JPH09330719A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery in which the battery characteristic is hardly reduced after storage when a charged battery is stored at high temperature by adding a prescribed transition metal oxide to a lithium-transition metal composite oxide as positive electrode active material to suppress the oxidation decomposition of the solvent of nonaqueous electrolyte. SOLUTION: This lithium secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte, the positive electrode contains a lithium-transition metal composite oxide as active material, the negative electrode contains a material capable of electrochemically storing and releasing lithium ions or lithium metal as active material. To the lithium-transition metal composite oxide which is the active material of the positive electrode, at least one transition metal oxide selected from FeOb , CoOc , MnOa , NiOe , TiOf and the like is added. The drawing shows the capacity residual factor, taking the volume residual ration (%) as the ordinate and the addition quantity ratio (wt.%) of transition metal oxide to lithium-transition metal composite oxide as the abscissa.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention uses a positive electrode having a lithium-transition metal composite oxide as an active material, and a material capable of electrochemically absorbing and releasing lithium ions or metallic lithium as an active material. Involved in a lithium secondary battery provided with a negative electrode and a non-aqueous electrolyte, specifically, for the purpose of providing a lithium secondary battery in which deterioration of battery characteristics does not easily occur when the battery in a charged state is stored at high temperature, It relates to the improvement of the positive electrode.

[0002]

2. Description of the Related Art As a positive electrode active material for a lithium secondary battery, a lithium-transition metal composite oxide that enables high voltage and high energy density is well known.

However, in a lithium secondary battery using a lithium-transition metal composite oxide as a positive electrode active material, when the battery in a charged state is stored at high temperature, oxygen in the lithium-transition metal composite oxide is released and released. The generated oxygen reacts with the solvent of the non-aqueous electrolyte to oxidatively decompose the solvent of the non-aqueous electrolyte. The surface of the positive electrode active material particles (lithium-transition metal composite oxide particles) is covered with the gas or decomposition product generated during the decomposition, and the internal resistance of the battery increases,
The charge / discharge capacity after storage may decrease.

The reason why the battery characteristics after the battery in a charged state is stored at a high temperature is deteriorated is that other than the oxidative decomposition of the solvent, the alkali remaining in the lithium-transition metal composite oxide (used as a synthetic raw material) LiOH) and water.

As a lithium secondary battery in which deterioration of battery characteristics due to alkali or moisture is suppressed, a positive electrode active material (L
It has been proposed that solid acid (SiO ₂ , Al ₂ O ₃ or the like) is added to iCoO ₂ ) to remove residual alkali and residual water in the positive electrode active material (Japanese Patent Laid-Open No. 4-355056).

However, the deterioration of the battery characteristics after storing the battery in a charged state at a high temperature is largely due to the oxidative decomposition of the solvent. It has been found that the decrease in γ cannot be sufficiently suppressed.

Therefore, an object of the present invention is to provide a lithium secondary battery in which deterioration of battery characteristics does not easily occur when the battery in a charged state is stored at a high temperature.

[0008]

A lithium secondary battery according to the present invention (a battery according to the present invention) for achieving the above object comprises a positive electrode using a lithium-transition metal composite oxide as an active material, and a lithium ion as an electrode. What is claimed is: 1. A lithium secondary battery comprising a negative electrode using a substance capable of chemically occluding and releasing or a metal lithium as an active material, and a non-aqueous electrolyte, wherein the lithium-transition metal composite oxide is FeO _b. (0 <b <1.
35), CoO _c (0 <c <1.35), MnO _d (0
<D <1.35), NiO _e (0 <e <1.1), Ti
_{O f (0 <f <2.0} ), VO g (0 <g <2.1),
CrO _h (0 <h <2.6) and CuO _i (0 <i <
1.35), and at least one transition metal oxide selected from the group consisting of 1.35) is added.

