Device and method for testing bubble lithium separation and membrane penetration boundary of negative electrode of lithium ion battery

Abstract

According to the lithium ion battery negative electrode bubble lithium precipitation membrane penetrating boundary testing device and method, porous conductive foamed nickel / copper is used as a monitoring electrode, the high porosity and conductivity of the porous conductive foamed nickel / copper provide a growth channel after lithium dendrites penetrate through a diaphragm, a reference electrode is plated with lithium to form a stable lithium metal reference potential, and therefore the change of the potential difference between the two is monitored; the lithium precipitation penetration behavior is monitored online in real time, whether the lithium dendrites pierce the diaphragm or not can be directly judged, and the detection period is greatly shortened. By preparing negative bubble pole pieces with different preset diameters and combining a charge-discharge cycle test, the safety boundary of the bubble size is accurately judged according to the corresponding relation between a voltage difference inflection point and the bubble size, and a key basis is provided for production line process parameter management and control. The method can guide a production line to adjust parameters before battery production, and eliminates the hidden danger of large-size bubbles. The device is made of low-cost materials, the process is standardized, the device has the advantages of low cost and high compatibility, and the safety and consistency of the battery are effectively improved.

Description

Technical Field

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

[0002] Lithium-ion battery negative electrode slurry is mainly composed of negative electrode active material, conductive agent, solvent, thickener, binder and deionized water. Its preparation process is mainly 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 glue solution, and then the conductive agent, negative electrode active material and binder are added in sequence and stirred to finally form a uniform negative electrode slurry. The wet mixing process adopts a premixing strategy. The conductive agent, negative electrode active material and thickener are premixed first, and then deionized water is added step by step for kneading and stirring. After forming a premixed slurry, the binder is added to complete the preparation of the final slurry.

[0003] However, during high-speed stirring, a large number of bubbles are easily introduced into the slurry. After these bubbles are applied to the surface of the copper foil substrate, they occupy the effective slurry volume, resulting in uneven coating. In the subsequent extrusion, rolling, and drying processes, the bubbles burst to form local defects, which reduces the surface density of the negative electrode. During charging, the lithium ions released from the positive electrode cannot be fully embedded due to insufficient negative electrode capacity in the bubble area, causing lithium precipitation. In severe cases, lithium dendrites penetrate the diaphragm, causing abnormal battery self-discharge and even short circuit risks.

[0004] Currently, the industry generally uses vacuum or ultrasonic vibration technology to eliminate bubbles, but there are still significant limitations. The vacuum method is limited by the viscosity of the slurry and the vacuum time (too long can easily lead to slurry deterioration). Small bubbles cannot completely overflow the surface, and ultimately form dark spots and exposed foil defects on the electrode. The ultrasonic method has high equipment costs and complex operation, and its effect on removing micron-level bubbles is limited, making it difficult to achieve efficient industrial application. In addition, whether dendrites will penetrate the diaphragm after lithium is deposited from bubbles of different sizes and cause battery self-discharge requires long-term self-discharge testing to confirm. As the battery capacity gradually increases, the detection time is further extended. There is currently no effective and rapid online method to confirm that lithium deposition has penetrated the diaphragm.

[0005] Based on this, a lithium-ion battery negative electrode bubble lithium deposition membrane boundary testing solution is needed to fill the technical gap of being unable to quickly determine online whether the bubble has penetrated the diaphragm after lithium deposition, which makes it difficult for the production line to accurately control the bubble specifications, and avoid problems such as abnormal pressure difference caused by large-sized bubbles flowing into the battery. Summary of the Invention

[0006] The present application aims to solve at least one of the above-mentioned technical defects. In view of this, the present application provides a device and method for testing the boundary of lithium-ion battery negative electrode bubble lithium deposition through the membrane. Through the collaborative design of a porous conductive monitoring electrode and a pre-lithium-plated reference electrode, the microscopic behavior is converted into a quantifiable signal, breaking through the limitations of traditional detection. At the same time, it provides a clear process control threshold for the production line, thereby improving battery safety and consistency.

