JPH10144346A - Secondary battery containing nonaqueous solvent electrolytic solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline, especially, lithium secondary battery with high withstand voltage, excellent charging and discharging performance of an anode, and excellent low temperature property. SOLUTION: In a secondary battery having a negative electrode which can charge and discharge alkali metal ion, a positive electrode which can reversely carry out electrochemical reaction with the alkali metal ion, and a non aqueous solvent electrolytic solution produced by dissolving an ion dissociable alkali metal salt, the non-aqueous solvent of the non-aqueous solvent electrolytic solution contains a dimethyl carbonate derivative. Dimethyl carbonate compounds of one hydrogen or more are substituted with halogens having formula CH3 -O- CO-O-CH2 -(-O-CO-O-CH2 )n-O-CO-O-CH3 (n = zero or positive integer) are examples of the dimethyl carbonate derivatives.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention particularly 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, the development of high energy density batteries as power sources has been required. 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 charging and discharging 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, and (iii) a negative electrode active material holder capable of charging and discharging lithium ions. The main component is a negative electrode. Examples of the lithium alloy negative electrode (ii) capable of charging and discharging lithium ions include Li and Al
Lithium alloy mainly composed of, Li and Cd, In, Pb,
A lithium alloy with Bi or the like, a lithium alloy with Li and Mg, and the like are known. Examples of the negative electrode mainly composed of the negative electrode active material holder capable of charging / discharging lithium ions of the above (iii) include various carbon materials, Nb ₂ O ₅ , W
Attempts have been made to use metal oxides such as O ₂ and Fe ₂ O ₃ and high molecular compounds such as polythiophene and polyacetylene. Examples of the positive electrode capable of performing a reversible electrochemical reaction (charge and discharge) with the lithium ion include Li _x CoO ₂ (0 ≦ x ≦ 1) and Li _x NiO _2.
(0 ≦ x ≦ 1), Li _x Mn ₂ O ₄ (0 ≦ x ≦ 1), crystalline or amorphous V ₂ O ₅ , polyaniline, polypyrrole, and the like are being studied. In this specification,
These batteries capable of charging and discharging lithium ions are referred to as lithium secondary batteries. As this type of battery, carbon is used as a negative electrode active material holder, and LiCoO is used as a positive electrode active material.
Cells using _2, carbon as an anode active material retainer, using V ₂ O ₅ cell using V ₂ O ₅ as a positive electrode active material, the Nb ₂ O ₅ as a negative electrode active material retainer, as a cathode active material Batteries are already commercially available. 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 material. The nonaqueous electrolyte to be used is required to have chemical stability (high reduction resistance) with respect to the negative electrode active material holder or lithium metal. In addition, when the voltage of this type of battery is a high voltage near 4 V, the electrolyte is also required to have high oxidation resistance (high oxidation potential). Therefore, the non-aqueous electrolyte used for this type of battery is required to have good charge / discharge performance of the negative electrode and high resistance to reduction and oxidation at the same time. In order to meet the above requirements for the non-aqueous electrolyte, an electrolyte having a particularly high oxidation potential has been studied. For example, an electrolyte using a dialkyl carbonate such as diethyl carbonate or an ester-based solvent having a linear structure such as methyl formate, methyl acetate, or ethyl acetate has been studied [Journal of Electrochemical Society].
ctrochemical Society), Vol.136, No.7, No.18
65-1869 (1985)]. However, an electrolytic solution using these solvents has a high oxidation potential, but a low reduction potential, and has high reactivity with a negative electrode that has stored lithium and lithium metal. Nitriles such as acetonitrile have high electrical conductivity, but cannot be used as a solvent for an electrolytic solution because of their extremely high reactivity with lithium metal.
Those known as having good charge / discharge characteristics of the negative electrode (eg, dioxolane and 2-methyltetrahydrofuran) are ethers, and have strong reduction resistance, but are easily oxidized, and have high charge / discharge characteristics and storage characteristics for high-voltage batteries. Sex is bad. Furthermore, cyclic carbonates such as propylene carbonate have oxidation potentials that are practically usable, but have reduction potentials higher than ethers, and do not provide sufficient charge / discharge performance of the negative electrode. For this reason, an electrolyte solution for a lithium secondary battery having good charge / discharge performance, high oxidation resistance, and high reduction resistance is required, but no electrolyte solution satisfying these conditions has been proposed. Dimethyl carbonate has a low viscosity, and the electrolyte containing it provides high lithium ion conductivity. Furthermore, even when lithium metal is used for the negative electrode, good charge / discharge characteristics are exhibited. However, since the melting point is as high as 3 ° C. and the boiling point is as low as 90 ° C., it is not sufficient for use in a wide temperature range. It has been proposed to mix dimethyl carbonate with various solvents, but this is not always sufficient.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has an alkali, which is excellent in high withstand voltage and excellent in charge / discharge characteristics and low-temperature characteristics of a negative electrode.
In particular, it is an object to provide a lithium secondary battery.

