JPH0461468B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a solid-state hydrogen battery in which a negative electrode active material, an electrolyte, and a positive electrode active material are all solid, and particularly relates to the positive electrode material thereof.

<Prior Art> In recent years, with the development of semiconductor technology and its applied technologies, the power consumption of electronic devices is gradually decreasing. In addition, batteries used in these electronic devices are desired to be smaller and thinner as power consumption decreases, and at the same time, they are also required to be highly reliable. Solid electrolyte batteries are generally known as batteries that meet these demands. Solid electrolyte batteries use a solid electrolyte with an ionic conductor as an electrolyte, so there is no leakage from the battery, and highly automated semiconductor manufacturing technology can be applied to the manufacturing process, making it easy to mass produce. It has unique characteristics.

Traditionally, such solid electrolytes include silver, copper,
Lithium-based batteries are being developed. In this,
Batteries using silver ions or copper ions have a property that the solid electrolyte has a relatively high ionic conductivity and can be discharged at a large current. On the other hand, lithium-based solid electrolyte batteries have high energy density and high output voltage, but cannot be discharged with a large current because the ionic conductivity of the solid electrolyte used is not very high. In addition, since lithium metal is extremely active, the battery manufacturing process and sealing technology are complicated due to oxidation and moisture resistance. Furthermore, when considering the use of solid-state batteries in any of the above systems as secondary batteries, there remains the major problem that the conductive species that are reduced at the negative electrode during charging precipitate in a dendritic form, resulting in poor cycle life and the inability to perform deep discharge. There is.

<Background of the Invention> The present inventor has developed a hydrogen storage material that stores hydrogen using a metal hydride as the negative electrode active material, a hydrogen ion conductor as the solid electrolyte, and a material that accepts hydrogen ions as a guest material as the positive electrode active material. He discovered that by doing so, it can be used as a battery. This battery is capable of discharging at a large current, and since the active material used in the negative electrode is hydrogen, it is a diffusion type electrode in which only the diffusion of hydrogen is involved in the reaction, so metal ions are not used as in conventional batteries. Unlike the precipitated electrodes used for the conductive species, there are no dendritic precipitates produced by repeated charging and discharging, and this has the advantage of a long cycle life.

It is possible to construct a battery using any material that accepts hydrogen ions as a guest material for the positive electrode mentioned above, but depending on the material used, the voltage that can be obtained, the current density that can be discharged, and the ability to make a secondary battery The cycle characteristics will vary depending on the case.

<Objective of the Invention> An object of the present invention is to provide a solid hydrogen battery having a positive electrode that can obtain a high voltage and a large discharge current, and has good repeated cycle characteristics during charging and discharging.

<Description of structure and effects> An alloy that stores hydrogen in the form of a metal hydride remains solid even in the state in which hydrogen is stored. Hydrogen storage alloys contain elements (Mg,
By combining elements with catalytic ability to activate hydrogen (Fe, Co, Ni, Cu, etc.) with Ca, La, Ti, V, etc., we have created products with various dissociation pressures and storage capacities. can do. This hydrogen storage alloy is used as a negative electrode. Solid electrolytes include hydrogen ion conductive oxides such as antimony pentoxide (Sb ₂ O ₅ , nH ₂ O) and tin dioxide (SnO ₂ , 3H ₂ O),
A solid polymer electrolyte, typified by a perfluorocarbon-based ion conversion membrane, etc., is used. As the positive electrode material, a substance that accepts hydrogen ions as a guest substance is used, and a battery having the structure as illustrated in FIG. 1 is constructed. In FIG. An electric body, 5 a lead wire, 6 a pressure plate, and 7 a screw.

The electromotive reaction of this battery is thought to be as follows.

Negative electrode: Metal−Hx discharge――→ ←− Charge Metal＋xH ⁺ ×xe ^- …(1) Positive electrode: xH ⁺ +ABn＋xe ^{-Discharge――} → ←− Charge HxABn …(2) or Negative electrode: Metal−Hx＋xH ₂ O discharge――→ ←―― Charge Metal＋xH ₃ O ⁺ ＋xe ^- ……(3) Positive electrode: xH ₃ O ⁺ ＋ABn＋xe ^{-Discharge−−} → ←―― Charge HxABn＋xH ₂ O ……(4) Here, Metal absorbs hydrogen ABn is a material that can incorporate hydrogen as a guest substance. The potential obtained varies depending on the negative electrode material and positive electrode material used. As a result of studying various electrode materials, we found that by using MnO ₂ as the positive electrode material and adding an appropriate amount of carbon powder such as acetylene black to this, it is possible to have a high equilibrium potential, enable large current discharge, and improve cycle characteristics. It has now become possible to create a good positive electrode.