As the lithium-transition metal composite oxide,
Formula: Li _x MO _y (0 <x <1.1, 1.9 <y <2.
2, M is a lithium-transition metal composite oxide substantially represented by at least one transition element selected from the group consisting of Ni, Co, Fe and Mn, and specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiFeO ₂ ,
Examples thereof include LiMnO ₂ and LiMn ₂ O ₄ .

Specific examples of the transition metal oxide include ferrous oxide (FeO), triiron tetraoxide (Fe ₃ O ₄ ), cobalt (II) oxide (CoO), and vanadium trioxide (V).
₂ O ₃ ), cuprous oxide (Cu ₂ O), titanium monoxide (T
iO), manganese (II) oxide (MnO), trimanganese tetraoxide (Mn ₃ O ₄ ), and chromium oxide (II) (CrO). These transition metal oxides may be used alone or in combination of two or more as needed.

The transition metal oxides having a relatively low oxidation number are limited to those having a high oxidation number because the reaction with the oxygen released from the lithium-transition metal composite oxide does not sufficiently occur. This is because the generated oxygen mainly reacts with the solvent of the non-aqueous electrolyte, so that the oxidative decomposition of the solvent cannot be effectively suppressed.

The preferred addition amount of the transition metal oxide is 1 to 20% by weight based on the lithium-transition metal composite oxide. If the amount of the transition metal oxide added is less than 1% by weight, the effect of suppressing the oxidative decomposition of the solvent is not sufficiently exhibited because the amount added is too small, while if the amount added exceeds 20% by weight. The presence of a large amount of a transition metal oxide having a low electric conductivity lowers the electron conductivity of the positive electrode, and the contact area between the positive electrode active material particles is reduced to hinder the diffusion of lithium ions, resulting in a decrease in the discharge capacity. .

The active material of the negative electrode is a material capable of electrochemically inserting and extracting lithium ions or metallic lithium. Examples of substances capable of electrochemically absorbing and desorbing lithium ions include lithium alloys (lithium-aluminum alloys, lithium-lead alloys, lithium-tin alloys, etc.) and carbon materials (graphite, coke, organic burned products, etc.). ) Is illustrated.

As the solute of the non-aqueous electrolyte, LiPF ₆ ,
LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiA
sF ₆ , LiN (CF ₃ SO ₂ ) ₂ and LiSO ₂ (C
F ₂ ) ₃ CF ₃ is exemplified, and examples of the solvent for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane,
2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate , Dipropyl carbonate, 1,
Examples are 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate and mixtures thereof.

In the battery of the present invention in which a transition metal oxide having a relatively low oxidation number is added to the lithium-transition metal composite oxide as the positive electrode active material, the transition to be added when the battery in the charged state is stored at high temperature. Since the metal oxide serves as a dummy (reducing agent) and reacts with oxygen released from the lithium-transition metal composite oxide, oxidative decomposition of the solvent is less likely to occur. Thus, when the battery of this type in a charged state is stored at a high temperature, the deterioration of the battery characteristics after the storage is largely due to the oxidative decomposition of the solvent. Therefore, according to the present invention, this is effectively suppressed.

[0016]

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 can be made without departing from the scope of the invention. Is possible.

Examples 1 to 6 [Preparation of positive electrode] Lithium raw material [Lithium hydroxide (LiO
H)] and nickel raw material [nickel hydroxide (Ni (OH)
₂ )] and cobalt raw material [cobalt hydroxide (Co (OH)
₂ ] with a molar ratio of 2: 1: 1 and calcined in a dry air atmosphere at 750 ° C. for 20 hours to give a formula: LiNi _0.5
A lithium-transition metal composite oxide represented by Co _0.5 O ₂ was obtained. Next, this lithium-transition metal composite oxide was pulverized using an Ishikawa type raid mortar to obtain a positive electrode active material powder having an average particle size of about 5 μm.

Next, 0.5 wt%, 1 wt%, 5 wt% of triiron tetroxide (Fe ₃ O ₄ ) was added to the positive electrode active material powder.
10% by weight, 20% by weight or 22% by weight was added to prepare a mixture powder, 90 parts by weight of each mixture powder, 5 parts by weight of artificial graphite powder as a conductive agent, and 5 parts by weight of PVdF (polyvinylidene fluoride). Parts of 5 wt% NMP (N-methyl-2-pyrrolidone) solution are kneaded to prepare slurries, and these slurries are applied to both sides of an aluminum foil as a positive electrode current collector by a doctor blade method, and then under vacuum. At 150
Heat treatment was performed at ° C for 2 hours and rolling was performed to produce a strip-shaped positive electrode.

[Production of Negative Electrode] Natural graphite powder (Lc> 10)
00Å, d ₀₀₂ = 3.35Å) 95 parts by weight and PVdF5
A slurry is prepared by kneading with 5 parts by weight of a 5 wt% NMP solution, and the slurry is applied to both sides of a copper foil as a negative electrode current collector by a doctor blade method, and the temperature is set to 150 ° under vacuum.
It was heat-treated at C for 2 hours and rolled to prepare a strip-shaped negative electrode.

[Preparation of Lithium Secondary Battery] Using the above positive electrodes and negative electrodes, cylindrical lithium secondary batteries A1 to A6 of AA size having a positive electrode capacity smaller than the negative electrode capacity were prepared. It should be noted that a polypropylene microporous film was used as a separator, and Li was added as a non-aqueous electrolyte to a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.
Those obtained by dissolving 1 mol / liter of PF ₆ were used.

Comparative Example 1 In the production of a positive electrode, triiron tetroxide was mixed with a lithium-transition metal composite oxide (LiNi _0.5 C).
o _0.5 O ₂ ) except that no additions were made to Examples 1-6.
Comparative battery B1 was prepared in the same manner as in.

(Examples 7 to 12) In the production of the positive electrode,
Instead of triiron tetraoxide, ferrous oxide (FeO) was added to lithium-
0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 20% by weight of transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ )
Examples 1 to 6 except that wt% or 22 wt% was added
Lithium secondary batteries A7 to A12 were produced in the same manner as in.

(Comparative Examples 2 to 5) In the production of the positive electrode, diiron trioxide (Fe ₂ O ₃ ) was replaced with lithium-transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ ) in place of triiron tetraoxide. Comparative battery B2 was manufactured in the same manner as in Examples 1 to 6 except that 5% by weight, 5% by weight, 10% by weight or 20% by weight was added.
~ B5 were produced.

(Examples 13 to 18) In the production of the positive electrode, manganese (II) oxide (MnO) was used instead of triiron tetroxide, and lithium-transition metal composite oxide (LiNi _0.5 Co _{0.5) was used.}
Lithium secondary battery A13 ~ in the same manner as in Examples 1 to 6 except that 0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 20% by weight or 22% by weight was added to O ₂ ). A1
No. 8 was produced.

(Examples 19 to 24) In the production of the positive electrode, trimanganese tetraoxide (Mn) was used instead of triiron tetraoxide.
₃ O ₄ ) as a lithium-transition metal composite oxide (LiNi
_0.5 Co _0.5 O ₂ ) was added in the same manner as in Examples 1 to 6 except that 0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 20% by weight or 22% by weight was added. Batteries A19 to A24 were produced.

(Comparative Examples 6 to 9) In the production of the positive electrode, manganese dioxide (MnO ₂ ) was used instead of triiron tetroxide, and lithium-transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ ) was used.
To Comparative Battery B in the same manner as in Examples 1 to 6 except that 1% by weight, 5% by weight, 10% by weight or 20% by weight was added to
6 to B9 were produced.

(Examples 25 to 30) In the production of the positive electrode, cobalt (II) oxide (CoO) was used instead of triiron tetroxide, and lithium-transition metal composite oxide (LiNi _0.5 Co _{0.5) was used.}
O ₂₎ to 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, except for adding 20 wt% or 22 wt% in the same manner as in Example 1 to 6, A25～ lithium secondary battery A3
0 was produced.

