CN110687469B - A kind of lithium ion battery constant capacity method - Google Patents

Abstract

The invention relates to a lithium ion battery constant volume method, and belongs to the technical field of lithium ion testing. The invention provides a novel lithium ion battery constant volume method, which comprises the following steps: 1) measuring the battery capacity of the battery to be measured in an n% SOC state; 2) substituting the battery capacity of the battery to be tested in the n% SOC state into a standard linear equation to calculate the battery capacity in the 100% SOC state; the standard linear equation is obtained by linearly fitting the acquired battery capacity data of the standard battery in the n% SOC state and the acquired battery capacity data of the standard battery in the 100% SOC state. When the method is used for testing the capacity of a new battery, the capacity of the battery in the SOC state of 100% can be obtained only by testing the capacity of the battery in the SOC state of n%. The lithium ion battery constant volume method greatly shortens the constant volume time, improves the productivity of the battery and reduces the production cost of enterprises.

Description

A kind of lithium ion battery constant capacity method

technical field

The invention relates to a method for constant capacity of a lithium ion battery, belonging to the technical field of lithium ion testing.

Background technique

At present, affected by the energy crisis and environmental crisis, lithium batteries have been widely used in energy, transportation, communications and other fields, and the lithium battery industry has been vigorously developed. Capacity refers to the size of the battery's stored power, and the unit of battery capacity is "mAh" or "Ah". The current calculation method of lithium-ion battery battery capacity (C): capacity C = discharge battery (constant current) I × discharge time (hour) T, and the test method of battery capacity is generally, charge the battery to full power (full voltage voltage The range is 3.65-4.2V), then constant current discharge to the lower limit voltage (the lower limit voltage range is 2.5V-3.0V), record the current and time during the battery discharge process, and calculate the battery capacity according to the recorded values.

The lithium-ion battery industry basically involves the capacity test process, but the battery capacity test requires the battery to be fully charged, and the process of charging to full power takes a long time, resulting in a large number of equipment purchased by enterprises and higher costs. The Chinese invention patent application with publication number CN108896920A discloses a method for constant capacity of lithium-ion batteries during low-temperature HPPC testing, which includes: S3. The battery is fully charged in a 25°C environmental chamber by means of constant current and constant voltage; S4. Place the battery in a -20°C environment chamber to make the battery reach thermal equilibrium; S5. Discharge the battery at 1C for 3 minutes in a -20°C environment chamber, and then let it stand for 1 hour; S6. Repeat step S5 until the voltage of the battery reaches Discharge is stopped at 2.8V; S7, the sum of the discharge capacities accumulated through steps S5-S6 is the battery capacity. In this method, the battery still needs to be fully charged, and in the whole process of constant capacity of the battery, not only a lot of time is wasted, but also excessive resources of the enterprise are consumed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a lithium ion battery constant capacity method, which can shorten the lithium ion battery capacity test time, not only can reduce the production cost of the enterprise, but also can greatly improve the production capacity of the enterprise.

A lithium-ion battery constant volume method, comprising the following steps:

1) Measure the battery capacity of the battery to be tested under n% SOC state;

2) Substitute the battery capacity of the battery to be tested in the n% SOC state into the standard linear equation to calculate the battery capacity in the 100% SOC state; the standard linear equation is based on the collected standard battery's battery capacity data in the n% SOC state and Obtained by linear fitting of battery capacity data under 100% SOC state;

The n is 50-80.

The present invention provides a new method for constant capacity of lithium ion batteries, which is to first select several standard batteries as samples, and calculate the linear relationship between the battery capacity in n% SOC state and the battery capacity in 100% SOC state. When testing the new battery capacity, it is only necessary to charge the battery to the corresponding voltage of n% SOC (the charging time is short), test the battery capacity in the n% SOC state, and put the data into the linear equation to get the 100% SOC state The battery capacity under 100% SOC state of the battery under test can be obtained without charging the battery to 4.2V. The method for constant capacity of the lithium ion battery in the present invention selects reasonable charging and discharging steps, shortens the time for constant capacity of the battery, increases the production capacity of the battery, and reduces the production cost of the enterprise.

In step 1) of the present invention, the method for measuring battery capacity under n% SOC state can be a conventional method, and the preferred method for measuring battery capacity under n% SOC state includes: A. Take the battery to be tested, and charge it with a first current constant current to n %SOC corresponds to the voltage, and then constant voltage charging to the termination current; the first current is 0.2C ~ 0.6C; the termination current is 2.0-3.0A; B. After standing for 5 ~ 30min, discharge to the termination voltage, according to The discharge current and time are used to calculate the battery capacity under n% SOC state; the termination voltage is 2.5V to 3.0V.

Generally, the corresponding voltages of n% SOC in step A are: when n is 50, the corresponding voltage is 3.68V; when n is 60, the corresponding voltage is 3.73V; when n is 70, the corresponding voltage is 3.8 V; when n is 80, the corresponding voltage is 3.87V.

Preferably, the discharge in step B adopts the following steps: I. discharge with a second current constant current to the termination voltage, and calculate the capacity data a1 according to the discharge current and time; the second current is 0.2C to 0.6C; II, static electricity After 5 to 30 minutes, discharge with the third current constant current to the final voltage, and calculate the capacity data a2 according to the discharge current and time; the third current is 0.05C to 0.15C; the sum of the capacity a1 and the capacity a2 is Battery capacity in n% SOC state. In the present invention, the battery capacity is obtained by two-stage constant current discharge of 0.2C～0.6C and 0.05C～0.15C, the steps are relatively simple, and the test accuracy is high and the error is small.

Specifically, the method for obtaining the standard linear equation described in step 2) is as follows: take several standard batteries, measure the battery capacity Y in the n% SOC state and the battery capacity X in the 100% SOC state, respectively; A standard linear equation was obtained by fitting the Y data. Preferably, the several standard batteries are 50-200 standard batteries.

In the present invention, the method for measuring the battery capacity under the n% SOC state of the standard battery is the same as the method for measuring the battery capacity under the n% SOC state of the battery to be tested. In order to maintain the consistency of the test method and improve the accuracy of constant volume.

The battery capacity of the standard battery in the 100% SOC state of the present invention can be obtained by conventional methods, and the preferred method for measuring the battery capacity of the standard battery in the 100% SOC state includes: a. Charge to 100% with a fourth current constant current SOC corresponds to the voltage, and then constant voltage charging to the termination current; the fourth current is 0.2C ~ 0.6C; b. After standing for 5 ~ 30min, discharge to the termination voltage, and calculate the battery under 100% SOC state according to the discharge current and time capacity.

Preferably, the voltage corresponding to 100% SOC in step a is 4.1-4.3V. Further preferably, the voltage corresponding to 100% SOC is 4.2V.

Preferably, the discharge in step b adopts the following steps: i. discharge with a fifth current constant current to the termination voltage, and calculate the capacity data b1 according to the discharge current and time; the fifth current is 0.2C to 0.6C; ii, static electricity After 5 to 30 minutes, discharge with the sixth current constant current to the final voltage, and calculate the capacity data b2 according to the discharge current and time; the sixth current is 0.05C to 0.15C; the sum of the capacity b1 and the capacity b2 is The battery capacity value at 100% SOC state.

Preferably, the fourth current is the same as the first current; the fifth current is the same as the second current; the sixth current is the same as the third current.

In the present invention, the linear relationship between the battery capacity in the n% SOC state of the standard battery and the battery capacity in the 100% SOC state can be obtained by conventional methods. Preferably, the linear equation can also be obtained by calculating with Minitab software.

Description of drawings

FIG. 1 is a linear relationship diagram between battery capacities under 70% SOC and 100% SOC states in Embodiment 1 of the present invention;

FIG. 2 is a linear relationship diagram between battery capacities under 50% SOC and 100% SOC states in Embodiment 2 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments. Unless otherwise specified, the equipment and reagents used in each example and test example can be obtained from commercial sources.

Example 1

The lithium-ion battery capacity-determining method of the present embodiment includes the following steps:

1) Take 170 standard batteries after formation, measure the battery capacity under 70% SOC state and the battery capacity under 100% SOC state; count and calculate the difference between the battery capacity under 70% SOC state and the battery capacity under 100% SOC state. Linear relationship, get a linear equation;

The method for measuring the battery capacity at 70% SOC state and the battery capacity at 100% SOC state of a battery sample is as follows:

A. Select the battery after formation, and let it stand for 10min;

B. Charge to 3.8V with a constant current of 0.3C, and then charge to 2.5A with a constant voltage;

C. After standing for 10 minutes, discharge to 2.7V with a constant current of 0.3C, and use the discharge current to multiply the time to obtain the capacity a1;

D. After standing for 10 minutes, discharge to 2.7V with a constant current of 0.1C, and multiply the discharge current by the time to obtain the capacity a2; a1+a2 is the battery capacity at 70% SOC;

E. Charge to 4.2V with a constant current of 0.3C, and then charge to 2.5A with a constant voltage;

F. After standing for 10min, discharge to 2.7V with a constant current of 0.3C, and use the discharge current to multiply the time to obtain the capacity b1;

G. After standing for 10 minutes, discharge to 2.7V with a constant current of 0.1C, and multiply the discharge current by the time to obtain the capacity b2; b1+b2 is the battery capacity at 100% SOC state.

