JP2000058076A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery, capable of effectively suppressing deterioration of discharge capacity and deterioration of high-rate discharging performance following the progress of charge/discharge cycles. SOLUTION: This nonaqueous electrolyte battery is equipped with a negative electrode, a positive electrode, and an electrolyte, the electrolyte contains an asymmetric non-cyclic sulfone explained in 'Chemistry 1' and a chain carbonate, and the chain carbonate comprises at least one kind of dimethyl carbonate(DMC), ethyl-methyl carbonate(EMC), and diethyl carbonate(DEC). The mixing ratio of the chain carbonate to the non-cyclic sulfone exists within a composition range expressed by a regulator tetrahedron of the figure, and exists within the compassion range expressed between a plane passing through points on respective sides, where the diethyl carbonate is 10 vol.%, the ethyl-methyl carbonate is 40 vol.%, and the diethyl carbonate is 80 vol.%, with respect to the non- cyclic sulfone, and a plane passing through points on the respective sides, where the diethyl carbonate is 80 vol.%, the ethyl-methyl carbonate is 90 vol.%, and the diethyl carbonate is 90 vol.%, with respect to the non-cyclic sulfone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery having high energy density and high reliability.

[0002]

2. Description of the Related Art Nonaqueous electrolyte batteries using lithium as an active material are known as high energy density batteries.
In particular, primary batteries using manganese dioxide, fluorocarbon, or the like for the positive electrode are used as power supplies for calculators and watches. Furthermore, with the rapid reduction in size and weight of electronic devices, there is an increasing demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged with respect to a battery as a power source thereof. As a secondary battery satisfying these requirements, a non-aqueous electrolyte secondary battery using a carbon material for a negative electrode has been developed, and is being used as a power source for portable communication devices and portable personal computers.

The negative electrode material of a non-aqueous electrolyte secondary battery is an L material capable of inserting and extracting lithium, including metallic lithium.
Various things such as i-Al alloys, graphite, low crystalline carbon materials, and metal oxides have been studied. Among them, a carbon material has an advantage that a battery having high safety and a long cycle life can be obtained.

Various positive electrode active materials for nonaqueous electrolyte secondary batteries such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been studied. ing. Among them, lithium cobalt composite oxide (Li
CoO ₂ ), lithium-containing nickel-cobalt composite oxide (LiNi _X Co _1-X O ₂ : 0.5 <X <0.9), and spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) are 4V (Li / Li +) Since charge and discharge are performed at the above extremely noble potential, a battery having a high discharge voltage can be realized by using the battery as a positive electrode.

[0005] However, in this type of battery, while lithium having a low potential is used as a negative electrode active material, while a metal oxide having a noble potential is used for a positive electrode, the electrolyte is easily decomposed in each of the negative electrode and the positive electrode. is there. Therefore, it is indispensable to adopt a configuration in consideration of these points in selecting an electrolyte, and it has been proposed to use various electrolytes. Most of them are dissolved in high dielectric constant solvents such as propylene carbonate, ethylene carbonate, γ-butyrolactone, and sulfolane as solvents.
-A mixture of low-viscosity solvents such as dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate. As the electrolyte salt, LiC
10 ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , Li
Lithium salts such as N (CF ₃ SO ₂ ) ₂ and LiN (C _n F _{2n + 1} SO ₂ ) ₂ (where n is 1, 2, 3, or 4 independently) are generally used. Above all, LiPF6 and Li
N (CF ₃ SO ₂ ) ₂ has been actively studied in recent years because of its high safety and high ionic conductivity of the dissolved electrolyte.

[0006]

However, even if the above-mentioned electrolyte is used, when the battery is stored at a high temperature for a long period of time, the electrolyte is decomposed in each of the negative electrode and the positive electrode,
There is a problem that the battery performance is significantly reduced. Therefore, the present inventors have attempted to solve the above problem by using an asymmetric acyclic sulfone represented by Chemical Formula 1 having excellent electrochemical stability as a solvent for the electrolyte. As a result, the battery using this type of electrolyte could suppress the deterioration of the battery performance due to storage, but when used as a power supply for driving electronic equipment or a battery for an electric vehicle requiring high rate discharge performance. It was found that the discharge capacity was sometimes reduced.

[0007]

The non-aqueous electrolyte battery according to the present invention comprises a negative electrode, a positive electrode, and an electrolyte, wherein the electrolyte is an asymmetric non-cyclic sulfone represented by the following formula (1): Carbonate, wherein the chain carbonate is at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0008]

Wherein R ₁ ≠ R ₂ and R ₁ and R ₂ are alkyl groups having 1 to 4 carbon atoms.

The second invention according to the first invention is characterized in that the chain carbonate is at least three of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.
The mixing ratio between the chain carbonate and the non-cyclic sulfone is within the composition range shown by the tetrahedron shown in FIG. 8, and dimethyl carbonate is 10% by volume, ethyl A surface passing through each side where the volume of methyl carbonate is 40% and the volume of diethyl carbonate is 80% by volume, and 80% by volume of dimethyl carbonate, 90% by volume of ethyl methyl carbonate and 90% by volume of diethyl carbonate with respect to the acyclic sulfone. It is characterized by a composition range shown between a plane passing through each side.

A third aspect of the present invention according to the first or second aspect is that the electrolyte comprises LiPF ₆ and LiN (CF ₃ SO ₂ ) _2.
Wherein the electrolyte salt is mixed at a molar ratio of 1: 9 to 9: 1. The present invention solves the above problem by the above configuration.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, when an asymmetric acyclic sulfone having excellent electrochemical stability is used as a solvent for an electrolyte, the reason why the high-rate discharge performance is lowered is that the viscosity of this kind of solvent is high. It is conceivable that the wettability of the electrode and the separator deteriorates, and the ionic conductivity of the electrolytic solution is low, so that the internal resistance of the battery has increased.

Therefore, by using a mixed solvent of an asymmetric acyclic sulfone and a chain carbonate for the electrolyte, the storage characteristics, cycle characteristics and high-rate discharge performance are better than when each solvent is used alone. The present inventors have found that a suitable battery can be obtained, and have completed the present invention.

That is, by adding a low-viscosity chain carbonate to an asymmetric acyclic sulfone, the viscosity of the solvent is reduced, the wettability of the electrode and the separator is improved, and the ionic conductivity of the electrolyte is improved. It is considered that a battery having good high-rate discharge performance was obtained. On the other hand, when the chain carbonate alone is used as the electrolyte, it is considered that the battery performance is deteriorated due to the low ionic conductivity and the poor electrochemical stability of the solvent.

Further, acyclic sulfones include asymmetrical sulfones and symmetrical sulfones. The symmetrical sulfones have a higher freezing point than the asymmetrical sulfones, and thus have a problem in that the battery operating temperature range becomes narrower. Therefore, it is preferable to use a non-cyclic asymmetric sulfone as the electrolyte solvent of the battery.

Hereinafter, the present invention will be described with reference to preferred embodiments.

[0016]

[Example 1] LiCoO ₂ was used as a positive electrode active material. 5% by weight of carbon black and 5% by weight of polyvinylidene fluoride (PVdF) were mixed with 90% by weight of LiCoO _2, and N-methyl-2-pyrrolidone (NMP) was appropriately added as a solvent to obtain a slurry. Thickness 20
A positive electrode mixture slurry was uniformly applied to a μm band-shaped aluminum foil, dried, and then roll-pressed to produce a band-shaped positive electrode.

As the negative electrode, a carbon material capable of doping / dedoping lithium ions (natural graphite whose surface is coated with hard carbon: product name GDA-2, manufactured by Mitsui Kinzoku Mining) was used. 10% by weight of PVdF was mixed with 90% by weight of the carbon material powder, and NMP was appropriately added as a solvent to obtain a slurry. This slurry was uniformly applied to a 20 μm-thick strip-shaped copper foil, dried, and then roll-pressed to produce a strip-shaped negative electrode.

