Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1999-03-02
2001-03-27
Tso, Edward H. (Department: 2838)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
Reexamination Certificate
active
06208147
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of and apparatus for measuring a unknown battery capacity by measuring and analyzing the characteristic impedance spectrum of primary and secondary batteries. Especially, the present invention relates to a method of and apparatus for measuring a unknown battery capacity by the impedance spectrum analysis, which is for the user to measure the battery capacity in a non-destructive way such as measuring a unknown remaining capacity of standardized cell product and grading the standardized capacity of product.
BACKGROUND OF THE RELATED ART
As a widely used measurement for battery capacity there is a real-time discharge method for measuring time td for which a battery connected to an electrical load can supply the power to a constant current Id.
Assuming that the battery capacity is expressed in ampere-hour (Ah). the battery capacity is given by Equation 1 which is used as a standard to evaluate the capacity of battery (e.g., the Korean Industrial Standards).
td=Ah/Id [Equation 1]
The real-time discharge method is to measure the capacity of battery directly and requires a long time for measurement as the battery is discharged in real time. To measure a plurality of batteries at the same time, a plurality of apparatuses is required for discharging the respective batteries separately in the real-time discharge method.
Especially, for the primary battery, the real-time discharge method is inapplicable to the measurement of battery capacity for purpose of quality management of products.
On the other hand, the time for measurement of impedance at a specified frequency is generally shorter than the time required for the real-time discharge method.
The time required for measuring, the impedance characteristic of battery is limited by the lowest frequency of an input/output signal to be measured.
If the result of the impedance measurement has a close correlation with battery capacity, therefore, the battery capacity can be measured more efficiently by measuring the impedance than by using the real-time discharge method.
There has already been reported a method of determining remaining capacity of battery or monitoring battery charge/discharge state by measuring impedance at a specified frequency.
U.S. Pat. No. 3,562,634 describes a method for determining the charge state of a secondary battery especially nickel-cadmium battery, from the measured Faraday's electric capacity by using a bridge.
According to U.S. Pat. No. 3,562,634, the relationship between the internal impedance of battery and the battery capacity substantially depends on the impedance response characteristic of chemical material used as an active material of the battery.
Therefore the specific relationship between the internal impedance of battery and the battery capacity measured at a specified frequency and for a specified kind of battery do not generally applies to determining battery capacity (Refer to Embodiment 4).
More general method of monitoring the state of charge by using the relationship between the internal impedance at a specified frequency and the remaining capacity of storage battery in U.S. Pat. No. 4,678,998, which proposes a method to sense the state of charge continuously by comparing impedances obtained at different frequencies.
Besides, U.S. Pat. No. 4,743,855 describes a method of using two complex impedances separately measured in the lower and higher frequency regions, and U.S. Pat. Nos. 5,241,275 and 5,717,336 disclose the use of the linear impedance characteristic in the lower frequency region. However, the related art method using the relationship between battery capacity and impedance at a specified frequency or in a narrow frequency region is hardly excellent in aspects of efficiency of measurement and accuracy of correlation.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of and apparatus for measuring battery capacity by impedance spectrum analysis that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a novel method of and apparatus for measuring battery capacity by the impedance spectrum analysis, which is to measure an unknown battery capacity accurately by measuring the characteristic impedance spectrum of primary and secondary batteries in a wide frequency band and analyzing the measured characteristic impedance spectrum.
Another object of the present invention is to provide a method of and apparatus for measuring battery capacity by the impedance spectrum analysis, which takes less time than the real-time discharge method and is excellent in efficiency and reliability.
To accomplish the objects of the present invention, a method of measuring battery capacity by impedance spectrum analysis, which is to measure a characteristic impedance spectrum of primary and secondary batteries and determine the battery capacity, includes the steps of: (1) measuring the characteristic impedance spectrum of primary and secondary batteries in a wide frequency range from the lower frequency of several mHz to the higher frequency of several KHz; (2) calculating model parameters by fitting the measured characteristic impedance spectrum to an equivalent circuit with distributed parameters such as resistance, capacitor and transmission line and (3) estimating the unknown battery capacity using parameters obtained in step (2) based on correlation between the capacity measured by the real time discharge method and the model parameters obtained in advance.
The present invention provides a method for measuring battery capacity with high efficiency and reliabiity by analyzing the impedance spectrum in a wide frequency range within short measurement time relative to the real-time discharge method and by determining model parameters of an equivalent circuit based on a close correlation with charge/discharge state of the battery.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
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Ho, C., Raistrick, I.D., and Huggins, R.A., Application of A-C Techniques to the Study of Lithium Diffusion in Tungsten Trioxide Thin Films,J. Electrochem.Soc., vol. 127, No. 2, pp. 343-350 (1980).
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Barsukov Yevgen
Kim Jong Hyun
Yoon Chul Oh
Davidson Davidson & Kappel LLC
Korea Kumho Petrochenical Co., Ltd.
Tso Edward H.
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