[0004]

SUMMARY OF THE INVENTION To summarize the present invention, a first invention of the present invention relates to a secondary battery having a non-aqueous solvent electrolyte, comprising a negative electrode capable of charging and discharging alkali metal ions. In a secondary battery having a positive electrode capable of performing a reversible electrochemical reaction with an alkali metal ion and a nonaqueous solvent electrolyte in which an ion dissociable alkali metal salt is dissolved, the nonaqueous solvent contains a dimethyl carbonate derivative. It is characterized by that. The second invention of the present invention is characterized in that the alkali metal of the first invention is lithium. Further, according to a third aspect of the present invention, the non-aqueous solvent according to the first aspect comprises:
The following structural formula (Formula 1):

[0005]

Embedded image

Wherein R _{1 to} R ₆ are the same or different;
Wherein at least one hydrogen in the molecule is substituted with a halogen. Further, according to a fourth aspect of the present invention, the dimethyl carbonate derivative of the first aspect is represented by the following structural formula (Formula 2):

[0007]

Embedded image CH ₃ —O—CO—O—CH ₂ — (— O—CO—O—CH ₂ ) _n —O—CO—O—CH ₃

(Wherein, n represents a zero or a positive integer).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. According to the present invention, for example, 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 Those in which cobalt, nickel, manganese, and iron are each partially substituted with another transition metal can be used.

As negative electrode materials capable of charging and discharging lithium ions, 1) a lithium metal negative electrode, 2) a lithium alloy negative electrode capable of charging and discharging lithium ions, for example, a lithium alloy mainly composed of Li and Al, and Li and Cd , In, P
b) Lithium alloy with Bi, etc. 3) Negative electrode mainly composed of negative electrode active material holder capable of charging and discharging lithium ions, for example, various carbon materials, Nb ₂ O ₅ , WO ₂ , Fe ₂ O ₃
Such as metal oxides, polymer compounds such as polythiophene and polyacetylene, Li _2.5 Co _0.5 N, Li _2.5 Cu _0.5
N, Li _2.5 Ni _0.5 N, Li ₃ FeN ₂ , Li ₇ Mn
A nitride such as N ₄ can be used. Examples of the electrolyte of the electrolyte include LiClO ₄ , LiPF ₆ , LiAsF ₆ ,
LiBF ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , Li
SbF ₆ , LiSCN, LiCl, LiC ₆ H ₅ S
O ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO
₂ ) ₃ and lithium salts such as LiCF ₃ SO ₃ can be used alone or in combination of two or more.

Examples of the dimethyl carbonate derivative contained in the solvent of the non-aqueous solvent electrolyte include the compound represented by the general formula (Chemical Formula 1) in the third aspect of the present invention. Examples thereof include methyl fluorocarbonate and difluorocarbonate. Bromine such as methyl carbonate, methyl chlorocarbonate, methyl dichlorocarbonate, methyl trichlorocarbonate and the like substituted with methyl chloride, methyl bromocarbonate, methyl dibromocarbonate, methyl tribromocarbonate, etc. Methyl carbonate substituted with iodine, such as methyl carbonate, methyl iodocarbonate, methyl diiodocarbonate, and methyl triiodocarbonate, and methyl carbonate substituted with hydrogen by using two or more halogens can be used. In addition, they can be used for all isomers. Another example of the dimethyl carbonate derivative is a compound represented by the general formula (Chemical Formula 2) in the fourth invention. The dimethyl carbonate derivative as described above may be used alone, or may be used as a mixture with another non-aqueous solvent. The non-aqueous solvent to be mixed with the dimethyl carbonate derivative is not particularly limited, and cyclic carbonates such as propylene carbonate and ethylene carbonate, cyclic fatty acid esters such as γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl propyl carbonate, and carbonic acid Chain carbonates such as dipropyl, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate,
Chain fatty acid esters such as methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, etc .; dimethoxyethane, diethoxyethane, straight-chain ethers such as ethoxymethoxyethane, etc.
Tetrahydrofuran and 2-methyltetrahydrofuran can be used alone or in combination of one or more. By using these as a solvent for the electrolytic solution, a secondary battery having a non-aqueous solvent electrolytic solution having a long life and a high energy density can be provided.

