Lithium iron phosphate battery lithium precipitation behavior monitoring method

Abstract

The invention belongs to the technical field of lithium battery detection, and discloses a lithium iron phosphate battery lithium precipitation behavior monitoring method, which comprises the following steps: sequentially carrying out a constant-current constant-voltage charging process, a standing process and a constant-current discharging process on a lithium iron phosphate battery, and collecting constant-voltage charging section data and constant-current discharging section data at a plurality of time points; and obtaining a first difference curve and a second difference curve according to the collected data, analyzing the lithium precipitation characteristics of the constant-current and constant-voltage charging process and the constant-current discharging process, and finally comprehensively judging the lithium precipitation state of the lithium iron phosphate battery. According to the method, the charging and discharging curve of the battery is processed and analyzed, the sampling interval time can be shortened during battery testing step setting, real-time monitoring of the whole life cycle of the lithium precipitation state of the battery can be simply, conveniently and accurately achieved in a lossless mode along with continuous updating of testing data, and compared with lossy detection, the method has the advantages of being low in cost, high in efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery testing technology, specifically, it relates to a method for monitoring lithium plating behavior in lithium iron phosphate batteries. Background Technology

[0002] Lithium iron phosphate (LiFePO4, LFP) batteries have become the core power source for electric vehicles and energy storage systems due to their high safety, long cycle life, and cost advantages. However, with the expansion of application scale and the increasing complexity of operating conditions, the performance limits and safety boundaries of batteries in actual operation have become key factors restricting the industry's development. Among these factors, lithium plating, as a major cause of battery failure and even thermal runaway, urgently requires effective monitoring.

[0003] Lithium plating essentially occurs when lithium ions break free from their normal intercalation pathway during charging and are reduced and deposited as metallic lithium on the graphite anode surface. Its root cause lies in the mismatch between battery kinetics and external operating conditions: at low temperatures (e.g., <0°C), the lithium-ion diffusion rate drops sharply, and the intercalation resistance increases dramatically; during high-current fast charging, the lithium-ion flux exceeds the upper limit of the anode intercalation rate. Both of these factors trigger the anode potential to drop below the metallic lithium deposition threshold, inducing lithium plating. Furthermore, this process exhibits a progressive deterioration characteristic: 1. Initial cycling: Trace amounts of lithium plating can reversibly re-intercalate during the constant-voltage stage, showing no obvious signs; 2. Mid-term accumulation: As the SEI film thickens and the electrolyte is consumed, the internal resistance increases, leading to a decrease in lithium-ion transport efficiency. Lithium plating intensifies at the end of the constant-current stage, and re-intercalation is incomplete during the constant-voltage stage; 3. Late-stage deterioration: Residual metallic lithium continues to accumulate until the discharge stage, forming irreversible deposits. Residual lithium not only consumes active lithium ions (accelerating capacity decay) but may also grow into lithium dendrites that pierce the separator, causing internal short circuits, or react with the electrolyte to release heat, inducing uncontrolled thermal runaway, significantly increasing safety risks.

[0004] Existing lithium plating monitoring technologies typically employ destructive testing and non-destructive electrochemical analysis, both of which have certain drawbacks: Destructive testing (such as SEM / XRD analysis after battery disassembly) involves expensive equipment, is time-consuming, and cannot be applied online. Non-destructive electrochemical analysis (such as dQ / dV and relaxation voltage models) relies on high-precision data and complex algorithms, exhibiting low sensitivity to early trace lithium plating, weak resistance to operating condition interference, and difficulty in achieving real-time monitoring throughout the entire lifecycle.

[0005] It is evident that the current lithium battery industry faces the challenge of simultaneously facing stringent cost reduction pressures and high-performance demands: while pursuing high energy density, fast charging, and long lifespan, intrinsic safety must be guaranteed. Therefore, developing a simple, low-cost, reliable, and online lithium plating real-time monitoring method suitable for battery system operation has become an urgent need to overcome industry bottlenecks. Summary of the Invention

[0006] Based on the above background, this invention proposes a method for monitoring lithium plating behavior in lithium iron phosphate batteries that is highly compatible with industry-standard battery testing methods and enables full-process monitoring. Compared with existing technologies, the method proposed in this invention is characterized by its ease of operation, low cost, and high accuracy, thereby improving the efficiency of battery research and development and failure analysis.

[0007] This invention provides a method for monitoring lithium plating behavior in lithium iron phosphate batteries, comprising:

[0008] S1: Perform a constant current and constant voltage charging process on the lithium iron phosphate battery and collect constant voltage charging data at least 500 time points.

[0009] S2: Allow the lithium iron phosphate battery to stand still;

[0010] S3: Perform a constant current discharge process on the lithium iron phosphate battery and collect constant current discharge segment data at at least 500 time points;

[0011] S4: Based on the constant voltage charging segment data obtained from S1 at multiple time points, the first differential curve is obtained. The lithium plating characteristics of the constant current and constant voltage charging process are analyzed based on the first differential curve, and the lithium plating state of the lithium iron phosphate battery is determined.

[0012] S5: Based on the constant current discharge segment data obtained from multiple time points in S3, the second differential curve is obtained. The lithium plating characteristics of the constant current discharge process are analyzed based on the second differential curve, and the lithium plating state of the lithium iron phosphate battery is determined.

[0013] Furthermore, S1 includes:

[0014] S101: Perform constant current and constant voltage charging on the lithium iron phosphate battery;

[0015] S102: Record the current, voltage and capacity at each time point in the constant voltage charging segment of S101.

[0016] S103: When the recorded current drops to 0.05C, proceed to S2; where 1C is the current intensity required for the lithium iron phosphate battery to be fully discharged in 1 hour.

[0017] Furthermore, S2 includes: letting the lithium iron phosphate battery stand for 10-60 minutes.

[0018] Furthermore, S3 includes:

[0019] S301: Perform constant current discharge on lithium iron phosphate batteries;

[0020] S302: Record the discharge time points of S301 and the corresponding current, voltage and capacity;

[0021] S303: When the recording voltage drops to the minimum operating voltage of the lithium iron phosphate battery, enter S4; the minimum operating voltage range is 2.0~2.5V.

[0022] Furthermore, S4 includes:

[0023] S401: Plot the constant voltage charging segment data collected by S1 at multiple time points into a time-current curve;

[0024] S402: Perform a differential processing on the time-current curve obtained in S401 to obtain the first differential curve;

[0025] S403: If the first difference curve obtained from S402 is in logarithmic form, then it is determined that there are no obvious lithium plating characteristics in stage S1.

[0026] If the first difference curve obtained by S402 has a characteristic peak, it is determined that lithium plating occurs in stage S1.

[0027] S404: For the first difference curve with characteristic peaks obtained from S403, the time corresponding to the peak position of the characteristic peak is the time when lithium deposition occurs; and the larger the peak value, the more lithium is deposited in the S1 stage.

[0028] Furthermore, S5 includes:

[0029] S501: Plot the constant current discharge segment data collected by S3 at multiple time points into a capacity-voltage curve;

[0030] S502: Perform a differential processing on the capacitance-voltage curve obtained in S401 to obtain a second differential curve;

[0031] S503: If the second difference curve obtained from S502 is in logarithmic form, then it is determined that there are no obvious lithium plating characteristics in the S1-S3 stage;

[0032] If the second difference curve obtained by S502 has a characteristic peak, it is determined that lithium plating occurs in the S1-S3 stage.

[0033] S504: For the second difference curve with characteristic peaks obtained from S503, determine the peak intensity of the characteristic peaks corresponding to the lithium deposition intensity; and the larger the peak value, the more lithium is deposited in the S1-S3 stage.

[0034] The beneficial effects of this invention are:

[0035] (i) This invention achieves full monitoring of the lithium plating state of the battery by adopting constant current and constant voltage charging, resting and constant current discharging processes for lithium iron phosphate batteries, combined with data acquisition from battery charging and discharging testing instruments. It eliminates the need to disassemble the battery, greatly simplifies the operation process and improves the testing efficiency.

[0036] (ii) The present invention uses differential processing of constant voltage segment data and constant current discharge segment data in constant current and constant voltage charging process, combined with differential curve analysis, to accurately identify lithium plating characteristics in battery charging segment and effectively judge the dissolution behavior of lithium ions in battery discharge segment, thus achieving accurate assessment of battery lithium plating state.

[0037] (iii) The present invention uses ≥500 data points as the judgment standard, which ensures the accuracy and stability of the data, improves the reliability of the detection, and overcomes the problem of insufficient accuracy and stability in the termination voltage detection and recording process in the prior art;

[0038] (iv) This invention enables real-time monitoring of the lithium plating state of a battery throughout its entire life cycle. Compared with destructive testing methods, it is non-destructive and non-invasive, and the test data is constantly updated, which can reflect the actual lithium plating state of the battery in a timely manner, providing an important basis for battery performance evaluation and fault early warning. Attached Figure Description

[0039] Figure 1 The first differential curve is the time-current difference curve of the constant voltage section of the charging curves at different rates (0.1C-0.4C) and different number of cycles in Example 1.

[0040] Figure 2 The capacity-voltage difference curves (second difference curves) are the discharge curves of different discharge cycles at different rates (0.1C-0.4C) in Example 1.

[0041] Figure 3 The images show the battery disassembly interfaces after 20 cycles at different rates (0.1C-0.4C) in Example 1; where: (a) has a rate of 0.1C, (b) has a rate of 0.2C, (c) has a rate of 0.3C, and (d) has a rate of 0.4C. Detailed Implementation

[0042] This invention provides a method for monitoring lithium plating behavior in lithium iron phosphate batteries, comprising:

[0043] S1: Perform constant current and constant voltage charging on lithium iron phosphate batteries, and collect constant voltage charging data at multiple time points using battery charge and discharge testing instruments.

[0044] Specifically, it includes:

[0045] S101: Perform constant current and constant voltage charging on the lithium iron phosphate battery;

[0046] S102: Record the current, voltage and capacity at each time point in the constant voltage charging segment of S101.

[0047] S103: When the recorded current drops to 0.05C, proceed to S2; where 1C is the current intensity required for the lithium iron phosphate battery to be fully discharged in 1 hour.

[0048] S2: Allow the lithium iron phosphate battery to stand still.

[0049] As a preferred embodiment, the settling time is 10-60 minutes.

[0050] S3: Perform a constant current discharge process on the lithium iron phosphate battery, and collect constant current discharge data at multiple time points using a battery charge and discharge test instrument.

[0051] Specifically including

[0052] S301: Perform constant current discharge on lithium iron phosphate batteries;

[0053] S302: Record the discharge time points of S301 and the corresponding current, voltage and capacity;

[0054] S303: When the recording voltage drops to the minimum operating voltage of the lithium iron phosphate battery, enter S4; the minimum operating voltage range is 2.0~2.5V.

[0055] For S1 and S3, the acquisition accuracy should be adjusted to ensure that the sum of the acquisition time points of S1 and S3 is ≥500.

[0056] S4: Based on the constant voltage charging segment data obtained from S1 at multiple time points, the first differential curve is obtained, and the lithium plating characteristics of the constant current and constant voltage charging process are analyzed based on the first differential curve.

[0057] Specifically, it includes:

[0058] S401: Plot the constant voltage charging segment data collected by S1 at multiple time points into a time-current curve;

[0059] S402: Perform a differential processing on the time-current curve obtained in S401 to obtain the first differential curve;

[0060] S403: If the first difference curve obtained from S402 is in logarithmic form, then it is determined that there are no obvious lithium plating characteristics in stage S1.

[0061] If the first difference curve obtained from S402 has a characteristic peak, it is determined that lithium plating occurs in stage S1 (the corresponding electrochemical reaction is Li⁺ + e⁻ → Li). 0 (Lithium metal));

[0062] S404: Based on the first difference curve with characteristic peaks obtained from S403, determine the time corresponding to the peak position of the characteristic peak in the S1 stage, which is the time when lithium deposition occurs; and the larger the peak value, the more lithium is deposited in the S1 stage.

