KR20030034853A - Method for evaluating their capacities using short-time high rate discharge characteristic of batteries - Google Patents

Abstract

PURPOSE: Provided is a method for sorting a capacity of battery, in which batteries having different discharge property are selectively separated by using instant high discharge property of battery. CONSTITUTION: The method comprises the steps of (i) charging an identical group of batteries produced at identical production condition, at identical charge condition, (ii) charging the battery at identical charge condition, and then discharging the battery at high discharge rate for predetermined time including a midterm shortcircuit procedure, and (iii) sorting a capacity of battery by comparing an open circuit voltage of initial state of charge(SOC) of predetermined value and a final instant high discharge rate profile of battery.

Description

Capacity selection method of battery using short-term high rate discharge characteristics {METHOD FOR EVALUATING THEIR CAPACITIES USING SHORT-TIME HIGH RATE DISCHARGE CHARACTERISTIC OF BATTERIES}

The present invention relates to a battery capacity screening method, and more particularly, to a battery capacity screening method capable of selectively separating power sources having different discharge characteristics by using instantaneous high rate discharge characteristics of a battery of 2.0C or more in a short section.

Recently, as home appliances, office supplies, and information and communication devices become portable and cordless, secondary batteries used as their driving power sources are also required to be miniaturized, lightweight, and high energy density.

In particular, among the secondary batteries, lithium ions are reversibly inserted / released, the battery voltage is 3 to 4V, and research and development on lithium ion secondary batteries having a high energy density of 100 Wh / kg is actively progressing. .

Since Sony started mass production of cylindrical lithium ion battery 18650 type in the early 90's, the battery capacity has recently been improved by improving electrode materials, lightening battery assembly parts, and precision battery assembly processes. Various types of rectangular and cylindrical batteries have been mass produced and marketed. These high-capacity batteries have recently increased the demand for multimedia in mobile information terminals, and are becoming an important energy source for delivering high quality image information. On the other hand, such batteries are used in the form of battery packs (battery packs: using a plurality of batteries in series or in parallel, in the form of a pack) together with the demand for unit cells (a device using one battery as a power source). The importance of screening the capacity of the battery is on the rise. Therefore, battery manufacturers are known to conduct impedance comparisons of specific frequencies, comparison of charging and discharging tests for a certain number of times, and the like before shipment of batteries.

However, the evaluation of the battery in the initial state is merely a criterion for determining whether the battery is defective or not, the former is sensitive to the measurement environment such as the measurement temperature and the measurement method, and the latter is a temporal time for evaluating the charging and discharging equipment for a large number of batteries. It has economic problems.

As for the characteristics related to the charge / discharge state of the battery, generally, the open circuit voltage of the battery, the voltage and change of the battery in the operating state, the characteristics of the output signal with respect to the input voltage or current applied to the battery, and Methods related to the measurement of internal resistance functions or impedance functions derived therefrom are well known. In the case of using these various methods, the battery capacity can be measured within a shorter time than the time required for the real-time discharge method of the battery. To this end, many studies have been conducted. For example, in US Pat. No. 4,952,862, the discharge characteristic of a battery is represented by a voltage-time function composed of a Peukert parameter, and the voltage measurement value of the battery and the voltage A method of calculating the remaining capacity of a battery from a time function is presented. European patent EP 119,547 also provides a method of measuring the discharge voltage of a discharged battery as a function of time and measuring the discharge state of the battery from the average rate of change of the discharge voltage over a period of time. US Pat. No. 3,984,762 refers to a method of measuring the phase difference between an alternating current applied to a battery and a measured alternating voltage. When the capacity is calculated by measuring the voltage or the amount of change in the discharge process, the accuracy of the correlation between the measured value and the capacity of the battery shows a sensitive dependence on the discharge characteristics of the battery. For example, in the case of a lithium ion secondary battery having excellent voltage flatness, there is little change in voltage with respect to a change in discharge state. Meanwhile, other researchers have proposed a method of determining battery deterioration using a charging voltage transient section for pulse current in Japanese Patent P2000-39471A. In this case, the arithmetic comparison comparison method for the slope of the charging voltage for continuous pulse current of 1.0C or less within the transient period within 100msec.This is because the difference in the internal resistance of the battery before measurement is already present. It is difficult to apply the battery produced by the same manufacturing conditions with little difference.

Accordingly, an object of the present invention is to provide a battery capacity screening method for selectively separating cells having different discharge characteristics by using high rate discharge characteristics of a battery having a temperature of 2.0C or higher within a short interval among secondary batteries produced under the same manufacturing conditions.

Another object of the present invention is to provide a battery capacity screening method that can maximize the energy efficiency of the assembled battery by separating the battery having a different discharge characteristics and assembled into a series or parallel combination battery.

1 is a graph showing discharge characteristics according to initial capacity distribution and discharge rate change of the same battery group.

