JP2908719B2 - Organic electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery having improved safety and storability and excellent battery performance.

[0002]

2. Description of the Related Art An organic electrolyte secondary battery is a secondary battery in which an organic solvent is used as a solvent for the electrolyte. This type of secondary battery has a large capacity, a high voltage and a high energy density. Therefore, the demand tends to increase more and more.

In such secondary batteries, organic solvents such as 1,2-dimethoxyethane and propylene carbonate have been used as a solvent for the electrolytic solution. Ethane belongs to Dangerous Goods Class 4,
Due to the low flash point and the high risk of ignition, use of such a flammable solvent has recently become unfavorable in terms of battery safety against fire.

On the other hand, phosphate triesters such as trialkyl phosphate are nonflammable or nonflammable (having a flash point of 10
(0 ° C. or higher)), which is particularly desirable as a solvent for an organic electrolyte secondary battery.

[0005]

However, in an electrolyte using a phosphoric acid triester, when lithium or an alloy thereof is used as a negative electrode with respect to an active positive electrode active material such as manganese dioxide, the negative electrode lithium is not used. There is a problem of storability that the reaction with the solvent occurs, the internal resistance is remarkably increased, and the battery performance is deteriorated.

The present invention solves the above-mentioned conventional problems,
An object of the present invention is to provide an organic electrolyte secondary battery having improved safety and storage properties and excellent battery performance.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, while using phosphoric acid triester as the main solvent of the organic electrolyte, lithium or its alloy was used for the negative electrode. By using a carbon material instead, an organic electrolyte secondary battery with excellent safety and storability can be obtained, in particular, a negative electrode made of a carbon material is brought into a specific surface state, or carbon dioxide is dissolved in the electrolyte. As a result, it was found that the above-mentioned secondary battery having excellent battery performance such as a closed circuit voltage, a retention (difference between a charged capacity and a discharged capacity), and a discharged capacity was obtained, and the present invention was completed.

That is, the present invention relates to an organic electrolyte secondary battery having a positive electrode, a negative electrode and an organic electrolyte, wherein a phosphate triester is used as a main solvent of the organic electrolyte and the negative electrode is made of a carbon material. In particular, the present invention relates to an organic electrolyte secondary battery characterized by a peak intensity (I) of about 285 eV of carbon by XPS analysis on the surface of a negative electrode.
₂₈₅₎ and peak near 289eV from 284eV carbon - configuration ratio I ₂₈₅ / Ic of the total click intensity (Ic) is 0.5 or less, also the phosphorus XPS analysis of the anode surface 135eV
From the peak intensity (I ₁₃₅ ) and 284 eV of carbon,
The ratio of the total peak intensity (Ic) near 89 eV, I ₁₃₅ /
A preferred embodiment has a configuration in which Ic is 0.05 or more and the ratio is larger than the above-described ratio inside the negative electrode, and further, a configuration in which carbon dioxide is dissolved in an organic electrolyte solution.

[0009]

In the present invention, the negative electrode is composed of a carbon material as a constituent element and a binder to which a binder or the like is appropriately added to form a mixture. The mixture is formed of a current collecting material such as a copper foil. As the core material, a finished product is used. here,
As the carbon material, any material capable of doping and undoping lithium ions may be used, such as graphite, pyrolytic carbons, cokes, glassy carbons, and a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fiber, activated carbon and the like can be used.

[0010] Such a carbon material is obtained by, for example, heat-treating heavy oil, coal tar, pitch fiber or the like, carbonizing it, and pulverizing it. That is, when the above-mentioned raw material is heated, an aromatic ring is formed with an increase in temperature to form a condensed polycyclic aromatic ring structure.
After heating to 0 ° C. or higher to partially treat the graphite-like structure, it is pulverized and dried, and used as a negative electrode active material precursor.

The negative electrode active material precursor has an interplanar distance d ₀₀₂ of the (002) plane of 3.3 ° or more, preferably 3.35 °.
Or more, most preferably 3.36 ° or more, and the upper limit is 3.5
Å, preferably 3.45 Å or less, more preferably 3.4 Å or less. The crystallite size Lc in the C-axis direction is 30 ° or more, preferably 80 ° or more,
It is more preferably at least 250 ° and the upper limit is at most 1,000 °, preferably at most 500 °. The average particle size is preferably 8 to 15 μm, particularly preferably 10 to 13 μm, and the purity is preferably 99.9% or more.

By using such a negative electrode active material precursor, the storability of an organic electrolyte secondary battery using a phosphoric acid triester as a main solvent of the electrolyte is improved, and the internal resistance is increased with time. It is possible to obtain excellent battery performance by suppressing it, but in order to further improve the battery performance, the negative electrode active material precursor or the negative electrode using the same is further subjected to an appropriate surface treatment. Is desirable.

As an example of the surface treatment, the object to be treated is immersed in a carbon treatment liquid, in which alkali metal ions are doped, and a small amount of Li element, oxygen element, phosphorus element and the like are removed. A method of performing a heat treatment under the included conditions may be mentioned. In the future, by adjusting the atmosphere for synthesizing the carbon material, it is considered that a desired surface state can be obtained without performing the above treatment.

