Lithium precipitation detection method and lithium precipitation detection system

Abstract

The invention provides a lithium precipitation detection method, and solves the technical problem that an inflection point of lithium precipitation cannot be quickly determined in the prior art. According to the lithium precipitation detection method provided by the invention, the whole battery is charged by adopting a plurality of charge-discharge cycle times, the last voltage value is recorded during each charge-discharge cycle, the impedance value corresponding to the target electric quantity value is calculated according to the last voltage value, and whether lithium precipitation occurs or not is determined according to the impedance values corresponding to the plurality of target electric quantity values. When the impedance values corresponding to a plurality of continuous target electric quantity values are found to be reduced, the lithium precipitation inflection point can be correspondingly obtained, the lithium precipitation behavior can be detected without damaging the whole battery and constructing a model, and the method for detecting the lithium precipitation behavior is simple and convenient. In addition, coupling with a battery charging and discharging program is easy, if a lithium precipitation behavior occurs, the charging and discharging program of the battery is adjusted during lithium precipitation, and the lithium precipitation behavior on the surface of the negative electrode of the battery is prevented, so that the overall safety performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium deposition detection, and in particular to a lithium deposition detection method and a lithium deposition detection system. Background Art

[0002] Currently, commercial lithium-ion batteries are widely used in 3C digital products, electric vehicles, energy storage equipment and other fields. In the context of the popularization of lithium-ion batteries, their safety and electrochemical performance are particularly important, especially the battery life, rate performance, safety performance and lithium plating characteristics. Among them, the lithium plating problem has always been the focus of attention. Lithium plating not only has a significant impact on the cycle performance of the battery, but also poses a hidden danger to the safety of the battery that cannot be ignored. Therefore, it is necessary to conduct lithium plating detection on the battery, so as to prevent battery accidents in advance.

[0003] In the prior art, the method for detecting lithium deposition in batteries is to use the principle that the overall impedance of the negative electrode surface decreases when lithium deposition occurs, and to determine the node where lithium deposition occurs by impedance monitoring. This method uses a pulse charging method to obtain the impedance value of the battery, wherein the pulse charging method means charging the battery using a cyclic charging-relaxation charging method. Since lithium deposition usually occurs when lithium ions cannot be embedded in the electrode material in time, lithium is deposited on the negative electrode surface in the form of metallic lithium, and pulse charging provides sufficient time for lithium ions to be fully embedded in graphite, thereby delaying the inflection point of lithium deposition. However, the time for analyzing the lithium deposition behavior of the battery using the pulse charging method is relatively long, and the inflection point of lithium deposition cannot be quickly determined, so that measures cannot be quickly taken to prevent lithium deposition from occurring on the negative electrode surface of the battery to improve the overall safety performance of the battery. Summary of the invention

[0004] In order to solve the above technical problems, the present application is proposed. The embodiment of the present application provides a lithium plating detection method, including: determining the number of charge and discharge cycles of a full battery and determining the power increase value corresponding to each charge and discharge cycle; based on a constant capacity current, discharging the full battery after each charge to a cut-off voltage and then standing for a first preset time period; wherein the full battery after charge is a full battery charged at a target rate; according to the target rate and the power increase value, charging the full battery so that the power value of the full battery after charge at the number of charge and discharge cycles reaches the target power value, and the target power value is the sum of the power value of the full battery before charging and the power increase value; according to the last voltage value of the full battery after charge, calculating the impedance value of the full battery at the target power value; according to the impedance value of the full battery at different target power values, determining the lithium plating inflection point; wherein the lithium plating inflection point indicates that when the full battery is charged at the target rate, the impedance value corresponding to multiple consecutive target power values ​​decreases.

[0005] In an embodiment of the present application, determining the lithium plating inflection point according to the impedance values of the full cell at different target state-of-charge (SOC) values includes: plotting the correspondence between different target SOC values and the impedance values of their corresponding full cells as first identification points; arranging multiple first identification points in sequence according to the magnitude of the target SOC values to form an impedance diagram; wherein, the abscissa of the impedance diagram is the SOC value and the ordinate is the impedance value; determining the identification point corresponding to the maximum value of the impedance drop in the impedance diagram as the lithium plating inflection point.

[0006] In an embodiment of the present application, determining the lithium plating inflection point according to the impedance values of the full cell at different target SOC values includes: testing the full cell impedance distribution curve of the full cell at the target SOC value;

[0007] In the full cell impedance distribution curve of the full cell at the target SOC value, disassembling the sub-impedance distribution curve corresponding to the charge transfer impedance; calculating the full cell impedance rate according to the full cell impedance distribution curve of the full cell at the target SOC value; calculating the charge transfer impedance rate according to the sub-impedance distribution curve corresponding to the charge transfer impedance; calculating the charge transfer impedance value according to the full cell impedance rate, the impedance value of the full cell, and the charge transfer impedance rate at the target SOC value; determining the lithium plating inflection point according to the charge transfer impedance values at different target SOC values. In an embodiment of the present application, the charge transfer impedance value is equal to the product of the ratio of the charge transfer impedance rate to the full cell impedance rate and the impedance value of the full cell.

[0008] In an embodiment of the present application, the product of the number of charge-discharge cycles and the increment of the SOC value is 1, and the increment of the SOC value ≤ 0.1.

[0009] In an embodiment of the present application, the sum of the increments of the SOC values corresponding to multiple charge-discharge cycles is equal to 1.

