JP2001118569A - Lithium secondary battery - Google Patents

Abstract

(57) [Problem] To provide a high-output lithium secondary battery having a Li _{1 + x} Mn ₂ -xO ₄ LiMn ₂ O ₄ -based positive electrode for an electric vehicle, particularly a hybrid electric vehicle requiring a high output. . An amorphous carbon or the negative electrode and / using graphite, with Li _{1+ x} Mn _2- xO ₄ to the positive electrode, Li of the current collector side of per unit area of the positive electrode 1 _{+ x} Mn _{2 -} xO ₄ to 6
By setting the content to be up to 36 mg / cm ² , a high-output lithium secondary battery for a hybrid electric vehicle that requires particularly high output can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high output 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-oriented 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 of the 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. 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 may be insecure in terms of resources and may be expensive. As a substitute material, lithium manganese composite oxide is expected, and the life of the lithium manganese composite oxide positive electrode battery is extended. A battery technology using a lithium manganese composite oxide cathode is disclosed in
It is disclosed in JP-A-120777.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open Publication No. 1-1
Japanese Patent No. 20777 proposes a battery using lithium metal for the negative electrode and LiMn ₂ O ₄ for the positive electrode. Since a lithium metal negative electrode battery generates inactive lithium by charging and discharging, it is difficult to extend the life of the battery. Such generation of inactive lithium deteriorates the performance of the negative electrode, and thus hinders not only the life characteristics but also the increase in output of the battery. In the case of a lithium metal negative electrode, the current value (3
Charge and discharge up to C) are possible. However, electric vehicles that require a high-power battery, especially hybrid electric vehicles, require a large current of 10 to 20 C or more. However, a lithium metal negative electrode cannot cope with such a large current. It is considered very difficult.

It is an object of the present invention to provide a high power density lithium secondary battery applicable to electric vehicles, particularly hybrid electric vehicles.

[0006]

When lithium metal is used for the negative electrode, not only lithium dendrite is generated at the time of charging but also inactive lithium is generated during charging and discharging, so that a high-output lithium secondary battery is obtained. It becomes difficult.

As a result of various studies to achieve the object of the present invention, the apparent density of the negative electrode mixture composed of amorphous carbon and / or graphite and a binder was determined with respect to the true density of the negative electrode mixture.
A negative electrode having a relative density of 55 to 70% was used.
_{1 + x Mn 2- xO 4 (} 0.05 ≦ x ≦ 0.2) using a lithium-manganese composite oxide represented by, 6～36Mg a lithium manganese composite oxide content per unit area of the double-sided collector of the positive electrode / Cm ² and the ratio of the amount of the positive electrode active material per unit area to the total amount of the positive electrode current collector and the amount of the positive electrode active material per unit area is 0.5 or more, whereby a lithium secondary battery having a high output density can be obtained. I found that it could be provided.

As the electrolyte, for example, at least one non-aqueous solution selected from propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, 1.2-diethoxyethane, etc. In the solvent, for example, LiClO
₄ , an organic electrolyte solution in which at least one lithium salt selected from LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like is dissolved, or a solid electrolyte having lithium ion conductivity, a gel electrolyte, or a molten salt. In general, a known electrolyte used in a battery using a carbon-based material, lithium metal, or a lithium alloy as a negative electrode active material can be used. Further, even if a microporous separator is used according to the necessity in the configuration of the battery, the effect of the present invention is not impaired at all.

The battery of the present invention can be used not only for electric vehicles, but also as a power source for devices requiring particularly high output, such as power storage and portable small devices.

That is, in a battery using a lithium manganese composite oxide as the positive electrode active material, the amount of the positive electrode active material per unit area on both surfaces of the current collector affects the battery characteristics. That is, when the amount of the positive electrode active material per unit area is reduced and the electrode is thinned, lithium ions in the electrode are easily diffused, and the charge / discharge characteristics of the battery are improved. However, if the electrode is too thin, the amount of active material becomes too small, so that a battery having a required weight output density cannot be obtained. Therefore, a lower limit is required for the amount of active material per unit area to obtain a required weight output density.

