A testing device and method for lithium-ion battery negative electrode bubble lithium deposition membrane boundary

Abstract

This application provides a device and method for testing the lithium dendrite penetration boundary of lithium-ion battery negative electrode bubbles. It utilizes porous, conductive nickel / copper foam as a monitoring electrode. Its high porosity and conductivity provide a growth channel for lithium dendrites to penetrate the separator. A reference electrode is plated with lithium to form a stable lithium metal reference potential. The potential difference between the two electrodes is monitored, enabling real-time online monitoring of lithium dendrite penetration behavior. This directly determines whether lithium dendrites have pierced the separator, significantly shortening the detection cycle. By preparing negative electrode bubble sheets of different preset diameters and combining them with charge-discharge cycle testing, the safe boundary of bubble size is accurately determined based on the correlation between the voltage difference inflection point and bubble size, providing crucial information for production line process parameter control. This application can guide production line parameter adjustments before battery production, eliminating the potential risks of large-size bubbles. The device uses low-cost materials and standardized processes, offering advantages of low cost and high compatibility, effectively improving battery safety and consistency.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a device and method for testing the boundary of lithium deposition through the film of a lithium-ion battery negative electrode bubble. Background Technology

[0002] Lithium-ion battery anode slurry mainly consists of anode active material, conductive agent, solvent, thickener, binder, and deionized water. Its preparation process is primarily divided into two types: dry mixing and wet mixing. In the dry mixing process, the thickener and deionized water are first mixed in a mixing tank to form a gel, followed by the sequential addition of the conductive agent, anode active material, and binder, and then stirred to finally form a homogeneous anode slurry. The wet mixing process employs a premixing strategy, first premixing the conductive agent, anode active material, and thickener, then adding deionized water step-by-step for kneading and stirring to form a premixed slurry, and finally adding the binder to complete the final slurry preparation.

[0003] However, during high-speed stirring, a large number of air bubbles are easily introduced into the slurry. These bubbles, after being coated onto the copper foil substrate, occupy an effective slurry volume, leading to uneven coating. In subsequent extrusion, rolling, and drying processes, the bursting of these bubbles creates localized defects, reducing the surface density of the negative electrode. During charging, lithium ions extracted from the positive electrode cannot be fully inserted due to insufficient capacity in the bubble-affected areas, causing lithium plating. In severe cases, lithium dendrites penetrate the separator, resulting in abnormal battery self-discharge or even a short circuit risk.

[0004] Currently, the industry commonly uses vacuuming or ultrasonic vibration techniques to eliminate bubbles, but these methods still have significant limitations. Vacuuming is limited by slurry viscosity and vacuuming time (excessive vacuuming can lead to slurry deterioration), making it difficult for tiny bubbles to completely escape the surface, ultimately forming dark spots and exposed foil defects on the electrode. Ultrasonic methods are expensive and complex to operate, and their effectiveness in removing micron-sized bubbles is limited, making efficient industrial application difficult. Furthermore, whether lithium deposition from bubbles of different sizes leads to dendrites penetrating the separator and causing battery self-discharge requires long-term self-discharge testing. As battery capacity increases, the testing time becomes even longer, and there is currently no effective method for rapid online confirmation of lithium deposition penetrating the separator.

[0005] Therefore, a test scheme for lithium-ion battery negative electrode bubble lithium penetration membrane boundary is needed to fill the technical gap that makes it impossible to quickly determine online whether lithium-ion bubbles have penetrated the membrane, which makes it difficult for production lines to accurately control the size of bubbles and avoid problems such as pressure difference that may be caused by large-sized bubbles flowing into the battery. Summary of the Invention

[0006] This application aims to address at least one of the aforementioned technical deficiencies. In view of this, this application provides a lithium-ion battery negative electrode bubble lithium deposition membrane boundary testing device and method. Through the collaborative design of porous conductive monitoring electrode and pre-plated lithium reference electrode, microscopic behavior is transformed into quantifiable signals, breaking through the limitations of traditional detection. At the same time, it provides clear process control thresholds for production lines, improving battery safety and consistency.

[0007] A lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device, characterized in that it includes a positive electrode sheet, a negative electrode sheet containing bubbles of a preset diameter, a multilayer separator, a monitoring electrode, a reference electrode, and a voltage monitoring device.

[0008] The diameter of the bubbles in the negative electrode sheet ranges from 0.1 mm to 2.5 mm;

[0009] The multilayer diaphragm includes a first diaphragm layer, a second diaphragm layer, and a third diaphragm layer;

[0010] The monitoring electrode is made of a porous conductive material, which is either nickel foam or copper foam with a porosity of 30% to 50%.

[0011] The reference electrode is located at the corresponding position at the center of the bubble;

[0012] The device includes the negative electrode, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer, and the positive electrode, which are stacked sequentially.

[0013] The monitoring electrode and the reference electrode are connected to the voltage monitoring device via tabs, and the reference electrode is lithium-plated to form a lithium metal reference standard;

[0014] The voltage monitoring device is used to monitor the potential difference between the monitoring electrode and the reference electrode in real time.

[0015] Optional, including:

[0016] The bubble is located in the central region of the negative electrode sheet;

[0017] The monitoring electrode is positioned to correspond to the center of the bubble in the negative electrode sheet;

[0018] One end of the reference electrode is plated with lithium, and the lithium-plated end is vertically aligned with the center of the bubble.

[0019] The positive electrode is positioned to correspond to the central region of the negative electrode.

[0020] Optionally, the tabs of the monitoring electrode and the reference electrode are fixed to a reserved area of ​​nickel foam or copper foam by a rolling process to form an electrical connection.

[0021] Optionally, the porosity of the porous conductive material is equal to the porosity of the multilayer membrane.

[0022] Optionally, one end of the reference electrode is plated with lithium, and the thickness of the lithium-plated reference electrode is the same as that of the foamed nickel or foamed copper.

[0023] A method for testing the boundary of lithium deposition through the film in the negative electrode of a lithium-ion battery, comprising:

[0024] Step 1: Prepare negative electrode sheets containing bubbles of different preset diameters, with the preset diameter range being 0.1 mm to 2.5 mm;

[0025] Step 2: Using the negative electrode sheets with bubbles of different preset diameters, assemble a test battery according to the device described in any one of claims 1-5, and perform lithium plating on the reference electrode included therein.

[0026] Step 3: Perform charge and discharge cycles on the assembled test battery. The charge and discharge conditions are as follows: charge to 3.65V at a constant current and constant voltage at the first preset charging rate, discharge to 2.5V at the second preset discharging rate, and cycle at a temperature of 25℃. The range of the first preset charging rate is 0.2C-1C, and the range of the second preset discharging rate is 0.2C-2C.

[0027] Step 4: Monitor the potential difference between the monitoring electrode and the reference electrode in real time;

[0028] Step 5: Determine whether to puncture the diaphragm based on the potential difference:

[0029] If the potential difference decreases, it is determined that the lithium plating of the bubble with the corresponding preset diameter has penetrated the membrane;

[0030] If the potential difference does not change, it is determined that the bubble of the corresponding preset diameter has not penetrated the membrane.

[0031] Optional, also includes:

[0032] Step 6: Determine the boundary of the bubble's diameter based on the potential difference:

[0033] If the potential difference corresponding to the preset diameter bubble does not change, the preset diameter is determined to be within the safe range;

[0034] If the potential difference corresponding to a bubble with a preset diameter decreases as time or the number of cycles increases, the preset diameter is determined to be the target diameter.

[0035] The smallest of the multiple target diameters is determined as the diameter boundary of the bubble.

[0036] Optionally, during the charge-discharge cycle, the voltage monitoring device records the curve of the potential difference changing with time or the number of cycles, and the critical number of cycles for lithium plating to penetrate the film is determined by combining the inflection point of the curve.

[0037] Optionally, if the porous conductive material is nickel foam, the initial value of the corresponding potential difference is 2.796V;

[0038] If the porous conductive material is copper foam, the initial value of the corresponding potential difference is 3.382V.

[0039] Optionally, the preparation of the negative electrode sheet containing bubbles of different preset diameters includes:

[0040] Collect negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm, and cut them into negative electrode bubble sheets of different sizes using a die cutter.

[0041] As can be seen from the above technical solutions, the lithium dendrite penetration test device and method for lithium-ion battery negative electrode provided in this application uses porous conductive foamed nickel or foamed copper as monitoring electrodes to provide growth space for lithium dendrites after penetrating the separator. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in potential difference between the electrode and the reference electrode, it is possible to directly determine whether lithium dendrites have pierced the separator, thereby significantly shortening the detection cycle.

[0042] To accurately determine the safety boundary of bubble size, negative electrode bubble sheets with different preset diameters are prepared, and a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size, in combination with charge-discharge cycle tests. This clarifies the critical value of whether lithium-deposited bubbles of different sizes penetrate the separator, providing a basis for the control of production line process parameters.

[0043] In terms of optimizing production processes and preventing safety hazards, the negative electrode slurry coating process is verified before battery production to clarify the allowable bubble size range. This guides the production line to adjust relevant parameters to eliminate large-sized bubbles, enabling rapid screening of high-risk bubble sizes and preventing large-sized bubble electrodes from flowing into the assembly process.

[0044] Furthermore, this application features low cost and high compatibility. It employs low-cost porous conductive nickel or copper foam with a lithium-plated reference electrode, standardizing electrode dimensions and assembly processes to adapt to mainstream battery manufacturing processes. This results in a simple device structure that eliminates the need for expensive equipment, making it suitable for various separator materials and battery systems. Through the synergistic design of the porous conductive monitoring electrode and the lithium-plated reference electrode, microscopic behavior is transformed into quantifiable signals, overcoming the limitations of traditional detection methods. Simultaneously, it provides clear process control thresholds for production lines, effectively improving battery safety and consistency. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the structure of the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device provided in the embodiments of this application;

[0047] Figure 2 This is a schematic diagram of another lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device disclosed in this application.

[0048] Figure 3 Microscopic illustration of the microporous structure of nickel foam provided in the embodiments of this application;

[0049] Figure 4 This is a flowchart illustrating a lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary test method as exemplified by an embodiment of this application;

[0050] Figure 5 The graph shows the voltage change between the monitoring electrode and the reference electrode during cycling of batteries with different bubble sizes, which are examples of embodiments of this application. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] The inventors discovered that during lithium plating detection, the white substrate of the separator is difficult to distinguish from the grayish-white of the lithium plating due to color difference. Furthermore, after lithium dendrites reach the positive electrode surface, they cannot continue to grow because the positive electrode potential is higher than the lithium plating potential. It is difficult to observe and define the boundary of lithium dendrites of different sizes passing through the separator and the distribution of lithium plating after passing through the separator, making it difficult to control the size of bubbles on the electrode during production and use.

[0053] Based on this, this application is hereby proposed. The following section will introduce the proposed solution. Please refer to the following text for details.

[0054] First, the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device provided in the embodiments of this application will be described. See [link to relevant documentation]. Figure 1 and Figure 2 , Figure 1This is a schematic diagram of the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device disclosed in the embodiments of this application. Figure 2 This is a schematic diagram of another lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary testing device disclosed in an embodiment of this application.

[0055] like Figure 1 and Figure 2 As shown, the device may include:

[0056] Positive electrode, negative electrode containing bubbles of a predetermined diameter, multilayer diaphragm, monitoring electrode, reference electrode, and voltage monitoring device.

[0057] The diameter of the bubbles in the negative electrode sheet ranges from 0.1 mm to 2.5 mm;

[0058] The multilayer diaphragm includes a first diaphragm layer, a second diaphragm layer, and a third diaphragm layer;

[0059] The monitoring electrode is made of a porous conductive material, which is either nickel foam or copper foam with a porosity of 30% to 50%.

[0060] The reference electrode is located at the corresponding position at the center of the bubble;

[0061] The device includes the negative electrode, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer, and the positive electrode, which are stacked sequentially.

[0062] The monitoring electrode and the reference electrode are connected to the voltage detection device via tabs, and the reference electrode is lithium-plated to form a lithium metal reference standard;

[0063] The voltage monitoring device is used to monitor the potential difference between the monitoring electrode and the reference electrode in real time.

[0064] Furthermore, the bubble is located at the center of the negative electrode sheet, the monitoring electrode is placed in a position corresponding to the center of the bubble in the negative electrode sheet, one end of the reference electrode is plated with lithium, and its lithium-plated end is vertically aligned with the center of the bubble, and the positive electrode sheet is placed in a position corresponding to the central region of the negative electrode sheet.

[0065] Furthermore, the tabs of the monitoring electrode and the reference electrode are fixed to a reserved area of ​​nickel foam or copper foam by a rolling process to form an electrical connection.

[0066] The porosity of the porous conductive material is equal to the porosity of the multilayer membrane.

[0067] Furthermore, one end of the reference electrode is plated with lithium, and the thickness of the lithium-plated reference electrode is the same as that of the foamed nickel or foamed copper.

[0068] Specifically, the positive electrode: As a key electrode component in the entire device, the positive electrode plays a crucial role in the redox reactions that occur during battery charging and discharging. Its dimensions are typically 5.0 × 6.0 cm², a specific size carefully designed to work in conjunction with other components to ensure the efficient execution of electrochemical reactions within the battery. It participates in the overall electrochemical process of the battery, providing a stable potential environment for the device, and together with the negative electrode, constitutes the core electrochemical reaction system of the battery.

[0069] Negative electrode sheet containing bubbles of a predetermined diameter: The negative electrode sheet is one of the core research objects of this device, and its unique feature is the presence of bubbles of a predetermined diameter. The bubble diameter is precisely controlled between 0.1 mm and 2.5 mm, and must be located as centrally as possible in the negative electrode sheet. The presence of these bubbles simulates defects that may occur in actual production, which is of crucial significance for studying the phenomenon of lithium plating and film penetration by bubbles in lithium-ion battery negative electrodes. Bubbles of different diameters will have different effects on the lithium plating process. By setting such diverse bubble sizes, the boundary conditions and laws of bubble lithium plating can be comprehensively and deeply explored. Through the scheme of this application, the influence of micron-sized bubbles on lithium plating can be explored, providing a practical and effective detection method for lithium plating detection.

[0070] Multilayer separator: The multilayer separator consists of a first separator layer, a second separator layer, and a third separator layer. Its main function is to isolate the positive and negative electrode plates, as well as the subsequent monitoring and reference electrodes, preventing internal short circuits in the battery, while allowing lithium ions to pass through and maintaining the normal electrochemical reaction of the battery. The separator can be made of PP (12µm thick) or PE (7+3+3+3) material and is cut to a size of 5.5×6.5cm². The appropriate material and size ensure that the separator can effectively perform its isolation function and remain stable in the complex electrochemical environment inside the battery, thus guaranteeing the safety and stability of the battery.

[0071] Monitoring Electrode: The monitoring electrode is made of a special porous conductive material, specifically foamed nickel or foamed copper with a porosity of 30% to 50%, and its porosity is consistent with that of the multilayer membrane in the device. It should be noted that the monitoring electrode needs to undergo a rolling process to improve porosity uniformity and reduce porosity, maintaining a match with the isolation porosity. For example, the foamed nickel used in the monitoring electrode typically has a porosity of 70-95% and a pore size range of 50-200μm before rolling. After rolling compression, its porosity can be precisely controlled at 30-50%, matching the membrane porosity. Simultaneously, the thickness of the compressed monitoring electrode can be equal to the thickness of the lithium-plated reference electrode. For example, the thickness of the rolled foamed nickel can be compressed to approximately 100μm, a thickness close to that of a conventional lithium-plated reference electrode, avoiding excessive local polarization due to excessive thickness, which could affect lithium-ion insertion / extraction efficiency. From a thickness perspective, the thickness of the nickel foam before rolling ranges from 167 to 1400 μm. During compression, the pore size decreases significantly due to the bending of the pore edges and their contact with the pore walls. Simultaneously, the specific surface area of ​​the material increases substantially, providing a larger surface area for contact with lithium dendrites, thus improving detection sensitivity. After compression, the porosity remains similar to that of the separator, providing a smooth path for lithium ion migration and avoiding hindering lithium dendrite growth. Furthermore, its three-dimensional porous structure provides space for the growth of lithium dendrites (approximately 300 nm in size), allowing them to form close electrical contact with the porous conductive network of the nickel foam itself during growth. This facilitates real-time capture of the boundary signal of lithium deposition through the membrane by monitoring the potential difference between the monitoring electrode and the reference electrode. In addition, rolling also enables the connection between the monitoring electrode and the tab, improving preparation efficiency while ensuring connection reliability.

[0072] In the entire testing setup, the monitoring electrode is located after the negative electrode and the first separator layer, and before the second separator layer, and is connected to the external circuit via a tab. It works in conjunction with a reference electrode, which is lithium-plated to form a lithium metal reference at the corresponding position in the bubble center. A voltage monitoring device monitors the potential difference between the two electrodes in real time to ensure detection accuracy. When lithium plating occurs in bubbles with a diameter of 0.1 mm to 2.5 mm in the central region of the negative electrode, and lithium penetrates the first separator layer, lithium dendrites can grow inside the nickel foam and form electrical contact with the nickel foam. The monitoring electrode can sensitively capture the potential changes caused by lithium ion migration, and through abrupt changes in the potential difference signal, it provides crucial data support for determining the lithium plating penetration boundary.

[0073] Figure 3This is a microscopic image illustrating the microporous structure of nickel foam, a porous conductive metal material that plays a significant role in lithium-ion battery-related testing. Its unique structure is crucial in detecting whether lithium plating has punctured the separator. Due to its numerous micropores, when lithium dendrites from lithium plating puncture the separator, they grow into the micropores of the nickel foam. The connection between the lithium dendrites and the porous material alters the local electrochemical environment, thereby reducing the potential of the porous material. By monitoring this potential change, it is possible to determine whether lithium plating has punctured the separator. Similar to nickel foam, copper foam is also a porous conductive metal and can be used in similar lithium plating detection scenarios, utilizing the potential change caused by the interaction between its porous structure and lithium dendrites for monitoring.

[0074] Reference electrode: Located between the second and third diaphragm layers, it is spaced apart from the monitoring electrode by the second diaphragm layer. This not only ensures spatial isolation between the two electrodes but also improves the accuracy of detecting potential difference changes between them. The reference electrode is a specially treated enameled copper wire with an internal copper wire diameter of 22 μm. One end is immersed in 98% concentrated sulfuric acid to a depth of 1 cm for 30 minutes to remove the surface insulation. After treatment, one end of the reference electrode is lithium-plated, with the lithium-plated end vertically aligned with the center of the bubble. The thickness of the lithium-plated reference electrode is the same as that of the foamed nickel or foamed copper. The lithium-plated reference electrode forms a stable lithium metal reference standard, providing an accurate potential reference standard for the voltage monitoring device. This allows for precise monitoring of potential difference changes between the monitoring electrode and the reference electrode, thereby effectively determining the penetration of lithium dendrites.

[0075] Voltage monitoring device: The voltage monitoring device plays a crucial role in data acquisition and analysis within the entire device. It monitors the potential difference between the monitoring electrode and the reference electrode in real time, collecting and recording this critical data. By analyzing the changes in potential difference, it is possible to intuitively understand whether lithium dendrites have penetrated the separator and the progress of the lithium deposition process. This data provides important quantitative evidence for studying the lithium deposition boundary of lithium-ion battery negative electrode bubbles, contributing to a deeper understanding of the electrochemical behavior inside the battery and providing strong support for improving battery performance and preventing safety hazards.

[0076] The lithium plating process for the reference electrode may specifically include:

[0077] ① The reference electrode is forward charged for 4 hours with a constant current of 20μA;

[0078] ② After switching the electrode polarity, the reference electrode is reverse charged for 4 hours with a constant current of 20μA.

[0079] Specifically, the lithium plating process of the reference electrode is extremely critical, as it provides a stable and accurate lithium metal reference for the device. This process includes the following two stages:

[0080] Forward charging stage: First, the positive electrode of the lithium plating equipment is connected to the reference electrode, and the reference electrode is forward-charged for up to 4 hours with a constant current of 20 μA. During this process, the current drives lithium ions to move towards the reference electrode and begin deposition. This stage is the initial step of lithium plating, laying the foundation for the subsequent uniform distribution of lithium metal. The continuous charging time of 4 hours ensures that a sufficient amount of lithium ions react and deposit on the surface of the reference electrode, initially building up a lithium metal layer.

[0081] Reverse charging phase: After forward charging is completed, the electrode polarity of the lithium plating equipment is switched, connecting the positive electrode to the negative electrode while the negative electrode remains connected to the reference electrode. The reference electrode is then reverse-charged again for 4 hours with a constant current of 20 μA. The reverse current promotes the redistribution of the deposited lithium metal on the reference electrode surface, reducing uneven lithium metal distribution or polarization that may occur during forward charging. After reverse charging, the lithium metal deposition on the reference electrode surface is more uniform, significantly improving the stability and accuracy of the reference electrode as a lithium metal reference standard.

[0082] After this complete lithium plating process, a stable and uniform lithium metal layer is formed at one end of the reference electrode. When precisely placed at the corresponding position in the center of the bubble, it can provide a highly accurate potential reference standard for the voltage monitoring device, thereby enabling the device to accurately monitor the potential difference change between the monitoring electrode and the reference electrode, and effectively determine whether lithium dendrites have penetrated the separator.

[0083] As can be seen from the above technical solutions, the lithium dendrite penetration test device and method for lithium-ion battery negative electrode provided in this application uses porous conductive foamed nickel or foamed copper as monitoring electrodes to provide growth space for lithium dendrites after penetrating the separator. This avoids affecting the growth of lithium dendrites while improving contact reliability. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in potential difference between the electrode and the reference electrode, it is possible to directly determine whether lithium dendrites have pierced the separator, thereby significantly shortening the detection cycle.

[0084] To accurately determine the safety boundary of bubble size, negative electrode bubble sheets with different preset diameters are prepared, and a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size, in combination with charge-discharge cycle tests. This clarifies the critical value of whether lithium-deposited bubbles of different sizes penetrate the separator, providing a basis for the control of production line process parameters.

[0085] In terms of optimizing production processes and preventing safety hazards, the negative electrode slurry coating process is verified before battery production to clarify the allowable bubble size range. This guides the production line to adjust relevant parameters to eliminate large-sized bubbles, enabling rapid screening of high-risk bubble sizes, preventing large-sized bubble electrodes from flowing into the assembly process, and improving production efficiency.

[0086] Furthermore, this application features low cost and high compatibility. It employs low-cost porous conductive nickel or copper foam with a lithium-plated reference electrode, standardizing electrode dimensions and assembly processes to adapt to mainstream battery manufacturing processes. This results in a simple device structure that eliminates the need for expensive equipment, making it suitable for various separator materials and battery systems. Through the synergistic design of the porous conductive monitoring electrode and the lithium-plated reference electrode, microscopic behavior is transformed into quantifiable signals, overcoming the limitations of traditional detection methods. Simultaneously, it provides clear process control thresholds for production lines, effectively improving battery safety and consistency.

[0087] The following describes the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary test method provided in the embodiments of this application. The lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary test method described below can be implemented using the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary test device described above, and can be referred to in correspondence with the lithium-ion battery negative electrode bubble lithium deposition membrane penetration boundary test device described above.

[0088] Figure 4 This is a flowchart of the lithium-ion battery negative electrode bubble lithium deposition membrane boundary test method disclosed in the embodiments of this application, as follows: Figure 4 As shown, the method may include:

[0089] Step 1: Prepare negative electrode sheets containing bubbles of different preset diameters, with the preset diameter range being 0.1 mm to 2.5 mm.

[0090] Specifically, the preparation of the negative electrode sheet containing bubbles of different preset diameters includes:

[0091] Collect negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm, and cut them with a die cutter to obtain multiple negative electrode bubble sheets.

[0092] Negative electrode sheets with varying bubble diameters, ranging from 0.1 mm to 2.5 mm (e.g., 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm), were collected. These sheets were then cut using a 5.2 × 6.2 cm² die-cutting tool to create negative electrode sheets containing bubbles of different sizes. During the cutting process, it was crucial to ensure that the bubbles were centered within the negative electrode sheet. This step is fundamental to the entire experiment; the different sizes of centrally located bubbles simulate potential defects that may occur during battery manufacturing, providing diverse and precise experimental samples for subsequent research on lithium plating penetration phenomena.

[0093] Step 2: Using the negative electrode sheets with bubbles of different preset diameters, assemble the test battery according to the aforementioned device, and perform lithium plating on the reference electrode included therein.

[0094] Specifically, using the negative electrode sheets with different preset diameter bubbles prepared in step one, the test battery is assembled according to the structure of the aforementioned device. The assembly method follows standard procedures and will not be elaborated further. After assembly, lithium plating is performed on the reference electrode included in the battery. The lithium plating process of the reference electrode is extremely critical, as it provides a stable and accurate lithium metal reference for the device. This process specifically includes the following two stages:

[0095] Forward charging stage: First, the positive electrode of the lithium plating equipment is connected to the reference electrode, and the reference electrode is forward-charged for up to 4 hours with a constant current of 20 μA. During this process, the current drives lithium ions to move towards the reference electrode and begin deposition. This stage is the initial step of lithium plating, laying the foundation for the subsequent uniform distribution of lithium metal. The continuous charging time of 4 hours ensures that a sufficient amount of lithium ions react and deposit on the surface of the reference electrode, initially building up a lithium metal layer.

[0096] Reverse charging phase: After forward charging is completed, the electrode polarity of the lithium plating equipment is switched, connecting the positive electrode to the negative electrode while the negative electrode remains connected to the reference electrode. The reference electrode is then reverse-charged again for 4 hours with a constant current of 20 μA. The reverse current promotes the redistribution of the deposited lithium metal on the reference electrode surface, reducing uneven lithium metal distribution or polarization that may occur during forward charging. After reverse charging, the lithium metal deposition on the reference electrode surface is more uniform, significantly improving the stability and accuracy of the reference electrode as a lithium metal reference standard.

[0097] Step 3: Perform charge and discharge cycles on the assembled test battery. The charge and discharge conditions are as follows: charge at a constant current and constant voltage at the first preset charging rate to 3.65V, discharge at the second preset discharging rate to 2.5V, and cycle at a temperature of 25℃. The range of the first preset charging rate is 0.2C-1C, and the range of the second preset discharging rate is 0.2C-2C.

[0098] Specifically, the assembled test battery with lithium-plated reference electrodes was subjected to cyclic testing under specific charge-discharge conditions. The charge-discharge conditions were set as follows: constant current and constant voltage charging at a first preset charge rate to 3.65V, followed by discharging at a second preset discharge rate to 2.5V. The temperature was maintained at 25℃ throughout the cycle. The first preset charge rate ranged from 0.2C to 1C, and the second preset discharge rate ranged from 0.2C to 2C. These charge-discharge conditions simulated the operating conditions of a real battery. Through continuous cycling, lithium plating was induced in the negative electrode bubble region, providing the necessary experimental environment for studying the lithium plating penetration boundary.

[0099] Step 4: Monitor the potential difference between the monitoring electrode and the reference electrode in real time.

[0100] Specifically, during the charge-discharge cycle of the test battery, the potential difference between the monitoring electrode and the reference electrode is monitored in real time. By continuously collecting this crucial data using a voltage monitoring device and tracking the changes in potential difference in real time, the progress of lithium plating inside the battery can be intuitively reflected, providing important data support for subsequent determination of whether lithium plating has penetrated the separator.

[0101] Step 5: Determine whether to puncture the diaphragm based on the potential difference:

[0102] If the potential difference decreases, it is determined that the lithium plating of the bubble with the corresponding preset diameter has penetrated the membrane;

[0103] If the potential difference does not change, it is determined that the bubble of the corresponding preset diameter has not penetrated the membrane.

[0104] Specifically, the lithium plating boundary is determined based on the monitored potential difference. If the potential difference continuously decreases from its initial value until it reaches 0V, then the lithium plating of the corresponding bubble size is considered to have penetrated the membrane; if the potential difference remains unchanged, then the lithium plating of the corresponding bubble size is considered not to have penetrated the membrane. Specifically, when the porous conductive material is nickel foam, the initial potential difference is 2.796V; for copper foam, the initial potential difference is 3.382V. The initial potential difference can be adjusted according to the material of the monitoring electrode to ensure detection accuracy. It should also be noted that no change in potential difference here includes no significant change, including millivolt-level drift or occasional spikes, which are not considered a decrease in potential difference.

[0105] Furthermore, this application can also determine the critical diameter at which lithium deposition bubbles in the negative electrode of a lithium-ion battery do not penetrate the separator.

[0106] This application also includes:

[0107] Step 6: Determine the boundary of the bubble's diameter based on the potential difference:

[0108] If the potential difference corresponding to the preset diameter bubble does not change, the preset diameter is determined to be within the safe range;

[0109] If the potential difference corresponding to a bubble with a preset diameter decreases as time or the number of cycles increases, the preset diameter is determined to be the target diameter.

[0110] The smallest of the multiple target diameters is determined as the diameter boundary of the bubble.

[0111] Specifically, if the potential difference between the monitoring electrode and the reference electrode remains unchanged throughout the entire charge-discharge cycle for a bubble of a predetermined diameter, this indicates that lithium plating in the bubble region does not pose a threat of penetration into the separator at this diameter, and this diameter is determined to be within the safe range. If the potential difference gradually decreases over time or with increasing cycle count, it means that lithium plating has affected the separator, and this predetermined diameter is the target diameter. Finally, by comparing multiple target diameters, the smallest value is selected as the bubble diameter boundary. This boundary value clarifies the maximum bubble diameter that can ensure the separator is not penetrated by lithium plating under the current test conditions.

[0112] In the lithium-ion battery negative electrode bubble lithium plating penetration boundary test system, potential detection is a key judgment method, and different detection combinations correspond to different dimensions for judging lithium plating behavior. First, by detecting the potential between the negative electrode and the reference electrode, it is possible to effectively determine whether lithium plating has occurred at the negative electrode bubble location. When lithium plating occurs in the negative electrode bubble region, the deposition of lithium metal will significantly change the local electrochemical environment, thereby causing abnormal fluctuations in the potential between the negative electrode and the reference electrode. Based on this potential change, the initial signal of lithium plating can be captured in time. Second, detecting the potential difference between the reference electrode and the monitoring electrode is an important basis for judging whether lithium dendrites grow from the negative electrode surface and penetrate the separator. Once lithium dendrites penetrate the separator and reach the monitoring electrode, their lithium intercalation process on the monitoring electrode will cause changes in the ion concentration and charge distribution in that region, resulting in a significant change in the potential difference between the reference electrode and the monitoring electrode. By monitoring this potential difference change in real time, the penetration behavior of lithium dendrites can be accurately confirmed. The testing apparatus and method described in this application can accurately track different stages of lithium plating, including the initial stage and the lithium plating puncture of the diaphragm, providing a precise and reliable detection method for lithium plating analysis.

[0113] Furthermore, during the charge-discharge cycle, this application can also record the change curve of the potential difference over time or the number of cycles using the voltage monitoring device, and determine the critical number of cycles for lithium plating to penetrate the film by combining the inflection point of the curve.

[0114] Specifically, after battery assembly and lithium plating of the reference electrode are completed, the battery enters the charge-discharge cycle stage. During this process, the voltage monitoring device, in addition to real-time monitoring of the potential difference, also plays a crucial role in recording the potential difference curve over time or the number of cycles. As the charge-discharge cycle continues, the lithium dendrite growth state changes continuously, and its impact on the potential difference between the monitoring electrode and the reference electrode gradually becomes apparent. When lithium dendrites begin to penetrate the separator, a clear inflection point appears on the potential difference curve. By carefully analyzing these inflection points, the critical number of cycles for lithium plating through the separator can be accurately determined. For example, when charging and discharging a test battery with a specific bubble size, the voltage monitoring device records the potential difference curve over the number of cycles. The curve shows that at the 115th cycle, the slope of the potential difference curve changes significantly, exhibiting a clear inflection point. The number of cycles corresponding to this inflection point is the critical number of cycles for lithium plating through the separator at that bubble size. By conducting similar analyses of batteries with different bubble sizes, we can comprehensively understand the critical cycle number for lithium plating and penetration corresponding to different bubble sizes. This provides more detailed data support for in-depth research on the lithium plating and penetration phenomenon of lithium-ion battery anodes, and helps to more accurately assess battery safety and optimize battery manufacturing processes.

[0115] Figure 5 This demonstrates the voltage changes between the monitoring electrode and the reference electrode during cycling of batteries with different bubble sizes. The figure shows that:

[0116] When the bubble diameter in the negative electrode is 0.5mm, 1mm, or 1.5mm, the voltage difference between the porous metal material (monitoring electrode) and the reference electrode remains basically unchanged throughout the entire battery cycle. Therefore, it can be determined that the bubbles of the corresponding size did not cause lithium plating to puncture the separator, and these bubble sizes are relatively safe under this detection system.

[0117] Perforated separator: When the bubble diameter is 2mm and 2.5mm, the voltage difference changes significantly during cycling and eventually drops to 0V. This indicates that lithium plating has perforated the separator. Such bubble size does not meet the production allowable range and should be avoided as much as possible in battery production to ensure the safety and stability of the battery.

[0118] As can be seen from the above technical solutions, the lithium dendrite penetration test device and method for lithium-ion battery negative electrode provided in this application uses porous conductive foamed nickel or foamed copper as monitoring electrodes to provide growth space for lithium dendrites after penetrating the separator. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in potential difference between the electrode and the reference electrode, it is possible to directly determine whether lithium dendrites have pierced the separator, thereby significantly shortening the detection cycle.

[0119] To accurately determine the safety boundary of bubble size, negative electrode bubble sheets with different preset diameters are prepared, and a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size, in combination with charge-discharge cycle tests. This clarifies the critical value of whether lithium-deposited bubbles of different sizes penetrate the separator, providing a basis for the control of production line process parameters.

[0120] In terms of optimizing production processes and preventing safety hazards, the negative electrode slurry coating process is verified before battery production to clarify the allowable bubble size range. This guides the production line to adjust relevant parameters to eliminate large-sized bubbles, enabling rapid screening of high-risk bubble sizes and preventing large-sized bubble electrodes from flowing into the assembly process.

[0121] Furthermore, this application features low cost and high compatibility. It employs low-cost porous conductive nickel or copper foam with a lithium-plated reference electrode, standardizing electrode dimensions and assembly processes to adapt to mainstream battery manufacturing processes. This results in a simple device structure that eliminates the need for expensive equipment, making it suitable for various separator materials and battery systems. Through the synergistic design of the porous conductive monitoring electrode and the lithium-plated reference electrode, microscopic behavior is transformed into quantifiable signals, overcoming the limitations of traditional detection methods. Simultaneously, it provides clear process control thresholds for production lines, effectively improving battery safety and consistency.

[0122] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0123] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0124] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A testing device for lithium-ion battery negative electrode bubble lithium deposition membrane boundary, characterized in that, It includes a positive electrode, a negative electrode containing bubbles of a predetermined diameter, a multilayer diaphragm, a monitoring electrode, a reference electrode, and a voltage monitoring device; The diameter of the bubbles in the negative electrode sheet ranges from 0.1 mm to 2.5 mm; The multilayer diaphragm includes a first diaphragm layer, a second diaphragm layer, and a third diaphragm layer; The monitoring electrode is made of a porous conductive material, which is either nickel foam or copper foam with a porosity of 30% to 50%. The reference electrode is located at the corresponding position at the center of the bubble; The device includes the negative electrode, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer, and the positive electrode, which are stacked sequentially. The monitoring electrode is connected to the voltage monitoring device via a tab, and the reference electrode is lithium-plated to form a lithium metal reference standard. The voltage monitoring device is used to monitor the potential difference between the monitoring electrode and the reference electrode in real time.

2. The apparatus according to claim 1, characterized in that, include: The bubble is located in the central region of the negative electrode sheet; The monitoring electrode is positioned to correspond to the center of the bubble in the negative electrode sheet; One end of the reference electrode is plated with lithium, and the lithium-plated end is vertically aligned with the center of the bubble. The positive electrode is positioned to correspond to the central region of the negative electrode.

3. The apparatus according to claim 1, characterized in that, The tabs of the monitoring electrode are fixed to a reserved area of ​​nickel foam or copper foam by a rolling process to form an electrical connection.

4. The apparatus according to claim 3, characterized in that, The porosity of the porous conductive material is equal to the porosity of the multilayer membrane.

5. The apparatus according to claim 1, characterized in that, One end of the reference electrode is plated with lithium, and the thickness of the lithium-plated reference electrode is the same as that of the foamed nickel or foamed copper.

6. A method for testing the boundary of lithium deposition through the film in the negative electrode of a lithium-ion battery, characterized in that, include: Step 1: Prepare negative electrode sheets containing bubbles of different preset diameters, with the preset diameter range being 0.1 mm to 2.5 mm; Step 2: Using the negative electrode sheets with bubbles of different preset diameters, assemble a test battery according to the device described in any one of claims 1-5, and perform lithium plating on the reference electrode included therein. Step 3: Perform charge and discharge cycles on the assembled test battery. The charge and discharge conditions are as follows: charge to 3.65V at a constant current and constant voltage at the first preset charging rate, discharge to 2.5V at the second preset discharging rate, and cycle at a temperature of 25℃. The range of the first preset charging rate is 0.2C-1C, and the range of the second preset discharging rate is 0.2C-2C. Step 4: Monitor the potential difference between the monitoring electrode and the reference electrode in real time; Step 5: Determine whether to puncture the diaphragm based on the potential difference: If the potential difference decreases, it is determined that the lithium plating of the bubble with the corresponding preset diameter has penetrated the membrane; If the potential difference does not change, it is determined that the bubble of the corresponding preset diameter has not penetrated the membrane.

7. The method according to claim 6, characterized in that, Also includes: Step 6: Determine the boundary of the bubble's diameter based on the potential difference: If the potential difference corresponding to the preset diameter bubble does not change, the preset diameter is determined to be within the safe range; If the potential difference corresponding to a bubble with a preset diameter decreases as time or the number of cycles increases, the preset diameter is determined to be the target diameter. The smallest of the multiple target diameters is determined as the diameter boundary of the bubble.

8. The method according to claim 6, characterized in that, During the charge-discharge cycle, the voltage monitoring device records the curve of the potential difference changing with time or the number of cycles, and the critical number of cycles for lithium plating to penetrate the film is determined by combining the inflection point of the curve.

9. The method according to claim 6, characterized in that, If the porous conductive material is nickel foam, the initial value of the corresponding potential difference is 2.796V; If the porous conductive material is copper foam, the initial value of the corresponding potential difference is 3.382V.

10. The method according to claim 6, characterized in that, The preparation of the negative electrode sheet containing bubbles of different preset diameters includes: Collect negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm, and cut them into negative electrode bubble sheets of different sizes using a die cutter.

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