JP2014182906A - Positive electrode active material for alkali storage batteries, and positive electrode for alkali storage batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for alkali storage batteries which enables suppression of the worsening of capacity characteristic in a high-temperature condition, and to provide a positive electrode for alkali storage batteries including the positive electrode active material for alkali storage batteries.SOLUTION: A positive electrode active material for alkali storage batteries comprises nickel hydroxide particles including nickel as a primary component, and a coating layer including cobalt and yttrium, and covering surfaces of the nickel hydroxide particles. The yttrium included by the coating layer accounts for 1-2 wt.% to 100 wt.% of the nickel hydroxide particles in terms of oxidation yttrium. In X-ray diffraction with Cu Kα rays, the half-peak width of (001)plane peak in the vicinity of 2θ ranging from 16.5 to 21.5° is 0.6 to 0.8°.

Description

  The present invention relates to a positive electrode active material for an alkaline storage battery used for an alkaline storage battery, and a positive electrode for an alkaline storage battery containing the positive electrode active material for an alkaline storage battery.

  As is well known, various alkaline storage batteries (secondary batteries) are used as power sources for portable electronic devices and as power sources for electric vehicles and hybrid vehicles. Among such alkaline storage batteries, there is a nickel-metal hydride storage battery as a storage battery having high energy density and excellent reliability. This nickel-metal hydride storage battery includes, for example, an electrode plate group in which a plurality of positive electrodes mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy are laminated via a separator, and an alkali composed of potassium hydroxide or the like. It is the storage battery comprised by accommodating in an accommodation container with electrolyte solution. Conventionally, an example of a positive electrode active material for an alkaline storage battery used in such a nickel metal hydride storage battery is described in Patent Document 1.

  The positive electrode active material for alkaline storage batteries described in Patent Document 1 is a positive electrode active material composed of hydroxide particles containing nickel as a main component. This positive electrode active material is coated with a phase layer in which the hydroxide particles consist of nickel and yttrium based hydroxides. The proportion of the hydroxide phase is 0.15 to 3% by weight of yttrium expressed as yttrium hydroxide with respect to the total weight of the hydroxide particles. As a result, an efficient alkaline storage battery active material composed of hydroxide particles mainly composed of nickel can be obtained.

Japanese Patent No. 3563586

  By the way, although an alkaline storage battery is often charged under temperature higher than normal temperature, there exists a tendency for charge efficiency to fall under high temperature compared with normal temperature (for example, 20 degree | times). Usually, an alkaline storage battery generates oxygen by overcharging after the end of charging. However, since generation of oxygen suppresses charging, a reduction in charging efficiency, that is, a reduction in capacity characteristics is inevitable. In particular, oxygen is easily generated at high temperatures, and such inconvenience cannot be ignored. In recent years, therefore, research and development have been conducted on alkaline storage batteries that can prevent a reduction in charging efficiency at high temperatures that are often charged and maintain capacity characteristics.

  The present invention has been made in view of such a situation, and an object thereof is a positive electrode active material for an alkaline storage battery capable of suppressing a decrease in capacity characteristics under high temperature, and a positive electrode active material for the alkaline storage battery. It is providing the positive electrode for alkaline storage batteries containing.

A positive electrode active material for an alkaline storage battery that solves the above problems is a positive electrode active material for an alkaline storage battery that includes nickel hydroxide particles mainly composed of nickel, and includes cobalt and yttrium as a layer covering the surface of the nickel hydroxide particles. The yttrium contained in the coating layer is represented by yttrium oxide (Y ₂ O ₃ ) and expressed as yttrium oxide (Y ₂ O ₃ ) in an amount of 1 wt% or more and 2 wt% or less. The half width of the peak on the (001) plane located in the vicinity of “2θ = 16.5 ° to 21.5 °” of X-ray diffraction using CuKα rays is “0.6 °” or more, and , “0.8 °” or less.

  The positive electrode for an alkaline storage battery that solves the above problem is a positive electrode for an alkaline storage battery that includes nickel hydroxide particles mainly composed of nickel as an active material for the alkaline storage battery, and the alkaline storage battery for the alkaline storage battery described above. The gist is that an active material is used.

