A method for detecting the limiting diffusion current density of lithium-ion batteries during fast charging

Abstract

This application discloses a method for detecting the limiting diffusion current density of a lithium-ion battery during fast charging. The method includes: obtaining the negative electrode system and electrolyte system in a testing device based on the lithium-ion battery system to be tested; sequentially stacking a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode in the first electrolyte of the testing device to form a battery circuit; the second electrode includes: a first current collector with a groove on one side, and two reference electrodes disposed in the groove; a negative electrode active material layer disposed on at least one side of the first current collector; and an insulating encapsulation film disposed between the negative electrode active material layer and the first current collector; operating the testing device and charging the battery circuit with a first preset current in i cycles and a second preset current in i+1 cycles; detecting the potential difference between the first reference electrode and the second reference electrode, determining the maximum potential difference, and taking the charging current density at the first occurrence of the maximum potential difference as the limiting diffusion current density.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a method for detecting the fast-charging limit diffusion current density of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, energy storage systems, consumer electronics, military equipment, and industrial equipment. With the development of lithium-ion battery technology, fast-charging performance has become a crucial research and engineering focus. However, under fast-charging conditions, lithium-ion batteries are prone to lithium plating, ohmic polarization, concentration polarization, and excessive heat generation. These problems not only limit their fast-charging performance but also pose safety hazards. Therefore, the key to improving fast-charging performance lies in accurately monitoring the extreme operating conditions during battery charging and making scientific optimizations in electrode structure and parameter design. The limiting diffusion current density under liquid-phase diffusion confinement can enable accurate assessment of the extreme operating conditions during battery charging.

[0003] In related research and engineering practice, methods such as rate performance testing and cyclic voltammetry are commonly used to test electrode diffusion performance. However, these methods have certain limitations, such as difficulty in distinguishing between solid-phase and liquid-phase diffusion contributions, cumbersome data processing, and large errors. Furthermore, they cannot achieve dynamic monitoring during the charging and discharging process, making it difficult to meet the need for real-time assessment of the limiting diffusion current density under fast charging conditions. Therefore, how to accurately detect the limiting diffusion current density of lithium-ion batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application aims to provide a method, apparatus, electronic device, and storage medium for detecting the limiting diffusion current density of lithium-ion batteries under fast charging conditions, thereby solving the technical problems of inaccurate detection results and complex operation of limiting diffusion current density under fast charging conditions in related technologies.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows:

[0006] In a first aspect, embodiments of this application propose a method for detecting the fast-charging limiting diffusion current density of a lithium-ion battery, comprising: obtaining a negative electrode system and an electrolyte system in a testing device based on the lithium-ion battery system to be tested, wherein the negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte; sequentially stacking a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode in the first electrolyte of the testing device to form a battery circuit; wherein the second electrode includes: a first current collector, which is formed by providing a groove on one side of the initial current collector connected to the electrode tab, and a second reference electrode disposed in the groove; the negative electrode... An active material layer is disposed on at least one side of the first current collector; an insulating encapsulation film is disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector; the detection device is run and the battery circuit is charged with a first preset current in i cycles and with a second preset current in i+1 cycles, wherein the second preset current is greater than the first preset current, i is a positive integer and i is greater than 1; the potential difference between the first reference electrode and the second reference electrode is detected, the maximum potential difference is determined during the multi-cycle charging phase of the battery circuit, and the charging current density at the first occurrence of the maximum potential difference is taken as the limiting diffusion current density of the lithium-ion battery under test.

[0007] In some embodiments, the insulating encapsulation film includes one or more of the following: lithium-ion battery separator material, single-ion conductor polymer, and composite material of single-ion conductor polymer and inorganic filler.

[0008] In some embodiments, the single-ion conductor polymer includes one or more of polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0009] In some embodiments, the insulating encapsulation film further includes an adhesive, which includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0010] In some embodiments, the inorganic filler includes one or more of alumina, cubic lithium lanthanum zirconium oxide, and lithium aluminum titanium phosphate.

[0011] In some embodiments, the material of the first reference electrode includes elemental lithium, Li4Ti4O3, etc. 12 One or more of LiFePO4.

[0012] In some embodiments, the material of the second reference electrode includes elemental lithium, Li4Ti4O4, etc. 12 One or more of LiFePO4.

[0013] In some embodiments, the first electrode includes one or more of elemental lithium, lithium alloy, and positive electrode containing positive active material;

[0014] In some embodiments, the first and second separators respectively comprise one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

[0015] In some embodiments, operating a detection device and charging with a first preset current in cycle i and with a second preset current in cycle i+1, wherein the second preset current is greater than the first preset current, includes: operating the detection device to achieve battery circuit formation; controlling the current of the battery circuit to charge with the first preset current during the charging phase of cycle i; and controlling the current of the battery circuit to charge with the second preset current during the charging phase of cycle i+1, wherein the second preset current is greater than the first preset current.

[0016] In some embodiments, the range of the first preset current and the second preset current is [1*C~10*C], where C is a multiple of the rated current of the lithium-ion battery.

[0017] In some embodiments, the second reference electrode includes a substrate and a lithium metal layer disposed on the surface of the substrate. The substrate is made of one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The method for preparing the second reference electrode includes: running a detection device; depositing lithium on the substrate to obtain a potential-stable second reference electrode.

[0018] In some embodiments, before determining the maximum value of the potential difference between the first reference electrode and the second reference electrode during the multi-cycle charging phase of the battery circuit, the method further includes: performing a formation process on the battery.

[0019] Secondly, embodiments of this application propose a lithium-ion battery fast-charging limiting diffusion current density detection device, comprising:

[0020] The first acquisition module is used to acquire the negative electrode system and electrolyte system in the testing device based on the lithium-ion battery to be tested. The negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte.

