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CN-121995254-A - Method for testing static state SOC-OCV of lithium ion battery

CN121995254ACN 121995254 ACN121995254 ACN 121995254ACN-121995254-A

Abstract

The invention relates to the technical field of lithium battery manufacturing, in particular to a method for testing static state of charge (SOC) -OCV of a lithium ion battery, which comprises the following steps of (1) DCIR testing and SOC partitioning, (2) determining OCV steady-state time of different SOC intervals, (3) adjusting load and testing OCV at different temperatures. By introducing a partition strategy based on the difference of Direct Current Internal Resistances (DCIR) of different SOC points and determining the standing time required by stabilizing the OCV voltage of each partition, the defect that the prior art adopts uniform standing time for all the SOC points is overcome, and the difference of battery polarization relaxation characteristics under different SOC states is fully considered, so that the accuracy of OCV test data is remarkably improved.

Inventors

  • QIN HONGLIAN
  • ZHANG YUAN
  • ZHENG LEI

Assignees

  • 中汽新能电池科技有限公司

Dates

Publication Date
20260508
Application Date
20260120

Claims (10)

  1. 1. The method for testing the static state SOC-OCV of the lithium ion battery is characterized by comprising the following steps of: 1. DCIR test and SOC partitioning: 1.1, at room temperature T1, carrying out charge-discharge circulation on a battery to be tested to determine the nominal capacity C0 of the battery at room temperature T1; 1.2, measuring the charging direct current internal resistance value and the discharging direct current internal resistance value of the battery to be measured at different SOC points; 1.3 calculating the difference of the charge DC internal resistance value of other SOC points relative to the reference value by taking the charge DC internal resistance value of 50% of the SOC as the reference, dividing all the SOC points into N charge SOC sections according to a preset difference threshold range, and Calculating the difference of the discharge direct current internal resistance values of other SOC points relative to the reference value by taking the discharge direct current internal resistance value of 50% of the SOC as the reference, and dividing all the SOC points into M discharge SOC sections according to a preset difference threshold range; 2. Determining OCV steady-state time of different SOC intervals: 2.1, selecting a representative SOC point from the N charge SOC intervals to serve as N target charge SOC points, and selecting a representative SOC point from the M discharge SOC intervals to serve as M target discharge SOC points; 2.2, preparing a plurality of groups of battery samples, wherein each group at least comprises two batteries, and adjusting one or more groups of batteries to the same target charge SOC point or target discharge SOC point; 2.3, standing each group of batteries at the same target SOC point for a long time at room temperature T1, and recording OCV values of each battery at a plurality of time points; 2.4, calculating the difference between the OCV value at each time point and a reference value by taking the OCV value at the end of standing as a reference, and determining the time point as the OCV steady-state time tN of the SOC section to which the target SOC point belongs when the OCV difference of all batteries in the same group at a certain time point is smaller than or equal to a preset voltage steady-state threshold value; 3. Load-adjusting and testing OCV at different temperatures: 3.1, preparing a plurality of battery samples, and respectively adjusting the battery samples to a plurality of different SOC states at room temperature T1, wherein each SOC state corresponds to at least two parallel samples; 3.2, simultaneously placing samples in different SOC states in an environment of a first temperature T2 to be detected, and standing for a first preset time, wherein the first preset time is the sum of the heat balance time tx at the temperature T2 and the OCV steady state time tN of the interval to which each SOC state belongs; 3.3, after standing, measuring and recording OCV values of all samples within a specified time, and taking an average value of the OCV values measured by the samples in the same SOC state as the OCV value of the SOC state at the temperature T2; 3.4, replacing to a second temperature T3 to be detected, and repeating the steps 3.2 to 3.3 to obtain an OCV value of the SOC at the temperature T3; and 3.5, repeating the steps 3.1 to 3.4, and respectively obtaining OCV values of different SOC states at a plurality of temperatures in a charging process and a discharging process, thereby obtaining a complete static SOC-OCV data table.
  2. 2. The method according to claim 1, wherein in step 1.3, the preset difference threshold range is that the difference is equal to or less than 5% divided into a first interval, the difference is equal to or less than 10% divided into a second interval, and so on.
  3. 3. The test method according to claim 1, wherein in step 2.4, the long-term standing time is not less than 48 hours, and the voltage stabilization threshold is 2mV.
  4. 4. The test method according to claim 1, wherein in step 3.1, adjusting the SOC state comprises discharging the battery to a plurality of discrete points between 0% SOC and 95% SOC at room temperature T1 for a discharging process, and charging the battery to a plurality of discrete points between 5% SOC and 100% SOC at room temperature T1 for a charging process.
  5. 5. The test method according to claim 1, wherein the room temperature T1 is 25±3 ℃.
  6. 6. The method according to claim 1, wherein the temperature T2, T3 to be measured has a value ranging from-35 ℃ to 60 ℃.
  7. 7. The method of testing according to claim 1, wherein the method of measuring the internal dc resistance in step 1.2 comprises: a. After the battery is adjusted to a specific SOC point and is kept stand until the battery is in thermal equilibrium, a first OCV value is recorded; b. applying a pulse discharge or pulse charge current for a first duration Δt1, recording a second OCV value at the end of the pulse; c. And calculating to obtain a discharge direct current internal resistance value or a charge direct current internal resistance value at the SOC point according to the first OCV value, the second OCV value and the amplitude of the pulse current.
  8. 8. The method of claim 7, wherein the first duration Δt1 is 10 seconds, the magnitude of the pulse discharging current is a maximum pulse discharging current of the battery at a corresponding SOC point, and the magnitude of the pulse charging current is a maximum pulse charging current of the battery at the corresponding SOC point.
  9. 9. The test method according to claim 1, wherein in steps 3.2 and 3.4, the OCV steady-state time tN thereof is referenced to the tN value determined for the 5% soc discharge interval for the 0% soc state and the OCV steady-state time tN thereof is referenced to the tN value determined for the 95% soc charge interval for the 100% soc state.
  10. 10. The test method of claim 1, wherein after OCV testing at all temperatures is completed, all test samples are again capacity calibrated at room temperature T1 to verify whether significant changes in battery capacity occurred during the test.

