region on the surface of the copper foil substrate.

[0008] Furthermore, the process of determining whether the stability of the hole-forming process is qualified based on the uniformity index includes: The uniformity index is compared with a preset uniformity index; The stability of the hole-forming process is determined to be qualified based on the comparison results where the uniformity index is greater than or equal to the preset uniformity index. Based on the comparison result that the uniformity index is less than the preset uniformity index, the stability of the hole forming process is determined to be unqualified.

[0009] Furthermore, under the condition that the stability of the pore-forming process is qualified, the process of determining whether the forming quality of the micropore is qualified based on the energy distribution ratio includes: Compare the energy allocation ratio with the preset allocation ratio; Based on the comparison result that the energy distribution ratio is less than the preset distribution ratio, it is determined that the forming quality of the micropores is unqualified; The energy distribution ratio is obtained by taking the square root of the product of the forward electrical conversion efficiency and the reverse electrolytic copper dissolution efficiency.

[0010] Furthermore, under the condition that the stability of the pore-forming process is unacceptable, the process of determining whether the micropore forming quality is acceptable based on the instability rate of the nucleation sites in the pore-forming distribution region includes: The instability rate of the nucleation site is compared with a preset instability rate; Based on the comparison result that the instability rate of the nucleation site is greater than the preset instability rate, it is determined that the forming quality of the micropore is unqualified.

[0011] Furthermore, the instability rate of the nucleation sites is determined based on the number of newly added nucleation sites and the number of disappeared nucleation sites in the pore distribution area.

[0012] Furthermore, under the condition that the micropore forming quality is unqualified, the process of adjusting the duty cycle of the reverse pulse based on the fluctuation amplitude of the electrolytic cell voltage includes: The fluctuation amplitude is compared with the preset amplitude respectively; Based on the comparison result that the fluctuation amplitude is greater than the first preset amplitude, the duty cycle of the reverse pulse is increased by the first duty cycle adjustment coefficient; Based on the comparison result that the fluctuation amplitude is less than the second preset amplitude, the duty cycle of the reverse pulse is reduced by the second duty cycle adjustment coefficient.

[0013] Furthermore, the skewness of the peak-valley distribution of the hole wall roughness is determined based on the height profile curve of the micropores of the porous copper foil sample within a single detection cycle.

[0014] Furthermore, the process of determining whether to optimize the preset uniformity index based on the skewness of the peak-valley distribution of the hole wall roughness includes: The skewness of the peak-valley distribution of the hole wall roughness is compared with the preset skewness. The preset uniformity index is optimized based on the comparison results of the peak-valley distribution skewness of the hole wall roughness being greater than the preset distribution skewness.

[0015] Furthermore, based on the difference between the skewness of the peak-valley distribution of the hole wall roughness and the preset distribution skewness, and the comparison result with the preset skewness difference, several index optimization coefficients are set to optimize the preset uniformity index.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: by monitoring the surface of the copper foil substrate in sections and comparing the slope of the time-series curve of the bubble coverage area in each region, the present invention constructs a bubble coverage area uniformity index based on the trend consistency ratio of the curve segments and the consistency ratio of the time-series curves. This quantifies the hydrogen evolution synchronization and distribution uniformity of the dynamic template of hydrogen bubbles from both spatiotemporal dimensions, which can accurately identify hidden anomalies such as local bubble aggregation and hydrogen evolution rate imbalance, and avoid problems such as uneven micropore density and excessive pore size dispersion caused by template instability. It ensures the uniformity of the porous structure from the initial stage of pore formation, thereby improving the pore formation quality of porous copper foil.

[0017] Furthermore, based on different working conditions of the hole-forming process stability, the present invention uses energy distribution ratio and nucleation site instability rate to classify and determine the forming quality. Under steady state, the energy distribution ratio characterizes the energy coupling efficiency of forward hydrogen evolution molding and reverse copper melting trimming. Under unsteady state, the instability rate of nucleation sites quantifies the dynamic replacement stability of hydrogen bubble sites, avoiding misjudgment of qualified products and omission of defective products, effectively reducing forming defects such as hole wall collapse and poor micropore penetration, thereby further improving the hole-forming quality of porous copper foil.

