Method and device for evaluating manganese dissolution of lithium manganese iron phosphate material

Abstract

The invention relates to the technical field of energy storage batteries, in particular to an evaluation method and an evaluation device for manganese dissolution of a lithium manganese iron phosphate material. By monitoring the capacity change rate of the to-be-detected battery in the initial charge-discharge cycle in the LMFP manganese characteristic high-voltage platform interval, the manganese dissolution of the lithium manganese iron phosphate material is predicted. The evaluation method for manganese dissolution of the lithium manganese iron phosphate material has the characteristics of rapidness, high efficiency, nondestructive detection, simple operation, low cost and high throughput potential, is standardized in process, is suitable for parallel rapid screening of a large number of samples, and is perfectly suitable for rapid evaluation and screening in the initial stage of material research and development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage batteries, in particular to a manganese dissolution evaluation method and device for lithium manganese iron phosphate material. BACKGROUND

[0002] Lithium manganese iron phosphate (LiMnxFe1-xPO4, LMFP) material has attracted extensive attention due to its high safety and high energy density. However, manganese dissolution is a major challenge, and the dissolved manganese ions will migrate to the negative electrode to destroy the SEI film, resulting in accelerated capacity decay. Accurate evaluation of the manganese dissolution tendency of the material is crucial for material development and quality control. The current mainstream methods in the industry all require destructive disassembly of the cycled battery, followed by detection of the positive or negative electrode material using inductively coupled plasma optical emission spectrometry (ICP-OES / MS) or X-ray fluorescence spectrometry (XRF) technology. Although these methods are accurate, they are time-consuming, labor-intensive, costly, and destructive to the sample, and cannot meet the needs of rapid iterative research and development. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies and shortcomings of the prior art and provide a manganese dissolution evaluation method for lithium manganese iron phosphate material.

[0004] To achieve the above-mentioned purpose, the following solutions are adopted in the present application:

[0005] A manganese dissolution evaluation method for lithium manganese iron phosphate material, which quickly predicts the manganese dissolution of lithium manganese iron phosphate material by monitoring the capacity change rate of the test battery in the initial charge-discharge cycle in the high-voltage platform interval of LMFP manganese characteristics.

[0006] Specifically comprising the following steps: 1) preparing a test battery; 2) forming a stable interface film by formation of the test battery; 3) performing charge-discharge cycling on the test battery obtained in step 2) from the 1st cycle to the nth cycle, and recording the characteristic capacity Q1 of the 1st cycle and the characteristic capacity Qn of the nth cycle; 4) judging the manganese dissolution of lithium manganese iron phosphate material by the characteristic capacity decay rate R. n

[0007] The R = (Q1-Qn) / Q1*100%. n

[0008] The charge-discharge cycling in step 3) is as follows: constant current charging to the upper limit voltage at the standard rate, then constant voltage charging until the current drops to the cutoff current; then constant current discharging at a small current in the high-voltage platform interval of LMFP manganese characteristics.

[0009] The high-voltage platform interval of LMFP manganese characteristics is 4.35V to 3.8V, preferably 4.25V to 3.9V.

[0010] ​​The small current is 0.01-0.1C; preferably 0.05C.

[0011] n in step 3) is 5-50; preferably 10.

[0012] The specific step of step 2) is: after the assembled battery to be tested is placed, constant current charging is performed at a standard rate to 4.25V, then constant voltage charging is performed until the current decreases to a cutoff current, and the battery is placed; constant current discharging is performed at a standard rate to 2.0V; the above steps are repeated for 1-3 cycles to complete the formation process of the battery, and a stable interface film is formed.

[0013] The higher the capacity attenuation rate R is, the higher the tendency of manganese dissolution is; the lower the capacity attenuation rate R is, the lower the tendency of manganese dissolution is; preferably, when n=10, R is less than 1%, it is considered that the tendency of manganese dissolution is low, R is in the range of [1%, 5%], it is considered that the tendency of manganese dissolution is moderate, and R is greater than 5%, it is considered that the tendency of manganese dissolution is high.

[0014] The application also includes a system for evaluating the manganese dissolution of a lithium iron manganese phosphate material, which is used to perform the evaluation method of the application; the system comprises:

[0015] The feature interval scanning test device is used to perform charge-discharge cycling on the battery to be tested and test the feature interval;

[0016] The data processing device is used to analyze and process the results obtained by the feature interval scanning test device;

[0017] The evaluation device is used to evaluate the results of the data processing device.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] The evaluation method of the manganese dissolution of the lithium iron manganese phosphate material of the application has the following characteristics: 1. fast and efficient: the evaluation period is shortened from several months to several days (only 5-20 cycles are required), which greatly improves the material screening efficiency; 2. non-destructive testing: the battery does not need to be disassembled, the same battery can be tested multiple times, and the integrity of the battery is maintained; 3. simple operation and low cost: only ordinary electrochemical test equipment (such as a blue electricity test system) is required, without expensive large-scale analytical instruments such as ICP and XRF and complex chemical digestion processes, which reduces the detection threshold and cost; 4. high-throughput potential: the method is standardized and suitable for parallel rapid screening of a large number of samples, and is perfectly suitable for rapid evaluation and screening in the early stage of material research and development. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a flowchart of the evaluation method of the manganese dissolution of the lithium iron manganese phosphate material of the application. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] Example 1:

[0023] Three lithium manganese iron phosphate materials with known differences in performance were selected and labeled as sample A (excellent), sample B (medium), and sample C (poor).

[0024] Evaluation method for manganese leaching from lithium manganese iron phosphate materials ( Figure 1 The flowchart shown below specifically includes the following steps:

[0025] 1) Preparation of the battery to be tested: The lithium manganese iron phosphate cathode material to be evaluated was assembled with the anode (lithium metal sheet), separator and electrolyte into an experimental CR2032 button cell, and three parallel samples were prepared for each group.

[0026] 2) Form the battery under test to generate a stable interface film; charge it at a constant current of 0.1C to 4.25V, charge it at a constant voltage of 4.25V until the current drops to 0.02C, let it stand for 15 minutes, then discharge it at a constant current of 0.1C to 2.0V, let it stand for 15 minutes to complete the first charge-discharge cycle, and repeat the above steps until 3 charge-discharge cycles are completed for activation.

[0027] 3) Perform charge-discharge cycles on the battery obtained in step 2) from the first cycle to the nth cycle, and record the characteristic capacity Q1 of the first cycle and the characteristic capacity Q of the nth cycle. n All batteries were tested at 25°C using the Blue Battery testing system.

[0028] Charge to 4.25V with a constant current (0.1C), then maintain a constant voltage of 4.25V until the current <0.02C, and let stand for 15 minutes. Discharge with a small current of 0.05C within the high-voltage plateau range of 4.25V to 3.9V for LMFP manganese, and record the characteristic capacity Q1 of the first cycle. Repeat this process for a total of 10 cycles, and record the characteristic capacity Q1 of the 10th cycle. 10 .

[0029] 4) The manganese dissolution of lithium manganese iron phosphate materials is determined by the characteristic capacity decay rate R. R = (Q1 - Q 10 ) / Q1*100%. If R is less than 1%, the manganese leaching tendency is considered low; if R is [1% to 5%], the manganese leaching tendency is considered moderate; and if R is greater than 5%, the manganese leaching tendency is considered high.

[0030] Table 1 shows the characteristic capacity and capacity decay rate of the three materials.

[0031] Table 1

[0032] Material Q1 (mAh / g) Q 10 (mAh / g) Attenuation rate R (%) Predicted tendency of manganese leaching A 73.0 72.5 0.68％ Low B 78.6 77.0 2.16％ Medium C 66.7 63.2 5.25％ High

[0033] To illustrate the effectiveness of the present application, the same batch of A, B, C samples were subjected to 500 standard cycles (1C, 2.0V-4.25V) to form soft package batteries, then the batteries were disassembled and the manganese content in the negative electrode was detected by ICP-OES, as shown in Table 2.

[0034] Table 2

[0035]

[0036]

[0037] The results show that the manganese content is in the order of C > B > A, which is completely consistent with the tendency predicted by the method of the present application through 10 cycles. This shows that the method of the present application can effectively and quickly screen out LMFP materials with better manganese dissolution resistance.

[0038] The present application also includes a system for evaluating the manganese dissolution of lithium manganese iron phosphate material, which is used to perform the evaluation method of the present application; comprising:

[0039] A characteristic interval scanning test device for charging and discharging the battery to be tested and testing the characteristic interval;

[0040] A data processing device for analyzing and processing the results obtained by the characteristic interval scanning test device;

[0041] An evaluation device for evaluating the results of the data processing device.

