A method for online detection of lithium evolution

Abstract

The present application belongs to the technical field of lithium ion batteries, and particularly relates to a method for on-line detection of lithium precipitation. The method comprises (1) performing a charging experiment on a battery containing a lithium metal reference electrode, monitoring the negative reference potential OCP and the full battery open circuit voltage OCV under different SOC states 负参电位 (2) obtaining the full battery threshold voltage of the battery containing the lithium metal reference electrode according to formula 1, and further obtaining the relationship curve between the full battery threshold voltage and the SOC of the battery containing the lithium metal reference electrode in the charging experiment; (3) performing a charging experiment on a battery to be tested, obtaining the full battery voltage of the battery to be tested; under the same SOC state, comparing the full battery voltage of the battery to be tested with the full battery threshold voltage of the battery containing the lithium metal reference electrode in step (2), and judging whether lithium precipitation occurs. The method can confirm whether lithium precipitation occurs according to the measured full battery actual voltage of the battery to be tested during the charging experiment, and has potential value for application to the BMS of a whole vehicle.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to an online method for detecting lithium plating. Background Technology

[0002] Lithium-ion batteries are widely used in electronic products such as watches, mobile phones, and computers due to their excellent performance, such as high power and energy density, environmental friendliness, and long cycle and calendar life. Currently, lithium-ion battery charging technology is one of the key aspects of their application and a hot research topic. To reduce the charging time of power batteries, high-current charging is often used. However, high-current charging of power lithium-ion batteries can lead to a rapid increase in battery temperature, capacity decay, and a decrease in lifespan. Lithium loss (LLI) is one of the main mechanisms of performance degradation and aging of power lithium-ion batteries, usually caused by electrolyte decomposition, SEI film formation, and lithium plating on the negative electrode. Among these factors, lithium plating leads to irreversible capacity decay and poses safety hazards. Lithium plating typically occurs during fast charging, low-temperature charging, and / or long-term cycling, and it occurs when the negative electrode potential is below 0V vs. Li / Li. + Furthermore, the deposited lithium not only reacts with the electrolyte but also becomes electrically isolated from the negative electrode, both of which lead to irreversible loss of active lithium and capacity. In addition, the deposited lithium formed during the lithium plating process can penetrate the separator, causing internal short circuits; and the active deposited lithium can lower the onset temperature of thermal runaway, thus leading to safety issues.

[0003] Considering the negative impacts of lithium plating, reliable, in-situ, and real-time detection methods are crucial for developing fast and safe charging processes. Furthermore, in-situ quantitative detection can estimate the aging state of LIBs in real time by analyzing the amount of lithium plating, while real-time detection can improve charging safety by adjusting charging strategies based on the presence of lithium plating. However, detecting lithium plating is very challenging because many factors influence it, including temperature, charge rate, state of charge (SOC), battery design, electrolyte composition, negative electrode capacity, N / P ratio, and battery defects. While significant efforts have been made in developing detection methods, some methods are only usable in laboratory settings where experimental conditions can be controlled and various instruments can be used. For automotive applications, where batteries operate under unpredictable conditions, detecting lithium plating is even more difficult due to the limited availability of instruments and measurement parameters.

[0004] To date, there are no reliable electrochemical manipulation methods or in-situ methods that can achieve early lithium plating detection in a given two-electrode full-cell system. Previously, differential analysis methods based on coulombic efficiency or voltage and / or capacity were generally used for early lithium plating detection, but these methods cannot detect lithium plating from the beginning; they can only detect lithium plating by processing the data after cycling. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art, such as the inability to detect the presence of lithium plating in batteries in real time, and thus provide a method for online detection of lithium plating.

[0006] To this end, the present invention provides the following technical solution.

[0007] This invention discloses an online method for detecting lithium plating, comprising the following steps:

[0008] (1) A charging experiment was conducted on a battery containing a lithium metal reference electrode, and the negative reference potential OCP at different SOC states was monitored. 负参电位 and the open-circuit voltage (OCV) of the full battery;

[0009] (2) The full cell threshold voltage of the battery containing the lithium metal reference electrode is obtained according to Equation 1, and then the relationship curve between the full cell threshold voltage and SOC of the battery containing the lithium metal reference electrode in the charging experiment is obtained.

