JP3384615B2 - Gel electrolyte battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel electrolyte battery, and more particularly, to a polymer having a high discharge capacity (high rate discharge capacity) at a high rate (large current). The present invention relates to a gel electrolyte battery using a gel electrolyte. 2. Description of the Related Art In recent years,
Solid electrolyte batteries have advantages that liquid electrolyte batteries do not have, such as being position-free because there is no risk of liquid leakage, and being easy to assemble the batteries because they do not require electrolyte injection. From, has attracted attention. [0003] However, since the ionic conductivity (conductivity) of the solid electrolyte is lower than that of the liquid electrolyte, the solid electrolyte battery has a disadvantage that its capacity is reduced when discharged at a high rate (large current discharge). Was. For this reason, the only solid electrolyte battery currently in practical use is a lithium battery used as a power source for a cardiac pacemaker. In order to improve the drawbacks of such a solid electrolyte battery and to increase the capacity during high-rate discharge, polyethylene oxide is converted from an electrolyte salt (solute) such as LiClO ₄ and a cyclic carbonate (a solvent such as propylene carbonate). Electrolyte battery using a polymer gel electrolyte impregnated with an electrolyte solution has been proposed, but a film such as Li ₂ O without electron conductivity is formed at the interface between the negative electrode and the polymer gel electrolyte. As a result, the contact resistance between the two increases, so that the battery does not have a sufficiently high high-rate discharge capacity for practical use. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gel electrolyte battery having a large high rate discharge capacity. A gel electrolyte battery according to the present invention (hereinafter, referred to as "battery of the present invention") for achieving the above object uses a positive electrode and lithium as an active material. A gel electrolyte battery comprising a negative electrode and a polymer gel electrolyte in which a polymer is impregnated with an electrolyte solution comprising an electrolyte salt and an aprotic solvent, wherein the polymer is a polyethylene.
And the aprotic solvent is a mixed solvent having the following composition. (Composition) High boiling point solvent: ethylene carbonate (238 ° C.), propylene carbonate (241 ° C.), butylene carbonate (240 ° C.), γ-butyrolactone (204 ° C.)
Solvent 2 selected from C) and sulfolane (285 ° C.)
Species: 5-50% by volume each, and low boiling solvent: 1,2-dimethoxyethane (84 ° C),
1,2-diethoxyethane (118 ° C), 1,2-ethoxymethoxyethane (104 ° C), tetrahydrofuran (66 ° C), 2-methyltetrahydrofuran (8
6 ° C.), 1,3-dioxolane (78 ° C.), 4-methyl-1,3-dioxolane (86 ° C.), dimethyl carbonate (90 ° C.), diethyl carbonate (12 ° C.)
6 ° C) and ethyl methyl carbonate (107 ° C)
One solvent selected from the following: 10 to 50% by volume. In parentheses are the boiling points of each solvent under atmospheric pressure. Examples of the negative electrode using lithium as an active material include metallic lithium or alloys, oxides, and carbon materials capable of inserting and extracting lithium. As alloys capable of inserting and extracting lithium, lithium-aluminum alloy, lithium-indium alloy, lithium-tin alloy, lithium-lead alloy, lithium-bismuth alloy, lithium-gallium alloy, lithium-zinc alloy, lithium-cadmium alloy,
Lithium-silicon alloys, lithium-calcium alloys, lithium-barium alloys, lithium-strontium alloys, and oxides capable of inserting and extracting lithium include iron oxide, tin oxide, niobium oxide, tungsten oxide, titanium oxide, and lithium oxide. Examples of the carbon material capable of storing and releasing carbon dioxide include coke, graphite, and a fired organic material. The active material of the positive electrode is not particularly limited, and includes, for example, lithium-containing manganese oxide, lithium-containing cobalt oxide, lithium-containing nickel oxide, and at least two metals selected from manganese, cobalt, and nickel. And the like. [0010] the polymer gel electrolyte of the present invention, especially
It is obtained by impregnating a fixed polymer with an electrolytic solution comprising an electrolyte salt and a specific aprotic solvent. As the polymer, polyethylene oxide or polypropylene oxide is used. The electrolyte salt includes lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium tetrafluoroborate (LiB 4).
F _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF _6), lithium trifluoromethanesulfonate imide [LiN (CF ₃
SO ₂ ) ₂ ]. As the aprotic solvent, specific 2
A ternary mixed solvent consisting of 5 to 50% by volume of each kind of high-boiling solvent and 10 to 50% by volume of a specific low-boiling solvent is used. When the ratio of each solvent is out of each regulation range, the high-rate discharge capacity decreases. The decrease in capacity during high-rate discharge is less likely to occur than in conventional gel electrolyte batteries. It is presumed that the contact resistance at the interface between the negative electrode and the polymer gel electrolyte is reduced because it is difficult to form a film such as Li ₂ O having no electron conductivity at the interface between the anode and the polymer gel electrolyte. Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the present invention is not limited to the following Examples at all, and may be modified as appropriate without departing from the scope of the invention. It can be implemented. (Examples 1 to 6 and Reference Example 1 ) [Positive electrode] Manganese dioxide as a positive electrode active material, graphite powder as a conductive agent, and PTFE (polytetrafluoroethylene)
Were mixed at a weight ratio of 8: 1: 1 to prepare a positive electrode mixture, which was formed into a disc shape, and dried at 100 ° C. under vacuum to prepare a positive electrode. [Negative electrode] A lithium-aluminum alloy was used. [Polymer Gel Electrolyte] The composition of a polyethylene oxide film, a polypropylene oxide film or a polyethyleneimine film having an average molecular weight of 60,000 is shown in Table 1 comprising two kinds of high-boiling solvents and one kind of low-boiling solvents. It was immersed in a solution (electrolyte solution) in which LiClO ₄ was dissolved at 1 mol / liter in a ternary mixed solvent to swell, thereby producing a polymer gel electrolyte. The weight ratio of the electrolyte to be impregnated to each film was 4: 1. The solvent ratio of the mixed solvent is 40% by volume (high-boiling solvent):
40% (high-boiling solvent): 20% (low-boiling solvent). [Table 1] [Gel Electrolyte Battery] Using the above positive electrode, negative electrode and each polymer gel electrolyte,
Flat gel electrolyte batteries A1 to A7 (theoretical capacity: 120 mAh; diameter: 20 mm, thickness: 2.5 mm) were assembled in this order. Batteries A1 to A6 are the batteries of the present invention,
Pond A7 is a reference battery. (Comparative Examples 1 to 18) The same kind of polyethylene oxide film, polypropylene oxide film or polyethylene imine film as those used in the examples was prepared by using one kind of high boiling point solvent shown in Table 2 or one kind Immersed in a solution (electrolyte solution) of LiClO ₄ dissolved at 1 mol / l in a binary mixed solvent consisting of a high boiling point solvent and one low boiling point solvent to swell to produce a polymer gel electrolyte . The weight ratio of the electrolyte to be impregnated to each film was 4: 1. The solvent ratio of the two-component mixed solvent was 80% (high boiling point solvent): 20% by volume.
(Low boiling point solvent). Gel electrolyte batteries B1 to B18 were assembled in the same manner as in the example except that these polymer gel electrolytes were used. Tables 2 and 3 show the solvents and polymers used for each gel electrolyte battery. [Table 2] [Table 3] Comparative Examples 19 to 21 Liquid electrolyte batteries B19 to B21 were prepared using LiClO ₄ dissolved in ethylene carbonate, propylene carbonate, or a mixture of these solvents in an equal volume of 1 mol / liter as an electrolyte.