[0018] Furthermore, this invention adjusts the reverse pulse duty cycle based on the amplitude of the cell voltage fluctuation in the electrolytic cell. The cell voltage fluctuation essentially reflects the ion mass transfer resistance at the cathode interface, the degree of concentration polarization, and the imbalance state of the electrochemical reaction. By precisely controlling the intensity of the reverse copper dissolution effect through graded adjustment coefficients, it can both enhance interfacial ion exchange to smooth reaction fluctuations when mass transfer is hindered and improve local deposition trimming efficiency when the reaction is slow, eliminate dendrite tip protrusion and edge effects, avoid local over-dissolution, under-dissolution, and grain coarsening problems, optimize pore wall morphology and porous structure stability, thereby further improving the pore formation quality of porous copper foil. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing porous copper foil for lithium batteries according to an embodiment of the present invention; Figure 2 A flowchart for determining whether the stability of the hole-forming process is qualified according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating how the forming quality of micropores is determined based on the energy distribution ratio in an embodiment of the present invention. Figure 4 This is a flowchart illustrating how to determine the quality of micropore formation based on the instability rate of nucleation sites in the pore distribution region, according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0021] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0022] Please see Figure 1 The diagram shown is a flowchart of a method for preparing porous copper foil for lithium batteries according to an embodiment of the present invention.

[0023] The present invention provides a method for preparing porous copper foil for lithium batteries, comprising: Step S1: Based on the comparison result of the uniformity index of the bubble coverage area on the copper foil substrate surface during the hole-forming process and the preset uniformity index, determine whether the stability of the hole-forming process is qualified. Step S2: Based on the energy distribution ratio determined by the forward electrical conversion efficiency during the forward pulse duration and the reverse copper dissolution efficiency during the reverse pulse duration, determine whether the micropore forming quality is qualified, or based on the instability rate of the nucleation sites in the pore distribution region, determine whether the micropore forming quality is qualified. Step S3: Under the condition that the micropore forming quality is unqualified, adjust the duty cycle of the reverse pulse based on the fluctuation amplitude of the electrolytic cell voltage. Step S4: Periodically detect the hole formation quality of the porous copper foil to optimize the preset uniformity index based on the peak-valley distribution skewness of the hole wall roughness.

[0024] This embodiment employs a pulsed reverse electrodeposition method combined with a hydrogen bubble template to prepare porous copper foil for lithium batteries. First, the copper foil substrate is pretreated by sequential cleaning, activation, and water washing and drying to obtain a clean copper foil substrate. Using the pretreated copper foil substrate as the working electrode, a platinum sheet or titanium mesh as the counter electrode, and a saturated calomel electrode or Ag / AgCl electrode as the reference electrode, electrodeposition is performed using a periodic forward-reverse pulsed power supply. The electrolyte is prepared by uniformly mixing a 0.3–0.6 mol / L copper sulfate solution with a 1.5–2.5 mol / L sulfuric acid solution at a volume ratio of 1:1, and then adding an additive. The additive is composed of polyethylene glycol PEG-2000 and sodium dodecyl sulfate, with the concentration of PEG-2000 being 0.3–0.8 g / L, the concentration of sodium dodecyl sulfate being 0.2–0.7 g / L, and the total concentration of the additive controlled at 0.5–1.5 g / L.

[0025] During preparation, a current density of 10–50 A / dm is first applied. 2 A positive high-current-density pulse is applied, at which point the copper foil substrate acts as the cathode. Under strong cathodic polarization, the hydrogen evolution reaction proceeds violently, and hydrogen bubbles rapidly nucleate and grow on the substrate surface. Simultaneously, Cu in the solution... 2+Dendritic copper crystals are reduced and deposited in the interbubble gaps, with hydrogen bubbles acting as dynamic negative templates to inhibit copper deposition in the bubble attachment areas. Immediately after the forward pulse ends, a short reverse pulse is applied, with a reverse current density of 1 / 3 to 1 / 2 that of the forward pulse. The copper foil substrate instantly becomes the anode, and surface protrusions such as dendrite tips preferentially undergo electrochemical dissolution, thereby eliminating edge effects, improving micropore uniformity, refining grains, and enhancing structural stability, preventing structural collapse caused by excessive dendrite growth. The forward-reverse pulses are cyclically applied at frequencies of 100–1000 Hz. Within a single pulse cycle, the forward pulse duration is 10–50 μs, and the reverse pulse duration is 5–20 μs. Hydrogen bubbles continuously complete the dynamic processes of nucleation, growth, merging, and detachment, forming a dynamic template. Copper continuously deposits in the bubble gaps, forming an interconnected porous network. The thickness of the porous layer gradually increases with the extension of deposition time.

[0026] After deposition is complete and the power is cut off, the substrate with the deposited porous copper layer is removed from the electrolyte and rinsed multiple times with deionized water to remove residual electrolyte and soluble impurities adhering to the surface. Then, the rinsed sample is placed in a vacuum drying environment for low-temperature drying to avoid deformation or oxidation of the porous structure caused by high temperature. After drying and shaping, a porous copper foil for lithium batteries with uniform micropores, stable structure and three-dimensional interconnection is finally obtained.

