JPH08250120A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery having an increased charge/ discharge cycle characteristic. CONSTITUTION: This lithium secondary battery is provided with a positive electrode wherein a lithium-'transition metals' composite oxide is adopted as positive electrode active material, a negative electrode, and a nonaqueous electrolyte containing an organic solvent. The lithium-'transition metals' composite oxide has the sulfide of B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Ru, Ag, Ta, Bi, In, Mo, or W, and a coating composed of selenide or telluride. Since the lithium-'transition metals' composite oxide, having a coating composed of specific chalcogenide on a particle surface, is used as positive electrode active material; the decomposition of the organic solvent is difficult to occur on the positive electrode side at the time of a charge/discharge cycle.

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 a positive electrode active material for the purpose of providing a lithium secondary battery having excellent charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art In recent years,
The lithium secondary battery is attracting attention because it is not necessary to consider the decomposition voltage of water and it is possible to achieve higher voltage by appropriately selecting the positive electrode active material.

A typical positive electrode active material for this type of battery is LiNiO ₂ , LiCoO ₂ , LiMn ₂ because it can be easily manufactured and has a large capacity.
Lithium-transition metal composite oxides such as O ₄ are mainly used.

However, the lithium secondary battery using the lithium-transition metal composite oxide as the positive electrode active material has a problem that the charge / discharge cycle characteristics are not yet sufficiently satisfactory for practical use. This is because the non-aqueous electrolytic solution (organic solvent) is decomposed in the highly active portion existing on the particle surface of the lithium-transition metal composite oxide.

The present invention has been made in view of the above circumstances, and an object thereof is to decompose the organic solvent on the positive electrode side by reducing the activity of the particle surface of the lithium-transition metal composite oxide. And to provide a lithium secondary battery having excellent charge / discharge cycle characteristics.

[0006]

A lithium secondary battery according to the present invention (a battery of the present invention) for achieving the above object comprises a positive electrode using a lithium-transition metal composite oxide as a positive electrode active material, a negative electrode, A lithium secondary battery comprising a non-aqueous electrolyte containing an organic solvent, wherein the lithium-transition metal composite oxide is B, Na, Mg, Al, S on the particle surface.
i, K, Ca, Sc, Ti, V, Cr, Mn, Fe, C
o, Ni, Cu, Zn, Ga, Ge, Zr, Nb, R
It has a coating film made of a sulfide, selenide or telluride of u, Ag, Ta, Bi, In, Mo or W.

As the above-mentioned coating, a coating made of TiS ₂ , MoS ₂ or a mixture thereof is particularly preferable in order to obtain a battery having particularly excellent charge-discharge cycle characteristics.

Typical examples of the lithium-transition metal composite oxide are LiMn ₂ O ₄ , LiMnO ₂ and L.
iNiO ₂ , LiCoO ₂ , LiNi _0.5 Co _0.5 O ₂
Is mentioned. In order to obtain a lithium secondary battery having particularly excellent charge / discharge cycle characteristics, the general formula Li _X Ni _y Co _z M
_1-yz O _a (where M is B, Na, Mg, Al, Si,
K, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu,
Zn, Ga, Ge, Zr, Nb, Ru, Ag, Ta, B
at least one element selected from the group consisting of i, In, Mo and W, 0 <x <1.3, 0 ≦ y ≦ 1, 0 ≦ z ≦
1, 0.5 ≦ y + z ≦ 1, 1.8 ≦ a ≦ 2.2)
Particularly preferred is a lithium-transition metal composite oxide represented by

A suitable ratio of the sulfide, selenide or telluride to the lithium-transition metal composite oxide is 0.1 to 20 mol%. The same ratio is 0.1
If it is less than mol%, the charge-discharge cycle characteristics are not sufficiently improved, while if it exceeds 20 mol%, the discharge capacity is reduced.

The lithium-transition metal composite oxide having a coating film made of a sulfide, a selenide or a telluride on the particle surface in the present invention is, for example, a lithium-transition metal composite oxide and a specific element such as B, Na or Mg. It can be easily obtained by a solid-phase method in which a mixture of the sulfide, selenide or telluride in a predetermined ratio is heat-treated at a predetermined temperature (usually 400 to 800 ° C.) for about 10 to 20 hours.

