JPH0569265B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to improvement of an electrolyte for an organic electrolyte battery that uses lithium as a negative electrode main active material and bismuth trioxide Bi ₂ O ₃ as a positive electrode main active material. An organic electrolyte battery that uses lithium as a negative electrode active material and Bi ₂ O ₃ as a positive electrode active material has an operating voltage of approximately 1.5V.
and alkaline manganese batteries, silver oxide batteries, etc.
It has approximately the same operating voltage as conventional commercially available batteries that use an aqueous alkaline electrolyte, so it is compatible with these batteries. Furthermore, since there is no creep phenomenon like with alkaline electrolytes, there is less electrolyte leakage, self-discharge is small, and energy density is high, so high energy density batteries with excellent long-term reliability can be used. You can expect it. [Prior Art] Conventionally, propylene carbonate (hereinafter abbreviated as PC), γ-
Butyrolactone, tetrahydrofuran, 1,2-
LiClO ₄ , LiBF ₄ , as a supporting electrolyte in a single or mixed solvent of aprotic organic solvents such as dimethoxyethane (hereinafter abbreviated as DME) and dioxolane.
A solution containing an ion dissociative salt such as LiPF ₆ or LiSO ₃ CF ₃ was used. In general, there are various characteristics required for a battery electrolyte, but the most important characteristics for battery performance are: 1. High ionic conductivity and fast electrode reaction rate. 2. High boiling point, low freezing point, and wide operating temperature range. 3. Stable to positive and negative electrode materials, and low solubility of positive and negative electrode materials. 4. High decomposition voltage, etc. From this point of view, high boiling points,
An organic electrolyte in which LiClO ₄ is dissolved in a mixed solvent of PC, which has a low freezing point, high dielectric constant, and high solubility as a supporting electrolyte, and DME, which has a low viscosity, is an excellent one and has been most often used in the past. [Problems to be solved by the invention] However, when this type of battery is conventionally installed in an actual device and discharged, as the battery discharge progresses, Li at the negative electrode dissolves into the electrolyte as Li ⁺ ions. As it moves through the electrolyte and reacts with the positive electrode, its volume decreases, but the volume of the positive electrode expands more than the decrease in volume of the negative electrode, causing the battery case to expand and, in extreme cases, preventing the battery from being used. There was a problem with the device itself being damaged. For this reason, in conventional batteries of this type, the amount of positive electrode and negative electrode active materials filled in a battery space of a certain size is reduced, and the battery capacity that can be discharged is kept low. battery case)
Methods have been developed to suppress the expansion of but,
This method has a problem in that the permissible discharge capacity per unit volume of the device using the battery becomes small. The present invention improves the organic electrolyte of this type of battery to reduce the volume expansion caused by discharge, thereby increasing reliability and safety in equipment using batteries, and at the same time reducing the volume per constant volume. The purpose is to improve discharge capacity. [Means for Solving the Problems] In order to solve the above problems, the present invention uses butylene carbonate (hereinafter abbreviated as BC) as a solvent for the organic electrolyte of this type of battery.

[Effect]

