JPS61227377A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To produce a high-performance nonaqueous secondary battery which exhibits good charge-and-discharge reversibility and has a long cycle life, high energy density, a very low self discharge rate and good thermal stability by using a liquid electrolyte which is composed of a special alkali metal salt and a mixture solvent composed of a phosphoric ester and an ether-system compound in a given ratio. CONSTITUTION:As compared to a secondary battery where propylene carbonate or tetrahydrofuran is used alone, a nonaqueous secondary battery where electro lyte represented by formula (1) or (2) is dissolved in an organic solvent consisting of a mixture solvent prepared by mixing a phosphoric ester re presented by formula (3) and an ether-system compound in a given ratio has the following advantages: (i) high energy density, (ii) good flatness of the volt age, (iii) minimal self discharge, (iv) long repetition life, (v) exhibiting special properties at low temperatures and (vi) good thermal stability. Due to its small weight, small size and high energy density, this battery can be advantageously used for portable apparatus, electric automobiles and gasoline automobiles as well as a battery for electric power storage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a battery that has high energy density, good charge/discharge reversibility, extremely low self-discharge rate, and excellent low-temperature characteristics and thermal stability. Regarding high performance non-aqueous secondary batteries.

[Problems to be solved by the prior art and the invention] Currently, commonly used secondary batteries include lead acid batteries, Ni/Cd batteries, and Ni/Cd batteries.
There are batteries etc. These secondary batteries have a single cell battery voltage of about 2.0V at most, and are generally aqueous batteries. BACKGROUND ART In recent years, research has been actively conducted on converting a battery using l-i as a negative electrode into a secondary battery as a secondary battery capable of achieving a high battery voltage.

When Ii is used as an electrode, it is necessary to use a non-aqueous electrolyte because of the high reactivity between water and Ij.

However, when carrying out a secondary battery reaction using Li as a negative electrode active material, dendrites occur when l-i+ is reduced during charging, resulting in problems such as a decrease in charge/discharge efficiency and a short circuit between the positive and negative electrodes. . Therefore, many technological developments have been reported to prevent dendrites and improve the charge/discharge efficiency and cycle life of negative electrodes.
K. M. Abraham et al. “Lithium Batches,
Edited by G.B. Kalbuff 2, published by Academic Press, London (1983).

K, M, Abraham et al, in″L
ithiumB atteries'', J, p, Q
abano, editor.

academic press, london
(1983)) and a method of preventing Li dendrites by adding additives to the electrolytic solution system or alloying the electrode itself with A1 [JP-A-59-108281].

Furthermore, in addition to alkali metals and alkali metal alloys such as L1/An, it is also known to use l[alpha] polymers having conjugated double bonds in their main chains as negative electrode active materials [G.H. 7 man.

G. Double Kaufer, N. G. Heeger, Earl Kerner, N. G. McDiarmid, Physics Review Volume 0,826.

No. 2327 (1982), J, H, Ka
ufman.

J, W, Kawfer, A, J, Heeg.
Er.

R,1(aner, A, G, MacQiarmi
d, phys.

Rev., 1'', 2327 (1982), )-
Well-known conductive polymers used in this method include polyacetylene, polythiophene, polyparaphenylene, and boribiol. It is also known to use graphite and other intercalation compounds as negative electrode active materials.

When a secondary battery is formed using the negative electrode active material as described above, it is necessary to use a non-aqueous solvent having a wide electrochemical stability range as the electrolyte for the battery.

However, when propylene carbonate, which is generally used as a non-aqueous solvent, performs a battery reaction by reversibly redoxing alkali metal cations with the negative electrode active material at the negative electrode, the electrochemical stability range of the negative electrode deteriorates. It has the disadvantage that it is too narrow to be used in such batteries (N.D., B.B. Sripan, Journal of Electrochemical Society, Vol. 117).

Na3. Pages 222-224 (1970).

A, N, Dey & B, P, 5ulli
van, J.

Electrochei, Soc,, Vol. 11
7. &, 2. 222-224 (1970)).

Similarly, even if conventionally known cyclic ether solvents such as tetrahydro7ran, dioxolane, 2-methyl-tetrahydrofuran, and 4-methyl-dioxolane are used alone, they exhibit high reactivity with alkali metal salts. However, there are problems such as low electrical conductivity of the electrolyte, making it impossible to charge and discharge at high electrical density (1 mA/lri or more), and it is difficult for the country to obtain high energy density secondary batteries. This is the number.