Description

Method for testing static state SOC-OCV of lithium ion battery Technical Field The invention belongs to the technical field of lithium batteries, and particularly relates to a method for testing static state of charge (SOC) -OCV of a lithium ion battery. Background Lithium ion batteries have been widely used in the fields of consumer electronics, electric power assisted vehicles, new energy automobiles, energy storage systems and the like due to the advantages of high specific energy, long cycle life and the like. The State of Charge (SOC) of the battery is used as a key parameter reflecting the current remaining power of the battery, and directly affects the judgment of the battery management system on the endurance mileage, the energy State and the safety boundary. Under certain conditions, the open-circuit voltage (Open Circuit Voltage, OCV) of the battery has a corresponding relation with the SOC, so that the OCV values corresponding to different SOC points are accurately obtained, and the method has important significance for improving the SOC estimation precision and optimizing the whole vehicle energy management, especially for static SOC-OCV data under the multi-temperature condition. Currently, a plurality of lithium ion battery SOC-OCV testing methods exist in the industry, but certain limitations still exist: For example, patent publication CN112014752a proposes a lithium battery SOC-OCV test method that performs capacity calibration on a battery several times at different temperatures, and adjusts SOC stepwise at the same temperature and tests OCV. The method has the advantages that the capacity calibration and the SOC adjustment are repeatedly carried out at different temperatures, so that the test period is long, the efficiency is low, meanwhile, the standing time before OCV test is set to be shorter (such as 30 minutes), the battery voltage is not fully stable, and the accuracy of the test result is affected. Patent publication No. CN112130080B discloses a method for measuring the SOC-OCV curve of a power lithium ion battery at low temperature, which attempts to match the dynamic and static OCV curves by comparing the two curves and performing current adjustment. However, due to the objective existence of the battery polarization effect, the dynamic OCV and the static OCV are difficult to completely coincide, and the theoretical basis of the method deviates from the actual physical characteristics, so that the accuracy of the measurement result is limited. The publication CN113985286a provides a solution for SOC-OCV testing at different temperatures, which uses room temperature calibration capability, but charges and discharges at different temperatures to adjust the SOC. Because the actual dischargeable capacity of the battery is obvious along with the temperature change, the method is easy to reach a voltage cut-off point in advance under the conditions of low temperature and the like, and cannot release all the calibrated capacity, so that the system error is introduced. The publication CN115128478a proposes to stand at various temperature points after adjusting the SOC at room temperature and to test the OCV, which has a certain similarity to the inventive concept. However, the method has obvious disadvantages that firstly, the time required by the battery to reach the heat balance in the low-temperature environment is not fully considered, and the fixed standing time (such as 2-5 hours) is uniformly set for all the SOC points, the difference of the battery polarization relaxation processes in different SOC states is not considered, secondly, the same battery sample is used for repeatedly standing and testing at different temperatures, the battery capacity can change in the temperature cycle, the corresponding relation between the finally measured OCV and the initial calibration SOC is offset, and the data accuracy is affected. In summary, the existing SOC-OCV test method generally has the problems of low test efficiency, insufficient consideration of polarization differences and relaxation characteristics of different SOC points, unreasonable setting of standing time, possible capacity drift errors in the test process, and the like. Disclosure of Invention The invention aims to provide a method for testing the static SOC-OCV of a lithium ion battery, so as to better meet the requirement of a battery management system on accurate SOC estimation. In order to achieve the above purpose, the present invention provides the following technical solutions: The invention provides a method for testing static state SOC-OCV of a lithium ion battery, which comprises the following steps: 1. DCIR test and SOC partitioning: 1.1, at room temperature T1, carrying out charge-discharge circulation on a battery to be tested to determine the nominal capacity C0 of the battery at room temperature T1; 1.2, measuring the charging direct current internal resistance value and the discharging direct current internal