JP2001196060A - Electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a lithium secondary battery using a lithium-titanium composite oxide as an active material, having an improved rate and power characteristics and durability by using a conductive assistant to be mixed therein in good particle shape and mixed condition to form a sufficient conductive network in the electrode. SOLUTION: The electrode for the lithium secondary battery comprises the active material of a lithium-titanium composite oxide represented by a composition formula, LixTiyO4 (0.5<=x<=3, 1<=y←h2.5), the conductive assistant containing carbon fibers and a binder for binding the active material and the conductive assistant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for storing and storing lithium.
The present invention relates to an electrode that can be used for a lithium secondary battery utilizing a desorption phenomenon.

[0002]

2. Description of the Related Art In the field of communication equipment and information-related equipment, lithium secondary batteries have already been put to practical use and spread widely because of the high energy density accompanying the miniaturization of mobile phones and notebook personal computers. Has reached. On the other hand, in the field of automobiles, early commercialization of electric vehicles is desired due to environmental problems such as air pollution and an increase in carbon dioxide, and the use of lithium secondary batteries as power sources for electric vehicles has been studied. I have. When a lithium secondary battery is used as a power source for an electric vehicle, in addition to high power and high energy density, it has good cycle characteristics such as long life, that is, the capacity does not decrease even after repeated charging and discharging. Required to have.

At present, lithium secondary batteries mainly use a lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material and a carbon material such as graphite as a negative electrode active material. However, both the positive electrode active material and the negative electrode active material have factors that cause cycle deterioration and the like, and even with this mainstream lithium secondary battery, sufficiently satisfactory durability (cycle characteristics, storage characteristics, etc.) ) Is not currently available.

As an electrode for a lithium secondary battery, Japanese Patent Application Laid-Open
As disclosed in JP-A-275263, an electrode using a lithium titanium composite oxide as an active material is also being studied.
Since the lithium-titanium composite oxide has excellent durability, it is considered that a lithium secondary battery using it as an active material will be a secondary battery having a longer life. In particular, lithium secondary batteries used as electric vehicle power supplies,
Since it is required to have a longer life in a wider temperature range than a lithium secondary battery used for a small consumer device, it is considered to be a suitable active material.

[0005] A transition metal composite oxide such as a lithium titanium composite oxide generally has low conductivity, and when used as an active material, at the same time, a conductive auxiliary material for ensuring conductivity in an electrode is required. At present, it is a general technique to use carbon black, acetylene black or the like as a conductive additive mixed in an electrode using a lithium titanium composite oxide as an active material. Lithium-titanium composite oxides have the same electronic conductivity as other active material materials such as lithium-cobalt composite oxides and lithium-nickel composite oxides (LiNiO ₂ ). Lithium secondary batteries composed of electrodes used as active materials tend to have poor rate characteristics and power characteristics. Therefore, it is necessary to ensure the conductivity of the electrode, and the mixed state of the active material and the conductive additive in the electrode becomes important.

[0006]

An electrode using a lithium-titanium composite oxide as an active material and using carbon black, acetylene black or the like as a conductive auxiliary material generally has a powdery active material and conductive auxiliary material. A mixture of these powders is formed by binding with a binder. When the present inventors investigated the mixed state of active material particles and conductive auxiliary particles,
Since the particles of carbon black, acetylene black and the like were minute spheres, it was found that the particles were easily aggregated and easily dispersed unevenly in the electrode. In addition, since the lithium-titanium composite oxide as an active material repeatedly undergoes expansion and contraction during charge and discharge, it was also found that a minute spherical shape easily causes poor current collection.

The present invention has been made based on the above findings. In an electrode for a lithium secondary battery using a lithium-titanium composite oxide as an active material, the particle shape of a conductive auxiliary material mixed therein and the mixed state thereof It is an object of the present invention to provide an electrode having an excellent rate characteristic and power characteristic and an excellent durability by forming a sufficient conductive network in the electrode by adjusting the value of.

