A lithium ion battery lithium precipitation detection method based on relaxation process heat generation characteristics

Abstract

The application discloses a lithium ion battery lithium precipitation detection method based on relaxation process heat generation characteristics, and relates to the field of lithium ion battery safety detection. Lithium precipitation is induced in the charging process of a lithium ion battery. By comparing dynamic in-situ heat generation curves of the lithium ion battery, it is found that an additional heat generation peak value appears in the relaxation process of the lithium precipitation battery after charging. The heat generation peak value corresponds to a mixed voltage platform generated by the simultaneous occurrence of lithium stripping and re-embedding graphite reaction, and the lithium precipitation battery can be identified through the heat generation peak value. Compared with the existing traditional dynamic detection method of lithium precipitation, the method comprehensively considers the dynamic and thermodynamic characteristics of the lithium precipitation battery, greatly improves the reliability of lithium precipitation detection, and is not limited by the lithium precipitation triggering condition, the battery type and the charging and discharging strategy. In addition, the method can also be used for lithium precipitation detection under fast charging and low temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery safety testing, specifically relating to a lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process. Background Technology

[0002] Currently, lithium-ion batteries are experiencing rapid growth, expanding from consumer electronics to new energy vehicles and energy storage. Lithium plating and the resulting lithium dendrites are considered major causes of capacity decay, internal short circuits, and safety issues in lithium-ion batteries. Therefore, lithium plating detection is a crucial step in ensuring the safety of lithium-ion batteries.

[0003] Current lithium plating detection methods mostly focus on its electrochemical kinetics, such as stripping voltage plateau, relaxation voltage plateau, and lithium plating voltage onset point (0V graphite anode voltage vsLi / Li). + Lithium plating detection methods often neglect the thermal characteristics of lithium plating and its correlation with kinetic properties. The evolution of battery thermal generation during lithium plating, its similarities and differences with lithium insertion / extraction thermal generation, and the relationship between the degree of lithium plating and thermal characteristics are not yet clearly understood, thus limiting the identification of lithium plating features. Relying on a single kinetic characteristic may lead to uncertainty in lithium plating detection; therefore, identifying lithium plating features from multiple perspectives is beneficial for improving detection capabilities and reliability. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process. The method induces lithium plating in the lithium-ion battery and subsequently relaxes it, simultaneously acquiring the battery voltage and heat generation curves during the relaxation process. The correlation between the peak heat generation and voltage plateau during relaxation can identify lithium-plated batteries. This invention achieves efficient and accurate detection of lithium-ion battery lithium plating from both thermodynamic and kinetic perspectives. By acquiring the heat generation characteristics during the relaxation process of lithium-plated batteries, this invention discovers the distinct heat generation peak of lithium-plated batteries compared to non-lithium-plated batteries, as well as the correspondence between the battery voltage plateau and the heat generation peak. Ultimately, it achieves lithium plating detection from both kinetic and heat generation characteristics perspectives, improving the reliability and accuracy of lithium plating detection.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for detecting lithium plating in lithium-ion batteries based on the heat generation characteristics of the relaxation process includes the following steps:

[0007] Step 1: For a target battery, select a charging method to trigger lithium plating, and simultaneously collect battery voltage and heat generation curves.

[0008] Step 2: Allow the charged battery to relax for at least 3 hours, and simultaneously collect battery voltage and heat generation curves.

[0009] Step 3: Detect changes in the battery's heat generation characteristics during relaxation to determine whether lithium plating has occurred in the battery.

[0010] Furthermore, in step one, the target battery can be a commercially available cylindrical or prismatic battery, or a self-made button, cylindrical, prismatic, or pouch battery.

[0011] Furthermore, in step one, the charging methods that induce lithium plating include low-temperature charging, high-rate charging, and overcharging.

[0012] Furthermore, in steps one and two, the device for collecting battery voltage is a charge-discharge cycle meter, and the device for collecting heat generation curves is a calorimeter, such as a coin cell calorimeter or an isothermal calorimeter. If the target battery is a coin cell battery, a coin cell calorimeter is selected; if the target battery is a commercial battery, an isothermal calorimeter is selected.

[0013] Furthermore, the relaxation time in step two is not less than 3 hours to ensure that the deposited lithium can complete the lithium stripping and re-intercalation into graphite reaction.

[0014] Furthermore, in step three, the change in battery heat generation characteristics is that lithium-plated batteries will experience a heat generation peak during relaxation, while the heat generation of non-lithium-plated batteries shows a decreasing trend during relaxation.

[0015] This invention is not limited by lithium plating triggering conditions or battery type, and has universal applicability in lithium plating safety detection.

[0016] The beneficial effects of this invention compared to the prior art are as follows:

[0017] 1. This invention innovatively proposes a method for detecting lithium plating in lithium-ion batteries based on heat generation characteristics. Compared with the traditional method of detection by electrical signals, multi-signal fusion can improve the reliability of detection.

[0018] 2. The lithium plating detection method in this invention is performed during the battery relaxation process, thus avoiding the influence of the charging and discharging strategy on the lithium plating detection;

[0019] 3. The lithium plating detection method in this invention is not limited by lithium plating triggering conditions and battery type, and has universality in lithium plating safety detection, thus safeguarding the safety of energy storage systems;

[0020] 4. Based on the heat generation characteristics of the relaxation process of lithium-plated batteries discovered in this invention, a battery thermal model can be further constructed and embedded into the battery management system, and the electrical and thermal signals can be used to jointly detect lithium-plated batteries in new energy vehicles and energy storage power stations. Attached Figure Description

[0021] Figure 1a The voltage-heat generation curves of a lithium-ion battery during discharge and relaxation processes under normal charge and discharge conditions are shown in the embodiments of the present invention.

[0022] Figure 1b The voltage-heat generation curves of a lithium-ion battery during discharge and relaxation processes under over-discharge (over-lithiation, corresponding to full-cell overcharge) conditions are shown in an embodiment of the present invention.

[0023] Figure 2 The image shows the surface morphology of the graphite negative electrode of a lithium-ion battery during normal charging and discharging in an embodiment of the present invention.

[0024] Figure 3 The image shows the surface morphology of the graphite anode of a lithium-ion battery under over-discharge (over-lithiation, corresponding to full-cell overcharge) conditions in an embodiment of the present invention. Detailed Implementation

[0025] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0026] Example

[0027] Taking the over-discharge (over-lithiation, corresponding to full-cell overcharge) induced lithium plating of a laboratory-made graphite / lithium coin cell as an example, this invention is described in a comprehensive and detailed manner. This method is not limited to this type of graphite / lithium coin cell, nor is it limited to the lithium plating process induced by over-lithiation. It is applicable to all commercial and self-made lithium-ion batteries and different lithium plating triggering methods.

[0028] The present invention provides a lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process, comprising the following steps:

[0029] Step 1: Perform a pre-cycle of the battery and determine its rated capacity;

[0030] Step 2: Conduct a heat generation test on a normally charged and discharged battery (non-lithium-plated battery);

[0031] Step 3: Conduct overcharge-triggered lithium plating and heat generation tests on the battery;

[0032] Step 4: Extract voltage and heat generation signals during battery charging and discharging;

[0033] Step 5: Perform lithium plating detection of the battery based on the heat generation characteristics of the relaxation process;

[0034] Step 6: Confirm lithium plating in the battery.