2 is a graph showing a capacity distribution diagram according to an embodiment of the present invention;

3 is a graph showing an impedance spectrum according to an embodiment of the present invention

Figure 4a is a graph showing the time-dependent pattern of the applied current in an embodiment of the present invention

4B is a graph showing a third high rate discharge profile of a lithium ion secondary battery according to an embodiment of the present invention;

5 is a graph showing a capacity distribution diagram according to another embodiment of the present invention;

6 is a graph illustrating an impedance spectrum according to another embodiment of the present invention.

7A is a graph showing a time-dependent pattern of applied current in another embodiment of the present invention;

7B is a graph illustrating a third high rate discharge profile of a lithium ion secondary battery according to another embodiment of the present invention.

8 is a graph showing a correlation between a voltage response change and a capacity obtained from a third high rate discharge profile of a lithium ion secondary battery according to another embodiment of the present invention.

The capacity selection method of the secondary battery of the present invention for achieving the above object is a step of charging the same group of batteries produced under the same manufacturing conditions under the same charging conditions, and the intermediate short-circuit after the battery is charged under the same conditions Performing a constant time high rate discharge including a process, and selecting a capacity of the battery by comparing the open circuit voltage of the initial specific SOC state with the instantaneous high rate discharge profile of the final battery.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation of the preferred embodiment of the present invention.

1 is a graph showing discharge characteristics according to changes in initial capacity distribution and discharge rate of the same battery group.

2 is a graph showing a capacity distribution diagram according to an embodiment of the present invention,

3 is a graph showing an impedance spectrum according to an embodiment of the present invention,

Figure 4a is a graph showing the time-dependent pattern of the applied current in an embodiment of the present invention,

4B is a graph illustrating a third high rate discharge profile of a lithium ion secondary battery according to an exemplary embodiment of the present invention.

5 is a graph showing a capacity distribution diagram according to another embodiment of the present invention,

6 is a graph showing an impedance spectrum according to another embodiment of the present invention,

7A is a graph illustrating a time-based pattern of applied current in another embodiment of the present invention.

7B is a graph showing a third high rate discharge profile of a lithium ion secondary battery according to another embodiment of the present invention.

8 is a graph showing a correlation between a voltage response change and a capacity obtained from a third high rate discharge profile of a lithium ion secondary battery according to another embodiment of the present invention.

1 to 8, the operation according to an embodiment of the present invention will be described in detail as follows.

As an example showing the discharge characteristics according to the initial capacity distribution and the discharge rate change of the same battery group used for the capacity selection of the secondary battery of the present invention, as shown in Figure 1, the capacity change with respect to the discharge rate of less than one hour rate (1.0C) Shows a very narrow dose distribution within 2%. However, as the number of charge / discharge cycles increased, the capacity distribution was observed to be different. On the other hand, the capacity change according to the increase of the cycle is similar to the high rate discharge characteristics of 2.0C, paying attention to the capacity selection using the instantaneous high rate discharge characteristics of the battery.

The battery producers ship secondary batteries according to the capacity distribution required by the battery buyer, and the open circuit voltage of the shipped batteries is considered to be partially discharged to avoid full charge or over discharge in consideration of stability during transportation and storage. To maintain it. As described in Korean Patent Publication No. 2000-264,515, the measurement of battery capacity through impedance spectrum analysis is based on the inherent impedance spectrum of the depth of discharge (DOD) of the battery being related to the remaining capacity of the battery. In order to compare the instantaneous discharge characteristics of the same battery group, it is necessary to maintain the same SOC state. Based on this fact, the Li-ion secondary battery charges an open circuit voltage below 4.0 volts, which is partially charged, that is, a 3.8 volt state of charge (SOC) state under a 0.5C charging condition. Charge to the amount of electricity corresponding to 0.5% of the nominal capacity under the termination condition of the charge, the open circuit voltage change does not exceed 20mV. At this time, it is preferable that the open circuit voltage is not lower than 3.0 volts in the SOC state. The distribution of internal resistance can also be confirmed by analyzing the impedance spectrum of the same cell group in a specific SOC state.

Observation of the instantaneous high rate discharge characteristics for the same group of cells in a particular SOC state prepared may use a general charge / discharge facility. At this time, the discharge pattern is performed within 60 seconds, preferably 2 seconds or more and 10 seconds or more, and one or more instantaneous short circuits within 1 second are performed continuously under the same conditions. The discharge current value to be applied is carried out at a discharge rate of 1.0C or more and 10.0C or less based on the nominal capacity. Preferably, it is preferable to set it as 1.5 C or more and 2.0 C or less. A comparison of the instantaneous high rate discharge characteristics for the same cell group can be obtained from the voltage response profile between the open circuit voltages and the discharge intervals in a particular SOC state.