[0010] In an embodiment of the present application, determining the lithium plating inflection point according to the charge transfer impedance rate of the full cell at different target SOC values, the electrochemical impedance of the full cell at different target SOC values, and the impedance values of the full cell at different target SOC values includes: performing integral processing on the electrochemical impedance of the full cell at different target SOC values to obtain the full cell impedance rate of the full cell at different target SOC values; calculating the ratio between the charge transfer impedance rate and the full cell impedance rate at the same target SOC value; calculating the charge transfer impedance value at the same target SOC value according to the ratio and the impedance value of the full cell at the same target SOC value to obtain the charge transfer impedance values at different target SOC values; determining the lithium plating inflection point according to the charge transfer impedance values at different target SOC values.

[0011] In an embodiment of the present application, determining the lithium plating inflection point according to the charge transfer impedance values at different target state of charge (SOC) values includes: plotting the corresponding relationship between different target SOC values and their corresponding charge transfer impedance values as identification points; arranging the multiple identification points in sequence from low to high according to the SOC values to form a charge transfer impedance diagram; wherein, the horizontal axis of the charge transfer impedance diagram is the SOC value, and the vertical axis is the charge transfer impedance value; determining the identification point corresponding to the maximum value of the decrease in the charge transfer impedance value in the charge transfer impedance diagram as the lithium plating inflection point.

[0012] In an embodiment of the present application, before discharging the fully charged battery after each charge based on the constant volume current until the cut-off voltage, it further includes: charging the fully charged battery to the target SOC value at the target rate to obtain a fully charged battery with the target SOC; allowing the fully charged battery with the target SOC to stand for a second preset time period; wherein, the second preset time period is less than the first preset time period; wherein, calculating the impedance value of the fully charged battery at the target SOC value according to the last voltage value of the fully charged battery after charging includes: calculating the difference between the last voltage value of the fully charged battery after charging and the earliest voltage value within the second preset time period; calculating the impedance value of the fully charged battery at the target SOC value according to the difference and the charging current.

[0013] As a second aspect of the present application, the present application provides a lithium plating detection system, including: a cycle number determination module, configured to determine the charge-discharge cycle number of the fully charged battery after the initial charge and determine the SOC increase value corresponding to each charge-discharge cycle; a discharge module, configured to discharge the fully charged battery after each charge based on the constant volume current until the cut-off voltage and then allow it to stand for a first preset time period; wherein, the fully charged battery after charging is a fully charged battery charged with the target rate charging current; a charging module, configured to charge the fully charged battery according to the target rate and the SOC increase value, so that the SOC value of the fully charged battery after charging reaches the target SOC value at the charge-discharge cycle number, and the target SOC value is the sum of the SOC value of the fully charged battery before charging and the SOC increase value; a calculation module, configured to calculate the impedance value of the fully charged battery at the target SOC value according to the last voltage value of the fully charged battery after charging; an inflection point determination module, configured to determine the lithium plating inflection point according to the impedance values of the fully charged battery at different target SOC values; wherein, the lithium plating inflection point represents the decrease in the impedance values corresponding to multiple consecutive target SOC values when the fully charged battery is charged at the target rate.

[0014] The lithium plating detection method provided by this application charges the full cell through multiple charge-discharge cycles during the charging process of the full cell. And during each charge-discharge cycle, the last voltage value is recorded, and the impedance value corresponding to the target charge value is calculated based on the last voltage value. Whether lithium plating occurs is determined according to the impedance values corresponding to multiple target charge values. When it is found that the impedance values corresponding to multiple consecutive target charge values decrease, the lithium plating inflection point can be correspondingly obtained. It is not necessary to damage the full cell or build a model, etc., to detect the lithium plating behavior, and the method for detecting the lithium plating behavior is simple. In addition, during the detection of the lithium plating behavior, it is easy to be coupled with the battery charge-discharge program. If it is determined that lithium plating has occurred, the battery charge-discharge program is adjusted during lithium plating to prevent lithium plating behavior on the surface of the battery negative electrode, thereby improving the overall safety performance of the battery, and can hinder the loss of active substances and interface degradation, and improve the service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By describing the embodiments of the present application in more detail in conjunction with the accompanying drawings, the above and other objects, features, and advantages of the present application will become more obvious. The accompanying drawings are used to provide a further understanding of the embodiments of the present application, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application. In the accompanying drawings, the same reference numerals generally represent the same components or steps.

[0016] Figure 1 is the equivalent circuit diagram of normal lithium battery charging provided by an exemplary embodiment of the present application.

[0017] Figure 2 is the equivalent circuit diagram of lithium-plated lithium battery charging provided by an exemplary embodiment of the present application.

[0018] Figure 3 The impedance distribution diagram at 20% SOC during the lithium battery charging process provided by an exemplary embodiment of the present application is shown.

[0019] Figure 4 The impedance distribution diagram at 50% SOC during the lithium battery charging process provided by an exemplary embodiment of the present application is shown.

[0020] Figure 5 The impedance distribution diagram at 80% SOC during the lithium battery charging process provided by an exemplary embodiment of the present application is shown.

[0021] Figure 6 is the flowchart of the lithium plating detection method provided by an exemplary embodiment of the present application.

[0022] Figure 7 is the flowchart of the lithium plating detection method provided by another exemplary embodiment of the present application.

[0023] Figure 8 It is a schematic flowchart of a lithium deposition detection method provided by another exemplary embodiment of the present application.

[0024] Figure 9 It is a schematic flowchart of a lithium deposition detection method provided by another exemplary embodiment of the present application.

[0025] Figure 10 It is a graph showing the change of voltage with charging time when the full battery is charged to the target power value provided by an exemplary embodiment of the present application.

[0026] Figure 11 It is an impedance graph and a charge transfer impedance graph of 1C charging provided by an exemplary embodiment of the present application.

[0027] Figure 12 It is an impedance graph and a charge transfer impedance graph of 3C charging provided by an exemplary embodiment of the present application.

[0028] Figure 13 It is a schematic structural diagram of a lithium deposition detection system provided by an exemplary embodiment of the present application.

