JPH10189040A - 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 composing a nonaqueous electrolyte of a nonaqueous solvent containing a phosphoric ester compound and a chained carbonate compound. 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 I and the chain carbonate compound expressed by the formula II, and an electrolyte. In the formula I, -C- stands for straight chain or branched hydrocarbon, and (k), (l) and (m) stand for an integer between 1 and 3. In addition, X1 to X3 may be identical to or different from each other, and a hydrogen atom, an alkoxy group or an alkyl group-substituted amino group. In the formula II, R<1> and R<2> are an alkyl group having carbons between 1 and 3. Also, lithium salt such as LiPF6 , LiBF4 , LiClO4 , and LiAsF6 is mentioned as an electrolyte dissolved in the nonaqueous electrolyte. The nonaqueous electrolyte may be used for a cylindrical nonaqueous electrolytic secondary battery.

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]

BACKGROUND OF THE INVENTION Non-aqueous electrolytes are used as electrolytes in energy storage devices such as lithium batteries and electric double layer capacitors, and these devices have high voltage, high energy density, and excellent reliability. Therefore, it is widely used as a power source for consumer electronic devices. The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte.As the non-aqueous solvent, propylene carbonate, which is a non-aqueous solvent generally having a high dielectric constant,
γ-butyrolactone, sulfolane, or low-viscosity non-aqueous solvents such as dimethyl carbonate, dimethoxyethane, tetrahydrofuran, and 1,3-dioxolane are used. As the electrolyte, Et ₄ NBF ₄ , LiB
_{F 4, LiPF 6, LiClO 4} , LiAsF 6, LiCF 3 S
O ₃ , LiAlCl ₄ , LiSiF _{6 and the} like are 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 to ensure the safety of this battery by experiments such as overcharging, external short-circuiting, nail penetration, and crushing. And in the future, if the energy density is significantly increased or the battery is enlarged,
Further improvement in safety is desired, and flammable non-aqueous electrolytes are required to have self-extinguishing properties.

[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 phosphoric acid ester such as triethyl phosphate is added is flame-retardant and has improved safety. There were problems in terms of battery charge / discharge efficiency, battery energy density, and battery life depending on the amount and the amount of addition. In order to solve such a problem, it has been proposed to limit the amount of the phosphoric acid ester to be added (see JP-A-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]

The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a phosphate compound represented by the following general formula [1], a chain carbonate compound, and an electrolyte. And

[0008]

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(In the formula,-(C)-is a linear or branched hydrocarbon, k, l and m each represent an integer of _{1 to 3} , and X _{1 to} X ₃ are the same as each other. A hydrogen atom, an alkoxy group, or an alkyl group-substituted amino group.) The chain carbonate compound is preferably a chain carbonate represented by the following general formula [2].

[0010]

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(In the formula, R ¹ and R ² may be the same or different from each other and are an alkyl group having 1 to 3 carbon atoms.) The non-aqueous solvent may further include a cyclic carbonate. It may contain a compound.

Such cyclic carbonate compounds include ethylene carbonate, propylene carbonate,
Desirably, it is a cyclic carbonate selected from butylene carbonate.

[0013] 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, as the negative electrode active material, metallic lithium, a lithium-containing alloy, a compound capable of doping / undoping lithium ions, and a carbon capable of doping / dedoping lithium ions are used. 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 a chain carbonate, and an electrolyte. First, the phosphate compound will be described.

Phosphate ester compound The phosphate ester compound contained in the non-aqueous solvent includes:
It is preferably a compound represented by the following general formula [1].

[0018]

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In the formula,-(C)-is a linear or branched hydrocarbon, and k, l and m each represent an integer of 1 to 3. X _{1 to} X ₃ may be the same or different and are a hydrogen atom, an alkoxy group or an alkyl-substituted amino group, preferably a hydrogen atom, an alkoxy group having 1 to 5 carbon atoms, 5 is an amino group substituted with an alkyl group.

