JPH10308237A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery, of which cycle lifetime characteristic is improved and which has a high energy density, by forming a lithium secondary battery of a positive electrode, a negative electrode of a lithium metal, and the organic electrolyte, which includes magnesium salt and CO2 gas at the time of forming a battery. SOLUTION: A gasket 3 is interposed between an outer can 1 for battery negative electrode and an outer can 2 for battery positive electrode, and a positive electrode 5, a negative electrode 4 and a separator impregnated with the organic electrolyte 6 are filled inside of the cans. At the time of charging a battery, in the lithium metal negative electrode 4, the CO2 gas, which exists in the organic electrolyte, is fixed to a surface of the lithium metal so as to generate LiCO3 . At the same time, magnesium ion is selectively deoxidized and deposited in a boundary of particles of a surface of the lithium metal so as to generate lithium and the alloy, and generation of lithium dendrite is restrained in the following charge and thereafter so as to improve the lifetime characteristic. Even in the case where a material, which can store and discharge lithium ion, is used for negative electrode, generation of lithium dendrite due to a quick charge is prevented so as to improve the lifetime characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in characteristics of a lithium secondary battery, and more particularly to a charge / discharge cycle life characteristic.

[0002]

2. Description of the Related Art A battery using lithium metal as a negative electrode active material was first studied in the United States in the late 1950's in a project to develop a new high-performance battery for military and space use. Since lithium has a low standard electrode potential and a large electrochemical equivalent, it was shown that when used as a negative electrode active material, a battery having a higher voltage and a higher energy density than conventional batteries, such as a dry battery or a lead storage battery, could be constructed. .
Research on lithium batteries began in Japan in the late 1960s, and the world's first lithium battery was 19
Developed in the early 70's. Although the chemical reactivity of lithium metal was extremely high, it was difficult to find a safe battery system. However, a highly safe lithium battery was developed by using an aprotic organic electrolyte as an electrolyte.

[0003] This lithium battery is a primary battery, and there are many problems in developing a chargeable / dischargeable secondary battery. The biggest problem is that when lithium ions are reduced to lithium metal and precipitate on the surface of the lithium metal substrate, needle-like or dendritic products, so-called lithium dendrites, are formed, and the separator between the positive electrode and the cathode Causes short circuit, causing various inconveniences. This phenomenon varies depending on the charge / discharge current density, but in any case, the problem that the battery cycle life is reduced occurs. A charging reaction in a battery corresponds to a reduction reaction of a negative electrode, and is a serious problem in a lithium secondary battery that repeatedly performs a charging and discharging reaction.

As a means for solving the above-mentioned problems and developing a stable lithium secondary battery, a method of using graphite or a carbon material, which absorbs and releases lithium ions, as the negative electrode active material instead of lithium metal as the negative electrode active material has been studied. 1990
In 2000, a lithium secondary battery (lithium ion secondary battery) using lithium cobalt oxide for the positive electrode and a carbon material for inserting and extracting lithium ions in the negative electrode was announced, and has been commercialized since 1991. Since this lithium secondary battery does not use lithium metal, it is considered to be safe without generating the above-mentioned lithium dendrite, and as a power source for small portable devices utilizing the features of long life and high energy density,
Currently its use is expanding rapidly.

[0005] However, when a carbon material is used for the negative electrode, the energy density per volume is lower than that of lithium metal, so that the energy density of the battery is relatively lower than that when lithium metal is used for the negative electrode. That is, the theoretical capacity of lithium metal is 3860 mAh / g, but the discharge capacity of the graphite negative electrode used in the lithium ion secondary battery is about 300 mAh / g, which is 1/10 or less of lithium metal. Although it depends on the size of the battery, when a battery is actually constructed, a lithium ion secondary battery using a graphite negative electrode has an energy density of 372 Wh / l at the maximum, while a secondary battery using a lithium metal has an energy density of about 400 Wh / l. / L
Energy density can be realized. Therefore, in order to improve the energy density, it is desired to use lithium metal as the negative electrode active material.