[0021] A battery circuit module is used to sequentially stack a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode in a first electrolyte of a testing device to form a battery circuit; wherein the second electrode includes: a first current collector, which is formed by providing a groove on one side of the initial current collector connecting to the tab, and the second reference electrode is disposed in the groove; a negative electrode active material layer, disposed on at least one side of the first current collector; and an insulating encapsulation film, disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector;

[0022] The current adjustment module is used to run the detection equipment and charge the battery circuit with a first preset current in i cycles and a second preset current in i+1 cycles, wherein the second preset current is greater than the first preset current, i is a positive integer and i is greater than 1;

[0023] The current density determination module is used to detect the potential difference between the first reference electrode and the second reference electrode, determine the maximum potential difference during the multi-cycle charging phase of the battery circuit, and take the charging current density at the first occurrence of the maximum potential difference as the limiting diffusion current density of the lithium-ion battery under test.

[0024] Thirdly, embodiments of this application provide an electronic device, the device comprising: a processor and a memory storing computer program instructions; the processor, when executing the computer program instructions, implements the method as described in any embodiment of the first aspect.

[0025] Fourthly, embodiments of this application provide a computer-readable storage medium storing computer program instructions that, when executed by a processor, implement the method as described in any embodiment of the first aspect.

[0026] Fifthly, embodiments of this application provide a computer program product in which instructions, when executed by a processor of an electronic device, cause the electronic device to perform the method as described in any embodiment of the first aspect.

[0027] In the detection method, apparatus, electronic device, and storage medium provided in this application embodiment, the second reference electrode is disposed between the negative electrode active material layer and the first current collector, and the ions of the negative electrode active material layer are transported through the insulating encapsulation film. The second reference electrode can reflect the potential of the negative electrode active material layer near the first current collector; the first reference electrode can reflect the potential of the surface of the second electrode. In the entire battery circuit, when the charging current is small, the lithium ion liquid phase diffusion matches the reaction kinetics of the second electrode, and at this time, the lithium ion concentration at the bottom and surface of the negative electrode active material layer is the same; when the charging current gradually increases, the lithium ion liquid phase diffusion lags behind the reaction of the second electrode, and at this time, the bottom of the negative electrode active material layer and the surface of the second electrode have the same lithium ion concentration. A concentration gradient appears on the surface of the electrode. The lithium-ion concentration at the bottom decreases as the current increases, while the lithium-ion concentration remains constant near the surface of the second electrode, close to the first reference electrode. Therefore, the difference in potential detected by the second reference electrode relative to the first reference electrode gradually increases. When the charging current density is too high, a "salt depletion" phenomenon occurs at the bottom of the negative electrode active material layer, meaning the lithium-ion concentration approaches zero. At this point, the difference in potential detected by the second reference electrode relative to the first reference electrode reaches its maximum. The current density under this charging condition is the limiting diffusion current density confined by liquid phase diffusion. Therefore, this method can detect the limiting diffusion current density in the lithium-ion battery system under test, with high accuracy and simple operation.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 A flowchart illustrating a method for detecting the fast-charging limiting diffusion current density of a lithium-ion battery according to an embodiment of this application is shown.

[0031] Figure 2 A schematic diagram of the structure of the second electrode provided in one embodiment of this application is shown;

[0032] Figure 3 A schematic diagram of the fabrication process of the second electrode sheet provided in one embodiment of this application is shown;

[0033] Figure 4 This illustration shows a schematic diagram of the potentials of the first and second reference electrodes under different current densities according to an embodiment of this application.

[0034] Figure 5 A graph showing the lithiation of a second reference electrode provided for an embodiment of this application is shown;

[0035] Figure 6 This invention provides a schematic diagram of the structure of a lithium-ion battery fast-charging limit diffusion current density detection device according to an embodiment of the present application.

[0036] Figure 7 A schematic diagram of the hardware structure of an electronic device provided in an embodiment of this application is shown.

[0037] Explanation of reference numerals in the attached figures:

[0038] 100. Second electrode; 10. Negative electrode current collector; 20. Second reference electrode; 30. Insulating encapsulation film; 40. Negative electrode active material layer; 200. Limiting diffusion current density detection device; 210. First acquisition module; 220. Battery circuit module; 230. Current adjustment module; 240. Current density determination module; 701. Processor; 702. Memory; 703. Communication interface; 710. Bus; Detailed Implementation

[0039] The features and exemplary embodiments of various aspects of this application will now be described in detail. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain this application and are not configured to limit this application. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples of this application.

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used merely 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..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0041] In lithium-ion batteries, the structural parameters of the negative electrode and the electrolyte significantly influence the diffusion behavior of lithium ions. Under high-rate charging conditions, the liquid-phase diffusion process can become a limiting step in the electrode reaction, leading to localized "salt depletion" and severely impacting battery capacity and charging efficiency. Therefore, accurately assessing the limiting diffusion current density under liquid-phase diffusion constraints is crucial for determining the fast-charging capability of lithium-ion batteries and provides important data support for the design of parameters such as the negative electrode and electrolyte systems.

[0042] To accurately assess extreme operating conditions during battery charging and address the challenge of accurately determining electrode reaction limits under fast-charging conditions for lithium-ion batteries due to limited liquid-phase diffusion, this application provides a method for detecting the limiting diffusion current density during fast charging of lithium-ion batteries. This method can dynamically and in-situ detect the limiting diffusion current density under liquid-phase diffusion constraints, providing data for designing electrode thickness, porosity, and other parameters. It also provides crucial data support for promoting the development of fast-charging technology and helps prevent safety hazards such as lithium plating.

[0043] Figure 1 A flowchart illustrating a method for detecting the fast-charging limiting diffusion current density of a lithium-ion battery according to an embodiment of this application is shown.

