JPH10189039A - 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 having a carbonyl group or an alkoxy group, as well as 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 an electrolyte. In the formula I, R<1> , R<2> and R<3> may be identical to or different from each other, and are a group containing a carbonyl group, or an alkoxy group having carbons between 1 and 4. Also, at least one of R<1> to R<3> is a group containing a carbonyl group. In this case, the group containing the carbonyl group is preferably a group expressed by one of the formulae II, III and IV. In the formulae II to IV, R<4> and R<5> are an alkyl group having carbons between 1 and 4. In this case, lithium salt such as LiPF6 , LiBF4 , and LiClO4 is mentioned, for example, 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.
Generally, propylene carbonate, γ-butyrolactone, and sulfolane, which are non-aqueous solvents having a high dielectric constant, or dimethyl carbonate, dimethoxyethane, tetrahydrofuran, and 1,3-dioxolane, which are low-viscosity non-aqueous solvents, are used. Et ₄ NBF ₄ , Li
BF ₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiCF ₃
SO 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 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 that the safety be further improved, and the flammable non-aqueous electrolyte has a self-extinguishing property. It has been demanded.

[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 problems, it has been proposed to limit the amount of phosphate 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]

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]

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[Wherein, R ¹ , R ² and R ³ may be the same or different and each is a group containing a carbonyl group or an alkoxy group having 1 to 4 carbon atoms, and R ^{1 to} R ³ At least one of them is a group containing a carbonyl group. The group containing a carbonyl group is preferably a group represented by any one of the following formulas [i] to [iii].

[0010]

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(In the formula, R ⁴ and R ⁵ may be the same or different from each other and are an alkyl group having 1 to 4 carbon atoms.) The electrolyte is preferably LiPF ₆ .

The concentration of such an electrolyte is preferably in the range of 0.5 to 2.0 mol / liter. The non-aqueous electrolyte secondary battery according to the present invention may be any of lithium metal, a lithium-containing alloy, a compound capable of doping / undoping lithium ions, and a carbon material capable of doping / dedoping lithium ions as a negative electrode active material. A negative electrode containing at least one of
It is characterized by having 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.
First, the phosphate compound will be described. 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.

[0015]

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[0016] In the ^{formula, R 1, R 2, R} 3 may be the being the same or different, a group or an alkoxy group having 1 to 4 carbon atoms containing a carbonyl group, the R ¹ to R ³ At least one of them is a group containing a carbonyl group.

The group containing a carbonyl group is preferably a group represented by any one of the following general formulas [i] to [iii].

[0018]

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In the formula, R ⁴ and R ⁵ may be the same or different from each other and are an alkyl group having 1 to 4 carbon atoms. As a group containing such a carbonyl group, specifically, a methoxycarbonyl group, an ethoxycarbonyl group,
N, N-dimethylcarbamyl group, N, N-diethylcarbamyl group, methoxycarbonylmethyl group, ethoxycarbonylmethyl group and the like.

Regarding the carbon number of R ^{1 to} R ^{5 in} the general formula [I], the higher the phosphorus content in the phosphate ester, the greater the self-extinguishing action of the phosphate ester tends to be. Specific examples of such a phosphate compound include trimethylphosphonoacetate, trimethylphosphonoformate, dibutyl N, N-diethylcarbamylphosphonate, triethylphosphonoacetate, triethylphosphonoformate, dimethyl N, N -Dimethylcarbamylphosphonate, dimethylethoxycarbonylphosphonate, diethylmethylcarbonylphosphonate, dimethylethoxycarbonylmethylphosphonate, diethylmethoxycarbonylmethylphosphonate, dimethyl N, N-diethylcarbamylphosphonate, diethyl N, N-dimethylcarbamylphosphonate and the like. Can be

Of these, trimethylphosphonoacetate, trimethylphosphonoformate, dimethyl N,
N-dimethylcarbamylphosphonate is preferred. Non-aqueous solvent The non-aqueous solvent used in the present invention may be composed of a phosphate ester compound as described above, or may be composed of a mixture of a phosphate ester 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 contained in the mixed solvent in an amount of 1.0% by volume or more, preferably 2% by volume or more.
Preferably it is present in an amount of up to 90% by volume, more preferably 5 to 70% 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 compound, a low-viscosity non-aqueous solvent and a high-dielectric-constant non-aqueous solvent are 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.

[0023]

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(In the formula, 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 these low-viscosity nonaqueous solvents are mixed with the above-mentioned phosphate compound [I], the viscosity of the electrolytic solution can be reduced, and the mobility of the electrolyte can be increased. Further, 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 a cyclic amide such as methylpyrrolidone are exemplified.

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

The above non-aqueous solvents may be used alone. However, 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 98% by volume, preferably 30 to 95% by volume, based on the whole nonaqueous solvent in the electrolytic solution.

[0029] As the electrolyte contained in the electrolyte a nonaqueous electrolyte solution, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, 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.

Of these lithium salts, LiPF ₆ is particularly preferred. When LiPF ₆ is used as the electrolyte, high self-extinguishing properties can be exhibited by synergistic action with the phosphate ester, so that it is preferably used.

