JP2000277113A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery excellent in charge/discharge characteristics compared with a lithium secondary battery with an active material of MoO3. SOLUTION: One of positive and negative electrodes has an active material of lithium containing composite oxides of orthorhombic system expressed by a formula MxMo1-xOy or these composite oxides containing Li. In the formula, M is at least one kind of transition element selected from Cu, V, Mn, Fe, Co and Ni and satisfies 0<x<=0.46; 2.6<=y<=3.1. A lithium secondary battery excellent in charge/discharge characteristics compared with a lithium secondary battery used with an active material of MoO3 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to improvement of an active material for the purpose of providing a lithium secondary battery having good charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art MoO
₃ (Molybdenum trioxide) has been proposed as a positive electrode active material for lithium secondary batteries (T. Tsumura, Solid Stat
e Ionic, Vol. 104, P183 (1997)).

MoO ₃ belongs to the orthorhombic system and is a relatively stable oxide among molybdenum oxides. However, the charge / discharge cycle characteristics of a lithium secondary battery using MoO ₃ as a positive electrode active material are not good. This is because the repetition of expansion and contraction during charging and discharging significantly changes the crystal structure of MoO ₃ .

Accordingly, an object of the present invention is to provide a lithium secondary battery having better charge / discharge cycle characteristics than a lithium secondary battery using MoO ₃ as an active material.

[0005]

According to the present invention, there is provided a lithium secondary battery according to the present invention.
The secondary battery (the battery of the present invention) includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.
And either one of the positive electrode or the negative electrode is
Formula: M_xMo_1-xO _y(M is Cu, V, Mn, Fe,
At least one selected from the group consisting of Co and Ni
Transition element; 0 <x ≦ 0.46; 2.6 ≦ y ≦ 3.1)
The orthorhombic composite oxide represented or the composite oxide
Rhodium containing orthorhombic lithium-containing composites
It has an oxide as an active material.

[0006] The composite oxide, part of Mo in the crystal lattice of the MoO ₃ phase has a crystal structure substituted with a specific transition element M, compared to MoO _3, crystals in the charge-discharge cycle The structure does not easily deteriorate. M and O in the crystal lattice
This is because the chemical bond with (oxygen) is stronger than the chemical bond between Mo and O.

The reason why x in the composition formula is limited to 0.46 or less is that if x exceeds 0.46, the composite oxide will contain an unstable transition element M oxide phase. This is because the charge / discharge cycle characteristics deteriorate. In order to obtain a lithium secondary battery having extremely excellent charge / discharge cycle characteristics, it is preferable to use a composite oxide in which x in the composition formula is 0.02 to 0.45, and x in the composition formula is 0.05 It is more preferred to use a composite oxide of ~ 0.40. The reason why y in the composition formula is limited to 2.6 to 3.1 is that although y varies depending on the kind of the transition element M and the firing temperature and the firing atmosphere when synthesizing the composite oxide, This is because they do not go outside the range. Note that the variation in stability (charge / discharge cycle characteristics) of the composite oxide due to y is extremely small.

Specific examples of the negative electrode material of the battery of the present invention having the above-mentioned composite oxide or lithium-containing composite oxide as a positive electrode active material include a substance capable of electrochemically occluding and releasing lithium ions and lithium. Metal. The charge voltage of this type of battery of the present invention is about 3V, and the discharge voltage is about 2V. Examples of the substance capable of electrochemically storing and releasing lithium ions include carbon materials such as graphite, coke, and fired organic materials; lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, and lithium-carbon alloy. A lithium alloy such as an aluminum-manganese alloy is exemplified. In order to obtain a lithium secondary battery having good charge / discharge cycle characteristics, it is preferable to use a carbon material that does not have a risk of internal short circuit caused by dendrite (dendritic lithium) penetrating the separator as a negative electrode material. . When using a lithium-containing composite oxide as the positive electrode active material, using a lithium-containing carbon material or a lithium-free carbon material as the negative electrode material, while using a lithium-free composite oxide as the positive electrode active material, A lithium-containing carbon material is used as a negative electrode material.

The above composite oxide or lithium-containing composite acid
Active material of the battery of the present invention having a nitride as a negative electrode active material
As a specific example, LiCoO_Two, LiNiO_Two, Li
Mn _TwoO_Four, LiMnO_Two, Lithium-containing MnO_Two, L
iCo_0.5Ni_0.5O_Two, LiCo_0.2Ni_0.7Mn
_0.1O_TwoSuch as lithium-containing transition metal oxides
You. The charging voltage of this type of battery of the present invention is about 2.5 V,
The voltage is about 1.5V, and the charge / discharge cycle characteristics are extremely
good. Since the charging voltage is as low as about 2.5V,
This is because the decomposition of the water electrolyte is suppressed.

The non-aqueous electrolyte is used when the solvent and solute are charged and discharged.
There is no particular limitation as long as it does not decompose at the voltage during storage and storage.
Non-aqueous electrolyte solvents include ethylene carbonate and
Cyclic such as propylene carbonate and butylene carbonate
Carbonic acid ester, dimethyl carbonate, diethyl car
Chain carbonates such as carbonate and methyl ethyl carbonate
A mixed solvent with ter, a cyclic carbonate, and 1,2
Ethane such as diethoxyethane, 1,2-dimethoxyethane, etc.
A mixed solvent with an ether-based solvent is exemplified. Non-aqueous electrolyte
As a solute, LiPF₆, LiBF_Four, LiCF_ThreeS
O_Three, LiN (CF_ThreeSO_Two)_Two, LiN (C_TwoF_FiveS
O_Two)_Two, LiN (CF_ThreeSO_Two) (C _FourF₉S
O_Two), LiC (CF_ThreeSO_Two)_ThreeAnd LiC (C_TwoF
_FiveSO_Two)_ThreeIs exemplified. These lithium salts are a kind
One type may be used alone, or two or more types may be used in combination as needed.
May be. Polyethyleneoxy as non-aqueous electrolyte
And non-aqueous electrolytes in polymers such as polyacrylonitrile.
A gel electrolyte immersed, or LiI, Li_ThreeN
And the like may be used.

[0011] The present invention battery, because it has a crystalline structure stable specific composite oxide or lithium-containing composite oxide compared to MoO ₃ as one of the active material of the positive electrode or the negative electrode, and the MoO ₃ active material Charge / discharge cycle characteristics are better than lithium secondary batteries.

[0012]

EXAMPLES 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 can be carried out by appropriately changing the scope without changing the gist. It is something.

(Experiment 1) A battery of the present invention and a comparative battery were prepared, and charge / discharge cycle characteristics were compared.

(Examples 1 to 6) [Preparation of positive electrode] Copper nitrate (Cu (NO ₃ ) ₂ ), vanadium chloride (VCl ₃ ), manganese acetate (Mn (CH ₃ CO ₃ ))
O) ₂ ), iron nitrate (Fe (NO ₃ ) ₃ ), cobalt acetate (Co (CH ₃ COO) ₂ ) or nickel nitrate (Ni
(NO ₃ ) ₂ ) and molybdenum carbonyl (Mo (C
O) ₆ ) and M (Cu, V, Mn, Fe, Co or N
i): Mo was weighed at an atomic ratio of 0.20: 0.80, mixed in a mortar, and molded at a molding pressure of 115 in a disk mold of 17 mm in diameter.
After molding under pressure at kg / cm ² , 700
° calcined 12 hours at C, and then pulverized in a mortar, respectively _{formula: Cu 0.20 Mo 0. 80 O 3} , V 0.20 Mo 0.80 O 3, M
n _0.20 Mo _0.80 O ₃ , Fe _0.20 Mo _0.80 O ₃ , Co _0.20
A composite oxide powder having an average particle diameter of 10 μm represented by Mo _0.80 O ₃ and Ni _0.20 Mo _0.80 O ₃ was produced.

