Negative active material

Abstract

Reduced capacity degradation. [Solution] The negative electrode active material is for a metal hydride battery. The negative electrode active material includes a substrate and an adhering material. The adhering material is attached to at least a portion of the surface of the substrate. The substrate contains a hydrogen storage alloy. The adhering material contains antimony.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode active material for a metal hydride battery.

Background Art

[0002] JP-A-10-270042 discloses adding a compound of antimony to a positive electrode paste.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A hydrogen storage alloy is used as a negative electrode active material of a metal hydride battery (hereinafter may be abbreviated as "MH battery"). The capacity of the MH battery depends on the hydrogen storage amount of the hydrogen storage alloy. The hydrogen storage amount may be reduced due to the aging deterioration (corrosion reaction) of the hydrogen storage alloy. That is, it is considered that the capacity deterioration of the MH battery progresses.

[0005] An object of the present disclosure is to reduce capacity deterioration.

Means for Solving the Problems

[0006] The negative electrode active material is for an MH battery. The negative electrode active material includes a base material and an adherent. The adherent is attached to at least a part of the surface of the base material. The base material includes a hydrogen storage alloy. The adherent includes antimony (Sb).

[0007] When Sb adheres to the surface of the hydrogen storage alloy, the corrosion reaction of the hydrogen storage alloy can be inhibited. Therefore, the capacity deterioration of the MH battery can be reduced. Note that on the surface of the hydrogen storage alloy, Sb may be a simple substance or may form a compound.

[0008] Hereinafter, one embodiment of the present disclosure (which may be abbreviated as "this embodiment") and one example of the present disclosure (which may be abbreviated as "this example") will be described. However, this embodiment and this example will not limit the technical scope of the present disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, it is intended from the outset that any configuration may be extracted from this embodiment and combined in any way. [Brief explanation of the drawing]

[0009] [Figure 1] This is a conceptual diagram of the negative electrode active material in this embodiment. [Figure 2] This table shows the battery configuration used in the first experiment. [Figure 3] This table shows the evaluation results of the first experiment. [Figure 4] This table shows the battery configuration used in the second experiment. [Figure 5] This table shows the evaluation results of the second experiment. [Modes for carrying out the invention]

[0010] -Negative electrode active material- Figure 1 is a conceptual diagram of the negative electrode active material in this embodiment. The negative electrode active material 1 includes a base material 2 and an adhering material 3. The base material 2 may be, for example, a powder. The powder may have any particle size. D50 may be, for example, 1 to 100 μm. D50 may be, for example, 10 to 20 μm. The range of D10 to D90 may be, for example, 1 to 100 μm. Note that "D10", "D50", and "D90" represent the particle sizes at which the cumulative values ​​in the volume-based particle size distribution (cumulative distribution) become 10%, 50%, and 90%, respectively.

[0011] The base material 2 includes any hydrogen storage alloy. The base material 2 may include, for example, at least one selected from the group consisting of A2B7 type alloy, AB5 type alloy, and AB2 type alloy. The hydrogen storage alloy may include, for example, Ni, RE (rare earth element), Al, Ti, Mn, Zr, Nb, Mg, Ca, Mm (mischmetal), etc. The hydrogen storage alloy may include, for example, RE, Mg, and Ni. The hydrogen storage alloy may be, for example, an A2B7 type alloy containing La, Mg, and Ni.

[0012] The deposit 3 contains Sb. The deposit 3 may contain at least one of Sb (elemental) and an Sb compound. "Sb compound" refers to a compound containing Sb. The Sb compound may be, for example, an oxide (Sb2O3, etc.), a hydroxide, etc.

[0013] The deposit 3 adheres to at least a portion of the surface of the substrate 2. The deposit 3 may adhere to substantially the entire surface of the substrate 2. The deposit 3 may adhere in layers. The thickness of the deposit 3 may be, for example, 1 nm to 1 mm. For example, 10% or more of the surface of the substrate 2 may be covered by the deposit 3. The deposit 3 may be referred to as, for example, a "coating layer". The surface coverage may be, for example, 30% or more, 50% or more, 70% or more, or 90% or more. The thickness and coverage of the deposit 3 can be determined, for example, by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy). The mass concentration of Sb on the surface of the substrate 2 may be measured by EDX. The mass concentration of Sb may be, for example, 0.01% or more, 0.1% or more, 1% or more, 3% or more, 5% or more, or 7% or more. The mass concentration of Sb may be, for example, 10% or less, 7% or less, or 5% or less.

[0014] -Method for manufacturing negative electrode active material- The negative electrode active material can be manufactured by surface treatment of a substrate 2 (hydrogen storage alloy). For example, surface treatment may be carried out by immersing the substrate in a treatment solution. The treatment solution may be acidic or alkaline. The pH (at 25°C) of the treatment solution may be, for example, 5 or higher, 7 or higher, 10 or higher, 12 or higher, or 14 or higher. For example, the treatment solution may be prepared by adding Sb to an acidic or alkaline base solution. Sb (elemental) or an Sb compound may be added. Regardless of the form in which Sb is added, Sb can be ionized in the treatment solution, so that an Sb-containing deposit 3 can be formed. The base solution may be, for example, an aqueous solution of HCl, an aqueous solution of H2SO4, an aqueous solution of NaOH, etc. For example, Sb2O3 may be added to an aqueous solution of NaOH. The amount of Sb compound added may be, for example, 0.01 to 10 g per 100 mL of base solution. The treatment solution may be a saturated solution of the Sb compound.