When a phosphate ester compound represented by the general formula [1] is added to the non-aqueous electrolyte, the higher the phosphoric acid content in the phosphate ester, the greater the self-extinguishing action of the phosphate ester. It is desirable that the number of carbon atoms is small.

As such a phosphate compound,
Specifically, the following compounds are mentioned.

[0022]

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Of these, trimethylolethane phosphate and glycerol phosphate are particularly preferred. The chain carbonate contained in the chain carbonate non-aqueous solvent is preferably a compound represented by the following general formula [2].

[0024]

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In the formula, R ¹ and R ² may be the same or different from each other, and represent an alkyl group having 1 to 3 carbon atoms. By mixing the chain carbonate represented by the general formula [2] with the phosphate ester, the viscosity of the non-aqueous electrolyte can be reduced, and the electrolyte has excellent electrical conductivity at normal temperature or low temperature. Is obtained.

Specific examples of the chain carbonate represented by the general formula [2] include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and ethyl propyl carbonate. .

Of these, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate are particularly preferred. Cyclic carbonate The non-aqueous solvent used in the present invention preferably further contains a cyclic carbonate.

Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and the like. By mixing such a cyclic carbonate, the dissociation of the electrolyte can be increased, and the electrical conductivity of the non-aqueous electrolyte can be increased.

Non-aqueous solvent The non-aqueous solvent used in the present invention comprises a mixed solvent of the above-mentioned phosphate compound, a chain carbonate, and, if necessary, a cyclic carbonate.

The phosphate compound is desirably present in the non-aqueous solvent in an amount of 5 to 90% by volume, preferably 10 to 70% by volume. The chain carbonate is desirably present in the non-aqueous solvent in an amount of 10 to 90% by volume, preferably 20 to 80% by volume.

The cyclic carbonate is contained in the non-aqueous solvent in an amount of from 1 to
Desirably it is present in an amount of 90% by volume, preferably 20-80% by volume. The non-aqueous electrolyte according to the present invention may contain other non-aqueous solvents in addition to the phosphate ester compound, the chain carbonate and the cyclic carbonate.

The mixed state of the phosphoric acid ester does not necessarily have to be dissolved and uniform in the liquid, but may be in a suspended state. Examples of such non-aqueous solvents include chain esters such as methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, chain ethers such as dimethoxyethane, and tetrahydrofuran. Such as cyclic ethers, chain amides such as dimethylformamide, methyl
Linear carbamates such as -N, N-dimethyl carbamate; cyclic esters such as γ-butyrolactone; cyclic sulfones such as sulfolane; cyclic carbamates such as N-methyloxazolidinone; and cyclic amides such as N-methylpyrrolidone. .

It is desirable that these solvents are contained in an amount of 80% by volume or less, preferably 1 to 60% by volume, based on the whole nonaqueous solvent in the electrolytic solution. As the electrolyte dissolved in the electrolyte the non-aqueous electrolyte, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, Li
CF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiAlCl ₃ , LiSi
Such as the F ₆ and the like. These lithium salts may be used alone or as a mixture of two or more lithium salts.

Of these lithium salts, LiPF ₆ is preferably used because of its high flame retardancy due to synergistic action with phosphate esters. Such electrolytes are usually 0.1 to 3
It is desirable that it is contained in the non-aqueous electrolyte in an amount 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 a negative electrode active material such as lithium metal, a lithium-containing alloy, a compound capable of doping and undoping lithium ions, and a lithium ion doping compound. 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 to, for example, 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.

Examples of the negative electrode active material constituting the negative electrode 1 include metal lithium, lithium alloys, compounds capable of doping / undoping lithium ions, and carbon materials capable of doping / dedoping 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 composed of 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.

[0040]

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.

