A rapid evaluation method for the cycle performance of negative electrode materials for lithium iron phosphate batteries

Abstract

The present invention relates to a rapid evaluation method for the cycle performance of negative electrode materials of lithium iron phosphate batteries, specifically: (1) comparing the room temperature 2C cycle and high temperature 55°C 1C cycle performance of a standard battery and a test battery, wherein the difference between the test battery and the standard battery is only the different negative electrode materials, and the standard negative electrode material with qualified cycle performance is used in the standard battery B. If the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery are better than or equal to the standard battery B, it can be used as a substitute for the standard negative electrode material, otherwise the next step is performed; (2) comparing the growth rate of the negative electrode Rct during the room temperature 1C cycle of the two standard batteries and the test battery, the negative electrode material with a smaller Rct growth rate has a better room temperature 1C cycle. The method of the present invention is simple, rapid, easy to operate, and can be used to quickly evaluate negative electrode materials.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for quickly evaluating the cycle performance of negative electrode materials of lithium iron phosphate batteries. Background Art

[0002] Lithium-ion batteries have outstanding advantages such as high energy density, no memory effect, long cycle life, fast charge and discharge, and low self-discharge. Lithium iron phosphate batteries, in particular, have a long cycle life and are safe. They are widely used in energy storage fields such as portable devices, electric vehicles, aerospace, and have huge market demand.

[0003] Generally, materials, processes, and tests will affect the cycle life of lithium iron phosphate batteries, and the negative electrode material has the greatest impact on its cycle life. The current method for evaluating the cycle performance of negative electrode materials for lithium iron phosphate batteries is mainly to make a full battery and then conduct a cycle life test according to a certain cycle format. Taking long-life energy storage batteries as an example, a cycle life of 3,000 to 6,000 times is generally required. Using a 1C charge and discharge format, it takes about 300 to 600 days to test a cycle life of 3,000 to 6,000 times. It can be seen that the traditional method of evaluating the cycle performance of the negative electrode is not only time-consuming and energy-intensive, but also increases costs (including manpower, material resources, and electricity consumption).

[0004] In summary, there is an urgent need for a rapid evaluation method for the cycle performance of lithium iron phosphate battery negative electrode materials. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quickly evaluating the cycle performance of negative electrode materials for lithium iron phosphate batteries, which can quickly evaluate the cycle performance of negative electrode materials and is convenient and simple to operate.

[0006] The technical solution adopted by the present invention to solve the above problem is: a method for quickly evaluating the cycle performance of negative electrode materials of lithium iron phosphate batteries, comprising the following steps:

[0007] (1) Test the 2C cycle performance at room temperature and 1C cycle performance at high temperature of 55°C for standard battery B;

[0008] (2) Test the 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C of the battery B-1 to be tested. The only difference between the battery B-1 to be tested and the standard battery B is the negative electrode material. The standard battery B uses a standard negative electrode material with qualified cycle performance, and the negative electrode material of the battery B-1 to be tested is the negative electrode material to be tested.

[0009] (3) Compare and analyze the results of step (1) and step (2). If the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery B-1 are both better than or equal to those of the standard battery B, it is determined that the room temperature 1C cycle performance of the test negative electrode material is better than or equal to that of the standard negative electrode material, and the evaluation ends; if at least one of the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery B-1 is worse than that of the standard battery B, proceed to the next test;

[0010] (4) Test the room temperature 1C cycle of standard battery B. When the number of cycles is 0, 200, 400 and 800, discharge the standard battery B, remove the negative electrode sheet of the battery, assemble it into a button half-cell, and perform EIS test to obtain the charge transfer internal resistance Rct(N(B))-0, Rct(N(B))-200, Rct(N(B))-400, Rct(N(B))-800 of the negative electrode material of standard battery B, and calculate the growth rate of Rct;

[0011] (5) Test the room temperature 1C cycle of the battery B-1 to be tested. When the number of cycles is 0, 200, 400 and 800, the battery B-1 is discharged, and then the negative electrode sheet of the battery is taken out and assembled into a button half-cell for EIS test. The charge transfer internal resistance of the negative electrode material of the battery B-1 is obtained as Rct(N(B-1))-0 times, Rct(N(B-1))-200 times, Rct(N(B-1))-400 times, Rct(N(B-1))-800 times, and the growth rate of Rct (relative to cycle 0) is calculated in turn;

[0012] Among them, the growth rate of Rct(N(B-1))-200 times = [Rct(N(B-1))-200 times - Rct(N(B-1))-0 times] / Rct(N(B-1))-0 times;

[0013] The growth rate of Rct(N(B-1))-400 times = [ Rct(N(B-1))-400 times — Rct(N(B-1))-0 times] / Rct(N(B-1))-0 times;

[0014] The growth rate of Rct(N(B-1))-600 times = [ Rct(N(B-1))-600 times — Rct(N(B-1))-0 times] / Rct(N(B-1))-0 times;

[0015] The growth rate of Rct(N(B-1))-800 times = [ Rct(N(B-1))-800 times — Rct(N(B-1))-0 times] / Rct(N(B-1))-0 times;

[0016] (6) Compare and analyze the results of step (4) and step (5). If the growth rate of Rct(N(B-1)) is less than or equal to Rct(N(B)), it is determined that the room temperature 1C cycle performance of the negative electrode material to be tested is better than or equal to that of the standard negative electrode material; conversely, if the growth rate of Rct(N(B-1)) is greater than Rct(N(B)), it is determined that the room temperature 1C cycle performance of the negative electrode material to be tested is worse than that of the standard negative electrode material.

[0017] Preferably, the room temperature 2C cycle test is specifically as follows: under room temperature conditions, the charge and discharge current of the battery is 2C, the charge and discharge voltage range is set to 2.5-3.65V, and the battery is left to stand after the charge and discharge are completed, and the standing time is 30 minutes.

[0018] Preferably, the 1C cycle test at a high temperature of 55°C is specifically as follows: under 55°C conditions, the charge and discharge current of the battery is 1C, the charge and discharge voltage range is set to 2.5-3.65V, and the battery is left to stand after the charge and discharge are completed, and the standing time is 30 minutes.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] The present invention provides a rapid evaluation method for negative electrode materials of lithium iron phosphate batteries, which can quickly screen negative electrode materials and shorten the evaluation period of negative electrode materials. The method is simple and easy to operate and implement. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to the embodiments.

[0022] Example 1

[0023] A method for quickly evaluating the cycle performance of a negative electrode material for a lithium iron phosphate battery comprises the following steps:

[0024] (1) Test the 2C cycle performance at room temperature and 1C cycle performance at high temperature of 55°C for standard battery B;

[0025] (2) Test the 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C of the battery B-1 to be tested. The only difference between the battery B-1 to be tested and the standard battery B is the negative electrode material. The standard battery B uses a standard negative electrode material with qualified cycle performance, and the negative electrode material of the battery B-1 to be tested is the negative electrode material to be tested.

[0026] (3) The results of step (1) and step (2) are shown in Table 1:

[0027] Table 1

[0028]

[0029] Note: 500 (80%) means the retention rate after 500 cycles is 80%, and so on.

[0030] It can be seen from Table 1 that the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery B-1 are better than or equal to the standard battery B. It is determined that the room temperature 1C cycle performance of the test negative electrode material is better than or equal to the standard negative electrode material, and it can be used as a substitute for the standard negative electrode material.

[0031] Example 2

[0032] A method for quickly evaluating the cycle performance of a negative electrode material for a lithium iron phosphate battery comprises the following steps:

[0033] (1) Test the 2C cycle performance at room temperature and 1C cycle performance at high temperature of 55°C for standard battery B;

[0034] (2) Test the 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C of the battery B-2 to be tested. The only difference between the battery B-2 to be tested and the standard battery B is the negative electrode material. The standard battery B uses a standard negative electrode material with qualified cycle performance, and the negative electrode material of the battery B-2 to be tested is the negative electrode material to be tested.

[0035] (3) The results of step (1) and step (2) are shown in Table 2:

[0036] Table 2

[0037]

[0038] Note: 600 (80%) means the retention rate after 600 cycles is 80%, and so on.

[0039] As shown in Table 2, the 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C of the battery B-2 to be tested have at least one performance worse than that of the standard battery B. The cycle performance of the negative electrode material to be tested cannot be determined yet, and the next step of testing is required;

[0040] (4) Test the room temperature 1C cycle of standard battery B. When the number of cycles is 0, 200, 400 and 800, discharge the standard battery B, remove the negative electrode sheet of the battery, assemble it into a button half-cell, and perform EIS test to obtain the charge transfer internal resistance Rct(N(B))-0, Rct(N(B))-200, Rct(N(B))-400, Rct(N(B))-800 of the negative electrode material of standard battery B, and calculate the growth rate of Rct;

[0041] (5) Test the room temperature 1C cycle of the battery B-2 to be tested. When the number of cycles is 0, 200, 400 and 800, the battery B-2 is discharged, and then the negative electrode sheet of the battery is taken out and assembled into a button half-cell. EIS test is performed to obtain the charge transfer internal resistance Rct(N(B-2))-0 times, Rct(N(B-2))-200 times, Rct(N(B-2))-400 times, Rct(N(B-2))-800 times of the negative electrode material of the battery B-2, and calculate the growth rate of Rct;

[0042] (6) The results of step (4) and step (5) are shown in Table 3:

[0043] Table 3

[0044]

[0045] Note: 80 (33%) means that the charge transfer internal resistance Rct of the battery under test after 200 cycles is 80, 33% is the growth rate (the growth rate of 200 cycles relative to 0 cycles), and so on.

