JP2014134395A - Short-circuit inspection method of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the time required for short-circuit inspection.SOLUTION: A secondary battery short-circuit inspection method includes: an initial activation step of initially charging a secondary battery for activation; an SOC adjustment step of adjusting an SOC value by discharging the secondary battery initially charged in the initial activation step; and a self-discharge step of self-discharging the secondary battery subjected to SOC adjustment in the SOC adjustment step. On the basis of an amount of voltage drop of the secondary battery in the self-discharge step, short-circuit is detected. In the SOC adjustment step, the SOC value is adjusted so that a value obtained by dividing an inclination of a discharge curve of the secondary battery by battery capacity is 0.05 or more.

Description

  The present invention relates to a technique for inspecting a short circuit of a secondary battery.

  Patent Document 1 discloses a technique for charging a first SOC, discharging to a second SOC lower than the first SOC, and detecting a micro short circuit in a state where the battery temperature is lowered after the discharging step. Is done.

JP 2011-69775 A

  In the technique described in Patent Document 1, the discharge current density is set to a value lower than the charge current density, and the discharge process is performed at a low rate. For this reason, the time required for the discharge becomes long, and as a result, the time required for the short circuit inspection becomes long.

The secondary battery short-circuit inspection method of the present invention includes an initial activation step of initially charging and activating the secondary battery, and discharging the secondary battery initially charged in the initial activation step to A SOC adjustment step for adjusting the value, and a self-discharge step for self-discharging the secondary battery after the SOC adjustment in the SOC adjustment step, and a short circuit based on the voltage drop amount of the secondary battery in the self-discharge step In the SOC adjustment step, the SOC value is obtained by dividing the slope of the discharge curve of the secondary battery by the battery capacity to be 0.05 or more. To a value of
According to this, it is possible to adjust to the optimum SOC regardless of the battery capacity of the secondary battery, and it is possible to shorten the time required for the short circuit inspection.

The amount of voltage drop in the self-discharge step is determined by the difference between the battery temperature of the secondary battery to be self-discharged from a predetermined battery temperature, the SOC value in the SOC adjustment step, and the battery of the secondary battery to be self-discharged. Using a correction voltage value obtained by adding a correction amount obtained by multiplying a correction coefficient calculated in advance according to a deviation direction of the temperature from the predetermined battery temperature to the voltage of the secondary battery to be self-discharged Calculated.
According to this, the voltage drop amount can be calculated with high accuracy regardless of the fluctuation of the environmental temperature in the self-discharge process.

  According to the present invention, the time required for the short circuit inspection can be shortened.

It is the schematic of a secondary battery. It is a flow which shows a short circuit inspection process. It is a graph which shows the correlation of the inclination / battery capacity of the discharge curve of a secondary battery, and SOC. In the Example and comparative example of this embodiment, it is a table | surface which shows the time required for the short circuit test process. It is a graph which shows the voltage fluctuation with respect to the battery temperature for every SOC. It is a graph which shows the fluctuation | variation of the battery voltage resulting from the fluctuation | variation of the battery temperature in a self-discharge process. It is a graph which shows the voltage value correct | amended as predetermined | prescribed battery temperature. It is a graph which shows the Example which calculates the amount of voltage drops.

FIG. 1 shows a schematic configuration of the secondary battery 1. The secondary battery 1 is a battery that can be repeatedly charged and discharged, for example, a square lithium ion secondary battery. The secondary battery 1 is configured by housing an electrode body 3 serving as a charge / discharge element in a sealed case 2. A positive electrode and a negative electrode external terminal 4 are connected to the electrode body 3 and are fixed to the case 2 so as to protrude outward.
The electrode body 3 is a wound body configured by laminating and winding a positive electrode current collector plate, a separator, and a negative electrode current collector plate. The positive electrode current collector plate and the negative electrode current collector plate are coated with a positive electrode electrode mixture and a negative electrode electrode mixture, respectively. In a lithium ion secondary battery, a positive electrode active material containing lithium ions, a positive electrode mixture containing a conductive additive, etc. are applied to the positive electrode current collector plate, and a negative electrode mixture containing a negative electrode active material containing a carbon-based material is a negative electrode It is applied to the current collector.

FIG. 2 shows a short circuit inspection step S <b> 1 of the secondary battery 1. The short circuit inspection step S1 is a step of inspecting a micro short circuit existing in the assembled secondary battery 1.
The short circuit inspection step S1 includes an initial activation step S11 in which the assembled secondary battery 1 is initially charged and activated, and an SOC adjustment in which the secondary battery 1 that has been initially charged is discharged to adjust the SOC value. Step S12 and a self-discharge step S13 for self-discharging the secondary battery 1 with the adjusted SOC value are included.

[Initial activation step S11]
First, an appropriate charging / discharging device is connected to the secondary battery 1 and charged to a first SOC at a predetermined current density. The value of the first SOC is set as a high SOC of 80% or more, for example. The predetermined current density used at this time is a C rate of 0.02 [C] or more. For example, the first SOC is charged to a charging state of 3.6 V or higher.

Next, the secondary battery 1 is held in a high temperature atmosphere, and a chemical substance (electrode active material) contained therein is activated. For example, it is exposed to an atmosphere at a high temperature (for example, about 40 ° C. to 85 ° C.) that is higher than normal temperature and that does not melt the separator included in the secondary battery 1.
In this way, by aging the secondary battery 1 at a high temperature, the chemical reaction inside the secondary battery 1 can be promoted, and a micro short circuit (chemical short circuit) resulting therefrom is actively generated to detect accuracy. Has improved.
The initial activation step S11 is applicable as long as it activates the secondary battery 1 and promotes an internal chemical reaction, and is not limited to the above.

[SOC adjustment step S12]
A charging / discharging device is connected to the secondary battery 1 and discharged to a second SOC lower than the first SOC at a current density equivalent to the initial activation step S11. That is, high-rate discharge (discharge of 0.02 [C] or more) is performed.

FIG. 3 shows a correlation between (inclination of discharge curve of secondary battery 1 [V / SOC] / battery capacity [Ah]) and SOC [%]. In the SOC adjustment step S12, the value obtained by the formula of (the slope of the discharge curve of the secondary battery 1 [V / SOC] / the battery capacity [Ah]), that is, the slope of the discharge curve of the secondary battery 1 is expressed by the battery capacity. Discharge is carried out until the SOC at which the divided value is 0.05 or more. That is, the SOC value adjusted in the SOC adjustment step S12 is changed according to the battery capacity and discharge characteristics of the secondary battery 1.
Thus, in SOC adjustment process S12, according to the battery capacity of the secondary battery 1, by adjusting to SOC in which the voltage drop in the self-discharge process S13 appears remarkably, the voltage divergence amount from the non-defective product of the defective product is adjusted. The detection sensitivity can be improved by increasing the voltage, and the voltage variation of non-defective products can be reduced.

[Self-discharge process S13]
The secondary battery 1 is self-discharged at room temperature, and the presence or absence of a micro short circuit is detected based on the amount of voltage drop after a predetermined time has elapsed.
At this time, the secondary battery 1 in which the amount of voltage drop at a predetermined measurement point of each secondary battery 1 is larger than the threshold value is determined as a short circuit and is determined as a defective product.

[Example]
FIG. 4 is a short circuit along the short circuit inspection process including the SOC adjustment process different from the SOC adjustment process S12 of the present embodiment, and Examples 1 to 3 in which the short circuit inspection is performed along the short circuit inspection process based on the present embodiment. The number of inspection days taken for Comparative Example 1 inspected is shown.

The secondary battery according to Example 1 has a battery capacity of 25 [Ah], and in the SOC adjustment step S12, a calculation formula of (slope of secondary battery discharge curve [V / SOC] / battery capacity [Ah]). After discharging to SOC: 9 [%], which is the SOC value that is obtained by 0.05, the number of days required for the short circuit inspection in the self-discharge step S13 was measured. At this time, the value obtained by the calculation formula of (the slope of the discharge curve of the secondary battery [V / SOC] / battery capacity [Ah]) is 0.05. The number of inspection days required for the secondary battery according to Example 1 was 10 days.
The secondary battery according to Example 2 has a battery capacity of 5 [Ah]. In the SOC adjustment step S12, a calculation formula of (slope of secondary battery discharge curve [V / SOC] / battery capacity [Ah]). After discharging to SOC: 20 [%], which is the SOC value that is obtained by 0.05, the number of days required for the short circuit inspection in the self-discharge step S13 was measured. At this time, the value obtained by the calculation formula of (gradient of discharge curve of secondary battery [V / SOC] / battery capacity [Ah]) is 0.09. The number of inspection days required for the secondary battery according to Example 2 was 5 days.
The secondary battery according to Example 3 has a battery capacity of 10 [Ah]. In the SOC adjustment step S12, a calculation formula of (slope of secondary battery discharge curve [V / SOC] / battery capacity [Ah]). After discharging to SOC: 15 [%], which is the SOC value that is obtained by 0.05, the number of days required for the short circuit inspection in the self-discharge step S13 was measured. At this time, the value obtained by the calculation formula of (gradient of discharge curve of secondary battery [V / SOC] / battery capacity [Ah]) is 0.06. The number of inspection days required for the secondary battery according to Example 3 was 15 days.

The secondary battery according to Comparative Example 1 has a battery capacity of 25 [Ah]. In the SOC adjustment step, the calculation formula of (gradient of discharge curve of secondary battery [V / SOC] / battery capacity [Ah]) is used. The number of days required for the short circuit inspection in the self-discharge process was measured after discharging to SOC: 20 [%], which is the SOC value at which the required value is less than 0.05. At this time, the value obtained by the calculation formula of (the slope of the discharge curve of the secondary battery [V / SOC] / battery capacity [Ah]) is 0.03, which is less than 0.05. It is different from the form. The number of inspection days required for the secondary battery according to Comparative Example 1 was 20 days.
As described above, the inspection days in Comparative Example 1 are longer than those in Example 1 to Example 3. That is, in the first to third embodiments, the time required for the short circuit inspection can be shortened.

[Temperature correction for voltage drop]
When the presence or absence of a short circuit is determined in the self-discharge process S13, it is performed by calculating a voltage drop amount per unit time within a predetermined time.
The amount of voltage drop in the self-discharge step S13 is calculated using the corrected value as the voltage value at the reference battery temperature T0 (for example, 20 ° C.). That is, by converting the battery temperature of the secondary battery 1 for obtaining the voltage drop amount to the reference temperature and obtaining the correction voltage value, the temperature fluctuation of the voltage that can fluctuate according to the environmental temperature is absorbed.

  As shown in FIG. 5, the battery voltage fluctuation amount ΔV [mV] with respect to the deviation of the battery temperature from the reference temperature T0 [° C.] is measured for each SOC by experiment, and the deviation direction from the reference temperature T0 (ascending side or A correction coefficient C [mV / ° C.] for the lowering side) is obtained.

Then, the voltage value V (T1) at the measurement point at which the battery temperature T1 is obtained is converted into the voltage value V (T0) at the reference temperature T0 using the following formula 1.
V (T0) = V (T1) + (T1−T0) × C (Equation 1)
In Equation 1, V (T) is a battery voltage variable depending on the temperature T, T0 is a reference temperature, T1 is a battery temperature at the time of measurement, and C is a correction coefficient.
In other words, the correction voltage value V (T0) is calculated in advance according to the SOC value and the deviation direction with respect to the reference temperature in the deviation amount (T1-T0) between the battery temperature (T1) and the reference temperature (T0) at the time of measurement. The correction amount ((T1−T0) × C) obtained by multiplying the correction coefficient C to be applied is added to the voltage (V (T1)) of the secondary battery 1.

As shown in FIG. 6, when the battery temperature during the self-discharge process S13 has a fluctuation of about ± 2 ° C., the battery voltage decreases while increasing or decreasing in conjunction with the fluctuation of the battery temperature.
In the present embodiment, as shown in FIG. 7, the voltage value at each measurement point is corrected as a voltage value at a predetermined reference temperature, thereby calculating a linear voltage drop. Thereby, the voltage drop amount can be calculated with high accuracy regardless of the environmental temperature fluctuation in the process, and the detection accuracy can be improved. In addition, the degree of freedom in voltage measurement timing is increased, process planning is facilitated, and inspection time can be shortened.

[Example]
FIG. 8 shows an example in which the voltage drop amount is calculated based on this embodiment.
The secondary battery 1 adjusted to SOC: 3 [%] in the SOC adjustment step S12 was subjected to a self-discharge step S13 for 5 days in an environment of room temperature: 20 [° C.]. The environmental temperature is assumed to fluctuate within a range of ± 0.8 [° C.], and the voltage drop is calculated by using a voltage value measured by a combination of times (t1, t2) that is maximum within the fluctuation range. The battery temperature T1 at t1 is 20.8 [° C.], and the battery temperature T2 at t2 is 19.2 [° C.].

The battery voltage V1 (T1) at t1 was 3.3815 [V], and the battery voltage V2 (T2) at t2 was 3.3801 [V].
When the voltage drop amount is calculated without correction, (3.3815-3.3801) /5=0.28 [mV / day].

When each battery voltage is corrected using Equation 1, the result is as follows.
The reference temperature T0 is 20 [° C.], and the correction coefficient C is 0.55 [mV / ° C.] on the lower side than the reference temperature, and 0.54 [mV / ° C.] on the higher side.
V1 (T0) = 3.3815 + (20.8-20) × 0.00055 = 3.3819
V2 (T0) = 3.3801 + (19.2-20) × 0.00054 = 3.3797
Therefore, the amount of voltage drop is (3.3819−3.3797) /5=0.44 [mV / day].

  As described above, by calculating the voltage drop amount using the correction voltage value calculated by substituting into Equation 1, a highly accurate short circuit inspection can be performed. Thereby, the quality of the secondary battery 1 which passed through short circuit test process S1 can be improved.

[Voltage stabilization process]
The SOC adjustment step S12 may include the following voltage stabilization step.
By leaving the secondary battery 1 at a room temperature (about 10 ° C. to about 30 ° C.) and within a range of ± 3 ° C. of the battery temperature after the SOC adjustment step S12, the secondary battery 1 Stabilize the voltage. Thereby, the jump of the voltage after the discharge of the secondary battery 1 (the voltage increase caused by the diffusion of the electrode active material) is reset.
In the voltage stabilization process, the secondary battery 1 after discharge is aged to stabilize the voltage, that is, by maintaining the internal chemical substance until it is stabilized, the voltage variation of each secondary battery 1 due to the voltage rise Can be absorbed. In addition, by performing the process while maintaining the temperature of the secondary battery 1 immediately after discharge as much as possible, voltage variations due to changes in battery temperature can be suppressed, and detection accuracy can be improved.

  1: Secondary battery, 2: Case, 3: Electrode body, 4: External terminal

Claims (2)

An initial activation step of initially charging and activating the secondary battery;
An SOC adjustment step of adjusting the SOC value by discharging the secondary battery initially charged in the initial activation step;
A self-discharge step of self-discharging the secondary battery after the SOC adjustment in the SOC adjustment step,
A secondary battery short circuit inspection method for detecting the presence or absence of a short circuit based on a voltage drop amount of the secondary battery in the self-discharge process,
In the SOC adjustment step, the SOC value is adjusted to a value such that a value obtained by dividing the slope of the discharge curve of the secondary battery by the battery capacity is 0.05 or more. Method. The amount of voltage drop in the self-discharge process is
The amount of deviation of the battery temperature of the secondary battery to be self-discharged from the predetermined battery temperature, the value of the SOC in the SOC adjustment step, and the direction of deviation of the battery temperature of the secondary battery to be self-discharged from the predetermined battery temperature 2. The calculation according to claim 1, wherein a correction amount obtained by multiplying a correction coefficient calculated in advance according to the value is applied to a voltage of the secondary battery to be self-discharged, and is calculated using a correction voltage value obtained by the correction voltage value. Secondary battery short circuit inspection method.

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