[0010] (3) Conduct a charging experiment on the battery under test to obtain the full cell voltage of the battery under test; under the same SOC state, compare the full cell voltage of the battery under test with the full cell threshold voltage of the battery containing the lithium metal reference electrode in step (2) to determine whether lithium plating has occurred.

[0011] U 全电池，阈值 =OCV+OCP 负参电位 Formula 1

[0012] Among them, OCP 负参电位 This refers to the potential difference between the negative electrode and the lithium metal reference electrode.

[0013] In step (1), the conditions for conducting the charging experiment on the battery containing the lithium metal reference electrode are: reaching the charge / discharge cutoff voltage at a charge / discharge rate of ≤0.05C.

[0014] The battery containing the lithium metal reference electrode is of the same type as the battery under test.

[0015] The battery under test is a two-electrode battery.

[0016] The battery under test is a lithium-ion battery.

[0017] The lithium metal reference electrode in the battery containing the lithium metal reference electrode is a lithium metal-coated conductive copper wire.

[0018] If the full-cell voltage of the battery under test is not less than the full-cell threshold voltage of the battery containing the lithium metal reference electrode, it indicates that lithium plating has occurred in the battery under test.

[0019] The online detection method for lithium plating provided by this invention includes the following principles:

[0020] Lithium plating in lithium-ion batteries primarily occurs at the negative electrode. Therefore, during use, overpotential at the negative electrode can cause the actual negative electrode potential to drop below 0V (vs Li / Li). + When this happens, lithium plating will occur at the negative electrode.

[0021] During charging, the voltage V at the negative terminal... 负极 Open circuit potential (OCP) 负极 and overpotential η 负极 The following relationship exists:

[0022] V 负极 =OCP 负极 -η 负极 Formula 2

[0023] During charging, the voltage V at the positive terminal... 正极 Open circuit potential (OCP) 正极 and overpotential η 正极 The following relationship exists:

[0024] V 正极 =OCP 正极 +η 正极 Formula 3

[0025] In actual cycling, for a normal two-electrode battery, only the full-cell voltage U can be directly measured; among which, the full-cell voltage U 全电池 and negative voltage V 负极 Positive voltage V 正极 The following relationship must be satisfied:

[0026] U 全电池 =V 正极 -V 负极 Formula 4

[0027] During charging and discharging, the full battery voltage U 全电池 and the open-circuit voltage OCV of the full battery 全电池 Full cell overpotential η 全电池 The following relationship must be satisfied:

[0028] U 全电池 =OCV 全电池 +η 全电池 Formula 5

[0029] Combining Equations 2 and 5, we can obtain the following relationship:

[0030] OCV 全电池 +η 全电池 =V 正极 -V 负极 Formula 6

[0031] OCV 全电池 +η 全电池 =OCP 正极 +η 正极 -OCP 负极 +η 负极 Formula 7

[0032] And due to OCV 全电池 =OCP 正极 -OCP 负极 The following relationship can be inferred:

[0033] η 全电池 =η 正极 +η 负极 Formula 8

[0034] In a two-electrode cell, the positive electrode overpotential η 正极 Negative overpotential η 负极 Full cell overpotential η 全电池 None of these can be measured directly; the only measurable value is the open-circuit voltage (OCV) of the full battery. 全电池 For the positive open-circuit potential OCP 正极 Open circuit potential (OCP) of negative electrode 负极 Neither of these can be directly measured, but the curve of open-circuit potential versus SOC can be obtained by measuring a battery containing a lithium metal reference electrode at a low rate, and then applied equivalently to a two-electrode battery. Therefore, in a two-electrode battery, when the open-circuit voltage OCV... 全电池 Knowing the situation, assuming the positive electrode overpotential is negligible, then there exists η. 全电池 =η 负极 It is approximated that the overpotential of the full cell is equal to the overpotential of the negative electrode. During charging, if lithium plating does not occur, the actual potential of the negative electrode should not be lower than 0V (vsLi / Li). + When considering the threshold case, i.e., the actual potential of the negative electrode is equal to 0V (vs Li / Li) + ), which is OCP 负极，阈值 =η 负极，阈值 .

