JP3374136B2 - 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 improvement of an electrolyte for a lithium secondary battery using a carbon material containing graphite as a single component or a main component as a negative electrode material.

[0002]

2. Description of the Related Art Recently, in recent years,
As a negative electrode material for a lithium secondary battery, a carbon material has been studied as a negative electrode material that replaces the conventional lithium alloy because it has excellent flexibility and there is no risk of electrodeposition of mossy lithium.

By the way, the carbon material that has been mainly studied in the past is coke, and graphite has been almost excluded from the subject of the study. However, in coke, since the amount of lithium inserted is not sufficiently large, it is difficult to obtain a large-capacity battery. As far as the inventors of the present invention know, as a document proposing a secondary battery using graphite as a negative electrode material, USP No.
Only 4,423,125 can be mentioned.

In the above-mentioned US Patent Publication, a carbon material capable of occluding lithium as an active material is used as a negative electrode material, and 1,3-dioxolane as a solvent and LiAsF ₆ as an electrolyte solute are dissolved in an electrolytic solution. A secondary battery using the above has been proposed, and the publication discloses that a secondary battery having excellent cycle characteristics can be obtained.

However, in the embodiment described later,
As shown in the characteristics of the conventional battery, the conventional secondary battery has not only cycle characteristics (cycle life), but also capacity per unit weight of graphite (mAh / g), initial charge / discharge efficiency (%), and battery capacity. (%), Self-discharge rate (% / month),
In many respects such as charge / discharge efficiency (%), the characteristics were inferior, and the secondary battery was not satisfactory in practical use.

It is speculated that this is because 1,3-dioxolane is polymerized on the negative electrode side (reduction side).

The present invention has been made in view of the above circumstances, and an object thereof is to provide a graphite having a large battery capacity, a small self-discharge rate, excellent cycle characteristics, and high charge-discharge efficiency. It is to provide a lithium secondary battery as a negative electrode material.

[0008]

In order to achieve the above object, in a lithium secondary battery according to the present invention, a positive electrode containing a compound capable of inserting and extracting lithium as a main material, and a c-axis in X-ray diffraction are used. Direction crystallite size Lc is 150Å
A negative electrode containing a carbon material as a main material, which is obtained by firing a mixture of the above graphite (except those having a crystallite size Lc in the c-axis direction in X-ray diffraction of less than 300 Å) and pitch.
A separator interposed between these positive and negative electrodes and an electrolytic solution in which an electrolyte solute is dissolved in a solvent, and as the above solvent, a mixed solvent of ethylene carbonate and a low boiling point solvent (excluding dimethoxyethane) Was used.

In the lithium secondary battery of the present invention, the compound capable of inserting and extracting lithium used for the positive electrode is Li ₂ FeO ₃ as an inorganic compound,
Examples thereof include oxides having so-called tunnel-shaped pores such as TiO ₂ and V ₂ O ₅ , and metal chalcogenides having a layered structure such as TiS ₂ and MoS _{2. The} composition formula is Li _x MO ₂ or Li _y.
M ₂ O ₄ (where M is a transition element, 0 ≦ x ≦ 1, 0 ≦ y ≦
The complex oxide represented by 2) is preferable, and specific examples thereof include LiCoO ₂ , LiMnO ₂ , and LiNiO.
₂ , LiCrO ₂ , LiMn ₂ O _{4, and the} like.

As the organic compound capable of occluding and releasing lithium used for the positive electrode, a conductive polymer such as polyaniline, a perfluorocarbon sulfonic acid represented by the following chemical formula 1 in a conductive polymer such as polyaniline (manufactured by DuPont, product Examples thereof include dopant-containing conductive polymers doped with the name “Nafion” or porphyrin.

[0011]

[Chemical 1]

Other compounds that can store and release lithium used for the positive electrode include LiCoO ₂ and L between graphite layers.
iMnO ₂ , LiNiO ₂ , Li ₂ FeO ₃ , LiCrO ₂
Intercalation compounds with metal oxides such as intercalation compounds, intercalation compounds with anions intercalated between graphite layers, intercalation compounds with halogen or halide intercalation between graphite layers, intercalation layers with porphyrin intercalation between graphite layers A compound etc. can also be used.

The positive electrode material is kneaded with a conductive agent such as acetylene black or carbon black and a binder such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PVdF) to prepare a positive electrode mixture. Used as. Among the above-mentioned conductive polymers and dopant-containing conductive polymers, those having excellent conductivity may be kneaded with a binder without blending a conductive agent to obtain a positive electrode mixture.

Further, in the lithium secondary battery of the present invention, as the material of the negative electrode, graphite having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more as described above (however, in the X-ray diffraction A carbon material obtained by firing a mixture of a crystallite size Lc in the c-axis direction Lc of less than 300Å) and a pitch is used.

Here, as the above-mentioned graphite, graphite having an average particle diameter in the range of 1 to 30 μm, and the d value (d ₀₀₂ ) of the lattice plane (002) plane in X-ray diffraction is 3.35-3.3. Four
Graphite having a specific surface area of 0.5 to 50 m ² within the range of 0Å
/ G in the range of true density of 1.9 to 2.3 g / g
It is preferable to use graphite in the range of cm ³ , and further, the crystallite size La in the a-axis direction in X-ray diffraction is La.
Is 150 Å or more, the atomic ratio of H / C is 0.1 or less, and the G value in Raman analysis (1360 cm ^-1 /
It is more preferable to use graphite whose 1590 cm ⁻¹ ) is 0.05 or more.

The graphite as described above may be natural graphite, artificial graphite or quiche graphite. By the way, quiche graphite is used in a blast furnace at an iron mill.
When iron was melted at a temperature of 00 ° C or higher, the carbon contained in the iron sublimated, adhered to the furnace wall, and recrystallized. It is a high carbon material. Moreover, you may make it use the mixture of 2 or more types of these graphites as needed. The artificial graphite referred to here also includes graphite-based substances such as expanded graphite obtained by further processing and modifying graphite.

Examples of the above-mentioned natural graphite include graphite from Sri Lanka, graphite from Madagascar, flake graphite from Korea, clay-like graphite from Korea, and graphite from China. Coke-based graphite is an example of artificial graphite. The lattice plane (002) in X-ray diffraction of these natural graphite and artificial graphite
Table 1 shows the d value (d ₀₀₂ ) of the plane and the crystallite size Lc in the c-axis direction in X-ray diffraction.

[0018]

[Table 1]

Commercial products of the above-mentioned natural graphite include
"NG-2", "NG-2L", "N" manufactured by Kansai Thermochemical Co., Inc.
"G-4", "NG-4L", "NG-7", "NG-7"
L "," NG-10 "," NG-10L "," NG-1 "
2 "," NG-12L "," NG-14 "," NG-1 "
4L "," NG-100 "," NG-100L "(above, high-purity graphite with a purity of 99% or more);" CX-3000 "," FBF "," BF "," CB "manufactured by Chuetsu Graphite Co., Ltd.
R ”,“ SSC-3000 ”,“ SSC-600 ”,
"SSC-3", "SSC", "CX-600", "C
"PF-8", "CPF-3", "CPB-6S", "C
PB "," 96E "," 96L "," 96L-3 ",
"90L-3", "CPC", "S-87", "K-"
3 "," CF-80 "," CF-48 "," CF-3 "
2 "," CP-150 "," CP-100 "," C
P "," HF-80 "," HF-48 "," HF-3 "
2 "," SC-120 "," SC-80 "," SC-6 "
0 "," SC-32 "(above, scaly graphite)," APF-
3000 "," APF "," AX-600 "," S- "
3 "," AP-6 "," AP-3 "," 300F ",
"150F" (above, soil graphite); "CSSP", "CSPE", "CSP", "special C" manufactured by Nippon Graphite Industry Co., Ltd.
P ”,“ CP ”,“ CP / B ”,“ CB-150 ”,
"CB-100", "F # 1", "F # 2", "F #
3 ”,“ SF • A ”,“ SF • B ”(above, scaly graphite),“ AOP ”,“ AUP ”,“ ASSP ”,“ AS ”
"P", "AP", "blue P", "APB", "PD",
"CA.C", "P # 1" (above, earth graphite), "AC
P-1000 "," ACP "," ACCB-150 ",
"SP-5", "SP-5L", "SP-10", "S"
P-10L "," SP-20 "," SP-20L ",
"SCB + 100", "SP-300", "HOP"
(The above is high-purity graphite having a purity of 97.5% or more).

Commercial products of the above-mentioned artificial graphite include
"RA-3000", "RA-15" manufactured by Chuetsu Graphite Co., Ltd.
"RA-44", "GX-600", "G-6S",
"G-3", "G-150", "G-100", "G-"
48 "," G-30 "," G-50 ";" HAG-150 "," HAG-15 "," HAG "manufactured by Nippon Graphite Industry Co., Ltd.
-5 "," PAG-15 "," PAG-5 "," PAG "
-80 "," PAG-60 "," SGS-100 ",
"SGS-50", "SGS-25", "SGS-1"
5 "," SGS-5 "," SGS-1 "," SGP-1 "
00 "," SGP-50 "," SGP-25 "," SG "
P-15 "," SGP-5 "," SGP-1 "," SG "
O-100 "," SGO-50 "," SGO-25 ",
"SGO-15", "SGO-5", "SGO-1",
"SGX-100", "SGX-50", "SGX-2"
5 "," SGX-15 "," SGX-5 "," SGX- "
1 ", 9QP% or more of high-purity artificial graphite," QP-2 "," QP-5 "," QP-10 ",
“QP-20” is exemplified.

Further, as a commercially available product of artificial graphite obtained by further processing and modifying natural graphite, natural graphite powder is pitched,
"AOP-" manufactured by Nippon Graphite Industry Co., Ltd., which has been surface-treated with acrylic, titanate or the like to improve dispersibility in a resin.
Pi5 "," AOP-B5 "," AOP-A5 "," A
OP-T1 "is illustrated.

Further, as a commercially available product of expanded graphite obtained by expanding the layers of natural graphite by acid treatment, "S" manufactured by Chuetsu Graphite Co., Ltd.
"SLF", "SSMF", "SSFF", "SLF",
"SMF", "SFF", "EMK", "ELF",
"EMF", "EFF", "CMF";"EXP-SPM","EXP-12M","EX" manufactured by Nippon Graphite Industry Co., Ltd.
P-80M "and" EXP-SM "are illustrated.

As the graphite other than the natural graphite and the artificial graphite, the above-mentioned Kish graphite which is commercially available from Kansai Thermal Chemical Co., Ltd. may be used.

The pitch mixed with the above graphite is
It may be either petroleum pitch or coal pitch.

As the carbon material obtained by firing the above mixture of graphite and pitch, it is preferable to use a carbon material having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more. Here, in order to obtain a carbon material having Lc of 150 Å or higher, it is necessary to set the firing temperature to 1000 ° C or higher, and normally the firing temperature is set to 1000 to 3000 ° C.

By thus mixing the graphite with the pitch and firing the graphite, the adhesion of the graphite to the core (conductive substrate) can be improved. The preferred addition ratio of pitch to graphite is in the range of 2 to 10 parts by weight with respect to 100 parts by weight of graphite. This is because if the addition ratio of pitch is less than 2 parts by weight, the above-mentioned effect of improving the adhesiveness is not sufficiently exhibited, while if the addition ratio exceeds 10 parts by weight, the energy density is lowered, and further, Both are not preferable because they lead to a decrease in battery capacity.

The carbon material obtained by firing the mixture of graphite and pitch as described above is kneaded by a conventional method with a binder such as polytetrafluoroethylene or polyvinylidene difluoride to prepare a negative electrode mixture. used.

In the lithium secondary battery according to the present invention, a mixed solvent of ethylene carbonate and a low boiling point solvent (excluding dimethoxyethane) is used as a solvent in the electrolytic solution as described above. . In addition,
In the present specification, the low boiling point solvent refers to a solvent having a boiling point of 150 ° C or lower.

Here, as the low boiling point solvent, 1,
Ether-based low boiling point solvents such as 2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), dimethyl carbonate (DMC), diethyl carbonate (DE
Ester low boiling point solvents such as C) can be used,
Particularly, it is preferable to use an ester low boiling point solvent such as dimethyl carbonate (DMC) or diethyl carbonate (DEC).

When dimethyl carbonate is used as the low boiling point solvent, the conductivity of dimethyl carbonate is high, so that the high-rate discharge characteristics are improved, and when diethyl carbonate is used, the viscosity of diethyl carbonate at low temperature is low and Since it has excellent conductivity, the low-temperature discharge characteristic is particularly improved.

When mixing the above-mentioned low boiling point solvent with ethylene carbonate, ethylene carbonate
It is preferable that the content is 0 to 80% by volume because the battery capacity at the time of high rate discharge becomes large.

In the lithium secondary battery of the present invention, examples of the electrolyte solute dissolved in the above mixed solvent include LiPF ₆ , LiBF ₄ , and LiClO.
₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃
SO ₂ ) ₂ , LiAsF ₆ or the like can be used. Then, in dissolving such an electrolyte solute in the solvent as described above, it is preferable that the ratio of the electrolyte solute is 0.1 to 3 mol / liter, and more preferably,
0.5 to 1.5 mol / liter.

Here, in the negative electrode, a lithium secondary battery using graphite satisfying the conditions shown in the present invention and a lithium secondary battery using coke not satisfying the conditions of the present invention were charged and discharged. The cycle characteristics were examined and the results are shown in FIG. Here, in FIG. 1, the vertical axis represents the negative electrode potential (V) with respect to the Li / Li + single electrode potential, and the horizontal axis represents the capacity per 1 g of the carbon material (graphite or coke) (mAh / g).
Is a graph showing the charge and discharge cycle characteristics of the lithium secondary battery using graphite satisfying the conditions of the present invention is shown by a solid line, the lithium secondary battery using coke not satisfying the conditions of the present invention The charge / discharge cycle characteristics are shown by the broken line. The direction of the arrow in the figure indicates the direction in which the negative electrode potential rises and falls during charging and discharging. The charge / discharge cycle characteristics shown are
Both are data for both batteries when a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 was used as an electrolyte solvent.

First, the charge / discharge cycle of a lithium secondary battery using coke which does not satisfy the conditions of the present invention will be described with reference to FIG. The potential of the negative electrode (point a), which was about 3 (V) before the initial charging, was Li / Li ⁺ single-pole potential (the negative electrode potential on the vertical axis is this as the initial charging progressed and Li was occluded in the coke). The potential approaches the reference (0 V), and when charging is completed, point b (negative electrode potential:
0 V, capacity: about 300 mAh / g). Note that b
The coke at the point is brown to red. Next, when the first discharge is performed, the potential of the negative electrode rises as the discharge progresses, and point c (capacity: 5) indicating the discharge end potential (about 1 V).
0 to 100 mAh / g). During the first discharge, the hysteresis reaches the point c without returning to the route followed during the initial charge, because Li corresponding to the capacity shown by P in the figure is trapped in the coke, This is because in the subsequent electrode reaction in charge and discharge, only Li in an amount corresponding to the capacity indicated by Q in the figure can participate in the reaction. By repeating the subsequent charge / discharge cycle, the potential of the negative electrode becomes c
It fluctuates in a cycle such as → b → c → b ....

Next, a charge / discharge cycle in a lithium secondary battery using graphite satisfying the conditions of the present invention will be described. Before the initial charging, the potential of the negative electrode (point a), which was about 3 (V) before the initial charging, was similar to that of the lithium secondary battery using the above-mentioned coke. / Li + approaches the unipolar potential, and when the charging is completed, the potential for the Li / Li + unipolar potential is 0 V d
It reaches the point (capacity: 375 mAh / g). It should be noted that the graphite at point d had a golden color, which confirms that C ₆ Li was also produced by X-ray diffraction. Then the first
When the second discharge is performed, the potential of the negative electrode rises as the discharge progresses, and point e (capacity:
25 mAh / g). By repeating the subsequent charge / discharge cycle, the potential of the negative electrode fluctuates in a cycle such as e → d → e → d.

Based on the charge / discharge cycle characteristics shown in FIG.
Comparing the battery characteristics of the lithium secondary battery using graphite satisfying the conditions of the present invention and the lithium secondary battery using coke not satisfying the conditions of the present invention, graphite satisfying the conditions of the present invention was obtained. The charging capacity per 1 g of graphite at the time of initial charging of the used lithium secondary battery was 375 m.
While it is as large as about Ah / g (point d), the charging capacity per 1 g of coke at the time of initial charging in the lithium secondary battery using the coke that does not satisfy the conditions of the present invention is 3
It is as small as about 00 mAh / g (point b), and the capacity per 1 g of graphite up to a discharge end potential of 1 V of a lithium secondary battery using the above graphite is about 350 mAh / g (de).
On the other hand, the capacity of the lithium secondary battery using the above coke per 1 g of coke up to the discharge end voltage of 1 V is as small as about 200 to 250 mAh / g (b-c).

This means that the charge / discharge efficiency of the lithium secondary battery using graphite satisfying the conditions of the present invention is higher than that of the lithium secondary battery using coke which does not satisfy the conditions of the present invention. .

The charging / discharging curve of the lithium secondary battery using graphite satisfying the conditions of the present invention is almost flat during the discharge from the point d to the point e, and the negative electrode potential sharply increases when approaching the point e. While rising, the charge / discharge curve of the lithium secondary battery using the coke that does not satisfy the conditions of the present invention gradually increases from point b to point c.

This also means that the lithium secondary battery using graphite satisfying the conditions of the present invention is flat in discharge voltage as compared with the lithium secondary battery using coke which does not satisfy the conditions of the present invention. Means superior.

As compared with the lithium secondary battery using the coke that does not satisfy the conditions of the present invention as described above, the lithium secondary battery using the graphite that satisfies the conditions of the present invention has a higher charge / discharge efficiency, and The fact that the discharge voltage is flat means that the discharge capacity of the lithium secondary battery using graphite satisfying the conditions of the present invention is larger than that of the lithium secondary battery using coke which does not satisfy the conditions of the present invention. It means that.

[0041]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

Reference Example 1 [Preparation of Positive Electrode] Cobalt carbonate and lithium carbonate were mixed at an atomic ratio of Co: Li of 1: 1 and then heat treated in air at 900 ° C. for 20 hours to obtain LiC.
oO ₂ was obtained.

LiC as the positive electrode material thus obtained
In oo ₂ , acetylene black as a conductive agent and a fluororesin dispersion as a binder were added in a weight ratio of 9
The mixture was mixed at a ratio of 0: 6: 4 to obtain a positive electrode mixture. And
This positive electrode mixture was rolled on an aluminum foil as a current collector and heat-treated under vacuum at 250 ° C. for 2 hours to produce a positive electrode.

[Preparation of Negative Electrode] Fluororesin dispersion as a binder was added to each of natural graphite, artificial graphite and Lonza graphite produced in China as a negative electrode material of 400 mesh pass in a weight ratio of 95: 5. The mixture was mixed to obtain a negative electrode mixture. Then, each of these negative electrode mixtures was rolled on an aluminum foil serving as a current collector, and heat-treated under vacuum at 250 ° C. for 2 hours to produce negative electrodes containing each carbon material as a main material. Here, the particle size of graphite used for the negative electrode is 40
0 mesh pass is preferable, and 2 to 14 μm is preferable.

The above-mentioned natural graphite, artificial graphite, and Lonza graphite produced in China all had a crystallite size Lc in the c-axis direction in X-ray diffraction of 300 Å or more.

Here, X-ray diffraction was performed under the following measurement conditions (the following X-ray diffraction was also under the same measurement conditions). Radiation source: CuKα Slit: Divergence slit 1 °, scattering slit 1 °, light receiving slit 0.3 mm Gonio radius: 180 mm Graphite curved crystal monochromator

[Preparation of Electrolyte Solution] In a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1,
LiPF ₆ was dissolved at 1 mol / liter to prepare an electrolytic solution. The mixing ratio is preferably in the range of 0.001: 1 to 1: 0.01.

[Production of Reference Batteries BA1 to BA3] A cylindrical non-aqueous electrolyte secondary battery was produced using the positive and negative electrodes and the electrolyte described above. Reference battery BA1 using natural graphite as the carbon material, reference battery BA using artificial graphite
2. Reference battery BA3 using Lonza graphite
It is represented by. As the separator, ion-permeable polypropylene (manufactured by Daicel, trade name "Duraguard") was used.

FIG. 2 is a cross-sectional view of the produced reference batteries BA1 to BA3. These reference batteries BA1 to BA3 include a positive electrode 1 and a negative electrode 2, a separator 3 separating these two electrodes, a positive electrode lead 4 and a negative electrode lead 5. , Positive electrode external terminal 6, negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a spirally wound state via the separator 3 into which the electrolytic solution is injected, and the positive electrode 1 is connected to the positive electrode external terminal 6 via the positive electrode lead 4. Further, the negative electrode 2 is connected to the negative electrode can 7 through the negative electrode lead 5 so that the chemical energy generated inside the battery BA1 can be taken out as electric energy to the outside.

(Comparative Example 1) As a negative electrode material, Lc was 26.
A comparative battery BC1 was produced in the same manner as in Reference Example 1 except that the coke of Å was used.

(Charge / Discharge Characteristics of Each Battery) FIG. 3 shows 250 mA of the above reference batteries BA1 to BA3 and comparative battery BC1.
FIG. 4 is a graph showing charge and discharge characteristics after the second cycle in (constant current discharge), with the vertical axis representing voltage (V) and the horizontal axis representing time (h), and FIG. 4 and FIG. The charge / discharge characteristics of the battery BA1 and the reference battery BA2 are compared with those of the comparative battery B.
The charge and discharge characteristics of C1 are compared, and the vertical axis shows Li /
3 is a graph showing the potential (V) of the negative electrode with respect to the Li + single electrode potential, with the horizontal axis representing the charge / discharge capacity (mAh / g).

From these figures, the reference batteries BA1 to BA3 using the Chinese-made natural graphite, artificial graphite and Lonza graphite as the negative electrode material are superior to the comparative battery BC1 using the coke as the negative electrode material in excellent charging / discharging. It is understood to have characteristics.

FIG. 6 shows the above reference batteries BA1 and BA.
2 is a graph showing the cycle characteristics of No. 2 and comparative battery BC1, with the vertical axis representing discharge capacity (mAh / g) and the horizontal axis representing cycle number. From the figure, reference battery cells BA1 and BA2 using Chinese-made natural graphite and artificial graphite as the negative electrode material are
Compared to the comparative battery BC1 using coke as the negative electrode material,
It can be seen that excellent cycle characteristics are exhibited.

The reference batteries BA1 to BA3 and the comparative battery BC1 were each charged and then stored at room temperature for 1 month, and the storage characteristics were measured. As a result, the self-discharge rate of the reference batteries BA1 to BA3 is 2 to 5% /
The month was 15% for the comparative battery BC1.

Example 1 As a negative electrode material, a carbon material obtained by firing a mixture obtained by adding 5 parts by weight of pitch to 100 parts by weight of the above-mentioned natural graphite produced in China at a temperature of 1000 ° C. was used. Example battery BA4 was made in the same manner as Example 1 except for the above. Here, in the carbon material obtained as described above, the crystallite size Lc in the c-axis direction in X-ray diffraction was 150Å.

FIG. 7 is a graph showing the cycle characteristics of the above-mentioned embodiment battery BA4, with the vertical axis representing the discharge capacity (mAh / g) of the battery and the horizontal axis representing the number of cycles. Note that FIG. 7 also shows, for comparison, the cycle characteristics of the reference battery BA1 using only the above-mentioned natural graphite as the negative electrode material and the comparative battery BC1 using the coke.

As can be seen from the figure, the example battery BA4 has less cycle characteristics than the comparative battery BC1 using coke and the reference battery BA1 using only natural graphite because the carbon material is less likely to fall off the electrode. It can be seen that it is expressed.

Reference Example 2 As a solvent for the electrolytic solution, ethylene carbonate (EC) and dimethyl carbonate (DM) were used.
Reference battery B instead of the mixed solvent having a volume ratio of 1: 1 with C).
In A6, a mixed solvent of ethylene carbonate and diethyl carbonate (DEC) in a volume ratio of 1: 1 was used as a comparative battery B.
In C2, a mixed solvent of ethylene carbonate and dipropyl carbonate (DPC) in a volume ratio of 1: 1 was used, and in a conventional battery, 1,3-dioxolane (1,3-DOL) was used.
Otherwise, in the same manner as in Reference Example 1 above, reference battery BA
6, comparative battery BC2 and conventional battery were produced.

FIG. 8 is a graph showing the charge / discharge characteristics of these batteries, with the vertical axis representing the negative electrode potential (V) and the horizontal axis representing the charge / discharge capacity.

From the figure, it can be seen that the reference battery BA6, like the reference battery BA1 described above, exhibits superior charge / discharge characteristics as compared with the comparative battery BC2 and the conventional battery. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 3 A lattice plane (0
13 types of batteries were produced in the same manner as in Reference Example 1 above, except that 13 types of carbon materials having different d values (d ₀₀₂ ) of the (02) plane were used.

FIG. 9 is a graph showing the relationship between the d ₀₀₂ value of the carbon material and the discharge capacity of the battery.
Ah / g) is plotted on the vertical axis, and the d ₀₀₂ value (Å) of the carbon material used is plotted on the horizontal axis.

From the figure, d ₀₀₂ is 3.35-3.40Å
It can be seen that the battery using graphite as a carbon material has a large discharge capacity. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 4 A negative electrode was prepared by using 12 kinds of carbon materials having different true densities, and other than that, the above Reference Example 1 was used.
Twelve types of batteries were prepared in the same manner as in.

FIG. 10 is a graph showing the relationship between the true density of the carbon material and the discharge capacity of the battery.
Ah / g) is plotted on the vertical axis, and the true density (g / cm ³ ) of the carbon material used is plotted on the horizontal axis.

From the figure, the true density is 1.9 to 2.3 g / c.
It can be seen that the battery using m ³ of graphite as the carbon material has a large discharge capacity. In addition, the above-mentioned Example 1
As shown in, even when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode, similar characteristics are obtained.

Reference Example 5 A negative electrode was prepared using nine kinds of carbon materials having different average particle diameters, and other than that, the above Reference Example 1 was used.
Nine kinds of batteries were produced in the same manner as in.

FIG. 11 is a graph showing the relationship between the average particle size of the carbon material and the discharge capacity of the battery. The discharge capacity (mAh / g) of the battery is plotted on the ordinate and the average particle size of the carbon material used. (Μm) is shown on the horizontal axis.

From the figure, it is understood that the battery using graphite having an average particle size of 1 to 30 μm as the carbon material has a large discharge capacity. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 6 Thirteen types of batteries were produced in the same manner as in Reference Example 1 except that negative electrodes were produced using 13 types of carbon materials having different specific surface areas.

FIG. 12 is a graph showing the relationship between the specific surface area of the carbon material and the discharge capacity of the battery. The discharge capacity (mAh / g) of the battery is plotted on the vertical axis and the specific surface area (m of the carbon material used is ² / g) is a graph showing the horizontal axis.

From the figure, the specific surface area is 0.5 to 50 m ² /
It can be seen that the battery using the graphite of g as the carbon material has a large discharge capacity. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 7 A negative electrode was prepared using 11 kinds of carbon materials having different crystallite sizes Lc in the c-axis direction in X-ray diffraction, and otherwise the same as in Reference Example 1 described above. Eleven types of batteries were produced.

FIG. 13 is a graph showing the relationship between the carbon material Lc and the discharge capacity of the battery. The discharge capacity (mA) of the battery is shown in FIG.
h / g) on the vertical axis and Lc (Å) of the carbon material used
Is a graph in which the horizontal axis represents.

From the figure, Lc is 150 Å or more, especially 30
It can be seen that a battery using graphite having a volume of 0 Å or more as a negative electrode material has a large discharge capacity. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 8 As Table 2 and Table 3 as electrolyte solutions
Twenty-one kinds of batteries were produced in the same manner as in Reference Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ in the mixed solvent shown in 1 at a ratio of 1 mol / liter was used.

Each battery in this reference example 8
After discharging at 00 mA, graphite characteristics [capacity per unit weight (mAh / g) and initial charge / discharge efficiency (%)] and battery characteristics [battery capacity (mAh), self-discharge rate (% / month), cycle life ( Times) and charge / discharge efficiency (%)] were measured, and the results are shown in Tables 2 and 3.

[0078]

[Table 2]

[0079]

[Table 3]

(Reference Example 9) As the electrolytic solution, Tables 4 and 5 were used.
Twenty-one kinds of batteries were produced in the same manner as in Reference Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ in the mixed solvent shown in 1 at a ratio of 1 mol / liter was used. Each battery in Reference Example 9 was also discharged at 100 mA as described above, the same items as in Reference Example 8 were measured, and the results are shown in Tables 4 and 5.

[0081]

[Table 4]

[0082]

[Table 5]

As is clear from the results shown in Tables 2 to 5, when a mixed solvent of a low boiling point solvent such as dimethyl carbonate or diethyl carbonate and ethylene carbonate is used, the above graphite characteristics and The battery characteristics were improved. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 10 As an electrolytic solution, as shown in Tables 6 and 7, dimethyl carbonate, diethyl carbonate, 1,2-diethoxyethane, ethoxymethoxyethane, which are low-boiling solvents, with respect to ethylene carbonate. In the same manner as in the above Reference Example 1, except that an electrolyte solution in which LiPF ₆ was dissolved at a ratio of 1 mol / liter was used in a mixed solvent in which 1: 1 and 4: 1 were mixed, respectively, was used. A seed battery was made. And, as for each battery in this reference example 10, as described above,
After discharging at mA, the same items as in Reference Example 8 were measured, and the results are shown in Tables 6 and 7.

[0085]

[Table 6]

[0086]

[Table 7]

As a result, when a mixed solvent in which dimethyl carbonate, diethyl carbonate, 1,2-diethoxyethane and ethoxymethoxyethane, which are low boiling point solvents, are mixed with ethylene carbonate is used, the above graphite characteristics and The battery characteristics were high. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 11 As an electrolytic solution, as shown in Tables 8 and 9, a mixed solvent prepared by mixing dimethyl carbonate, which is a low boiling point solvent, with ethylene carbonate in a volume ratio of 1: 1 was used. Six types of batteries were produced in the same manner as in Reference Example 1 except that the electrolyte solution obtained by dissolving each of the electrolyte solution solutes described above at a rate of 1 mol / liter was used. Then, with respect to each of the batteries in Reference Example 11, the same items as in Reference Example 8 were measured by discharging at 100 mA as described above, and the results are shown in Table 8 and Table 9.
It was shown to.

[0089]

[Table 8]

[0090]

[Table 9]

As a result, when each electrolyte solution obtained by dissolving each electrolyte solution solute shown in the same table in a mixed solvent prepared by mixing dimethyl carbonate, which is a low boiling point solvent, with ethylene carbonate in a volume ratio of 1: 1 Also in the above, the above-mentioned graphite characteristics and battery characteristics were high. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 12 Ethylene carbonate (EC) and dimethyl carbonate (D
MC), volume mixing ratio is 100: 0, 90:10, 8
0:20, 70:30, 60:40, 50:50, 4
0:60, 30:70, 20:80, 10:90, 0:
Using 11 kinds of solvents that became 100, and using an electrolyte solution in which LiPF ₆ was dissolved in each solvent at a ratio of 1 mol / liter, LiNiO ₂ was used as the positive electrode material, and other than that, the above reference example was used. Eleven types of batteries were produced in the same manner as in 1.

Then, for each battery in Reference Example 12, the battery capacity (mAh) was obtained by discharging at 1 A, and the volume mixing ratio (volume%) of ethylene carbonate (EC) and dimethyl carbonate (DMC) and the battery capacity were calculated. (M
The relationship with Ah) was investigated, and the results are shown in the graph of FIG.

As a result, when the mixed solvent of ethylene carbonate and dimethyl carbonate was used, the battery capacity when discharged at 1 A as described above was a mixture of ethylene carbonate and 20 to 80% by volume. It was higher in the battery using the solvent.
As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 13 As a solvent for the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (D
EC) volume mixing ratio is 100: 0, 90:10, 8
0:20, 70:30, 60:40, 50:50, 4
0:60, 30:70, 20:80, 10:90, 0:
Using 11 kinds of solvents that became 100, and using an electrolyte solution in which LiPF ₆ was dissolved in each solvent at a ratio of 1 mol / liter, LiNiO ₂ was used as the positive electrode material, and other than that, the above reference example was used. Eleven types of batteries were produced in the same manner as in 1.

Then, for each of the batteries in Reference Example 13, the battery capacity (mAh) was obtained by discharging at 1 A,
Volume mixing ratio (volume%) of ethylene carbonate (EC) and diethyl carbonate (DEC) and battery capacity (m
The relationship with Ah) was investigated, and the results are shown in the graph of FIG.

As a result, when a mixed solvent of ethylene carbonate and diethyl carbonate was used, the battery capacity when discharged at 1 A as described above was a mixture containing ethylene carbonate in the range of 20 to 80% by volume. It was higher in the battery using the solvent.
As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 14 As solvents for the electrolytic solution, ethylene carbonate (EC) and dimethyl carbonate (D
The volume mixing ratio of MC) and diethyl carbonate (DEC) is 100: 0: 0, 90: 5: 5, 80: 10: 1.
0, 70:15:15, 60:20:20, 50: 2
5:25, 40:30:30, 30:35:35, 2
11 kinds of solvents, 0:40:40, 10:45:45, and 0:50:50, were used, and LiPF was used for each solvent.
Eleven batteries were prepared in the same manner as in Reference Example 1 except that an electrolyte solution in which ₆ was dissolved at a ratio of 1 mol / liter was used, LiNiO ₂ was used as the positive electrode material.

Then, for each of the batteries in Reference Example 14, the battery capacity (mAh) was obtained by discharging at 1 A,
The relationship between the volume mixing ratio (volume%) of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) and the battery capacity (mAh) was examined, and the result is shown in the graph of FIG. 16.

As a result, when the mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate was used, the battery capacity when discharged at 1 A as described above was 20 to 8 ethylene carbonate.
It was higher in the battery using the mixed solvent contained in the range of 0% by volume. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 15 In Reference Example 15, 16 types of intercalation compounds in which metal oxides or chalcogenides shown in Tables 10 and 11 below were inserted into graphite were used as materials for the positive electrode. did.

In producing these intercalation compounds, 200 g of the metal oxides and chalcogenides shown in Tables 10 and 11 and KMnO _{4 as a} catalyst were stirred in glacial acetic acid, and then the graphite powder Name "NG-7") 10
g, and stirred at 45 ° C for 3 days.

Next, this was filtered, washed with acetic acid, and then dried under reduced pressure at 80 ° C. for 2 days, and the metal oxide residue, metal oxide and metal chalcogenide were separated by centrifugation. It was separated into powder of intercalation compound inserted in graphite. In addition, the case where the thus obtained product is used as it is is shown as a manufacturing method 1 in Tables 10 and 11.

Further, V ₂ O ₅ and Mo containing no Li
O ₃ , CrO ₃ , VO ₂ , MnO ₂ , WO ₃ , Ti
S ₂ , TiSe ₂ , VS ₂ , VSe ₂ , K _0.3 MoO ₃
For the intercalation compound inserted in graphite, LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 in an electrolytic solution of 1 mol / liter, 3mA /
Cathode reduction with a constant current of cm ²
i was inserted. In addition, the case of using the one in which Li is inserted in this way is shown as a manufacturing method 2 in Tables 10 and 11.

The 16 types of intercalation compounds obtained as described above were used as positive electrode materials, and the 16 types of batteries of Reference Example 15 were used in the same manner as in Reference Example 1 except for the above. It was made.

Then, the batteries of Reference Example 15 were each discharged at 100 mA to obtain a positive electrode capacity (mAh / g), a battery capacity (mAh), a self-discharge rate (% / month), a cycle life (times) and a charge. The discharge efficiency (%) was measured, and the results are shown in Tables 10 and 11.

[0107]

[Table 10]

[0108]

[Table 11]

As a result, in each battery using 16 kinds of intercalation compounds in which the above metal oxides or metal chalcogenides are inserted in graphite, the battery capacity, self-discharge rate,
The characteristics of cycle life and charge / discharge efficiency were improved.
As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 16 In Reference Example 16, 24 kinds of positive electrode materials prepared by inserting anions shown in Tables 12 to 14 into graphite by any of the following Production Method 1 to Production Method 3 were used. Was used.

(Production Method 1) BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , ClO
^{_{4 -, B 10 Cl 10 -}} , B 12 Cl 12 -, PF 6 -, wherein the perfluorocarbon sulfonic acid ion (manufactured by DuPont, trade name "Nafion" (Nafion)), CF ₃ COO
^- , S ₂ O ₄ ²⁻ , NO ₃ ⁻ , SO ₄ ²⁻ 6 g of KMnO ₄ was added to 1 liter of a 1M aqueous acid solution containing anions, and the mixture was stirred and then graphite powder (trade name “NG-7”) was added. ) 10 g was added and the mixture was stirred at 60 ° C. for 3 days and then filtered,
It was washed with water and then dried at 60 ° C. for 3 days to obtain an intercalation compound in which the above anion was inserted into graphite.

(Production Method 2) In order to obtain an intercalation compound in which an anion such as TiF ₄ ⁻ or VF ₅ ⁻ is inserted into graphite, Ti is used.
After F ₄ and VF ₅ were put into the chamber and filled with fluorine gas, 10 g of graphite powder (trade name “NG-7”) was put, and 160 ° C. for TiF _{4 and} 180 ° for VF ₅ .
It was exposed to C for 3 days and TiF ₄ ⁻ and VF ₅ ⁻ anions were inserted into graphite.

(Production Method 3) BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , ClO ₄ ⁻ , B ₁₀ C were added to a mixed solvent prepared by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.
l ₁₀ ⁻ , B ₁₂ Cl ₁₂ ⁻ , PF ₆ ⁻ , the above-mentioned perfluorocarbon sulfonate ion (manufactured by DuPont, trade name “Nafion” (Nafion)), CF ₃ COO ⁻ , S ₂ O.
₄ ^2-, NO ₃ ^-, using an electrolytic solution obtained by dissolving Li salt containing anions consisting of SO ₄ ^2-, using graphite in the cathode and anodic oxidation in these electrolytes, said shade graphite After obtaining the intercalation compound into which the ions were inserted, this was washed with the above mixed solvent and dried at 60 ° C for 3 days.

The 24 types of intercalation compounds prepared as described above were used for the positive electrode material, and graphite (trade name "NG-7") was used for the negative electrode in a ratio of 1: 1 ethylene carbonate and dimethyl carbonate. C ₆ Li obtained by cathodic reduction in an electrolytic solution in which LiPF ₆ was dissolved at a ratio of 1 mol / liter in a mixed solvent mixed in a volume ratio was used. Other than that, the case of Reference Example 1 described above was used. In the same manner, 24 types of batteries of Reference Example 16 were produced.

Then, the batteries of Reference Example 16 were each discharged at 100 mA to obtain a positive electrode capacity (mAh / g), a battery capacity (mAh), a self-discharge rate (% / month), a cycle life (times) and a charge. The discharge efficiency (%) was measured, and the results are shown in Tables 12 to 14.

[0116]

[Table 12]

[0117]

[Table 13]

[0118]

[Table 14]

As a result, in each battery of Reference Example 16 using 24 kinds of intercalation compounds in which the above-mentioned anions were inserted into graphite as the positive electrode, the battery capacity, self-discharge rate, cycle life and charge / discharge efficiency were also improved. Each property was improved. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 17 In Reference Example 17, as the material for the positive electrode, 10 kinds of the halogens shown in Tables 15 and 16 below were inserted into graphite by either of the following Production Method 1 and Production Method 2. An intercalation compound was used.

(Production method 1) Graphite powder (trade name "NG-
7 ") was immersed in a fluid of 1 liter of halogen for 24 hours, and unreacted halogen was evaporated near the saturated vapor pressure of the inserted halogen.

(Production Method 2) Graphite powder (trade name "NG-7") was allowed to stand in a halogen gas.

Further, after inserting halogen into graphite by the above-mentioned manufacturing method 1 or manufacturing method 2, LiPF ₆ is mixed at a ratio of 1 mol / l in a mixed solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1. In the electrolytic solution dissolved in, the cathode was reduced with a constant current of 3 mA / cm ² to insert Li.

Then, the ten kinds of intercalation compounds prepared as described above were used for the positive electrode material, and the ten kinds of batteries of Reference Example 17 were prepared in the same manner as in Reference Example 1 except for the above. It was made.

The batteries of Reference Example 17 were each discharged at 100 mA to obtain positive electrode capacity (mAh / g), battery capacity (mAh), self-discharge rate (% / month), cycle life (times) and charge. The discharge efficiency (%) was measured and the results are shown in Table 1.
5 and Table 16.

[0126]

[Table 15]

[0127]

[Table 16]

As a result, also in each battery of Reference Example 17 in which 10 kinds of intercalation compounds in which each of the above halogens was inserted into graphite was used for the positive electrode, the battery capacity, self-discharge rate, cycle life and charge / discharge efficiency were The characteristics were improved. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 18 In Reference Example 18, 10 g of graphite powder (trade name "NG-7") was used in Table 17 below.
Further, vapors of the respective metal chlorides (halides) shown in Table 18 were brought into contact with each other to prepare nine types of intercalation compounds in which the respective metal chlorides were inserted into graphite.

Further, the nine kinds of intercalation compounds thus obtained were dissolved in LiPF ₆ at a ratio of 1 mol / liter in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1. In the electrolytic solution, Li was inserted by performing cathodic reduction with a constant current of 3 mA / cm ² .

Then, the nine kinds of intercalation compounds produced as described above are used for the positive electrode material, and otherwise,
In the same manner as in Reference Example 1 above, nine types of batteries of Reference Example 18 were produced.

The batteries of Reference Example 18 were each discharged at 100 mA to obtain a positive electrode capacity (mAh / g), a battery capacity (mAh), a self-discharge rate (% / month), a cycle life (times) and a charge. The discharge efficiency (%) was measured and the results are shown in Table 1.
7 and Table 18.

[0133]

[Table 17]

[0134]

[Table 18]

As a result, also in each battery of Reference Example 18 using as a positive electrode nine kinds of intercalation compounds in which each of the above metal chlorides (halides) was inserted into graphite, the battery capacity, self-discharge rate, and cycle life , Each property of charge and discharge efficiency was improved. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Reference Example 19 In Reference Example 19, a conductive polymer and a dopant-containing conductive polymer obtained by doping a conductive polymer with a dopant were used for the positive electrode.

Here, in order to obtain the conductive polymer, 0.5 mol of each monomer was dissolved in 1 liter of a 1N aqueous solution of borofluoric acid, and 0.5 mol of ammonium persulfate was added to 1N of borofluoride. A solution dissolved in 1 liter of an aqueous solution of hydrogen acid was added dropwise to cause precipitation. Then, 1N sodium hydroxide aqueous solution was added thereto to remove anions, which were thoroughly washed with water, washed with methanol, and then vacuum dried at 80 ° C. Five kinds of conductive polymer powders of polyaniline, polypyrrole, polythiophene, polycarbazole and polyiminodibenzyl shown in Table 21 were obtained.

Next, each of the above conductive polymer powders was pressure-molded, and the molded body was used for the positive electrode, while lithium metal was used for the negative electrode. Nafion (trade name), polyvinyl polyvinyl sulfonate, lithium persulfate, para It was charged in a non-aqueous solvent in which a dopant selected from lithium toluenesulfonate was dissolved, and each conductive polymer powder used for the positive electrode was doped with the dopant, and the results are shown in Table 19 below.
~ Ten kinds of dopant-containing conductive polymers shown in Table 21 were obtained.

Then, in a mixed solvent of ethylene carbonate and dimethyl carbonate mixed at a volume ratio of 1: 1 LiPF ₆ was dissolved at a ratio of 1 mol / liter, in an electrolytic solution, each of the above conductive polymers and The dopant-containing conductive polymer was subjected to cathodic reduction with a constant current of 3 mA / cm ² , and lithium was inserted into each conductive polymer and the dopant-containing conductive polymer.

Then, 15 kinds of conductive polymers obtained as described above were used as the positive electrode material, and other than that, in the same manner as in Reference Example 1 described above, Reference Example 19
15 kinds of batteries were prepared.

Then, each of the batteries of Reference Example 19 was discharged at 100 mA to obtain a positive electrode capacity (mAh / g), a battery capacity (mAh), a self-discharge rate (% / month), a cycle life (times) and a charge. The discharge efficiency (%) was measured, and the results are shown in Tables 19 to 21.

[0142]

[Table 19]

[0143]

[Table 20]

[0144]

[Table 21]

As a result, Reference Example 19 using each of the above conductive polymers and the conductive polymer containing a dopant as the positive electrode
In each battery, the characteristics of battery capacity, self-discharge rate, and cycle life were improved. As shown in Example 1 above, similar characteristics are obtained when a carbon material obtained by firing a mixture of graphite and pitch is used for the negative electrode.

Further, although the specific examples in which the present invention is applied to the cylindrical battery have been described in the above-mentioned embodiments, the shape of the battery is not particularly limited, and the present invention is applicable to various shapes such as prismatic and flat lithium batteries. It can be applied to a secondary battery.

[0147]

INDUSTRIAL APPLICABILITY The lithium secondary battery according to the present invention has a large battery capacity and a high charge / discharge efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing charge / discharge cycle characteristics of reference batteries BA1 to BA3 and a comparative battery BC1.

FIG. 2 is a cross-sectional view of a cylindrical battery.

FIG. 3 is a diagram showing charge / discharge characteristics of reference batteries BA1 to BA3 and comparative battery BC1.

FIG. 4 is a diagram showing charge / discharge characteristics of a reference battery BA1.

FIG. 5 is a diagram showing charge / discharge characteristics of a reference battery BA2.

FIG. 6 is a diagram showing cycle characteristics of reference batteries BA1 and BA2 and a comparative battery BC1.

FIG. 7 is a diagram showing charge / discharge characteristics of Example battery BA4.

FIG. 8 is a diagram showing cycle characteristics of a reference battery BA6, a comparative battery BC2, and a conventional battery.

FIG. 9 is a diagram showing the relationship between the d ₀₀₂ value of a carbon material and the discharge capacity of a battery.

FIG. 10 is a diagram showing the relationship between the true density of a carbon material and the discharge capacity of a battery.

FIG. 11 is a diagram showing the relationship between the average particle size of a carbon material and the discharge capacity of a battery.

FIG. 12 is a diagram showing the relationship between the specific surface area of a carbon material and the discharge capacity of a battery.

FIG. 13 is a diagram showing the relationship between the crystallite size Lc in the c-axis direction of a carbon material in X-ray diffraction and the discharge capacity of a battery.

FIG. 14 is a diagram showing the relationship between the volume mixing ratio (volume%) of ethylene carbonate (EC) and dimethyl carbonate (DMC) and the battery capacity (mAh) in Reference Example 12.

15 is a diagram showing the relationship between the volume mixing ratio (volume%) of ethylene carbonate (EC) and diethyl carbonate (DEC) and the battery capacity (mAh) in Reference Example 13. FIG.

16 is a diagram showing the relationship between the volume mixing ratio (volume%) of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) and the battery capacity (mAh) in Reference Example 14. FIG. .

[Explanation of symbols]

BA1 battery 1 positive electrode 2 Negative electrode 3 separator 4 Positive lead 5 Negative electrode lead 6 Positive external terminal 7 Negative electrode can

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiro Furukawa 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Toshiyuki Noma, 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Denki Co., Ltd. (72) Inventor Masatoshi Takahashi 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Denki Co., Ltd. (56) Reference JP-A-4-337247 (JP, A) Kaihei 5-28996 (JP, A) JP 64-2258 (JP, A) JP 59-96666 (JP, A) JP 3-8270 (JP, A) JP 2-172162 ( JP, A-JP 63-102166 (JP, A) JP-A 63-121260 (JP, A) JP 4-171675 (JP, A) JP 1-31565 (JP, A) JP 61-111907 (JP, A) JP-A-59-121782 (JP, A) JP-A-60 182670 (JP, A) JP 5-41251 (JP, A) JP 4-332465 (JP, A) JP 4-155775 (JP, A) JP 64-14880 (JP, A) JP-A-4-280068 (JP, A) JP-A-7-320783 (JP, A) JP-A-1-248469 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 10/40 H02M 4/02 H02M 4/58 H02M 4/62

Claims (12)

(57) [Claims] 1. A positive electrode containing a compound capable of occluding and releasing lithium as a main material, and graphite having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more (provided that the crystallite size in the c-axis direction in X-ray diffraction is A negative electrode containing a carbon material as a main material obtained by firing a mixture of a crystallite size Lc of less than 300Å) and a pitch, a separator interposed between the positive and negative electrodes, and an electrolyte in a solvent. A lithium secondary battery comprising an electrolytic solution in which a solute is dissolved, and a mixed solvent of ethylene carbonate and a low boiling point solvent (excluding dimethoxyethane) is used as the solvent. 2. The lithium secondary battery according to claim 1, wherein the low boiling point solvent is an ester low boiling point solvent. 3. The low boiling point solvent is at least one solvent selected from dimethyl carbonate, diethyl carbonate, 1,2-diethoxyethane and ethoxymethoxyethane. Rechargeable lithium battery. 4. The lithium secondary battery according to claim 1, wherein the mixed solvent comprises ethylene carbonate, dimethyl carbonate and diethyl carbonate. 5. The lithium secondary battery according to claim 1, wherein the mixed solvent contains 20 to 80% by volume of ethylene carbonate. 6. The (00) in the X-ray diffraction of the graphite
2) The lithium secondary battery according to any one of claims 1 to 5, wherein the d value of the plane is 3.35-3.40Å. 7. (00) in X-ray diffraction of said graphite
2) The lithium secondary battery according to any one of claims 1 to 5, wherein the d value of the plane is 3.554 to 3.365Å. 8. The lithium secondary battery according to claim 1, wherein the average particle diameter of the graphite is 1 to 30 μm. 9. The specific surface area of the graphite is 0.5 to 50 m.
^{It is 2} / g, The lithium secondary battery in any one of Claims 1-12 characterized by the above-mentioned. 10. The true density of the graphite is 1.9 to 2.3.
It is g / cm < ³ >, The lithium secondary battery in any one of Claims 1-9 characterized by the above-mentioned. 11. The composition formula Li _x MO ₂ or Li _y M ₂ used for the positive electrode is capable of inserting and extracting lithium.
O ₄ (where M is a transition element, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2)
It is represented by any one of Claims 1-10 characterized by the above-mentioned.
The lithium secondary battery according to the item. 12. The lithium secondary battery according to claim 1, wherein LiPF ₆ is dissolved as a solute in the electrolytic solution.