KR20150033267A - Method for Estimating Quality Specification of Battery Cell and Quality Control System Using the Same - Google Patents

Abstract

The present invention relates to a method for estimating a quality standard to determine whether battery cells are defective, comprising the steps of (a) sampling battery cells according to sigma levels, (b) performing battery keeping test on the sampled battery cells and inputting a resultant value to a database, (c) estimating a representative quality standard from the input resultant value, and (d) setting optimal process capability (optimal sigma level) as a reference for setting a quality standard of each tray from the representative quality standard.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for estimating a quality standard of a battery cell and a quality management system using the same,

The present invention relates to a method for estimating a quality standard for a battery cell and a quality management system using the same. More particularly, the present invention relates to a method for estimating a quality standard for selecting the presence / Sampling the battery cells, performing a battery storage test on the sampled battery cells, inputting the result into a database, calculating a representative quality standard from the input result, and (d) And setting the optimal process capability (optimum sigma level), which is a setting reference of the quality standard of each tray, from the representative quality standard, and a quality management method using the same ≪ / RTI >

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

Generally, a lithium secondary battery comprises an anode, a cathode, and a separator disposed between both electrodes and an electrolyte. In order to increase the reliability of the secondary battery, it is important to provide a standardized product having a certain performance to the consumer.

Therefore, it is possible to promptly determine whether or not the battery cell is deviated from the quality standard through the quality inspection of the battery cell during the production process of the battery cell, to prevent the occurrence of the nonconforming product in advance and to select the defective product before the produced non- I am doing work.

In the prior art, even when there is a process deviation between battery cells in the case of a normal battery cell, a voltage variation in a normal range at the time of charging and discharging is maintained, while in the case of a deteriorated or defective battery cell, The leakage of the defective battery cells was prevented by detecting the battery cells out of the normal voltage behavior distribution among the plurality of battery cells. In particular, in order to reduce the risk of erroneous detection, an average of voltage deviation values was used as a quality standard to perform screening.

However, although battery cells made under the same process conditions can have uniform quality, substantially mass-produced products are subject to variations in process conditions during many manufacturing processes. Therefore, in order to uniformly provide a better product to the consumer, it is necessary to set a more detailed quality standard in consideration of the deviation of process conditions of the produced battery cells.

For example, the magnitude of the voltage drop of the battery cell may be relatively different depending on the manufacturing conditions of the battery cell (for example, by the production lane of the electrode or by the position of the activation device). Therefore, when one quality standard is applied to all 1 lot, the battery cells of some of the trays can appropriately select the defective battery cells, but it is suitable as a criterion of the defect selection of a plurality of trays A large amount of normal battery cells were selected as defective.

Therefore, it is necessary to devise a method of selecting a new quality specification (specification) considering the deviation of process conditions of the battery cells in order for the producer to rationally perform the faulty sorting operation and satisfy the satisfaction of the consumer.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that a new method of estimating a quality standard in consideration of the quality fluctuation of battery cells in a tray and between trays due to deviation of process conditions It is possible to estimate a quality standard that can prevent the outflow of the defective battery cells more effectively, and have accomplished the present invention.

Accordingly, the present invention is a method for estimating a quality standard for selecting the presence or absence of defective battery cells,

(a) sampling battery cells by sigma level;

(b) performing a battery storage test on the sampled battery cells and inputting the result into a database;

(c) calculating a representative quality standard from the input result;

(d) setting an optimum process capability (optimum sigma level) as a setting reference of the quality standard of each tray from the representative quality standard;

As shown in FIG.

Generally, mass-produced battery cells have a quality deviation in each tray and between trays, so that the optimal values of the voltage difference? OCV of the battery cells are different for each tray. Therefore, it is not possible to effectively select the defective battery cells by applying the quality standard collectively without considering the deviation of the process conditions of the produced battery cells.

Therefore, the method for estimating the quality of a battery cell according to the present invention classifies and samples the battery cells according to the sigma level in order to set a quality standard in consideration of the quality deviation between the trays and the trays, It is possible to set a reasonable standard quality standard that can represent a lot.

Here, the process capability is a numerical value indicating the degree of quality fluctuation of a product produced in the process when the process is in a controlled state, and the quality fluctuation level of a product having a standardized standard is analyzed through the process capability It can be expressed at the sigma level.

The sigma level is a quantitative expression of the process capability, and indicates how many standard deviations (sigma) are included in the standard. For example, the larger the standard deviation of the product quality data produced in a certain standard, the smaller the sigma level becomes, and the smaller the standard deviation, the larger the sigma level becomes.

In one specific example, in the step (a), a test group is divided into a plurality of test groups according to elements of a manufacturing process which generate quality deviations of battery cells to be produced for each sigma level, and at least one test group The above trays can be selected.

Also, the battery cells in the tray can calculate the sigma level of each battery cell in the tray using the voltage difference [Delta] OCV measured during the production process, and sample the battery cells according to the calculated sigma level.

In one specific example, the sampling of the step (a) can set a test group by designating a tray for each production lane in consideration of a quality deviation between the trays generated due to a deviation of each process condition.

Specifically, the manufacturing process of the battery cell may include coating an electrode active material on a single electrode plate, cutting the electrode plate by a plurality of lanes, and supplying the electrode active material. At this time, the coating amount of the active material coated on the electrode plate is different from that of the active material coated on the electrode plate, thereby causing a difference in the loading amount of the electrode active material for each lane. Therefore, since the deviation of the minimum voltage drop value actually occurs between the trays produced for each lane in the room temperature atmospheric air, the test group can be set by designating trays for each production lane.

In addition, sampling of the step (a) can set a test group by designating a tray for each charging / discharging position of the activating device in consideration of quality deviation between trays generated due to deviation of each process condition.

Specifically, the activation device of the battery cell is composed of a plurality of layers, and one tray is positioned for each of the layers to charge the battery cells. At this time, since the variation in voltage characteristics between the trays appears due to the difference in the idling conditions (e.g., the supply voltage difference) charged in each layer, a test group can be set by designating a tray for each charge / discharge position.

In one specific example, the battery storage test may be performed according to the standard test method of the Institute of Electrical and Electronics Engineers of the United States,

(i) a battery activating step of fully charging each battery cell according to a full charge specification;

(ii) measuring the voltage of the battery cells after standing at room temperature for one day;

(iii) storing the battery cells in a high-temperature chamber set at 45 degrees Celsius for 7 days;

(iv) measuring the voltage 2 after waiting the battery cells for one day at room temperature again;

(v) calculating a voltage difference? OCV by calculating the difference between the voltage 1 and the voltage 2.

In one specific example, the step (c) is a step of calculating the upper specification limit by applying the result of the battery retention test to the following formula 1, and applying the lower specification limit ), And the upper limit standard and the lower limit standard can be set as the representative quality standard.

M + 4 × P (1)

M - 4 x P (2)

Where M is the ΔCOC center value of the result of calculating the difference between voltage 1 and voltage 2 of all the battery cells and P is the standard deviation of the square root of the amount distributed in the ΔOCV values.

In one specific example, the representative quality specification may have only an upper specification limit depending on the characteristics of the battery cell to which it is applied.

The method of calculating a quality standard according to the present invention is characterized in that the step (d) analyzes a scatter diagram according to a sigma level using the representative quality standard calculated in the step (c) ) Can be calculated. In detail, the range in which the defective battery cells are not included can be set to an optimal sigma level based on the samples of the normal battery cells in the representative quality standard.

In yet another aspect, a battery cell quality specification estimating system can be constructed using the method of estimating a quality standard according to the present invention. The battery cell quality standard calculation system, specifically,

An input unit for receiving a result of a battery retention test of sampled battery cells according to a sigma level;

A database storing results of the battery retention test;

A specification setting unit that receives information from the database and calculates a representative quality standard; And

A process capability calculating unit for calculating an optimal process capability (optimum sigma level) by utilizing the quality standard generated by the representative quality standard setting unit;

. ≪ / RTI >

In one specific example, the sigma level sampling of the battery cell quality standard calculation system is performed by setting a test group by designating a tray for each production lane or for each charging / discharging position of the activation device, sampling the battery cells from each test group can do.

In one specific example, the standard setting unit can calculate the representative quality standard having only the upper limit specification according to the characteristics of the battery cell to be applied.

As described above, it is possible to effectively prevent the leakage of the defective-product battery cell by using the method of calculating the quality standard considering the quality dispersion of the battery cells in the tray and between the trays due to the deviation of the process conditions according to the present invention, It is possible to prevent the false discrimination and to reduce the production cost of the producer and to provide an excellent battery cell to consumers.

1 is a flowchart of a method of calculating a quality standard of a battery cell according to an embodiment of the present invention;
FIG. 2 is a graph showing voltage (Volt) change over time for explaining the battery storage test method of the present invention; FIG.
3 is an exemplary graph showing sigma levels according to the OCV value of the IEEE battery storage test for selecting the optimum process capability (optimal sigma level) of the present invention and the OCV value measured during the production process.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the scope of the present invention is not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart of a method for calculating a quality standard of a battery cell according to an embodiment of the present invention. FIG.

As shown in the flowchart of FIG. 1, the method for estimating the quality standard of the battery cell according to the present invention includes (a) to (d) steps 10, 20, 30 and 40.

First, in (a) step (10), a test group is set for each charge / discharge position of the sampling and activation device for each production lane as follows, and the battery cells of the selected tray are classified according to the sigma level and sampled do.

Sampling by production lane

Sampling is performed so that the battery cells produced in all the lanes are included in the test group to represent the entire data of one lot of the production product. For example, four or five trays containing battery cells manufactured for each production lane may be designated, and voltage values of the battery cells measured during the production process of each of the specified trays may be used to determine the number of trays The level of each battery cell in the set tray is calculated, and the battery cells are classified and sampled according to each sigma level. At this time, the sampling quantity is determined proportionally to represent the sigma level of the whole lot.

Sampling by charging and discharging position

In order to represent the entire data of one lot of production product, four to five trays including activated battery cells for each layer of the battery cell activating device are designated, and then, during the production process of each designated tray, Voltage values are used to calculate the sigma level of each battery cell in the tray set to the test group, and the battery cells are classified and sampled according to each sigma level. At this time, the sampling quantity is determined proportionally to represent the sigma level of the whole lot.

In the step (b) of FIG. 1, the sampled battery cells are performed according to the battery storage test method of IEEE Institute of Electrical and Electronics Engineers as follows.

IEEE battery storage test

FIG. 2 is a graph showing a change in voltage (Volt) over time to explain the battery storage test method of the present invention.

The IEEE battery storage test method will be described with the graph of FIG. First, full charge is carried out according to the full charge specification of each battery cell, followed by waiting at room temperature for one day. At this time, the voltage 1 (OCV1) is measured, and the battery cells are stored in the high-temperature chamber set at 45 degrees Celsius for 7 days. Thereafter, the battery cells again wait at room temperature for one day, and measure the voltage 2 (OCV2).

1 (b), the voltage difference (OCV) between the measured voltages 1 (OCV1) and 2 (OCV2) is calculated, and the resultant value is input to the database.

In step (c) of FIG. 2, the center value and the standard deviation (sigma) value of the test groups are calculated from the input result values, and applied to the equations (1) and (2) And the range of the upper limit standard and the lower limit standard is set as the representative quality standard.

In step (d) 40 of FIG. 1, (c) the optimum process capability (optimal sigma level) is selected according to the representative quality standard calculated in step (30).

3 shows an exemplary graph showing the ΔCOC values of the IEEE battery storage test for selecting the optimal sigma level of the present invention and the sigma levels according to the ΔOCV values measured to select defects in the production process .

Referring to the graph of FIG. 3, the upper limit of the IEEE-OCV value of 57.4 is calculated from the result of the IEEE battery storage test according to the standard quality standard, and is shown in the graph. It can be seen that the range of the OCV sigma level is 5 or less in the process, and the optimum sigma level is 5.

The selected optimal sigma level is applied to the sigma level of each tray classified according to the production lane or the charging / discharging position of the activating device, thereby setting the quality standard for each tray.

Therefore, the method of calculating the quality standard of the battery cell according to the present invention can estimate the quality standard considering the dispersion of the quality of the battery cells in the tray and between the trays due to the deviation of the process condition.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (13)

A method for estimating a quality standard for selecting the presence or absence of defects of battery cells,
(a) sampling battery cells by sigma level;
(b) performing a battery storage test on the sampled battery cells and inputting the result into a database;
(c) calculating a representative quality standard from the input result;
(d) setting an optimal processing capability (optimal sigma level) from the representative quality standard;
Wherein the method further comprises the steps of: 2. The method according to claim 1, wherein in step (a), in order to sample the battery cells according to the sigma level, a test group is divided into elements of a manufacturing process for generating quality deviations of produced battery cells, Wherein at least one of the trays is selected. 3. The method of claim 2, wherein the battery cells in the tray use a voltage difference [Delta] OCV measured during the production process to calculate a sigma level of each battery cell in the tray, Of the battery cell. The method of claim 1, wherein the sampling of the step (a) is performed by designating a tray for each production lane or for each charging / discharging position of the activating device. The method of claim 1, wherein the battery storage test is performed according to a representative test method of the Institute of Electrical and Electronics Engineers of the United States of America. The method according to claim 1,
(i) a battery activating step of fully charging each battery cell according to a full charge specification;
(ii) measuring the voltage of the battery cells after standing at room temperature for one day;
(iii) storing the battery cells in a high-temperature chamber set at 45 degrees Celsius for 7 days;
(iv) measuring the voltage 2 after waiting the battery cells for one day at room temperature again;
(v) calculating a voltage difference? OCV by calculating a difference between the voltage 1 and the voltage 2;
Wherein the method further comprises the step of: The method according to claim 1, wherein the step (c) comprises: calculating an upper specification limit by applying a result of the battery retention test to the following formula 1, and applying the lower specification limit ), And the upper limit specification and the lower limit specification are set as a representative quality standard.
M + 4 × P (1)
M - 4 x P (2)
Where M is a voltage difference? OCV center value calculating the difference between voltage 1 and voltage 2 of all the battery cells, and P is a representative deviation that is a square root of the amount distributed in? OCV values. 8. The method of claim 7, wherein the representative quality standard has only an upper specification limit. The method according to claim 1, wherein the step (d) comprises the steps of: analyzing a scatter diagram according to a sigma level using the representative quality standard calculated in step (c), and calculating an optimal process capability (optimal sigma level) Wherein the method comprises the steps of: 10. The method of claim 9, wherein an optimal sigma level is set based on samples of a normal battery cell in the representative quality standard. A system for estimating a battery cell quality standard using the method of calculating a quality standard according to claim 1,
An input unit for receiving a result of a battery retention test of sampled battery cells according to a sigma level;
A database storing results of the battery retention test;
A specification setting unit that receives information from the database and calculates a representative quality standard;
A process capability calculating unit for calculating an optimal process capability (optimum sigma level) by utilizing the quality standard generated by the representative quality standard setting unit;
The battery cell quality standard calculation system comprising: 12. The system of claim 11, wherein the sigma level sampling is performed by designating a tray for each production lane or a charging / discharging position of the activation device. 12. The system according to claim 11, wherein the standard setting unit calculates a representative quality standard having only the upper limit specification.

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