JP2003308885A - Method of diagnosing deterioration of lithium ion battery and apparatus incorporating the method of diagnosing deterioration - Google Patents

Abstract

The present invention relates to a deterioration diagnosis method for analyzing deterioration of active materials of a positive electrode and a negative electrode, which are deterioration factors of a lithium ion battery, and an increased state of a resistance component, and an apparatus incorporating the deterioration diagnosis method. Kind Code: A1 A change in a plateau voltage in the vicinity of immediately before the end of charge / discharge of an initial charge / discharge due to a constant current of a battery is detected, and each capacity of a normal time rate and a long time rate in the initial charge / discharge of each voltage change range is detected. The charge / discharge time in the confirmation test and the charge / discharge time in each capacity confirmation test of the normal time rate and the long time rate in each of the voltage change ranges after the cycle test were measured, and the charge / discharge time during the initial charge / discharge was measured. From the ratio of each charge / discharge time and each charge / discharge time after the cycle test, the deterioration rate of the entire negative electrode and the positive electrode, and the deterioration rate of each active material of the negative electrode and the positive electrode, and the deterioration of the entire negative electrode and the positive electrode The rate of increase in the impedance of each of the negative electrode and the positive electrode is determined from the difference between the rate and the deterioration rate of each active material of the negative electrode and the positive electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for diagnosing deterioration of a lithium ion battery, and in particular, deterioration of active materials of positive electrode and negative electrode and resistance component which are deterioration factors of decrease in battery capacity of lithium ion battery. The present invention relates to a method for diagnosing deterioration of a lithium-ion battery capable of measuring the increase state of the battery and an apparatus incorporating the method for diagnosing deterioration.

[0002]

2. Description of the Related Art Battery capacity decreases due to repeated charge and discharge of a lithium ion battery. The main causes of this battery capacity decrease are deterioration of the active material of the positive electrode and the negative electrode and growth on the surface of the positive electrode and the negative electrode. This is an increase in internal impedance due to the resistive thin film. As a method for inspecting or observing the degree of these deteriorations, for example, inspection of active materials of positive and negative electrodes by x-ray diffraction method, x-ray microanalyzer, etc., inspection of resistive thin film by x-ray photoelectron spectroscopy, impedance method, etc. It has been known.

[0003]

However, all of the above-mentioned measuring methods require expensive dedicated devices and special auxiliary devices for the measurement, and the measuring requires a lot of time and skill. In addition, the data obtained is qualitative and difficult to grasp quantitatively.
The present invention is an analysis method for obtaining a deterioration mechanism of a lithium-ion battery and a ratio of the deterioration factor affecting the deterioration from a function of voltage and time, and this deterioration diagnosis method and its device provide useful information on battery deterioration in a simple and easy manner. It can be provided in a short time, and is extremely useful for research and development of lithium-ion batteries or inspection work.

[0004]

According to a first aspect of the present invention, there is provided a method for diagnosing deterioration of a lithium-ion battery, which is provided near the end of charge in a normal time rate charge / discharge test in initial charge / discharge with a constant current of a lithium-ion battery. Detecting a plateau voltage change that occurs immediately before the end of discharge, measuring each lower limit voltage value and each upper limit voltage value of each voltage change portion, and lowering the lower limit voltage value in the capacity confirmation test at the normal time rate. To the upper limit voltage value, the first charging time required to change the charging voltage and the first discharging time required to change the discharging voltage from the upper limit voltage value to the lower limit voltage value are measured, and A capacity confirmation test is performed at a time rate of time, a second charging time required for the charging voltage change and a second discharging time required for the discharge voltage change are measured, and after the initial charge / discharge test, A third time required for the charging voltage change and a third charging time required for the charging voltage change in the capacity confirmation test at the normal time ratio after the cycle test after performing a normal time rate charge / discharge cycle test. And the fourth discharge time required for the change in the discharge voltage by performing the capacity confirmation test at a long time rate after the cycle test and measuring the discharge time of Is measured, and the deterioration rate of the entire positive electrode of the lithium ion battery based on the ratio between the first charging time and the third charging time, and the lithium ion battery based on the ratio between the first discharging time and the third discharging time. Of the deterioration rate of the whole negative electrode, and the deterioration rate of the active material of the positive electrode, the second discharge time, and the fourth ratio according to the ratio of the second charging time to the fourth charging time.
The deterioration rate of the active material of the negative electrode is obtained by the ratio with the discharge time, and the impedance increase rate of the positive electrode and the deterioration rate of the entire negative electrode are subtracted from the deterioration rate of the positive electrode as a whole. Is obtained by subtracting the deterioration rate of the active material of the negative electrode from the above.