The secondary battery having the non-aqueous solvent electrolyte of the present invention has, for example, the following features. That is, a battery using a composite oxide of lithium and manganese as a positive electrode active material is characterized by being inexpensive and having a long cycle life. Batteries using a composite oxide of lithium and cobalt are characterized by high voltage and high energy density. Batteries using a composite oxide of lithium and nickel are characterized by high charge / discharge capacity and high energy density. A battery using a composite oxide of lithium and iron has the characteristics of being inexpensive and light. In addition, the composite oxides in which cobalt, nickel, manganese, and iron are partially substituted with other transition metals, respectively, have a characteristic that the substitution results in a particularly stable crystal structure and a long charge / discharge life. A long charge / discharge life can be achieved by using, as the solvent, a halogen-substituted product of methyl carbonate, which has high reduction resistance and oxidation resistance and can realize high conductivity, as the solvent.

[0013]

EXAMPLES The present invention will be described more specifically with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples.

First, according to the third aspect of the present invention, an example using a compound represented by the general formula (Formula 1) as a dimethyl carbonate derivative will be described. Table 1 shows an example of a dimethyl carbonate derivative in which at least one hydrogen is substituted with a halogen. In these solvents, the numbers shown in Table 1 were used in the following Examples. In Table 1 and the following description, DMC
Is an abbreviation for dimethyl carbonate.

[0015]

[Table 1]

FIG. 1 is a sectional view of a secondary battery having a non-aqueous solvent electrolyte according to the present invention. In FIG. 1, reference numeral 1 denotes a negative electrode case made of stainless steel. Reference numeral 2 denotes a negative electrode, in which a lithium foil having a predetermined thickness punched out to a diameter of 16 mm is pressure-bonded to 1. Reference numeral 3 denotes an electrolytic solution using a non-aqueous solvent, and uses the electrolytic solutions described in the following Examples and Comparative Examples. Reference numeral 4 denotes a separator, for example, a porous film of polypropylene or polyethylene.
Reference numeral 5 denotes a stainless steel positive electrode case. 6 is the opposite pole,
The electrodes, stainless steel substrates, acetylene black, and LiMn described in the following Examples and Comparative Examples
_1.9 Co _0.1 O ₄ . Reference numeral 7 denotes a gasket, which maintains electrical insulation between the negative electrode 1 and the positive electrode case 5, and
The opening of the negative electrode case is bent inward and crimped to seal and seal the battery contents.

Examples 1 to 21 and Comparative Examples 1 and 2 (Charge / Discharge Efficiency of Li Electrode) By changing the halogen of the dimethyl carbonate derivative, an electrolyte was prepared by dissolving 1 M of lithium perchlorate LiClO ₄ . The counter electrode was a stainless steel substrate, and after lithium was electrochemically deposited on the substrate by 2 mAh, the average value of the charge and discharge efficiency up to 20 cycles when the lithium was electrochemically discharged and melted, and as a comparative example 1M-LiClO ₄ −
Table 2 shows the values when DMC and 1M-LiClO ₄ -PC (PC: propylene carbonate) electrolytes were used. From the results shown in Table 2, it can be seen that the dimethyl carbonate derivative shows almost the same high properties as DMC, and shows higher properties than the PC electrolyte. In addition, these use LiPF _{6 as} an electrolyte,
Almost the same results can be obtained with LiBF ₄ , LiAsF _6, etc., even when the electrolyte concentration is set to 0.5 to 2.0 M.

[0018]

[Table 2]

Examples 22 to 42 and Comparative Examples 3 and 4 (Cycle Characteristics of Carbon Electrode) Electrolyte was prepared by dissolving 1 M of lithium perchlorate LiClO ₄ by changing the halogen of the dimethyl carbonate derivative. A coin-type battery was manufactured using acetylene black which is a kind of carbon (interlayer distance is 3.47 to 3.48 angstroms). For these batteries, at a discharge and charge current density of 0.5 mA / cm ² , the lower limit of the discharge voltage was 0 V and the upper limit of the charge voltage was 2.0 V.
The voltage regulation charge / discharge cycle was repeated. In this test, lithium was occluded in acetylene black by discharging, and lithium absorbed in acetylene black was released by charging. Lithium was occluded in the negative electrode holder (acetylene black in this example and comparative example). This is a test for knowing the influence of the electrolyte material on the charge / discharge performance of the negative electrode. As a comparative example, 1M-LiClO ₄ -D
MC 1 when, using a 1M-LiClO ₄ -PC electrolyte
Table 3 shows the obtained capacities at 0, 40, and 100 cycles, respectively.
Shown in From the results shown in Table 3, it can be seen that the dimethyl carbonate derivative shows almost the same properties as DMC and shows high properties. In these, electrolytes are LiPF ₆ , LiB
Even when F ₄ , LiAsF ₆ or the like is used, the electrolyte concentration is further reduced to 0.1.
Approximately the same result can be obtained even with 5 to 2.0M.