[0042] In summary, the evaluation method for manganese dissolution of lithium manganese iron phosphate material of the present application has the following characteristics: 1. Fast and efficient: the evaluation period is shortened from several months to several days (only 5-20 cycles are required), which greatly improves the material screening efficiency. 2. Non-destructive testing: the battery does not need to be disassembled, the same battery can be tested multiple times, and the integrity of the battery is maintained; 3. Simple operation and low cost: only ordinary electrochemical test equipment (such as a blue electricity test system) is needed, without the need for expensive large-scale analytical instruments such as ICP and XRF and complex chemical digestion processes, reducing the detection threshold and cost. 4. High throughput potential: the method is standardized and suitable for parallel rapid screening of a large number of samples, and is perfectly suitable for rapid evaluation and screening in the early stage of material research and development.

[0043] The foregoing merely illustrates the principles of the application and various embodiments are now described with reference to the drawings. This application is not limited to the precise details and

[0044] Thus, the embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the application to be indicated by the appended claims rather than the foregoing description, all changes which come within the meaning and range of equivalency of the claims are to be embraced therein.

[0045] Furthermore, it is to be understood that the application can be carried out by specifically different embodiments and that each disclosed embodiment is only representative of the many alternatives and combinations of different embodiments. Accordingly, other arrangements and methods can be devised in practice that are intended to fall within the scope of the present application.

Claims

1. A method for evaluating manganese leaching from lithium manganese iron phosphate materials, characterized in that, By monitoring the capacity change rate of the battery under test within the high-voltage plateau range characteristic of LMFP manganese during the initial charge-discharge cycle, the manganese dissolution of lithium manganese iron phosphate material can be predicted.

2. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 1, characterized in that, Specifically, the process includes the following steps: 1) preparing the battery to be tested; 2) forming the battery to be tested to generate a stable interface film; 3) performing charge-discharge cycles on the battery to be tested obtained in step 2) from the first cycle to the nth cycle, and recording the characteristic capacity Q1 of the first cycle and the characteristic capacity Q of the nth cycle. n ;4) The manganese dissolution of lithium manganese iron phosphate materials is judged by the characteristic capacity decay rate R.

3. The evaluation method for manganese leaching from lithium manganese iron phosphate materials according to claim 3, characterized in that, The R = (Q1 - Q) n ) / Q1*100%.

4. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 3, characterized in that, The charge-discharge cycle in step 3) is as follows: charge at a standard rate with constant current to the upper limit voltage, then charge at a constant voltage until the current drops to the cutoff current; then discharge at a small current in the high-voltage plateau range characteristic of LMFP manganese.

5. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 4, characterized in that, The characteristic high-voltage plateau range of LMFP manganese is 4.35V to 3.8V, preferably 4.25V to 3.9V.

6. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 4, characterized in that, The small current is 0.01-0.1C; preferably 0.05C.

7. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 4, characterized in that, In step 3), n is 5-50; preferably 10.

8. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 1, characterized in that, Step 2) The specific steps are as follows: After the assembled battery to be tested is left to stand, it is charged at a constant current at a standard rate to 4.25V, and then charged at a constant voltage until the current drops to the cutoff current, and then left to stand; it is discharged at a constant current at a standard rate to 2.0V; the above steps are repeated for a total of 1-3 cycles to complete the battery formation process and form a stable interface film.

9. The method for evaluating manganese leaching from lithium manganese iron phosphate materials according to claim 1, characterized in that, The higher the capacity decay rate R, the higher the manganese leaching tendency; the lower the capacity decay rate R, the lower the manganese leaching tendency. Preferably, when n=10, if R is less than 1%, the manganese leaching tendency is considered low; if R[1%-5%], the manganese leaching tendency is considered moderate; and if R is greater than 5%, the manganese leaching tendency is considered high.

10. An evaluation system for manganese leaching from lithium manganese iron phosphate materials, characterized in that, For performing the evaluation method according to any one of claims 1-9; comprising: The feature interval scanning test device is used to perform charge-discharge cycles on the battery under test and test the feature interval. A data processing device is used to analyze and process the results obtained from the feature interval scanning test device; An evaluation device is used to evaluate the results of the data processing device.

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