[0044] like Figure 1As shown, the method for detecting the fast-charging limit diffusion current density of lithium-ion batteries includes steps 100 to 400.

[0045] Step 100: Based on the lithium-ion battery system to be tested, obtain the negative electrode system and electrolyte system in the testing device. The negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte.

[0046] The lithium-ion battery system under test may include a positive electrode, a negative electrode, and an electrolyte. The positive electrode may be made of lithium-containing materials such as lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiMn2O4), lithium manganese oxide (LiCoO2), and lithium nickel oxide (LiNiO2); the negative electrode may be made of carbon materials, silicon materials, and metal oxide materials, with carbon materials including artificial graphite, mesophase carbon microspheres, and hard carbon; the electrolyte may be a liquid electrolyte, such as a lithium salt solution. In addition, a lithium-ion battery may also include a casing and battery electrode leads. The casing may be made of steel, aluminum, nickel-plated iron, or aluminum-plastic film.

[0047] The negative electrode system and electrolyte system in the testing equipment are determined based on the negative electrode and electrolyte in the lithium-ion battery system under test. For example, the first electrolyte in the testing equipment is determined by the electrolyte in the lithium-ion battery system under test; the negative electrode active material layer and the initial current collector in the testing equipment are determined by the negative electrode in the lithium-ion battery system under test. The first electrolyte, negative electrode active material layer, and initial current collector can be freshly prepared based on the lithium-ion battery system under test, or they can be customized based on the lithium-ion battery system under test, for example, they can be stored for a period of time, such as 1 to 10 days.

[0048] The negative electrode active material layer may include a negative electrode active material, an optional binder, and an optional conductive agent. The negative electrode active material may be a material such as graphite, silicon, or silicon carbide; the initial current collector may be a material such as copper foil.

[0049] The initial current collector may include a substrate layer and an electroplated layer. The substrate layer may be made of PET material, and the electroplated layer may be made of metal such as copper. For example, copper can be electroplated onto PET using a water electroplating method, and the groove is formed by using a mask to cover it without electroplating copper.

[0050] Step 200: The first electrode, the first separator, the first reference electrode, the second separator, and the second electrode are sequentially stacked in the first electrolyte of the detection device to form a battery circuit; wherein, the second electrode includes: a first current collector, which is formed by providing a groove on one side of the initial current collector connecting to the tab, and the second reference electrode is disposed in the groove; a negative electrode active material layer, disposed on at least one side of the first current collector; and an insulating encapsulation film, disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector.

[0051] In some embodiments, the insulating encapsulation film includes one or more of the following: lithium-ion battery separator material, single-ion conductor polymer, and composite material of single-ion conductor polymer and inorganic filler.

[0052] As an example, the separator material for lithium-ion batteries can be one or more of the following: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0053] Alternatively, an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may be applied to the surface of the separator.

[0054] In some embodiments, the single-ion conductor polymer includes one or more of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA).

[0055] In some embodiments, the inorganic filler includes one or more of alumina (Al2O3), cubic lithium lanthanum zirconium oxide (LLZO), and lithium aluminum titanium phosphate (LATP).

[0056] In some embodiments, the insulating encapsulation film further includes an adhesive, which includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0057] It is understandable that the insulating encapsulation film has electronic insulation and ion conduction properties, which can achieve the functions of electronic insulation and ion conduction between the negative electrode active material layer and the first current collector.

[0058] The first current collector is formed by providing a groove on one side of the initial current collector connected to the tab. For example, in a battery circuit, a tab is connected to one side of the second electrode, and the tab is connected to the second electrode; a tab is also connected to the side parallel or opposite to this side, and the tab is connected to the second reference electrode.

[0059] The second reference electrode is disposed within the groove to detect the lithium-ion concentration in the negative electrode active material layer and provide feedback on the potential at that location. It can be understood that the second reference electrode acts as a potential sensor, converting changes in the lithium-ion concentration on the negative electrode current collector side into a potential signal, reflecting the potential at that location. For example, if the lithium-ion concentration on the negative electrode current collector side decreases, the potential of the second reference electrode decreases, thereby increasing the potential deviation between the second and first reference electrodes. Throughout the fast charging process, the potential of the first reference electrode remains relatively stable, reflecting the lithium-ion concentration on the surface of the negative electrode.

[0060] The first electrolyte may include an electrolyte salt and an organic solvent.

[0061] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0062] In some embodiments, the organic solvent may include one or more of cyclic carbonate solvents, chain carbonate solvents, carboxylic acid ester solvents, ether solvents, nitrile solvents, and sulfone solvents.

[0063] As an example, the organic solvent may include, but is not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0064] In some embodiments, the concentration of the electrolyte salt can be between 0.6 mol / L and 4 mol / L, for example, it can be 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, or any range of the above values. Those skilled in the art can adjust the concentration of the electrolyte salt according to the type of battery cell.

[0065] In some embodiments, the first electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the secondary battery cell, such as additives that improve overcharge performance, additives that improve high-temperature performance, additives that improve low-temperature performance, etc.

[0066] In some embodiments, the material of the first reference electrode includes elemental lithium, Li4Ti4O3, etc. 12 One or more of LiFePO4.

[0067] In some embodiments, the material of the second reference electrode includes elemental lithium, Li4Ti4O4, etc. 12 One or more of LiFePO4.

[0068] The second reference electrode can be entirely composed of elemental lithium. The second reference electrode may further include a current collector substrate and a lithium layer disposed on the surface of the current collector substrate; the lithium layer can be elemental lithium. The lithium layer can be obtained by electroplating. When the second reference electrode is assembled with the second electrode sheet, an insulating encapsulation film is disposed on the surface of the second reference electrode and the surface of the first current collector.

