JPH10189038A - Nonaqueous electrolyte and nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic secondary battery having a high degree of incombustibility and safety, having the capability of generating high voltage and further having a high charging and discharging function by composting a nonaqueous electrolyte of a nonaqueous solvent containing a phosphoric ester compound having a group with an ether linkage and an electrolyte. SOLUTION: The nonaqueous electrolyte of a secondary battery is composed of a nonaqueous solvent containing the phosphoric ester compound expressed by the formula and an electrolyte. In the formula, R<1> , R<2> and R<3> may be identical to or different from each other, and are an alkyl group having carbons between 1 and 4, or a group having the ether linkage expressed by -R<4> -O-R<5> . Also, R<4> and R<5> stand for a hydrocarbon group having carbons between 1 and 10. Furthermore, lithium salt such as LiPF6 , LiBF4 , LiClO4 , LiAsF6 , and LiCF3 SO3 is mentioned, for example, as an electrolyte dissolved in the nonaqueous electrolyte. Also, the electrolyte is preferably contained in the nonaqueous electrolyte at a level of concentration between 0.5 and 2mol/L. The nonaqueous electrolyte may be used for a cylindrical nonaqueous electrolytic secondary battery or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery which are safe, capable of generating a high voltage, and excellent in battery charge / discharge performance. The present invention relates to a water electrolyte and a non-aqueous electrolyte secondary battery containing the electrolyte.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION Non-aqueous electrolytes are
Electrolysis of energy storage devices such as gas double layer capacitors
Used in high quality, high voltage, high energy
With high energy density and excellent reliability
It is used as a power source for electronic equipment for home use. Non-aqueous electrolyte
Is composed of a non-aqueous solvent and an electrolyte.
In general, propylene carbonate is a high dielectric constant organic solvent
G, γ-butyrolactone, sulfolane, or low viscosity
Dimethyl carbonate, dimethoxy
For use with tan, tetrahydrofuran, 1,3-dioxolan, etc.
It has been. The electrolyte is Et._FourNBF_Four, Li
BF_Four, LiPF₆, LiClO_Four, LiAsF₆, LiCF _ThreeS
O_Three, LiAlCl_Four, LiSiF₆Are used.

[0003] Among energy storage devices using a non-aqueous electrolyte, a secondary battery called a lithium ion battery is rapidly spreading. It is necessary for this battery to ensure its safety by experiments such as overcharging, external short-circuiting, nail penetration, and crushing. In the future, if the energy density is significantly increased or the size of the battery is increased, it is desired to further improve the safety, and the flammable non-aqueous electrolyte must have self-extinguishing properties. Have been.

[0004] For this reason, it has been proposed to add a phosphate ester known as a compound having a self-extinguishing property to an electrolytic solution (for example, see JP-A-4-184870).

[0005] However, an electrolytic solution to which a general phosphate such as triethyl phosphate is added is flame-retardant and the safety is improved, but the reductive decomposition reaction of the phosphate tends to occur at the negative electrode. Therefore, there are problems in terms of battery charge / discharge efficiency, battery energy density, and battery life depending on the type and the amount of addition. In order to solve such a problem, it has been proposed to limit the amount of phosphate ester to be added (for example, see Japanese Patent Application Laid-Open No. 8-22839).

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous electrolyte which has high flame retardancy, is safe, can generate a high voltage, and has excellent battery charge / discharge performance. And a secondary battery containing the non-aqueous electrolyte.

[0007]

SUMMARY OF THE INVENTION The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a phosphate compound represented by the following general formula [I], and an electrolyte.

[0008]

Embedded image

[Wherein R ¹ , R ² and R ³ may be the same or different and each is an alkyl group having 1 to 4 carbon atoms or an ether represented by —R ⁴ —O—R ^5. a group containing a bond (a hydrocarbon group of R ⁴ and R ⁵ may C1-10 optionally being the same or different), R ¹
At least one of to R ³ indicates a group containing an ether bond represented by -R ⁴ -O-R ^5. It is preferable that the group containing an ether bond is a methoxyethyl group or a methoxyphenyl group.

Further, the electrolyte is preferably LiPF _6. Such an electrolyte concentration is preferably in the range of 0.5 to 2.0 mol / liter.

In the nonaqueous electrolyte secondary battery according to the present invention, the negative electrode active material includes lithium metal, a lithium-containing alloy, a compound capable of doping / undoping lithium ions, and a carbon capable of doping / dedoping lithium ions. It is characterized by including a negative electrode containing any one of the materials, a positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material, and a nonaqueous electrolyte as described above.

[Detailed Description of the Invention] A non-aqueous electrolyte according to the present invention and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte will be specifically described below.

The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a specific phosphate compound and an electrolyte. Phosphate ester compound As the phosphate ester compound contained in the non-aqueous solvent,
The compound represented by the following general formula [I] is preferable.

[0014]

Embedded image

In the formula, R ¹ , R ² and R ³ may be the same or different from each other, and have an alkyl group having 1 to 4 carbon atoms or an ether bond represented by —R ⁴ —O—R ^5. And at least one of R ^{1 to} R ³ is -R ⁴ -O-
A group containing an ether bond represented by R ⁵ is shown.

R ⁴ and R ⁵ may be the same or different and represent a hydrocarbon group having 1 to 10 carbon atoms.
Examples of the group containing an ether bond represented by -R ⁴ -OR ⁵ include a methoxymethyl group, a methoxyethyl group, a methoxypropyl group, a methoxyphenyl group, an ethoxymethyl group, an ethoxyethyl group, an ethoxypropyl group, and an ethoxy group. Phenyl group, methoxyethoxyethyl group (CH ₃ OCH ₂ CH ₂ OC
H ₂ CH ₂ —), and a 2,2-dimethoxyethyl group.

As for the carbon number of R ^{1 to} R ⁵ , the self-extinguishing action of the phosphate ester tends to increase as the phosphorus content in the phosphate ester increases. As such a phosphate compound, specifically, trimethoxyethyl phosphate,
Di (methoxy) methoxyphenyl phosphate, tri (methoxyphenyl) phosphate, di (methoxyethyl) phosphate
(Methyl), (methoxyethyl) phosphate di (methyl) phosphate,
Di (methoxyphenyl) methyl phosphate, tri (ethoxyethyl) phosphate, (methoxyethyl) di (ethoxyethyl) phosphate, di (methoxyethyl) ethoxyethyl phosphate, (methoxyethyl) di (methoxyphenyl) phosphate , Di (methoxyethyl) methoxyphenyl phosphate,
Methyl (methoxyethyl) phosphate (methoxyphenyl), tri (methoxymethyl) phosphate and the like can be mentioned.

Of these, trimethoxyethyl phosphate and di (methoxy) methoxyphenyl phosphate are particularly preferred. Non-aqueous solvent The non-aqueous solvent used in the present invention may be composed of a phosphate ester compound as described above,
Further, it may be composed of a mixture of a phosphate compound and another non-aqueous solvent. When the non-aqueous solvent is a mixed solvent of a phosphate compound and another non-aqueous solvent, the phosphate compound is 1.0% by volume or more in the mixed solvent.
Preferably 5 to 90% by volume, more preferably 10 to 7% by volume.
It is present in an amount of 0% by volume.

Within such a range, sufficient self-extinguishing properties can be obtained, and high battery performance can be maintained. As the non-aqueous solvent other than the phosphate ester compound, a low-viscosity non-aqueous solvent, a high-dielectric-constant non-aqueous solvent, or the like is preferably used in order to improve the conductivity of the electrolytic solution.

As the low-viscosity nonaqueous solvent, for example, a chain ester represented by the following general formula [II] can be used.

[0021]

Embedded image

(Wherein R ⁶ represents a hydrogen atom, a methyl group, an ethyl group, a methoxy group, or an ethoxy group, and R ⁷ represents a chain or branched alkyl group having 1 to 3 carbon atoms). Specific examples of the chain ester represented by the formula [II] include chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and ethyl propyl carbonate, methyl formate, and formic acid. Examples thereof include chain esters such as ethyl, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate.

Examples of low-viscosity non-aqueous solvents other than the formula [II] include chain ethers such as dimethoxyethane, cyclic ethers such as tetrahydrofuran, amides such as dimethylformamide, and methyl-N, N-dimethylcarbamate. Can also be used.

When such a low-viscosity non-aqueous solvent is mixed with the phosphate compound [I], the viscosity of the electrolytic solution can be reduced and the mobility of the electrolyte can be increased.
As the high dielectric constant non-aqueous solvent, ethylene carbonate, propylene carbonate, cyclic carbonates such as butylene carbonate, cyclic esters such as γ-butyrolactone, cyclic sulfones such as sulfolane, cyclic carbamates such as N-methyloxazolidinone, N- Non-aqueous solvents having a cyclic polar group, such as cyclic amides such as methylpyrrolidone and cyclic ureas such as N, N-dimethylimidazolidone.

