JP2003142153A - Non-aqueous electrolyte secondary battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life non-aqueous electrolyte secondary battery free of the risk that the discharge capacity in the initial period drops and showing a less deterioration in the capacity during the charge-discharge cycle. SOLUTION: The electrolyte of this non-aqueous electrolyte secondary battery contains 1,4,7-trioxonin expressed by Formula (1) and/or its derivative....(1) This allows formation of a protection film in good workmanship on the surface of a negative electrode active material, which suppresses decomposition of the non-aqueous electrolyte on the surface of the negative electrode active material, and as a result, the intended secondary battery of long lifetime showing a less deterioration in the capacity during the chargedischarge cycle can be achieved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable devices, personal digital assistants, etc., a battery as a power source thereof is small, lightweight and has high energy density, Furthermore, there is a strong demand for the development of secondary batteries that can be repeatedly charged and discharged for a long period of time. Above all,
Compared to lead batteries and nickel-cadmium batteries that use aqueous electrolytes, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are the most promising and active research sources for secondary batteries that meet these needs. It is done.

Positive electrode active materials for non-aqueous electrolyte secondary batteries include titanium disulfide, vanadium pentoxide and molybdenum trioxide, as well as lithium cobalt composite oxide, lithium nickel composite oxide and spinel manganese oxide. Various compounds represented by the formula Li _x MO ₂ (where M is one or more transition metals) have been investigated. Among them, lithium cobalt composite oxides, lithium nickel composite oxides, spinel type lithium manganese oxides, and the like charge and discharge at an extremely noble potential of 4 V (vs Li / Li ⁺ ) or more, and thus can be used as a positive electrode. It is possible to realize a battery having a high discharge voltage.

As the negative electrode active material of the non-aqueous electrolyte secondary battery, various materials such as metallic lithium, lithium alloys, and carbon materials capable of inserting and extracting lithium have been studied. Among them, carbon materials are used. Then, there is an advantage that a battery having a long cycle life can be obtained and the safety is high.

As an electrolyte of a non-aqueous electrolyte secondary battery, generally, a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate is used as a mixed solvent such as LiPF ₆ or LiBF ₄ . An electrolyte solution in which a supporting salt is dissolved is used.

[0006]

However, in the non-aqueous electrolyte secondary battery, as the charge / discharge cycle progresses, the decomposition of the supporting salt and the solvent in the non-aqueous electrolyte progresses on the negative electrode, and the electrolyte solution decreases. However, there is a problem that the decomposition product of the solvent is deposited on the surface of the negative electrode to hinder the movement of lithium ions, and the discharge capacity is reduced.

The present invention has been made in order to solve the above problems, and an object of the present invention is to reduce the initial discharge capacity, reduce the capacity deterioration during charge / discharge cycles, and prolong the service life. Another object is to provide a non-aqueous electrolyte secondary battery.

[0008]

According to the invention of claim 1, in a non-aqueous electrolyte secondary battery, 1,4,7- is contained in the non-aqueous electrolyte.
It is characterized by containing trioxonine and / or a derivative thereof. According to the above invention, it is possible to suppress capacity deterioration during charge / discharge cycles and prolong the cycle life.

Preferably, the above-mentioned 1, in the non-aqueous electrolyte is
The content of 4,7-trioxonine and / or its derivative is preferably less than 5.0 wt%. This is because the initial discharge capacity decreases if 5.0 wt% or more is added. More preferably, it is less than 2.0 wt%, and more preferably,
It is preferably 0.01 wt% or more and 1.0 wt% or less. This is because the life can be extended and the initial discharge capacity can be increased.

The invention of claim 3 is characterized in that, in the method for producing a non-aqueous electrolyte secondary battery, there is a step of adding 1,4,7-trioxonine and / or its derivative. According to the above invention, it is possible to manufacture a non-aqueous electrolyte secondary battery in which suppressing the capacity deterioration during charge / discharge cycles can prolong the life.

Preferably, the 1,4,7-trioxonine and / or its derivative is added in an amount of less than 5.0 wt% with respect to the non-aqueous electrolyte.
This is because the initial discharge capacity of the manufactured non-aqueous electrolyte secondary battery decreases if 5.0 wt% or more is added. More preferably, it is less than 2.0 wt%, and more preferably 0.01 wt% or more and 1.0 wt% or less. This is because the life can be extended and a non-aqueous electrolyte secondary battery having a large initial discharge capacity can be manufactured.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. As the positive electrode active material of the non-aqueous electrolyte secondary battery according to the present invention, any kind of compound can be used as long as it is a compound that occludes / releases lithium ions. In particular, Li _x MO ₂ (where M is one or more). A transition metal) and a compound mainly composed of Li _x M ₂ O ₄ are preferably used alone or in combination of two or more,
Furthermore, from the height of the discharge voltage, the transition metal M is C
It is more preferable to use at least one transition metal selected from the group consisting of o, Ni and Mn.

For the negative electrode, carbon materials such as cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, and metallic lithium, lithium alloys, polyacene, etc. may be used alone or in combination. Although the above can be mixed and used, it is particularly preferable to use a carbonaceous material because of its high safety.

As the solvent for the non-aqueous electrolyte, ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, sulfolane, 1,
2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3
A non-aqueous solvent such as methyl-1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, methylpropyl carbonate, alone or These mixed solvents can be used.

The non-aqueous electrolyte is a supporting salt in these non-aqueous solvents.
Dissolve and use. As the supporting salt, LiClO_Four,
LiPF₆, LiBF_Four, LiAsF₆, LiCF_ThreeC
O_Two, LiCF_ThreeSO_Three, LiCF_ThreeCF_TwoSO_Three, L
iCF_ThreeCF_TwoCF_TwoSO_Three, LiN (SO_TwoCF_Three)
_Two, LiN (SO_TwoCF_TwoCF_Three)_Two, LiN (COC
F_Three)_Two, LiN (COCF_TwoCF_Three)_TwoAnd LiP
F_Three(CF_TwoCF_Three) _ThreeSuch as salt or a mixture of these
Can be used.

The present invention relates to a non-aqueous electrolyte secondary battery,
1,4,7- represented by the following [Chemical Formula 1] in a non-aqueous electrolyte
It is characterized by containing trioxonine or a derivative thereof. Alternatively, 1,4,7-trioxonine and its derivative may be contained.

[0017]

[Chemical 1]

By including 1,4,7-trioxonine in the non-aqueous electrolyte, good SEI is formed on the surface of the negative electrode active material, so that the non-aqueous electrolyte is subsequently decomposed on the surface of the negative electrode active material. Is suppressed, and as a result, a long-life non-aqueous electrolyte secondary battery with little capacity deterioration during charge / discharge cycles is obtained.

Here, SEI (Solid Electric)
lyte interphase) means that when the lithium metal or carbon material is charged for the first time in a non-aqueous electrolyte, the solvent in the electrolyte and the components contained in the electrolyte are reduced to form on the surface of the lithium metal or carbon material. Refers to the passivation film. The SEI formed on the surface of the metallic lithium or carbon material acts as a lithium ion conductive protective film, and the subsequent reaction between the metallic lithium or carbon material and the solvent is suppressed.

Further, it is preferable that the non-aqueous electrolyte contains less than 5.0 wt% of 1,4,7-trioxonine or its derivative in total. 1,4,7 in non-aqueous electrolyte
-If trioxonine is contained in an appropriate amount, good SEI is formed on the surface of the negative electrode active material, but when the content of 1,4,7-trioxonine in the non-aqueous electrolyte is 5.0 wt% or more. As a result, the irreversible capacity at the time of initial charge / discharge becomes large, and as a result, the initial discharge capacity becomes significantly small.

Instead of the liquid electrolyte, a solid ion conductive polymer electrolyte can be used. When the polymer electrolyte membrane is polyethylene oxide, polyacrylonitrile, polyethylene glycol, or modified products thereof, it is lightweight and flexible, which is advantageous when used for a wound electrode plate. Furthermore, an ion conductive polymer electrolyte membrane and an organic electrolytic solution can be used in combination. Further, as the electrolyte, other than the polymer electrolyte,
A mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used.

The non-aqueous electrolyte secondary battery according to the present invention usually comprises a combination of a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte as its constitution. The separator is a porous polyvinyl chloride film. Porous polymer membranes such as and lithium ion or ion conductive polymer electrolyte membranes can be used alone or in combination.

In the method for producing a non-aqueous electrolyte secondary battery according to the present invention, it is preferable to add 1,4,7-trioxonine or its derivative to the non-aqueous electrolyte. Further, the 1,4,7-trioxonine and its derivative may be mixed and used.

[0024]

EXAMPLES The present invention will be described below with reference to the preferred examples, but it goes without saying that the present invention is not limited to the following unless the gist of the present invention is exceeded.

Example 1 A prismatic non-aqueous electrolyte secondary battery was prepared using lithium cobalt oxide as the positive electrode active material and a carbon material as the negative electrode active material. FIG. 1 is a view showing a cross-sectional structure of a prismatic nonaqueous electrolyte secondary battery. In FIG. 1, 1 is a prismatic nonaqueous electrolyte secondary battery, 2 is a wound electrode group, 3 is a positive electrode, 4
Is a negative electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8 is a safety valve, 9 is a positive electrode terminal, and 10 is a positive electrode lead. The wound electrode group 2 is formed by winding a positive electrode 3 and a negative electrode 4 with a separator 5 in between. The wound electrode group 2 is housed in a battery case 6, a safety valve 8 is provided in the battery case 6, and the battery lid 7 and the battery case 6 are sealed by laser welding. The positive electrode terminal 9 is connected to the positive electrode lead 10, and the negative electrode 4 is connected to the inner wall of the battery case 6 by contact.

The positive electrode mixture contains LiCoO ₂ 9 as an active material.
0 parts by weight and 5 parts by weight of conductive agent acetylene black,
A paste was prepared by mixing 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder to prepare a positive electrode mixture and dispersing it in N-methyl-2-pyrrolidone (NMP). This paste was uniformly applied to an aluminum current collector having a thickness of 20 μm, dried, and then compression molded by a roll press to produce a positive electrode.

The negative electrode mixture was prepared by mixing 90 parts by weight of a carbon material capable of occluding and releasing lithium ions and 10 parts by weight of PVdF as a binder, and adding NMP as appropriate to disperse the mixture to prepare a slurry. The slurry was uniformly applied to a copper current collector having a thickness of 15 μm, dried, dried at 100 ° C. for 5 hours, and compression-molded with a roll press to prepare a negative electrode.

A microporous polyethylene film having a thickness of about 20 μm was used as the separator. These positive
The negative electrode and the separator were wound to form a wound electrode group. For the electrolyte, 1.1 M of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7.
A prismatic nonaqueous electrolyte secondary battery was prepared using a nonaqueous electrolytic solution containing 0.01 wt% of 4,7-trioxonine.

Example 2 A prismatic nonaqueous electrolyte secondary battery of Example 2 was prepared in the same manner as in Example 1 except that the content of 1,4,7-trioxonine was 0.1 wt%.

Example 3 A prismatic nonaqueous electrolyte secondary battery of Example 3 was prepared in the same manner as in Example 1 except that the content of 1,4,7-trioxonine was 0.5 wt%.

Example 4 A prismatic nonaqueous electrolyte secondary battery of Example 4 was prepared in the same manner as in Example 1 except that the content of 1,4,7-trioxonine was 1.0 wt%.

Example 5 A prismatic non-aqueous electrolyte secondary battery of Example 5 was prepared in the same manner as in Example 1 except that the content of 1,4,7-trioxonine was 2.0 wt%.

Example 6 A prismatic nonaqueous electrolyte secondary battery of Example 6 was prepared in the same manner as in Example 1 except that the content of 1,4,7-trioxonine was 5.0 wt%.

Comparative Example 1 A prismatic non-aqueous electrolyte secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that 1,4,7-trioxonine was not contained.

The batteries of Examples 1 to 6 and Comparative Example 1 were produced in units of 10 cells. Charge these batteries to 1
Charge with constant current and constant voltage to 4.2V with CA current for 3 hours,
After that, discharge was performed up to 3 V at a current value of 1 CA, and the initial discharge capacity was confirmed. Thereafter, the same charge / discharge cycle was repeated 500 times, and the capacity retention rate (%) after 500 cycles was measured. The results are shown in Table 1. The “capacity retention rate” here is 500 with respect to the initial discharge capacity.
The ratio (%) of the discharge capacity after the cycle shall be shown.

[0036]

[Table 1]

From Table 1, it is seen that when a non-aqueous electrolyte containing 1,4,7-trioxonine is used, that is, in Examples 1 to 1.
It can be seen that in Example 6, the capacity retention rate after 500 cycles is significantly higher than in Comparative Example 1. In particular, by setting the content of 1,4,7-trioxonine to the non-aqueous electrolyte to be less than 5.0 wt%, the capacity retention rate can be improved without significantly reducing the initial capacity. Furthermore, regarding the initial discharge capacity, 1, 4, 7-
Example 1 in which trioxonine was added in an amount of 2 wt% or less
It is understood that the examples up to the example 5 are equal to or larger than the comparative example 1. Further, it can be seen that the initial discharge capacity is increased in Examples 1 to 4 in which the addition amount is 0.01 wt% or more and 1 wt% or less.

In the case of Example 6 in which the content of 1,4,7-trioxonine was 5% by weight, the capacity retention rate after the charge / discharge cycle was as high as 95%, but the initial discharge capacity was largely reduced.
The reason for this is that when the amount added to the non-aqueous electrolyte is large, S
It is considered that the amount of electricity required for forming the EI increased and that the formed SEI hindered the Li insertion reaction into the negative electrode to reduce the amount of electricity charged.

Thus, it was found that the inclusion of 1,4,7-trioxonine in the non-aqueous electrolyte improves the cycle life characteristics of the battery. Although the reason for this is not clear, by incorporating 1,4,7-trioxonine in the electrolyte, a good SEI film is formed on the surface of the negative electrode active material, and then the nonaqueous electrolyte on the negative electrode is formed. It is thought that the decomposition of the was suppressed.

In order to prevent the initial discharge capacity from decreasing,
The amount of 1,4,7-trioxonine added to the non-aqueous electrolyte is preferably less than 5 wt%, more preferably less than 2 wt%.

In the examples and comparative examples, the electrolyte solvent is described as EC: EMC system, but when the ratio of cyclic carbonate to chain carbonate is changed or as chain carbonate, DMC or EMC system is used. The same tendency was observed when the γ-BL was used instead of the chain carbonate, and the same tendency was observed. The same tendency was observed when the concentration of the electrolyte salt was changed.

[0042]

According to the present invention, in a non-aqueous electrolyte, 1,
By including 4,7-trioxonine and / or its derivative, good SEI can be obtained on the surface of the negative electrode active material.
Therefore, the decomposition of the non-aqueous electrolyte on the surface of the negative electrode active material after that is suppressed, and as a result, the capacity deterioration during charge / discharge cycles is small, and a long-life non-aqueous electrolyte secondary battery can be obtained. It has become possible. When the content of 1,4,7-trioxonine and / or its derivative in the non-aqueous electrolyte is less than 5.0 wt%, the initial discharge capacity is large and the capacity deterioration during charge / discharge cycle is small and long. It has become possible to obtain a non-aqueous electrolyte secondary battery with a long life.

According to the manufacturing method of the present invention, it is possible to manufacture a non-aqueous electrolyte secondary battery which has a small capacity deterioration during charge / discharge cycles and has a long life. In addition, the content is 5.0 wt%
When it is less than the above range, a non-aqueous electrolyte secondary battery having a large initial discharge capacity, a small capacity deterioration during charge / discharge cycles and a long life can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of prismatic batteries of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

1 Rectangular non-aqueous electrolyte secondary battery 2-roll type electrode group 3 positive electrode 4 Negative electrode 5 separator 6 battery case 7 Battery lid 8 safety valve 9 Positive terminal 10 Positive electrode lead

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery containing 1,4,7-trioxonine and / or a derivative thereof in the non-aqueous electrolyte. 2. The content of the 1,4,7-trioxonine and / or its derivative in the non-aqueous electrolyte is 5.0.
It is less than wt%, The non-aqueous electrolyte secondary battery according to claim 1. 3. A method for manufacturing a non-aqueous electrolyte secondary battery,
A method for producing a non-aqueous electrolyte secondary battery, comprising the step of adding 1,4,7-trioxonine and / or its derivative. 4. The 1,4,7-trioxonine and / or
Or 5.0 wt% of this derivative with respect to the non-aqueous electrolyte
% Is added so as to be less than%.
The method for producing a non-aqueous electrolyte secondary battery according to 1.