[0069] The first and second reference electrodes can be the same or different. When the first and second reference electrodes are made of the same material, it is beneficial to determine the maximum potential difference more accurately.

[0070] In some embodiments, the first electrode includes one or more of elemental lithium, lithium alloy, and positive electrode containing positive active material.

[0071] It is understood that the positive electrode active material in a positive electrode sheet containing a positive electrode active material can include ternary positive electrode materials (NCM), lithium iron phosphate, and other positive electrode active materials. The positive electrode sheet can be a positive electrode sheet known in the art. For example, the positive electrode sheet can include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can include the aforementioned positive electrode active materials, etc.

[0072] In some embodiments, the first and second separators respectively comprise one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

[0073] It is understandable that the first electrode, the first separator, the first reference electrode, the second separator, the second electrode, and the electrolyte form the battery circuit.

[0074] Step 300: Run the detection device and charge the battery circuit with a first preset current in i cycles and a second preset current in i+1 cycles, wherein the second preset current is greater than the first preset current, i is a positive integer and i is greater than 1.

[0075] Based on constant voltage charging of the battery circuit, an increased current is applied to the battery circuit for different predetermined durations during multiple electrochemical cycles.

[0076] Step 400: Detect the potential difference between the first reference electrode and the second reference electrode, determine the maximum potential difference during the multi-cycle charging phase of the battery circuit, and take the charging current density at the first occurrence of the maximum potential difference as the limiting diffusion current density of the lithium-ion battery under test.

[0077] It is understandable that during the multi-cycle process of the battery circuit, in any cycle including the charging phase and / or discharging phase, the battery can be charged with a first preset current or a second preset current, for example, it can be charged from 0% to 100% SOC.

[0078] It is understandable that during normal charging, the potential of the first reference electrode is greater than that of the second reference electrode.

[0079] The instantaneous voltage responses of the first and second reference electrodes are collected to obtain their potential difference. The maximum potential difference is determined during the multi-cycle charging phase of the battery circuit. The charging current density at which the maximum potential difference first appears is taken as the limiting diffusion current density of the lithium-ion battery under test. This also reflects the critical change point of the limiting current density, thus determining the fast-charging limit under the current electrode structure. If the current in the battery circuit continues to gradually increase, i.e., the actual current exceeds the limiting diffusion current density, it indicates that lithium-ion diffusion cannot meet the reaction requirements, and a "salt depletion" phenomenon exists. The obtained limiting diffusion current density can then be used as a fast-charging limit indicator and fed back into the design of lithium-ion batteries.

[0080] For example, when the current is gradually increased to a certain current (e.g., 60mA), when the charge reaches 100% SOC (i.e., fully charged state), the potential difference reaches its maximum for the first time (the potential difference is larger than the previous detection current, e.g., 58mA, but the potential difference after 62mA, 65mA, etc. is almost the same as 60mA). The current at this time (60mA) is the limiting current, and the limiting current density is obtained by dividing 60mA by the area of ​​the electrode.

[0081] According to the Nernst equation, the negative electrode active material layer and the first current collector can provide feedback on the potential change based on the change in lithium ion concentration; the second reference electrode is disposed between the negative electrode active material layer and the first current collector, and the ions of the negative electrode active material layer are transported through the insulating encapsulation film. The second reference electrode can reflect the potential of the negative electrode active material layer near the first current collector; the first reference electrode can reflect the potential of the surface of the second electrode.

[0082] In the entire battery circuit, when the charging current is small, the lithium-ion liquid-phase diffusion matches the reaction kinetics of the second electrode. At this time, the lithium-ion concentration at the bottom and surface of the negative electrode active material layer is the same. As the charging current gradually increases, the lithium-ion liquid-phase diffusion lags behind the reaction of the second electrode. At this time, a concentration gradient appears between the bottom of the negative electrode active material layer and the surface of the second electrode. The lithium-ion concentration at the bottom decreases with increasing current, while the first reference electrode is close to the surface of the second electrode, and the lithium-ion concentration remains unchanged. Thus, the difference between the potential detected by the second reference electrode and that of the first reference electrode gradually increases. When the charging current density is too high, a "salt depletion" phenomenon occurs at the bottom of the negative electrode active material layer, that is, the lithium-ion concentration approaches 0. At this time, the difference between the potential detected by the second reference electrode and that of the first reference electrode reaches its maximum. The current density under this charging condition is the limiting diffusion current density restricted by liquid-phase diffusion. Therefore, this method can detect the limiting diffusion current density in the lithium-ion battery system under test, with high accuracy and simple operation.

[0083] The method described in this application constructs a detection system including a first reference electrode and a second reference electrode, collects the potential change behavior at different positions of the second electrode under different operating conditions or different current densities, and then determines the diffusion limit behavior of the battery circuit. This detection method does not rely on complex modeling, has real-time performance and adaptability, and is suitable for fast-charging optimization design in actual lithium batteries.

[0084] Figure 2 A schematic diagram of the structure of the second electrode and the second reference electrode provided in one embodiment of this application is shown. Please refer to... Figure 2 The second electrode includes a negative current collector, which includes a groove, and a second reference electrode is disposed in the groove. The second electrode also includes an insulating encapsulation film disposed on one side of the negative current collector, and a negative active material layer located on the side of the insulating encapsulation film opposite to the negative current collector.

[0085] Figure 3 A schematic diagram of the fabrication process of the second electrode provided in one embodiment of this application is shown.

[0086] Please see Figure 3 In some embodiments, the method for preparing the second electrode includes steps 150 to 153.

[0087] Step 150: A groove is provided on the side of the initial current collector connecting to the electrode tab to obtain the first current collector;

[0088] Step 151: Place the second reference electrode in the groove;

[0089] Optionally, the gap between the edge of the second reference electrode and the groove wall is less than or equal to 1 mm, optionally 0.8 mm, and further optionally 0.5 mm.