[0041]

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

[0042]

Example 1 Preparation of Nonaqueous Electrolyte LiPF ₆ is represented by propylene carbonate (PC), dimethyl carbonate (DEC) and the following formula [i] so that the electrolyte concentration becomes 1.0 mol / liter. Mixed solvent with trimethylolethane phosphate (TMLEP)
(Mixing volume ratio PC: DMC: TMLEP = 40: 40:
20) to prepare a non-aqueous electrolyte solution.

[0043]

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Evaluation of Self-extinguishing Properties of Nonaqueous Electrolyte A manila paper sheet for separator having a thickness of 0.04 mm and cut into strips of 15 mm and 30 cm in length was immersed in a beaker containing the nonaqueous electrolyte for 1 minute or more. did. 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. Place the sample stand with the fixed Manila paper in a metal box of 25 cm x 25 cm x 50 cm, ignite one end with a lighter, measure the burned length of the separator paper and the time required for combustion three times, and average Was calculated.

The results are shown in Table 1.

[0046]

Example 2 In Example 1, the mixing volume ratio of the solvent was changed to P
The self-extinguishing property was evaluated in the same manner as in Example 1 except that C: DMC: TMLEP = 40: 50: 10.

Table 1 shows the results.

[0048]

Example 3 In Example 1, the mixing volume ratio of the solvent was changed to P
The self-extinguishing property was evaluated in the same manner as in Example 1 except that C: DMC: TMLEP = 40: 55: 5.

Table 1 shows the results.

[0050]

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

Table 1 shows the results.

[0052]

[Table 1]

[0053]

Embodiment 4 LiPF₆3.8 g (25 mmol) of ethylene
Carbonate (EC) and dimethyl carbonate (DM
C) and trimethylolethane phosphate (TMLE)
P) and a mixed solvent (mixing volume ratio EC: DMC: TMLE)
P = 40: 40: 20) and 25 ml
A non-aqueous electrolyte was prepared.Measurement of withstand voltage and electric conductivity of electrolyte Glassy carbon for working electrode, platinum for counter electrode, gold for reference electrode
Prepared in a three-electrode withstand voltage measurement cell using lithium
Fill the solution and set the potential at 10 mV / sec with a potentiostat.
Run, and decompose based on the potential of lithium metal.
Current is 0.1mA / cm ^TwoThe potential that did not flow above is defined as the withstand voltage range.
And evaluated.

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

[0055]

Comparative Example 2 In Example 4, a mixed solvent of propylene carbonate (PC) and trimethyl phosphate (TMPA) (mixed volume ratio PC: TM
Withstand voltage and electric conductivity were measured in the same manner as in Example 4 except that PA = 80: 20) was used.

Table 2 shows the results.

[0057]

[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-type 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 (7)

[Claims] 1. A non-aqueous electrolyte comprising: a non-aqueous solvent containing a phosphate compound represented by the following general formula [1]; a chain carbonate compound; and an electrolyte. Embedded image (Wherein-(C)-is a linear or branched hydrocarbon, k, l and m each represent an integer of ₁ to 3, and X ₁ to
X ₃ may be the same or different and is a hydrogen atom, an alkoxy group or an alkyl-substituted amino group. ) 2. The non-aqueous electrolyte according to claim 1, wherein the chain carbonate compound is a chain carbonate represented by the following general formula [2]. Embedded image (In the formula, R ¹ and R ² may be the same or different from each other, and are an alkyl group having 1 to 3 carbon atoms.) 3. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent further contains a cyclic carbonate compound. 4. The non-aqueous electrolyte according to claim 3, wherein the cyclic carbonate compound is a cyclic carbonate selected from ethylene carbonate, propylene carbonate and butylene carbonate. 5. The non-aqueous electrolyte according to claim 1, wherein said electrolyte is LiPF ₆ . 6. The non-aqueous electrolyte according to claim 1, wherein the electrolyte concentration is 0.5 to 2.0 mol / liter. 7. 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 nonaqueous electrolyte secondary battery comprising: a positive electrode; and the nonaqueous electrolyte according to claim 1 as an electrolyte.