JP2020071924A - Positive electrode material for nickel hydrogen battery - Google Patents

Abstract

To provide a positive electrode material for nickel hydrogen batteries, capable of improving capacity.SOLUTION: A positive electrode material for nickel hydrogen batteries contains a positive electrode active material and a conductive assistant, the conductive assistant being CoCO.SELECTED DRAWING: None

Description

  The present application discloses a positive electrode material for a nickel hydrogen battery.

  Non-Patent Document 1 discloses a nickel-hydrogen battery that uses Co as a conductive additive for the positive electrode, and describes that the use of Co improves the electrochemical performance of the battery.

M.G.Ortiz et.al, International journal of hydrogen energy, 39, 2014, 8661-8666.

  However, since Co has a property of being difficult to elute in the electrolytic solution, it is considered that a sufficient amount of conductive paths cannot be formed between the positive electrode active materials. If a sufficient amount of conductive paths are not formed, the capacity of the battery becomes small. Therefore, there is still room for improvement in the conductive auxiliary material used for the positive electrode of the nickel hydrogen battery.

  Then, this application makes it a subject to provide the positive electrode material for nickel hydrogen batteries which can improve capacity.

As a result of earnest studies, the present inventor has found that the battery capacity is improved by using CoCO ₃ as the conductive auxiliary material.

Therefore, the present application discloses a positive electrode material for a nickel-hydrogen battery, which contains a positive electrode active material and a conductive auxiliary material, and the conductive auxiliary material is CoCO ₃ , as one means for solving the above problems based on the above findings.

  According to the positive electrode material for a nickel-hydrogen battery disclosed by the present application, the capacity of the battery can be improved.

It is a figure explaining the presumed mechanism of conductive path formation when Co is used as a conductive auxiliary material. In the case of using a CoCO ₃ as a conductive auxiliary material is a diagram for explaining the estimation mechanism of conductive paths formed. It is an XRD result of the conductive auxiliary material used in the Example. It is an XRD result of the conductive auxiliary material used for the comparative example. It is a charging / discharging curve of an Example. It is a charge-discharge curve of a comparative example. It is a result of impedance measurement of an example. It is a result of impedance measurement of a comparative example.

  In the following, regarding the numerical values A and B, the notation “A to B” means “above A and below B”. In this notation, when a unit is attached only to the numerical value B, the unit is also applied to the numerical value A.

<Cathode material for nickel-hydrogen battery>
The positive electrode material for a nickel-hydrogen battery of the present disclosure includes a positive electrode active material and a conductive auxiliary material, and the conductive auxiliary material is CoCO ₃ . Thereby, the capacity of the battery can be improved.

  The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in a nickel hydrogen battery, and a nickel compound such as nickel hydroxide or a hydrate of the nickel compound can be used. The content of the positive electrode active material in the positive electrode material is not particularly limited, but is preferably 80.0 mass% or more and 99.8 mass% or less.

As the conductive material, CoCO ₃ is used as described above. The content of the conductive additive in the positive electrode material is not particularly limited, but is preferably 0.1% by mass or more and 10% by mass or less. However, it does not prevent the use of a conductive auxiliary material other than CoCO _{3 for} the positive electrode material.

  In addition, the positive electrode material for a nickel-hydrogen battery of the present disclosure can include a known binder in addition to the positive electrode active material and the conductive auxiliary material. For example, SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) can be mentioned. The binder may be used alone or in combination of two or more. The content of the binder in the positive electrode material is not particularly limited, but is preferably 0.1% by mass or more and 10% by mass or less.

  Here, an estimation mechanism by which the battery capacity is improved by using the positive electrode material for a nickel-hydrogen battery according to the present disclosure will be described.

First, a case where a conventional positive electrode material using Co as a conductive additive is used in a battery will be described with reference to FIG. As shown in FIG. 1, Co reacts with OH ⁻ in the electrolytic solution to become Co (OH) ₄ ²⁻ and is eluted into the electrolytic solution. Then, Co (OH) ₄ ²⁻ is further oxidized to CoOOH, which forms a conductive path between the positive electrode active materials.
However, as shown in FIG. 1, generally, Co is difficult to be eluted in the electrolytic solution used in the nickel-hydrogen battery, so that the amount of CoOOH produced tends to be small. Therefore, a sufficient conductive path is not formed between the positive electrode active materials, reaction resistance tends to increase, and capacity tends to decrease.

On the other hand, in the positive electrode material of the present disclosure, CoCO ₃ is used as a conductive auxiliary material. Since CoCO ₃ is more easily eluted into the electrolytic solution than Co, a sufficient amount of conductive paths (CoOOH) can be formed between the positive electrode active materials, as shown in FIG. Therefore, by using the positive electrode material for a nickel-hydrogen battery of the present disclosure in a battery, formation of a conductive path is promoted, so that the reaction resistance can be reduced and the capacity can be improved.