[0007] A lithium-ion battery negative electrode bubble lithium deposition membrane boundary test device, characterized by comprising a positive electrode plate, a negative electrode plate containing bubbles of a preset diameter, a multi-layer diaphragm, 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 multi-layer 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, and the porous conductive material is nickel foam or copper foam with a porosity of 30% to 50%;

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

[0012] The device comprises the negative electrode sheet, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer and the positive electrode sheet stacked in sequence;

[0013] The monitoring electrode and the reference electrode are connected to the voltage monitoring device through tabs, and the reference electrode is plated with lithium 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 bubbles are located in the central area of ​​the negative electrode sheet;

[0017] The monitoring electrode is placed at a position corresponding to the center of the bubble of the negative electrode;

[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 placement position of the positive electrode plate corresponds to the central area of ​​the negative electrode plate.

[0020] Optionally, the tabs of the monitoring electrode and the reference electrode are fixed to a reserved area of ​​the 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 nickel foam or copper foam.

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

[0024] Step 1: preparing a negative electrode sheet containing bubbles of different preset diameters, wherein the preset diameter ranges from 0.1 mm to 2.5 mm;

[0025] Step 2: using the negative electrode sheets with bubbles of different preset diameters, assembling a test battery according to the device of any one of claims 1 to 5, and performing 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: charging at a first preset charge rate with constant current and constant voltage to 3.65V, and discharging at a second preset discharge rate to 2.5V. The cycle temperature is 25°C. The first preset charge rate range is 0.2C-1C, and the second preset discharge rate range is 0.2C-2C.

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

[0028] Step 5: Determine whether the diaphragm is punctured based on the potential difference:

[0029] If the potential difference becomes smaller, it is determined that the lithium deposition of the bubble corresponding to the preset diameter has penetrated the diaphragm;

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

[0031] Optionally, also include:

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

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

[0034] If the potential difference corresponding to the bubble of the preset diameter decreases with the increase of time or the number of cycles, 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 and discharge cycle, the voltage monitoring device records a curve showing a change in the potential difference over time or the number of cycles, and the critical number of cycles for lithium deposition through the membrane is determined in combination with the inflection point of the curve.

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

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

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

[0040] Negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm were collected and cut using a die cutter to obtain negative electrode bubble sheets of different sizes.

[0041] It can be seen from the above technical solution that the embodiment of the present application provides a device and method for testing the boundary of lithium-ion battery negative electrode bubble lithium deposition through the membrane. In monitoring the lithium deposition penetration behavior, porous conductive foam nickel or foam copper is used as a monitoring electrode to provide growth space for lithium dendrites after penetrating the diaphragm. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in the potential difference between the electrode and the reference electrode, it can be directly determined whether the lithium dendrites have pierced the diaphragm, thereby greatly shortening the detection cycle.

[0042] In order to accurately determine the safety boundary of bubble size, negative electrode bubble pole pieces with different preset diameters are prepared, and combined with charge and discharge cycle tests, a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size. In this way, the critical value of whether bubbles of different sizes penetrate the diaphragm after lithium precipitation is clarified, providing a basis for the control of production line process parameters.

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

[0044] In addition, this application features low cost and high compatibility. It uses low-cost porous conductive nickel foam or copper foam and lithium-plated reference electrodes, standardizes electrode size and assembly processes to adapt to mainstream battery production processes, and makes the device structure simple and eliminates the need for expensive equipment. It is suitable for a variety of diaphragm materials and battery systems. Through the coordinated design of porous conductive monitoring electrodes and lithium-plated reference electrodes, microscopic behavior is converted into quantifiable signals, breaking through the limitations of traditional detection. At the same time, it provides clear process control thresholds for production lines, effectively improving battery safety and consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0046] Figure 1 A schematic diagram of the structure of a lithium-ion battery negative electrode bubble lithium deposition membrane boundary test device provided in an embodiment of the present application;

[0047] Figure 2 Schematic diagram of another lithium-ion battery negative electrode bubble lithium penetration boundary test device disclosed in the embodiment of the present application

[0048] Figure 3 A microscopic view showing the microporous structure of nickel foam provided in the examples of the present application;

[0049] Figure 4 This is a flow chart of a method for testing the boundary of lithium-ion battery negative electrode bubble deposition through the membrane according to an embodiment of the present application;

[0050] Figure 5 This is a curve diagram of the voltage change between the monitoring electrode and the reference electrode during the cycling process of batteries with different bubble sizes according to an embodiment of the present application. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0052] The inventors have found that during lithium deposition detection, the white base of the diaphragm is difficult to distinguish from the grayish white color of the deposited lithium in terms of color difference. Moreover, after the lithium dendrites reach the surface of the positive electrode, the positive electrode potential is higher than the lithium deposition potential, and the lithium dendrites cannot continue to grow. It is difficult to observe and define the boundaries of lithium deposition dendrites of different sizes passing through the diaphragm and the distribution of lithium deposition after passing through the diaphragm, making it difficult to control the size of bubbles on the electrode during production and use.

