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CN-122017611-A - Screening method for self-discharge performance of lithium iron phosphate battery

CN122017611ACN 122017611 ACN122017611 ACN 122017611ACN-122017611-A

Abstract

The invention relates to the field of lithium ion battery preparation and discloses a screening method of self-discharge performance of a lithium iron phosphate battery, which comprises the steps of performing discharge operation on a single lithium battery to discharge electric quantity of the single lithium battery, charging the single lithium battery to a charge state of 3-10% of nominal capacity of the single lithium battery by using a current of 0.1-0.3C, after the charged single lithium battery is placed at room temperature for a first preset time T1, measuring voltage V1 of the single lithium battery, after the single lithium battery after the voltage V1 is measured is placed at room temperature for a second preset time T2, measuring voltage V2 of the single lithium battery, calculating a K value of the single lithium battery according to K= (V1-V2)/(T2-T1), comparing the K value with a preset screening standard, and eliminating the single lithium battery which does not meet the standard.

Inventors

  • WU HOUXING
  • ZHANG YANPING
  • ZHANG LANG
  • ZHAO YANSHUAI

Assignees

  • 湖南格瑞普新能源有限公司

Dates

Publication Date
20260512
Application Date
20251014

Claims (10)

  1. 1. The screening method for the self-discharge performance of the lithium iron phosphate battery is characterized by comprising the following steps of: Performing a discharging operation on the single lithium battery to discharge the electric quantity thereof; charging the lithium cell to a state of charge of 3% to 10% of its nominal capacity using a current of 0.1C to 0.3C; After the charged single lithium battery is placed at room temperature for a first preset time T1, measuring the voltage V1 of the single lithium battery; The single lithium battery after the voltage V1 is measured is placed at room temperature for a second preset time T2, and the voltage V2 is measured; calculating the K value of the single lithium battery according to K= (V1-V2)/(T2-T1); comparing the K value with a preset screening standard, and eliminating the single batteries which do not meet the standard.
  2. 2. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 1, characterized in that, The step of performing a discharging operation to discharge the amount of electricity thereof includes, Discharging the single lithium battery to 2.0V with a current of 0.1-0.3C, and standing for 3-10 minutes; The single lithium battery was discharged to 2.0V at a current of 0.005C to 0.02C.
  3. 3. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 1, characterized in that, The single lithium battery was charged to a state of charge of 6% of its nominal capacity using a current of 0.2C.
  4. 4. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 1, characterized in that, The room temperature is 25 ℃ to 28 ℃.
  5. 5. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 1, characterized in that, The first predetermined time T1 is 20 to 28 hours.
  6. 6. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 5, characterized in that, The first predetermined time T1 is 24 hours.
  7. 7. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 5, characterized in that, The second predetermined time T2 is 100 to 140 hours.
  8. 8. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 5, characterized in that, The second predetermined time T2 is 120 hours.
  9. 9. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 5, characterized in that, The values of the voltage V1 and the voltage V2 are in the range of 3090mV to 3240 mV.
  10. 10. The method for screening self-discharge performance of lithium iron phosphate battery according to claim 5, characterized in that, The preset screening standard is K value between 0mV/h and 0.06 mV/h.

Description

Screening method for self-discharge performance of lithium iron phosphate battery Technical Field The invention relates to the field of lithium ion battery preparation, in particular to a screening method for self-discharge performance of a lithium iron phosphate battery. Background In the production process of lithium ion batteries, particularly lithium iron phosphate (LiFePO 4) batteries, there are unavoidable differences in the performance of individual batteries (cells) due to fluctuations in various factors such as equipment accuracy, raw material lot, test method, and production environment. The quality and consistency of the single battery performance directly determine the overall performance, the cycle life and the safety reliability of the final battery pack. Therefore, the adoption of a correct self-discharge screening method to remove the cells with poor consistency or defects is an important link in the manufacturing process before sorting and matching. At present, screening of self-discharge performance (generally represented by K value) of lithium iron phosphate batteries in industry generally adopts a normal-temperature semi-electric state standing test method. The method generally charges a battery to a medium state of charge (for example, 30% -80% state of charge (english StateofCharge, abbreviated as SOC)), then stands for a long time (about 20 days) at normal temperature, calculates a K value by measuring a voltage drop thereof, and performs screening accordingly. However, the present inventors have found during the course of the research of the present invention that the prior art methods have the following drawbacks: First, the lithium iron phosphate material itself has a very flat voltage plateau. In particular, in the wide range of 30% to 80% SOC, the relationship between the terminal voltage of the battery and the SOC is approximately a straight line, and the voltage variation is extremely small. In this "voltage plateau", the voltage change signal caused by the small self-discharge difference is very weak, as if it were difficult to detect a fine gradient on a flat road. This results in an insufficient sensitivity of the method, and it is difficult to effectively reject "edge" cells that have a slightly higher self-discharge rate than standard, but have poor potential for uniformity, thereby burying the potential for overall quality of the battery pack. Second, prior methods have to rely on ultra-long stationary screening cycles (about 20 days) in order to capture sufficiently resolved voltage differences. This greatly extends the production cycle of the product, results in a high inventory enterprise in the production, severely impacts capital turnover efficiency, and creates significant pressure on production cost control and customer lead time response. In view of the foregoing, there is a strong need in the art for a self-discharge screening method that overcomes the voltage plateau characteristics of lithium iron phosphate batteries, and has both short cycle and high precision, so as to improve the production efficiency and reduce the overall cost while ensuring the battery quality. Disclosure of Invention One of the purposes of the embodiments of the present invention is to provide a screening method capable of overcoming the voltage platform characteristic of a lithium iron phosphate battery, and having both a short period and high precision, so as to improve the production efficiency and reduce the comprehensive cost while ensuring the battery quality. In a first aspect, a method for screening self-discharge performance of a lithium iron phosphate battery provided by an embodiment of the present invention includes the following steps: Performing a discharging operation on the single lithium battery to discharge the electric quantity thereof; charging the lithium cell to a state of charge of 3% to 10% of its nominal capacity using a current of 0.1C to 0.3C; After the charged single lithium battery is placed at room temperature for a first preset time T1, measuring the voltage V1 of the single lithium battery; The single lithium battery after the voltage V1 is measured is placed at room temperature for a second preset time T2, and the voltage V2 is measured; calculating the K value of the single lithium battery according to K= (V1-V2)/(T2-T1); comparing the K value with a preset screening standard, and eliminating the single batteries which do not meet the standard. Optionally, the step of performing a discharging operation to discharge its power includes, Discharging the single lithium battery to 2.0V with a current of 0.1-0.3C, and standing for 3-10 minutes; The single lithium battery was discharged to 2.0V at a current of 0.005C to 0.02C. Alternatively, the single lithium battery is charged to a state of charge of 6% of its nominal capacity using a current of 0.2C. Alternatively, the room temperature is 25 ℃ to 28 ℃. Optionally, the first predetermined time T1 is 20 to 28