  The method for producing a positive electrode using the positive electrode material for a nickel-hydrogen battery of the present disclosure is not particularly limited, and a known method can be adopted. For example, a method of mixing and rolling the positive electrode material for nickel hydrogen battery of the present disclosure and a method of applying a slurry containing the positive electrode material for nickel hydrogen battery of the present disclosure and a solvent can be mentioned.

  Moreover, the nickel-hydrogen battery configured using the above positive electrode is not particularly limited, and a known configuration can be adopted. For example, the nickel-hydrogen battery can have a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode. In addition, it is preferable that current collectors are arranged on the positive electrode and the negative electrode.

Here, as the negative electrode, a negative electrode containing a known negative electrode active material used in nickel-hydrogen batteries can be used. For example, the negative electrode active material may be a hydrogen storage alloy used in nickel-hydrogen batteries. Further, the negative electrode may contain a conductive auxiliary material or a binder.
As the electrolyte layer, an electrolyte layer containing a known electrolyte (liquid electrolyte or the like) used in nickel hydrogen batteries can be used. However, when a liquid electrolyte (electrolyte solution) is used as the electrolyte, it is necessary to dispose a separator, which is an insulating porous body, between the positive electrode and the negative electrode to ensure insulation between the positive electrode and the negative electrode. Examples of the liquid electrolyte include known ones such as potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, and lithium hydroxide aqueous solution. These liquid electrolytes may be used alone or in combination. The concentration of the liquid electrolyte is not particularly limited, but is preferably 4 mol / kg to 8 mol / kg.
A known collector such as nickel can be used as the collector.

  The method for manufacturing the above nickel hydrogen battery is not particularly limited, and an optimal method can be adopted as appropriate according to the configuration of the nickel hydrogen battery.

  The positive electrode material for a nickel-hydrogen battery of the present disclosure will be described in detail with reference to Examples and Comparative Examples.

[Identification of conduction aid]
XRD measurement was performed for each of the conductive auxiliary materials used in Examples and Comparative Examples. The results are shown in FIGS. From FIG. 3, it was confirmed that the conductive auxiliary material used in the examples was CoCO ₃ . From FIG. 4, it was confirmed that the conductive additive used in the comparative example was Co.

  Here, the conditions of the XRD measurement performed above are shown. In addition, the XRD measurement used the Rigaku XRD measuring device. The condition was 2θ = 20 ° to 80 ° with CuKα ray.

[Production of Battery According to Example]
<Production of positive electrode>
A positive electrode active material (β-Ni (OH) ₂ ), a conductive auxiliary material (CoCO ₃ ), SBR, and CMC were mixed in a mass ratio of 95: 3: 1: 1, and further mixed with a solvent (NMP). Was added and mixed to form a slurry. Then, the obtained slurry was applied to a current collector (nickel) and dried to prepare a positive electrode.

<Production of negative electrode>
Hydrogen storage alloy, SBR, and CMC were mixed in a mass ratio of 98: 1: 1, and a solvent (NMP) was further added and mixed to obtain a slurry. Then, the obtained slurry was applied to a current collector (nickel) and dried to prepare a negative electrode.
LaNi ₅ was used as the hydrogen storage alloy.

<Production of nickel-hydrogen battery>
A separator (a non-woven fabric made of polyethylene / polypropylene) was sandwiched between the positive electrode and the negative electrode produced as described above, and further, pressed by an acrylic plate from both sides and fixed. Then, a 6 mol / kg potassium hydroxide aqueous solution was used as an electrolytic solution to prepare a nickel hydrogen battery for evaluation. A mercury oxide electrode (Hg / HgO) was used as a reference electrode.

[Preparation of Battery According to Comparative Example]
A nickel-metal hydride battery was manufactured by replacing Co in the conductive auxiliary material of the example.

[Evaluation]
The nickel-metal hydride batteries according to Examples and Comparative Examples were evaluated for discharge capacity and reaction resistance.
First, a nickel hydrogen battery was connected to a charging / discharging device, and charging / discharging was performed at a temperature of 25 ° C. Then, 10 cycles of charging and discharging were repeated at a temperature of 25 ° C. The results of the charge / discharge capacity at that time are shown in FIGS. The charge / discharge was performed at a current value of 0.2 mA / cm ² , and the lower limit voltage was 1.0V. Then, impedance measurement was performed. The results are shown in FIGS. The obtained results are summarized in Table 1.

From Table 1, the batteries of Examples using CoCO ₃ as a conductive additive for the positive electrode had a lower reaction resistance and a higher discharge capacity than the batteries using Co. It is considered that this is because CoCO ₃ is more likely to be eluted into the electrolyte than Co and the amount of CoOOH produced is increased (the conductive path between the positive electrode active materials is increased).

Claims (1)

A positive electrode material for a nickel-hydrogen battery, comprising a positive electrode active material and a conductive auxiliary material, wherein the conductive auxiliary material is CoCO ₃ .