[Means for Solving the Problems] The present invention was completed based on the discovery that a high-performance non-aqueous secondary battery that is rechargeable and has good thermal stability can be obtained by using an electrolytic solution consisting of a mixed solvent. I ended up doing it.

That is, in the present invention, the alkali metal and the alkali metal preliquid have the following general formula (1) or (2) (where M is an alkali metal, X is an element of Group Va of the periodic table, and R1-R6 may be different or the same and represent a hydrogen atom, a halogen atom, an alkyl group having 15 or less carbon atoms, an aryl group, an allyl group, an aralkyl group, or a halogenated alkyl group.) [In the formula, M is an alkali metal , X represents an element of Group 11a of the periodic table, and R-R. may be different or the same, and represents a hydrogen atom, a halogen atom, an alkyl group having 15 or less carbon atoms, an aryl group, an allyl group, an aralkyl group, or a halogenated alkyl group. ] Alkali gold JIjW represented by and the following general formula (3)
(In the formulas, R11 to R13 represent a hydrogen atom, an alkyl group having 15 or less carbon atoms, an aryl group, an allyl group, an aralkyl group, or a halogenated alkyl group.

However, R11 to R13 are never hydrogen atoms at the same time. ) The mixed solvent consists of a mixed solvent of a phosphoric ester and an ether compound represented by
The present invention relates to a non-aqueous secondary battery characterized by containing 0% glue.

[Function] In the present invention, the effect of using an electrolytic solution consisting of an alkali metal salt and a mixed solvent formed by mixing a phosphoric acid ester and an ether compound in a specific ratio is extremely remarkable, and the mechanism of its action is Although the details are not clear, a mixed solvent consisting of a phosphate ester and an ether compound is thermally stable with respect to an alkali metal salt as an electrolyte, and the mixed solvent has the effect of suppressing the decomposition of the electrolyte itself. Furthermore, the electrolyte has good solubility in the mixed solvent and the electrical conductivity of the electrolytic solution is higher than that of conventionally known single solvent systems, so it is thought that the effects of the present invention are achieved. In particular, in the mixed solvent of the present invention, when the phosphoric acid ester is used at 5 volume % to 30 volume % based on the entire mixed solvent, the ability to maintain the electrical conductivity of the electrolyte specifically high is also a great effect. This is thought to be the reason for this.

[Means for Solving the Problems] The alkali metal salt used as the electrolyte in the present invention is represented by the general formula (1) or (2).

Examples of the alkali metal cation of the alkali gold m-salt include L j ++ Na ++ K++*Rb'. Specific examples of alkali metal salts include Li BF
, LiPFe, LiAsF6.

LiB(Et), LiBPh4゜Li BPh 3F, Li BPh 3C1, Na B
F4゜Na B (Bu), Na PF6. Na
Examples include As F6°Rb BF and Rb PF6.

Examples of the ether compound that is one component of the mixed solvent used in the present invention include aliphatic ethers, saturated cyclic ethers, and aromatic ethers. Specific examples of these ether compounds include 1,2-dimethoxyethane, 1,2-jethoxyethane, 1,3-dioxolane, 4-methyl-1°3-dioxolane, 4,4-dimethyl-1,3-dioxolane. , 4,5-dimethyl-1,3
-dioxolane, 2-methyl-1,3-dioxolane,
2,4-dimethyl-1,3-dioxolane, tetrahydrofuran, tetrahydrobyran, 2-methyl-tetrahydrofuran, 2,5-dimethyl-tetrahydrofuran, 2-methoxydetrahydrofuran, anisole, etc. can give.

In addition, the other component of the mixed solvent, the general formula (3
) Specific examples of phosphate esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate,
Triphenyl phosphate, tricresyl phosphate, trioctyl phosphate, tris(2-chloroethyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, tris(2°3-dibromopropyl) phosphate, Tris phosphate (4
-tert-butylphenyl) and tritolyl phosphate.

The mixing ratio of the phosphoric acid ester and the ether compound is such that the phosphoric acid ester is in a range of 5 to 30% by volume based on the total amount of the mixed solvent.

If the mixing ratio of the phosphate ester is outside the range of the present invention, the electrolytic solution has a narrow electrochemical stability range and low electrical conductivity, making it difficult to obtain a battery with good performance.

The concentration of the alkali metal salt as an electrolyte is 0.5 to 5 mol/min, preferably 1.0 to 2 at a high electrical conductivity concentration.
．． It is within the range of 5 mol/liter. The electrolytic solution may be used in a state in which the alkali metal salt is completely dissolved in the mixed solvent, or in a state in which the alkali metal salt is precipitated in the mixed solvent at a concentration higher than saturation. . The electrolyte solution obtained by this method has an extremely wide electrochemical stability range.