[0008]

The electrode for a lithium secondary battery of the present invention has a composition formula of Li _x Ti _y O ₄ (0.5 ≦ x ≦ 3,
An active material comprising a lithium-titanium composite oxide represented by 1 ≦ y ≦ 2.5), a conductive auxiliary material containing carbon fibers, and a binder for binding the active material and the conductive auxiliary material. Is characterized by the following. That is, in the electrode for a lithium secondary battery using the lithium-titanium composite oxide as an active material, the conductive auxiliary material mixed therein is a fibrous carbon material.

The conductivity of carbon fibers is as high as that of metals, and a sufficient current collecting effect can be obtained as compared with conventionally used carbon black, acetylene black and the like. The carbon fibers are uniformly dispersed without agglomeration in the electrodes during electrode formation due to their shape characteristics, and have high flexural rigidity.
It is possible to sufficiently cope with shrinkage, and it is possible to suppress poor current collection due to charge / discharge cycles. Furthermore, it has a larger DBP oil absorption than carbon black, acetylene black, and the like, and is excellent in retention of an electrolytic solution, so that a larger amount of electricity can be taken out at high current density discharge. Therefore, the electrode for a lithium secondary battery of the present invention is excellent in rate characteristics and power characteristics, and excellent in cycle characteristics, storage characteristics, and the like, due to the formation of a sufficient current collection network in the electrodes. Good electrode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of an electrode for a lithium secondary battery according to the present invention will be described with reference to a lithium-titanium composite oxide as an active material, a carbon fiber as a conductive additive, the structure and manufacture of the electrode, and the present electrode. Will be described in detail in the order of the lithium secondary batteries.

<Lithium-titanium composite oxide> A lithium-titanium composite oxide (hereinafter, referred to as “lithium-titanium composite oxide”) as an active material of the electrode for a lithium secondary battery of the present invention has a composition formula of Li _x Ti _y O ₄ (0.5 ≦ x ≦ 3, 1 ≦
y ≦ 2.5). The lithium titanium composite oxide has a spinel structure or a structure similar thereto,
According to powder X-ray diffraction using CuKα ray, the interplanar spacing in the crystal structure was at least 4.84 °, 2.53 °, 2.0
There is a diffraction peak on the diffraction surface (reflection surface) at 9 ° and 1.48 ° (± 0.1 ° between each surface).

The present lithium-titanium composite having this crystal structure
Oxide has a stable crystal structure, and lithium
The basic structure is destroyed by the absorption and desorption of um.
Lithium secondary batteries that are hard to break and have good cycle characteristics
It can be a configurable active material. Among various compositions
However, in terms of stability of the crystal structure, the composition formula Li_0.8Ti
_2.2O_Four, LiTi_TwoO_Four, Li_1.33Ti_1.67O_Four, Li
_1.14Ti_1.71O_FourWhat is represented by is excellent,
One type alone or a mixture of two or more types
It is desirable to use them together. Place used as active material
The change in volume due to charge and discharge is small and the crystal structure is
In terms of stability, the composition formula Li _1.33Ti
_1.67O_FourIt is more desirable to use the one represented by
By the way, the composition formula Li_0.8Ti_2.2O_Four, Li_1.33Ti
_1.67O_Four, Li_1.14Ti_1.71O_FourIs the composition formula Li
_FourTi₁₁O₂₀, Li_FourTi_FiveO₁₂, Li_TwoTi_ThreeO₇Express
Can also be.

The production method of the present lithium-titanium composite oxide is not particularly limited, but a lithium compound as a lithium source and titanium oxide as a titanium source are mixed, and the mixture is easily synthesized by firing. be able to. As the lithium compound, Li ₂ CO ₃ , Li
(OH) or the like can be used. The firing is performed in an oxygen stream or in the atmosphere. The mixing ratio of each raw material may be a ratio according to the composition of the lithium titanium composite oxide to be synthesized. If the temperature is too low, it is not possible to obtain a particle having a particle size that has grown so as to have good characteristics as an active material. If the temperature is too high, a rutile-type titanium oxide phase (TiO ₂ ), The firing temperature is 500 to 1000 ° C.
It is desirable that More preferably, 700 to 900
℃ is good.

It is difficult to completely eliminate the titanium oxide phase generated as a sub phase. Since this titanium oxide phase is generated in a mixed crystal state with the main phase of the lithium-titanium composite oxide, if present in a small amount, the charge-discharge characteristics and cycle characteristics when used as an active material are extremely deteriorated. It does not matter. Therefore, the present lithium-titanium composite oxide may contain this titanium oxide in a mixed crystal state, and in the present specification, “lithium-titanium composite oxide” means containing the same. .

<Carbon Fiber> The type of the carbon fiber used as the conductive additive of the electrode for a lithium secondary battery of the present invention is not particularly limited. For example, carbonaceous whiskers such as carbon whiskers and graphite whiskers, PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, and vapor-grown carbon fibers can be used. Among these, vapor-grown carbon fibers are preferably used in view of the advantage that carbon fibers having a uniform shape can be easily produced and synthesized.

The carbon fiber used has an average fiber length of 0.1.
It is desirable that the thickness be 1 μm or more and 10 μm or less. When the average fiber length is less than 0.1 μm, it is inferior in forming a sufficient conductive network in the electrode.
If the thickness exceeds 0 μm, the moldability of the electrode deteriorates because the viscosity of the electrode paste prepared when forming the electrode by binding with a binder becomes too high. In consideration of the formability of the electrode, it is more desirable that the carbon fibers used have an average fiber diameter of 1 μm or less.

<Constitution and Production of Electrode> The electrode for a lithium secondary battery of the present invention comprises an active material comprising the lithium-titanium composite oxide, a conductive auxiliary material containing the carbon fiber, the active material and the conductive auxiliary material. And a binder for binding the material.

As the active material, the above-mentioned lithium titanium composite oxide is used. For reasons such as improvement of electrode characteristics, if the lithium-titanium composite oxide is used as a main active material and the present electrode is used as a positive electrode, a known Li
A positive electrode active material such as a lithium transition metal composite oxide such as CoO ₂ or LiNiO ₂ may be mixed in a positive manner to form an active material, or a carbon material such as graphite or hard carbon if the negative electrode is used. It is also conceivable to mix an already known negative electrode active material such as the above as a secondary material to form an active material. The electrode of the present invention does not prevent such a mixture from being used as an active material. The lithium-titanium composite oxide includes various lithium-titanium composite oxides depending on the composition, and one of them can be used alone.
Two or more kinds may be used as a mixture.

An electrode can be formed by using only the above-mentioned carbon fiber as the conductive auxiliary material, or a conductive auxiliary material can be prepared by mixing a carbon material such as carbon black and acetylene black with the carbon fiber. . As shown in the examples described later, it has been clarified by an experiment performed by the present inventor that when carbon fibers such as carbon black and acetylene black are mixed as a conductive auxiliary material, Are excellent in terms of rate characteristics and longer-term charge / discharge cycle characteristics. It is considered that the reason for this is that the conductivity was further improved by using conductive assistants having different shapes. In this case, it is desirable that the mixing ratio of the carbon fiber to the carbon black, acetylene black or the like is 2: 8 to 9: 1 by weight.

The binder is not particularly limited, and any known binder may be used. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used.

The method for producing the electrode of the present invention is not particularly limited, and may be in accordance with a generally practiced method for producing an electrode for a lithium secondary battery. For example, the active material is mixed with the conductive additive and the binder, and an appropriate amount of a solvent (dispersion medium) is added as necessary to obtain a paste-like electrode mixture. It can be prepared by coating and drying on the body surface and then increasing the density of the electrode mixture by pressing or the like as necessary. As the current collector, an aluminum foil or the like may be used when the present electrode is used as a positive electrode, and a copper foil or the like may be used when the current electrode is used as a negative electrode. Further, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. According to this manufacturing method, the produced electrode becomes a sheet-like electrode. This sheet-shaped electrode may be cut into a size according to the specification of the lithium secondary battery to be manufactured.

