JPH04284369A - Nickel-metal hydride storage battery - Google Patents

Abstract

PURPOSE:To provide a nickel-metal hydride battery in which the rise of internal resistance, the lowering of discharge capacity, and the reduction of a charge/ discharge cycle life are eliminated by preventing positive electrode expansion, following the progress of a charge/ discharge cycle, without adding cadmium to a positive electrode. CONSTITUTION:An alkaline electrolyte, containing zinc of 0.1M or more and saturated concentration or below, is used in a nickel-metal hydride storage battery composed of a negative electrode having a main body of a hydrogen storage alloy, a positive electrode having a main active material of nickel hydroxide, and an alkaline electrolyte.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel/metal hydride storage battery using a hydrogen storage alloy as a negative electrode, nickel hydroxide as the main active material of a positive electrode, and an aqueous alkaline solution as an electrolyte.

0002

BACKGROUND OF THE INVENTION Hydrogen storage alloys are used for hydrogen storage electrodes, which are negative electrodes of nickel metal hydride batteries. This hydrogen storage alloy has a charge/discharge cycle when used in an alkaline storage battery by replacing component elements such as AB5 type intermetallic compound LaNi5 and AB2 type Laves phase intermetallic compound ZrNi2 with various other metal elements. It has improved various characteristics such as life characteristics, equilibrium hydrogen pressure, and amount of hydrogen storage and release.

[0003]The positive electrode of this battery uses a sintered type or foamed metal type nickel hydroxide electrode similar to those used in conventional nickel-cadmium batteries.

[0004] The electrolyte of this battery is an alkaline aqueous solution mainly containing potassium hydroxide, sodium hydroxide, or the like.

A hydrogen storage electrode operates at a potential comparable to that of a cadmium hydroxide electrode, and has a discharge capacity per volume that is significantly larger than that of a cadmium hydroxide electrode. Therefore, in a nickel metal hydride battery,
By reducing the volume of the negative plate and increasing the volume of the positive plate while keeping the capacity ratio between the positive and negative electrodes at the same level as nickel-cadmium batteries, the operating voltage of the battery is almost the same as that of nickel-cadmium batteries. Moreover, a high capacity battery with a discharge capacity about 1.5 times that of a nickel-cadmium battery can be obtained.

[0006] In such high-capacity nickel metal hydride batteries, the packing density of the active material in the positive electrode plate is increased, so that the phenomenon of swelling of the positive electrode active material becomes noticeable as the charge/discharge cycle progresses. , the alkaline electrolyte held in the separator is absorbed into the swollen pores of the positive electrode as charging and discharging progresses, and the amount of liquid in the separator tends to decrease significantly. When this phenomenon occurs, the internal resistance of the battery increases significantly, and when discharging at a relatively large current of about an hourly rate, the polarization of the battery increases, reducing the discharge capacity and shortening the charge/discharge cycle life. An inconvenience occurred in that it became shorter.

The cause of this phenomenon is thought to be as follows.

That is, there are two types of charged products of nickel hydroxide: a β phase with a small interlayer distance and a γ phase with a large interlayer distance, both of which have a layered crystal structure. When the nickel hydroxide electrode is charged with a large current or the amount of overcharged electricity is increased, the amount of γ phase produced increases and the nickel hydroxide electrode swells. Therefore, when the packing density of the positive electrode active material in the positive electrode plate is increased, the volume of the pores in the positive electrode plate becomes smaller, the contact between the electrolyte and the positive electrode active material becomes uneven, and the charging current is locally reduced. If the size of the positive electrode active material increases and the formation of γ phase is promoted, or even if a small amount of γ phase is formed, it becomes difficult for the pores in the positive electrode plate to absorb the increased volume of the positive electrode active material, and the positive electrode plate The swelling becomes noticeable.

[0009] Therefore, in conventional nickel metal hydride storage batteries and nickel cadmium storage batteries, in order to prevent such a phenomenon, it is known that cadmium hydroxide is added to the nickel hydroxide of the positive electrode.

[0010] That is, when cadmium hydroxide is co-precipitated with nickel hydroxide or added as a precipitate on the surface of nickel hydroxide, the formation of γ phase is suppressed during charging, and therefore the swelling of nickel hydroxide is suppressed. This has the effect of lengthening the charge/discharge cycle life of the nickel hydroxide electrode.

[0011] However, due to concerns about the impact that cadmium contained in discarded batteries would have on the global environment,
A storage battery that does not contain cadmium has become desirable. Therefore, it has been desired that a nickel metal hydride storage battery that does not use cadmium as a negative electrode active material also does not use cadmium as a positive electrode.

[0012] Furthermore, if the nickel/metal hydride storage battery is an open type (vent type) or semi-closed type, charging of the negative electrode is completed in the overcharge region from the end of charging.
Negative polarization is negative. In nickel/metal hydride storage batteries with cadmium added to the positive electrode plate, some of the cadmium added to the positive electrode dissolves in the electrolyte, and this cadmium forms resinous crystals of metallic cadmium when the battery is overcharged. It deposits on the negative electrode as a moss-like substance, causing an internal short circuit in the battery.

[0013] When the nickel metal hydride storage battery is a sealed type, during normal charging, the amount of uncharged hydrogen storage alloy is increased so that the charge of the negative electrode is not completed even when the charge of the positive electrode is completed. Configure the battery as follows. Therefore, in the case of this type of battery, if all the oxygen gas generated from the positive electrode during overcharging is reduced and absorbed at the negative electrode, charging of the negative electrode will stop, and the negative electrode will be polarized to the base and become metal cadmium. There is no risk of internal short circuit due to electrodeposition. However, this type of battery cannot absorb all of the generated oxygen gas because the oxygen gas absorption rate decreases at extremely low temperatures.

[0014] As described above, if the negative electrode cannot absorb all of the oxygen gas generated from the positive electrode during overcharging, the unabsorbed oxygen gas will be released to the outside of the battery system, and the uncharged hydrogen storage alloy at the negative electrode will , charged by an amount equivalent to its released oxygen gas. Therefore, if overcharging is continued at low temperatures where the oxygen gas absorption rate is low, the uncharged hydrogen storage alloy provided in excess at the negative electrode will be charged and consumed.

Therefore, even in the case of a sealed nickel/metal hydride storage battery, if cadmium is added to the positive electrode plate,
When overcharging of this battery is continued at low temperatures where the rate of oxygen gas absorption is low, charging of the negative electrode is completed and the negative electrode becomes negatively polarized, causing metal cadmium to be deposited and causing an internal short circuit.

In nickel-metal hydride storage batteries, the addition of cadmium to the positive electrode can thus prevent internal short circuits in the battery when overcharging under conditions where excess uncharged hydrogen storage alloy is not provided at the negative electrode. This is not desirable because it invites

[0017] Therefore, without adding cadmium to the positive electrode, it is possible to prevent the swelling of the positive electrode as the charge/discharge cycle progresses, thereby preventing an increase in internal resistance, a decrease in discharge capacity, and a decrease in charge/discharge cycle life. Metal hydride batteries were desired.

[0018]

[Means for solving the problems] Nickel according to the present invention
In order to solve the above-mentioned problems, metal hydride storage batteries
It consists of a negative electrode mainly made of a hydrogen storage alloy, a positive electrode mainly made of nickel hydroxide, and an alkaline electrolyte.
The alkaline electrolyte is characterized in that it contains zinc at a saturation concentration of 0.1M or more and a saturation concentration or less.

[0019]

[Effect] When the alkaline electrolyte contains zinc at a concentration of 0.1M or more and less than the saturation concentration, the charged product will Generation of γ phase is suppressed. Therefore, swelling of the nickel hydroxide positive electrode plate as the charge/discharge cycle progresses is effectively suppressed, and an increase in internal resistance is prevented.

[0020] Note that when the concentration of zinc in the alkaline electrolyte is 0,
．． If it is less than 1M, it is not preferable because the effect of suppressing the formation of γ phase in the nickel hydroxide electrode is small.

[0021]Also, when the concentration of an alkaline electrolyte such as KOH or NaOH is lower than about 1N, the saturation concentration of zinc becomes lower than 0.1M, but at such a low concentration, it is difficult to add zinc. Even when the nickel hydroxide is not charged, the amount of γ phase produced in the charged product of nickel hydroxide is originally small, so there is no need to add zinc to the electrolyte. however,
At such a low concentration, the resistance of the electrolyte increases, resulting in an increase in the internal resistance of the battery and a high freezing point of the electrolyte, making it impossible to use the battery at low temperatures. Therefore, in the case of a battery that does not reduce internal resistance and can be used even at low temperatures, it is necessary to use an alkaline electrolyte with a high concentration of 1M or more.
The effects of the present invention can be obtained by containing zinc at a saturation concentration or lower.

Furthermore, in the present invention, when overcharging is carried out with a large current at a low temperature, zinc contained in the alkaline electrolyte is not deposited on the negative electrode, so that no internal short circuit occurs. The reason is as follows.

That is, the standard electrode potential of zinc in an alkaline electrolyte is about 0.4 V less noble than that of cadmium, and the standard electrode potential of cadmium and hydrogen storage alloys used in alkaline batteries are extremely close. It is a value. Therefore, in order for zinc to be deposited, the hydrogen storage electrode must be negatively polarized by about 0.4V. However, hydrogen storage electrodes have extremely low hydrogen overvoltage, so even if a sealed battery is overcharged with a large current at low temperatures and the negative electrode is overcharged,
The potential does not polarize basely to the value at which metallic zinc is deposited. Therefore, if cadmium is not added to the positive electrode, neither metal cadmium nor metal zinc will be deposited on the negative electrode, so no internal short circuit will occur.

