JPS6129102B2 - - Google Patents

Description

[Detailed description of the invention]

In particular, the present invention relates to a battery using a solid electrolyte obtained by dissolving a soluble salt in a compound having water of crystallization, and aims to improve the shelf life characteristics of the battery by improving the solid electrolyte. purpose. BACKGROUND ART In recent years, advances in electronics technology have led to the development of small devices, and as a result, the number of uses for incorporating batteries has increased. Particularly in these applications, corrosion of equipment by electrolytes is extremely disliked, and therefore great efforts have been devoted to sealing batteries that use conventional electrolytes, regardless of whether they are primary batteries or secondary batteries.
On the other hand, as a way to fundamentally solve the problem of corrosion caused by electrolytes, attempts have been made to use solid electrolytes, and several solid electrolytes have been developed so far. Among these, the present inventors have focused on compounds that have water of crystallization but have low solubility in water and are stable against atmospheric humidity, such as subsalt phosphates, iron phosphates, and zinc oxalate. By mixing soluble salts such as zinc halides, tin halides, iron halides, or by making an aqueous solution of the above soluble salts, mixing them with salts having water of crystallization, and evaporating to dryness. It was discovered that a solid electrolyte exhibiting remarkable ionic conductivity can be obtained. This solid electrolyte is different from conventional solid electrolytes such as AgI or LiI, in which the salt exhibits electrochemical reactivity with many metals and oxides, just like an aqueous solution, and has a wide range of The possibility of using the active material was recognized. On the other hand, in order to take advantage of these characteristics and use them as actual batteries, not only conductivity but also shelf life is an important factor, especially for primary batteries. Here, when a battery was constructed using the above solid electrolyte, some self-discharge sometimes occurred. One cause of this self-discharge is on the negative electrode side. For example, if the negative electrode is made of iron and a halide is used as the salt constituting the solid electrolyte, iron halide is generated in the iron that comes into contact with the solid electrolyte. This is thought to be due to oxidation of the negative electrode metal due to salt in the electrolyte. The purpose of the present invention is to prevent such phenomena as much as possible and improve the reliability of the battery. It is characterized in that at least one compound selected from the group consisting of acid salts and hypophosphites is added and present in the solid electrolyte. According to the present invention, due to the presence of these phosphorus compounds, corrosion of the negative electrode is significantly suppressed, and self-discharge of the negative electrode due to this corrosion is reduced. Among these phosphorus compounds, alkali metals have relatively little influence on battery characteristics. For example, potassium pyrophosphate K ₄ P ₂ O ₇ , sodium hexametaphosphate (NaPO ₃ ) ₆ , sodium tripolyphosphate Na ₅ P ₃ O ₁₀ ,
Sodium hypophosphite NaH ₂ PO ₂ ·2H ₂ O, sodium phosphite Na ₂ PHO ₃ ·5H ₂ O, etc. dissolve in the solid electrolyte and do not impart deliquescent properties to the obtained crystals. In the method of adding these phosphorus compounds, even if the above-mentioned phosphorus compounds are mixed in powder form into the solid electrolyte obtained by the above-mentioned manufacturing method, they will dissolve to some extent in the crystallization water and exhibit the effect. It is preferable to dissolve the above-mentioned phosphorus compound in water, mix it with a solid electrolyte, and evaporate it to dryness because uniform dispersion can be achieved. Furthermore, in the process of producing a solid electrolyte, when a method is used in which a mixture of a compound having crystal water and an aqueous solution of a salt dissolved therein is evaporated to dryness, the phosphorus compound is simultaneously dissolved in the mixture of the aqueous solutions. However, if it is evaporated and dried, it can be added uniformly into the solid electrolyte. Regarding the amount of these phosphorus compounds added, an effect can be recognized even when the amount is about 0.1 mol% based on the total number of moles of the crystal water compound and the salt to be dissolved, but from the viewpoint of preventing self-discharge, the more the better. However, since these substances originally have poor properties of increasing ionic conductivity even when dissolved in crystal water, if the amount added is extremely increased, the resistance tends to increase. Although it varies depending on the type, up to about 10 mol% of the total number of moles of the crystal water compound and the salt dissolved therein has little effect on the specific resistance. Of course, in the case of a battery with a small permissible current, an even higher addition ratio is possible. Hereinafter, the features and effects of the present invention will be described with reference to Examples. In the examples, as a method with particularly excellent uniformity, a tetracrystalline hydrate of zinc phosphate was used as the compound having water of crystallization. The standard method (comparative example) is to separate iron, add water until it is completely dissolved, mix this aqueous solution with the above zinc phosphate, and evaporate to dryness to obtain a solid electrolyte. The effects based on the present invention when various additives are mixed into the mixture are shown. Further, in order to demonstrate the effects of the present invention, a battery as shown in FIG. 1 was constructed. Here, 1 is the negative electrode, and a mixture of 10% by weight of fluororesin and iron powder is added to the 400% negative electrode.
It is a pellet molded at a pressure of Kg/cm ² . 2 is the solid electrolyte obtained above, which is also molded at a pressure of 400 Kg/cm ² . 3 is a positive electrode, which is molded at 400 kg/cm ² from a positive electrode mixture containing 10% by weight of fluororesin as a binder based on mercury oxide. Both have a diameter of 10 mm. This is sandwiched between conductors 4 made of stainless steel plates, and resin plates 5,
Press down further with 6 and tighten with bolt 7 to form a battery. The following table shows typical additives selected from among the evaluated electrolytes containing various phosphorus compounds and their initial capacity retention rates after three months of battery storage. The composition of the additive is 5% based on the total number of moles of the compounds constituting the solid electrolyte mentioned above.
It was expressed as mol%.

[Table] As is clear from the results, the battery using the solid electrolyte of the present invention exhibits a higher capacity retention rate than the battery without additives. Further, as an example of the amount of addition, FIG. 2 shows the relationship between the amount of addition and the capacity retention rate of the battery when Na ₂ PHO ₃ .5H ₂ O is added. As shown by this result, the capacity retention rate due to addition is effective even at 0.1 mol%, and becomes even better as it increases. However, although not shown in this figure,
If it exceeds 10 mol%, it will be about 2/
The conductivity decreases to 3. However, this range is not necessarily impractical and is suitable for use with very small currents. The reason for the above effect is still not clear, but the presence of these phosphorus compounds in an aqueous solution system causes passivation of iron, etc., so this solid electrolyte, which is composed mainly of crystalline water, It can be inferred that these partially dissolved phosphorus compounds form a weak inert layer on the negative electrode metal and have the effect of suppressing the progress of chemical corrosion due to contact with the salt that provides conductivity. As described above, the present invention significantly improves storage characteristics, particularly in a battery using a solid electrolyte obtained by mixing a soluble salt with a compound having water of crystallization.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a battery used in an example of the present invention, and FIG. 2 shows the relationship between the amount of phosphorus compound added to the electrolyte and the capacity retention rate.

Claims (1)

[Scope of Claims] 1. A battery using a solid electrolyte in which a soluble salt is dissolved in a compound having water of crystallization, wherein the solid electrolyte contains metal pyrophosphate, hexametaphosphate, tripolyphosphate, phosphite and A solid electrolyte battery comprising at least one selected from the group consisting of hypophosphites. 2. A compound having water of crystallization, a soluble salt dissolved in this compound, and a phosphorus compound selected from the group consisting of metal pyrophosphates, hexametaphosphates, tripolyphosphates, phosphites, and hypophosphites. , and a method for producing a solid electrolyte, comprising evaporating to dryness a mixture of the soluble salt and water dissolving the phosphorus compound.