A method for characterizing a lithium precipitation window using battery polarization potential

Abstract

The application discloses a method for characterizing lithium precipitation window by using battery polarization potential, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: obtaining a standard charge-discharge potential curve through a discharged battery; setting different rates, and performing charge-discharge tests on a three-electrode battery at different rates to obtain positive and negative charge-discharge potential curves of the three-electrode battery at each rate; comparing the positive and negative charge-discharge potential curves of the three-electrode battery at each rate with the standard charge-discharge potential curve, and calculating the polarization potential of the three-electrode battery at each rate through the potential difference at the maximum deviation of the two curves; and disassembling the three-electrode battery to obtain the polarization potential and the charge-discharge rate when lithium precipitation starts. The main use of the application is to further reduce the risk of lithium precipitation of lithium ion batteries, utilize the correlation between battery lithium precipitation and polarization, utilize the polarization potential to characterize the lithium precipitation window, and predict the internal condition of the battery in advance, so that a more optimal charging strategy can be formulated, and the battery performance can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a method for characterizing the lithium plating window using battery polarization potential. Background Technology

[0002] With energy scarcity and environmental degradation, new energy technologies are being used and promoted more and more. Among them, lithium-ion batteries, due to their high energy density, low self-discharge, and good cycle performance, are environmentally friendly products, leading to their rapid development.

[0003] During the charging and discharging process of a battery, when current flows through the battery, a phenomenon occurs where the battery potential deviates from the equilibrium potential; this phenomenon is called battery polarization. The polarization potential is the difference between the actual potential and the equilibrium potential, and it is used to measure the degree of polarization. Polarization is divided into three categories: electrochemical polarization, concentration polarization, and ohmic polarization. Ohmic polarization is caused by the contact resistance between the electrolyte, electrode materials, separator resistance, and various components; it occurs instantaneously and is constant, affected only by the magnitude of the current. Concentration polarization and electrochemical polarization can be mitigated and reduced through various means, and reducing polarization can further improve battery performance.

[0004] During charging, lithium-ion batteries allow Li+ ions to be extracted from the positive electrode and inserted into the negative electrode. However, when abnormal conditions occur, such as insufficient space for lithium insertion in the negative electrode, excessive resistance to Li+ insertion into the negative electrode, or Li+ ions rapidly extracting from the positive electrode but failing to insert an equal amount into the negative electrode, the Li+ ions that cannot be inserted into the negative electrode can only gain electrons on the surface of the negative electrode, forming silvery-white metallic lithium, commonly known as lithium plating. Lithium plating not only degrades battery performance and significantly shortens cycle life but also limits the battery's fast-charging capacity and may potentially cause catastrophic consequences such as combustion and explosion. Therefore, developing a good charging strategy to avoid lithium plating and improve battery performance is crucial. Summary of the Invention

[0005] 1. The technical problem that the invention aims to solve

[0006] This invention provides a method for characterizing the lithium plating window using battery polarization potential, which is used to address the problem of further reducing the risk of lithium plating in lithium-ion batteries. By utilizing the correlation between lithium plating and polarization, the polarization potential is used to characterize the lithium plating window, allowing for early prediction of the internal conditions of the cell, thereby enabling the development of a better charging strategy and improving battery performance.

[0007] 2. Technical Solution

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0009] A method for characterizing the lithium deposition window using battery polarization potential includes the following steps:

[0010] S1. To manufacture a button cell including a positive electrode and a lithium plate, a button cell including a negative electrode and a lithium plate, and a button cell including a positive electrode and a negative electrode.

[0011] S2. Charge and discharge the coin cell at a set rate to obtain the standard charge and discharge potential curves of the positive and negative electrodes of the coin cell.

[0012] S3. Fabricate a wound cell and set a reference electrode on the wound cell to obtain a three-electrode cell;

[0013] S4. Set different rates and perform charge and discharge tests on the three-electrode battery at different rates to obtain the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate.

[0014] S5. Compare the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate with the standard charge and discharge potential curve, and calculate the polarization potential of the three-electrode battery at each rate by the potential difference at the point where the two curves deviate the most.

[0015] S6. Disassemble the three-electrode battery to obtain the polarization potential and charge / discharge rate at the start of lithium plating.

[0016] Furthermore, in step S1, the electrode sheet for making the button cell is taken from the electrode sheet for making the wound cell in step S3.