A deterioration diagnosing device for a lithium ion battery, which is a second invention of the present application, occurs near the end of charging and near the end of discharging in the initial charge / discharge of a normal time rate charge / discharge test by a constant current of a lithium ion battery. Voltage change detection means for detecting each plateau voltage change, storage means for measuring and storing each lower limit voltage value and each upper limit voltage value of each plateau voltage change portion, and capacity confirmation test at the normal time rate The first charging time required to change the charging voltage from the lower limit voltage value to the upper limit voltage value and the first charging time to change the discharge voltage from the upper limit voltage value to the lower limit voltage value in
First charging / discharging time storage means for measuring and storing the discharging time, and a second charging time required for the charging voltage change in the capacity confirmation test at a long time rate in the initial charging / discharging state, Second charging / discharging time storage means for measuring and storing the second discharging time required for the discharge voltage change, and the normal time after the normal charge / discharge cycle test after the initial charge / discharge test. Charging / discharging time storage means for measuring and storing the third charging time required for the charging voltage change and the third discharging time required for the discharge voltage change in the capacity confirmation test at a rate, and the cycle test. Fourth charge / discharge time for measuring and storing the fourth charge time required for the change in the charge voltage and the fourth discharge time required for the change in the discharge voltage in the capacity confirmation test at the later long time rate. Storage means and during the first charging And a third charging time and a ratio of the first discharging time and the third discharging time to obtain respective deterioration rates of the entire positive electrode and the entire negative electrode of the lithium ion battery, and the second charging time. And a ratio of the fourth charging time and a ratio of the second discharging time and the fourth discharging time to calculate a deterioration rate of each active material of the positive electrode and the negative electrode, and a deterioration rate of the entire positive electrode. A means for calculating the respective impedance increase rates of the positive electrode and the negative electrode from the difference between the deterioration rate of the active material of the positive electrode, the deterioration rate of the entire negative electrode and the deterioration rate of the active material of the negative electrode. Is.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for diagnosing a lithium ion battery according to the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 shows charge / discharge voltage characteristics of a cylindrical lithium-ion battery in a constant current test, and a peak 1 of a voltage change called a plateau at the beginning and end of charging and discharging of the charge / discharge voltage characteristics. ~ 4 appears. These peaks 1 to 4 appear reversibly with charge and discharge, peaks 1 and 4 are due to the stage structure change of the negative electrode (graphite carbon), and peaks 2 and 3 are due to the structure change of the positive electrode (LiCoO2). Appears due to. The present invention was made by focusing on the fact that it is possible to determine the degree of deterioration of the active material by comparing the time required for the voltage range in which each peak appears as a function of cycle.

However, the internal resistance of the battery increases with the cycle test, and the polarization increases due to the increase of the resistance component.
As a result, the initial charge at peak 1 and the initial discharge at peak 3 may become undetectable as the polarization increases. Therefore, analysis of deterioration due to the positive electrode is peak 2, and deterioration due to the negative electrode is peak 4 as well. Is to be analyzed. Moreover, the confirmation test of the battery capacity reduction is usually performed at a charge / discharge current value corresponding to a rate of 8 to 10 hours (normal rate).

FIG. 2 shows the details of the analysis by enlarging the peaks 2 and 4 shown in FIG. 1, and the deterioration of the positive electrode is from the lower limit voltage value of 4.0 V at the end of charging to the upper limit voltage value. 4.
15V, the deterioration of the negative electrode is 3.75V which is the upper limit voltage value at the end of discharge.
Based on the voltage range of 3.6V, which is the lower limit voltage value, as a reference, the degree of deterioration is analyzed from the time difference between the initial charge / discharge test required for the change of the voltage range and after the cycle test. That is, as an initial charge / discharge test, for example, the average charge time and the discharge time in the voltage range of three times of the charge / discharge test are each ΔT, and for example, the charge time and the discharge time required for the same voltage range after the 970 cycle test are each ΔTn. As a result, the capacity reduction rates of the positive electrode and the negative electrode can be obtained from the following equation (1).

[0009]   Capacity decrease rate = [1- (ΔTn / ΔT)] × 100 (1)

However, since the current value is large in the capacity decrease rate obtained from the capacity confirmation test at the charge / discharge current value corresponding to the 8 to 10 hour rate, not only the active material but also the polarization component (resistance component) is affected. It will be the included value.