That is, a positive electrode active material layer having a predetermined amount or more that can satisfy a required weight output density, that is, an active material layer having a ratio of 0.5 or more to the total weight of the current collector and the active material is formed as a current collector. It is necessary to provide. In order to enable charging and discharging with such an electrode at a large current of 10 to 20 C or more, it cannot be solved simply by specifying the amount of the positive electrode active material. That is, in order to obtain a lithium secondary battery having excellent weight output density, Li having better load characteristics than LiMn ₂ O ₄ is used.
₁ + x Mn _2- xO ₄ be used (0.05 ≦ x ≦ 0.2) is important.

On the other hand, the density of the negative electrode is another key point in constituting the present invention. It is well known that graphite has a layered structure, but amorphous carbon also basically has a layered structure, and many of the lithium ion insertion / desorption sites are occupied by this layered structure. I have. That is, when the electrode density is excessively increased, the ratio of graphite or amorphous carbon particles having a hexagonal mesh plane oriented parallel to the current collector increases, and the speed of lithium ion insertion / desorption decreases. Along with this, the load characteristics of the negative electrode decrease, and it becomes impossible to increase the output of the battery.

On the other hand, when the electrode density is reduced, the influence of the orientation is reduced, but the contact state between the particles is deteriorated, and a desired load characteristic cannot be obtained. That is, in order to obtain a negative electrode in which the particles are in good contact with each other without being affected by the orientation, it is preferable that the apparent density of the negative electrode mixture be 55 to 70% of the relative density of the true density.

[0014]

Embodiments of the present invention will be described below. Note that the present invention is not limited to the embodiments described below.

(Example 1) LiOH and MnO ₂ were converted to Li:
Mn was mixed at a ratio of Mn = 1.15: 1.85 and calcined at 500 ° C. to obtain a lithium manganese composite oxide. The positive electrode material was made of graphite, a conductive agent, and polyvinylidene fluoride, a binder.
It was weighed at a weight ratio of 5: 10: 5. These were kneaded for 30 minutes by a mill, and then applied to a 20 μm-thick aluminum foil to obtain a positive electrode. The amount of the positive electrode active material per unit area is as follows: 1) 4.3 mg / cm ² , 2) 6.1 mg / cm ² ,
3) 13.1 mg / cm ² , 4) '19 .0 mg / c
m ² , 5) 24.2 mg / cm ² , 6) 35.5 mg / c
m ² , 7) 44.7 mg / cm ² . Amorphous carbon was used for the negative electrode material, and polyvinylidene fluoride was used for the binder.
It was applied to a 0 μm copper foil.

FIG. 1 illustrates 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 apparent density of the negative electrode mixture after pressing was 65% of the true density. 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 the battery can 4. The negative electrode terminal 7 connected to the negative electrode 2 was welded to the bottom of the battery can 4. The positive electrode terminal 5 connected to the positive electrode 1 was welded to the back surface of the battery lid 6. As the electrolytic solution, LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate so as to have a concentration of 1 mol / l was used and injected into the battery can 4. After the injection of the electrolyte, a cylindrical battery was produced by caulking between the battery lid 6 and the battery can 4 as a load via a packing 10. The packing 9 is interposed between the back surface of the battery cover 6 and the positive terminal 5, and a rupture valve is attached between the positive terminals 5.

The above-mentioned amount of the polar active material of the manufactured battery 1) to
7) in the order of batteries 1-1, 1-2, 1-3, 1-4, 1-
5, 1-6, and 1-7. The battery was charged to 4.2 V with a current of 0.2 C, and then discharged to 2.8 V in a current range of 0.2 C to 15 C. FIG.
Shown in The discharge capacity maintenance ratio in FIG. 2 is a value in which the discharge capacity at each current value is represented by%, with the discharge capacity at 0.2 C as 100%. The batteries 1-1 to 1-6 exhibited a capacity retention ratio of about 80% even at a large current of 15C, but the battery 1-7 having a large amount of the positive electrode active material of 44.7 (mg / cm ² ) had a capacity of 40%. %, And cannot be used.

[0018]

[Table 1]

Next, batteries 1-1, 1-2, 1-3,1-
The output densities of 4,1-5,1-6,1-7 at the time of 15C discharge were examined. The results are shown in Table 1 in terms of output density per positive electrode (total of the current collector and the positive electrode active material). The positive electrode of the battery 1-1 has a large weight of the current collector in the electrode, that is, the ratio of the positive electrode active material (positive electrode active material / positive electrode active material + Al
Since the current collector is small, the weight output density in terms of the weight of the positive electrode is about 1600 W / kg. When the amount of the positive electrode active material per unit area is reduced and the electrode is thinned, lithium ions in the electrode are easily diffused, and the charge and discharge characteristics of the battery are improved. However, as shown in Table 1, if the electrode is made too thin, the amount of active material becomes too small, so that a battery having a required weight output density cannot be obtained. Therefore, a lower limit is required for the amount of active material per unit area to obtain a required weight output density. That is, a positive electrode active material layer of a certain amount or more that can satisfy the required weight output density, in other words, an active material layer having a ratio of 0.5 or more to the total weight of the current collector and the active material is provided on the current collector. It is necessary.

On the other hand, since the discharge characteristics of the battery 1-7 at a high rate are low as shown in FIG. 2, the weight output density also becomes a low value of about 1600 W / kg. Also in the case of the battery 1-1, the weight output density is about 1600 W / kg.
The value is as low as about, and a high output current cannot be obtained.

On the other hand, the range from the positive electrode active material amount of 6.0 (mg / cm ² ) or more in the range of batteries 1-2 to 1-6 to the positive electrode active material amount of 36.0 (mg / cm ² ). Then
Power density of about 2020 (W / kg) to power density of about 300
0 (W / kg), and a high-output battery can be obtained.

The amount of the positive electrode active material was 19.0 (mg / c).
m ² ) or less, the thickness of the positive electrode is
A step of removing coarse particles of the lithium manganese composite oxide is required, and it is difficult to avoid high cost. However, when the amount of the positive electrode active material is 19.0 (mg / cm ² ) or more, since the thickness of the positive electrode coating is large, coarse particles of the lithium manganese composite oxide are not exposed from the coated surface, and coarse particles are collected. The removal process is no longer necessary. Therefore, high cost can be avoided.

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 amount of the positive electrode active material was adjusted to the range of 20 to 22 (mg / cm ² ), and the composition of the positive electrode active material was 1) LiMn ₂ O ₄ , 2) Li ₁ .
₀₅ Mn ₁ . ₉₅ O ₄ , 3) Li ₁ . ₁ Mn ₁ . ₉ O ₄ , 4) L
i ₁ . ₁₅ Mn ₁ . ₈₅ 5O ₄ , 5) Li ₁ . ₂ Mn ₁ . ₈ O ₄ ,
6) Li ₁ . ₂₅ Mn ₁ . There were six types of ₇₅ O ₄ .

The prepared battery was prepared using the above-described positive electrode active material composition 1).
6) in the order of the batteries 2-1, 2-2, 2-3, 2-4, 2
-5 and 2-6. The test conditions were the same as in Example 1. The battery was charged to 4.2 V with a current of 0.2 C, then discharged to 2.8 V in a current range of 0.2 C to 15 C, and the load characteristics were examined. Shown in Battery 2-1 and 2
-6 has a retention rate at 15 C of about 40%, which is low and cannot be used for discharging a large current. However, the batteries 2-2 to 2-5 show a capacity retention rate of about 80% even when discharging a large current of 15 C.
A high output battery can be obtained.

Example 3 Graphite was used as a negative electrode material and polyvinylidene fluoride was used as a binder, and a negative electrode was produced in the same manner as in Example 1 at a weight ratio of 90:10. After the application, the press pressure was changed to press the electrode. The apparent density of the negative electrode mixture after pressing is 1) 74%, 2) relative to the true density.
69%, 3) 63%, 4) 56%, 5) 50%.

For the positive electrode, a material having the same composition as in Example 1 was used.
The amount of the positive electrode active material was set to 20 to 22 mg / cm as in Example 2.
Adjusted to the range of ² . The produced batteries were compared with batteries 3-1 and 3 in the order of degrees 1) to 5) with respect to the apparent density of the negative electrode.
-2, 3-3, 3-4 and 3-5. The test conditions were the same as in Example 1. The battery was charged to 4.2 V at a current of 0.2 C, and then discharged to 2.8 V in a current range of 0.2 C to 15 C. Shown in Battery 3
-1 and 3-5 have a low retention rate of about 40% at 15C, but the batteries 2-2 to 2-4 exhibited a capacity retention rate of about 80% even when discharging a large current of 15C. Can be used to discharge current.

Example 4 Batteries 1-3 and 1 of Example 1
7 were connected in series, and two sets of assembled batteries were produced. Each battery pack is referred to as a battery pack 4-3, 4-7. The assembled battery is charged at a current of 0.2 C until the voltage reaches 33.6 V, and then the discharge voltage is set to 22.4 V, and the battery is charged at 0.2 C to
FIG. 5 shows the result of the discharge in the current range of 15 C and the discharge characteristics were examined. The battery pack 4-3 composed of the battery 1-3 having a high output exhibited a capacity retention ratio of about 80% even in a large current region of 15C. However, batteries 1-7 having poor output characteristics
Was less than 40%.

The lithium secondary battery of the present invention described in the above embodiments can be used for notebook personal computers, pen input personal computers, pocket personal computers, notebook word processors, pocket word processors,
E-book player, mobile phone, cordless phone handset, pager, handy terminal, mobile copy, electronic organizer, calculator, LCD TV, electric shaver, power tool, electronic translator, car phone, transceiver, voice input device,
Memory card, backup power supply, tape recorder, radio, headphone stereo, portable printer, handy cleaner, portable CD, video movie, navigation system, refrigerator, air conditioner, TV, stereo, water heater, oven microwave, dishwasher, washing machine, Needless to say, it can be used for a dryer, a game device, a lighting device, a toy, a road conditioner, a medical device, an automobile, an electric vehicle, a golf cart, an electric cart, and a power storage system.

[0029]

As described above, according to the present invention, a lithium secondary battery having excellent high-output characteristics can be obtained, and thereby a high-output-density battery applicable to electric vehicles, particularly for hybrid electric vehicles, can be provided. .

[Brief description of the drawings]

FIG. 1 is a side sectional view of a lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing discharge characteristics of the lithium secondary battery of Example 1.

FIG. 3 is a characteristic diagram showing a relationship between a discharge current and a discharge capacity retention ratio when the composition of a positive electrode active material according to an example of the present invention is changed.

FIG. 4 is a characteristic diagram showing a relationship between a discharge current and a discharge capacity retention ratio when the density of a negative electrode mixture according to an example of the present invention is changed.

FIG. 5 is a characteristic diagram showing a relationship between a discharge current and a discharge capacity retention ratio of a battery pack in which a plurality of lithium secondary batteries according to an embodiment of the present invention are connected.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Battery can, 5
... Positive electrode terminal, 6 ... Battery lid, 7 ... Negative electrode terminal, 8 ... Burst valve
9,10 ... Packing.

[Procedure amendment]

[Submission date] November 17, 1999 (1999.11.
17)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

As a result of various studies to achieve the object of the present invention, the apparent density of the negative electrode mixture composed of amorphous carbon and / or graphite and a binder was determined with respect to the true density of the negative electrode mixture.
A negative electrode having a relative density of 55 to 70% was used.
_Using a lithium manganese composite oxide represented by _{1 + x} Mn _{2- x} O ₄ (0.05 ≦ x ≦ 0.2), the amount of lithium manganese composite oxide per unit area on both surfaces of the current collector in the positive electrode is 6 to By setting the ratio of the amount of the positive electrode active material per unit area to the total amount of the positive electrode current collector and the amount of the positive electrode active material per unit area to 0.5 or more, a high output density lithium secondary battery is set to 36 mg / cm ^2. Was found to be available.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

That is, a positive electrode active material layer having a predetermined amount or more that can satisfy a required weight output density, that is, an active material layer having a ratio of 0.5 or more to the total weight of the current collector and the active material is formed as a current collector. It is necessary to provide. In order to enable charging and discharging with such an electrode at a large current of 10 to 20 C or more, it cannot be solved simply by specifying the amount of the positive electrode active material. That is, in order to obtain a lithium secondary battery having excellent weight output density, Li having better load characteristics than LiMn ₂ O ₄ is used.
It is important to use _{1 + x} Mn _{2- x} O ₄ (0.05 ≦ x ≦ 0.2).

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

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 the present example, the amount of the positive electrode active material was adjusted to a range of 20 to 22 (mg / cm ² ), and the composition of the positive electrode active material was changed to ( 1) LiMn ₂ O ₄ , ( 2) L
i _1.05 Mn _1.95 O ₄ , ( 3) Li _1.1 Mn ₁ . ₉ O ₄ ,
( 4) Li _1.15 Mn _1.85 O ₄ , ( 5) Li _1.2 Mn
Six types of _1.8 O ₄ and ( 6) Li _1.25 Mn _1.75 O ₄ were used.

Continued on the front page F term (reference) 5H003 AA01 BB04 BB05 BB11 BD03 BD05 5H014 AA02 AA04 EE08 EE10 HH01 HH08 5H029 AJ02 AK03 AL07 AL08 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ07 DJ09 HJ01 HJ08

Claims (6)

[Claims] 1. A positive electrode mainly composed of a lithium manganese composite oxide, a negative electrode mainly composed of amorphous carbon or graphite or amorphous carbon and graphite, and a lithium secondary composed of a non-aqueous electrolyte containing a lithium salt. In the battery, the amount of lithium manganese composite oxide on both surfaces of the current collector per unit area of the positive electrode is 6 to 36 mg / cm ² . 2. The lithium manganese composite oxide is Li _{1 + x}
The lithium secondary battery according to claim 1, characterized by being represented by _{Mn 2- xO 4 (0.05 ≦ x} ≦ 0.2). 3. The lithium secondary battery according to claim 1, wherein the ratio of the amount of the cathode active material per unit area to the total amount of the cathode current collector and the cathode active material per unit area is 0.5 or more. Next battery. 4. The apparent density of the negative electrode mixture containing amorphous carbon and / or graphite or amorphous carbon and graphite and a binder is lower than the true density of the negative electrode mixture containing amorphous carbon and / or graphite and a binder. The lithium secondary battery according to claim 1, wherein the relative density is 55 to 70%. 5. A lithium secondary battery comprising a plurality of the lithium secondary batteries according to claim 1 connected in series and parallel. 6. A notebook personal computer, a pen input personal computer, a pocket personal computer, a notebook word processor, a pocket word processor, an electronic book player, a mobile phone, a cordless phone handset, a pager, a handy terminal, a mobile copy, an electronic organizer, a calculator, an LCD television, Electric shavers, power tools,
Electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, portable printer, handy cleaner, portable CD, video movie, navigation system, refrigerator, air conditioner, television, stereo, Water heaters, microwave ovens, dishwashers, washing machines, dryers, game equipment, lighting equipment, toys, road conditioners, medical equipment, automobiles, electric vehicles, golf carts, electric carts, power storage systems The lithium secondary battery according to any one of claims 1 to 5, wherein: