JP2003163029A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Abstract] (with correction) [PROBLEMS] In a non-aqueous electrolyte secondary battery using Li _4/3 Ti _5/3 O ₄ as a negative electrode active material, a negative electrode without increasing the rate of addition of a conductive material , The high load discharge characteristics are improved. SOLUTION: In a battery comprising a negative electrode mainly composed of lithium titanium oxide having a spinel structure, a nonaqueous electrolytic solution contains propane sultone and ethylene sulphite having an S ＝ O bond.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composition formula Li _4/3 T
A non-aqueous electrolyte secondary with improved high-load discharge characteristics using a spinel-type lithium titanium oxide represented by i _5/3 O ₄ (hereinafter referred to as Li _4/3 Ti _5/3 O ₄ ) as a negative electrode active material. Regarding batteries.

[0002]

2. Description of the Related Art Due to the rapid development of electronic technology in recent years, miniaturization of electronic devices has progressed, and there has been an increasing demand for batteries that are small and lightweight and have a high energy density as a main power source and a backup power source for these devices. Li _4/3 Ti _5/3 O is used as a battery active material that meets these demands.
₄ is drawing attention. Since Li _4/3 Ti _5/3 O ₄ has a crystal structure that is strong against a lithium occlusion / desorption reaction, the rate of progress of deterioration due to repeated charging / discharging is small and very stable. In addition, overcharge / the dendrite-like metallic lithium does not deposit due to overcharge, resulting in excellent safety. Due to these characteristics, it has been put to practical use as a backup power source. Recently, however, the environment in which backup batteries are used has become more severe with the diversification of equipment applications, and in addition to the characteristics of over-discharge and over-charge resistance, it is extremely important to satisfy discharge characteristics at high loads. It is an issue.

To address such problems, the negative electrode is made of Li _4/3.
For batteries that use Ti _5/3 O ₄ and a lithium-containing transition metal oxide such as cobalt or manganese for the positive electrode, it is proposed to improve the over-discharge resistance and over-charge resistance by configuring the negative electrode capacity regulation. (Japanese Patent Laid-Open No. 7-335261)
Japanese Patent Laid-Open No. 10-27626 and Japanese Patent Laid-Open No.
0-69922).

[0004]

However, even with the above proposal, it is difficult to obtain a battery satisfying the high load discharge characteristics. This is because the above proposal is intended to improve the overcharge / overdischarge characteristics by adopting the negative electrode capacity regulation, and no consideration is given to the high load discharge characteristics. Generally, the high load discharge characteristics are greatly affected by the conductivity of the electrodes. Conductive Li _4/3 Ti _5/3 O lithium titanium oxide such as _4, in the state of inserting lithium observed a slight increase, significantly lower than the carbon material. Therefore, it is apparent that the high load discharge characteristics are inferior to the battery using the carbon material. Therefore, in order to improve the conductivity of an electrode using lithium titanium oxide as an active material, a method has been proposed in which a conductive material such as graphite or carbon black is added to the electrode in a predetermined ratio. However, although the high-load discharge characteristics can be improved by increasing the addition ratio of the conductive agent, the active material amount relatively decreases as the addition amount increases. For this reason, there is a problem that the electric capacity density of the electrode is lowered and the practicality of the battery is greatly impaired.

The present invention improves the conductivity of a lithium titanium oxide negative electrode in a battery using Li _4/3 Ti _5/3 O ₄ as a negative electrode active material without increasing the addition ratio of a conductive material,
This aims to improve the high load discharge characteristics.

[0006]

[Means for Solving the Problems] To achieve the above object
The non-aqueous electrolyte secondary battery of the present invention is_4/3Ti_5/3O _Four
Non-aqueous electrolyte secondary battery using
Propane sultone or ethylene sulfite etc.
By containing a compound having an S═O bond of
Li_4/3Ti_5/3O_FourWhen the conductivity of the electrode containing
It is based on the findings.