  According to this configuration, with respect to the crystal structure of the surface of the positive electrode active material, the half width of the peak of the (001) plane is set to “0.6 °” or more and “0.8 °” or less. The utilization factor of the positive electrode active material in a high temperature environment is maintained high. In addition, with this crystal structure, the tap density is also maintained high, so the density of the positive electrode active material is increased and the capacity density as the positive electrode is also maintained high. Thereby, the positive electrode active material for alkaline storage batteries and the positive electrode for alkaline storage batteries in which a decrease in capacity characteristics at high temperatures is suppressed can be obtained.

As a preferable configuration, the above-described positive electrode active material for alkaline storage battery is summarized in that the average particle size of the positive electrode active material for alkaline storage battery is 5 μm or more and 20 μm or less.
According to such a configuration, by making the average particle size in the range of 5 [μm] or more and 20 [μm] or less, the utilization factor in a high temperature environment is maintained high and the tap density is also high. The positive electrode active material for alkaline storage batteries to be maintained can be obtained.

The gist is that the coating layer is formed by simultaneous crystallization of cobalt and yttrium.
According to such a configuration, a positive electrode active material that maintains a high utilization rate in a high-temperature environment is preferable by uniformizing the dispersion of cobalt and yttrium in the coating layer by simultaneous crystallization of cobalt and yttrium. It will be obtained.

A preferred configuration is that the simultaneous crystallization is crystallization by a reaction crystallization method.
According to such a configuration, a coating layer in which cobalt hydroxide and yttrium are simultaneously crystallized on nickel hydroxide particles can be formed by a reactive crystallization method.

  According to such a positive electrode active material for alkaline storage batteries and a positive electrode for alkaline storage batteries including the positive electrode active material for alkaline storage batteries, a decrease in capacity characteristics at high temperatures is suppressed.

The graph shown about the relationship between the half value width of the peak of the (001) plane which shows the crystal structure of the coating layer, and high temperature utilization factor in one Embodiment of the positive electrode active material for alkaline storage batteries. In the positive electrode active material for alkaline storage batteries of the same embodiment, the graph which shows about the relationship between the half value width of the peak of (001) plane and the tap density which show the crystal structure of the coating layer.

Hereinafter, an embodiment in which a positive electrode active material for an alkaline storage battery (hereinafter, positive electrode active material) is embodied and an example of an alkaline storage battery positive electrode including the positive electrode active material will be described.
In this embodiment, the case where the positive electrode active material is an active material constituting the positive electrode of a nickel-metal hydride storage battery as an alkaline storage battery is illustrated. This nickel metal hydride storage battery is a sealed battery, and is a battery used as a power source for electric vehicles and hybrid vehicles. The nickel-metal hydride storage battery includes, for example, a separator composed of a non-woven fabric of an alkali-resistant resin, a predetermined number of negative electrodes (not shown) including a hydrogen storage alloy, and a predetermined number of positive electrodes including nickel hydroxide (Ni (OH) ₂ ). And an electrode group laminated. The negative electrode is manufactured by applying hydrogen storage alloy powder to an electrode support as a substrate made of punching metal or the like. The positive electrode is manufactured by filling a substrate made of a foamed nickel substrate, which is a metal porous body, with the above-described positive electrode active material containing nickel hydroxide particles. The nickel-metal hydride storage battery has the positive electrode of the electrode group connected to the current collector plate on the positive electrode side, the negative electrode of the electrode group connected to the current collector plate on the negative electrode side, and is housed in a resin battery case together with the electrolyte. Composed.

Next, production of this nickel metal hydride storage battery will be described.
[Production of nickel hydroxide particles]
In this embodiment, the nickel hydroxide particles contained in the positive electrode plate were produced as nickel hydroxide particles containing magnesium in a solid solution state.

  That is, a mixed solution containing nickel sulfate and magnesium sulfate, an aqueous sodium hydroxide solution, and an aqueous ammonia solution were prepared, and each was supplied into a reaction vessel to produce nickel hydroxide that solid-dissolves a predetermined amount of magnesium. As a result, the average particle diameter of the nickel hydroxide powder was 10 [μm]. The average particle diameter of the nickel hydroxide powder was measured with a laser diffraction / scattering particle size distribution analyzer.

  The average particle diameter of the nickel hydroxide powder can be manufactured with a size other than 10 [μm]. However, in order to produce a positive electrode active material having an average particle size smaller than 5 [μm], the residence time (reaction time) in the reaction vessel must be shortened. Since the particles become bulky, the positive electrode packing density decreases. For this reason, the positive electrode active material having an average particle size smaller than 5 [μm] reduces the capacity density of the positive electrode. On the contrary, when a positive electrode active material having an average particle size larger than 20 [μm] is used, the positive electrode expands significantly due to the influence of the crystal structure of nickel hydroxide in the charge / discharge process. Due to this influence, the electrolyte in the separator is reduced (and eventually depleted), and the cycle life characteristics are deteriorated. Therefore, the nickel hydroxide powder is preferably produced with an average particle diameter of 5 [μm] or more and 20 [μm] or less.

[Production of positive electrode active material]
Next, a coating layer in which cobalt hydroxide and yttrium hydroxide are precipitated (crystallized) on the surface of the nickel hydroxide particles obtained as described above (hereinafter also referred to as yttrium-containing cobalt hydroxide coating). Form. Thus, a positive electrode active material composed of nickel hydroxide particles coated with a coating layer in which a cobalt compound and an yttrium compound were mixed was manufactured.

Specifically, first, an aqueous cobalt sulfate solution and an aqueous yttrium sulfate solution (an aqueous solution containing a cobalt salt and an yttrium salt) are supplied into an aqueous solution (suspension) containing nickel hydroxide particles in the reaction vessel. At the same time, an aqueous sodium hydroxide solution (alkaline aqueous solution) is supplied. Then, the inside of the reaction vessel is stirred to cause the cobalt sulfate aqueous solution and the yttrium sulfate aqueous solution to react with the sodium hydroxide aqueous solution, so that cobalt hydroxide and yttrium hydroxide are formed on the surface of the nickel hydroxide particles in the reaction vessel. Were simultaneously precipitated (simultaneous crystallization) (reaction crystallization method). By depositing the cobalt hydroxide and the yttrium hydroxide simultaneously, the yttrium hydroxide is uniformly contained in the cobalt hydroxide. Subsequently, air was supplied into the reaction vessel, and nickel hydroxide particles on which cobalt hydroxide and yttrium hydroxide were precipitated were oxidized by air bubbling in an alkaline aqueous solution, and cobalt oxide and yttrium oxidation were performed. A covering layer made of a material was formed. Thereafter, the positive electrode active composed of nickel hydroxide particles having a coating layer made of a yttrium-containing cobalt hydroxide coating is dried in an air atmosphere at a temperature of 100 ° C. or higher and 130 ° C. or lower after washing and dehydration. Obtained material. The positive electrode active material has a cobalt compound coating amount of 5% by weight and a yttrium compound (Y ₂ O ₃ ) coating amount of 1% by weight to 100% by weight of the nickel hydroxide particles. It adjusted so that it might become 2 weight%. Moreover, the average valence of cobalt was 2.9.

  In general, when nickel hydroxide particles contain a magnesium compound, magnesium solid solution nickel hydroxide particles containing magnesium having a high charging potential increase the battery output, but lower the oxygen overvoltage that generates oxygen during charging. Therefore, the high-temperature charging efficiency is remarkably reduced. Therefore, in the present embodiment, by including yttrium oxide in the cobalt oxide coating layer, the oxygen overvoltage at the end of charging of the positive electrode active material is increased to suppress the generation of oxygen, thereby suppressing the decrease in high-temperature charging efficiency. To be. By the way, it is known that when the cobalt oxide coating layer contains yttrium oxide, the oxygen overvoltage is remarkably increased, and the effect of the yttrium oxide is uniformly applied to the cobalt oxide coating layer which is a reaction field in charging. It is thought that it can be enhanced by distribution.

  Since the coating layer is thin, the average particle diameter of the positive electrode active material made of nickel hydroxide particles having this coating layer is also 10 [μm]. Moreover, the average particle diameter of a positive electrode active material can also be manufactured between 5 [micrometers] or more and 20 [micrometers] or less.

  Next, X-ray diffraction measurement using CuKα rays was performed, and the crystal structure of the coating layer containing the cobalt compound and the yttrium compound was investigated. As a result, in this X-ray diffraction pattern, the half width of the peak on the (001) plane located in the vicinity of “2θ = 16.5 ° to 21.5 °” was “0.6 °”. In addition, RINT2200 made from Rigaku Corporation is used as the X-ray diffraction apparatus, and the measurement conditions are as follows.

<X-ray diffraction measurement conditions>
X-ray: CuKα, 45kV, 40mA
Slit: SS = 0.04 rad, DS = 0.5 °
Scanning mode: continuous
Step Size: 0.017 °
Time per Step: 50sec
Scan Speed: 0.042 ° / sec
[Production of nickel positive electrode]
Next, the nickel positive electrode which comprises a positive electrode plate was produced. Specifically, first, a predetermined amount of an additive such as cobalt metal, water, and a thickener are added to the positive electrode active material powder obtained as described above, and kneaded to form a paste. did.

  The paste was filled into a foamed nickel substrate, dried, and then pressure-molded to produce a nickel positive electrode plate. Subsequently, this nickel positive electrode plate was cut into a predetermined size, and a nickel positive electrode, that is, a positive electrode plate was obtained. The theoretical capacity of the nickel electrode (positive electrode plate) is calculated on the assumption that nickel in the active material undergoes a one-electron reaction.

[Production of alkaline storage batteries]
Next, a negative electrode containing a hydrogen storage alloy was manufactured by a known method. Specifically, by applying a predetermined amount of hydrogen storage alloy powder adjusted to a predetermined particle size to the electrode support, a negative electrode plate having a capacity larger than that of the positive electrode could be obtained.

  Next, the negative electrode plate and the positive electrode plate are laminated via a separator made of a non-woven fabric of alkali-resistant resin, connected to a current collector plate, and an electrolytic solution mainly composed of potassium hydroxide (KOH) A rectangular sealed nickel-metal hydride storage battery was produced by housing the battery in a resin battery case.

  Further, by the manufacturing method similar to that of the present embodiment described above, the (001) plane located near “2θ = 16.5 ° to 21.5 °” as the crystal structure of the coating layer containing the cobalt compound and the yttrium compound. A positive electrode active material composed of nickel hydroxide particles having a half width of the peak in the vicinity of “0.5 °” was obtained. Similarly, a positive electrode active material composed of nickel hydroxide particles near “0.65 °”, a positive electrode active material composed of nickel hydroxide particles near “0.7 °”, and around “0.8 °” Positive electrode active material composed of nickel hydroxide particles and a positive electrode active material composed of nickel hydroxide particles in the vicinity of “0.85 °”. And the alkaline storage battery which has a positive electrode plate containing the positive electrode active material comprised from each nickel hydroxide particle was produced, respectively.

[Relationship between high temperature utilization factor and half-width of peak of (001) plane]
As shown in FIG. 1, the coating layer is composed of nickel hydroxide particles whose (001) plane peak half-widths are “0.5 °”, “0.6 °”, and “0.8 °”. Each high-temperature utilization rate [%] was measured for each alkaline storage battery having a positive electrode plate containing a positive electrode active material. The high-temperature utilization ratio [%] is about 79.5% (graph A1) when the half width is “0.5 °”, and about 82% (graph) when the half width is “0.6 °”. A2) When the half width was “0.5 °”, a value of about 87.5% (graph A3) was obtained. That is, the high temperature utilization rate is about 2.5% higher when the half width is “0.6 °” than when the half width is “0.5 °”. At “0.8 °”, the value was about 8% higher.

  By the way, the “high temperature utilization rate” of the present embodiment is the ratio of the capacity discharged from the nickel-metal hydride storage battery charged by a predetermined charge capacity under the environmental temperature of “60 ° C.” to the charge capacity, Is calculated by

High temperature utilization rate [%] = discharge capacity [Ah] / charge capacity [Ah] × 100
Here, the discharge capacity is obtained by charging a nickel hydride storage battery for a predetermined charge capacity under an environmental temperature of “60 ° C.”, and then discharging a discharge current of 1/10 of the charge capacity from the storage battery. Capacity [Ah]. At this time, the discharge capacity is represented by the product of the measured discharge current and the measured time from the start of discharge to the end-of-discharge voltage (1 V). In general, it is judged that the storage battery is more excellent as the discharge capacity is larger.

