JP2002270173A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery exhibiting high energy density and enhanced high rate discharge efficiency. SOLUTION: A lithium manganese composite oxide used as a positive electrode active material for this non-aqueous electrolyte secondary battery is expressed by a general formula, Lix Mn(3-x-y) My O4 (wherein 1<=x<=2, 0.01<=y<=0.1, and M is at least one of elements selected from Co, Ni, V, Fe, Ti, Cr, Cu, Ca, Al, In, Ga, B and Si), and is constituted by a sintered body of a primary particle of which average particle diameter is 0.1 μm or more and 1 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery has a feature that it has a high energy density, and is suitable for a power supply for electronic equipment such as a cellular phone and a power supply for an electric vehicle. In particular, in recent years, hybrid electric vehicles using both a motor and an engine have attracted attention, and lithium secondary batteries for this purpose have been actively developed.

When a lithium secondary battery is put into practical use as a battery for a hybrid electric vehicle, good high-rate discharge characteristics and a large output are required. Therefore, in order to reduce the internal resistance of the battery and obtain a large output, it is necessary to reduce the electrode thickness to increase the area of the electrode housed in the battery as much as possible and to reduce the particle size of the positive electrode active material and the negative electrode material. Thus, the specific surface area of the electrode was increased to increase the output of the battery.

[0004]

SUMMARY OF THE INVENTION In a battery, in order to charge and discharge with a large current, the particle size of the active material is reduced.
It is necessary to increase the surface area. However, in the case of a positive electrode active material having lower electron conductivity than the negative electrode material, if the particle size of the active material is reduced, the number of active materials per unit weight in the positive electrode mixture increases. In order to increase the conductivity inside, a large amount of a conductive auxiliary material is required, and the amount of the active material per unit volume is reduced by that much, which causes a problem that the capacity of the battery is reduced.

An object of the present invention is to solve such a problem and to provide a non-aqueous electrolyte secondary battery having a high energy density and excellent high-rate discharge characteristics.

[0006]

According to the first aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising a general formula Li as a positive electrode active material.
_x Mn _{(3-xy) MyO 4} (where 1 ≦ x
≦ 2, 0.01 ≦ y ≦ 0.1, M is Co, Ni, V, F
e, at least one element selected from the group consisting of Ti, Cr, Cu, Ca, Al, In, Ga, B, and Si). , The average particle diameter is 0.1 μm or more,
It is made of a sintered body of primary particles of 1 μm or less.

According to the first aspect of the present invention, in the positive electrode active material, the primary particle diameter is reduced and the specific surface area is increased without changing the size of the secondary particles formed of the sintered particles of the primary particles. In addition, since the number of contact points between the secondary particles of the positive electrode active material does not change, it is not necessary to increase the amount of the conductive auxiliary material, so that the output of the battery can be increased.

According to a second aspect of the present invention, in the above non-aqueous electrolyte secondary battery, the secondary particles formed of a sintered body have an average particle diameter of 5
It is not less than μm and not more than 20 μm.

According to the second aspect of the present invention, a non-aqueous electrolyte secondary battery having a high energy density and excellent high-rate discharge characteristics can be obtained.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery.
The general formula Li as the positive electrode active material_xMn
_(3-xy)M_yO₄(Where 1 ≦ x ≦ 2,
0.01 ≦ y ≦ 0.1, M is Co, Ni, V, Fe, T
i, Cr, Cu, Ca, Al, In, Ga, B and S
at least one element selected from the group consisting of i)
Using lithium-manganese composite oxide
This positive electrode active material has an average particle diameter of 0.1 μm or less.
Above, consisting of a sintered body of primary particles of 1 μm or less,
In addition, the average particle diameter of the secondary particles made of this sintered body is 5 μm.
As described above, the thickness is not more than 20 μm. lithium
-As M in the above general formula representing a manganese composite oxide
Means transition metal elements, alkaline earth elements,
Elements and the like can also be used.

An example of the method for producing the lithium-manganese composite oxide of the present invention will be described below, but the production method is not limited to this example. First, electrolytic manganese dioxide, lithium hydroxide serving as a lithium source, and a compound containing an element that partially replaces a manganese site are mixed by a bead mill in an aqueous state at a ratio according to a composition ratio. Next, the mixed aqueous solution is made into a spray state, and is heated and dried in that state to obtain primary particles. Thereafter, sintering is performed at a high temperature in the atmosphere to promote crystallization and obtain secondary particles.