As mentioned above, BC and DME are used as solvents for organic electrolytes.
In the case of batteries using a mixed solvent mainly consisting of
Compared to batteries using conventional mixed solvents of PC and DME, the expansion of battery volume for a given discharge capacity is significantly smaller, so a larger amount of positive and negative active materials can be filled in a given battery space. The discharge capacity per unit volume can be significantly improved. The reason why the expansion of battery volume due to discharge is improved is not necessarily clear, but it is presumed as follows. The battery discharge reaction between bismuth trioxide and lithium is shown by the following equation (1), and the reaction products are Bi and Li ₂ O
It is. 6Li+Bi ₂ O ₃ −→2Bi+3Li ₂ O ...(1) In this reaction, as shown in Table 1, Li, Bi ₂
From the respective densities and formula weights of O ₃ , Bi, and Li ₂ O, Bi ₂
In terms of the volume calculated from the reaction amount in equation (1) for 1 mole of O ₃ , the sum of the volumes of Bi and Li ₂ O after the battery reaction is the sum of the volumes of Li and Bi ₂ O ₃ before the reaction. less than the value. Nevertheless, the reason why the battery actually expands when it is discharged is that the reaction products at the positive electrode are not simply generated as shown in equation (1), but the reaction progresses while incorporating electrolyte. It is estimated to be. In fact, when we disassemble the battery after the reaction, we find that almost all of the electrolyte is occluded in the positive electrode reaction product.
Almost no liquid is visible. Since the positive electrode expands due to the electrolyte solvent being occluded in the positive electrode reaction product, it is presumed that the type and state of the electrolyte solvent have a significant effect on the expansion of the positive electrode due to discharge.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples. FIG. 1 is a sectional view of a button-type battery showing an example of the present invention. In the figure, 1 is a negative electrode can which also serves as a negative electrode terminal, and is made by drawing a three-layer Ni-SUS-Ni clad plate. Negative electrode 2 has a thickness of 1.4
A lithium sheet with a diameter of 1 mm is punched out and crimped onto the inner surface of the negative electrode can. 6 is a positive electrode can made of SUS plated with Ni, which also serves as a positive electrode terminal. This positive electrode can is filled with a positive electrode 5, which will be described later, and a separator 4 made of a microporous polypropylene sheet is placed thereon. 3 is an impregnating material that holds the electrolyte between the positive electrode and the negative electrode, and is made of a nonwoven fabric whose main element is polypropylene. 7 is a gasket mainly made of polypropylene, and the negative electrode can 1
It is interposed between the positive electrode can 6 and maintains electrical insulation between the positive electrode and the negative electrode, and at the same time, the opening edge of the positive electrode can is bent inward and caulked to seal and seal the battery contents. There is. The positive electrode 5 is made of bismuth trioxide powder with a purity of 99.99%, which is a positive electrode active material, which is melt-heat treated at 900°C in the air for 5 hours, cooled, and then crushed to a particle size of 100 μm or less, and a carbon conductive agent (graphite or carbon black). etc.) and a binder made of fluororesin at a weight ratio of 95.7:4:0.3 to form an L-shaped cross-section.
After being pressure-molded into a pellet shape together with the positive electrode holding ring 8 made of SUS, the pellet was thoroughly dried under vacuum heating at 100°C. The weight of the positive electrode mixture is 0.26 per battery.
It was hot at g. The electrolytes used in this example were (a) 1 mol/LiClO ₄ dissolved in a mixed solvent of BC and DME in a volume ratio of 1:1, and (b) EC in a volume ratio of BC and DME.
LiClO ₄ in a mixed solvent mixed at a ratio of 45:50:5
1 mol/dissolved and as a conventional example,
(c) 1 mole/LiClO ₄ dissolved in a 1:1 mixed solvent of PC and DME; Using each electrolyte solution, three types of batteries were fabricated as described above, except for the type of electrolyte solution. The size of the battery is 9.45 mm in diameter and 3.0 mm in height, and the amount of electrolyte injected is
It was 45μ. Figure 2 shows the 7.5KΩ constant resistance discharge characteristics of the battery made in this way at 20°C, and Table 2 shows the discharge capacity up to a cut-off voltage of 1.2V and the 7.5KΩ constant resistance discharge characteristic at 20°C.
The result of the difference between the height of the battery after overdischarging for up to 550 hours (at this time all batteries were completely discharged and the operating voltage was 0V) and the height of the battery before discharge (swelling due to discharge) showed that. As is clear from these results, the battery of the present invention (b)
There is almost no difference in discharge capacity up to a cut-off voltage of 1.2V between the conventional battery (c) and the conventional battery (c), but the swelling of the battery due to discharge is significantly smaller in the battery according to the present invention (b) than in the conventional battery (c). It's summery. In other words, if the maximum height of the battery allowed by the battery-using device is 3.2mm,
With the battery (b) according to the present invention, it is possible to extract a discharge capacity of at least 76mAh, but with the conventional battery (c), the battery height increases when 76mAh is discharged.
Since it expands to 3.36 mm or more, in order to make it 3.2 mm or less, it is necessary to reduce the amount of positive and negative active materials by about 10%, and the discharge capacity that can be taken out decreases accordingly. In (a), as shown in Figure 2, the internal resistance increases at the end of discharge, so the operating voltage decreases slightly, and the discharge capacity up to the cut-off voltage of 1.2V is slightly smaller than in (b) and (c). However, similarly to (b), the swelling of the battery due to discharge is significantly smaller than that in (c). Therefore, the battery (a) according to the present invention has a larger allowable capacity per the same volume than the conventional battery (c). Further, the small change in shape of the battery is an extremely important advantage for the reliability and safety of devices using batteries.

〔Effect of the invention〕

As detailed above, the present invention uses a mixed solvent mainly consisting of butylene carbonate and 1,2-dimethoxyethane or a mixed solvent containing ethylene carbonate as an electrolyte solvent. It can significantly reduce the expansion of Bi ₂ O ₃ batteries due to discharge, significantly improving the discharge capacity per unit volume, and at the same time significantly reducing changes in battery shape that are unfavorable for the reliability and safety of battery-using equipment. It has excellent effects such as

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a battery implemented in the present invention, and FIG. 2 is a comparison diagram of 7.5KΩ constant resistance discharge characteristics. DESCRIPTION OF SYMBOLS 1... Negative electrode can, 2... Negative electrode lithium, 3... Impregnating material, 4... Separator, 5... Positive electrode, 6... Positive electrode can, 7... Gasket, 8... Positive electrode holding ring.

Claims (1)

[Scope of Claims] 1 Consists of at least a negative electrode having lithium as the main active material, an organic electrolyte, and a positive electrode having bismuth trioxide Bi ₂ O ₃ as the main active material, and butylene carbonate and 1 as a solvent for the organic electrolyte. , 2-dimethoxyethane. 2. The organic electrolyte battery according to claim 1, wherein a mixed solvent further containing ethylene carbonate is used as a solvent for the organic electrolyte. 3. The organic electrolyte battery according to claim 1 or 2, characterized in that lithium perchlorate LiClO ₄ is used as a supporting electrolyte dissolved in the organic electrolyte.