Of these high dielectric constant non-aqueous solvents, it is preferable to use ethylene carbonate and propylene carbonate or a mixture thereof. When such a high dielectric constant non-aqueous solvent is mixed with the phosphate compound [I], the dissociation of the electrolyte can be increased, and the electric conductivity of the electrolyte can be increased.

The above non-aqueous solvents may be used alone, but when a high dielectric constant non-aqueous solvent and a low-viscosity non-aqueous solvent are used in combination, the effect of decreasing the viscosity and the effect of dissociating the electrolyte are reduced. It is preferable for synergism, and it is particularly preferable to use a combination of a cyclic carbonate and a chain carbonate. These solvents are desirably contained in a range of less than 99% by volume, preferably 10 to 95% by volume, more preferably 30 to 90% by volume, based on the whole nonaqueous solvent in the electrolytic solution.

The electrolyte dissolved in the non-aqueous electrolyte includes, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , and Li
CF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiAlCl ₃ , LiSi
Lithium salts such as F ₆ and the like. These lithium salts may be used alone or as a mixture of two or more lithium salts.

Among these lithium salts, LiPF ₆ is preferably used because of its high flame retardancy due to the synergistic action with the phosphate ester. Such electrolytes are usually 0.1 to 3
It is desirable that it be contained in the non-aqueous electrolyte at a concentration of mol / l, preferably 0.5 to 2 mol / l.

Non-Aqueous Electrolyte Secondary Battery The non-aqueous electrolyte secondary battery according to the present invention comprises, as a negative electrode active material, metallic lithium, a lithium-containing alloy, a compound capable of doping / undoping lithium ions, It is characterized by including a negative electrode containing any of undoped carbon materials, a positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material, and the above-mentioned non-aqueous electrolyte.

Such a non-aqueous electrolyte secondary battery can be applied, for example, to a cylindrical non-aqueous electrolyte secondary battery. As shown in FIG. 1, a cylindrical nonaqueous electrolyte secondary battery has a negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound through a separator 3 into which a non-aqueous electrolyte is injected, and is housed in a battery can 5 in a state where insulating plates 4 are placed above and below the wound body. A battery lid 7 is attached to the battery can 5 by caulking via a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. It is configured to function as. The separator is a porous film.

In this battery, the positive electrode lead 12 may be electrically connected to the battery lid 7 via the current interrupting thin plate 8. In such a battery, when the internal pressure of the battery increases, the current interrupting thin plate 8 is pushed up and deformed,
The positive electrode lead 12 is cut leaving a portion welded to the thin plate 8 so as to cut off the current.

The negative electrode active material constituting the negative electrode 1 may be any of lithium metal, a lithium alloy, a compound capable of doping and undoping lithium ions, and a carbon material capable of doping and undoping lithium ions. Can be used. Among these, it is preferable to use a carbon material capable of doping and undoping lithium ions. Such a carbon material may be graphite or amorphous carbon, and any carbon material such as activated carbon, carbon fiber, carbon black, and mesocarbon microbeads is used.

As the positive electrode active material constituting the positive electrode 2, a composite oxide comprising lithium and a transition metal, such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ , is used. The non-aqueous electrolyte secondary battery according to the present invention includes the non-aqueous electrolyte described above as the electrolyte, and the shape of the battery is not limited to that shown in FIG. 1 and is shown in FIG. Such a coin type or a square type may be used.

[0034]

The non-aqueous electrolyte according to the present invention is flame-retardant and has excellent charge / discharge performance. A non-aqueous electrolyte secondary battery using such a non-aqueous electrolyte is safe and has a high voltage. And excellent charge / discharge characteristics.

[0035]

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

[0036]

Example 1 Preparation of Nonaqueous Electrolyte LiPF ₆ was mixed with propylene carbonate (PC), dimethyl carbonate (DMC) and trimethoxyethyl phosphate (M) so that the electrolyte concentration was 1.0 mol / l.
eOEtPA) with a mixed solvent (mixing volume ratio PC: DMC:
(MeOEt PA = 40: 40: 20) to prepare a non-aqueous electrolyte. Evaluation of Self-extinguishing Property of Nonaqueous Electrolyte In a beaker containing the above nonaqueous electrolyte, a 0.04 mm-thick manila paper cut into a strip having a length of 15 mm and a length of 30 cm was immersed for 1 minute or more. Excess non-aqueous electrolyte dripping from the manila paper was wiped off with a beaker wall, and the manila paper was pierced at intervals of 2.5 cm into the support needle of the sample stand having the support needle to be fixed horizontally. The sample table with the manila paper fixed was placed in a 25 cm x 25 cm x 50 cm metal box, one end of which was ignited with a lighter, and the burned length of the separator paper and the time required for combustion were measured three times, and the average was measured. I took it.

The results are shown in Table 1.

[0038]

Example 2 The self-extinguishing property was evaluated in the same manner as in Example 1 except that the mixing volume ratio of the non-aqueous solvent was changed to PC: DMC: MeOEtPA = 40: 50: 10.

Table 1 shows the results.

[0040]

Comparative Example 1 The self-extinguishing property was evaluated in the same manner as in Example 1 except that a mixed solvent in which LiPF ₆ was not dissolved was used.

The results are shown in Table 1.

[0042]

[Table 1]

[0043]

Embodiment 3 LiPF ₆ was mixed with ethylene carbonate (EC), dimethyl carbonate (DMC) and trimethoxyethyl phosphate (MeOEtPA) in a mixed solvent (mixed volume) such that the electrolyte concentration was 1.0 mol / l. Ratio E
C: DMC: MeOEtPA = 40: 40: 20) to prepare a non-aqueous electrolyte. Measurement of withstand voltage and electric conductivity of electrolyte solution Withstand voltage and electric conductivity were measured using the electrolyte solution prepared as described above. The withstand voltage of the electrolytic solution is as follows. The electrolytic solution is placed in a three-electrode withstand voltage measuring cell using glassy carbon for the working electrode, platinum for the counter electrode and metallic lithium for the reference electrode, and the potential is swept at 10 mV / sec with a potentiostat. And
Decomposition current is 0.1 mA based on the potential of lithium metal
/ Cm ² or less was defined as the withstand voltage range.

The electric conductivity of the electrolytic solution was measured at 10 kHz using an impedance meter. Table 2 shows the results.

[0045]

Comparative Example 2 In Example 3, a mixed solvent of propylene carbonate (PC) and trimethyl phosphate (TMPA) (mixing volume ratio PC: TM
Withstand voltage and electric conductivity were measured in the same manner as in Example 1 except that PA = 80: 20) was used.

Table 2 shows the results.

[0047]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a cylindrical battery showing one embodiment of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a schematic sectional view of a coin battery showing one embodiment of the non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 1, 13 ··· Negative electrode 2, 14 ··· Positive electrode 3, 15 ··· Separator 4 ··· Insulating plate 5 ··· Battery can 6 ··· Sealing gasket 7 ··· Battery lid 8: Current interrupting thin plate 9: Negative electrode current collector 10: Positive electrode current collector 11: Negative electrode lead 12: Positive electrode lead 16: Sealing plate 17 ··· Case 18 ··· Gasket

Claims (5)

[Claims] 1. A non-aqueous electrolyte comprising a non-aqueous solvent containing a phosphate compound represented by the following general formula [I] and an electrolyte. Embedded image [Wherein, R ¹ , R ² , and R ³ may be the same or different from each other, and may be an alkyl group having 1 to 4 carbon atoms or —R ⁴
-O-R group containing an ether bond represented by ⁵ (R ⁴ and R ⁵ may be each different even in the same show also good hydrocarbon group having 1 to 10 carbon atoms) and, R ¹ ~ At least one of R ³ represents a group containing an ether bond represented by —R ⁴ —O—R ⁵ . ] 2. The non-aqueous electrolyte according to claim 1, wherein the group containing an ether bond represented by -R ⁴ -O-R ⁵ is a methoxyethyl group or a methoxyphenyl group. 3. The non-aqueous electrolyte according to claim 1, wherein the electrolyte is LiPF ₆ . 4. The non-aqueous electrolyte according to claim 1, wherein the electrolyte concentration is in the range of 0.5 to 2.0 mol / liter. 5. A negative electrode containing any of lithium metal, a lithium-containing alloy, and a carbon material capable of doping / dedoping lithium ions as a negative electrode active material, and a composite oxide of lithium and a transition metal as a positive electrode active material. A non-aqueous electrolyte secondary battery comprising: a positive electrode; and the non-aqueous electrolyte according to claim 1 as an electrolyte.