A feature of the present invention is that, as a positive electrode active material, a specific sulfide on the surface of particles of a lithium-transition metal composite oxide,
The point is that a film formed of selenide or telluride is used. Therefore, for other members constituting the battery, such as the negative electrode material and the non-aqueous electrolyte containing the organic solvent, various materials conventionally proposed or practically used for lithium secondary batteries should be used without particular limitation. Is possible.

For example, as the negative electrode material, a substance capable of electrochemically absorbing and desorbing lithium ions or metallic lithium can be used. Examples of the substance capable of electrochemically absorbing and desorbing lithium ions include carbon materials such as graphite, coke, and organic burned material,
Examples include metal oxides such as LiNb ₂ O ₅ and lithium alloys (lithium-aluminum alloys, lithium-lead alloys, lithium-tin alloys).

The organic solvent for the non-aqueous electrolyte may be a high dielectric constant solvent such as ethylene carbonate, vinylene carbonate or propylene carbonate, or diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-dicarbonate or the like. A mixed solvent with a low-boiling-point solvent such as ethoxyethane or ethoxymethoxyethane has the same solute as LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₄ .
₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiAs
Each of F ₆ is exemplified. The non-aqueous electrolyte containing an organic solvent in the present invention also includes a gelled solid electrolyte (pseudo solid electrolyte).

[0014]

[Function] Since a film made of a specific chalcogenide is formed on the surface of particles of a lithium-transition metal composite oxide as a positive electrode active material and its surface activity is reduced, organic compounds on the positive electrode side during charge / discharge cycles are reduced. Decomposition of the solvent (organic solvent in the non-aqueous electrolytic solution or organic solvent in the gelled solid electrolyte) is less likely to occur.

[0015]

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

Example 1 A flat type lithium secondary battery (the battery of the present invention) was assembled.

[Positive electrode] Li ₂ CO ₃ and MnO ₂ were mixed in a mortar at a molar ratio of 1: 4, and were mixed in a dry air atmosphere at 75
The mixture was heat-treated at 0 ° C. for 20 hours and crushed in an Ishikawa type mortar mortar to obtain LiMn ₂ O ₄ (positive electrode active material).

Next, 100 parts by mole of this LiMn ₂ O ₄ and 10 parts by mole of TiSe ₂ were mixed, and the mixture was heated at 650 ° C. for 10 minutes.
After heat treatment for a long time, TiSe ₂ was formed on the surface of the LiMn ₂ O ₄ particles.
To form a positive electrode active material. LiMn ₂ O
It was confirmed by X-ray photoelectron spectroscopy (X-ray Photoelectron Spectroscopy) that the coating film was formed on the particle surface of ₄ (the following coating films were also confirmed by the same method).

This positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are mixed at a weight ratio of 90: 6: 4 to prepare a positive electrode mixture, and this positive electrode mixture is prepared. With a molding pressure of 2 tons / cm ² and a diameter of 20
After pressure-molding into a disk shape of mm, heat treatment was carried out at 250 ° C. for 2 hours to prepare a positive electrode.

[Negative Electrode] A rolled lithium metal plate having a predetermined thickness was punched into a disk shape having a diameter of 20 mm to prepare a negative electrode.

[Non-Aqueous Electrolyte] Lithium perchlorate was dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 at a ratio of 1 M (mol / liter) to obtain a non-aqueous electrolyte. Was prepared.

[Battery Assembly] A flat type battery BA1 of the present invention was assembled using the above positive electrode, negative electrode and non-aqueous electrolyte (battery size: diameter 24.0 mm, thickness 3.0 mm). As the separator, a polypropylene microporous film was used, which was impregnated with the above non-aqueous electrolyte solution.

FIG. 1 is a sectional view schematically showing the produced battery BA1 of the present invention. The illustrated battery BA1 of the present invention comprises a positive electrode 1, a negative electrode 2, a separator 3 for separating these electrodes 1, 2 from each other, It comprises a positive electrode can 4, a negative electrode can 5, a positive electrode current collector 6, a negative electrode current collector 7, an insulating packing 8 made of polypropylene, and the like.

The positive electrode 1 and the negative electrode 2 are housed in a battery case formed by positive and negative electrode cans 4 and 5 facing each other with a separator 3 impregnated with a non-aqueous electrolytic solution interposed therebetween. The positive electrode 1 is a positive electrode current collector. The negative electrode 2 is connected to the positive electrode can 4 via 6 and the negative electrode 2 is connected to the negative electrode can 5 via the negative electrode current collector 7, and the chemical energy generated inside the battery is converted into electrical energy from both terminals of the positive electrode can 4 and the negative electrode can 5. It can be taken out.