In the electrode for a lithium secondary battery of the present invention, since the mixed state of the active material and the conductive auxiliary in the electrode is important, the mixing ratio of the active material and the conductive auxiliary in the electrode mixture is important. There is also a more appropriate range. In the electrode for a lithium secondary battery of the present invention, it is desirable that the mixing ratio of the conductive additive to the active material is 0.005 or more and 0.2 or less by weight. In other words, it is desirable to mix the conductive aid in a ratio of 0.5 part by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the active material. The mixing ratio of the conductive additive is 0.00
When the number is less than 5, that is, when the amount of the conductive aid is too small, an efficient conductive network cannot be formed. When the number is more than 0.2, that is, when the amount of the conductive aid is too large, the moldability of the electrode is poor. Is also too low. From the viewpoint of satisfying all of the battery capacity, the conductive network, and the moldability of the electrode, the mixing ratio of the conductive auxiliary to the active material is 0.05 to 0.15 by weight.
It is more desirable to set the following.

<Lithium Secondary Battery> In a lithium secondary battery using the electrode of the present invention, the electrode of the present invention can be used as a positive electrode or a negative electrode.
The lithium-titanium composite oxide has a reduction potential of Li / Li ⁺
Is about 1.5 V, and an electrode using an active material having a higher potential than this, for example, a lithium transition metal composite oxide such as LiCoO ₂ or LiNiO ₂ as an active material is used as a positive electrode. May be used as a negative electrode to constitute a lithium secondary battery. Conversely, an active material having a potential lower than 1.5 V, such as lithium metal, a lithium alloy,
A lithium secondary battery may be formed by using an electrode using a carbon material such as graphite, coke, hard carbon or the like as an active material as a negative electrode and using the electrode of the present invention as a positive electrode. Each electrode facing the electrode of the present invention may be manufactured by a general manufacturing method according to the above-described method of manufacturing the electrode of the present invention.

In a lithium secondary battery using the electrode of the present invention,
Is the same as the general lithium secondary battery,
In addition, a separator sandwiched between the positive and negative electrodes,
The lysis solution is a constituent element. The separator consists of a positive electrode and a negative electrode.
To separate the electrolyte and retain the electrolyte.
A thin microporous membrane such as polypropylene can be used.
You. In addition, the non-aqueous electrolyte is made up of an organic solvent such as lithium.
Is a non-prototype organic solvent.
Organic solvents such as ethylene carbonate, propylene
Carbonate, dimethyl carbonate, diethyl carbonate
Bonate, ethyl methyl carbonate, γ-butyrolact
Ton, acetonitrile, 1,2-dimethoxyethane,
1 such as trahydrofuran, dioxolan, methylene chloride, etc.
Species or a mixture of two or more of these can be used.
You. The electrolyte to be dissolved is LiI, LiC
10_Four, LiAsF₆, LiBF_Four, LiPF₆, LiN
(CF _ThreeSO_Two)_TwoEtc. can be used
You.

The lithium secondary battery using the electrode of the present invention configured as described above can have various shapes such as a cylindrical type, a laminated type and a coin type. Regardless of the shape used, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and a current collecting lead extends from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal that lead to the outside. The electrode body is sealed together with the non-aqueous electrolyte in a battery case to complete the battery.

As described above, since the lithium-titanium composite oxide has a relatively high reduction potential of about 1.5 V, when the electrode of the present invention is used as a negative electrode, the nonaqueous electrolyte The effect of suppressing the decomposition of the compound can also be expected, and the effect of improving the cycle characteristics based on this effect can be obtained.

