JPH09298068A - Lithium secondary battery - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To use a non-aqueous solvent electrolytic solution which uses a new material replacing an existing negative electrode and has high conductivity, good temperature characteristics and load characteristics, and also excellent redox resistance. Provided is a lithium secondary battery which has a high energy density, enables high-current discharge rapid charging, and has a long charge / discharge life by using an optimal combination of electrodes. A formula for the negative electrode active material _{6 Li 1 + x M y N} ( where, M represents an element belonging to the transition metal, x is -0.2
In the range of 2.0, y is 0. an amorphous lithium-containing transition metal nitride represented by the formula (1 to 0.5)),
As the non-aqueous solvent used in the non-aqueous solvent electrolyte solution 3, a mixed solvent containing propylene carbonate is used. [Effect] High energy density, good temperature characteristics,
Moreover, a lithium secondary battery having a long charge / discharge life can be provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The lithium secondary battery of the present invention, in particular,
The present invention relates to a lithium secondary battery having high energy density, high charge / discharge density, and long cycle life.

[0002]

2. Description of the Related Art As portable electronic devices have become smaller and lighter, their power sources are (1) high voltage, high energy density, and (2) large current discharge and rapid charge from their use.
There is a demand for (3) a long charge / discharge life and (4) an inexpensive secondary battery. As a battery that meets such demands, development of a high-performance secondary battery having a negative electrode capable of charging and discharging lithium ions and a positive electrode capable of charging and discharging lithium ions, that is, a lithium secondary battery is expected.

The secondary batteries currently on the market, nickel-cadmium batteries, nickel-hydrogen batteries, and lead-acid batteries, have the characteristics that they can be rapidly charged, but their battery voltage and energy density are low, and they are currently required. I can not meet the demand. On the other hand, it is expected to realize a lithium secondary battery using metallic lithium whose active material has a very high energy density as a negative electrode material. However, generally, when lithium metal is used as the negative electrode active material, acicular lithium (dendrites) are generated during charging, and when discharging,
Since the acicular lithium is detached from the broken electrode, so-called "dead lithium" that does not participate in charge / discharge is generated. Therefore, the metallic lithium charged in the battery cannot be fully utilized. Therefore, in a battery system using lithium metal or a lithium alloy similar thereto as the negative electrode active material, it is difficult to secure its cycle life.

As an anode active material replacing lithium metal or a lithium alloy, a material utilizing the intercalation reaction of lithium is drawing attention. Typical examples thereof include carbonaceous materials such as natural graphite and artificial graphite and Nb ₂
Inorganic materials such as O ₅ , MoO ₂ and TiS ₂ are being investigated. Since these materials are retained in the skeletal structure in the state where lithium is ionized, they are stable as compared with the metal lithium negative electrode, and the cycle life is improved because there is no generation of dendrite seen in lithium metal.

Among them, the carbonaceous material is capable of inserting and desorbing lithium ions within a range of a base electrode potential of 0 to 1 V with respect to a lithium reference electrode (metallic lithium), and has a charge of 150 to 370 mAh / g. Has a discharge capacity.
Graphite-based material, which is one type of carbonaceous material, has a large capacity especially in the electrode potential range of 0 to 0.5 V, and has a total capacity of 3
It is possible to secure a capacity close to 70 mAh / g.
At present, lithium-ion secondary batteries using a graphite-based material as the negative electrode active material have been put into practical use.

[0006]

When a carbonaceous material is used and the maximum lithium ion capacity is LiC ₆ ,
The capacity per weight is relatively large at 370 mAh / g. However, this value is a theoretical value, and from the viewpoint of safety, only a capacity of 200 to 300 mAh / g is actually used.

On the other hand, when lithium metal is used as the negative electrode, the energy density of the negative electrode is as high as 3860 mAh / g, but normally, as described above, in order to compensate for the deterioration, it is generally higher than the positive electrode capacity. And about 4 times as much lithium is filled in the battery. However, as described above, the use of the above energy density is insufficient due to the large production of dead lithium, and it is difficult to achieve a long cycle life as when using a carbonaceous material.

When a graphite material, which is a carbonaceous material, is used, propylene carbonate decomposes in an electrode potential range of about 1 V with respect to a lithium reference electrode (metal lithium) and cannot be used as it is in an electrolytic solution. . However, if propylene carbonate having a melting point of −49 ° C. can be used, it is considered that sufficient battery characteristics can be obtained without solidification of the electrolytic solution when the battery is used at a temperature of −20 ° C.

The present invention is intended to solve such problems of the prior art, uses a new material replacing the conventional negative electrode, has high conductivity, good temperature characteristics and load characteristics, and further has a redox resistance. Using a non-aqueous solvent electrolyte with excellent properties, by providing an optimal combination of each electrode, it is possible to provide a lithium secondary battery with high energy density, high-current discharge rapid charge, and long charge / discharge life. To aim.

[0010]

As a result of various studies to achieve the above object, the present inventors have found that the composition formula Li _{1 + x} M _y N (where M is a transition) is added to the negative electrode active material. Which represents an element belonging to a metal, x is in the range of -0.2 to 2.0, and y is in the range of 0.1 to 0.5). It was found that it was effective to use a mixed solvent containing propylene carbonate as the non-aqueous solvent used in the non-aqueous solvent electrolytic solution, and the present invention was completed.

That is, according to the present invention, a positive electrode material capable of charging / discharging lithium ions, particularly a positive electrode active material requiring a charge end voltage of 3.5 V or higher, can be charged / discharged with lithium ion. such, in particular the composition formula Li _{1 +} x M _y
N (however, M represents an element belonging to a transition metal, and x represents −
In the range of 0.2 to 2.0, y is in the range of 0.1 to 0.5), the amorphous lithium-containing transition metal nitride represented by By including propylene carbonate, discharge characteristics at low temperature, large current discharge,
A lithium secondary battery that enables quick charging can be provided.

Hereinafter, the present invention will be described in detail.

[0013] The present invention, as the lithium ion that can be charged and discharged in the negative electrode material family, in particular the composition formula Li 1 _{+ x} M _y N (where, M
Represents an element belonging to a transition metal, and x is -0.2 to 2.0.
In the range of y, y is in the range of 0.1 to 0.5), and an amorphous lithium-containing transition metal nitride represented by the following formula is used, and propylene carbonate is contained as a non-aqueous solvent of the electrolytic solution. I am trying.

Here, M is not particularly limited as long as it is a transition metal, but Co, Ni or Cu is preferably used. Further, x is -0.2 to 2.0 and y is 0.1 to 0.5, but if it deviates from this range, cycle characteristics may be deteriorated, and charging / discharging may not be possible at a high energy density. .

The solvent to be mixed with propylene carbonate is not particularly limited, but it is preferable to use at least one of chain ester and chain ether. Furthermore, it is more preferable to use one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate as the chain ester and dimethoxyethane and diethoxyethane as the chain ether.

Further, the electrolyte of the electrolytic solution is not particularly limited, and examples thereof include LiClO ₄ , LiPF ₆ , and LiAsF.
₆ , LiBF ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , Li
SbF ₆ , LiSCN, LiCl, LiC ₆ H ₅ SO ₃ , L
iN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC
Lithium salts such as F ₃ SO ₃ can be used alone or in admixture of two or more. Of these, especially LiPF ₆ , L
It is preferable to use iClO ₄ , LiBF ₄ , and LiAsF ₆ .

The positive electrode is not particularly limited, but it is 3.5 in the present invention because it enables a high energy density.
A positive electrode active material that requires a cut-off voltage of V or more, especially L
i _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ (0 ≦ x ≦
It is preferable to use a complex oxide mainly containing 1.2), a complex oxide mainly containing Mn ₂ O ₄ , or a complex sulfate mainly containing Fe ₂ (SO ₄ ) ₃ .

[0018]

The secondary battery having the non-aqueous solvent electrolyte according to the present invention has the following features. That is, in the lithium secondary battery, the composition formula Li1 + xMyN is added to the negative electrode active material.
(However, M represents an element belonging to a transition metal, and x represents −0.
2 to 2.0, and y is in the range of 0.1 to 0.5). By using an amorphous lithium-containing transition metal nitride represented by
An energy density of Ah / g is obtained, which makes it possible to obtain a capacity that is more than double that when a carbon-based material is used for the negative electrode, and to exhibit high cycle characteristics, which results in a long cycle life as a secondary battery. can get.

A positive electrode active material which requires a cut-off voltage of 3.5 V or more, particularly Li _x CoO ₂ , Li _x NiO ₂ and Li _x.
By using a composite oxide mainly composed of Mn ₂ O ₄ (0 ≦ x ≦ 1.2) or Mn ₂ O ₄ , each has the following characteristics.

As a positive electrode active material, Li _x CoO ₂ (0 ≦ x ≦
The battery using the complex oxide mainly composed of 1.2) is characterized by high voltage and high energy density.

As the positive electrode active material, Li _x NiO ₂ (0 ≦
x ≦ 1.2) using a composite oxide mainly composed of
It has the characteristics of large charge / discharge capacity and large energy density.

A battery using a composite oxide mainly composed of Li _x Mn ₂ O ₄ (0 ≦ x ≦ 1.2) is characterized by being inexpensive.

A battery using a composite sulfate mainly composed of Fe ₂ (SO ₄ ) ₃ is characterized by being inexpensive and lightweight.

As described above, a high voltage and a high energy density can be obtained by using a positive electrode active material that requires 3.5 V or more as the final charging voltage for the positive electrode in the positive electrode, and the lithium ion interface can be obtained. Curation,
It is suitable for high-current discharge rapid charging due to the rapid diffusion of deintercalation.

By using propylene carbonate as the electrolytic solution and mixing it with another solvent, particularly a linear ester or a linear ether, it is possible to simultaneously have a low freezing point and a high electric conductivity. Therefore, it becomes possible to sufficiently improve the load characteristics and the low temperature characteristics of the battery.

[0026]

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

[0027]

EXAMPLE 1 FIG. 1 is a sectional view of a lithium secondary battery according to the present invention. In FIG. 1, 1 is a stainless steel counter electrode case. Reference numeral 2 is metallic lithium, and here, a lithium foil having a predetermined thickness punched out to a diameter of 16 mm is pressure-bonded to 1. 3 is an electrolytic solution using a non-aqueous solvent. 4 is a separator made of a polypropylene or polyethylene porous film. 5 is a pole case for stainless steel production. 6 is a working electrode composed of Li _2.6 Co _0.4 N. This is Li _2.6 Co _0.4 N above
Is mixed with a conductive agent and a binder and rolled to form a sheet,
It is punched out to a diameter of 16 mm. Reference numeral 7 denotes a gasket, which maintains electrical insulation between the counter electrode case 1 and the working electrode case 5, and at the same time, the working electrode case opening edge is bent inward and caulked to seal and seal the battery contents. ing.

With respect to the coin type batteries of Examples 1 to 7 and Comparative Example 1 produced as described above, the current value during charging / discharging was set at 20 ° C. with a charge end voltage of 1.4 V and a discharge end voltage of 0 V. A cycle test was performed at 1 mA.

In FIG. 2a, propylene carbonate (PC) and dimethyl carbonate (DMC) are used as the electrolyte solution.
The results of a cycle test using lithium hexafluorophosphate LiPF ₆ dissolved at 1 mol / liter in a mixed solvent having a volume mixing ratio of 1: 1 are shown. As is clear from this, the battery showed good cycle characteristics with almost no capacity deterioration even up to 100 cycles.

[0030]

Comparative Example 1 For comparison, in the secondary battery of Example 1, a battery was prepared in the same manner as in Example 1 except that the graphite-based carbon material was used for the working electrode, and this battery was the same as in Example 1. A charge / discharge cycle test was performed under charge / discharge conditions.
However, in this secondary battery, decomposition of PC was observed at the time of initial charging, and charging was not possible.

[0031]

[Example 2] In the secondary battery of Example 1, P was added to the electrolytic solution.
A battery was produced in the same manner as in Example 1 except that C and ethyl methyl carbonate (EMC) were used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Figure 2b shows the charge and discharge capacity and cycle life. As is clear from this, the battery showed good cycle characteristics with almost no capacity deterioration even up to 100 cycles.

[0032]

Comparative Example 2 For comparison, in the secondary battery of Example 2, a battery was prepared in the same manner as in Example 1 except that the graphite-based carbon material was used for the working electrode. A charge / discharge cycle test was conducted under discharge conditions.
However, in this secondary battery, decomposition of PC was observed at the time of initial charging, and charging was not possible.

[0033]

[Embodiment 3] In the secondary battery of Embodiment 1, the electrolyte solution contains P
A battery was prepared in the same manner as in Example 1 except that C and dimethoxyethane (DME) were used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. FIG.
Charge / discharge capacity and cycle life are shown in c. As is clear from this, the battery showed good cycle characteristics with almost no capacity deterioration even up to 100 cycles.

[0034]

[Comparative Example 3] For comparison, a battery was prepared in the same manner as in Example 1 except that a graphite-based carbon material was used for the working electrode in the secondary battery of Example 2, and the same charge as in Example 1 was applied to this battery. A charge / discharge cycle test was conducted under discharge conditions.
However, in this secondary battery, decomposition of PC was observed at the time of initial charging, and charging was not possible.

[0035]

[Embodiment 4] In the secondary battery of Embodiment 1, the electrolyte solution contains P
A battery was produced in the same manner as in Example 1 except that C and diethoxyethane (DEE) were used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. FIG.
Charge / discharge capacity and cycle life are shown in d. As is clear from this, the battery showed good cycle characteristics with almost no capacity deterioration even up to 100 cycles.

[0036]

[Comparative Example 4] For comparison, a battery was prepared in the same manner as in Example 1 except that a graphite-based carbon material was used for the working electrode in the secondary battery of Example 2, and the same charge as in Example 1 was applied to this battery. A charge / discharge cycle test was conducted under discharge conditions.
However, in this secondary battery, decomposition of PC was observed at the time of initial charging, and charging was not possible.

[0037]

[Embodiment 5] In the secondary battery of Embodiment 1, the electrolyte solution contains P
A battery was produced in the same manner as in Example 1 except that C and ethoxymethoxyethane (EME) were used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Figure 2e shows the charge / discharge capacity and cycle life. As is clear from this, the battery showed good cycle characteristics with almost no capacity deterioration even up to 100 cycles.

[0038]

Comparative Example 5 For comparison, a battery was prepared in the same manner as in Example 1 except that a graphite-based carbon material was used for the working electrode in the secondary battery of Example 2, and the same charge as in Example 1 was applied to this battery. A charge / discharge cycle test was conducted under discharge conditions.
However, in this secondary battery, decomposition of PC was observed at the time of initial charging, and charging was not possible.

In addition, the lithium salt for the electrolytic solution may be LiP.
Almost the same result was obtained even when F ₆ was changed to LiClO ₄ , LiBF ₄ or LiAsF ₆ . In addition, LiP
Similar results were obtained even when the concentration of F ₆ , LiClO ₄ , LiBF ₄ or LiAsF ₆ was set to 0.5-2.0 mol / l.

[0040]

As described above, according to the present invention,
In the lithium secondary battery, the above Li _2.6 is used as the negative electrode active material.
Co _0.4 N and the composition formula Li _{1 +} x M _y N (where, M represents an element belonging to the transition metal, x is in the range of -0.2～2.0,
y is in the range of 0.1 to 0.5), by using an amorphous lithium-containing transition metal nitride represented by the following, and by using an electrolyte solution containing propylene carbonate, high energy density and temperature characteristics It is also possible to provide a lithium secondary battery which is excellent and has a long charge / discharge life.

[Brief description of drawings]

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

2A is a diagram showing the results of a cycle test in Example 1. FIG.

2B is a diagram showing the result of a cycle test in Example 2. FIG.

FIG. 2c is a diagram showing the result of a cycle test in Example 3.

FIG. 2d is a diagram showing the result of a cycle test in Example 4.

2e is a diagram showing the results of a cycle test in Example 5. FIG.

[Explanation of symbols]

 1 Stainless steel counter electrode case 2 Counter electrode 3 Electrolyte using non-aqueous solvent 4 Separator 5 Stainless steel manufacturing electrode case 6 Working electrode 7 Gasket

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

Claims (5)

[Claims] 1. A negative electrode capable of charging and discharging lithium ions,
In a secondary battery having a positive electrode capable of performing a reversible electrochemical reaction with lithium ions and an electrolytic solution in which an ionic dissociative lithium salt is dissolved in a negative electrode, a composition formula Li is used as the negative electrode active material.
_{1 + x} M _y N (where, M represents an element belonging to the transition metal, x
Is in the range of -0.2 to 2.0, and y is in the range of 0.1 to 0.5), and an amorphous lithium-containing transition metal nitride represented by A lithium secondary battery characterized by using an electrolytic solution. 2. The lithium secondary according to claim 1, wherein propylene carbonate and one or more selected from the group consisting of chain ester or chain ether are used as a solvent for the electrolytic solution. battery. 3. The chain ester or chain ether is a mixture of at least one selected from the group consisting of dimethyl carbonate, ethylmethyl carbonate, dimethoxyethane, diethoxyethane and ethoxymethoxyethane. The lithium secondary battery according to claim 2. 4. LiPF ₆ , L as the solute for the electrolytic solution
The secondary battery having the non-aqueous solvent electrolyte according to claim 1, wherein one or more of iClO ₄ , LiBF ₄ , and LiAsF ₆ is used. Wherein the composition formula Li _{1 +} x M _y N (where, M represents an element belonging to the transition metal, x is in the range of -0.2~2.0, y is from 0.1 to 0. In the amorphous lithium-containing transition metal nitride represented by
It is Ni or Cu, The lithium secondary battery in any one of Claim 1 to 4 characterized by the above-mentioned.