JP3406843B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having an improved negative electrode structure.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have been attracting attention as high energy density batteries, and manganese dioxide (MnO ₂ ) has been used as a positive electrode active material.
Fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl
₂ ) The primary batteries using these are already widely used as calculators, clock power supplies, and memory backup batteries.

Further, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, the demand for high energy density secondary batteries as their power source has increased, and lithium secondary batteries using lithium as a negative electrode active material. Batteries are being actively researched.

Lithium secondary batteries use lithium for the negative electrode and use propylene carbonate (PC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-) as an electrolyte.
BL), tetrahydrofuran (THF) or the like, a non-aqueous electrolyte solution or a lithium ion conductive solid electrolyte in which a lithium salt such as LiClO ₄ , LiBF ₄ , or LiAsF ₆ is dissolved in a non-aqueous solvent, and a positive electrode active material is mainly used. TiS ₂ ,
The use of compounds such as MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , and MnO ₂ that undergo a topochemical reaction with lithium has been studied.

However, the lithium secondary battery described above has not yet been put into practical use. The main reason for this is that the charging / discharging efficiency is low and the number of times charging / discharging is possible (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the negative electrode lithium and the non-aqueous electrolyte. That is, lithium that has been dissolved in the non-aqueous electrolyte as lithium ions during discharge reacts with the solvent during precipitation during charging, and its surface is partially inactivated. Therefore, when charging and discharging are repeated, lithium deposits in a dendrite-like (dendritic) or small spherical shape, and further lithium is desorbed from the current collector.

From the above, by using a carbonaceous material that absorbs and releases lithium, such as coke, a resin fired body, carbon fiber, and pyrolytic vapor phase carbon, as a negative electrode incorporated in a lithium secondary battery, It has been proposed to improve the reaction with the non-aqueous electrolyte and further the deterioration of the negative electrode characteristics due to the deposition of dendrites.

The negative electrode containing the carbonaceous material has a structure (graphite structure) in which hexagonal mesh plane layers mainly composed of carbon atoms are stacked in the carbonaceous material, and lithium ions are present between the layers. It is considered to charge and discharge by going in and out. Therefore, it is necessary to use a carbonaceous material having a graphite structure developed to some extent for the negative electrode of the lithium secondary battery. However, when a carbonaceous material obtained by pulverizing giant crystals having advanced graphitization is used as a negative electrode in a non-aqueous electrolytic solution, the non-aqueous electrolytic solution is decomposed, resulting in low battery capacity and charge / discharge efficiency. In particular, when the battery is operated at a high current density, the capacity, charging / discharging efficiency, and the voltage during discharging remarkably decrease. Further, as the charging / discharging cycle progresses, the crystal structure or the fine structure of the carbonaceous material collapses, the lithium storage / release capacity deteriorates, and the cycle life decreases.

Further, since the powder of the graphitized product is flaky, the c of the graphite crystallite in which lithium ions are inserted is used.
Since the area where the axial surface is exposed to the electrolytic solution becomes smaller, there is a problem that the capacity rapidly decreases in a high-rate charge / discharge cycle. Therefore, although improvement has been made by adding carbon black or the like, there is a problem that the negative electrode packing density is lowered. As a result, a high-capacity lithium secondary battery could not be realized with the conventional graphitized product.

Further, even in the case of carbon fiber having advanced graphitization, the non-aqueous electrolytic solution is decomposed when powdered, and the problem that the performance as the negative electrode is significantly lowered is the same as when the powder of giant crystals is used. Had a point.

On the other hand, in the case of carbonization products such as coke and carbon fiber having a low degree of graphitization, although the decomposition of the solvent can be suppressed to some extent, the capacity and charge / discharge efficiency are low, and the overvoltage of charge / discharge is large, and the discharge voltage of the battery is large. Has a low flatness and a low cycle life.

Previously disclosed in JP-A-62-168058, JP-A-2-824466, JP-A-4-61747, JP-A-4-115458, JP-A-4-184862, JP-A-4-190557 and the like. It has been proposed to control the graphitization degree of various carbonized materials and graphitized materials as described above and to optimize parameters of the graphite structure, but a negative electrode having sufficient characteristics has not been obtained. In addition, JP-A-4-79
No. 170 and JP-A-4-82172 disclose a carbon fiber used as a negative electrode, but the performance of a negative electrode using a carbonaceous material obtained by pulverizing the carbon fiber has a problem.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having high capacity and excellent battery characteristics such as charge / discharge efficiency, cycle life, discharge voltage flatness, and rapid charge / discharge cycle. It is a thing.

[0013]

A lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, and a non-aqueous electrolyte, The carbonaceous material has an X-ray diffraction odor
And the interplanar spacing d ₀₀₂ of the (002) plane of the graphite structure is 0.337.
Flake graphite showing a diffraction peak derived from 0 nm or less, and
Black consisting of at least one kind selected from flaky graphitized coke showing the above-mentioned diffraction peak in X-ray diffraction
The spacing between the lead compound powder and the (002) plane of the graphite structure d ₀₀₂
Is larger than the interplanar spacing d ₀₀₂ of the graphitized powder.
And the diffraction peak derived from the range of 0.340 nm or less
And a mesophase pitch-based carbon fiber, which shows the blackness in X-ray diffraction .

In the above mesophase pitch carbon fiber, it is preferable that the crystallite orientation in a cross section perpendicular to the fiber length direction is radial, lamellar or Brookstaylor type.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a lithium secondary battery (for example, a cylindrical lithium secondary battery) according to the present invention will be described in detail with reference to FIG. The bottomed cylindrical container 1 has an insulator 2 arranged at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3 includes a strip-shaped product obtained by stacking a positive electrode 4, a separator 5 and a negative electrode 6 in this order.
Has a structure in which it is spirally wound so that it is located outside.

An electrolytic solution is contained in the container 1. The insulating paper 7 having a central opening is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is
The sealing plate 8 is arranged in the upper opening of the container 1 and the vicinity of the upper opening is caulked inward.
Is liquid-tightly fixed to the container 1. The positive electrode terminal 9 is
It is fitted in the center of the insulating sealing plate 8. Positive electrode lead
One end of the battery 10 is connected to the positive electrode 4 and the other end is connected to the positive electrode terminal 9
Respectively connected to. The negative electrode 6 is connected to the container 1, which is a negative electrode terminal, via a negative electrode lead (not shown).

The container 1 is made of, for example, stainless steel. The positive electrode 4 is prepared by suspending a conductive agent and a binder in a positive electrode active material in an appropriate solvent, applying the suspension to a current collector, and drying the suspension to form a thin plate.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Examples thereof include lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium cobalt oxide (LiCoO
₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ , LiMnO ₂ )
Is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
E), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and the like can be used.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is 80 to 95% by weight of the positive electrode active material and the conductive agent 3 to 2.
It is preferable that the content is 0% by weight and the binder is 2 to 7% by weight.

As the current collector, for example, aluminum foil, stainless foil, nickel foil or the like can be used. As the separator 5, for example, a synthetic resin non-woven fabric, a polyethylene porous film, a polypropylene porous film, or the like can be used.

The negative electrode 6 contains the carbonaceous material described in (1) to (4) below. However, La, d ₀₀₂ , Lc and intensity ratio (P ₁₀₁ / P ₁₀₀ ) for determining carbonaceous matter
The measurement and definition of are as follows.

(A) For all data measured by the X-ray diffraction method, CuKα was used as the X-ray source, and high-purity silicon was used as the standard substance. La, d ₀₀₂ , and Lc were obtained from the position of each diffraction peak and the full width at half maximum. The half-width half-point method was used as the calculation method.

(B) The crystallite length La in the a-axis direction and the crystallite length Lc in the c-axis direction are values when K, which is the form factor of Scherrer's equation, is 0.89. (C) Intensity ratio (P ₁₀₁ / P of (101) diffraction peak P ₁₀₁ and (100) diffraction peak P ₁₀₀ by X-ray diffraction method
₁₀₀ ) is obtained from the height ratio of those peaks.

(1) Carbonaceous Material This carbonaceous material has a graphite structure of (00
2) The interplanar spacing d ₀₀₂ is in the range of 0.335 to 0.336 nm, and the (101) diffraction peaks P ₁₀₁ and (100)
The peak intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the diffraction peak P ₁₀₀ exceeds 2.2, and the ratio of the crystallite length La in the a-axis direction to the crystallite length Lc in the c-axis direction (La / Lc) Is less than 1.5.

The carbonaceous material has an average interplanar spacing d ₀₀₂ of (002) planes obtained by X-ray diffractometry of 0.335 to 0.
336 nm. In such a carbonaceous material, the number of sites into which lithium ions can be inserted increases, and the capacity increases.
However, a carbonaceous material having an average interplanar spacing that deviates from the above range has a low capacity and a low flatness of voltage when the battery is discharged.

The carbonaceous material having a strength ratio (P ₁₀₁ / P ₁₀₀ ) of more than 2.2 has a very developed graphite structure. Such a graphite structure has few deviations, twists, and angles between the stacked hexagonal mesh plane layers. Since this has the characteristics of conventional natural graphite, the capacity decreases under high-rate charge / discharge conditions. Therefore, by setting the ratio (La / Lc) of the crystallite length La in the a-axis direction to the crystallite length Lc in the C-axis direction by the X-ray diffraction method to be less than 1.5, the high rate It was possible to obtain a graphitized product that avoids a decrease in capacity under charge and discharge conditions. That is, by making the La shorter and the Lc longer than in the conventional graphite, it is possible to smoothly carry out the insertion / desorption reaction of lithium ions, and it becomes possible to overcome the problems of the layer structure. A high capacity can be obtained under the charge and discharge conditions.

In the carbonaceous material, the crystallite length La in the a-axis direction of the graphite structure according to the diffraction peak of the (110) plane obtained by X-axis diffraction is 20 to 100 nm, more preferably 40 to 80 nm. desirable. Further, the shape of the a-axis surface in the graphite structure of the carbonaceous material is preferably rectangular.

The carbonaceous material having La in the above range is
Since the graphite structure is moderately developed and the length of the crystallite in the a-axis direction is moderate, lithium ions easily diffuse between the layers of the hexagonal network plane layer, and the site where lithium ions come in and out It has the property of increasing the number of lithium ions and storing and releasing more lithium ions.

The carbonaceous material in which La exceeds 100 nm becomes a huge crystal, and it becomes difficult for lithium ions to diffuse between the layers of the hexagonal mesh plane layer, and it becomes difficult to secure the amount of occlusion / release of lithium ions. Further, the surface thereof is active with respect to the non-aqueous solvent, and the solvent is easily reductively decomposed. On the other hand, since the carbonaceous matter having La of less than 20 nm is mixed with a large amount of carbonaceous matter having an undeveloped graphite structure, it is possible to reduce reversible occlusion / release of lithium ions between the hexagonal mesh plane layers. There is a risk of becoming.

The carbonaceous material preferably has a crystallite size Lc in the c-axis direction obtained by X-ray diffractometry of 15 nm or more, more preferably 20 to 100 nm. The carbonaceous material having Lc in such a range has a property that the graphite structure is appropriately developed and a large amount of lithium ions are reversibly stored and released.

As a measure of the ratio of the graphite structure and the turbostratic structure constituting the carbonaceous material, an argon laser (wavelength 51
There is a Raman spectrum of the carbonaceous material measured by using (4.5 nm) as a light source. In the Raman spectrum measured for the carbonaceous material, there are a peak derived from a turbostratic structure appearing in the vicinity of 1360 cm ⁻¹ and a peak originating in the graphite structure appearing in the vicinity of 1580 cm ⁻¹ . The peak intensity ratio, i.e. the argon laser Raman spectrum peak intensity 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in (wavelength 514.5 nm) (R2) (R
It is preferable to use a carbonaceous material having a ratio (R1 / R2) of 1) of 0.2 or less.

The carbonaceous material preferably has a true density of 2.20 g / cm ³ or more, which is a measure of the degree of graphitization. The carbonaceous material has a particle size distribution of 90% by volume or more in a range of 1 to 100 μm and an average particle size of 1 to 80 μm.
It is preferably m. Also, BET for N ₂ gas adsorption
The specific surface area according to the method is preferably 0.1 to 40 m ² / g. The carbonaceous material having such a particle size distribution and specific surface area can improve the packing density of the negative electrode, and at the same time reduce the content of the carbonaceous material or the amorphous carbon in which the graphite crystal structure which is active to the non-aqueous solvent is broken, The reductive decomposition of the non-aqueous solvent can be suppressed. Furthermore, a carbonaceous material containing fine particles having a particle diameter of 0.5 μm or less in an amount distribution of 5% by volume or less further reduces carbonaceous material in which the graphite crystal structure is broken or amorphous carbon, and effectively reduces reductive decomposition of a non-aqueous solvent. It becomes possible to suppress. Conversely, the particle size distribution and N ₂
If the specific surface area of the gas adsorption by the BET method becomes too large, the content of amorphous carbonaceous material and the content of carbonaceous material in which the graphite crystal structure is collapsed increase, and the reductive decomposition of the solvent easily occurs. Moreover, the packing density of the negative electrode Is reduced.

The carbonaceous material has a sulfur content of 1000 pp.
It is preferably m or less (including 0 ppm). Such a carbonaceous material having a low sulfur content increases the amount of occlusion / release of lithium ions and reduces the reductive decomposition of the non-aqueous solvent.

In a carbonaceous material in which the graphite structure is developed to some extent, the sulfur content is 1000 ppm or less (0 ppm
(Including), there are few defects in the graphite structure,
As a result, the collapse of the graphite structure is unlikely to occur, and moreover the amount of occlusion / release of lithium ions increases.
Therefore, the capacity, charge / discharge efficiency, and cycle life of the lithium secondary battery can be improved. Further, it is considered that the decomposition of the non-aqueous solvent and the inhibition of the electrode reaction due to the reaction between the non-aqueous solvent and the lithium ion and sulfur or the sulfur compound are reduced, and the charge / discharge efficiency and the cycle life can be improved. That is, when sulfur in the carbonaceous material reacts with lithium ions, stable groups such as LiS- and LiS-
And other compounds. It is considered that the lithium does not contribute to the reversible occlusion / release reaction. In addition, the resulting compound becomes an obstacle between hexagonal network plane layers,
It is believed to prevent smooth insertion. These factors reduce charge / discharge efficiency and cycle life.

It is preferable that oxygen, nitrogen, silicon, or metal elements such as Fe and Ni as other impurities in the carbonaceous material are as small as possible. Specifically, the oxygen content is 500 ppm or less, and the nitrogen content is 10 ppm.
It is preferable that the amount of each metal element such as Fe and Ni is 50 ppm or less and that of each metal element is 50 ppm or less. If the amount of these impurity elements exceeds the above range, lithium ions existing between carbon layers may react with the impurity elements and be consumed. However, the inclusion of aluminum, boron, phosphorus, calcium, tin, etc. is allowed.

An example of the method for producing the carbonaceous material will be described below. First, a short fiber having a fiber length of 200 to 300 μm is spun by a melt blowing method using mesophase pitch as a raw material, and then carbonized to an extent that it can be infusibilized and pulverized. The heat treatment for carbonization is desirably performed at 600 to 2000 ° C, preferably 800 to 1500 ° C. The carbonized mesophase pitch carbon fiber has a (002) plane spacing d ₀₀₂ of 0.344 nm or more according to an X-ray diffraction method,
More preferably, it is 0.357 nm or more. Such a carbon fiber has a fine structure suitable for shortening the fiber length, and thus is suitable for pulverization. On the other hand, when the carbon fibers having the interplanar spacing d ₀₀₂ of less than 0.344 nm are crushed, vertical cracks occur and it becomes difficult to shorten the fiber length. Subsequently, the carbonized and crushed carbon fiber is 2000 ° C. or higher, more preferably 2500.
The above-mentioned carbonaceous material is manufactured by graphitizing at ~ 3200 ° C. At this time, the crushing and firing steps are extremely important, and at the time of crushing, a ball mill, a jet mill or the like is used for crushing for an appropriate time (within 20 hours) to obtain spherical particles,
It is preferable to graphitize a granular, block-shaped, or columnar material. In addition, it is necessary to prevent the crystal structure of the graphitized product from having a rhombohedral crystal system of 30% or more. This is because the hexagonal graphite structure is destroyed by crushing,
This is because a rhombohedral structure is formed, but it is preferably adjusted to 0 to 30% by volume by appropriately pulverizing. If it exceeds this range, the electrolytic solution is decomposed and the negative electrode performance is deteriorated.

The La of the carbonaceous material produced by the above method
The ratio of Lc to Lc and the crystal structure can be controlled by defining the crushing conditions (crushing time, atmosphere, crushing force).

When the carbonaceous material is produced by the above method, it is desirable that the particle size distribution and the specific surface area of the obtained carbonaceous material have the above-mentioned values. In addition to the carbonaceous material obtained by the above-mentioned method, the carbonaceous material can be obtained, for example, by graphitizing coke or bulk mesophase obtained from low-sulfur petroleum pitch, coal tar, etc. at 2500 to 3200 ° C.

In the carbonaceous material, the ratio of the rhombohedral system to the hexagonal system can be defined such that the ratio of (101) diffraction peaks by X-ray diffraction method is 0.6 or less. A carbonaceous material having a rhombohedral structure with such a ratio can increase the negative electrode charge / discharge efficiency.

(2) Carbonaceous Material This carbonaceous material has a graphite structure of (00
Plane spacing d ₀₀₂ of 2) plane is from below 0.340nm
The diffraction peak and the interplanar spacing d ₀₀₂ are 0.344 to 0.37.
It is a powder in which a diffraction peak derived from the range of 0 nm appears.

The carbonaceous material has a surface spacing d of the (002) plane.
₀₀₂ is a diffraction peak derived from the range of 0.340 nm or less
A huge graphite crystal (thickness La in the a-axis direction is 20 nm)
Diffraction peak derived from the graphitized product and the (002) plane spacing d ₀₀₂ of 0.344 to 0.370 nm.
Since it is made of a carbonized product having a small graphite crystal (Lc of 6 nm or less) exhibiting a crack, it is possible to maintain a high capacity with little cycle deterioration even during rapid charging. Carbonized product the latter (002) diffraction peak derived from a range of from 0.356 to 0.370 nm is more preferable.

Conventionally, the negative electrode made of the above graphitized product exhibits a large cycle deterioration and a small capacity in the rapid charge, which shows a diffraction peak derived from the range of the (002) plane spacing d ₀₀₂ of 0.340 nm or less. Become. Also on the (002) plane
Why the plane spacing d ₀₀₂ is in the range of 0.344~0.370nm
The carbonaceous material showing an upcoming diffraction peak has a true density of 1.
Since it is 70 to 2.15 / cm ^3, it is smaller than the above graphitized product, and the capacity per unit volume of the negative electrode (mAh / c
m ³ ) has a problem that it becomes small.

In order to solve such a problem, the carbonaceous material constituting the negative electrode of the present invention has both the graphitized material and the carbonized material having the above-mentioned characteristics, whereby the rapid charging characteristics and the capacity are significantly improved. It has become possible. This is because when the rapid charge at a constant current ( ² mA / cm ² or more) , the surface spacing d ₀₀₂ of the (002) plane is 0.344 to 0.
Lithium ions are selectively inserted into a graphite crystal showing a diffraction peak derived from a range of 370 nm. At this time, the diffusion rate of lithium ions is much faster than that of the graphitized product showing a diffraction peak derived from the (002) plane spacing d ₀₀₂ of 0.340 nm or less , so that rapid charging is possible. When the rapid charging progresses further, the charging end voltage is reached, and when switching to constant voltage charging at that voltage , the (002) plane is mainly used.
Diffraction peak derived from an interval d ₀₀₂ of 0.340 nm or less
Lithium ions are selectively inserted into the graphite crystal showing the above at a slow rate. By such a selective insertion reaction of lithium ions, rapid charging is possible and high capacity can be maintained.

Examples of the carbonaceous material include X-ray diffraction
Plane spacing d ₀₀₂ of (002) plane of Oite graphite structure is 0.3
Diffraction peaks derived from 40 nm or less and 0.344 to 0.
Multiphase graphite product and diffraction peak appears to be derived from a range of 370nm or (002) plane face spacing d ₀₀₂ of 0.3
Graphite showing a diffraction peak derived from 40 nm or less and the interplanar spacing d ₀₀₂ between the (002) plane are 0.344 nm to 0.3
An example is a mixture of carbonized products showing a diffraction peak originating in the range of 70 nm.

Examples of the multi-phase graphitized product include polyvinylidene chloride, phenol resin, furfural resin, charcoal, anthracite, sugar and pitch under normal pressure or high pressure.
It is obtained by carrying out non-uniform graphitization at a temperature of 500 to 3000 ° C. to carry out multiphase graphitization. By non-uniformly graphitizing in this way, the surface spacing d ₀₀₂ of the (002) plane is
Shows a diffraction peak derived from 0.340 nm or less and the interplanar spacing d ₀₀₂ between the (002) plane and the graphitized phase is 0.34.
It is possible to obtain a coexisting phase with a low blackening phase which exhibits a diffraction peak derived from 4 nm to 0.370 nm.

Examples of the graphitized product which is one of the components of the mixture include powders of graphite, anisotropic pitch carbon fiber, spherical carbon, pyrolytic vapor grown carbon body, coke and the like. The graphitized product has a specific surface area of 0.5 to 10
Graphite in the range of m ² / g, powder of mesophase pitch carbon fiber, and mesophase spherules are more preferable.

Examples of the carbonized material which is the other component of the mixture include coke having a low sulfur content (2000 ppm or less) and low nitrogen content (1000 pmm or less), high purity anisotropic pitch carbon fiber, spherical carbon, heat Powders such as decomposed vapor grown carbon bodies and resin fired bodies are mentioned. The carbonized product is a powder of carbon fiber made of synthetic pitch (such as naphthalene) having a specific surface area of ² to 30 m ² / g, a powder of high-purity mesophase pitch-based carbon fiber, mesophase microspheres, and a low sulfur content. Is more preferred. Since any of the carbonized products has a firing temperature in the range of 600 to 1200 ° C., it is important to reduce impurities such as sulfur and transition metals (iron, nickel) in the carbonized products. Therefore, it is necessary to select petroleum pitch, mesophase pitch, or coal tar that has a small amount of impurities as the raw material.

(3) Carbonaceous Material This carbonaceous material is a graphitized product mainly having a block shape, a fibrous shape or a spherical shape, and the interplanar spacing d ₀₀₂ of the (002) plane of the graphite structure by the X-ray diffraction method is 0. 335 to 0.337
the (101) diffraction peak P ₁₀₁ and (1
00) Peak intensity ratio of diffraction peak P ₁₀₀ (P ₁₀₁ / P
₁₀₀ ) has a property exceeding 2.2.

The carbonaceous material has an average interplanar spacing d ₀₀₂ of (002) planes of 0.335 to 0.
337 nm. In such a carbonaceous material, the number of sites into which lithium ions can be inserted increases, and the capacity increases.
However, a carbonaceous material having an average interplanar spacing that deviates from the above range has a low capacity and a low flatness of voltage when the battery is discharged.

The carbonaceous material having a strength ratio (P ₁₀₁ / P ₁₀₀ ) of more than 2.2 has a very developed graphite structure. Such a graphite structure has few deviations, twists, and angles between the stacked hexagonal mesh plane layers. Since this has the characteristics of conventional natural graphite, there is a possibility that the capacity may decrease under high-rate charge / discharge conditions. Therefore, the X
The ratio (La / Lc) of the crystallite length La in the a-axis direction to the crystallite length Lc in the C-axis direction by the line diffraction method is preferably less than 1.5. By defining La / Lc in this way, it is possible to obtain a graphitized product that avoids a decrease in capacity under the high-rate charge / discharge conditions. That is,
By making the La shorter and the Lc longer than in conventional graphite, it is possible to smoothly carry out the insertion / desorption reaction of lithium ions, and it becomes possible to overcome the problems of the layered structure and to satisfy the high rate. High capacity can be obtained under discharge conditions.

The carbonaceous material has a block shape,
It has a fibrous or spherical shape. Here, the block shape is a grain shape other than a flaky shape and has a ratio of major axis to minor axis (major axis / minor axis) of 5
The following means that it is more preferably 2 or less. The term “fibrous” means the ratio of fiber length to fiber diameter (fiber length / fiber diameter)
Is in the range of 0.5 to 10, and the crystallite orientation is preferably radial, lamellar or Brookstellar in a cross section perpendicular to the fiber length direction. The spherical shape is a sphere having a ratio of major axis to minor axis (major axis / minor axis) in the range of 1 to 2, and crystallite orientation is preferably radial, lamellar or brook stella type in its cross section.
Such a carbonaceous material having a block shape, a fibrous shape, or a spherical shape can increase the exposed area in the c-axis direction, so that a high-capacity secondary battery can be obtained under high-rate charge / discharge conditions. . In particular, a carbonaceous material having a fibrous or spherical shape in which the crystallite orientation is radial, lamellar, or Brooks-Stella type can further increase the exposed area in the c-axis direction, and the insertion / desorption reaction of lithium ions can be performed. It becomes possible to carry out smoothly.

In the carbonaceous material, the crystallite length La in the a-axis direction of the graphite structure according to the diffraction peak of the (110) plane obtained by the X-ray diffraction method is 20 to 100 nm, more preferably 40 to 80 nm. Is desirable. Further, the shape of the a-axis surface in the graphite structure of the carbonaceous material is preferably rectangular.

The carbonaceous material in which La is within the above range is
Since the graphite structure is moderately developed and the length of the crystallite in the a-axis direction is moderate, lithium ions easily diffuse between the layers of the hexagonal network plane layer, and the site where lithium ions come in and out It has the property of increasing the number of lithium ions and storing and releasing more lithium ions.

The carbonaceous material in which La exceeds 100 nm becomes a huge crystal, and it becomes difficult for lithium ions to diffuse into the layers of the hexagonal net surface layer, and it becomes difficult to secure the amount of occlusion / release of lithium ions. Further, the surface thereof is active with respect to the non-aqueous solvent, and the solvent is easily reductively decomposed. On the other hand, since the carbonaceous matter having La of less than 20 nm is mixed with a large amount of carbonaceous matter having an undeveloped graphite structure, it is possible to reduce reversible occlusion / release of lithium ions between the hexagonal mesh plane layers. There is a risk of becoming.

In the carbonaceous material, the crystallite size Lc in the c-axis direction obtained by X-ray diffractometry is preferably 15 nm or more, and more preferably 25 to 200 nm. The carbonaceous material having Lc in such a range has a property that the graphite structure is appropriately developed and a large amount of lithium ions are reversibly stored and released.

As a measure of the ratio of the graphite structure and the turbostratic structure constituting the carbonaceous material, an argon laser (wavelength 51
There is a Raman spectrum of the carbonaceous material measured by using (4.5 nm) as a light source. In the Raman spectrum measured for the carbonaceous material, there are a peak derived from a turbostratic structure appearing in the vicinity of 1360 cm ⁻¹ and a peak originating in the graphite structure appearing in the vicinity of 1580 cm ⁻¹ . The peak intensity ratio, i.e. the argon laser Raman spectrum peak intensity 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in (wavelength 514.5 nm) (R2) (R
It is preferable to use a carbonaceous material having a ratio (R1 / R2) of 1) of 0.2 or less.

The carbonaceous material preferably has a true density of 2.20 g / cm ³ or more, which is a measure of the degree of graphitization. The carbonaceous material has a particle size distribution of 90% by volume or more in a range of 1 to 100 μm and an average particle size of 1 to 80 μm.
It is preferably m. Also, BET for N ₂ gas adsorption
The specific surface area according to the method is preferably 0.1 to 10 m ² / g. The carbonaceous material having such a particle size distribution and specific surface area can improve the packing density of the negative electrode, and at the same time reduce the content of the carbonaceous material or the amorphous carbon in which the graphite crystal structure which is active to the non-aqueous solvent is broken, The reductive decomposition of the non-aqueous solvent can be suppressed. Furthermore, a carbonaceous material containing fine particles having a particle diameter of 0.5 μm or less in an amount distribution of 5% by volume or less further reduces carbonaceous material in which the graphite crystal structure is broken or amorphous carbon, and effectively reduces reductive decomposition of a non-aqueous solvent. It becomes possible to suppress. Conversely, the particle size distribution and N ₂
If the specific surface area of the gas adsorption by the BET method becomes too large, the content of amorphous carbonaceous material and the content of carbonaceous material in which the graphite crystal structure is collapsed increase, and the reductive decomposition of the solvent easily occurs. Moreover, the packing density of the negative electrode Is reduced.

The carbonaceous material has a sulfur content of 1000 pp.
It is preferably m or less (including 0 ppm). Such a carbonaceous material having a low sulfur content increases the amount of occlusion / release of lithium ions and reduces the reductive decomposition of the non-aqueous solvent.

In a carbonaceous material in which the graphite structure is developed to some extent, the sulfur content is 1000 ppm or less (0 ppm
(Including), there are few defects in the graphite structure,
As a result, the collapse of the graphite structure is unlikely to occur, and moreover the amount of occlusion / release of lithium ions increases.
Therefore, the capacity, charge / discharge efficiency, and cycle life of the lithium secondary battery can be improved. Further, it is considered that the decomposition of the non-aqueous solvent and the inhibition of the electrode reaction due to the reaction between the non-aqueous solvent and the lithium ion and sulfur or the sulfur compound are reduced, and the charge / discharge efficiency and the cycle life can be improved. That is, when sulfur in the carbonaceous material reacts with lithium ions, stable groups such as LiS- and LiS-
And other compounds. It is considered that the lithium does not contribute to the reversible occlusion / release reaction. In addition, the resulting compound becomes an obstacle between hexagonal network plane layers,
It is believed to prevent smooth insertion. These factors reduce charge / discharge efficiency and cycle life.

As the other impurities in the carbonaceous material, oxygen, nitrogen, silicon, or metal elements such as Fe and Ni are preferably contained as little as possible. Specifically, the oxygen content is 500 ppm or less, and the nitrogen content is 10 ppm.
It is preferable that the amount of each metal element such as Fe and Ni is 50 ppm or less and that of each metal element is 50 ppm or less. If the amount of these impurity elements exceeds the above range, lithium ions existing between carbon layers may react with the impurity elements and be consumed. However, the inclusion of aluminum, boron, phosphorus, calcium, tin, etc. is allowed.

An example of the method for producing the carbonaceous material will be described below. First, a short fiber having a fiber length of 200 to 300 μm is spun by a melt blowing method using mesophase pitch as a raw material, and then carbonized to an extent that it can be infusibilized and pulverized. The infusibilization condition at this time has a great influence on the graphitization described later, and it is desirable that the infusibilization is slow. The heat treatment for carbonization is 600 to 2000 ° C., preferably 800 to 15 ° C.
It is desirable to carry out at 00 ° C. Plane spacing d ₀₀₂ of (002) plane measured by X-ray diffraction of the mesophase pitch carbon fibers the carbonization, or 0.344 nm, it is preferable and more preferably not less than 0.357Nm. Such a carbon fiber has a fine structure suitable for shortening the fiber length, and thus is suitable for pulverization. On the other hand, when the carbon fibers having the interplanar spacing d ₀₀₂ of less than 0.344 nm are crushed, vertical cracks occur and it becomes difficult to shorten the fiber length. Subsequently, the carbon fiber subjected to the carbonization and pulverization treatment is 2000 ° C. or higher, more preferably 2500 to 3200.
The above-mentioned carbonaceous material is manufactured by graphitizing at ℃. At this time, the crushing and firing steps are extremely important,
At the time of pulverization, it is necessary to pulverize a spherical, block-shaped or fibrous substance by pulverizing for a suitable time (within 20 hours) using a ball mill, jet mill or the like.
Further, it may be a mixture containing at least two kinds of graphitized products of spherical, block-like and fibrous. In addition, it is necessary to prevent the crystal structure of the graphitized product from having a rhombohedral crystal system of 30% or more. This is because the hexagonal graphite structure is broken by pulverization and a rhombohedral structure is formed, but it is preferably adjusted to 0 to 30% by volume by appropriate pulverization. If it exceeds this range, the electrolytic solution is decomposed and the negative electrode performance is deteriorated.

The La of the carbonaceous material produced by the above method
The ratio of Lc to Lc and the crystal structure can be controlled by defining the crushing conditions (crushing time, atmosphere, crushing force).

When the carbonaceous material is produced by the above method, it is desirable that the particle size distribution and the specific surface area of the obtained carbonaceous material have the above-mentioned values. In addition to the carbonaceous material obtained by the above-described method, for example, coke, mesophase spherules, or bulk mesophase obtained from low-sulfur petroleum pitch, coal tar, etc.
It can be obtained by graphitizing at 500 to 3200 ° C.

The ratio of the rhombohedral crystal system to the hexagonal system of the carbonaceous material can be specified such that the ratio of (101) diffraction peaks by X-ray diffraction method is 0.6 or less. A carbonaceous material having a rhombohedral structure with such a ratio can increase the negative electrode charge / discharge efficiency.

[0066] (4) carbonaceous material this carbonaceous material, the graphite structure in X-ray diffraction (00
2) The surface spacing d ₀₀₂ is 0.3370 nm or less .
Graphite showing a diffraction peak and graphite in X-ray diffraction
The interplanar spacing d ₀₀₂ of the (002) plane of the structure is 0.3370 nm
Diffraction peaks originating in the range of 0.340 nm or less
It is composed of a graphitized material showing a black mark .

The carbonaceous material has a surface spacing d of the (002) plane.
Diffraction peak derived from _{002 in} the range of 0.3370 nm or less
A huge graphite crystal with a thickness of 40 n in the a-axis direction.
m or more) and the interplanar spacing d ₀₀₂ between the (002) plane
Is over 0.3370 nm and below 0.340 nm
Since it is composed of a graphitized product having a relatively small size (La is 40 nm or less) of a graphite crystal exhibiting a diffraction peak derived from, it is possible to maintain a high capacity with little cycle deterioration even in rapid charging. The latter graphitized product is (00
2) The diffraction peak is preferably derived from the range of 0.3370 to 0.3380 nm.

The surface spacing d ₀₀₂ of the (002) plane is 0.337.
The negative electrode made of the above-mentioned graphitized product showing a diffraction peak derived from a range of 0 nm or less has large cycle deterioration and a small capacity in rapid charging. Also, the surface spacing of the (002) plane
The negative electrode made of a graphitized product having a d _{002 of more} than 0.3370 nm and a diffraction peak derived from the range of 0.340 nm has a problem that the capacity is 200 to 280 mAh / cm ³ and the capacity is smaller than that of the graphitized product. ing.

In order to solve such a problem, the carbonaceous material constituting the negative electrode of the present invention has two types of graphitized products having the above characteristics, whereby the rapid charging characteristics and the capacity can be significantly improved. It has become possible. This rapid charging (2 mA / cm ² or higher) of the constant current sometimes mainly, (0
02) surface spacing d ₀₀₂ exceeds 0.3370 nm,
Lithium ions are selectively inserted into a graphite crystal that exhibits a diffraction peak derived from a range of 0.340 nm or less. At this time, the diffusion rate of lithium ions is the interplanar spacing of the (002) plane
d ₀₀₂ has a diffraction peak derived from 0.3370 nm or less
Since it is much faster than the graphitized product shown, rapid charging is possible. When the rapid charging progresses further, the charging end voltage is reached,
When switching to constant voltage charging at that voltage , (00
2) The surface spacing d ₀₀₂ is 0.3370 nm or less .
Lithium ions are selectively inserted into the graphite crystal exhibiting a diffraction peak at a slow rate. By such a selective insertion reaction of lithium ions, rapid charging is possible and high capacity can be maintained.

Examples of the carbonaceous material include X-ray diffraction
Plane spacing d ₀₀₂ of (002) plane of Oite graphite structure is 0.3
Graphite showing a diffraction peak derived from 370 nm or less and a range of more than 0.3370 nm and 0.340 nm or less
Ru multiphase graphite product name and a graphite product having a diffraction peak derived from or (002) plane face spacing d ₀₀₂ of, 0.337
Graphitized products showing a diffraction peak derived from 0 nm or less and (0
02) surface spacing d ₀₀₂ exceeds 0.3370 nm,
An example is a mixture of graphitized products showing a diffraction peak derived from a range of 0.340 nm or less.

Examples of the multi-phase graphitized product include polyvinylidene chloride, phenol resin, furfural resin, charcoal, anthracite, sugar, pitch, etc. under normal pressure or high pressure.
It is obtained by carrying out non-uniform graphitization at a temperature of 500 to 3000 ° C. to carry out multiphase graphitization. By non-uniformly graphitizing in this manner, the interplanar spacing d ₀₀₂ of the (002) plane is d _002.
Shows a diffraction peak derived from 0.3370 nm or less and the interplanar spacing d ₀₀₂ between the phase with advanced blackening and the (002) plane is 0.3.
Derived from the range of more than 370 nm and less than 0.340 nm
It is possible to obtain a coexistence of a low graphitization phase showing a diffraction peak .

One component of the mixture (002)
Number of times when the surface spacing d ₀₀₂ is 0.3370 nm or less
Examples of the graphitized product exhibiting a folding peak include graphite and 230
Anisotropic pitch-based carbon fiber graphitized at 0 to 3200 ° C,
Examples of the powder include spherical carbon, pyrolytic vapor grown carbon body, and coke powder. The graphitized product has a specific surface area of 2-1.
Graphite, mesophase pitch carbon fiber powder, and mesophase spherules having an average particle diameter of 0 m ² / g and in the range of 1 to 30 μm are more preferable.

The other component of the mixture (002)
The surface spacing d ₀₀₂ exceeds 0.3370 nm and is 0.34
As the graphitized product showing a diffraction peak derived from a range of 0 nm or less, for example, a low sulfur content (2000 ppm or less),
Examples thereof include coke having a low nitrogen content (1000 pmm or less), high-purity anisotropic pitch-based carbon fiber, spherical carbon, pyrolytic vapor-deposited carbon body, and powdered resin. The graphitized product contains carbon fiber powder made of synthetic pitch (such as naphthalene) having a specific surface area in the range of 1 to 10 m ² / g, high-purity mesophase pitch carbon fiber powder, mesophase microspheres, and low sulfur content. Is more preferred. The above graphitized materials are obtained by using 2300 to 3 of the above raw materials.
It is obtained by firing at a temperature in the range of 000 ° C.

The surface spacing d ₀₀₂ of the (002) plane is 0.3.
The mixing weight ratio of the graphitized product showing a diffraction peak derived from 370 nm or less is preferably 5 to 30% by weight. If the mixing weight ratio exceeds 30% by weight, the rate characteristics may deteriorate. On the other hand, if the mixing weight ratio is 5
If it is less than wt%, the battery capacity may decrease.

The negative electrode 6 containing the carbonaceous material described in (1) to (4) above is specifically manufactured by the following method. The binder is suspended in a suitable solvent in the carbonaceous material, and the suspension is applied to a current collector and dried to form a thin plate, thereby producing the positive electrode.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The mixing ratio of the carbonaceous material and the binder is
The carbon material is preferably in the range of 90 to 98% by weight and the binder in the range of 2 to 10% by weight. Particularly, the carbonaceous material is preferably in the range of 5 to ²⁰ mg / cm ² in the state where the negative electrode 6 is manufactured.

As the current collector, for example, copper foil, stainless foil, nickel foil or the like can be used. The non-aqueous electrolytic solution contained in the container 1 is prepared by dissolving an electrolyte in a non-aqueous solvent.

The non-aqueous solvent may be a non-aqueous solvent known as a solvent for lithium secondary batteries, and is not particularly limited, but it has a lower melting point than ethylene carbonate (EC) and the above-mentioned ethylene carbonate, and a donor. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with one or more non-aqueous solvents having a number of 18 or less (hereinafter referred to as a second solvent). Such a non-aqueous solvent has the advantages that it is stable with respect to the carbonaceous material with a developed graphite structure that constitutes the negative electrode, that reductive decomposition or oxidative decomposition of the electrolytic solution does not easily occur, and that it has high conductivity.

The non-aqueous electrolytic solution containing only ethylene carbonate has an advantage that it is difficult to undergo reductive decomposition with respect to the graphitized carbonaceous material, but has a high melting point (39 ° C. to 40 ° C.).
(° C) High viscosity makes it unsuitable for secondary batteries operating at room temperature because of its low electrical conductivity. The second solvent mixed with ethylene carbonate makes the mixed solvent have a lower viscosity than the ethylene carbonate and improves the conductivity. Further, by using a second solvent having a donor number of 18 or less (however, the donor number of ethylene carbonate is 16.4), it becomes difficult for the ethylene carbonate to be selectively solvated with lithium ions, and a graphite structure is developed. It is considered that the reduction reaction of the second solvent with respect to the carbonaceous material is suppressed. Further, by setting the number of donors of the second solvent to 18 or less, the oxidative decomposition potential becomes 4 relative to the lithium electrode.
It also has an advantage that a lithium secondary battery having a high voltage is easily realized and a high voltage can be realized.

Examples of the second type solvent include dimethyl carbonate (DMC) and diethyl carbonate (D
EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene or methyl acetate (MA). These second solvents are
They can be used alone or in the form of a mixture of two or more kinds. In particular, it is more preferable that the second type solvent has a donor number of 16.5 or less.

The viscosity of the second solvent is 2 at 25 ° C.
It is preferably 8 mp or less. The blending amount of the ethylene carbonate in the mixed solvent is 10 to 10 by volume.
It is preferably 80%. If you deviate from this range,
There is a possibility that charge and discharge efficiency may decrease due to decrease in conductivity or decomposition of solvent. A more preferable blending amount of ethylene carbonate is 20 to 75% by volume. By increasing the blending amount of ethylene carbonate in the non-aqueous solvent to 20% by volume or more, solvation of ethylene carbonate to lithium ions is facilitated, so that the effect of suppressing decomposition of the solvent can be improved.

A more preferable composition of the mixed solvent is EC
And DMC, EC and PC and DMC, EC and DEC, EC and PC and DEC, EC and γ-BL and DEC mixed solvent,
The volume ratio of DMC or DEC is preferably 60% or less. By thus setting the DEC ratio to 60% or less, more preferably 35% or less, the flash point of the mixed solvent can be increased and safety can be improved. However, from the viewpoint of further reducing the viscosity, ethers such as diethoxyethane may be added in an amount of 30% by volume or less.

Main impurities present in the mixed solvent (non-aqueous solvent) include water and organic peroxides (eg glycols, alcohols, carboxylic acids). It is considered that each of the impurities forms an insulating film on the surface of the graphitized product and increases the interfacial resistance of the electrode. Therefore, the cycle life and the capacity may be reduced. In addition, self-discharge during storage at high temperature (60 ° C or higher) may increase. Therefore, it is preferable that the impurities are reduced as much as possible in the electrolytic solution containing the non-aqueous solvent. Specifically, the water content is 50 pp
m or less, and the organic peroxide content is preferably 1000 ppm or less.

As the electrolyte contained in the non-aqueous electrolyte, for example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride ( LiAs
F ₆ ), lithium trifluorometasulfonate (LiC
F ₃ SO _3), bis (trifluoromethylsulfonyl) imide lithium _{[LiN (CF 3 SO 2)} 2] Lithium salt such as (electrolyte) can be mentioned. Among them, LiP F _6, LiB
It is preferable to use F ₄ and LiN (CF ₃ SO ₂ ) ₂ . In particular, when LiN (CF ₃ SO ₂ ) ₂ is used, there is little reaction with the positive electrode active material at high temperature (for example, 60 ° C.), and excellent charge / discharge cycle characteristics can be obtained at high temperature. Further, it has the advantage that it is stable with respect to the carbonaceous material and the cycle life can be improved. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / 1.

[0086]

Embodiments of the present invention will now be described in detail with reference to FIG. Reference Example 1 First, lithium cobalt oxide (Li _x CoO ₂ (0.
8 ≦ x ≦ 1)) 91% by weight of powder is mixed with 3.5% by weight of acetylene black, 3.5% by weight of graphite and 2% by weight of ethylene propylene diene monomer powder and toluene, and mixed together to collect an aluminum foil (30 μm). A positive electrode was produced by pressing after applying on an electric body.

Coke made from low-sulfur (content 8000 ppm or less) petroleum pitch as a raw material was carbonized at 1000 ° C. in an argon atmosphere, and then 90% by volume was found to have an average particle size of 40 μm and a particle size of 1 to 80 μm. In addition, a carbonaceous material was produced by appropriately pulverizing particles having a particle diameter of 0.5 μm or less so as to be small (5% or less) and then graphitizing at 3000 ° C. under vacuum.

The carbonaceous material obtained was a graphitized carbon powder having an average particle size of 40 μm, and a particle size distribution of 90 to 90 μm.
The volume distribution of particles having a volume percentage of 0.5% or less was 0 volume%. The specific surface area according to the N ₂ gas adsorption BET method was 3 m ² / g. The powder had a block shape. Intensity ratio by X-ray diffraction (P ₁₀₁ / P
The value of ₁₀₀ ) was 3.6. d ₀₀₂ is 0.3354
nm, Lc is 43 nm, La is 43 nm, and La / Lc
Was 1. The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system by X-ray diffraction was 0.4. The content of sulfur in the carbonaceous material was 100 ppm or less. In addition, the oxygen content was 100 ppm or less, the nitrogen content was 100 ppm or less, and each of Fe and Ni was 1 ppm.

Next, 96.7% by weight of the carbonaceous material was mixed with 2.2% by weight of styrene-butadiene rubber and 1.1% by weight of carboxymethyl cellulose, and this was applied to a copper foil as a current collector and dried. The negative electrode was produced by.

The positive electrode, the separator made of a polyethylene porous film, and the negative electrode were laminated in this order, and then spirally wound so that the negative electrode was located outside, to prepare an electrode group.

Furthermore, lithium hexafluorophosphate (LiP
F ₆ ) as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC)
1.0 to the mixed solvent (mixed volume ratio 40:30:30)
Mol / 1 was dissolved to prepare a non-aqueous electrolytic solution.

The electrode group and the electrolytic solution were respectively housed in a stainless steel bottomed cylindrical container to assemble the cylindrical lithium secondary battery shown in FIG. Reference Example 2 First, an anisotropic bulk mesophase pitch obtained from petroleum pitch was carbonized at 1000 ° C. in an argon atmosphere, and then the average particle size was 15 μm and the particle size was 1 to 80 μm.
The particles were appropriately pulverized so that 0% by volume was present and the number of particles having a particle size of 0.5 μm or less was reduced (5% or less).
Then, a carbonaceous material was produced by heat treatment under vacuum at a temperature of 3000 ° C. to graphitize.

The obtained carbonaceous material was a graphitized carbon powder having an average particle size of 15 μm and had a particle size distribution of 90 to 90 μm.
The distribution of particles having a volume ratio of 0.5% or less was 1% by volume. The specific surface area measured by the N ₂ gas adsorption BET method was 7 m ² / g. The shape of the powder was spherical. The value of the intensity ratio (P ₁₀₁ / P ₁₀₀ ) by X-ray diffraction was 2.6. d ₀₀₂ is 0.3357nm, Lc is 45nm, La in 58nm, La / Lc was 1.29. The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system was 0.5. Moreover, the content of sulfur in the carbonaceous material was 100 ppm or less. In addition, the oxygen content is 100ppm or less, and the nitrogen content is 100p.
pm or less, and Fe and Ni were each 1 ppm.

A negative electrode was produced in the same manner as in Reference Example 1 using the carbonaceous material. Except for using such a negative electrode, ginseng
Assembling a cylindrical lithium secondary battery shown in FIG. 1 described above the same as considered Example 1.

Reference Example 3 Mesophase pitch carbon fiber powder A carbonized at 900 ° C. has an average fiber length of 30 μm, an average fiber diameter of 7 μm, and N
Specific surface area by ₂ gas adsorption BET method is 5 m ² / g, sulfur content is 1600 ppm, nitrogen content is 200 ppm, Fe is 5 ppm, Ni is 3 ppm, and the interplanar spacing d ₀₀₂ of the (002) plane of the graphite structure is 0 in X-ray diffraction. The diffraction peak derived from 0.361 nm was shown, Lc was 1.4 nm and La was 3.9 nm.

The powder B of mesophase pitch carbon fiber graphitized at 3100 ° C. has an average fiber length of 40 μm, an average fiber diameter of 12 μm, a specific surface area of 3.8 m ² / g by N ₂ gas adsorption BET method, and a sulfur content of 100 ppm or less. , the following nitrogen content 100 ppm, the surface spacing d ₀₀₂ of (002) plane of Oite graphite structure in X-ray diffraction from 0.3365nm
Shows a diffraction peak of Lc of 37 nm and La of 67 n.
m, P ₁₀₁ / P ₁₀₀ was 2.3.

The weight ratio of the powder A and the powder B is 1: 2.
The carbonaceous material obtained by mixing with the above was used to prepare a negative electrode by the same method as in Reference Example 1. A cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1 except that this negative electrode was used.

Reference Example 4 Mesophase pitch carbon fiber powder A carbonized at 1000 ° C. had an average fiber length of 30 μm, an average fiber diameter of 7 μm,
Specific surface area by N ₂ gas adsorption BET method 5 m ² / g, sulfur content rate 1500 ppm, nitrogen content rate 100 ppm, Fe
Is 5 ppm, Ni is 3 ppm, shows diffraction peaks plane spacing d ₀₀₂ of (002) plane of the graphite structure in X-ray diffraction is from 0.360 nm, Lc is 1.48 nm, La
Was 3.4 nm.

The artificial graphite powder B obtained by graphitizing coke at 3000 ° C. has an average particle size of 40 μm, a specific surface area of 3.3 m ² / g by the N ₂ gas adsorption BET method, and a sulfur content of 100 p.
pm or less, the nitrogen content of 100ppm or less, Fe, Ni in each 1 ppm, of Oite graphite structure in X-ray diffraction (00
2) Number of times when the interplanar spacing d ₀₀₂ is 0.3354 nm
Fold peaks were observed, Lc was 45 nm, and La was 60 nm.

The powder A and the powder B are in a weight ratio of 1: 1.
A negative electrode was produced by the same method as in Reference Example 1 using the carbonaceous material obtained by mixing with. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1 except that this negative electrode was used.

Comparative Example 1 Graphite powder was obtained by crushing natural graphite to an average particle size of 6 μm. This graphite powder had 85% by volume of particles having a particle size distribution of 1 to 80 μm, and the distribution of particles having a particle size of 0.5 μm or less was 10% by volume. N ₂ gas adsorption B
The specific surface area according to the ET method was 10 m ² / g. The value of the intensity ratio (P ₁₀₁ / P ₁₀₀ ) by X-ray diffraction was 2.1. d ₀₀₂ is 0.3357 nm, Lc is 33 nm, L
a was 60 nm. La / Lc is 1.82.
The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system was 0.85.

A negative electrode was produced in the same manner as in Reference Example 1 using the above graphite powder. Except for using such a negative electrode, ginseng
Assembling a cylindrical lithium secondary battery shown in FIG. 1 described above the same as considered Example 1.

Comparative Example 2 Reference Example 1 using only the artificial graphite powder B of Reference Example 4
A negative electrode was produced in the same manner as in. A cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1 except that this negative electrode was used.

Comparative Example 3 Mesophase pitch carbon fiber powder A of Reference Example 3
A negative electrode was produced in the same manner as in Reference Example 1 using only the above. A cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1 except that this negative electrode was used.

Obtained Reference Examples 1 to 4 and Comparative Examples 1 to 3
This lithium secondary battery is charged at a charging current of 400 mA to 4.2 V for 3 hours and then repeatedly charged and discharged at a high rate current of 1 A to 2.7 V, and the discharge capacity and cycle life of each battery are measured. did. The result is shown in FIG.

As is clear from FIG. 2, the lithium secondary batteries of Reference Examples 1 to 4 have higher capacities even at high rate discharge and the cycle life is remarkably improved as compared with the batteries of Comparative Examples 1 to 3. I understand that

On the other hand, LiN (CF ₃ S was added to the electrolyte of the electrolytic solution.
When the same evaluation was performed using O ₂ ) ₂ , it was confirmed that the cycle life was longer than in Reference Examples 1 to 4. Reference Example 5 First, lithium cobalt oxide (Li _x CoO ₂ (0.
8 ≦ x ≦ 1)) 91% by weight of powder is mixed with 3.5% by weight of acetylene black, 3.5% by weight of graphite and 2% by weight of ethylene propylene diene monomer powder and toluene, and mixed together to collect an aluminum foil (30 μm). A positive electrode was produced by pressing after applying on an electric body.

Coke made from low-sulfur (content 8000 ppm or less) petroleum pitch as a raw material was carbonized at 1000 ° C. in an argon atmosphere, and then 90% by volume was found to have an average particle size of 20 μm and a particle size of 1 to 80 μm. And crushed into blocks so that particles having a particle diameter of 0.5 μm or less are reduced (5% or less), and then 300 in an argon atmosphere.
A carbonaceous material was produced by graphitizing at 0 ° C.

The carbonaceous material obtained was a block-like graphitized carbon powder having an average particle size of 20 μm and had a particle size distribution of 1-8.
90% by volume or more was present in 0 μm, and the particle size distribution of particles having a particle size of 0.5 μm or less was 0% by volume. The specific surface area according to the N ₂ gas adsorption BET method was 3 m ² / g. The shape of the powder was granular. Intensity ratio (P
₁₀₁ / value of P ₁₀₀₎ was 3.6. d ₀₀₂ is 0.
3354nm, Lc 43nm, La 43nm, L
a / Lc was 1. The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system by X-ray diffraction is 0.4.
Met. The sulfur content in the carbonaceous material is 100 p
It was pm or less. In addition, the oxygen content is 100pp
m or less, the content of nitrogen was 100 ppm or less, and each of Fe and Ni was 1 ppm.

Then, 96.7% by weight of the carbonaceous material was mixed with 2.2% by weight of styrene-butadiene rubber and 1.1% by weight of carboxymethylcellulose, and this was applied to a copper foil as a current collector and dried. The negative electrode was produced by.

The positive electrode, the separator made of a polyethylene porous film, and the negative electrode were laminated in this order, and then spirally wound so that the negative electrode was located outside to prepare an electrode group.

Furthermore, lithium hexafluorophosphate (LiP
F ₆ ) as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC)
1.0 to the mixed solvent (mixed volume ratio 40:30:30)
Mol / 1 was dissolved to prepare a non-aqueous electrolytic solution.

The electrode group and the electrolytic solution were respectively housed in a bottomed cylindrical container made of stainless steel, and the cylindrical lithium secondary battery shown in FIG. 1 was assembled. Reference Example 6 First, anisotropy mesophase pitch obtained from petroleum pitch was spun and infusibilized, and the obtained carbon fiber was carbonized at 1000 ° C. under an argon atmosphere, and then the average fiber diameter was 15 μm and the particle size was 15 μm. 90% by volume exists at 1 to 80 μm, and the number of particles having a particle size of 0.5 μm or less is reduced (5%
The following) was appropriately pulverized. Then, a fibrous carbonaceous material was manufactured by heat-treating at a temperature of 3100 ° C. in an argon atmosphere and graphitizing. The carbonaceous material is
The orientation in the cross section perpendicular to the length direction of the fiber was radial.

The carbonaceous material obtained had an average fiber diameter of 15 μm.
Graphitized carbon powder of 9 to 1-80 μm in particle size distribution
0% by volume or more was present, and the distribution of particles having a particle size of 0.5 μm or less was 1% by volume. The specific surface area measured by the N ₂ gas adsorption BET method was 4 m ² / g. The shape of the powder was a fiber having a ratio of length to diameter (length / diameter) of 3. The value of the intensity ratio (P ₁₀₁ / P ₁₀₀ ) by X-ray diffraction was 2.6. d ₀₀₂ is 0.3357 nm, Lc is 45 nm, La
Was 58 nm and La / Lc was 1.29. In addition,
The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system was 0.5. Moreover, the content of sulfur in the carbonaceous material was 100 ppm or less. Others, oxygen content 10
0ppm or less, nitrogen content 100ppm or less, F
e and Ni were 1 ppm each.

A negative electrode was produced in the same manner as in Reference Example 5 using the carbonaceous material. Except for using such a negative electrode, ginseng
Assembling a cylindrical lithium secondary battery shown in FIG. 1 described above the same as considered Example 5.

Example 7 Mesophase pitch carbon fiber powder A graphitized at 3000 ° C. had an average fiber length of 40 μm and an average fiber diameter of 7 μm.
N ₂ gas adsorption BET specific surface area 3 m ² / g, sulfur content 1600 ppm, nitrogen content 200 ppm, Fe
0.3375nm is 5 ppm, Ni is 3 ppm, the surface spacing d ₀₀₂ of (002) plane of Oite graphite structure in X-ray diffraction
The diffraction peak derived from was shown , Lc was 30 nm and La was 60 nm.

The petroleum coke powder B obtained by graphitizing at 3100 ° C. and pulverizing had an average particle size of 6 μm.
A flaky powder having a specific surface area by N ₂ gas adsorption BET method 9m ² / g, sulfur content 100ppm or less, or less nitrogen content 100ppm, spacing of (002) plane of Oite graphite structure in X-ray diffraction d ₀₀₂ is derived from 0.3358 nm
Showing a diffraction peak of Lc of 60 nm and La of 120
nm, P ₁₀₁ / P ₁₀₀ was 2.5.

The powder A and the powder B are mixed in a weight ratio of 4: 1.
A negative electrode was produced by the same method as in Reference Example 5 using the carbonaceous material obtained by mixing with. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 5 except that this negative electrode was used.

Reference Example 8 The mesophase pitch microspheres graphitized at 3000 ° C. are those in which the surface layer having an average particle size of 20 μm and a thickness of 1 to 5 μm is oxidized and removed to expose the lamella layer. Also,
The mesophase pitch microspheres have a specific surface area of 5 m ² / g and a sulfur content of 200 pp according to the N ₂ gas adsorption BET method.
m, nitrogen content is 100 ppm, Fe is 5 ppm, Ni
Is 3 ppm, and (002) having a graphite structure in X-ray diffraction
A spherical graphitized product having a diffraction peak with a surface spacing d ₀₀₂ of 0.3365 nm, Lc of 60 nm, La of 100 nm, and an intensity ratio (P ₁₀₁ / P ₁₀₀ ) of 2.3 by X-ray diffraction. .

A negative electrode was produced in the same manner as in Reference Example 5 using the above graphitized material (carbonaceous material). The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 5 except that this negative electrode was used.

Comparative Example 4 Flake graphite powder was obtained by crushing natural graphite to an average particle size of 6 μm. This graphite powder has a particle size distribution of 1 to 8
There are 85% by volume of particles having a particle size of 0 μm, and the particle size is 0.
The distribution of particles of 5 μm or less was 5% by volume. The specific surface area according to the N ₂ gas adsorption BET method was 10 m ² / g.
The value of the intensity ratio (P ₁₀₁ / P ₁₀₀ ) by X-ray diffraction is 3.
It was 6. d ₀₀₂ is 0.3357 nm, Lc is 60 n
m and La were 120 nm. La / Lc is 1.82
Is. The ratio of the (101) diffraction peak intensities of the rhombohedral system and the hexagonal system was 0.85.

A negative electrode was produced using the above graphite powder in the same manner as in Reference Example 5. Except for using such a negative electrode, ginseng
Assembling a cylindrical lithium secondary battery shown in FIG. 1 described above the same as considered Example 5.

Comparative Example 5 A negative electrode was produced in the same manner as in Reference Example 5 using only the graphitized petroleum coke powder B of Example 7 above. The same as in Reference Example 5 except that this negative electrode was used.
The cylindrical lithium secondary battery shown in was assembled.

Comparative Example 6 Mesophase pitch carbon fiber powder A of Example 7
A negative electrode was produced in the same manner as in Reference Example 5 using only the above. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 5 except that this negative electrode was used.

The obtained lithium secondary batteries of Example 7, Reference Examples 5 to 6 and 8 and Comparative Examples 4 to 6 were charged at a charging current of 400 mA to 4.2 V for 3 hours and then 2.7 V.
Up to and including 1 A of high rate current, charging and discharging were repeated, and the discharge capacity and cycle life of each battery were measured. The result is shown in FIG.

As is clear from FIG. 3, the lithium secondary battery of Example 7 has a higher capacity even at high rate discharge and the cycle life is remarkably improved as compared with the batteries of Comparative Examples 4 to 6. I understand.

On the other hand, LiN (CF ₃ S was added to the electrolyte of the electrolytic solution.
When the same evaluation was performed using O ₂ ) ₂ , it was confirmed that the cycle life was longer than that in Example 7 . In addition, although the example applied to the cylindrical lithium secondary battery has been described in the above embodiment, the present invention can be similarly applied to the prismatic lithium secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, and may have a form in which a plurality of positive electrodes, separators and negative electrodes are laminated in this order.

[0128]

As described in detail above, according to the present invention, it is possible to provide a lithium secondary battery having a high capacity, an excellent cycle life, and a high voltage that can be maintained even during long-term use. .

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical lithium secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between charge / discharge cycle and discharge capacity in the lithium secondary batteries of Reference Examples 1 to 4 and Comparative Examples 1 to 3.

FIG. 3 Example 7, Reference Examples 5 to 6 and 8 and Comparative Example 4 to
6 is a characteristic diagram showing the relationship between the charge / discharge cycle and the discharge capacity in the lithium secondary battery of No. 6.

[Explanation of symbols]

1 ... container, 3 ... electrode group, 4 ... Positive electrode, 6 ... Negative electrode, 8 ... Sealing plate.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-237971 (JP, A) JP-A-5-36440 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (3)

(57) [Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, and a non-aqueous electrolyte, wherein the carbonaceous material has a graphite structure of (00
2) The surface spacing d ₀₀₂ is 0.3370 nm or less.
Before the flake graphite and X-ray diffraction shows diffraction peaks that
Graphite powder consisting of at least one kind selected from flaky graphitized coke showing a diffraction peak, and graphite
The interplanar spacing d ₀₀₂ of the (002) planes of the structure is the graphitized powder.
Is larger than the above-mentioned surface spacing d ₀₀₂ of 0.340n
Diffraction peaks derived from the range of m or less in X-ray diffraction
A lithium secondary battery comprising: the mesophase pitch carbon fiber shown . 2. The mesophase pitch-based carbon fiber,
The lithium secondary battery according to claim 1, wherein the orientation of the crystallites in a cross section perpendicular to the fiber length direction is radial, lamella or Brooks Stella type. 3. A mixture of the graphitized powder in the carbonaceous material.
The total weight ratio is in the range of 5 to 30% by weight.
Lithium according to any one of claims 1 to 2
Secondary battery.