Lithium ion battery fast charge limit diffusion current density detection method

Abstract

The invention discloses a lithium ion battery fast charge limit diffusion current density detection method. The method comprises the following steps: acquiring a negative electrode system and an electrolyte system in detection equipment according to a to-be-detected lithium ion battery system; sequentially laminating the first pole piece, the first isolating membrane, the first reference electrode, the second isolating membrane and the second pole piece in the first electrolyte of the detection equipment to form a battery loop; the second pole piece comprises a first current collector, one side of the first current collector is provided with a groove, and the two reference electrodes are arranged in the groove; the negative electrode active material layer is arranged on at least one side of the first current collector; the insulating packaging film is arranged between the negative electrode active material layer and the first current collector; the detection device is operated, and the battery loop is charged with a first preset current in the i circles of circulation and charged with a second preset current in the i + 1 circles of circulation; and detecting the potential difference between the first reference electrode and the second reference electrode, determining the maximum value of the potential difference, and taking the charging current density when the maximum value of the potential difference appears for the first time as the limit diffusion current density.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a method for detecting the fast-charging limit diffusion current density of a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in many fields, including electric vehicles, energy storage systems, consumer electronics, military equipment, and industrial equipment. With the development of lithium-ion battery technology, the fast-charging performance of lithium-ion batteries has become an important direction of current research and engineering development. 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 risks. 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 limitation can accurately assess the extreme operating conditions during battery charging.

[0003] In related research and engineering practice, electrode diffusion performance is typically measured using methods such as rate performance testing and cyclic voltammetry. However, these methods have limitations, such as difficulty distinguishing the contributions of solid-phase and liquid-phase diffusion, cumbersome data processing, and large errors. Furthermore, they cannot achieve dynamic monitoring during the charge and discharge process, making it difficult to meet the demand for real-time assessment of the limiting diffusion current density under fast-charging conditions. Accurately measuring the limiting diffusion current density of lithium-ion batteries has become a pressing technical issue. Summary of the Invention

[0004] The present application aims to provide a method, device, electronic device and storage medium for detecting the limiting diffusion current density of a lithium-ion battery during fast charging, so as to solve the technical problems in the related art of inaccurate detection results of the limiting diffusion current density under fast charging conditions and complex operation.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] In the first aspect, the embodiment of the present application proposes a method for detecting the fast-charging limit diffusion current density of a lithium-ion battery, comprising: obtaining a negative electrode system and an electrolyte system in a detection device according to 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; stacking a first electrode piece, a first isolation membrane, a first reference electrode, a second isolation membrane, and a second electrode piece in sequence in the first electrolyte of the detection device to form a battery circuit; wherein the second electrode piece includes: a first current collector, the first current collector is obtained by providing a groove on one side of the initial current collector for connecting the electrode ear, and the second reference electrode is arranged in the groove; a negative electrode A negative electrode active material layer is provided on at least one side of a first current collector; an insulating packaging film is provided between the negative electrode active material layer and the first current collector to fix the second reference electrode and the first current collector; a detection device is operated to 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; a potential difference between the first reference electrode and the second reference electrode is detected, a maximum value of the potential difference is determined during the charging stage of multiple cycles of the battery circuit, and a charging current density when the maximum potential difference first occurs is used as the limiting diffusion current density of the lithium-ion battery to be tested.

[0007] In some embodiments, the insulating packaging film includes one or more of a separator material for lithium-ion batteries, a single-ion conductor polymer, and a composite material of a single-ion conductor polymer and an 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 packaging film further includes a binder, and the binder 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 lithium, Li4Ti4O 12 , LiFePO4 or more.

[0012] In some embodiments, the material of the second reference electrode includes lithium, Li4Ti4O 12 , LiFePO4 or more.

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

[0014] In some embodiments, the first isolation membrane and the second isolation membrane respectively include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

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

[0016] In some embodiments, the first preset current and the second preset current are in a range of [1*C to 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, and the material of the substrate includes one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy; the preparation method of the second reference electrode includes: operating the detection equipment; and depositing lithium on the substrate to obtain a second reference electrode with stable potential.