That is, the present invention relates to the composition formula Li _4/3 Ti
_5/3 O ₄ , a negative electrode using a lithium titanium oxide having a spinel structure as an active material, and 3 V (vsLi / Li
⁺ ) A secondary battery having a positive electrode whose active material is a substance capable of inserting and desorbing lithium ions at a potential of the above potential, and a nonaqueous electrolytic solution, wherein the nonaqueous electrolytic solution is propane sultone, It is characterized by containing at least one of ethylene sulfite.

Li _4/3 Ti _5/3 O ₄ , which is the negative electrode active material, is
Usually, it is synthesized through a heat treatment process at 500 to 1000 ° C. At this time, the product obtained by the heat treatment is not a perfect homogeneous phase, and becomes a mixed crystal in which a part of the particle surface is covered with the rutile type titanium dioxide layer. As a result of a detailed study conducted by the present inventors, the amount of rutile-type titanium dioxide coating the surface of Li _4/3 Ti _5/3 O ₄ is very small, but the titanium dioxide has negative conductivity of the negative electrode. It was also found that the high load discharge characteristics of the battery are significantly deteriorated, and the cause of the deterioration is due to the following reasons.

That is, the reaction potential of Li _4/3 Ti _5/3 O ₄ and lithium is about 1.55 V based on the lithium electrode, whereas the reaction potential of rutile titanium dioxide is 1.
It is in the range of 5 to 1.3 V, which is a little lower than the potential of Li _4/3 Ti _5/3 O ₄ . Therefore, during charging, lithium is first inserted into Li _4/3 Ti _5/3 O ₄ and then into rutile titanium dioxide. On the other hand, during discharge, the rutile type titanium dioxide releases lithium first, and then Li _4/3 Ti.
_{5/3 Desorbed from} O ₄ . Therefore, the charge / discharge reaction of Li _4/3 Ti _5/3 O ₄ proceeds due to the movement of lithium ions through the rutile-type titanium dioxide phase in which lithium does not exist. The rutile-type titanium dioxide phase in which lithium is not present has low conductivity and therefore inhibits the migration of lithium. Thus, high rate of discharge becomes difficult in batteries using the extraction of lithium from Li _4/3 Ti _5/3 O ₄ is suppressed _{,, Li 4/3 Ti 5/3 O} 4 anode active material In particular, the discharge characteristics at a high load are significantly impaired.

As described above, the present invention includes a substance having an S═O bond in its molecular structure contained and added to the non-aqueous electrolyte. Among them, in a battery using a non-aqueous electrolytic solution containing at least one of propane sultone and ethylene sulfite (hereinafter referred to as an additive) and using Li _4/3 Ti _5/3 O ₄ for the negative electrode, Li _{4 /} Rutile titanium dioxide forming the surface phase of ₃ Ti _5/3 O ₄ reacts with a substance having an S═O bond to form a Ti—O—S ternary compound. Since the conductivity of this compound is significantly better than that of rutile titanium dioxide, it is speculated that this compound contributed to the improvement of the high load discharge characteristics. The ternary compound of Ti-OS is L
Formation on the surface of i _4/3 Ti _5/3 O ₄ was confirmed by the introduction of S in the surface analysis.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below.

The non-aqueous electrolyte secondary battery of the present invention comprises Li _4/3
A negative electrode whose main active material is Ti _5/3 O ₄ and 3V (vsL
A battery comprising a positive electrode using a substance capable of inserting and desorbing lithium ions at an electric potential of i / Li ⁻ ) or higher and a nonaqueous electrolytic solution composed of a solute and a nonaqueous solvent, wherein the nonaqueous electrolytic solution is propane. At least one of sultone and ethylene sulfite is contained.

As the negative electrode applied to the battery of the present invention,
It may contain Li _4/3 Ti _5/3 O ₄ as a main component and may be a mixed crystal of another negative electrode active material. In addition, acetylene black, carbon black, graphite or the like can be used as a conductive agent used for the negative electrode, and styrene-butadiene latex (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE) can be used as a binder. ), Polyvinylidene fluoride (PVDF), ethylene propylene diene copolymer (EPDM), tetrafluoroethylene / hexafluoropropylene copolymer (FEP) and the like can be used.

On the other hand, as the positive electrode, 3 V (vsLi / L
i⁺) It is possible to insert and desorb lithium ions at the above potential.
Transition metal oxides are used. Specifically, 3V (vsL
i / Li⁺3V class LiMnO having a potential of about₂，
V₂O_FiveIn addition to 4V (vsLi / Li⁺) Potential
4V class LiCoO shown₂, LiNiO₂, LiMn₂O _Four
And transition metal oxides are applied. And these activities
As a binder or conductive agent that is combined with the quality to form the positive electrode
As the negative electrode, the same one as the above negative electrode can be used.

Further, as a method of incorporating lithium in the positive electrode, in the case of a transition metal oxide of 3V class, lithium metal is brought into contact with Li _4/3 Ti _5/3 O ₄ of the negative electrode during battery assembly and incorporated. Thus, a battery having a discharge voltage of about 1.5 V can be obtained. On the other hand, in the case of a transition metal composite oxide of 4V class, since it is contained during the synthesis of the active material, a battery having a discharge voltage of about 2.5V can be obtained without the above treatment.

As the non-aqueous solvent that constitutes the non-aqueous electrolyte,
Propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), sulfolane (SLF), γ-butyrolactone (γ-BL), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC). , 1,
It is preferably at least one selected from 2-dimethoxyethane (DME), tetrahydrofuran (THF) and dioxolane (DOL).

As the solute lithium salt constituting the non-aqueous electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiC are used.
F ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ S
O ₂ ) _{2 and the} like can be used alone or in combination. LiPF ₆ and LiBF ₄ are preferable. The concentration of solute in the electrolytic solution is preferably 0.3 to 2.0 mol / l, more preferably 0.8 to 1.5 mol / l.

The amount of propane sultone added to the non-aqueous electrolyte is preferably 0.1 to 10% by weight. If it is less than 0.1% by weight, the organic coating formed by propane sultone may not be able to completely cover the surface of the lithium titanium oxide. On the other hand, if it is more than 10% by weight, the resistance component of the organic coating increases as the organic coating resulting from propane sultone becomes thicker. Therefore, the polarization resistance during charge / discharge of the negative electrode increases, and the electric load characteristics deteriorate.

The amount of ethylene sulfite added to the non-aqueous electrolyte is preferably 0.05 to 2.0% by weight.
If it is less than 0.05% by weight, the organic coating formed by ethylene sulfite may not be able to completely cover the surface of Li _4/3 Ti _5/3 O ₄ . On the other hand, if it exceeds 3.0% by weight, the resistance component of the organic coating increases as the thickness of the organic coating resulting from ethylene sulfite increases. Therefore, the polarization resistance during charge / discharge of the negative electrode increases, and the electric load characteristics deteriorate.

As described in detail above, the present invention comprises a negative electrode containing Li _4/3 Ti _5/3 O ₄ as a main component, a positive electrode capable of inserting and desorbing lithium ions, a non-aqueous solvent and a solute. A non-aqueous electrolyte secondary battery comprising the following non-aqueous electrolyte solution containing 0.1 to 10% by weight of propane sultone or 0.05 to 2.0% by weight of ethylene sulfite. By using the liquid, it has become possible to obtain a lithium-ion secondary battery having excellent high-load discharge characteristics.

[0021]

The present invention will be described in detail below with reference to examples.

FIG. 1 shows a sectional view of the coin type battery used in this embodiment. Each of the positive electrode case 1 and the negative electrode case 2 is made of stainless steel, and the inner surface of the positive electrode case 1 in contact with the electrolytic solution is completely covered with aluminum on the surface of the stainless steel. The insulating packing 3 is made of polypropylene and insulates and seals the positive electrode case 1 and the negative electrode case 2.

For the positive electrode 4, 88% by weight of lithium cobalt oxide (LiCoO ₂ ) as an active material, 5% by weight of acetylene black as a conductive agent, and 7% by weight of polytetrafluoroethylene as a binder were mixed. And dried mixture 2
50 mg was pressure-molded at ² ton / cm ² into pellets having a diameter of 16 mm, and dried at 200 ° C. to prepare. The negative electrode 5 had an active material of Li _4/3 Ti _5/3 O ₄ of 88% by weight, an acetylene black of 5% by weight as a conductive agent, and a styrene-butadiene latex aqueous dispersion of 7% by solid as a binder.
Approximately 185 mg of the mixed material which was mixed and dried at a mixing ratio of 2 wt.
Pellets having a diameter of 16 mm at ton / cm ² were pressure-molded and dried at 200 ° C. to prepare. The positive electrode 4 and the negative electrode 5 are
They are arranged opposite to each other with a separator 6 made of polypropylene non-woven fabric interposed therebetween.

In the non-aqueous electrolytic solution, lithium phosphorus hexafluoride was dissolved at a concentration of 1 mol / l in a non-aqueous solvent prepared by mixing ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 1: 1. Then, the product prepared by adding 1.0% by weight of propane sultone as an additive was used. 90 mg of the above electrolytic solution was injected into the battery. This battery has a diameter of 20 mm and a thickness of 2.0 mm. The battery A of the present invention was produced with the above-mentioned structure.

In Battery A, ethylene sulfite was added in an amount of 0.5% by weight in place of propane sultone as an additive, and Battery B of the present invention was prepared in the same manner as in the above.

Further, as a comparative battery, lithium phosphorus hexafluoride was dissolved at a concentration of 1 mol / l in a non-aqueous solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1. A battery having the same configuration as the battery A was assembled except that the water electrolytic solution was used.

The discharge rate characteristics of three non-aqueous electrolyte secondary batteries of the batteries A and B and the comparative battery of the present invention were evaluated as follows. Charging was carried out at an ambient temperature of 25 ° C. for 24 hours with a constant voltage of 2.6 V applied voltage by connecting a charging resistor of 5Ω to an external circuit. On the other hand, the discharge was performed at the same temperature for each current value of 2, 5, 10, 15, and 20 mA at a constant current up to a final voltage of 1.5 V, and the discharge capacity was measured. The results are shown in Table 1. Here, the discharge current 5 to
In the discharge at 15mA, after discharging to the final voltage,
Subsequently, after discharging at 2 mA to a final voltage of 1.5 V, the next charging was performed.

[0028]

[Table 1]

As is clear from the results shown in Table 1, the batteries A and B of the present invention obtained a larger capacity than the batteries of the comparative examples at a discharge current of 5 mA or more, and propane sultone or ethylene sulfite was added. The effect is confirmed.

In this embodiment, lithium cobalt oxide was used as the positive electrode, but similar results can be obtained with lithium nickel oxide and lithium manganate. The shape of the battery is not limited to the coin type described in this embodiment, but can be applied to a cylindrical type or a rectangular type.

[0031]

As is clear from the above description, Li
_In a non-aqueous electrolyte secondary battery using _4/3 Ti _5/3 O ₄ as the negative electrode active material, by incorporating propane sultone and ethylene sulfite in the non-aqueous electrolyte, excellent high load discharge characteristics were achieved. It is possible to provide a lithium ion secondary battery, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a non-aqueous electrolyte battery in this example.

[Explanation of symbols]

1 positive electrode can 2 Negative electrode can 3 gasket 4 positive electrode 5 Negative electrode 6 separator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuharu Koshiba             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5H029 AJ06 AK03 AL03 AM00 AM07                       BJ03 BJ12 HJ02 HJ18                 5H050 AA12 BA17 CA08 CA09 CB03                       FA02 HA02 HA18

Claims (2)

[Claims] 1. A negative electrode represented by the composition formula Li _4/3 Ti _5/3 O ₄ and having a spinel-type structure and a lithium titanium oxide as an active material, and lithium at a potential of 3 V (vsLi / Li ⁺ ) or more. A secondary battery having a positive electrode having a substance capable of inserting and desorbing ions as an active material, and a nonaqueous electrolytic solution as a basic component, wherein the nonaqueous electrolytic solution contains at least one of propane sultone and ethylene sulfite. A non-aqueous electrolyte secondary battery characterized by containing. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is a lithium composite oxide containing at least one of cobalt, nickel and manganese.