Therefore, as a means for estimating (measuring) the deterioration of the active material by eliminating the influence of the polarization component as much as possible,
A capacity confirmation test at an extremely low rate corresponding to a 50 hour rate (long time rate) is performed in parallel. Also in the capacity confirmation test at this extremely low rate, the difference between the lower limit voltage value and the upper limit voltage value of each of peaks 2 and 4 detected during the capacity confirmation test at the charge / discharge current value at the aforementioned 8 to 10 hour rate. The charge time ΔT or the discharge time ΔT required for the change of the voltage range by the initial 30 to 50 hour rate of the charge / discharge test, and the 30 to 50 hour rate after the cycle test have elapsed. Is calculated from the time difference from the charging time ΔTn or the discharging time ΔTn required for the change of the voltage range.

According to the capacity confirmation test at the extremely low rate, the resistance thin film grown on the surface of the positive electrode and the negative electrode transmits the charging current or the discharging current, so that the influence of the resistance thin film can be neglected. This is detected as the capacity decrease rate of the deterioration amount of the active material. Therefore, the capacity decrease rate obtained by subtracting the capacity decrease rate of the deterioration amount of the active material of the positive electrode and the negative electrode from the capacity decrease rate obtained in the charge / discharge test by the above-mentioned 8 to 10 hours rate grows on the surface of the positive electrode and the negative electrode. It can be estimated (measured) as the rate of capacitance decrease due to the resistance component of the resistance thin film. That is, by using an extremely low rate capacity test with a rate of 30 to 50 hours in combination with a normal capacity confirmation test of 8 to 10 hours, deterioration of the active material of the positive electrode and the negative electrode and an increase in the resistance component are separated, and quantitatively determined. It is possible to measure in.

[0013]

EXAMPLE A plurality of patterns of a charge / discharge cycle of a cylindrical 18650 type lithium ion battery were prepared using the method for diagnosing deterioration of a lithium ion battery of the present invention or its apparatus, and the results of analysis are shown in FIGS. 3 and 4. 3 is a data table showing the ratio of each deterioration factor to the battery capacity reduction rate, and FIG. 4 is a bar graph showing the data shown in FIG.

This test data shows that the capacity decrease rate of the entire battery, the deterioration rate of the entire negative electrode, the deterioration rate of the negative electrode active material, and the increase rate of the negative electrode resistance component (impedance) under each test condition of temperature and charge / discharge rate ( Deterioration rate of the entire negative electrode −
The deterioration rate of the negative electrode active material), the deterioration rate of the entire positive electrode, the deterioration rate of the positive electrode active material, and the increase rate of the positive electrode resistance component (impedance) (deterioration rate of the entire positive electrode-deterioration rate of the positive electrode active material). is there. As is clear from FIGS. 3 and 4, the breakdown of the cause of the battery capacity decrease can be quantitatively shown, and the accuracy of the analysis is such that the deterioration rate of the entire negative electrode is 90% to the battery capacity decrease rate. It is included in the 110% range, and the test can be performed with considerably high accuracy.

Next, a deterioration diagnosis device for a lithium ion battery according to the present invention will be described. This deterioration diagnosing device uses a capacity testing device for charging and discharging a lithium ion battery with a constant current, and is performed at a normal time rate, for example, 8 to 10 hours. In the initial charge / discharge test of this capacity test, a detecting means for detecting a plateau voltage change immediately before the end of charging and immediately before the end of discharging, and a lower limit voltage value and an upper limit voltage value of each voltage change are read and stored in a memory. And a storage means for storing, and a capacity confirmation test at the above-mentioned normal time rate during the initial charge / discharge test and after the cycle charge / discharge test, for example, 8 to 10 hour rate, and a long time rate, for example, 30 to 50 hour. It has a measuring means for measuring the charging time and the discharging time required for each voltage change described above when performing the capacity confirmation test at a rate, and a storage means for storing the measurement result in a memory.

That is, during the initial charge / discharge test, the change of the charging voltage from the lower limit voltage value to the upper limit voltage value and the change of the discharge voltage from the upper limit voltage value to the lower limit voltage value are performed at a normal time rate and a long time. Each charging time (first charging time and second charging time) and each discharging time (first discharging time and second discharging time) in time rate, and from the lower limit voltage value to the upper limit voltage value after the cycle charge / discharge test Charging voltage change and the discharge voltage change from the upper limit voltage value to the lower limit voltage value, the charging time (the third charging time and the fourth charging time) at the normal time rate and the long time rate, and Discharge time (3rd
It has a measuring means for measuring the discharging time and the fourth discharging time and a storing means for storing the measurement result.