The specific process is shown in Table 1. In Table 1, step 4 obtains capacity a1, step 6 obtains capacity a2; step 10 obtains capacity b1, step 12 obtains capacity b2; a1+a2 is the battery capacity under 70% SOC state, b1+ b2 is the battery capacity under 100% SOC state; 170 sets of data are obtained, of which 3 sets of data are shown in Table 2.

Table 1 Lithium-ion battery constant capacity capacity determination process table

Step number Process name current Voltage Deadline 1 stand still / / 10min 2 Constant current and constant voltage charging 0.3C 3.8V 2.5A 3 stand still / / 10min 4 Constant current discharge 0.3C 2.7V 5 stand still / / 10min 6 Constant current discharge 0.1C 2.7V 7 stand still / / 10min 8 Constant current and constant voltage charging 0.3C 4.2V 2.5A 9 stand still / / 10min 10 Constant current discharge 0.3C 2.7V 11 stand still / / 10min 12 Constant current discharge 0.1C 2.7V 13 stand still / / 10min

Table 2 Lithium-ion battery 70% SOC, 100% SOC constant capacity capacity measurement results table

Input the data of 170 sets of battery capacity under 70% SOC state and battery capacity under 100% SOC state into Minitab software, and calculate the linear relationship between the battery capacity under n% SOC state and the battery capacity under 100% SOC state (as shown in Figure 1). shown), the linear equation is obtained: Y=-5.344+0.778X, X is the battery capacity at 100% SOC state, and Y is the battery capacity at 70% SOC state.

2) Take a new battery to be tested, and then measure its battery capacity at 70% SOC state according to the method in step 1). 0.1C discharge) = 35.582Ah.

Substitute the battery capacity under the 70% SOC state of the battery to be tested into the linear equation described in step 1), and calculate the 100% SOC battery capacity; Substitute Y into the formula: Y=-5.344+0.778X (R-Sq=94.7%) ; 100% SOC theoretical capacity X _theoretical = 52.604Ah can be obtained.

Test the actual 100% SOC battery capacity of the new battery according to the method in step 1): X _actual =51.751Ah (0.3C discharge)+0.987Ah (0.1C discharge)=52.738Ah; error= _∣Xactual - _{Xtheoretical∣} /X _actual = 0.25%, the error is small.

Example 2

The lithium-ion battery capacity-determining method of the present embodiment includes the following steps:

1) Take the 64 batteries after formation, measure the battery capacity at 50% SOC state and the battery capacity at 100% SOC state; count and calculate the linearity between the battery capacity at 50% SOC state and the battery capacity at 100% SOC state relationship, get a linear equation;

The method for measuring the battery capacity at 50% SOC state and the battery capacity at 100% SOC state of a battery sample is as follows:

A. Select the formed battery and let it stand for 10min;

B. Charge to 3.68V with a constant current of 0.3C, and then charge to 2.5A with a constant voltage;

C. After standing for 10min, discharge to 2.7V with a constant current of 0.3C, and use the discharge current to multiply the time to obtain the capacity a1;

D. After standing for 10 minutes, discharge to 2.7V with a constant current of 0.1C, and multiply the discharge current by the time to obtain the capacity a2; a1+a2 is the battery capacity at 50% SOC;

E. Charge to 4.2V with a constant current of 0.3C, and then charge to 2.5A with a constant voltage;

F. After standing for 10min, discharge to 2.7V with a constant current of 0.3C, and use the discharge current to multiply the time to obtain the capacity b1;

G. After standing for 10 minutes, discharge to 2.7V with a constant current of 0.1C, and use the discharge current to multiply the time to obtain the capacity b2; b1+b2 is the battery capacity at 100% SOC state.

The specific process is shown in Table 3. In Table 3, step 4 obtains capacity a1, step 6 obtains capacity a2; step 10 obtains capacity b1, step 12 obtains capacity b2; a1+a2 is the battery capacity under 50% SOC state, b1+ b2 is the battery capacity at 100% SOC; 64 sets of data are obtained, 3 of which are shown in Table 4.

Table 3 Lithium-ion battery constant capacity capacity determination process table

Step number Process name current Voltage Deadline 1 stand still / / 10min 2 Constant current and constant voltage charging 0.3C 3.68V 2.5A 3 stand still / / 10min 4 Constant current discharge 0.3C 2.7V 5 stand still / / 10min 6 Constant current discharge 0.1C 2.7V 7 stand still / / 10min 8 Constant current and constant voltage charging 0.3C 4.2V 2.5A 9 stand still / / 10min 10 Constant current discharge 0.3C 2.7V 11 stand still / / 10min 12 Constant current discharge 0.1C 2.7V 13 stand still / / 10min

Table 4 Lithium-ion battery 50% SOC, 100% SOC constant capacity capacity measurement results table

Input 64 sets of battery capacity data at 50% SOC state and battery capacity at 100% SOC state into Minitab software, and calculate the linear relationship between battery capacity at n% SOC state and battery capacity at 100% SOC state (as shown in Figure 2). shown), a linear equation is obtained: Y=-7.548+0.627X, X is the battery capacity at 100% SOC state, and Y is the battery capacity at 50% SOC state.

2) Take a new battery to be tested, and then measure its battery capacity at 50% SOC state according to the method in step 1); battery capacity at 50% SOC state: Y=24.674Ah (0.3C discharge)+1.074Ah (0.1 C discharge) = 25.748 Ah.

Substitute the battery capacity under the 50% SOC state of the battery to be tested into the linear equation described in step 1), and calculate the 100% SOC battery capacity; Substitute Y into the formula: Y=-7.548+0.627X (R-Sq=92.9%) ; 100% SOC theoretical capacity X _theoretical = 53.104Ah can be obtained.

Test the actual 100% SOC battery capacity of the new battery according to the method in step 1): X _actual =51.672Ah (0.3C discharge)+1.043Ah (0.1C discharge)=52.715Ah; error= _∣Xactual - _{Xtheoretical∣} / X _actual = 0.74%, the error is small.

Claims (7)

1. a lithium ion battery constant volume method, is characterized in that, comprises the steps: 1) Measure the battery capacity of the battery to be tested under n% SOC state; 2) Substitute the battery capacity of the battery to be tested in the n% SOC state into the standard linear equation to calculate the battery capacity in the 100% SOC state; the standard linear equation is based on the collected standard battery's battery capacity data in the n% SOC state and The battery capacity data is obtained by linear fitting under 100% SOC state; The n is 50-80; The method for determining the battery capacity in the n% SOC state in step 1) includes: A. Take the battery to be tested, charge it with the first current constant current to the voltage corresponding to n% SOC, and then charge it with constant voltage to the termination current; the first current is 0.2C～0.6C; the termination current is 2.0-3.0A ; B. After standing for 5 to 30 minutes, discharge to the end voltage, and calculate the battery capacity under n% SOC state according to the discharge current and time; the end voltage is 2.5V to 3.0V; The discharging described in step B adopts the following steps: I. Discharge with a second current constant current to the termination voltage, and calculate the capacity data a1 according to the discharge current and time; the second current is 0.2C to 0.6C; II. After standing for 5 to 30 minutes, discharge with a third current constant current to the termination voltage, and calculate the capacity data a2 according to the discharge current and time; the third current is 0.05C to 0.15C; The sum of the capacity a1 and the capacity a2 is the battery capacity in the n% SOC state. 2 . The lithium-ion battery capacity-determining method according to claim 1 , wherein the corresponding voltages of n% SOC described in step A are respectively: when n is 50, the corresponding voltage is 3.68V; when n is 60 , the corresponding voltage is 3.73V; when n is 70, the corresponding voltage is 3.8V; when n is 80, the corresponding voltage is 3.87V. 3. The lithium-ion battery capacity-determining method according to claim 1, wherein the method for obtaining the standard linear equation in step 2) is: Take several standard batteries and measure the battery capacity Y in the n% SOC state and the battery capacity X in the 100% SOC state respectively; the X and Y data of all standard batteries are fitted to obtain a standard linear equation. 4. The lithium-ion battery capacity-determining method according to claim 3, characterized in that, the battery capacity measuring method under the n% SOC state of the standard battery is the same as the battery capacity measuring method under the n% SOC state of the battery to be tested. 5. The lithium-ion battery capacity-determining method according to claim 3, wherein the battery capacity determination method under the 100% SOC state of the standard battery comprises: a. Charge with a fourth current constant current to the corresponding voltage of 100% SOC, and then charge with constant voltage to the termination current; the fourth current is 0.2C～0.6C; b. After standing for 5-30 minutes, discharge to the final voltage, and calculate the battery capacity under 100% SOC state according to the discharge current and time. 6 . The method for constant capacity of a lithium ion battery according to claim 5 , wherein the voltage corresponding to 100% SOC in step a is 4.1-4.3V. 7 . 7. The lithium-ion battery constant-capacity method according to claim 5, wherein the discharging described in step b adopts the following steps: i. Discharge at a constant current of the fifth current to the termination voltage, and calculate the capacity data b1 according to the discharge current and time; the fifth current is 0.2C to 0.6C; ii. After standing for 5 to 30 minutes, discharge with a sixth current constant current to the termination voltage, and calculate the capacity data b2 according to the discharge current and time; the sixth current is 0.05C to 0.15C; The sum of the capacity b1 and the capacity b2 is the battery capacity value in the 100% SOC state.

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