JP2001217011A - Lithium secondary battery - Google Patents

Abstract

[PROBLEMS] To provide a LiMn ₂ O ₄ -based positive electrode long-life lithium secondary battery for electric power storage, electric vehicles and the like. SOLUTION: In a lithium secondary battery having a positive electrode mainly composed of a lithium manganese composite oxide, a negative electrode storing and releasing lithium, and a non-aqueous electrolyte containing a lithium salt, the capacity per unit weight of the positive electrode active material is converted. 55-80Ah /
A lithium secondary battery characterized in that a capacity corresponding to kg is a rated capacity of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery using a positive electrode mainly composed of a lithium manganese composite oxide.

[0002]

2. Description of the Related Art With the development of the information society, it is expected that the spread of personal computers, mobile phones and the like will increase further in the future.
Lithium secondary batteries have a high battery voltage and a high energy density, and have been actively developed, and some batteries have been put to practical use as power sources for personal computers, mobile phones, and the like.

However, for applications other than portable devices, power sources for power storage, electric vehicles, and the like are conceivable. However, in order to apply to these applications, the battery must be large, have a long service life, have a high output, and be low in cost. Is essential.

[0004] Since a large amount of electrode material is used in a large-sized battery, a lithium-cobalt composite oxide positive electrode material of a commercially available battery containing cobalt, which is a rare metal as a main component, is insecure in terms of resources and may be expensive. . As an alternative material, lithium manganese composite oxide is expected. However, in using the lithium manganese composite oxide positive electrode battery as a power source for power storage, electric vehicles, and the like, extending the life is a particularly important issue. Japanese Patent Application Laid-Open No. 9-120843 discloses a technique for extending the life.

[0005]

The above-mentioned Japanese Patent Application Laid-Open No. 9-12 / 1997
No. 0843, the carbon is used for the negative electrode, and LiCoO ₂ is used for the positive electrode.
Discloses a charging / discharging method for prolonging the life of a battery using a battery. That is, there is disclosed a method of increasing the upper limit voltage of charging and lowering the lower limit voltage of discharging with the increase of the charge / discharge cycle to secure the capacity of the battery. However, if the charging voltage is increased in order to secure the battery capacity, decomposition of the electrolyte may occur, especially when a long life is required for large batteries such as electric power storage and electric vehicles. It is considered that such techniques are difficult to adapt.

[0006] In view of the above, an object of the present invention is to provide a long-life lithium secondary battery applicable for electric power storage, electric vehicles and the like.

[0007]

Means for Solving the Problems] a result of various studies in order to achieve the object of the present _{invention, Li 1 + x Me y Mn} 2-xy O
₄ (0 ≦ x ≦ 0.2, Me = Co, Cr, 0 ≦ x ≦ 0.2
In a lithium secondary battery having a positive electrode mainly composed of the lithium-manganese composite oxide represented by 2), a negative electrode that inserts and desorbs lithium, and a non-aqueous electrolyte containing a lithium salt, the capacity per unit weight of the positive electrode active material is reduced. Converted to 55 to 80 Ah
It is an object of the present invention to provide a lithium secondary battery having a capacity corresponding to / kg as a rated capacity and a rated capacity as a maximum charge capacity during charge and discharge.

[0008] As the electrolyte, for example, at least one non-electrolyte selected from propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, 1,2-diethoxyethane and the like. In an aqueous solvent, for example, LiClO ₄ , L
an organic electrolyte solution in which at least one lithium salt selected from iAsF ₆ , LiBF ₄ , LiPF _{6 and the} like is dissolved, a solid electrolyte having lithium ion conductivity, a gel electrolyte or a molten salt, and a carbon-based material; A known electrolyte used for a battery using lithium metal or a lithium alloy as a negative electrode active material can be used.

Further, a microporous separator can be used as required in the structure of the battery.

The battery of the present invention can be used not only for electric vehicles and electric power storage, but also as a power source for other uses requiring a long life.

In the present invention, the rated charge capacity of the lithium secondary battery is set based on the capacity per unit weight of the positive electrode active material, and the charge capacity is set to be equal to or less than the rated capacity, thereby keeping the charge end voltage of the battery low. In addition, the battery life can be extended.

The capacity per unit weight of the positive electrode active material as a reference of the rated capacity, that is, the capacity per unit weight of the lithium manganese composite oxide as the positive electrode active material is 55 to 80 Ah /
kg is preferred. 55 Ah / k capacity per unit weight
Even if it is less than g, a remarkable effect on the improvement of the life is not obtained, and the energy density of the battery is also reduced. On the other hand, 80Ah
If the pressure exceeds / kg, the battery will operate for a long time in the high voltage range, and it is estimated that the decomposition of the electrolyte is one of the causes.
The decrease in battery capacity becomes remarkable.

Using a lithium metal counter electrode, the discharge capacity of the lithium manganese composite oxide is measured at a charge end voltage of 4.2 to 4.3 V, a discharge end voltage of 3 to 3.5 V, and a constant voltage of 3 to 4 hour rate. As a result, the discharge capacity per unit weight was 100
１１０110 Ah / kg.

That is, the present invention shows that a battery having a long life can be provided by setting the rated capacity to a value determined based on 50 to 80% of the discharge capacity per unit weight measured as described above. It is a thing.

By measuring the weight of the electrode of a commercially available battery and calculating (rated capacity / amount of positive electrode active material), it is possible to determine how much capacity (Ah / kg) per unit weight of the active material is rated.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically based on embodiments.

Example 1 LiOH and MnO ₂ were converted to L
i: Mn = 1.15: 1.85 mixed at a ratio of 500 ° C.
To obtain a lithium manganese composite oxide.

For the positive electrode material, graphite as a conductive agent, polyvinylidene fluoride as a binder and a solvent were weighed at a weight ratio of 85: 10: 5, and the mixture was kneaded with a triturator for 30 minutes.
m of aluminum foil to form a positive electrode.

Graphite was used as a negative electrode material, and polyvinylidene fluoride was used as a binder. The mixture was kneaded at a weight ratio of 90:10 in the same manner as the positive electrode, and applied to a copper foil having a thickness of 20 μm.

FIG. 1 shows a schematic cross-sectional view of the manufactured battery.
The positive and negative coated electrodes were roll-formed by a press machine, spot-welded the terminals, and then vacuum-dried at 150 ° C. for 5 hours.

The positive electrode 1 and the negative electrode 2 were laminated via a microporous polypropylene separator 3 and spirally wound, and the wound group was inserted into a battery can. The negative electrode terminal 7 was welded to the bottom of the battery can, and the positive electrode terminal 5 was welded to the back of the battery lid 6.

The electrolyte contains LiPF ₆ at a concentration of 1 mol / l.
Using a solution dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate, the mixture was poured into a battery can. After the injection of the electrolyte, the battery lid 6 was caulked via the packing 10 to produce a cylindrical battery.

The produced battery is charged at 40 Ah per unit weight.
/ Kg, 50Ah / kg, 55Ah / kg, 60
Capacity calculated at each capacity of Ah / kg, 70 Ah / kg, 80 Ah / kg, and 85 Ah / kg (capacity per unit weight of positive electrode active material x amount of charged positive electrode active material of battery)
Was set to the rated capacity.

The above-mentioned batteries were designated as Battery No. 1-1 and Battery N
o-1, battery No. 1-3, battery No. 1-4, battery No. 1-5, battery No. 1-6, and battery No. 1-7.

Next, a cycle test was performed under the following conditions.
The charge / discharge current is 0.2 with respect to the rated capacity for both charge and discharge.
The current is set to 5C, and the charging is performed under the condition that the charging time is 12 hours, the constant current and constant voltage charging of the charging upper limit voltage is 4.2 V, and the capacity regulation in which the rated capacity is set to the charging termination capacity, and the discharging is the termination voltage. It carried out at 3.0V.

FIG. 2 shows a cycle test result of Battery No. 1-5 in which the capacity was set to 70 Ah / kg. FIG. 2 shows the relationship between the discharge capacity maintenance ratio% (discharge capacity / first discharge capacity in the cycle test) and the number of cycles.

The battery reaches a final voltage of 4.2 V at the time of charging the rated capacity in 2,300 cycles. Thereafter, the battery is charged at a constant voltage of 4.2 V after the constant current charging. Was stopped and discharged.

Further, after 2580 cycles, the charge capacity did not reach the rated capacity within a predetermined charge time (12 hours), and the discharge capacity tended to decrease gradually. The cycle life at which the maintenance rate reaches the life evaluation standard of 70% is 40.
10 cycles.

FIG. 3 shows the relationship between the capacity per unit weight of the positive electrode active material and the cycle life. Battery No. 1-7 had a short cycle life of 1580 cycles. The battery of Battery No. 1-6 showed a long life of 3520 cycles.

On the other hand, battery No. 1-1 and battery No. 1-2
Means that the capacity per unit weight of the positive electrode active material is 40 Ah / kg,
55 Ah / kg, despite being reduced to 50 Ah / kg
4530 compared to the cycle life of battery No. 1-3 of No. 1-3
560 cycles and 4590 cycles, no significant improvement in cycle life was observed.

In the positive electrode material of the lithium manganese composite oxide other than this example, the discharge capacity per unit weight of the active material measured using the lithium metal counter electrode was 50 to 80.
By using the value determined based on the% as the rated capacity, a long-life battery can be obtained.

Example 2 A battery was manufactured in the same manner as in Example 1 except that the composition of the positive electrode active material was changed. In this example, the composition of the positive electrode active material was LiMn ₂ O ₄ , Li _1.05 Mn.
_1.95 O ₄ , Li _1.1 Mn _1.9 O ₄ , Li _1.15 Mn _1.85 O
_{4, Li 1.2 Mn 1.8 O 4} , and, Li _1.25 Mn _{1. 75}
There were six types of O ₄ .

Each of the manufactured batteries was used in the order of the above-described positive electrode active material composition to batteries No. 2-1, No. 2-2, and No. 2
-3, No. 2-4, No. 2-5, and No. 2-
6 is assumed.

The cycle test conditions were the same as in Example 1, except that the capacity per unit weight of the positive electrode active material was 70 A.
The rated capacity was set as h / kg. FIG. 4 shows the cycle test results.

Each of the batteries No. 2-1 to No. 2-5 had a cycle life of 3600 to 4000 cycles and exhibited a long life. On the other hand, Battery No. 2-6 had a short life of less than 2000 cycles.

Example 3 A battery was manufactured in the same manner as in Example 1. This embodiment differs from the first embodiment in that the composition of the positive electrode is Li _1.1 Mn _1.9 O ₄ . The capacity of the produced battery was set at 75 Ah / kg per unit weight of the positive electrode active material, and the rated capacity was set.

The charging / discharging current is 0.1 with respect to the rated capacity.
25C (8 hour rate) and 0.25C (4 hour rate) were set. The respective batteries were designated as Battery No. 3-1 and Battery No. 3
-2. Charge time 12 hours, charge upper limit voltage 4.2V
Was the same as in Example 1. The discharge end voltage is also 3.0.
V and the same as in Example 1.

FIG. 5 shows the cycle test results. Battery N
o.3-1 has a cycle life of 3560 cycles,
The cycle life of battery No. 3-2 was 3,780 cycles.

Example 4 Two types of batteries were produced in the same manner as in Examples 1 and 2. The battery having the same specification as that of the first embodiment is the battery No. 4-1 and the battery having the same specification as the second embodiment is the battery No.
4-2. 70 A capacity per unit weight of positive electrode active material
The rated capacity was set as h / kg. The charge / discharge current was set to 0.25 C with respect to the rated capacity.

In this embodiment, charging was performed only by constant current charging. The charge upper limit voltage of 4.2 V and the discharge end voltage of 3.0 V were the same as in Examples 1 and 2. FIG. 6 shows the results of the cycle test.

The cycle life of battery No. 4-1 was 358.
The cycle life was 0, and the cycle life of Battery No. 4-2 was 3,470 cycles.

Embodiment 5 In this embodiment, Li _1.1 M
n _1.85 Co _0.05 O ₄ was used as a positive electrode active material. Otherwise, the procedure of Example 1 was followed to fabricate a battery. The capacity per unit weight of the positive electrode active material was set to 70 Ah / kg, and the rated capacity was set. A cycle test was performed under the same test conditions as in Example 1. The cycle life was 3940 cycles, indicating a long life.

Example 6 A battery was manufactured in the same manner as in Example 1. Here, amorphous carbon was used as the negative electrode active material. The rated capacity was set with a capacity per unit weight of the positive electrode active material of 70 Ah / kg.

A cycle test was performed under the same test conditions as in Example 1 except that the discharge end voltage was changed to 2.8V. The cycle life was 3,880 cycles, indicating a long life.

[Embodiment 7] An assembled battery was formed by connecting the same four batteries as in Embodiment 1 in series. The rated capacity was set at a capacity per unit weight of the positive electrode active material of 70 Ah / kg and 85 Ah / kg. The charge / discharge current was set to 0.25 C with respect to the rated capacity, and only the constant current charge was performed in the same manner as in Example 4. The charge upper limit voltage was 16.8 V and the discharge end voltage was 12.0 V. FIG. 7 shows the results of the cycle test.

The cycle life of battery No. 5-1 was 347
0 cycle, and the cycle life of Battery No. 4-2 was 1,530 cycles.

[0047]

According to the present invention, it is possible to provide a long-life lithium secondary battery that can be used for electric power storage, electric vehicles, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a cylindrical battery of the present invention.

FIG. 2 is a graph showing cycle characteristics of the battery of Example 1.

FIG. 3 is a graph showing the relationship between the rated capacity and the life of the battery of Example 1.

FIG. 4 is a graph showing the relationship between the positive electrode composition and the life of the battery of Example 2.

FIG. 5 is a graph showing cycle characteristics of the battery of Example 3.

FIG. 6 is a graph showing cycle characteristics of the battery of Example 4.

FIG. 7 is a graph showing cycle characteristics of the battery pack of Example 7.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Battery can, 5
... positive electrode lead, 6 ... battery cover, 7 ... negative electrode lead, 8 ... burst valve, 9, 10 ... packing.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeo Yamagata 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hisashi Ando 7-1 Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd., Hitachi Research Laboratory (72) Inventor Ren Muranaka 7-1-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Hitachi Research Laboratory F-term (reference) 5H029 AJ05 AJ07 AK03 AL07 AM03 AM04 AM05 AM07 AM16 BJ02 BJ14 HJ02 HJ19

Claims (4)

[Claims] 1. In a lithium secondary battery having a positive electrode mainly composed of a lithium-manganese composite oxide, a negative electrode storing and releasing lithium, and a non-aqueous electrolyte containing a lithium salt, the positive electrode active material is converted into a capacity per unit weight. 55 to 80 Ah
A lithium secondary battery characterized in that a capacity corresponding to / kg is defined as a rated capacity of the battery. 2. In a lithium secondary battery having a positive electrode mainly composed of a lithium-manganese composite oxide, a negative electrode storing and releasing lithium, and a non-aqueous electrolyte containing a lithium salt, the positive electrode active material is converted into a capacity per unit weight. 55 to 80 Ah
A rechargeable lithium battery characterized by being charged / discharged at a capacity corresponding to / kg. 3. The lithium manganese composite oxide is Li _{1 + x}
Me _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.2, Me = Co, C
2. The lithium secondary battery according to claim 1, wherein r, 0 ≦ x ≦ 0.2). 4. An assembled battery comprising a plurality of the lithium secondary batteries connected in series and / or parallel.