JP3456217B2 - Nickel-based secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention examines a battery configuration necessary for performing rapid charging of 1 C or more. The present invention provides a nickel-based secondary battery such as a highly reliable nickel-cadmium battery for ultra-rapid charging. As a result, the simplicity of a portable device or the like is further improved, and the expansion of applications can be expected. [0002] In recent years, with the development of electronic equipment, the appearance of new high-performance secondary batteries is expected. At present, nickel-cadmium batteries, nickel-zinc batteries, nickel-based batteries such as nickel-hydride batteries, and lead batteries are used as power supplies for electronic devices. These secondary batteries are required to have an improved rapid charging performance as well as a higher capacity. Among them, a nickel-based secondary battery uses a nickel hydroxide electrode as a positive electrode plate. The electrode reaction of the positive electrode plate is diffusion of H ⁺ ions, and does not have a dissolution / precipitation mechanism unlike the electrode reaction of the positive electrode of a lead battery. Therefore, it is used as a long-life high-performance electrode. When this electrode is charged, nickel hydroxide becomes nickel oxyhydroxide (NiOOH). Nickel oxyhydroxide has β-form and γ-form.When γ-NiOOH is generated during charging, volume expansion of 31% occurs, and when it becomes α-NiOOH, which is the discharge product of γ-NiOOH, expansion of 59% Becomes In recent years, in order to increase the energy density of a battery, when the active material is filled in a large amount, the residual porosity of the electrode decreases, and when the active material expands, the electrode becomes thicker. A so-called "dry-up" phenomenon in which the internal resistance increases by moving to the electrode may occur, or the electrode may collapse and a short circuit may occur. Furthermore, in applications where the charging time is required to be shortened, that is, in the case of performing quick charging, since γ-NiOOH is particularly easily generated, measures have been required. Conventionally, a method of adding cobalt hydroxide to an active material for the purpose of improving the utilization rate of the nickel hydroxide active material (for example, Electrochemistry 31, 47 (1936), Patent Publication 50-1)
32441) Also, after filling the nickel substrate with the active material, Co (O
H) Method for forming ₂ (for example, Patent Publication Showa 57-005018)
A method of forming a binary system of Cd (OH) ₂ -Ni (OH) ₂ (for example, Japanese Patent Publication No. 2-39063, US Pat.
-36796)-A method of forming a ternary system of Ni (OH) ₂ -Co (OH) ₂ -Cd (OH) ₂ (for example, Patent Publication Hei 3-20860, US Pat.
76)) has been proposed. Furthermore, a method has been proposed in which metallic cobalt is contained in a sintered nickel substrate, which is a holder for an active material (for example, Japanese Patent Publication No. 54-1010). However, it was insufficient from the viewpoint of suppressing the production of γ-NiOOH. Further, in order to develop a sealed battery for quick charging, it is necessary to improve gas absorption performance.
Achieving the above gas absorption performance was extremely difficult in principle and also due to deterioration of the battery due to heat generated by gas absorption. In addition, rapid charging and discharging
Temperature rise and increase in overvoltage cause migration of cadmium hydroxide, internal short circuit due to cadmium dendrite growth, or abnormal heat generation during charging due to a gas absorption reaction. There is a proposal to use a microporous separator as a means for suppressing internal short-circuiting of the battery and extending the life (for example, Japanese Patent Laid-Open Publication No. Hei 1-264167). Further optimization is needed. [0007] For example, nickel cadmium batteries are required to have a high energy density and an improved fast charging performance. However, the nickel hydroxide positive electrode plate used for high energy density batteries and quick charge batteries swells and becomes thicker as the charge / discharge cycle progresses, and the electrolyte of the separator moves to the electrodes to increase the internal resistance. There is a drawback that a so-called dry-up phenomenon occurs and battery life is shortened. In particular, when a nickel substrate serving as an active material holder has a porosity of 80% or more, particularly 85% or more, there is a problem that the swelling of the positive electrode plate becomes large because the strength of the substrate is low. Further, when a rapid charge of 1 C or more is performed, rapid heat generation due to gas absorption deteriorates the material of the separator to increase the internal resistance or increase the solubility of cadmium in the electrolyte. There is a problem that an internal short circuit easily occurs due to migration of cadmium. Further, when the degree of the short circuit is small, a new problem that the battery becomes high temperature due to Joule heat when rapid charging, that is, when a large current flows, occurs, and a countermeasure is desired. According to the present invention, there is provided a battery comprising a positive electrode plate using a nickel substrate containing metallic cobalt and an electrolytic solution of an alkaline aqueous solution having a molar concentration of 6.5 to 14M .
It is a nickel-based secondary battery . Particularly, by using a negative electrode plate of a plastic bonded electrode and a microporous film separator, a highly reliable nickel-based secondary battery such as a sealed nickel-cadmium battery capable of quick charging can be obtained. In particular, the porosity of the nickel substrate is 85-98
% Of the positive electrode plate having a high energy density, the life of the positive electrode plate having a high energy density can be extended. In addition, metallic nickel is used as the active material.
And Molar Concentration of Negative Plastic Bonded Electrode
With an alkaline aqueous electrolyte solution with a degree of more than 7M and 14M or less.
Nickel-cadmium for quick charging of 1C or more
Battery. In order to suppress the change of the active material of the nickel hydroxide positive electrode plate into γ-NiOOH by charging and to improve the utilization factor, cobalt hydroxide is added to the active material to reduce the nickel hydroxide. Means for forming a solid solution or adding cadmium hydroxide to form a solid solution in the same manner are known as universal techniques. According to the present invention, a nickel hydroxide positive electrode plate used in a high energy density battery or a battery for rapid charging swells and becomes thicker as the charge / discharge cycle proceeds, and the electrolyte of the separator moves to the electrode to increase the internal resistance. In addition to the conventionally known phenomenon that γ-NiOOH is generated as a charge product of the nickel hydroxide active material, the cause of the drawback that the dry-up phenomenon occurs and the battery life is shortened is increased, The nickel porous material used as the active material support is oxidized by charging and discharging to become nickel hydroxide, which is γ-NiO
It is based on the finding that the major cause is that the positive electrode plate swells and becomes thicker to become OH, whereby the electrolyte of the separator moves to the electrode plate. As a countermeasure, the present invention provides a means for containing nickel in the nickel of the active material holder to suppress nickel hydroxide generated by oxidation of the substrate from being further oxidized to γ-NiOOH. . In addition, the nickel porous body is oxidized by charge and discharge to become nickel hydroxide, and an electrolytic solution that compensates in advance for excess potassium hydroxide necessary for it to become γ-NiOOH, that is, a high-concentration electrolytic solution is used. By doing so, it is possible to suppress an increase in internal resistance with the passage of cycles. Further, when a high-concentration electrolytic solution is used, the solubility of cadmium is increased, and hydrogen is generated from the negative electrode due to an abnormally high initial charging voltage that occurs in the case of ultra-rapid charging, and consequently from the positive electrode. Generation of oxygen gas can be suppressed. In addition, the battery for ultra-rapid charging has a new problem that the current density is concentrated at the time of charging, so that a minute short-circuit is likely to occur. Therefore, there is a new problem that a large current flows and the battery generates heat. There is a need. As a countermeasure, if a microporous film separator, particularly one having a porosity of 30% or more, is used, the occurrence of micro short circuit can be suppressed without impairing gas absorption performance, and abnormal heat generation of the battery does not occur. Further, when the negative electrode of the plastic bonded electrode is used, a change in the final voltage at the time of charging is larger than when a sintered cadmium negative electrode plate is used. A charging method for limiting a current in an overcharge region where oxygen gas is generated, that is, a constant voltage method or a method of charging with a small current can be applied. By applying this method, overcharging is not performed more than necessary, so that the above-mentioned various problems associated with rapid charging can be reduced. Hereinafter, a preferred embodiment of the present invention will be described. [Example 1] Carbonyl nickel powder and 2 wt% metal cobalt powder are mixed, and then kneaded with a 0.1 wt% aqueous methylcellulose solution to form a slurry. This slurry was applied to a nickel-plated 0.1 mm perforated plate, dried with a heater, and then sintered at 950 ° C. in a reducing atmosphere of hydrogen to produce a sintered nickel substrate having a porosity of 87%. Next,
5M containing 2mol% of cobalt nitrate on this sintered nickel substrate
Of nickel nitrate aqueous solution at 80 ° C
M sodium hydroxide aqueous solution. After that, the operation of washing with hot water and drying was performed eight times. After that, it is washed with hot water and dried, the theoretical capacity is 350 mAh, and the dimensions are 0.8 × 14 ×
A 52 (mm) positive electrode plate was manufactured. In Example 1, the content of metallic cobalt powder was reduced to 0,
Two positive electrode plates of 1,3,5 wt% were changed and three sintered cadmium negative electrode plates of conventionally known theoretical capacity of 500 mAh and dimensions of 0.7 × 15 × 52 (mm) were produced. Next, this positive electrode plate was
After wrapping with a non-woven polyamide nonwoven fabric separator, heat sealing was performed. Subsequently, a positive electrode plate and a negative electrode plate were alternately stacked to form an electrode plate group. A prismatic nickel-cadmium battery using a nickel-plated iron battery container having a nominal capacity of 650 mAh was manufactured using the electrode group and 2.5 ml of an aqueous solution of potassium hydroxide having a different concentration of 5 to 14 M as an electrolytic solution. External dimensions are 67 x 1
A 6.5 × 8 (mm), and with a safety valve operating at 0.5 kg / cm ² in the battery. Metal cobalt content of 0,1,3,5w
A, B, C, D are used for the sign of the battery of t% After charging these batteries with a large current of 25 ° C. and 5 C until the voltage reaches 1.65 V, a set voltage lower than the detection voltage is set to 1.50 V (the total time is 15 minutes). Then, a cycle test of discharging to 1.0 V at a current of 0.5 C was performed. FIG. 1 shows the change in the retention rate of the discharge capacity with the passage of the cycle. From the figure, the content of cobalt contained in the nickel substrate was 0 w
In the case of t% (A), the discharge capacity decreases when the number of charge / discharge cycles exceeds 400, but 1wt% (B), 3wt% (C) and 5wt%
It can be seen that the capacity of (D) is stable and good. FIG. 2 shows the relationship between the internal resistance at the 500th cycle of these batteries and the concentration of the used electrolyte. It can be seen that the values of the internal resistance of the metallic cobalt content of 1 wt% (B), 3 wt% (C) and 5 wt% (D) are lower than those of the cobalt content of 0 wt% (A). . It can also be seen that the value of the internal resistance is greatly affected by the concentration of the electrolytic solution, and decreases as the concentration increases. Also, when the value of the internal resistance sharply increased, the discharge capacity of the battery decreased, and the charge voltage increased and the discharge voltage decreased. Battery A having a metal cobalt content of 0% was disassembled, and the elements of the battery were examined. As a result, the electrolyte in the separator was depleted, and the positive electrode plate was thick and swollen. Since the weight of the battery hardly decreased, it is considered that the case where the content of metallic cobalt is 0% means that the nickel substrate is oxidized and γ-NiOOH is generated. The characteristic formula of this γ-NiOOH is K _0.33 NiO ₂ · 0.67H ₂ O, which means that the electrolyte is absorbed by the positive electrode. On the other hand, when a battery using a nickel substrate containing metallic cobalt was disassembled and examined, the swelling of the positive electrode plate was smaller than that of battery A in which the content of metallic cobalt was 0%, and a separator was used. Was wet with electrolyte. This means that the positive electrode plate using a nickel substrate containing metallic cobalt is less likely to become γ-NiOOH during charging because nickel contained in the nickel substrate is oxidized and nickel hydroxide contains cobalt. It is considered that swelling is reduced. Generally, when the electrode swells, the electrolyte of the separator moves to the electrode, and the value of the internal resistance of the battery increases. It has been empirically found that when the value of the internal resistance is increased to exceed 70 mΩ, the discharge capacity is significantly reduced. In order to set the value of the internal resistance to 70 mΩ or less, it can be seen from FIG. 2 that the value of the metal cobalt content of the nickel substrate is 8.5 M for 1 wt% (B) and 7.6 for 3 wt% (C). M, 5
It can be seen that in the case of wt% (D), an electrolyte concentration of 6.5 M or more is required. That is, the required OH ^- ion concentration of the electrolytic solution is determined by the content of metallic cobalt contained in the substrate. When the content of metallic cobalt is 3 wt% or less, an alkaline aqueous electrolyte having an OH ^- ion concentration of 6.5 to 14M is preferable. As an electrolytic solution, a mixed aqueous solution of potassium hydroxide and sodium hydroxide was examined.
It was found that the performance was largely influenced by the total concentration of the used OH ^- ions. As described above, when a nickel substrate containing metallic cobalt is used and a nickel hydroxide positive electrode plate and a high concentration electrolytic solution are used, the battery can be charged with an extremely large current of 10 C. After detecting a constant voltage, it is necessary to charge by a constant voltage method or a constant current method under conditions that allow gas absorption. A general nickel-cadmium battery charging method employs a method of charging at a constant current and controlling charging by detecting a temperature rise or a voltage drop due to a gas absorption reaction (−ΔV method). With this method, rapid charging over 1C was difficult. For example,
When performing 2C charging, the gas absorption performance corresponding to the current is difficult, and the unabsorbed oxygen gas is dissipated from the safety valve set at 6 to 15 kg / cm ² , causing the electrolyte to decrease and the internal resistance to increase. As a result, charging becomes impossible, and the discharge capacity is significantly reduced. In addition, heat generation due to gas absorption is large, and performance is also deteriorated due to an increase in carbonate groups of the electrolytic solution due to deterioration of the separator. A method for detecting such a voltage and controlling charging is disclosed in Japanese Patent Laid-Open Publication No. Hei 309265, US Pat. No. 5,077,
As in the case of a lead-acid battery, a method of detecting the potential change of the negative electrode and controlling the charging is desirable, as proposed in 151 etc.
For such a function, it is desirable to apply a plastic bonded negative electrode plate having a larger hydrogen overvoltage than a negative electrode plate using a sintered nickel substrate having a small hydrogen overvoltage as described above. In this case, the reserve in the negative electrode active material is Cd (O
When the amount of H) ₂ is reduced, the potential change based on the polarization of the negative electrode appears significantly. Next, an embodiment in which a plastic bonded negative electrode plate is applied will be described in detail. 100 parts of cadmium hydroxide powder, 20 parts of metal cadmium powder, and 0.1 part of short polypropylene fiber having a length of 1 mm are mixed with ethylene glycol containing 0.1% by weight of polyvinyl alcohol to form a paste. The paste is applied to a 0.5 μm nickel-plated perforated steel sheet having a thickness of 0.1 mm, dried at 150 ° C., and then pressed to obtain a theoretical capacity of 500 mAh and a size of 0.7 × 1.
A 5 × 52 (mm) plastic bonded cadmium negative electrode plate was manufactured. Next, nickel contained in the active material holder
0,1Wt% and changing porosity of the content of the metallic cobalt powder to
After mixing 100 parts of spherical nickel hydroxide powder having a diameter of 5 μm containing 2 wt% of cobalt hydroxide and 10 parts of metallic cobalt in a 90% foamed nickel substrate, 0.1 wt% of methylcellulose is mixed.
Then, 50 ml of an aqueous solution is added, and the mixture is mixed and pasted. Thereafter, it is dried with hot air at 100 ° C., immersed in a 40 wt% dispersion solution of polytetrafluoroethylene powder, and dried again at the same temperature. afterwards,
In a 5M aqueous sodium hydroxide solution, use a smooth nickel plate as the counter electrode, charge at 0.1C (based on the theoretical capacity when the charge and discharge reaction is a one-electron reaction) for 15 hours, and then at 0C (Hg /
HgO). The electrode plate is further dried with hot air at 100 ° C., and then pressed under pressure to obtain a theoretical capacity of 350 m.
Ah, a positive electrode plate having dimensions of 0.8 × 14 × 52 (mm) was manufactured. The two positive plates were wrapped with a 0.12 mm polyamide nonwoven fabric separator, and then heat sealed. Subsequently, a positive electrode plate and a negative electrode plate were alternately stacked to form an electrode plate group. A square nickel-cadmium battery using a nickel-plated iron battery case with a nominal capacity of 650 mAh was manufactured using the electrode group and 2.5 ml of a potassium hydroxide aqueous solution having different concentrations of 5 to 14 M as an electrolyte. The external dimensions are 67 × 16.5 × 8 (mm), and the battery is equipped with a safety valve that operates at 0.5 kg / cm ² . The symbols of the batteries having a metal cobalt content of 0.1 wt% are E and F, respectively. After charging these batteries with an extremely large current of 25 ° C. and 10 C until the voltage reaches 1.65 V, a constant voltage of 1.65 V is applied without changing the set voltage.
(Total time was 10 minutes), then 1.0 at 0.5C current
A cycle test of discharging to v was performed. FIG. 3 shows the relationship between the internal resistance value at the 300th cycle of these batteries and the electrolyte concentration. Also in the case of a battery using a plastic bonded cadmium negative electrode plate, the content of metallic cobalt is 1 wt%.
The value of the internal resistance of (F) is that the cobalt content is 0 wt%.
It turns out that it is lower than that of (E). It can also be seen that the value of the internal resistance is greatly affected by the concentration of the electrolytic solution, and decreases as the concentration increases. In particular, when a plastic-bonded cadmium negative electrode plate is used, the battery's internal resistance can be reduced to a practical number of charge / discharge cycles up to 300 times when the concentration of the electrolyte exceeds 8.5 M, even at an ultra-rapid charge of 10 C.
It can be suppressed to 70 mΩ or less. As described above, good cycle characteristics can be obtained by using a plastic bonded cadmium negative electrode plate because, as described above, the hydrogen overvoltage of this negative electrode plate is much larger than that of a sintered nickel substrate, so that a constant voltage is obtained. This is considered to be due to the fact that the local generation of hydrogen is suppressed in the region and the degree of depletion of the electrolyte is small. Further, the increase in internal resistance is suppressed when the concentration of the electrolytic solution is more than 8.5M, when nickel nickel substrate as described above to produce nickel hydroxide undergo oxidation, OH ^- ions In addition to being based on consumption, the use of high-concentration electrolytes increases the solubility of cadmium, which results in the formation of hydrogen from the negative electrode due to an abnormally high initial charging voltage that occurs during ultra-rapid charging, and Accordingly, there is a point that generation of oxygen gas from the positive electrode can be suppressed. As an example, FIG. 4 shows the 5C and 10C charging characteristics of batteries E, that is, the batteries G and H when the electrolyte concentration is 7 M and 10 M, respectively, for a positive electrode plate having a metal cobalt content of 0 wt%. When a battery G using an electrolyte having a commonly used concentration is charged at 5C or 10C, the voltage reaches 1.6V or more from the beginning of charging, then gradually decreases and then increases again. Appears. When the gas composition inside the battery was analyzed by gas chromatography, generation of small amounts of hydrogen gas and oxygen gas was detected in the initial stage of charging. The concentration at which such a phenomenon was observed was 8.5 M or less. Even when the amount of the electrolytic solution was increased to 3 ml, a slight decrease in polarization was observed, but the same phenomenon was observed. On the other hand, at 10 M, no generation of hydrogen gas or oxygen gas was observed even when charged at 10 C. Therefore, when the concentration of the electrolyte is low, the amount of cadmium ions dissolved in the electrolyte decreases, so that the charging reaction of the negative electrode plate, which is a dissolution / precipitation reaction, hardly progresses. It is considered that the polarization also increases at the same time, and oxygen gas is generated from the positive electrode. Then, when hydrogen gas is generated from the negative electrode, the gas absorption capacity on the negative electrode decreases, so the generated oxygen gas escapes through the valve, so that the electrolyte decreases, and the electrolyte contained in the separator is reduced. It is considered that the exhaustion occurs and the internal resistance increases. When the concentration of the electrolytic solution is high, the solubility of cadmium ions in the electrolytic solution is increased, so that the charging reaction of the negative electrode plate, which is a dissolution / precipitation reaction, is facilitated, and the polarization of the negative electrode is reduced. It is conceivable that the generation of oxygen gas from the positive electrode was reduced, and the generation of oxygen gas from the positive electrode was also suppressed. In the example, the porosity of the nickel substrate was 87%.
