CN105738814A - Method for evaluating capacity attenuation degree of lithium ion battery online - Google Patents

Abstract

The invention relates to a method for evaluating the degree of capacity attenuation of a lithium-ion battery on-line. The method establishes the relationship between the degree of capacity attenuation and the accumulated processing energy of the battery at different depths of charge and discharge through cycle tests of the battery at different depths of charge and discharge. , and its correlation is applied to the energy storage system monitoring system, which can realize the online evaluation of the capacity decay degree of lithium-ion batteries.

Description

A Method for Evaluating the Degree of Lithium-ion Battery Capacity Fading Online

Technical field:

The invention relates to a method for evaluating the degree of capacity decay of a battery, and more particularly relates to a method for evaluating the degree of capacity decay of a lithium-ion battery online.

Background technique:

At present, the evaluation of the degree of capacity fading of lithium-ion batteries is carried out offline, that is, the battery or battery pack is taken out of the energy storage system, and then connected to a high-precision battery tester, at room temperature (25°C) with a standard The charging and discharging method charges and discharges the battery or battery pack to obtain the capacity of the battery, and compares it with its initial capacity to calculate the capacity decay rate of the lithium-ion battery. Although this method can accurately assess the degree of capacity fading of lithium-ion batteries, it will affect the normal operation of the energy storage system because the battery or battery pack will be taken out of the energy storage system. At the same time, since the energy storage system is composed of a large number of lithium-ion battery cells or battery packs, it will inevitably consume a lot of manpower and material resources to evaluate the degree of capacity decay of so many cells or battery packs offline. It is equivalent to an additional increase in the operating cost of the battery energy storage system.

Lithium-ion batteries are used in energy storage systems, mainly to deal with the unstable electric energy generated by renewable energy power generation. Every time the battery is charged and discharged, a certain amount of energy is processed, and as the accumulated processing energy of the battery increases, the capacity of the battery Decay gradually. In the energy storage system, the energy of each charge and discharge of the lithium-ion battery is a parameter that is easy to collect and store. If the relationship between the cumulative processing energy of the battery and the decay degree of the battery capacity can be established, the lithium-ion battery in the energy storage system can be realized. On-line assessment of the degree of capacity fading.

Invention content:

The purpose of the present invention is to provide an online method for evaluating the degree of capacity decay of a lithium-ion battery. The method evaluates the degree of capacity decay of the battery by establishing the relationship between the cumulative processing energy of the battery and the rate of capacity decay.

In order to achieve the above object, the present invention adopts the following technical solutions: a method for online evaluation of the degree of capacity decay of lithium-ion batteries, comprising the following steps:

(1) Determine the relationship between the degree of battery capacity attenuation, the working range of battery capacity and the accumulated processing energy;

(2) On-line evaluation of the degree of battery capacity decay.

A kind of method that the present invention provides on-line evaluation lithium-ion battery capacity attenuation degree, described step (1) comprises the following steps:

(1-1) Calibrate the capacity of the battery;

(1-2) Test the battery with different discharge depth cycles.

The invention provides a method for online evaluation of the degree of capacity attenuation of lithium-ion batteries, the calibration process of the step (1-1) is: select more than 30 batteries of the same type, and in an environment of 25 ° C, the battery and high Connect to the precision charge and discharge detector, and conduct a charge and discharge test on the battery at a discharge rate of 1/3. The upper and lower limit voltages of the battery’s charge and discharge adopt the voltage range recommended by the battery manufacturer, cycle 3 times, and record the discharge capacity of each battery.

Another preferred method provided by the present invention is an online method for evaluating the degree of capacity decay of a lithium-ion battery. The high-precision charge and discharge detector includes a charge and discharge module, a voltage and temperature acquisition device, and a charge and discharge control system.

Another preferred method for evaluating the degree of capacity decay of lithium-ion batteries on-line provided by the present invention, the test process of the non-chasing (1-2) is: in an environment of 25 ° C, the battery and the high-precision charging The discharge detector is connected, and the battery is cycle-tested with different discharge depths and 1/3 discharge rates; the discharge depths are respectively selected as 80%, 60%, 40%, 20% and 10%, and the batteries tested for each discharge depth No less than 5 samples.

Another preferred method for evaluating the degree of capacity decay of lithium-ion batteries on-line provided by the present invention, when tested with 80% depth of discharge, the battery remaining capacity working range of the battery sample is 10-90%, and the battery sample is charged and discharged The cut-off is not performed by the voltage, but by the charge-discharge capacity, and the charge-discharge capacity of the battery sample each time is 80% of the calibration.

Another preferred method for evaluating the degree of capacity decay of lithium-ion batteries on-line provided by the present invention, when tested with 60% depth of discharge, the battery remaining capacity working range of the battery sample is 20-80%, and the battery sample Each charge and discharge capacity is 60% of the calibration.

Another preferred method for evaluating the capacity fading degree of lithium-ion batteries on-line provided by the present invention, when tested with 40% depth of discharge, the battery remaining capacity working range of the battery sample is 30-70%, and the battery sample Each charge and discharge capacity is 40% of the calibration.

Another preferred method for evaluating the degree of capacity decay of lithium-ion batteries on-line provided by the present invention, when tested with 20% depth of discharge, the battery remaining capacity working range of the battery sample is 40-60%, and the battery sample Each charge and discharge capacity is 20% of the calibration.

Another preferred method for evaluating the degree of capacity decay of lithium-ion batteries on-line provided by the present invention, when tested with 10% depth of discharge, the battery remaining capacity working range of the battery sample is 45-55%, and the battery sample Each charge and discharge capacity is 10% of the calibration.

Another preferred method provided by the present invention is to record the energy of each charging and discharging of the battery sample, and accumulate the energy of the battery sample every 200 cycles. Carry out a capacity calibration; establish the relationship between the capacity decay rate of the battery and its accumulated processing energy.

Another preferred method for evaluating the degree of capacity fading of lithium-ion batteries on-line provided by the present invention is to determine the online capacity by the relationship between the cumulative processing energy and the capacity fading rate when the battery is operating within the range of 10% to 90% SOC. The capacity decay rate of the running lithium-ion battery can be used to evaluate the degree of capacity decay of the lithium-ion battery online.

Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects

1. The method of the present invention evaluates the degree of capacity fading of the battery by establishing the relationship between the cumulative battery processing energy and the capacity fading rate;

2, the method of the present invention is easy and simple to operate, easy to implement, saves manpower and material resources;

3. The method of the present invention realizes the linear evaluation of battery capacity attenuation by accumulating the processing energy during the operation of the battery, without affecting the normal operation of the energy storage system;

4. The method of the present invention improves the application rate of the energy storage system and reduces its operating cost;

5. The method of the present invention accurately evaluates the capacity fading degree of the lithium-ion battery.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention.

detailed description

Below in conjunction with embodiment the invention is described in further detail.

Example 1:

As shown in Figure 1, the invention of this example provides an online method for assessing the degree of capacity decay of lithium-ion batteries, the steps of which are:

1 Research on the relationship between the degree of battery capacity attenuation, the working range of battery capacity and the accumulated processing energy

When a lithium-ion battery is used in an energy storage system, its depth of discharge (DOD) will not reach 100%, and under different energy storage conditions, the depth of charge and discharge of the battery is also different. Charge and discharge the battery at different depths of discharge, calculate the cumulative processing energy and capacity decay rate of the battery, and establish the relationship between the two. The specific plan is as follows:

(1) Battery capacity calibration: select more than 30 batteries of the same type, connect the battery to a high-precision charge and discharge detector in an environment of 25°C, and conduct a charge and discharge test on the battery at a rate of 1/3C. The upper and lower limit voltages of the discharge adopt the voltage range recommended by the battery manufacturer, cycle 3 times, and record the discharge capacity of each battery.

(2) Battery cycle test at different discharge depths: In an environment of 25°C, connect the battery to a high-precision charge and discharge detector to test the cycle performance of the battery at different discharge depths, and perform cycle tests on the battery at a rate of 1/3C. The depth of discharge is selected to be 80%, 60%, 40%, 20%, and 10%, respectively, and no less than 5 battery samples are tested for each depth of discharge. During the 80% discharge depth test, the SOC working range of the battery is 10-90%. The battery charge and discharge are not cut off by the voltage, but by the charge and discharge capacity. The charge and discharge capacity of the battery each time is 80% of the calibration; 60 When testing the depth of discharge, the SOC working range of the battery is 20-80%, and the charging and discharging capacity of the battery each time is 60% of the calibration; when testing the depth of discharge at 40%, the SOC working range of the battery is 30-70%. The charge and discharge capacity each time is 40% of the calibration; when the 20% depth of discharge test, the SOC working range of the battery is 40-60%, the charge and discharge capacity of the battery each time is 20% of the calibration; 10% depth of discharge test , the SOC working range of the battery is 45-55%, and the charge and discharge capacity of the battery each time is 10% of the calibration. Record the energy of each charge and discharge of the battery and accumulate it. The battery is calibrated every 200 cycles, and the capacity calibration method is the same as (1). Establish the relationship between the capacity decay rate of the battery and its accumulated processing energy.

2. On-line evaluation of the degree of battery capacity decay

Through experiment 1, it is found that when the battery works within the SOC range of 10% to 90%, the capacity decay rate has little correlation with the depth of discharge (DOD), but only with the accumulated processing energy. In the actual application process of the battery, especially in the application of energy storage, the operating SOC range is usually set within the range of 10% to 90% SOC. In addition, for the energy storage battery system operating online, the cumulative processing energy is very large. Therefore, the relationship between the accumulated processing energy and the capacity fading rate can be used to determine the capacity fading rate of the lithium-ion battery running online, so as to evaluate the capacity fading degree of the lithium-ion battery online.

Through the energy storage system monitoring system, the processing energy of the battery is accumulated, and then according to the correlation between the accumulated processing energy and the battery capacity decay rate, the capacity decay degree of the battery can be judged online.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those of ordinary skill in the art should understand with reference to the above embodiments that the specific implementation methods of the present invention can still be modified or equivalent. Replacement, any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending application.

Claims (12)

1. A method for online assessment of lithium-ion battery capacity decay degree, characterized in that: comprise the following steps: (1) Determine the relationship between the degree of battery capacity attenuation, the working range of battery capacity and the accumulated processing energy; (2) On-line evaluation of the degree of battery capacity decay. 2. a kind of method of on-line assessment lithium-ion battery capacity fading degree as claimed in claim 1, is characterized in that: described step (1) comprises the following steps: (1-1) Calibrate the capacity of the battery; (1-2) Test the battery with different discharge depth cycles. 3. a kind of method for on-line evaluation of lithium-ion battery capacity attenuation degree as claimed in claim 2, is characterized in that: the calibration process of described step (1-1) is: choose more than 30 batteries of the same model, in 25 In an environment of ℃, connect the battery to a high-precision charge and discharge detector, and conduct a charge and discharge test on the battery at a discharge rate of 1/3. The upper and lower limit voltages of the battery are within the voltage range recommended by the battery manufacturer. Cycle 3 times and record The discharge capacity of each battery. 4. A method for online evaluation of lithium-ion battery capacity attenuation as claimed in claim 3, wherein the high-precision charge and discharge detector includes a charge and discharge module, a voltage and temperature acquisition device, and a charge and discharge control system. 5. A method for online evaluation of lithium-ion battery capacity fading degree as claimed in claim 2, characterized in that: the test process of the non-chasing (1-2) is: in an environment of 25 ° C, the battery and The high-precision charge and discharge detector is connected, and the battery is cycle tested with different discharge depths and 1/3 discharge rates of the battery; the discharge depths are respectively selected from 80%, 60%, 40%, 20% and 10%, each There are no less than 5 battery samples for the depth of discharge test. 6. A method for online evaluation of lithium-ion battery capacity fading degree as claimed in claim 5, characterized in that: when tested with 80% depth of discharge, the battery remaining capacity working range of the battery sample is 10-90% , the charge and discharge of the battery sample is not cut off by the voltage, but by the charge and discharge capacity, and the charge and discharge capacity of the battery sample each time is 80% of the calibration. 7. A method for online evaluation of lithium-ion battery capacity fading degree as claimed in claim 5, characterized in that: when tested with 60% depth of discharge, the battery remaining capacity working range of the battery sample is 20-80% , the charging and discharging capacity of the battery sample each time is 60% of the calibration. 8. A method for online evaluation of lithium-ion battery capacity fading degree as claimed in claim 5, characterized in that: when tested with 40% depth of discharge, the battery remaining capacity working range of the battery sample is 30-70% , the charging and discharging capacity of the battery sample each time is 40% of the calibration. 9. A method for online evaluation of lithium ion battery capacity fading degree as claimed in claim 5, characterized in that: when tested with 20% depth of discharge, the battery remaining capacity working range of the battery sample is 40-60% , the charging and discharging capacity of the battery sample each time is 20% of the calibration. 10. A method for online evaluation of lithium ion battery capacity fading degree as claimed in claim 5, characterized in that: when tested with 10% depth of discharge, the battery remaining capacity working range of the battery sample is 45-55% , the charging and discharging capacity of the battery sample each time is 10% of the calibration. 11. A method for on-line evaluation of the degree of capacity decay of a lithium-ion battery as claimed in any one of claims 5-10, wherein: the energy of each charge and discharge of the battery sample is recorded and accumulated, and the battery The capacity of the sample is calibrated every 200 cycles; the relationship between the capacity decay rate of the battery and its accumulated processing energy is established. 12. A method for online evaluation of the degree of capacity fading of a lithium-ion battery as claimed in claim 1, characterized in that: when the battery is operating within the SOC range of 10% to 90%, the difference between the accumulated processing energy and the capacity fading rate is calculated. The relationship between them determines the capacity fading rate of the lithium-ion battery running online, so as to evaluate the degree of capacity fading of the lithium-ion battery online.