Although the embodiment of the electrode for a lithium secondary battery of the present invention has been described above, the above-described embodiment is merely an embodiment, and the electrode for a lithium secondary battery of the present invention is
The present invention can be implemented in various forms including various modifications and improvements based on the knowledge of those skilled in the art, including the above embodiment.

[0028]

EXAMPLE Based on the above embodiment, an electrode for a lithium secondary battery including a lithium-titanium composite oxide as an active material and carbon fibers as a conductive additive was produced. Further, for comparison, an electrode for a lithium secondary battery using only carbon black as a conductive additive was prepared. Then, lithium secondary batteries using these electrodes as negative electrodes were produced, and the characteristics of these secondary batteries were evaluated, thereby confirming the superiority of the lithium secondary battery electrodes of the present invention. Hereinafter, these will be described.

<Electrode for Lithium Secondary Battery of Example 1> A lithium-titanium composite oxide represented by a composition formula of Li _1.33 Ti _1.67 O ₄ was used as an active material of the present electrode. This lithium-titanium composite oxide was synthesized by using Li ₂ CO ₃ as a Li source and anatase TiO ₂ as a titanium source, mixing these at a predetermined ratio, and calcining at 800 ° C. for 12 hours in an oxygen stream. The synthesized lithium titanium composite oxide was subjected to powder X-ray diffraction analysis using CuKα radiation,
4.83４, 2.52Å, 2.09Å, 1.48
It was confirmed that there were respective diffraction peaks obtained by the diffractive surface (reflective surface) as Å. The conductive material of the present electrode has an average fiber diameter of 0.2 μm and an average fiber length of 2 μm.
Only the μm vapor-grown carbon fiber was used.

90 parts by weight of the lithium-titanium composite oxide was mixed with 10 parts by weight of the carbon fiber, and 5 parts by weight of polyvinylidene fluoride was further mixed as a binder.
Methyl-2-pyrrolidone was added and kneaded well to prepare a paste-like electrode mixture. Next, this electrode mixture was applied to both surfaces of a copper foil current collector having a thickness of 10 μm, dried, and pressed to prepare a sheet-like electrode. This electrode was used as the electrode for a lithium secondary battery of Example 1.

<Electrode for Lithium Secondary Battery of Example 2> The electrode of this example is an electrode using a mixture of carbon fiber and carbon black as a conductive additive. The same lithium-titanium composite oxide as in Example 1 was used as the active material, and the same carbon fibers as those in Example 1 were used as the conductive assistant. 90 parts by weight of the lithium-titanium composite oxide was mixed with 5 parts by weight of the carbon fiber and 5 parts by weight of carbon black, and 5 parts by weight of polyvinylidene fluoride was further mixed as a binder. Pyrrolidone was added and kneaded well to prepare a paste-like electrode mixture. Next, this electrode mixture was applied to both surfaces of a copper foil current collector having a thickness of 10 μm, dried, and pressed to prepare a sheet-like electrode. The amount of active material per unit area of the electrode was the same as in Example 1. This electrode was used as an electrode for a lithium secondary battery of Example 2.

<Electrode for Lithium Secondary Battery of Comparative Example 1> The electrode of this comparative example is an electrode using only carbon black as a conductive additive. As the active material, the same lithium titanium composite oxide as in Example 1 was used. 90 parts by weight of the lithium-titanium composite oxide is mixed with 10 parts by weight of carbon black, 5 parts by weight of polyvinylidene fluoride is further mixed as a binder, and an appropriate amount of N-methyl-2-pyrrolidone is added and kneaded sufficiently. Thus, a paste-like electrode mixture was prepared.
Next, this electrode mixture was applied to both surfaces of a copper foil current collector having a thickness of 10 μm, dried, and pressed to prepare a sheet-like electrode. The amount of active material per unit area of the electrode was the same as in Example 1. This electrode was used as an electrode for a lithium secondary battery of Comparative Example 1.

<Preparation of Lithium Secondary Battery> A lithium secondary battery using the electrodes of the above Examples and Comparative Examples as negative electrodes was prepared. The positive electrode to be opposed is composed of LiNi
A layered rock-salt lithium nickel composite oxide represented by _0.85 Co _0.1 Al _0.05 O ₂ was used as an active material. To 85 parts by weight of this lithium nickel composite oxide, 10 parts by weight of acetylene black as a conductive additive and 5 parts by weight of polyvinylidene fluoride as a binder were mixed, and an appropriate amount of N-methyl-2-
Pyrrolidone was added and sufficiently kneaded to prepare a paste-like positive electrode mixture. Next, this positive electrode mixture was applied to a thickness of 20 μm.
Was coated on both sides of an aluminum foil current collector, dried and pressed to produce a sheet-shaped positive electrode.

The above-mentioned positive electrode and the negative electrode which is each electrode of the above-mentioned Examples and Comparative Examples were cut to a predetermined size, and a polyethylene separator having a thickness of 25 μm was sandwiched between them and wound. A roll-shaped electrode body was formed. A positive electrode and a negative electrode current collecting lead were attached to this electrode body, housed in a 18650 type battery case, a non-aqueous electrolyte was injected, and then the battery case was sealed to produce a cylindrical lithium secondary battery. The non-aqueous electrolyte was prepared by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 3:
A solution obtained by dissolving LiPF ₆ at a concentration of 1 M in the mixed solvent mixed in Example 7 was used.

The lithium secondary battery using the electrode of Example 1 as a negative electrode was the lithium secondary battery of Example 1, and the secondary battery using the electrode of Example 2 was the lithium secondary battery of Example 2. The secondary battery using the electrode of Comparative Example 1 and the secondary battery was defined as a lithium secondary battery of Comparative Example 1.

<Characteristic Evaluation of Lithium Secondary Battery> A charge / discharge test was performed on each of the above lithium secondary batteries, and the initial discharge capacity and rate characteristics were evaluated. First, 20 ° C
Under the ambient temperature, the current density is 1m up to the charging end voltage 2.7V.
After charging at a constant current of A / cm ² , discharging was performed at a constant current of 1 mA / cm ^{2 at} a current density of 1 mA / cm ² until the discharge end voltage was 1.5 V, and the discharge capacity at the time of discharging was defined as the initial discharge capacity. Next, after charging under the same conditions, the battery was discharged at a constant current of a current density of 10 mA / cm ^{2 to} a discharge end voltage of 1.5 V, the discharge capacity at this time was determined, and the discharge capacity was compared with the initial discharge capacity. The ratio (percentage) was determined. Table 1 below shows the initial discharge capacity and the discharge capacity ratio per unit weight of the positive electrode active material of each lithium secondary battery.

[0037]

[Table 1] As can be seen from Table 1 above, the secondary batteries of Example 1 and Example 2 have a larger initial discharge capacity than the secondary battery of Comparative Example 1. Further, the secondary batteries of Example 1 and Example 2 are also superior in terms of the discharge capacity ratio when discharging at a high current density. From this, in the case of a lithium secondary battery using an electrode using a lithium-titanium composite oxide as an active material, the lithium secondary battery containing carbon fiber as a conductive additive for the electrode has excellent rate characteristics. You can check. When the secondary battery of Example 1 was compared with the secondary battery of Example 2, both the initial discharge capacity and the rate characteristics were measured using an electrode in which carbon fiber and carbon black were mixed and used as a conductive auxiliary material. It was found that the secondary battery of Example 2 was more excellent.

Further, each of the above secondary batteries was subjected to a charge / discharge cycle test to evaluate the cycle characteristics.
The charge / discharge cycle test is performed in a high temperature environment of 60 ° C., which is considered to be the upper limit temperature at which the lithium secondary battery is actually used. The conditions of the charge / discharge cycle are as follows. Charging at a constant current of ² and then discharging at a constant current of ² mA / cm ^{2 to} a discharge end voltage of 1.5 V were defined as one cycle, and the cycle was performed up to 500 cycles. As a result of this test, FIG. 1 shows the capacity retention ratio of each secondary battery in each cycle (discharge capacity of that cycle / discharge capacity of first cycle × 100%).

As can be seen from FIG. 1, as compared with the secondary battery of Comparative Example 1, the secondary batteries of Examples 1 and 2 showed a small decrease in the discharge capacity even when charging and discharging were repeated. Has become a battery. Therefore, in the case of a lithium secondary battery using an electrode using a lithium-titanium composite oxide as an active material, a lithium secondary battery containing carbon fiber as a conductive additive of the electrode has excellent cycle characteristics, particularly excellent high-temperature cycle characteristics. Can be confirmed. In addition, when comparing the secondary battery of Example 1 with the secondary battery of Example 2, the secondary battery of Example 2 using an electrode in which carbon fiber and carbon black were mixed and used as a conductive auxiliary material was better. It can be confirmed that the cycle characteristics after a longer period, that is, after many cycles, are excellent.

[0040]

The electrode for a lithium secondary battery according to the present invention is an electrode using a lithium-titanium composite oxide as an active material, and is constituted so that its conductive auxiliary material contains carbon fibers. With such a configuration, the lithium secondary battery using the present electrode becomes a lithium secondary battery having excellent rate characteristics, power characteristics, and excellent cycle characteristics and excellent durability due to the above-described operation. .

[Brief description of the drawings]

FIG. 1 shows the capacity retention ratio in each cycle of each secondary battery as a result of a charge / discharge cycle test performed on lithium secondary batteries of Examples and Comparative Examples.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takuaki Okuda 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. (72) Inventor Takeshi Sasaki, Nagakute-machi, Aichi-gun, Aichi Prefecture No. 41, Chochu-Yokomichi, at Toyota Central Research Institute, Inc. (72) Inventor Koji Takeuchi, No. 41, Nagachute-cho, Aichi-gun, Aichi Prefecture, Japan No. 41, Toyota Chuo Research Institute, Inc. (72) Inventor, Tetsuro Kobayashi No. 41, Toyota Chuo R & D Co., Ltd., No. 41, Nagakute-cho, Aichi-gun, Aichi-gun, Toyota-Central Research Institute, Inc. (72) Inventor Yoshio Ukyo Yoshichio Ukyo 41, Toyota-Chuo Central Research Institute, F-41, Nagakute-cho, Aichi-gun, Aichi Terms (reference) 4G047 CA05 CB04 CC03 CD07 5H003 AA01 AA04 BB05 BB15 BC02 BC06 BD00 BD02 5H014 AA02 EE07 EE10 HH00 HH06 5H029 AJ02 AJ05 AK03 AM03 A M04 AM05 AM07 BJ02 BJ03 DJ08 DJ15 HJ05

Claims (4)

[Claims] A composition formula Li _x Ti _y O ₄ (0.5 ≦ x ≦
3, 1 ≦ y ≦ 2.5), an active material composed of a lithium-titanium composite oxide, a conductive auxiliary material containing carbon fibers, and a binder for binding the active material and the conductive auxiliary material. An electrode for a lithium secondary battery comprising: 2. The carbon fiber has an average fiber length of 0.1 μm.
The electrode for a lithium secondary battery according to claim 1, wherein the electrode has a length of not less than m and not more than 10 µm. 3. The electrode for a lithium secondary battery according to claim 1, wherein a mixing ratio of the conductive auxiliary to the active material is 0.005 to 0.2 in weight ratio. 4. The lithium-titanium composite oxide has a composition of Li _0.8 Ti _2.2 O ₄ , LiTi ₂ O ₄ , Li _1.33 T
_{4. The} electrode for a lithium secondary battery according to claim 1, wherein the electrode is at least one member selected from the group consisting of i _1.67 O ₄ and Li _1.14 Ti _1.71 O ₄ .