[0020]

[Table 3]

Examples 43 to 63 and Comparative Examples 5 and 6 (Cycle Characteristics of Full Cell) The counter electrode in FIG. 1 was a positive electrode composed of LiMn _1.9 Co _0.1 O ₄ . This is because a slurry prepared by mixing the above-mentioned positive electrode active material with a conductive agent and a binder is applied to an Al foil to a predetermined thickness, dried, and then dried to a diameter of 14 m.
It is cut out to a size of 16 mm in diameter having m electrode portions. With respect to the coin-type battery manufactured as described above, at 20 ° C., the charge end voltage was set to 4.3 V, the discharge end voltage was set to 3.3 V, the charge current density was 1 mA / cm ² , and the discharge current density was 3 mA. / Cm ² was subjected to a cycle test. In these batteries, the halogen in the dimethyl carbonate dielectric was changed to produce lithium perchlorate Li.
An electrolytic solution in which 1 M of ClO ₄ was dissolved was prepared and adapted. In the battery using each electrolytic solution, the cycle life at half of the initial discharge capacity was defined as the cycle life at that time, and the results are shown in Table 4. From the results shown in Table 4, it can be seen that the dimethyl carbonate derivative shows almost the same characteristics as DMC, and shows higher characteristics than the PC electrolyte. In these, the electrolyte is Li
Almost the same results can be obtained by using PF ₆ , LiBF ₄ , LiAsF _6, etc. even when the electrolyte concentration is set to 0.5 to 2.0 M.

[0022]

[Table 4]

Examples 64 to 84 and Comparative Examples 7 and 8 (low-temperature discharge characteristics in full cell) A charge / discharge cycle was performed in the same manner as when the cycle life was evaluated in order to evaluate low-temperature characteristics. ° C
After that, discharge was performed at 6 mA / cm ² , and the discharge capacity at that time was estimated. Table 5 shows the results. The dimethyl carbonate derivative provided a very high discharge capacity as compared with DMC and PC. In these, electrolytes are LiPF ₆ , LiB
Almost the same results can be obtained by using F ₄ , LiAsF ₆ or the like. It is clear that not only normal cycle characteristics but also high load characteristics and low temperature characteristics are excellent.

[0024]

[Table 5]

Hereinafter, according to the fourth aspect of the present invention, an example using a compound represented by the general formula (Formula 2) as a dimethyl carbonate derivative will be described. Examples 85 to 88 and Comparative Examples 9 and 10 (Charging / Discharging Efficiency of Li Electrode) The dimethyl carbonate derivative represented by the general formula (Chemical Formula 2) was used to change n to make the volume mixing ratio with PC 1: 1. An electrolyte was prepared by dissolving lithium acid LiClO ₄ at 1M. FIG.
Was used as a counter electrode in a stainless steel substrate, and lithium was electrochemically deposited on the substrate by 2 mAh, and then this was electrochemically discharged and melted. The average value of charge and discharge efficiency up to 20 cycles and 1 M as a comparative example —LiClO ₄ —PC /
DMC (1: 1), 1M-LiClO ₄ -PC / DME
Table 6 shows the values when the (1: 1) (DME: dimethoxyethane) electrolyte was used. From the results in Table 6, the dimethyl carbonate derivative shows almost the same high properties as DMC,
It can be seen that the characteristics are higher than those of the C / DME-based electrolyte. In these, electrolytes are LiPF ₆ , LiBF
₄ , even with LiAsF ₆ etc., the electrolyte concentration is further reduced to 0.5
Approximately the same result can be obtained even when it is set to 2.0M. Also,
Substantially similar results can be obtained by using EC (ethylene carbonate) instead of PC.

