JPH1114717A - Deterioration detecting method of secondary battery and capacity estimating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method unitedly and quantitatively detecting the deterio rating condition of a secondary battery after repeated charging/discharging cycle. SOLUTION: Voltage after impressing a fixed current for a fixed time on a secondary battery to be detected is measured, the decrement (or increment) from the initial voltage of the battery is computed, the value is fitted by a secondary function indicated by V=ai<2> +bi+c (V: voltage decrement, i: impressed current), and the degree of deterioration of the secondary battery to be detected is quantitatively indicated by a secondary factor (a) obtained by this. By inputting and computing the parameter (a) to discharge capacity = k1 -ak2 (k1 , k2 are constants particular to the battery), the discharge capacity of the battery to be detected is estimated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection method for detecting the degree of deterioration of a secondary battery such as a lithium ion secondary battery, and a method of estimating a discharge capacity of the battery based on the method. It relates to a capacity estimation method.

[0002]

2. Description of the Related Art Currently, notebook computers, mobile phones, etc.
Portable devices using a high-capacity secondary battery as a power source are rapidly spreading. These devices are usually equipped with a remaining capacity meter that indicates the available time, which is convenient for users. However, the performance of the secondary battery, which is the power source of these portable devices, always decreases when the number of times of charging and discharging is repeated. However, there are very few cases in which the degree of this deterioration is indicated to the user of the device, and the user only feels that the performance of the battery has deteriorated in a form that the working time of the used device is somewhat reduced. Absent. The methods for detecting the degree of deterioration of a secondary battery proposed so far can be broadly classified into the following methods. (1) Method for measuring the internal impedance of a battery (JP-A-53-42327, JP-A-61-170678, JP-A-1-253175, JP-A-4-141966, JP-A-8-254573, JP-A-8-273705) (2) A method of measuring the internal impedance of a battery with signals having different frequencies and processing the value according to an arithmetic expression (JP-A-8-43506, JP-A-8-250159). Method for measuring electric resistance (JP-A-56-103875) (4) A method for measuring a voltage when a predetermined current is applied and comparing the measured voltage with a predetermined reference value (JP-A-59-48)
661, JP-A-3-95872, JP-A-8-25457
3, JP-A-8-55642, JP-A-9-33620. (5) A method of counting the number of charge / discharge cycles (JP-A-5-74501).

[0003]

As described above, many methods have been proposed for detecting performance degradation of a secondary battery. However, it goes without saying that the performance deterioration of the secondary battery greatly depends on the method of use, that is, the charge / discharge current, the charge / discharge voltage, the charge / discharge time, and the like. In other words, even if the number of charge / discharge cycles is simply counted, the degree of deterioration in performance of a battery that has undergone the same charge / discharge cycle is not the same between a shallow charge / discharge cycle and a deep charge / discharge cycle near complete discharge. Unlike this, it was difficult to quantify the degree of deterioration using a uniform method. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of easily detecting the degree of deterioration of a battery by a simple test regardless of a past charge / discharge history.

[0004]

Means for Solving the Problems The present inventors conducted a charge / discharge cycle test in different discharge current modes using a currently marketed lithium ion battery, examined common deterioration characteristics, and determined this from outside. And found a way to detect it. The common deterioration characteristics indicate the same deterioration characteristics even if the charging current or the environmental temperature is changed, as long as the charge conditions and discharge stop voltage recommended by the test battery manufacturer are observed. It was said that the current rate characteristics deteriorated. Therefore, when a method for quantitatively and quickly detecting the rate characteristic of the output current was studied, a plurality of currents different from each other were applied to the test secondary battery for a predetermined time, and the secondary battery at this time was applied. By measuring the voltage value, inputting it to a predetermined formula, and expressing the obtained value as an index of the characteristic deterioration of the battery, it was found that the degree of deterioration of the secondary battery could be qualitatively evaluated. The invention has been completed.

