RU2295139C2 - Method for determining remaining capacity of primary current source - Google Patents

Abstract

FIELD: technology for controlling chemical current sources, namely, non-destructive control of their condition, and can be used for determining remaining capacity of primary chemical current sources, on anodes of which passive film is formed.

SUBSTANCE: method for determining remaining capacity of primary current source includes feeding advance current impulse onto primary chemical current source, which destroys pacifying film on anode. Immediately after letting of advance current impulse through primary current source, measurements of its impedance are performed in frequency range ranging from fractions of hertz to 1 kHz, and on basis of produced locus diagram of impedance, value of phase angle is computed in point wherein module of extreme of imaginary part of locus diagram has maximal value. Remainder capacity is determining by comparing resulting value of phase angle to calibration curve.

EFFECT: realization of impedance method for measuring remainder capacity of primary current source, on anode of which passive film is present, with minimal losses of element capacity during measurement.

Description

The present invention relates to the control of chemical current sources (CIT), and in particular to the field of non-destructive control of their condition, and can be used to determine the residual capacity of the primary CIT, on the anode of which a passive film is formed.

A known method for determining the residual capacitance of Leklanshe elements based on measurements of impedance [1]. The specified method is as follows. The impedance of the current source is measured in the frequency range from fractions of a hertz to 10 kHz. The capacitance value Rx is calculated from the obtained spectrum at a fixed frequency value of 31.2 Hz. The determination of the value of the residual capacity is carried out by comparing the obtained value with a calibration curve, measured by the specified method on the elements, with a known value of the residual capacity.

The disadvantage of this method is that it determines the residual capacity in the range of 100-90%, in which a linear dependence of the value of Rx on the residual capacity is observed.

This drawback is also inherent in the methods for determining the residual capacity of current sources proposed in [2, 3]. In [2], as a parameter by which the residual capacitance is determined, the difference in the values of the resistance of the current source is used at two fixed frequency values (6 Hz and 10 kHz). In [3], the residual capacity of the primary lithium thionyl chloride chemical current source was determined by the value of the charge transfer resistance or by the value of the double layer capacitance.

The closest analogue is a method of measuring the residual capacity of a lead battery by the values of the phase angle of the impedance at a fixed frequency [4]. This method is implemented by measuring the impedance, constructing the frequency-phase hodograph, calculating the phase angle value at the selected fixed frequency, comparing the obtained phase angle value with the calibration curve, and determining the value of the residual current source capacitance.

The choice of a fixed frequency value at which the phase angle is calculated and the calibration graph is constructed is carried out as follows. The battery is initially charged for 5 hours, kept without load for 1 hour and discharged to a final voltage value of 1.7 V on each element. After several charge-discharge cycles, the battery impedance is measured at various values of the residual capacity (from 0 to 100%) . Measurements are initially carried out on a fully discharged battery. After obtaining the impedance spectrum at a residual capacity of 0%, the battery is charged to a certain value of the residual capacity, the battery is held for 8 hours without load and the impedance is measured again. The battery is discharged again in order to control the set value of the residual capacity of the current source. This procedure is carried out for each value of the residual capacity until a full battery charge is reached. From the impedance spectra (frequency-phase hodographs) obtained for each value of the residual capacitance, the values of the phase angle in the frequency range 25 Hz-0.01 Hz are calculated. The obtained data are tabulated and fixed frequencies are chosen at which monotonic dependences of the phase angle value on the residual battery capacity are observed, which are subsequently used as calibration curves.

The main disadvantage of this method is that the determination of fixed frequencies must be carried out for each batch of the same type of batteries, and even more so in the case of studies of batteries produced by different manufacturers, where the difference between these frequencies reaches several orders of magnitude. In addition, this method cannot be used to study the state of primary current sources in which it is impossible to conduct charge-discharge cycles when constructing a calibration curve.

The problem of determining the degree of discharging of primary lithium current sources has been studied in detail in [5]. However, the results cannot be called encouraging, since the impedance, for example, of lithium thionyl chloride elements does not directly correlate with the degree of discharge and cannot serve as a quantitative characteristic. One of the reasons for this is the specific features of elements of this type, associated, in particular, with the strong oxidizing ability of thionyl chloride. As a result, the lithium anode is passivated by a thin oxide film during storage, which leads to irreproducibility of the results and to the loss of the expected correlation between the degree of discharge (residual capacity) and impedance characteristics.