[0046] It can be seen from Table 3 that if the growth rate of Rct(N(B-2)) is less than Rct(N(B)), it is determined that the room temperature 1C cycle performance of the negative electrode material to be tested is better than that of the standard negative electrode material, and it can be used as a substitute for the standard negative electrode material.

[0047] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A rapid evaluation method for the cycle performance of negative electrode materials for lithium iron phosphate batteries, characterized in that: The following steps are involved: (1) Test the 2C cycle performance at room temperature and 1C cycle performance at high temperature of 55°C for standard battery B; (2) Test the 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C of the battery B-1 to be tested. The only difference between the battery B-1 to be tested and the standard battery B is the negative electrode material. The standard battery B uses a standard negative electrode material with qualified cycle performance, and the negative electrode material of the battery B-1 to be tested is the negative electrode material to be tested. (3) Compare and analyze the results of step (1) and step (2). If the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery B-1 are both better than or equal to those of the standard battery B, it is determined that the room temperature 1C cycle performance of the test negative electrode material is better than or equal to that of the standard negative electrode material, and the evaluation ends; if at least one of the room temperature 2C cycle performance and the high temperature 55°C 1C cycle performance of the test battery B-1 is worse than that of the standard battery B, proceed to the next test; (4) Test the room temperature 1C cycle of standard battery B. When the number of cycles is 0, 200, 400 and 800, discharge the standard battery B, remove the negative electrode sheet of the battery, assemble it into a button half-cell, and perform EIS test to obtain the charge transfer internal resistance Rct(N(B))-0, Rct(N(B))-200, Rct(N(B))-400, Rct(N(B))-800 of the negative electrode material of standard battery B, and calculate the growth rate of Rct; (5) Test the room temperature 1C cycle of the battery B-1 to be tested. When the number of cycles is 0, 200, 400 and 800, the battery B-1 is discharged, and then the negative electrode sheet of the battery is taken out and assembled into a button half-cell. EIS test is performed to obtain the charge transfer internal resistance of the negative electrode material of the battery B-1 Rct(N(B-1))-0 times, Rct(N(B-1))-200 times, Rct(N(B-1))-400 times, Rct(N(B-1))-800 times, and calculate the growth rate of Rct; (6) Compare and analyze the results of step (4) and step (5). If the growth rate of Rct(N(B-1)) is less than or equal to Rct(N(B)), it is determined that the room temperature 1C cycle performance of the negative electrode material to be tested is better than or equal to the standard negative electrode material; conversely, if the growth rate of Rct(N(B-1)) is greater than Rct(N(B)), it is determined that the room temperature 1C cycle performance of the negative electrode material to be tested is worse than that of the standard negative electrode material; The 2C cycle performance at room temperature and the 1C cycle performance at high temperature of 55°C in step (1) and step (2) are both evaluated based on the number of cycles corresponding to 80% capacity retention; the number of cycles of the standard battery B at room temperature 2C cycling to 80% capacity retention, and the number of cycles of the standard battery B at high temperature of 55°C 1C cycling to 80% capacity retention are recorded; the number of cycles of the test battery B-1 at room temperature 2C cycling to 80% capacity retention, and the number of cycles of the test battery B-1 at high temperature of 55°C 1C cycling to 80% capacity retention are recorded.

2. The rapid evaluation method for the cycle performance of the negative electrode material of a lithium iron phosphate battery according to claim 1, characterized in that: The room temperature 2C cycle test is specifically as follows: under room temperature conditions, the charge and discharge current of the battery is 2C, the charge and discharge voltage range is set to 2.5-3.65V, and the battery is left to stand after the charge and discharge are completed, and the standing time is 30 minutes.

3. The rapid evaluation method for the cycle performance of the negative electrode material of a lithium iron phosphate battery according to claim 1, characterized in that: The 1C cycle test at high temperature of 55°C is specifically as follows: under 55°C conditions, the charge and discharge current of the battery is 1C, the charge and discharge voltage range is set to 2.5-3.65V, and the battery is left to stand after the charge and discharge are completed, and the standing time is 30 minutes.

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