JPH1114718A - Secondary battery deterioration detection method and capacity detection method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for quantitatively evaluating the degree of deterioration regardless of past charge / discharge histories, and estimating the current discharge capacity without actually discharging the current discharge capacity. SOLUTION: The nominal capacity of a test secondary battery at an hourly rate is C
(MAh), a large current of 5 C (mA) or more is applied to the battery, and the time T required for the battery voltage to reach a specific value is T
Thus, the degree of deterioration of the secondary battery is qualitatively evaluated by expressing it as an index of the characteristic deterioration of the battery. Further, the time T is calculated by the following equation (where i = 1, 2,... N, k _i
Is input to the printout current, the stop voltage, and a specific value which is clearly determined by the battery type), thereby estimating the discharge capacity of the test battery. (Equation 1)

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 battery capacity detection method for estimating a discharge capacity of a battery based on the detection method. It is about.

[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 roughly 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-59-1983)
-48661, JP-A-3-95872, JP-A-8-25
4573, JP-A-8-55642, JP-A-9-3362
0) (5) A method of counting the number of charge / discharge cycles (JP-A-5-74501).

[0004]

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.

[0005]

The inventor of the present invention has conducted charge / discharge cycle tests in different discharge current modes using currently marketed lithium ion batteries, examined common deterioration characteristics, and externally examined the deterioration characteristics. And found a way to detect it. The common deterioration characteristics are the same deterioration characteristics even if the discharge current is changed, as long as the charge conditions and the discharge stop voltage recommended by the test battery manufacturer are observed. It was said that the characteristics deteriorated.

[0006] Then, when a method for quantitatively detecting the rate characteristic of the output current in a short time was examined, when the nominal capacity of the test secondary battery at one hour rate is C (mAh), A large current of 5 C (mA) or more is applied to the secondary battery, a time T until the battery voltage reaches a specific value is measured, and this value is input to a predetermined formula to calculate a numerical parameter. The present inventors have found that the degree of deterioration of a secondary battery can be qualitatively evaluated by expressing it as an index of battery characteristic deterioration, and have completed the present invention.

This method 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 it has a low ionic conductivity like a lithium battery. In a battery system using an organic electrolyte, when a large current value is applied to a battery, which is generally considered insane, a battery with a more severe capacity deterioration due to a charge / discharge cycle has a larger voltage drop. This is a point that was in an inversely proportional relationship linearly.

More importantly, even if the current mode of the charge / discharge cycle is different, the magnitude of the voltage drop when a current value as large as normally considered insane is applied to the battery is used as a parameter. When used, the state of deterioration of a battery that has been subjected to repeated charge / discharge cycles can be uniformly and quantitatively detected. For example, C _cap = k ₁ T ³
+ K ₂ T ² + k ₃ T + k ₄ (C _cap is discharge capacity, k _{1 to} k ₄ are applied current, stop voltage, and a specific value determined in advance by battery type). It became possible to estimate the discharge capacity of the battery at that time regardless of the discharge history.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 constituent devices. The measurement process applies, for example, a current of 5 A to the test secondary battery,
The time T required for the battery voltage to reach 1 V is measured, and it can be determined that the smaller the value T, the greater the capacity deterioration of the battery. Furthermore, by inputting and calculating the value of T into a polynomial expression relating to T, for example, Expression (1), it is possible to estimate the discharge capacity of the test battery in advance.

[0010]

(Equation 2)

Where i = 1, 2,... N, k _i is the applied current,
This is a unique value determined in advance by the stop voltage and the battery type.

[0012]

EXAMPLES The method of the present invention will be specifically described below with reference to examples. << Example 1 >> A charge / discharge cycle under different discharge conditions described in Table 1 was performed, and before the charge / discharge cycle, 100, 300,
The deterioration detection measurement of the secondary battery according to the present invention was performed on the battery after 500 or 700 cycles, and the validity of the detection method of the present invention was verified. The measurement was performed according to the procedure described below.

[0013]

[Table 1]

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.
Charging was completed in a total of 2 hours by applying a constant current of 500 mA and maintaining the voltage at a constant voltage of 4.1 V when the voltage reached 4.1 V. The discharge conditions were set in three different current modes described in Table 1, and the discharge stop voltage was all set to 3.0 V. All tests were performed in a constant temperature room at 20 ° C. The result is shown in FIG.

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. Deterioration parameter measurement: 1 above
In the charging / discharging process C described in -1, the battery before and after the charging / discharging cycle, 100, 300, 500, and 700 cycles was subjected to the secondary battery deterioration detection measurement according to the present invention. After the completion of the charging process according to the charging method described above, the state of the battery voltage drop when a current of 4.9 A was applied was measured, and the results are shown in FIG. In FIG. 2, it can be seen that, when charge and discharge cycles are repeated, the voltage drop rate increases even when the same current is applied. further,
After the current was applied, the time required for the battery voltage to drop to 1.0 V was measured, and this was taken as a time factor T and is shown in FIG. 3 together with the discharge capacity for each cycle. The time factor T and the discharge capacity shown in FIG. 3 can be correlated by a cubic function, and the coefficients are also shown in the figure.

Next, with respect to the charge / discharge processes A and B described in the above 1-1, the same measurement as in the method described above was performed, and the time factor T was calculated. The results are shown in FIGS. 4 and 5, respectively. Indicated. Further, FIGS. 3, 4, and 5
All plot points of the time factor T-discharge capacity described in the above are plotted in FIG. Normally, 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 charge / discharge conditions. However, as can be seen from FIG. 6, according to the present example, even if the battery was subjected to a charge / discharge cycle with a different discharge current, the discharge capacity was calculated using the time factor T obtained in this measurement. (MAh) = aT ³ + bT ² + c
T + d (a = 0.066, b = −4.0, c = 86, d
= 19), it was found that the discharge capacity, which is the ability of the battery at that time, can be expressed numerically.

The equation for estimating the discharge capacity used in this method is a cubic equation relating to the time factor T.
Needless to say, setting the parameters more accurately improves the estimation accuracy of the capacity.

[0019]

According to the present invention, even if a battery has undergone charge / discharge cycles under different conditions, the degree of deterioration is quantitatively evaluated, and even if the current discharge capacity is not actually discharged, this can be achieved. Can be estimated.

[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 a voltage-time characteristic when a current is applied to a battery in a discharge process C at the end of each cycle.

FIG. 3 is a diagram showing a relationship between a time factor T determined based on FIG. 2 and a discharge capacity in each cycle.

FIG. 4 is a diagram showing a relationship between a time factor T in a discharge process A and a discharge capacity in each cycle.

FIG. 5 is a diagram showing a relationship between a time factor T in a discharge process B and a discharge capacity in each cycle.

FIG. 6 is a diagram illustrating a relationship between a time factor T and a discharge capacity of all discharge processes A, B, and C.

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

Claims (2)

[Claims] 1. The nominal capacity of the test secondary battery at an hourly rate of C
(MAh), a large current of 5 C (mA) or more is applied to the secondary battery, a time T until the battery voltage reaches a specific value is measured, and this value is input and calculated in a predetermined calculation formula. A deterioration parameter of the secondary battery is quantitatively determined based on the calculated numerical parameter. 2. The time T is expressed by the following equation: (Where i = 1, 2,... N, k _i are specific values predetermined in accordance with the applied current, stop voltage, and battery type) to estimate the discharge capacity of the battery under test. Battery capacity detection method.