CN117434453B - Method for detecting service life abnormality of lithium ion battery - Google Patents

Abstract

The invention provides a lithium-ion battery life abnormality detection method. The method first performs calibration of the Coulombic efficiency of the target lithium-ion battery, obtains two Coulombic efficiency curves, and then obtains the equation of the corrected first fitting curve and the corrected The equation of the second fitting curve, and then for an electric vehicle loaded with the same type of lithium-ion battery as the target lithium-ion battery, obtain the Coulomb efficiency _ys and the number of cycles of the lithium-ion battery of the electric vehicle, and then based on the lithium of the electric vehicle The number of cycles of the ion battery is used to obtain the upper limit of the standard Coulombic efficiency y _max and the lower limit of the standard Coulombic efficiency y _min . If y _s > y _max or y _s < y _min is satisfied, the lithium-ion battery life of the electric vehicle is determined to be abnormal. And issuing an early warning, the present invention has the advantages of low cost and short time consumption.

Description

A method for detecting abnormal lithium-ion battery life

Technical field

The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for detecting abnormality in the life of lithium-ion batteries.

Background technique

Electric vehicles are the development direction of the automotive field, and as a key component of electric vehicles, the performance of lithium-ion batteries directly affects the experience of using electric vehicles. The life of a lithium-ion battery is one of the important indicators of the battery. However, during the charge and discharge cycle of the lithium-ion battery, some irreversible processes will occur inside the battery, resulting in changes in internal impedance, output current, etc., thus causing capacity and energy The loss affects the cycle life of the battery.

Generally speaking, when the lithium-ion battery capacity drops to 80% of the rated capacity, the cycle life of the lithium-ion battery reaches the end. In the normal decay process of lithium-ion batteries, this process is long. However, lithium-ion batteries will undergo complex and changeable working conditions and abuse during the cycle, causing the cycle life to end prematurely. Therefore, the lithium-ion batteries for electric vehicles will Detect lifecycle anomalies.

However, most of the existing methods for detecting abnormal lithium-ion battery life require sophisticated testing equipment and complex calculations, making detection costly and time-consuming.

Contents of the invention

The purpose of the present invention is to provide a lithium-ion battery life abnormality detection method to solve the problems of high detection cost and long time consumption in the existing technology.

A method for detecting lithium-ion battery life anomalies, including the following steps:

Step 1: Calibrate the Coulombic efficiency of the target lithium-ion battery, and obtain the first Coulombic efficiency curve with a Coulombic efficiency value greater than 100% and the second Coulombic efficiency curve with a Coulombic efficiency value less than 100% in the target coordinate system. The abscissa is the number of cycles, and the ordinate is the Coulomb efficiency value;

Step 2: Perform logarithmic fitting on the first Coulomb efficiency curve and the second Coulomb efficiency curve respectively to obtain the equation of the first fitting curve and the equation of the second fitting curve;

Step 3: When the correlation coefficient between the first Coulomb efficiency curve and the second Coulomb efficiency curve is not less than the preset value, correct the coefficients of the equation of the first fitting curve and the equation of the second fitting curve to obtain the corrected the equation of the first fitting curve and the equation of the modified second fitting curve;

Step 4: For an electric vehicle loaded with a lithium-ion battery of the same type as the target lithium-ion battery, obtain the charge and discharge data of the electric vehicle that meets the preset conditions, and obtain the Coulombic efficiency y _s of the lithium-ion battery of the electric vehicle based on the charge and discharge data. , and convert the driving mileage of the electric vehicle into the number of cycles of the lithium-ion battery of the electric vehicle;

Step 5: Substitute the number of cycles of the lithium-ion battery of the electric vehicle into the equation of the revised first fitting curve and the equation of the revised second fitting curve to obtain the standard Coulomb efficiency upper limit value y _max and the standard Coulomb efficiency lower limit value y _min ;

Step 6: If y _s > y _max or y _s < y _min is satisfied, it is determined that the lithium-ion battery life of the electric vehicle is abnormal and an early warning is issued.