(Example 2) LiMn ₂ O ₄ mol part and Ti
10 parts by mole of Te ₂ was mixed and heat-treated at 650 ° C. for 10 hours to form a TiTe ₂ coating film on the surface of the LiMn ₂ O ₄ particles to prepare a positive electrode active material. The battery BA of the present invention was prepared in the same manner as in Example 1 except that this positive electrode active material was used.
Assembled 2.

Example 3 100 parts by mole of LiMn ₂ O ₄ and 10 parts by mole of TiS ₂ were mixed and heat-treated at 650 ° C. for 10 hours to form a TiS ₂ coating on the surface of LiMn ₂ O ₄ particles. A positive electrode active material was produced. Battery B of the present invention was prepared in the same manner as in Example 1 except that this positive electrode active material was used.
Assembled A3.

Example 4 100 mol parts of LiMn ₂ O _{4 and} 10 mol parts of MoS ₂ were mixed and heat-treated at 650 ° C. for 10 hours to form a MoS ₂ coating on the surface of LiMn ₂ O ₄ particles. A positive electrode active material was produced. Battery B of the present invention was prepared in the same manner as in Example 1 except that this positive electrode active material was used.
Assembled A4.

(Example 5) 100 parts by mole of LiMn ₂ O _4, 5 parts by mole of MoS _{2 and} 5 parts by mole of TiS ₂ were mixed, and 6
A heat treatment was performed at 50 ° C. for 10 hours to form a coating film composed of MoS ₂ and TiS _{2 on the} surface of the LiMn ₂ O ₄ particles to prepare a positive electrode active material. A battery BA5 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 6 LiOH, Ni (OH) ₂ and Co (OH) ₂ were mixed in a mortar at a molar ratio of 2: 1: 1 and heat-treated at 750 ° C. for 20 hours in a dry air atmosphere. Then, crush it with an Ishikawa type Raikai mortar and add LiNi _0.5 C
o _0.5 O ₂ (positive electrode active material) was obtained.

Next, this LiNi _0.5 Co _0.5 O ₂ 1
650 parts by mole and TiSe ₂ 10 parts by mole were mixed, and 650
A heat treatment was performed at 10 ° C. for 10 hours to form a TiSe ₂ film on the surface of the LiNi _0.5 Co _0.5 O ₂ particles, thus preparing a positive electrode active material. Example 1 except that this positive electrode active material was used
Battery BA6 of the present invention was assembled in the same manner as in.

Example 7 LiNi _0.5 Co _0.5 O ₂ 1
650 parts by mole and TiTe ₂ 10 parts by mole were mixed, and 650
A positive electrode active material was prepared by forming a TiTe ₂ film on the surface of LiNi _0.5 Co _0.5 O ₂ particles by heat treatment at ° C for 10 hours. Example 1 except that this positive electrode active material was used
Battery BA7 of the present invention was assembled in the same manner as in.

Example 8 LiNi _0.5 Co _0.5 O ₂ 1
00 parts by mole and TiS ₂ 10 parts by mole were mixed, and 650 °
A heat treatment was performed for 10 hours at C to form a TiS ₂ film on the surface of the LiNi _0.5 Co _0.5 O ₂ particles, and a positive electrode active material was produced. A battery BA8 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 9 LiNi _0.5 Co _0.5 O ₂ 1
00 parts by mole and 10 parts by mole of MoS ₂ were mixed together, and 650 °
A heat treatment was performed for 10 hours in C to form a TiSe ₂ coating on the surface of the LiNi _0.5 Co _0.5 O ₂ particles, and a positive electrode active material was produced. A battery BA9 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

(Example 10) LiNi _0.5 Co _0.5 O ₂
100 mol parts, 5 mol parts of TiS _{2 and} 5 mol parts of MoS ₂ are mixed and heat treated at 650 ° C. for 10 hours to obtain LiNi.
_A film made of TiSe ₂ and MoS ₂ was formed on the surface of _0.5 Co _0.5 O ₂ particles to prepare a positive electrode active material. In the same manner as in Example 1 except that this positive electrode active material was used,
The battery BA10 of the present invention was assembled.

Comparative Example 1 LiMn ₂ as a positive electrode active material
A comparative battery BC1 was assembled in the same manner as in Example 1 except that O ₄ was used.

