JP3493988B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source for small portable electronic devices or a large industrial secondary battery for automobiles, power storage, and the like.

[0002]

_2. Description of the Related Art Conventionally, transition metal oxides represented by LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like have been used as positive electrode materials for Li secondary batteries. It has considerably lower conductivity than metals or lithium alloyed metals. Therefore, graphite or an amorphous carbon material is mixed as a conduction aid to improve the conductivity inside the electrode, and mixed with a binder to prepare an electrode coated on a metal substrate.

The carbon material, which is a conduction aid, and the positive electrode active material are in contact with each other at a point or a surface. However, due to repeated expansion and contraction of the positive electrode active material itself due to charging and discharging, the contact area between the conduction aid and the positive electrode active material is increased. It will decrease and the continuity will gradually disappear. Therefore, it has been impossible to make full use of the ability of the positive electrode active material.

As a method for solving this problem, for example, in Japanese Unexamined Patent Publication (Kokai) No. 105459/1998, LiMn ₂ O ₄ is used with graphite as a conductive auxiliary agent, and the ratio of graphite to the total weight of LiMn ₂ O ₄ and graphite is from 8 to 8. Two
It is disclosed that the charge / discharge cycle characteristics are improved by setting the content to 2% by weight.

However, according to this method, even if the cycle characteristics are improved, the characteristics in high-efficiency discharge are not sufficient unless more graphite is used. If the amount of graphite increases, the packing density of the active material of the battery increases. It has the drawback of lowering, and is not sufficient to realize a high-capacity, high-power battery.

The reason for this is considered as follows. Since graphite creates a conductive path by contact between particles,
This is because the material itself does not have a conductive network, and thus many particles are required to obtain high current collecting property. In an electrode using graphite as a conductive agent, when discharged with high efficiency, the amount of particles is small, so that the number of contact points with the active material is small, the current collecting property is insufficient, and the discharge capacity is reduced.

In order to improve the cycle characteristics, the dibutyl phthalate (DBP) oil absorption is 50 ml / 100 g to 3
It has been proposed in JP-A 7-296794 to use less than 00 ml / 100 g of carbon black. This is because the large amount of oil absorption is used to soak the electrolyte solution in the battery and the swelling of the electrodes is used to eliminate the insufficient pressurization due to loose winding between the electrodes even in the battery.
It has been proposed that the charge / discharge cycle characteristics be improved.

However, in practice, when a carbon material or carbon black having a large oil absorption is used, the oil absorption is large, so that it is difficult to prepare a slurry during electrode coating, and a large amount of a binder is also absorbed. It is difficult to manufacture a positive electrode which maintains the mechanical strength while maintaining the bond between particles.

Therefore, it is necessary to increase the amount of binder,
As a result, there is a drawback that the packing density of the positive electrode active material decreases.

Further, since carbon black has a large bulk density, it is difficult to obtain a high electrode density. To increase the electrode density, it is necessary to increase the pressing pressure. However, in order to obtain a high electrode density, the pressing pressure is increased. If it is increased, the problem that the substrate and the mixture are separated occurs. Therefore, it is difficult to increase the volumetric energy density of the battery. Furthermore, since the mechanical strength of the electrode was insufficient in a long-term cycle, the current collector and the mixture were peeled off, and there was a problem in cycle characteristics.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having improved positive electrode conductivity and electrode strength, and excellent charge / discharge cycle characteristics and high rate output characteristics. To provide.

[0012]

The present invention has been completed by adopting the following technical means in order to solve the above-mentioned problems.