[Relationship between tap density and half width of peak of (001) plane]
As shown in FIG. 2, the half-value widths of the peaks on the (001) plane of the coating layer are “0.65 °”, “0.7 °”, “0.8 °”, and “0.85 °”. About each alkaline storage battery which has a positive electrode plate containing the positive electrode active material comprised from nickel hydroxide particle, each tap density [g / cc] was measured. Each tap density [g / cc] is about 2.05 (point B1) when the half width is “0.65 °”, and about 2.05 when the half width is “0.7 °”. When the point B2) is about 2.04 (point B3) and the half-value width is “0.8 °”, about 2.02 (point B4) or about 2.00 (point B5), and the half-value width is “0. When the angle was 85 °, a value of about 1.97 (point B6) was obtained. That is, the tap density is 2-3% when the half width is “0.8 °” or “0.85 °” than when the half width is “0.65 °” or “0.7 °”. Degraded to some extent.

By the way, the tap density was measured in accordance with Japanese Industrial Standard metal powder-tap density measurement method (JIS Z 2512: 2006).
[High temperature capacity]
The nickel-metal hydride storage battery has a relatively high “high temperature capacity” as the “high temperature utilization rate” increases, and a “high temperature capacity” also decreases as the “high temperature utilization rate” decreases. . That is, according to the relationship between the “high temperature utilization factor” and the half width of the peak on the (001) plane shown in FIG. 1, the half width of the peak on the (001) plane of the coating layer is “0.5 °”. A nickel-metal hydride battery having a larger “high temperature capacity” can be obtained when it is larger than “0.6 °” or “0.8 °”.

  As a characteristic of the nickel-metal hydride battery, it is considered that the “high temperature utilization factor” is preferably 80% or more. Therefore, on the basis of “high temperature utilization rate”, the nickel hydride storage battery having a preferable “high temperature capacity” characteristic has a positive electrode active material coating layer having a (001) plane peak half width of “0.6 °”. It is preferable that nickel hydroxide particles having a coating layer as described above are included.

  In addition, as a characteristic of the nickel metal hydride battery, when the “tap density” is lower than 2.02 [g / cc], the positive electrode filling density of the positive electrode active material is lowered and the capacity density is lowered, so-called positive electrode capacity density is insufficient. It is thought to be. Therefore, based on the “tap density”, the nickel-metal hydride storage battery having a preferable “high-temperature capacity” characteristic has a half-width of the peak of the (001) plane of the coating layer of the positive electrode active material of “0.8”. It is preferable that nickel hydroxide particles having a coating layer of “°” or less are included.

The operation of this embodiment will be described.
As described above, in the nickel metal hydride storage battery having a high “high temperature capacity”, the half width of the peak on the (001) plane of the coating layer of the positive electrode active material is “0.6 °” based on the “high temperature utilization rate”. On the other hand, when “tap density” is used as a reference, it is “0.8 °” or less. That is, the nickel-metal hydride storage battery has a “high temperature capacity” when the half-value width of the peak of the (001) plane of the coating layer of the positive electrode active material is “0.6 °” or more and “0.8 °” or less. Get higher.

  Accordingly, a positive electrode active material for a nickel storage battery having a coating layer in which the half width of the peak of the (001) plane is “0.6 °” or more and “0.8 °” or less, and the positive electrode for the nickel storage battery According to the positive electrode for a nickel storage battery containing an active material, a nickel hydride storage battery having a high “high temperature capacity” can be obtained.

  As explained above, according to the positive electrode active material for alkaline storage battery of this embodiment and the positive electrode for alkaline storage battery containing the positive electrode active material for alkaline storage battery, the effects listed below can be obtained.

  (1) Regarding the crystal structure of the surface of the positive electrode active material, by setting the half-value width of the peak of the (001) plane to “0.6 °” or more and “0.8 °” or less, the positive electrode active material The utilization factor (high temperature utilization factor) in a high temperature environment is maintained high. In addition, with this crystal structure, the tap density is also maintained high, so the density of the positive electrode active material is increased and the capacity density as the positive electrode is also maintained high. Thereby, the positive electrode active material for alkaline storage batteries in which a decrease in capacity characteristics at high temperatures is suppressed can be obtained.