[0017] Furthermore, in step S2, the set multiplier is below 0.1C.

[0018] Furthermore, in step S3, copper wire is used to connect the wound cell, with one end of the copper wire serving as a reference electrode to form a three-electrode cell.

[0019] Furthermore, in step S4, the method for setting different magnifications is to take values ​​around 1C for each magnification.

[0020] Furthermore, the different multiplier values ​​increase in a stepwise manner from small to large.

[0021] Furthermore, in step S4, the method for conducting charge-discharge tests on the three-electrode battery at different rates and obtaining the charge-discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate is as follows: a multi-channel instrument is used to connect the three voltage channels of the three-electrode battery: positive electrode-reference electrode, negative electrode-reference electrode, and positive electrode-negative electrode. At the same time, the electrical performance test cabinet is connected to the positive and negative electrodes of the three-electrode battery, and charge-discharge tests at different rates are started.

[0022] Furthermore, in step S6, the charge / discharge rate at the start of lithium plating is the minimum rate corresponding to the battery that undergoes lithium plating among the different rates in step S4.

[0023] Furthermore, the polarization potential at the start of lithium plating is the polarization potential corresponding to the minimum rate of operation.

[0024] Furthermore, the positive and negative electrode plates for making button batteries are first wiped on one side with a reagent before manufacturing.

[0025] 3. Beneficial effects

[0026] Compared with existing known technologies, the technical solution provided by this invention has the following significant advantages:

[0027] (1) The present invention provides a method for characterizing the lithium plating window using battery polarization potential. Lithium plating typically occurs at the end of charging, when lithium ions are enriched inside the negative electrode, resulting in greater polarization and increased risk of lithium plating. This method, which uses battery polarization potential to characterize the lithium plating window, helps to predict the internal condition of the cell in advance, which is beneficial for subsequent optimization of charging strategies and improvement of battery performance. It can improve battery cycle life without changing the original battery design or increasing material and labor costs, thereby saving costs.

[0028] (2) The present invention provides a method for characterizing the lithium plating window using battery polarization potential. This method obtains standard charge-discharge potential curves for the positive and negative electrodes, compares the potential curves of a three-electrode battery at different charge-discharge rates with the standard potential curves, determines the polarization potential at different rates, and then, by disassembling the battery, determines the minimum charge rate that causes lithium plating, thus obtaining the polarization potential at the start of lithium plating. Based on this potential, it determines whether subsequent charge-discharge strategies will cause lithium plating. This method can more accurately reflect and predict the occurrence of lithium plating in a battery at a certain charge rate.

[0029] (3) The present invention provides a method for characterizing the lithium plating window using battery polarization potential. By comparing the charge-discharge curves at each rate with the standard curve, the difference between the charge-discharge curves at different rates and the standard curve can be obtained. This difference represents the polarization of the rechargeable battery at that rate. By comparing the negative electrode potential curve under charging conditions, the difference between the standard potential and the operating potential can be obtained at the end of charging, which is the polarization potential for lithium plating.

[0030] (4) A method for characterizing the lithium deposition window using battery polarization potential according to the present invention is to manufacture a coin cell by using positive and negative single-sided electrode sheets and lithium sheets separately, using the lithium sheet as the counter electrode to eliminate the influence of the counter electrode, and using a small rate to further eliminate polarization, thereby obtaining a standard potential curve of positive and negative electrodes that is closer to the standard curve. Attached Figure Description

[0031] Figure 1 Standard charge / discharge curves for coin cells;

[0032] Figure 2 This is a comparison chart of the negative electrode potential curves of a three-electrode battery and a coin cell. Detailed Implementation

[0033] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments.

[0034] Since lithium plating and battery polarization are correlated, lithium ions accumulate inside the negative electrode at the end of battery charging, increasing polarization and raising the risk of lithium plating. Therefore, this embodiment provides a method for characterizing the lithium plating window using battery polarization potential. Characterizing the lithium plating window using polarization potential helps to predict the internal condition of the cell in advance, which is beneficial for subsequent optimization of charging strategies and improvement of battery performance.

[0035] The method for characterizing the lithium plating window using battery polarization potential in this embodiment includes the following steps:

[0036] S1. To manufacture a button cell including a positive electrode and a lithium plate, a button cell including a negative electrode and a lithium plate, and a button cell including a positive electrode and a negative electrode.

[0037] S2. Charge and discharge the coin cell at a set rate to obtain the standard charge and discharge potential curves of the positive and negative electrodes of the coin cell.

[0038] S3. Fabricate a wound cell and set a reference electrode on the wound cell to obtain a three-electrode cell;

[0039] S4. Set different rates and perform charge and discharge tests on the three-electrode battery at different rates to obtain the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate.

[0040] S5. Compare the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate with the standard charge and discharge potential curve, and calculate the polarization potential of the three-electrode battery at each rate by the potential difference at the point where the two curves deviate the most.

[0041] S6. Disassemble the three-electrode battery to obtain the polarization potential and charge / discharge rate at the start of lithium plating.

[0042] To provide a more detailed understanding of the solution in this embodiment, each step will be explained in detail.

[0043] S1. To manufacture a button cell including a positive electrode and a lithium plate, a button cell including a negative electrode and a lithium plate, and a button cell including a positive electrode and a negative electrode.

[0044] A portion of the positive and negative electrode sheets after rolling is taken as the positive and negative electrode sheets for making the button cell. Before making the button cell, the positive and negative electrode sheets are wiped on one side with a reagent.

[0045] Specifically, the positive and negative electrode sheets used in the fabrication of the coin cell were tested. The thickness of both electrodes was required to be 123±2 μm, with a 24-hour rebound thickness of 130 μm. Resistivity and peel strength tests showed no abnormalities. The positive and negative electrodes were then wiped on one side only. The positive electrode was wiped with NMP (N-methylpyrrolidone), and the negative electrode with alcohol. During the process, the electrodes were sealed with tape around their perimeter to prevent the reagents from seeping into the other side. After wiping, the positive and negative electrodes were assembled with lithium-ion cells to form the coin cell.

[0046] S2. Charge and discharge the coin cell at a set rate to obtain standard charge and discharge potential curves for the positive and negative electrodes of the coin cell. The set rate is below 0.1C.

[0047] The charging and discharging current of the coin cell is determined based on its parameters, i.e., the vertical setting of the set rate mentioned in step S2 is determined. In this embodiment, the specific parameters of the coin cell are: the weight of the positive and negative electrode sheets used to manufacture the coin cell, and the areal density of the foil material is 53 g / m². 2 The active materials in the positive and negative electrodes account for 96.8% and 96.5% respectively, with the positive electrode having a specific capacity of 145 mAh / g and the negative electrode having a specific capacity of 350 mAh / g. Based on the obtained parameters, the charge / discharge current was determined, and the battery was subjected to a 0.1C (0.08 mA) charge / discharge test to obtain the standard charging potential curves for the positive and negative electrodes, as shown below. Figure 1 As shown, a coin cell battery is charged at a rate of 0.1C. Curve ① represents the full-cell potential trend, where the full-cell battery includes a positive electrode and a negative electrode. Curve ② represents the potential trend of the positive electrode, where the battery includes a positive electrode and a lithium plate. Curve ③ represents the potential trend of the negative electrode, where the battery includes a negative electrode and a lithium plate. In this embodiment, the potential trend is calculated using the State of Charge (SOC), which is calculated based on the percentage of the battery's remaining capacity. In this embodiment, the coin cell battery is tested at a low rate (0.1C). Using a coin cell battery eliminates the influence on the electrodes, and using a low rate further eliminates polarization, thus obtaining the standard potential curves of the positive and negative electrodes. Comparing these curves with the test results of a three-electrode battery clearly reveals the polarization potentials of the positive and negative electrodes of the three-electrode battery.

[0048] S3. Fabricate a wound cell and set a reference electrode on the wound cell to obtain a three-electrode cell.

[0049] The positive and negative electrode sheets after rolling in step S1 are wound to form a wound cell. Copper wire is used to connect the wound cell, and one end of the copper wire is used as a reference electrode to form a three-electrode cell.

[0050] The copper wire used needs to have its surface oxide layer removed first. The copper wire includes a connecting end and a free end. The connecting end of the copper wire is connected to the battery, and the free end of the copper wire is led out from the battery's explosion-proof valve as a reference electrode. The connecting end of the copper wire is connected to the large surface of the battery core, and a diaphragm is installed at the copper wire. The free end of the copper wire is led out from the battery's explosion-proof valve and fixed to the cover plate.

[0051] The specific process for manufacturing a three-electrode battery is as follows: disassemble the last few folds of the wound battery core, remove the copper wire with the oxide layer removed, and place it on the large surface of the cell electrode. Fix a certain area of ​​separator at the copper wire to prevent the copper wire from directly contacting the positive and negative electrodes.

[0052] After the copper wires are laid out, the core electrode sheets are restored, and the other end of the copper wire is fixed to the core with tape. The core then undergoes hot pressing and assembly processes. After the cover plate is welded, the free end of the copper wire is removed and led out from the explosion-proof valve, fixed to the cover plate, and placed into the assembly line for laser welding. After laser welding, the cell is removed, and the opening at the explosion-proof valve is sealed with glue. After the glue has completely cured, the battery undergoes subsequent baking, electrolyte filling, formation, and capacity testing processes. Leading out the copper wire and fixing it to the cover plate prevents the copper wire from melting during subsequent laser welding of the cell.

[0053] After the three-electrode batteries have been tested for capacity, select batteries with qualified capacity and internal resistance to plate lithium on copper wires. Set the lithium plating current to 0.02mA for both forward and reverse plating. Select a smaller lithium plating current to ensure uniform lithium plating.

[0054] S4. Set different rates and perform charge and discharge tests on the three-electrode battery at different rates to obtain the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate.

[0055] The method for setting different multipliers is to take values ​​around 1C for different multipliers, and to increase the values ​​of different multipliers in a stepwise manner from small to large.

[0056] The method for conducting charge-discharge tests on the three-electrode battery at different rates and obtaining the charge-discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate is as follows: a multi-channel instrument is used to connect the three voltage channels of the three-electrode battery: positive electrode-reference electrode, negative electrode-reference electrode, and positive electrode-negative electrode. The three potentials are observed to see if they are normal. At the same time, the electrical performance test cabinet is connected to the positive and negative electrodes of the three-electrode battery. After all the wiring is completed, the time interval between the acquisition of the multi-channel instrument and the electrical performance test cabinet is set to be consistent, and then the charge-discharge tests at different rates are started.

[0057] In this embodiment, five three-electrode batteries were fabricated, and charge-discharge tests were performed on the five three-electrode batteries at rates of 0.7C, 0.8C, 0.9C, 1C, and 1.1C, respectively. The charge-discharge potential curves of the batteries at different rates were recorded. Figure 2As shown, the charging and discharging potential trend curve of the negative electrode of the three-electrode battery at a 0.9C rate is obtained ④.

[0058] S5. Compare the charge-discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate with the standard charge-discharge potential curve, and calculate the polarization potential of the three-electrode battery at each rate by using the potential difference at the point where the two curves deviate the most.

[0059] The polarization potential at different rates is determined by comparing the potential curves between the positive and negative electrodes of a three-electrode battery with standard charge-discharge potential curves. Specifically, in this embodiment, the method for determining the polarization potential at different rates is as follows: Figure 2 As shown, curve ④, representing the negative electrode potential trend of a three-electrode battery at a 0.9C rate, is obtained. Curve ④ is then compared with... Figure 1 Comparing curve ③, near the end of charging, the negative electrode potential decreases and then begins to rise. At the inflection point where the decrease turns into the rise, the difference between curve ④ and curve ③ is the largest. At this charging rate, the negative electrode potential of the three-electrode battery deviates most from the standard curve at the lowest point of the curve. The potential difference at the point of maximum deviation between the two curves is taken as the polarization potential of the three-electrode battery, and the difference between the actual negative electrode potential of the three-electrode battery at the lowest point and the actual potential of the standard battery is taken as the polarization potential. For example, in this embodiment... Figure 2 At the mid-inflection point, the difference between the actual potential of the negative electrode of the three-electrode battery and the actual potential of the standard battery at a 0.9C rate was measured to be 0.12V.

[0060] Similarly, using the same method, the negative electrode potential trend curves during charging tests at 0.7C, 0.8C, 1C, and 1.1C rates were compared with curve ③ to obtain the polarization potential of the battery at different rates, as shown in the table below:

[0061] Table 1. Polarization potential of the battery at different rates

[0062]

[0063] S6. Disassemble the three-electrode battery to obtain the polarization potential and charge / discharge rate at the start of lithium plating.

[0064] In this step, the charge / discharge rate at the start of lithium plating is the minimum charge / discharge rate corresponding to the battery that undergoes lithium plating among the different rates in step S4; the polarization potential at the start of lithium plating is the polarization potential corresponding to the minimum charge / discharge rate.

[0065] For example, in this embodiment, batteries tested at different charging rates were disassembled. It was found that batteries tested at 0.7C and 0.8C rates did not exhibit lithium plating, while batteries tested at 0.9C, 1C, and 1.1C rates did. Therefore, lithium plating occurs at the interface when charging at rates above 0.9C. The negative electrode lithium plating polarization potential at 0.9C is 0.12V, thus the polarization potential of the lithium plating window is determined to be 0.12V. When subsequently charging this battery, the charging strategy should ensure that the charging rate does not exceed 0.9C.

[0066] In this embodiment, standard charge-discharge potential curves for the positive and negative electrodes are obtained. The potential curves of the three-electrode battery at different charge-discharge rates are compared with the standard potential curves to determine the polarization potential at different rates. Then, by disassembling the battery, the minimum charge rate that causes lithium plating is determined, yielding the minimum negative parameter polarization potential for lithium plating. Based on this potential, it is determined whether subsequent charge-discharge strategies will cause lithium plating. Compared to the usual method of using three-electrode battery testing to determine lithium plating potential, which typically only focuses on changes in the negative parameter potential and has a larger error, the lithium plating determination method in this embodiment can more accurately reflect and predict the occurrence of lithium plating at a certain charge rate.

[0067] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for characterizing the lithium plating window using battery polarization potential, characterized in that: Includes the following steps, S1. To manufacture a button cell including a positive electrode and a lithium plate, a button cell including a negative electrode and a lithium plate, and a button cell including a positive electrode and a negative electrode. S2. Charge and discharge the coin cell at a set rate to obtain the standard charge and discharge potential curves of the positive and negative electrodes of the coin cell. S3. Fabricate a wound cell and set a reference electrode on the wound cell to obtain a three-electrode cell; S4. Set different rates and perform charge and discharge tests on the three-electrode battery at different rates to obtain the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate. S5. Compare the charge and discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate with the standard charge and discharge potential curve, and calculate the polarization potential of the three-electrode battery at each rate by the potential difference at the point where the two curves deviate the most. S6. Disassemble the three-electrode battery to obtain the polarization potential and charge / discharge rate at the start of lithium plating.

2. The method for characterizing the lithium plating window using battery polarization potential according to claim 1, characterized in that: In step S1, the electrode sheet used to make the button cell is taken from the electrode sheet used to make the wound cell in step S3.

3. The method for characterizing the lithium plating window using battery polarization potential according to claim 1, characterized in that: In step S2, the set magnification is below 0.1C.

4. The method for characterizing the lithium plating window using battery polarization potential according to claim 2 or 3, characterized in that: In step S3, copper wire is used to connect the wound cell, with one end of the copper wire serving as a reference electrode to form a three-electrode cell.

5. The method for characterizing the lithium plating window using battery polarization potential according to claim 4, characterized in that: In step S4, the method for setting different magnifications is to take values ​​around 1C for each magnification.

6. The method for characterizing the lithium plating window using battery polarization potential according to claim 5, characterized in that: The different multiplier values ​​increase in a stepwise manner from small to large.

7. The method for characterizing the lithium plating window using battery polarization potential according to claim 5, characterized in that: In step S4, the method for conducting charge-discharge tests on the three-electrode battery at different rates and obtaining the charge-discharge potential curves of the positive and negative electrodes of the three-electrode battery at each rate is as follows: a multi-channel instrument is used to connect the three voltage channels of the three-electrode battery: positive electrode-reference electrode, negative electrode-reference electrode, and positive electrode-negative electrode. At the same time, the electrical performance test cabinet is connected to the positive and negative electrodes of the three-electrode battery, and charge-discharge tests at different rates are started.

8. The method for characterizing the lithium plating window using battery polarization potential according to claim 7, characterized in that: In step S6, the charge / discharge rate at the start of lithium plating is the minimum rate corresponding to the battery that undergoes lithium plating among the different rates in step S4.

9. The method for characterizing the lithium plating window using battery polarization potential according to claim 8, characterized in that: The polarization potential at the start of lithium plating is the polarization potential corresponding to the minimum rate.

10. The method for characterizing the lithium plating window using battery polarization potential according to claim 2, characterized in that: Before manufacturing the positive and negative electrodes for button batteries, they are first wiped on one side with a reagent.

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