JPH08190932A - Secondary battery having nonaqueous solvent electrolyte - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery with excellent high voltage resistance and high negative electrode charging characteristics by using diethyl malonate as an electrolyte. CONSTITUTION: A lithium secondary battery comprises a stainless steel negative case 1, a negative electrode 2, an electrolyte 3 using a nonaqueous solvent, a separator 4, a positive electrode 5, a stainless steel positive case 6, and a gasket 7. As the positive electrode 5, a composite oxide of a composite oxide of Li and Co, or Li and Ni with Li and a transition metal can be used. As the negative electrode, a material capable of charging/discharging a lithium ion, such as lithium metal, a lithium alloy, and others is used. As an electrolyte of the electrolyte solution, LiClO4 , LiPF6 , LiAsF6 , LiBrF4 , or LiAlCl4 alone or a mixture of these compounds is used. By using diethyl malonate as the solvent of a nonaqueous solvent electrolyte, the secondary battery with long life and high energy density is obtained. For example, the electrolyte prepared by dissolving one molar LiClO4 in diethyl malonate is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery having a non-aqueous solvent electrolyte having a high voltage, a high energy density and a large charge / discharge capacity.

[0002]

2. Description of the Related Art As portable electronic devices have become smaller and lighter, it has been required to develop a high energy density battery as a power source thereof. As a battery that meets such requirements, development of a high-performance secondary battery having a negative electrode capable of charging and discharging lithium ions and a positive electrode capable of reversible electrochemical reaction with lithium ions is expected. Examples of the negative electrode capable of charging and discharging lithium ions include (i) a lithium metal negative electrode, (ii) a lithium alloy negative electrode capable of charging and discharging lithium ions,
(Iii) A negative electrode mainly composed of a negative electrode active material holder capable of charging and discharging lithium ions can be mentioned. Examples of the lithium alloy negative electrode (ii) capable of charging and discharging lithium ions include, for example, a lithium alloy mainly composed of Li and Al, Li and C
Known lithium alloys such as d, In, Pb, and Bi, lithium alloys of Li and Mg, and the like are known. Also, in (iii) above,
Examples of the negative electrode mainly composed of a negative electrode active material holder capable of charging and discharging lithium ions include various carbon materials, Nb ₂
Attempts have been made to use metal oxides such as O ₅ , WO ₂ and Fe ₂ O ₃ and polymer compounds such as polythiophene and polyacetylene. Examples of the positive electrode capable of reversible electrochemical reaction (chargeable and dischargeable) with the lithium ion include Li _x CoO ₂ (0 ≦ x ≦ 1), Li _x
NiO ₂ (0 ≦ x ≦ 1), Li _x Mn ₂ O ₄ (0 ≦ x ≦
1), crystalline or amorphous V ₂ O ₅ , polyaniline,
The use of polypyrrole or the like is being studied. In the present specification, a battery capable of charging and discharging these lithium ions is referred to as a lithium secondary battery. As this type of battery, a battery using carbon as a negative electrode active material holder and LiCoO ₂ as a positive electrode active material, a battery using carbon as a negative electrode active material holder and V ₂ O ₅ as a positive electrode active material, a negative electrode active material Batteries using Nb ₂ O ₅ as the substance holder and V ₂ O ₅ as the positive electrode active material are already on the market. This type of lithium secondary battery is basically required to have a long charge / discharge cycle life, and the charge / discharge performance is greatly affected by the selected non-aqueous electrolyte solution material. The non-aqueous electrolyte used is required to have chemical stability (high reduction resistance) to the negative electrode active material holder or lithium metal. Also, when the voltage of this type of battery is a high voltage around 4V,
The electrolytic solution is also required to have high oxidation resistance (high oxidation potential). Therefore, the non-aqueous electrolytic solution used in this type of battery is required to have good negative electrode charge / discharge performance and high reduction resistance and oxidation resistance. In order to meet the above-mentioned requirements for the non-aqueous electrolytic solution, an electrolytic solution having a particularly high oxidation potential has been studied. For example, a dialkyl carbonate such as dimethyl carbonate or diethyl carbonate or methyl formate,
Electrolytes using ester-based solvents with a linear structure such as methyl acetate and ethyl acetate have been investigated [Jiorna
l of Electrochemical Society), Vol. 136, No. 7
No., 1865-1869 (1985)]. But,
The electrolytic solution using these solvents has a high oxidation potential, but has a low reduction potential, and has a high reactivity with the negative electrode that has occluded lithium and lithium metal. Further, what is known to have good charge and discharge characteristics of the negative electrode (for example, dioxolane and 2-methyltetrahydrofuran) are ethers,
Although it has strong resistance to reduction, it is easily oxidized, and the charge / discharge characteristics and storage stability of high-voltage batteries are poor. Further, cyclic carbonates such as propylene carbonate have a practically usable value for the oxidation potential, but the reduction potential is higher than that of ethers, and sufficient charge / discharge performance of the negative electrode cannot be obtained. Therefore, there is a demand for an electrolytic solution for a lithium secondary battery, which has good charge / discharge performance, high oxidation resistance, and high reduction resistance, but no electrolytic solution satisfying these conditions has been proposed.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a lithium secondary battery having excellent withstand high voltage and excellent charge / discharge characteristics of the negative electrode. To do.