[0053] Based on this, this application is proposed. The application scheme is introduced below. Please see below for details.

[0054] First, the lithium-ion battery negative electrode bubble lithium deposition membrane boundary test device provided in the embodiment of the present application is described. Figure 1 and Figure 2 , Figure 1This is a schematic diagram of the structure of the lithium-ion battery negative electrode bubble lithium membrane boundary test device disclosed in the embodiment of the present application. Figure 2 This is a structural schematic diagram of another lithium-ion battery negative electrode bubble lithium deposition membrane boundary testing device disclosed in an embodiment of the present application.

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

[0056] A positive electrode sheet, a negative electrode sheet containing bubbles of a preset diameter, a multi-layer diaphragm, a monitoring electrode, a reference electrode and a 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 multi-layer 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, and the porous conductive material is nickel foam or copper foam with a porosity of 30% to 50%;

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

[0061] The device comprises the negative electrode sheet, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer and the positive electrode sheet stacked in sequence;

[0062] The monitoring electrode and the reference electrode are connected to a voltage detection device through tabs, and the reference electrode is plated with lithium 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 placement position of the monitoring electrode corresponds to the center of the bubble of 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 placement position of the positive electrode sheet corresponds to the central area of ​​the negative electrode sheet.

[0065] Furthermore, the tabs of the monitoring electrode and the reference electrode are fixed to the reserved area of ​​the 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 separator.

[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 nickel foam or copper foam.

[0068] Specifically, the positive electrode sheet: As a key electrode component in the entire device, the positive electrode sheet plays a crucial role in the redox reaction during the battery's charge and discharge processes. Its dimensions are typically 5.0 × 6.0 cm². This specific size is carefully designed to work in conjunction with other components to ensure the efficient electrochemical reactions within the battery. It participates in the battery's overall electrochemical process, providing a stable potential environment for the device and, together with the negative electrode sheet, forming the battery's core electrochemical reaction system.

[0069] Negative electrode sheet containing bubbles of preset diameter: The negative electrode sheet is one of the core objects of research of this device, and its uniqueness lies in that it contains bubbles of preset diameter. The bubble diameter range is precisely controlled between 0.1mm and 2.5mm, and must be located as close as possible to the center area of ​​the negative electrode sheet. The existence of these bubbles simulates the defects that may occur in actual production, which is of vital importance for studying the phenomenon of lithium deposition and membrane penetration of bubbles in the negative electrode of lithium-ion batteries. Bubbles of different diameters will have different effects on the lithium deposition process. By setting such diverse bubble sizes, the boundary conditions and laws of bubble lithium deposition can be fully and deeply explored. Through the solution of this application, the effect of micron-sized bubbles on lithium deposition can be explored, providing a practical and effective detection method for lithium deposition detection.

[0070] Multilayer diaphragm: The multilayer diaphragm consists of a first, second, and third diaphragm layer. Its primary function is to isolate the positive and negative electrodes, as well as the subsequent monitoring and reference electrodes, to prevent internal short circuits in the battery while allowing lithium ions to pass through, maintaining normal electrochemical reactions. The diaphragm can be made of either PP (12µm thick) or PE (7+3+3+3) and is cut to a size of 5.5 x 6.5 cm². This appropriate material and size ensures that the diaphragm effectively isolates the battery while remaining stable in the complex electrochemical environment within the battery, guaranteeing battery safety and stability.

[0071] Monitoring electrode: The monitoring electrode is made of a special porous conductive material, specifically nickel foam or copper foam with a porosity of 30% to 50%, and its porosity is consistent with the porosity of the multi-layer diaphragm in the device. It should be noted that the monitoring electrode needs to undergo a roller pressing process to improve the porosity uniformity and reduce the porosity so that it matches the isolation porosity. For example, the porosity of the nickel foam used in the monitoring electrode is usually 70-95% before rolling, and the pore size is in the range of 50-200μm. After roller compression, its porosity can be precisely controlled at 30-50%, matching the porosity of the diaphragm. At the same time, 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 nickel foam after rolling can be compressed to about 100μm, which is close to the thickness of the conventional lithium-plated reference electrode, which can avoid the local polarization being too strong due to excessive thickness and affecting the lithium ion deintercalation efficiency. In terms of thickness parameters, the thickness of nickel foam before rolling is between 167-1400μm. During the compression process, the pore-strut bending and contact with the pore wall significantly reduce the pore diameter. At the same time, the specific surface area of ​​the material increases significantly, and a larger specific surface area is in contact with the lithium dendrites, which can improve the detection sensitivity. After compression, the porosity is maintained similar to that of the separator, which can not only provide a smooth path for lithium ion migration and avoid hindering the growth of lithium dendrites, but also provide space for the growth of lithium dendrites (about 300nm in size) with its three-dimensional porous structure. When the lithium dendrites grow inside the nickel foam, they form close electrical contact with the porous conductive network of the nickel foam itself, making it easier to capture the boundary signal of lithium plating through the membrane in real time by monitoring the change in the potential difference between the electrode and the reference electrode. In addition, through rolling, the connection between the monitoring electrode and the tab can be achieved at the same time, which improves the preparation efficiency while ensuring the reliability of the connection.

[0072] In the entire test device, the monitoring electrode is located behind the negative electrode, the first diaphragm layer, and before the second diaphragm layer, and is connected to the external circuit through the tab. It cooperates with the reference electrode located at the corresponding position in the center of the bubble, which is lithium-plated to form a lithium metal reference standard. The voltage monitoring device monitors the potential difference between the two in real time to ensure detection accuracy. When lithium is deposited in bubbles with a diameter of 0.1mm to 2.5mm in the central area of ​​the negative electrode, and lithium penetrates the first diaphragm layer, lithium dendrites can grow inside the nickel foam and form electrical contact with the nickel foam. The monitoring electrode can keenly capture the potential changes caused by lithium ion migration, and provide key data support for the determination of the boundary of lithium deposition through the membrane through the mutation of the potential difference signal.

[0073] Figure 3This is a microscopic display of the microporous structure of nickel foam. Nickel foam is a porous conductive metal material and plays a significant role in lithium-ion battery-related testing. Its unique structure plays a key role in detecting whether lithium plating has punctured the diaphragm. Because it has many micropores, when the lithium dendrites produced by lithium plating puncture the diaphragm, they will grow into the micropores of the nickel foam. The lithium dendrites are connected to the porous material of nickel foam, which will change the local electrochemical environment and thus reduce the potential of the porous material. By monitoring this potential change, it can be determined whether the lithium plating has punctured the diaphragm. Copper foam is similar to nickel foam. It is also a porous conductive metal and can also be used in similar lithium plating detection scenarios. It uses the potential change caused by the interaction between its porous structure and lithium dendrites for monitoring.

[0074] Reference electrode: Located between the second diaphragm layer and the third diaphragm layer, it is spaced apart from the monitoring electrode by the second diaphragm layer. This not only ensures the spatial isolation between the two, but also improves the accuracy of detecting the change in the potential difference between the monitoring electrode and the reference electrode. The reference electrode is a specially treated enameled copper wire with an internal copper wire diameter of 22um. One end is soaked in 98% concentrated sulfuric acid to a depth of 1cm for 30 minutes to remove the surface insulation. One end of the treated reference electrode is plated with lithium, and the lithium-plated end is vertically aligned with the center of the bubble, and the thickness of the lithium-plated reference electrode is the same as that of the nickel foam or copper foam. The reference electrode after lithium plating forms a stable lithium metal reference benchmark, providing an accurate potential reference standard for the voltage monitoring device, so that the potential difference change between the monitoring electrode and the reference electrode can be accurately monitored, thereby effectively judging 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. Analysis of changes in the potential difference provides an intuitive understanding of whether lithium dendrites have penetrated the separator and the progress of the lithium deposition process. This data provides important quantitative evidence for studying the boundaries of lithium-ion battery anode bubbles and lithium deposition through the membrane, facilitating in-depth exploration of the electrochemical behavior within the battery, and providing strong support for improving battery performance and preventing safety hazards.

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

[0077] ① Forward charging the reference electrode at a constant current of 20 μA for 4 hours;

[0078] ② After switching the electrode polarity, the reference electrode was reversely charged at a constant current of 20 μA for 4 hours.

[0079] Specifically, the lithium plating process of the reference electrode is extremely critical, providing a stable and accurate lithium metal reference for the device. This process specifically 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 at a constant current of 20μA. During this process, the current drives the lithium ions to move toward the reference electrode and begin to deposit. This stage is the starting step of lithium plating and lays the foundation for the subsequent uniform distribution of lithium metal. The 4-hour charging time ensures that there are sufficient lithium ions to react and deposit on the surface of the reference electrode, initially building a lithium metal layer.

[0081] Reverse charging phase: After the forward charge is completed, the electrode polarity of the lithium plating equipment is switched, and the positive electrode is connected to the negative electrode column, while the negative electrode is still connected to the reference electrode. The reference electrode is reverse charged again at a constant current of 20μA for 4 hours. The reverse current causes the deposited lithium metal to redistribute on the surface of the reference electrode, reducing the uneven distribution or polarization of lithium metal that may be caused by forward charging. After reverse charging, the lithium metal is deposited more evenly on the surface of the reference electrode, greatly 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 forms on one end of the reference electrode. When precisely placed at the center of the bubble, it provides a highly accurate potential reference for the voltage monitoring device, enabling the device to precisely monitor the potential difference between the monitoring electrode and the reference electrode, effectively determining whether lithium dendrites have penetrated the diaphragm.

[0083] It can be seen from the above technical solution that the embodiment of the present application provides a device and method for testing the boundary of lithium-ion battery negative electrode bubble lithium deposition through the membrane. In monitoring the lithium deposition penetration behavior, porous conductive foam nickel or foam copper is used as a monitoring electrode to provide growth space for lithium dendrites after penetrating the diaphragm. While avoiding affecting the growth of lithium dendrites, the contact reliability is improved. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in the potential difference between the electrode and the reference electrode, it can be directly determined whether the lithium dendrites have pierced the diaphragm, thereby greatly shortening the detection cycle.

[0084] In order to accurately determine the safety boundary of bubble size, negative electrode bubble pole pieces with different preset diameters are prepared, and combined with charge and discharge cycle tests, a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size. In this way, the critical value of whether bubbles of different sizes penetrate the diaphragm after lithium precipitation is clarified, providing a basis for the control of production line process parameters.

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

[0086] In addition, this application features low cost and high compatibility. It uses low-cost porous conductive nickel foam or copper foam and lithium-plated reference electrodes, standardizes electrode size and assembly processes to adapt to mainstream battery production processes, and makes the device structure simple and eliminates the need for expensive equipment. It is suitable for a variety of diaphragm materials and battery systems. Through the coordinated design of porous conductive monitoring electrodes and lithium-plated reference electrodes, microscopic behavior is converted into quantifiable signals, breaking through the limitations of traditional detection. At the same time, it provides clear process control thresholds for production lines, effectively improving battery safety and consistency.

[0087] The following describes a method for testing the boundary of lithium-ion battery negative electrode bubble deposition through the membrane provided in an embodiment of the present application. The method for testing the boundary of lithium-ion battery negative electrode bubble deposition through the membrane described below can be implemented using the lithium-ion battery negative electrode bubble deposition through the membrane boundary testing device described above, and can be referenced to each other with the lithium-ion battery negative electrode bubble deposition through the membrane boundary testing device described above.

[0088] Figure 4 Flowchart of the method for testing the boundary of lithium-ion battery negative electrode bubble deposition through the membrane disclosed in the embodiment of the present application, as shown in FIG. Figure 4 As shown, the method may include:

[0089] Step 1: Prepare a negative electrode sheet containing bubbles of different preset diameters, where the preset diameter ranges from 0.1 mm to 2.5 mm.

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

[0091] Negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm are collected and cut using a die cutter to obtain multiple negative electrode bubble sheets.

[0092] Collect negative electrode sheets with different bubble diameters, ranging from 0.1mm to 2.5mm, such as 0.1mm, 0.5mm, 1mm, 1.5mm, 2mm, and 2.5mm. Subsequently, a die cutter with a specification of 5.2×6.2cm² is used to cut these negative electrode sheets to produce negative electrode bubble sheets containing bubbles of different sizes. During the cutting process, it is necessary to ensure that the bubbles are located in the center of the negative electrode sheet as much as possible. This step is the basis of the entire experiment. Bubbles of different sizes and located in the center simulate the defects that may occur in the battery production process, providing diverse and accurate experimental samples for subsequent research on the phenomenon of lithium plating through the membrane.

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

[0094] Specifically, the negative electrode sheets with bubbles of different preset diameters prepared in step 1 are used to assemble the test battery according to the structure of the aforementioned device. The assembly method follows the conventional settings and will not be described in detail. After the assembly is completed, the reference electrode contained in the battery is subjected to lithium plating. The lithium plating process of the reference electrode is extremely critical, as it provides a stable and accurate lithium metal reference benchmark for the device. The 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 at a constant current of 20μA. During this process, the current drives the lithium ions to move toward the reference electrode and begin to deposit. This stage is the starting step of lithium plating and lays the foundation for the subsequent uniform distribution of lithium metal. The 4-hour charging time ensures that there are sufficient lithium ions to react and deposit on the surface of the reference electrode, initially building a lithium metal layer.

[0096] Reverse charging phase: After the forward charge is completed, the electrode polarity of the lithium plating equipment is switched, and the positive electrode is connected to the negative electrode column, while the negative electrode is still connected to the reference electrode. The reference electrode is reverse charged again at a constant current of 20μA for 4 hours. The reverse current causes the deposited lithium metal to redistribute on the surface of the reference electrode, reducing the uneven distribution or polarization of lithium metal that may be caused by forward charging. After reverse charging, the lithium metal is deposited more evenly on the surface of the reference electrode, greatly 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: charging to 3.65V at a first preset charge rate with constant current and constant voltage, discharging to 2.5V at a second preset discharge rate, and a cycle temperature of 25°C. The first preset charge rate range is 0.2C-1C, and the second preset discharge rate range is 0.2C-2C.

[0098] Specifically, the assembled test battery with the reference electrode plated with lithium was placed under specific charge and discharge conditions for cycle testing. The charge and discharge conditions were set as follows: charging to 3.65V at a first preset charge rate with constant current and constant voltage, and then discharging to 2.5V at a second preset discharge rate. The temperature of the entire cycle was maintained at 25°C, where the first preset charge rate ranged from 0.2C to 1C, and the second preset discharge rate ranged from 0.2C to 2C. Such charge and discharge conditions simulate the actual working conditions of the battery. Through continuous cycling, lithium deposition is promoted in the bubble area of ​​the negative electrode, providing the necessary experimental environment for studying the boundary of lithium deposition through the membrane.

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

[0100] Specifically, during the test battery's charge and discharge cycles, the potential difference between the monitoring electrode and the reference electrode is monitored in real time. This critical data is continuously collected by the voltage monitoring device. By tracking the changes in the potential difference in real time, the progress of lithium deposition within the battery can be intuitively reflected, providing important data support for subsequent determination of whether the deposited lithium has penetrated the separator.

[0101] Step 5: Determine whether the diaphragm is punctured based on the potential difference:

[0102] If the potential difference becomes smaller, it is determined that the lithium deposition of the bubble corresponding to the preset diameter has penetrated the diaphragm;

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

[0104] Specifically, the boundary of lithium deposition through the membrane is determined based on the monitored potential difference. If the potential difference continues to decrease from the initial value until it drops to 0V, it is determined that the lithium deposition of the corresponding bubble size has penetrated the membrane; if the potential difference does not change, it is determined that the lithium deposition of the corresponding bubble size has not penetrated the membrane. Among them, when the porous conductive material is nickel foam, the corresponding initial value of the potential difference is 2.796V; if it is copper foam, the corresponding initial value of the potential difference is 3.382V. The initial value of the potential difference can be adjusted according to the different materials of the monitoring electrode to ensure detection accuracy. At the same time, it should be noted that the potential difference here does not change, including no significant changes, including some millivolt drift or occasional glitches, etc., which does not fall into the category of smaller potential difference.

[0105] Furthermore, the present application can also determine the critical diameter of lithium-ion battery negative electrode bubbles that do not penetrate the diaphragm during lithium deposition.

[0106] This application also includes:

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

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

[0109] If the potential difference corresponding to the bubble of the preset diameter decreases with the increase of time or the number of cycles, 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 corresponding monitoring electrode and the reference electrode of a bubble of a preset diameter remains unchanged throughout the entire charge and discharge cycle, this indicates that at this diameter, lithium deposition in the bubble region does not pose a penetration threat to the diaphragm, and the diameter is determined to be within a safe range; if the potential difference gradually decreases over time or as the number of cycles increases, it means that lithium deposition has affected the diaphragm, and this preset 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 that the diaphragm is not penetrated by lithium deposition under the current test conditions.

[0112] In the lithium-ion battery anode bubble penetration boundary testing system, potential detection is a key determination method, and different detection combinations correspond to different dimensions of lithium deposition behavior. First, by measuring the potential between the anode and reference electrodes, it is possible to effectively determine whether lithium deposition is occurring at the anode bubble location. When lithium deposition occurs in the anode bubble region, the deposition of lithium metal significantly changes the local electrochemical environment, causing abnormal fluctuations in the potential between the anode and reference electrodes. Based on this potential change, the initial signal of lithium deposition can be captured in a timely manner. Second, measuring the potential difference between the reference electrode and the monitoring electrode is an important basis for determining whether lithium dendrites have grown from the anode surface and penetrated the separator. Once a lithium dendrite penetrates the separator and reaches the monitoring electrode, its lithium insertion process on the monitoring electrode causes changes in the ion concentration and charge distribution in that area, resulting in a significant change in the potential difference between the reference and monitoring electrodes. By monitoring this potential difference in real time, the penetration of lithium dendrites can be accurately confirmed. Through the testing device and method of the present application, the initial stage of lithium plating and the different stages of lithium plating piercing the diaphragm can be accurately tracked, providing an accurate and reliable detection means for lithium plating analysis.

[0113] In addition, during the charge and discharge cycle, the present application can also record the change curve of the potential difference over time or cycle number through the voltage monitoring device, and determine the critical cycle number of lithium deposition through the membrane in combination with the inflection point of the curve.

[0114] Specifically, after the battery assembly and lithium plating of the reference electrode are completed, the charge and discharge cycle stage begins. During this process, in addition to real-time monitoring of the potential difference, the voltage monitoring device also undertakes the important task of recording the curve of the potential difference changing with time or the number of cycles. As the charge and discharge cycle continues, the growth state of the lithium dendrites continues to change, and its influence on the potential difference between the monitoring electrode and the reference electrode gradually becomes apparent. When the lithium dendrites begin to penetrate the diaphragm, a clear inflection point will appear in the potential difference change curve. By carefully analyzing the inflection points of these curves, the critical number of cycles for lithium plating through the membrane can be accurately determined. For example, when a test battery with a specific bubble size is charged and discharged, the voltage monitoring device records the curve of the potential difference changing with the number of cycles. It is found from the curve that at the 115th cycle, the slope of the potential difference curve changes significantly, and a clear inflection point appears. The number of cycles corresponding to this inflection point is the critical number of cycles for lithium plating through the membrane under this bubble size. Through similar analysis of test batteries with different bubble sizes, we can fully understand the critical cycles of lithium plating and membrane penetration corresponding to different bubble sizes, providing more detailed data support for in-depth research on the phenomenon of lithium plating and membrane penetration caused by bubbles in the negative electrode of lithium-ion batteries, which will help to more accurately evaluate battery safety and optimize battery production processes.

[0115] Figure 5 The voltage change between the monitoring electrode and the reference electrode during the cycling of batteries with different bubble sizes is shown in the figure.

[0116] The diaphragm is not punctured: When the bubble diameters in the negative electrode are 0.5mm, 1mm, and 1.5mm, the voltage difference between the porous metal material (monitoring electrode) and the reference electrode remains basically unchanged during the entire battery cycle. This indicates that bubbles of the corresponding sizes do not cause lithium deposition and puncture the diaphragm. These bubble sizes are relatively safe under this detection system.

[0117] Diaphragm puncture situation: When the bubble diameter is 2mm and 2.5mm, the voltage difference changes significantly during the cycle and eventually drops to 0V, indicating that lithium plating has punctured the diaphragm. The size of such bubbles does not meet the production allowable range and should be avoided as much as possible in battery production to ensure battery safety and stability.

[0118] It can be seen from the above technical solution that the embodiment of the present application provides a device and method for testing the boundary of lithium-ion battery negative electrode bubble lithium deposition through the membrane. In monitoring the lithium deposition penetration behavior, porous conductive foam nickel or foam copper is used as a monitoring electrode to provide growth space for lithium dendrites after penetrating the diaphragm. The reference electrode is plated with lithium to form a stable lithium metal reference potential. By monitoring the change in the potential difference between the electrode and the reference electrode, it can be directly determined whether the lithium dendrites have pierced the diaphragm, thereby greatly shortening the detection cycle.

[0119] In order to accurately determine the safety boundary of bubble size, negative electrode bubble pole pieces with different preset diameters are prepared, and combined with charge and discharge cycle tests, a judgment standard is established based on the correspondence between the voltage difference inflection point and the bubble size. In this way, the critical value of whether bubbles of different sizes penetrate the diaphragm after lithium precipitation is clarified, providing a basis for the control of production line process parameters.

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

[0121] In addition, this application features low cost and high compatibility. It uses low-cost porous conductive nickel foam or copper foam and lithium-plated reference electrodes, standardizes electrode size and assembly processes to adapt to mainstream battery production processes, and makes the device structure simple and eliminates the need for expensive equipment. It is suitable for a variety of diaphragm materials and battery systems. Through the coordinated design of porous conductive monitoring electrodes and lithium-plated reference electrodes, microscopic behavior is converted into quantifiable signals, breaking through the limitations of traditional detection. At the same time, 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, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

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

[0124] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium-ion battery negative electrode bubble lithium deposition membrane boundary testing device, characterized in that: It includes a positive electrode sheet, a negative electrode sheet containing bubbles of a preset diameter, a multi-layer 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 multi-layer 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, and the porous conductive material is nickel foam or copper foam with a porosity of 30% to 50%; The reference electrode is located at a position corresponding to the center of the bubble; The device comprises the negative electrode sheet, the first diaphragm layer, the monitoring electrode, the second diaphragm layer, the reference electrode, the third diaphragm layer and the positive electrode sheet stacked in sequence; The monitoring electrode is connected to the voltage monitoring device via a tab, and the reference electrode is plated with lithium 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 device according to claim 1, characterized in that include: The bubbles are located in the central area of ​​the negative electrode sheet; The monitoring electrode is placed at a position corresponding to the center of the bubble of the negative electrode; 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 placement position of the positive electrode plate corresponds to the central area of ​​the negative electrode plate.

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

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

5. The device 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-ion battery negative electrode bubble lithium deposition through the membrane, characterized in that: include: Step 1: preparing a negative electrode sheet containing bubbles of different preset diameters, wherein the preset diameter ranges from 0.1 mm to 2.5 mm; Step 2: using the negative electrode sheets with bubbles of different preset diameters, assembling a test battery according to the device of any one of claims 1 to 5, and performing 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: charging at a first preset charge rate with constant current and constant voltage to 3.65V, and discharging at a second preset discharge rate to 2.5V. The cycle temperature is 25°C. The first preset charge rate range is 0.2C-1C, and the second preset discharge rate range is 0.2C-2C. Step 4: monitoring the potential difference between the monitoring electrode and the reference electrode in real time; Step 5: Determine whether the diaphragm is punctured based on the potential difference: If the potential difference becomes smaller, it is determined that the lithium deposition of the bubble corresponding to the preset diameter has penetrated the diaphragm; If the potential difference does not change, it is determined that the bubble of the corresponding preset diameter has not penetrated the diaphragm.

7. The method according to claim 6, characterized in that Also includes: Step 6: Determine the diameter boundary of the bubble based on the potential difference: If the potential difference corresponding to the bubble of the preset diameter does not change, it is determined that the preset diameter is within the safe range; If the potential difference corresponding to the bubble of the preset diameter decreases with the increase of time or the number of cycles, 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 and discharge cycle, the voltage monitoring device records the curve of the potential difference changing with time or the number of cycles, and the critical cycle number for lithium deposition through the membrane is determined in combination with 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 corresponding initial value of the potential difference is 2.796V; If the porous conductive material is foamed copper, the corresponding initial value of the potential difference is 3.382V.

10. The method according to claim 6, characterized in that The method of preparing a negative electrode sheet containing bubbles of different preset diameters comprises: Negative electrode sheets with bubble diameters ranging from 0.1 mm to 2.5 mm were collected and cut using a die cutter to obtain negative electrode bubble sheets of different sizes.

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