The positive electrode and the negative electrode thus produced were wound through a separator made of a microporous polyethylene film to obtain a power generating element having an oval cross section. After connecting the positive and negative electrode current collectors to the power generating element, a long cylindrical battery container (50 m long)
mx 130 mm wide x 210 mm high) and sealed. At this time, the positive electrode current collector and the negative electrode current collector were connected to the positive electrode terminal and the negative electrode terminal provided on the battery container, respectively, via connection leads.

Next, asymmetric acyclic sulfones (ethyl methyl sulfone (EMS), ethyl isopropyl sulfone (EIPS)) and chain carbonates (dimethyl carbonate (DMC), ethyl methyl carbonate ( EM
C), diethyl carbonate (DEC))
0.5 mol / l (liter) LiPF ₆ and 0.5 m
ol / l of LiN (CF ₃ SO ₂ ) ₂ dissolved together with an electrolytic solution under reduced pressure, and then sealed to obtain a battery.

Comparative Example 1 The procedure of Example 1 was repeated except that a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) having the composition shown in FIG. 7 was used instead of the electrolyte solvent described in Example 1. A similar battery was manufactured.

[Evaluation] The battery has a current of 50 A at a temperature of 25 ° C.
/ Constant voltage at 4.1V for 4 hours / After charging at constant voltage, at current of 100A
The cycle of discharging at a high rate to 2.75 V was repeated. The discharge capacity at the 100th charge / discharge cycle is summarized in FIGS.

[0022]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

FIG. 7 clearly shows that when a mixed solvent of asymmetric acyclic sulfone and a chain carbonate is used as the electrolyte solvent, the content of the chain carbonate is 10% by volume or more and 80% or more in the case of dimethyl carbonate. % By volume, 40% by volume or more and 90% by volume or less in the case of ethyl methyl carbonate, 80% by volume or more in the case of diethyl carbonate and 9%
0% by volume or less, the conventional electrolytic solution (EC
+ DMC (2: 8 volume ratio)).

The reason for this is that the addition of a low-viscosity chain carbonate to the asymmetric acyclic sulfone lowers the viscosity of the solvent, improves the wettability of the electrodes and the separator, and simultaneously reduces the ionic conductivity of the electrolyte. It is thought that it improved.

The optimum content of the chain carbonate varies depending on the type of the solvent. That is, dimethyl carbonate is
Among the three types of chain carbonates, the viscosity was the lowest, but the dielectric constant was the highest, so the effect was seen from the content as low as 10% by volume, but the content was 80% by volume due to poor stability.
When it exceeded, capacity decreased.

Diethyl carbonate has the highest viscosity among the three types of chain carbonates but has the lowest dielectric constant, so a content of 80% by volume or more was required. High capacity was maintained even at 90% by volume.

Ethyl methyl carbonate has an intermediate property among the three types of chain carbonates, and an effect was observed when the content was reduced from 40% by volume to 90% by volume.

FIG. 8 shows the composition of a mixed solvent of ethyl methyl sulfone, which is an asymmetric acyclic sulfone, and dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, which are chain carbonates.

The open circles in the figure indicate the composition of the two-component mixture system in which the effect was observed in the above embodiment. The open triangles in the figure indicate the experimental results of a three-component mixed system. The composition of each point was as follows: 80% by volume of ethyl methyl sulfone, 10% by volume of dimethyl carbonate, 10% by volume of ethyl methyl carbonate, 16% by volume of ethyl methyl sulfone , Dimethyl carbonate 4
2% by volume, 42% by volume of ethyl methyl carbonate, 60% by volume of ethyl methyl sulfone, 30% by volume of ethyl methyl carbonate, 30% by volume of diethyl carbonate, and 10% by volume of ethyl methyl sulfone, 45% by volume of ethyl methyl carbonate; It is of 45% by volume of diethyl carbonate. The open squares are the experimental results of the four-component mixed system, which are 25% by volume of ethyl methyl carbonate, 25% by volume of dimethyl carbonate, 25% by volume of ethyl methyl carbonate, and 25% by volume of diethyl carbonate.

The same experiment as in the above example was conducted with the mixed solvent of the above three components and four components, and it was confirmed that the same effect as that of the two component system was obtained. That is, the mixing ratio between the chain carbonate and the non-cyclic sulfone is as shown in FIG.
A composition range represented by the described tetrahedron, and 10% of dimethyl carbonate with respect to the acyclic sulfone;
The surface passing through each side of 40% of ethyl methyl carbonate and 80% of diethyl carbonate and the side of 80% of dimethyl carbonate, 90% of ethyl methyl carbonate and 90% of diethyl carbonate with respect to the acyclic sulfone It was found that the effects of the present invention were exhibited if the composition range was shown between the surface and the passing surface. It goes without saying that the composition in the case of the two-component system, the three-component system, and the four-component system is obvious from individual composition diagrams. In addition, it goes without saying that the composition range includes the composition on the surface.

In the above embodiment, the case where ethyl methyl sulfone and ethyl isopropyl sulfone are used as the asymmetric acyclic sulfone has been described.
_{When 1} ≠ R ₂ , the same effect can be obtained if R ₁ and R ₂ are alkyl groups having 1 to 4 carbon atoms. Examples thereof include methyl isopropyl sulfone, ethyl propyl sulfone, propyl isopropyl sulfone, butyl methyl sulfone, butyl ethyl sulfone and the like, and these can be used alone or in combination of two or more.

In the above embodiment, the case where a liquid is used as an electrolyte has been described. However, the present invention can be applied to a solid polymer electrolyte or a gel electrolyte. As an example, a polymer solid electrolyte obtained by adding the above-mentioned mixed solvent to a fluororubber-based polymer material, or a gel electrolyte obtained by adding an acrylic monomer to the above-mentioned solvent and polymerizing the same can be used.

Further, in this embodiment, the case where the carbon material is used for the negative electrode has been described. However, the negative electrode material used for the lithium battery, for example, metallic lithium, lithium alloy, highly crystalline carbon material (artificial graphite, natural graphite), Low crystalline carbon (hard carbon, low-temperature fired carbon), metal oxides, and the like can be applied to the negative electrode alone or in combination of two or more. However, considering the charge-discharge cycle life performance, the carbon material of the lattice spacing d ₀₀₂ is more than 0.338nm material to or graphite surface is coated like a low crystalline carbon material, is preferred.

In the above embodiment, the case where the lithium-cobalt composite oxide (LiCoO ₂ ) is used as the positive electrode active material has been described. However, manganese dioxide which is the active material for the primary battery and the active material for the secondary battery are used. The present invention can be applied to various substances such as titanium disulfide, spinel lithium manganese oxide, vanadium pentoxide, and molybdenum trioxide. In particular, the electrolyte used in the battery of the present invention is superior in electrochemical stability to the conventional electrolyte, and therefore, the lithium-cobalt composite oxide and the lithium-containing nickel-cobalt composite oxide (LiNi _X Co _1-X O ₂ : 0.5 <X <0.9), and 4V such as spinel type lithium manganese oxide (LiMn ₂ O ₄ )
(Li / Li ⁺ ) It has a great effect on an active material that charges and discharges at a very noble potential of above.

In the above embodiment, Li was used as the electrolyte salt.
Although the case where PF ₆ and LiN (CF ₃ SO ₂ ) ₂ are mixed has been described, an electrolyte used in conventional primary batteries and secondary batteries can be applied. For example, LiCl
O ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiN
(CF ₃ SO ₂ ) ₂ , LiN (C _n F _{2n + 1} SO ₂ ) ₂ (however,
n can be independently 1, 2, 3, or 4) alone or as a mixture of two or more. Above all, LiN
(CF ₃ SO ₂ ) ₂ is the most suitable electrolyte salt in that the ionic conductivity is increased with respect to the mixed solvent of the asymmetric acyclic sulfone and the chain carbonate. But,
With LiN the (CF ₃ SO _{2) 2} alone, since the aluminum foil Seikyokumoto material is corroded, LiPF ₆ and L
It is preferable to use an electrolyte salt obtained by mixing iN (CF ₃ SO ₂ ) ₂ with a molar ratio of 1: 9 to 9: 1. In this mixed electrolyte salt, the ionic conductivity of the electrolyte is increased by the effect of adding LiN (CF ₃ SO ₂ ) ₂ , and the aluminum foil of the positive electrode substrate is hardly corroded by the effect of adding LiPF ₆ . If the molar ratio of LiN (CF ₃ SO _{2) 2} with respect to LiPF ₆ is 10% or less, high-rate discharge performance of the battery because the ion conductivity of the electrolyte is low is reduced, LiN for LiPF ₆ (CF ₃ SO ₂ ) When the molar ratio of ₂ is 90% or more, the aluminum foil of the positive electrode substrate is corroded, and the battery performance is reduced. The concentration of the electrolyte dissolved in the electrolyte is suitably 0.5 to 1.5 mol / l.