It is desirable that such an electrolyte is usually contained in the nonaqueous electrolyte at a concentration of 0.1 to 3 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 has metallic lithium, a lithium-containing alloy, a compound capable of doping and undoping lithium ions as a negative electrode active material, and doping and undoping of lithium ions. It is characterized by including a negative electrode containing any of the possible 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 cover 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 metallic lithium, a lithium alloy, a compound capable of doping / undoping lithium ions, and a carbon material 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.

[0036]

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.

[0037]

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

[0038]

Example 1 Preparation of Nonaqueous Electrolyte LiPF ₆ is represented by the following formula [1] with propylene carbonate (PC) and dimethyl carbonate (DMC) so that the electrolyte concentration becomes 1.0 mol / L. Mixed solvent with trimethylphosphonoacetate (TMPAc) (mixing volume ratio PC: DMC: TMPAc = 40: 40: 20)
To prepare a non-aqueous electrolyte.

[0039]

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Evaluation of Self-extinguishing Properties of Nonaqueous Electrolyte In a beaker containing the nonaqueous electrolyte, a strip of 0.04 mm thick manipulator paper having a thickness of 15 mm and a length of 30 cm was immersed 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.

[0042]

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: TMPAc = 40: 50: 10.

Table 1 shows the results.

[0044]

Example 3 In Example 1, dibutyl N, N-diethylcarbamylphosphonate (D) represented by the following formula [2] was substituted for trimethylphosphonoacetate (TMPAc).
BDECP) and the mixing volume ratio is PC: DM
C: The self-extinguishing property was evaluated in the same manner as in Example 1 except that DBDECP was set to 40:50:10.

[0045]

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Table 1 shows the results.

[0047]

Example 4 In Example 1, dibutyl N, N-diethylcarbamylphosphonate (DBDECP) was used in place of trimethylphosphonoacetate (TMPAc), and the mixing volume ratio was PC: DMC: DBDECP = 4.
Except having set it to 0:40:20, it carried out similarly to Example 1, and
The self-extinguishing properties were evaluated.

Table 1 shows the results.

[0049]

Example 5 In Example 1, dibutyl N, N-diethylcarbamylphosphonate (DBDECP) was used instead of trimethylphosphonoacetate (TMPAc), and the mixing volume ratio was PC: DMC: DBDECP = 4.
Except having set it to 0:30:30, it carried out similarly to Example 1, and
The self-extinguishing properties were evaluated.

Table 1 shows the results.

[0051]

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.

[0053]

[Table 1]

[0054]

Embodiment 6: LiPF₆3.8 g (25 mmol) of propylene
Carbonate (PC) and trimethylphosphonoacetate
(TMPAc) (mixing volume ratio PC: TM
PAc = 80: 20) and 25 ml of non-
A water 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.

[0056]

Example 7 In Example 6, propylene carbonate (PC) and dibutyl N,
N-diethylcarbamylphosphonate (DBDECP)
Mixed solvent (mixing volume ratio PC: DBDECP = 80:
Withstand voltage and electric conductivity were measured in the same manner as in Example 6, except that 20) was used.

Table 2 shows the results.

[0058]

Example 8 In Example 6, propylene carbonate (PC) and trimethylphosphonoformate (TMPF) represented by the following formula [3] were used as a mixed solvent of the non-aqueous electrolyte.
M) (mixing volume ratio PC: TMPFM = 8)
0:20), except that the withstand voltage and the electric conductivity were measured in the same manner as in Example 6.

[0059]

Embedded image

Table 2 shows the results.

[0061]

Comparative Example 2 In Example 6, 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.

[0063]

Embodiment 9 In Embodiment 6, the mixed solvent of the non-aqueous electrolyte was ethylene carbonate (EC), dimethyl carbonate (DMC) and trimethyl phosphonoacetate (T
MPAc) (mixed volume ratio EC: DMC: T
The electric conductivity was measured in the same manner as in Example 6, except that MPAc = 40: 40: 20) was used.

Table 2 shows the results.

[0065]

Example 10 In Example 6, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and dibutyl N, N-diethylcarbamylphosphonate (DBDECP) (mixing volume ratio) was used as the mixed solvent of the nonaqueous electrolyte. EC: DMC: DBDECP = 40: 40: 2
Electric conductivity was measured in the same manner as in Example 6, except that 0) was used.

Table 2 shows the results.

[0067]

Example 11 In Example 6, the mixed solvent of the non-aqueous electrolyte was ethylene carbonate (EC), dimethyl carbonate (DMC) and triphosphonoformate (TM).
PFM) and a mixed solvent (mixing volume ratio EC: DMC: TM)
Example 6 except that PFM = 40: 40: 20) was used.
The electric conductivity was measured in the same manner as described above.

Table 2 shows the results.

[0069]

[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 (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 include a carbonyl group-containing group or
And at least one of R ^{1 to} R ³ is a group containing a carbonyl group. ] 2. The non-aqueous electrolyte according to claim 1, wherein the group containing a carbonyl group is a group represented by any one of the following general formulas [i] to [iii]. Embedded image (In the formula, R ⁴ and R ⁵ may be the same or different from each other, and are an alkyl group having 1 to 4 carbon atoms.) 3. The non-aqueous electrolyte according to claim 1, wherein said 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.