[0029] Figure 14 It is a structural diagram of an electronic device provided by an exemplary embodiment of the present application. Detailed implementation manners

[0030] In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of the present invention, all directional indications (such as up, down, left, right, front, back, top, bottom...) are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally further include steps or units not listed, or may optionally further include other steps or units inherent to these processes, methods, products or devices.

[0031] In addition, referring to "embodiments" in this article means that specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present invention. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0032] Overview of the Application

[0033] There are mainly two methods for detecting lithium plating in batteries:

[0034] (1) Destructive lithium plating detection: The battery is disassembled, and then the surface phenomenon of the electrode sheet and physical characterization are combined to judge whether the battery has lithium plating. However, this method is time-consuming and laborious, and additional physical and chemical analysis and characterization are required to confirm lithium plating;

[0035] (2) Non-destructive lithium plating detection: Non-destructive detection is carried out for the phenomenon that lithium ions may precipitate in the form of metallic lithium on the negative electrode surface during the charging process of lithium-ion batteries (i.e., lithium plating). For example, Coulomb efficiency method, voltage relaxation method, three-electrode method, dQ / dV extreme value method, etc.

[0036] However, some of these methods require constructing a battery with a special structure, such as the three-electrode method; some require long-term testing, such as the Coulomb efficiency method, and some have low detection accuracy, such as the voltage relaxation method and the dQ / dV extreme value method.

[0037] The inventor found during the research process that Figure 1 For the circuit diagram of charging a normal lithium battery, when lithium plating occurs in the lithium battery, the lithium plated on the surface of the graphite negative electrode introduces a new charge transfer process, which is equivalent to connecting a small impedance in parallel to the graphite negative electrode. At this time, the circuit diagram of charging the lithium battery with lithium plating is as Figure 2 shown, and the overall impedance of the negative electrode decreases.

[0038] As Figures 3 - 5 shown, the impedance of different SOC full batteries, positive electrode-lithium, and negative electrode-lithium is decomposed into different parts, where P1 is the film impedance of the SEI film, P2 is the charge transfer impedance, P3 is the liquid-phase diffusion impedance, and P4 is the solid-phase diffusion impedance. During the charging process of the lithium battery, the charge transfer impedance of the negative electrode-lithium under different SOC (State of Charge) values controls the charge transfer impedance of the full battery, and the charge transfer impedance of the positive electrode has little effect. Therefore, if lithium plating occurs on the surface of the negative electrode, it can be directly detected by the full battery (i.e., the produced conventional battery, without additional production) without implanting a three-electrode to monitor the negative electrode. That is, when the charge transfer impedance value of the full battery does not change, the battery does not have lithium plating, and when the charge transfer impedance value of the full battery suddenly drops, it indicates that the battery has lithium plating.

[0039] Based on the above concept, an embodiment of the present invention provides a method for detecting lithium plating. The lithium plating detection method provided in this application charges the full cell with multiple charge-discharge cycles during the charging process of the full cell. And during each charge-discharge cycle, the last voltage value is recorded, and the impedance value corresponding to the target charge value is calculated based on the last voltage value. Whether lithium plating occurs is determined based on the impedance values corresponding to multiple target charge values. When it is found that the impedance values corresponding to multiple consecutive target charge values decrease, the lithium plating inflection point can be correspondingly obtained. It is not necessary to damage the full cell or construct a model, etc., to detect the lithium plating behavior, and the method for detecting the lithium plating behavior is simple. In addition, during the detection of the lithium plating behavior, it is easy to be coupled with the battery charge-discharge program. If it is determined that lithium plating has occurred, the battery charge-discharge program is adjusted during lithium plating to prevent lithium plating behavior from occurring on the surface of the battery negative electrode, thereby improving the overall safety performance of the battery, and can prevent the loss of active substances and interface degradation, and improve the service life of the battery.

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] Exemplary Method

[0042] As the first aspect of this application, this application provides a method for detecting lithium plating, as Figure 6 shown, a method for detecting lithium plating includes the following steps:

[0043] S1: Determine the charge-discharge cycle number of the full cell and determine the charge increment corresponding to each charge-discharge cycle;

[0044] Specifically, the method for determining the rated capacity of the full cell is as follows: The full cell is charged and discharged for 3 weeks at room temperature, and the constant current for constant volume is: 0.33C to 0.5C of the nominal capacity of the full cell; and the discharge data of the third week is taken as the rated capacity C of the full cell 0 . Charging and discharging the full cell at 0.33C to 0.5C can play a role in constant volume of the full cell, that is, the rated capacity of the full cell can be determined through charge-discharge tests, so that the active substances inside the battery can be fully activated, improving the stability of subsequent charge-discharge cycles, and providing basic data support for subsequent detections.

[0045] Specifically, during the charging process of the full battery, a method of multiple charge-discharge cycles is adopted. For example, after the first charge-discharge to n% SOC and then discharge, and then the second charge-discharge to (n + m)% SOC and then discharge, until the full battery is charged to the target power value (for example, the target power value is 100% SOC). Among them, n% SOC is the power increase value corresponding to the first charge-discharge cycle, and m% SOC is the power increase value corresponding to the second charge-discharge cycle.

[0046] The power increase value corresponding to each charge-discharge cycle can be the same (for example, m = n), or different.

[0047] When the power increase value corresponding to each charge-discharge cycle is the same, the product of the number of charge-discharge cycles and the power increase value is equal to 1 to detect the lithium plating situation during the entire charging stage. Optionally, the power increase value is less than or equal to 0.1, that is, the number of charge-discharge cycles is greater than or equal to 10 times to improve the detection accuracy.