[0026]

[Table 6]

Examples 89 to 92 and Comparative Examples 11 and 12
(Cycle Characteristics of Carbon Electrode) An electrolyte was prepared by changing n with a dimethyl carbonate derivative represented by the general formula (Chemical Formula 2) to a volume mixing ratio of 1: 1 with PC and dissolving 1 M of lithium perchlorate LiClO _4. did. FIG.
A coin-type battery was manufactured using acetylene black, a kind of carbon (interlayer distance: 3.47 to 3.48 angstroms), as a counter electrode in. For these batteries, at a discharge and charge current density of 0.5 mA / cm ² , the lower limit of the discharge voltage was 0 V and the upper limit of the charge voltage was 2.0 V.
The voltage regulation charge / discharge cycle was repeated. In this test, lithium was occluded in acetylene black by discharging, and lithium absorbed in acetylene black was released by charging. Lithium was occluded in the negative electrode holder (acetylene black in this example and comparative example). This is a test for knowing the influence of the electrolyte material on the charge / discharge performance of the negative electrode. As a comparative example, 1M-LiClO ₄ -P
C / DMC (1: 1), 1M-LiClO ₄ -PC / D
10, 40, 100 when using ME (1: 1) electrolyte
Table 7 shows the obtained capacity during the cycle. From the results in Table 7, it can be seen that the dimethyl carbonate derivative shows almost the same properties as DMC, and shows high properties. Note that these are also the electrolyte LiPF _6, LiBF _4, LiAsF _6, etc., to obtain substantially the same results as further 0.5~2.0M the electrolyte concentration. Almost the same result can be obtained by using EC instead of PC.

[0028]

[Table 7]

Examples 93 to 96 and Comparative Examples 13 and 14
(Cycle Characteristics of Full Cell) The counter electrode in FIG. 1 was a positive electrode composed of LiMn _1.9 Co _0.1 O ₄ . This is because a slurry prepared by mixing the above-mentioned positive electrode active material with a conductive agent and a binder is applied to an Al foil to a predetermined thickness, dried, and then dried to a diameter of 14 m.
It is cut out to a size of 16 mm in diameter having m electrode portions. In order to evaluate the battery characteristics of the coin-type battery manufactured as described above, at 20 ° C., the charge end voltage was set to 4.3 V, the discharge end voltage was set to 3.3 V, the charge current density was 3 mA / cm ² , and the discharge current density was 0. The cycle test was performed at 0.5 mA / cm ² . In these batteries, n was changed with a dimethyl carbonate dielectric represented by the general formula (Formula 2) to make the volume mixing ratio with PC 1: 1 and lithium perchlorate L
An electrolytic solution in which 1M iClO ₄ was dissolved was prepared and adapted. As a comparative example, 1M-LiClO ₄ -PC / DMC (1:
_{1), 1M-LiClO 4 -PC} / DME (1: 1) using the electrolytic solution. The cycle life was defined as the time when the initial discharge capacity was 電池 of the battery using each electrolytic solution. From the results in Table 8, it can be seen that the dimethyl carbonate derivative shows almost the same high properties as DMC, and shows higher properties than the PC / DME-based electrolyte. In these, the electrolyte is LiP
Even when F ₆ , LiBF ₄ , LiAsF ₆ or the like is used, the similar result can be obtained even when the electrolyte concentration is set to 0.5 to 2.0 M. Almost the same result can be obtained by using EC instead of PC.

[0030]

[Table 8]

[0031]

As described in detail above, according to the present invention, a secondary battery having a non-aqueous solvent electrolyte having excellent charge / discharge characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a battery of the present invention.

[Explanation of symbols]

1: negative electrode case made of stainless steel, 2: negative electrode, 3: electrolytic solution using non-aqueous solvent, 4: separator, 5: positive electrode case,
6: Counter electrode, 7: Gasket

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Junichi Yamaki Nippon Telegraph and Telephone Corporation 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (4)

[Claims] An anode comprising a negative electrode capable of charging / discharging an alkali metal ion, a positive electrode capable of reversible electrochemical reaction with the alkali metal ion, and a non-aqueous solvent electrolyte in which an ion-dissociable alkali metal salt is dissolved. A secondary battery comprising a nonaqueous solvent electrolyte, wherein the nonaqueous solvent contains a dimethyl carbonate derivative. 2. The secondary battery according to claim 1, wherein the alkali metal according to claim 1 is lithium. 3. The non-aqueous solvent according to claim 1, wherein the non-aqueous solvent has the following structural formula (Formula 1): (Wherein, R _{1 to} R ₆ are the same or different and represent hydrogen or halogen, but at least one R represents halogen)
The secondary battery having a non-aqueous solvent electrolyte according to claim 1, wherein the secondary battery comprises a dimethyl carbonate derivative in which at least one hydrogen in the molecule has been replaced with a halogen represented by the formula: 4. The dimethyl carbonate derivative according to claim 1,
The following structural formula (Chemical formula 2): embedded image CH ₃ —O—CO—O—CH ₂ — (— O—CO—O—CH ₂ ) _n —O—CO—O—CH ₃ (wherein, n Is a dimethyl carbonate derivative represented by the following formula: