JP2003346905A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the life of a nonaqueous electrolyte secondary battery. <P>SOLUTION: The nonaqueous electrolyte secondary battery uses a spinel- structure lithium-manganese compound oxide as a positive electrode active material, and a carbon material as a negative electrode active material. The discharging capacity of the positive electrode active material when the battery is charged so that the open terminal voltage after charging becomes 4.1 V is 70 to 80% of the discharging capacity of the positive electrode active material in discharging at a voltage between 4.3 V and 3.0 V. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonaqueous electrolyte secondary battery using a lithium manganese composite oxide having a spinel structure as a positive electrode active material.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries are widely used as power sources for mobile phones and the like because of their characteristics of being lightweight and having a high energy density. This non-aqueous electrolyte secondary battery includes a lithium or lithium alloy, a negative electrode containing lithium, a positive electrode containing a lithium composite oxide, a separator disposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. And a secondary battery comprising:

A non-aqueous electrolyte secondary battery that is often used in mobile phones and the like is called a small non-aqueous electrolyte secondary battery, and uses a lithium-cobalt composite oxide as a positive electrode active material and a negative electrode active battery. A graphite-based carbon material is used as the substance. The battery capacity is relatively small at about 1 Ah, and the discharge rate during normal use is relatively small at less than 1 C.

[0004]

In contrast to the above-mentioned small non-aqueous electrolyte secondary battery, the practical use of a large non-aqueous electrolyte secondary battery which can be used for electric vehicles such as electric vehicles and emergency uninterruptible power supplies. Is desired. Such a large non-aqueous electrolyte secondary battery is required to have a longer life than that required for a small non-aqueous electrolyte secondary battery for its use and to be capable of discharging at a high rate. Year,
Performance such as 5C discharge is required.

[0005] Further, since it is necessary to consider the large battery capacity and the environmental load when the future demand increases, it is desired to use a lithium manganese composite oxide as the positive electrode active material.

However, simply increasing the size of a small non-aqueous electrolyte secondary battery that is already widely used,
At present, the required life performance and discharge performance cannot be satisfied, and further, the life performance deteriorates when a lithium manganese composite oxide is used.

In view of the above, the present invention uses a lithium manganese composite oxide having a spinel structure as a positive electrode active material, has a capacity of 5 Ah or more (at 1C discharge), and has a ratio of a capacity at 3C discharge to a capacity at 1C discharge. It is an object of the present invention to improve the life performance of a non-aqueous electrolyte secondary battery satisfying a rate performance of 90% or more.

[0008]

The present invention relates to a nonaqueous electrolyte secondary battery using a lithium manganese composite oxide having a spinel structure as a positive electrode active material and a carbon material as a negative electrode active material,
3. The open terminal voltage after charging the non-aqueous electrolyte secondary battery is 4.
The discharge capacity of the positive electrode active material when charged to 1 V is 70 to 80% of the discharge capacity of the positive electrode active material when discharged between 4.3 V and 3.0 V. It is a water electrolyte secondary battery.

Here, "the open terminal voltage after charging is 4.1
The “discharge capacity of the positive electrode active material when charged to V” is based on 1C discharge. In addition, "" with respect to "the discharge capacity of the positive electrode active material when discharged between 4.3 V and 3.0 V"
The ratio of the “discharge capacity of the positive electrode active material when charged so that the open terminal voltage after charging is 4.1 V” is defined as “utilized capacity ratio (%)”.

[0010] By charging and discharging the positive electrode in such a range of the used capacity, destruction of the positive electrode active material structure and elution of Mn are suppressed, and the capacity retention rate of the battery is improved.

Particularly, as the lithium-manganese composite oxide, Li _{1 + x} Mn _{2- xy My} O ₄ (0.05 ≦ x
≤ 0.15, 0.02 ≤ y ≤ 0.15), the capacity retention of the battery is further improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the nonaqueous electrolyte secondary battery of the present invention, the open terminal voltage after charging with respect to the discharge capacity of the positive electrode active material when discharged between 4.3 V and 3.0 V is 4.1.
V, the discharge capacity of the positive electrode active material (1
C), that is, the used capacity ratio is 70% to 80%.

When the discharge capacity is measured by changing the current between 4.3 V and 3.0 V, the discharge capacity of the positive electrode active material increases as the current value decreases.
Below a certain current value, the discharge capacity of the positive electrode active material reaches saturation and becomes almost constant. Here, "4.3V to 3.
The term “discharge capacity of the positive electrode active material when discharged between 0 V” means the discharge capacity of the positive electrode active material that has reached saturation.

For this purpose, for example, the irreversible capacity of the negative electrode active material carbon material to be used is adjusted, or the amount of the negative electrode active material is relatively increased. However, if the irreversible capacity is increased, the utilization rate decreases. However, since decreasing the utilization rate decreases the energy density of the positive electrode, it is meaningless to reduce the utilization rate to less than 70%. The reason is that the life is not changed even if the length is further reduced.

The positive electrode active material used in the present invention includes:
Li _{1 + x} Mn _{2 - xy My} O having a spinel structure
₄ (0.05 ≦ x ≦ 0.15, 0.02 ≦ y ≦ 0.1
5, M is Ti, Cr, Fe, Co, Ni, Zn, A
and at least one metal element selected from Mg) is preferable. In particular, the metal element M is more preferably Al because the metal element M has a longer life and good heavy load characteristics. It is to be noted that, although it is basically represented by the above-mentioned composition, it is also preferable that the oxygen site is partially replaced by sulfur or a halogen element, or that the oxygen content is somewhat non-stoichiometric.

When lithium manganese composite oxide particles are used, primary particles having a polygonal appearance are aggregated into spherical secondary particles having a large number of irregularities on the surface. It is more preferable to use one having a particle size of 10 μm to 20 μm, and it is more preferable to use one having a specific surface area of 0.1 m ² / g or more and 1.0 m ² / g or less.
By using such a powder, it becomes easy to manufacture the electrode having the wound structure in a favorable state in which peeling or the like does not occur, and the life performance can be favorably maintained. When the specific surface area is smaller than 0.1 m ² / g, the high rate discharge performance is deteriorated, and when the specific surface area exceeds 1.0 m ² / g, the life is sharply deteriorated.

The lithium-manganese composite oxide particles as described above can be produced, for example, by mixing starting materials containing lithium, manganese and a metal element, followed by firing and cooling in the presence of oxygen. Lithium compounds used as starting materials include Li ₂ CO ₃ and LiNO
_3, LiOH, LiCl, there are Li ₂ O, as the manganese compound used as a starting _material, Mn ₂ O _3, Mn
Manganese oxides such as O ₂ , MnCO ₃ , Mn (NO ₃ )
There are ₂ etc. Examples of the compound of the other metal element used as a starting material of the other metal element include an oxide, a hydroxide, a nitrate, a carbonate, a dicarboxylate, a fatty acid salt, and an ammonium salt.

The carbon material used in the present invention is not particularly limited as long as it allows lithium ions to be inserted and desorbed, but the plane distance d (002) in the C-axis direction is 0.337 n.
It is particularly preferable to use a carbon material of m or less in a proportion of 90% or more of the negative electrode active material. This is because a battery having a large energy density and a high discharge rate performance can be manufactured in this manner.

Further, the surface distance d in the C-axis direction is added to the negative electrode active material.
It is more preferable to use a carbon material having a (002) of 0.337 nm or less, which is spherical or massive and scaly. This makes it possible to maintain better discharge performance.

As the spherical carbon material, for example, a material obtained by firing mesophase pitch small spheres can be used, and as the massive carbon material, for example, a material obtained by firing and grinding pulverized coke can be used. It is preferable to use those having an average particle size of 20 to 35 μm.
m. This is a large current, especially 5C
In a battery premised on use at a large current as described above, it is preferable that the thickness of the carbon material layer of the negative electrode be 80 μm or less on one side, and that the use of a material having the above particle size or less can improve coating properties. This is because the film density can be increased. If the average particle size is 20 μm or less, the life is likely to be deteriorated.

As the scaly carbon material, scaly natural graphite or scaly artificial graphite is preferably used. The size in the plane direction is smaller than the particle diameter of the spherical or massive carbon material, so that the capacity density can be increased. Therefore, the average particle diameter is the average particle diameter of the spherical or massive carbon material, or the average of these mixtures. It is preferable to use one smaller than the particle size. The average particle size can be measured using, for example, a laser diffraction / scattering type particle size distribution analyzer. This is the same in other cases.

The content of the flaky carbon material is preferably smaller than the content of the spherical (or massive) carbon material, and more preferably the total weight of the carbon material capable of doping and undoping lithium ions. Therefore, the weight ratio is preferably 30% or less, more preferably 25% or less. This is because when the amount increases, the flaky carbon material is oriented when the negative electrode is pressed, and the charge / discharge capacity under a large current decreases.

The positive electrode and the negative electrode are formed by coating each active material mixture on a current collector of a metal foil, and the porosity of the positive electrode is 31 to 36%, more preferably 32 to 35%. The porosity of the negative electrode is preferably 32 to 37%, more preferably 33 to 36%. This is because the porosity is too small or too large to shorten the life of the battery,
Further, as the size increases, the energy density of the battery decreases.

It is preferable that the porosity of the negative electrode is larger than the porosity of the positive electrode in order to obtain a battery having a longer life and good high-rate discharge performance.
It is better to be less than μm. It is particularly preferable that the difference in porosity between the positive electrode and the negative electrode is 3% or less. This is because the balance of the liquid amount becomes better and the life is prolonged.

The porosity can be adjusted by controlling the coating weight and the thickness of the mixture layer. For example, the porosity is calculated as (1− (application weight / (mixture layer volume × mixture true density))) × 100 (%), and the porosity is controlled by this. When the porosity of a battery is measured, for example, the electrode is taken out in a discharged state and measured by a mercury porosimeter.

As a separator used for producing the battery of the present invention, for example, a microporous polyolefin film such as a polyethylene film or a polypropylene film can be used, and preferably, the thickness (one side) of the negative electrode active material layer When the sum of the thickness of the active material layer of the positive electrode and the thickness (one side) of the positive electrode is defined as a, and the thickness of the separator is defined as b, 0.
It is preferable that the relation of 05 ≦ b / (a + b) ≦ 0.25 is satisfied, and the air permeability of the separator is 300 to 700 sec / 100 cc. By thus defining the relationship between the thickness of the active material layer and the thickness of the separator and the air permeability of the separator, a long life of the battery and good high-rate discharge performance can be achieved.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, chain carbonates such as diethyl carbonate and dimethyl carbonate, carboxylate esters such as methyl propionate and methyl butyrate, and γ-butyl. Lactone, sulfolane, ethers such as 2-methyltetrahydrofuran and dimethoxyethane can be used. In particular, in the case of the battery of the present invention, a mixed solvent of ethylene carbonate and a chain carbonate is preferably used. The effect of is exhibited well. Further, vinylene carbonate is preferably added to the non-aqueous solvent, and an electrolyte using lithium hexafluorophosphate is preferred as the electrolyte.

The amount of the electrolyte is preferably from 6 g to 8 g per Ah, and more preferably from 6.3 g to Ah.
7.5 g is preferable because the life can be improved.

FIG. 1 is an exploded perspective view showing an example of a battery according to the present invention. This non-aqueous electrolyte secondary battery is a battery in which four long cylindrical wound power generating elements 1 are closely arranged and connected in parallel. These power generating elements 1 are connected in parallel with positive and negative electrodes connected and fixed to current collectors 2 arranged at both end faces. The current collecting connector 2 is made of an aluminum plate on the positive electrode side and a copper plate on the negative electrode side, and is a horizontal, approximately isosceles triangle. The positive electrode or the negative electrode of the power generation element 1 is connected and fixed to the connection portion protruding in the shape. The plate-shaped main bodies of these current collectors 2 are respectively provided with lower insulating sealing plates 3.
Are disposed at both ends of the back surface of the cover plate 4. Cover plate 4
Is made of a rectangular stainless steel plate, is fitted into an upper end opening of a battery case 5 which is a stainless steel container for housing the power generating element 1, and is fixed by welding. The cover plate 4 and the battery housing 5 constitute a battery case of the non-aqueous electrolyte secondary battery.

Terminals are arranged on both ends of the upper surface of the cover plate 4 via upper insulating sealing plates 6 respectively. The terminal is made of a metal material made of aluminum on the positive electrode side and made of copper on the negative electrode side, and is composed of a rivet terminal 7, a terminal block 8 and a terminal bolt 9, respectively.

[0031]

EXAMPLE Lithium-manganese composite oxide Li _1.1 M in which polygonal primary particles aggregate to form spherical secondary particles
n _1.82 Al _0.08 O ₄ (specific surface area 0.7 m ² /
g, average particle size of 15 μm) using acetylene black and polyvinylidene fluoride (PVdF) in a weight ratio of 8
The mixture was mixed at a ratio of 8: 5: 7 to prepare a mixture. The mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry. The slurry was applied to both sides of a 20-μm-thick aluminum foil, dried, and dried. By pressing, a belt-shaped positive electrode having a porosity of 33% and a thickness of 220 μm was produced. This positive electrode was cut out, and 4.3
The discharge capacity of the positive electrode active material determined by discharging between V and 3.0 V was 109 mAh / g. The average particle size is a value of d50 measured by a laser diffraction scattering method,
The specific surface area is measured by a BET method using nitrogen gas as an adsorption gas.

Spherical artificial graphite powder 75 having an average particle size of 26 μm
Parts (average spacing of 0.335 nm in the C-axis direction), 15 parts by weight of flaky artificial graphite powder (average spacing of 0.335 nm in the C-axis direction) having an average particle diameter of 27 μm, and 10 parts by weight of PVdF were mixed together to form a negative electrode. After adjusting the agent, N-methyl-
The slurry was dispersed in 2-pyrrolidone to form a slurry. The slurry was applied to both sides of a 15-μm-thick copper foil, dried, and then compression-molded at a constant pressure to prepare a strip-shaped negative electrode having a porosity of 34% and a thickness of 120 μm. This negative electrode was cut out and its irreversible capacity was measured to be 33 mAh / g.