The features of the lithium secondary battery according to the present invention are:
In a lithium secondary battery including a positive electrode, a negative electrode and a non-aqueous electrolyte solution and utilizing a lithium ion insertion / desorption reaction, a positive electrode mixture is composed of a positive electrode active material, a conductive auxiliary agent, and a binder, The agent is a carbon material, and is composed of a fibrous carbon material and granular carbon, and the ratio of the fibrous carbon is 1 to 20% by weight, when the total amount of the conductive additive is 100% by weight.
The granular carbon is composed of 99 to 80% by weight. By adding the fibrous carbon, it becomes possible to relieve the volume stress against the expansion and contraction of the electrode and facilitate the maintenance of the structure. In addition, the addition of granular carbon increases the number of contact points with the active material, resulting in low resistance. By mixing the fibrous carbon in a weight ratio smaller than that of the granular carbon, it becomes possible to suppress the decrease in conductivity of the electrode due to expansion and contraction.

Another feature of the lithium secondary battery according to the present invention is that the lithium secondary battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, and utilizes a lithium ion insertion / desorption reaction. It is composed of an active material, a conductive auxiliary agent, and a binder, and the conductive auxiliary agent is a carbon material and includes a fibrous carbon material and granular carbon, and the granular carbon is crystalline carbon and amorphous carbon. And the ratio of the fibrous carbon is 1 to 20
%, The granular carbon is composed of 99 to 80% by weight, and the ratio of crystalline carbon to amorphous carbon in the granular carbon is 9% by weight with the granular carbon being 100% by weight.
It is composed of 0 to 60% by weight and 10 to 40% of the amorphous carbon.

Still another characteristic is that the fibrous carbon of the conductive additive of the positive electrode has an aspect ratio of length to fiber diameter (hereinafter referred to as aspect ratio) of 20 to 100,000 and a fiber diameter of 0.001. ˜2 μm, the ratio of the average particle size of crystalline carbon to the average particle size of amorphous carbon in the conductive additive of the positive electrode is amorphous when the average particle size of amorphous carbon is 1. The quality carbon is in the range of 0.004 to 0.05.

Fibrous carbon has a longer conductive path than graphite, but if the fiber diameter is about 5 μm or more, it is difficult to efficiently contact the surface of the active material, and electrons are not sufficiently supplied to the active material. High efficiency discharge is difficult.

Therefore, in the present invention, it is desirable that the fiber diameter is small and the length is such that a sufficient conductive path can be formed in the electrode. The fibrous carbon forms a conductive path in the electrode, and the material having a fiber diameter of 0.001 to 2 μm and a length of about 20 μm can easily maintain the electrode. .

As the granular carbon mixed with the carbon fiber, crystalline carbon represented by graphite in the granular carbon is used. This increases the electrode density, and the average particle size is 1
By mixing fine amorphous carbon black carbon having a size of μm or less, the lack of contact points of crystalline carbon is compensated for, the conductivity in the electrode is increased, and the liquid collecting property is improved.

By mixing these, the electrode density can be improved, and the active material filling amount can be increased. Therefore, a battery having a high volume energy density and excellent cycle characteristics and high rate discharge characteristics can be realized.

The present invention relates to a lithium secondary battery, wherein the conductive auxiliary agent of the electrode is 1 to 20 carbon fibers based on the whole conductive auxiliary agent.
%, And 99% to 80% of granular carbon are mixed to form an electrode, the battery has less problems of peeling of the electrode, has a long life, has a high volume energy density, and further has 10% of the entire granular carbon.
A battery using an electrode in which 40% is amorphous carbon and the remaining 90 to 60% is graphite carbon is based on the finding of higher performance.

[0021]

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

First, the features of the lithium secondary battery according to the present invention will be described as a summary of the findings obtained by the present inventors, and the outline of the embodiment will be described. Specific examples obtained as knowledge will be described later.

The lithium secondary battery according to the present invention for achieving the above object is composed of a positive electrode, a negative electrode and an organic electrolytic solution. In a secondary battery utilizing a lithium ion insertion / desorption reaction, a positive electrode or a negative electrode is added. The conductive additive used is a mixture of fibrous carbon, granular crystalline carbon and / or amorphous carbon.

