WO2014019314A1

WO2014019314A1 - Selection and evaluation method for gradient utilization of power cell

Info

Publication number: WO2014019314A1
Application number: PCT/CN2012/086542
Authority: WO
Inventors: 吴文龙; 赵光金; 郭静娟; 李臻; 邱武斌; 刘韶林; 王刚
Original assignee: 河南省电力公司电力科学研究院; 国家电网公司
Priority date: 2012-07-31
Filing date: 2012-12-13
Publication date: 2014-02-06
Also published as: CN102755966A; CN102755966B

Abstract

The present invention relates to a selection and evaluation method for gradient utilization of a power cell. The method comprises: (1) performing appearance recognition and selection on a power cell recycled from an electric motor, and determining whether the power cell enters a gradient utilization stage; (2) performing performance characteristic analysis on a power cell that enters the gradient utilization stage, and determining whether the cell has a gradient utilization value; and (3) detecting changes of the internal microstructure of the power cell for gradient utilization, and evaluating safety and health of the cell.

Description

Power battery step utilization sorting evaluation method

Technical field

The invention belongs to the technical field of batteries, and particularly relates to a power battery step utilization sorting evaluation method, which specifically comprises a power battery step utilization appearance identification sorting, performance characteristic analysis, internal structure detection imaging and phase phase analysis.

Background technique

Electric vehicles have high performance requirements for power batteries. When the capacity of the power battery drops to a certain level, it must be replaced in order to ensure the power performance, driving range and safety performance of the electric vehicle. The battery that has been replaced from the electric car still has a high remaining capacity. Lithium-ion batteries have the advantages of high specific energy, high temperature characteristics, long cycle life, etc. After being decommissioned as electric vehicle power batteries, they may be applied to relatively good working conditions and relatively low battery performance requirements after screening and re-matching. In the case of the use of the power battery cascade. The power battery cascade utilization refers to the continued use of the electric energy storage device in other fields after the performance of the power battery is degraded and the electric vehicle usage requirement cannot be met.

For batteries that have been retired from electric vehicles and are likely to be used for cascade use, there has not been a concept of battery sorting evaluation, and there is no relevant sorting evaluation method, and it does not involve non-destructive testing and three-dimensional imaging of the internal structure of the battery. Methods Report on battery sorting evaluation. Before the lithium-ion battery is used in groups, it is usually based on the external characteristics of the battery, including: battery capacity, internal resistance, charge and discharge curve, self-discharge, etc., to judge and sort the performance of the battery, and The basis for battery grouping. For the power battery used by the cascade, due to its safety performance and electrochemical performance decline, it is necessary to evaluate its health status and safety before use, including: historical operation of the battery, performance characteristics, etc., to determine whether the battery is Cascade utilization and how to use cascades. The external characteristic parameters of the battery can only reflect the changes of some of its main parameters, and can not reflect the factors that cause the battery performance to decline from the internal mechanism, and can not accurately evaluate the health and safety of the battery. Based on the analysis of battery performance characteristic parameters and the analysis of internal structural characteristics of the battery, the present invention fundamentally grasps the cause of battery performance degradation, and then evaluates the safety and health status of the battery to realize the sorting evaluation of the power battery. .

Summary of the invention

The object of the present invention is to provide a power battery step utilization sorting evaluation method, which can detect and image the internal structure of the power battery by using non-destructive testing means and methods, and determine the capacity retention, health state and safety performance of the power battery. The cascade uses the non-destructive sorting evaluation of the power battery.

To achieve the above object, the present invention adopts the following technical solutions:

A power battery cascade utilization sorting evaluation method includes the following steps:

(1) Performing appearance identification and sorting on the decommissioned power battery of the electric vehicle to determine whether the power battery enters the cascade utilization link;

(2) Perform performance analysis on the power battery entering the step utilization section to determine whether the battery has a step utilization value;

(3) Detecting the internal microstructural changes of the power battery in the cascade, and evaluating the safety and health of the battery.

In the first preferred technical solution provided by the present invention, the appearance identification sorting in the step (1) includes: whether the appearance is intact, whether the surface is flat and dry, whether there is damage, whether there is deformation, whether there is any stain, whether there is gas or not. Bulging phenomenon, whether the mark is clear, correct, etc., the appearance recognition needs to be carried out under good lighting conditions.

In a second preferred technical solution provided by the present invention, performance characteristics analysis of the power battery is performed in the step (2), including historical operation parameter analysis and basic performance parameter test analysis.

The historical operating parameter analysis includes analyzing the overcharge, overdischarge condition, operating environment, service life, and available capacity of each battery. Specifically, when analyzing the historical operating parameters, if any of the following conditions are not met, the possibility of using the cascade is directly excluded: 1 Charging at a rate of 0.5-1.0 times, until the voltage reaches 4.5-5.0 V times ≤ 5 times;

2 discharge at a rate of 0.5-1.0 times, until the voltage reaches 1.0-2.0V times ≤ 5 times;

3 The number of times of operation at 50-80 ° C high temperature is less than ≤ 5 times;

4 The number of years of use is less than 8 years;

5 The battery's normal temperature 3h rate discharge capacity is greater than 60% of the nominal value.

The basic performance parameter test analysis refers to testing and recording the main parameters of the battery, including: voltage, internal resistance, capacity, high and low temperature performance, and charge retention capability. The specific values of normal temperature and high and low temperature are: 20 ° C ± 5 ° C, 50 ± 5 ° C, -20 ± 5 ° C. Specifically, when analyzing the basic performance parameter test, if any of the following conditions are not met, the possibility of step utilization is directly excluded:

1 Voltage detection: If the detection value is zero or lower than the discharge cut-off voltage, the possibility of step utilization is directly excluded; the discharge termination voltage is the discharge termination voltage specified in the technical conditions of the enterprise, and the range is 1.90 to 3.00. V, depending on the type of lithium battery;

2 Internal resistance test: For the battery with qualified voltage test, measure the internal resistance. If the internal resistance increases by more than 1.5 times of the initial value, the possibility of step utilization is directly excluded. The initial value of the internal resistance of the lithium battery is ≤ 5mΩ;

3 Under the condition of normal temperature 20 ° C ± 5 ° C, the discharge capacity at 0.3 times is greater than 75% of the rated value;

4 Under the condition of normal temperature 20 ° C ± 5 ° C, the discharge capacity at 0.5 times is greater than 70% of the rated value;

5 Discharge at a low temperature of -20 ± 5 ° C at a rate of 0.3 times, the capacity of which is not less than 85% of the actual capacity of normal temperature;

6 Discharge at a high temperature of 50 ± 5 ° C at a rate of 0.3 times, the capacity of which is not less than 65% of the actual capacity of normal temperature;

7 The charge retention capacity of the power battery at room temperature 20 ° C ± 5 ° C should be greater than 80% of the rated value, the charge retention capacity of the battery at a high temperature of 50 ± 5 ° C and a temperature of -50 ± 5 ° C is not less than 70% of the rated value. .

Specifically, the experimental procedure of the charge retention capability includes: performing a normal temperature 0.3-fold capacity test, recording the actual capacity released and performing full charge, and the battery ambient temperature is 20° C. and 5° C. open storage for 28 days. After 28 days of open storage, the room temperature 0.3-fold capacity test was performed under no-charge conditions and the remaining capacity after storage was recorded.

The capacity test steps of

steps

3, 4, 5, 6, and 7 in the basic performance parameter test analysis include: charging at a constant rate of 0.3 times (or 0.5 times) under a predetermined temperature condition (normal temperature and high temperature) to the battery When the voltage reaches the charging termination voltage, the constant voltage charging is turned on, and when the charging current is reduced to 0.1 times of the constant current charging current value, the charging is stopped, and the measured capacity is the battery charging capacity. Under the condition of full battery capacity, under the specified temperature conditions (normal temperature and high temperature), the power battery discharges at 0.3 times (or 0.5 times), and stops discharging when the battery voltage reaches the discharge termination voltage. The measured capacity is the battery. Discharge capacity.

Specifically, the charging termination voltage, that is, the charging termination voltage specified in the technical conditions of the enterprise, ranges from 3.50V to 4.20V, which is different depending on different types of lithium batteries.

In the third preferred technical solution provided by the present invention, the detecting means used in the step (3) comprises: an industrial CT, a 7Li nuclear magnetic resonance imager.

In the fourth preferred technical solution provided by the present invention, in step (3), the internal microstructural changes of the power battery are detected, and the safety and health status of the battery are evaluated, including: using industrial CT non-destructive testing and three-dimensional imaging technology to realize The internal structure of the decommissioned battery is tested and three-dimensional imaging is realized. Observe whether there is a drum up phenomenon in the internal electrode piece of the battery to judge the health status of the battery. The 7Li nuclear magnetic resonance image non-destructive testing technology is used to analyze the composition of the carbon negative electrode of the lithium battery. There is fiber lithium to judge battery safety. The standard for judging safety: the lithium fiber content on the carbon negative electrode is ≤15% (Li/C, Wt/wt).