Using these electrodes and a polypropylene (PP) / polyethylene (PE) / polypropylene (PP) laminated separator having a thickness of 40 μm, a long cylindrical wound-type power generating element is produced. By arranging and connecting in parallel, a battery having the same structure as that shown in FIG. 1 was produced. The outer shape of the battery is W170 × D47 × H115 (m
m), and the container is made of stainless steel having a thickness of 1 mm.

As an electrolytic solution, vinylene carbonate (VC) was added to a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 3: 4: 3 and vinylene carbonate (VC) in a volume ratio of 1%.
And an electrolyte solution containing 1 mol / l of LiPF ₆
00 g was injected.

The discharge capacity (lower limit voltage of 2.7 V) of this battery (battery 1) at the time of 4.1 V charge is 4 A at a constant current discharge of 46 A.
6 Ah, and 43.2 Ah at 230 A constant current discharge. The discharge capacity of the positive electrode active material calculated from the value at 1 C discharge was 85 mAh / g, which was 4.3 V and 3.
It was 78% (= utilized capacity ratio) of the discharge capacity of 109 mAh / g of the positive electrode active material obtained by discharging between 0 V.

Apart from the above-mentioned battery, the irreversible capacity of the negative electrode was increased by increasing the thickness of the negative electrode to reduce the available capacity (battery 2), and the irreversible capacity of the negative electrode was changed to reduce the available capacity. A battery (battery 3) and a larger one (battery 4) were produced. The other configurations were the same. These batteries were repeatedly charged and discharged at 25 ° C.
The ratio of the discharge capacity at the 1000th cycle to the initial discharge capacity was determined, and the ratio expressed as a percentage was defined as the capacity retention ratio. The charging was performed at a constant current (46 A) / constant voltage (3H) with a final voltage of 4.1 V, and the charging and discharging was performed with a constant current (46 A) with a final voltage of 2.7 V. The results are shown in Table 1 below.

[0037]

[Table 1]

The batteries 1 and 2 differed only in the thickness of the negative electrode, and the capacity retention rate hardly changed. However, when the deterioration of each electrode after the cycle was compared, the capacity deterioration of the positive electrode was smaller in the battery 2 than in the battery 2. It was small. Battery 3 has the same configuration as battery 1 except that hard carbon is used instead of flaky artificial graphite for the negative electrode, and the irreversible capacity of the negative electrode is 40 m.
Ah / g.

The battery 4 has the same configuration as the battery 1 except that both the spherical artificial graphite and the flaky artificial graphite used for the negative electrode have a surface coated with a CVD carbon thin film, and the irreversible capacity of the negative electrode is 21 mAh. / G. In the battery 4, the utilization capacity ratio was 82%, but it was found that the capacity maintenance rate was rapidly deteriorated.

Although the above is only an example, the results of the study were conducted by finely changing the used capacity ratio by charging the positive electrode or the negative electrode to a predetermined state before assembling the battery without changing the irreversible capacity or thickness. From this, it is known that, by reducing the used capacity ratio, the deterioration of the positive electrode is reduced and the amount of Mn deposited on the negative electrode is also reduced, and it is understood that the difference is almost eliminated when the used capacity ratio is 70% or less. ing. Further, it is known that when the utilization capacity ratio exceeds 80%, the deterioration of the positive electrode and the deposition of Mn on the negative electrode increase. On the other hand, for example, the capacity of the battery 2 is as small as 43 Ah, but it is not advisable to reduce the used capacity from the viewpoint of the energy density of the battery. Therefore, it is preferable that the utilization capacity ratio be 70% or more and 80% or less.

[0041]

According to the present invention, a lithium manganese composite oxide having a spinel structure is used as a positive electrode active material, and has a capacity of 5 Ah or more (at 1C discharge), and a ratio of a capacity at 3C discharge to a capacity at 1C discharge. Satisfies the rate performance of 90% or more, and a non-aqueous electrolyte secondary battery having a good life can be manufactured.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an example of a battery according to the present invention.

[Explanation of symbols]

1 Power generation element 2 Current collector 3 Lower insulating sealing plate 4 lid plate 5 Battery case

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium manganese composite oxide having a spinel structure as a positive electrode active material and a carbon material as a negative electrode active material, the open terminal after charging the non-aqueous electrolyte secondary battery The discharge capacity of the positive electrode active material when charged so that the voltage becomes 4.1 V is 70 to 80% of the discharge capacity of the positive electrode active material when discharged between 4.3 V and 3.0 V. Characteristic non-aqueous electrolyte secondary battery. 2. The lithium manganese composite oxide is Li
_{1 + x}Mn_2-xyM _yO₄(0.05 ≦ x ≦ 0.1
5, 0.02 ≦ y ≦ 0.15)
2. The non-aqueous electrolyte secondary battery according to claim 1.