JP2003346904A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the trickle charging life of a nonaqueous electrolyte secondary battery. <P>SOLUTION: The nonaqueous electrolyte secondary battery uses a spinel lithium-manganese compound oxide as a positive electrode active material, and a carbon material having an average spacing in a C-axial direction of 0.337 nm of less as a negative electrode active material. Discharging capacity of the battery at 4.1 V charging is 5 Ah or more, and the rate of the discharging capacity at 5C discharging to that at 1C discharging is 90% or more. The charging rate for the carbon material (the value of x when expressed as Li<SB>x</SB>C<SB>6</SB>) as the negative electrode active material when the battery voltage is 4.1 V is 0.6 or greater and 0.75 or smaller. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having a relatively large capacity and used for discharging at a relatively high rate.

[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 has a capacity of 5 Ah or more (at the time of 1 C discharge) and has a capacity of 5 C with respect to the capacity at the time of 1 C discharge.
An object of the present invention is to improve the float charge life performance of a nonaqueous electrolyte secondary battery that satisfies a rate performance in which a capacity ratio at the time of discharging is 90% or more.

[0008]

The present invention uses a spinel-type lithium manganese composite oxide as a positive electrode active material and a carbon material having an average plane spacing of 0.337 nm or less in the C-axis direction as a negative electrode active material. When the discharge capacity at the time of charging 1 V is 5 Ah or more,
A nonaqueous electrolyte secondary battery in which the ratio of the discharge capacity at the time of 5C discharge to the discharge capacity at the time of 1C discharge is 90% or more,
When the battery voltage is 4.1 V, the charge rate (the value of x when written as Li _x C ₆ ) of the carbon material as the negative electrode active material is 0.6 or more and 0.75 or less. It is a non-aqueous electrolyte secondary battery.

By setting x to 0.75 or less, the deterioration of the performance of the negative electrode is suppressed. By setting x to 0.6 or more, the potential at the time of charging the positive electrode is reduced and the performance deterioration of the positive electrode is suppressed. As a result, the discharge capacity after float charging at 4.1 V at normal temperature for one year can be maintained at 85% or more.

Further, in the above battery, by setting the volume energy density of the battery to be 150 wh / l or more and 200 wh / l or less, it is possible to maintain the volume energy density at room temperature after 1500 cycles.
0% or more capacity can be maintained.

[0011]

As the positive electrode active material used in the Detailed Description of the Invention The present invention, a spinel structure _{Li 1 + x Mn 2- x-} y M y
O ₄ (0.05 ≦ x ≦ 0.15, 0.02 ≦ y ≦ 0.1
5, M is Ti, Cr, Fe, Co, Ni, Zn, A
At least one or more metal elements selected from l and Mg) is preferable. As the metal element M, it is particularly preferable to use Al or Mg because the life can be prolonged and the capacity can be kept large. Because the load characteristics are good,
More preferably, Al is used. 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 above-mentioned lithium-manganese composite oxide particles 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, etc., as the manganese compound used as a starting _material, Mn _{2 O} 3, M
manganese oxides such as nO ₂ , MnCO ₃ , Mn (N
O ₃ ) _{2 and the} like. 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 has a plane distance d (002) in the C-axis direction of 0.337 nm or less.
It is preferable to use a negative electrode containing this at a ratio of 90% or more of the negative electrode active material. More suitable are such carbon materials including spherical or massive ones and scale-like ones.

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 flaky carbon material, flaky natural graphite or flaky 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 being doped and dedoped with 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.

In the battery of the present invention, when the battery voltage is 4.1 V, the charge rate of the negative electrode active material carbon material (the value of x when written as Li _x C ₆ ) is 0.6 or more and 0.75 or less. However, by adjusting the ratio between the usage amount of the positive electrode active material and the usage amount of the negative electrode active material, it is possible to control such a usage rate.

The volume energy density of the battery is set to 150
The wh / l or more and 200 wh / l or less are preferably adjusted by adjusting the porosity of the electrode and the thickness of the separator.
It is preferable that the power generating element is housed in the battery container without any gap so that pressure is applied.

The positive electrode and the negative electrode are formed by applying each active material mixture on a current collector made of a metal foil.
It 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.