[0063] S5: Based on the constant current discharge segment data obtained from multiple time points in S3, a second differential curve is obtained, and the lithium plating characteristics of the constant current discharge process are analyzed based on the second differential curve.

[0064] S501: Plot the constant current discharge segment data collected by S3 at multiple time points into a capacity-voltage curve;

[0065] S502: Perform a differential processing on the capacitance-voltage curve obtained in S401 to obtain a second differential curve;

[0066] S503: If the second difference curve obtained from S502 is in logarithmic form, then it is determined that there are no obvious lithium plating characteristics in the S1-S3 stage;

[0067] If the second difference curve obtained by S502 has a characteristic peak, it is determined that lithium plating occurs in the S1-S3 stage.

[0068] S504: Based on the second difference curve with characteristic peaks obtained in S503, determine that the peak intensity of the characteristic peak corresponds to the lithium deposition intensity in the S1-S3 stage; and the larger the peak value, the more lithium is deposited in the S1-S3 stage.

[0069] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the protection scope of the present invention.

[0070] In the description of this invention, it should be understood that the term "C" refers to the battery rate, which means the current intensity required for the battery to release its rated capacity within a specified time during charging or discharging. In this invention, the battery 1C is 4A. The terms "t", "I", "Q" and "V" refer to the test time, current, capacity and voltage of the battery being tested, respectively.

[0071] This embodiment uses a freshly manufactured 4Ah lithium iron phosphate pouch battery as the test subject, with an ambient temperature of -10℃. The battery was subjected to a charge-discharge cycle of 20 cycles at a rate of 0.1 / 0.2 / 0.3 / 0.4C.

[0072] The weekly charge and discharge operation includes the battery undergoing constant current and constant voltage charging, resting, and constant current discharging. The battery charge and discharge test instrument collects time, current, voltage, and capacity data for each battery at each stage. The acquisition accuracy is adjusted to ensure that the amount of data obtained in the constant voltage stage of the constant current and constant voltage charging process and the amount of data obtained in the constant current discharging process are ≥500 each.

[0073] Starting from week 1, the battery charge-discharge curves are processed at 5-week intervals to determine the lithium plating boundary of the battery.

[0074] Perform a differential processing on the constant voltage section of the charging curve, see [link / reference]. Figure 1 At 0.1C, the curve is logarithmic in form with no obvious lithium plating characteristics. At 0.2-0.4C, the curve shows obvious lithium plating characteristic peaks in the initial stage, which gradually become stronger as the rate increases. At the same current density, the time of lithium plating also increases with the number of cycles, indicating that lithium plating begins at 0.2C, accumulates with the number of cycles, and gradually intensifies with the rate.

[0075] Perform a differential processing on the discharge curve, see [link / reference] Figure 2 At 0.1C, the curve showed no obvious lithium plating characteristics. At 0.2-0.4C, the curve showed obvious lithium plating characteristic peaks in the initial stage, which gradually became stronger as the rate increased, indicating that lithium plating began to occur at 0.2C and gradually intensified with the increase of the rate.

[0076] Cycle the battery 20 times at 0.1 / 0.1C, 0.2 / 0.2C, 0.3 / 0.3C, and 0.4 / 0.4C rates respectively. After disassembly, observe the negative electrode interface. (See [reference needed]). Figure 3 Analysis of the disassembly photos shows that after 30 cycles at 0.1C, the battery exhibits no obvious lithium plating at the interface, indicating good lithium intercalation. This suggests that no lithium plating occurs at 0.1C, while at 0.2C, lithium plating is evident at the edge of the negative electrode, with the center appearing golden yellow (indicating a high degree of lithium intercalation). At 0.3C, the lithium intercalation area further expands. As the rate increases, the central portion gradually changes from golden yellow to grayish-black, indicating a gradual decrease in the degree of lithium intercalation at the negative electrode. With increasing rate, the lithium plating area continuously increases, until at 0.4C, the electrode is essentially covered by grayish-white deposits.

[0077] The results above show that lithium plating occurs in the range of 0.2-0.4C, and the plating intensifies with increasing rate of change. The effectiveness of each method in detecting lithium plating is judged based on the disassembly results.