Examples of alkali metals used as the negative electrode active material in the present invention include Li, Na, etc., and examples of alkali metal alloys include Li/AN, Li/Hg, and Li/Z.
n, Li/Cd, etc.

Examples of conductive polymers include polymers of polypyrrole and virol derivatives, polymers of polythiophene and thiophene derivatives, polyquinoline, polyacene, polyvaraphenylene, polyacetylene, etc., and examples of interlayer compounds include graphite, TiS2, etc. It will be done. Furthermore, examples of the composite include, for example, a composite of Li/A1 alloy and various conductive polymers. The term "composite" as used herein means a homogeneous mixture of two or more components, a laminate, and a modified product in which a base component is modified with another component.

As the counter electrode, that is, the positive electrode active material used in the non-aqueous secondary battery of the present invention, any substance that can undergo reversible oxidation and reduction reactions within the electrochemical stability range of the electrolyte of the present invention can be used. . Typical examples of positive electrode active materials include TiS2. ■ Conductive polymers such as polypyrrole and virol derivative polymers, polyaniline and aniline derivative polymers, polythiophene and thiophene derivative polymers, and polyacetylene, which are doped or undoped with intercalation compounds such as 205 and electrolyte anions. I can give it to you. Preferred examples of these positive electrode active materials include TiS2, polypyrrole, poly-3-methyl-vinyl, polyacetylene, polythiophene, and polyaniline.

As is well known to those skilled in the art, the conductive polymer used as the electrode of the nonaqueous secondary battery of the present invention may include other suitable conductive materials such as carbon black, acetylene black, metal powder, and metal fiber. , carbon fiber, etc. may be mixed. Also, polyethylene, modified polyethylene, polypropylene, polytetrafluoroethylene, ethylene-propylene-terpolymer (EPDM), sulfonated EP
It may be reinforced with thermoplastic resin such as DM.

In the present invention, if necessary, a porous membrane made of synthetic resin such as polyethylene or polypropylene, natural 11m paper or glass! l fibers or the like may be used as a diaphragm.

In addition, some of the electrodes used in the 31 aqueous secondary battery of the present invention may react with oxygen or water and reduce the performance of the battery, so the battery should be sealed and substantially oxygen-free. and preferably in an anhydrous state.

[Effect of the invention] A non-aqueous secondary battery using the mixed solvent of the present invention, which is a mixture of a phosphoric acid ester and an ether compound in a specific ratio, as an organic solvent of an electrolytic solution, can be manufactured by using conventionally known propylene carbonate or tetrahydrofuran alone. Compared to the secondary battery used, (+) the energy density is large, (t+) the flatness of the z-pressure is good, (iii) there is little self-discharge, and (i
It has the following advantages: V) long cycle life, (V) good low-temperature properties, and (Vi) good thermal stability.

The nonaqueous secondary battery of the present invention is lightweight, compact, and has a high energy density, so it is useful as portable devices, electric vehicles, gasoline vehicles, and power storage batteries.

[Example] Hereinafter, the present invention will be explained in further detail by giving Examples and Comparative Examples.

Example 1 A Li/A gold alloy with an atomic ratio of Li and heli of 40:60 was used as the negative electrode, polypyrrole produced by electrolytic polymerization was used as the positive electrode, and the mixing ratio of LiPF6 electrolyte and trimethyl phosphate was used as the electrolyte. 20 volume d% trimethyl phosphate and 1.2
A cycle test of the battery was carried out using the experimental cell shown in FIG. 1, using a solution of LiPF6 containing a mixed solvent of -dimethoxyethane and having a concentration of 17 liters/liter.

The current density for charging and discharging was set at a constant current of 2.0rrt A/cd, and the end-of-discharge voltage was set at 2.0V.Start with discharging, and then immediately charge the amount of electricity at 25 mol per molecule per repeating unit of the positive electrode polypyrrole. % (this amount of electricity corresponds to 2/3 of the total reaction field of lithium in the Li/A 1 alloy used for the negative electrode), and when charging and discharging were repeated, the discharge voltage reached the 500th repetition. The relationship with time was the curve shown in FIG. 2(a). The charge/discharge efficiency at that time was 98%. In addition, after charging for the fifth time, we opened the circuit and discharged it immediately after leaving it for 24 hours.
The charging efficiency at the fourth repetition was 99%, while the charging/discharging efficiency in the 24-hour self-discharge test was 99%.
It was 6%. The energy density of both the positive and negative electrodes and the electrolyte used, calculated from the 500th discharge curve of this battery, is 78 W -hr/K
It was g. Note that all battery experiments were conducted at room temperature (20° C.).

