CN106199452B - Power lithium ion battery functional state estimation method - Google Patents

Abstract

The invention discloses a method for estimating the functional state of a power lithium-ion battery, which comprises the steps of charging and discharging the lithium battery after capacity division by using a current less than 1C, measuring its weight, AC internal resistance, thickness and appearance rating; re-discharging , to detect its discharge capacity and discharge energy; when the lithium battery is discharged to its remaining power of 30-80%, use the mixed pulse power test method to test its power to obtain the power density; and then perform a full charge and full discharge cycle, And after every 100 cycles, repeat the above steps until the functional state SOF is less than 0.6, and record the values measured for each operation; the functional state of the lithium battery is obtained by using the weighted average method. Through the evaluation of battery function status, hidden dangers can be found early, and targeted defense measures can be taken, which is beneficial to the maintenance and use of batteries.

Description

A method for estimating the functional state of a power lithium-ion battery

technical field

The invention relates to the technical field of lithium-ion batteries, in particular to a method for estimating the functional state of a power lithium-ion battery.

Background technique

In recent years, in the face of the threat of increasingly serious problems such as environmental pollution and energy crisis, countries all over the world are stepping up the research and development of electric vehicles. Electric vehicles have become the focus of future industrial development due to their safety, environmental protection and pollution-free features, but the battery as the power source of electric vehicles has become a bottleneck restricting the development of electric vehicles. As the key to monitoring and managing the battery system, the battery management system ensures the normal and reasonable operation of the battery system through charge and discharge balance management, and the battery management system's estimation of the functional state (SOF) of the battery and battery pack is crucial to the management of the battery management system , through accurate and reasonable functional state input, the service life of the battery system can be improved, and the utilization rate of the battery can be improved.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for estimating the functional state of a power lithium-ion battery.

The technical scheme adopted in the present invention is:

A method for estimating the functional state of a power lithium-ion battery, comprising the following steps:

(1) Use a current of less than 1C to charge and discharge the lithium battery after capacity division, and cycle full charge and full discharge for five weeks;

(2) Detecting the weight, AC internal resistance, thickness and appearance rating of the lithium battery after step (1) treatment;

(3) re-discharging the lithium battery after the detection of step (2), and detecting its discharge capacity and discharge energy values;

(4) When the lithium battery is discharged to its residual power of 30-80%, test its power with the hybrid pulse power test method (HPPC), then divide the power value by the weight of the lithium battery to obtain the power density;

(5) After the remaining power of the lithium battery is discharged, it is fully charged and fully discharged, and the above steps (2)-(4) are repeated after 100 cycles of each cycle until the functional state SOF is less than 0.6, and Record the values of lithium battery weight, AC internal resistance, thickness, appearance rating, discharge capacity, discharge energy and power density measured for each operation;

(6) Calculate the thickness increase rate D, internal resistance increase rate R, capacity retention rate C, energy retention rate Q, and power retention rate P of the lithium battery during each detection relative to the previous detection, specifically:

rate of increase in thickness Among them, n represents the number of times of detection; Dn and Dn+1 respectively represent the thickness of the lithium battery detected twice;

Internal resistance increase rate Where n represents the number of detections; R _n and R _n+1 represent the AC internal resistance of the lithium battery tested twice;

Capacity retention Where n represents the number of detections; C _n , C _n+1 represent the discharge capacity of the lithium battery detected twice;

energy retention Among them, n represents the number of times of detection; Q _n and Q _n+1 respectively represent the discharge energy of the lithium battery detected twice;

power retention Where n represents the number of detections; P _n and P _n+1 respectively represent the power density of the lithium battery detected twice;

(7) Using the weighted average method, the functional state SOF of the lithium battery is calculated according to the following formula,

SOF＝(C+R+P+Q+D+W)/6

In the formula: SOF is the functional state, C is the capacity retention rate, R is the internal resistance increase rate, P is the power retention rate, Q is the energy retention rate, D is the thickness increase rate, and W is the appearance score.