[0035] Specifically, in step 1, the pre-cycled button cell battery is first subjected to a pre-cycle treatment to determine its rated capacity, including:

[0036] After the fabricated coin cells were relaxed for 8 hours to ensure electrolyte wetting, a pre-cycling treatment was initiated: discharge to 0.001V at 0.1C (based on the theoretical graphite capacity of 372 mAh / g) to allow lithium insertion into the graphite electrode, relax for 3 minutes, and then charge at 0.1C to 1.5V to allow delithiation. This process was repeated three times to complete the pre-cycling treatment, ensuring the formation of a stable solid electrolyte interphase (SEI) film on the graphite electrode surface. The capacity obtained from the third charge was the rated capacity of the coin cell (Q). t (Unit: mAh)

[0037] Step 2 includes: subsequently performing normal charge and discharge on the coin cell to obtain the voltage and heat generation of the unplated lithium battery, including:

[0038] Step 2.1) Place the button cell in the button cell calorimeter and connect it to the circulation instrument simultaneously;

[0039] Step 2.2) Subsequently, the button cell battery is charged and discharged normally, as shown in Table 1, including:

[0040] Step 2.2.1) Perform a 3-hour relaxation to ensure uniform heating of the battery and stable ambient temperature.

[0041] Step 2.2.2): Perform constant current discharge at 0.8C until the cutoff voltage is 0.001V to allow the graphite electrode to complete lithium intercalation;

[0042] Step 2.2.3), relax for 1 hour to ensure the battery heat generation recovers;

[0043] Step 2.2.4): Charge at 0.8C to 1.5V to allow the graphite electrode to complete lithium removal;

[0044] Step 2.2.5), relax for 1 hour to ensure the battery heat generation recovers;

[0045] Step 2.2.6), repeat steps 2.2.2) to 2.2.5) three times to ensure the regularity of the heat generation curve.

[0046] Specifically, normal charge and discharge refers to normal cycles that do not involve fast charging, overcharging, or low temperatures, which may induce lithium plating. During normal charge and discharge, only lithium delithiation / lithiation reactions occur, and lithium plating does not occur.

[0047] Specifically, the constant current charge and discharge current needs to be between 0.5C and 1C. Since the capacity of coin cells is relatively small, the current should not be too small in order to ensure that the heat generation curve is clearly visible. In order to avoid the impact of fast charging on lithium plating, the current should not be too large either. Therefore, it should be maintained between 0.5C and 1C.

[0048] Specifically, the charging and discharging current here is calculated based on the rated capacity.

[0049] Table 1

[0050]

[0051] Step 3 includes subsequently triggering lithium plating in the battery based on overcharge and testing its heat generation, including:

[0052] Step 3.1) Place the battery in the button cell calorimeter and connect it to the circulation instrument simultaneously;

[0053] Step 3.2) Overcharge the battery to trigger lithium plating, as shown in Table 2, including:

[0054] Step 3.2.1) Perform a 3-hour relaxation to ensure uniform heating of the battery and stable ambient temperature.

[0055] Step 3.2.2): Perform constant current discharge at 0.8C, with the discharge capacity set to 1.5 times the rated capacity, so that the graphite electrode can complete lithium insertion and lithium plating;

[0056] Step 3.2.3), relax for 1 hour to ensure the battery heat generation recovers;

[0057] Step 3.2.4): Charge at 0.8C to 1.5V to allow the graphite electrode to complete lithium removal;

[0058] Step 3.2.5), relax for 1 hour to ensure the battery heat generation recovers;

[0059] Step 3.2.6), repeat steps 3.2.1) to 3.2.5) a total of three times to ensure the regularity of the heat generation curve.

[0060] Specifically, over-discharge in graphite / lithium coin cells corresponds to overcharging in full cells. The principle is to perform over-lithiation on the graphite electrode to cause lithium deposition on the graphite electrode.

[0061] Table 2

[0062]

[0063] Step 4 includes: extracting voltage and heat generation signals from the discharge and relaxation processes of the above tests, and selecting the second or third voltage-heat generation data from the three repeated steps (steps 3.2.1 to 3.2.5) as the basis for analysis. Since the internal environment of the coin cell calorimeter is unstable during the first cycle, but relatively stable in the second and third cycles, the measured heat generation curves have higher accuracy and are more reasonable. The voltage-heat generation curves of the battery during discharge and relaxation processes under normal charge and discharge conditions are as follows: Figure 1aAs shown, the voltage-heat generation curves of the battery during discharge and relaxation processes under overcharge conditions are as follows: Figure 1b As shown.

[0064] Step 5, the battery lithium plating detection based on the heat generation characteristics of the relaxation process, includes:

[0065] Step 5.1) For a battery that is charging and discharging normally, during the relaxation process, the battery voltage immediately recovers to the open circuit voltage of the lithium-intercalated graphite, which is about 86mV, and the heat generation also drops rapidly to 0mW.

[0066] Step 5.2) For overcharged (over-lithiated) batteries, during relaxation, the battery voltage first appears in a plateau region near 0V. This voltage plateau is a mixed voltage plateau formed by lithium stripping and re-intercalation into graphite. Subsequently, it recovers to the open-circuit voltage of the lithium-intercalated graphite. Simultaneously, unlike normally charged and discharged batteries, the heat generated during relaxation after overcharging does not directly drop to 0V, but rather exhibits an additional heat generation peak, which corresponds precisely to the mixed voltage plateau. Therefore, detecting the appearance of this heat generation peak can indirectly confirm the occurrence of lithium plating.

[0067] In step 6, to confirm overcharge-induced lithium plating, the normally charged / discharged and overcharged batteries were disassembled to obtain the graphite negative electrode, which was then subjected to scanning electron microscopy (SEM) testing. It was observed that the graphite surface was clearly visible during normal charge / discharge, as shown in the image. Figure 2 As shown; however, in an overcharged battery, the surface of the graphite negative electrode is covered with bent and entangled lithium dendrites, as... Figure 3 As shown, this proves that lithium plating does indeed occur, further demonstrating the feasibility of detecting lithium plating using the heat generation peak during relaxation.

[0068] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for detecting lithium plating in lithium-ion batteries based on the heat generation characteristics of the relaxation process, characterized in that, Includes the following steps: Step 1: For a target battery, select an overcharge charging method to trigger lithium plating in the target battery, and simultaneously collect the battery voltage and heat generation curves. Step 2: Relax the charged target battery for no less than 3 hours, and simultaneously collect battery voltage and heat generation curves. Step 3: Detect changes in the heat generation characteristics of the target battery during the relaxation process to determine whether lithium plating has occurred in the target battery, including: For batteries that are charging and discharging normally, the battery voltage immediately recovers to the open-circuit voltage of the lithium-intercalated graphite during the relaxation process. For overcharged batteries, during the relaxation process, the battery voltage first appears in a plateau region near 0V. This voltage plateau is a mixed voltage plateau formed by lithium stripping and lithium reintercalation into graphite. Subsequently, it also recovers to the open-circuit voltage of the lithium-intercalated graphite. At the same time, after overcharging, the battery generates additional heat peaks during the relaxation process. These peaks correspond exactly to the mixed voltage plateau. The occurrence of lithium plating is indirectly confirmed by detecting the appearance of these heat peaks.

2. The lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process according to claim 1, characterized in that, In step one, the target battery is a commercially available cylindrical or square battery, or a self-made button, cylindrical, square, or pouch battery.

3. The lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process according to claim 1, characterized in that, The device for collecting battery voltage in steps one and two is a charge-discharge cycle meter, and the device for collecting heat generation curves is a calorimeter, including a button cell calorimeter or an isothermal calorimeter.

4. The lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process according to claim 1, characterized in that, The relaxation time of not less than 3 hours in step two ensures that the deposited lithium can complete the lithium stripping and re-intercalation into graphite reaction.

5. The lithium-ion battery lithium plating detection method based on the heat generation characteristics of the relaxation process according to claim 1, characterized in that, In step three, the changes in the heat generation characteristics of the target battery are as follows: lithium-plated batteries exhibit a heat generation peak during relaxation, while the heat generation of non-lithium-plated batteries shows a decreasing trend during relaxation.

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