Was assembled. A nonwoven fabric made of polypropylene was used as the separator. Table 3 shows the solvents used for each liquid electrolyte battery. <Decomposition Current> A test cell was assembled using each electrolyte, a platinum electrode as a working electrode, and a lithium electrode as a counter electrode and a reference electrode. Then, the potential of the platinum electrode was set to 0 V to the reference electrode (Li / Li ⁺ ) was measured to determine the difficulty of decomposability of each electrolyte by measuring the reduction current (decomposition current μA / cm ² ). The higher the decomposition current, the more easily the electrolyte is decomposed. The results are shown in Tables 1 to 3 above. According to Tables 1 to 3, Example 1 in which a mixed solvent of two kinds of high-boiling solvents and one kind of low-boiling solvents was used as the solvent.
It can be seen that the polymer gel electrolytes of Nos. 6 to 6 have a smaller decomposition current and are less likely to be decomposed than the liquid electrolytes of Comparative Examples 19 to 21 and the polymer gel electrolytes of Comparative Examples 1 to 18. <High-rate discharge capacity and internal resistance> 1 for each battery
A high-rate discharge test was performed at room temperature (25 ° C.) by connecting an external resistor of 0 kΩ to obtain a high-rate discharge capacity of each battery. The internal resistance of each battery was also examined. The results are shown in Tables 1 to 3 above. As can be seen from Tables 1 to 3, the gel electrolyte batteries A1 to A6 using the polymer gel electrolyte having a small decomposition current (the batteries of the present invention) are the batteries B using the electrolyte having a large decomposition current.
It can be seen that the internal resistance of the battery is smaller than that of 1 to B21 (comparative battery), and therefore the high rate discharge capacity is large. <Relationship between Solvent Ratio of Mixed Solvent and High-Rate Discharge Capacity> The solvent is composed of ethylene carbonate (high-boiling solvent), propylene carbonate (high-boiling solvent), and 1,2-dimethoxyethane (low-boiling solvent). A polymer gel electrolyte was prepared and a gel electrolyte battery was assembled in the same manner as in Examples 1 to 6 , except that 25 kinds of mixed solvents were used. FIG.
Is a plot of the composition of each mixed solvent in a triangular diagram. In FIG. 1, the composition of each mixed solvent is represented by a line segment AB (ratio of ethylene carbonate), BC (ratio of propylene carbonate) and CA
It is represented by the intersection of line segments AB, BC and CA when a parallel line is drawn to (ratio of 1,2-dimethoxyethane). Next, a high-rate discharge test was performed on each of the gel electrolyte batteries under the same conditions as the above-mentioned high-rate discharge test, and a high-rate discharge capacity (mAh) was obtained. The high-rate discharge capacity of each gel electrolyte battery is shown in parentheses in FIG. As shown in FIG. 1, when a ternary mixed solvent consisting of 5 to 50% by volume of ethylene carbonate and propylene carbonate and 10 to 50% by volume of 1,2-dimethoxyethane is used (shaded area in the figure) Further, it can be seen that a gel electrolyte battery having a large high rate discharge capacity can be obtained. It was also confirmed that good results were obtained with other mixed solvents at the same solvent ratio. The high-rate discharge capacity is large because the polymer gel electrolyte to be used is hardly decomposed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a triangular diagram showing a relationship between a solvent ratio of a mixed solvent and a high-rate discharge capacity.

Continuation of the front page (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo (56) References JP-A-1-281679 (JP, A) JP-A-60-121676 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 6 / 18 H01M 6/22 H01M 10/40

Claims (1)

(57) [Claim 1] A positive electrode, a negative electrode using lithium as an active material,
A gel electrolyte comprising a polymer impregnated with an electrolyte solution comprising an electrolyte salt and an aprotic solvent, wherein the polymer is a polyethylene oxide.
A gel electrolyte battery , which is sid or polypropylene oxide, and wherein the aprotic solvent is a mixed solvent having the following composition. (Composition) High-boiling solvents: two solvents selected from ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and sulfolane: 5 to 50 vol% each; and low-boiling solvents: 1,2-dimethoxyethane, 1, 2-diethoxyethane, 1,2-ethoxymethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,
One kind of solvent selected from 3-dioxolan, 4-methyl-1,3-dioxolan, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate: 10
~ 50% by volume