The above composite oxide powder as a positive electrode active material, carbon powder as a conductive agent, and polyvinylidene fluoride powder as a binder are mixed in a weight ratio of 85: 10: 5 to obtain a mixture. The obtained mixture was mixed with NMP (N-methylpyrrolidone) to prepare a slurry, and this slurry was applied to one surface of a 20 μm-thick aluminum current collector by a doctor blade method, and dried at 150 ° C. ,
The blank was punched out to produce a disk-shaped positive electrode having a diameter of 10 mm and a thickness of about 80 μm.

Each of the above positive electrodes and a disc-shaped lithium metal as a counter electrode are laminated with a separator (ion-permeable polypropylene film) interposed therebetween to produce an electrode body. This electrode body is made of ethylene carbonate. Immersed in a non-aqueous electrolyte obtained by dissolving 1 mol / l of LiPF _{6 in} a mixed solvent of
Electrolyze to 1.5 V (vs. Li ^/ Li ⁺ ) with μA,
The composite oxide of each positive electrode contained lithium.

[Preparation of Negative Electrode] A natural graphite powder and a polyvinylidene fluoride powder as a binder were mixed at a weight ratio of 95: 5.
And the obtained mixed powder is mixed with NMP (N-methylpyrrolidone) to prepare a slurry. The slurry is applied to one surface of a 20 μm-thick copper current collector by a doctor blade method, After drying at ° C., punching was performed to produce a disk-shaped negative electrode having a diameter of 10 mm and a thickness of about 60 μm.

[Preparation of Nonaqueous Electrolyte] A nonaqueous electrolyte was prepared by dissolving 1 mol / l of LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.

[Preparation of Lithium Secondary Battery] Flat lithium secondary batteries A1 to A6 (the batteries of the present invention) were prepared using the above positive electrode, negative electrode and nonaqueous electrolyte. An ion-permeable polypropylene film was used for the separator. FIG. 1 is a cross-sectional view of a manufactured lithium secondary battery. The illustrated lithium secondary battery A has a positive electrode 1, a negative electrode 2,
Separator 3, positive electrode can 4, negative electrode can 5, separating them
It comprises 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 face each other via a separator 3 impregnated with a nonaqueous electrolyte, and are housed in a battery can formed by a positive electrode can 4 and a negative electrode can 5.
The positive electrode 1 is connected to the positive electrode can 4 via the positive electrode current collector 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 in the battery can is supplied to the outside as electric energy. It can be taken out.

(Examples 7 and 8) A positive electrode was manufactured in the same manner as in the method of manufacturing the positive electrode in Example 1. However, electrolysis, which is an operation for incorporating lithium into the composite oxide (Cu _0.20 Mo _0.80 O ₃ ) of the positive electrode, was not performed. Further, a lithium rolled sheet and a lithium-aluminum alloy sheet (lithium content: 20.6% by weight) were punched out to produce two kinds of disc-shaped negative electrodes having a diameter of 10 mm and a thickness of 1.0 mm. Batteries A7 and A8 of the present invention were produced in the same manner as in Example 1 except that the above-mentioned positive electrode and each negative electrode were used as the positive electrode and the negative electrode, respectively.

(Examples 9 to 11) L as a positive electrode active material
iCoO ₂ , LiNiO ₂ or LiMn ₂ O ₄ , carbon powder as a conductive agent, and polyvinylidene fluoride powder as a binder were mixed at a weight ratio of 85: 10: 5, and the obtained mixture was mixed with NMP ( N-methylpyrrolidone) to prepare a slurry.
It was applied to one side of an aluminum current collector by a doctor blade method, dried at 150 ° C., and punched out.
A disk-shaped positive electrode having a diameter of 10 mm and a thickness of about 80 μm was produced. Further, a composite oxide powder having an average particle size of 10 μm represented by the composition formula: Cu _0.20 Mo _0.80 O ₃ (the same as that prepared in Example 1), a carbon powder as a conductive agent, and a binder as a binder Of polyvinylidene fluoride powder at a weight ratio of 8
The mixture was mixed at 5: 10: 5, and the resulting mixture was mixed with NMP (N-
Methylpyrrolidone) to prepare a slurry,
The slurry was applied to one surface of a copper current collector having a thickness of 20 μm by a doctor blade method, dried at 150 ° C., and punched out to produce a disk-shaped negative electrode having a diameter of 10 mm and a thickness of 1.0 mm. Batteries A9 to A11 of the invention were produced in the same manner as in Example 1, except that the above-described positive electrode and negative electrode were used as the positive electrode and the negative electrode.

Comparative Example 1 MoO ₃ as a positive electrode active material
Powder, carbon powder as a conductive agent, and polyvinylidene fluoride powder as a binder are mixed at a weight ratio of 85: 10: 5, and the obtained mixed powder and NMP are mixed to prepare a slurry. Then, this slurry was applied to one side of a 20 μm-thick aluminum current collector by a doctor blade method, dried at 150 ° C., punched out, and punched to a diameter of 10 m.
m, a disc-shaped positive electrode having a thickness of about 80 μm was prepared. MoO
_{As the three} powders, those fired at 600 ° C. were used. All of the MoO ₃ powders described below were fired at 600 ° C. Next, electrolysis was performed under the same conditions as those performed in Example 1 so that MoO ₃ of the positive electrode contained lithium. A comparative battery B1 was produced in the same manner as in Example 1 except that the above positive electrode was used as the positive electrode.

(Comparative Examples 2 and 3) M as a positive electrode active material
An oO ₃ powder, a carbon powder as a conductive agent, and a polyvinylidene fluoride powder as a binder were mixed at a weight ratio of 85: 1.
The mixture was mixed at 0: 5, and the obtained mixed powder and NMP were mixed to prepare a slurry. The slurry was applied to one side of a 20 μm-thick aluminum current collector by a doctor blade method, , And punched out to produce a disk-shaped positive electrode having a diameter of 10 mm and a thickness of about 80 µm. A lithium rolled sheet and a lithium-aluminum alloy sheet (lithium content: 20.6% by weight) were punched out to produce two kinds of disc-shaped negative electrodes having a diameter of 10 mm and a thickness of 1.0 mm. Comparative batteries B2 and B3 were produced in the same manner as in Comparative Example 1 except that the above positive electrode and each negative electrode were used as the positive electrode and the negative electrode, respectively.

<Charge / Discharge Cycle Characteristics of Each Battery> For the batteries A1 to A6 of the present invention and the comparative battery B1, 100 μA
The battery was charged to 3.0 V and then charged and discharged at 100 μA to 1.5 V for 50 cycles, and the capacity retention ratio of each battery at the 50th cycle was determined by the following equation. Invention battery A7
And A8 and comparative batteries B2 and B3
The battery was discharged at 0 μA to 1.5 V, then charged at 100 μA to 3.0 V, and then charged and discharged at 100 μA to 1.5 V for 50 cycles. I asked. Inventive batteries A9 to
As for A11, after charging to 2.5 V at 100 μA, discharging and discharging to 0.5 V at 100 μA was performed for 50 cycles, and the capacity retention ratio of the 50th cycle of each battery was determined by the following formula. All charge and discharge cycle tests were performed at room temperature (25 °
C). Table 1 shows the discharge voltage (average discharge voltage until reaching the discharge end voltage), initial capacity (discharge capacity in the first cycle), and capacity retention of each battery.