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

[0019] In a second aspect, the present application provides a device for detecting the fast-charging limit diffusion current density of a lithium-ion battery, comprising:

[0020] A first acquisition module is configured to acquire a negative electrode system and an electrolyte system in a testing device according to a 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;

[0021] A battery circuit module is configured to sequentially stack a first electrode sheet, a first separator, a first reference electrode, a second separator, and a second electrode sheet in a first electrolyte of a detection device to form a battery circuit; wherein the second electrode sheet comprises: a first current collector, the first current collector being formed by providing a groove on a side of the initial current collector for connection to the electrode tab, with the second reference electrode disposed within the groove; a negative electrode active material layer disposed on at least one side of the first current collector; and an insulating packaging film disposed between the negative electrode active material layer and the first current collector to secure the second reference electrode and the first current collector.

[0022] a current adjustment module, configured to operate the detection device 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, and i is a positive integer 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 value of the potential difference during the charging stage of multiple cycles of the battery circuit, and use the charging current density when the maximum potential difference first appears as the limiting diffusion current density of the lithium-ion battery to be tested.

[0024] In a third aspect, an embodiment of the present application proposes an electronic device, comprising: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the method in any embodiment of the first aspect is implemented.

[0025] In a fourth aspect, an embodiment of the present application proposes a computer-readable storage medium having computer program instructions stored thereon. When the computer program instructions are executed by a processor, a method as in any embodiment of the first aspect is implemented.

[0026] In a fifth aspect, an embodiment of the present application provides a computer program product. When the instructions in the computer program product are executed by a processor of an electronic device, the electronic device executes the method in any embodiment of the first aspect.

[0027] In the detection method, device, electronic device and storage medium provided in the embodiments of the present application, the second reference electrode is arranged between the negative electrode active material layer and the first current collector, and the ions of the negative electrode active material layer are transmitted through the insulating packaging film, and the second reference electrode can reflect the potential of the negative electrode active material layer close to 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 liquid phase diffusion of lithium ions 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 liquid phase diffusion of lithium ions lags behind the reaction of the second electrode, and at this time, the bottom of the negative electrode active material layer of the second electrode is aligned with the reaction kinetics of the second electrode. A concentration gradient appears on the surface of the electrode, and the lithium ion concentration at the bottom decreases with increasing current. The first reference electrode is close to the surface of the second electrode, and the lithium ion concentration remains unchanged. It can be seen that the difference between the potential detected by the second reference electrode and the first reference electrode gradually increases. When the charging current density is too large, "salt depletion" 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 the first reference electrode reaches the maximum. The current density under this charging condition is the limiting diffusion current density limited by liquid phase diffusion. Therefore, this method can detect the limiting diffusion current density in the lithium-ion battery system to be tested. The detection results are highly accurate and easy to operate.

[0028] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 1 A schematic diagram of a process for detecting the fast-charging limit diffusion current density of a lithium-ion battery provided in one embodiment of the present application is shown;

[0031] Figure 2 A schematic structural diagram of a second pole piece provided in one embodiment of the present application is shown;

[0032] Figure 3 A schematic diagram of the process for preparing a second pole piece provided in one embodiment of the present application is shown;

[0033] Figure 4 A schematic diagram of the potentials of the first reference electrode and the second reference electrode at different current densities provided in one embodiment of the present application is shown;

[0034] Figure 5 A graph showing the lithiation of the second reference electrode provided in one embodiment of the present application is shown;

[0035] Figure 6 A schematic diagram of the structure of a device for detecting the fast-charging limit diffusion current density of a lithium-ion battery provided in one embodiment of the present application is shown;

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

[0037] Description of reference numerals:

[0038] 100, second pole piece; 10, negative electrode current collector; 20, second reference electrode; 30, insulating packaging 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 DESCRIPTION

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

[0040] 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, so 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..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0041] In lithium-ion batteries, the structural parameters of the negative electrode and the electrolyte have a significant impact on the diffusion behavior of lithium ions. Under high-rate charging conditions, the liquid-phase diffusion process may become the limiting step of the electrode reaction, leading to local "salt depletion" of the electrode, seriously affecting the battery capacity and charging efficiency. Therefore, accurately assessing the limiting diffusion current density under liquid-phase diffusion limitations helps to determine the fast-charging capability of lithium-ion batteries and also provides important data support for the design of parameters such as the negative electrode system and electrolyte system of lithium-ion batteries.