Comparative Example 1 An experiment was conducted in exactly the same manner as in Example 1, except that the conventionally known propylene carbonate was used alone as the solvent for the electrolyte, except for the materials and weights of both electrodes.
The relationship between discharge voltage and time at the 500th repetition became the curve shown in FIG. 2(b). The charging/discharging efficiency at that time is 68%
Met. In addition, after charging for the fifth time, we conducted a 24-hour self-discharge test with an open circuit, and found that the charge-discharge efficiency for the fourth time was 92%, whereas the charge-discharge efficiency in the self-discharge test was was 88%. Also,
The energy density with respect to the weight of the positive electrode, negative electrode and electrolyte calculated from the 500th repetition discharge curve is 51W −
hr/ Kyte Atsuta.

Example 2 For the negative electrode, polyacetylene obtained by chemical polymerization using a Ziegler-Natsuta catalyst was electrochemically doped with 8 mol% of lithium per 4 units of acetylene repeating molecules, and for the positive electrode, a commercially available polyacetylene was used. using TiS2, LiBF4 electrolyte as electrolyte, and LiBF consisting of a mixed solvent of triethyl phosphate and 2-methyl-tetrahydrofuran with a mixing ratio of triethyl phosphate of 10% by volume.
A cycle test of the battery was carried out using a solution having a concentration of 17 l/l and using the same cell as in Example 1.

The charging and discharging current density was set at a constant current of 5.07FLA/1-111, and the discharge end voltage was set at 0.5■, and discharge was started in the same manner as in Example 1. Next, immediately charged N electric cup equivalent to 8 mol % with respect to the negative electrode polyacetylene (this electric surface is calculated as the amount released and intercalated with respect to the TiS2 used in the positive electrode, and the amount of T t S 2 used is 5
This corresponds to 0 mol%. ) and repeated charging and discharging, the charging and discharging efficiency at the 50th repetition was 99% or more.

Further, when a 24-hour self-discharge test was conducted at the fifth repetition as in Example 1, the charging/discharging efficiency at that time was 96%.

The energy density with respect to Wffi of both the positive and negative electrodes and the electrolyte used was calculated from the discharge curve after the 50th repetition of this battery was 72 W-hr/Ky.

Comparative Example 2 A battery cycle test was conducted in exactly the same manner as in Example 2, except that 2-methyl-tetrahydrofuran as a single solvent was used instead of the mixed solvent used in Example 2.

When this battery was subjected to a 24-hour self-discharge test for the fifth time, the charging/discharging efficiency was 92%.

Also, the energy density of this battery at the 50th repetition is 58W -hr/? It was rg.

Example 3 The battery used in Example 1 and gold (to configure a similar battery and examine the temperature characteristics, cycle 4 was conducted under the same conditions as Example 1)
Up to the 5th cycle, battery experiments were conducted at room temperature (20°C), and from the 5th cycle onwards, the battery system was maintained at -30°C. We conducted repeated charging and discharging experiments. The charging/discharging efficiency of this battery at the 20th repetition was 99% or more, and the energy density calculated from the discharge curve at the 20th repetition using the same method as in Example 1 was 73 W-hr/
It was Nf. Furthermore, when a 24-hour self-discharge test was conducted at the 25th repetition, the charging/discharging efficiency at this time was 98%. Next, from the 26th cycle, we raised the temperature of the battery system to 40°C and conducted a repeated charging/discharging experiment while keeping the temperature constant at 40°C, and the charging/discharging efficiency at the 30th cycle was 98. %Met.

The energy density at this time was 12W-117Kg. Furthermore, in order to investigate the self-discharge rate at 40° C., a 24-hour self-discharge test was conducted for the 35th time, and the charge/discharge efficiency at that time was 93%.

Comparative Example 3 A battery exactly the same as the battery used in Comparative Example 1 was constructed, and its temperature characteristics were examined under exactly the same conditions as in Example 3.

The charge/discharge efficiency of this battery at -30℃ is 97%, -
The energy density at 30°C was 57 W-hr/9.

Furthermore, when a self-discharge test was conducted at this temperature, the charge-discharge efficiency was 94%. Further, the charging/discharging efficiency at the 30th repetition at 40° C. was 81%, and the energy density at this time was 46 W-hr/Kg.