The batteries according to the above-described embodiments are all long-cylindrical batteries having a capacity of 100 Ah, but the same effects can be obtained by applying the present invention to cylindrical, square or paper batteries. In the above embodiment, an example of application to a secondary battery has been described, but the present invention is also applicable to a primary battery.

[0036]

As described above, according to the present invention, it is possible to effectively suppress a decrease in discharge capacity and a decrease in high-rate discharge performance accompanying the progress of a charge / discharge cycle, and its industrial value is extremely large. is there.

[Brief description of the drawings]

FIG. 1 shows discharge capacity and EMS + at the 100th charge / discharge cycle.
It is a figure which shows the relationship with the DMC content in a DMC mixed solvent.

FIG. 2 shows discharge capacity and EMS + at the 100th charge / discharge cycle.
It is a figure which shows the relationship with EMC content in an EMC mixed solvent.

FIG. 3 shows discharge capacity and EMS + at the 100th charge / discharge cycle.
It is a figure which shows the relationship with the DEC content rate in a DEC mixed solvent.

FIG. 4 shows discharge capacity and EIPS at the 100th charge / discharge cycle.
It is a figure which shows the relationship with the DMC content rate in + DMC mixed solvent.

FIG. 5: Discharge capacity and EIPS at the 100th charge / discharge cycle
It is a figure which shows the relationship with the EMC content rate in + EMC mixed solvent.

FIG. 6 shows discharge capacity and EIPS at the 100th charge / discharge cycle.
It is a figure which shows the relationship with the DEC content rate in + DEC mixed solvent.

FIG. 7 shows the discharge capacity and EC + E at the 100th charge / discharge cycle.
It is a figure which shows the relationship with EMC content in MC mixed solvent.

FIG. 8 is a composition diagram of a mixed solvent of ethyl methyl sulfone, which is an asymmetric acyclic sulfone, and dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, which are chain carbonates.

Claims (3)

[Claims] 1. An electrolyte comprising: a negative electrode, a positive electrode, and an electrolyte, wherein the electrolyte contains an asymmetric acyclic sulfone represented by the following formula (1) and a chain carbonate, wherein the chain carbonate is: A non-aqueous electrolyte battery comprising at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Wherein R ₁ ≠ R ₂ and R ₁ and R ₂ are alkyl groups having 1 to 4 carbon atoms. 2. The mixing ratio between the chain carbonate and the non-cyclic sulfone is within the composition range shown by the tetrahedron shown in FIG. 8, and dimethyl carbonate is 10% by volume with respect to the non-cyclic sulfone; 40% by volume of ethyl methyl carbonate, 80% by volume of diethyl carbonate passing through each side, and 80% by volume of dimethyl carbonate and 9% of ethyl methyl carbonate with respect to the acyclic sulfone.
2. The nonaqueous electrolyte battery according to claim 1, wherein the composition range is between 0% by volume and a plane passing through each side of 90% by volume of diethyl carbonate. 3. The method according to claim 1, wherein the electrolyte comprises LiPF ₆ and LiN (C
F ₃ SO _{2) 2} and the molar ratio of 1: 9 to 9: The non-aqueous electrolyte battery according to claim 1 or 2, characterized in that it contains an electrolyte salt were mixed in a 1.