Example 1

The results of five charge / discharge cycles of five identical battery groups of 18650 cylindrical lithium ion secondary batteries are shown in FIG. 2. At this time, the measurement conditions were performed under 0.5C charge rate and 1.0C discharge rate conditions. After five charge / discharge cycles, the cell voltage was maintained at 3.8 volts under the charging condition to achieve the same SOC state, and the impedance spectrum of these cells was measured and analyzed for internal resistance comparison before the instantaneous high rate discharge. . Impedance measurement was performed in the frequency range between 10 kHz and 10 mHz using BPS 1000FL model (manufactured by Kumho Petrochemical Co., Ltd.), and the results are shown in FIG. 3 and specific test analysis was performed using Korean Patent Publication No. 2000-264,515. Cited. The instantaneous discharge was performed three times for a group of cells in the same SOC state of 3.8 volts, and the discharge pattern was carried out three times for 16 consecutive intervals with a short time of 0.5 seconds each time. At this time, the applied discharge current was 3,600 mA. The change from the open circuit voltage of the initial SOC state after the three instantaneous high rate discharge patterns was completed was shown in FIG. 4B by monitoring the voltage response profile. As shown in the capacity distribution of FIG. 2, the battery 4 shows the largest discharge capacity, and this fact should be a small value in the capacity correlation with the change in the size of the spectral semicircle associated with the charge transfer resistance from the impedance spectrum. The case could not be distinguished. On the other hand, comparing the instantaneous high rate discharge profile of the present invention was able to make a clear selection as shown in Figure 4b.

Example 2

The capacity distribution of the same cell group of nine lithium-ion secondary batteries of 650 mAh square type is shown in FIG. 5. In order to maintain the same SOC state, the cell voltage was maintained at 3.72 volts under the charging condition, and the impedance spectrum of these cells was measured and analyzed for internal resistance comparison before the instantaneous high rate discharge. Impedance measurement was performed in the frequency range between 10 kHz and 10 mHz using BPS 1000FL model (manufactured by Kumho Petrochemical Co., Ltd.), and the results are shown in FIG. 6 and specific test analysis was performed using Korean Patent Publication No. 2000-264,515. Cited. The instantaneous discharge was performed three times for a group of cells in the same SOC state of 3.72 volts, and the discharge pattern was performed three times in a 10 second interval with a short circuit of 1.0 seconds each time. At this time, the applied high rate discharge current was 1,200 mA. The change from the open circuit voltage of the initial SOC state after the three instantaneous high rate discharge patterns was completed was shown in FIG. 7B by monitoring the voltage response profile. As shown in the capacity distribution of FIG. 5, the cell 5 shows the largest discharge capacity, which indicates the smallest semicircle in the capacity correlation and the magnitude change of the spectral semicircle associated with the charge transfer resistance from the impedance spectrum. The case of 1 showed the largest value. On the other hand, comparing the instantaneous high rate discharge profile of the present invention, as shown in Figure 6, the same result as the impedance spectrum distribution tendency was obtained. These results compare the rate of change of the voltage response between the termination voltage and the initial SOC open circuit voltage obtained from the third instantaneous high rate discharge profile with the correlation with the battery capacity.

As described above, in taking advantage of the short high rate discharge characteristics of the same group secondary batteries produced under the same manufacturing conditions according to the present invention, a battery of a specific SOC state corresponding to a partial discharge state is prepared to have a nominal capacity of 2.0 High-rate discharges are continuously performed at a high rate discharge rate of C or more, two or more times, and within one second between each discharge step, thereby comparing voltage response profiles to selectively separate cells having different discharge characteristics. There is an advantage that the capacity granularity of the shipment battery can be selected.

In addition, there is an effect that can maximize the energy efficiency of the combination battery to the user to use the battery assembled in series or parallel combination.

Claims (6)

In the capacity selection method of the same group of batteries produced under the same manufacturing conditions, Charging the same group of batteries produced under the same manufacturing conditions under the same charging conditions; Charging the battery under the same conditions and performing a high rate discharge for a predetermined time including an intermediate short circuit; A capacity selection method of a battery using a high-rate discharge characteristic of a short period, characterized in that the step of selecting the capacity of the battery by comparing the open circuit voltage of the initial specific SOC state and the instantaneous high rate discharge profile of the final battery. The method of claim 1, The high rate discharge rate is a capacity selection method of a battery using a high rate discharge characteristics of a short section, characterized in that the nominal capacity of the measurement battery 1.5C or more within 10.0C. The method according to claim 1 or 2, The high-rate discharge is characterized in that the battery capacity selection method using the high-rate discharge characteristics of the short section, characterized in that at least one time, the application time is 2 seconds or more and less than 60 seconds. The method of claim 3, wherein A method of selecting a capacity of a battery using a high-rate discharge characteristic of a short period, characterized in that it further comprises the step of performing at least one continuous short-circuit within 1 second between the high rate discharge. The method of claim 1, In the charging process, the charging condition is a capacity selection method of a battery using a high rate discharge characteristic of a short period, characterized in that the charging to 0.5C by applying a voltage of 3.8V. The method according to claim 1 or 2, The battery is a lithium ion, lithium ion polymer, lithium polymer secondary battery characterized in that the capacity selection method of the battery using a high rate discharge characteristics of a short section.