This technique is similar to chronopotentiometry usually used when analyzing the polarization characteristics of an electrochemical reaction system, but a new finding in the present invention is that the applied current value is measured by i. When the voltage value is set to V and fitted with a quadratic function represented by the equation V = ai ² + bi + c, the quadratic coefficient a is very large in the case where the charge / discharge cycle is not performed, that is, the applied current and the polarization Although the voltage is in a substantially proportional relationship, when the charge / discharge cycle is repeated, this value gradually decreases, that is, the polarization voltage increases at an accelerated rate by the applied current. More importantly, even when charging and discharging are performed in various modes, the use of this parameter a makes it possible to uniformly and quantitatively detect the state of deterioration of a battery that has been repeatedly charged and discharged. became. For example, the above parameter a is calculated by the formula C _cap
= K ₁ -ak ₂ (where C _cap is the discharge capacity and k ₁ and k ₂ are predetermined battery-specific values) to estimate the discharge capacity of the battery at that time regardless of the past charge / discharge history. Became possible.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, according to the present invention, a plurality of different currents are applied to a test secondary battery for a predetermined time, and the voltage value of the secondary battery measured at this time is calculated by a predetermined calculation. Calculate numerical parameters by performing input arithmetic processing on the formula,
The degree of deterioration of the secondary battery is quantitatively determined based on the numerical parameters. In particular, as the method of calculating, the applied current value i _n independent variables, the measured voltage value V _n corresponding thereto as the dependent variable, the formula V = ai ² this value
A method of determining the degree of deterioration of the test secondary battery based on the magnitude of the secondary coefficient a when approximated by a quadratic function represented by + bi + c. Further, the method of estimating the capacity of the secondary battery is to estimate the discharge capacity of the test secondary battery by inputting and calculating the coefficient a in the formula C _cap = k ₁ -ak ₂ .

In order to carry out the method for detecting deterioration of a secondary battery according to the present invention, a current application circuit, a voltage measurement circuit and a measurement data calculation circuit are provided in the components. The measurement process is
For example, 0.1A, 0.5A, 1A, 2
A and 3A currents were applied continuously for 1 second, the voltage after 1 second after each application was measured, the amount of drop (or rise) from the initial voltage of the battery was calculated, and the value was calculated as V = ai ² + bi.
By fitting with a quadratic function represented by + c (V: voltage drop, i: applied current), a obtained by inputting and calculating it into the previously recorded equation C _cap = k ₁ −ak ₂ is obtained by The discharge capacity of the test battery is expressed numerically. The fitting algorithm for calculating a in the present process does not need to be particularly limited, and a known method such as a least square method can be used.

[0008]

EXAMPLES The method of the present invention will be specifically described below with reference to examples. << Embodiment 1 >> A charge / discharge cycle under different discharge conditions described in Table 1 was performed, and deterioration of a secondary battery according to the present invention was detected before and after the charge / discharge cycle, when 300 cycles had elapsed, and when 500 cycles were completed. The method was performed to verify the validity of the detection method of the present invention. The measurement was performed according to the procedure described below.

1-1. Battery charge / discharge cycle test: Test battery is a lithium-ion battery (model number CG) manufactured by Matsushita Electric Industrial Co., Ltd.
R17500: Recommended upper limit voltage 4.1 V, lower limit voltage 3.0 V, nominal discharge capacity 720 mAh). Charging conditions are according to the constant current-constant voltage charging method, which is the recommended charging method for this battery.
When a constant current of 500 mA was applied and the voltage reached 4.1 V, the charging was completed in a total of 2 hours of maintaining the constant voltage at 4.1 V. The discharge conditions were different for each of the three conditions described in Table 1.
The operation was performed in various types of current modes, and the discharge stop voltage was set to a common value of 3.0 V. All tests were performed in a constant temperature room at 20 ° C. The result is shown in FIG.

[0010]

[Table 1]

In FIG. 1, the vertical axis shows the discharge capacity and the horizontal axis shows the number of charge / discharge cycles. As you can see from this,
It was shown that the state of cycle deterioration of the discharge capacity was different when the discharge current was different.