[0024] In the case of a cadmium electrode, since the hydrogen overvoltage of cadmium is extremely high, the cadmium electrode is polarized to be extremely negative at the end of charging. Therefore, if zinc is added to the alkaline electrolyte of a battery using a cadmium negative electrode, resinous crystals of metallic zinc will be deposited on the negatively polarized negative electrode plate at the end of charging, causing an internal short circuit in the battery. There is.

That is, in the present invention, the effect of containing zinc in the alkaline electrolyte does not hold in the case of a battery that uses a cadmium electrode as the negative electrode, but uses a hydrogen storage electrode as the negative electrode and hydroxide as the positive electrode. This is true in alkaline storage batteries that use nickel electrodes, and is unique to this type of storage battery.

[0026]

EXAMPLES The present invention will be explained by means of preferred examples. [Batteries A, B, C, D, E and F] (Embodiment of the present invention)
The positive electrode plate was manufactured as follows. That is, a known sintered nickel substrate having a porosity of about 82% was impregnated with nickel hydroxide by a known chemical impregnation method. Co-precipitated cobalt hydroxide is added to this nickel hydroxide in an amount of about 5% by weight based on the total of nickel hydroxide and cobalt hydroxide,
Thereafter, this positive electrode plate was further impregnated with about 2% by weight of cobalt hydroxide based on the weight of nickel hydroxide by a chemical impregnation method, and then cut. Co-precipitated cobalt hydroxide is mainly added to lower the charging potential of cobalt hydroxide to increase charging efficiency, and cobalt hydroxide impregnated alone mainly increases the active material utilization rate of the positive electrode plate. It was added to increase the height.

[0027] The dimensions of this positive electrode plate are approximately 0.8 in thickness.
mm, the width is about 3.5 cm, the length is about 10 cm, and the total amount of nickel hydroxide and cobalt hydroxide is about 5.1 cm.
When assembled into a battery, it contains approximately 1.4 g.
A discharge capacity of Ah is obtained.

The negative electrode plate was manufactured as follows. That is, the chemical formula is LmNi3.8 Co0.7 Al0.5
(Here, Lm represents lanthanum-rich misch metal with a La content of approximately 80% by weight) having the composition of , 2 parts by weight of furnace black as a conductive additive per 100 parts by weight of alloy powder,
A paste was created by dispersing it in an aqueous solution of polyvinyl alcohol, which is a thickener and binder, and this paste was applied to both sides of nickel-plated iron punching metal, dried, pressed, and cut to produce a negative electrode plate. . The dimensions of one negative electrode plate are approximately 0.5 mm thick and approximately 3.5 cm wide.
m, the length is about 15 cm, and contains about 10 g of hydrogen storage alloy, and this hydrogen storage electrode alone has a discharge capacity of about 3 Ah.

The separator used was a polysulfone nonwoven fabric with a thickness of about 0.15 mm and a width of about 39 mm, which was treated with a surfactant to make it hydrophilic.

Then, one positive electrode plate and one negative electrode plate were wound together with one separator in between, and placed in a cylindrical case made of nickel-plated iron and having an outer diameter of about 16.3 mm. and the concentration is 0.68M (this is
This is almost the saturation concentration of zinc. ), 0.6M, 0.4M,
After injecting a 7M concentration KOH alkaline electrolyte with 0.3M, 0.2M, and 0.1M zinc dissolved in it,
Sealed nickel/metal hydride storage batteries A, B,
C, D, E and F were manufactured. The height of the battery is approximately 42m
It is m. [Battery G] (Comparative Example) A nickel metal hydride storage battery G for comparison was made with the same configuration as Battery B of the present invention except that the concentration of zinc contained in the alkaline electrolyte was 0.05M. Manufactured. [Battery H] (Conventional Example) A conventional sealed nickel-metal hydride storage battery H was manufactured with the same configuration as Battery B of the present invention except that zinc was not added to the alkaline electrolyte. [Battery I] (Conventional example) The positive electrode plate of Battery B of the present invention is further impregnated with cadmium hydroxide alone by a known chemical impregnation method, and the addition rate of cadmium hydroxide is changed to nickel hydroxide and cobalt hydroxide. The amount was 3% by weight based on the total amount. The battery B of the present invention, except for using this positive electrode plate and not adding zinc to the alkaline electrolyte,
Nickel metal hydride storage battery I was manufactured in the same manner as above.

Two of each of the above nine types of nickel metal hydride batteries A to I were manufactured, and each battery was charged for 2.5 hours at 25° C. with a current of 0.7 A. A charge/discharge cycle test was conducted under the condition that the battery was discharged at a current of 1.4 A until the terminal voltage reached 0.8 V.

[0032] Internal resistance and discharge capacity at the 2nd cycle and 200th cycle of this charge/discharge cycle test,
Table 1 also shows the charge/discharge cycle life (defined as "the number of charge/discharge cycles until the discharge capacity decreases to 60% of the second cycle discharge capacity").

[0033] Also, the remaining one of each of the nine types of batteries A to I was heated to 0.7A at 25°C.
Charge for 2.5 hours at a current of -10 °C.
The battery was overcharged at a current of 2.8 A for 10 hours, and the occurrence of an internal short circuit in the battery was examined. The results are also shown in Table 1.

[0034]

[Table 1] The following is clear from Table 1.

First, no large difference was observed in the internal resistance and discharge capacity in the second cycle among the batteries. However, the internal resistance and discharge capacity at the 200th cycle,
The following significant differences in charge/discharge cycle life are observed.

That is, without adding cadmium to the positive electrode plate, the concentration of zinc contained in the alkaline electrolyte is 0.
．． Batteries A, B, C, D, E according to the present invention which are 1M or more
and F have the same low internal resistance at the 200th cycle and the same large discharge capacity as the conventional product I, which has cadmium added to the positive electrode plate and no zinc added to the alkaline electrolyte. It is a long value with a charge/discharge cycle life of the same or higher value.

On the other hand, without adding cadmium to the positive electrode plate, the concentration of zinc contained in the alkaline electrolyte is 0.1.
Comparative battery G and conventional battery H, which are lower than M, include batteries A, B, C, D, E, and F of the present invention in which the concentration of zinc contained in the alkaline electrolyte is 0.1 M or more, and batteries containing cadmium in the positive electrode plate. Compared to the conventional example in which the compound was added, the internal resistance at the 200th cycle is high, the discharge capacity is small, and the charge/discharge cycle life is short.

Furthermore, when overcharging was continued at low temperatures, an internal short circuit occurred in conventional battery I in which cadmium was added to the positive electrode plate, but in comparison with batteries A to F of the present invention in which cadmium was not added to the positive electrode plate. No internal short circuit occurred in battery G and conventional battery H.

Therefore, the nickel/metal hydride storage battery constructed according to the present invention does not contain cadmium added to the positive electrode plate, which causes an internal short circuit in the battery when overcharged with a large current at low temperatures, and also has a short charging/discharging cycle. It can be said that it is possible to effectively suppress the increase in internal resistance, decrease in discharge capacity, and decrease in charge/discharge cycle life as the battery progresses.

In this example, the hydrogen storage alloy has the chemical formula LmNi3.8 Co0.7 Al0.5
However, other rare earth type AB5 type hydrogen storage alloys, Laves phase hydrogen storage alloys, TiNi
Even in the case of hydrogen storage alloys such as alloys used in conventional nickel/metal hydride storage batteries, the effects of the present invention can be obtained in the same manner as in the above embodiments.

[0041]Also, in this embodiment, a case where a paste type hydrogen storage electrode is used for the negative electrode plate and a sintered type nickel hydroxide electrode is used for the positive electrode plate is described. In cases where the alloy is filled into an alkali-resistant conductive three-dimensional porous material such as foamed nickel, when a sintered body of a hydrogen-absorbing alloy is used, or when the active material is filled in an alkali-resistant three-dimensional porous material such as foamed nickel as a positive electrode plate. Even in the case of using a container filled with , the effects of the present invention can be obtained in the same manner as in the embodiments.

Furthermore, in this example, the effect of the present invention in the case of a sealed nickel/metal hydride storage battery was explained, but by not adding cadmium to the positive electrode plate, the effect of overcharging at low temperature is improved. The effect of preventing internal short circuits is the open type (vented type) and semi-closed type nickel
Exactly the same result can be obtained when a metal hydride storage battery is overcharged.

[0043]

[Effects of the Invention] As described above, the nickel of the present invention
Metal hydride storage batteries can be used without adding cadmium to the positive electrode, which can cause internal short circuits in the battery or cause environmental pollution when overcharging under conditions where excess uncharged hydrogen storage alloy cannot be present in the negative electrode. It is possible to provide a nickel/metal hydride storage battery that effectively suppresses a decrease in charge/discharge cycle life due to an increase in internal resistance as the charge/discharge cycle progresses.

Claims (1)

[Claims] Claim 1: A nickel metal hydride storage battery comprising a negative electrode mainly composed of a hydrogen storage alloy, a positive electrode mainly composed of nickel hydroxide, and an alkaline electrolyte,
A nickel/metal hydride storage battery, wherein the alkaline electrolyte contains zinc at a saturation concentration of 0.1 M or more and less than a saturation concentration.