[0027] Please see Figure 2 As shown, it is a flowchart for determining whether the stability of the hole-forming process is qualified according to an embodiment of the present invention.

[0028] Specifically, the process of determining whether the stability of the hole-forming process is acceptable based on the uniformity index includes: The surface of the copper foil substrate is divided into several detection areas of equal area; Several frames of images are acquired for a single detection region, and a time-series curve of the bubble coverage area of ​​a single detection region is established based on the bubble coverage area of ​​a single frame image; Using the time nodes on the horizontal axis as the dividing criterion, the time series curve of each bubble coverage area is divided into several continuous curve segments; Compare the time series curves of all bubble coverage areas one by one according to the curve segments of the corresponding time intervals; Curve segments with consistent slopes are identified as having consistent bubble change trends. Based on the comparison results that the proportion of curve segments is greater than or equal to a preset proportion, several time-series curves of bubble coverage area are identified as having consistent change trends. The ratio of the number of time series curves showing a consistent trend in bubble coverage area to the total number of time series curves showing a consistent trend in bubble coverage area is determined as the uniformity index of bubble coverage area. The uniformity index is compared with a preset uniformity index; The stability of the hole-forming process is determined to be qualified based on the comparison results where the uniformity index is greater than or equal to the preset uniformity index. Based on the comparison results where the uniformity index is less than the preset uniformity index, the stability of the hole forming process is determined to be unqualified. The percentage of curve segments is the ratio of the number of curve segments with the same trend to the total number of curve segments in the time series curve of the corresponding bubble coverage area.

[0029] Specifically, the images acquired for a single area are high-definition microscopic images with a frame rate of no less than 100fps and a resolution of no less than 1280×1024 pixels. Backlit transmission imaging is used to avoid interference from reflections from the electrolyte and the metal surface, ensuring that the edges of the bubbles are clearly visible. The time point can be 0.5s, but no specific limitation is made.

[0030] Specifically, the preset percentage is 72%. At least 200 groups of porous copper foil samples with stable hole formation, uniform micropore distribution and qualified forming quality are selected during the historical pulse reverse electrodeposition hole formation process. The percentage of samples with consistent change trends in the time-series curve segment of bubble coverage area in different detection areas on the copper foil substrate surface is detected for each group. The arithmetic mean of the percentage data of all qualified samples is determined as the preset percentage.

[0031] Specifically, the preset uniformity index is set at 83%. Based on no less than 200 historical samples with qualified pore quality, the uniformity index of bubble coverage area of ​​the corresponding sample is calculated for each group, and the lower limit of the 95% confidence interval of the data group is extracted as the preset uniformity index.

[0032] Specifically, in the process of creating micropores using the hydrogen bubble template method combined with pulsed reverse electrodeposition, hydrogen bubbles act as dynamic forming templates that directly determine the location, size, and distribution of micropores. The evolution of the bubble coverage area in different regions and at different times directly corresponds to the intensity of hydrogen evolution reaction, ion mass transfer state, and uniformity of the pulsed electric field on the cathode surface. The uniformity index of the bubble coverage area quantifies the consistency of the changing trends of the bubble coverage time-series curves in each detection area, objectively reflecting the uniformity and synchronous evolution of the hydrogen bubble template on the copper foil substrate surface in the spatiotemporal dimension. If the uniformity index meets the preset requirements, it indicates that the hydrogen nucleation, bubble growth, and detachment behaviors in each region of the substrate tend to be consistent throughout the entire process of creating the micropores. The electric field distribution, mass transport, and electrochemical reaction rate during the pulsed electrodeposition process are stable and controllable, without local bubble aggregation, insufficient local hydrogen evolution, or instability of nucleation sites. This ensures the uniformity of the micropore formation location, pore size, and microporosity.

[0033] Please see Figure 3 As shown, it is a flowchart of an embodiment of the present invention for determining whether the forming quality of micropores is qualified based on the energy distribution ratio.

[0034] Specifically, under the condition that the stability of the hole-forming process is qualified, the process of determining whether the forming quality of the microhole is qualified based on the energy distribution ratio determined by the forward electrical conversion efficiency of the forward pulse and the reverse electrolytic copper dissolution efficiency of the reverse pulse includes: The square root of the product of the forward electrical conversion efficiency and the reverse electrolytic copper dissolution efficiency is determined as the energy distribution ratio; Compare the energy allocation ratio with the preset allocation ratio; Based on the comparison result that the energy distribution ratio is greater than or equal to the preset distribution ratio, the forming quality of the micropores is determined to be qualified. Based on the comparison result that the energy distribution ratio is less than the preset distribution ratio, it is determined that the forming quality of the micropores is unqualified.

[0035] Specifically, the preset allocation ratio is 0.78. At least 200 qualified samples were selected from historical pore-forming processes, showing a pore diameter uniformity deviation of ≤5%, good micropore connectivity, no pore wall collapse, and no local over-dissolution / under-dissolution defects. The preset allocation ratio was 1.1 times the arithmetic mean of the energy allocation ratios of the samples during the pore-forming process.

[0036] Specifically, forward electrical conversion efficiency represents the conversion capacity of a unit pulse of electricity for generating hydrogen bubble templates. It directly determines the generation rate, coverage uniformity, and temporal stability of the hydrogen bubble template, and is the foundation for the formation of micropores. Reverse electrocopper dissolution efficiency represents the electrochemical trimming capacity of a unit reverse charge for copper deposition protrusions and dendrite tips. It directly determines the regularity of the pore wall and the connectivity of the micropores, and can avoid pore wall collapse, local over-dissolution, or under-dissolution defects. A higher energy distribution ratio indicates a more balanced distribution of electrical energy between bubble template construction and pore structure trimming, and a higher overall energy utilization efficiency. This results in better pore size uniformity and connectivity of the formed micropores, and reduces the likelihood of pore wall collapse and local defects. Conversely, a lower ratio indicates an unbalanced energy distribution, which can easily lead to template instability or excessive dissolution of the structure.

[0037] Specifically, the process for determining the forward electrical conversion efficiency is as follows: During the duration of the forward pulse, the first amount of electricity passing through during the forward pulse is accumulated by a coulomb counter connected in series in the electrolytic cell circuit, while the actual volume of hydrogen gas being released is recorded by a gas flow meter connected to the gas collecting hood above the cathode; the theoretical volume of hydrogen gas under the first amount of electricity is calculated based on Faraday's law of electrolysis, and the ratio of the actual volume of hydrogen gas to the theoretical volume of hydrogen gas is determined as the forward electrical conversion efficiency.

[0038] Specifically, the formula for calculating the theoretical hydrogen volume based on the first charge is as follows:

[0039] Where V is the theoretical hydrogen volume, Q1 is the first charge passing through during the duration of the positive pulse, Vm is the molar volume of the gas, and F is the Faraday constant.

[0040] Specifically, the process for determining the reverse electrolytic copper dissolution efficiency is as follows: During the duration of the reverse pulse, the second charge passing through during the reverse pulse is accumulated by a coulomb counter connected in series in the electrolytic cell circuit. At the same time, the mass change of the copper foil substrate before and after the application of the reverse pulse is measured by a precision balance to obtain the actual dissolved mass of copper during the reverse pulse. Based on Faraday's law of electrolysis, the theoretical dissolved mass of copper is calculated from the second charge. The ratio of the actual dissolved mass of copper to the theoretical dissolved mass is determined as the reverse electrolytic copper dissolution efficiency.

[0041] Specifically, the formula for calculating the theoretical dissolved mass based on the second charge is as follows:

[0042] Where m is the theoretical dissolved mass, Q2 is the second charge passing through during the reverse pulse duration, M is the molar mass of copper, and F is the Faraday constant.

[0043] Please see Figure 4 As shown, it is a flowchart of an embodiment of the present invention for determining whether the forming quality of micropores is qualified based on the instability rate of nucleation sites in the pore distribution region.

[0044] Specifically, under the condition that the stability of the pore-forming process is unacceptable, the process of determining whether the micropore forming quality is acceptable based on the instability rate of the nucleation sites in the pore-forming distribution region includes: The instability rate of the nucleation site is compared with a preset instability rate; Based on the comparison results of the nucleation site instability rate being greater than the preset instability rate, it is determined that the micropore forming quality is unqualified. Based on the comparison results of the nucleation site instability rate being less than or equal to the preset instability rate, the micropore forming quality is determined to be qualified.

[0045] Specifically, the preset instability rate is set at 15%. At least 200 samples were selected from historical tests where the stability of the pore formation process was deemed unqualified, but the final micropore forming quality was qualified. The instability rate of the nucleation sites of the samples was statistically analyzed, and the median value obtained from the statistics was taken as the preset instability rate.

[0046] Specifically, the nucleation site instability rate characterizes the degree of dynamic fluctuation of hydrogen bubble nucleation sites over time. The smaller the value, the closer the rate of new addition and disappearance of nucleation sites per unit time, and the smoother the site replacement. The number and spatial distribution of hydrogen bubble templates on the copper foil surface are always in a relatively stable dynamic equilibrium state, which can ensure that the hole position, hole size and micropore distribution height are uniform, the hole wall is well formed and there are no obvious defects, and the micropore forming quality is better. Conversely, the larger the nucleation site instability rate, the more explosive the addition or mass disappearance of hydrogen bubble nucleation sites, the more the bubble template is in a state of violent instability, which can easily cause local holes to be too dense or too sparse or the hole size to be large, which in turn leads to forming defects such as hole wall collapse and poor micropore connectivity, resulting in a decrease in micropore forming quality.

[0047] Specifically, the process of determining the instability rate of nucleation sites includes: Bubble images of the pore distribution area are collected at preset time intervals. After preprocessing the bubble images, image algorithms are used to identify the number of hydrogen bubble nucleation sites, the number of newly added nucleation sites, and the number of disappeared nucleation sites in the bubble images. The ratio of the number of newly added nucleation sites to the area of ​​the pore distribution region to the time interval is determined as the density change rate of newly added nucleation sites. The ratio of the number of disappearing nucleation sites to the area of ​​the pore distribution region to the time interval is determined as the rate of change of the density of disappearing sites. The relative difference between the density change rate of the newly added nucleation sites and the density change rate of the disappeared sites is determined as the nucleation site instability rate; The number of newly added nucleation sites refers to the number of sites identified in bubble images acquired after a preset time interval, and for which there is no matching hydrogen bubble nucleation site at the corresponding position in bubble images acquired before the preset time interval; the number of disappeared nucleation sites refers to the number of sites identified in bubble images acquired before the preset time interval, and for which there is no matching hydrogen bubble nucleation site at the corresponding position in bubble images acquired after the preset time interval.

[0048] Specifically, the relative difference between the density change rate of newly added nucleation sites and the density change rate of disappearing sites refers to the percentage of the absolute difference between the density change rate of newly added nucleation sites and the density change rate of disappearing sites to the density change rate of disappearing sites.

[0049] Specifically, the preset time interval is 200 μs. Bubble images are acquired using a high-speed microscopic imaging system with a resolution of at least 1280 × 1024 pixels. Backlit transmission imaging is employed to avoid interference from electrolyte and metal surface reflections, ensuring clear identification of bubble edges and nucleation sites. An 8-bit grayscale bitmap format is used, resulting in images free from motion blur, overexposure, and underexposure. Image algorithms employ Gaussian filtering to remove noise, adaptive threshold segmentation to distinguish bubble regions from the substrate background, and morphological opening operations to eliminate minute impurities, preserving the complete outline of hydrogen bubble nucleation sites. This is existing technology and will not be elaborated further.

[0050] Specifically, the matching and comparison of nucleation sites is carried out by using the Euclidean distance matching algorithm of pixel coordinates to perform spatial location matching of nucleation sites in two adjacent bubble images. Sites with an Euclidean distance of less than 3 pixels are determined to be the same matching site, thereby distinguishing between newly added nucleation sites and disappeared nucleation sites.

[0051] Specifically, when the stability of the hole-forming process is qualified, the temporal changes and spatial distribution of bubble coverage in each region of the copper foil substrate surface are in a uniform and controllable state. The electric field distribution, material transport and electrochemical reaction environment of the overall hole-forming process remain stable. At this time, the energy matching relationship between forward hydrogen evolution to construct bubble template and reverse copper dissolution to repair hole structure becomes the core dominant factor that determines the uniformity of micropore diameter, connectivity and regularity of hole wall. The energy distribution ratio can accurately characterize the rationality of the distribution of electrical energy in the hole-forming and hole-repairing stages. Therefore, the micropore forming quality can be directly judged based on this index.

[0052] When the stability of the pore-forming process is unsatisfactory, the spatiotemporal uniformity of bubble coverage on the substrate surface deviates, the overall process environment is in a non-steady state, and the energy distribution ratio can no longer objectively reflect the actual pore-forming effect. At this time, the dynamic stability of the hydrogen bubble nucleation sites becomes the key direct factor determining whether micropores can be formed normally. The instability rate of the nucleation sites can intuitively characterize the local dynamic stability of the bubble template, accurately determine whether the nucleation sites are within a controllable fluctuation range, and thus accurately determine the final micropore forming quality under non-steady-state conditions.

[0053] Meanwhile, the failure to meet the stability requirements of the pore-forming process only indicates fluctuations in the spatiotemporal uniformity of bubble coverage on the substrate surface, and does not directly equate to final forming defects such as micropore morphology, pore size, and connectivity. This pore-forming process itself has a certain tolerance range, and some process fluctuations can be corrected by subsequent pulse action and dynamic bubble equilibrium, without being transmitted to the final micropore structure. If only process stability is used as the criterion, products with acceptable forming quality are easily misjudged as unacceptable, thereby increasing production losses and costs. However, secondary judgment through the instability rate of nucleation sites can directly reflect the local dynamic forming capability of the hydrogen bubble template. As long as the replacement of nucleation sites is stable and no drastic instability occurs, qualified micropores with uniformity and connectivity and no structural defects can be formed, thus effectively avoiding the one-sidedness of judging by a single process indicator.

[0054] Specifically, under the condition that the micropore forming quality is unqualified, the process of adjusting the duty cycle of the reverse pulse based on the fluctuation amplitude of the electrolytic cell voltage includes: The fluctuation amplitude is compared with the preset amplitude respectively; Based on the comparison result that the fluctuation amplitude is greater than the first preset amplitude, the duty cycle of the reverse pulse is increased by the first duty cycle adjustment coefficient; Based on the comparison result that the fluctuation amplitude is less than the second preset amplitude, the duty cycle of the reverse pulse is reduced by the second duty cycle adjustment coefficient; Based on the comparison result that the fluctuation amplitude is less than or equal to the first preset amplitude and greater than or equal to the second preset amplitude, the duty cycle of the reverse pulse is not adjusted.

[0055] Specifically, the first preset amplitude is 80mV, the second preset amplitude is 20mV, and no less than 200 samples with qualified pore formation quality and stable pore formation process are selected in the historical pore formation process; during the pore formation stage of each sample, the working cell pressure time sequence data of the electrolytic cell is continuously collected, and the corresponding cell pressure fluctuation amplitude is calculated.

[0056] Statistical analysis was performed on the voltage fluctuation amplitude of the qualified samples, and a 95% confidence interval was extracted. The upper limit of the confidence interval was determined as the first preset amplitude, and the lower limit was determined as the second preset amplitude.

[0057] Specifically, the formula for calculating the first duty cycle adjustment coefficient k1 is as follows:

[0058] Wherein, λ1 is the positive duty cycle adjustment gain coefficient, with a value of 0.1, V0 is the fluctuation amplitude of the electrolytic cell voltage, and V1 is the first preset amplitude.

[0059] Specifically, the formula for calculating the second duty cycle adjustment coefficient k2 is as follows:

[0060] Where λ2 is the negative duty cycle adjustment gain coefficient, with a value of 0.1, V0 is the fluctuation amplitude of the electrolytic cell voltage, and V2 is the second preset amplitude.

[0061] Specifically, the product of the determined duty cycle adjustment coefficient and the original duty cycle of the reverse pulse is determined as the adjusted duty cycle of the reverse pulse.

[0062] Specifically, excessively large cell pressure fluctuations indicate impaired mass transfer at the cathode interface and an imbalance in the hydrogen evolution / copper dissolution reaction. Therefore, increasing the reverse pulse duty cycle is necessary to improve interfacial ion transport. Conversely, excessively small cell pressure fluctuations indicate that the interfacial reaction is too gradual. Therefore, decreasing the reverse pulse duty cycle is necessary to enhance the local reaction intensity.

[0063] Specifically, the detection cycle for the pore quality of porous copper foil is determined based on the ratio of the consumption rate of additives and copper ions in the electrolyte.

[0064] Specifically, the process for determining the consumption rate ratio of additives and copper ions is as follows: real-time monitoring of the concentrations of additives and copper ions in the electrolyte, with the monitoring duration as the abscissa and the corresponding concentration as the ordinate, is used for linear fitting to obtain the linear decrease slope of the additive concentration per unit time and the linear decrease slope of the copper ion concentration per unit time, respectively; the ratio of the decrease slope of the additive concentration to the decrease slope of the copper ion concentration is determined as the consumption rate ratio of additives and copper ions.

[0065] Specifically, the process of determining the detection cycle of the porous copper foil's hole formation quality based on the consumption rate ratio includes: The consumption rate ratio is compared with the preset rate ratio respectively; Based on the comparison result that the consumption rate ratio is greater than the first preset rate ratio, the detection cycle of the hole formation quality of the porous copper foil is set as the first cycle. Based on the comparison result that the consumption rate ratio is less than or equal to the first preset rate ratio and greater than or equal to the second preset rate ratio, the detection cycle of the hole formation quality of the porous copper foil is set as the second cycle. Based on the comparison result that the consumption rate ratio is less than the second preset rate ratio, the detection cycle of the porous copper foil hole formation quality is set as the third cycle.

[0066] Specifically, the first preset rate ratio is set to 0.55, the second preset rate ratio is set to 0.35, and no less than 200 groups of continuous production samples with qualified hole formation quality are selected. The consumption rate ratio of additives to copper ions for each group is statistically analyzed, and its 95% confidence interval is extracted. The upper limit of the confidence interval is determined as the first preset rate ratio, and the lower limit is determined as the second preset rate ratio.

[0067] Specifically, the first testing cycle is 30 minutes, the second testing cycle is 60 minutes, and the third testing cycle is 45 minutes.

[0068] Specifically, the process of determining the skewness of the peak-valley distribution of the hole wall roughness includes: Random sampling of porous copper foil produced in a single testing cycle; The height profile curve of a single micropore is obtained by scanning along the pore wall axially for each micropore in a single sample. Determine the peak height and trough depth of the height profile curve of a single micropore, and determine the third-order skewness coefficient of the mixed array consisting of the peak heights and trough depths of all micropores in a single sample. The arithmetic mean of the absolute values ​​of the third-order skewness coefficients of all samples is determined as the skewness of the peak-valley distribution of the pore wall roughness.

[0069] Specifically, 3-5 samples are randomly selected at equal intervals within a single detection cycle. The selected samples are pretreated by ultrasonic cleaning with anhydrous ethanol for 5-10 minutes and air-dried naturally. A high-precision laser profilometer is used to scan the contour of the micropores along the axial direction of the pore wall with a scanning step size of 50-100 nm. The contour curve of the pore wall height corresponding to each micropore is obtained. The curve represents the roughness of the pore wall with the axial position of the pore wall as the abscissa and the pore wall surface height as the ordinate.

[0070] All peak heights and valley depths in each height profile curve are identified and integrated to form a mixed data array. The third-order skewness coefficient of the mixed data array is calculated, and the arithmetic mean of the absolute values ​​of the third-order skewness coefficients of all samples is determined as the skewness of the peak-valley distribution of the hole wall roughness in a single detection cycle.

[0071] Specifically, the formula for calculating the third-order skewness coefficient is as follows:

[0072] Among them, S k The third-order skewness coefficient is represented by n, which represents the number of data points in the mixed array, and x represents the third-order skewness coefficient. i This represents a single data point in the mixed array, where x0 represents the arithmetic mean of the mixed array, and S represents the standard deviation of the mixed array.

[0073] Specifically, the third-order skewness coefficient represents the degree of asymmetry in the mixed distribution of peak height and trough depth. Positive and negative values ​​indicate the direction of distribution skewness, and absolute values ​​indicate the degree of skewness in distribution.

[0074] Specifically, a peak refers to a local extreme point where at least three consecutive scanning sampling points form a local bulge, and the height difference between the highest point of the local bulge and the reference plane is greater than or equal to 0.08 μm; a trough refers to a local extreme point where at least three consecutive scanning sampling points form a local depression, and the depth difference between the lowest point of the local depression and the reference plane is greater than or equal to 0.08 μm. The reference plane is obtained by fitting using the least squares method.

[0075] Specifically, the process of determining whether to optimize the preset uniformity index based on the skewness of the peak-valley distribution of the hole wall roughness includes: The skewness of the peak-valley distribution of the hole wall roughness is compared with the preset skewness. Based on the comparison result that the skewness of the peak-valley distribution of the hole wall roughness is greater than the preset distribution skewness, the preset uniformity index is optimized. Based on the comparison result of the skewness difference between the peak-valley distribution skewness of the hole wall roughness and the preset distribution skewness, several index optimization coefficients are set to optimize the preset uniformity index. Based on the comparison results of the peak-valley distribution skewness of the hole wall roughness being less than or equal to the preset distribution skewness, it is determined that the preset uniformity index will not be optimized.

[0076] Specifically, based on the comparison result that the skewness difference is greater than or equal to the preset skewness difference, the preset uniformity index is determined to be optimized with a first index optimization coefficient; Based on the comparison result that the skewness difference is less than the preset skewness difference, the preset uniformity index is determined to be optimized with the second index optimization coefficient.

[0077] Specifically, the preset distribution skewness is set to 0.35, the preset skewness difference is set to 0.12, and no fewer than 200 sets of porous copper foil samples with hole formation quality that meet the design requirements are selected from historical production. The peak-valley distribution skewness of hole wall roughness corresponding to each sample is measured, and the value corresponding to the median is taken as the preset distribution skewness. The preset skewness difference is determined by taking 1.5 times the sample standard deviation of the peak-valley distribution skewness of hole wall roughness corresponding to each sample.

[0078] Specifically, the formula for calculating the first exponential optimization coefficient is as follows:

[0079] Where y1 represents the first exponential optimization coefficient, α represents the first skewness gain coefficient with a value of 0.25, ΔS represents the skewness difference, and S0 represents the preset distribution skewness.