[0004]

The present invention will be described in brief. The present invention relates to a secondary battery having a non-aqueous solvent electrolyte, which is a negative electrode capable of charging and discharging lithium ions, and reversible with lithium ions. In a secondary battery having a positive electrode capable of electrochemical reaction and an electrolytic solution in which an ion dissociative lithium salt is dissolved in a non-aqueous solvent, the following structural formula (Formula 1) is added to the non-aqueous solvent:

[0005]

Embedded image CH ₃ —CH ₂ —O—CO—CH ₂ —CO—O
-CH ₂ -CH ₃

It is characterized by using diethyl malonate represented by

According to the present invention, for example, as a positive electrode, a composite oxide of lithium and cobalt, a composite oxide of lithium and nickel, a composite oxide of lithium and manganese, a composite oxide of lithium and iron, or the above composite oxide. It is possible to use those obtained by partially substituting cobalt, nickel, manganese, and iron with other transition metals.

As the negative electrode, one capable of charging and discharging lithium ions can be used. As the negative electrode material capable of charging and discharging lithium ions, (1) lithium metal negative electrode and (2) lithium capable of charging and discharging lithium ions. Alloy negative electrode, for example, lithium alloy mainly composed of Li and Al, Li and C
Lithium alloys such as d, In, Pb and Bi, (3) Negative electrodes mainly containing a negative electrode active material holder capable of charging and discharging lithium ions, for example, various carbon materials, Nb ₂ O ₅ , WO ₂ ,
Examples include metal oxides such as Fe ₂ O ₃ and polymer compounds such as polythiophene and polyacetylene.

LiClO ₄ , L is used as the electrolyte of the electrolytic solution.
_{iPF 6, LiAsF 6, LiBF 4} , LiAlC
l ₄ , LiCF ₃ SO ₃ , LiSbF ₆ , LiSCN,
LiCl, LiC ₆ H ₅ SO ₃ , LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ SO
Lithium salts such as ₃ can be used alone or in admixture of two or more. By using diethyl malonate as the solvent of the non-aqueous solvent electrolytic solution, it is possible to provide a secondary battery having a non-aqueous solvent electrolytic solution having a long life and a high energy density.

The secondary battery having the non-aqueous solvent electrolyte of the present invention has the following features, for example. That is, a battery using a composite oxide of lithium and manganese as a positive electrode active material is inexpensive and has a long cycle life. A battery using a composite oxide of lithium and cobalt has features of high voltage and high energy density. A battery using a composite oxide of lithium and nickel has characteristics of high charge / discharge capacity and high energy density. A battery using a composite oxide of lithium and iron is inexpensive and lightweight. In addition, each of the above composite oxides in which cobalt, nickel, manganese, and iron are partially replaced with another transition metal has a characteristic that the crystal structure is particularly stable and the charge / discharge life is extended by the replacement. By using diethyl malonate, which has high reduction resistance and oxidation resistance, as a solvent for the electrolytic solution, a long charge / discharge life can be achieved.

[0011]

EXAMPLES The effects of the present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

EXAMPLE 1 Lithium perchlorate (LiClO ₄ ) in diethyl malonate
Was dissolved in 1 M, and the voltage was swept at 0.1 mV / sec using the glassy carbon as a working electrode. At this time, the potential at which the current value rises rapidly can be regarded as the oxidation potential. For comparison, 1M LiClO ₄ -PC / DM
The E (PC: propylene carbonate, DME: dimethoxyethane) electrolytic solution was also measured in the same manner. 1M LiClO
_4- PC / DME is decomposed by an increase in current due to the oxidation of the solvent at around 4.8 V, whereas it is 5.6 V in the electrolytic solution in which 1 M of LiClO ₄ is dissolved in diethyl malonate.
Up to this point, no increase in current value due to decomposition of the solvent, that is, decomposition of the electrolytic solution was observed. In addition, in these, the electrolyte is LiPF
₆ , LiBF ₄ , LiAsF _6, etc. are almost the same.