The positive electrode active material can be realized by using a transition metal oxide, a transition metal sulfide, a polyaniline type organic compound, or any other active material, but Li _x Ni _1-y M is particularly preferable. _y O ₂ , Li _x M _1-y Co _y O ₂ , Li
_{x Mn 1-y M y O} 2 (0 <x ≦ 1.3, 0 ≦ y ≦ 1,0 ≦ z
<2, M: Al, Fe, Cu, Co, Mg, Ca, V,
Ni, Ag, Sn, at least one of n second transition metal elements), lithium-containing manganese oxide such as LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ or Li _x Mn _{2- y My} O
_4-z (0 <x ≦ 1.3, 0 ≦ y <2, 0 ≦ z <2, M: A
l, Fe, Cu, Co, Mg, Ca, V, Ni, Ag,
Sn, a lithium-containing oxide represented by the chemical formula of at least one kind of a second transition metal element).

On the other hand, examples of the negative electrode active material include metallic lithium and lithium alloys (eg, LiAl, LiPb, LiS).
n, LiBi, LiCd, etc.), a conductive polymer doped with lithium ions (eg, polyacetylene, polypyrrole, etc.), an intercalation compound with lithium ions mixed in the crystal (eg, TiS ₂ , MoS _2, etc., containing lithium between layers). However, a carbonaceous material that can be doped or dedoped with lithium, an intermetallic compound such as silicide, a metal oxide, or any material that can store and release lithium can be used.

As the electrolytic solution, an aprotic organic electrolytic solution in which a lithium salt is used as an electrolyte and the electrolyte is dissolved in an organic solvent is used. Here, as the organic solvent, esters, ethers, 3-substituted-2-oxazolidinones, and a mixed solvent of two or more of these are used. Specific examples include esters such as alkylene carbonates (ethylene carbonate, propylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone, etc.), chain dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, etc. Is.

As the ethers, diethyl ether,
Dimethoxyethane, diethoxyethane, cyclic ether,
For example, the ether having a 5-membered ring is tetrahydrofuran and its substitution product, dioxolane and the like, and the ether having a 6-membered ring is 1,4-dioxolane, pyran, dihydropyran, tetrahydropyran and the like. As the electrolyte, lithium perchlorate, lithium borofluoride, lithium chloroaluminate, lithium halide, lithium trifluoromethanesulfonate, LiPF ₆ , LiAs
F ₆ and LiB (C ₆ H ₅ ) ₄ can be used, and among these, lithium phosphorus fluoride, lithium borofluoride, and lithium perchlorate are preferable.

However, all organic electrolytic solutions using a lithium salt as a supporting electrolyte can be used and are not limited to the above examples.

As a conductive additive for the positive electrode, a fibrous carbon material and a granular carbon material are mixed, and the granular carbon material is mixed with graphite particles and an amorphous carbon material to activate the electrode. By optimizing the proportion of the substance to 90% by weight or more and reducing the proportion of the weight of the binder and the conductive assistant to optimize, a battery having high volume energy density, high rate characteristics and long life can be realized.

As described above, the drawback of the fibrous carbon material is that the number of contact points with the active material is small, and it is necessary to increase the amount of addition in the electrode by itself. Further, compared with graphite, since it has a fibrous shape, there is no collapse like graphite, and it is difficult to increase the electrode density. In addition, since carbon fibers represented by vapor-phase synthetic carbon fibers and the like have a higher synthesis cost than other carbon materials, the use of a large amount increases the cost of the battery.

On the other hand, the advantage of the fibrous carbon material is that it forms a conductive path in the electrode, enables the relaxation of the volume stress due to the expansion and contraction of the electrode, and facilitates the maintenance of the structure. Further, there is an advantage that the specific surface area is small and the slurry can be easily prepared.