Comparative Example 2 LiNi as a positive electrode active material
_A comparative battery BC2 was assembled in the same manner as in Example 1 except that _0.5 Co _0.5 O ₂ was used.

[Charge / Discharge Cycle Test] Battery BA1 of the Invention
-BA10 and comparative batteries BC1 and BC2 were charged with a charging current density of 1 mA / cm ² to 4.3 V and then discharged with a discharging current density of 3 mA / cm ² to 2.5 V.
Cycle, a charge-discharge cycle test is performed, and the capacity deterioration rate of the discharge capacity at the 150th cycle relative to the discharge capacity at the first cycle [capacity deterioration rate (%) = {(discharge capacity at the first cycle−discharge capacity at the 150th cycle ) / 1st cycle discharge capacity} × 100]. The results are shown in Table 1.

[0038]

[Table 1]

From Table 1, the batteries BA1 to BA10 of the present invention using the lithium-transition metal composite oxide having a specific coating on the particle surface as the positive electrode active material show the lithium-transition metal composite oxide having no coating on the particle surface. It can be seen that the capacity deterioration rate is smaller than that of the comparative batteries BC1 and BC2 using the materials as the positive electrode active material. When the film forming materials are the same, LiNi _{0.5 is} used as the lithium-transition metal composite oxide.
Since the capacity deterioration rate of the battery using Co _0.5 O ₂ is particularly small, it is understood that the Li-Ni-Co-based composite oxide is particularly preferable.

Example 11 LiNi _0.5 Co _0.5 O ₂
100 parts by mole and 0.05 parts by weight of TiS ₂ are mixed to obtain 6
LiNi _0.5 Co _0.5 O after heat treatment at 50 ° C. for 10 hours
A film of TiS ₂ was formed on the surface of particles ₂ to prepare a positive electrode active material. Battery BA11 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 12 LiNi _0.5 Co _0.5 O ₂
100 parts by mole and 0.1 parts by weight of TiS ₂ are mixed to obtain 65
LiNi _0.5 Co _0.5 O _{2 after} heat treatment at 0 ° C for 10 hours
A TiS ₂ film was formed on the surface of the particles to prepare a positive electrode active material. Example 1 except that this positive electrode active material was used
The battery BA12 of the present invention was assembled in the same manner as.

Example 13 LiNi _0.5 Co _0.5 O ₂
100 parts by mole and ₂ parts by mole of TiS ₂ are mixed, and 650 °
A heat treatment was performed for 10 hours at C to form a TiS ₂ film on the surface of the LiNi _0.5 Co _0.5 O ₂ particles, and a positive electrode active material was produced. A battery BA13 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 14 LiNi _0.5 Co _0.5 O ₂
Mix 100 parts by mole and 20 parts by weight of TiS ₂ to obtain 650
The positive electrode active material was produced by forming a TiS ₂ film on the surface of LiNi _0.5 Co _0.5 O ₂ particles by heat treatment at ° C for 10 hours. A battery BA14 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

(Example 15) LiNi _0.5 Co _0.5 O ₂
Mix 100 parts by mole and 22 parts by mole of TiS ₂ to obtain 650
The positive electrode active material was produced by forming a TiS ₂ film on the surface of LiNi _0.5 Co _0.5 O ₂ particles by heat treatment at ° C for 10 hours. A battery BA15 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 16 100 parts by mole of LiMn ₂ O ₄ and 0.05 parts by weight of MoS ₂ were mixed and heat-treated at 650 ° C. for 10 hours to form MoS on the particle surface of LiMn ₂ O _4.
The coating film of ₂ was formed to prepare a positive electrode active material. A battery BA16 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 17 100 parts by mole of LiMn ₂ O ₄ and 0.1 part by mole of MoS ₂ were mixed and the mixture was mixed at 650 ° C. for 1 hour.
After heat treatment for 0 hours, MoS ₂ was formed on the surface of the LiMn ₂ O ₄ particles.
To form a positive electrode active material. A battery BA17 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 18 100 parts by mole of LiMn ₂ O ₄ and ₂ parts by mole of MoS ₂ were mixed and heat-treated at 650 ° C. for 10 hours to form a MoS ₂ film on the surface of LiMn ₂ O ₄ particles. A positive electrode active material was prepared. A battery BA18 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 19 100 parts by mole of LiMn ₂ O ₄ and 20 parts by mole of MoS ₂ were mixed and the mixture was heated at 650 ° C. for 10 minutes.
Heat treatment was carried out for a period of time to form a MoS ₂ film on the surface of the LiMn ₂ O ₄ particles, and a positive electrode active material was produced. A battery BA19 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

Example 20 100 parts by mole of LiMn ₂ O ₄ and 22 parts by mole of MoS ₂ were mixed and the mixture was heated at 650 ° C. for 10 minutes.
Heat treatment was carried out for a period of time to form a MoS ₂ film on the surface of the LiMn ₂ O ₄ particles, and a positive electrode active material was produced. A battery BA20 of the present invention was assembled in the same manner as in Example 1 except that this positive electrode active material was used.

[Charge / Discharge Cycle Test] Battery BA1 of the present invention
For 1 to BA20, a charge / discharge cycle test was performed under the same conditions as above to determine the capacity deterioration rate of each battery. Table 2 shows the results.

[0051]

[Table 2]

As shown in Table 2, the batteries BA11 to BA11 of the present invention.
The capacity deterioration rate of BA12 to BA14 of BA15 is 5%
The following is particularly small, and the batteries of the present invention BA16 to BA20
Among them, the capacity deterioration rate of BA17 to BA19 is particularly small at 15% or less. From this, it is understood that the ratio (average coverage) of the sulfide, selenide or telluride to the lithium-transition metal composite oxide is preferably in the range of 0.1 to 20 mol%.

(Examples 21 to 46) LiNi _0.5 Co
100 parts by mole of _0.5 O ₂ and 10 parts by mole of various sulfides shown in Table 3 were mixed and heat treated at 650 ° C. for 10 hours to obtain Li.
A coating film made of each of these sulfides was formed on the surface of Ni _0.5 Co _0.5 O ₂ particles to prepare a positive electrode active material. Inventive batteries BA21 to 46 were assembled in the same manner as in Example 1 except that each of these positive electrode active materials was used.

[Charge / Discharge Cycle Test] Battery BA2 of the present invention
For 1 to BA46, a charge-discharge cycle test was performed under the same conditions as above to determine the capacity deterioration rate of each battery. The results are shown in Table 3. It should be noted that in Table 3, the capacity deterioration rates of the batteries BA8 and BA9 of the present invention are also transcribed from Table 1.

[0055]

[Table 3]

As shown in Table 3, among the batteries of the present invention, the capacity deterioration rate of BA8 and BA9 is 5% or less, which is particularly small.
This and the battery BA10 of the present invention as shown in Table 1.
It can be seen that TiS ₂ , MoS ₂ or a mixture thereof is particularly preferable as the film forming material since the capacity deterioration rate of 4 is as small as 4%.

[0057]

Since the lithium-transition metal composite oxide having a coating film made of a specific chalcogenide on the particle surface is used as the positive electrode active material, the organic solvent is unlikely to be decomposed on the positive electrode side during the charge / discharge cycle. Therefore, the battery of the present invention has excellent charge / discharge cycle characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a flat type lithium secondary battery (the battery of the present invention) assembled in an example.

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A lithium secondary battery comprising a positive electrode using a lithium-transition metal composite oxide as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte containing an organic solvent, wherein the lithium-transition metal composite oxide is used. B, Na, M on the particle surface
g, Al, Si, K, Ca, Sc, Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Zn, Ga, Ge, Z
r, Nb, Ru, Ag, Ta, Bi, In, Mo or W
A lithium secondary battery having a coating film made of the sulfide, selenide, or telluride of the above. 2. The lithium-transition metal composite oxide has a general formula of Li _X Ni _y Co _z M _1-yz O _a (wherein M is B,
Na, Mg, Al, Si, K, Ca, Sc, Ti, V,
Cr, Mn, Fe, Cu, Zn, Ga, Ge, Zr, N
b, Ru, Ag, Ta, Bi, In, Mo, and at least one element selected from the group consisting of W, 0 <x <1.
3, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0.5 ≦ y + z ≦ 1,
1.8 ≦ a ≦ 2.2), The lithium secondary battery according to claim 1. 3. The lithium secondary battery according to claim 1, wherein the coating film is made of TiS ₂ , MoS ₂ or a mixture thereof. 4. The lithium secondary battery according to claim 1, wherein the ratio of the sulfide, the selenide, or the telluride to the lithium-transition metal composite oxide is 0.1 to 20 mol%.