Further, from the above-mentioned first charging time to fourth charging time and first discharging time to fourth discharging time, the deterioration rate of the entire positive electrode and the entire negative electrode, the deterioration rate of the active material of the positive electrode, and And a calculation circuit for calculating the deterioration rate of the negative electrode active material, the increase rate of impedance due to the resistance thin film growing on the surface of the positive electrode, and the increase rate of the same impedance of the negative electrode.

That is, by substituting the first charging time ΔT and the third charging time ΔTn into the equation (1), the deterioration rate of the entire positive electrode is obtained, and the first discharging time ΔT and the third discharging time ΔTn are obtained. Similarly, the deterioration rate of the entire negative electrode is obtained. Further, by substituting the second charging time ΔT and the fourth charging time ΔTn into the formula (1), the deterioration rate of the positive electrode active material is obtained, and the second discharging time ΔT and the fourth
Similarly, the deterioration rate of the negative electrode active material is obtained from the discharge time ΔTn. Furthermore, the rate of increase of the impedance of the positive electrode is obtained by subtracting the rate of deterioration of the positive electrode active material from the rate of deterioration of the entire positive electrode described above, and the rate of increase of the impedance of the negative electrode is subtracted from the rate of deterioration of the negative electrode active material from the rate of deterioration of the entire negative electrode. It has respective arithmetic circuits to be obtained.

FIG. 5 shows the processing steps of the test, measurement, and calculation by the above-described lithium ion battery deterioration diagnosing device. Figure 5
In the above, F1 is a point measurement of the rate of 8 to 10 hours during initial charge and discharge and time required for the plateau portion, F2 is a time measurement of the plateau section at a rate of 30 to 50 hour during initial charge and discharge, and F3
Indicates various cycle tests, F4 indicates 8 to 10 after the cycle test.
The time rate measurement and the required time measurement of the plateau part, F5 is the required time measurement of the plateau part at the rate of 30 to 50 hours after the test, F6 is the calculation part of each measurement data of F1, F2, F4 and F5. Factor analysis of the capacity decrease is performed along with the capacity decrease rate of the lithium-ion battery. That is, the deterioration rates of the positive electrode and the negative electrode, the deterioration rates of the active materials of the positive electrode and the negative electrode, and the increase rates of the impedances of the positive electrode and the negative electrode are obtained. The cycle test of the battery is completed at F7.

In the above description of the method for diagnosing the deterioration of the lithium ion battery and the apparatus for diagnosing the deterioration, in the initial charge / discharge test and after the completion of the cycle test of, for example, 970 times, the capacity confirmation at the normal time rate and the long time rate is performed. A test is conducted to measure the respective deterioration rates of the positive electrode and the negative electrode. For example, 200 cycles, 500 cycles, etc. during the cycle test described above. Similar measurement in the middle of 800 cycles,
By calculation, it is possible to diagnose the deterioration state of the battery. The data collection required for this diagnostic analysis and the calculation program required for diagnostic analysis can be easily incorporated into a conventional battery charge / discharge test system, which allows
It is possible to automatically analyze and output the deterioration process accompanying the progress of the cycle test.

The subject of the method and apparatus for diagnosing deterioration of a lithium-ion battery of the present invention is mainly a transition metal oxide (LiCoO2, LiN) as a positive electrode for a lithium-ion battery.
iO2, LiMn2O4, etc.), and a battery system using a graphite-based carbon material as the negative electrode for a lithium ion battery.

[0022]

As is apparent from the above description, the present invention obtains the deterioration state of a battery from voltage, time, and current as cycle test data. It can be safely, promptly and quantitatively evaluated regardless of cell size without the need for skill, etc., and will contribute significantly to accelerating development of lithium-ion batteries and improving inspection efficiency. Is.

[Brief description of drawings]

FIG. 1 shows typical charge / discharge voltage characteristics of a lithium ion battery to which the present invention is applied.

FIG. 2 is a characteristic diagram illustrating an example of a relationship between voltage and time, which is a main configuration for deterioration diagnosis of the lithium-ion battery of the present invention.

FIG. 3 is a data table showing an example of the ratio of each deterioration factor to the battery capacity reduction rate obtained from the relationship between voltage and time measured according to the present invention.

FIG. 4 is a bar graph showing the data shown in the data table of FIG.

FIG. 5 is a process step diagram in the deterioration diagnostic apparatus for a lithium ion battery of the present invention.

Claims (5)

[Claims] 1. A plateau voltage change that occurs near the end of charge and near the end of discharge in a normal time rate charge / discharge test in the initial charge / discharge of a lithium ion battery with constant current is detected, and each of the voltage change parts is detected. The first charging time and the upper limit voltage required to change the charging voltage from the lower limit voltage value to the upper limit voltage value in the capacity confirmation test at the normal time rate while measuring the lower limit voltage value and each upper limit voltage value respectively. First required to change the discharge voltage from the voltage value to the lower limit voltage value
Second discharge time required for the change in the charging voltage and the second discharge time required for the change in the charging voltage by performing a capacity confirmation test at a long time rate in the initial charge / discharge. After the initial charge / discharge test, the normal time rate charge / discharge cycle test was performed, and the third time required for the charging voltage change in the capacity confirmation test at the normal time rate after the cycle test was performed.
Charging time and the third discharge time required for the discharge voltage change, and a capacity confirmation test at a long time rate after the cycle test was performed to perform the fourth charge time required for the charge voltage change. And a fourth discharge time required for the change in the discharge voltage is measured, and the deterioration rate of the entire positive electrode of the lithium ion battery is determined by the ratio of the first charge time to the third charge time, and the first charge time.
The deterioration rate of the entire negative electrode of the lithium ion battery according to the ratio of the discharge time and the third discharge time, and the deterioration rate of the positive electrode active material according to the ratio of the second charge time and the fourth charge time, While determining the deterioration rate of the active material of the negative electrode by the ratio of the second discharge time and the fourth discharge time,
The impedance increase rate of the positive electrode is subtracted from the deterioration rate of the positive electrode from the deterioration rate of the entire positive electrode, and the impedance increase rate of the negative electrode is subtracted from the deterioration rate of the negative electrode active material from the deterioration rate of the entire negative electrode. A method for diagnosing the deterioration of a lithium-ion battery that is required. 2. The lithium ion according to claim 1, wherein the capacity reduction rate of the lithium ion battery is obtained from the measured capacity at the initial charge / discharge test by the constant current and the measured capacity after the cycle test. Battery deterioration diagnosis method. 3. A voltage change detecting means for detecting each plateau voltage change occurring immediately before the end of charging and immediately before the end of discharging in the initial charge and discharge of a normal time rate charge and discharge test of a constant current of a lithium ion battery. Storage means for measuring and storing each lower limit voltage value and each upper limit voltage value of each plateau voltage change part, and charging voltage change from the lower limit voltage value to the upper limit voltage value in the capacity confirmation test at the normal time rate. A first charge / discharge time storage means for measuring and storing a first charge time required and a first discharge time required for a discharge voltage change from the upper limit voltage value to the lower limit voltage value; and the initial charge / discharge state. The second charging time required for the charging voltage change in the capacity confirmation test at a long time rate at
And second charging / discharging time storage means for measuring and storing the second discharging time required for the discharge voltage change, and the normal charging rate after the normal charging / discharging cycle test after the initial charging / discharging test. Third charging / discharging time storage means for measuring and storing a third charging time required for the charging voltage change and a third discharging time required for the discharge voltage change in a capacity confirmation test at a time rate; Fourth charging / discharging for measuring and storing a fourth charging time required for the charging voltage change and a fourth discharging time required for the discharge voltage change in the capacity confirmation test at the long time rate after the test. The time storage means, and the deterioration rates of the entire positive electrode and the entire negative electrode of the lithium ion battery based on the ratio of the first charging time to the third charging time and the ratio of the first discharging time to the third discharging time. The calculation means to be calculated, An arithmetic means for obtaining a deterioration rate of each active material of the positive electrode and the negative electrode according to a ratio of the second charging time and the fourth charging time and a ratio of the second discharging time and the fourth discharging time, and the positive electrode. Calculation for obtaining each impedance increase rate of the positive electrode and the negative electrode from the difference between the overall deterioration rate and the deterioration rate of the positive electrode active material, and the difference between the deterioration rate of the entire negative electrode and the deterioration rate of the negative electrode active material. Deterioration diagnosis apparatus for lithium ion battery, comprising: 4. A means for measuring the capacity of the lithium-ion battery during the initial charge / discharge test by the constant current and after the cycle test, and the capacity decrease rate from the measured capacity during the initial charge / discharge test and after the cycle test. The deterioration diagnosis device for a lithium ion battery according to claim 3, further comprising: 5. The deterioration diagnosis of the lithium ion battery according to claim 1, 2, 3 or 4, wherein the normal time rate is 8 to 10 hour rate and the long time rate is 30 to 50 hour rate. An apparatus incorporating a method and its deterioration diagnosis method.