Here, an example in which a negative electrode using a negative electrode active material precursor is treated in a carbon treatment liquid will be described.
Although the concentration of the electrolyte in the carbon treatment liquid is not particularly limited, usually, the carbon treatment liquid contains 0.01 to 4 mol / liter, particularly 0 to 4 mol / liter of a metal salt as an electrolyte in an organic solvent. What dissolves about 0.5 to 1.5 mol / liter is preferably used. Further, it is preferable to use a solution obtained by dissolving carbon dioxide in the carbon treatment liquid, because a negative electrode in which the reactivity between the negative electrode surface and the electrolytic solution is further suppressed can be formed.

As a solvent for the treatment liquid, for example, a mixed solvent of a phosphoric acid triester and an ester having a high dielectric constant is preferably used. Triester phosphates include trialkyl phosphates such as trimethyl phosphate, triethyl phosphate, and tributyl phosphate. Esters having a high dielectric constant include ethylene carbonate and propylene carbonate.
Butylene carbonate, γ-butyrolactone, and the like.

The electrolyte of the treatment liquid is LiCl
O ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiS
bF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ and the like,
Other Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1}
SO ₃ (n> = 2).

By performing such a surface treatment, the hydrogen bonds (CH) existing on the surface of the negative electrode active material precursor are reduced, and C * -OR, C * (= O) -OR, C *-(OR)
(OR ′), functional groups such as C * ＝ O (where C * indicates a carbon atom on the surface of the negative electrode, R and R ′ are H, and have 1 to 1 carbon atoms).
0, an alkyl group or an alkali metal), and as a result, the surface state of the negative electrode becomes 2% of carbon in the XPS analysis.
Peak intensity (I ₂₈₅ ) near 85 eV and 284 e of carbon
The ratio I ₂₈₅ / Ic of the total peak intensity (Ic) from V to around 289 eV becomes 0.5 or less, preferably 0.1 or less. In this case, the reactivity between the negative electrode surface and the electrolyte further increases. As a result, more favorable results can be obtained due to the improvement in storability, and a higher closed circuit voltage can be obtained.

Further, by including a phosphorus-based substance such as trialkyl phosphate in the treatment solution, the amount of phosphorus element on the surface of the negative electrode is increased, and as a result, the surface state of the negative electrode is reduced by the XPS analysis. The ratio I ₁₃₅ / Ic of the peak intensity (I ₁₃₅ ) around ₁₃₅ eV to the total (Ic) of the peak intensity around 284 eV to 289 eV of carbon is 0.05 or more, preferably 0.1 or more, more preferably Is 0.2 or more, and this ratio is larger than the above-mentioned ratio inside the negative electrode. In this case, in addition to the improvement in storage property, the effect of reducing the retention (difference between charge capacity and discharge capacity) is obtained. Can be

The ratio I ₁₃₅ / Ic of the negative electrode surface is the same as the above ratio inside the negative electrode, that is, the ratio I ₁₃₅ / Ic inside the negative electrode after etching with an argon ion sputter of 2 KeV and 7 to 8 μA for 10 minutes. When the ratio I ₁₃₅ / Ic of the negative electrode surface is set to 1, the ratio I ₁₃₅ / Ic inside the negative electrode is 0.95 or less, preferably 0.9 or less.
It is more preferably about 0.7 or less.

In the present invention, manganese dioxide, vanadium pentoxide, chromium oxide, LiNiO ₂
Such as lithium nickel oxide, lithium cobalt oxide such as LiCoO ₂ , lithium manganese oxide such as LiMn ₂ O ₄ , or metal sulfide such as titanium disulfide and molybdenum disulfide, or a positive electrode thereof A mixture obtained by appropriately adding a conductive additive, a binder such as polytetrafluoroethylene, or the like to the active material, and finishing the formed body with a current collector material such as a stainless steel net as a core material is used.

In the present invention, the organic electrolyte is prepared by dissolving the electrolyte in an organic solvent. As the organic solvent, the general formula: (RO) ₃ P = O (where R
Is an organic group, and the three organic groups may be the same or different), preferably a trialkyl phosphate wherein R is an alkyl group having 1 to 6 carbon atoms For example, trimethyl phosphate, triethyl phosphate,
Tripropyl phosphate, tributyl phosphate and the like are used as the main solvent. Here, the main solvent may be such that all of the solvent of the organic electrolyte is phosphate triester, or that most of the solvent of the organic electrolyte is phosphate triester, and the other solvent is one. It means that some parts may be used together.

When another organic solvent is used in combination, the content of the phosphoric acid triester should be at least 40% by volume, preferably at least 60% by volume, more preferably at least 90% by volume, based on the total solvent of the organic electrolytic solution. When the proportion of the phosphoric acid triester is large, the non-flammable or flame-retardant property of the solvent is sufficiently exhibited, and the fire safety is improved. On the other hand, considering the discharge performance and the like, it is preferable to use another solvent in combination as long as safety against fire based on phosphoric acid triester can be ensured.

As the other solvent, an ester having a dielectric constant of 30 or more, particularly preferably 50 or more, is preferable. When this solvent is used, a flame-retardant electrolytic solution having high solubility of the electrolyte can be obtained, and the active site of the reaction between the carbon material surface of the negative electrode and the electrolytic solution can be further reduced. That is, when the phosphoric acid triester and the ester having a high dielectric constant are used in combination, the solubility of the electrolyte is improved,
The conductivity is also increased, and the capacity is also improved. In particular, the size Lc of the crystallite in the C-axis direction in the negative electrode is 30 ° or more, preferably 80 °
It is desirable to use a carbon material having a thickness of Å or more, especially 250 ° or more, since the capacity is remarkably improved.

As such an ester having a high dielectric constant, an alkylene carbonate having 2 to 10 carbon atoms, preferably 2 to 6 carbon atoms, is used. For example, ethylene carbonate, propylene carbonate, butylene carbonate
G, butyrolactone, ethylene glycol sulfite and the like. Among them, those having a cyclic structure are particularly preferable, and a cyclic carbonate is particularly preferable. The most preferred ester is ethylene carbonate
And its dielectric constant is 95.

These esters having a high dielectric constant are used for improving the discharge performance. However, when carbon dioxide is dissolved in the electrolytic solution, a sufficiently high capacity can be obtained by the dissolution as described later. To achieve this, it is desirable to keep the amount of the above-mentioned ester having a high dielectric constant as small as possible in consideration of safety. That is, since the ester having a high dielectric constant is flammable, it is preferable that the ester having a high dielectric constant be used in combination with a phosphoric acid triester from the viewpoint of safety. Middle one
It is preferably 0% by volume or less, more preferably 5% by volume or less, and still more preferably 3% by volume or less. The capacity improvement by these esters having a high dielectric constant appears when the amount of the ester is 1% by volume or more in the total solvent of the electrolytic solution, and when the amount of the ester reaches 2% by volume, a remarkable improvement is observed.

As described above, when carbon dioxide is dissolved in an organic electrolytic solution, when the ester having a high dielectric constant and the phosphoric acid triester are used in combination, the ester having a high dielectric constant is dissolved in the electrolytic solution. 1 to 10% by volume in all solvents, especially 2 to
Preferably it is 5% by volume, especially 2-3% by volume. The difference in boiling point between the phosphoric acid triester and the ester having a high dielectric constant is preferably 150 ° C. or less, more preferably 100 ° C. or less, further preferably 50 ° C. or less, and most preferably 10 ° C. or less. This is because the flammable ester and the flame-retardant phosphoric acid triester azeotropically make the ester less likely to ignite.

In addition to such an ester having a high dielectric constant, 1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether and the like can be used in combination. Further, an amine imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, or the like may be used in combination. However, these solvents also
It is preferably 10% by volume or less in the total solvent of the electrolytic solution.

As the electrolyte of the electrolytic solution, for example, Li
ClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , L
iSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ ,
LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , Li
N (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , L
iC _n F _{2n + 1} SO ₃ (n ≧ 2) alone or 2
Used as a mixture of more than one species. Among them, LiPF ₆ and Li
C ₄ F ₉ SO ₃ is preferably used because of its good charge / discharge characteristics. The concentration of these electrolytes in the electrolyte is not particularly limited, but is usually about 0.1 to 2 mol / liter, preferably about 0.4 to 1 mol / liter.

In the present invention, it is particularly preferable to dissolve carbon dioxide in such an organic electrolytic solution because a high capacity can be achieved. This is because even when a carbon material is used for the negative electrode, a reaction between the carbon material and the solvent of the organic electrolyte still occurs, and the reaction product tends to hinder the charge / discharge reaction or decrease the capacity. Can be However, when carbon dioxide is dissolved in the organic electrolyte, a thin composite film of organic or inorganic carbonate or phosphate is formed on the surface of the carbon material. The reaction is suppressed, and the composite film does not adversely affect the charge / discharge reaction and does not cause a decrease in capacity, so that the ability of the positive electrode material and the negative electrode material can be maximized and the capacity of the battery can be reduced. It is thought to improve.

The dissolution of carbon dioxide is determined by using a lithium composite oxide, such as LiNiO ₂ , LiCoO ₂ , or LiMn ₂ O ₄ , having a closed circuit voltage of 4 V or more based on Li as a positive electrode active material. It is valid. These positive electrode active materials have a high voltage, and under normal conditions, the organic electrolyte is oxidized and the discharge performance deteriorates.However, when carbon dioxide having excellent oxidation resistance is dissolved in the organic electrolyte, the carbon dioxide becomes a positive electrode. Suppress decomposition of the electrolyte due to oxidation on the surface. In particular, LiNiO ₂ cannot be used from the viewpoint of reactivity with the electrolyte than other metal oxides. However, even in the case of such LiNiO ₂ , the reaction with the organic electrolyte is suppressed, and a high capacity battery is achieved. Is done.

The amount of carbon dioxide dissolved in the organic electrolyte is 0.03 mol / mol with respect to the organic electrolyte in the battery.
The amount is preferably not less than 0.1 liter (carbon dioxide is 0.03 mol per liter of organic electrolyte), more preferably 0.1 liter.
It is at least mol / litre, more preferably at least 0.3 mol / litre. The larger the amount of carbon dioxide, the more stably the reaction activity of the carbon material is extracted, and the more the positive electrode active material is suppressed from reacting with the organic electrolyte. In such a case, the internal pressure of the battery may be increased to cause the battery to burst. Therefore, in consideration of the pressure resistance of the battery case and the sealing member, the amount is preferably 2 mol / liter or less. Here, carbon dioxide that has been put into the battery and has not been dissolved in the organic electrolyte also dissolves in the organic electrolyte when the carbon dioxide is consumed in the organic electrolyte or when the temperature is lowered. So that it is considered substantially dissolved.

As a method of dissolving carbon dioxide in the organic electrolyte, for example, a method of bubbling carbon dioxide into the organic electrolyte, a method of dissolving liquefied carbon dioxide, and the like can be adopted. The pressure of carbon dioxide during bubbling is preferably higher. In addition, the method of putting the organic electrolyte solution and carbon dioxide in a closed pressurized container and applying pressure to dissolve the carbon dioxide in the organic electrolyte solution, or the method of putting dry ice in the battery case and sealing it, etc. are adopted. Yes, but not necessarily.

The partial pressure of carbon dioxide during dissolution of carbon dioxide is preferably 0.5 kgf / cm ² or more, and 1.0 kgf / cm ² or more.
^Two or more are more preferable. The injection of the organic electrolyte is also preferably performed in a dry atmosphere containing carbon dioxide. further,
The temperature of the organic electrolytic solution at the time of injecting the electrolyte and the temperature of the battery before the injection are preferably 10 ° C. or lower, particularly preferably −20 ° C. or lower. It is preferable to use dry ice or liquefied carbon dioxide because these are easily satisfied.
It is also preferable to put dry ice into the battery. In this case, it is preferable not to put it in the organic electrolytic solution and to put it on a separator or the like. After charging, it is preferable to seal within 1 minute, more preferably within 20 seconds, further preferably within 10 seconds.

As a method of injecting the organic electrolytic solution after dissolving the carbon dioxide into the battery case, for example, the battery case and the organic electrolytic solution are cooled to -20 ° C. or lower for several hours and then cooled. A method of injecting the organic electrolyte into a cooled battery case can be adopted. Also, a battery case is attached to the centrifuge.
How to set the solution and quickly inject the organic electrolyte,
A method in which the battery case is evacuated and then an organic electrolytic solution is injected can be adopted, but this is not necessarily required.

In the organic electrolyte secondary battery according to the present invention, the above-described positive electrode and the negative electrode comprising a carbon material as components are arranged in a battery case so as to face each other via a separator, and a phosphate triester is provided. Inject the organic electrolyte with the main solvent as
Preferably, carbon dioxide is dissolved in this, and the battery form includes various forms such as a tubular form, a button form, a coin form and the like.

[0036]

Next, an embodiment of the present invention will be described in more detail. However, the present invention is not limited only to the following embodiments.

Example 1 LiC ₄ F ₉ SO ₃ (hereinafter, referred to as NFB) was dissolved in trimethyl phosphate, and propylene carbonate (hereinafter, referred to as PC) was added thereto.
A mixed solvent of C and trimethyl phosphate in a volume ratio of 1: 2
An organic electrolyte in which FB was dissolved at 0.6 mol / liter was prepared.

Further, lithium cobalt oxide (LiCo
6 parts by weight of graphite and 3 parts by weight of polyvinylidene fluoride were added to 91 parts by weight of O ₂ ), mixed and dispersed with a solvent to form a slurry. This positive electrode material mixture slurry is uniformly applied to both sides of the aluminum foil of the positive electrode current collector having a thickness of 20 μm, dried and then compression molded by a roller press machine, and the lead body is welded. Thus, a belt-shaped positive electrode was manufactured.

Separately, 90 parts by weight of coke having an inter-plane distance d ₀₀₂ of (002) plane of 3.43 ° and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to form a negative electrode mixture. This was dispersed in a solvent to form a slurry. This negative electrode mixture slurry has a thickness of 20 μm as a negative electrode current collector.
Uniformly applied on both sides of the strip of copper foil and dried, then
After compression molding with a roller press, the lead body was welded to produce a strip-shaped negative electrode precursor.

Next, a processing solution for the negative electrode precursor was prepared.
That is, first, NFB is dissolved in trimethyl phosphate, and then ethylene carbonate (hereinafter, referred to as EC) is added and mixed to obtain a mixed solvent of EC and trimethyl phosphate at a volume ratio of 1: 1. A treatment solution was prepared by dissolving 0.6 mol / liter of NFB. Next, a lead body was sandwiched between pressurized Li oils via a polypropylene separator impregnated with the above-mentioned treatment solution on both sides of the negative electrode precursor, and placed in a polypropylene holder. , Li electrode as a negative electrode and 0 at 300 mA
250mAh / g per unit weight of carbon material of electrode up to V
After discharging, the battery was charged to 1.5 V at 300 mA. Thereafter, the resultant was decomposed, the negative electrode precursor was washed with dimethyl carbonate, and dried to prepare a negative electrode.

Next, the above-mentioned strip-shaped positive electrode was put in a thickness of 25 μm.
The sheet-shaped negative electrode is overlapped with a sheet-shaped negative electrode through a separator made of a microporous polypropylene film having a diameter of 15 m, and spirally wound to form a spiral electrode body. After filling the lead and welding the lead bodies of the positive electrode and the negative electrode, the above-mentioned organic electrolytic solution was injected into the battery case. Then, the opening of the battery case was sealed, and the battery was precharged to produce a cylindrical organic electrolyte secondary battery.

FIG. 1 is a schematic view of a battery according to the present invention.
1 is a positive electrode, 2 is a negative electrode. In this figure, for the sake of simplicity, current collectors and the like used for producing the positive electrode 1 and the negative electrode 2 are not shown. 3 is a separator and 4 is an organic electrolyte.

5 is a stainless steel battery case,
Also serves as the negative terminal. An insulator 6 made of polytetrafluoroethylene sheet is arranged at the bottom of the battery case 5, and an insulator 7 made of polytetrafluoroethylene sheet is also arranged at the inner periphery. A spiral electrode body composed of a positive electrode 1, a negative electrode 2, and a separator 3, an organic electrolytic solution 4, and the like are housed in the battery case 5.

Reference numeral 8 denotes a stainless steel sealing plate having a gas vent 8a at the center. 9 is an annular packing made of polypropylene, and 10 is a flexible thin plate made of titanium. Reference numeral 11 denotes an annular polypropylene heat-deformable member which is deformed by temperature and has an effect of changing the breaking pressure of the flexible thin plate 10.

Reference numeral 12 denotes a nickel-plated rolled steel terminal plate provided with a cutting blade 12a and a gas discharge hole 12b, and gas is generated inside the battery to increase the internal pressure.
When the flexible thin plate 10 is deformed due to this rise, the flexible thin plate 10 is broken by the cutting blade 12a, and gas inside the battery is discharged to the outside of the battery from the gas discharge hole 12b, and the battery is removed. Designed to prevent destruction.

Reference numeral 13 denotes an insulating packing, 14 denotes a lead body, which electrically connects the positive electrode 1 and the sealing plate 8, and the terminal plate 12 functions as a positive terminal by contact with the sealing plate 8. Reference numeral 15 denotes a lead body for electrically connecting the negative electrode 2 and the battery case 5.

Example 2 The same procedure as in Example 1 was carried out except that the amount of discharge electricity was set to 210 mAh / g per unit weight of the carbon material of the electrode when treating the negative electrode precursor. A battery was manufactured.

Example 3 The same procedure as in Example 1 was carried out except that the amount of electric discharge was 50 mAh / g per unit weight of the carbon material of the electrode when the negative electrode precursor was treated. A battery was manufactured.

Example 4 A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 1 except that the negative electrode precursor was used as it was without treatment.

Comparative Example 1 Example 1 was repeated except that a lithium metal plate was used as the negative electrode.
In the same manner as in the above, a cylindrical organic electrolyte secondary battery was produced.

With respect to the cylindrical organic electrolyte secondary batteries of Examples 1 to 4 and Comparative Example 1, the rate of change in internal resistance before and after storage was examined in the following manner. Further, the closed circuit voltage of the battery after the storage test (the minimum discharge voltage when a constant current of 0.3 A was applied for 10 ms) was examined. These results were as shown in Table 1 below.

<Rate of change in internal resistance> The battery was charged at 0.1 C to 4.1 V, and then stored at 80 ° C for 10 days.
The change in the impedance at 1 KHz before and after storage was examined, and the rate of change in the internal resistance was calculated by the following formula to examine the deterioration of the battery performance.

[0053]

Table 1

As is clear from Table 1 above, Comparative Example 1
Of the organic electrolyte secondary battery, the internal resistance after storage is about 11 times higher than the initial value, but each of the organic electrolyte secondary batteries of Examples 1 to 4, the internal resistance of the storage 2-4 rise
It is relatively low and has a high closing voltage.
Moreover, about each organic electrolyte secondary battery of Examples 1-4,
Overdischarge was performed up to -4V with 4A as the maximum battery.
There were no batteries that could cause ignition, etc., and the safety was excellent.

Example 5 After dissolving NFB in trimethyl phosphate, EC was added and mixed, and a solution composed of 0.5 mol / liter of NFB / EC: trimethyl phosphate (volume ratio 1: 2), that is, A solution was prepared by dissolving 0.5 mol / liter of NFB in a mixed solvent of EC and trimethyl phosphate at a volume ratio of 1: 2, followed by bubbling carbon dioxide for 10 minutes. And The dissolved amount of carbon dioxide in this treatment liquid was 0.1 mol / liter.

Next, as the negative electrode active material precursor, (00
2) 90 parts by weight of carbon having a plane-to-plane distance d ₀₀₂ of 3.43 °, a crystallite size Lc in the C-axis direction of 32 °, an average particle size of 12 μm, a purity of 99%, and a Si content of 10 ppm are provided. Then, 10 parts by weight of polyvinylidene fluoride was used as a binder, the two were mixed to form a negative electrode mixture, and this was dispersed in N-methylpyrrolidone to form a slurry.

This slurry-shaped negative electrode mixture was coated with a thickness of 18 μm.
m is uniformly coated on both sides of a negative electrode current collector made of a copper foil in a strip shape, dried, and then compression molded by a roller press machine, and the lead body is welded to form a strip electrode body. Produced. This electrode body was short-circuited for 48 hours with Li as a counter electrode in the above-mentioned carbon treatment liquid to dope lithium, and then
A voltage of 1.5 V (vs. Li / Li ⁺ ) was removed for 3 days, followed by vacuum drying to obtain a strip-shaped negative electrode.

For this negative electrode, a solution consisting of 0.5 mol / liter of NFB / EC: trimethyl phosphate (volume ratio 1: 2), that is, a mixed solvent of EC and trimethyl phosphate in a volume ratio of 1: 2 was mixed with NFB. Was dissolved in a solution prepared by dissolving 0.5 mol / liter in a solution prepared by bubbling carbon dioxide for 10 minutes as an electrolyte (0.1 mol / liter of dissolved carbon dioxide). Retention in the first cycle was as low as 1.8%.

Separately, 91 parts by weight of LiCoO _2, 6 parts by weight of graphite and 6 parts by weight of polyvinylidene fluoride were added, mixed and dissolved with N-methylpyrrolidone to form a slurry.
This positive electrode material mixture slurry is uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm, dried, and then compressed and formed by a roller press.
The strip body was welded to produce a belt-shaped positive electrode. The negative electrode was stacked on the positive electrode via a separator made of a microporous polypropylene film having a thickness of 25 μm and spirally wound to obtain a spiral electrode body.

The spiral electrode body is provided with an outer diameter of 15 mm and a height of 4 mm.
After filling a 0 mm bottomed cylindrical battery case and welding the positive and negative electrode leads, 0.5 mol / liter of NFB / EC: trimethyl phosphate (volume ratio 1:
A solution obtained by bubbling carbon dioxide into the solution obtained in 2) for 10 minutes was used as an electrolytic solution (0.1 mol / liter of dissolved carbon dioxide), and this electrolytic solution was injected into the battery case.
At the time of injection, the battery case and the electrolyte were cooled to −20 to −40 ° C. using dry ice, and the electrolyte was injected while the surroundings were in a carbon dioxide dry atmosphere. Thereafter, the opening of the battery case was sealed according to a conventional method to produce a cylindrical organic electrolyte secondary battery having the structure shown in FIG.

Example 6 A strip-shaped electrode body produced by using a negative electrode active material precursor was carved.
The time for short-circuiting with Li as the counter electrode in
A strip-shaped negative electrode was obtained in the same manner as in Example 5, except that the time was changed. Further, using this band-shaped negative electrode, a cylindrical organic electrolyte secondary battery was manufactured in the same operation as in Example 5.

In the same manner as in Example 5, 0.5 mol / liter of NFB / E
C: Evaluated with a model cell using an electrolytic solution (0.1 mol / liter of dissolved carbon dioxide) in which a solution of trimethyl phosphate (volume ratio 1: 2) was bubbled with carbon dioxide for 10 minutes. In the first cycle, the retention was 3%.

Example 7 In short-circuiting a strip-shaped electrode body prepared using a negative electrode active material precursor with Li as a counter electrode in a carbon treatment liquid, carbon dioxide was not bubbled into the carbon treatment liquid. Except for the above, processing was performed in the same manner as in Example 2 to obtain a strip-shaped negative electrode. Further, a cylindrical organic electrolyte secondary battery was produced using the strip-shaped negative electrode by the same operation as in Example 5 except that carbon dioxide was not bubbled into the electrolyte.

In the same manner as in Example 5, 0.5 mol / liter of NFB / E
C: Evaluated with a model cell using an electrolytic solution (0.1 mol / liter of dissolved carbon dioxide) in which a solution of trimethyl phosphate (volume ratio 1: 2) was bubbled with carbon dioxide for 10 minutes. Of the first cycle was 4%.

Example 8 A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 5 except that an untreated negative electrode was used in place of the negative electrode treated in the carbon treating solution. Was prepared. For the untreated negative electrode, in the same manner as in Example 5, an electrolytic solution obtained by bubbling carbon dioxide into a solution containing 0.5 mol / liter of NFB / EC: trimethyl phosphate (volume ratio 1: 2) for 10 minutes. When the evaluation was performed using a model cell using (amount of dissolved carbon dioxide of 0.1 mol / liter), the retention of the first cycle of the negative electrode was 21%, and the retention of the third cycle was 4%.

The organic electrolyte secondary batteries of Examples 5 to 8 were charged and discharged at 0.1 C in a voltage range of 2.7 to 4.2 V, and the first cycle retention was examined. The results were as shown in Table 2 below. The retention is determined according to the following formula: retention (%) = [(charge capacity−discharge capacity) / (charge capacity)] × 100.

In Table 2, for reference, the ratio of I ₂₈₅ / Ic of the negative electrode carbon material in each example , that is, the negative
XPS analysis of the extreme surface was performed, and the photoelectron spectrum
Peak intensity around 285 eV and 284 eV to 289 eV
The ratio I ₂₈₅ / Ic of the sum of the peak intensities around V was examined, and the results are also shown. In each example, the ratio of I ₁₃₅ / Ic of the negative electrode carbon material, that is, XPS analysis of the negative electrode surface was performed, and the peak intensity of 135 eV of phosphorus and the peak intensity of 284 eV to 289 eV of carbon in the photoelectron spectrum were observed. The total ratio I ₁₃₅ / Ic was examined, and the results are also shown.
Further, the same ratio I ₁₃₅ / Ic inside the electrode (after etching for 10 minutes with an argon ion sputter at 2 KeV and 7 to 8 μA) was also examined, and the results are also shown.

[0069]

[Table 2]

As is clear from the results in Table 2 above, in the organic electrolyte secondary batteries of Examples 5 to 7 in which the ratio of I ₁₃₅ / Ic on the surface of the negative electrode carbon material was set high, the ratio was set low. It can be seen that the retention of the battery is smaller than that of the battery of Example 8, and the battery has more excellent performance as a secondary battery.

Example 9 Trimethyl phosphate and EC were mixed at a volume ratio of 98: 2,
NFB was dissolved in 1.0 mol / liter in this mixed solvent to prepare an organic electrolyte. Carbon dioxide was bubbled into the solution, and carbon dioxide was dissolved in the electrolyte at a partial pressure of 1 kgf / cm ² .

Separately, 91 parts by weight of LiNiO ₂ was mixed with 6 parts by weight of phosphorous graphite as a conductive assistant, and a mixture of this mixture and 3 parts by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone was used. Was mixed into a slurry. The positive electrode mixture slurry was passed through a mesh of 70 mesh to remove large particles, and then uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, followed by drying. Then, after compression-forming with a roller press machine, it cut | disconnected and welded the lead body, and produced the strip | belt-shaped positive electrode.

Further, separately from this, a carbon material (however,
d ₀₀₂ = 3.37 °, Lc = 290 °, average particle size = 10
(μm, purity = 99%) 90 parts by weight and a solution prepared by dissolving 10 parts by weight of polyvinylidene fluoride in N-methylpyrrolidone were mixed to form a slurry. The negative electrode mixture slurry was passed through a mesh of 70 mesh to remove large pieces, and then uniformly applied to both surfaces of a negative electrode current collector made of a 18 μm-thick strip-shaped copper foil, followed by drying. Then, after compression forming with a roller press machine, cut,
The strip was welded to produce a strip-shaped negative electrode.

Next, the strip-shaped positive electrode produced by the above-described method is superimposed on the strip-shaped negative electrode produced by the above-described method via a microporous polypropylene film having a thickness of 25 μm, and spirally wound. After forming the spiral electrode body, it was filled into a cylindrical battery case with a bottom having an outer diameter of 15 mm, and the positive and negative electrode leads were welded.

The battery case filled with the spiral electrode body and the organic electrolytic solution in which the above-mentioned carbon dioxide was dissolved were cooled to -20 to -40 ° C. with dry ice. The electrolyte is injected into the battery case, and after the organic electrolyte has sufficiently penetrated into the separator or the like, about 0.1%.
02 g of dry ice was put in the organic electrolyte so as not to get wet, and after 5 seconds, the container was sealed to produce a cylindrical organic electrolyte secondary battery having the structure shown in FIG. When the amount of carbon dioxide in the battery produced in the same manner was measured, about 0.35 mol / liter of carbon dioxide per unit volume of the electrolyte was detected.

Example 10 NFB was dissolved at 1.0 mol / liter in trimethyl phosphate to prepare an organic electrolytic solution, and carbon dioxide was bubbled into the organic electrolytic solution to dissolve carbon dioxide in the electrolytic solution. Except that this organic electrolytic solution was used, the same as in Example 9,
A cylindrical organic electrolyte secondary battery was produced. The amount of carbon dioxide in the battery was the same as in Example 9.

Example 11 As the carbon material for the negative electrode, d ₀₀₂ = 3.42 ° and Lc = 3
A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 9, except that a carbon material having characteristics of 2Å, an average particle size of 12 μm, and a purity of 99% or more was used. The amount of carbon dioxide in the battery was the same as in Example 9.

Example 12 A cylindrical organic electrolyte secondary battery was manufactured in the same manner as in Example 9 except that the amount of carbon dioxide dissolved in the organic electrolyte was changed to 0.1 mol / liter. . In this battery, dry ice was not supplied to the battery when the electrolyte was injected.