(Examples 31 to 36) In the production of the positive electrode, titanium monoxide (TiO) was replaced with lithium-transition metal composite oxide (LiNi _0.5 Co) in place of triiron tetraoxide.
_0.5 O ₂ ) 0.5% by weight, 1% by weight, 5% by weight, 10
In the same manner as in Examples 1 to 6 except that 20% by weight, 22% by weight or 22% by weight was added, the lithium secondary battery A31 to
A36 was produced.

(Comparative Examples 10 to 13) In the production of the positive electrode, manganese dioxide (TiO ₂ ) was used in place of triiron tetroxide, and lithium-transition metal composite oxide (LiNi _0.5 Co _{0.5) was used.}
O ₂₎ to 1 wt%, 5 wt%, except for adding 10 wt% or 20 wt% in the same manner as in Example 1-6 was fabricated comparative battery B10～B13.

(Examples 37 to 42) In the production of the positive electrode, chromium oxide (CrO) was used instead of triiron tetroxide, and lithium-transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ ) was used.
0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 2
Example 1 except that 0 wt% or 22 wt% was added
Lithium secondary batteries A37 to A42 were produced in the same manner as in No. 6.

(Examples 43 to 48) In the preparation of the positive electrode, cuprous oxide (Cu ₂ O) was replaced with lithium-transition metal composite oxide (LiNi _0.5 Co) instead of triiron tetraoxide.
_0.5 O ₂ ) 0.5% by weight, 1% by weight, 5% by weight, 10
Lithium secondary battery A43 ~ in the same manner as in Examples 1 to 6 except that 20% by weight, 20% by weight or 22% by weight was added.
A48 was produced.

(Comparative Examples 14 to 17) In the production of the positive electrode, cupric oxide (CuO) was replaced by lithium-transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ ) instead of triiron tetraoxide.
To Comparative Battery B in the same manner as in Examples 1 to 6 except that 1% by weight, 5% by weight, 10% by weight or 20% by weight was added to
14-B17 were produced.

(Examples 49 to 54) In the production of the positive electrode, divanadium trioxide (V
₂ O ₃ ) as a lithium-transition metal composite oxide (LiNi
_0.5 Co _0.5 O ₂ ) was added in the same manner as in Examples 1 to 6 except that 0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 20% by weight or 22% by weight was added. Next batteries A49 to A54 were produced.

(Comparative Examples 18 to 21) In the production of the positive electrode, vanadium pentoxide (V ₂ O ₅ ) was used instead of triiron tetroxide.
A lithium-transition metal composite oxide (LiNi _0.5 Co
_0.5 O ₂ ) 1% by weight, 5% by weight, 10% by weight or 20%
In the same manner as in Examples 1 to 6 except that the addition of wt% was performed,
Comparative batteries B18 to B21 were produced.

(Examples 55 to 60) In the preparation of the positive electrode, nickel oxide (NiO) was used instead of triiron tetroxide to form a lithium-transition metal composite oxide (LiNi _0.5 Co).
_0.5 O ₂ ) 0.5% by weight, 1% by weight, 5% by weight, 10
Lithium secondary battery A5 in the same manner as in Examples 1 to 6 except that 20% by weight, 20% by weight or 22% by weight was added.
5 to A60 were produced.

<Charge storage characteristics of each battery> At room temperature (25 ° C), each battery was charged to 4.2 V at 200 mA and then discharged to 2.75 V at 200 mA to store the internal resistance R1 before storage. And the discharge capacity C1 were determined. Then, each of the discharged batteries was charged at 200 mA to 4.2 V and stored at 60 ° C. for 20 days, and then at 200 mA for 2.
After discharging to 75 V, the internal resistance R2 and the discharge capacity C2 after storage were obtained. From the respective values of the discharge capacity C1 before storage and the discharge capacity C2 after storage, the capacity remaining rate was calculated based on the following formula.

Capacity remaining rate (%) = (C2 / C1) × 100

The internal resistance R1 before storage and the internal resistance R2 after storage of each battery are shown in Tables 1 to 8, and the remaining capacity ratio of each battery is shown in FIGS. In each of FIGS. 1 to 4, the vertical axis represents the capacity residual ratio (%), and the horizontal axis represents the addition amount ratio (% by weight) of the transition metal oxide to the lithium-transition metal composite oxide (LiNi _0.5 Co _0.5 O ₂ ). ) Are orthogonal axis coordinate graphs.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

[0045]

[Table 7]

[0046]

[Table 8]

As shown in Tables 1 to 8 and FIGS. 1 to 4,
Inventive batteries A1 to A60 have a smaller increase in internal resistance after storage and a higher capacity remaining rate than comparative batteries B1 to B21. From this fact, it can be seen that the batteries A1 to A60 of the present invention are less likely to deteriorate in battery characteristics after storage when the batteries in the charged state are stored at a higher temperature than the comparative batteries B1 to B21. In addition, comparing the batteries of the present invention to which the same transition metal oxide was added, the batteries of the present invention A2 to A5, A
8-A11, A14-A17, A20-A23, A26
~ A29, A32 to A35, A38 to A41, A44 ~
Since the storage characteristics of A47, A50 to A53, and A56 to A59 are particularly excellent, it is understood that the addition% of the transition metal oxide to the lithium-transition metal composite oxide is preferably 1 to 20% by weight.

[0048]

In the battery of the present invention, the transition metal oxide added suppresses the oxidative decomposition of the solvent of the non-aqueous electrolyte, so that when the battery in a charged state is stored at a high temperature, the battery characteristics are unlikely to deteriorate after storage. .

[Brief description of drawings]

FIG. 1 is a graph showing a capacity remaining rate when a battery of the present invention and a comparative battery are stored in a charged state.

FIG. 2 is a graph showing a capacity remaining rate when the battery of the present invention and the comparative battery are stored in a charged state.

FIG. 3 is a graph showing a capacity remaining rate when the battery of the present invention and the comparative battery are stored in a charged state.

FIG. 4 is a graph showing a capacity remaining rate when a battery of the present invention and a comparative battery are stored in a charged state.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 in Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A positive electrode using a lithium-transition metal composite oxide as an active material, a negative electrode using a material capable of electrochemically absorbing and desorbing lithium ions or a lithium metal as an active material, and non-aqueous electrolysis. Lithium secondary battery including a liquid, wherein FeO _{b is} added to the lithium-transition metal composite oxide.
(0 <b <1.35), CoO _c (0 <c <1.3
5), MnO _d (0 <d <1.35), NiO _e (0 <
e <1.1), TiO _f (0 <f <2.0), VO
at least one transition metal oxide selected from the group consisting of _g (0 <g <2.1), CrO _h (0 <h <2.6) and CuO _i (0 <i <1.35). A lithium secondary battery characterized by being added. 2. The lithium-transition metal composite oxide,
Formula: Li _x MO _y (0 <x <1.1, 1.9 <y <2.
The lithium secondary battery according to claim 1, wherein 2, M are lithium-transition metal composite oxides substantially represented by at least one transition element selected from the group consisting of Ni, Co, Fe and Mn. 3. The transition metal oxide is ferrous oxide (Fe
O), triiron tetroxide (Fe ₃ O ₄ ), cobalt (II) oxide
(CoO), divanadium trioxide (V ₂ O ₃ ), cuprous oxide (Cu ₂ O), titanium monoxide (TiO), manganese (II) oxide (MnO), trimanganese tetraoxide (Mn ₃ O ₄₎ )
And at least one transition metal oxide selected from the group consisting of chromium oxide (II) (CrO).
The lithium secondary battery described. 4. The lithium secondary battery according to claim 1, wherein 1 to 20% by weight of the transition metal oxide is added to the lithium-transition metal composite oxide.