  (2) Alkaline storage battery in which the average particle size is in the range of 5 [μm] or more and 20 [μm] or less, so that the utilization rate in a high temperature environment is maintained high and the tap density is also maintained high. A positive electrode active material is obtained.

  (3) By making the dispersion of cobalt and yttrium uniform in the coating layer by simultaneous crystallization of cobalt and yttrium, a positive electrode active material that maintains a high utilization rate in a high temperature environment can be suitably obtained.

(4) A coating layer in which cobalt hydroxide and yttrium are simultaneously crystallized from nickel hydroxide particles can be formed by a reactive crystallization method.
(Other embodiments)
In addition, the said embodiment can also be implemented with the following aspects.

  -Even if it is a method other than the said embodiment, if a nickel hydroxide particle is producible, a well-known method can be used for preparation of a nickel hydroxide particle. Thereby, the improvement of the manufacturing freedom of the positive electrode active material for alkaline storage batteries comes to be achieved.

  -In above-mentioned embodiment, the nickel hydroxide particle illustrated about the case where a magnesium compound is included. However, the present invention is not limited thereto, and the nickel hydroxide particles may contain a zinc compound, a cobalt compound, or the like in addition to the magnesium compound as long as the nickel hydroxide particles can be coated with the coating layer. Thereby, the improvement of the manufacturing freedom of the positive electrode active material for alkaline storage batteries comes to be achieved.

  -In the said embodiment, it illustrated about the case where the average valence of cobalt of a coating layer is 2.9. However, the present invention is not limited to this, and the average valence of cobalt in the coating layer may be any value of 2.6 or more and 3.0 or less. Thereby, the improvement of the manufacturing freedom of the positive electrode active material for alkaline storage batteries comes to be achieved.

  -In the said embodiment, it illustrated about the case where a coating layer is formed by the reaction crystallization method. However, the present invention is not limited to this, and a known method other than the reaction crystallization method can be used for forming the coating layer as long as the coating layer in which the cobalt compound and the yttrium compound are uniformly distributed can be formed. Thereby, the improvement of the manufacturing freedom of the positive electrode active material for alkaline storage batteries comes to be achieved.

  -In the said embodiment, the nickel hydride storage battery illustrated about the case where it is used as a power supply of a motor vehicle. However, the present invention is not limited to this, and the nickel-metal hydride storage battery may be used as a power source other than an automobile as long as it requires a power source. Thereby, the application range of the positive electrode active material for alkaline storage batteries and the positive electrode for alkaline storage batteries is expanded.

  A1, A2, A3 ... graph, B1, B2, B3, B4, B5, B6 ... points.

Claims (5)

A positive electrode active material for an alkaline storage battery comprising nickel hydroxide particles mainly composed of nickel,
A coating layer containing cobalt and yttrium as a layer covering the surface of the nickel hydroxide particles;
The yttrium contained in the coating layer is expressed by yttrium oxide (Y ₂ O ₃ ) and is 1% by weight or more and 2% by weight or less with respect to 100% by weight of the nickel hydroxide particles, and uses CuKα rays. The half width of the peak on the (001) plane located in the vicinity of “2θ = 16.5 ° to 21.5 °” of X-ray diffraction is “0.6 °” or more and “0.8 °” A positive electrode active material for an alkaline storage battery, characterized by: In the positive electrode active material for alkaline storage batteries according to claim 1,
The average particle size of the positive electrode active material for alkaline storage batteries is 5 μm or more and 20 μm or less. The positive electrode active material for an alkaline storage battery according to claim 1, wherein the coating layer is formed by simultaneous crystallization of cobalt and yttrium. The positive electrode active material for an alkaline storage battery according to claim 3, wherein the simultaneous crystallization is crystallization by a reactive crystallization method. A positive electrode for an alkaline storage battery comprising nickel hydroxide particles mainly composed of nickel as an active material for an alkaline storage battery,
The positive electrode for alkaline storage batteries, wherein the alkaline storage battery active material according to any one of claims 1 to 4 is used as the alkaline storage battery active material.

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