During the sintering, the sintering temperature is preferably set to 700 ° C. to 850 ° C. in order to adjust the primary particle diameter to be in the range of 0.1 μm to 1 μm. In addition,
In this sintering step, it is very difficult to control the particle diameter of the primary particles in the obtained secondary particles to a value smaller than 0.1 μm. The secondary particles thus obtained are further pulverized and sieved to select, whereby a lithium-manganese composite oxide having a desired secondary particle diameter is obtained. The average particle diameter of the secondary particles is 5 μm to 20 μm in consideration of the simplicity of the coating process, in which the secondary particles are made by aggregating as many primary particles as possible to enhance the electron conductivity between the active materials. A range is preferred.

FIG. 1 shows a scanning electron microscope (SEM) photograph of the obtained lithium-manganese composite oxide.
Here, the average particle diameter of the primary particles was measured by a laser scattering particle size distribution measuring method, and the average particle diameter of the secondary particles was calculated from an SEM photograph. As can be seen from FIG. 1, the average particle size of the primary particles of the lithium-manganese composite oxide is about 0.3 μm,
The average particle diameter of the secondary particles is about 15 μm, and both the primary particles and the secondary particles are substantially spherical. The shape of the particles is not limited to a spherical shape, but may be a substantially spherical shape, a spheroidal shape, a rectangular parallelepiped, a cube, or the like, depending on manufacturing conditions.

In the non-aqueous electrolyte secondary battery of the present invention,
As the negative electrode material, a carbon-based material, lithium metal, Al,
A lithium alloy of lithium with Si, Pb, Sn, Zn, Cd, or the like, or an oxide material is used. As the carbon-based material, for example, artificial or natural graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, activated carbon, graphite, carbon fibers, and the like are used. As the oxide, a compound mainly composed of tin oxide is used. These are used in a powder state. LiFe ₂ O ₃ ,
Transition metal oxides such as WO ₂ and MoO ₂ , Li ₅ (Li ₃
N) or the like may be used.

In the non-aqueous electrolyte secondary battery of the present invention, the solvent for the organic electrolytic solution includes cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, and γ. -Butyrolactone,
Sulfolane, dimethyl sulfoxide, acetonitrile,
Dimethylformamide, dimethylacetamide, 1,2
Polar solvents such as -dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof can be used. Examples of the lithium salt dissolved in the organic solvent include LiPF ₆ , LiBF
_{4, LiAsF 6, LiCF 3 CO} 2, LiCF 3 SO
₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂₎
CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (C
A salt such as OCF ₂ CF ₃ ) ₂ or a mixture thereof may be used. Further, as the separator, an insulating polyolefin microporous membrane such as polyethylene or polypropylene, a polymer solid electrolyte, a gel electrolyte in which an electrolyte is contained in a polymer solid electrolyte, or the like can be used. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination.
Further, when using a porous solid polymer electrolyte membrane as the solid polymer electrolyte, an electrolytic solution to be contained in the polymer,
The electrolyte to be contained in the pores may be different.

The power generating element composed of the positive electrode, the separator and the negative electrode may be of a wound type or a laminated type, and the shape of the battery may be a square type, a cylindrical type, a long cylindrical type or the like. , Any shape battery can be used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on preferred embodiments. Here, ten types of non-aqueous electrolyte secondary batteries with battery symbols A to J were produced and their characteristics were compared.

The ones commonly used for the batteries are as follows. As the positive electrode active material, Li _{1 . 1} Mn _1.805
Al _0.095 O ₄ was used. The positive electrode plate is prepared by mixing a positive electrode active material, graphite as a conductive agent and PTFE as a binder on both surfaces of an aluminum foil having a thickness of 0.02 mm as a current collector, and adding an organic solvent as a dispersant. It is applied, dried, and rolled in a state.
In the batteries 1 to 9, the mixing ratio of the positive electrode mixture is
Parts by weight, 10 parts by weight of graphite and 8 parts by weight of PTFE, and in the battery 10, 72 parts by weight of the positive electrode active material, 20 parts by weight of graphite and 8 parts by weight of PTFE. The scanning electron microscope (SEM) photograph of the positive electrode active material used here is the same as that shown in FIG. The specific surface area of the positive electrode active material was measured based on the BET multipoint method.

The negative electrode plate has a thickness of 0.01 m as a current collector.
A mixture of 92 parts by weight of a carbon material capable of being doped with and dedoped with lithium as a negative electrode material and 8 parts by weight of polyvinylidene fluoride as a binder was added to both surfaces of a copper foil of m, and an organic solvent as a dispersant was added. After being formed into a paste, applied, dried, and rolled, a negative electrode lead made of nickel is attached to an end of the negative electrode by ultrasonic welding.

Next, the positive electrode plate and the negative electrode plate are
After drying at 20 ° C. for 10 hours, a spirally wound power generating element was wound through a separator, and the power generating element was housed in a cylindrical battery case.

FIG. 2 shows a structural example of a cylindrical organic electrolyte secondary battery. 2, reference numeral 1 denotes a battery case also serving as a negative electrode terminal, 2 denotes a positive electrode plate, 3 denotes a negative electrode plate, 4 denotes a separator, 5 denotes a positive electrode lead, 6 denotes a negative electrode lead, 7 denotes a positive electrode terminal, 8 denotes a safety valve, and 9 denotes a PTC element. Reference numeral 10 denotes a gasket, 11 denotes an insulating plate, and the positive electrode plate 2, the separator 4, and the negative electrode plate 3 are wound and housed in a case. As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a ratio of 1 mol / l in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is used. The battery capacity was 5 Ah.

Table 1 summarizes data on the positive electrode active materials used in each battery.

[0023]

[Table 1]

Next, the following measurements were performed for each battery, and the results are summarized in Table 2. First, at room temperature, a terminal voltage of 4.1 V was obtained at a current of 5 A corresponding to 1 C.
After constant-current charging was performed, the battery was further charged for 3 hours based on the constant-voltage charging method. Subsequently, a constant current discharge was performed at a current of 5 A corresponding to 1 C until the terminal voltage reached 2.75 V. Furthermore, after charging under the same conditions, discharging was performed by changing the current during constant current discharging to a current of 100 A corresponding to 20 C. 1C and 20 at this time
The ratio of the discharge capacity obtained at the time of C discharge and the discharge capacity at the time of 20C discharge to the discharge capacity at the time of 1C discharge was defined as a high rate / low rate capacity ratio. FIG. 3 shows a discharge curve of each battery at the time of discharging at 20C.

In order to compare the output characteristics of the batteries, in a fully charged state (battery open circuit voltage: 4.1 V), at 25 ° C., a current of 5 A was used for 10 seconds, and then a current of 20 A was used for 10 seconds.
Second, discharge for 10 seconds at a current of 50 A, and plot each current value and the battery voltage after 10 seconds, and extrapolate and calculate the current value at which the battery voltage becomes 2.5 V from their approximate straight lines. The output value of each battery was determined, and the internal resistance of each battery was determined from the approximate straight line at this time. The results are shown in Table 2. Note that the values in Table 2 were the average values of the measured values for every 10 batteries for each battery.

[0026]

[Table 2]

From Tables 1 and 2, and FIG. 3, the following has become clear. In the batteries A to E, the average particle diameter of the secondary particles of the positive electrode active material was the same, but the average particle diameter of the primary particles was changed. As shown in Table 1, these positive electrode active materials have a relationship that the smaller the average particle diameter of the primary particles, the larger the BET specific surface area. In comparing these batteries, a high rate /
The low-rate capacity ratio increased from 97 for Battery A to 78 for Battery E as the average particle size of the primary particles of the positive electrode active material became smaller. In other words, it was found that the higher the specific surface area of the positive electrode active material, the higher the high ratio / low ratio capacity ratio.

That is, it was found that reducing the average particle diameter of the primary particles of the positive electrode active material was more advantageous for the high rate discharge characteristics of the battery. In addition, the average particle diameter of the primary particles is 0.1.
It was very difficult to control to a value smaller than 0.1 μm, such as 05 μm.

The average primary particle diameter is 1.5 μm.
In battery E, the high ratio / low ratio capacity ratio was extremely small, and the output value was 808 W, which was inferior to other batteries.

The batteries F, G, C, H and I have the same primary particle diameter of the primary particles of the positive electrode active material, but are different from the average particle diameter of the secondary particles.
In addition, in these positive electrode active materials, as shown in Table 1, the smaller the average particle diameter of the secondary particles, the larger the BET specific surface area. In the comparison of these batteries, the high ratio / low ratio capacity ratio increased from 76 of battery F to 92 of battery C as the average particle diameter of the secondary particles of the positive electrode active material increased.

On the other hand, in the batteries H and I, the high ratio / low ratio capacity ratio was small. This is because if the particle size of the secondary particles is too large to a certain extent, the specific surface area becomes too small, and the effect of the particle size of the primary particles is reduced.

That is, it was found that increasing the average particle diameter of the secondary particles of the positive electrode active material was advantageous for the high rate discharge characteristics of the battery. However, considering the simplicity of the workability in the step of applying the positive electrode mixture layer containing the positive electrode active material to the current collector, the average particle diameter of the secondary particles is preferably 20 μm or less.

In the batteries F and J, the primary particles and the secondary particles used the positive electrode active material having the same average particle diameter, but the mixing ratio of the positive electrode active material and the amount of the conductive additive in the positive electrode mixture was different. Things. It was found that the battery F had a smaller high rate / low rate capacity ratio than the battery J. However, as in the case of the battery J, it was found that when the amount of the conductive additive was increased, the 1C discharge capacity was reduced. From these facts, the secondary particles 1 of the positive electrode active material 1
In the case of the positive electrode active material used for the battery F in which the number of primary particles aggregated per unit is small, more primary particles are sintered, compared with the positive electrode active material used for the battery B or the battery C,
As a result of the low electron conductivity of the positive electrode active material, more conductive assistants must be mixed into the positive electrode mixture, and when the positive electrode active material used in Battery J is used, the high-rate discharge characteristics are improved. It was found that the discharge capacity had to be sacrificed in order to achieve this.

From these results, according to the present invention, a lithium-manganese composite oxide comprising a sintered body of primary particles having an average particle diameter of 0.1 μm or more and 1 μm or less, among which the average particle diameter of the secondary particles is 5 μm As described above, in a nonaqueous electrolyte secondary battery using a lithium-manganese composite oxide having a size of 20 μm or less as a positive electrode active material, as shown in Table 2, 1 C
Discharge capacity is 5.0Ah or more, high rate / low rate capacity ratio is 90%
As described above, the output value is 1000 W or more, and the internal resistance is 4.0 mΩ.
The following excellent characteristics were exhibited.

[0035]

According to the present invention, a lithium-manganese composite oxide obtained by sintering primary particles having an average particle diameter within a certain range is used as a positive electrode active material, so that energy density can be reduced in a simple manufacturing process. It is possible to provide a non-aqueous electrolyte secondary battery having a high discharge rate and excellent high-rate discharge characteristics.

[Brief description of the drawings]

FIG. 1 is an SEM photograph of a positive electrode active material A.

FIG. 2 is a diagram showing a structural example of a cylindrical non-aqueous electrolyte secondary battery.

FIG. 3 is a diagram comparing discharge curves at the time of 20C discharge of each battery.

[Brief explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5 Positive electrode lead 6 Negative electrode lead 7 Positive electrode terminal 8 Safety valve 9 PTC element 10 Gasket 11 Insulating plate

Continued on the front page F-term (reference)

Claims (2)

[Claims] 1. The general formula Li _x Mn _{(3-xy) MyO
4} (where 1 ≦ x ≦ 2, 0.01 ≦ y ≦ 0.
1, M is Co, Ni, V, Fe, Ti, Cr, Cu, C
a, at least one element selected from the group consisting of Al, In, Ga, B and Si).
In a nonaqueous electrolyte secondary battery using a manganese composite oxide as a positive electrode active material, the positive electrode active material has an average particle diameter of 0.1
A non-aqueous electrolyte secondary battery comprising a sintered body of primary particles of 1 μm or more and 1 μm or less. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the average particle diameter of the secondary particles made of the sintered body is 5 μm or more and 20 μm or less.