JP2861665B2 - Maintenance and inspection method and capacity recovery method for nickel-cadmium batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maintenance and inspection method and a method for restoring the capacity of a battery of a nickel-cadmium battery.

[0002]

2. Description of the Related Art Storage batteries are used in a wide variety of fields as emergency power supplies. As a charging method, a rectifier, a storage battery, and a load are connected in parallel, and the voltage is used to maintain a constant value called a floating charging voltage. In the floating charging method, the storage battery is always in a standby state, but charge control or the like is performed to compensate for self-discharge and maintain the battery in a fully charged state.

However, during long-term use, variations in battery voltage and the like occur, so that maintenance management such as uniform charging is required. As a check method, measure the charging voltage of each cell and empirically define the range. For example, the upper limit is specified as + 0.02V of the maximum value, and the lower limit is specified as -0.05V of the maximum value. Was always there. Furthermore, when a voltage variation occurs during use, as a method of correcting the voltage variation, an overdischarge method or an overcharge method has been empirically performed. In particular, recently, the application of sealed batteries to an emergency power supply has increased, and conventional maintenance methods cannot sufficiently cope with them.

[0004]

According to the conventional maintenance and inspection method, when a voltage variation occurs, the cell is removed and then overdischarged or overcharged, or the entire assembled battery is overcharged. Therefore, the method of eliminating voltage variations is applied, but depending on the conditions, the durability of the effect is not constant, and overcharging may be performed more than necessary, which adversely affects the life performance of the battery. Was. More importantly, such maintenance and inspection methods have been empirically performed, and the reasons therefor are not clear, and optimization thereof is required.

[0005]

SUMMARY OF THE INVENTION The present invention is to optimize the maintenance by systematically conducting experiments and considerations on voltage change and capacity change of a battery pack of a sealed battery. That is, a method of recognizing a battery having a float voltage outside the range of 1.23 to 1.48 V as abnormal and performing maintenance and inspection, and for a battery having a voltage of 1.40 V or higher, changing the battery to 1.48 V There is a method of reducing the voltage variation by charging at a constant voltage of up to 1.70 V and restoring the battery capacity. In particular, the effect is further obtained by removing the valve and charging.

[0006]

The unit cell voltage V ₁ of the group battery during the float operation
^{_{V 1 = E 01 + + η}} + that expressed by the following formula ^{_{- (E 01 - -η -)}} (1) E 01 +: equilibrium potential of the positive electrode, E ₀₁ ^-: equilibrium potential of the negative electrode, eta ^+: positive electrode overvoltage ( ^{_{a 1 + + b 1 + LogI}} ), η -: negative overvoltage ^{_{(a 1 - + b 1 -}} LogI) a 1 +, b 1 +: data - coefficient Fell ^{_{a 1 = a 1 + + a}} 1 -, B 1 = ^{_{b 1 + + b 1 -,}} E 01 =
Assuming that E ₀₁ ⁺ −E ₀₁ ⁻ , the total number of group batteries is n, the set voltage is V _s , and the internal resistance of the unit battery is r, the following equation is established.

[0007] _{V S = I (r 1 +} r 2 + ... r n) + (E 01 + E 02 + ... E 0n) + (A 1 + A 2 + ... A n) + (B 1 + B 2 + ... B n) Log I (2) Since values other than the current value are constants, when the type of battery reaction, that is, the type of positive / negative electrode reaction is determined, the voltage of each unit battery is determined. Therefore, it is considered that the variation of the battery voltage during the float is caused by the difference between the positive and negative reactions. The main electrode reactions that occur in a floating battery are considered as follows.

[0008] The reaction of the reaction the negative electrode of the positive electrode _{1) Ni (OH) 2 →} NiOOH + H + + e - (3) Cd (OH) 2 + 2e - → Cd + 2OH - (5) 2) 4OH - → O 2 + 2H 2 ^{O + 4e - (4) Cd} (OH) 2 + 2e - → Cd + 2OH - 3) 4OH - → O 2 + 2H 2 O + 4e - 2H 2 O + 2e - → H 2 + 2OH - (6) 4) 4OH - → O 2 ^{_{+ 2H 2 O + 4e - O}} 2 + 2H 2 O + 4e - → 4OH - (7) 5) Ni (OH) 2 → NiOOH + H + + e - 2H 2 O + 2e - → H 2 + 2OH - 6) Ni (OH) ^{_{2 → NiOOH + H + + e}} - O 2 + 2H 2 O + 4e - → 4OH - causes variation of the battery will be caused by the presence of these various electrode reactions. Note that the battery voltage also varies due to the difference in battery internal resistance.
In particular, in the case of a sealed battery, since the gas absorption reaction performance is affected by the amount of the electrolytic solution, it is considered that the type of electrode reaction changes during long-term use. It is concluded that the battery voltage during the float of a battery with a large liquid volume and limited gas absorption reaction varies according to the following mechanism. First stage After the start of use, for several years, the reaction of 4), in which oxygen is generated at the positive electrode and oxygen is absorbed at the negative electrode, and the reduction of Cd (OH) ₂ occurs at the negative electrode as a side reaction, 2) There is almost no voltage variation. Second stage In a battery in which the gas absorption performance of the negative electrode is not sufficient because the float current is small, the remaining reserve Cd (OH) ₂ is almost completely reduced to Cd several years after the start of use. Therefore, the reserve Cd (OH) ₂ is almost eliminated, the polarization of the reaction of the negative electrode in 2) increases, and the battery voltage gradually increases. The voltage rise value is equally distributed to other battery voltages. Therefore, although the float voltage is constant,
The float current is reduced. This remaining reserve Cd (OH) ₂
In the process of increasing the polarization due to the decrease in the voltage, the battery voltage increases, but the polarization occurs and the positive electrode potential gradually becomes lower. The process in which the potential of the positive electrode becomes lower is that the NiOOH of the charge product decomposes water by the formula (8) and degrades the oxygen by the formula (8), compared with the progress of the charge reaction of the formula (3) or the oxygen generation reaction of the formula (4). This is a process in which the reaction that generates gas or generates Ni (OH) ₂ by self-discharge by the shuttle mechanism progresses at a high rate.

4NiOOH + 2H ₂ O → 4Ni (OH) ₂ + O ₂ (8) Third Stage When the state of the second stage is continued, hydrogen gas from the negative electrode and oxygen gas from the positive electrode escape outside the system. In addition, the electrolyte decreases. When the electrolyte solution decreases and the gas absorption performance improves, the battery voltage decreases because the gas absorption reaction of the formula (7) occurs at the negative electrode. Note that, since the potential of the positive electrode is low in the second stage, the battery voltage is lower than in the first stage. Fourth stage When the third stage is maintained, the float current becomes larger than that of the second stage and approaches the state of the first stage. Therefore, the charging voltage during the float varies greatly from the first stage to the fourth stage, but has little effect on the capacity of the unit cell itself. In order to confirm this, a capacity test was performed on the battery in which the voltage fluctuation occurred in the assembled battery. As a result, when the battery voltage was in the range of 1.23 to 1.48 V, the capacity was slightly reduced. It was confirmed that there was almost no variation and the condition was good. Then, when a battery having a high battery voltage was charged at a constant voltage of 1.48 to 1.70 V, the voltage dropped, and the voltage of the entire battery group was reduced. At the same time, the discharge capacity was restored to the initial state. Therefore, it can be said that such a means is effective in eliminating voltage variations and recovering capacitance.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described. (Example 1) Twelve positive electrode plates having a size of 70 ^W x 165 ^L x 0.90 ^T mm which were sintered nickel hydroxide electrode plates,
The negative electrode plate is a sintered cadmium electrode plate of 70 ^W x 165 ^L x
13 sheets of 0.82 ^T mm, and the separator has a thickness of 0.1 mm.
Two 2 mm polyamide non-woven fabrics, electrolyte having specific gravity of 1.2
5 (20 ° C.) aqueous KOH solution was used, and a sealed 35 Ah solution having a
Cells and 8 cells were fabricated. The five cells having a liquid volume of 105 ml were prepared by intentionally mixing fragments of the positive electrode plate between the separator and the positive electrode plate. The adjustment of the amount of the electrolyte was performed by charging the battery at 0.1 C for 16 hours to make the battery charged, and then discharging the excess solution.

The capacity when these batteries were discharged at 1 C was 107% ± 2% of the nominal capacity ratio, with little variation. 80 cells of these batteries are connected in series,
After charging for 5 hours, the capacity was confirmed to be 107% of the nominal capacity. Next, in order to perform an accelerated test,
Float charging was performed for 1.5 years at an average set voltage of 1.36 V per unit battery connected in series at 45 ° C. Initially, the range of battery voltage variation is 1.
Although it was almost 35 to 1.37 V, it became 1.15 to 1.42 V after 1.5 years.

The discharge capacity of this battery was examined for each unit battery. FIG. 1 shows a relationship between a typical float voltage value and a nominal capacity ratio of a discharge capacity. It should be noted that those having a battery voltage of 1.40 V or more had a large liquid volume of 140 ml, and most of them had limited gas absorption. From FIG. 1, it can be seen that even if such a voltage fluctuation occurs, the range of 1.23 to 1.48 V is good, and there is almost no variation in capacitance.

On the other hand, the battery showing a low voltage of 1.15 V was one cell in which fine fragments of the positive electrode plate were mixed. The capacity was only 60% of the nominal capacity. When the battery was disassembled and the state of the electrode plate was examined, a minute short-circuit occurred in a portion of the positive electrode plate where fine fragments were mixed. Therefore, 1.
The reason why the capacity of the battery showing a low voltage of 15 V was small was that energy was consumed by the occurrence of this minute short circuit.

Next, as a means for eliminating the variation of the float voltage, a battery having a float voltage exceeding 1.40 V is charged at a constant voltage for 3 hours while changing various set voltages, and then the float charge is performed. Where
The timing at which the voltage fluctuates and rises differs depending on the value of the set voltage. Table 1 shows the set voltage and the time when the voltage fluctuates. That is, the voltage at a constant voltage of 1.48 V or higher was 1.36 V in three years, whereas the voltage at a set voltage of 1.45 V was 1.41 V.
Five years later, the constant voltage of 1.48 V with the valve opened was 1.36 V.

From this, the recovery charge required 1.48 V or more, and the voltage was stable especially when the valve was opened. The reason is that when the set voltage becomes 1.48 V or more, the positive electrode reaches a potential required to recover a potential decrease corresponding to the amount of electricity whose capacity has been reduced by self-discharge. When the valve is opened, oxygen in the air is sucked in, and the metal cadmium on the negative electrode reacts with the water in the electrolytic solution to form Cd.
It is probable that (OH) ₂ was formed, resulting in an increase in the amount of the reserve Cd (OH) ₂ .

Next, the same battery as in Example 1 was float-charged at a set voltage of 1.36 V and 45 ° C. for 1.5 years. The charging voltage had little variation at the beginning, but the range of the voltage variation after 1.5 years was 1.26.
４７1.47V.

FIG. 2 shows the relationship between the nominal capacity ratio when these batteries are discharged at 1 C and typical float voltage values.
It is shown in (C). These battery packs are used as battery packs,
Charge to 1.48V / cell at 2C, then 1.48V
/ Cell for 3 hours at a constant voltage and then discharged at 1C, the discharge capacity was 106-107% of the nominal capacity ratio (FIG. 2).
D) and had recovered to the initial value.

Subsequently, when float charging was performed for three years, the range of voltage variation was 1.35.
It was as small as 1.37V. In this way, capacity recovery and elimination of voltage fluctuations can be achieved without changing the assembled battery.

It should be noted that when the set voltage is increased, the same effect is obtained. However, when the voltage exceeds 1.7 V, particularly 1.8 V / cell, gassing occurs and a problem occurs that liquid leaks from the valve. Voltage is 1.48-1.70V
Met.

[0020]

[Table 1]

Note) The test marked * was performed with the valve opened during constant voltage charging for 3 hours.

Next, in order to clarify the cause of the fluctuation of the charging voltage and the relationship between the magnitude of the fluctuation value and the battery capacity, consideration was made from the elementary reaction between the positive electrode and the negative electrode during charging of the battery.
First, although there are various combinations of reactions in batteries, the difference in potential may be attributed to the difference between the oxygen gas absorption reaction and the hydrogen generation reaction of the negative electrode. The electrode potential of the oxygen evolution reaction can be expressed by equation (1).

[0023] _{E = E 02 -b O2 logI 0} , O2 + b O2 logI (1) E O2: equilibrium potential of oxygen, b _O2: Tafel coefficient of oxygen generating I _{0, O2:} exchange of oxygen evolution current density hydrogen generation The electrode potential for the reaction can be expressed by equation (2).

E = E _H2 + b _H2 log I _{0, H 2} −b _H2 log I (2) E _H2 : Equilibrium potential of hydrogen, b _H2 : Tafel coefficient of hydrogen generation I _{0, H2} : Exchange current density of hydrogen generation Oxygen gas Assuming that the electrode potential of the absorption reaction is governed by the charging potential of the cadmium electrode of the negative electrode, the charging electrode potential of the negative electrode can be expressed by equation (3), and the gas absorption reaction occurs at that potential.

E = E _Cd + b _Cd logI _{0, Cd} −b _Cd logI (3) E _Cd : Equilibrium potential of cadmium, b _Cd : Tafel coefficient of cadmium pole I _{0, Cd} : Exchange current density of cadmium pole In this case, since the negative electrode has a reserve Cd (OH) ₂ , the battery voltage Vs is given by the following equation (1)-(3).

[0026] _{Vs = E O2 - E Cd -} (b O2 logI 0, O2 - b
_Cd logI _{0, Cd} ) + (b _O2 + b _Cd ) During use, reserve Cd (OH) ₂ disappears, and when a battery generating hydrogen gas is generated, the battery voltage Vv is expressed by the following equation (1). Equation (2) is obtained.

[0027] _{Vv = E O2 - E H2 -} (b O2 logI 0,02 + b H2
_{logI 0, H2) + (b} O2 + b H2) logI such batteries Consider the case arising _one n of the total number n. The current through the set voltage Vset, initially I _1, n
When the current _{when one} battery has occurred and I _2, Vset
Can be expressed by equations (4) and (5). Where the internal resistance r of the battery
Is constant. _{Vset = I 1 · n · r} + n · {E O2 - E Cd - (b O2 logI 0,02 - b Cd logI 0, Cd) + (b O2 + b Cd) logI 1} (4) Vset = I _{2 · n · r + (n-} n 1) · {E O2 - E Cd - (b O2 logI 0,02 - b Cd logI 0, Cd) + (b O2 + b Cd) logI 2} + n 1 { _{E O2 - E H2 - (b} O2 logI 0,02 + b H2 logI 0, H2) + (b O2 + b H2) logI 2} (5) (4) equation, the equation (5) from equation (6) To establish. {LogI ₂ = K / {(b _O2 + b _Cd ) + n ₁ / n (b _H2 −b _Cd )} (6) K = r · (I ₁ −I ₂ ) + n ₁ / n (E _H2 − E _Cd −b _Cd logI _{0, Cd} + b _H2 logI _{0, H2} ) + (b _O2 + b _Cd ) logI ₁ Here, the term relating to the internal resistance of the battery, r · (I ₁ −I ₂ )
Is almost negligible and is set to 0, and the positive and negative electrode IV
Substituting these values obtained from the _{characteristics, b O2 = 0.051, b H2} = 0.055, b Cd = 0, I 0, H2 = 5 * 10 -5 logI 2 = (- 0.242 · n 1 / n + 0.051logI ₁ ) / (0.055 · n ₁ /n+0.051) (7) When the equation (7) is substituted into the equation (1), E = E _O2 −b _O2 logI _0,02 + b _O2 (−0.242 · n ₁ / n + 0.051logI ₁ ) / (0.055 · n ₁ /n+0.051) (8) Here, the numerical values of E _O2 = 0.302V, I _0,02 = 2 * 10 ^-5 are substituted, and E and n ₁ / FIG. 3 shows the relationship with n. Here is an important finding. That is, this electrode potential is the potential for generating oxygen at the positive electrode, and the positive electrode is considered to have a charge level corresponding to a potential equal to this potential.
Since the potential of the nickel hydroxide electrode, which is the positive electrode of the alkaline battery, differs depending on the depth of discharge, the depth of discharge can be determined from this electrode potential. However, there is no result of investigating the relationship between the open circuit potential of the positive electrode after use of the long-term float and the depth of discharge.

FIG. 4 (F) shows the result of an examination of a battery float-charged at 1.36 V at 45 ° C. for 1.5 years. FIG. 4 also shows the result immediately after the use of the float (G). From the figure, it can be seen that the open circuit potential of the positive electrode is extremely low when the float is used. Although the details of the process of shifting the potential are not clear, it is considered that nickel oxyhydroxide, which is a charge product, undergoes aging and its crystallinity increases.