[0015] The temperature of the processing solution may be, for example, 40°C or higher, 65°C or higher, 80°C or higher, or 95°C or higher. The temperature of the processing solution may also be, for example, 135°C or lower, or 110°C or lower.

[0016] For example, the base material 2 (powder) may be stirred in the processing liquid. The stirring time may be, for example, 10 minutes or more, 30 minutes or more, or 60 minutes or more. The stirring time may be, for example, 120 minutes or less, 90 minutes or less, or 60 minutes or less. After stirring, the processing liquid and the powder may be separated, for example, by filtration. After filtration, the powder may be washed, for example, with pure water. After washing with pure water, the powder may be washed with hydrogen peroxide solution. Furthermore, the negative electrode active material 1 can be produced by subjecting the powder to dehydration treatment and drying treatment.

[0017] -Metal Hydride Battery- The MH battery includes an arbitrary positive electrode. The MH battery may be, for example, a nickel-metal hydride battery (Ni-MH) or the like. The MH battery may have a monopolar structure or a bipolar structure. In the bipolar structure, for example, when a large current flows, the amount of heat generated tends to increase. Also, in the bipolar structure, there is little surplus space and the amount of electrolyte tends to decrease. Due to these circumstances, in the bipolar structure, the corrosion reaction of the hydrogen storage alloy may be promoted. The negative electrode active material in the present embodiment is considered to be suitable for the MH battery having a bipolar structure.

[0018] -Other applications- The negative electrode active material (hydrogen storage alloy after surface treatment) in the present embodiment may be used, for example, as a hydrogen storage material for hydrogen storage. In the hydrogen storage material for hydrogen storage, a decrease in the hydrogen storage amount due to corrosion of the hydrogen storage alloy is one of the problems.

Examples

[0019] -First experiment- No.1 An aqueous NaOH solution with a concentration of 42% by mass fraction was prepared. By dissolving a saturated amount of Sb2O3 in the aqueous NaOH solution, the first treatment solution was adjusted. The concentration of Sb2O3 in the first treatment solution was 1 g / 100 mL. The first treatment solution had a pH (converted value at 25°C) of 14 or more. The temperature of the first treatment solution was adjusted to 110°C. As a substrate, powder of an A2B7 type alloy (La-Mg-Ni system) was prepared. The powder was put into the first treatment solution and stirred. After stirring for 30 to 60 minutes, the powder was recovered by filtration. The negative electrode active material was produced by sequentially performing pure water washing, hydrogen peroxide water washing, dehydration, and drying. The mass concentration of Sb on the surface of the substrate measured by EDX was about 3.5%. The coverage rate by the deposit was 90% or more.

[0020] Figure 2 is a table showing the battery configuration in the first experiment. A test cell (nickel-metal hydride battery) having the battery configuration of Figure 2 was manufactured.

[0021] No.2 The second treatment solution was prepared by dissolving Ca(OH)2 in an aqueous NaOH solution. The test cell was manufactured in the same manner as in No. 1, except that the second treatment solution was used instead of the first treatment solution.

[0022] No.3 The test cell was manufactured in the same manner as No. 1, except that an untreated hydrogen storage alloy was used as the negative electrode active material.

[0023] Evaluation method and evaluation results The initial capacity of the test cell was measured at 25°C. After measuring the initial capacity, the test cell was stored for 7 days in a constant temperature bath set to 85°C. After storage, the capacity after durability was measured, similar to the initial capacity. Figure 3 is a table showing the evaluation results of the first experiment. The relative capacity in Figure 3 is a relative value with the capacity after durability of No. 3 set to 100. A larger relative capacity is considered to indicate reduced capacity degradation.

[0024] Compared to No. 2 and No. 3, No. 1 showed reduced capacity degradation. It is thought that the Sb adhering to the surface of the hydrogen storage alloy due to the surface treatment inhibited the corrosion reaction of the hydrogen storage alloy. With Ca, a similar effect to that of Sb was hardly observed.

[0025] -Experiment 2- No. 4 Figure 4 is a table showing the battery configuration in the second experiment. In experiment No. 4, an untreated hydrogen storage alloy was used as the negative electrode active material. In experiment No. 4, no additives were used for the negative electrode composite material, and the test cell was manufactured.

[0026] No. 5 In No. 5, an untreated hydrogen storage alloy was used as the negative electrode active material. In No. 5, 3% Sb2O3 was added by mass fraction to the negative electrode mixture. Except for this, the test cell was manufactured in the same manner as in No. 4.

[0027] Evaluation method and evaluation results Similar to the first experiment, a durability test (85°C for 7 days) was conducted. Figure 5 is a table showing the evaluation results of the second experiment. The relative capacity in Figure 5 is a relative value with the durability capacity of No. 4 set to 100. Even when Sb2O3 (powder) was mixed into the negative electrode mixture, the capacity degradation was not reduced. Rather, there was a tendency for the capacity degradation to increase. [Explanation of Symbols]

[0028] 1. Negative electrode active material, 2. Substrate, 3. Adhering material.

Claims

[Claim 1] Including the base material and attached substances, The aforementioned deposit is attached to at least a portion of the surface of the substrate, The aforementioned substrate contains a hydrogen storage alloy, The aforementioned deposit contains antimony, A negative electrode active material for metal hydride batteries.

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