In a further solution, the appearance score refers to observing the appearance of the lithium battery with a microscope. If the appearance is intact and undamaged, it is recorded as 1, and if there is damage, the SOF evaluation of the functional state is 0;

When the capacity retention rate drops to 80% of the initial capacity retention rate, the functional state SOF is evaluated as 0;

When the power retention rate drops to 50% of the first power retention rate, the functional state SOF is evaluated as 0;

When the internal resistance increase rate drops to 50% of the first internal resistance increase rate drop, the functional state SOF is evaluated as 0;

When the thickness increase rate drops to 30% of the initial thickness increase rate, the functional state SOF is rated as 0.

As a further solution, the charging and discharging operation of the lithium battery and the detection of the weight, AC internal resistance, thickness, appearance score, discharge capacity, discharge energy and power density of the lithium battery are all carried out at a temperature of 23±2°C.

The invention calculates the capacity retention rate, internal resistance increase rate, power retention rate, energy retention rate, and thickness increase by detecting the quality, thickness, internal resistance increase rate, appearance score, discharge capacity, and discharge energy of the lithium battery. rate; thus the functional state SOF of the lithium battery can be obtained, thereby improving the service life of the battery system and improving the utilization rate of the battery.

The beneficial effects of the present invention are:

Through the construction of six functional state estimation models of capacity retention rate, internal resistance increase rate, power retention rate, energy retention rate, thickness increase rate and appearance score, the present invention breaks through the current method of only using capacity as a judgment of the state of a power lithium-ion battery. The status quo, so as to more truly reflect the functional state of the lithium battery, provide a reliable data basis for the power lithium-ion battery management system, more realistically estimate the comprehensive state of the battery system, and bring better driving experience to new energy vehicle users .

By evaluating the functional state of the battery, the functional state level of the battery in terms of capacity, energy, power, resistance, appearance and structural parts can be obtained, hidden dangers can be found early, and targeted defense measures can be made, which is beneficial to battery maintenance and maintenance. use.

Detailed ways

Example 1:

A method for estimating the functional state of a power lithium-ion battery, comprising the following steps:

(1) Use a current of less than 1C to charge and discharge the lithium battery after capacity division, and cycle full charge and full discharge for five weeks;

(2) Detecting the weight, AC internal resistance, thickness and appearance rating of the lithium battery after step (1) treatment;

(3) re-discharging the lithium battery after the detection of step (2), and detecting its discharge capacity and discharge energy values;

(4) When the lithium battery is discharged to its residual power of 30-80%, test its power with the hybrid pulse power test method (HPPC), then divide the power value by the weight of the lithium battery to obtain the power density;

(5) After the remaining power of the lithium battery is discharged, it is fully charged and fully discharged, and the above steps (2)-(4) are repeated after 100 cycles of each cycle until the functional state SOF is less than 0.6, and Record the values of lithium battery weight, AC internal resistance, thickness, appearance score, discharge capacity, discharge energy and power density measured for each operation;

(6) Calculate the thickness increase rate D, internal resistance increase rate R, capacity retention rate C, energy retention rate Q, and power retention rate P of the lithium battery during each detection relative to the previous detection, specifically:

rate of increase in thickness Among them, n represents the number of times of detection; Dn and Dn+1 respectively represent the thickness of the lithium battery detected twice;

Internal resistance increase rate Where n represents the number of detections; R _n and R _n+1 represent the AC internal resistance of the lithium battery tested twice;

Capacity retention Where n represents the number of detections; C _n , C _n+1 represent the discharge capacity of the lithium battery detected twice;

energy retention Among them, n represents the number of times of detection; Q _n and Q _n+1 respectively represent the discharge energy of the lithium battery detected twice;

power retention Where n represents the number of detections; P _n and P _n+1 respectively represent the power density of the lithium battery detected twice;

(7) Using the weighted average method, the functional state SOF of the lithium battery is calculated according to the following formula,

SOF＝(C+R+P+Q+D+W)/6

In the formula: SOF is the functional state, C is the capacity retention rate, R is the internal resistance increase rate, P is the power retention rate, Q is the energy retention rate, D is the thickness increase rate, and W is the appearance score.

In a further solution, the appearance score refers to observing the appearance of the lithium battery with a microscope. If the appearance is intact and undamaged, it is recorded as 1, and if there is damage, the SOF evaluation of the functional state is 0;

When the capacity retention rate drops to 80% of the initial capacity retention rate, the functional state SOF is evaluated as 0;

When the power retention rate drops to 50% of the first power retention rate, the functional state SOF is evaluated as 0;

When the internal resistance increase rate drops to 50% of the first internal resistance increase rate drop, the functional state SOF is evaluated as 0;

When the thickness increase rate drops to 30% of the initial thickness increase rate, the functional state SOF is rated as 0.

As a further solution, the charging and discharging operation of the lithium battery and the detection of the weight, AC internal resistance, thickness, appearance score, discharge capacity, discharge energy and power density of the lithium battery are all carried out at a temperature of 23±2°C.

Example 2:

(1) Receive one IFP20100140-20Ah square battery cell from the production workshop. At this time, the state of charge of the cell is fully charged; charge and discharge with a current of 0.1C (6.6A) for five weeks, The charge and discharge voltage range is 2.0-3.7V, standby;

(2) The mass of the cell is 439.5g, the thickness is 20.12mm, the AC internal resistance is 0.65mΩ, the appearance is good by visual inspection, no damage is observed by microscope, and the appearance state is recorded as 1.0;

(3) Discharge to 2.0V with 20A current, the discharge capacity at this time is 20170mAh, and the discharge energy is 64.544Wh;

(4) Discharge with a current of 20A to half of the power, and record its open circuit voltage OCV as 3286.8mV after standing for 1 hour; then discharge with a current of 100A for 10 seconds, and record the voltage V ₁ at the end of discharge as 2660.5mV, then according to the mixed pulse The power measured by the power test method = [(OCV-2000)*2*I/(OCV-V ₁ )], the calculated value is 410.9193W, divided by the mass of 439.5g, the power density P ₀ is 934.97W/KG ;

(5) Then use 1C to fully charge and fully discharge at room temperature to cycle, repeat steps (2), (3) and (4) every 100 weeks, until the functional state SOF is below 0.6, that is, the functional state is not satisfied Requirements. And record the lithium battery weight, AC internal resistance, thickness, appearance score, discharge capacity, discharge energy and power density values measured for each operation, as shown in Table 1;

Table 1. 5-week test data:

(6) According to the data in Table 1, calculate the thickness increase rate D, the internal resistance increase rate R, the capacity retention rate C, the energy retention rate Q and the power retention rate of the lithium battery during each test relative to the previous test. P, specifically:

rate of increase in thickness Among them, n represents the number of times of detection; Dn and Dn+1 respectively represent the thickness of the lithium battery detected twice;

Internal resistance increase rate Where n represents the number of detections; R _n and R _n+1 represent the AC internal resistance of the lithium battery tested twice;

Capacity retention Where n represents the number of detections; C _n , C _n+1 represent the discharge capacity of the lithium battery detected twice;

energy retention Among them, n represents the number of times of detection; Q _n and Q _n+1 respectively represent the discharge energy of the lithium battery detected twice;

power retention Where n represents the number of detections; P _n , P _n+1 represent the power density of the lithium battery detected twice; and recorded in Table 2;

(7) Using the weighted average method, the functional state SOF of the lithium battery is calculated according to the following formula,

SOF＝(C+R+P+Q+D+W)/6

In the formula: SOF is the functional state, C is the capacity retention rate, R is the internal resistance increase rate, P is the power retention rate, Q is the energy retention rate, D is the thickness increase rate, and W is the appearance score.