According to the lithium-ion battery life abnormality detection method provided by the present invention, the Coulombic efficiency of the target lithium-ion battery is first calibrated to obtain two Coulombic efficiency curves, and then the equation of the corrected first fitting curve and the corrected second fitting curve are obtained. The equation of the fitting curve, and then for an electric vehicle loaded with the same type of lithium-ion battery as the target lithium-ion battery, obtain the Coulomb efficiency _ys and the number of cycles of the lithium-ion battery of the electric vehicle, and then based on the lithium-ion battery of the electric vehicle The standard Coulomb efficiency upper limit value y _max and the standard Coulomb efficiency lower limit value y _min are obtained by the number of cycles. If y _s > y _max or y _s < y _min is satisfied, it means that the cycle life of the lithium-ion battery of the electric vehicle has been reached in advance. Finally, it is determined that the lithium-ion battery life of the electric vehicle is abnormal and an early warning is issued. This invention does not require sophisticated testing equipment and complex calculations. It only needs to perform calibration and calculation fitting of the Coulombic efficiency of the target lithium-ion battery, and then performs calculations on the electric vehicle. Comparative analysis of lithium-ion batteries in cars can quickly detect lithium-ion battery life anomalies, which is low-cost and time-consuming, helping to improve the safety of electric vehicles.

In addition, the lithium-ion battery life abnormality detection method provided by the present invention also has the following technical features:

Further, the steps to calibrate the Coulombic efficiency of the target lithium-ion battery specifically include:

Step 1.1, adjust the temperature of the target lithium-ion battery to 25°C and let it stand for 120 minutes;

Step 1.2, convert the target lithium-ion battery to Charge with a constant current to the maximum termination voltage specified by the target lithium-ion battery, then perform constant voltage charging, stop charging when the charging current drops to 0.02I ₁ , and then let it stand for 5 minutes, where I ₁ is the 1-hour discharge of the target lithium-ion battery. rate current;

Step 1.3, convert the target lithium-ion battery to Discharge with a constant current to the minimum termination voltage specified by the target lithium-ion battery, and then let it sit for 5 minutes;

Step 1.4: Charge the target lithium-ion battery at a constant current with the average current of the electric vehicle to the maximum termination voltage of the target lithium-ion battery allowed by the electric vehicle, then switch to constant voltage charging, and stop charging when the charging current drops to the minimum charging current allowed by the electric vehicle. Then let it sit for 10 minutes;

Step 1.5, simulate the operating conditions of the electric vehicle, discharge the target lithium-ion battery at the electric vehicle average current rate to the target lithium-ion minimum termination voltage allowed by the electric vehicle, and then let it stand for 10 minutes;

Step 1.6, take step 1.4 to step 1.5 as one charge and discharge cycle, and perform 20 charge and discharge cycles;

Step 1.7, cycle steps 1.2 to 1.6 until the capacity of the target lithium ion decays to 80% of the rated capacity, record the charge and discharge capacity of each charge and discharge cycle, and calculate the Coulombic efficiency of each charge and discharge cycle.

Further, in step 2, the expression of the equation of the first fitting curve is:

y ₁ =A ₁ ×ln(x)+B ₁ ;

Among them, y ₁ represents the Coulomb efficiency value corresponding to the first fitting curve, x represents the number of cycles, A ₁ and B ₁ represent the equation coefficients corresponding to the first fitting curve;

The expression of the equation of the second fitting curve is:

y ₂ =A ₂ ×ln(x)+B ₂ ;

Among them, y ₂ represents the Coulomb efficiency value corresponding to the second fitting curve, and A ₂ and B ₂ represent the equation coefficients corresponding to the second fitting curve.

Further, in step 3, the expression of the equation of the modified first fitting curve is:

y ₁ =A ₁ ×(1+0.5%)×ln(x)+B ₁ ×(1+0.5%);

The expression of the equation of the modified second fitting curve is:

y ₂ =A ₂ ×(1-0.5%)×ln(x)+B ₂ ×(1-0.5%).

Further, in step 4, the charge and discharge data of the electric vehicle that meets the preset conditions are obtained, and the Coulomb efficiency y _s of the lithium-ion battery of the electric vehicle is obtained based on the charge and discharge data, which specifically includes:

Obtain charge and discharge data with a temperature range of 20℃-30℃ and a SOC interval greater than 20% during charge and discharge. The charge and discharge data include charging capacity and discharge capacity, and calculate the Coulombic efficiency y _s of the lithium-ion battery of the electric vehicle according to the following formula:

y _s = (C ₁ /C ₂ )×100%;

Among them, C ₁ represents the discharge capacity and C ₂ represents the charging capacity.

Further, in step 4, the formula for converting the driving mileage of the electric vehicle into the number of cycles of the lithium-ion battery of the electric vehicle is:

x _s =S ₂ /S ₁ ;

Among them, x _s represents the number of cycles of the lithium-ion battery of the electric vehicle, S ₁ represents the maximum single driving mileage of the electric vehicle, and S ₂ represents the cumulative driving mileage of the electric vehicle.

Further, the preset value is 90%.

Description of the drawings

Figure 1 is a flow chart of a lithium-ion battery life abnormality detection method provided by an embodiment of the present invention;

Figure 2 is an exemplary first Coulomb efficiency curve and a second Coulomb efficiency curve.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Please refer to Figure 1. An embodiment of the present invention provides a lithium-ion battery life abnormality detection method, which includes the following steps 1 to 6:

Step 1: Calibrate the Coulombic efficiency of the target lithium-ion battery, and obtain the first Coulombic efficiency curve with a Coulombic efficiency value greater than 100% and the second Coulombic efficiency curve with a Coulombic efficiency value less than 100% in the target coordinate system. The abscissa is the number of cycles, and the ordinate is the Coulomb efficiency value.

Among them, the steps to calibrate the Coulombic efficiency of the target lithium-ion battery specifically include:

Step 1.1, adjust the temperature of the target lithium-ion battery to 25°C and let it stand for 120 minutes;

Step 1.2, convert the target lithium-ion battery to Charge with a constant current to the maximum termination voltage specified by the target lithium-ion battery, then perform constant voltage charging, stop charging when the charging current drops to 0.02I ₁ , and then let it stand for 5 minutes, where I ₁ is the 1-hour discharge of the target lithium-ion battery. rate current;

Step 1.3, convert the target lithium-ion battery to Discharge with a constant current to the minimum termination voltage specified by the target lithium-ion battery, and then let it sit for 5 minutes;

Step 1.4: Charge the target lithium-ion battery with a constant current using the average current of the electric vehicle to the maximum termination voltage of the target lithium-ion battery allowed by the electric vehicle, then switch to constant voltage charging, and stop charging when the charging current drops to the minimum charging current allowed by the electric vehicle. Then let it sit for 10 minutes;

Step 1.5, simulate the operating conditions of the electric vehicle, discharge the target lithium-ion battery at the electric vehicle average current rate to the target lithium-ion minimum termination voltage allowed by the electric vehicle, and then let it stand for 10 minutes;

Step 1.6, take step 1.4 to step 1.5 as one charge and discharge cycle, and perform 20 charge and discharge cycles;

Step 1.7, cycle steps 1.2 to 1.6 until the capacity of the target lithium ion decays to 80% of the rated capacity, record the charge and discharge capacity of each charge and discharge cycle, and calculate the Coulombic efficiency of each charge and discharge cycle.

Specifically, by obtaining the charge and discharge capacity of each charge and discharge cycle, the Coulomb efficiency of each charge and discharge cycle can be calculated, and then the target coordinate system is drawn with the number of cycles as the abscissa and the Coulomb efficiency value as the ordinate, and then By plotting the Coulomb efficiency of each charge and discharge cycle in the target coordinate system, the first Coulomb efficiency curve with a Coulomb efficiency value greater than 100% and the second Coulomb efficiency curve with a Coulomb efficiency value less than 100% can be obtained. An example The first Coulomb efficiency curve and the second Coulomb efficiency curve are shown in Figure 2.

Step 2: Perform logarithmic fitting on the first Coulombic efficiency curve and the second Coulombic efficiency curve respectively to obtain the equation of the first fitting curve and the equation of the second fitting curve.

Among them, the expression of the equation of the first fitting curve is:

y ₁ =A ₁ ×ln(x)+B ₁ ;

Among them, y ₁ represents the Coulomb efficiency value corresponding to the first fitting curve, x represents the number of cycles, A ₁ and B ₁ represent the equation coefficients corresponding to the first fitting curve;

The expression of the equation of the second fitting curve is:

y ₂ =A ₂ ×ln(x)+B ₂ ;

Among them, y ₂ represents the Coulomb efficiency value corresponding to the second fitting curve, and A ₂ and B ₂ represent the equation coefficients corresponding to the second fitting curve.

Step 3: When the correlation coefficient between the first Coulomb efficiency curve and the second Coulomb efficiency curve is not less than the preset value, correct the coefficients of the equation of the first fitting curve and the equation of the second fitting curve to obtain the corrected The equation of the first fitted curve and the equation of the modified second fitted curve.

Among them, the correction is to eliminate the difference between the calibration environment of the lithium-ion battery (mainly the calibration test instrument) and the environment of the cells in the battery pack (mainly the collection equipment - BMS).

Preferably, the default value is 90%.

The expression of the equation of the modified first fitting curve is:

y ₁ =A ₁ ×(1+0.5%)×ln(x)+B ₁ ×(1+0.5%);

The expression of the equation of the modified second fitting curve is:

y ₂ =A ₂ ×(1-0.5%)×ln(x)+B ₂ ×(1-0.5%).

It should be pointed out that during specific implementation, if the correlation coefficient between the first Coulomb efficiency curve and the second Coulomb efficiency curve is less than 90%, other mathematical function fitting (such as exponential, polynomial and other functions) needs to be performed until the correlation coefficient is no longer If it is less than 90%, the coefficient of the corresponding function will be corrected.

Step 4: For an electric vehicle loaded with a lithium-ion battery of the same type as the target lithium-ion battery, obtain the charge and discharge data of the electric vehicle that meets the preset conditions, and obtain the Coulombic efficiency y _s of the lithium-ion battery of the electric vehicle based on the charge and discharge data. , and convert the driving mileage of the electric vehicle into the number of cycles of the lithium-ion battery of the electric vehicle.

Among them, the charge and discharge data of the electric vehicle that meets the preset conditions are obtained, and the Coulomb efficiency _ys of the lithium-ion battery of the electric vehicle is obtained based on the charge and discharge data, which specifically includes:

Obtain charge and discharge data with a temperature range of 20℃-30℃ and a SOC interval greater than 20% during charge and discharge. The charge and discharge data include charging capacity and discharge capacity, and calculate the Coulombic efficiency y _s of the lithium-ion battery of the electric vehicle according to the following formula:

y _s = (C ₁ /C ₂ )×100%;

Among them, C ₁ represents the discharge capacity and C ₂ represents the charging capacity.

The formula for converting the driving range of an electric vehicle into the number of cycles of the electric vehicle's lithium-ion battery is:

x _s =S ₂ /S ₁ ;

Among them, x _s represents the number of cycles of the lithium-ion battery of the electric vehicle, S ₁ represents the maximum single driving mileage of the electric vehicle, and S ₂ represents the cumulative driving mileage of the electric vehicle.

Step 5: Substitute the number of cycles of the lithium-ion battery of the electric vehicle into the equation of the revised first fitting curve and the equation of the revised second fitting curve to obtain the standard Coulomb efficiency upper limit value y _max and the standard Coulomb efficiency lower limit value y _min .

Step 6: If y _s > y _max or y _s < y _min is satisfied, it is determined that the lithium-ion battery life of the electric vehicle is abnormal and an early warning is issued.

It should be pointed out that if y _min ≤ _{y s} ≤ y _max , it means that the cycle life of the lithium-ion battery of the electric vehicle has not ended, and the electric vehicle is continuously monitored.

In summary, according to the lithium-ion battery life abnormality detection method provided in this embodiment, the Coulombic efficiency of the target lithium-ion battery is first calibrated to obtain two Coulombic efficiency curves, and then the equation and correction of the corrected first fitting curve are obtained. The equation of the second fitting _curve after The standard Coulomb efficiency upper limit value y _max and the standard Coulomb efficiency lower limit value y _min are obtained from the number of cycles of the lithium-ion battery. If y _s > y _max or y _s < y _min is satisfied, it means that the lithium-ion battery for electric vehicles has The cycle life reaches the end in advance, and the lithium-ion battery life of the electric vehicle is determined to be abnormal and an early warning is issued. This invention does not require sophisticated testing equipment and complex calculations, and only requires the calibration of the Coulombic efficiency of the target lithium-ion battery and calculation fitting. , and then comparative analysis of lithium-ion batteries in electric vehicles can quickly detect lithium-ion battery life anomalies, which is low-cost and time-consuming, helping to improve the safety of electric vehicles.

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "an example," "specific examples," or "some examples" or the like means that specific features are described in connection with the embodiment or example. , structures, materials or features are included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and purposes of the invention. The scope of the invention is defined by the claims and their equivalents.

Claims (3)

1. The method for detecting the service life abnormality of the lithium ion battery is characterized by comprising the following steps of:

step 1, calibrating the coulomb efficiency of a target lithium ion battery to obtain a first coulomb efficiency curve with the coulomb efficiency value more than 100% and a second coulomb efficiency curve with the coulomb efficiency value less than 100% in a target coordinate system, wherein the abscissa of the target coordinate system is the cycle number and the ordinate of the target coordinate system is the coulomb efficiency value;

step 2, carrying out logarithmic fitting on the first coulomb efficiency curve and the second coulomb efficiency curve respectively to obtain an equation of the first fitted curve and an equation of the second fitted curve;

step 3, when the correlation coefficient of the first coulomb efficiency curve and the second coulomb efficiency curve is not smaller than a preset value, correcting the coefficient of the equation of the first fitting curve and the coefficient of the equation of the second fitting curve to obtain a corrected equation of the first fitting curve and a corrected equation of the second fitting curve;

step 4, for the electric automobile loaded with the lithium ion battery of the same model as the target lithium ion battery, acquiring charge and discharge data of the electric automobile meeting preset conditions, and acquiring the coulomb efficiency y of the lithium ion battery of the electric automobile according to the charge and discharge data _s Converting the driving mileage of the electric automobile into the cycle number of the lithium ion battery of the electric automobile;

step 5, substituting the cycle number of the lithium ion battery of the electric automobile into the equation of the corrected first fitting curve and the equation of the corrected second fitting curve to respectively obtain the standard coulomb efficiency upper limit value y _max And a standard coulombic efficiency lower limit y _min ；

Step 6, if y is satisfied _s ＞y _max Or y _s ＜y _min Judging that the service life of the lithium ion battery of the electric automobile is abnormal, and giving an early warning;

the step of calibrating the coulomb efficiency of the target lithium ion battery specifically comprises the following steps:

step 1.1, regulating the temperature of a target lithium ion battery to 25 ℃, and standing for 120min;

step 1.2, the target lithium ion battery is used forThe constant current of the lithium ion battery is charged to the maximum termination voltage regulated by the target lithium ion battery, and then the constant voltage charging is carried out until the charging current is reduced to 0.02I ₁ Stopping charging, standing for 5min, wherein I ₁ Is the discharge rate current of the target lithium ion battery for 1 hour;

step 1.3, the target lithium ion battery is used forDischarging to the minimum termination voltage specified by the target lithium ion battery, and then standing for 5min;

step 1.4, charging the target lithium ion battery to the maximum end voltage of the target lithium ion battery allowed by the electric automobile in a constant current manner by using the average current of the electric automobile, turning into constant voltage charging, stopping charging when the charging current is reduced to the minimum charging current allowed by the electric automobile, and standing for 10min;

step 1.5, simulating the operation condition of the electric automobile, discharging a target lithium ion battery to the minimum termination voltage of the target lithium ion allowed by the electric automobile according to the average current multiplying power of the electric automobile, and standing for 10min;

step 1.6, taking the steps 1.4 to 1.5 as a circle of charge-discharge cycle, and carrying out 20 circles of charge-discharge cycle;

step 1.7, cycling the steps 1.2-1.6 until the capacity of target lithium ions is attenuated to 80% of rated capacity, recording the charge-discharge capacity of each circle of charge-discharge cycle, and calculating the coulomb efficiency of each circle of charge-discharge cycle;

in step 2, the expression of the equation of the first fitted curve is:

y ₁ =A ₁ ×ln(x)+B ₁ ；

wherein y is ₁ The coulomb efficiency value corresponding to the first fitting curve is represented, x represents the cycle number, A ₁ And B ₁ Equation coefficients corresponding to the first fitting curve are represented;

the expression of the equation for the second fitted curve is:

y ₂ =A ₂ ×ln(x)+B ₂ ；

wherein y is ₂ Representing the coulomb efficiency value corresponding to the second fitting curve, A ₂ And B ₂ Equation coefficients corresponding to the second fitting curve are represented;

in step 3, the expression of the equation of the modified first fitting curve is:

y ₁ =A ₁ ×(1+0.5%)×ln(x)+B ₁ ×(1+0.5%)；

the expression of the equation of the modified second fitted curve is:

y ₂ =A ₂ ×(1－0.5%)×ln(x)+B ₂ ×(1－0.5%)；

in step 4, charge and discharge data of the electric vehicle meeting the preset conditions are obtained, and the coulomb efficiency y of the lithium ion battery of the electric vehicle is obtained according to the charge and discharge data _s The method specifically comprises the following steps:

acquiring charge and discharge data with the temperature interval of 20-30 ℃ and the SOC interval of more than 20% during charge and discharge, wherein the charge and discharge data comprise charge capacity and discharge capacity, and calculating the coulomb efficiency y of the lithium ion battery of the electric automobile according to the following formula _s ：

y _s =（C ₁ /C ₂ ）×100%；

Wherein C is ₁ Represents discharge capacity, C ₂ Indicating the charge capacity.

2. The method for detecting abnormal life of a lithium ion battery according to claim 1, wherein in the step 4, a formula for converting a driving range of an electric vehicle into a number of cycles of the lithium ion battery of the electric vehicle is:

x _s =S ₂ /S ₁ ；

wherein x is _s Represents the cycle number of the lithium ion battery of the electric automobile, S ₁ Represents the single maximum driving mileage of the electric automobile, S ₂ Indicating the accumulated driving mileage of the electric automobile.

3. The method for detecting abnormal life of a lithium ion battery according to claim 1, wherein the preset value is 90%.