[0090] Step 152: An insulating encapsulation film is disposed on the surface of the first current collector and the second reference electrode to fix the first current collector and the second reference electrode.

[0091] Optionally, the outline projections of the negative electrode active material layer and the insulating encapsulation film are matched. The outer contour of the negative electrode current collector matches the outline projection of the insulating encapsulation film.

[0092] Step 153: Coat the surface of the insulating encapsulation film with a negative electrode active slurry and dry it to obtain a second electrode sheet, which includes a negative electrode active material layer.

[0093] In some embodiments, after coating the surface of the insulating encapsulation film with a negative electrode active slurry and drying it, the method for preparing the second electrode further includes: step 154, removing excess negative electrode current collector compared to the outline of the negative electrode active material layer to obtain the second electrode.

[0094] The negative electrode active material layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0095] In some embodiments, the initial current collector or the negative current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0096] The negative electrode active material is a material capable of extracting and inserting active ions, and can be any material known in the art. As examples, negative electrode active materials include, but are not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0097] This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of the following: superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0099] As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0100] Figure 4 This illustration shows a schematic diagram of the potentials of the first and second reference electrodes under different current densities according to an embodiment of this application; Figure 4 As shown in (a), at a current density of 40 mA, the potential difference between the first and second reference electrodes in the charging curve tends to stabilize, and a potential difference can be obtained; through Figure 4 As shown in (b), at a current density of 70mA, the potential difference between the first and second reference electrodes in the charging curve tends to stabilize, and another potential difference can be obtained. Therefore, when multiple potential differences are compared at different current densities, and multiple potential differences remain constant at their maximum as the current changes, the first current density at which the maximum potential difference appears can be taken as the limiting diffusion current density.

[0101] The second reference electrode can be prepared by applying an electrode with pre-existing reference conditions into the groove of the second electrode, or by placing the raw material of the second reference electrode into the groove of the second electrode and preparing it within the battery circuit after the battery circuit is formed. When the raw material or substrate of the second reference electrode is copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy, a uniform lithium layer can be obtained by lithium deposition on the substrate. When the raw material of the second reference electrode is either lithium titanate or lithium phosphate, the material can be delithiated to obtain the second reference electrode.

[0102] In some embodiments, in step 200, the second reference electrode includes a substrate and a lithium metal layer disposed on the surface of the substrate. The substrate is made of one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The method for preparing the second reference electrode includes:

[0103] Before running the testing equipment to achieve battery circuit formation, i.e. before step 300, lithium is deposited on the substrate to obtain a potential-stable second reference electrode.

[0104] In this embodiment, a dense and uniform lithium metal layer is formed on the substrate through constant current electroplating. This electrochemical "deposition" of a stable lithium metal layer gives it the property of "0V vs. Li". + The reference capability of / Li, Li in metallic lithium and electrolyte + A balanced lithium battery pair provides a stable reference potential, which is beneficial for subsequent detection; it can also reduce interfacial side reactions and improve long-term stability.

[0105] Figure 5 A graph showing the lithiation of a second reference electrode provided in an embodiment of this application is illustrated; Figure 5 It can be seen that the lithium metal reference electrode formed by electroplating has a stable reference potential.

[0106] In some embodiments, step 300, operating the detection device and charging it with a first preset current in cycle i, and charging it with a second preset current in cycle i+1, wherein the second preset current is greater than the first preset current, includes:

[0107] Step 310: Run the testing equipment;

[0108] It is understandable that the battery circuit formation has been achieved before the maximum potential difference is determined, or before or after the detection equipment is run.

[0109] Step 320: During the charging phase of the i-cycle, control the current of the battery circuit to charge at a first preset current.

[0110] Optionally, the first preset current is greater than or equal to the rated current of the lithium-ion battery.

[0111] Step 330: During the charging phase of the i+1 cycle, the current of the battery circuit is controlled to charge at a second preset current, which is greater than the first preset current.

[0112] The i-cycle and i+1-cycle include the charging phase and the discharging phase.

[0113] Alternatively, pulse charging or constant voltage charging can be used during the charging process.

[0114] The current can increase in a gradient over different time periods.

[0115] In some embodiments, a detection device is operated to achieve battery circuit formation, thereby forming a solid electrolyte membrane and meeting the basic conditions for battery circuit cycling. This allows lithium ions to fully re-intercalate into the second electrode via diffusion, and the potential of the second reference electrode can be accurately measured. For example, a first preset current and a second preset current are increased in a gradient. In the first charging cycle, the current is 1.0C; in the second charging cycle, the current is 1.1C; in the third charging cycle, the current is 1.2C, and so on. The duration of the charging and discharging cycles in any given cycle can be the same or different. Thus, by increasing the current, the lithium ion supply in the battery circuit can be determined in real time and accurately, yielding an accurate limiting diffusion current density.

[0116] In some embodiments, the range of the first preset current and the second preset current is [1*C~10*C], where C is a multiple of the rated current of the lithium-ion battery.

[0117] The rated current of a lithium-ion battery refers to the current that the battery can fully discharge at its rated capacity within one hour or a specified time under standard test conditions, measured in amperes (A). This current value represents the standard operating current at which the battery can operate stably within its design life without causing performance degradation or safety risks. The range of the first and second preset currents is [1C~10C], selectable as 1.1C, 1.2C, 1.3C, 1.4C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, etc. Having the first and second preset currents greater than or equal to the rated current facilitates testing with increased current, allowing for real-time detection of the precise limiting diffusion current density.

[0118] This allows for a balance between testing efficiency and improved testing accuracy.