As described above, the float voltage is 1.23 to
The capacity of the battery showing a voltage in the range of 1.48V was good during float use. The reason why the capacity is sufficient even when the float voltage is as low as 1.23 V is based on the fact that the positive electrode potential shifts to a low value during the float.

In FIG. 4, at the initial stage of the potential at which the capacity indicates 80% (corresponding to the discharge depth of 20%), the initial voltage is 0.370 V, that is, the terminal voltage is 1.291 V (0.370 V + negative electrode potential 0.
921 V) required, but 0.340 V in float
That is, the terminal voltage is (0.340V + 0.921V)
It turns out that it is 1.261V. This positive electrode potential varies depending on the content of cobalt hydroxide added to the active material, and decreases by 2 mV when the content increases by 1 mol.
Since the potential decreases as the temperature rises, the potential of the positive electrode may be practically considered to be about 0.31 V. Therefore, the lower limit of the voltage may be 1.231 V (0.31 V + 0.921 V).

When the float voltage is 1.48V, the capacity is not reduced because the positive electrode is sufficiently noble. However, when the voltage becomes 1.48 V or more, the battery generates heat due to the generation of hydrogen and oxygen, and the liquid decreases. Therefore, there is a danger of an increase in the internal resistance of the battery and the occurrence of a short circuit phenomenon due to the growth of cadmium dendrite. Increase. An inspection is required for that. That is, a battery showing 1.48 V or more is normal if it shifts to a process in which the float voltage decreases due to the decrease in the liquid and the improvement in gas absorption performance, but the battery voltage continues to increase or the voltage becomes 1.
If the voltage drops to 23 V and shifts to a minute short circuit, it can be recognized as an abnormality.

The value of 1.23 V corresponds to the theoretical decomposition voltage of water calculated from free energy, and the value of 1.48 V matches the theoretical decomposition voltage calculated from enthalpy change.

As described above, it has been found that even a low voltage, which has been conventionally recognized as abnormal, is good, and the inspection method of the group battery is as follows. It has been found that it is appropriate to use a maintenance and inspection method for recognizing a battery having a value outside the range of -1.48 V as abnormal.

Here, a further important conclusion is drawn. Generally, like a lead battery, an alkaline storage battery is subjected to recovery charging about once every several months. From this experiment and detailed considerations, it was found that even if the float voltage fluctuated, if the value was in the range of 1.23 to 1.48 V, no significant capacity reduction occurred. On the other hand, in the case of a lead battery, the float voltage fluctuates and its electromotive force is 2.03.
When the voltage falls below V, not only does the capacity significantly decrease due to self-discharge, but also during use, the capacity varies due to the stratification of the electrolytic solution, so that recovery charging is essential. Therefore, it can be said that a sealed alkaline battery does not require frequent equal charging as in the case of a lead battery.

[0035]

As described above, the effect of the present invention is obtained when a sealed battery assembly is used, in which some of the batteries whose gas absorption performance is difficult due to the amount of liquid and the thickness of the separator are mixed. Optimizing conventional maintenance and inspection methods and capacity recovery methods that have recognized abnormal batteries as abnormal due to fluctuations in float voltage and that overcharged or overdischarged more than necessary and had a negative impact on service life This improves the efficiency of maintenance and inspection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a value of a float voltage and a capacitance;

FIG. 2 is a diagram showing the relationship between the discharge capacity and the value of the float voltage before and after the recovery charge according to the present invention is performed.

FIG. 3 is a diagram showing a relationship between E and n ₁ / n.

FIG. 4 is a diagram showing a relationship between an open circuit potential of a positive electrode plate used in a float and a depth of discharge.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-109273 (JP, A) JP-A-58-134778 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 10/42-10/48 H02J 7/00

Claims (2)

(57) [Claims] Claims 1. A plurality of nickel-cadmium unit batteries
Constant value for nickel-cadmium batteries connected in series
Of each unit cell measured with the floating charge voltage of
Float voltage, float charging, characterized in that recognizes an abnormal unit cells indicating a value outside the range of 1.23~1.48V
Maintenance and inspection method for nickel-cadmium battery packs. By 2. A maintenance method according to claim 1, single float voltage has a value outside the range of 1.23~1.48V
A method for recovering the capacity of a nickel-cadmium battery pack for floating charging, comprising performing constant-voltage charging at an average set voltage of 1.48 to 1.70 V after recognizing and replacing an abnormal battery .