1-2. Measurement of deterioration parameter: 1-
In the charge / discharge process C described in No. 1, the method for detecting deterioration of a secondary battery according to the present invention was performed before the charge / discharge cycle, when 300 cycles had elapsed, and when 500 cycles were completed. The measurement is performed after the charging process is completed according to the charging method described above, and then 0.1A, 0.5A, 1A, 1.5A, 2A,
The measurement was performed by measuring the drop of the battery voltage from the completion of charging when the current of 2.5 A, 3 A, 4 A, and 5 A was continuously supplied (discharged) for 1 second. The result is shown in FIG. 2 together with the energizing current. In FIG. 2, it can be seen that when the charge and discharge cycles are repeated, the voltage drop becomes larger even when the same current is applied. The data shown in FIG.
Table 2 shows parameters a, b, and c obtained by quadratic function fitting represented by i ² + bi + c (V: drop voltage, i: applied current).

[0013]

[Table 2]

Next, the parameter a obtained for each cycle and the discharge capacity at that time are plotted in FIG.
In FIG. 4, the plotted four points have a substantially linear relationship, and fitting them by the least squares method has established the relationship shown by discharge capacity (mAh) = 680-490 · a.

Next, with respect to the charging / discharging processes A and B described in the above 1-1, exactly the same measurement as in the method described above was performed, the parameter a was calculated, and the results are shown in FIGS. 4 and 5, respectively. Was. Usually, the discharge capacity varies greatly depending on the discharge current, and when the charge / discharge cycle is repeated,
The degree of deterioration naturally depends on the conditions of charge and discharge. However, as can be seen from a combination of FIGS. 3, 4 and 5, according to the present embodiment, even in a battery which has been subjected to a charge / discharge cycle having a different discharge current, the discharge capacity is measured by measuring the initial discharge current. From the value and the parameter a obtained by the method of the present invention, it was found that the actual capacity of the battery at that time can be expressed numerically by the equation of discharge capacity (mAh) = initial capacity−500 · a. In the above example, the voltage drop was measured using the current applied to the battery as the discharge current.
The discharge capacity can be similarly estimated by measuring the voltage rise with the applied current as the charging current.

[0016]

According to the present invention, a plurality of currents different from each other are applied to a test secondary battery for a predetermined period of time, and the voltage value of the secondary battery at this time is measured and input to a predetermined calculation formula. By doing so, the degree of deterioration of the secondary battery can be qualitatively evaluated using the parameters obtained. Further, even when charging and discharging are performed in various modes, it is possible to estimate the discharge capacity of the battery at that time regardless of the past charging and discharging history by using this parameter.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of cycles and the discharge capacity in charge / discharge cycles performed under different conditions.

FIG. 2 is a diagram showing an applied current-drop voltage characteristic for a battery in a discharge process C.

FIG. 3 is a diagram showing a relationship between a parameter a obtained by fitting an applied current-drop voltage characteristic with a quadratic function based on FIG. 2 and a discharge capacity.

FIG. 4 is a diagram showing a relationship between a parameter a and a discharge capacity for a battery in a discharge process A.

FIG. 5 is a diagram showing a relationship between a parameter a and a discharge capacity for a battery in a discharge process A.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Takeyama 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A plurality of currents different from each other are respectively applied to a test secondary battery for a predetermined time, and a voltage value of the secondary battery measured at this time is input and processed into a predetermined calculation formula to calculate a numerical parameter. A deterioration detection method for a secondary battery, wherein the degree of deterioration of the secondary battery is quantitatively determined based on the numerical parameters. Wherein said calculation method, the applied current value i _n independent variables, the measured voltage value V _n corresponding thereto as the dependent variable, quadratic function expressed this value in equation V = ai ² + bi + c 2. The deterioration detection method for a secondary battery according to claim 1, wherein the degree of deterioration of the test secondary battery is determined based on the magnitude of the secondary coefficient a when approximation is performed. 3. The coefficient a is calculated as follows: discharge capacity = k ₁ −ak
_{2 A} method for estimating the discharge capacity of a secondary battery by estimating the discharge capacity of the secondary battery by inputting and calculating in an expression represented by ₂ (k ₁ and k ₂ are predetermined specific values).