Example 13 Triethyl phosphate and EC were mixed at a volume ratio of 98: 2,
NFB was dissolved in 1.0 mol / liter in this mixed solvent to prepare an organic electrolyte. This was bubbled with carbon dioxide to dissolve carbon dioxide in the electrolytic solution. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 9 except that this organic electrolyte was used. The amount of carbon dioxide in the battery was the same as in Example 9.

Each of the organic electrolyte secondary batteries of Examples 9 to 13 was charged and discharged at a voltage of 2.7 to 4.1 V at 35 mA, and the discharge capacity at the first cycle was examined. The results were as shown in Table 3 below.

[0081]

[Table 3]

As is clear from the results in Table 3 above, each of the organic electrolyte secondary batteries of Examples 9 to 13 in which carbon dioxide was dissolved in the organic electrolyte solution had a high discharge capacity. It can be seen that high capacity can be achieved by dissolving carbon dioxide.

Next, in order to examine the stability of each of the organic electrolyte secondary batteries of Examples 9 to 13 against fire, the following comparison was conducted using a normal organic solvent other than trialkyl phosphate as the organic electrolyte. In comparison with the organic electrolyte secondary battery of Example 2, a safety test was performed in the following manner. The results were as shown in Table 4 below.

Comparative Example 2 1,2-Dimethoxyethane and EC were mixed at a volume ratio of 1: 1 and NFB was dissolved at 1.0 mol / liter in this mixed solvent to prepare an organic electrolytic solution. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 9 except that the organic electrolyte was used and the battery was directly assembled without dissolving carbon dioxide therein.

<Safety Test> When the battery was heated to a high temperature,
When the safety valve is operated (that is, in the battery shown in FIG. 1, gas is generated inside the battery due to evaporation of the solvent from the electrolytic solution, etc., and the internal pressure of the battery is increased.
Expands toward the terminal plate 12 and comes into contact with the cutting blade 12a, thereby breaking the flexible thin plate 10 and discharging gas inside the battery into the gas discharge hole 1.
2b), the flexible thin plate 10 is broken in advance, and the battery is heated to 100 ° C. in this state, and the gas exhaust hole 1 of the battery is discharged.
A fire was brought close to 2b, and it was examined whether or not it would ignite.

[0086]

[Table 4]

As is clear from the results in Table 4 above, Comparative Example 2 using a normal organic solvent as the solvent for the organic electrolyte solution.
The battery of Example 9 ignited and burned out when heated to about 40 ° C., but Example 9 using a trialkyl phosphate as a main solvent
Each battery of ~ 13 does not ignite even when heated to 100 ° C,
High safety against fire. In particular, the flash point of the electrolyte solution of the batteries of Examples 1 to 4 was 200 ° C. or higher.

[0088]

According to the present invention, a phosphoric acid triester is used as a main solvent of an organic electrolytic solution, while a carbon material is used for a negative electrode. Dissolved carbon dioxide in the inside, it is excellent in safety and storability, closed circuit voltage,
An organic electrolyte secondary battery having excellent battery performance such as retention (difference between charge capacity and discharge capacity) and discharge capacity can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration example of an organic electrolyte secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Organic electrolyte 5 Battery case

────────────────────────────────────────────────── ─── of the front page continued (72) inventor Akira Kawakami Ibaraki, Osaka Ushitora chome No. 1 No. 88 Hitachi Maxell, Ltd. in the (58) investigated the field (Int.Cl. ^6, DB name) H01M 10/40 H01M 4/02 H01M 4/58

Claims (8)

(57) [Claims] 1. An organic electrolyte secondary battery having a positive electrode, a negative electrode, and an organic electrolyte, wherein a phosphate triester is used as a main solvent of the organic electrolyte, and the negative electrode is made of a carbon material. Organic electrolyte secondary battery. 2. The organic electrolyte secondary battery according to claim 1, wherein the phosphate triester is a trialkyl phosphate. 3. 285e of carbon by XPS analysis of the negative electrode surface
The ratio I ₂₈₅ of the peak intensity (I ₂₈₅ ) around V and the sum (Ic) of the peak intensity around 284 eV to 289 eV of carbon _.
The organic electrolyte secondary battery according to claim 1, wherein / Ic is 0.5 or less . 4. 135e of phosphorus by XPS analysis of the negative electrode surface
The ratio I ₁₃₅ of the peak intensity (I ₁₃₅ ) around V and the sum (Ic) of the peak intensity around 284 eV to 289 eV of carbon.
2. The organic electrolyte secondary battery according to claim 1, wherein / Ic is 0.05 or more, and the ratio is larger than the above ratio inside the negative electrode. 5. The organic electrolyte secondary battery according to claim 1, wherein an ester having a dielectric constant of 30 or more is used together with a phosphoric acid triester as a solvent of the organic electrolyte. 6. The organic electrolyte secondary battery according to claim 1, wherein carbon dioxide is dissolved in the organic electrolyte. 7. The organic electrolyte secondary battery according to claim 6, wherein the dissolved amount of carbon dioxide is 0.03 mol / liter or more. 8. The organic electrolyte secondary battery according to claim 6, wherein the solvent of the organic electrolyte contains 1 to 10% by volume of an ester having a dielectric constant of 30 or more.