[0119] In some embodiments, the method further includes performing a formation process on the battery before determining the maximum value of the potential difference between the first reference electrode and the second reference electrode during a multi-cycle charging phase of the battery circuit, after detecting the potential difference between the first and second reference electrodes. This improves the accuracy of the detection results.

[0120] In some embodiments, before operating the detection equipment, the detection method further includes:

[0121] When the battery circuit performs a first operation, the lithium-ion battery is controlled to operate within a preset current range, wherein the first operation includes at least one of the following:

[0122] 1) Perform a charging operation on the battery circuit;

[0123] 2) Control the battery circuit to discharge at the rated current.

[0124] The first operation includes, but is not limited to: after depositing lithium on the substrate of the second reference electrode, continuing to charge and discharge the lithium-ion battery, and then controlling the lithium-ion battery to charge with an increasing current in order to determine the potential difference between the first reference electrode and the second reference electrode.

[0125] Figure 6 A schematic diagram of the structure of a lithium-ion battery fast-charging limit diffusion current density detection device provided in an embodiment of this application is shown;

[0126] Please see Figure 6 The lithium-ion battery fast-charging limit diffusion current density detection device 200 includes: a first acquisition module 210, a battery circuit module 220, a current adjustment module 230, and a current density determination module 240.

[0127] The first acquisition module 210 is used to acquire the negative electrode system and electrolyte system in the testing device based on the lithium-ion battery to be tested. The negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte.

[0128] The battery circuit module 220 is used to sequentially stack a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode in the first electrolyte of the testing device to form a battery circuit; wherein the second electrode includes: a first current collector, which is formed by providing a groove on one side of the initial current collector connecting to the tab, and the second reference electrode is disposed in the groove; a negative electrode active material layer, disposed on at least one side of the first current collector; and an insulating encapsulation film, disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector;

[0129] The current adjustment module 230 is used to run the detection equipment and charge the battery circuit with a first preset current in i cycles and with a second preset current in i+1 cycles, wherein the second preset current is greater than the first preset current, i is a positive integer and i is greater than 1.

[0130] The current density determination module 240 is used to detect the potential difference between the first reference electrode and the second reference electrode, determine the maximum potential difference during the multi-cycle charging phase of the battery circuit, and take the charging current density when the maximum potential difference first appears as the limiting diffusion current density of the lithium-ion battery under test.

[0131] In some embodiments, the current adjustment module 230:

[0132] The formation module is used to run the testing equipment to achieve battery circuit formation;

[0133] The first current regulation module is used to control the current of the battery circuit to charge at a first preset current during the charging phase of the i-cycle.

[0134] The second current regulation module is used to control the current of the battery circuit to charge at a second preset current during the charging phase of the i+1 cycle. The second preset current is greater than the first preset current.

[0135] Figure 7 A schematic diagram of the hardware structure of an electronic device provided according to an embodiment of this application is shown.

[0136] Please see Figure 7 The electronic device may include a processor 701 and a memory 702 storing computer program instructions.

[0137] Specifically, the processor 701 may include a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits that can be configured to implement the embodiments of this application.

[0138] Memory 702 may include mass storage for data or instructions. For example, and not limitingly, memory 702 may include a hard disk drive (HDD), floppy disk drive, flash memory, optical disk, magneto-optical disk, magnetic tape, or Universal Serial Bus (USB) drive, or a combination of two or more of these. Where appropriate, memory 702 may include removable or non-removable (or fixed) media. Where appropriate, memory 702 may be internal or external to the integrated gateway disaster recovery device. In a particular embodiment, memory 702 is non-volatile solid-state memory.

[0139] Memory may include read-only memory (ROM), random access memory (RAM), disk storage media devices, optical storage media devices, flash memory devices, and electrical, optical, or other physical / tangible memory storage devices. Therefore, typically, memory includes one or more tangible (non-transitory) computer-readable storage media (e.g., memory devices) encoded with software including computer-executable instructions, and when the software is executed (e.g., by one or more processors), it is operable to perform the operations described with reference to the methods according to one aspect of this disclosure.

[0140] The processor 701 implements any of the detection methods described in the above embodiments by reading and executing computer program instructions stored in the memory 702.

[0141] In one example, the electronic device may also include a communication interface 703 and a bus 710. For example, Figure 4 As shown, the processor 701, memory 702, and communication interface 703 are connected through bus 710 and complete communication with each other.

[0142] Communication interface 703 is primarily used to enable communication between modules, devices, units, and / or equipment in the embodiments of this application. Bus 710 includes hardware, software, or both, that couples components of the online data traffic metering device together. For example, and not limitingly, the bus may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a Front Side Bus (FSB), HyperTransport (HT) interconnect, an Industry Standard Architecture (ISA) bus, an Infinite Bandwidth Interconnect, a Low Pin Count (LPC) bus, a memory bus, a Microchannel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a Serial Advanced Technology Attachment (SATA) bus, a Video Electronics Standards Association Local (VLB) bus, or other suitable buses, or combinations of two or more of these. Where appropriate, bus 710 may include one or more buses. Although specific buses are described and illustrated in the embodiments of this application, this application contemplates any suitable bus or interconnect.

[0143] The electronic device can perform the detection method in the embodiments of this application, thereby achieving a combination Figure 1 The detection method described.

[0144] Furthermore, in conjunction with the detection methods in the above embodiments, this application embodiment can provide a computer-readable storage medium for implementation. This computer-readable storage medium stores computer program instructions; when these computer program instructions are executed by a processor, they implement any of the detection methods in the above embodiments.

[0145] In conjunction with the detection methods described in the above embodiments, this application can provide a computer program product for implementation. When the instructions in the computer program product are executed by the processor of an electronic device, they implement any of the detection methods described in the above embodiments.

[0146] It should be clarified that this application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of this application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of this application.

[0147] The functional blocks shown in the above structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this application are programs or code segments used to perform the required tasks. Programs or code segments can be stored in a computer-readable storage medium or transmitted over a transmission medium or communication link via data signals carried on a carrier wave. "Computer-readable storage medium" can include any medium capable of storing or transmitting information. Examples of computer-readable storage media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0148] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0149] The above are merely specific embodiments of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

[0150] The beneficial effects of the detection method provided in this application will be illustrated by the following examples.

[0151] Example 1

[0152] This embodiment provides a method for detecting the fast-charging limiting diffusion current density of lithium-ion batteries, including:

[0153] S100, based on the lithium-ion battery to be tested, obtain the negative electrode system and electrolyte system in the testing equipment, wherein the negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte;

[0154] Specifically, the initial current collector is a copper foil with a thickness of 9 μm; the negative electrode active material layer comprises, by mass percentage, 80% graphite, 10% conductive carbon black (SupperP), 5% sodium carboxymethyl cellulose (CMC), and 5% styrene-butadiene rubber (SBR); the first electrolyte comprises lithium hexafluorophosphate (LiPF6), ethylene carbonate, and dimethyl carbonate; the concentration of lithium hexafluorophosphate (LiPF6) is 1 M, and the volume ratio of ethylene carbonate to dimethyl carbonate is 3:7;

[0155] S200, a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode are sequentially stacked in the first electrolyte of the detection device to form a battery circuit; wherein, the second electrode includes:

[0156] The first current collector is formed by providing a groove on one side of the initial current collector connecting to the electrode tab, and the second reference electrode is disposed in the groove;

[0157] A negative electrode active material layer is disposed on at least one side of the first current collector;

[0158] An insulating encapsulation film is disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector;

[0159] Specifically, the first and second separators are made of polyethylene material with a thickness of 25 μm; the first electrode is a lithium metal sheet with a thickness of 30 μm and an area of ​​28 cm². 2 The first reference electrode is a lithium metal filament with a diameter of 0.1 mm; the second reference electrode is made of copper foil; the gap between the wall of the groove and the second reference electrode is 0.6 cm; the insulating encapsulation film is made of polyvinylidene fluoride (PVDF), which is dissolved in NMP to prepare a 15 wt% solution to encapsulate the second electrode and the second reference electrode. The encapsulation film is prepared by gradient drying, which includes volatilization at room temperature (25°C) for 1 hour, drying at 70°C for 1 hour in a forced-air drying oven, drying at 140°C for 3 minutes in a forced-air drying oven, and drying at 80°C for 20 minutes.

[0160] Preparation of the negative electrode active material layer: 1200-mesh fine-particle graphite powder was used as the raw material, and sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were used as the binders. First, sodium carboxymethyl cellulose (CMC) was dissolved in water to obtain a 1 wt% transparent liquid. A slurry was prepared by mixing graphite powder, conductive carbon black (SupperP), and sodium carboxymethyl cellulose (CMC) in a mass ratio of 8:1:1 with a certain amount of water and mixing evenly until fully dispersed and free of obvious particles. Then, 5% (by weight of total solids) of styrene-butadiene rubber (SBR) was added, and the mixture was stirred at 200 rpm for 1 hour using a magnetic stirrer. The negative electrode slurry was evenly coated onto the surface of the negative electrode current collector copper foil and the insulating encapsulation film using a 100 μm scraper, forming a 30 μm negative electrode active material layer. The layer was then dried in a vacuum dryer for 24 hours. The second reference electrode and the first reference electrode were then connected to tabs.

[0161] Preparation of the second reference electrode: The assembled soft-pack battery has the raw material for the second reference electrode, namely copper foil, connected to one side of the positive electrode, and metallic lithium connected to the negative electrode. The embedded copper foil is uniformly deposited with lithium for 40 hours using a current of 0.02mA to form a dense second reference electrode with a long-term stable potential.

[0162] Assemble a graphite four-electrode soft-pack half-cell, perform formation and capacity testing: After assembly, the battery undergoes formation and is charged and discharged for 3 cycles with a small current of 0.05C to activate the active material and form a stable solid electrolyte membrane, thereby obtaining the actual capacity of the battery.

[0163] S300, the detection device is run and charged with a first preset current in the i-th cycle, and charged with a second preset current in the i+1-th cycle, wherein the second preset current is greater than the first preset current;

[0164] Specifically, the battery's rated current is 20mA, and it is charged and discharged at a current of 20mA, then the current is increased by 10mA, and the current is increased in this way.

[0165] S400 detects the potential difference between the first and second reference electrodes. During the multi-cycle charging phase of the battery circuit, the maximum potential difference is determined, and the charging current density at the first occurrence of this maximum potential difference is taken as the limiting diffusion current density of the lithium-ion battery under test. A current of 76 mA is detected as the limiting diffusion current density of this lithium-ion battery.

[0166] The experimental results were verified using the limiting diffusion current density formula:

[0167] Limiting diffusion current density formula:

[0168]

[0169] Among them, i d,lim The limiting diffusion current density of the electrolyte, in A / m³.2 ;

[0170] n: Lithium-ion migration charge number, usually a constant 1;

[0171] F: Faraday constant, 96485 C / mol;

[0172] D Li + Diffusion coefficient of lithium ions in electrolyte, unit: m 2 / s; This diffusion coefficient is obtained by detection using EIS or GITT methods.

[0173] C bulk : Bulk concentration of lithium ions in the first electrolyte, unit: mol / m 3 The bulk concentration in this application is 1 mol / m 3 ;

[0174] δ: Thickness of the negative electrode active material layer, in meters (m);

[0175] According to calculations, the result of the limiting diffusion current density formula is 75mA, and the results of the test in this application are relatively accurate.

[0176] Example 2

[0177] The difference between this embodiment and Embodiment 1 is that the thickness of the negative electrode active material layer is different. Specifically, the thickness of the negative electrode active material layer is 50 micrometers. The limiting diffusion current density measured using the method of this embodiment is 69 mA. The limiting diffusion current density is calculated using the formula, and the result is 71 mA. The results detected by this embodiment are more accurate.

[0178] Example 3

[0179] The difference between this embodiment and Embodiment 1 lies in the composition of the first electrolyte. Specifically, the first electrolyte comprises LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate):DEC (diethyl carbonate), wherein the volume ratio of EC to DEC is 3:7. Using the method of this embodiment, the limiting diffusion current density was measured to be 83 mA. Calculated using the limiting diffusion current density formula, the result is 81 mA. The results obtained in this embodiment are relatively accurate.

[0180] Example 4

[0181] The difference between this embodiment and Embodiment 1 is that the composition of the negative electrode active material layer is different. Specifically, the negative electrode active material layer includes, by mass percentage, 60% graphite, 20% conductive carbon black (SupperP), 10% sodium carboxymethyl cellulose (CMC), and 10% styrene-butadiene rubber (SBR). The limiting diffusion current density measured using the method of this embodiment is 73 mA. The limiting diffusion current density is calculated using the formula, and the result is 75 mA. The results detected by this embodiment are more accurate.

[0182] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0183] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for detecting the limiting diffusion current density of a lithium-ion battery during fast charging, characterized in that, include: Based on the lithium-ion battery system to be tested, the negative electrode system and electrolyte system in the testing equipment are obtained, wherein the negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte; A first electrode, a first separator, a first reference electrode, a second separator, and a second electrode are sequentially stacked in the first electrolyte of the detection device to form a battery circuit; wherein, the second electrode includes: The first current collector is formed by providing a groove on one side of the initial current collector connecting tab, and the second reference electrode is disposed in the groove; The negative electrode active material layer is disposed on at least one side of the first current collector; An insulating encapsulation film is disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector; Operate the testing equipment; During the charging phase of the i-th cycle, the current of the battery circuit is controlled to charge at a first preset current, where i is a positive integer and i is greater than 1; During the charging phase of the i+1 cycle, the current of the battery circuit is controlled to charge at a second preset current, which is greater than the first preset current. The potential difference between the first reference electrode and the second reference electrode is detected, and the maximum potential difference is determined during the multi-cycle charging phase of the battery circuit. The charging current density at which the maximum potential difference first appears is taken as the limiting diffusion current density of the lithium-ion battery under test.

2. The detection method according to claim 1, characterized in that, The insulating encapsulation film includes one or more of the following: lithium-ion battery separator material, single-ion conductor polymer, and composite material of single-ion conductor polymer and inorganic filler.

3. The detection method according to claim 2, characterized in that, The single-ion conductor polymer includes one or more of polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate; and / or The inorganic filler includes one or more of alumina, cubic lithium lanthanum zirconium oxide, and lithium aluminum titanium phosphate.

4. The detection method according to claim 2, characterized in that, The insulating encapsulation film also includes an adhesive, which includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

5. The detection method according to claim 1, characterized in that, The materials of the first reference electrode and the second reference electrode include elemental lithium, LiFePO4, and Li4Ti5O, respectively. 12 One or more of the following.

6. The detection method according to claim 1, characterized in that, The first electrode comprises one or more of elemental lithium, lithium alloy, and a positive electrode containing a positive electrode active material; and / or, The first and second separators respectively comprise one or more of the following: glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

7. The detection method according to claim 1, characterized in that, The range of the first preset current and the second preset current is [1*C~10*C], where C is a multiple of the rated current of the lithium-ion battery.

8. The detection method according to claim 1, characterized in that, The second reference electrode includes a substrate and a lithium metal layer disposed on the surface of the substrate. The substrate is made of one or more of the following materials: copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The method for preparing the second reference electrode includes: Before the testing equipment is operated to achieve the battery circuit formation, The substrate is subjected to lithium deposition to obtain a potential-stable second reference electrode.

9. The detection method according to claim 1, characterized in that, The method of detecting the potential difference between the first reference electrode and the second reference electrode, before determining the maximum value of the potential difference during the multi-cycle charging phase of the battery circuit, further includes: performing a formation process on the battery.

10. A device for detecting the limiting diffusion current density of a lithium-ion battery during fast charging, characterized in that, include: The first acquisition module is used to acquire the negative electrode system and electrolyte system in the testing device based on the lithium-ion battery to be tested, wherein the negative electrode system includes a negative electrode active material layer and an initial current collector, and the electrolyte system includes a first electrolyte. A battery circuit module is used to sequentially stack a first electrode, a first separator, a first reference electrode, a second separator, and a second electrode in the first electrolyte of the detection device to form a battery circuit; wherein the second electrode includes: a first current collector, which is formed by providing a groove on one side of the initial current collector connecting to the tab, and a second reference electrode disposed in the groove; a negative electrode active material layer disposed on at least one side of the first current collector; and an insulating encapsulation film disposed between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector; The current adjustment module is used to control the current of the battery circuit to charge at a first preset current during the charging phase of the i-th cycle of the detection device, where i is a positive integer and i is greater than 1; and to control the current of the battery circuit to charge at a second preset current during the charging phase of the i+1-th cycle, where the second preset current is greater than the first preset current. The current density determination module is used to detect the potential difference between the first reference electrode and the second reference electrode, determine the maximum potential difference during the multi-cycle charging phase of the battery circuit, and take the charging current density at the first occurrence of the maximum potential difference as the limiting diffusion current density of the lithium-ion battery under test.

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