[0048] When the power increase values corresponding to each charge-discharge cycle are not the same, then the sum of the power increase values corresponding to multiple charge-discharge cycles is equal to 1.

[0049] S2: Based on the constant current, discharge the fully charged battery after each charge to the cut-off voltage and then let it stand for the first preset time period; among them, the fully charged battery after charging is the fully charged battery charged at the target rate.

[0050] During each charge-discharge cycle, charge the full battery to the target power value (equal to the sum of the power value of the full battery before charging and the power increase value) at the target rate, and then based on the constant current, discharge the fully charged battery to the cut-off voltage and then let it stand for the first preset time period to make the full battery stable and reach chemical equilibrium.

[0051] Among them, the cut-off voltage is a fixed value related to the type of battery. For example, the cut-off voltage corresponding to a lithium iron phosphate battery is 2.5V, and the cut-off voltage corresponding to a ternary lithium battery is 2.8V. The positive electrode material of the ternary lithium battery is mainly composed of a ternary polymer of nickel, cobalt, and manganese (or aluminum).

[0052] Discharging with a constant current can avoid excessive battery polarization and ensure the discharge capacity.

[0053] The first preset time period can be 20 - 60 minutes. Optionally, the first preset time period is 30 minutes, 40 minutes, or 50 minutes.

[0054] S3: Charge the full battery according to the target rate and the power increase value so that the power value of the fully charged battery after charging reaches the target power value under the number of charge-discharge cycles. The target power value is the sum of the power value of the full battery before charging and the power increase value.

[0055] During each charge-discharge cycle, the full battery is charged at the target rate to the target charge value corresponding to that charge-discharge cycle number. Here, the target charge value is equal to the sum of the charge value before charging the full battery and the charge increment value. That is, the target charge value is equal to the charge value before charging the full battery, which is the sum of the target charge value of the previous charge-discharge cycle and the charge increment value. For example, if the charge increment value corresponding to the second charge-discharge cycle number is m% SOC, and the target charge value corresponding to the first charge-discharge cycle of the full battery is n% SOC, then the target charge value corresponding to the second charge-discharge cycle number is: (n + m)% SOC. If the charge increment value corresponding to the third charge-discharge cycle number is m% SOC, then the target charge value corresponding to the third charge-discharge cycle number is: (n + 2m)% SOC. If the charge increment value corresponding to each charge-discharge cycle number is equal (i.e., all are m% SOC), then the target charge value corresponding to the Nth charge-discharge cycle number is:

[0056] (n + (N - 1)m)% SOC.

[0057] Among them, the charge rate refers to the rate at which the battery is charged to its rated capacity with a certain current value within a specific time. The charge rate reflects the speed of battery charging. The charge rate is usually represented by the letter C. For example, a 1C rate means that the battery is charged to its rated capacity within 1 hour. If the rated capacity of the battery is 25 Ah, then the 1C charging current is 25 A.

[0058] The rated capacity of the full battery in this application is fixed. Therefore, the product of the target rate and the rated capacity of the full battery is the charging current.

[0059] Among them, the target rate in this application can be 1C, or 2C, or 3C, etc. This application does not make any restrictions.

[0060] S4: Calculate the impedance value of the full battery at the target charge value according to the last voltage value of the charged full battery;

[0061] After each charge-discharge cycle, the last voltage value of the full battery after each charge-discharge cycle can be obtained;

[0062] Then, according to the last voltage value obtained after each charge-discharge cycle, calculate the impedance value of the full battery at the target charge value. When the full battery is fully charged, that is, when the charge value of the full battery is 100% SOC, after multiple charge-discharge cycles, then multiple impedance values of the full battery at different target charge values will be obtained.

[0063] S5: Determine the lithium plating inflection point according to the impedance values of the full battery at different target charge values; among them, the lithium plating inflection point means that when the full battery is charged at the target rate, the impedance values corresponding to multiple consecutive target charge values decrease.

[0064] Determine the lithium plating inflection point based on the impedance values of the full cell at multiple different target state-of-charge (SOC) values. Herein, the lithium plating inflection point indicates that when the full cell is charged at a target rate, the impedance values corresponding to multiple consecutive target SOC values decrease.

[0065] In the lithium plating detection method provided by this application, during the charging process of the full cell, the full cell is charged with multiple charge-discharge cycles, and the last voltage value is recorded during each charge-discharge cycle. Then, the impedance value corresponding to the target SOC value is calculated based on the last voltage value. Whether lithium plating occurs is determined based on the impedance values corresponding to multiple target SOC values. When it is found that the impedance values corresponding to multiple consecutive target SOC values decrease, the lithium plating inflection point can be correspondingly obtained. It is not necessary to damage the full cell or construct a model, etc., to detect the lithium plating behavior, and the method for detecting the lithium plating behavior is simple. In addition, during the detection of the lithium plating behavior, it is easy to be coupled with the battery charge-discharge program. If it is determined that lithium plating occurs, the battery charge-discharge program is adjusted during lithium plating to prevent lithium plating behavior on the surface of the battery negative electrode, thereby improving the overall safety performance of the battery and being able to prevent the loss of active substances and interface degradation, and improving the battery service life.

[0066] In an embodiment of this application, for "determining the lithium plating inflection point based on the impedance values of the full cell at different target SOC values", there are the following two specific determination methods:

[0067] (1) As Figure 7 shown, S5 (determining the lithium plating inflection point based on the impedance values of the full cell at different target SOC values) specifically includes the following steps:

[0068] S51: Plot the correspondence between different target SOC values and the impedance values of their corresponding full cells as the first identification points;

[0069] For example, during the charge-discharge process, the target SOC value and the impedance value corresponding to each charge-discharge cycle are used as a first identification point, as Figure 12 shown (the full cell is charged and discharged at a target rate of 3C).