The aim of the invention is to determine the residual capacity of the primary chemical current source, on the anode of which a passive film is formed, in particular a lithium current source.

The essence of the invention lies in the fact that the primary chemical current source is supplied with a preliminary current pulse, the amplitude of which does not exceed the maximum discharge current of an element of a given size, and the duration is chosen such that the change in the capacitance of the element during measurement should be at least 0.5 % of the nominal capacity of the element. In this case, the passivation of the film at the anode is degraded. Immediately after passing the preliminary current pulse through the primary current source, its impedance is measured in the frequency range from fractions of a hertz to 1 kHz, and the magnitude of the phase angle at the point at which the absolute value of the imaginary part of the hodograph has the maximum value is calculated from the obtained impedance hodograph. The residual capacity is determined by comparing the obtained value of the phase angle with the calibration curve.

The technical result of the claimed invention is the implementation of the impedance method of measuring the residual capacitance of the primary current source, on the anode of which there is a passive film, with minimal loss of capacitance of the element during measurement.

Comparison of the invention with the prototype allows you to establish compliance with its criterion of "novelty."

In the prototype, the measurement of the impedance at the current source is carried out after a long pause, during which all processes occurring in the source come into equilibrium. In the present invention, on the contrary, before measuring the impedance, the element is unbalanced by passing a preliminary current pulse through it. This operation is necessary because the phase angle measured on the element after long-term storage does not depend on the residual capacity of the element and has a very low value. After passing a preliminary current pulse, the phase angle for non-discharged elements increases by almost an order of magnitude.

In the prototype, the phase angle value is calculated at a fixed frequency value. In the present invention, the phase angle value is calculated at the point of the hodograph of the impedance, in which the extremum modulus of the imaginary part has a maximum value. Thus, the parameter “measurement frequency” is not at all decisive, and the choice of the extremum point made it possible to significantly reduce the processing time of the obtained impedance spectra. In addition, the relationship between the phase angle at the extremum point and the residual capacity does not depend on the geometry of the current source, which allows us to use the proposed criterion not only for elements of the same type, but also for elements of various sizes and various electrochemical systems containing anodes of passivable materials .

The authors are not aware of other technical solutions that allow determining the residual capacity of elements whose anodes are coated with a passive film. On the contrary, literature data indicate the “impossibility” of determining the residual capacity of elements with a passive film, for example, primary lithium current sources [5], by impedance methods.

One of the options for implementing the invention is as follows. A preliminary current pulse with an amplitude of 10 mA and a duration of 15 minutes was passed through a LT 14500 V5 lithium cell with a nominal capacity of 1.2 A · h and a maximum discharge current of 30 mA, after which the impedance was measured in the frequency range from 1.6 · 10 ^-3 Hz - 1.00 kHz. Then, the frequency-phase hodograph of the impedance was calculated and the point at which the absolute value of the imaginary extremum had the maximum value was determined on it. At this point, the values of the phase angle were measured. The obtained value was compared with the calibration curve. The time of measuring the phase angle during computer construction of the hodograph did not exceed 30 minutes.

Bibliography

1. S.A.G.R. Karunathilaka, N.A. Hampson, R. Leek, T.J.Sinclain. Journal of applied Electrochemisty 10 (1980) 799-806.

2. S.A.G.R. Karunathilaka, N.A. Hampson, T.P. Haas, R. Leek, T.J.Sinclain. Journal of applied Electrochemisty 11 (1981) 573.

3. M. Hughes, S. A. G. G. Karunathilaka, N. A. Hampson, T. J. Sinclain. Journal of applied Electrochemisty 13 (1983) 669-678.

4. V.V. Viswanuthan, A.J. Sulhind, J.J. Kelley, J.B. Ockerman. Journal of applied Electrochemisty 25 (1995) 729-739.

5. L.S. Kanevsky, B.C. Bagotsky, E.A. Nizhnikovsky. Electrochemistry 31 (1995) 376-382.

Claims (1)

A method for determining the residual capacity of a primary current source, including the operation of measuring the impedance of the current source, constructing the impedance hodograph, determining the phase angle of the impedance and comparing it with a calibration curve, characterized in that a preliminary current pulse whose amplitude is passed through the current source does not exceed the maximum discharge current of the primary current source of this size, and the duration of the preliminary current pulse provides If the capacitance of the primary current source during the measurement is reduced by at least 0.5% of its nominal capacity, the impedance hodograph point is determined at which the imaginary part extremum modulus has a maximum value, and the phase angle value is determined at this point.