[0042] In order to achieve accurate assessment of the extreme operating conditions during battery charging and solve the problem of difficulty in accurately judging the electrode reaction limit under fast charging conditions of lithium-ion batteries due to the limited liquid phase diffusion process, the embodiment of the present application provides a method for detecting the extreme diffusion current density of lithium-ion batteries under fast charging. This method can dynamically and in situ detect the extreme diffusion current density under liquid phase diffusion limitation, providing a data basis for designing the thickness, porosity, etc. of the electrode, providing key data support for promoting the development of fast charging technology, and helping to prevent safety hazards such as lithium plating.

[0043] Figure 1 A schematic diagram of a process for detecting the fast-charging limit diffusion current density of a lithium-ion battery provided in one embodiment of the present application is shown;

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

[0045] Step 100: Obtain a negative electrode system and an electrolyte system in a testing device according to a 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.

[0046] The lithium-ion battery system to be tested may include a positive electrode, a negative electrode, and an electrolyte. The positive electrode can 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 can be made of carbon materials, silicon materials, and metal oxide materials, such as artificial graphite, mesophase carbon microbeads, and hard carbon. The electrolyte can be an electrolyte solution, such as a lithium salt solution. Furthermore, the lithium-ion battery may also include a casing, battery electrode terminals, and other components. The casing can be made of steel, aluminum, nickel-plated iron, or aluminum-plastic film.

[0047] The negative electrode system and electrolyte system in the testing device are determined based on the negative electrode and electrolyte in the lithium-ion battery system to be tested. For example, the first electrolyte in the testing device is determined by the electrolyte in the lithium-ion battery system to be tested; the negative electrode active material layer and initial current collector in the testing device are determined by the negative electrode in the lithium-ion battery system to be tested. The first electrolyte, negative electrode active material layer, and initial current collector can be freshly prepared based on the lithium-ion battery system to be tested, or they can be customized based on the lithium-ion battery system to be tested, for example, after being 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 graphite, silicon, silicon carbon, or other materials; the initial current collector may be made of materials such as copper foil.

[0049] The initial current collector may include a base layer and an electroplated layer. The base layer may be made of PET, and the electroplated layer may be made of a metal such as copper. For example, copper may be electroplated on PET using water electroplating. The grooves are formed by masking the grooves without electroplating copper.

[0050] In step 200, the first electrode, the first isolation membrane, the first reference electrode, the second isolation membrane and the second electrode are stacked in sequence in the first electrolyte of the detection equipment to form a battery circuit; wherein the second electrode includes: a first current collector, the first current collector is made by providing a groove on one side of the initial current collector connecting the electrode ear, and the second reference electrode is arranged in the groove; a negative active material layer is arranged on at least one side of the first current collector; an insulating packaging film is arranged between the negative 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 packaging film includes one or more of a separator material for lithium-ion batteries, a single-ion conductor polymer, and a composite material of a single-ion conductor polymer and an inorganic filler.

[0052] As an example, the separator material for lithium-ion batteries can be one or more of 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. In the case of a multi-layer composite film, the materials of each layer can be the same or different.

[0053] Optionally, an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may be coated on the surface of the isolation membrane.

[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 (Al 2 O 3 ), cubic lithium lanthanum zirconium oxide (LLZO), and lithium aluminum titanium phosphate (LATP).

[0056] In some embodiments, the insulating packaging film further includes a binder, and the binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0057] It can be understood that the insulating packaging film has electronic insulation and ion conductivity properties, and can achieve the functions of electronic insulation and ion conductivity between the negative electrode active material layer and the first current collector.

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

[0059] The second reference electrode is arranged in the groove to facilitate the detection of the lithium ion concentration in the negative electrode active material layer and feedback of the potential at that position. It can be understood that the second reference electrode can act as a potential sensor to convert the change in lithium ion concentration on the negative electrode current collector side into a potential signal to reflect the potential at that position. For example, the lithium ion concentration on the negative electrode current collector side becomes smaller, and the potential of the second reference electrode decreases, thereby increasing the potential deviation between the second reference electrode and the first reference electrode. During the entire fast charging process, the potential of the first reference electrode remains basically stable, reflecting the lithium ion concentration on the surface of the negative electrode sheet.

[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 bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0062] In some embodiments, the organic solvent may include one or more of a cyclic carbonate solvent, a chain carbonate solvent, a carboxylate solvent, an ether solvent, a nitrile solvent, and a sulfone solvent.