[0070] S52: Arrange multiple first identification points in sequence according to the magnitude of the target SOC value to form an impedance diagram; wherein, the abscissa of the impedance diagram is the SOC value, and the ordinate is the impedance value;

[0071] When multiple first identification points are determined, an impedance diagram can be formed, as Figure 12 shown.

[0072] S53: Determine the identification point corresponding to the maximum decrease in impedance value in the impedance diagram as the lithium plating inflection point.

[0073] Determine whether the impedance value has decreased based on the magnitude between every two adjacent marked points in the impedance diagram, calculate the specific value of the impedance value decrease, and determine the marked point corresponding to the maximum value of the impedance value decrease as the lithium plating inflection point, that is, the marked point corresponding to the mutation of the impedance value is the lithium plating inflection point.

[0074] The marked point corresponding to the maximum value of the impedance value decrease in the impedance diagram is the lithium plating inflection point. For example, Figure 12 as shown, the lithium plating inflection point is 55% SOC.

[0075] (2) As Figure 8 shown, S5 (determine the lithium plating inflection point according to the impedance value of the full cell at different target state of charge values) specifically includes the following steps:

[0076] S54: Test the full cell impedance distribution curve of the full cell at the target state of charge value;

[0077] Specifically, the impedance value of the full cell includes: electrochemical impedance value and other impedance values (such as DC internal resistance, AC internal resistance, etc.). During the charge and discharge process of the full cell, both the electrochemical impedance value and other impedance values may change, and the changes in the electrochemical impedance value and other impedance values will cause the impedance value of the full cell to change. For example, when the impedance value decreases, the possible reasons are: ① other impedance values decrease and the electrochemical impedance value increases; ② other impedance values decrease and the electrochemical impedance value remains unchanged; ③ other impedance values decrease and the electrochemical impedance value decreases; ④ other impedance values remain unchanged and the electrochemical impedance value decreases; ⑤ other impedance values increase and the electrochemical impedance value decreases.

[0078] Therefore, lithium plating detection is mainly related to the charge transfer impedance. It is necessary to exclude the influence of other impedance values on the impedance value of the full cell, calculate the charge transfer impedance value through the proportion of the charge transfer impedance in the impedance value of the full cell, and determine the lithium plating inflection point according to the charge transfer impedance values at different target state of charge values, which can further improve the detection accuracy of the lithium plating inflection point.

[0079] The full cell impedance distribution curves corresponding to different target state of charge values can be obtained through testing.

[0080] Specifically, test the impedance at the target state of charge value through an electrochemical workstation (connect the positive electrode wire to the positive electrode and the negative electrode wire to the negative electrode). Decompose the impedance of the battery into ohmic impedance, film impedance, electrochemical impedance, diffusion impedance, etc. through numerous differential RC elements. Take tau (time) as the x-axis and gamma(tau) (resistance value) as the y-axis to obtain the full cell impedance distribution curve, as Figures 3 - 5 shown. This test also belongs to non-destructive testing and does not require disassembling the battery, improving the detection convenience.

[0081] S55: Extract the sub-impedance distribution curve corresponding to the charge transfer impedance from the full-cell impedance distribution curve at the target state of charge;

[0082] Decompose the electrochemical impedance distribution line of the full cell into: the sub-impedance distribution curve corresponding to the charge transfer impedance, the sub-impedance distribution curve corresponding to the ohmic impedance value, the sub-impedance distribution curve corresponding to the film impedance value, and the sub-impedance distribution curve corresponding to the diffusion impedance value. As Figures 3 - 5 shown, P1 is the sub-impedance distribution curve corresponding to the film impedance, P2 is the sub-impedance distribution curve corresponding to the charge transfer impedance, P3 is the sub-impedance distribution curve corresponding to the liquid-phase diffusion impedance, and P4 is the sub-impedance distribution curve corresponding to the solid-phase diffusion impedance.

[0083] The charge transfer impedance describes the resistance encountered by charges during transmission. Specifically, it refers to the resistance encountered by charges when transferring from one position to another in electronic components, circuits, or within a battery. When lithium plating occurs in a lithium-ion battery, lithium ions begin to transform into metallic lithium on the surface of the graphite negative electrode. The charging current is divided into an intercalation current and a lithium plating current, generating a new equivalent circuit branch. At this time, the impedance of the charge transfer process decreases due to the addition of a parallel branch. Therefore, the occurrence of the lithium plating reaction can be accurately detected through the charge transfer impedance.

[0084] S56: Calculate the full-cell impedance rate based on the full-cell impedance distribution curve of the full cell at the target state of charge;

[0085] Specifically, the calculation method of the full-cell impedance rate can be: perform an integral calculation on the full-cell impedance distribution curve of the full cell at the target state of charge to calculate the full-cell impedance rate r 总,n％SOC。

[0086] S57: Calculate the charge transfer impedance rate based on the sub-impedance distribution curve corresponding to the charge transfer impedance;

[0087] Specifically, the calculation method of the charge transfer impedance rate can be: perform an integral calculation on the sub-impedance distribution curve corresponding to the charge transfer impedance at the target state of charge (such as Figures 3 - 5 the P2 curve in) to calculate the charge transfer impedance rate r P2,n％SOC。

[0088] S58: Calculate the charge transfer impedance value based on the full-cell impedance rate, the impedance value of the full cell, and the charge transfer impedance rate at the target state of charge;

[0089] Specifically, the charge transfer impedance value is equal to the product of the ratio of the charge transfer impedance rate to the full-cell impedance rate and the impedance value R n％SOC of the full cell, that is, the charge transfer impedance value = (r P2,n％SOC / r 总,n％SOC ) * R n％SOC .

[0090] The charge transfer impedance value at each target battery level can be calculated by S54 - S58.