Example 1 Commercially available titanium (Ti) (purity 99.5%) and nickel (Ni) (purity 99.95%) were weighed and mixed in an atomic ratio of 1:1. This is melted in an arc melting furnace. This alloy is placed in a stainless steel reaction vessel, high-pressure hydrogen gas is introduced, and the alloy is heated and hydrogenated. Take out the hydrogenated alloy and put it in an argon gas atmosphere.
Grind to 44μm or less. 0.3 g of this powder, 0.015 g of Teflon powder and 0.01 g of acetylene black are mixed, 0.08 g of a solid electrolyte to be described later is added, and the mixture is molded into pellets using a tablet molding machine. This is used as the negative electrode.

Next, antimony pentachloride (SbCl ₅ ) was dropped into pure water to obtain a white precipitate of antimony hydroxide. This was washed and dried to obtain antimony pentoxide. Use 0.1 g of this to make pellets using a tablet machine. This is used as a solid electrolyte.

Next, using 0.5 g of electrolytic manganese, 0.01 g of acetylene black and 0.2 g of the solid electrolyte mentioned above are mixed therewith, and pelletized using a tablet molding machine. This is used as the positive electrode. Using these, a battery having a structure as shown in FIG. 1 is constructed. The initial open-circuit potential in this case was about 860 mV. Thereafter, discharge was performed at a current density of 100 μA/cm ² . The results are shown in FIG. The horizontal axis represents time, and the vertical axis represents volts (voltage).

Example 2 A negative electrode and solid electrolyte of TiNiMn0.01Hx are produced from Ti-Ni and Mitsushi Metal in the same manner as in Example 1. Next, using 0.5 g of electrolytic manganese, add 0.02 g of acetylene black and 0.2 g of solid electrolyte.
g is mixed and a battery is constructed using this as a positive electrode. The initial open-circuit potential in this case was about 1100 mV. Thereafter, the battery was discharged at a cell density of 100 μA/cm ² . The results are shown in FIG. In addition, this battery can be used at 100μA/cm ²
A cycle life test was conducted in which charging and discharging were repeated every 2 hours at a current density of . The results are shown in FIG. After 100 charging and discharging tests, no deterioration was observed. The reason why the open circuit potentials of the batteries configured as described above are different is as follows. That is, the open-circuit potential varies greatly depending on the hydrogen content when the hydrogen storage alloy used is hydrogenated. Particularly, in materials such as Ti--Ni that do not have a flat area in hydrogen dissociation pressure, there is a difference in open-circuit potential depending on the hydrogen content. The material used in this example is Ti-Ni:
H0.8, the material used in Example 2 is Ti-Ni:
Mn0.01H1.2.

As described above, in an all-solid-state hydrogen battery, by using manganese dioxide for the positive electrode and mixing carbon powder with it, it is possible to construct an all-solid-state hydrogen battery that can be used as both a primary battery and a secondary battery. can.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram illustrating a solid hydrogen battery used for explaining the present invention. FIGS. 2 and 3 are discharge characteristic diagrams of solid hydrogen batteries according to each embodiment of the present invention. FIG. 4 is a diagram showing the charging and discharging characteristics of the solid hydrogen battery according to the embodiment of the present invention. 1... Negative electrode, 2... Solid electrolyte, 3... Positive electrode,
4... Current collector, 5... Lead wire, 6... Pressure plate, 7... Screw.

Claims (1)

[Scope of Claims] 1. A secondary battery comprising a negative electrode made of a hydrogen storage material that stores hydrogen as a metal hydride, a solid electrolyte made of a hydrogen ion conductor, and a positive electrode made of manganese dioxide, the negative electrode and A solid hydrogen battery characterized in that the positive electrode is a mixture of hydrogen ion conductors constituting the solid electrolyte.