JPH04296471A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a non-aqueous electrolyte secondary battery having a long charging-discharging cycle lie and high capacity by using a carbonaceous material for an anode and a sydnone compound as an organic solvent of the non- aqueous electrolyte. CONSTITUTION:A carbonaceous material is used as a carrier of an anode 5 and novolak resin is fired to be used as the material. A cathode 7 is prepared by applying and drying LiCoO2 as a cathode active mass to which acetylene black and a binder are added. An electrolyte is prepared by dissolving LiPF6 in a sydnone compound having a formula I or a non-aqueous solvent mixture containing the sydnone compound. The mixing amount of 3-propylsydnone (a sydnone compound) is preferably no less than 10 volume%. Since the diameter of the complex obtained by solvating the sydnone compound-containing non- aqueous solvent and the Li ion is small and easy to enter into the interlayers of the carbonaceous material and occludes a large amount of Li. Consequently, the discharging capacity is improved and the charging-discharging cycle properties are remarkably improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an electrolyte in a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode carrier.

0002

BACKGROUND OF THE INVENTION In recent years, with the development of electronic devices, there has been a demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged. This type of secondary battery is known to use lithium or lithium alloy as the negative electrode active material and oxides, sulfides, selenides, etc. of molybdenum, vanadium, titanium, niobium, etc. as the positive electrode active material. There is.

Recently, spinel-type LiMn2O4 and other lithium-manganese composite oxides, which have improved cycle characteristics of manganese oxides having high energy density, have been actively studied.

[0004] In these battery systems that use lithium manganese oxide as a positive electrode active material and lithium as a negative electrode active material, by repeating the cycle, the dissolution and precipitation reactions of lithium, which is the negative electrode active material, are repeated, and eventually the lithium substrate A problem arises with the formation of acicular lithium dendrite precipitates on top.

Therefore, in this battery system, the battery life is limited by the gradual collapse of the crystal structure in the positive electrode active material, the formation of dendrites on the negative electrode side, and the decomposition reaction of the solvent, and the battery life is limited to more than 500 cycles. Manufacturing batteries with long-term reliability has been extremely difficult.

[0006] The above-mentioned deterioration of lithium is greatly affected by the combination of electrolyte and non-aqueous solvent, so the optimum combination thereof is being studied. For example, among various mixed solvents being considered as non-aqueous solvents, a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran is known to be a stable solvent for lithium. In the case of such a mixed solvent, it has been reported that high lithium charging and discharging efficiency can be obtained with a nonaqueous electrolyte in which 1.5 mol/l of LiAsF6 is dissolved as an electrolyte (Electro-chem, Acta, 30 ,1
715 (1985)). However, LiAsF6 has problems in terms of toxicity.

For this reason, the use of lithium hexafluorophosphate (LiPF6) and lithium borofluoride (LiBF4), which have a molar conductivity as high as that of LiAsF6, is being considered. However, LiPF6 and LiBF4 have problems such as poor chemical stability, so it is difficult to obtain sufficient lithium charging and discharging efficiency with non-aqueous electrolytes in which these electrolytes are dissolved, and there are problems in that storage properties are also poor. Ta.

On the other hand, electrode active materials utilizing the intercalation or doping phenomenon of layered compounds are attracting attention. Since these electrode active materials do not cause complicated chemical reactions during charge and discharge reactions, they are expected to have extremely excellent charge and discharge cycles. Among these, those using carbonaceous materials as a carrier are attracting attention. This carbonaceous material is used as a negative electrode carrier, and as a positive electrode active material, for example, L
The iCoO2/LiNiO2 system has been proposed.

[0009]

[Problems to be Solved by the Invention] However, since the amount of intercalation and desorption of lithium ions is still small, there is a problem in that the negative electrode specific capacity (mAh/g) is small. Therefore, even if a carbonaceous material is used as a negative electrode, it is difficult to obtain sufficient battery capacity and cycle life at the same time.

The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a non-aqueous electrolyte secondary battery with excellent charge/discharge cycle life. In particular, when a carbon material, which is a fired body of an organic compound, and lithium or an alkali metal mainly composed of lithium supported on the carbonaceous material are used in the negative electrode body, a non-aqueous material with excellent charge/discharge cycle characteristics and high capacity can be used. The purpose is to provide an electrolyte secondary battery.

[0011]

[Means for Solving the Problems] That is, the present invention provides general formula (I):

0012

[Case 2]

(In the formula, R1 represents an alkyl group, an aralkyl group, or an aryl group, R2 represents a hydrogen atom, an alkyl group, an aralkyl group, or an aryl group, and the dotted line represents a resonance hybrid structure.)

[0014]

[Chemical formula 3]

Regarding the non-aqueous electrolyte for batteries, which is formed by dissolving an electrolyte in a sydone compound (a type of mesoionic compound) represented by In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, the non-aqueous electrolyte secondary battery is characterized in that a sydone compound represented by the aforementioned general formula (I) is used as an organic solvent. be.

The non-aqueous electrolyte for batteries of the present invention is one in which an electrolyte is dissolved in sydone compound (I). The sydone compound used as an organic solvent in the present invention is the most characteristic one and is represented by the above-mentioned general formula (I). R1 is methyl, ethyl, propyl, isopropyl, butyl, hexyl, heptyl, octyl, nonyl,
Examples include linear or branched alkyl groups such as decyl and dodecyl, aralkyl groups such as benzyl, phenylethyl and phenylpropyl, and aryl groups such as phenyl and tolyl, and the viscosity and melting point increase as the number of carbon atoms increases. As a result, the low-temperature characteristics of the battery deteriorate. Therefore, an alkyl group having 1 to 6 carbon atoms is preferable;
The alkyl group of No. 3 is particularly preferred.

In addition to a hydrogen atom, R2 is exemplified by those within the same range as R1, and may be the same or different from R1. R2 is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

In the non-aqueous electrolyte of the present invention, sydone (I) may be used as a solvent in combination with other non-aqueous solvents to form a mixed solvent. Examples of electrolytes that can be used in combination with Sidonone include DME, THF, 2Me-THF, acetonitrile (AN), dioxolane (DOL), PC, and ethylene carbonate (EC). The amount of sydone in the mixed solvent is preferably 5% by volume or more, more preferably 10% by volume or more.

[0019] Examples of the electrolyte used in the present invention include LiBF4, LiPF6, LiClO4, LiAsF
6, 1 selected from LiCF3SO3, LiAlCl4
A species or more than one lithium salt can be used. It is desirable that such a lithium salt be dissolved in the solvent in an amount of 0.2 to 1.5 mol/l. The reason for this is that deviating from the above range may lead to a decrease in electrical conductivity and a decrease in lithium charging/discharging efficiency. The amount of electrolyte in the nonaqueous electrolyte is preferably 0.5 to 1.5 mol/l, and 0.5 to 1.5 mol/l.
-1.2 mol/l is particularly preferred.

[0020] Before storing the non-aqueous electrolyte in the battery container, the non-aqueous electrolyte is treated by being adsorbed onto an insoluble adsorbent, or treated with electricity, or both of these treatments in order to remove moisture and impurities. It is desirable to apply

The above treatment with an insoluble adsorbent can be carried out by, for example, adding an insoluble adsorbent that does not react with the electrolytic solution, such as activated alumina or molecular sieve, to the electrolytic solution and stirring, and then filtering the insoluble adsorbent. A method of separation by,
Alternatively, a method can be adopted in which the electrolyte is passed through a column filled with an insoluble adsorbent.

[0022] The above-mentioned energization treatment is carried out, for example, by immersing an electrode made of lithium as an anode in an electrolytic solution and immersing an electrode made of lithium or a metal other than lithium as a cathode, and then applying a constant current between the anode and the cathode. Alternatively, lithium can be deposited on the cathode by applying continuous waves or pulses at a constant voltage, or a method of repeating deposition and dissolution can be adopted.

[0023] In the non-aqueous electrolyte secondary battery of the present invention, the organic compound serving as the raw material for the carbonaceous material constituting the negative electrode is not particularly limited as long as it is commonly used. For example, epoxy Resin; Phenolic resin; Acrylic resin such as polyacrylonitrile, poly(α-halogenated acrylonitrile); Halogenated vinyl resin such as polyvinyl chloride, polyvinylidene chloride, polychlorinated vinyl chloride; Poamide-imide resin; Polyamide resin; Polyacetylene, poly Any organic polymer compound such as a conjugated resin such as (p-phenylene); For example, naphthalene, phenanthrene, anthracene, triphenylene,
A condensed polycyclic hydrocarbon compound formed by condensing two or more monocyclic hydrocarbon compounds with three or more members, such as pyrene, chrysene, naphthacene, picene, perylene, pentaphene, and pentacene, or a carboxylic acid of the above compound, Various pitches whose main components are derivatives such as carboxylic acid anhydrides, carboxylic acid imides, and mixtures of the above compounds; for example,
At least two or more 3-membered or more-membered heterocyclic compounds such as indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, and phenathridine are bonded to each other,
or a fused heterocyclic compound bonded to one or more 3-membered or more monocyclic carbon compounds, derivatives of the above compounds such as carboxylic acids, carboxylic acid anhydrides, and carboxylic acid imides, and further benzene 1 and 2 , 4,5-tetracarboxylic acid, its dianhydride, or its diimide. Furthermore, coke and the like can also be used as raw materials for carbonaceous materials.