The porosity of the positive electrode is preferably 31 to 36%, more preferably 32 to 35%, and the porosity of the negative electrode is preferably 32 to 37%, more preferably 33 to 36%. . This is because, if the porosity is too small or too large, the life of the battery deteriorates, and if the porosity is too large, the energy density of the battery decreases. Further, 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. The thickness of one side of the negative electrode active material layer is preferably 80 μm or less. good.
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.

As the 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. 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 6 g to 8 g per Ah, more preferably 6.3 g to 7.5 per Ah.
It is good to set it to g 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 disposed at 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.

[0027]

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 15 μm) powder, and acetylene black and polyvinylidene fluoride (PVdF) in a weight ratio of 9%.
The mixture was mixed at a ratio of 0: 5: 5 to prepare a mixture. The mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry. By pressing, a belt-shaped positive electrode having a porosity of 33% and a thickness of 220 μm was produced. The average particle size is a value of d50 measured by a laser diffraction scattering method, and 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.

Using these electrodes and a 40 μm-thick polypropylene (PP) / polyethylene (PE) / polypropylene (PP) laminated separator, a long cylindrical wound-type power generating element is produced, and two of these are closely adhered. 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 by 1% by volume.
And an electrolyte solution containing 1 mol / l of LiPF ₆
00 g was injected.

The capacity of this battery at the time of 4.1 V charging is 46
A discharge is 46 Ah and 230 A discharge is 43.2 Ah
It is. The charging rate is 0.66, and the volume energy density is 180 Wh / l. The charge rate was calculated from the total weight of the negative electrode active material and the battery capacity, assuming that the amount of electricity obtained by discharging all the lithium inserted in the form of Li _x C ₆ appeared as the battery capacity. Was.

Furthermore, the thickness of the positive electrode and the negative electrode were changed, and the other components were the same, and batteries having different charging rates but the same capacity were produced. 25 ° C for these batteries
The battery was charged at a constant current (46 A) and a constant voltage (3 H) with a final voltage of 4.1 V, and left as it was for one year with a float voltage of 4.1 V applied. Then, a constant current (46 A) discharge with a final voltage of 2.7 V was performed to measure the discharge capacity, and the ratio to the discharge capacity before standing was determined as a percentage, which was defined as the capacity retention rate. The results are shown in Table 1 below.

[0033]

[Table 1]

According to the above results, the charging rate was from 0.6 to 0.7.
It turns out that the range of 5 is preferable. Further, when the 1C discharge capacity and the 5C discharge capacity of the battery after standing were compared, the ratio was 90% or more in each case. Furthermore, the charging rate is 0.6
When a cycle test was performed on the batteries of 0 to 0.75 under the above-mentioned charge / discharge conditions at 25 ° C., all the batteries maintained 80% or more capacity at 1500 cycles. On the other hand, the other batteries did not reach the capacity of 80%, and the ratio between the 1C discharge capacity and the 5C discharge capacity was 9%.
Less than 0%. When the battery after the float charge was disassembled, when the charge rate was 0.87 or 0.95, the amount of coating on the negative electrode surface was large, the distribution of the electrolyte solution was noticeable, and the deterioration in the negative electrode was the capacity retention rate. Probable cause of the decline. Further, in the case of 0.55, the deterioration of the positive electrode was larger than that of the other samples, and it is considered that the positive electrode potential became a potential with large deterioration.

[0035]

According to the present invention, the float charge life performance is good, and the capacity at the time of 5 Ah or more (at the time of 1 C discharge) and the ratio of the capacity at the time of 5 C discharge to the capacity at the time of 1 C discharge become 90% or more. A non-aqueous electrolyte secondary battery satisfying the performance 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 positive electrode active material comprising a spinel-type lithium manganese composite oxide, and a carbon material having an average plane spacing of 0.337 nm or less in the C-axis direction being used as a negative electrode active material, having a discharge capacity at the time of 4.1 V charging of 5 Ah. As described above, the nonaqueous electrolyte secondary battery in which the ratio of the discharge capacity at the time of 5C discharge to the discharge capacity at the time of 1C discharge is 90% or more, and the carbon material as the negative electrode active material when the battery voltage is 4.1V A non-aqueous electrolyte secondary battery, wherein the charge rate (value of x when written as Li _x C ₆ ) is 0.6 or more and 0.75 or less. 2. The battery has a volume energy density of 150 wh.
2. The ratio is not less than / l and 200 wh / l.
The non-aqueous electrolyte secondary battery according to the above.