Example 2 Using an electrolytic solution in which 1M of LiClO ₄ was dissolved in diethyl malonate, lithium was electrochemically treated in an amount of 2 m on a stainless plate.
A in FIG. 1 shows the change in charging / discharging efficiency when Ah was electrodeposited and then electrochemically dissolved by discharge. For comparison, a change in charge / discharge efficiency when a 1M LiClO ₄ -PC / DME electrolyte solution was also used is shown in b in FIG. 1. In FIG. 1, the horizontal axis represents the number of cycles and the vertical axis represents the charge / discharge efficiency (%). From the results in FIG. 1, it can be seen that b shows a stable characteristic while the charge / discharge cycle sharply decreases with the charge / discharge cycle. In addition, these are electrolytes with LiP
The same applies to F ₆ , LiBF ₄ , LiAsF _6, etc.

Example 3 An electrolytic solution of 1M LiClO ₄ dissolved in diethyl malonate was used, and acetylene black, which is a kind of carbon (interlayer distance: 3.47-3.48 Å), was used as a negative electrode. Coin battery shown in (diameter 23m
m, thickness 2 mm) was prepared (this battery is referred to as "battery c"). That is, FIG. 2 is a cross-sectional view of the battery of the present invention, in which reference numeral 1 is a negative electrode case made of stainless steel, 2 is a negative electrode, and 3 is a negative electrode.
Is an electrolytic solution using a non-aqueous solvent, 4 is a separator, 5 is a positive electrode, 6 is a stainless steel positive electrode case, and 7 is a gasket. Further, as a comparison for showing the effect of the present invention,
A coin battery identical to that described above was prepared except that 1M LiClO ₄ -PC / DME electrolyte was used (this battery is referred to as “battery d”). 0.5 mA for these batteries
At the discharge and charging current densities of / cm ² , the voltage-controlled charging / discharging cycle in which the lower limit of the discharging voltage was 0 V and the upper limit of the charging voltage was 2.0 V was repeated. This test is a test in which lithium is occluded in acetylene black by discharging and releasing lithium occluded in acetylene black by charging,
This is a test for knowing the influence of the electrolyte solution material on the charge and discharge performance of the negative electrode in which lithium is stored in the negative electrode holder (acetylene black in this example). In this test,
Discharge capacity per acetylene black weight (mAh / g,
The relationship between the vertical axis) and the number of cycles (horizontal axis) is shown as c and d in FIG.
Shown in The “battery d” (d in FIG. 3) of the comparative example is about 50.
The discharge capacity decreased to 50% of the initial capacity with cycling. On the other hand, the “battery c” of the present invention (c in FIG. 3) has a larger discharge capacity per cycle than the “battery d” of the comparative example, and a stable charge / discharge cycle of 50 cycles or more was possible.
In addition, these electrolytes are LiPF ₆ , LiBF ₄ , and Li.
The same applies to AsF ₆ etc.

[0015]

As described above, according to the present invention, by using diethyl malonate as the electrolytic solution, a secondary battery having a non-aqueous solvent electrolytic solution excellent in charge / discharge characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in charge / discharge efficiency of an electrolytic solution in Example 2 of the present specification, in which a is an electrolytic solution (1M L
iClO ₄ -diethyl malonate), b is 1M LiCl
O ₄ is a diagram showing a case of -PC / DME.

FIG. 2 is a cross-sectional view of the battery of the present invention.

FIG. 3 is a diagram showing a change in discharge capacity per weight of acetylene black in Example 3 of the present specification, where c is an electrolyte solution of the present invention (1M LiClO ₄ -diethyl malonate),
d is a diagram showing a case of 1M LiClO ₄ -PC / DME.

[Explanation of symbols]

1: Stainless steel negative electrode case, 2: Negative electrode, 3: Electrolyte using non-aqueous solvent, 4: Separator, 5: Positive electrode, 6: Stainless steel positive electrode case, 7: Gasket

Claims (1)

[Claims] 1. A negative electrode capable of charging and discharging lithium ions,
In a secondary battery having a positive electrode capable of reversibly electrochemically reacting with lithium ions and an electrolytic solution in which an ion dissociative lithium salt is dissolved in a non-aqueous solvent, the non-aqueous solvent is represented by the following structural formula (Formula 1). A secondary battery having a non-aqueous solvent electrolyte, characterized by using diethyl malonate represented. Embedded image CH ₃ —CH ₂ —O—CO—CH ₂ —CO—O
-CH ₂ -CH ₃