[0091] After calculating the charge transfer impedance values at different target battery levels, the lithium plating inflection point can be determined based on the charge transfer impedance values at different target battery levels, that is, execute S59.

[0092] S59: Determine the lithium plating inflection point according to the charge transfer impedance values at different target battery levels.

[0093] The identification point corresponding to the maximum value of the impedance decrease in the impedance diagram is the lithium plating inflection point. For example Figure 12 As shown, the lithium plating inflection point determined by the charge transfer impedance is 58% SOC. It can be seen that compared with determining the lithium plating inflection point by the full - cell impedance, determining the lithium plating inflection point by the charge transfer impedance further improves the detection accuracy.

[0094] Among them, S59 (determine the lithium plating inflection point according to the charge transfer impedance values at different target battery levels) specifically includes the following steps:

[0095] (1) Plot the corresponding relationship between different target battery levels and their corresponding charge transfer impedance values as identification points;

[0096] Combine the target battery level and the corresponding charge transfer impedance value into an identification point.

[0097] (2) Arrange multiple identification points in sequence from low to high according to the battery level to form a charge transfer impedance diagram; wherein, the horizontal axis of the charge transfer impedance diagram is the battery level, and the vertical axis is the charge transfer impedance value;

[0098] (3) Determine the identification point corresponding to the maximum value of the charge transfer impedance decrease in the charge transfer impedance diagram as the lithium plating inflection point.

[0099] Determine whether the charge transfer impedance value has decreased according to the magnitude between every two adjacent identification points in the charge transfer impedance diagram, calculate the specific value of the charge transfer impedance decrease, and determine the identification point corresponding to the maximum value of the charge transfer impedance decrease as the lithium plating inflection point, that is, the identification point corresponding to the mutation of the charge transfer impedance value is the lithium plating inflection point.

[0100] In an embodiment of the present application, as Figure 9 shown, before S1 (discharge the fully charged battery to the cut - off voltage based on the constant - volume current after each charge), the lithium plating detection method further includes the following steps:

[0101] S10: Charge the fully charged battery to the target battery level at the target rate to obtain a fully charged battery with the target battery level;

[0102] Before discharging the full battery to the cut-off voltage after each charge and discharge, first charge the full battery to the target state of charge (SOC) value.

[0103] Specifically, charge the full battery to the target SOC value at the target rate (e.g., 1C rate or 3C rate) to obtain the target SOC value of the full battery. For example, the target SOC value is n% SOC.

[0104] S11: Let the full battery with the target SOC stand for a second preset time period; where the second preset time period is less than the first preset time period.

[0105] After charging the full battery to the target SOC value, let the full battery with the target SOC value stand for a second preset time period, where the second preset time period is less than the first preset time period. For example, the second preset time period is: 1 - 5 seconds. Optionally, the second preset time period is 2 seconds, 3 seconds, or 4 seconds. The second preset time is much less than the first preset time, which improves the overall detection efficiency, ensures that the voltage change is not too large, and improves the detection accuracy. Preferably, the second preset time period is 1 second.

[0106] At this time, the specific calculation method for calculating the impedance value of the full battery, that is, S4 (calculate the impedance value of the full battery at the target SOC value according to the last voltage value of the full battery after charging) specifically includes the following steps:

[0107] S41: Calculate the difference between the last voltage value of the full battery after charging and the earliest voltage value within the second preset time period.

[0108] After charging the full battery to the target SOC value, the difference between the last voltage value after charging and the earliest voltage value within the second preset time period (i.e., the voltage value collected for the first time when starting to stand) can be determined.

[0109] For example, as Figure 10 shown. If the voltage acquisition accuracy (i.e., time interval) during charging is 0.1 second, the last voltage value after charging the full battery to the target SOC value is V1, and the earliest voltage value within the second preset time period (i.e., the voltage value at 0.1 second of standing) is V2, then the difference is V1 - V2. If the voltage acquisition accuracy (i.e., time interval) during charging is 0.05 second, then the earliest voltage value within the second preset time period is the voltage value at 0.05 second of standing. By setting the second preset time period to detect the last voltage value after charging and the earliest voltage value within the second preset time period, and then calculating the impedance value of the full battery from these two values, the detection efficiency can be improved.

[0110] S42: Calculate the impedance value of the full battery at the target SOC value according to the difference and the charging current.

[0111] Based on the difference obtained from S41 and the charging current, the impedance value of the full battery at the target state of charge can be calculated.

[0112] The following will more specifically implement the lithium plating detection method of the present invention by showing specific embodiments.

[0113] Example 1:

[0114] The present invention takes a certain model of 104 Ah battery cell as the experimental object, and performs constant current and constant voltage charging at 0.33C (34.32 Ah) and discharging at 0.33C at room temperature, cycles 3 times, performs volume calibration on the battery, with a voltage range of 2.5 - 3.65V, and takes the discharge capacity of 104.4412 Ah in the third week as the calibrated capacity.

[0115] Charge the battery at a rate of 1C0 (i.e., 104.4412 Ah) for the first time, charge to 5% SOC, stand still for 1 s (1 s is the second preset time mentioned above), with a sampling interval of 0.01 s. Among them, the last voltage when charging to 5% SOC is 3.2546V, and the earliest first voltage during the 1 s standstill is 3.2022V. Discharge at 0.33C to 2.5V and stand still for 30 min (30 min is the first preset time mentioned above); repeat this charge and discharge step. Each time during charging, increase the charging amount by 5% SOC (5% SOC is the state of charge increment mentioned above) until the charging amount reaches 100% SOC and ends. The last voltage during charging and the first voltage during standstill for each target state of charge (the sum of the target state of charge of the previous charge and the state of charge increment) are shown in Table 1. The relationship diagram between the impedance value of the full battery at each target state of charge and the target state of charge is as Figure 11 shown. Charging at this target rate (1C0) will not cause lithium plating on the battery cell. After disassembling the battery cell, it is confirmed that there is no lithium plating on the negative electrode interface.

[0116] Table 1

[0117]

[0118]

[0119] Example 2:

[0120] The present invention takes a certain model of 104 Ah battery cell as the experimental object, and performs constant current and constant voltage charging at 0.33C (34.32 Ah) and discharging at 0.33C at room temperature, cycles 3 times, performs volume calibration on the battery, with a voltage range of 2.5 - 3.65V, and takes the discharge capacity of 104.24 Ah in the third week as the calibrated capacity.

[0121] Charge at 300.72 Ah (i.e., 3C0 rate) until 5% SOC, let it stand for 1 s, with a sampling interval of 0.01 s. The last voltage when charging to 5% SOC is 3.4076 V, and the first voltage during standing is 3.3028 V. Discharge to 2.5 V at 0.33C and let it stand for 30 min. Repeat this charge-discharge step. Each time during charging in a cycle, increase the charge amount by 5% SOC until the charge amount reaches 100% SOC and ends. The last voltage when charging for each target charge value and the first voltage during standing are shown in Table 2. The relationship graph between the impedance value of the full cell and the target charge value at each target charge value is as Figure 12 shown. When charging at this target rate (3C0), lithium plating occurs in the cell at 55% SOC.

[0122] Table 2

[0123]

[0124] Exemplary System

[0125] As the second aspect of the present application, the present application also provides a lithium plating detection system, as Figure 13 shown. The lithium plating detection system 20 includes:

[0126] A cycle number determination module 201 for determining the charge-discharge cycle number of the full cell after initial charging and determining the charge increment corresponding to each charge-discharge cycle;

[0127] A discharge module 202 for discharging the full cell after each charging to the cut-off voltage based on a constant volume current and then letting it stand for a first preset period; wherein, the full cell after charging is the full cell charged with a target rate charging current;

[0128] A charging module 203 for charging the full cell according to the target rate and the charge increment, so that the charge value of the full cell after charging reaches the target charge value at the charge-discharge cycle number, and the target charge value is the sum of the charge value of the full cell before charging and the charge increment;

[0129] A calculation module 204 for calculating the impedance value of the full cell at the target charge value according to the last voltage value of the full cell after charging;

[0130] An inflection point determination module 205 for determining the lithium plating inflection point according to the impedance values of the full cell at different target charge values; wherein, the lithium plating inflection point indicates that when the full cell is charged at the target rate, the impedance values corresponding to multiple consecutive target charge values decrease.

[0131] The lithium plating detection system provided by this application charges the full cell with multiple charge-discharge cycles during the charging process of the full cell. And during each charge-discharge cycle, the last voltage value is recorded, and the impedance value corresponding to the target charge value is calculated based on the last voltage value. And whether lithium plating occurs is determined based on the impedance values corresponding to multiple target charge values. When it is found that the impedance values corresponding to multiple consecutive target charge values decrease, the lithium plating inflection point can be correspondingly obtained. It is not necessary to damage the full cell or build a model, etc., to detect the lithium plating behavior, and the method for detecting the lithium plating behavior is simple. In addition, during the process of detecting the lithium plating behavior, it is easy to be coupled with the battery charge-discharge program. If it is determined that lithium plating has occurred, the battery charge-discharge program is adjusted during lithium plating to prevent lithium plating behavior on the surface of the battery negative electrode, thereby improving the overall safety performance of the battery, and can prevent the loss of active substances and interface degradation, and improve the service life of the battery.

[0132] Exemplary Electronic Device

[0133] Figure 14 The block diagram of an electronic device according to an embodiment of the present application is illustrated.

[0134] As Figure 14 shown, the electronic device 10 includes one or more processors 11 and a memory 12.

[0135] The processor 11 may be a central processing unit (CPU) or other forms of processing units with data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device 10 to perform desired functions.

[0136] The memory 12 may include one or more computer program products, and the computer program products may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory, etc. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 11 may run the program instructions to implement the lithium plating detection method of various embodiments of the present application described above and / or other desired functions. Various contents such as input signals, signal components, and noise components may also be stored in the computer-readable storage medium.

[0137] In one example, the electronic device 10 may further include: an input device 13 and an output device 14, and these components are interconnected through a bus system and / or other forms of connection mechanisms (not shown).

[0138] When the electronic device 10 is a stand-alone device, the input device 13 can be a communication network connector for receiving the collected input signals from the first device and the second device.

[0139] In addition, the input device 13 can also include, for example, a keyboard, a mouse, and the like.

[0140] The output device 14 can output various information to the outside, including the determined distance information, direction information, etc. The output device 14 can include, for example, a display, a speaker, a printer, a communication network, and remote output devices connected thereto, and the like.

[0141] Of course, for simplicity, Figure 14 only some of the components related to the present application in the electronic device 10 are shown, and components such as a bus, an input / output interface, etc. are omitted. In addition, according to specific application situations, the electronic device 10 can also include any other appropriate components.

[0142] The computer program product can be written in any combination of one or more programming languages for executing the program code of the operations of the embodiments of the present application. The programming languages include object-oriented programming languages such as Java, C++, etc., and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code can be executed entirely on the user computing device, partially on the user device, executed as an independent software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0143] The computer-readable storage medium can adopt any combination of one or more readable media. The readable media can be a readable signal medium or a readable storage medium. The readable storage medium can, for example, include but is not limited to an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (non-exhaustive list) of the readable storage medium include: an electrical connection having one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0144] The above description has been given for purposes of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions, and sub-combinations thereof.