Furthermore, when a self-discharge test was conducted at the 35th repetition, the charging/discharging efficiency was 78%.

Comparative Examples 4 to 8 Battery experiments were conducted in exactly the same manner as in Example 1, except that the solvents shown in the table were used instead of the mixed solvent used in Example 1. The results are shown in the table.

Table Example 4 An experiment was conducted in exactly the same manner as in Example 1, except that Li gold metal pressure-molded onto a nickel wire mesh was used instead of the Li/A1 alloy used for the negative electrode in Example 1.

However, the Li! used for the negative electrode! On Day I, a weight equivalent to twice the reaction amount of tourmaline was used to dope the positive electrode polypyrrole with 25 mol % of anions.

The charging and discharging efficiency of this battery at the fourth cycle was 97%, and the charging and discharging efficiency at the fifth cycle after the 24-hour self-discharge test was 94%.

The energy density calculated from the discharge curve at the 50th repetition was 71 W-hr/Ky.

Comparative Example 9 Trimethyl phosphate used as wJIs in Example 4 and 1
, 2-dimethoxyethane, an experiment was carried out in exactly the same manner as in Example 4, except that propylene carbonate was used alone.

The charging/discharging efficiency of this battery after the fourth repetition was 90%. Further, the charging/discharging efficiency at the fifth cycle after the 24-hour self-discharge test was 85%.

Note that this battery could hardly be discharged after the 37th repetition, and the charging/discharging efficiency was 7%.

Example 5 Instead of the li metal used as the negative electrode active material in Example 4, 20% by weight of polyacetylene, 11% by weight of gold 11AJL60fi, and 120% by weight of li alloy were mixed with a pestle under an argon gas atmosphere. An experiment was conducted in exactly the same manner as in Example 4, except that the mixture was uniformly mixed and molded and used as the negative electrode.

However, among the composite electrodes used for the negative electrode, the weight of l-i is equivalent to 1.2 times that of tourmaline doped with 25 mol% of the molecular weight per repeating unit of the polypyrrole used for the positive electrode. did.

The charging/discharging efficiency of this battery at the fourth cycle was 99%, and the charging/discharging efficiency at the fifth cycle after the 24-hour self-discharge test was 98%.

The charge/discharge efficiency at the 50th repetition was 99%, and the energy density calculated from the discharge curve at the 50th repetition was 79 W-hr/Ky.

Comparative Example 10 An experiment was conducted in exactly the same manner as in Example 5, except that tetrahydrofuran was used as a comparative experiment solvent instead of the solvent used in Example 5.

The charging/discharging efficiency of this battery at the fourth cycle was 77%, and the charging/discharging efficiency at the fifth cycle after a 24-hour self-discharge test was 70%.

The charging/discharging efficiency at the 50th repetition was 36%, and the energy density calculated from the discharge curve at that time was 28W −
It was hr/Kg.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a battery cell for measuring characteristics of a non-aqueous secondary battery, which is an example of the present invention, and FIG.
and FIG. 9 is a diagram showing the relationship between the discharge voltage and the discharge time at the 50th repetition in Comparative Example 1. 1... Negative electrode lead wire 2... Negative electrode current collector 3...
・Negative pole

Claims (1)

[Claims] In a secondary battery using an alkali metal, an alkali metal alloy, a conductive polymer, an intercalation compound, or a composite thereof as a negative electrode active material, the electrolyte has the following general formula (1) or (2). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, M represents an alkali metal, X represents an element of Group Va of the periodic table, R_1 to R_6 may be different or the same, and may be a hydrogen atom, a halogen atom, It represents an alkyl group, aryl group, allyl group, aralkyl group, or halogenated alkyl group having 15 or less carbon atoms. ] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [In the formula, M represents an alkali metal, X represents an element of group IIIa of the periodic table, R_7 to R_10 may be different or the same, and may be a hydrogen atom, a halogen atom, It represents an alkyl group, aryl group, allyl group, aralkyl group, or halogenated alkyl group having 15 or less carbon atoms. ] and the following general formula (3) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [In the formula, R_11 to R_13 are hydrogen atoms, and the number of carbon atoms is 15
represents an alkyl group, an aryl group, an allyl group, an aralkyl group or a halogenated alkyl group. However, R_11 to R_13 are never hydrogen atoms at the same time. ] The mixed solvent consists of a mixed solvent of a phosphoric ester and an ether compound represented by
A non-aqueous secondary battery characterized by containing 30% by volume.