[0078] As can be seen, by processing and analyzing the battery charge and discharge curves, this invention can shorten the sampling interval time when setting up battery testing steps. With the continuous updating of test data, it can easily, accurately and non-destructively achieve real-time monitoring of the lithium plating state of the battery throughout its entire life cycle. Compared with destructive testing, it has the characteristics of low cost and high efficiency.

[0079] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A method for monitoring lithium precipitation behavior of a lithium iron phosphate battery, characterized in that, The method comprises the following steps: S1: constant current and constant voltage charging process is performed on the lithium iron phosphate battery, and constant voltage charging segment data at at least 500 time points are collected; S2: the lithium iron phosphate battery is subjected to static treatment; S3: constant current discharging process is performed on the lithium iron phosphate battery, and constant current discharging segment data at at least 500 time points are collected; S4: a first differential curve is obtained according to the constant voltage charging segment data at the plurality of time points obtained in S1, the lithium precipitation characteristics of the constant current and constant voltage charging process are analyzed according to the first differential curve, and the lithium precipitation state of the lithium iron phosphate battery is judged; S5: a second differential curve is obtained according to the constant current discharging segment data at the plurality of time points obtained in S3, the lithium precipitation characteristics of the constant current discharging process are analyzed according to the second differential curve, and the lithium precipitation state of the lithium iron phosphate battery is judged.

2. The method for monitoring lithium precipitation behavior of a lithium iron phosphate battery according to claim 1, characterized in that, S1 comprises: S101: constant current and constant voltage charging is performed on the lithium iron phosphate battery; S102: each time point in the constant voltage charging segment of S101 and the current, voltage and capacity corresponding to each time point are recorded; S103: when the recorded current decreases to 0.05C, S2 is entered; wherein 1C is the current intensity required for the lithium iron phosphate battery to be completely discharged in 1 hour.

3. The method for monitoring lithium precipitation behavior of a lithium iron phosphate battery according to claim 1, characterized in that, S2 comprises: The lithium iron phosphate battery is statically treated for 10-60 min. 4.The lithium precipitation behavior monitoring method of a lithium iron phosphate battery according to claim 1, wherein S3 S301: constant current discharging is performed on the lithium iron phosphate battery; S302: each time point in the discharging of S301 and the current, voltage and capacity corresponding to each time point are recorded; S303: when the recorded voltage decreases to the minimum working voltage of the lithium iron phosphate battery, S4 is entered; the minimum working voltage is in the range of 2.0-2.5 V. S401: the constant voltage charging segment data at the plurality of time points collected in S1 are plotted into a time-current curve; 5. The method for monitoring lithium precipitation behavior of a lithium iron phosphate battery according to claim 1, wherein S4 S402: the time-current curve obtained in S401 is subjected to first-order differential processing to obtain a first differential curve; S403: when the first differential curve obtained in S402 is in a logarithmic form, it is judged that there is no obvious lithium precipitation characteristic in the S1 stage; When the first differential curve obtained in S402 has a characteristic peak, it is judged that lithium precipitation occurs in the S1 stage; S404: for the first differential curve with a characteristic peak obtained in S403, the time corresponding to the peak position of the characteristic peak is judged as the time when lithium precipitation occurs; And the greater the peak value is, the more lithium is precipitated in the S1 stage. S501: the constant current discharging segment data at the plurality of time points collected in S3 are plotted into a capacity-voltage curve; S502: the capacity-voltage curve obtained in S401 is subjected to first-order differential processing to obtain a second differential curve; 6.The lithium plating behavior monitoring method of a lithium iron phosphate battery according to claim 1, wherein S5 S503: when the second differential curve obtained in S502 is in a logarithmic form, it is judged that there is no obvious lithium precipitation characteristic in the S1-S3 stage; When the second differential curve obtained in S502 has a characteristic peak, it is judged that lithium precipitation occurs in the S1-S3 stage; S504: for the second differential curve with a characteristic peak obtained in S503, the peak intensity of the characteristic peak is judged as the lithium precipitation intensity; and the greater the peak value is, the more lithium is precipitated in the S1-S3 stage. ​ ​ ​

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