Claims

1. A lithium precipitation detection method, characterized in that: include: Determine the number of charge and discharge cycles of the full battery and determine the amount of power increase corresponding to each charge and discharge cycle; Based on the constant capacity current, the full battery after each charge is discharged to a cut-off voltage and then left to stand for a first preset time period; wherein the full battery after charge is a full battery charged at a target rate; According to the target rate and the power increase value, the full battery is charged so that the power value of the full battery after charging reaches the target power value at the number of charge and discharge cycles, and the target power value is the sum of the power value of the full battery before charging and the power increase value; according to the last voltage value of the full battery after charging, the impedance value of the full battery at the target power value is calculated; The lithium deposition inflection point is determined according to the impedance value of the full battery at different target power values; wherein the lithium deposition inflection point indicates that when the full battery is charged at the target rate, the impedance values ​​corresponding to multiple consecutive target power values ​​decrease.

2. The lithium precipitation detection method according to claim 1, characterized in that: Determining the lithium deposition inflection point according to the impedance value of the full battery at different target power values ​​includes: The corresponding relationship between different target power values ​​and the impedance values ​​of the corresponding full battery is plotted as a first identification point; Arrange the plurality of first identification points in sequence according to the target power value to form an impedance diagram; wherein the abscissa of the impedance diagram is the power value, and the ordinate is the impedance value; The identification point corresponding to the maximum value of the impedance value drop in the impedance diagram is determined as the lithium deposition inflection point.

3. The lithium precipitation detection method according to claim 1, characterized in that: Determining the lithium deposition inflection point according to the impedance value of the full battery at different target power values ​​includes: Test the electrochemical impedance of the full battery at different target charge values; Decomposing a sub-impedance distribution curve corresponding to the charge transfer impedance from a full-battery impedance distribution curve of the full-battery at the target power value; Calculating the full battery impedance rate according to the full battery impedance distribution curve of the full battery at the target power value; Calculating the charge transfer impedance ratio according to the sub-impedance distribution curve corresponding to the charge transfer impedance; Calculating a charge transfer impedance value according to the full battery impedance rate at the target power value, the impedance value of the full battery, and the charge transfer impedance rate; The lithium deposition inflection point is determined according to the charge transfer impedance value at different target power values.

4. The lithium precipitation detection method according to claim 3, characterized in that: The charge transfer impedance value is equal to the product of the ratio of the charge transfer impedance rate to the full battery impedance rate and the impedance value of the full battery.

5. The lithium precipitation detection method according to claim 1, characterized in that: The product of the number of charge and discharge cycles and the amount of electricity increase is 1, and the amount of electricity increase is ≤0.

1.

6. The lithium precipitation detection method according to claim 1, characterized in that: The sum of the increase in charge corresponding to multiple charge and discharge cycles is equal to 1.

7. The lithium precipitation detection method according to claim 4, characterized in that: Determining the lithium precipitation inflection point according to the charge transfer impedance rate of the full battery at different target power values, the electrochemical impedance of the full battery at different target power values, and the impedance value of the full battery at different target power values ​​includes: Integrating the electrochemical impedance of the full battery at different target power values ​​to obtain the full battery impedance rate of the full battery at different target power values; Calculate the ratio between the charge transfer impedance and the full battery impedance at the same target charge value; Calculating the charge transfer impedance value at the same target power value according to the ratio and the impedance value of the full battery at the same target power value to obtain the charge transfer impedance value at different target power values; The lithium deposition inflection point is determined based on the charge transfer impedance value at different target charge values.

8. The lithium precipitation detection method according to claim 7, characterized in that: Determining the lithium deposition inflection point according to the charge transfer impedance values ​​at different target power values ​​includes: The corresponding relationship between different target power values ​​and their corresponding charge transfer impedance values ​​is plotted as identification points; Arrange the multiple identification points in order from low to high according to the electric quantity value to form a charge transfer impedance diagram; wherein the horizontal axis of the charge transfer impedance diagram is the electric quantity value, and the vertical axis is the charge transfer impedance value; The identification point corresponding to the maximum value of the charge transfer impedance value drop in the charge transfer impedance diagram is determined as the lithium deposition inflection point.

9. The lithium precipitation detection method according to claim 1, characterized in that: Based on the constant capacity current, the full battery after each charge is discharged to the cut-off voltage, and also includes: Charging the full battery to a target power value at the target rate to obtain a full battery with the target power; Allowing the full battery of the target power level to rest for a second preset time period; wherein the second preset time period is shorter than the first preset time period; Wherein, calculating the impedance value of the full battery at the target power value according to the last voltage value of the full battery after charging includes: Calculating the difference between the last voltage value of the charged full battery and the earliest voltage value within the second preset time period; The impedance value of the full battery at the target power value is calculated based on the difference and the charging current.

10. A lithium deposition detection system, characterized in that: include: The number determination module is used to determine the number of charge and discharge cycles of the full battery after the initial charge and determine the power increase value corresponding to each charge and discharge cycle; A discharge module, for discharging the full battery after each charge to a cut-off voltage based on a constant capacity current and then standing for a first preset time period; wherein the full battery after charge is a full battery charged with a target rate charging current; A charging module, used for charging the full battery according to the target rate and the power increase value, so that the power value of the full battery after charging reaches the target power value under the number of charge and discharge cycles, and the target power value is the sum of the power value of the full battery before charging and the power increase value; A calculation module, used to calculate the impedance value of the full battery at the target power value according to the last voltage value of the full battery after charging; The inflection point determination module is used to determine the lithium deposition inflection point according to the impedance value of the full battery at different target power values; wherein the lithium deposition inflection point indicates that when the full battery is charged at the target rate, the impedance values ​​corresponding to multiple consecutive target power values ​​decrease.

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