[0006] Various reports have been made on the mechanism by which lithium dendrite is generated, but many unclear portions have not been determined. One of them is "Analysis of Lithium Precipitation and Dissolution Process, Takuya Fujieda, Osaka Institute of Technology, The 24th Seminar on Electrochemistry", especially in batteries using lithium metal, the grain boundaries existing between lithium crystallites. Reports that dendrites are easily formed.
That is, since the energy state of the grain boundary portion is high and the precipitation reaction of lithium metal during charging is likely to be concentrated, dendritic lithium is generated. Therefore, by lowering the energy of the grain boundary or extinguishing the grain boundary itself,
It is expected that a lithium metal negative electrode having a uniform energy state as a whole is obtained, and that lithium metal is uniformly and smoothly deposited on the lithium negative electrode even during charging.

Several studies have been made for the purpose of suppressing the grain boundary of lithium metal. For example, alloys are used by adding aluminum or boron to lithium metal at the negative electrode, or various kinds of electrolytes are used in the battery electrolyte. Attempts have been made to uniformly deposit lithium metal by adding an organic or inorganic substance. For example, with respect to the invention in which an aluminum salt is added to an organic electrolytic solution, JP-A-63-25
No. 7183.

[0008] A method of adding CO ₂ gas to an organic electrolyte is disclosed in Japanese Patent Application Laid-Open No. 7-176323, in order to suppress LiOH in which lithium is not uniformly generated during charging. Further, a method of using metallic lithium treated in a CO ₂ gas atmosphere as a negative electrode in a battery is disclosed in
There is 124700 publication. All aim at forming a Li ₂ CO ₃ film on the surface of metallic lithium.
Since this Li ₂ CO ₃ film has good electric conductivity and a uniform energy state on the surface, generation of lithium metal dendrite during charging is suppressed.

[0009]

The charge / discharge cycle characteristics of a battery using a lithium metal negative electrode are certainly improved by the above-mentioned means known in the art. However, compared to current lithium-ion batteries, they do not always have sufficient cycle characteristics.

Accordingly, the present invention provides a lithium secondary battery which realizes a high energy density and further improves the charge / discharge cycle characteristics of a battery by using a lithium metal negative electrode by suppressing the generation of dendritic lithium. Using a material that can store and release lithium ions for the negative electrode,
It is an object of the present invention to provide a lithium secondary battery that has a long life even when quick charging is performed.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, suppresses the generation of dendritic lithium, and improves the cycle life characteristics. It is intended to provide a long-life lithium secondary battery. In the present invention, CO ₂ gas is added to the organic electrolytic solution to chemically fix CO ₂ on the lithium metal surface to form a Li ₂ CO ₃ film. Furthermore, by adding a salt containing a magnesium element to the organic electrolyte, dissolved magnesium ions are preferentially reduced at the grain boundaries on the lithium metal negative electrode when the battery is charged, and magnesium metal is generated. Reacts with lithium metal to form an alloy in the surface layer, that is, the surface has a tilting function. As a result, due to the synergistic effect of the alloy and the effect of the Li ₂ CO ₃ film, the production of dendrite-like lithium is further suppressed as compared to the single method, and the lithium is deposited smoothly, and a safe, long-life and high energy density battery can be realized. It is.

Further, when a carbon material negative electrode having a function of inserting and extracting lithium ions is used, the energy density is the same as that of the conventional one, and a long-life lithium ion is added by adding a magnesium salt and CO ₂ gas. A secondary battery can be realized. The reason is that when a carbon material is used for the negative electrode, the generation of dendritic lithium does not occur, but in a special case, that is, during rapid charging performed by increasing the charging current density, the carbon material negative electrode absorbs lithium ions. , And as a result, formation of dendritic lithium may occur. For this reason, the cycle life characteristics of the lithium ion secondary battery that has been rapidly charged are reduced. Therefore, by adding the magnesium salt to the organic electrolyte, a long-life lithium-ion secondary battery can be realized even when quick charging is performed. This effect can be similarly obtained even when another polymer, alloy or metal compound capable of inserting and extracting lithium is used for the negative electrode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be implemented by the embodiments described in the claims. That is, claim 1
As in the invention according to the description, the present invention can be implemented by using, as constituent elements, a positive electrode, a negative electrode of lithium metal, and an organic electrolyte containing both a magnesium salt and CO ₂ gas when constituting a battery. According to the present invention, at least at the time of charging the battery, in the lithium metal negative electrode, the CO ₂ gas dissolved in the organic electrolyte is fixed to the lithium metal surface, and Li ₂ CO ₃ is generated. At the same time, magnesium ions are selectively reduced and precipitated at the grain boundaries on the lithium metal surface, and form an alloy with lithium in the surface layer. Therefore, in the subsequent charging, the generation of lithium dendrite can be suppressed, and the cycle life characteristics can be improved.