[0024] This carbonaceous material is produced by heating one or more of the above-mentioned compounds in a non-oxidizing atmosphere at a temperature of 1000 to 300.
It can be prepared by calcination, thermal decomposition, and carbonization at 0° C. for 2 to 3 hours.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode may be, for example, amorphous vanadium pentoxide, manganese oxide such as manganese dioxide or lithium manganese composite oxide, titanium disulfide, molybdenum disulfide, Examples include molybdenum selenide, lithium cobalt composite oxide, lithium cobalt nickel composite oxide, and the like.

[0026]

[Operation] According to the present invention, by using a carbonaceous material for the negative electrode and using the sydone compound (I) as the organic solvent of the non-aqueous electrolyte, the non-aqueous electrolyte has an excellent charge/discharge cycle life and a high capacity. A liquid secondary battery can be obtained.

The mechanism by which the effects of the present invention are obtained is that the diameter of the solvated complex of the non-aqueous solvent containing the sydone compound and the Li ion is relatively small, and that the solvated complex is formed between the layers of the carbonaceous material, which is the fired product of the organic material. Due to the ease of insertion, Li easily diffuses between the layers of the negative electrode carbon-based material.
This is believed to be because the solvent of the present invention is able to absorb more Li, and is chemically and electrochemically stable, does not react with the negative electrode carbon-based material, and does not cause collapse of the structure of the negative electrode carbon-based material. It will be done.

[0028] Also, for example, Li, which is used as an electrolyte,
PF6 and LiBF4 are unstable to moisture and heat, so
It decomposes to produce Lewis acids such as PF5 and BF3. Such Lewis acids tend to react with solvents, producing impurities that degrade the solvent.

Furthermore, according to the present invention, by using the sydone compound (I) which is strong due to the oxidation reaction with Lewis acid, the reaction between the solvent and the Lewis acid can be suppressed, and as a result, the formation of impurities that deteriorate the negative electrode carbonaceous material can be reduced. can. This also makes it possible to obtain a non-aqueous electrolyte secondary battery with an excellent charge/discharge cycle life.

Further, the dielectric constant ε of the above sydone compound is:
For example, 3-methylsydone is 144.0 (40°C),
3-propylcydonone is 95.0 (25℃), 3-isopropylcydonone is 66.0 (60℃), 3-butylcydonone is 52.8 (25℃), and PC is 64.4 (
25℃), DME is 7.20 (25℃), γ-BL is 3
9.1 (25°C), THF is higher than other organic solvents such as 7.58 (25°C). Furthermore, for example, 3-propylsidone exhibits a very high dielectric constant at low temperatures (around 0° C.), as shown in FIG. From this, when a sydone compound is used as an organic solvent for a nonaqueous electrolyte, its high dielectric constant easily causes ion dissociation of lithium salt, which is an electrolyte, even at low temperatures. It is possible to obtain a non-aqueous electrolyte secondary battery with superior low-temperature operation characteristics compared to conventional batteries.

[0031] Before placing the non-aqueous electrolyte having the above composition into the battery container, the negative electrode carbonaceous material and the non-aqueous electrolyte can be brought into contact with an insoluble adsorbent and/or subjected to an electric current treatment. The deterioration of the carbonaceous material due to the reaction can be significantly suppressed, and a non-aqueous electrolyte secondary battery having extremely good charge/discharge cycle life and storage property can be obtained. This is considered to be because impurities in the electrolyte are removed by the above treatment, resulting in a highly pure non-aqueous electrolyte.

[0032]

EXAMPLE Hereinafter, an example in which the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery will be described in detail with reference to FIG. In addition, although a secondary battery with a cylindrical structure was used in the example,
The technology of the present invention is not limited to this structure, and can also be applied to non-aqueous electrolyte secondary batteries having shapes such as coin shape, flat shape, and square shape.

Example 1 90% by weight of LiCoO as a positive electrode, 7% by weight of acetylene black as a conductive material, and 3% by weight of an ethylene-propylene-cyclic diene terpolymer as a binder were kneaded in hexane to form a slurry. A positive electrode mixture was prepared, and this positive electrode mixture was applied onto a titanium substrate with a thickness of 15 μm, air-dried, and then pressurized to a constant thickness. A plate-shaped positive electrode having a positive electrode mixture layer with a thickness of .26 mm was manufactured.

