JP3244389B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode comprising lithium-containing cobalt oxide, lithium-containing nickel oxide or lithium-containing nickel-cobalt composite oxide as an active material;
A lattice capable of inserting and extracting lithium ions
D value (d ₀₀₂ ) on plane (002) plane is 3.39 ° or less
And the crystallite size (Lc) in the c-axis direction is 1
The present invention relates to a lithium secondary battery provided with a negative electrode using a carbon material of 50 ° or more as a negative electrode material, and more particularly, to an electrolyte (non-aqueous electrolyte) intended to provide a lithium secondary battery having excellent low-temperature characteristics. It relates to improvement of the solvent.

[0002]

2. Description of the Related Art In recent years,
Carbon materials, such as graphite, coke, amorphous carbon, and non-graphitizable carbon, that can occlude and release lithium ions are different from the metallic lithium used before, due to the growth of dendritic lithium. Since there is no fear of internal short-circuit, there is a great deal of attention as a new negative electrode material for lithium secondary batteries.

Generally, in a lithium secondary battery using a carbon material as a negative electrode material, a high dielectric constant solvent such as ethylene carbonate, propylene carbonate, 1,2-butylene carbonate and a dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. A mixed solvent with a low melting point / low viscosity solvent is used.

For example, as a solvent for a non-aqueous electrolyte of a lithium secondary battery using graphite as a negative electrode material, which is considered to be most advantageous for achieving high energy density, a mixed solvent of ethylene carbonate and dimethyl carbonate (US Pat. 19
No. 2,629) and a mixed solvent of 4,5-dichloroethylene carbonate and dimethyl carbonate (see JP-A-5-325985).
In this publication, "3,4-dichloroethylene carbonate" is an erroneous description of "4,5-dichloroethylene carbonate".

However, a lithium secondary battery using a mixed solvent of ethylene carbonate and dimethyl carbonate has a melting point of ethylene carbonate (3
9-40 ° C.), low temperatures, especially -2
It has been found that when the temperature is lower than 0 ° C., the conductivity of the non-aqueous electrolytic solution is significantly reduced, so that there is a problem that the discharge capacity at low temperatures becomes extremely small.

[0006] Further, in a lithium secondary battery using a mixed solvent of 4,5-dichloroethylene carbonate and dimethyl carbonate, the solvent is decomposed at the time of charge and discharge at room temperature, so that the discharge capacity near room temperature is small. It turned out that there was a problem.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a lithium secondary battery with a small decrease in discharge capacity at low temperatures, that is, excellent in low-temperature characteristics. is there.

[0008]

In order to achieve the above object, a lithium secondary battery (battery of the present invention) according to the present invention comprises a lithium-containing cobalt oxide, a lithium-containing nickel oxide or a lithium-containing nickel-cobalt composite oxide. Positive electrode using a material as an active material, and a d value (d) on a lattice plane (002) plane capable of inserting and extracting lithium ions.
₀₀₂ ) is 3.39 ° or less and a crystallite in the c-axis direction
In a lithium secondary battery including a negative electrode using a carbon material having a size (Lc) of 150 ° or more as a negative electrode material, a nonaqueous electrolyte solution including a solvent and a solute, and a separator,
The solvent is chloroethylene carbonate 10 to 100.
Volume% (except 100 volume%), 90 to 0 volume% (excluding 0 volume%) of at least one acyclic carbonate selected from the group consisting of methyl propyl carbonate and methyl isopropyl carbonate. Consists of

In the present invention, the solvent of the nonaqueous electrolyte is chloroethylene carbonate (melting point -40 ° C. or less).
100 vol% (excluding 100 vol%) excluding the at least one non-cyclic carbonic ester 90-0 vol% selected from the group consisting of methylation propyl carbonate and methyl isopropyl carbonate (provided that 0% by volume ) . When the mixing ratio of chloroethylene carbonate and acyclic carbonate is out of the above range, the low-temperature characteristics are deteriorated.

As the solute, LiPF ₆ , LiBF ₄ ,
LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li
N (CF ₃ SO ₂ ) ₂ is exemplified. A suitable addition ratio of these solutes to the solvent is 0.5 to 3 mol / l.

[0011] The positive electrode active substance include lithium-containing cobalt oxides (such as LiCoO _2), lithium-containing nickel oxides (such as LiNiO ₂₎ or lithium-containing nickel-cobalt composite oxide (such as Li ₂ NiCoO _4).

The negative electrode material has a lattice plane (002) plane.
The d value (d ₀₀₂ ) is equal to or less than 3.39 ° and the c-axis direction
Material having a crystallite size (Lc) of at least 150 °
(Material belonging to graphite). Use this kind of carbon material
To obtain a high capacity and flat discharge potential
You. In the present invention, lithium alloys such as a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-lead alloy, and metallic lithium cannot be used as a negative electrode material.
This is because the solvent (chloroethylene carbonate) is decomposed.

[0013]

As a high dielectric constant solvent, chloroethylene carbonate having a lower melting point than ethylene carbonate (the dielectric constant of chloroethylene carbonate is almost the same as that of ethylene carbonate) is used. Less decrease. Therefore, Ru excellent low-temperature characteristics.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be carried out by appropriately changing the scope of the present invention. Is possible.

Examples 1 to 5 AA size lithium secondary batteries (batteries of the present invention) A17 to A21 were assembled using the following positive electrode, negative electrode and nonaqueous electrolyte. A polyethylene microporous membrane was used as the separator.

[Positive electrode] Lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a molar ratio of 1: 2, and the obtained mixture is baked at 850 ° C. for 20 hours.
LiCoO ₂ powder was produced. This LiCoO ₂ powder was pulverized in an Ishikawa-type raisable mortar for 4 hours to obtain a fine LiCoO ₂ powder having an average particle size of about 5 μm.

10 parts by weight of carbon (artificial graphite) as a conductive agent is mixed with 85 parts by weight of this LiCoO ₂ fine powder, and the resulting mixture is mixed with 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder. A 5% by weight N-methylpyrrolidone (NMP) solution was dispersed to form a slurry. The slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector by a doctor blade method, and dried to obtain a film having a thickness of 2 mm.
A positive electrode in which an active material layer having a thickness of 50 μm was formed on each surface of a 0 μm aluminum foil was prepared.

[Anode] Graphite powder (d ₀₀₂ = 3.35 °;
Lc> 1000 °) 95 parts by weight of a polyvinylidene fluoride 5 parts by weight as a binder is dispersed in a 5% by weight N-methylpyrrolidone solution to form a slurry. 18μ
m, and applied to both sides of a copper foil, followed by drying to prepare a negative electrode having a 50 μm-thick active material layer formed on each side of the copper foil.

[0019] and [non-aqueous electrolyte] chloroethylene carbonate (CEC) Mechirupuropi
80: 20,6 by volume ratio with lucarbonate (MPC)
LiPF ₆ was dissolved in each of the mixed solvents of 0:40, 40:60, 20:80 or 10:90 at 1 mol / L to prepare a non-aqueous electrolyte.

FIG. 1 is a sectional view of the assembled battery A17 of the present invention. The illustrated battery A17 has a positive electrode 1, a negative electrode 2, a separator 3, a positive electrode lead 4, and a negative electrode lead for separating the electrodes 1 and 2 from each other. 5, a positive electrode external terminal 6, a negative electrode can 7, and the like.

The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 while being spirally wound through a separator 3 impregnated with a non-aqueous electrolyte. The negative electrode 2 is connected to the positive electrode external terminal 6 and the negative electrode 2 is connected to the negative electrode can 7 via the negative electrode lead 5 so that the chemical energy generated inside the battery can be taken out from the positive external terminal 6 and the negative electrode can 7 as electric energy. It has become.

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] (Comparative Example 1) Example except for using the LiPF ₆ methyl propyl carbonate 1 mol / liter dissolved non-aqueous electrolyte
A comparative battery B4 was assembled in the same manner as in Nos. 1 to 5 .

Examples 6 to 10 The volume ratio of chloroethylene carbonate to methyl isopropyl carbonate (MiPC) 80:20, 60: 4.
The present invention is carried out in the same manner as in Examples 1 to 5 , except that a non-aqueous electrolyte obtained by dissolving LiPF ₆ at 1 mol / L in each of the mixed solvents of 0, 40:60, 20:80 or 10:90 is used. The batteries A22 to A26 were assembled.

Comparative Example 2 A comparative battery B5 was assembled in the same manner as in Examples 1 to 5 , except that a nonaqueous electrolyte obtained by dissolving 1 mol / liter of LiPF _{6 in} methyl isopropyl carbonate was used.

( Comparative Examples 3 to 8 ) Ethylene carbonate (EC), volume ratio of ethylene carbonate to diethyl carbonate 80:20, 60:
Example 1 except that a non-aqueous electrolyte obtained by dissolving LiPF ₆ at 1 mol / liter in a mixed solvent of 40, 40:60 or 20:80 or diethyl carbonate was used.
Comparative batteries B6 to B11 were assembled in the same manner as in Nos. 1 to 5 .

[Low temperature characteristics] Battery of the present inventionA17 to A26And comparative batteriesB4-B11
With a cut-off voltage of 4.1 mA at −20 ° C. and 200 mA.
After charging to 200 V, the final voltage is 2.75 V at 200 mA.
To determine the discharge capacity of each battery at -20 ° C.
Was. The results are shown in FIGS.FIG.Shown in

FIGS. 2 to 4 show -20 ° C. of each battery on the vertical axis .
4 is a graph showing the discharge capacity (mAh) in Table 1 and the volume mixing ratio of the solvent used on the horizontal axis. According to these figures, chloroethylene carbonate is 10 to 100% by volume.
(Excluding 100% by volume) and acyclic carbonate 90 to 90 %
0% by volume (excluding 0% by volume)
It can be seen that a lithium secondary battery having a large discharge capacity at −20 ° C. and excellent in low-temperature characteristics can be obtained in the case of using a medium .

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

In the above embodiment, the case where the present invention is applied to a cylindrical battery has been described as an example. However, the present invention is not particularly limited in the shape of the battery, and various shapes such as a flat type and a square type are available. It can be applied to a lithium secondary battery.

[0049]

According to the battery of the present invention, as a solvent for the non-aqueous electrolyte, chloroethylene carbonate containing at least 10% by volume of chloroethylene carbonate having a high dielectric constant and a low melting point and a specific non-cyclic carbonate are used. Since a mixed solvent is used, it has excellent low-temperature characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery assembled in an example.

FIG. 2 Chloroethylene carbonate and methyl propyl
The relationship between the volume mixing ratio with carbonate and discharge capacity is shown.
This is a graph.

FIG. 3 Chloroethylene carbonate and methyl isopro
Relationship between volumetric mixing ratio with pill carbonate and discharge capacity
FIG.

FIG. 4 Ethylene carbonate and diethyl carbonate
5 is a graph showing the relationship between the volume mixing ratio of
You.

[Description of Signs ] A17 cylindrical lithium secondary battery (battery of the present invention) 1 positive electrode 2 negative electrode 3 separator

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikiya Yamazaki 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP 4-104468 (JP, A) JP 62-290072 (JP, A) JP-A-6-176768 (JP, A) JP-A-6-20719 (JP, A) JP-A-5-2111070 (JP, A) JP-A-7-240232 (JP) JP-A-6-140076 (JP, A) JP-A-8-37025 (JP, A) JP-A-3-1555061 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01M 10/40 H01M 4/02 H01M 4/58

Claims (2)

(57) [Claims] 1. A positive electrode comprising a lithium-containing cobalt oxide, a lithium-containing nickel oxide or a lithium-containing nickel-cobalt composite oxide as an active material, and a lattice surface capable of inserting and extracting lithium ions. On the surface
(D ₀₀₂ ) is less than 3.39 ° and the c-axis
Lithium secondary battery including a negative electrode using a carbon material having a crystallite size (Lc) in the direction of 150 ° or more as a negative electrode material, a non-aqueous electrolyte solution comprising a solvent and a solute, and a separator In the above, the solvent may be chloroethylene carbonate 1
0 to 100% by volume (excluding 100% by volume), and 90 to 0% by volume of at least one acyclic carbonate selected from the group consisting of methyl propyl carbonate and methyl isopropyl carbonate (however, 0% by volume Excluding). 2. The method according to claim 1, wherein said solute is LiPF ₆ , LiBF ₄ , L
iClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ or Li
_2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is N (CF ₃ SO ₂ ) ₂ .