When a graphite material is used as the conductive additive for the positive electrode, if the average particle size is 5 μm or less and the specific surface area is 10 m ² / g or more, the resistance is increased when a large current of about 2 C is applied. There is a problem in that the capacity characteristics are large and inferior.
However, the oil absorption is small and the slurry preparation is easy.
Further, when the electrodes are pressed, graphite is easily oriented, so that a high electrode density can be easily obtained, and a large amount of active material can be filled in the battery, which is effective in improving the energy density of the battery.

Carbon black-based Ketjen black and acetylene black have a large oil absorption amount, making it difficult to prepare a slurry and having a low bulk density, making it difficult to obtain a high mixture density and also adsorbing a binder to form an electrode substrate. There is a problem of weak mechanical adhesion with. However, these have a well-developed structure with good electron conductivity,
Moreover, since the average particle size is as small as 0.1 μm or less, there are many contact points with the active material in the electrode, and the current collecting property is high, so that the rate characteristics are very good. Furthermore, it is considered that the cycle characteristics are good because the electrolyte can be sufficiently captured in the electrode.

In the present invention, the constitution of the conductive auxiliary agent of the electrode is as follows. Carbon fibers with a fiber diameter of 0.001 to 2 μm and an aspect ratio of more than 200 are
Addition of ~ 20% by weight makes it easy to maintain the structure in the electrode and 99-80% of granular carbon having an average particle size of 5 μm or less is added.
Add wt% to increase the contact points between the conductive additive and the positive electrode active material. In addition, the particle size of the granular carbon contained in the conductive additive is 0.1.
Graphite having a particle size of 5 to 5 μm is used in an amount of 60 to 90% by weight to increase the electrode density, and further, amorphous carbon such as carbon black-based Ketjen black or acetylene black having a particle size of 80 nm or less is less than half of the total amount of granular carbon, preferably 10-40
By adding the weight%, the contact points with the active material were increased to form a conductive network, and an electrode with high performance was realized effectively.

By adding the carbon fiber, it becomes possible to relieve the volume stress against the expansion and contraction of the electrode. In addition, the addition of carbon black also improves the liquid catching property,
The resistance drops. Here, the particle size of the carbon black-based carbon material that is amorphous carbon is 0.0 with respect to the particle size of graphite.
When the ratio is 04 or more and 0.05 or less, it is possible to efficiently enter the positive electrode active material and the graphite, or the graphites, or the fibrous carbon material and the gap where these cannot be sufficiently contacted, increasing the number of contact points, An electrode with higher conductivity can be realized. By mixing these carbon materials and using them as a conductive additive, it is possible to obtain a high density electrode and increase the amount of the active material filled. for that reason,
A battery with high volume energy density can be realized.

Further, by compounding the conductive auxiliary agent in this way, the cycle characteristics, particularly the capacity characteristics when the discharge rate is increased, are realized, and the synergistic effect of a long life is exhibited.

The carbon fibers which can be used in the conductive additive of the present invention are vapor phase synthetic carbon fibers having a fiber diameter of 1 to 20 μm, and a fiber diameter of 1
˜50 nm nanotubes, pitch-based fibers, PAN-based fibers, mesophase pitch-based fibers and the like can be used, but vapor phase synthetic carbon fibers or nanotubes are preferable in view of their tensile strength and resistance. Among the carbonaceous materials and the graphite materials, the graphite materials have a lower resistance value, a larger density and a greater effect of improving the electrode density, and are more preferable.

The crystalline carbon used in the present invention is an artificial graphite or natural graphite having an average particle size of 1 to 5 μm, mainly having an aspect ratio of the major axis to the minor axis of 1 or more and 5 or less.
Specific surface area by BET method is 10 m ² / g or more 300 m ²
/ G or less is desirable, and the ash content is low, and L
It is preferable that both c and La are 240 Å or more.

The particle shape may be scale-like, lump-like, or anisotropic. As the amorphous carbon material, carbon black is not limited in type and production history, and various types such as furnace black, channel black, thermal black, acetylene black, and Ketjen black can be applied. Preferable are those having a hollow shell structure such as Ketjen black or acetylene black having a developed structure structure. Most preferably, it is desirable to use a system in which the electrode density increases.

In the constitution of the positive electrode of the present invention, a mixture of carbon fiber, artificial graphite and carbon black is used as a conductive additive, and it is mixed with a positive electrode active material which is a lithium-containing transition metal oxide to form a binder. The positive electrode was produced in. With this configuration, the contact area between the positive electrode active material and the conductive additive is larger than in the conventional case, the resistance in the electrode is reduced, and the overvoltage during charging / discharging is reduced, so that the capacity characteristics are improved.

Furthermore, when granular carbon is simply mixed with the positive electrode active material as a conduction aid as in the conventional case, the expansion and contraction of the lattice of the positive electrode active material accompanying charge and discharge causes a gap between the positive electrode active material and the conduction aid. Peeling gradually progressed, there was a problem that charge and discharge to the positive electrode active material is not performed smoothly, when using the conductive additive of the present invention, the positive electrode active material and fibrous carbon,
Since the granular carbon coexists, the positive electrode active material and the conductive additive are kept in good contact with each other, so that a battery with less deterioration of the positive electrode due to cycling can be realized.

By the electrode using the conductive additive of the present invention,
Suppression of electrode collapse and improvement of electronic conductivity are realized, and cycle characteristics and output characteristics can be improved.

Comparative Example 1 First, a comparative example will be described. The positive electrode was manufactured as follows. Artificial graphite having an average particle size of 5 μm (8.7% by weight) as a conductive additive and lithium manganate having an average particle size of about 20 μm (87% by weight) which is a positive electrode active material.
PVDF (polyvinylidene fluoride) (4.3% by weight), which is a binder dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), is mixed with the mixture to form a paste.
Both sides were applied to an Al foil having a thickness of 20 μm and dried at 80 ° C. for 3 hours. Then, after press-molding at a pressure of about 2.0 ton / cm ² , it was heat-treated in vacuum at 120 ° C. for 3 hours to obtain a positive electrode. The density of the mixture layer of this positive electrode was about 3.0 g / cm ³ .

The negative electrode was manufactured by the following method. As a binder to artificial graphite, PVDF solution was added to carbon material as P
The mixture was mixed so that VDF was 10% by weight, and NMP was added to form a paste, which was applied on both surfaces of a copper foil current collector having a thickness of 23 μm and dried at 80 ° C. for 3 hours. After that, the mixture was roll-formed by a roll press until the mixture density became about 1.57 g / cm ^3, and then dried in vacuum at 120 ° C for 2 hours.

The positive electrode and the negative electrode were combined with a polyethylene porous membrane separator having a thickness of 25 μm, which was wound as shown in FIG. 1 and housed in a battery can having an outer dimension of 14 mm × 47 mm. 1M-LiPF ₆ / EC ₊ DMC as electrolyte
The characteristic was evaluated using (1: 1).

Similarly as the second and third comparative examples, a positive electrode was prepared by using acetylene black as the conductive additive, and the electrode density was 2.4 g / cm ³ . When Ketjen Black was used as the conductive additive, when the conductive additive was 8.7% by weight and the binder was 4.3%, peeling occurred due to drying after coating the electrode, making it impossible to manufacture the electrode. . Therefore, in Ketjen Black, the conductive additive was made 6 wt% and the binder was made 7 wt%. The other electrodes were treated in the same manner, and the electrode density of the obtained electrode was 2.6 g / cm ³ .

The obtained positive electrode was prepared under exactly the same conditions except that the positive electrode was removed, and the characteristics were evaluated as in the case where graphite was used as the conductive additive.

Example 1 A conductive auxiliary agent (8.7% by weight) in which various fibrous carbons and granular carbons were mixed and lithium manganate (87% by weight) as a positive electrode active material were added to N-methyl-2-. PVDF (polyvinylidene fluoride) (4.3% by weight), which is a binder dissolved in pyrrolidone (hereinafter abbreviated as NMP), is mixed to form a paste, which is then applied on both sides of an Al foil having a thickness of 20 μm, It was dried at 80 ° C. for 3 hours. After that, about 2 to
After pressure molding at a pressure of n / cm ² , heat treatment was performed in vacuum at 120 ° C. for 3 hours to obtain a positive electrode.

[0049]

[Table 1]

Table 1 shows the mixing ratio of carbon of these electrodes and the density of the mixture layer. Further, when a battery was prepared in the same manner as in Comparative Example 1 except for the positive electrode, the battery capacity and current density were 0.2C.
Then, when the charge / discharge test was performed in the voltage range of 4.2V to 3.5V, the discharge capacity maintenance ratio (discharge capacity in n cycles / initial discharge capacity) at 500 cycles, the discharge rate at 3 CmA, and the lower limit voltage 3 The discharge capacity retention ratio vs. 0.2 C (discharge capacity at 3 CmA / 0.2 CmA discharge capacity) when discharged to 0.5 V is also shown in Table 1 together with the comparative example. It can be seen that, by combining the fibrous carbon and the granular carbon with the conductive additive, the coatability at the time of producing the electrode is improved and the battery performance is also improved as compared with the comparative example.

(Example 2)

[0052]

[Table 2]

As a second embodiment, carbon black, acetylene black, which is amorphous carbon, and crystalline artificial graphite are mixed with granular carbon excluding fibrous carbon which is a conductive additive, and the respective ratios are changed. In Examples 2A to 2K, electrodes were prepared in the same manner as in Example 1. In Example 2L, an electrode was prepared under the same conditions as in Example 1 except that 90% by weight of the positive electrode active material, 6.7% of the conductive auxiliary agent and 3.3% by weight of the binder were mixed. . These granular carbons had a shape with an aspect ratio in the range of 1.0 to 5.0. The fibrous carbon was a mixture of fibers having a fiber diameter of 0.2 μm and an aspect ratio of 100 or more at a ratio of 20% by weight.

The carbon mixing ratio of these electrodes, the density of the mixture layer, the battery capacity when a battery was prepared in the same manner as in Comparative Example 1 except for the positive electrode, and the current density was 0.2 C and 4.2 V. ~ 3.5
The discharge capacity retention rate (discharge capacity in n cycles / initial discharge capacity) at 500 cycles when the charge / discharge test was performed in the voltage range of V, the discharge rate at 3 CmA to the lower limit voltage of 3.5 V vs. Table 2 shows the 0.2 C discharge capacity retention rate (discharge capacity at 3 CmA / 0.2 CmA discharge capacity).

In these examples, both the coating property and the adhesive property were good, the discharge capacity retention rate was as high as 80% or more, and the rate characteristics were 3C discharge, and a discharge capacity of 80% or more was obtained. The rate characteristics are improved and improved. In particular, it has been found that high performance is obtained when the ratio of amorphous carbon in the granular carbon is 10% to 40%.

It has been found that when carbon black is used as the granular carbon and artificial graphite having an average particle size of 1 μm is used to manufacture a battery, a battery having improved rate characteristics, capacity density and cycle characteristics can be obtained.

(Embodiment 3) Next, an embodiment of an apparatus using the lithium secondary battery according to the present invention will be described. As a built-in power supply for a portable personal computer, it has the same structure as the battery described in Example 2, and the outer dimension is 18 mm in diameter.
A × 65 mm cylindrical type single cell was produced, and an assembled battery was produced using this to prepare a battery pack. For comparison, a battery configuration similar to that shown in Comparative Example 1 was used with a diameter of 18 mm ×
A 65 mm cylindrical unit cell was prepared and a battery pack was prepared.

The battery pack to which the present invention was applied had a good rate characteristic, and it was possible to shorten the charging time by 50% as compared with Comparative Example 1. In addition, the capacity retention rate after 100 times of charge and discharge showed good characteristics of 99% or more. As described above, it was found that the portable personal computer incorporating the lithium secondary battery according to the present invention has a short waiting time for charging and the usability for the user is significantly improved. Also,
Even as a backup power supply, it can be used for a long time and the possibility of memory loss is avoided.

In this embodiment, a portable personal computer has been described as an example, but a radio, a compact disc player, a cassette recorder, a magneto-optical disc player, an MD player, a portable device which employs the lithium secondary battery according to the present invention as a power source. TV, mobile phone, pager, PHS, pocket computer,
Laptop personal computer, mobile terminal,
Electronic devices such as electronic notebooks, portable electric devices, shavers, and other portable devices, electronic devices used as backup power sources such as arithmetic units and storage devices containing lithium secondary batteries, communication devices such as facsimiles and cordless telephones, refrigerators, and air. Conditioners, rechargeable vacuum cleaners, household electronic / electric devices such as cordless irons, electric vehicles, motorcycles, bicycle golf carts with motors, electric wheelchairs,
Needless to say, even in the case of electric power storage equipment such as a motor-assisted bicycle and an outdoor emergency power source, the performance can be improved as compared with the conventional one, as in the present embodiment.

[0060]

As is clear from the above description, according to the present invention, the strength of the electrode and the conductivity in the electrode are increased and the mixture density of the electrode is improved to increase the filling rate of the active material. Easy to create. As a result, it is possible to realize a high-performance lithium secondary battery with high volume energy density, which has good discharge rate characteristics and further improved charge / discharge cycle characteristics.

In addition, any device or system that employs the lithium secondary battery according to the present invention has the effect of realizing lightweight, high performance, and stable operation. And miniaturization of devices and systems using the lithium secondary battery according to the present invention,
This has the effect of extending the service life.

[Brief description of drawings]

FIG. 1 is a perspective view showing an exploded configuration of a cylindrical lithium secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Positive electrode terminal, 2 ... Separator, 3 ... Negative electrode, 4 ... Positive electrode,
5 ... Negative electrode terminal.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ren Muranaka 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (56) Reference JP-A-8-138678 (JP, A) JP-A-9-27344 (JP, A) JP-A-8-222206 (JP, A) JP-A-7-296794 (JP, A) JP-A-2-262243 (JP, A) JP-A-7-211320 (JP, A) JP 4-289658 (JP, A) JP 4-345760 (JP, A) JP 11-3710 (JP, A) JP 10-312811 (JP, A) Kaihei 9-306502 (JP, A) JP-A-8-153539 (JP, A) International Publication 98/003710 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4 / 62 H01M 4/02 H01M 10/40

Claims (6)

(57) [Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution and utilizing a lithium ion insertion / elimination reaction, wherein the positive electrode mixture is a positive electrode active material, a conductive auxiliary agent, and a binder. The conductive auxiliary agent is a carbon material, and includes fibrous carbon and granular carbon, the granular carbon includes crystalline carbon and amorphous carbon, and the total amount of the conductive auxiliary agent is 100% by weight. %, The fibrous carbon content is 1 to 20% by weight, and the granular carbon content is 99 to
80% by weight, and the ratio of crystalline carbon and amorphous carbon in the granular carbon is 90 to 60% by weight when the granular carbon is 100% by weight, 10 to 40% by weight of the amorphous carbon
A lithium secondary battery, which is characterized in that 2. A portable electronic device, wherein the lithium secondary battery according to claim 1 is used as a power source of a portable device. 3. An electronic device using the lithium secondary battery according to claim 1 as a backup power source. 4. A household electronic / electrical device comprising the lithium secondary battery according to claim 1 as a power source. 5. A running electric motor comprising the lithium secondary battery according to claim 1 as a power source. 6. A power storage device using the lithium secondary battery according to claim 1 as a battery for power storage.