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CN-122017623-A - Self-discharge high-precision screening method for lithium ion battery

CN122017623ACN 122017623 ACN122017623 ACN 122017623ACN-122017623-A

Abstract

The invention discloses a self-discharge high-precision screening method of a lithium ion battery, which comprises the steps of S1, obtaining a self-discharge rate parameter K and residual capacity C of the battery, S2, detecting whether a battery capacity retention ratio C/C 0 is smaller than a preset threshold value, judging as an unqualified battery if the battery capacity retention ratio C/C 0 is smaller than the preset threshold value, otherwise, executing S3, calculating a battery comprehensive evaluation function F (K, C) in the step S3, S4, detecting whether the F value is in a preset gray area range, judging as a battery to be rechecked and returning to execute the steps S11 to S17 if the F value is larger than a range maximum value, judging as the unqualified battery if the F value is smaller than a range minimum value, and judging as the qualified battery. The invention combines the self-discharge rate parameter K and the residual capacity C obtained by directly metering the electric quantity, and utilizes the comprehensive evaluation function to quantitatively judge the battery cell, thereby obviously reducing the misjudgment and the omission ratio in a flat system of a voltage platform and ensuring the judgment reliability.

Inventors

  • DUAN ZHENG
  • Xu Kaizheng
  • ZHANG JING
  • YIN ZIZHEN
  • MA MENG

Assignees

  • 天津力神超电科技有限公司

Dates

Publication Date
20260512
Application Date
20260130

Claims (10)

  1. 1. The self-discharge high-precision screening method for the lithium ion battery is characterized by comprising the following steps of: step S1, for a battery to be detected, acquiring a self-discharge rate parameter K of the battery and acquiring the residual capacity C of the battery, wherein the acquisition process comprises steps S11 to S17; Step S2, performing a primary judgment operation, namely detecting whether the capacity retention ratio C/C 0 of the battery is smaller than a preset threshold value, wherein C 0 is an initial reference capacity; if yes, judging that the battery is a self-discharge unqualified battery; otherwise, continuing to execute the step S3; Step S3, calculating a comprehensive evaluation function F (K, C) of the battery according to the self-discharge rate parameter K of the battery and the residual capacity C of the battery; s4, detecting whether the F value is in a range of a preset gray area; if yes, judging the battery as the battery to be rechecked, returning to the steps S11 to S17, and finally judging according to a preset secondary judging operation after rechecking; If the F value is larger than the maximum value of the preset gray area range, judging that the battery is a self-discharge unqualified battery; and if the F value is smaller than the minimum value of the range of the preset gray zone, judging the battery to be a self-discharge qualified battery.
  2. 2. The method for screening lithium ion battery self-discharge high precision according to claim 1, wherein an initial reference capacity C 0 = nominal rated capacity x preset coefficient; The value range of the preset coefficient is 30% -80%.
  3. 3. The method for screening the lithium ion battery self-discharge high precision according to claim 1, wherein the step S1 specifically comprises the following operations: step S11, preprocessing operation, namely performing charge and discharge operation on the battery, and then charging the battery with a constant flow rate of 1C to be equal to half rated capacity; step S12, standing, namely standing the battery for 72 hours in a 45 ℃ environment; Step S13, balancing at normal temperature, namely placing the battery in a 25 ℃ environment for standing for 24 hours, and measuring and recording the voltage V1 of the battery at the moment; Step S14, standing at normal temperature, namely standing the battery in a 25 ℃ environment for 72 hours, and measuring and recording the voltage V2 of the battery at the moment; step S15, obtaining a self-discharge rate parameter K of the battery according to a calculation formula of the self-discharge rate parameter K value; step S16, storing for a long time, namely placing the battery in a 25 ℃ environment for standing for 21 days; and S17, measuring discharge, namely discharging to the discharge cut-off voltage of the battery at a constant current with a 1C multiplying power, and measuring the residual capacity C.
  4. 4. The method for screening lithium ion battery self-discharge high precision according to claim 3, wherein in step S11, the battery is charged and discharged at a rate of 0.5C.
  5. 5. The method for screening lithium ion battery self-discharge high precision according to claim 3, wherein in step S15, a calculation formula of the self-discharge rate parameter K value is as follows: K=ΔOCV/Δt; Wherein, the Δocv=ocv_initial-ocv_final; ΔOCV is the voltage drop in mV; OCV_initial is the battery open-circuit voltage before the self-discharge begins; OCV_final is the battery open-circuit voltage at the time of discharged storage time Deltat; Δt is the storage time in h.
  6. 6. The method according to claim 1, wherein in step S2, the preset threshold is 95%.
  7. 7. The method for screening lithium ion battery self-discharge high precision according to claim 1, wherein in step S3, the comprehensive evaluation function F (K, C) of the battery is calculated as follows: F(K,C)=α·K+β·(1-C/C 0 ); wherein, K is the self-discharge rate, C is the residual capacity; C/C 0 is the capacity retention ratio of the battery, α is the voltage decay weight coefficient, and β is the capacity loss weight coefficient.
  8. 8. The method for screening the lithium ion battery with high self-discharge precision according to claim 7, wherein the value range of alpha is 0.5-0.7; The value range of beta is 0.3-0.5.
  9. 9. The method of claim 1, wherein in step S4, the range of the preset gray scale of the F value is F 1 ≤F≤F 2 , wherein F 1 =0.04,F 2 =0.06.
  10. 10. The method for screening lithium ion battery cells according to claim 1 to 9, wherein in step S4, a predetermined secondary judgment operation is performed, specifically, if the F value obtained after the battery cells to be retested are returned to the steps S11 to S17 and the step S3 is re-performed is smaller than the minimum value of the predetermined gray zone range and the conditions that the self-discharge rate parameter K <0.04mV/h and the capacity retention ratio C/C 0 >95% of the battery cells are satisfied, the battery cells are judged to be qualified, otherwise, the battery cells are judged to be unqualified.

Description

Self-discharge high-precision screening method for lithium ion battery Technical Field The invention relates to the technical field of lithium ion battery detection and screening, in particular to a lithium ion battery self-discharge high-precision screening method. Background At present, the lithium ion battery has the advantages of high energy density, good cycle performance, green pollution-free property and the like, and is widely applied to the fields of digital products, electric automobiles and energy storage. The self-discharge characteristic of lithium ion batteries is an important indicator for measuring the consistency and reliability of the battery cells. For batteries with flat SOC (residual charge) -OCV (open circuit voltage) characteristics, such as Lithium Titanate (LTO) and lithium iron phosphate (LFP), the voltage change in the intermediate SOC region is extremely small, and conventional methods for determining battery self-discharge have low sensitivity and are prone to missed detection or erroneous determination. Note that the flat SOC (remaining charge) -OCV (open circuit voltage) characteristic of the battery refers to the flat characteristic of the SOC-OCV curve of the battery, that is, refers to a phenomenon in which the Open Circuit Voltage (OCV) varies little in a specific section of the state of charge (SOC) of the battery, which generally occurs in the middle SOC range (e.g., 20% to 80%) of the battery. ‌ A The existing methods for judging the self-discharge of the battery all take voltage as the only judgment dimension. The single dimension cannot effectively identify multiple types of self-discharge defects in a lithium ion battery with flat SOC-OCV characteristics, namely, the continuous capacity loss in the battery can be missed, and instantaneous electrical anomalies of the battery can be ignored. Therefore, there is an urgent need to develop a method capable of solving the above technical problems. Disclosure of Invention The invention aims at providing a self-discharge high-precision screening method for lithium ion batteries, aiming at the technical defects existing in the prior art. Therefore, the invention provides a lithium ion battery self-discharge high-precision screening method, which comprises the following steps: step S1, for a battery to be detected, acquiring a self-discharge rate parameter K of the battery and acquiring the residual capacity C of the battery, wherein the acquisition process comprises steps S11 to S17; Step S2, performing a primary judgment operation, namely detecting whether the capacity retention ratio C/C 0 of the battery is smaller than a preset threshold value, wherein C 0 is an initial reference capacity; if yes, judging that the battery is a self-discharge unqualified battery; otherwise, continuing to execute the step S3; Step S3, calculating a comprehensive evaluation function F (K, C) of the battery according to the self-discharge rate parameter K of the battery and the residual capacity C of the battery; s4, detecting whether the F value is in a range of a preset gray area; if yes, judging the battery as the battery to be rechecked, returning to the steps S11 to S17, and finally judging according to a preset secondary judging operation after rechecking; If the F value is larger than the maximum value of the preset gray area range, judging that the battery is a self-discharge unqualified battery; and if the F value is smaller than the minimum value of the range of the preset gray zone, judging the battery to be a self-discharge qualified battery. Compared with the prior art, the technical proposal provided by the invention provides a lithium ion battery self-discharge high-precision screening method system, which is a lithium ion battery self-discharge high-precision screening method with an ash region judging mechanism, the method combines the self-discharge rate parameter K and the residual capacity C obtained by directly metering the electric quantity, and utilizes the comprehensive evaluation function to quantitatively judge the battery cell, so that the misjudgment and the omission rate are obviously reduced in a flat system of a voltage platform, the judgment reliability is ensured through a gray area rechecking mechanism, and the method has great practical significance. According to the self-discharge high-precision screening method for the lithium ion battery, disclosed by the invention, the direct metering dimension of the electric quantity is introduced on the basis of a traditional K value method, a gray zone rechecking mechanism is established, and a robust quality control system combining high-precision screening with low misjudgment is realized through double-index cooperative judgment. The method of the invention is a self-discharge evaluation method based on double-parameter cooperative judgment, namely, the K value and the capacity attenuation C/C 0 of the battery are considered at the same time. The K value reflects t