Also, as in the invention according to claim 2,
Even when a material capable of occluding and releasing lithium ions is used as the negative electrode without using lithium metal for the negative electrode, even if the battery is rapidly charged, dendrite-like lithium is not generated. A secondary battery can be realized.

Further, as in the invention according to claim 3,
Magnesium salt is 1m of lithium ion in organic electrolyte.
Good results can be obtained by adding 0.01 to 1 mol to ol.

That is, if the addition amount of the magnesium salt to 1 mol of lithium ion is 0.01 mol or less, the magnesium alloy does not function sufficiently. Further, when the addition amount of the magnesium salt is 1 mol or more, precipitation of magnesium occurs more than required precipitation of lithium,
By inhibiting the deposition and diffusion of lithium ions,
It is not preferable because high-rate charge / discharge characteristics and low-temperature charge / discharge characteristics deteriorate.

Further, as in the invention according to claim 4, even if the solvent of the organic electrolytic solution is an organic electrolytic solution alone,
Alternatively, a mixture of an organic electrolyte and a polymer electrolyte may be used.

Further, as in the invention according to claim 5,
Magnesium salts are commercially available Mg (ClO
It is practical to choose from ₄ ) ₂ , MgSO ₄ , Mg (PO ₄ ) ₂ , and MgBr ₂ .

Further, as in the invention according to claim 6,
Good results can be obtained by adding CO ₂ gas to 1 L of the organic electrolyte at a flow rate of 2 L / min for 1 to 5 minutes.

That is, the addition amount of the CO ₂ gas to the organic electrolyte is 2 L per minute, and if the addition amount is less than this, Li ₂ CO ₃ is not generated on the surface of the lithium metal. Also,
Since the CO ₂ gas concentration in the organic electrolyte solution reaches saturation in 5 minutes of the addition time, the addition of more than this is not only wasteful but also decreases the amount of organic electrolyte solution produced per hour, which is not preferable.

In the case where a material capable of inserting and extracting lithium ions without using lithium metal is used for the negative electrode as in the invention according to claim 7, the material may be a polymer, You can choose from carbon, graphite, metal oxides or alloys.

[0022]

Next, a specific example of the present invention will be described with reference to the drawings.

(Example 1) An organic electrolyte prepared by adding LiPF ₆ as an electrolyte to a solvent in which ethylene carbonate and propylene carbonate are mixed in an equal volume to give a concentration of 1 mol / dm ³ was used as a standard. The amount of CO ₂ gas in the organic electrolyte was 1 L, and the flow rate was ₂ L / min for 5 minutes.
Organic electrolyte solution A was obtained by adding 1 mol of gBr ₂ to 1 mol of lithium ions.

<Evaluation of Battery Performance> FIG. 1 shows a configuration diagram of a coin-type battery. In FIG. 1, reference numeral 1 denotes a battery cathode outer can, which is filled with a cathode 4, an anode 5, and an organic electrolyte 6 impregnated in a separator via a gasket 3 between the battery anode outer can 2 and a battery anode outer can 2.

In the coin-type battery shown in FIG. 1, a negative electrode 5 made of lithium metal having a thickness of 15 mm and a thickness of 0.3 mm and a thickness of 0.08
A positive electrode 4 made of LiCoO ₂ having a diameter of 15 mm is used. A 25 μm-thick polyethylene separator is impregnated with the organic electrolyte solution A between the positive electrode 4 and the negative electrode 5 to form an organic electrolyte 6.
As a result, a coin-type battery A having a total height of 1.6 mm and a theoretical capacity of 5 mAh was formed.

Comparative Example For comparison, a coin-type battery B having a capacity of 5 mAh was constructed in the same manner as in Example 1 using a standard organic electrolyte solution to which neither CO ₂ gas nor magnesium salt was added.

FIG. 2 shows the cycle life characteristics of the coin batteries A and B. The test conditions were as follows: the battery was charged at a current of 1 mA until the battery voltage reached 4.2 V, and then shifted to constant voltage charging.
The battery was charged at 4.2 V until the capacity reached 5 mAh.
The discharge was performed at a current of 1 mA until the battery voltage reached 3.0 V. The rest time between charge and discharge was 5 minutes. Cycle life is 60% of discharge capacity with respect to theoretical capacity
And when it reaches. All tests were performed at 20 ° C.

FIG. 2 shows that the conventional coin-type battery B was used.
Although the cycle life was 70 cycles, the coin-type battery A of the present invention could be improved up to 200 cycles.

Example 2 An organic electrolyte prepared by mixing LiPF ₆ as an electrolyte at 1 mol / dm ³ in a solvent in which ethylene carbonate and propylene carbonate were mixed in equal volumes was used as a standard. The organic electrolyte solution contains CO ₂ gas at a flow rate of 2 L / min.
gBr ₂ is 1 mol per 1 mol of lithium ion,
Organic electrolytes A, C and D were obtained by adding 0.01 mol and 10 mol, respectively.

<Evaluation of Battery Performance> In the same manner as in Example 1,
A negative electrode 5 made of lithium metal having a thickness of 0.3 mm and a diameter of 15φ
And a positive electrode 4 made of LiCoO ₂ having a thickness of 0.08 mm and having a diameter of 15φ, and a 25 μm-thick polyethylene separator provided between the positive electrode and the negative electrode.
Are respectively impregnated into an organic electrolyte 6, and a total height of 1.6 m
m, coin type batteries A, C and D having a theoretical capacity of 5 mAh were constructed.

(Comparative Example) For comparison, a coin-type battery having a capacity of 5 mAah was prepared in the same manner as in the batteries A, C and D shown in Example 2 using a standard organic electrolyte solution to which neither CO ₂ gas nor magnesium salt was added. Battery B was configured. The CO ₂ gas in the standard electrolyte against 1L, is contained 5 minutes at a flow rate of 2L / min, to give an organic electrolyte E and F with 0.001mol and 2mol added MgBr ₂ the lithium ion 1mol A coin-type battery E having a capacity of 5 mAh was formed in the same manner as the batteries A, C, and D shown in Example 2.

FIG. 3 shows the cycle life characteristics of these coin-type batteries. The conditions were the same as in Example 1. After charging the battery with a current of 1 mA until the battery voltage reached 4.2 V, the operation was shifted to constant voltage charging, and charging was continued at 4.2 V until the capacity reached 5 mAh. The discharge was performed at a current of 1 mA until the battery voltage reached 3.0 V. The rest time between charge and discharge was 5 minutes. The cycle life was determined when the discharge capacity reached 60% of the theoretical capacity. All tests are 2
Performed at 0 ° C.

As shown in FIG. 3, the cycle life of the standard coin-type battery B was 70 cycles, while that of the coin-type battery C was 110 cycles. Although the life could be prevented from being shortened, the coin-type battery A of the present invention 2
The effect is smaller than in the 00 cycle. In addition, the coin-type battery D has 120 cycles and has a longer life than the coin-type battery B, but the effect is smaller than that of the coin-type battery A of the present invention. This is because lithium dendrite could be suppressed by the formation of the alloy, but the precipitation of magnesium occurred more excessively than the required precipitation of lithium, so the effect was canceled out and no significant improvement in cycle life characteristics was observed. .

Since the coin-type battery E has 72 cycles and is equivalent to the coin-type battery B, it is considered that an effect of 0.001 mol of the coin-type battery E is not effective.
Also, the coin-type battery F had 45 cycles, which was lower than that of the coin-type battery B. This is considered to be due to the added amount being as large as 2 mol.

Example 3 An organic electrolyte prepared by mixing LiPF ₆ as an electrolyte at a concentration of 1 mol / dm ³ in a solvent in which ethylene carbonate and propylene carbonate were mixed in equal volumes was used as a standard. For 1 L of CO ₂ gas in the organic electrolyte, the flow rate was ₂ L / min for 5 minutes, and MgBr ₂
Was added to 1 mol of lithium ion to obtain an organic electrolyte solution A.

<Evaluation of Battery Performance> Using the organic electrolytic solution A obtained by the above method, a negative electrode 5 made of lithium metal having a thickness of 15 mm and a thickness of 0.3 mm and a Li electrode having a thickness of 0.08 mm and a thickness of 15 φ
A coin-type battery A having a total height of 1.6 mm and a theoretical capacity of 5 mAh was formed using a positive electrode 4 made of CoO ₂ and a 25-μm-thick polyethylene separator between the positive electrode and the negative electrode.

(Comparative Example) For comparison, it is the same to add carbon dioxide gas using a standard organic electrolyte solution and then add 1 mol of MgBr ₂ to 1 mol of lithium ion. On the other hand, organic electrolytes G and H were added at a flow rate of 2 L / min for 30 seconds and 30 minutes, respectively. Then, in the same manner as in the first embodiment, the capacity is 5 m
Ah coin type batteries G and H were configured.

FIG. 4 shows the cycle life characteristics of these coin-type batteries. The conditions were the same as in Example 1. After charging the battery with a current of 1 mA until the battery voltage reached 4.2 V, the operation was shifted to constant voltage charging, and charging was continued at 4.2 V until the capacity reached 5 mAh. The discharge was performed at a current of 1 mA until the battery voltage reached 3.0 V. The rest time between charge and discharge was 5 minutes. The cycle life was determined when the discharge capacity reached 60% of the theoretical capacity. All tests are 2
Performed at 0 ° C.

FIG. 4 shows that the cycle life of the coin-type battery G was 72 cycles, but the coin-type battery A of the present invention could be improved up to 200 cycles. Coin-cell battery G
Can be prevented from shortening the service life, but the effect is smaller than that of the coin-type battery A. Also coin-cell battery H
The life was improved up to 220 cycles. But battery A
There is no advantage in battery characteristics compared to
Is 6 times longer to prepare the electrolytic solution than the coin-type battery A, which is not preferable from the viewpoint of mass productivity, and it can be said that the coin-type battery A is preferable.

Example 4 An organic electrolyte prepared by mixing LiPF ₆ as an electrolyte at a concentration of 1 mol / dm ³ in a solvent in which ethylene carbonate and propylene carbonate were mixed in equal volumes was used as a standard. For 1 L of CO ₂ gas in the organic electrolyte, the flow rate was ₂ L / min for 5 minutes, and MgBr ₂
Was added to 1 mol of lithium ion to obtain an organic electrolyte solution A. This organic electrolytic solution A was added to polyethylene oxide having a thickness of 25 μm to form a gel polymer electrolyte I.
I got

<Evaluation of Battery Performance> Using the organic electrolyte solution A obtained by the above method, in the same manner as in Example 1, a thickness of 0.3 m
A negative electrode 5 made of lithium metal having a diameter of 15 m and a thickness of 0.
A positive electrode 4 made of LiCoO ₂ having a diameter of 15 mm and a diameter of 15 mm was used, and a 25 μm-thick polyethylene separator was impregnated between the positive electrode and the negative electrode with the organic electrolyte solution A obtained by the above method to obtain an organic electrolyte. A coin-type battery A of 5 mAh was configured.

In the same manner as in Example 1, the thickness was 0.3 m
A negative electrode 5 made of lithium metal having a diameter of 15 m and a thickness of 0.
A coin-type battery having a total height of 1.6 mm and a theoretical capacity of 5 mAh, using a positive electrode 4 made of LiCoO ₂ having a diameter of 15 mm and a diameter of 15φ, and using the gel polymer electrolyte H obtained by the above method as an organic electrolyte between the positive electrode and the negative electrode. I was constructed.

(Comparative Example) For comparison, using a standard organic electrolyte solution to which neither CO ₂ gas nor magnesium salt was added, a capacity of 5 was obtained in the same manner as in the batteries A and I shown in Example 4.
A coin-type battery B of mAh was configured. A standard electrolytic solution was added to a 25 μm-thick polyethylene oxide to obtain a gel polymer electrolyte J. A coin-type battery J having a capacity of 5 mAh was constructed in the same manner as the batteries A and I shown in Example 4.

FIG. 5 shows the cycle life characteristics of these coin-type batteries. The conditions were the same as in Example 1. After charging the battery with a current of 1 mA until the battery voltage reached 4.2 V, the operation was shifted to constant voltage charging, and charging was continued at 4.2 V until the capacity reached 5 mAh. The discharge was performed at a current of 1 mA until the battery voltage reached 3.0 V. The rest time between charge and discharge was 5 minutes. The cycle life was determined when the discharge capacity reached 60% of the theoretical capacity. All tests are 2
Performed at 0 ° C.

FIG. 5 shows that the coin-type battery B has a cycle life of 70 cycles, and the coin-type battery I of the present invention has a cycle life of 250 cycles with respect to 100 cycles of the coin-type battery J.
This was a cycle, and the cycle life characteristics were improved as compared with 200 cycles of the coin-type battery A. Coin type battery A
The reason why the cycle life characteristics were improved compared to
There is a difference in properties between the polymer electrolyte and the organic electrolyte. This is because, since the polymer electrolyte is in a solid state, the dendritic lithium can be suppressed, and the current flows uniformly over the entire surface of the electrolyte, so that the dendritic lithium is less likely to be generated.

Example 5 An organic electrolyte prepared by mixing LiPF ₆ as an electrolyte at 1 mol / dm ³ in a solvent in which ethylene carbonate and propylene carbonate were mixed in equal volumes was used as a standard. For 1 L of CO ₂ gas in the organic electrolyte, the flow rate was ₂ L / min for 5 minutes, and MgBr ₂
Was added to 1 mol of lithium ion to obtain an organic electrolyte solution A.

<Evaluation of Battery Performance> In the same manner as in Example 1,
A negative electrode 5 made of lithium metal having a thickness of 0.3 mm and a diameter of 15φ
And a positive electrode 4 made of LiCoO ₂ having a thickness of 0.08 mm and a diameter of 15φ, and a 25 μm-thick polyethylene separator was impregnated with the organic electrolyte solution A obtained by the above method between the positive electrode and the negative electrode to form an organic electrolyte. .6mm, theoretical capacity 5m
A coin-type battery A of Ah was constructed.

Similarly, when the thickness is 0.3 mm and the diameter is 15 mm
Negative electrode 5 made of a carbon material of
A coin-type battery L having a total height of 1.6 mm and a theoretical capacity of 5 mAh was formed using a positive electrode 4 made of LiCoO ₂ having a diameter of φ and a separator made of polyethylene having a thickness of 25 μm between the positive electrode and the negative electrode. In this case, since the organic electrolytic solution A cannot be used, an organic electrolytic solution L was prepared and used by using diethyl carbonate instead of propylene carbonate. The reason is that the carbon anode reacts with propylene carbonate to generate gas and rupture the battery.

(Comparative Example) For comparison, a standard organic electrolytic solution B to which neither CO ₂ gas nor magnesium salt was added was used.
By the same method as the battery A shown in Example 5, the capacity was 5 mA.
h coin type battery B was constructed.

Further, among the standard organic electrolytic solutions, an organic electrolytic solution M using diethyl carbonate instead of propylene carbonate was prepared, and the organic electrolytic solution M was used.
By the same method as the battery L shown in Example 5, the capacity was 5 mA.
h coin type battery M was constructed.

FIG. 6 shows the cycle life characteristics of these batteries. The conditions were as follows: for rapid charging, the battery was charged at a current of 3 mA until the battery voltage reached 4.2 V, and then the operation was shifted to constant voltage charging, and charging was continued at 4.2 V until the capacity reached 5 mAh. The discharge was performed at a current of 1 mA until the battery voltage reached 3.0 V. The rest time between charge and discharge was 5 minutes. The cycle life is 6 times the discharge capacity with respect to the theoretical capacity.
0% was reached. All tests were performed at 20 ° C.

FIG. 6 shows that the coin-type battery B has a cycle life of 20 cycles, and the coin-type battery L of the present invention has a cycle life of 200 cycles compared to 50 cycles of the coin-type battery M.
This was a cycle, and the cycle life characteristics were improved as compared with 150 cycles of the coin-type battery A. In the case of rapid charging, dendrite-like lithium is more likely to be generated.
The cycle life characteristics are lower than when charged with a current of mA. In addition, a lithium ion secondary battery using a carbon material for the negative electrode shows a cycle life characteristic of 500 cycles or more at a current of 1 mA at a current of 1 mA, but a cycle of 3 mA at a current of 3 mA generates dendritic lithium. The life characteristics deteriorate. However, the addition of the magnesium salt and CO ₂ gas of the present invention suppresses the generation of dendritic lithium, thereby preventing a decrease in cycle life characteristics. In the case of a lithium ion secondary battery, lithium ions which cannot be involved in charge / discharge are generated during the initial charge / discharge while being taken in from the positive electrode into the carbon negative electrode.
A decreased.

In the embodiment of the present invention, MgBr ₂ was used as the magnesium salt.
O ₄ ) ₂ , MgSO ₄ , Mg (PO ₄ ) _2, etc.

Although LiPF ₆ is used as the electrolyte salt, LiBF ₄ or LiClO ₄ may be used.

In the embodiment of the present invention, the solvent for the organic electrolyte is ethylene carbonate, propylene carbonate,
Although diethyl carbonate is used, other carbonate solvents such as dimethyl carbonate and ethyl methyl carbonate, and ether solvents such as dimethoxyethane may be used.

Further, in the embodiments of the present invention, polyethylene oxide is used as the polymer electrolyte, but a polyether compound such as polypropylene oxide or polyacrylonitrile may be used.

In the embodiment of the present invention, LiCoO ₂ was used as the positive electrode of the lithium secondary battery.
iO ₂ , LiMn ₂ O ₄ , V ₆ O ₁₃ or the like may be used.

In the embodiments of the present invention, lithium metal and a carbon material are used as the negative electrode of the lithium secondary battery. However, other polymers, metal compounds, alloys and the like capable of inserting and extracting lithium may be used.

[0059]

As described above, according to the present invention, lithium
In a secondary battery, the organic electrolyte contains CO _TwoGas and at least
Also add both one or more magnesium salts
With improved cycle life characteristics and high energy density
Lithium secondary battery can be produced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a configuration of a coin-type battery of the present invention and a comparative example.

FIG. 2 is a diagram showing cycle charge / discharge characteristics of coin batteries of the present invention and a comparative example.

FIG. 3 is a diagram showing cycle charge / discharge characteristics of coin batteries of the present invention and a comparative example.

FIG. 4 is a diagram showing cycle charge / discharge characteristics of coin type batteries of the present invention and a comparative example.

FIG. 5 is a diagram showing cycle charge / discharge characteristics of coin batteries of the present invention and a comparative example.

FIG. 6 is a diagram showing cycle charge / discharge characteristics of coin batteries of the present invention and a comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Battery negative case 2 Battery positive case 3 Gasket 4 Negative electrode 5 Positive electrode 6 Organic electrolyte A Cycle charge / discharge characteristics of coin battery A B Cycle charge / discharge characteristics of coin battery B C Cycle charge / discharge characteristics of coin battery C D Cycle charge / discharge characteristics of coin type battery D E Cycle charge / discharge characteristics of coin type battery E F Cycle charge / discharge characteristics of coin type battery F G Cycle charge / discharge characteristics of coin type battery G H Cycle charge / discharge characteristics of coin type battery H I Cycle charge / discharge characteristics of coin battery I J Cycle charge / discharge characteristics of coin battery J K Cycle charge / discharge characteristics of coin battery K L Cycle charge / discharge characteristics of coin battery L M Cycle charge / discharge characteristics of coin battery M

Continuing on the front page (72) Inventor Ken Nishimura 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a lithium metal negative electrode, and an organic electrolyte containing both a magnesium salt and CO ₂ gas when constituting the battery. 2. Components comprising a positive electrode, a negative electrode made of a substance capable of inserting and extracting lithium ions, and an organic electrolyte containing both a magnesium salt and CO ₂ gas at the time of battery construction. A rechargeable lithium battery. 3. The lithium secondary battery according to claim 1, wherein the magnesium salt is contained in an amount of 0.01 to 1 mol based on 1 mol of lithium ions in the organic electrolyte. 4. An organic electrolyte containing both a magnesium salt and CO ₂ gas comprises a solute and either an organic electrolyte or a mixture of an organic electrolyte and a polymer electrolyte. Or the lithium secondary battery according to 2. 5. The magnesium salt is Mg (ClO ₄ ) ₂ , M
The lithium secondary battery according to claim 1, wherein the lithium secondary battery is at least one magnesium salt selected from the group consisting of gSO ₄ , Mg (PO ₄ ) ₂ , and MgBr ₂ . 6. The lithium secondary battery according to claim 1, wherein the CO ₂ gas is added to 1 L of the organic electrolyte at a flow rate of 2 L / min for 1 minute to 5 minutes. 7. The substance having a function of occluding and releasing lithium ions is a substance selected from the group consisting of polymers, carbon, graphite, metal oxides and alloys, and occluding and releasing lithium ions. The lithium secondary battery according to claim 2, wherein the lithium secondary battery is a substance having a function of performing an operation.