JP3311104B2 - 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 lithium secondary battery, and more particularly to a lithium secondary battery having improved nonaqueous electrolyte and exhibiting excellent battery characteristics.

[0002]

2. Description of the Related Art In recent years, nonaqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries. For example, manganese dioxide (Mn)
Primary batteries using O ₂ ), fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl ₂ ), and the like have already been widely used as power sources for calculators, watches, and as backup batteries for memories.

Further, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, a demand for a high-energy-density secondary battery as a power source for them has been increasing. In response to such demands, research on lithium secondary batteries using lithium as a negative electrode active material has been actively conducted.

A lithium secondary battery is composed of a negative electrode made of lithium and a non-aqueous solvent such as propylene carbonate (PC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-BL), and tetrahydrofuran (THF). To LiCl
A non-aqueous electrolyte or a lithium ion conductive solid electrolyte in which lithium salts such as O ₄ , LiBF ₄ , and LiAsF ₆ are dissolved;
Mainly TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , MnO
Research has been conducted on a structure provided with a positive electrode containing an active material composed of a compound that undergoes a topochemical reaction with lithium such as ₂ .

[0005] However, the lithium secondary battery having the above configuration has not yet been put to practical use. The main reason for this is that the charge / discharge efficiency is low and the number of times that charge / discharge can be performed (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the lithium of the negative electrode and the non-aqueous electrolyte. That is, lithium dissolved in the non-aqueous electrolyte as lithium ions during discharge is:
When deposited from the non-aqueous electrolyte during charging, it reacts with the non-aqueous solvent contained in the electrolyte to partially inactivate the surface. As a result, when charge and discharge are repeated, lithium precipitates in a dendritic (dendritic) or small spherical shape, and further, a phenomenon such as detachment of lithium from the current collector of the negative electrode occurs.

In view of the above, a lithium secondary battery having a negative electrode containing a carbonaceous material that occludes and releases lithium, such as coke, resin fired body, carbon fiber, and pyrolytic gas phase carbon, has been proposed. ing. The lithium secondary battery provided with the negative electrode can suppress the reaction between lithium and the non-aqueous electrolyte, and further suppress the dendrite deposition to improve the deterioration of the negative electrode characteristics.

[0007] The negative electrode containing the carbonaceous material has a structure (graphite structure) in which hexagonal mesh layers mainly composed of carbon atoms are stacked, and in particular, lithium ions enter and exit at a portion between the hexagonal mesh layers. It is considered that charging and discharging are performed. Therefore, it is necessary to use a carbonaceous material having a developed graphite structure to some extent as the negative electrode of the lithium secondary battery. However, a negative electrode containing a carbonaceous material obtained by pulverizing a graphitized giant crystal decomposes a non-aqueous electrolyte, thereby lowering battery capacity and charge / discharge efficiency. In particular, when a lithium secondary battery provided with the negative electrode is operated at a high current density, the capacity, charge / discharge, and voltage at the time of discharge are significantly reduced. Further, as the charge / discharge cycle progresses, the crystal structure or microstructure of the carbonaceous material is destroyed, and the ability to occlude and release lithium is deteriorated, so that the cycle life is shortened.

Further, the negative electrode containing a powdered carbon fiber having advanced graphitization decomposes the non-aqueous electrolyte in the same manner as the negative electrode containing the powdered carbonaceous material of the giant crystal, so that the performance as the negative electrode is greatly improved. And the like.

On the other hand, for the positive electrode, lithium lithium oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO) are used.
O ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), or the like can provide a high voltage of 4 V. Therefore, it is necessary to select an electrolyte and a non-aqueous solvent which do not decompose at a high voltage of 4 V or more.

Conventionally, electrolytes include lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiB
Although F ₄ ) is mainly used, it has problems in high-temperature operation (40 ° C. or higher) performance, storage performance, cycle life, and the like due to low chemical stability. As the non-aqueous solvent, a solvent having excellent oxidation-reduction resistance, such as ethylene carbonate, propylene carbonate, γ-butyrolactone or diethyl carbonate, is selected. However, these non-aqueous solvents have low conductivity and the LiPF ₆ ,
The non-aqueous electrolyte prepared by dissolving LiBF ₄ has a problem of poor chemical stability. Among them, when γ-butyrolactone is used, there is a problem that the high-temperature operation (40 ° C. or higher) performance, storage performance, and cycle life are significantly reduced.

Therefore, the electrolyte is excellent in chemical stability, and the non-aqueous electrolyte obtained by dissolving the electrolyte in a non-aqueous solvent is excellent in high conductivity and oxidation-reduction resistance, and has a high flash point and no toxicity. High security is required. Also,
The non-aqueous electrolyte needs to have low reactivity with a simple substance as a negative electrode material and high reversibility of occlusion and release of lithium ions.

From the above, LiPF ₆ , LiB
F _4, LiAsF bistrifluoromethylsulfonylimide lithium as high electrolyte chemical stability in place of the electrolyte, such as _{6 [Li (CF 3 SO 2} ) 2 N] is Sho 59-14263 discloses, J.Electrochem.Soc ., Are disclosed. Further, as a solvent for dissolving the electrolyte, a single or mixed solvent of tetrahydrofuran, 1,2-dimethoxyethane, propylene carbonate, ethyl carbonate, 2-methyltetrahydrofuran, and dioxolane is known. However, the Li (CF ₃ S
Since the non-aqueous electrolyte comprising O ₂ ) ₂ N and the above-mentioned solvent is easily oxidized and decomposed at a high temperature of 4 V, the aforementioned positive electrode material Li
There are problems such as reaction with CoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , reduction and decomposition with a carbonaceous material as a negative electrode material, and low conductivity. As a result, although the chemical stability is improved, the cycle life and the rate characteristics of the secondary battery are reduced.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having improved high temperature performance, storage performance, rate characteristics and cycle life by improving a non-aqueous electrolyte. .

[0014]

A lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode uses a mesophase pitch as a raw material, And the non-aqueous electrolyte contains at least one solvent selected from ethylene carbonate and propylene carbonate having a content of 1000 ppm or less (including 0 ppm).
A non-aqueous solvent obtained by mixing 80% by volume and 20 to 90% by volume of at least one solvent selected from diethoxyethane, chain carbonate and acetonitrile is mixed with a compound of the formula Li (C
_n X _{2n + 1} Y) ₂ N (where X is a halogen, n is an integer of 1 to 4, and Y is a CO group or an SO ₂ group). 1 characterized by being dissolved.

Another lithium secondary battery according to the present invention is a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a mesophase pitch as a raw material and a sulfur content is lower. The non-aqueous electrolyte contains carbonaceous material of 1000 ppm or less (including 0 ppm), and the non-aqueous electrolyte contains 10 to 80% by volume of γ-butyrolactone and at least one selected from cyclic carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile. A non-aqueous solvent mixed with 20 to 90% by volume of a solvent of the formula Li (C
_n X _{2n + 1} Y) ₂ N (where X is a halogen, n is an integer of 1 to 4, and Y is a CO group or an SO ₂ group). 1 characterized by being dissolved.

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. For example, a cylindrical container 1 with a bottom made of stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
It has a structure in which a belt-like material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5 is formed of, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, or a polypropylene porous film.

The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8
The sealing plate 8 is disposed at the upper opening of the container 1 and caulked in the vicinity of the upper opening inward.
Is fixed to the container 1 in a liquid-tight manner. The positive terminal 9 is
The insulating sealing plate 8 is fitted at the center. Positive lead
One end of the cathode 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9.
Connected to each other. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative lead (not shown).

Next, the configurations of the positive electrode 4, the negative electrode 6, and the non-aqueous electrolyte will be specifically described. 1) Configuration of Positive Electrode 4 The positive electrode 4 is produced by, for example, suspending a conductive agent and a binder in an active material in an appropriate solvent, applying the suspension to a current collector, and drying to form a thin plate. Is done.

The active material is preferably a metal compound mainly composed of at least one metal selected from the group consisting of cobalt, nickel, manganese, vanadium, titanium, molybdenum and iron, and containing lithium. As the metal compound, for example, manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide,
Examples include a lithium-containing cobalt compound, a lithium-containing nickel cobalt oxide, a vanadium oxide containing lithium, and a lithium-containing chalcogen compound such as titanium disulfide or molybdenum disulfide. Among these metal compounds, lithium cobalt oxide (LiCoO
₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganese oxide (LiMn ₂ O ₄ ) are preferable because a high voltage of 4 V 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 current collector has a thickness of, for example, 10 to 10.
It is preferable to use a 40 μm aluminum foil, stainless steel foil, nickel foil or the like. 2) Configuration of Negative Electrode 6 The negative electrode 6 includes, for example, lithium metal, a carbonaceous material that occludes and releases lithium ions, a chalcogen compound that occludes and releases lithium ions, and a lithium ion that occludes and releases lithium ions.
Including light metals to release. When a carbonaceous material or a chalcogen compound is used as the negative electrode material, the negative electrode material is suspended in a suitable solvent together with a binder, and the suspension is applied to a current collector and dried to form a thin plate. It is produced by In particular, the carbonaceous material is 5 to 5 when the negative electrode 6 is manufactured.
It is preferable to contain it in the range of 20 mg / cm ² .

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.

Examples of the chalcogen compound for absorbing and releasing lithium ions include titanium disulfide (TiS).
₂ ), molybdenum disulfide (MoS ₂ ), niobium selenide (NbSe ₃ ), and the like.

Light metals that occlude and release lithium ions include, for example, aluminum, aluminum alloys,
A magnesium alloy, a lithium alloy, and the like can be given. The carbonaceous material that occludes and releases lithium ions,
The following (2-1) to (2-3) can be used. However, differential thermal analysis for determining carbonaceous material, La, d ₀₀₂ , Lc and intensity ratio P ₁₀₁ / P
_{The 100} measurements and definitions are as follows.

(A) The value of the differential thermal analysis indicates that the heating rate is 10 ° C. /
(B) All data measured by X-ray diffraction were obtained by converting CuKα to X
High-purity silicon was used as a radiation source and a standard substance. La, d
₀₀₂ and Lc were determined from the position of each diffraction peak and the half width. As a calculation method, a half-width midpoint method was used.

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

(2-1) Carbonaceous matter This carbonaceous matter has an exothermic peak of 700 according to differential thermal analysis.
° C or higher, preferably 800 ° C or higher, more preferably 8 ° C or higher.
It has a temperature of 40 ° C or higher. The value of the exothermic peak by the differential thermal analysis is a measure of the carbon-carbon bonding force of the carbonaceous material. The carbonaceous material having an exothermic peak in this range has a graphite structure that is appropriately developed, and exhibits a property that lithium ions are reversibly inserted and released between hexagonal mesh layers in the graphite structure. Further, it is considered that the carbonaceous material has a small amount of amorphous carbon active in the non-aqueous solvent.

In the carbonaceous material in which the exothermic peak is present only at a temperature of less than 700 ° C., the carbonaceous material having an undeveloped graphite structure is mixed in the carbonaceous material. It is considered that reversible occlusion and release are small. Further, it is considered that there are many fine powders of amorphous carbon active in the non-aqueous solvent, and the non-aqueous solvent is easily reduced and decomposed.

In the carbonaceous material having an exothermic peak only at a temperature of less than 700 ° C., the carbonaceous material having an undeveloped graphite structure is mixed in the carbonaceous material. It is considered that reversible bust / release is small. Further, it is considered that there are many fine powders of amorphous carbon active in the non-aqueous solvent, and the non-aqueous solvent is easily reduced and decomposed.

The carbonaceous material has an intensity ratio P ₁₀₁ / P ₁₀₀ of (101) diffraction peak P ₁₀₁ and (100) diffraction peak P ₁₀₀ by X-ray diffraction of a graphite structure of 0.7 to 2.2. It is necessary to be. In particular, the carbonaceous material wherein the intensity ratio P ₁₀₁ / P ₁₀₀ is 0.8 - 1.8 is preferred because it can further improve the battery capacity, charge and discharge efficiency and cycle life.

The carbonaceous material having the above-mentioned strength ratio P ₁₀₁ / P ₁₀₀ has a moderately developed graphite structure, and the hexagonal mesh layers stacked in the graphite structure have moderate deviation, twist, and angle from each other. It is thought that it is doing. If the hexagonal mesh layers stacked in this way have an appropriate shift, twist, or angle to each other, lithium ions can easily diffuse between the hexagonal mesh layers, and many lithium ions are reversibly occluded.・ Shows the nature of release. Also,
The carbonaceous material having the above-described structure is capable of intercalating lithium ions between layers.
Disruption of the graphite structure due to release is unlikely to occur. When the graphite structure collapses due to occlusion / release of lithium ions between layers, the amount of occlusion / release of lithium ions decreases, and a surface active with respect to the non-aqueous solvent is generated, so that the non-aqueous solvent is easily reduced and decomposed. Further, the broken fine crystals also reductively decompose the non-aqueous solvent.

The carbonaceous material having the strength ratio P ₁₀₁ / P ₁₀₀ exceeding 2.2 develops a graphite structure (for example, natural graphite) and has a small displacement, twist and angle between hexagonal mesh layers. Such a carbonaceous material is particularly, for example, 0.5 mA /
Under high-rate charge / discharge conditions such as cm ² or more, the amount of occluded / released lithium ions is rather reduced. Further, the surface of the carbonaceous material having the above structure is active against a non-aqueous solvent. For this reason, the non-aqueous solvent is easily reduced and decomposed by the carbonaceous material, and the capacity, charge / discharge efficiency, and cycle life characteristics of the lithium secondary battery deteriorate.

On the other hand, when the intensity ratio P ₁₀₁ / P ₁₀₀ is 0.7
As for the carbonaceous materials of less than one, many of those having an undeveloped graphite structure are mixed, and the misalignment, twist, and angle between the hexagonal mesh layers become too large. For this reason, the carbonaceous material having the above-mentioned structure has little reversible occlusion and release of lithium ions between hexagonal mesh layers, and the capacity, charge / discharge efficiency, and cycle life characteristics of the lithium secondary battery are reduced.

The carbonaceous material preferably has the following characteristics (1) to (8) in addition to the above-mentioned characteristics. (1) The average length La of the crystallite in the a-axis direction of the graphite structure by the diffraction peak of the (110) plane obtained by X-ray diffraction is 2
A carbonaceous material having a thickness of 0 to 100 nm, more preferably 40 to 80 nm. The shape of the a-axis surface in the graphite structure of the carbonaceous material is preferably rectangular.

In the carbonaceous material having La in the above range, the graphite structure is moderately developed and the length of the crystallite in the a-axis direction is moderate, so that lithium ions diffuse between the hexagonal mesh layers. Easier to do. In addition, the carbonaceous material having the above-described structure has a property that the number of sites where lithium ions enter and exit is increased, so that more lithium ions can be inserted and extracted.

The carbonaceous material whose La exceeds 100 nm becomes a giant crystal, making it difficult for lithium ions to diffuse between the layers of the hexagonal mesh layer, making it difficult to secure occlusion and release of lithium ions. Further, since the surface of the carbonaceous material is active with respect to the non-aqueous solvent, the non-aqueous solvent is easily reduced and decomposed. On the other hand, since the carbonaceous material having La of less than 20 nm contains a large amount of carbonaceous material having an undeveloped graphite structure, reversible occlusion and release of lithium ions between hexagonal mesh layers may be reduced.

(2) A carbonaceous material having an average interplanar spacing d ₀₀₂ of the (002) plane obtained by X-ray diffraction of 0.370 nm or less, more preferably 0.340 nm or less. In particular, a carbonaceous material having an average plane distance d ₀₀₂ of 0.3358 to 0.3440 nm, more preferably 0.3359 to 0.3380 nm, and still more preferably 0.3370 to 0.3380 nm is desirable.

The carbonaceous material having an average interplanar spacing d ₀₀₂ in the above range is suitable for the occlusion / release reaction between hexagonal reticulated layers in which the spacing between the hexagonal reticulated layers is smooth.

The carbonaceous material having an average plane distance d _{002 of more} than 0.370 nm tends to have a low capacity, a large overvoltage during charge and discharge, and a decrease in rapid charge and discharge performance. In addition, there is a tendency for battery performance to deteriorate such as flatness of voltage at the time of battery discharge.

(3) The crystallite size Lc in the c-axis direction obtained by X-ray diffraction is 15 nm or more, more preferably 20 nm or more.
Carbonaceous material of 〜100 nm. A carbonaceous material having an Lc in the above range exhibits a property that a graphite structure is appropriately developed and a large amount of lithium ions is inserted and released reversibly.

(4) A carbonaceous material having a La / Lc ratio of La / Lc in the range of 1.3 to 2.5. The La / Lc
When the carbonaceous material has a value of less than 1.3, the number of sites where lithium ions can enter and exit between the carbon layers decreases, and thus the negative electrode capacity may decrease. On the other hand, the carbonaceous material having a ratio of La / Lc of more than 2.5 has a possibility that the overvoltage accompanying the occlusion / release of lithium ions becomes large and the rapid charge / discharge performance is lowered.

(5) As a measure of the ratio of the graphite structure constituting the carbonaceous material to the turbostratic structure, an argon laser (wavelength 51
(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 near 1360 cm ^-1 and a peak derived from a graphite structure appearing near 1580 cm ^-1 . The peak intensity ratio, that is, the peak intensity (R2) of 1360 cm ^{-1 to} the peak intensity (R2) of 1580 cm ^-1 in the argon laser Raman spectrum (wavelength 414.5 nm).
A carbonaceous material in which the value of the ratio R1 / R2 of 1) is 0.7 or less is preferable.

(6) A carbonaceous material having a true density of 2.15 g / cm ³ or more. The true density is a measure of the degree of graphitization of the carbonaceous material. (7) A carbonaceous material having a sulfur content of 0 to 1,000 ppm.

The carbonaceous material containing or not containing sulfur in the above range increases the amount of lithium ions inserted and extracted, and reduces reductive decomposition of the non-aqueous solvent. This is because, in a carbonaceous material in which a graphite structure exhibiting an exothermic peak at 700 ° C. or more in differential thermal analysis has been developed to some extent, if the sulfur content is 1,000 ppm or less (including 0 ppm), the graphite structure has defects. As a result, the graphite structure is less likely to collapse, and the amount of occluded and released lithium ions is increased. Therefore, the lithium secondary battery including the negative electrode including the carbonaceous material has improved capacity, charge / discharge efficiency, and cycle life.

The sulfur content is 1,000 pp.
m or less (including 0 ppm) of the carbonaceous material can reduce the decomposition of the non-aqueous solvent due to the reaction of the non-aqueous solvent and lithium ions with sulfur or a sulfur compound, and reduce the inhibition of the electrode reaction. Therefore, the lithium secondary battery including the negative electrode containing the carbonaceous material has improved charge / discharge efficiency and cycle life.

That is, when sulfur in a carbonaceous material reacts with lithium ions, a stable group such as LiS—
And the like. It is considered that the formation of such a group or a compound prevents the lithium from contributing to a reversible storage / release reaction. Further, it is considered that the generated compound such as LiS acts as an obstacle between the hexagonal mesh layers and prevents the smooth insertion of lithium ions.

Therefore, by setting the sulfur content that inhibits the performance of the carbonaceous material to 1,000 ppm or less or not including it at all, it is possible to improve the charge / discharge efficiency and cycle life of the lithium secondary battery. it can.

(8) The content of various metal elements such as Fe and Ni is 0 to 50 ppm, and the content of silicon is 0 to 50 pp.
m, a carbonaceous material having an oxygen content of 0 to 500 ppm.
In a carbonaceous material in which the content of each of the impurity elements exceeds the above range, lithium ions present between the carbon layers react with the impurity elements and are consumed, and there is a possibility that lithium involved in the battery reaction may be reduced.

The carbonaceous material has a fiber shape in which 90% by volume or more is distributed in a length range of 0.5 to 100 μm and an average fiber diameter is 1 to 30 μm.
It is preferable that 90% by volume or more is distributed in a particle size range of 0 μm, and the particles have a particle shape with an average particle size of 1 to 80 μm. In addition, the carbonaceous material having the above shape is a BET of N ₂ gas adsorption.
The specific surface area by the method is preferably from 0.1 to 100 m ² / g.

The packing density of the carbonaceous material having the above-described shape can be increased when a negative electrode is manufactured. Further, the carbonaceous material having the above shape is a carbonaceous material having a graphite crystal structure which is active against a non-aqueous solvent,
Alternatively, the content of amorphous carbon can be reduced, and reductive decomposition of the non-aqueous solvent can be suppressed.

In particular, the carbonaceous material containing fine fibers or particles having a diameter of 0.5 μm or less and containing only 5% by volume or less has a further reduced carbonaceous material or amorphous carbon having a broken graphite crystal structure, and has a non-aqueous solvent content. Conversely it becomes possible to reduce the reductive decomposition, carbonaceous material having a specific surface area by the BET method of the particle size distribution and N ₂ gas adsorption is out of the range, collapsed in containing and graphite crystal structure of amorphous carbonaceous material carbon And the reductive decomposition of the solvent is likely to occur. Also,
It becomes difficult to produce a negative electrode with a high filling amount of carbonaceous material.

Next, the carbonaceous material of the (2-1), i.e. fever peak to 700 ° C. or higher in differential thermal analysis - has a click, the graphite structure by X-ray diffraction (101) diffraction peak - a click P ₁₀₁ (1
00) the diffraction peak - intensity ratio P ₁₀₁ / P ₁₀₀ of click P ₁₀₀ is zero.
A method for producing a carbonaceous material having a size of 7 to 2.2 will be described.

I) First, for example, using a coal tar, petroleum pitch or synthetic pitch as a raw material, 1500 ° C. to 3000 ° C.
Baking at high temperature to produce coke or anisotropic pitch.

It is preferable to use a coal tar, petroleum pitch or synthetic pitch having a low sulfur content. When such a raw material is used, coke or anisotropic pitch having few defects in the lattice of the graphite structure can be obtained by heat treatment at a relatively low temperature. In particular, it is preferable to select and use one having a small carbon-sulfur chemical bond in the condensed aromatic carbon constituting the organic substance. That is, the carbon-sulfur chemical bond in the aromatic condensed carbon is less likely to be broken than a C—S bond in which a sulfur atom is present as a part of a substituent, and it is difficult to remove sulfur. Therefore, a raw material having a small carbon-sulfur chemical bond in the condensed aromatic carbon is preferable.

The above-mentioned cold tar, petroleum pitch or synthetic pitch preferably has a low nitrogen content. In addition, the smaller the proportion of alkyl side chains such as methyl carbon or methylene carbon in the aromatic ring in the coal tar, petroleum pitch or synthetic pitch, the more the graphite structure develops,
A carbonaceous material having a large value of La by line diffraction is obtained. However, if La is too large as 100 nm, it is not preferable in terms of negative electrode performance.

From the pitch having the anisotropy, a fibrous carbon-based material and a spherical carbon-based material can be obtained. In particular, among the fibrous carbon-based materials, the short fibrous carbon-based material has advantages in that the cost is low and the packing density of the negative electrode can be increased.

The anisotropic pitch preferably has a purity of 95 vol% or more, more preferably 98 vol% or more. This is because the fibrous carbon-based material extracted from the anisotropic pitch containing a large amount of isotropic pitch as an impurity, when the spherical carbon-based material is graphitized as described below, the graphite structure collapses, and amorphous carbon is removed. It causes the occurrence. However, if the heat treatment temperature of the fibrous carbon-based material and the spherical carbon-based material extracted from the pitch having high anisotropy pitch is high at a heat treatment temperature of 2800 ° C. or higher, the graphitization proceeds excessively. . For this reason, the pitch having the anisotropy may include an isotropic pitch of about 1 to 2% by volume.

The high-purity anisotropic pitch includes a mesophase pitch. The fibrous carbon-based material and spherical carbon-based material obtained from the mesophase pitch have, for example, a radial, lamellar, or Brooks-Teller type orientation. In particular, when a spherical carbon-based material is obtained from the mesophase pitch, when extracting the mesophase spherulites from the coal tar, the fine mesophase spherulites having a particle size of 0.5 μm or less are removed. It is effective to perform processing.
It is also effective to perform a heat treatment at 300 to 700 ° C. in an oxygen atmosphere after the extraction. By such treatment, the fine mesophase spherulites attached to the mesophase spherulites and the extra carbon component attached to the surface are burned off and removed. The resulting carbonaceous material can suppress the inhibition of the lithium ion occlusion / release reaction.

Ii) Next, at least one selected from the above-mentioned coke, fibrous carbon-based material and spherical carbon-based material is heat-treated to be carbonized. The heat treatment temperature is from 600 to
It is desirable that the temperature be 1900 ° C, more preferably 800 to 1500 ° C. Preferably, the heat treatment is performed in an argon stream. Further, the heat treatment time is preferably in the range of 0.5 to 30 hours.

Iii) Next, the obtained carbon body is pulverized. When the finally obtained carbonaceous material is in the form of particles, the pulverizing treatment is preferably performed under the following conditions. That is, 90% by volume in the particle size range of 1 to 100 μm.
The above is distributed, more preferably, fine particles having a particle diameter of 0.5 μm or less are distributed at 5% by volume or less, and the average particle diameter is 1 to 1.
Pulverization is performed by selecting appropriate pulverization conditions so as to be 80 μm, or sieving is performed after the pulverization. When the finally obtained carbonaceous material is in the form of fibers, it is preferable to perform the treatment under the following conditions. That is, 0.5 to 100 μm
Appropriate grinding conditions such that 90% by volume or more are distributed in the length range, more preferably 5% by volume or less of fine fibers having a diameter of 0.5 μm or less and an average fiber diameter of 1 to 30 μm. And pulverizing or sieving after pulverization. The pulverization and sieving are preferably performed in an inert atmosphere.

IV) Next, the pulverized carbon body was
It is graphitized by heat treatment at a temperature of 000 ° C. or more to produce a carbonaceous material having the above-described characteristics. The graphitization treatment has an effect of graphitizing amorphous carbon or carbon with a low degree of graphitization generated by grinding the carbon body.

The heat treatment temperature is 2000-3000 ° C.
It is preferable to set the temperature range. Preferably, the heat treatment is performed in an argon stream. Further, the heat treatment time may be in the range of 1 hour to 30 hours.

When the coke is carbonized, pulverized, and graphitized to produce the carbonaceous material, the coke is formed into a granular or spherical powder using a ball mill or a jet mill during the pulverization. Is preferred.

In order to obtain a carbonaceous material having a small amount of impurities such as sulfur as described above, it is preferable to remove impurities during the production of the carbonaceous material. In order to remove sulfur or a sulfur compound from the carbonaceous material, it is necessary to use 2000 to 3000
C, more preferably at a temperature of 2300-2800 ° C.
A method in which a heat treatment is performed by allowing a Lewis acid such as Cl ₃ , a chlorine gas, or metallic sodium to act thereon can be employed. The heat treatment may be performed simultaneously with the carbonization step or the graphitization step, or may be separately performed after the graphitization step.

Further, the characteristic (1) and (2) described above, that is, the plane spacing d ₀₀₂ of the (002) plane obtained by X-ray diffraction is 0.
3360 to 0.3380 nm, lengths La and c in the a-axis direction
When the axial length ratio La / Lc is 1.3 to 2.5,
The carbonaceous material having a thickness of 20 to 100 nm is produced by the method described below.

I) First, a fibrous carbon-based material obtained from a mesophase pitch among the high-purity anisotropic pitches described above is used. In order to obtain a fibrous carbon-based material from the mesophase pitch, first, the mesophase pitch is spun into a short fiber having a fiber length of 200 to 300 μm by a melt blow method. The spinning conditions at this time affect the orientation and crystal structure of the finally obtained carbonaceous material. By properly adjusting the nozzle shape, discharge speed, cooling speed, and thinning speed during spinning, it is possible to control the crystal parameters, microstructure, and orientation.
After spinning, a fibrous carbon-based material is obtained by infusibilizing treatment.

Ii) Next, the fibrous carbon-based material is heat-treated to form a carbon body. The fibrous carbon body obtained by the heat treatment has a plane distance d ₀₀₂ of the (002) plane obtained by X-ray diffraction.
Is preferably 0.344 to 0.380 nm.
The carbon body having the interplanar spacing d ₀₀₂ in this range can be easily converted into a fibrous carbon body having a short fiber length by a pulverization process described later. In addition, the fibrous carbon body in which the interplanar spacing d ₀₀₂ is out of the range is cracked in the longitudinal direction (fiber length direction) in the pulverizing treatment step, and it becomes difficult to shorten the fiber length.

The heat treatment temperature is 600 to 1900 ° C., preferably 800 to 1500 ° C. The heat treatment is preferably performed in an argon stream. The heat treatment time may be in the range of 0.5 hours to 30 hours.

Iii) Next, the fibrous carbon body is pulverized. In the pulverization treatment, 90% by volume or more of the finally obtained carbonaceous material is distributed in a length range of 0.5 to 100 μm, and more preferably 5% by volume or less of fine fibers having a diameter of 0.5 μm or less. Then, pulverization is performed by selecting appropriate pulverization conditions so that the average diameter is 1 to 30 μm, or sieving is performed after the pulverization. The pulverization and sieving are preferably performed in an inert atmosphere.

IV) Subsequently, the fibrous carbon body subjected to the pulverization treatment is heated to 2000 ° C. or more, preferably 2000 ° C. to
The fibrous carbonaceous material having the above-mentioned properties is produced by heat-treating at 3000 ° C., more preferably at 2600-3000 ° C. to graphitize.

The heat treatment for graphitization is preferably performed in an argon gas stream. The heat treatment time may be in the range of 0.5 hours to 30 hours. (2-2) Carbonaceous matter This carbonaceous matter was heated to 700 ° C or higher by differential thermal analysis.
Length L of the crystal structure in the a-axis direction of the graphite structure by the diffraction peak of the (110) plane obtained by X-ray diffraction
a is 20 to 100 nm and the sulfur content is 1000 p
pm or less (including 0 ppm).

It is necessary that the carbonaceous material has an exothermic peak of 700 ° C. or more by differential thermal analysis. An exothermic peak by the differential thermal analysis is preferably 800 ° C. or more,
More preferably, the temperature is 840 ° C. or higher. The value of the exothermic peak by the differential thermal analysis is a measure of the carbon-carbon bonding force of the carbonaceous material. A carbonaceous material having an exothermic peak in this range has a property in which a graphite structure is appropriately developed and lithium ions are reversibly inserted and released between hexagonal mesh layers in the graphite structure. Further, it is considered that the carbonaceous material has a small amount of amorphous carbon active in the non-aqueous solvent. It should be noted that a carbonaceous material having an exothermic peak of less than 700 ° C. by differential thermal analysis is not preferable as a negative electrode material for the same reason as described in the carbonaceous material (2-1).

The carbonaceous material has an average length La of crystallites in the a-axis direction of the graphite structure by diffraction peaks of the (110) plane obtained by X-ray diffraction, 20 to 100 nm, more preferably 40 to 80 nm. It is necessary to be. The shape of the a-axis surface in the graphite structure of the carbonaceous material is preferably rectangular.

In the carbonaceous material having La in the above range, the graphite structure is moderately developed and the length of the crystallite in the a-axis direction is moderate, so that lithium ions diffuse between the hexagonal mesh layers. Easier to do. In addition, the carbonaceous material having the above-described structure has a property that the number of sites where lithium ions enter and exit is increased, so that more lithium ions can be inserted and extracted. In addition,
The carbonaceous material whose La deviates from the above range is not preferable as the negative electrode material for the same reason as described in the carbonaceous material (2-1).

Further, the carbonaceous material has a sulfur content of 0%.
It needs to be ~ 1,000 ppm. The carbonaceous material containing or not containing sulfur in the above range has an increased amount of absorbing and releasing lithium ions and reduces reductive decomposition of a non-aqueous solvent.

This is because, in a carbonaceous material in which a graphite structure exhibiting an exothermic peak at 700 ° C. or more in differential thermal analysis has developed to some extent, the sulfur content is 1,000 ppm or less (0 pp).
m (including m), there are few defects in the graphite structure, and as a result, the graphite structure is less likely to collapse and the amount of lithium ions absorbed and released is increased. The carbonaceous material having a sulfur content of 1,000 ppm or less (including 0 ppm) reduces decomposition of the non-aqueous solvent due to the reaction of the non-aqueous solvent and lithium ion with sulfur or a sulfur compound, and reduces the inhibition of the electrode reaction. It is possible to In addition, the sulfur is 1000
The carbonaceous matter whose content exceeds ppm is the carbonaceous matter (2
It is not preferable as a negative electrode material for the same reason as described in -1).

The carbonaceous material allows the content of various metal elements such as Fe and Ni to be 0 to 50 ppm, the content of silicon to be 0 to 50 ppm, and the content of oxygen to be 0 to 500 ppm.

Examples of the carbonaceous material include graphite which is graphitized from a high-purity raw material having a low sulfur content, a high-purity petroleum pitch having low sulfur content, coal tar, heavy oil, and the like. Graphite or carbonized coke from synthetic pitch, synthetic polymer, organic resin, etc.
Examples include carbon fiber, spherical carbon, fired resin, and vapor-grown carbon.

(2-3) Carbonaceous matter The carbonaceous matter was heated to 700 ° C. or more by differential thermal analysis.
And the content of each metal element is 0 to 50 pp
m, the content of silicon is 0 to 50 ppm, the content of nitrogen is 0 to 1000 ppm, and the content of sulfur is 0 to 1000 pp.
m.

It is necessary that the carbonaceous material has an exothermic peak of 700 ° C. or more by differential thermal analysis. An exothermic peak by the differential thermal analysis is preferably 800 ° C. or more,
More preferably, the temperature is 840 ° C. or higher. The value of the exothermic peak by the differential thermal analysis is a measure of the carbon-carbon bonding force of the carbonaceous material. The carbonaceous material having an exothermic peak in this range has a graphite structure that is appropriately developed, and exhibits a property that lithium ions are reversibly inserted and released between hexagonal mesh layers in the graphite structure. Further, it is considered that the carbonaceous material has a small amount of amorphous carbon active in the non-aqueous solvent. It should be noted that a carbonaceous material having an exothermic peak of less than 700 ° C. by differential thermal analysis is not preferable as a negative electrode material for the same reason as described in the carbonaceous material (2-1).

The carbonaceous material has a content of various metal elements such as Fe and Ni of 0 to 50 ppm, a content of silicon of 0 to 50 ppm, and a content of oxygen of 0 to 500 pp.
m, the content of sulfur must be 0 to 1000 ppm.

The carbonaceous material containing or not containing sulfur in the above range increases the amount of lithium ions stored and released, and reduces reductive decomposition of the non-aqueous solvent. The carbonaceous material containing more than 1000 ppm of sulfur is not preferable as a negative electrode material for the same reason as described in the carbonaceous material (2-1).

In the carbonaceous material in which the content of each of the impurity elements other than the above-mentioned sulfur exceeds the above range, lithium ions present between the carbon layers react with the impurity elements and are consumed, so that lithium involved in the battery reaction is reduced.

As such a carbonaceous material, a high-purity pitch-based raw material, specifically, coal tar, petroleum pitch, or synthetic pitch obtained by heat-treating at about 800 ° C. to about 2000 ° C. Mix, fired resin, or the same raw material for about 2
Graphite and graphite obtained by heat-treating at a temperature of 000 ° C. to about 3000 ° C. are exemplified. Preferably, mesophase microspheres obtained from mesophase pitch or mesophase pitch-based carbon fibers are treated at about 800 ° C. to about 200 ° C.
A lithium secondary battery provided with a negative electrode containing a carbonaceous material carbonized at 0 ° C. or graphitized at about 2000 ° C. to about 3000 ° C. has excellent capacity, charge / discharge efficiency, and cycle life.

3) Structure of Nonaqueous Electrolyte The nonaqueous electrolyte contained in the container 1 is prepared by dissolving an electrolyte in a nonaqueous solvent.

As the non-aqueous solvent, (a) at least one solvent selected from ethylene carbonate (EC) and propylene carbonate (PC)
A mixed solvent of 80% by volume and 20 to 90% by volume of at least one kind of solvent selected from diethoxyethane, chain carbonate and acetonitrile; (b) 10 to 80% by volume of γ-butyrolactone (γ-BL) and cyclic A mixed solvent of 20 to 90% by volume of at least one solvent selected from carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile is used.

As the chain carbonate used in the mixed solvent (a), dimethyl carbonate (DM
C) or diethyl carbonate (DEC) is preferred. The reason for limiting the blending amount of EC and PC (first component) in the mixed solvent (a) to 10 to 80% by volume is as follows.
If the amount of the component is out of the above range, the conductivity of the non-aqueous electrolyte decreases and the charge and discharge efficiency of the negative electrode decreases, and the capacity and cycle life of the battery decrease.

The cyclic carbonate used in the mixed solvent (b) is preferably EC or PC. As the chain carbonate, dimethyl carbonate (DMC) or diethyl carbonate (DEC) is preferable.

The reason that the amount of γ-BL (first component) in the mixed solvent (b) is limited to 10 to 80% by volume is that if the amount of the first component deviates from the above range, the non-aqueous This is because a decrease in the conductivity of the liquid and a decrease in the charge / discharge efficiency of the negative electrode are caused, and the capacity and cycle life of the battery are reduced.

The electrolyte contained in the non-aqueous electrolyte is represented by the formula L
i (C _n X _{2n + 1} Y) ₂ N (where X is halogen, n is 1
-4, and Y represents a CO group or an SO ₂ group). Examples of the imide-based lithium salt include lithium bistrifluoromethylsulfonylimide [Li (CF ₃ SO ₂ ) ₂ N] and lithium bistrifluoromethylacetylimide [Li (CF
₃ CO) ₂ N]. These imide-based lithium salts have high electrical conductivity.

The non-aqueous electrolyte contains the imide-based lithium salt (electrolyte) in an amount of 0.1 mol / l to 3.0 mol / l with respect to the non-aqueous solvent.
It is prepared by dissolving an amount of 0 mol / l. The main impurities present in the non-aqueous electrolyte are water and
Examples include organic peroxides (eg, glycols, alcohols, carboxylic acids), halides, sulfur oxides, nitrides, heavy metals, and the like. These impurities are preferably reduced as much as possible because they adversely affect the negative electrode and the like. In particular, water is 50 ppm or less, and organic peroxide is 1 ppm.
It is preferable that the concentration is not more than 000 ppm. By reducing the amount of impurities in the non-aqueous electrolyte, the charge / discharge efficiency of the negative electrode is increased, and the cycle life is improved.

[0092]

The lithium secondary battery according to the present invention comprises at least one solvent selected from EC and PC.
0% by volume and 20 to 90% by volume of at least one solvent selected from diethoxyethane, chain carbonate and acetonitrile in a non-aqueous solvent mixed with the formula Li (C _n
X _{2n + 1} Y) ₂ N (where X is a halogen, n is an integer of 1 to 4, and Y is a CO group or an SO ₂ group). Since it has a non-aqueous electrolyte dissolved in mol / l, it has excellent high-temperature operation performance, storage performance, rate characteristics and cycle life.

That is, the non-aqueous electrolyte having the above composition has high conductivity. In addition, the non-aqueous electrolyte is excellent in stability against carbonaceous materials that occlude and release lithium ions as a negative electrode material, chalcogen compounds, light metals or lithium metals, and LiCoO ₂ , LiNiO ₂ , as positive electrode materials.
It is stable when extracting a high voltage of 4 V using LiMn ₂ O ₄ . Further, since the reactivity between the mixed solvent and the imide-based lithium salt is low, the non-aqueous electrolyte comprising them has excellent chemical stability at high temperatures. Therefore, the lithium secondary battery including the non-aqueous electrolyte having the above composition has excellent high-temperature operation performance, storage performance, rate characteristics, and cycle life.

Another lithium secondary battery according to the present invention comprises 10 to 80% by volume of γ-butyrolactone and at least one selected from the group consisting of cyclic carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile.
Formula _{Li (C n X 2n + 1} Y) 2 N ( provided that X in the non-aqueous solvent mixture of 20 to 90% by volume seed more solvents halogen, n
Is an integer of 1 to 4, and Y represents a CO group or a SO ₂ group). Has high temperature operation performance, storage performance, rate characteristics and cycle life.

That is, the non-aqueous electrolyte having the above composition has a higher conductivity than the non-aqueous electrolyte containing the mixed solvent containing EC and PC as the first components. This is because γ-BL was used as the first component in the mixed solvent. Further, the non-aqueous electrolyte has excellent stability for the negative electrode and the positive electrode. Further, since the reactivity between γ-BL and the imide-based lithium salt in the mixed solvent is extremely low,
The non-aqueous electrolyte composed of these has extremely excellent chemical stability at high temperatures (45 ° C. or higher). Therefore,
The lithium secondary battery including the non-aqueous electrolyte having the above-described composition has better high-temperature operation performance and storage than the secondary battery using the non-aqueous electrolyte including the mixed solvent including EC and PC as the first component. Has performance, rate characteristics and cycle life.

Further, the aforementioned (2-1) to (2-3)
A negative electrode containing a carbonaceous material that absorbs and releases lithium ions, which has the characteristics described above, can rapidly store and release lithium ions. Therefore, a secondary battery with significantly improved high-rate (rapid charge and discharge) performance can be used. Obtainable. In addition, when the negative electrode and the above-mentioned non-aqueous electrolyte are combined, the charge and discharge efficiency of the positive electrode and the negative electrode is greatly improved, and the cycle life can be extended. This is because the growth of the organic film generated on the surface of the carbonaceous material in the nonaqueous electrolyte is suppressed, and the resistance of the film is small, so that the reversibility of occlusion and release of lithium ions is increased. Conceivable.

Further, if the above-described chalcogen compound that absorbs and releases lithium ions is used as a negative electrode material,
Although the battery voltage decreases, the negative electrode capacity increases, so that the battery capacity can be increased. In addition, since the diffusion rate of lithium ions in the negative electrode can be increased, high-rate performance can be significantly improved.

[0098]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the aforementioned cylindrical lithium secondary battery shown in FIG. Example 1 First, lithium cobalt oxide (Li _x CoO ₂ (0.
8 ≦ x ≦ 1)) Toluene is added to 91% by weight of powder, 3.5% by weight of acetylene black, 3.5% by weight of graphite, and 2% by weight of ethylene propylene diene monomer powder, and the mixture is mixed. A positive electrode was produced by applying the composition to a current collector made of an aluminum foil and pressing it.

Further, after mesophase carbon fiber using mesophase pitch as a raw material is heat-treated at 1000 ° C. in an argon atmosphere to be carbonized, 90 volume% is present in an average particle size of 25 μm and a particle size distribution of 1 to 80 μm. Then, after appropriately pulverizing so that particles having a particle size of 0.5 μm or less become 4% or less, a carbonaceous material was produced by graphitizing at 3000 ° C. in an argon atmosphere.

The obtained carbonaceous material had an average particle size of 25 μm.
And a particle size distribution of 9 to 1 to 80 μm.
0% by volume was present, and the particle size distribution of the particles having a particle size of 0.5 μm or less was 0% by volume. Further, the carbonaceous substance is N ₂
The specific surface area measured by the gas adsorption BET method was 3 m ² / g.

[0102] Various parameters by X-ray diffraction for the carbonaceous material - was measured by the half width midpoint method data, P ₁₀₁
/ Value of P ₁₀₀ was 1.5. d ₀₀₂ is 0.336
It was 8 nm. The exothermic peak by differential thermal analysis was 810 ° C.

Next, 96.7% by weight of the carbonaceous substance was mixed with 2.2% by weight of styrene-butadiene rubber and 1.1% by weight of carboxymethylsemelose, and the mixture was applied to a copper foil as a current collector. By drying, a negative electrode was produced.

After laminating the positive electrode, the separator made of a porous film made of polypropylene, and the negative electrode in this order, the electrode was formed by spirally winding the negative electrode so as to be positioned outside.

Further, lithium bistrifluoromethylsulfonylimide [Li (CF ₃ SO
_{2) 2} N] the Echirenka - Bonnet - DOO (EC), propylene carbonate (PC) and Jiechiruka - BONNET - a mixed solvent (mixing volume ratio of the bets (DEC) 40: 20: 4
0) was dissolved in 1.0 mol / l to prepare a non-aqueous electrolyte.

The above-mentioned electrode group and the above-mentioned electrolytic solution were respectively housed in a stainless steel bottomed cylindrical container to assemble the above-mentioned cylindrical lithium secondary battery shown in FIG. Example 2 As a non-aqueous solvent, a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) (mixing volume ratio 50: 10: 4)
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the above-mentioned (0) was used.

Example 3 Ethylene carbonate (EC), propylene carbonate (PC) and acetonitrile (A) were used as non-aqueous solvents.
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that the mixed solvent (N) was used (mixed volume ratio: 40:20:40).

Example 4 Ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (D)
MC) and diethyl carbonate (DEC) in the same manner as in Example 1 except that a mixed solvent (mixed volume ratio of 40: 10: 25: 25) was used. The battery was assembled.

Example 5 As a non-aqueous solvent, a mixed solvent of γ-butyrolactone (γ-BL), ethylene carbonate (EC) and propylene carbonate (PC) (mixing volume ratio: 50: 15: 3)
The cylindrical lithium secondary battery shown in FIG. 1 described above was assembled in the same configuration as in Example 1 except that 5) was used.

Example 6 The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the following carbonaceous substance and nonaqueous electrolyte were used.

First, carbon fibers made from mesophase pitch were heat-treated at 800 ° C. in an argon atmosphere to be carbonized, and then had an average particle size of 20 μm and a particle size distribution of 1 to 80 μm.
The carbonaceous material was produced by appropriately pulverizing so that 90% by volume was present. The obtained carbonaceous substance had a specific surface area of 5 m ² / g by N ₂ gas adsorption BET method, a d ₀₀₂ of 0.360 nm by X-ray diffraction, and an exothermic peak of 690 ° C. by differential thermal analysis.

The non-aqueous electrolyte is γ-butyrolactone (γ-butyrolactone).
BL), a mixed solvent of ethylene carbonate (EC) and diethoxyethane (DEE) (mixing volume ratio: 20: 5)
0:30), except that the composition was the same as in Example 1.

Example 7 The same carbonaceous substance as in Example 6 and γ-butyrolactone (γ-BL) and ethylene carbonate (E
C) and 2-methyltetrahydrofuran (2MeTH
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled with the same configuration as in Example 1 except that the mixed solvent (F) (mixing volume ratio: 30:50:20) was used.

Example 8 The same carbonaceous substance as in Example 6 and γ-butyrolactone (γ-BL) and ethylene carbonate (E
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled with the same configuration as in Example 1 except that a mixed solvent of C) and acetonitrile (AN) (mixing volume ratio: 20:50:30) was used.

Example 9 As a non-aqueous electrolytic solution, lithium bistrifluoromethylacetylimide [Li (CF ₃ CO) ₂ N]
The procedure was performed except that a solution prepared by dissolving 1.0 mol / l in a mixed solvent (mixing volume ratio: 60:10:30) of carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used. The cylindrical lithium secondary battery shown in FIG. 1 described above was assembled in the same configuration as in Example 1.

Example 10 Titanium disulfide was used as a negative electrode material, and Li was used as a nonaqueous electrolyte.
(CF ₃ SO ₂ ) ₂ Nγ-butyrolactone (γ-B
L), a mixed solvent of ethylene carbonate (EC) and acetonitrile (AN) (mixing volume ratio 20: 50: 3)
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the solution prepared by dissolving 1.0 mol / l in 0) was used.

Example 11 Except that the negative electrode was formed of an aluminum manganese alloy,
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1.

Comparative Example 1 As a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF
₆ ) is a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (γ-BL) (mixing volume ratio: 50:
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the solution prepared by dissolving 1.0 mol / l in Example 50) was used.

Comparative Example 2 As a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF
₆ ) as a mixed solvent of ethylene carbonate (EC) and diethoxyethane (DME) (mixing volume ratio: 50: 5)
The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the solution prepared by dissolving 1.0 mol / l in 0) was used.

Comparative Example 3 As a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF
₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) and acetonitrile (AN) (mixing volume ratio: 50:50) at a ratio of 1.0 mol / l, and the same configuration as in Example 1 was used. The above-described cylindrical lithium secondary battery shown in FIG. 1 was assembled.

The obtained Examples 1 to 11 and Comparative Example 1
About 3 lithium secondary batteries at a temperature of 45 ° C. and a charging current of 500 mA for up to 4.2 V for 3 hours;
Charging and discharging were performed repeatedly at a high rate of 1 A up to 2.7 V, and the discharge capacity and cycle life of each battery were measured. The result is shown in FIG.

As is apparent from FIG.
It can be seen that the lithium secondary battery has a higher capacity even at a high rate of discharge than the batteries of Comparative Examples 1 to 3, and the cycle life is significantly improved.

In the repetitive charge / discharge test at room temperature (25 ° C.), the lithium secondary batteries of Examples 1 to 11 had higher capacities and longer life than the batteries of Comparative Examples 1 to 3.

In the above embodiment, an example in which the present invention is applied to a cylindrical lithium secondary battery has been described. However, the present invention can be similarly applied to a prismatic lithium secondary battery. Further, the electrode group accommodated in the battery container is not limited to a spiral shape, but may be a form in which a plurality of positive electrodes, separators, and negative electrodes are stacked in this order.

[0124]

As described above, according to the present invention, a lithium secondary battery having a high capacity and an excellent cycle life can be provided even when used at a high temperature.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between a charge / discharge cycle and a discharge capacity in the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 3 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 3 ... electrode group, 4 ... positive electrode, 6 ... negative electrode, 8 ... sealing plate.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-211070 (JP, A) JP-A-5-74491 (JP, A) JP-A-5-129018 (JP, A) JP-A-5-129018 275321 (JP, A) JP-A-6-318459 (JP, A) Material Database Editing Committee, Material Database-Inorganic Materials, Japan, Nikkan Kogyo Shimbun, January 25, 1989, first edition, P715-717 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/00-4/62

Claims (2)

(57) [Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is made of a mesophase pitch as a raw material, and has a sulfur content of 1000 ppm or less (including 0 ppm). And the non-aqueous electrolyte contains 10 to 80% by volume of at least one solvent selected from ethylene carbonate and propylene carbonate and at least one solvent selected from diethoxyethane, chain carbonate and acetonitrile. non-aqueous solvent mixture of 20 to 90 vol% formula _{Li (C n X 2n + 1} Y) 2 n ( provided that X
Is a halogen, n is an integer of 1 to 4, Y is a CO group or SO
Imide lithium salt represented by ₂ )
A lithium secondary battery comprising 3 mol / l dissolved. 2. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is made of a mesophase pitch as a raw material and has a sulfur content of 1000 ppm or less (including 0 ppm). And the non-aqueous electrolyte contains 10 to 80% by volume of γ-butyrolactone and at least one solvent 20 to 90 selected from the group consisting of cyclic carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile.
The formula Li (C _n X _{2n + 1} Y) is added to a non-aqueous solvent mixed with
₂ N (where X is halogen, n is an integer of 1-4, Y is C
A lithium secondary battery characterized by comprising 0.1 to 3 mol / l of an imide-based lithium salt represented by the formula: O group or SO ₂ group).