Compared with the prior art, the present invention provides an electric vehicle power battery cascade utilization sorting evaluation method, and the battery sorting evaluation process adopts non-destructive testing methods and means, which can ensure that the sorted battery can satisfy the step. The requirements of utilization avoid the damage to the battery; and through the combination of internal and external characteristics, reveal the reasons for the decline of the performance of the power battery in the cascade, and based on this, carry out battery health and safety assessment; The safety and reliability of the power battery during the cascade utilization process.

DRAWINGS

Figure 1 is a three-dimensional image of the internal structure of the #4 battery obtained by industrial CT non-destructive testing;

2 is a three-dimensional image of the internal structure of the #5 battery obtained by industrial CT non-destructive testing;

Figure 3 is a capacity attenuation diagram of the #6 battery at 0.2C;

Figure 4 is a charge and discharge curve of the #6 battery at 0.2C;

Figure 5 is a capacity attenuation diagram of the #6 battery at 0.3C;

Figure 6 is a charge and discharge curve of a #6 battery at 0.3C.

detailed description

Hereinafter, the process of the present invention will be further described in detail by way of specific examples, but the scope of the present invention is not limited thereto.

Example 1

An electric vehicle power battery cascade utilization sorting evaluation method includes the following steps:

(1) Select 6 power batteries that have been retired from a pure electric bus, numbered #1, #2, #3, #4, #5, #6, and the factory specifications are: square soft package lithium iron phosphate Battery, nominal capacity 25Ah, nominal voltage: 3.20V, charge cut-off voltage: 3.65V, discharge cut-off voltage: 2.00V, internal resistance ≤ 5 MΩ.

Firstly, the six power batteries were visually identified and sorted. The appearance was sorted under the conditions of good outdoor light. It was found that the #1 battery had obvious air swelling, and the battery's logo was blurred. According to the appearance sorting principle, # 1 The battery directly excludes the possibility of use of the ladder; the appearance recognition of the remaining 5 batteries meets the requirements of the cascade utilization, that is, the appearance is intact, the surface is smooth and dry, no damage, no deformation, no stain, no inflation, and the mark is clear and correct. According to the appearance sorting results, 5 power batteries can enter the step utilization.

(2) For the performance characteristics analysis of the power battery entering the step utilization section (including historical operation parameter analysis and basic performance parameter test analysis), determine whether the battery has the value of the cascade utilization. According to the historical data of 5 batteries recorded by the power station, analyze the overcharge, overdischarge, operating environment, service life and available capacity of each battery. Specifically, when analyzing the historical operating parameters, if any of the following conditions are not met, the possibility of using the cascade is directly excluded:

1 charging at a rate of 0.5-1.0 times, to a voltage of 4.5-5.0 V times ≤ 5 times;

3 The number of runs at 50-80 ° C high temperature ≤ 5 times;

4 The number of years of use is less than 8 years;

The analysis results of the historical data of 5 batteries are shown in Table 1. According to the analysis results, the #2 battery does not have the value of the cascade utilization.

Then test the basic performance parameters of the remaining 4 batteries, test and record the main parameters of the battery, including: voltage, internal resistance, capacity, high and low temperature performance, and charge retention. Specifically, when analyzing the basic performance parameter test, if any of the following conditions are not met, the possibility of step utilization is directly excluded:

1 Voltage detection: If the detected value is zero or lower than the discharge cut-off voltage, the possibility of step utilization is directly excluded; the discharge cut-off voltage is 1.90~3.00 V, depending on the type of lithium battery;

3 Under the condition of 20 ° C ± 5 ° C, the discharge capacity at 0.3 times is greater than 75% of the rated value;

4 Under the condition of 20 ° C ± 5 ° C, the discharge capacity at 0.5 times is greater than 70% of the rated value;

5 Discharge at a rate of 0.3 times at a low temperature of -20 ± 5 ° C, the capacity of which is not less than 85% of the actual capacity of normal temperature;

6 Discharge at a rate of 0.3 times at a temperature of 50 ± 5 ° C, the capacity of which is not less than 65% of the actual capacity of normal temperature;

7 At normal temperature (20 ° C ± 5 ° C), the charge retention capacity of the power battery should be greater than 80% of the rated value, the charge retention of the battery at high temperature (50 ± 5 ° C) and low temperature (-20 ± 5 ° C) The capacity is not less than 70% of the rated value.

The charging maintenance test procedure includes: performing a normal temperature 0.3 times capacity test, recording the actual capacity released and performing full charge at a normal temperature of 0.3 times, and the battery ambient temperature is 20 ° C ± 5 ° C open storage for 28 days. After 28 days of open storage, the room temperature 0.3-fold capacity test was performed under no-charge conditions and the remaining capacity after storage was recorded.

The basic performance parameter test analysis, in

steps

3, 4, 5, 6, and 7, the capacity test step includes: charging at a constant rate of 0.3 times (or 0.5 times) under a predetermined temperature condition (normal temperature and high temperature). When the battery voltage reaches the charging termination voltage, the constant voltage charging is performed, and when the charging current is reduced to 0.1 times of the constant current charging current value, the charging is stopped, and the measured capacity is the battery charging capacity. Under the condition of full battery capacity, under the specified temperature conditions (normal temperature and high temperature), the power battery discharges at 0.3 times (or 0.5 times), and stops discharging when the battery voltage reaches the discharge termination voltage. The measured capacity is the battery. Discharge capacity. The charge termination voltage, that is, the charge termination voltage specified in the technical conditions of the enterprise, ranges from 3.50V to 4.20V, depending on different types of lithium batteries.

The test results of the performance measurement parameters of the four batteries are shown in Table 2. According to the data results of Table 2, it is judged that the #3 battery has no step utilization value.

(3) Detecting the internal microstructural changes of the power battery in the cascade, evaluating the battery safety and health status, and classifying the battery. First use industrial CT pairs #4, #5, #6 Three batteries were used for non-destructive testing of internal structure to realize three-dimensional imaging. It was found that there was a phenomenon of pole piece protrusion inside the #4 battery (see Figure 1), which could not be seen by the naked eye in the appearance identification sorting of step 1. The energy storage battery safety and reliability requirements, #4 battery belongs to the sub-health grade decommissioned battery. The test shows that the #5 (see Figure 2) and #6 batteries have good internal structure and belong to the healthy grade decommissioned battery. Next, use the 7Li NMR imager for #5, #6 The carbon negative electrode of the two batteries was subjected to non-destructive testing to analyze the presence or absence of lithium fiber. It was found that a certain amount of lithium fiber was present on the carbon negative electrode of the #5 battery, and the content was 16% (Li/C, Wt / wt), the detection value exceeds the limit value of 15%, therefore, from a safety point of view, #5 battery belongs to the sub-safety level decommissioned battery. No lithium fiber was detected on the #6 battery carbon negative electrode. Finally, the #6 battery sorted by non-destructive testing was evaluated and verified. The specific steps were as follows: the #6 battery was tested for room temperature capacity, and the remaining capacity of the #6 battery was 21 Ah. At the same time, the cycle performance of #6 battery was tested. The specific result: charging and discharging at 0.2C, the capacity retention rate of the cycle is still above 98% (see Figure 3, Figure 4), charging and discharging at 0.3C, cycle 10 The secondary capacity retention rate is still above 95% (see Figure 5 and Figure 6), reflecting good cycle performance. The results show that the batteries sorted by the method provided by the present invention have good performance.

Claims

A power battery cascade utilization sorting evaluation method, characterized in that the sorting evaluation method comprises the following steps: (1) performing appearance identification sorting on an electric vehicle decommissioned power battery to determine whether the power battery enters a step utilization link; 2) Analyze the performance characteristics of the power battery entering the step utilization section to determine whether the battery has the value of the cascade utilization; (3) Detect the internal microstructural changes of the power battery in the step, and evaluate the battery safety and health status.
The power battery step utilization sorting evaluation method according to claim 1, wherein the appearance identification sorting in the step (1) comprises: whether the appearance is intact, whether the surface is flat and dry, whether there is damage, whether there is deformation or not. Whether there is any stain, whether there is swelling or not, whether the mark is clear and correct, and the appearance recognition needs to be carried out under good light conditions.
The power battery step utilization sorting evaluation method according to claim 1, wherein in step (2), the performance characteristics of the power battery are analyzed, including historical operation parameter analysis and basic performance parameter test analysis.
The power battery step utilization sorting evaluation method according to claim 3, wherein the historical operation parameter analysis comprises analyzing an overcharge, an overdischarge condition, an operating environment, a service life, and an available capacity of each battery; Basic performance parameter test analysis refers to testing and recording the main parameters of the battery, including: voltage, internal resistance, capacity, high and low temperature performance, and charge retention.
The power battery step utilization sorting evaluation method according to claim 1, wherein in step (3), the internal microstructural changes of the power battery are detected by the step, and the detection means used include: industrial CT, 7Li nuclear magnetic resonance. Imager.
The power battery step utilization sorting evaluation method according to claim 1, wherein in step (3), the internal microstructure change of the power battery is detected, and the battery safety and health status are evaluated, including: utilizing Industrial CT non-destructive testing and three-dimensional imaging technology, to achieve the detection of the internal structure of the decommissioned battery and to achieve three-dimensional imaging, to determine the health of the battery; 7Li magnetic resonance imaging non-destructive testing technology for the composition of lithium battery carbon negative electrode, to detect the presence of fiber lithium To determine battery safety.