Capacity retention (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) × 100

[0026]

[Table 1]

Table 1 shows that the batteries A1 to A11 of the present invention have a larger capacity retention ratio and better charge / discharge cycle characteristics than the comparative batteries B1 to B3. Also, from the comparison of the capacity retention ratio between the battery A1 of the present invention and the batteries A7 and A8 of the present invention, in order to obtain a lithium secondary battery having good charge / discharge cycle characteristics, dendrite was used as a negative electrode material even after repeated charge / discharge. It can be seen that it is preferable to use graphite (carbon material) that is not likely to be generated. Further, among the batteries of the present invention, the batteries A9 to A11 of the present invention have particularly high capacity retention rates. Therefore, a lithium-containing transition metal oxide is used as the positive electrode active material, and the composite oxide defined by the present invention is used as the negative electrode active material. It turns out that it is preferable to use. The reason why the capacity retention ratios of the batteries A9 to A11 of the present invention are particularly large as 90 to 91% is that the decomposition of the non-aqueous electrolyte is suppressed because the charging voltage is as low as 2.5 V.

(Experiment 2) Composition formula: The relationship between _{x in} M _x Mo _1-x O ₃ and charge / discharge cycle characteristics was examined.

Copper nitrate (Cu (NO ₃ ) ₂ ) and molybdenum carbonyl (Mo (CO) ₆ ) are converted to a Cu: Mo atomic ratio of 0.02: 0.98, 0.05: 0.95, 0 .1
0: 0.90, 0.30: 0.70, 0.40: 0.6
0, 0.45: 0.55, 0.46: 0.54 and 0.
47: weighed at 0.53 and mixed in a mortar, 17m in diameter
After molding under pressure with a molding pressure of 115 kg / cm ² in a disc mold of m, calcining was performed at 700 ° C. for 12 hours in an oxygen stream,
Pulverized in a mortar, each having the composition formula: Cu _0.02 Mo _0.98
O ₃ , Cu _0.05 Mo _0.95 O ₃ , Cu _0.10 Mo _0.90 O ₃ ,
_{Cu 0.30 Mo 0. 70 O 3,} Cu 0.40 Mo 0.60 O 3, Cu
_0.45 Mo _0.55 O ₃ , Cu _0.46 Mo _0.54 O ₃ and Cu _0.47
A composite oxide powder having an average particle size of 10 μm represented by Mo _0.53 O ₃ was produced. In the preparation of the positive electrode, the composition formula: Cu
Instead of the composite oxide powder represented by _0.20 Mo _0.80 O ₃ ,
Example 1 except that each of the above composite oxide powders was used.
In the same manner as in, batteries X1 to X7 and a battery B4 were sequentially manufactured. The batteries X1 to X7 are the batteries of the present invention, and the battery B4
Is a comparative battery. For each battery, a charge / discharge cycle test was performed under the same conditions as those performed for the batteries A1 to A6 of the present invention and the comparative battery B1 in Experiment 1, and the capacity retention ratio was examined. Table 2 shows the discharge voltage (the average discharge voltage up to the discharge end voltage), the initial capacity (the first cycle discharge capacity), and the capacity retention rate of each battery. FIG. 2 shows the composition formula: Cu _x M
o _1-x The relationship between _{x in} O ₃ and charge / discharge cycle characteristics, the capacity retention rate (%) is plotted on the vertical axis, and the composition formula: Cu _x Mo _{1-x is} plotted on the horizontal axis.
5 is a graph showing values of x in O ₃ . Table 2 and FIG. 2 also show the capacity retention ratio of the battery A1 of the present invention and the comparative battery B1.

[0030]

[Table 2]

From Table 2 and FIG. 2, the use of a composite oxide in which x is greater than 0 and 0.46 or less improves the charge-discharge cycle characteristics. However, in order to greatly improve the charge-discharge cycle characteristics, , X is preferably from 0.02 to 0.45, and x is from 0.05 to 0.40.
It can be seen that it is more preferable to use the composite oxide of the above. In Experiment 2, the relationship between _x in the composition formula: Cu _x Mo _1-x O ₃ and charge / discharge cycle characteristics was examined by taking the case where the transition element M is Cu as an example. Regardless, in order to greatly improve the charge / discharge cycle characteristics, _{x in} the composition formula: M _x Mo _1-x O ₃ is 0.02 to 0.02.
It was confirmed that it is preferable to use a composite oxide of 0.45, and it is more preferable to use a composite oxide of x of 0.05 to 0.40.

In the above embodiment, the case where the present invention is applied to a flat type lithium secondary battery has been described as an example.
The present invention is not limited to the shape of the battery, and is applicable to lithium secondary batteries having various shapes such as a cylindrical shape.

[0033]

According to the present invention, a lithium secondary battery having better charge / discharge cycle characteristics than a lithium secondary battery using MoO ₃ as an active material is provided.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between _{x in the} composition formula: Cu _x Mo _1-x O ₃ and charge / discharge cycle characteristics.

[Explanation of symbols]

 A Lithium secondary battery 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode can 5 Negative electrode can 6 Positive current collector 7 Negative current collector 8 Insulation packing

Continuation of the front page (72) Inventor Shin Fujitani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5H003 AA04 BB05 BC01 BC06 BD00 5H014 AA01 AA06 EE07 EE10 HH00 5H029 AJ05 AK03 AL06 AM03 AM04 AM05 AM07 BJ03 BJ16 DJ16 DJ17 HJ02

Claims (6)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein one of the positive electrode and the negative electrode has a composition formula: M _x Mo _1-x O _y (M is Cu,
At least one transition element selected from the group consisting of V, Mn, Fe, Co and Ni; 0 <x ≦ 0.46; 2.6
.Ltoreq.y.ltoreq.3.1), characterized by having as an active material an orthorhombic lithium-containing composite oxide obtained by adding lithium to the composite oxide. Rechargeable lithium battery. 2. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a composition formula: M _x M
o _1-x O _y (M is Cu, V, Mn, Fe, Co and Ni
At least one transition element selected from the group consisting of: 0
<X ≦ 0.46; 2.6 ≦ y ≦ 3.1) An orthorhombic lithium-containing composite oxide obtained by adding lithium to an orthorhombic composite oxide represented by the following formula: A lithium secondary battery, wherein the negative electrode includes, as a lithium ion storage material, a carbon material or a lithium-containing carbon material obtained by adding lithium to a carbon material. 3. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a composition formula: M _x M
o _1-x O _y (M is Cu, V, Mn, Fe, Co and Ni
At least one transition element selected from the group consisting of: 0
<X ≦ 0.46; 2.6 ≦ y ≦ 3.1) lithium as an active material, wherein the negative electrode contains lithium in a carbon material. A lithium secondary battery having a carbon material as a lithium ion storage material. 4. A rechargeable battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte.
In the lithium secondary battery, the positive electrode is a lithium-containing
Having a transfer metal oxide as an active material, wherein the negative electrode has a composition
Formula: M _xMo_1-xO_y(M is Cu, V, Mn, Fe, C
at least one transition selected from the group consisting of o and Ni
Transfer element; 0 <x ≦ 0.46; 2.6 ≦ y ≦ 3.1)
With orthorhombic composite oxide as active material
Rechargeable battery. 5. The composite oxide has a composition formula: M _x Mo _1-x
O _y (M is at least one transition element selected from the group consisting of Cu, V, Mn, Fe, Co and Ni; 0.02
≦ x ≦ 0.45; 2.6 ≦ y ≦ 3.1), the lithium secondary battery according to claim 1. 6. The composite oxide has a composition formula: M _x Mo _1-x
O _y (M is at least one transition element selected from the group consisting of Cu, V, Mn, Fe, Co and Ni; 0.05
≤x≤0.40; 2.6≤y≤3.1), wherein the lithium secondary battery according to any one of claims 1 to 4.