On the other hand, the carbonaceous material that is the negative electrode carrier is prepared by baking a novolak resin at 950°C in a nitrogen atmosphere.
It was further produced by heating to 2,000°C to carbonize it, and pulverizing it into a powder with an average particle size of 10 μm.

A ternary copolymer of ethylene-propylene-cyclic diene as a binder was dissolved in hexane and dispersed in a ratio of carbonaceous material:adhesive=97:3 to prepare a slurry-like negative electrode mixture. did. This slurry was applied onto a stainless steel substrate with a thickness of 10 μm and dried to form a negative electrode mixture with a thickness of 0.2 mm.

Using the positive and negative electrodes thus obtained, a non-aqueous solvent secondary battery of AA size as shown in FIG. 1 was assembled. That is, the non-aqueous solvent secondary battery 1 has a bottomed cylindrical stainless steel container 3 with an insulator 2 disposed at the bottom and also serving as a negative electrode terminal. This container 3 includes an electrode group 4
is stored. This electrode group 4 consists of a strip of a negative electrode 5, a separator 6, and a positive electrode 7 laminated in this order.
It has a structure in which it is wound in a spiral shape so that it is located on the outside. The separator 6 is formed from a polypropylene porous film impregnated with an electrolytic solution.

The electrolytic solution used was one in which 0.8 molar concentration of lithium hexafluorophosphate (LiPF6) was dissolved in 3-propylcydonone (formula (II)).

[0038]

[C4]

An insulating plate 8 with an open center is arranged above the electrode group 4 in the battery container 3. An insulating sealing body 9 is hermetically caulked and fixed to the upper opening of the container 3. A positive electrode terminal 10 is fitted into the central opening of the insulating sealing plate 8 . This positive electrode terminal 10 is connected to the above-mentioned positive electrode 7 via a positive electrode lead 11. Note that the negative electrode 5 is connected to the container 3, which is a negative electrode terminal, via a negative electrode lead (not shown).

Example 2 As a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF6) was mixed with 3-propylsidenon: formula (I
A nonaqueous electrolyte secondary battery having the same configuration as in Example 1 was assembled, except that a battery having a composition dissolved in a mixed solvent of I) and DME (mixed volume ratio 50:50) was used.

Comparative Example 1 A non-aqueous electrolyte having the same structure as in Example 1 except that an electrolyte in which 0.8 molar concentration of lithium hexafluorophosphate (LiPF6) was dissolved in PC was used as the non-aqueous electrolyte. I assembled a liquid secondary battery.

Comparative Example 2 As a non-aqueous electrolyte, 0.8 molar concentration of lithium hexafluorophosphate (LiPF6) was used in a mixed solvent of PC and 1,2-dimethoxyethane (DME) (mixed volume ratio 50:50). A non-aqueous electrolyte secondary battery having the same configuration as in Example 1 was assembled, except that a battery having a composition dissolved in .

The nonaqueous electrolyte secondary batteries of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 were repeatedly charged and discharged at a charging current of 100 mA and a discharging current of 100 mA, and the discharge capacity and cycle life of each battery were determined. It was measured. The results are shown in FIG.

[0044]

[Effect of the invention] As is clear from FIG. 2, this embodiment 1,
The non-aqueous electrolyte secondary battery of No. 2 has almost the same initial discharge capacity as the batteries of Comparative Examples 1 and 2, but the decrease in discharge capacity is small even when the number of cycles increases, and the cycle life is shortened. It can be seen that it has become significantly longer.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a cylindrical non-aqueous electrolyte secondary battery in Example 1 of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the discharge capacity and the number of charge/discharge cycles of cylindrical nonaqueous electrolyte secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2.

[Figure 3] Temperature (°C) and dielectric constant (
ε) is a characteristic diagram showing the relationship with ε).

[Explanation of symbols]

1 battery 4 electrode group 5 negative electrode 6 separator 7 positive electrode 9 sealing body A Example 1 B Example 2 C Comparative example 1 D Comparative example 2

Claims (1)

[Claims] Claim 1: A non-aqueous electrolyte secondary battery using a carbon material as a negative electrode carrier, comprising a positive electrode, and an electrolyte solution formed by dissolving an electrolyte in a non-aqueous solvent, which has the general formula (I): 1] (In the formula, R1 represents an alkyl group, an aralkyl group, or an aryl group, R2 represents a hydrogen atom, an alkyl group, an aralkyl group, or an aryl group, and the dotted line represents a resonance hybrid structure) A non-aqueous electrolyte secondary battery characterized in that a non-aqueous mixed solvent containing the compound or the sydone compound is used.