JPH0785888A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain a lithium secondary battery having excellent high temperature performance, storage performance, rate characteristic and cycle lifetime by improving nonaqueous electrolyte. CONSTITUTION:A lithium secondary battery is provided with a positive electrode 4, a negative electrode 6, which includes lithium metal and carbonaceous material, which stores and emits lithium ion, and chalcogen compound or light metal, and nonaqueous electrolyte. The nonaqueous electrolyte has the composition that 0.1-3mole/l of imide group lithium salt expressed with a formula Li(CnX2n+1 Y)2N (X means halogen, n means integral number in a range of l-4, and Y means CO group or SO2, group) is dissolved in the nonaqueous solvent, obtained by mixing at least one kind of solvent selected among ethylenecarbonate and propylenecarbonate at 10-80volume % and at least one kind solvent selected among diethoxyethane, chain carbonate and acenitryl at 20-90volume %.

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 which has improved non-aqueous electrolyte and exhibits excellent battery characteristics.

[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. For example, manganese dioxide (Mn
A primary battery using O ₂ ), carbon fluoride [(CF ₂ ) _n ], thionyl chloride (SOCl ₂ ) or the like is already widely used as a power source for calculators, watches, and backup batteries for memories.

Further, in recent years, with the miniaturization and weight reduction of various electronic devices such as VTRs and communication devices, there is an increasing demand for high energy density secondary batteries as their power sources. 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 manufactured by using 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). LiCl
A non-aqueous electrolyte solution or a lithium ion conductive solid electrolyte in which a lithium salt such as O ₄ , LiBF ₄ , LiAsF ₆ is dissolved;
Mainly TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , MnO
A structure having a positive electrode containing an active material composed of a compound that undergoes a topochemical reaction with lithium such as ₂ has been studied.

However, the lithium secondary battery having the above structure 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, the lithium dissolved in the non-aqueous electrolyte as lithium ions during discharge is
When it precipitates from the non-aqueous electrolyte solution during charging, it reacts with the non-aqueous solvent contained in the electrolyte solution to partially inactivate the surface. As a result, when charging / discharging is repeated, lithium deposits in a dendritic (dendritic) or small spherical shape, and further, lithium is separated from the current collector of the negative electrode.

In view of the above, a lithium secondary battery provided with a negative electrode containing a carbonaceous material that absorbs and releases lithium such as coke, a resin fired body, carbon fiber, and pyrolysis vapor-phase carbon has been proposed. ing. The lithium secondary battery including 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.

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, and in particular, lithium ions come in and out at a portion between the hexagonal mesh plane layers. It is considered to be charged and discharged. Therefore, it is necessary to use a carbonaceous material having a graphite structure developed to some extent as the negative electrode of the lithium secondary battery. However, the negative electrode containing the carbonaceous material obtained by pulverizing the giant crystal having advanced graphitization decomposes the non-aqueous electrolytic solution, so that the capacity and charge / discharge efficiency of the battery are reduced. In particular, when the lithium secondary battery provided with the negative electrode is operated at a high current density, the capacity, charge / discharge, and voltage during discharge are significantly reduced. Further, as the charge / discharge cycle progresses, the crystal structure or the fine structure of the carbonaceous material collapses, and the lithium occlusion / desorption ability deteriorates, so that the cycle life is shortened.

Further, the negative electrode containing the powdered carbon fiber having advanced graphitization decomposes the non-aqueous electrolytic solution similarly to the negative electrode containing the powdery carbonaceous material of giant crystals, and therefore the performance as the negative electrode is greatly improved. There is a problem such as a decrease.

On the other hand, the positive electrode has lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNi
By using O ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ) or the like, a high voltage of 4 V can be obtained. Therefore, as the non-aqueous electrolyte, it is necessary to select an electrolyte and a non-aqueous solvent that do not decompose at a high voltage of 4 V or higher.

Lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiB) have hitherto been used as electrolytes.
F ₄ ) is mainly used, but it has problems in terms of high temperature operation (40 ° C. or higher) performance, storage performance, cycle life, etc. due to its low chemical stability. Moreover, as the non-aqueous solvent, a solvent having excellent redox resistance such as ethylene carbonate, propylene carbonate, γ-butyrolactone or diethyl carbonate is selected. However, these non-aqueous solvents have low electric conductivity, and LiPF ₆ ,
The non-aqueous electrolyte prepared by dissolving LiBF ₄ has a problem that it has 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 prepared by dissolving the electrolyte in a non-aqueous solvent has high conductivity and redox resistance, and has a high flash point and no toxicity. High safety is required. Also,
It is necessary that the non-aqueous electrolyte has low reactivity with the monolithic substance as the negative electrode material and high reversibility of occlusion / release of lithium ions.

From these facts, LiPF ₆ , LiB
Bistrifluoromethylsulfonylimide lithium [Li (CF ₃ SO ₂ ) ₂ N] is used as an electrolyte having a high chemical stability in place of an electrolyte such as F ₄ or LiAsF ₆ , and JP-A-59-14263 and J. Electrochem. Soc. ., Are disclosed. Further, as a solvent for dissolving the electrolyte, tetrahydrofuran, 1,2-dimethoxyethane, propylene carbonate, ethyl carbonate, 2-methyltetrahydrofuran, dioxolane alone or in a mixed solvent is known. However, the Li (CF ₃ S
Since the non-aqueous electrolytic solution containing O ₂ ) ₂ N and the solvent is easily oxidized and decomposed at a high temperature of 4 V, the positive electrode material Li described above is used.
There are problems such as reacting with CoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ , being reductively decomposed by a carbonaceous material which is a negative electrode material, and having low conductivity. As a result, although the chemical stability is improved, the cycle life and rate characteristics of the secondary battery are reduced.

[0013]

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

[0014]

A lithium secondary battery according to the present invention comprises a positive electrode, a lithium metal, a carbonaceous material that absorbs and releases lithium ions, a chalcogen compound that absorbs and releases lithium ions, or a lithium ion.・
In a lithium secondary battery comprising a negative electrode containing a light metal to be released and a non-aqueous electrolytic solution, the non-aqueous electrolytic solution contains 10 to 80% by volume of at least one solvent selected from ethylene carbonate and propylene carbonate. diethoxyethane, chain carbonate and a non-aqueous solvent obtained by mixing at least one kind of a solvent 20 to 90 vol% selected from acetonitrile formula _{Li (C n X 2n + 1} Y) 2
N (however, X is halogen, n is an integer of 1 to 4, Y is CO)
Group or SO ₂ group) is dissolved in an amount of 0.1 to 3 mol / l of an imide-based lithium salt.

Another lithium secondary battery according to the present invention is
A lithium secondary battery including a positive electrode, a negative electrode containing lithium metal, a carbonaceous material that absorbs and releases lithium ions, a chalcogen compound that absorbs and releases lithium ions, or a light metal that absorbs and releases lithium ions, and a non-aqueous electrolyte. In the secondary battery, the non-aqueous electrolyte solution contains 10 to 80% by volume of γ-butyrolactone and at least one solvent 20 to 90 selected from cyclic carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile.
In a non-aqueous solvent mixed with vol%, the formula Li (C _n X _{2n + 1} Y)
₂ N (where X is halogen, n is an integer of 1 to 4, Y is C
An imide type lithium salt represented by O group or SO ₂ group) is dissolved in an amount of 0.1 to 3 mol / l.

Hereinafter, a lithium secondary battery (eg, a cylindrical lithium secondary battery) according to the present invention will be described in detail with reference to FIG. For example, a bottomed cylindrical container 1 made of stainless steel has an insulator 2 arranged at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 is
The positive electrode 4, the separator 5, and the negative electrode 6 are laminated in this order, and a band-shaped material is spirally wound so that the negative electrode 6 is located outside. The separator 5 is made of, for example, a synthetic resin non-woven fabric, a polyethylene porous film, or a polypropylene porous film.

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).

Next, the constitutions 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, for example, by suspending a conductive agent and a binder in an active material in an appropriate solvent, applying the suspension on a current collector, and drying the suspension to form a thin plate. To be done.

It is preferable that the active material is a metal compound containing at least one metal selected from the group consisting of cobalt, nickel, manganese, vanadium, titanium, molybdenum and iron as a main component and also containing lithium. Examples of the metal compound include manganese dioxide, lithium manganese oxide, lithium-containing nickel oxide,
Examples thereof include a lithium-containing cobalt compound, a lithium-containing nickel cobalt oxide, a lithium-containing vanadium oxide, 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 10 to 10, for example.
It is preferable to use 40 μm aluminum foil, stainless steel foil, nickel foil, or the like. 2) Configuration of Negative Electrode 6 The negative electrode 6 contains, for example, lithium metal, a carbonaceous material that occludes and releases lithium ions, a chalcogen compound that occludes and releases lithium ions, or a occludes lithium ions.
Contains light metals that are released. When a carbonaceous material or 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 preferably contained 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 which absorbs and releases lithium ions include titanium disulfide (TiS).
₂ ), molybdenum disulfide (MoS ₂ ), niobium selenide (NbSe ₃ ), and the like.

Examples of the light metal which absorbs and releases lithium ions include aluminum, aluminum alloys,
Examples thereof include magnesium alloys and lithium alloys. The carbonaceous material that occludes and releases the lithium ions is
The following (2-1) to (2-3) can be used. However, differential thermal analysis for determining carbonaceous matter, 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 is the temperature rising rate of 10 ° C. /
Min, sample weight 3 mg, measured in air (b) All data measured by X-ray diffraction was CuKα 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. The half-width half-point method was used as the calculation method.

(C) 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. (D) The intensity ratio P ₁₀₁ / P ₁₀₀ between the (101) diffraction peak P ₁₀₁ and the (100) diffraction peak P ₁₀₀ by X-ray diffraction is obtained from the peak height ratio.

(2-1) Carbonaceous Material This carbonaceous material has an exothermic peak of 700 due to differential thermal analysis.
℃ or more, preferably 800 ℃ or more, more preferably 8
It has a temperature of 40 ° C or higher. The value of the exothermic peak obtained by the differential thermal analysis is a measure of the carbon-carbon bond strength of the carbonaceous material. The carbonaceous material having an exothermic peak in this range has an appropriately developed graphite structure, and exhibits a property of reversibly occluding / desorbing lithium ions between the layers of the hexagonal network surface layer in the graphite structure. In addition, it is considered to be a carbonaceous material having a small amount of amorphous carbon which is active in a nonaqueous solvent.

In the carbonaceous material whose exothermic peak exists only below 700 ° C., carbonaceous material in which the graphite structure is undeveloped is mixed in the carbonaceous material. It is considered that reversible occlusion / release is small. In addition, it is considered that there are many fine powders of amorphous carbon that are active in the non-aqueous solvent, and the non-aqueous solvent is likely to be reductively decomposed.

In the carbonaceous material whose exothermic peak exists only below 700 ° C., the carbonaceous material in which the graphite structure is undeveloped is mixed in the carbonaceous material, so that the intercalation between the hexagonal mesh planes in the graphite structure of lithium ion It is considered that there are few reversible busts / emissions. In addition, it is considered that there are many fine powders of amorphous carbon that are active in the non-aqueous solvent, and the non-aqueous solvent is likely to be reductively 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 graphite structure of 0.7 to 2.2. It is necessary to be. In particular, a carbonaceous material having a strength ratio P ₁₀₁ / P ₁₀₀ of 0.8 to 1.8 is preferable because it can further improve battery capacity, charge and discharge efficiency, and cycle life.

In the carbonaceous material in which the strength ratio P ₁₀₁ / P ₁₀₀ is in the above range, the graphite structure is appropriately developed, and the hexagonal mesh plane layers stacked in the graphite structure have appropriate deviations, twists, and angles. It is thought that it is doing. When the stacked hexagonal mesh plane layers have an appropriate offset, twist, or angle with respect to each other, lithium ions easily diffuse between the layers of the hexagonal mesh plane layers, and many lithium ions are reversibly occluded.・ Shows the property of being released. Also,
The carbonaceous material having the above-mentioned structure absorbs lithium ions between layers.
Breakdown of the graphite structure due to release is unlikely to occur. When the graphite structure collapses due to storage / release of lithium ions between layers, the storage / release amount of lithium ions decreases, and an active surface for the non-aqueous solvent is generated to facilitate the reductive decomposition of the non-aqueous solvent. Also, the collapsed fine crystals similarly reductively decompose the non-aqueous solvent.

The carbonaceous material having a strength ratio P ₁₀₁ / P ₁₀₀ exceeding 2.2 develops a graphite structure (for example, natural graphite), and has less deviation, twisting and angle between hexagonal mesh plane layers. Such a carbonaceous material is, for example, especially 0.5 mA /
Under high-rate charging / discharging conditions such as cm ² or more, the amount of lithium ion stored / released is rather reduced. In addition, the surface of the carbonaceous material having the above structure is active with respect to the non-aqueous solvent. Therefore, 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 are deteriorated.

On the other hand, the intensity ratio P ₁₀₁ / P ₁₀₀ is 0.7.
The carbonaceous materials of less than 5 are mixed with many undeveloped graphite structures, resulting in misalignment between the hexagonal mesh plane layers, twisting, and an excessively large angle. For this reason, the carbonaceous material having the above-described structure has less reversible occlusion / release of lithium ions between the layers of the hexagonal net surface layer, and the capacity, charge / discharge efficiency, and cycle life characteristics of the lithium secondary battery are deteriorated.

The carbonaceous material preferably has the characteristics (1) to (8) described below in addition to the characteristics described above. (1) The average length La of crystallites 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 appropriately developed, and the length of the crystallite in the a-axis direction is appropriate, so that lithium ions diffuse between the layers of the hexagonal net surface layer. Easier to do. In addition, the carbonaceous material having the above structure has a large number of sites where lithium ions enter and leave, and exhibits a property of being able to store and release 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 net surface layer, and it becomes difficult to secure the occlusion / release of lithium ions. Further, since the surface of the carbonaceous material is active with respect to the non-aqueous solvent, it facilitates the reductive decomposition of the non-aqueous solvent. On the other hand, the carbonaceous material having an La of less than 20 nm contains a large amount of carbonaceous material with an undeveloped graphite structure, and therefore reversible occlusion / release of lithium ions between the layers of the hexagonal network layer may be reduced.

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

The carbonaceous material having the average interplanar spacing d ₀₀₂ within the above range is suitable for the storage / release reaction between the layers of the hexagonal net-like layer in which the spacing between the layers of the hexagonal net-like layer is smooth.

The carbonaceous material having an average interplanar spacing d _{002 of more} than 0.370 nm has a low capacity and a large overvoltage during charging / discharging, which tends to deteriorate rapid charging / discharging performance. Further, the battery performance tends to be deteriorated such that the flatness of the voltage when the battery is discharged becomes low.

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

(4) A carbonaceous material having a La / Lc ratio La / Lc in the range of 1.3 to 2.5. La / Lc
If the carbonaceous material has a ratio of less than 1.3, the number of sites where lithium ions can enter and leave between the carbon layers is reduced, and thus the negative electrode capacity may be reduced. On the other hand, a carbonaceous material having a La / Lc of more than 2.5 has a large overvoltage associated with the absorption / desorption of lithium ions, which may deteriorate the rapid charge / discharge performance.

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

(6) 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 which contains sulfur or does not contain sulfur in the above range has an increased storage / release amount of lithium ions and reduces reductive decomposition of the non-aqueous solvent. This is because, in a carbonaceous material in which a graphite structure showing an exothermic peak at 700 ° C. or higher in a differential thermal analysis has developed to some extent, if the sulfur content is 1,000 ppm or less (including 0 ppm), a defect in the graphite structure will occur. As a result, the collapse of the graphite structure hardly occurs, and the amount of occlusion / release of lithium ions is increased. Therefore, the lithium secondary battery including the negative electrode containing the carbonaceous material has improved capacity, charge / discharge efficiency, and cycle life.

The sulfur content is 1,000 pp
The carbonaceous material of m or less (including 0 ppm) 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 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 the carbonaceous material reacts with lithium ions, stable groups such as LiS- and LiS-
To produce a compound such as. It is considered that the formation of such a group or compound prevents the lithium from contributing to the reversible occlusion / release reaction. Further, it is considered that the produced compound such as LiS becomes an obstacle between the hexagonal mesh plane layers and prevents the smooth insertion of lithium ion.

Therefore, the charging / discharging efficiency and cycle life of the lithium secondary battery can be improved by reducing the sulfur content, which hinders the performance of the carbonaceous material, to 1,000 ppm or less. it can.

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

90% by volume or more of the carbonaceous material is distributed in a length range of 0.5 to 100 μm and has a fiber shape with an average fiber diameter of 1 to 30 μm, or 1 to 10
It is preferable that 90% by volume or more is distributed in the particle size range of 0 μm and that the particles have an average particle size of 1 to 80 μm. Further, the carbonaceous material having the above-mentioned shape is a BET for N ₂ gas adsorption
The specific surface area according to the method is preferably 0.1 to 100 m ² / g.

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

Particularly, a carbonaceous material containing fine fibers or particles having a diameter of 0.5 μm or less in an amount of 5% by volume or less is further reduced in the carbonaceous material in which the graphite crystal structure is broken or the amorphous carbon, and the non-aqueous solvent On the contrary, it is possible to reduce the reductive decomposition. On the contrary, the carbonaceous material having the particle size distribution and the specific surface area of the N ₂ gas adsorption by the BET method outside the above range is a carbon material containing an amorphous carbonaceous material and a carbon having a broken graphite crystal structure. The content of the substance increases, and the reductive decomposition of the solvent easily occurs. Also,
It becomes difficult to produce a negative electrode having a high filling amount of carbonaceous material.

Next, the carbonaceous material of the above (2-1), that is, a (101) diffraction peak P ₁₀₁ having a graphite structure having a heat generation peak at 700 ° C. or higher by differential thermal analysis and having a graphite structure by X-ray diffraction was obtained. (1
00) the diffraction peak - intensity ratio P ₁₀₁ / P ₁₀₀ of click P ₁₀₀ is zero.
A method for producing a carbonaceous material of 7 to 2.2 will be described.

I) First, for example, using a raw material such as coal tar, petroleum pitch or synthetic pitch, 1500 ° C. to 3000 ° C.
A pitch having coke or anisotropy is produced by firing at a high temperature.

It is preferable to use one having a low sulfur content as the above-mentioned coal, petroleum pitch or synthetic pitch. By using such a raw material, a coke or a pitch having anisotropy with 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 number of carbon-sulfur chemical bonds in the aromatic condensed carbon constituting the organic substance. That is, the carbon-sulfur chemical bond in the aromatic condensed carbon is more difficult to be cleaved than the C—S bond in which the sulfur atom is present as a part of the substituent, and the removal of sulfur is difficult. Therefore, a raw material having few carbon-sulfur chemical bonds in the aromatic condensed carbon is preferable.

It is preferable that the above-mentioned coal, petroleum pitch or synthetic pitch has a small nitrogen content. Further, the smaller the proportion of the alkyl side chain such as methyl carbon or methylene carbon in the aromatic ring in the coal, petroleum pitch or synthetic pitch, the more the graphite structure is developed,
A carbonaceous material having a large value of La can be obtained by linear diffraction. However, if the La is too large as 100 nm, it is not preferable in terms of negative electrode performance.

Fibrous carbonaceous materials and spherical carbonaceous materials can be obtained from the anisotropic pitch. In particular, among the fibrous carbon-based materials, the short fibrous carbon-based material has advantages that the cost is low and the negative electrode packing density can be increased.

As for the pitch having anisotropy, the purity of the anisotropic pitch is preferably 95% by volume or more, more preferably 98% by volume or more. This is because when the fibrous carbon-based material extracted from the anisotropic pitch containing a large amount of isotropic pitch as an impurity, and the spherical carbon-based material is graphitized later, the graphite structure collapses, and the amorphous carbon It causes the occurrence. However, when the fibrous carbon-based material or spherical carbon-based material extracted from the pitch having anisotropy with a high amount of anisotropic pitch is graphitized at a high heat treatment temperature of 2800 ° C. or higher, graphitization proceeds too much. . Therefore, the anisotropic pitch may include an isotropic pitch of about 1 to 2% by volume.

Examples of the high-purity anisotropic pitch include mesophase pitch. The fibrous carbon-based material and the spherical carbon-based material obtained from mesophase pitch have, for example, radial, lamellar or Brooks-Stella type orientation. In particular, when a spherical carbon-based material is obtained from the mesophase pitch, fine mesophase spherulites having a particle size of 0.5 μm or less are removed when extracting the mesophase spherulites from the cotter. It is effective to perform processing.
It is also effective to perform heat treatment at 300 to 700 ° C in an oxygen atmosphere after extraction. By such treatment, the fine mesophase spherulites adhering to the mesophase spherulites and further the excess carbon component adhering to the surface are burned and removed. The obtained carbonaceous material suppresses the inhibition of lithium ion storage / release reaction.

Ii) Next, at least one selected from the coke, the fibrous carbonaceous material and the spherical carbonaceous material is heat-treated to carbonize it. The heat treatment temperature is 600 to
It is desirable to set the temperature to 1900 ° C, more preferably 800 to 1500 ° C. Further, the heat treatment is preferably performed in an argon stream. Further, the heat treatment time is preferably in the range of 0.5 hours to 30 hours.

Iii) Next, the obtained carbon body is pulverized. The pulverization treatment is preferably performed under the following conditions when the finally obtained carbonaceous material has a particle shape. 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 size of 0.5 μm or less are distributed in an amount of 5% by volume or less, and the average particle size is 1 to
Appropriate pulverization conditions are selected so as to have a particle size of 80 μm for pulverization, or sieving is performed after pulverization. When the finally obtained carbonaceous material has a fiber shape, it is preferably carried out under the following conditions. That is, 0.5 to 100 μm
90% by volume or more is distributed in the length range, more preferably 5% by volume or less of fine fibers having a diameter of 0.5 μm or less are distributed, and suitable pulverization conditions are such that the average fiber diameter is 1 to 30 μm. Is pulverized, or is sieved after pulverization. The crushing and sieving are preferably performed in an inert atmosphere.

IV) Then, the pulverized carbon body is mixed with 2
It is graphitized by heat treatment at a temperature of 000 ° C. or higher to produce a carbonaceous material having the above-mentioned characteristics. The graphitization treatment has a function of graphitizing amorphous carbon generated by pulverizing the carbon body or carbon having a low graphitization degree.

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

In the case of producing the carbonaceous material by carbonizing, crushing and graphitizing the coke, a granular or spherical powder is used at the time of crushing by using a ball mill or a jet mill. It is preferable.

Further, in order to obtain the above-mentioned carbonaceous material containing a small amount of impurities such as sulfur, it is preferable to remove impurities during the production of the carbonaceous material. To remove sulfur or sulfur compounds from the carbonaceous matter, 2000-3000.
Cu, more preferably at a temperature of 2300 to 2800 ° C.
It is possible to employ a method in which a Lewis acid such as Cl ₃ or chlorine gas or metallic sodium is used to perform heat treatment. The heat treatment may be performed simultaneously with the carbonization process or the graphitization process, or may be performed separately after the graphitization process.

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

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

Ii) Next, the fibrous carbonaceous material is heat-treated into a carbon body. The fibrous carbon body obtained by the heat treatment has an interplanar spacing d ₀₀₂ of (002) planes by X-ray diffraction.
Is preferably 0.344 to 0.380 nm.
The carbon body having the interplanar spacing d ₀₀₂ within this range can be easily made into a fibrous carbon body having a short fiber length by a pulverization treatment described later. A fibrous carbon body having a surface distance d _{002 outside the} above range is cracked in the longitudinal direction (fiber length direction) in the pulverization process, 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 the 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. And crushing by selecting appropriate crushing conditions so that the average diameter is 1 to 30 μm, or sieving after crushing. The crushing and sieving are preferably performed in an inert atmosphere.

IV) Next, the pulverized fibrous carbon body is heated to 2000 ° C. or higher, preferably 2000 ° C. or higher.
The fibrous carbonaceous material having the above-mentioned properties is manufactured by heat treatment at 3000 ° C., more preferably at a temperature of 2600 to 3000 ° C., and graphitization.

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 material This carbonaceous material has a heat generation peak of 700 ° C. or higher by differential thermal analysis.
Average length L 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.
a is 20 to 100 nm and the sulfur content is 1000 p
pm or less (including 0 ppm).

The carbonaceous material must have an exothermic peak of 700 ° C. or higher as measured by differential thermal analysis. The exothermic peak by the differential thermal analysis is preferably 800 ° C. or higher,
More preferably, it is 840 ° C or higher. The value of the exothermic peak obtained by the differential thermal analysis is a measure of the carbon-carbon bond strength of the carbonaceous material. The carbonaceous material having an exothermic peak in this range has an appropriately developed graphite structure and exhibits the property that lithium ions are reversibly occluded and released between the layers of the hexagonal mesh plane layer in the graphite structure. In addition, it is considered to be a carbonaceous material having a small amount of amorphous carbon which is active in a non-aqueous solvent. A carbonaceous material whose exothermic peak by differential thermal analysis is less than 700 ° C. is not preferable as a negative electrode material for the same reason as explained in the above-mentioned carbonaceous material (2-1).

The carbonaceous material has an average length La of crystallites in the a-axis direction of the graphite structure of the (110) plane diffraction peak obtained by X-ray diffraction of 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, since the graphite structure is appropriately developed and the length of the crystallite in the a-axis direction is appropriate, lithium ions are diffused between the layers of the hexagonal mesh plane layer. Easier to do. In addition, the carbonaceous material having the above structure has a large number of sites where lithium ions enter and leave, and exhibits a property of being able to store and release more lithium ions. In addition,
A carbonaceous material in which La deviates from the above range is not preferable as a 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.
~ 1000 ppm is required. The carbonaceous material that contains sulfur or does not contain sulfur in the above range has an increased storage / release amount of lithium ions 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 by differential thermal analysis is developed to some extent, the sulfur content is 1,000 ppm or less (0 pp
(including m), there are few defects in the graphite structure, as a result, collapse of the graphite structure is less likely to occur, and the amount of occlusion / release of lithium ions is increased. In addition, the carbonaceous material having a sulfur content of 1,000 ppm or less (including 0 ppm) reduces 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 the inhibition of the electrode reaction. It is possible to In addition, the sulfur is 1000
The content of carbonaceous matter exceeding the ppm is the above-mentioned 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 graphitized from a high-purity raw material having a particularly low sulfur content, and high-purity petroleum pitch, a cortall, a heavy oil having a low sulfur content, Graphite or carbonized coke made from synthetic pitch, synthetic polymer, organic resin, etc.
Examples thereof include carbon fibers, spherical carbon bodies, resin fired bodies, and vapor grown carbon bodies.

(2-3) Carbonaceous Material This carbonaceous material has a heat generation peak of 700 ° C. or more in the differential thermal analysis.
And each metal element content is 0 to 50 pp
m, silicon content 0 to 50 ppm, nitrogen content 0 to 1000 ppm, sulfur content 0 to 1000 pp
m.

The carbonaceous material must have an exothermic peak of 700 ° C. or higher as measured by differential thermal analysis. The exothermic peak by the differential thermal analysis is preferably 800 ° C. or higher,
More preferably, it is 840 ° C or higher. The value of the exothermic peak measured by the differential thermal analysis is a measure of the carbon-carbon bond strength of the carbonaceous material. The carbonaceous material having an exothermic peak in this range has an appropriately developed graphite structure, and exhibits a property of reversibly occluding / desorbing lithium ions between the layers of the hexagonal network surface layer in the graphite structure. In addition, it is considered to be a carbonaceous material having a small amount of amorphous carbon which is active in a nonaqueous solvent. A carbonaceous material whose exothermic peak by differential thermal analysis is less than 700 ° C. is not preferable as a negative electrode material for the same reason as explained in the above-mentioned carbonaceous material (2-1).

The carbonaceous material contains 0 to 50 ppm of various metal elements such as Fe and Ni, 0 to 50 ppm of silicon, and 0 to 500 pp of oxygen.
It is necessary that the content of m and sulfur is 0 to 1000 ppm.

The carbonaceous material containing sulfur in the above range or containing no sulfur increases the occlusion / release amount of lithium ions and reduces the reductive decomposition of the non-aqueous solvent. The carbonaceous material having a sulfur content of more than 1000 ppm is not preferable as the 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 impurity element other than sulfur exceeds the above range, the lithium ions existing between the carbon layers react with the impurity element and are consumed, and the lithium involved in the battery reaction is reduced.

As such a carbonaceous material, a pitch-based raw material of high purity, specifically, coal, petroleum pitch, or synthetic pitch is obtained by heat treatment at about 800 ° C. to about 2000 ° C. Box, resin fired body, or about 2
Examples thereof include graphitized products and graphite obtained by heat treatment at a temperature of 000 ° C to about 3000 ° C. Preferably, mesophase spherules obtained from mesophase pitch, or mesophase pitch-based carbon fibers are used at about 800 ° C to about 200 ° C.
A lithium secondary battery having a negative electrode containing a carbonaceous material carbonized at 0 ° C. or a carbonaceous material graphitized at about 2000 ° C. to about 3000 ° C. has excellent capacity, charge / discharge efficiency, and cycle life.

3) Composition of Non-Aqueous Electrolyte Solution The non-aqueous electrolyte solution contained in the container 1 is prepared by dissolving an electrolyte in a non-aqueous solvent.

The non-aqueous solvent includes (a) at least one solvent selected from ethylene carbonate (EC) and propylene carbonate (PC).
Mixed solvent of 80% by volume and 20 to 90% by volume of at least one 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.

The chain carbonate used in the mixed solvent (a) is dimethyl carbonate (DM
C) or diethyl carbonate (DEC) are 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 the first
This is because if the amounts of the components deviate from the above ranges, the conductivity of the non-aqueous electrolytic solution and the charging / discharging efficiency of the negative electrode are reduced, and the capacity and cycle life of the battery are reduced.

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

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

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

The non-aqueous electrolytic solution contains the imide-based lithium salt (electrolyte) in an amount of 0.1 mol / l to 3.
Prepared by dissolving an amount of 0 mol / l. The main impurities present in the non-aqueous electrolyte are water and
Examples thereof include organic peroxides (eg glycols, alcohols, carboxylic acids), halides, sulfur oxides, nitrides and heavy metals. Since these impurities adversely affect the negative electrode and the like, it is preferable to reduce them as much as possible. Especially, the water content is 50ppm or less, and the organic peroxide is 1
It is preferably 000 ppm or less. By reducing the amount of impurities in the non-aqueous electrolyte as described above, the charge / discharge efficiency of the negative electrode is improved and the cycle life is improved.

[0092]

The lithium secondary battery according to the present invention comprises at least one solvent 10 to 8 selected from EC and PC.
In a non-aqueous solvent prepared by mixing 0% by volume with 20 to 90% by volume of at least one solvent selected from diethoxyethane, chain carbonate and acetonitrile, 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) is an imide lithium salt in an amount of 0.1 mol / l to 3 It has excellent high temperature operation performance, storage performance, rate characteristics and cycle life because it has a non-aqueous electrolyte solution dissolved in mol / l.

That is, the non-aqueous electrolyte having the above composition has a high electric conductivity. In addition, the non-aqueous electrolyte is a carbonaceous material that absorbs and releases lithium ions, which is a negative electrode material, a chalcogen compound, is excellent in stability against light metal or lithium metal, and is a positive electrode material, LiCoO ₂ , LiNiO ₂ ,
It is stable when taking out a high voltage of 4 V using LiMn ₂ O ₄ . Furthermore, since the reactivity of the mixed solvent and the imide-based lithium salt is low, the non-aqueous electrolytic solution composed of these 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 has 10 to 80% by volume of γ-butyrolactone and at least one selected from 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), and is excellent because it has a non-aqueous electrolyte solution in which 0.1 mol / l to 3 mol / l of an imide-based lithium salt is dissolved. It 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 component. This is because γ-BL was used as the first component in the mixed solvent. Also, the non-aqueous electrolyte has excellent stability with respect to the negative electrode and the positive electrode. Furthermore, since the reactivity of γ-BL in the mixed solvent with the imide-based lithium salt is very 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 composition has higher high-temperature operating performance and storage than the secondary battery including the non-aqueous electrolyte containing the mixed solvent containing EC and PC as the first component. Has performance, rate characteristics and cycle life.

Furthermore, the above-mentioned (2-1) to (2-3)
Since a negative electrode containing a carbonaceous material that absorbs and releases lithium ions having the characteristics described above can achieve rapid absorption and release of lithium ions, a secondary battery with significantly improved high rate (rapid charge / discharge) performance can be obtained. Obtainable. Further, by combining the negative electrode with the above-mentioned non-aqueous electrolyte, the charge and discharge efficiency of the positive electrode and the negative electrode can be significantly improved and the cycle life can be lengthened. This is because the growth of the organic film formed on the surface of the carbonaceous material in the non-aqueous electrolyte is suppressed, and the resistance value of the film is small, so that reversibility of occlusion / release of lithium ions is increased. Conceivable.

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

[0098]

EXAMPLES The present invention will be described in detail below with reference to the cylindrical lithium secondary battery shown in FIG. Example 1 First, lithium cobalt oxide (Li _x CoO ₂ (0.
8 ≦ x ≦ 1)) 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, toluene was added and mixed, and this mixture was mixed with a thickness of 30 μm. A positive electrode was produced by applying it to a current collector made of aluminum foil and then pressing.

Further, after the mesophase carbon fibers made of mesophase pitch as a raw material were carbonized by heat treatment at 1000 ° C. in an argon atmosphere, 90% by volume was found to have an average particle size of 25 μm and a particle size distribution 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 to 4 %% or less and then graphitizing at 3000 ° C. in an argon atmosphere.

The carbonaceous material obtained had an average particle size of 25 μm.
Graphitized carbon powder of 9 to 1-80 μm in particle size distribution
0% by volume was present, and the particle size distribution of particles having a particle size of 0.5 μm or less was 0% by volume. The carbonaceous material 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
The value of / P ₁₀₀ was 1.5. d ₀₀₂ is 0.336
It was 8 nm. The exothermic peak measured by differential thermal analysis was 810 ° C.

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 semellose, and this was coated on a copper foil as a current collector, A negative electrode was produced by drying.

The positive electrode, the separator made of a polypropylene 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, bistrifluoromethylsulfonylimide lithium [Li (CF ₃ SO
₂ ) ₂ N] is a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) (mixing volume ratio 40: 20: 4).
0) was dissolved in 1.0 mol / l to prepare a non-aqueous electrolytic solution.

The electrode group and the electrolytic solution were respectively housed in a stainless steel cylindrical container having a bottom, and the cylindrical lithium secondary battery shown in FIG. 1 was assembled. 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).
0) was used, and the cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1.

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

Example 4 Ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (D) as a non-aqueous solvent
MC) and diethyl carbonate (DEC) mixed solvent (mixed volume ratio 40: 10: 25: 25) except that the cylindrical lithium secondary battery shown in FIG. I assembled the battery.

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

Example 6 The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that the carbonaceous materials and non-aqueous electrolytes shown below were used.

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

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

Example 7 Carbonaceous materials similar to those in Example 6 and γ-butyrolactone (γ-BL) and ethylene carbonate (E) were used as the non-aqueous solvent.
C) and 2-methyltetrahydrofuran (2MeTH
The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that the mixed solvent (F) (mixed volume ratio 30:50:20) was used.

Example 8 Carbonaceous materials similar to those in Example 6 and γ-butyrolactone (γ-BL) and ethylene carbonate (E) were used as the non-aqueous solvent.
The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that a mixed solvent of C) and acetonitrile (AN) (mixed volume ratio 20:50:30) was used.

Example 9 As a non-aqueous electrolyte, bistrifluoromethylacetylimide lithium [Li (CF ₃ CO) ₂ N] was used as ethylene carbonate.
Other than using a solution of 1.0 mol / l in a mixed solvent (mixing volume ratio 60:10:30) of carbonic acid (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The cylindrical lithium secondary battery shown in FIG. 1 and having the same configuration as in Example 1 was assembled.

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

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

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

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

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

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

As is apparent from FIG. 2, the present Examples 1 to 11
It can be seen that the lithium secondary battery of No. 1 has a higher capacity even at high rate discharge than the batteries of Comparative Examples 1 to 3 and the cycle life is remarkably improved.

[0122] In a repeated test of similar charge and discharge at room temperature (25 ° C), the lithium secondary batteries of Examples 1 to 11 had higher capacity and longer life than the batteries of Comparative Examples 1 to 3.

In the above embodiment, an example in which the invention is applied to a cylindrical lithium secondary battery is explained, but the invention is also applicable to a prismatic lithium secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, and a plurality of positive electrodes, separators and negative electrodes may be laminated in this order.

[0124]

As described above, according to the present invention, it is possible to provide a lithium secondary battery having a high capacity and an excellent cycle life even when used at high temperatures.

[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 the charge / discharge cycle and the 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]

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

Claims (2)

[Claims] 1. A positive electrode, a negative electrode containing lithium metal, a carbonaceous material that absorbs and releases lithium ions, a chalcogen compound that absorbs and releases lithium ions, or a light metal that absorbs and releases lithium ions, and a non-aqueous electrolyte solution. In the lithium secondary battery, the non-aqueous electrolyte solution is at least one solvent selected from ethylene carbonate and propylene carbonate at 10 to 80% by volume and at least diethoxyethane, chain carbonate and acetonitrile. 1
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 an SO ₂ group), and the imide-based lithium salt is dissolved in an amount of 0.1 to 3 mol / l. 2. A positive electrode, a negative electrode containing lithium metal, a carbonaceous material that absorbs and releases lithium ions, a chalcogen compound that absorbs and releases lithium ions, or a light metal that absorbs and releases lithium ions, and a non-aqueous electrolyte. In the lithium secondary battery comprising, the non-aqueous electrolytic solution comprises 10 to 80% by volume of γ-butyrolactone and at least one solvent 20 selected from cyclic carbonate, chain carbonate, diethoxyethane, cyclic ether and acetonitrile. ˜90% by volume in a non-aqueous solvent of the formula Li (C _n X _{2n + 1} Y) ₂ N (where X
Is halogen, n is an integer of 1 to 4, Y is a CO group or SO
_The imide-based lithium salt represented by
A lithium secondary battery, characterized in that it is formed by dissolving 3 mol / l.