Method for detecting lithium precipitation of secondary battery, detection system, secondary battery, and battery pack

Abstract

The application discloses a lithium precipitation detection method and system for a secondary battery, a secondary battery and a battery pack. The detection method comprises the following steps: obtaining a first discharge capacity of a button cell at a first discharge rate and a second discharge capacity of the button cell at a second discharge rate, wherein the first discharge rate is less than the second discharge rate; and determining a lithium precipitation rate of the secondary battery by a linear corresponding relationship between a preset ratio of the second discharge capacity to the first discharge capacity and the lithium precipitation rate, when the ratio of the second discharge capacity to the first discharge capacity meets a preset numerical range. The application can accurately detect the lithium precipitation window of the secondary battery and improve the lithium precipitation detection efficiency, thereby improving the development speed of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a method, system, secondary battery and battery pack for detecting lithium plating in secondary batteries. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) are widely used in energy storage, consumer electronics, and new energy electric vehicles due to their advantages such as high energy density, no memory effect, and long life. However, this also places higher demands on their performance and safety.

[0003] Lithium deposition on the negative electrode surface (i.e., lithium plating) is a major cause of capacity decay and safety issues in secondary batteries. This is mainly because the deposited metallic lithium reacts with the electrolyte, consuming active lithium and accelerating capacity decay; at the same time, dendritic lithium may puncture the separator, causing a short circuit and leading to safety problems.

[0004] In current technologies for detecting lithium plating in secondary batteries, the process typically involves first preparing a full cell (usually a pouch cell) and then performing the detection based on that full cell. However, the complex structure of a full cell leads to a long sample preparation cycle, which in turn results in a time-consuming lithium plating detection process. This is particularly problematic for rapidly evolving lithium-ion batteries, hindering the improvement of lithium plating detection efficiency and consequently impeding the speed of lithium-ion battery development. Summary of the Invention

[0005] To address the aforementioned technical problems, this application discloses a method, system, secondary battery, and battery pack for detecting lithium plating in secondary batteries, which improves lithium plating detection efficiency while accurately detecting the lithium plating window of the secondary battery.

[0006] In a first aspect, this application provides a method for detecting lithium plating in secondary batteries, the method comprising:

[0007] The first discharge capacity of the coin cell at a first discharge rate and the second discharge capacity at a second discharge rate are obtained, wherein the first discharge rate is less than the second discharge rate.

[0008] When the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range, the lithium plating rate of the secondary battery is determined by the preset linear correspondence between the ratio and the lithium plating rate.

[0009] In some embodiments of this application, the linear correspondence is expressed as:

[0010] y = -0.41 + 24.47x

[0011] In the formula, x represents the ratio of the second discharge capacity to the first discharge capacity, and 0.05≤x≤0.32; y represents the lithium plating rate of the coin cell.

[0012] In some embodiments of this application, the first discharge rate is 0.01C to 0.4C, and the second discharge rate is 1C to 4C.

[0013] In some embodiments of this application, 1 ≤ y ≤ 4.

[0014] In some embodiments of this application, the method further includes:

[0015] The coin cell is subjected to a first constant current discharge operation at the first discharge rate to obtain the first discharge capacity.

[0016] After charging the coin cell to the target voltage at a first charging rate, the coin cell is subjected to a second constant current discharge operation at a second discharge rate to obtain the second discharge capacity.

[0017] In some embodiments of this application, the method further includes:

[0018] The first button cell is subjected to a first constant current discharge operation at the first discharge rate to obtain the first discharge capacity.

[0019] The second button cell is subjected to a second constant current discharge operation at the second discharge rate to obtain the second discharge capacity, wherein the first button cell and the second button cell have the same specifications and state.

[0020] In some embodiments of this application, the specifications include at least one of the following: shape, size, type of positive electrode material, type of negative electrode material, type of separator, and type of electrolyte of the coin cell; and the state includes at least one of the following: voltage, internal resistance, and state of charge of the coin cell.

[0021] In some embodiments of this application, the button cell has the same type of negative electrode material as the secondary battery.

[0022] In some embodiments of this application, the negative electrode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon-carbon.

[0023] Secondly, this application provides a lithium plating detection system for secondary batteries, the system comprising:

[0024] A discharge capacity acquisition module is used to acquire the first discharge capacity of the coin cell at a first discharge rate and the second discharge capacity at a second discharge rate, wherein the first discharge rate is less than the second discharge rate.

[0025] The lithium plating rate determination module is used to determine the lithium plating rate of the secondary battery by means of a preset linear correspondence between the ratio between the second discharge capacity and the first discharge capacity, provided that the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range.

[0026] Thirdly, this application provides a secondary battery whose lithium plating window is determined by the secondary battery lithium plating detection method described in the first aspect.

[0027] Fourthly, this application provides a battery pack including a housing and at least one secondary battery as described in the third aspect, the secondary battery being housed within the housing.

[0028] Fifthly, this application provides an electrical device including the secondary battery described in the third aspect or the battery pack described in the fourth aspect.

[0029] Compared with the prior art, this application has at least the following beneficial effects:

[0030] This application provides a method, system, battery, and battery pack for detecting lithium plating in secondary batteries. The method obtains the first discharge capacity of a coin cell at a first discharge rate and the second discharge capacity at a second discharge rate, thus determining the ratio between the second and first discharge capacities. When this ratio meets a preset range, the lithium plating rate of the secondary battery is determined through a preset linear relationship between this ratio and the lithium plating rate. This lithium plating rate is the lithium plating window of the secondary battery. On one hand, the lithium plating detection method of this application is based on the discharge operation of the coin cell, which has a shorter sample preparation cycle compared to a full cell, thus reducing the overall time spent on the lithium plating detection process. On the other hand, the lithium plating rate of this application is directly determined through a preset linear relationship between the ratio and the lithium plating rate, eliminating the need for complex calculations. Furthermore, this lithium plating detection method is a non-destructive testing method that does not require battery disassembly, avoiding the time spent on battery disassembly. Therefore, compared with existing lithium plating detection methods based on full cells, this application can not only accurately detect the lithium plating window of secondary batteries, but also improve the lithium plating detection efficiency, thereby accelerating the development of secondary batteries. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1This is a flowchart illustrating a method for detecting lithium plating in a secondary battery according to one embodiment of this application.

[0033] Figure 2 This is a schematic diagram of the structure of a secondary battery lithium plating detection system according to one embodiment of this application;

[0034] Figure 3 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application;

[0035] Figure 4 This is a schematic diagram of the energy storage system in one embodiment of this application;

[0036] Figure 5 This is a schematic diagram showing the relationship between different discharge rates and specific capacities of the coin cell prepared in Example 1-1 of this application;

[0037] Figure 6 This is a schematic diagram illustrating the lithium plating window characterization based on the determined linear correspondence and the actual lithium plating rate of the full cell in this application.

[0038] Explanation of reference numerals in the attached drawings: 1-Energy storage device, 2-Electric power conversion device, 3-First user load, 4-Second user load, 200-Lithium plating detection system, 201-Discharge capacity acquisition module, 202-Lithium plating rate determination module, 400-Energy storage system, 410-High voltage cable, 420-First electric power conversion device, 430-Second electric power conversion device. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0041] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0042] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0043] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, components, or parts (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, components, or parts. Unless otherwise stated, "a plurality of" means two or more.

[0044] It should be noted that in this application, lithium-ion batteries or full batteries are used as examples of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries or full batteries.

[0045] Among related technologies, commonly used lithium plating detection methods include electrochemical testing and in-situ spectroscopic analysis. Electrochemical testing can perform in-situ analysis, but its detection accuracy is low, and lithium plating signals cannot be observed at room temperature. In-situ spectroscopic analysis requires expensive specialized instruments and equipment, making it difficult to use in actual lithium-ion batteries designed and put into production.

[0046] In view of this, this application provides a method for detecting lithium plating in secondary batteries, such as... Figure 1 As shown, it includes the following steps:

[0047] S101, obtain the first discharge capacity of the coin cell at the first discharge rate and the second discharge capacity at the second discharge rate.

[0048] The executing entity of this application may be a testing device. For example, when the executing entity is a testing device, the testing device can obtain the first discharge capacity of the coin cell at a first discharge rate, and obtain the second discharge capacity of the coin cell at a second discharge rate, wherein the first discharge rate is less than the second discharge rate.

[0049] The button cell in this application refers to a coin cell battery, which typically includes a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. The coin cell battery can be circular or rectangular in shape, and the casing can be made of steel. The positive electrode of the coin cell battery is made of lithium.

[0050] During the discharge of the coin cell battery at a first discharge rate, the coin cell battery can be discharged from its full charge voltage to a first preset voltage, and then discharged at a constant voltage to the first preset rate. For example, the full charge voltage can be 1.5V, the first preset voltage can be 0.01V, and the first preset rate can be 0.01C. During the discharge of the coin cell battery at a second discharge rate, the coin cell battery can be charged to a second preset voltage, and then discharged from the second preset voltage to a third preset voltage. For example, the second preset voltage can be 1.5V, and the third preset voltage can be 0.01V. The first preset voltage and the third preset voltage can be the same or different.

[0051] The secondary battery of this application includes a full battery, which typically includes a positive electrode, a negative electrode, a separator, an electrolyte, and a casing, the casing being made of a soft-pack material. The negative electrode of the secondary battery includes a negative electrode material layer, and the negative electrode material layer includes negative electrode material.

[0052] S102, when the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range, the lithium plating rate of the secondary battery is determined by the preset linear correspondence between the ratio and the lithium plating rate.

[0053] In the electrochemical system of a full cell (such as a pouch cell), assuming other conditions such as the positive electrode, separator, and electrolyte remain constant, the kinetic performance of the negative electrode material determines the lithium plating window of the full cell. During high-power charging of a full cell, lithium ions cannot be completely intercalated into the negative electrode material, thus depositing on its surface and causing lithium plating. The inventors discovered that current lithium plating detection methods typically use full cells for testing because it is generally believed that lithium plating usually only occurs in full cells and is difficult to occur in coin cells. This common understanding leads battery developers to determine the lithium plating window solely based on lithium plating detection of full cells, without considering other possibilities. The inventors' research revealed that in coin cells, since the potential of the lithium electrode is usually lower than that of the negative electrode material, the lithium electrode can be considered the negative electrode, and the negative electrode material can be considered the positive electrode. Therefore, the discharge process of a coin cell can be viewed as a lithium intercalation process of the negative electrode material. Furthermore, when the discharge rate remains constant, the negative electrode discharge capacity of the negative electrode material can represent its ability to intercalate lithium ions. Further research by the inventors revealed a positive correlation between the ratio of discharge capacities at different discharge rates and the lithium plating rate of the full cell when coin cells are discharged at different rates. Based on this finding, this application creatively determines the lithium plating rate of the full cell by discharging coin cells and observing the positive correlation between the ratio of discharge capacities at different discharge rates and the lithium plating rate of the full cell. The lithium plating rate refers to the charging rate at which lithium plating occurs in a secondary battery, and it can be used to represent the lithium plating window of the secondary battery. Using the lithium plating detection method of this application, only coin cells can be prepared for new negative electrode material samples to test the ratio of discharge capacities at different discharge rates, thereby determining the lithium plating rate of the full cell, i.e., the lithium plating window. This allows for parallel comparison with negative electrode material samples whose lithium plating windows have been previously tested. Furthermore, negative electrode material samples whose lithium plating windows have been previously tested do not require the preparation of coin cells, significantly saving time and resources.

[0054] This application provides a lithium plating detection method for secondary batteries. Firstly, this method is based on the discharge operation of coin cells, resulting in a shorter sample preparation cycle compared to full cells, thus reducing the overall lithium plating detection time. Secondly, the lithium plating rate is directly determined through a preset linear relationship between a ratio and the lithium plating rate, eliminating the need for complex calculations. Furthermore, this method is a non-destructive testing method that does not require battery disassembly, avoiding the time spent on battery disassembly. Therefore, compared to existing lithium plating detection methods based on full cells, this application can accurately detect the lithium plating window of secondary batteries while improving detection efficiency, thereby accelerating the development of secondary batteries.

[0055] In some embodiments of this application, the linear correspondence is expressed as:

[0056] y = -0.41 + 24.47x

[0057] In the formula, x represents the ratio of the second discharge capacity to the first discharge capacity, and 0.05≤x≤0.32; y represents the lithium plating rate of the coin cell.

[0058] Through the above linear correspondence, the lithium plating rate of secondary batteries can be detected simply, quickly, efficiently, and accurately, thereby improving the lithium plating detection efficiency, accelerating the lithium plating detection cycle of secondary batteries, and thus increasing the research and development speed of secondary batteries. This is conducive to the development of lithium-ion batteries with better kinetic performance and greater safety.

[0059] In some embodiments of this application, the first discharge rate is 0.01C to 0.4C, and the second discharge rate is 1C to 4C; in some embodiments, the first discharge rate is 0.19C to 0.21C, and the second discharge rate is 1.9C to 2.1C. For example, the first discharge rate is 0.01C, 0.04C, 0.1C, 0.15C, 0.19C, 0.2C, 0.21C, 0.3C, or 0.4C; and the second discharge rate is 1C, 1.5C, 1.9C, 2C, 2.1C, 2.5C, 3C, or 4C. The inventors discovered that a larger ratio of the second discharge capacity at the second discharge rate to the first discharge capacity at the first discharge rate indicates better kinetic performance of the negative electrode material, higher lithium intercalation efficiency, and a correspondingly higher lithium plating window; conversely, a smaller ratio indicates poorer kinetic performance of the negative electrode material, lower lithium intercalation efficiency, and a lower lithium plating window. Based on this, this application, by adjusting the first and second discharge rates within the aforementioned ranges, can better characterize the kinetic performance of the negative electrode material, thereby accurately detecting the lithium plating window of the secondary battery.

[0060] In some embodiments of this application, 1 ≤ y ≤ 4. When the lithium plating rate is within the above range, the lithium plating window determined by the linear correspondence is closer to the actual lithium plating window of the secondary battery, thus reflecting the lithium plating window of the secondary battery more accurately.

[0061] In some embodiments of this application, the lithium plating detection method further includes:

[0062] i. Perform a first constant current discharge operation on the button cell at a first discharge rate to obtain the first discharge capacity;

[0063] ii. After charging the button cell to the target voltage at the first charging rate, perform a second constant current discharge operation on the button cell at the second discharge rate to obtain the second discharge capacity.

[0064] Step i can be placed before step S101. In this application, the same coin cell can be used to perform the first constant current discharge operation and the second constant current discharge operation to obtain the first discharge capacity and the second discharge capacity. This reduces the detection error caused by using different coin cells and improves the accuracy of lithium plating detection.

[0065] In some embodiments of this application, the lithium plating detection method further includes:

[0066] i' Perform a first constant current discharge operation on the first button cell at a first discharge rate to obtain the first discharge capacity;

[0067] ii'. Perform a second constant current discharge operation on the second button cell at a second discharge rate to obtain a second discharge capacity, wherein the first button cell and the second button cell have the same specifications and state.

[0068] Step i' can be performed before step S101. In this application, coin cells of the same specifications and condition can be used to perform a first constant current discharge operation and a second constant current discharge operation, respectively, to obtain a first discharge capacity and a second discharge capacity. Thus, the first and second constant current discharge operations can be performed in parallel, thereby improving the lithium plating detection efficiency. Using coin cells of the same specifications and condition reduces detection errors and improves the accuracy of lithium plating detection.

[0069] In some embodiments of this application, the specifications of the coin cell include at least one of the following: shape, size, type of positive electrode material, type of negative electrode material, type of separator, and type of electrolyte. The state of the coin cell includes at least one of the following: voltage, internal resistance, and state of charge (SOC). This application improves the accuracy of lithium plating detection by selecting coin cells of the same specifications and state.

[0070] In some embodiments of this application, the coin cell and the secondary battery have the same type of negative electrode material. For example, when the negative electrode material of the secondary battery is natural graphite, the negative electrode material of the coin cell is also natural graphite; or, when the negative electrode material of the secondary battery is artificial graphite, the negative electrode material of the coin cell is also artificial graphite. Thus, the lithium plating window determined by the lithium plating detection method of this application is closer to the actual lithium plating window of the secondary battery, and therefore can more accurately reflect the lithium plating window of the secondary battery.

[0071] In some embodiments of this application, the negative electrode material includes at least one selected from artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon-carbon. These negative electrode materials exhibit excellent kinetic performance, thus the resulting secondary batteries are less prone to lithium plating, resulting in higher battery safety and making them more suitable for energy storage applications.

[0072] In some embodiments of this application, the negative electrode material can be secondary particles obtained by granulation of primary particles, which is beneficial to obtaining a negative electrode material with the desired particle size distribution.

[0073] Based on the aforementioned embodiments, this application provides a secondary battery lithium plating detection system. The modules and units included in the system can be implemented by a processor; of course, they can also be implemented by specific logic circuits. In the implementation process, the processor can be a central processing unit (CPU), a microprocessor (MPU), a digital signal processor (DSP), or a field programmable gate array (FPGA), etc.

[0074] Figure 2 This is a schematic diagram of the secondary battery lithium plating detection system provided in this application, as shown below. Figure 2 As shown, the lithium plating detection system 200 includes a discharge capacity acquisition module 201 and a lithium plating rate determination module 202, wherein,

[0075] The discharge capacity acquisition module is used to acquire the first discharge capacity of the coin cell at a first discharge rate and the second discharge capacity at a second discharge rate, wherein the first discharge rate is less than the second discharge rate.

[0076] The lithium plating rate determination module is used to determine the lithium plating rate of the secondary battery by means of a preset linear correspondence between the ratio between the second discharge capacity and the first discharge capacity, provided that the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range.

[0077] This application provides a lithium plating detection system for secondary batteries. A discharge capacity acquisition module obtains the first discharge capacity of a coin cell at a first discharge rate and the second discharge capacity at a second discharge rate, thus obtaining the ratio between the second and first discharge capacities. When this ratio meets a preset range, a lithium plating rate determination module determines the lithium plating rate of the secondary battery through a preset linear correspondence between the ratio and the lithium plating rate. This lithium plating rate is the lithium plating window of the secondary battery. On one hand, this application is based on the discharge operation of coin cells, which has a shorter sample preparation cycle compared to full cells, thus reducing the overall lithium plating detection time. On the other hand, the lithium plating rate of this application is directly determined through a preset linear correspondence between the ratio and the lithium plating rate, eliminating the need for complex calculations. Furthermore, the lithium plating detection method of this application is a non-destructive testing method that does not require battery disassembly, avoiding the time spent on battery disassembly. Therefore, this application can accurately detect the lithium plating window of secondary batteries while improving lithium plating detection efficiency, thereby accelerating the development of secondary batteries.

[0078] The secondary battery of this application also includes a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode and plays a role in isolation.

[0079] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet typically includes a positive current collector and a positive electrode material layer. The positive electrode material layer can be disposed on one surface or two surfaces in the thickness direction of the positive current collector. In this application, the positive electrode material layer is disposed on the surface of the positive current collector, that is, the positive electrode material layer can be disposed on a portion of a surface of the positive current collector or on the entire surface of a surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application, such as including but not limited to aluminum foil, aluminum alloy foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application, such as a thickness of 10 μm to 20 μm. The thickness of the positive electrode material layer in this application can be 150 μm to 400 μm.

[0080] In this application, the positive electrode material layer includes a positive electrode material. This application does not have any particular restrictions on the positive electrode material, as long as it can achieve the purpose of this application. For example, it may include at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, and lithium titanate.

[0081] In this application, the positive electrode material layer may further include a positive electrode conductive agent. This application does not impose any particular limitation on the positive electrode conductive agent, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, acetylene black, and graphene. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. In this application, the positive electrode material layer may further include a positive electrode binder. This application does not impose any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of fluorinated resins, polypropylene resins, fiber-type binders, rubber-type binders, or polyimide-type binders.

[0082] This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet typically includes a negative current collector and a negative electrode material layer. The negative electrode material layer can be disposed on one or both surfaces of the negative current collector in the thickness direction. In this application, the negative electrode material layer is disposed on the surface of the negative current collector, that is, the negative electrode material layer can be disposed on a portion of one surface of the negative current collector, or it can be disposed on the entire surface of one surface of the negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative current collector, as long as it achieves the purpose of this application, for example, a thickness of 4 μm to 12 μm. The thickness of the negative electrode material layer in this application can be 70 μm to 200 μm.

[0083] In this application, the negative electrode material layer may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, it may include at least one of acrylate, polyamide, polyimide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0084] This application does not impose any particular limitation on the diaphragm; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0085] The secondary battery of this application also includes a casing. This application does not impose any particular restrictions on the casing, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the casing may include an aluminum-plastic film.

[0086] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, separator and negative electrode in sequence, and winding and folding them as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0087] The negative electrode, separator, and electrolyte of the button cell in this application can be the same as those of the secondary battery, and this application does not make any specific limitations.

[0088] This application also provides a battery pack, including a housing and at least one secondary battery as described in any of the above embodiments, the secondary battery being housed within the housing. The battery pack with this secondary battery exhibits excellent performance, which is beneficial for its use. Housed within the housing, the battery is secured and protected, thus extending the battery pack's lifespan. It is understood that the battery pack may contain one or more secondary batteries, and when the battery pack contains multiple secondary batteries, these batteries can be connected in at least one manner, such as parallel or series connection.

[0089] This application also provides an electrical device including a secondary battery or battery pack as described in any of the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In an optional embodiment, the electrical device includes an electrical device body, and the secondary battery or battery pack is used to supply power to the electrical device body. In an optional embodiment, the electrical device body includes a positive terminal and a negative terminal, the positive terminal of the secondary battery or battery pack is used to electrically connect to the positive terminal of the electrical device body, and the negative terminal of the secondary battery or battery pack is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0090] The electrical equipment covered by this application may include, but is not limited to: containers, household energy storage systems, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0091] Please see Figure 3 , Figure 3 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application, and this application... Figure 3 The implementation plan is illustrated using the residential energy storage scenario in user-side energy storage as an example. The energy storage device in this application is not limited to the residential energy storage scenario.

[0092] This application provides a residential energy storage system, which includes a power conversion device 2 (photovoltaic panel), a first user load 3 (streetlight), a second user load 4 (e.g., household appliances such as air conditioners), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 1 is used to store this electrical energy and supply it to streetlights and household appliances during periods of high electricity prices, or to provide power during power outages / power failures.

[0093] Please see Figure 4 , Figure 4 This is a schematic diagram of the structure of an energy storage system 400 according to one embodiment of this application, and this application Figure 4 The implementation plan is illustrated using the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1 in this application is not limited to the power generation / distribution side energy storage scenario.

[0094] This application provides an energy storage system 400, which includes a high-voltage cable 410, a first power conversion device 420, a second power conversion device 430, and the energy storage device 1 provided in this application. During power generation, the first power conversion device 420 and the second power conversion device 430 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable 410 and supplied to the power consumption side of the distribution network. When the power load is low and the first conversion device 420 and the second power conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1, along with the high-voltage cable 410, in a grid-connected mode to supply power to the power consumption side. This provides various services such as peak shaving, frequency regulation, and backup for the power grid operation, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0095] Optionally, the first power conversion device 420 and the second power conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0096] The number of energy storage devices 1 can be multiple, and these devices can be connected in series or in parallel. The multiple energy storage devices 1 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" refers to two or more. An energy storage box can also be provided outside the energy storage device 1 to house it.

[0097] Optionally, the energy storage device 1 may include, but is not limited to, a single battery cell, a battery module, a battery pack, or a battery system. The actual application form of the energy storage device 1 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 1. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 1 is a single battery cell, the energy storage device 1 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0098] Example

[0099] The following examples, embodiments, and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0100] Preparation Example 1-1

[0101] Preparation of button cell (half-cell):

[0102] <Preparation of Negative Electrode Sheets>

[0103] The negative electrode material is artificial graphite (average particle size D). 50 A mixture of 13μm secondary particles, conductive carbon black (Super-P), and carboxymethyl cellulose (CMC) was prepared at a mass ratio of 80:10:10. Deionized water was added to form a negative electrode slurry with a solid content of 60wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6μm thick copper foil current collector, and dried to obtain a negative electrode sheet. The obtained negative electrode sheet was rolled and then punched to obtain a circular negative electrode sheet with a diameter of 12mm and a thickness of 100μm.

[0104] <Preparation of Electrolyte>

[0105] In an argon-atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Lithium salt LiPF6 was then added and dissolved in the solvent. After thorough mixing, the electrolyte was obtained. The molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0106] <Preparation of the diaphragm>

[0107] A porous polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0108] Assembly of button batteries

[0109] The prepared 12mm diameter circular lithium sheet, separator, and circular negative electrode are stacked in sequence, with the separator positioned between the circular lithium sheet and the negative electrode to act as a separator. Then, the prepared electrolyte is injected to assemble a coin cell.

[0110] Preparation Examples 1-2

[0111] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the secondary particles being 15 μm, the preparation method was the same as in Preparation Example 1-1.

[0112] Preparation Examples 1-3

[0113] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles of 9 μm, the preparation method is the same as in Preparation Example 1-1.

[0114] Preparation Examples 1-4

[0115] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the 11 μm single particles, the preparation method is the same as in Preparation Example 1-1.

[0116] Preparation Examples 1-5

[0117] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the 13μm single particles, the preparation method is the same as in Preparation Example 1-1.

[0118] Preparation Examples 1-6

[0119] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles being 15 μm in size, the preparation method was the same as in Preparation Example 1-1.

[0120] Preparation Example 2-1

[0121] Preparation of lithium-ion batteries (full cells):

[0122] <Preparation of the positive electrode>

[0123] Lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and binder PVDF were mixed in a mass ratio of 94:3:3. Then, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 60wt%, and stirred evenly. The positive electrode slurry was then uniformly coated on one surface of a 10μm thick aluminum foil for the positive electrode current collector. After drying, cold pressing, slitting, and cutting, a positive electrode sheet with a thickness of 250μm was obtained.

[0124] <Preparation of Negative Electrode Sheets>

[0125] Artificial graphite (same as in Preparation Example 1-1), conductive carbon black (Super-P), and carboxymethyl cellulose (Carboxymethyl cellulose) were mixed in a mass ratio of 80:10:10. Deionized water was added to prepare a negative electrode slurry with a solid content of 60 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated on one surface of a 6 μm thick copper foil current collector. After drying, cold pressing, slitting, and cutting, a negative electrode sheet with a thickness of 100 μm was obtained.

[0126] <Preparation of Electrolyte>

[0127] Same as preparation example 1-1.

[0128] <Preparation of the diaphragm>

[0129] Same as preparation example 1-1.

[0130] <Preparation of Lithium-ion Batteries>

[0131] The positive electrode, separator, and negative electrode obtained above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0132] Preparation Example 2-2

[0133] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the secondary particles being 15 μm, the preparation method is the same as in Preparation Example 2-1.

[0134] Preparation Examples 2-3

[0135] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles of 9 μm, the preparation method is the same as in Preparation Example 2-1.

[0136] Preparation Examples 2-4

[0137] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles being 11 μm in size, the preparation method was the same as in Preparation Example 2-1.

[0138] Preparation Examples 2-5

[0139] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles being 13 μm, the preparation method was the same as in Preparation Example 2-1.

[0140] Preparation Examples 2-6

[0141] In addition to adjusting the average particle size D of artificial graphite in the <Preparation of Negative Electrode Sheets>, 50 Except for the single particles being 15 μm in size, the preparation method was the same as in Preparation Example 2-1.

[0142] Example 1

[0143] Determination of Discharge Capacity Ratio

[0144] The coin cell prepared in Preparation Example 1-1 was fully charged (1.5V), left to stand at 25°C for 15 minutes, then discharged to 0.01V at 0.2C (first discharge rate), and then discharged at a constant voltage to 0.01C. The sampling points were spaced 20 seconds apart to obtain the first discharge capacity of the coin cell at the first discharge rate. Then, it was left to stand for 15 minutes, charged to 1.5V at a charging rate of 0.2C, left to stand for 15 minutes, and then discharged to 0.01V at 2C (second discharge rate). The sampling points were spaced 2 seconds apart to obtain the second discharge capacity of the coin cell at the second discharge rate. The ratio of the second discharge capacity to the first discharge capacity was then calculated and denoted as 2DC / 0.2DC.

[0145] <Determination of Theoretical Lithium Plating Ratio>

[0146] Substituting the ratio of the second discharge capacity to the first discharge capacity into the expression: y = -0.41 + 24.47x, the theoretical lithium plating rate is calculated, as detailed in Table 1.

[0147] Examples 2 to 6

[0148] Except for the coin cells selected from Preparation Examples 1-2 to 1-6 as shown in Table 1, the rest were the same as in Example 1. The ratio of the second discharge capacity to the first discharge capacity is shown in Table 1.

[0149] Examples 7 to 8

[0150] Except for adjusting the first discharge rate and the second discharge rate as shown in Table 2, the rest is the same as in Example 1. The ratio of the second discharge capacity to the first discharge capacity is shown in Table 1.

[0151] Comparative Example 1

[0152] The full cell prepared in Preparation Example 2-1 was selected, allowed to stand at 25°C for 15 min, fully charged (3.65V), discharged at 2C to 2.5V, and then allowed to stand for 15 min. Immediately afterwards, it was charged at 2C to 3.65V, and then allowed to stand for 15 min. This constituted one cycle. The above charge-discharge cycle was repeated 10 times, and the actual lithium plating rate of the full cell was measured.

[0153] Comparative Examples 2 to 6

[0154] Except for the full cells selected from Preparation Examples 2-2 to 2-6 as shown in Table 1, the rest are the same as those in Comparative Example 1.

[0155] Table 1 Performance parameters of Examples 1-6 and Comparative Examples 1-6

[0156]

[0157]

[0158] Table 2 Performance parameters of Examples 1, 7-8

[0159] First discharge rate (C) Second discharge rate (C) Lithium plating rate (C) Example 1 0.2 2 2.89 Example 7 0.01 1 2.76 Example 8 0.4 4 3.22

[0160] As can be seen from Examples 1 to 6 and Comparative Examples 1 to 6, the lithium plating rate determined by the lithium plating detection method of this application is very close to the actual lithium plating rate obtained based on full-cell testing. Furthermore, the lithium plating detection method of this application is based on the discharge operation of coin cells, which has a shorter sample preparation cycle compared to full-cell testing, thus reducing the overall lithium plating detection time. Therefore, the lithium plating detection method of this application can accurately detect the lithium plating window of secondary batteries while also improving lithium plating detection efficiency.

[0161] The first and second discharge rates typically also affect the detected lithium plating rate. As can be seen from Examples 1 and 7-8, by controlling the first and second discharge rates within the scope of this application, the lithium plating rate of the secondary battery can be accurately detected.

[0162] Figure 5 This diagram illustrates the relationship between different discharge rates and specific capacities for three coin cells (denoted as A-1, A-2, and A-3) prepared in Example 1-1 of this application. The numbers 1, 2, 3, 4, 5, and 6 represent the corresponding cycle numbers. From cycle 1 to cycle 6, the discharge rates for each cycle are 0.1C, 0.2C, 0.2C, 0.2C, 1C, and 2C, respectively, while the charging rate is 2C for all cycles, and all cycles are performed after a full charge. The diagram shows that the three broken lines largely overlap, indicating that the coin cells based on the same negative electrode material exhibit stable test results and effectively reflect the relationship between different discharge rates and specific capacities.

[0163] Figure 6 This is a schematic diagram characterizing the lithium plating window of the actual lithium plating rate of the full cell measured by Comparative Examples 1 to 6, based on the linear correspondence determined by the second discharge capacity / first discharge capacity ratio of Examples 1 to 6 in this application. Figure 6 In the diagram, the dashed line represents the expression for the linear correspondence in this application, and each point represents the actual lithium plating rate. From... Figure 6 As can be seen, the points are distributed near both sides of the imaginary line, indicating that the linear correspondence expression of this application can accurately reflect the lithium plating window of the full cell.

[0164] The foregoing has provided a detailed description of a lithium plating detection method, detection system, secondary battery, and battery pack for secondary batteries disclosed in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for detecting lithium plating in secondary batteries, characterized in that, The method includes: The first discharge capacity of the coin cell at a first discharge rate and the second discharge capacity at a second discharge rate are obtained, wherein the first discharge rate is less than the second discharge rate. When the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range, the lithium plating rate of the secondary battery is determined by the preset linear correspondence between the ratio and the lithium plating rate. The coin cell includes a lithium sheet and a negative electrode material, and the coin cell has the same type of negative electrode material as the secondary battery.

2. The lithium plating detection method according to claim 1, characterized in that, The linear correspondence is expressed as follows: y = -0.41 + 24.47x In the formula, x represents the ratio of the second discharge capacity to the first discharge capacity, and 0.05≤x≤0.32; y represents the lithium plating rate of the coin cell.

3. The lithium plating detection method according to claim 1 or 2, characterized in that, The first discharge rate is 0.01C to 0.4C, and the second discharge rate is 1C to 4C.

4. The lithium plating detection method according to claim 2, characterized in that, 1≤y≤4。 5. The lithium plating detection method according to claim 1 or 2, characterized in that, The method further includes: The coin cell is subjected to a first constant current discharge operation at the first discharge rate to obtain the first discharge capacity. After charging the coin cell to the target voltage at a first charging rate, the coin cell is subjected to a second constant current discharge operation at a second discharge rate to obtain the second discharge capacity.

6. The lithium plating detection method according to claim 1 or 2, characterized in that, The method further includes: The first button cell is subjected to a first constant current discharge operation at the first discharge rate to obtain the first discharge capacity. The second button cell is subjected to a second constant current discharge operation at the second discharge rate to obtain the second discharge capacity, wherein the first button cell and the second button cell have the same specifications and state.

7. The lithium plating detection method according to claim 6, characterized in that, The specifications include at least one of the following: shape, size, type of positive electrode material, type of negative electrode material, type of separator, and type of electrolyte of the coin cell; the state includes at least one of the following: voltage, internal resistance, and state of charge of the coin cell.

8. The lithium plating detection method according to claim 1, characterized in that, The negative electrode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon-carbon.

9. A lithium plating detection system for secondary batteries, characterized in that, The system includes: A discharge capacity acquisition module is used to acquire the first discharge capacity of the coin cell at a first discharge rate and the second discharge capacity at a second discharge rate, wherein the first discharge rate is less than the second discharge rate. The lithium plating rate determination module is used to determine the lithium plating rate of the secondary battery by means of a preset linear correspondence between the ratio between the second discharge capacity and the first discharge capacity, provided that the ratio between the second discharge capacity and the first discharge capacity meets a preset numerical range. The coin cell includes a lithium sheet and a negative electrode material, and the coin cell has the same type of negative electrode material as the secondary battery.

Images