And a substrate as high as 90% was used, but it was found that these tendencies were remarkable when the porosity was above 80%, especially above 85%. As the life mode of the battery, there is an increase in internal resistance due to depletion of the electrolyte and a short circuit. In the short-circuit mode, when quick charging is performed in the case where a micro short-circuit occurs, the current is large, so a new problem that the battery becomes high temperature due to Joule heat occurs,
It is necessary to suppress the occurrence of a micro short circuit. In particular, when the constant voltage method is applied in the charge control method, the maximum current of the charger flows at the constant voltage. In order to suppress such a minute short circuit, the use of a microporous film separator as a separator has a remarkable effect. A battery with the same configuration as Battery F,
2.5 ml of 10 M potassium hydroxide aqueous solution as electrolyte and 60% porosity polypropylene as separator
Battery J ', in which a 20 μm microporous film separator was applied in combination with a nonwoven fabric, and battery J, in which a microporous film separator was not applied, were manufactured in 10 cells each, and the voltage was increased to 1.65 V at 25 ° C and 10 C current. After the battery was charged until it reached, a cycle test was performed in which a constant voltage of 1.65 V was further applied (total time was 10 minutes), and then the battery was discharged to 1.0 V with a current of 0.5 C. When the number of cycles exceeds 500, a phenomenon in which the current once attenuates in the constant voltage region and then increases in three cells of the battery without the microporous film separator, and the battery temperature rises to around 100 ° C. Came to reach. When the battery was disassembled and inspected, the amount of electrolyte solution in the separator was reduced, and migration of cadmium hydroxide occurred, and a slight short circuit was observed. On the other hand, the battery provided with the microporous film separator did not have such a rise in temperature, and did not cause any abnormal phenomenon even after reaching 1,000 cycles. FIG. 5 shows typical changes in voltage, current, and temperature during charging. As described above, the battery provided with the microporous film separator does not generate abnormal heat in the constant voltage region because the microporous film separator suppresses the occurrence of micro short circuit due to migration of cadmium hydroxide, It is considered that transmission of oxygen generated from the positive electrode is suppressed and abnormal heat generation due to gas absorption performance is restricted. As a function of the microporous film separator, it is necessary to suppress the occurrence of a micro short circuit due to the migration of cadmium hydroxide, and the pore size is set to be 0.1 μm.
It is sufficient that the porosity is 1 to 20 μm and the porosity is 20 to 90%. The present invention relates to a battery provided with a positive electrode plate using a nickel substrate containing metallic cobalt and an electrolytic solution of an alkaline aqueous solution having an OH ^- ion concentration of 6.5 to 14M. A nickel-based secondary battery that can be charged quickly, such as a sealed nickel-cadmium battery that can be charged. Particularly, the reliability is further improved by using a negative electrode plate of a plastic bonded electrode, a microporous film separator, or the like. In addition, since a high-energy-density positive electrode plate using a nickel substrate having a porosity of 85 to 98% can be extended, a high-energy-density rapid charging battery can be obtained. [0037]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram comparing the capacity retention of a sealed nickel-cadmium battery with a configuration according to the present invention and a conventional battery with the progress of charge / discharge cycles. FIG. 2 is a diagram comparing a change in internal resistance between a positive electrode plate using substrates having different cobalt contents and a battery using electrolyte solutions having different concentrations. FIG. 3 is a diagram comparing a change in internal resistance of a battery using a plastic-bonded cadmium negative electrode plate, using a metal-cobalt-containing substrate and a metal-cobalt-containing positive electrode plate, and further using an electrolyte having a different concentration. . FIG. 4 is a diagram showing 5C and 10C charging characteristics of batteries having different electrolyte concentrations on a positive electrode plate using a substrate containing no metallic cobalt. FIG. 5 is a diagram showing typical changes in voltage, current and temperature during charging when a battery having a microporous film separator and a battery having no microporous film separator exceed 500 cycles.

Claims (1)

(57) [Claim 1] A nickel secondary battery comprising a positive electrode plate using a nickel substrate containing metallic cobalt and an electrolytic solution of an alkaline aqueous solution having a molar concentration of 6.5 to 14M.