JP3229757B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a positive electrode using a material capable of charging and discharging at 3 V (vs. Li / Li ⁺ ) or more as a positive electrode active material, and having a Lc of 150 °
As described above, a non-aqueous electrolyte for increasing the capacity of a lithium secondary battery including a negative electrode using a carbon material (graphite) having a d ₀₀₂ of 3.37 ° or less, an electrode material, a non-aqueous electrolyte, and a separator Regarding improvement.

[0002]

2. Description of the Related Art In recent years,
BACKGROUND ART A lithium secondary battery using a carbon material, particularly graphite, as an anode active material has attracted attention as a high energy density battery.

[0003] As a solvent for an electrolytic solution of this type of lithium secondary battery, a mixed solvent of a high dielectric constant solvent and a low viscosity solvent is usually used. For example, US Patent Publication (USP) 5
192629 discloses a mixed solvent of ethylene carbonate (high-dielectric-constant solvent) and dimethyl carbonate (low-viscosity solvent) as a solvent for an electrolytic solution of a lithium secondary battery.

However, when this mixed solvent is used, the amount of lithium inserted (doped) between layers of graphite by charging is limited to one lithium (Li) for six carbon atoms (C). Therefore, the discharge capacity of the negative electrode was 372 mAh /
g (theoretical capacity per gram of graphite calculated from C ₆ Li).

In Japanese Patent Application Laid-Open No. Hei 5-212070, ethylene carbonate, γ-butyrolactone, sulfolane, and 1,2-dimethoxy are used as solvents for a non-aqueous electrolyte of a lithium secondary battery using graphite as a negative electrode. A four-component mixed solvent comprising ethane and ethane has been proposed.

However, as a result of investigations by the present inventors, when a mixed solvent containing 1,2-dimethoxyethane or γ-butyrolactone is used as a solvent for a non-aqueous electrolyte of a lithium secondary battery using graphite as a negative electrode, Since these solvents react with C ₆ Li generated in the negative electrode at the end of charging, it was found that there was a problem that the discharge capacity of the negative electrode was reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-capacity lithium secondary battery in which the discharge capacity of a negative electrode exceeds 372 mAh / g.

[0008]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
Of the lithium secondary battery according to the present invention has a 3V (vs. Li /
Li⁺The positive and negative chargeable and dischargeable materials are used as positive electrode active materials.
The size of the pole and the crystallite in the c-axis direction (Lc) is 150 ° or less.
D value on the lattice plane (002) plane (d
₀₀₂) Is less than 3.37 °, occludes lithium ions
And a carbon material that can be released
Electrode, non-aqueous electrolyte comprising solvent and solute, and separator
In a lithium secondary battery comprising:
, Diethyl carbonate (EC), dimethyl carbonate
(DMC), methyl ethyl carbonate (ME
C), methyl propyl carbonate (MPC) and methyl
Group consisting of luisopropyl carbonate (MiPC)
At least one acyclic carbonate (A) selected from
5 to 65% by volumeAnd tetramethylene sulfoxide (TM
SO), a sulfone represented by the following formula 4, and a sulfone represented by the following formula 5
And a sulfoxide represented by the following formula:
Orchid (SL) and its derivatives
At least one kind of sulfur-containing compound (B)5 to 65% by volume
And ethylene carbonate (EC) (C)5 to 65 volumes
%And a mixed solvent consisting of

[0009]

Embedded image

(However, m = 1, 2, 3 or 4)

[0011]

Embedded image

(However, n = 1, 3 or 4)

[0013]

Embedded image

(However, A ^{1 to} A ⁴ are each independently a hydrogen atom or a methyl group)

When the mixing ratio of the above-mentioned mixed solvents is
Steal (A) 10 to 75% by volume, sulfur-containing compound (B)
5 to 65% by volume, ethylene carbonate (C) 5 to 65
What is limited to volume% is that the negative electrode
High capacity lithium secondary battery with extremely large discharge capacity
Because it can be done.

The chargeable / dischargeable material (positive electrode active material) at 3 V (vs. Li / Li ⁺ ) or more includes lithium-containing nickel oxide, lithium-containing cobalt oxide, and lithium-containing cobalt-nickel composite oxide. You.

The solute is LiPF ₆ , L
iBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiAs
F ₆ and LiN (CF ₃ SO ₂ ) ₂ are exemplified.

[0018]

[Function] As a solvent for a non-aqueous electrolyte of a lithium secondary battery,
Acyclic carbonates such as diethyl carbonate (A) 1
0 to 75% by volume , a sulfur-containing compound such as sulfolane (B) 5 to 65% by volume , and ethylene carbonate (C)
Since a mixed solvent of 5 to 65% by volume is used, the discharge per unit weight of the negative electrode graphite is lower than that in the case of using a conventional binary solvent of a two-component system composed of diethyl carbonate and ethylene carbonate. The capacity increases. This is achieved by adding a sulfur-containing compound (B) to a binary mixed solvent consisting of an acyclic carbonate (A) and an ethylene carbonate (C), thereby forming lithium ions (solute) in the non-aqueous electrolyte. Energy is reduced when lithium ions are inserted between graphite layers, so that C ₆ L
This is considered to be due to the fact that Li is inserted more than the ratio of i (C: Li = 6: 1). As described above, since the discharge capacity per unit weight of the negative electrode graphite increases,
For example, the filling amount of graphite in the negative electrode of the positive electrode-dominated lithium secondary battery can be reduced, and the filling amount of the positive electrode active material can be increased. As a result, a high capacity lithium secondary battery can be obtained.

Although the reason is not clear, when the specific mixed solvent in the present invention is used, the mixed solvent of the acyclic carbonate (A) and the ethylene carbonate (C), that is, the sulfur-containing compound (B) is not contained. The cycle characteristics at high temperatures are improved as compared with the case where a mixed solvent is used.

[0020]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples, and can be carried out by appropriately changing the scope of the invention without changing its gist. Things.

(Test Example 1: EC + SL + DEC) [Assembly of Triode Test Cell] Graphite powder (Lc = 3.35)
{; D ₀₀₂ > 1000}) is dispersed in an NMP (N-methylpyrrolidone) solution of PVdF (polyvinylidene fluoride) to prepare a slurry, and the slurry is then subjected to a doctor blade method to form a copper foil as a negative electrode current collector Was coated on both sides and dried to prepare a negative electrode having a 50 μm-thick active material layer (carbon material layer) formed on both sides of a copper foil.

Next, the negative electrode serving as the test electrode and the lithium metal foil serving as the counter electrode were spirally wound through a polyethylene porous film serving as a separator to produce an electrode body.

Next, the electrode body and a reference electrode made of lithium metal were incorporated into a test cell into which a non-aqueous electrolyte was injected to assemble a three-electrode test cell. Various non-aqueous electrolytes shown in the following (1) to (3) were prepared as the non-aqueous electrolyte.

(1) LiPF ₆ was added to seven kinds of mixed solvents obtained by mixing ethylene carbonate and sulfolane in an equal volume mixed solvent, and further mixing diethyl carbonate in various ratios.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

(2) LiPF _{6 is} added to six kinds of mixed solvents obtained by mixing an equal volume mixed solvent of ethylene carbonate and diethyl carbonate with sulfolane at various ratios.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

(3) LiPF _{6 is} added to six kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of sulfolane and diethyl carbonate.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

The three-electrode test cells assembled in this manner are respectively referred to as A1 to A7, B1 to B6, C1 to C6.
Called.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged at 25 ° C. at a current density of 0.1 mA / cm ² to a final voltage of 0 V.
Discharge to a final voltage of 1 V at 0.1 mA / cm ² , 3
The discharge capacity of the negative electrode of the polar test cell was examined. Figure 1 shows the results
(Equilateral triangle). In FIG. 1, the ratio of each solvent in the mixed solvent of the non-aqueous electrolyte used in each of the three-electrode test cells is:
It is obtained from the coordinates of the intersection with each side when three straight lines parallel to each side of the triangle are drawn from each point. That is, SL
-A straight line parallel to the DEC line and the EC-SL line or EC-DE
The intersection with the line C indicates the ratio of ethylene carbonate,
Straight line parallel to C-SL line and SL-DEC line or EC-D
The intersection with the EC line represents the ratio of diethyl carbonate,
Also, a straight line parallel to the EC-DEC line and the EC-SL line or S
The intersection with the L-DEC line indicates the ratio of sulfolane. For example, the solvent ratio (volume%) of the non-aqueous electrolyte in the three-electrode test cell A6 is ethylene carbonate: sulfolane: diethyl carbonate = 45: 45: 10 (see FIG. 3 described later).
11 to 11 are graphs of the same coordinate system. ). FIG. 2 shows the results of the charge / discharge test for the three-electrode test cells B1 to B6 in FIG. 1, the vertical axis represents the discharge capacity (mAh) of the negative electrode, and the horizontal axis represents each solvent of the nonaqueous electrolyte used. 3 is a graph showing the ratio of the values.

As shown in FIGS. 1 and 2, the discharge capacity of the negative electrode of the three-electrode test cell B6 in which sulfolane was not mixed was 372 mAh / g (theoretical capacity in the case of C ₆ Li). And 5% by volume of sulfolane, the discharge capacity of the three-electrode test cell B5 is as large as 380 mAh / g. As described above, even if the amount of sulfolane mixed is small, the effect of the mixture of sulfolane on the increase in the discharge capacity of the negative electrode is extremely large, and the discharge capacity of the negative electrode greatly changes with the mixed amount of sulfolane of 5% by volume as a critical value. . In addition, in FIG. 1, a portion A is a solvent composition region in which the discharge capacity of the negative electrode is 380 m to 400 mAh / g, and a portion B is 40
This is a solvent composition range of 0 mAh / g or more.

[0030] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 2: EC + SL + DMC) [Assembly of Triode Test Cell] The following non-aqueous electrolytes (1) to (3) were prepared.

(1) LiPF _{6 is} added to seven kinds of mixed solvents obtained by mixing dimethyl carbonate in various ratios with an equal volume mixed solvent of ethylene carbonate and sulfolane.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

(2) LiPF _{6 is} added to six kinds of mixed solvents obtained by mixing ethylene carbonate and dimethyl carbonate in an equal volume mixed solvent and sulfolane in various ratios.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

(3) LiPF _{6 is} added to six kinds of mixed solvents obtained by mixing an equal volume mixed solvent of sulfolane and dimethyl carbonate with ethylene carbonate at various ratios.
Non-aqueous electrolyte prepared by dissolving 1 mol / l.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-electrode test cells assembled in this manner are referred to as D1 to D7, E1 to E6, and F1 to F6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. The results are shown in FIG.

In FIG. 3, the portion A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0038] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 3: EC + SL + MEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) LiP is added to seven kinds of mixed solvents obtained by mixing ethylene carbonate and sulfolane in an equal volume mixed solvent, and further mixing methyl ethyl carbonate in various ratios.
Nonaqueous electrolyte was prepared F ₆ was dissolved 1 mol / liter.

(2) LiP is added to six kinds of mixed solvents obtained by mixing an equal volume mixed solvent of ethylene carbonate and methyl ethyl carbonate with sulfolane at various ratios.
Nonaqueous electrolyte was prepared F ₆ was dissolved 1 mol / liter.

(3) LiP is added to six kinds of mixed solvents obtained by mixing an equal volume mixed solvent of sulfolane and methyl ethyl carbonate with ethylene carbonate at various ratios.
Nonaqueous electrolyte was prepared F ₆ was dissolved 1 mol / liter.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as G1 to G7, H1 to H6, and I1 to I6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged / discharged under the same charge / discharge conditions as in Test Example 1 to determine the discharge capacity of the negative electrode of each triode test cell. Examined. FIG. 4 shows the results.

In FIG. 4, the portion A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0046] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 4: EC + SL + MiPC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) Non-aqueous solution prepared by dissolving 1 mol / l of LiPF ₆ in seven kinds of mixed solvents obtained by mixing methyl isopropyl carbonate in various ratios with an equal volume mixed solvent of ethylene carbonate and sulfolane Electrolyte.

(2) Non-aqueous solution prepared by dissolving LiPF ₆ at 1 mol / l in six kinds of mixed solvents obtained by mixing sulfolane in various ratios with an equal volume mixed solvent of ethylene carbonate and methyl isopropyl carbonate Electrolyte.

(3) Non-aqueous solution prepared by dissolving 1 mol / l of LiPF ₆ in six kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of sulfolane and methyl isopropyl carbonate Electrolyte.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as J1 to J7, K1 to K6, and L1 to L6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge and discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. The results are shown in FIG.

In FIG. 5, part A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0054] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 5: EC + SL + MPC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) Seven kinds of mixed solvents obtained by mixing various volumes of methyl propyl carbonate with an equal volume mixed solvent of ethylene carbonate and sulfolane
Non-aqueous electrolyte solution was prepared PF ₆ by dissolving 1 mol / liter.

(2) Six kinds of mixed solvents obtained by mixing an equal volume mixed solvent of ethylene carbonate and methyl propyl carbonate with sulfolane at various ratios are used to prepare Li.
Non-aqueous electrolyte solution was prepared PF ₆ by dissolving 1 mol / liter.

(3) Six kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of sulfolane and methyl propyl carbonate
Non-aqueous electrolyte solution was prepared PF ₆ by dissolving 1 mol / liter.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as M1 to M7, N1 to N6, and O1 to O6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge and discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. FIG. 6 shows the results.

In FIG. 6, part A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0062] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 6: EC + TMSO + DEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) LiPF ₆ was prepared by dissolving 1 mol / l in 6 kinds of mixed solvents obtained by mixing diethyl carbonate in various ratios with an equal volume mixed solvent of ethylene carbonate and tetramethylene sulfoxide. Water electrolyte.

(2) LiPF ₆ was prepared by dissolving 1 mol / l of LiPF ₆ in six kinds of mixed solvents obtained by mixing tetramethylene sulfoxide at various ratios with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate. Water electrolyte.

(3) LiPF ₆ was prepared by dissolving 1 mol / l in 6 kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of tetramethylene sulfoxide and diethyl carbonate. Water electrolyte.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as P1 to P6, Q1 to Q6, and R1 to R6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge and discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was reduced. Examined. FIG. 7 shows the results.

In FIG. 7, the portion A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0070] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 7: EC + PS + DEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) Six types of mixed solutions obtained by mixing diethyl carbonate in various ratios with an equal volume mixed solvent of ethylene carbonate and propyl sulfone (PS) (m = 3 in the above formula 4) A non-aqueous electrolyte prepared by dissolving LiPF ₆ at 1 mol / L in a solvent.

(2) Five types of mixed solvents obtained by mixing propyl sulfone at various ratios with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate are mixed with Li.
Non-aqueous electrolyte solution was prepared PF ₆ by dissolving 1 mol / liter.

(3) Lithium is mixed with four kinds of mixed solvents obtained by mixing propylene sulfone and diethyl carbonate in an equal volume mixed solvent and ethylene carbonate in various ratios.
Non-aqueous electrolyte solution was prepared PF ₆ by dissolving 1 mol / liter.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as S1 to S6, T1 to T5, and U1 to U4, respectively.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged / discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was reduced. Examined. FIG. 8 shows the results.

In FIG. 8, part A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0078] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used. Further, methyl sulfone (m in the above chemical formula 4)
= 1), ethyl sulfone (m = 2 in the above chemical formula 4) and butyl sulfone (m = 4 in the above chemical formula 4), similar results were obtained.

(Test Example 8: EC + PSO + DEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) Six kinds of mixed solutions obtained by mixing diethyl carbonate in various ratios with an equal volume mixed solvent of ethylene carbonate and propyl sulfoxide (PSO) (n = 3 in the above formula) A non-aqueous electrolyte prepared by dissolving LiPF ₆ at 1 mol / L in a solvent.

(2) Non-aqueous solution prepared by dissolving 1 mol / l of LiPF ₆ in six kinds of mixed solvents obtained by mixing propyl sulfoxide at various ratios with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate Electrolyte.

(3) Non-aqueous solution prepared by dissolving 1 mol / l of LiPF ₆ in 6 kinds of mixed solvents obtained by mixing propylene sulfoxide and diethyl carbonate in an equal volume mixed solvent and ethylene carbonate in various ratios. Electrolyte.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as V1 to V6, W1 to W6, and X1 to X6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge and discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was reduced. Examined. FIG. 9 shows the results.

In FIG. 9, part A indicates that the discharge capacity of the negative electrode is 38.
The composition region of the solvent where the discharge capacity is 0 to 400 mAh / g, and the portion B is the composition region of the solvent where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0086] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used. Further, the same results were obtained for methyl sulfoxide (n = 1 in the above formula) and butyl sulfoxide (n = 4 in the above formula).

(Test Example 9: EC + 3-MSL + DEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) Diethyl carbonate is mixed at various ratios with an equal volume mixed solvent of ethylene carbonate and 3-methylsulfolane (3-MSL).
A non-aqueous electrolyte prepared by dissolving 1 mol / L of LiPF ₆ in various kinds of mixed solvents.

(2) LiPF ₆ was dissolved at 1 mol / L in six kinds of mixed solvents obtained by mixing 3-methylsulfolane in various ratios with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate. Non-aqueous electrolyte.

(3) LiPF ₆ was dissolved at 1 mol / L in six kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of 3-methylsulfolane and diethyl carbonate. Non-aqueous electrolyte.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole test cells assembled in this manner are referred to as Y1 to Y7, Z1 to Z6, and AA1 to AA6, respectively.

[Charge / Discharge Test with Triode Test Cell] Each of the assembled triode test cells was charged and discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was reduced. Examined. The results are shown in FIG.

In FIG. 10, part A indicates that the discharge capacity of the negative electrode is 3
The solvent composition region where the discharge capacity is 80 to 400 mAh / g, and the portion B is the solvent composition region where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0094] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Test Example 10: EC + 2,4-DMSL + DEC) [Assembly of Triode Test Cell] The following nonaqueous electrolytes (1) to (3) were prepared.

(1) LiPF ₆ was added to seven kinds of mixed solvents obtained by mixing ethylene carbonate and 2,4-dimethylsulfolane (2,4-DMSL) in an equal volume, and diethyl carbonate in various ratios. Non-aqueous electrolyte prepared by dissolving 1 mol / l.

(2) LiPF ₆ was dissolved at 1 mol / L in six kinds of mixed solvents obtained by mixing 2,4-dimethylsulfolane in various ratios with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate. The prepared non-aqueous electrolyte.

(3) LiPF ₆ was dissolved at 1 mol / L in six kinds of mixed solvents obtained by mixing ethylene carbonate in various ratios with an equal volume mixed solvent of 2,4-dimethylsulfolane and diethyl carbonate. The prepared non-aqueous electrolyte.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.
The three-pole type test cells assembled in this manner are respectively referred to as AB1 to AB7, AC1 to AC6, and AD1 to AD6.
Called.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged / discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. The results are shown in FIG.

In FIG. 11, part A indicates that the discharge capacity of the negative electrode is 3
The solvent composition region where the discharge capacity is 80 to 400 mAh / g, and the portion B is the solvent composition region where the discharge capacity of the negative electrode is 400 mAh / g or more.

[0102] 0.5 to 3 mol / l LiPF ₆ concentration similar to the above results for the can be obtained and LiBF ₄
The same results as above were obtained when other solutes were used.

(Comparative Test Example 1: EC + SL + DME) [Assembly of a three-electrode test cell] A single mixture obtained by further mixing 1,2-dimethoxyethane in various proportions in an equal volume mixed solvent of ethylene carbonate and sulfolane. Six kinds of non-aqueous electrolytes were prepared by dissolving 1 mol / liter of LiPF ₆ in a solvent or a mixed solvent.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these nonaqueous electrolytes were used.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged / discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. The result is shown in FIG.

In FIG. 12, the vertical axis represents the discharge capacity (mAh) of the negative electrode.
/ G) and the ratio of the solvent is plotted on the horizontal axis. FIG. 12 shows that the discharge capacity of the negative electrode decreases as the mixing ratio of 1,2-dimethoxyethane increases.

(Comparative Test Example 2: EC + SL + γ-BL) [Assembly of Tripolar Test Cell] A single solvent obtained by mixing γ-butyrolactone in various ratios with an equal volume mixed solvent of ethylene carbonate and sulfolane Alternatively, LiPF ₆ was dissolved at 1 mol / L in a mixed solvent to prepare six types of non-aqueous electrolytes.

A three-electrode test cell was assembled in the same manner as in Test Example 1 except that these non-aqueous electrolytes were used.

[Charge / Discharge Test with Triode Test Cell] Each assembled triode test cell was charged / discharged under the same charge / discharge conditions as in Test Example 1, and the discharge capacity of the negative electrode of each triode test cell was measured. Examined. FIG. 13 shows the results.

In FIG. 13, the vertical axis represents the discharge capacity (mAh) of the negative electrode.
/ G) and the ratio of the solvent is plotted on the horizontal axis. FIG. 13 shows that the discharge capacity of the negative electrode decreases as the mixing ratio of γ-butyrolactone increases.

(Example 1) [Preparation of positive electrode] Lithium carbonate (Li ₂ CO ₃ ) and nickel carbonate (NiCO ₃ ) were mixed at an atomic ratio of Li: Ni of 1: 1.
The mixture obtained by the above was fired at 850 ° C. for 20 hours to produce LiNiO ₂ (lithium-containing nickel oxide) powder as a positive electrode active material. This powder was ground in an Ishikawa-type rai mortar for 4 hours to obtain a fine powder having an average particle size of about 5 μm.

A mixture of the thus-obtained LiNiO ₂ fine powder and carbon as a conductive agent was dispersed in an NMP solution of PVdF to prepare a slurry. A positive electrode having an active material layer with a thickness of 50 μm formed on both sides of an aluminum foil was applied to both sides of an aluminum foil as a body and dried.

[Production of Negative Electrode] Graphite powder (Lc = 3.35)
{ _D002 > 1000}) was dispersed in an NMP solution of PVdF to prepare a slurry. The slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, dried, and dried. A negative electrode having an active material layer having a thickness of 50 μm formed on both surfaces of the foil was produced.

[Preparation of electrolyte solution] The volume ratio of ethylene carbonate, sulfolane and diethyl carbonate was 20:
A non-aqueous electrolyte was prepared by dissolving 1 mol / liter of LiPF ₆ in a 20:60 mixed solvent.

[Assembly of Battery] An AA-size cylindrical lithium secondary battery (battery of the present invention) BA1 was assembled using the above positive electrode, negative electrode and electrolytic solution. A polyethylene porous membrane was used as a separator.

FIG. 14 is a cross-sectional view schematically showing the assembled lithium secondary battery. The illustrated battery BA1 has a positive electrode 1, a negative electrode 2, a separator 3 separating these two electrodes, a positive electrode lead 4, and a negative electrode lead. 5, positive external terminal 6, negative can 7
Etc. The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 in a state of being spirally wound through a separator 3 into which a non-aqueous electrolyte is injected. The terminal 6 and the negative electrode 2 are connected to a negative electrode can 7 via a negative electrode lead 5, so that chemical energy generated inside the battery can be taken out as electric energy.

Example 2 Lithium carbonate (Li ₂ C)
O ₃ ) and cobalt carbonate (CoCO ₃ )
The mixture obtained by mixing at an atomic ratio of 1: 1 was calcined at 850 ° C. for 20 hours to obtain LiCoO 2 as a positive electrode active material.
₂ (Lithium-containing cobalt oxide) powder was produced. This powder was ground in an Ishikawa-type rai mortar for 4 hours to obtain a fine powder having an average particle size of about 5 μm.

An AA-size cylindrical lithium secondary battery (battery of the present invention) BA2 was prepared in the same manner as in Example 1 except that the fine powder of LiCoO ₂ was used instead of LiNiO ₂ as the positive electrode active material. Produced.

Example 3 Lithium carbonate (Li ₂ C)
O ₃ ), nickel carbonate (NiCO ₃ ), and cobalt carbonate (CoCO ₃ ) in a Li: Ni: Co atomic ratio of 2:
The mixture obtained by mixing at a ratio of 1: 1 was calcined at 850 ° C. for 20 hours to prepare Li ₂ NiCoO ₄ (lithium-containing cobalt-nickel composite oxide) powder as a positive electrode active material. This powder was ground in an Ishikawa-type rai mortar for 4 hours to obtain a fine powder having an average particle size of about 5 μm.

AA size cylindrical lithium secondary battery (battery of the present invention) was carried out in the same manner as in Example 1 except that the fine powder of Li ₂ NiCoO ₄ was used as the positive electrode active material instead of LiNiO _2. BA3 was produced.

(Comparative Examples 1 to 3) LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 40:60 by 1 mol / l to prepare a non-aqueous electrolyte.

An AA-size cylindrical lithium secondary battery (comparative example) was used in the same manner as in Example 1, Example 2 or Example 3 except that the above-mentioned non-aqueous electrolyte was used as the electrolyte. Battery) BC1, BC2, and BC3 were produced.

[Charge / Discharge Cycle Test] Battery BA1 of the Present Invention
About BA3 and comparative batteries BC1 to BC3,
In C, a charge / discharge cycle test was performed in which charging was performed at 200 mA to a cut-off voltage of 4.1 V, and discharging at 200 mA to a cut-off voltage of 2.75 V was one cycle, and the cycle characteristics of each battery were examined. FIG. 15 shows the results.

FIG. 15 shows the battery capacity (mAh) on the vertical axis.
Also, the horizontal axis is a graph showing the number of cycles (times). FIG. 15 shows that the batteries BA1 to BA3 of the present invention are much superior in cycle characteristics at high temperatures as compared with the comparative batteries BC1 to BC3.

[0125]

The battery of the present invention has a large discharge capacity per unit weight of the carbon material of the negative electrode and has excellent cycle characteristics at high temperatures.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + DEC) and the discharge capacity of a negative electrode.

FIG. 2 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + DEC) and the discharge capacity of a negative electrode.

FIG. 3 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + DMC) and the discharge capacity of a negative electrode.

FIG. 4 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + MEC) and the discharge capacity of a negative electrode.

FIG. 5 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + MiPC) and the discharge capacity of a negative electrode.

FIG. 6 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + MPC) and the discharge capacity of a negative electrode.

FIG. 7 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + TMSO + DEC) and the discharge capacity of the negative electrode.

FIG. 8 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + PS + DEC) and the discharge capacity of the negative electrode.

FIG. 9 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + PSO + DEC) and the discharge capacity of the negative electrode.

FIG. 10 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + 3-MSL + DEC) and the discharge capacity of the negative electrode.

FIG. 11: Mixed solvent (EC + 2,4-DMSL + DE)
It is a graph which shows the relationship between the ratio of each solvent in C), and the discharge capacity of a negative electrode.

FIG. 12 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + DME) and the discharge capacity of the negative electrode.

FIG. 13 is a graph showing the relationship between the ratio of each solvent in a mixed solvent (EC + SL + γ-BL) and the discharge capacity of the negative electrode.

FIG. 14 is a cross-sectional view of a cylindrical lithium secondary battery manufactured in an example.

FIG. 15 shows the high temperature (60 ° C.) of the battery of the present invention and the comparative battery.
5 is a graph showing cycle characteristics in FIG.

[Explanation of symbols]

 BA1 cylindrical lithium secondary battery (battery of the present invention) 1 positive electrode 2 negative electrode 3 separator

──────────────────────────────────────────────────続 き Continuing on the front page (72) Mikiya Yamazaki 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Inside Sanyo Electric Co., Ltd. (72) Yuji Yamamoto 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Inside Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5, Keihanhondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (56) References JP-A-6-223874 (JP, A) JP-A-5-211070 (JP, A) JP-A-6-36802 (JP, A) JP-A-3-3 152879 (JP, A) JP-A-3-11563 (JP, A) JP-A-2-14863 (JP, A) JP-A-7-230825 (JP, A) JP-A-7-230824 (JP, A) JP-A-3-214566 (JP, A) -307974 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) H01M 10/40 H01M 4/02 H01M 4/58

Claims (4)

(57) [Claims] 1. A positive electrode comprising a material capable of being charged and discharged at 3 V (vs. Li / Li ⁺ ) or more as a positive electrode active material, a crystallite size (Lc) in the c-axis direction of 150 ° or more, and a lattice A negative electrode having a d value (d ₀₀₂ ) of 3.37 ° or less on the (002) plane, using a carbon material capable of occluding and releasing lithium ions as an electrode material, and a non-aqueous electrolyte comprising a solvent and a solute. And a separator, wherein the solvent is at least one acyclic carbonate (A) selected from the group consisting of diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and methyl isopropyl carbonate. 10 to 75% by volume , tetramethylene sulfoxide, a sulfone represented by the following chemical formula 1, and a chemical formula represented by the following chemical formula 2 At least one sulfur-containing compound (B) selected from the group consisting of sulfoxides, sulfolane and sulfolane derivatives represented by the following formula (3) :
% By volume and ethylene carbonate (C) 5 to 65% by volume
A lithium secondary battery characterized by being a mixed solvent consisting of: Embedded image (However, m = 1, 2, 3 or 4) (However, n = 1, 3, or 4) (However, A ^{1 to} A ⁴ are each independently a hydrogen atom or a methyl group) 2. The method according to claim 1, wherein the sulfolane derivative is 3-methylsulfolane or 2,4-dimethylsulfolane.
The lithium secondary battery according to the above. 3. The method according to claim 1, wherein the positive electrode active material is lithium-containing nickel.
Oxide, lithium-containing cobalt oxide or lithium-containing
2. The resin according to claim 1, which is a cobalt-nickel composite oxide.
Rechargeable lithium battery. 4. The method according to claim 1, wherein the solute is LiPF ₆ , LiBF ₄ , L
iClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ or Li
_2. The lithium secondary battery according to claim 1, which is N (CF ₃ SO ₂ ) _2.
Next battery.