[0035] Based on the above assumptions and derivations, the lithium plating threshold of the full cell voltage can be obtained through the following relationship:

[0036] U 全电池，阈值 =OCV 全电池，阈值 +η 全电池，阈值 =OCV 全电池，阈值 +η 负极，阈值 =OCV 全电池，阈值 +OCP 负极，阈值

[0037] During the battery charging experiment containing a lithium metal reference electrode, OCP负极，阈值 The potential difference between the negative electrode and the reference electrode is denoted as OCP. 负参电位 OCV 全电池，阈值 This is the open-circuit voltage of the full cell containing a lithium metal reference electrode, which satisfies Equation 1:

[0038] U 全电池，阈值 =OCV+OCP 负参电位 Formula 1.

[0039] In this invention, the battery containing a lithium metal reference electrode and the battery under test are of the same type. The relationship curve between the lithium plating threshold voltage and the state of charge (SOC) of this type of battery can be obtained first using the battery containing the lithium metal reference electrode. Then, the full cell voltage of the battery under test is tested in real time. When the full cell voltage of the battery under test exceeds the lithium plating threshold voltage of the same SOC state, it indicates that the battery under test has lithium plating.

[0040] The method provided by this invention can detect whether lithium plating occurs in batteries of the same type as those containing a lithium metal reference electrode. After obtaining the relationship curve between the lithium plating threshold voltage and the state of charge (SOC), this invention can perform real-time detection of lithium plating in batteries of the same type. When the battery type changes, the relationship curve between the lithium plating threshold voltage and SOC for the changed battery type is obtained again, thereby detecting lithium plating in that type of battery.

[0041] The technical solution of this invention has the following advantages:

[0042] 1. The present invention provides an online method for detecting lithium plating, the method comprising (1) performing a charging experiment on a battery containing a lithium metal reference electrode and monitoring the negative reference potential OCP under different SOC states. 负参电位 (1) Obtain the open-circuit voltage (OCV) of the full battery; (2) Obtain the full battery threshold voltage of the battery containing the lithium metal reference electrode according to Equation 1, and then obtain the relationship curve between the full battery threshold voltage and SOC of the battery containing the lithium metal reference electrode in the charging experiment; (3) Conduct a charging experiment on the battery to be tested to obtain the full battery voltage of the battery to be tested; Under the same SOC state, compare the full battery voltage of the battery to be tested with the full battery threshold voltage of the battery containing the lithium metal reference electrode in step (2) to determine whether lithium plating has occurred. This method can confirm whether lithium plating has occurred based on the actual full battery voltage measured during the charging experiment of the battery to be tested, and has potential value for application to the whole vehicle BMS. The online detection method for lithium plating provided by this invention, through reasonable assumptions, can be applied to lithium-ion batteries with different material systems, and can test the lithium plating phenomenon under different temperatures and different charging rates. The test results are highly accurate and have the advantages of wide applicability and high efficiency.

[0043] The online lithium plating detection method provided by this invention can accurately determine whether lithium plating exists in the battery under test by comparing the full-cell voltage of the battery under test during the charging experiment with the full-cell threshold voltage of the battery containing a lithium metal reference electrode. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is the relationship curve between the full-cell threshold voltage and the state of charge (SOC) of the battery containing a lithium metal reference electrode in Embodiment 1 of the present invention.

[0046] Figure 2 This is the relationship curve between the full cell voltage and the state of charge (SOC) of the lithium-ion battery under test in Example 2 of this invention.

[0047] Figure 3 This is the relationship curve between the full cell voltage and the state of charge (SOC) of the lithium-ion battery under test in Example 3 of this invention.

[0048] Figure 4 This is the relationship curve between the full cell voltage and the state of charge (SOC) of the lithium-ion battery under test in Example 4 of this invention.

[0049] Figure 5 This is the curve showing the relationship between the full-cell voltage and SOC of the lithium-ion battery under test in Example 5 of this invention. Detailed Implementation

[0050] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0051] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0052] Example 1

[0053] This embodiment provides a method for online detection of lithium plating, specifically including the following steps:

[0054] The lithium-ion battery with a lithium metal reference electrode used in this embodiment has a capacity of 100mAh. This battery contains one positive electrode, two negative electrodes, and one reference electrode. This lithium-ion battery with a lithium metal reference electrode is a three-electrode battery, wherein the positive electrode material is LiNi. 0.6 Co 0.1 Mn 0.3 O2, the negative electrode is made of graphite, and the reference electrode is lithium metal coated conductive copper wire.

[0055] A charging experiment was conducted on the lithium-ion battery containing a lithium metal reference electrode. The battery was charged to 4.35V at 0.05C, and the full-cell voltage and negative reference potential were monitored. The full-cell voltage was approximated as the open-circuit voltage OCV, and the negative reference potential OCP was approximated as OCP. 负参电位 As the open-circuit voltage of the negative electrode, the negative reference potential refers to the potential difference between the negative electrode and the lithium metal reference electrode.

[0056] Based on Equation 1, the full-cell threshold voltage U of a three-electrode lithium-ion battery containing a lithium metal reference electrode under different states of charge (SOC) is calculated. 全电池，阈值 OCP 负参电位 OCV was obtained through charging experiments, U 全电池，阈值 U is obtained through calculation using Equation 1. 全电池，阈值 The relationship curve with SOC, such as Figure 1 As shown, Figure 1 The curve shown is the relationship between the lithium plating threshold voltage and the state of charge (SOC). 全电池，阈值 It is the lowest voltage at which lithium-ion batteries will exhibit lithium plating, also known as the lithium plating threshold voltage.

[0057] U 全电池，阈值 =OCV+OCP 负参电位 Formula 1

[0058] A charging experiment was conducted on the battery under test to obtain the full-cell voltage of the battery under test. The voltage under test was compared with the full-cell threshold voltage of a lithium-ion battery containing a lithium metal reference electrode to determine whether lithium plating has occurred.

[0059] When the full-cell voltage of the battery under test is not lower than the lithium plating threshold voltage of a lithium-ion battery containing a lithium metal reference electrode, it indicates that lithium plating has occurred in the battery under test.

[0060] Example 2

[0061] This embodiment provides a method for online detection of lithium plating, specifically including the following steps:

[0062] The battery under test in this embodiment is the same type of battery as the lithium-ion battery containing a lithium metal reference electrode in Example 1. The battery under test in this embodiment has a capacity of 100mAh, contains one positive electrode and two negative electrodes, and is a two-electrode lithium-ion battery. The material of the positive electrode is LiNi. 0.6 Co 0.1 Mn 0.3 O2, the negative electrode is made of graphite.

[0063] The lithium-ion battery under test was charged at 0.5C to a cutoff voltage of 4.35V at 25℃ to obtain the full-cell voltage of the lithium-ion battery under test. Figure 2 As shown, the relationship curve between lithium plating threshold voltage and SOC in Example 1 is compared. From Figure 2 As can be seen, the full-cell voltage of the lithium-ion battery under test in this embodiment never exceeded the lithium plating threshold voltage, indicating that the lithium-ion battery under test in this embodiment did not exhibit lithium plating when charged at a 0.5C rate. To verify this accuracy, the battery cell was disassembled, and no lithium plating was observed.

[0064] Example 3

[0065] This embodiment provides a method for online detection of lithium plating, specifically including the following steps:

[0066] The battery under test in this embodiment is the same type of battery as the lithium-ion battery containing a lithium metal reference electrode in Example 1. The battery under test in this embodiment has a capacity of 100mAh, contains one positive electrode and two negative electrodes, and is a two-electrode lithium-ion battery. The material of the positive electrode is LiNi. 0.6 Co 0.1 Mn 0.3 O2, the negative electrode is made of graphite.

[0067] The lithium-ion battery under test was charged at 1.0C to a cutoff voltage of 4.35V at 25℃ to obtain the full-cell voltage of the lithium-ion battery under test. Figure 3 As shown, the relationship between lithium plating threshold voltage and SOC is compared with that in Example 1. From Figure 3 As can be seen, the full-cell voltage of the lithium-ion battery under test in this embodiment exceeds the lithium plating threshold voltage at 40% SOC, indicating that lithium plating occurs in the lithium-ion battery under test in this embodiment. To verify the accuracy, the cell was disassembled, and slight lithium plating was found.

[0068] Example 4

[0069] This embodiment provides a method for online detection of lithium plating, specifically including the following steps:

[0070] The battery under test in this embodiment is the same type of battery as the lithium-ion battery containing a lithium metal reference electrode in Example 1. The battery under test in this embodiment has a capacity of 100mAh, contains one positive electrode and two negative electrodes, and is a two-electrode lithium-ion battery. The material of the positive electrode is LiNi. 0.6 Co 0.1 Mn 0.3 O2, the negative electrode is made of graphite.

[0071] The lithium-ion battery under test was charged at 3.0C to a cutoff voltage of 4.35V at 25℃ to obtain the full-cell voltage of the lithium-ion battery under test. Figure 4 As shown, the relationship between lithium plating threshold voltage and SOC is compared with that in Example 1. From Figure 4 As can be seen, the full-cell voltage of the lithium-ion battery under test in this embodiment exceeded the lithium plating threshold voltage at the very beginning of the charging experiment, indicating that lithium plating occurred in the lithium-ion battery under test in this embodiment. To verify the accuracy, the battery cell was disassembled, and severe lithium plating was found.

[0072] Example 5

[0073] This embodiment provides a method for online detection of lithium plating, specifically including the following steps:

[0074] The battery under test in this embodiment is the same type of battery as the lithium-ion battery containing a lithium metal reference electrode in Example 1. The battery under test in this embodiment has a capacity of 100mAh, contains one positive electrode and two negative electrodes, and is a two-electrode lithium-ion battery. The material of the positive electrode is LiNi. 0.6 Co 0.1 Mn 0.3 O2, the negative electrode is made of graphite.

[0075] The lithium-ion battery under test was charged at 0°C and 1.0C to a cutoff voltage of 4.35V to obtain the full-cell voltage of the lithium-ion battery under test. Figure 5 As shown, the relationship between lithium plating threshold voltage and SOC is compared with that in Example 1. From Figure 5 As can be seen, the full-cell voltage of the lithium-ion battery under test in this embodiment exceeded the lithium plating threshold voltage at the very beginning of the charging experiment, indicating that lithium plating occurred in the lithium-ion battery under test in this embodiment. To verify the accuracy, the battery cell was disassembled, and severe lithium plating was found.

[0076] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for online detection of lithium plating, characterized in that, Includes the following steps: (1) A charging experiment was conducted on a battery containing a lithium metal reference electrode, and the negative reference potential OCP at different SOC states was monitored. 负参电位 and the open-circuit voltage (OCV) of the full battery; (2) The full cell threshold voltage of the battery containing the lithium metal reference electrode is obtained according to Equation 1, and then the relationship curve between the full cell threshold voltage and SOC of the battery containing the lithium metal reference electrode in the charging experiment is obtained. (3) Perform a charging experiment on the battery to be tested to obtain the full cell voltage of the battery to be tested; under the same SOC state, compare the full cell voltage of the battery to be tested with the full cell threshold voltage of the battery containing the lithium metal reference electrode in step (2) to determine whether lithium plating has occurred. Formula 1 Among them, OCP 负参电位 This refers to the potential difference between the negative electrode and the lithium metal reference electrode.

2. The method according to claim 1, characterized in that, In step (1), the conditions for conducting the charging experiment on the battery containing the lithium metal reference electrode are: reaching the charge / discharge cutoff voltage at a charge / discharge rate of ≤0.05C.

3. The method according to claim 1 or 2, characterized in that, The battery containing the lithium metal reference electrode is of the same type as the battery under test.

4. The method according to claim 1 or 2, characterized in that, The battery under test is a two-electrode battery.

5. The method according to claim 1 or 2, characterized in that, The battery under test is a lithium-ion battery.

6. The method according to claim 1 or 2, characterized in that, The lithium metal reference electrode in the battery containing the lithium metal reference electrode is a lithium metal-coated conductive copper wire.

7. The method according to claim 1 or 2, characterized in that, If the full-cell voltage of the battery under test is not less than the full-cell threshold voltage of the battery containing the lithium metal reference electrode, it indicates that lithium plating has occurred in the battery under test.

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