[0063] As an example, the organic solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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, methyltetrahydrofuran, diphenyl ether, and crown ether.

[0064] In some embodiments, the concentration of the electrolyte salt can be 0.6 mol / L-4 mol / L, for example, 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 a range consisting of any 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, or additives capable of improving certain properties of the secondary battery cell, such as additives that improve overcharge performance, additives that improve high-temperature performance, and additives that improve low-temperature performance.

[0066] In some embodiments, the material of the first reference electrode includes lithium, Li4Ti4O 12 , LiFePO4 or more.

[0067] In some embodiments, the material of the second reference electrode includes lithium, Li4Ti4O 12 , LiFePO4 or more.

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

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

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

[0071] It is understood that the positive electrode active material in the positive electrode sheet containing the positive electrode active material may include a ternary positive electrode material (NCM), lithium iron phosphate, or other positive electrode active materials. The positive electrode sheet may be any known positive electrode sheet in the art. For example, the positive electrode sheet may 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 may include the aforementioned positive electrode active materials, among others.

[0072] In some embodiments, the first isolation membrane and the second isolation membrane respectively include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

[0073] It can be understood that the first electrode, the first isolation membrane, the first reference electrode, the second isolation membrane, the second electrode and the electrolyte form a battery circuit.

[0074] Step 300: Run the detection device 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.

[0075] On the basis of constant voltage charging of the battery circuit, increasing currents for different predetermined time periods are applied to the battery circuit in a plurality of electrochemical cycles.

[0076] Step 400 , detecting the potential difference between the first reference electrode and the second reference electrode, determining the maximum value of the potential difference during the charging phase of multiple cycles of the battery circuit, and using the charging current density when the maximum potential difference first appears as the limiting diffusion current density of the lithium-ion battery to be tested.

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

[0078] It can be understood that: during a normal charging process, the potential of the first reference electrode is greater than the potential of the second reference electrode.

[0079] The instantaneous voltage response of the first reference electrode and the second reference electrode is collected to obtain the potential difference between the two. The maximum value of the potential difference is determined during the charging stage of multiple cycles of the battery circuit. The charging current density when the maximum value of the potential difference first appears is used as the limiting diffusion current density of the lithium-ion battery to be tested. This also reflects that this is the critical change point of the limiting current density, and the fast charging limit under the current electrode structure can be determined. If the current in the battery circuit continues to increase gradually, that is, the actual current is greater than the limiting diffusion current density, it indicates that the diffusion of lithium ions cannot meet the reaction requirements and there is a "salt depletion" phenomenon. Subsequently, the obtained limiting diffusion current density can be used as a fast charging limit indicator and fed back into the design of the lithium-ion battery.

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

[0081] According to the Nernst equation, the potential between the negative electrode active material layer and the first current collector can be fed back according to the change of lithium ion concentration; the second reference electrode is arranged between the negative electrode active material layer and the first current collector, and the ions of the negative electrode active material layer are transmitted through the insulating packaging film. The second reference electrode can reflect the potential of the negative electrode active material layer close to the first current collector; the first reference electrode can reflect the potential of the surface of the second electrode piece.

[0082] In the entire battery circuit, when the charging current is small, the liquid-phase diffusion of lithium ions matches the reaction kinetics of the second electrode, and the lithium ion concentrations at the bottom and surface of the negative electrode active material layer are the same; when the charging current gradually increases, the liquid-phase diffusion of lithium ions lags behind the reaction of the second electrode. At this time, a concentration gradient appears at the bottom of the negative electrode active material layer of the second electrode and the surface of the second electrode, and 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. Therefore, it can be seen that the difference between the potential detected by the second reference electrode and the first reference electrode gradually increases. When the charging current density is too large, "salt depletion" 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 the first reference electrode reaches the maximum. The current density under this charging condition is the limiting diffusion current density limited by liquid phase diffusion. Therefore, this method can detect the limiting diffusion current density in the lithium-ion battery system to be tested, with high detection accuracy and simple operation.

[0083] The method in this application embodiment constructs a detection system comprising a first reference electrode and a second reference electrode. This system collects the potential changes at different locations on the second electrode under different operating conditions or current densities, thereby determining the diffusion-limited behavior of the battery circuit. This detection method, independent of complex modeling, is both real-time and adaptable, making it suitable for fast-charging optimization design in practical lithium batteries.

[0084] Figure 2 Schematic diagram of the structure of the second electrode and the second reference electrode provided in one embodiment of the present application is shown. Figure 2 The second electrode sheet includes a negative electrode current collector, the negative electrode current collector includes a groove, and the second reference electrode is arranged in the groove; the second electrode sheet also includes an insulating packaging film arranged on one side of the negative electrode current collector, and a negative electrode active material layer located on the side of the insulating packaging film away from the negative electrode current collector.

[0085] Figure 3 A schematic diagram of the preparation process of the second pole piece provided in one embodiment of the present application is shown.

[0086] See Figure 3 In some embodiments, the method for preparing the second pole piece includes: steps 150 to 153.

[0087] Step 150 , providing a groove on one side of the initial current collector connected to the tab to obtain a first current collector;

[0088] Step 151, placing a 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, may be 0.8 mm, and may further be 0.5 mm.

[0090] Step 152 , placing an insulating packaging film on the surfaces of the first current collector and the second reference electrode to fix the first current collector and the second reference electrode;

[0091] Optionally, the negative electrode active material layer and the insulating packaging film have matching outer projections. The outer contour of the negative electrode current collector matches the outer projection of the insulating packaging film.

[0092] Step 153 : coating the negative electrode active slurry on the surface of the insulating packaging film and drying it to obtain a second electrode sheet, which includes a negative electrode active material layer.

[0093] In some embodiments, after the negative electrode active slurry is coated on the surface of the insulating packaging film and dried, the method for preparing the second electrode sheet 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 sheet.

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

[0095] In some embodiments, the initial current collector or the negative electrode 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 polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer 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 that can extract and embed active ions, and the negative electrode active material can be a material known in the art. As an example, the negative electrode active material includes but is 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 alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present 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] The present application has no particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] The present application has no particular restriction on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (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 auxiliary agents may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like.

[0100] Figure 4 Schematic diagram of the potential of the first reference electrode and the second reference electrode at different current densities provided by an embodiment of the present application is shown; Figure 4 As shown in (a), at a current density of 40 mA, in the charging curve, the potential difference between the first reference electrode and the second reference electrode of the charging curve tends to be stable, and a potential difference can be obtained; Figure 4 As shown in (b), at a current density of 70 mA, in the charging curve, the potential difference between the first reference electrode and the second reference electrode of the charging curve tends to be stable, and another potential difference can be obtained; from this, it can be seen that at multiple different current densities, multiple potential differences are compared. When multiple potential differences are constant and maximum as the current changes, the first current density at which the potential difference maximum value appears can be taken as the limiting diffusion current density.

[0101] The second reference electrode can be prepared by placing an electrode that already meets the reference conditions in the groove of the second electrode piece, or by placing the raw material of the second reference electrode in the groove of the second electrode piece and preparing it in 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 produce 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, and the substrate is made of one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The preparation method of the second reference electrode includes:

[0103] Before operating the detection device to realize the battery circuit formation, that is, before step 300, lithium is deposited on the substrate to obtain a second reference electrode with stable potential.

[0104] In this embodiment, a dense and uniform metallic lithium layer is formed on the substrate by constant current electroplating. This electrochemical method "deposits" a layer of stable metallic lithium, making it have "0Vv.Li + / Li”, the reference capacity of metallic lithium and Li in electrolyte + Balance, forming a lithium battery pair, and a stable reference potential are beneficial for subsequent detection; it can also reduce interface side reactions and improve long-term stability.

[0105] Figure 5 A graph showing the lithiation of the second reference electrode provided in one embodiment of the present application is shown; 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 of operating the detection device and charging 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, includes:

[0107] Step 310, running the detection equipment;

[0108] It is understood that: before determining the maximum potential difference, before or after running the detection device, the battery circuit has been formed;

[0109] Step 320, during the charging phase of the i-cycle, controlling 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 a 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, where the second preset current is greater than the first preset current.

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

[0113] Optionally, during the charging process, pulse charging or constant voltage charging may be used.

[0114] The current can be increased in a gradient manner over different time periods.

[0115] In some embodiments, the detection equipment is operated to realize the battery circuit formation so as to form a solid electrolyte membrane and achieve the basic conditions for the battery circuit cycle, so that the lithium ions can be fully re-embedded into the second electrode by diffusion, and the potential of the second reference electrode can be accurately measured. For example, the first preset current and the second preset current increase in a gradient. In the charging stage of the first circle, the current is 1.0C, in the charging stage of the second circle, the current is 1.1C, in the charging stage of the third circle, the current is 1.2C, and so on. In the charging and discharging stages of any circle, the duration of the charging stage can be the same or different. Thus, by increasing the current, the lithium ion supply situation in the battery circuit can be judged in real time and accurately, and an accurate limiting diffusion current density can be obtained.

[0116] In some embodiments, the first preset current and the second preset current are in a range of [1*C to 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 corresponding to the full discharge of the lithium-ion battery at rated capacity within 1 hour or a specified time under standard test conditions, and the unit is ampere (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 preset current and the second preset current is [1*C~10*C], and can be selected as 1.1*C, 1.2*C, 1.3*C, 1.4*C, 1.5*C, 2*C, 3*C, 4*C, 5*C, 6*C, 7*C, 8*C, 9*C, 10*C, etc. The first preset current and the second preset current are greater than or equal to the rated current, which is conducive to increasing the current for testing and detecting the precise limiting diffusion current density in real time.

[0118] In this way, the efficiency of detection can be taken into account while improving the accuracy of detection.

[0119] In some embodiments, before detecting the potential difference between the first reference electrode and the second reference electrode and determining the maximum value of the potential difference during the charging phase of the multiple cycles of the battery circuit, the method further includes: performing a formation treatment on the battery. This helps improve the accuracy of the detection results.

[0120] In some embodiments, before running the detection device, 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) Charging 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, controlling the lithium-ion battery to charge with an increasing current 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 device for detecting the fast-charging limit diffusion current density of a lithium-ion battery provided in one embodiment of the present application is shown;

[0126] See Figure 6 The lithium-ion battery fast charge 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] A first acquisition module 210 is configured to acquire a negative electrode system and an electrolyte system in a testing device according to 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;

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

[0129] a current adjustment module 230 for operating the detection device and causing the battery circuit to charge with a first preset current during an i-cycle and a second preset current during an i+1-cycle, wherein the second preset current is greater than the first preset current, and i is a positive integer 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 value of the potential difference during the charging stage of multiple cycles of the battery circuit, and use the charging current density when the maximum potential difference first appears as the limiting diffusion current density of the lithium-ion battery to be tested.

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

[0132] Formation module, used to run the test equipment to achieve battery circuit formation;

[0133] A first current regulating 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 cycle;

[0134] The second current regulating module is used to control the current of the battery circuit to charge at a second preset current during the charging stage of the i+1 cycle, where 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 for an embodiment of the present application is shown.

[0136] 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), or an application-specific integrated circuit (ASIC), or may be configured to implement one or more integrated circuits of the embodiments of the present application.

[0138] The memory 702 may include a large capacity memory for data or instructions. By way of example and not limitation, the memory 702 may include a hard disk drive (HDD), a floppy disk drive, a flash memory, an optical disk, a magneto-optical disk, a magnetic tape, or a universal serial bus (USB) drive, or a combination of two or more of these. Where appropriate, the memory 702 may include removable or non-removable (or fixed) media. Where appropriate, the memory 702 may be inside or outside the integrated gateway disaster recovery device. In a specific embodiment, the memory 702 is a non-volatile solid-state memory.

[0139] The memory may include read-only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical or other physical / tangible memory storage devices. Thus, generally, the 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 method according to an aspect of the present disclosure.

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

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

[0142] Communication interface 703 is mainly used to realize the communication between each module, device, unit and / or equipment in the embodiment of the present application. Bus 710 includes hardware, software or both, and couples the components of the online data flow metering device to each other. For example, but not limitation, the bus may include Accelerated Graphics Port (AGP) or other graphics bus, Enhanced Industrial Standard Architecture (EISA) bus, Front Side Bus (FSB), HyperTransport (HT) interconnect, Industrial Standard Architecture (ISA) bus, InfiniBand interconnect, Low Pin Count (LPC) bus, memory bus, Micro Channel Architecture (MCA) bus, Peripheral Component Interconnect (PCI) bus, PCI-Express (PCI-X) bus, Serial Advanced Technology Attachment (SATA) bus, Video Electronics Standards Association Local (VLB) bus or other suitable bus or a combination of two or more of these. In appropriate cases, bus 710 may include one or more buses. Although the embodiment of the present application describes and shows a specific bus, the present application considers any suitable bus or interconnect.

[0143] The electronic device can execute the detection method in the embodiment of the present application, thereby realizing the combination Figure 1 Describe the detection method.

[0144] In addition, in conjunction with the detection methods in the above embodiments, embodiments of the present application may provide a computer-readable storage medium for implementation. The computer-readable storage medium stores computer program instructions; when the computer program instructions are executed by a processor, any one of the detection methods in the above embodiments is implemented.

[0145] In combination with the detection methods in the above embodiments, the embodiments of the present application may be implemented by providing a computer program product. When the instructions in the computer program product are executed by a processor of an electronic device, any one of the detection methods in the above embodiments is implemented.

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

[0147] The functional blocks shown in the above block 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 the present application are programs or code segments that are used to perform the required tasks. The program or code segment can be stored in a computer-readable storage medium, or transmitted on a transmission medium or a communication link by a data signal carried in a carrier wave. "Computer-readable storage medium" can include any medium that can store or transmit information. Examples of computer-readable storage media include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical disks, hard disks, optical fiber media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0148] It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, this application is not limited to the order of the above steps. In other words, 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 is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the scope of protection of the present application.

[0150] The beneficial effects of the detection method provided in this application are illustrated below through examples.

[0151] Example 1

[0152] This embodiment provides a method for detecting the fast-charging limit diffusion current density of a lithium-ion battery, comprising:

[0153] S100, obtaining a negative electrode system and an electrolyte system in a testing device according to 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;

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

[0155] S200, stacking a first electrode piece, a first isolation membrane, a first reference electrode, a second isolation membrane, and a second electrode piece in sequence in a first electrolyte of a detection device to form a battery circuit; wherein the second electrode piece includes:

[0156] A first current collector is prepared by providing a groove on one side of the initial current collector for connecting to the tab, and a 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 packaging 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;

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

[0160] Preparation of the negative electrode active material layer: 1200-mesh small-particle graphite powder was used as the raw material, and sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were used as the binder. First, sodium carboxymethyl cellulose (CMC) was dissolved in a certain amount of water to form a 1wt% transparent liquid. Graphite powder: conductive carbon black (SupperP): sodium carboxymethyl cellulose (CMC) was mixed with a certain amount of water in a mass ratio of 8:1:1 to prepare a slurry and evenly mixed. After fully dispersing without obvious particles, styrene-butadiene rubber (SBR) accounting for 5% of the total solid mass was added. The mixture was stirred at 200 rpm in a magnetic stirrer for 1 hour. A 100μm scraper was used to evenly apply the negative electrode slurry to the surface of the negative electrode current collector copper foil and the insulating packaging film. The negative electrode active material layer was 30μm thick and dried in a vacuum dryer for 24 hours. The second reference electrode and the first reference electrode were connected to the tabs respectively.

[0161] Preparation of the second reference electrode: For the assembled soft-pack battery, one side of the positive electrode is connected to the raw material of the second reference electrode, i.e. copper foil, and the negative electrode is connected to metallic lithium. A current of 0.02 mA is used to uniformly deposit lithium on the embedded copper foil for 40 hours to form a dense second reference electrode with long-term stable potential.

[0162] Assembly of graphite four-electrode soft-pack half-cells, formation and capacity testing: The assembled batteries were formed and cycled three times with a low current of 0.05C to activate the active materials and form a stable solid electrolyte membrane to obtain the actual capacity of the battery.

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

[0164] Specifically, the rated current of the battery is 20 mA, and the battery is charged and discharged at a current of 20 mA, and then the current is increased by 10 mA, and the current is continued to increase in this manner;

[0165] S400: Detecting the potential difference between the first reference electrode and the second reference electrode, determining the maximum potential difference during the charging phase of multiple cycles of the battery circuit, and using 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. A current of 76 mA is detected as the limiting diffusion current density of the lithium-ion battery.

[0166] The limiting diffusion current density formula is used to verify the experimental results:

[0167] Limiting diffusion current density formula:

[0168]

[0169] Among them, i d,lim is the limiting diffusion current density of the electrolyte, unit: A / m2 ;

[0170] n: The number of lithium ion transfer charges, usually a constant of 1;

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

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

[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, unit: m;

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

[0176] Example 2

[0177] The difference between this embodiment and Example 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 microns. The limiting diffusion current density is measured by the method of the embodiment of the present application, and is 69 mA. The limiting diffusion current density formula is used for calculation, and the calculation result of the limiting diffusion current density formula is 71 mA. The detection results of this application are more accurate.

[0178] Example 3

[0179] This embodiment differs from Example 1 in that the composition of the first electrolyte is different. Specifically, the first electrolyte includes LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate):DEC (diethyl carbonate), wherein the volume ratio of EC (ethylene carbonate):DEC (diethyl carbonate) is 3:7. Using the method of this embodiment, the limiting diffusion current density was measured to be 83 mA. Using the limiting diffusion current density formula, the calculated result was 81 mA, indicating that the test results of this embodiment are more accurate.

[0180] Example 4

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

[0182] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0183] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and intent of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for detecting the fast-charging limit diffusion current density of a lithium-ion battery, characterized in that: include: According to the lithium-ion battery system to be tested, obtaining a negative electrode system and an 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; The first electrode piece, the first isolation membrane, the first reference electrode, the second isolation membrane and the second electrode piece are sequentially stacked and arranged in the first electrolyte of the detection device to form a battery circuit; wherein the second electrode piece includes: a first current collector, wherein the first current collector is formed by providing a groove on one side of the initial current collector connecting tab, and a 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 packaging 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; Running the detection device and charging 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; The potential difference between the first reference electrode and the second reference electrode is detected, a maximum value of the potential difference is determined during a charging phase of multiple cycles of the battery circuit, and a charging current density when the maximum potential difference first occurs is used as the limiting diffusion current density of the lithium-ion battery to be tested.

2. The detection method according to claim 1, wherein The insulating packaging film comprises one or more of a lithium-ion battery separator material, a single-ion conductor polymer, and a composite material of a single-ion conductor polymer and an 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 aluminum oxide, cubic lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate; and / or, The insulating packaging film further includes a binder, and the binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

4. The detection method according to claim 1, wherein The materials of the first reference electrode and the second reference electrode include lithium, LiFePO4, Li4Ti5O 12 One or more of.

5. The detection method according to claim 1, wherein The first electrode sheet comprises one or more of lithium, lithium alloy, and a positive electrode sheet containing a positive electrode active material; and / or, The first isolation membrane and the second isolation membrane respectively include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride and ceramics.

6. The detection method according to claim 1, characterized in that The step of operating the detection device and charging the battery with a first preset current in an i-cycle and a second preset current in an i+1-cycle, wherein the second preset current is greater than the first preset current, includes: operating the detection equipment; During a charging phase in an i-cycle cycle, controlling the current of the battery circuit to charge at a first preset current; 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.

7. The detection method according to claim 6, characterized in that The range of the first preset current and the second preset current is [1*C to 10*C], where C is a multiple of the rated current of the lithium-ion battery.

8. The detection method according to claim 6, characterized in that The second reference electrode includes a substrate and a lithium metal layer disposed on the surface of the substrate, wherein the material of the substrate includes one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy; The preparation method of the second reference electrode comprises: Before operating the detection device to realize the battery circuit formation, Lithium is deposited on the substrate to obtain a second reference electrode with stable potential.

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

10. A device for detecting the fast-charging limit diffusion current density of a lithium-ion battery, characterized in that: include: A first acquisition module is configured to acquire a negative electrode system and an electrolyte system in a testing device according to a 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, configured to sequentially stack a first electrode sheet, a first separator, a first reference electrode, a second separator, and a second electrode sheet in the first electrolyte of the detection device to form a battery circuit; wherein the second electrode sheet comprises: a first current collector, the first current collector being formed by providing a groove on one side of the initial current collector for connection to the electrode tab, the second reference electrode being disposed in the groove; the negative electrode active material layer being disposed on at least one side of the first current collector; and an insulating packaging film being disposed between the negative electrode active material layer and the first current collector to secure the second reference electrode and the first current collector; a current adjustment module, configured to operate the detection device 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, and i is a positive integer greater than 1; a current density determination module, configured to detect the potential difference between the first reference electrode and the second reference electrode, determine the maximum value of the potential difference during the charging phase of multiple cycles of the battery circuit, and use the charging current density when the maximum potential difference first occurs as the limiting diffusion current density of the lithium-ion battery to be tested.

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