[0080] Specifically, the formula for calculating the second exponential optimization coefficient is as follows:

[0081] Where y2 represents the second exponential optimization coefficient, β represents the second skewness gain coefficient with a value of 0.12, ΔS represents the skewness difference, and S0 represents the preset distribution skewness.

[0082] Specifically, the product of the determined index optimization coefficient and the preset uniformity index is the adjusted preset uniformity index.

[0083] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing porous copper foil for lithium batteries, characterized in that, include: Based on the comparison between the uniformity index of the bubble coverage area on the copper foil substrate surface during the hole-forming process and the preset uniformity index, it is determined whether the stability of the hole-forming process is qualified. The quality of micropore formation is determined by the energy distribution ratio based on the forward electrical conversion efficiency during the forward pulse duration and the reverse copper dissolution efficiency during the reverse pulse duration, or by the instability rate of nucleation sites in the pore distribution region. Under the condition that the forming quality of micropores is unqualified, the duty cycle of the reverse pulse is adjusted based on the fluctuation amplitude of the electrolytic cell voltage. The hole formation quality of the porous copper foil is periodically tested, and the preset uniformity index is optimized based on the skewness of the peak and valley distribution of the hole wall roughness.

2. The method for preparing porous copper foil for lithium batteries according to claim 1, characterized in that, The uniformity index is determined based on the time-series curve of bubble coverage area in a single detection region on the surface of the copper foil substrate.

3. The method for preparing porous copper foil for lithium batteries according to claim 2, characterized in that, The process of determining whether the stability of the hole-forming process is qualified based on the uniformity index includes: The uniformity index is compared with a preset uniformity index; The stability of the hole-forming process is determined to be qualified based on the comparison results where the uniformity index is greater than or equal to the preset uniformity index. Based on the comparison result that the uniformity index is less than the preset uniformity index, the stability of the hole forming process is determined to be unqualified.

4. The method for preparing porous copper foil for lithium batteries according to claim 3, characterized in that, Under the condition that the stability of the pore-forming process is qualified, the process of determining whether the forming quality of the micropore is qualified based on the energy distribution ratio includes: Compare the energy allocation ratio with the preset allocation ratio; Based on the comparison result that the energy distribution ratio is less than the preset distribution ratio, it is determined that the forming quality of the micropores is unqualified; The energy distribution ratio is obtained by taking the square root of the product of the forward electrical conversion efficiency and the reverse electrolytic copper dissolution efficiency.

5. The method for preparing porous copper foil for lithium batteries according to claim 4, characterized in that, Under the condition that the stability of the pore-forming process is unacceptable, the process of determining whether the micropore forming quality is acceptable based on the instability rate of the nucleation sites in the pore distribution region includes: The instability rate of the nucleation site is compared with a preset instability rate; Based on the comparison result that the instability rate of the nucleation site is greater than the preset instability rate, it is determined that the forming quality of the micropore is unqualified.

6. The method for preparing porous copper foil for lithium batteries according to claim 5, characterized in that, The instability rate of the nucleation sites is determined based on the number of newly added nucleation sites and the number of disappeared nucleation sites in the pore distribution area.

7. The method for preparing porous copper foil for lithium batteries according to claim 6, characterized in that, Under conditions where the micropore forming quality is unqualified, the process of adjusting the duty cycle of the reverse pulse based on the fluctuation amplitude of the electrolytic cell voltage includes: The fluctuation amplitude is compared with the preset amplitude respectively; Based on the comparison result that the fluctuation amplitude is greater than the first preset amplitude, the duty cycle of the reverse pulse is increased by the first duty cycle adjustment coefficient; Based on the comparison result that the fluctuation amplitude is less than the second preset amplitude, the duty cycle of the reverse pulse is reduced by the second duty cycle adjustment coefficient.

8. The method for preparing porous copper foil for lithium batteries according to claim 7, characterized in that, The skewness of the peak-valley distribution of the pore wall roughness is determined based on the height profile curve of the micropores in the porous copper foil sample within a single detection cycle.

9. The method for preparing porous copper foil for lithium batteries according to claim 8, characterized in that, The process of determining whether to optimize the preset uniformity index based on the skewness of the peak-valley distribution of the hole wall roughness includes: The skewness of the peak-valley distribution of the hole wall roughness is compared with the preset skewness. The preset uniformity index is optimized based on the comparison results of the peak-valley distribution skewness of the hole wall roughness being greater than the preset distribution skewness.

10. The method for preparing porous copper foil for lithium batteries according to claim 9, characterized in that, Based on the difference between the skewness of the peak-valley distribution of the hole wall roughness and the preset distribution skewness, and the comparison result with the preset skewness difference, several index optimization coefficients are set to optimize the preset uniformity index.

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