Table 2 Data processing

From the data in Table 2, the following conclusions can be drawn:

1. The single-use capacity retention rate cannot truly reflect the true functional state of the power lithium-ion battery;

2. The increase rate of internal resistance is larger than the parameters of other modules;

3. Thickness increase rate and appearance are cumulative decisive parameters;

4. The functional state is closer to the state of energy retention rate and power retention rate, that is, it is considered that the energy retention rate and power retention rate are close to the parameters actually used by the power lithium-ion battery.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. All modifications, equivalent replacements and improvements made within the principles of the present invention should be included in the protection scope of the present invention. Inside.

Claims (2)

1. a kind of evaluation method of power lithium-ion battery functional status, it is characterised in that：Include the following steps：

(1) electrically operated to the lithium battery progress charge and discharge after partial volume using the electric current less than 1C, and completely fill, completely put circulation five weeks；

(2) weight, AC internal Resistance, thickness and appearance scoring through step (1) treated lithium battery are detected respectively；

(3) it is discharged again the lithium battery after step (2) detection, detects to obtain its discharge capacity and discharge energy numerical value；

(4) when it is 30-80% that lithium battery, which is discharged to its remaining capacity, it is tested with mixed pulses power testing method (HPPC) Then the performance number is obtained power density divided by the weight of lithium battery by power；

(5) after discharging lithium battery remaining capacity, then it is completely filled, completely puts circulation, and every circulation is repeatedly above-mentioned after 100 weeks Step (2)-(4) operate until its functional status SOF is less than 0.6, and record operates measured lithium battery every time respectively Weight, AC internal Resistance, thickness, appearance scoring, discharge capacity, discharge energy and power density numerical value；

(6) the increment rate D of the thickness of lithium battery when calculating separately each detection relative to previous detection, internal resistance increase rate R, Capacity retention ratio C, energy conservation rate Q and power conservation rate P, specially：

The increment rate of thicknessWherein n indicates the number of detection；Dn,D_n+1Respectively indicate the lithium detected twice The thickness of battery；

Internal resistance increase rateWherein n indicates the number of detection；R_n、R_n+1Respectively indicate the lithium electricity detected twice The AC internal Resistance in pond；

Capacity retention ratioWherein n indicates the number of detection；C_n、C_n+1Respectively indicate the electric discharge of the lithium battery detected twice Capacity；

Energy conservation rateWherein n indicates the number of detection；Q_n、Q_n+1Respectively indicate putting for the lithium battery detected twice Electric flux；

Power conservation rateWherein n indicates the number of detection；P_n、P_n+1Respectively indicate the power of the lithium battery detected twice Density；

(7) weighted mean method is used, calculates the functional status SOF of lithium battery as follows,

SOF=(C+R+P+Q+D+W)/6

In formula：SOF is functional status, and C is capacity retention ratio, and R is internal resistance increase rate, and P is power conservation rate, and Q is energy holding Rate, D is thickness increment rate, W is appearance scoring；

The appearance scoring refers to be observed with appearance of the microscope to lithium battery, and complete appearance is unabroken to be denoted as 1, has broken Then functional status SOF is assessed as 0 to damage；

When capacity retention ratio is down to the 80% of capacity retention ratio for the first time, then functional status SOF is assessed as 0；

When power conservation rate is down to the 50% of power conservation rate for the first time, then functional status SOF is assessed as 0；

When internal resistance increase rate is down to the 50% of internal resistance increase rate drop for the first time, then functional status SOF is assessed as 0；

When thickness increment rate is down to the 30% of thickness increment rate for the first time, then functional status SOF is assessed as 0.

2. evaluation method according to claim 1, it is characterised in that：The charge and discharge of lithium battery is electrically operated and lithium battery weight, AC internal Resistance, thickness, appearance scoring, discharge capacity, discharge energy and power density detection at a temperature of 23 ± 2 DEG C into Row.