JP2002279985A - Positive electrode active material for non-aqueous lithium secondary battery and the non-aqueous lithium secondary battery using the active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase capacity when a large current is discharged by reducing an internal resistance in a non-aqueous lithium secondary battery, in which a composite oxide of Li and a transient metal is used for a positive electrode. SOLUTION: After at least one of transient metal compounds of Co and Mn and a lithium compound are mixed to form a composite oxide of lithium transition metal in α-NaFeO2 structure, primary particles are coagulated to form in spherical shape. As a result of this, the peak intensity ratio of X-ray diffraction (110)/(003), when the composite oxide is applied/pressed on the electrode, is set to 0.1 or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a non-aqueous lithium secondary battery. The present invention relates to a positive electrode active material. The present invention relates to reducing the internal resistance of the battery, and thereby enabling large current discharge as a non-aqueous lithium secondary battery.

[0002]

2. Description of the Related Art A lithium secondary battery has a higher energy density than a nickel cadmium battery or a nickel hydride battery, and has rapidly spread in the field of portable terminals and the like. Also EV
And in the field of power storage. A lithium secondary battery has a structure in which a positive electrode, a negative electrode, and a separator are arranged in a container, and is filled with a nonaqueous electrolyte using an organic solvent. The positive electrode is obtained by applying a positive electrode active material to a current collector such as an aluminum foil and press-molding the same. Α-NaFeO ₂ as the positive electrode active material
Complex oxides of lithium and transition metals (typically lithium manganate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) having a spinel structure) , A lithium transition metal oxide) is mainly used.
Japanese Patent No. 17471 discloses the production method in detail. In particular, lithium cobaltate having an α-NaFeO ₂ structure (L
iCoO ₂ ) and lithium nickelate (LiNiO ₂ ) have a large discharge capacity compared to lithium manganate (LiMn ₂ O ₄ ) having a spinel structure and have been put to practical use as positive electrode active materials for Li-ion batteries for mobile terminals . Synthesis is generally lithium compounds of these positive electrode active material (LiOH, Li ₂ CO _3, etc.) powder and the transition metal compound (CoO, NiO, etc.) were mixed powder, sintering, wide method of the ground to the lithium transition metal oxide Has been adopted. When applying the positive electrode active material to the current collector, carbon powder is mixed with the positive electrode active material in a weight ratio of several percent to several tens percent, and further, PVDF is added.
(Polyvinylidene fluoride), PTFE (polytetrafluoroethylene), etc., kneaded with a binder, and made into a paste, applied on a current collector foil to a thickness of 20 to 100 μm, dried, and pressed to form a positive electrode. ing.

[0003] These positive electrode active materials have an electric conductivity of 10 ^-1 to 10 ^-1 .
At 10 ^-6 S / cm ² , which is lower than that of general conductors, when applied to electrodes as it is, a battery with high internal resistance is obtained, and no output can be obtained in situations where large current discharge is required. In order to further increase the electrical conductivity between the aluminum current collector and the positive electrode active material or between the active materials, a positive electrode is formed by adding a conductive auxiliary material such as carbon powder having a higher electrical conductivity than the positive electrode active material. Is done. In addition, attempts have been made to apply a positive electrode active material having a small particle size and a large specific surface area to the electrode surface by pulverization to increase the contact area with an electrolytic solution.

[0004]

In the prior art described above, a conductive auxiliary such as carbon powder having a higher electric conductivity than the positive electrode active material is added, or the positive electrode active material is used to increase the contact area with the electrolyte. Although the output at the time of large current discharge is improved to some extent by the method of pulverizing the substance to reduce the particle diameter, it is still insufficient to meet the demand. In order to stably discharge such a large current, it is necessary to increase the diffusion rate of Li ions in the positive electrode active material. LiCoO ₂ and LiNiO ₂ commonly used as a positive electrode active material are generally α-NaFeO ₂
Has a layered rock salt structure represented by This structure
For example, as described in a lithium ion secondary battery (Nikkan Kogyo Shimbun), lithium and a transition metal are each (1)
11) A single layer arranged between oxygen layers is formed and alternately laminated to form a hexagonal superlattice (hexagonal layered rock salt structure). In this case, the diffusion path of the Li ion is (003) of the hexagonal layered rock salt structure as shown in FIG.
The direction is parallel to the plane. That is, Li ions cannot enter and exit the positive electrode active material from a direction perpendicular to the (003) plane. In the synthesis methods commonly used in, i.e. lithium compound (LiOH, Li ₂ CO _3, etc.) powder and the transition metal compound (MnO _2, CoO, NiO, etc.) powder were mixed, firing the - was triturated alpha-NaFeO _When a positive electrode active material such as LiCoO ₂ or LiNiO _{2 having two} structures is obtained, as shown in FIG. 2, flat particles are obtained because they are easily cleaved parallel to the (003) plane during pulverization after firing. This was applied to a current collector such as an Al foil and pressed to obtain a positive electrode, as shown in FIG.
3) The surface is easily oriented in parallel with the electrode surface. Since Li ions in charge and discharge move in a direction perpendicular to the electrode surface, it is necessary to move in a direction parallel to the (003) plane in order to enter and exit the positive electrode active material. For this reason, when the (003) plane is oriented parallel to the electrode surface as described above, it is difficult for Li ions to enter and exit the positive electrode particles during rapid charge and discharge, and the Li ion concentration on the positive electrode active material surface increases. I will.
Since the electrode potential is affected by the Li ion concentration in the positive electrode active material, the electrode potential decreases, and as a result, the output as a battery cannot be obtained.

[0005] Methods for controlling this orientation are also being studied. For example, Japanese Patent Application Laid-Open No. 2001-23639 discloses that the particle size and the sintering temperature of Co ₃ O ₄ as a raw material before sintering are controlled, and the intensity ratio of X-ray diffraction of the obtained LiCoO ₂ is I (003) / (1
10) ≦ 5.6 and I (105) / (113) ≧ 0.9
And I (110) / (113) ≦ 1.35, it is possible to provide a non-aqueous electrolyte secondary battery which is safe and has a high energy density even at a high charging temperature. However, even when the orientation of LiCoO ₂ is controlled during firing, it is necessary to pulverize the particles to an average particle diameter of about 10 to 20 μm when applying to the electrode. At this time, as described above, the particles are parallel to the (003) plane. The particles are easily cleaved and tend to be flat particles. This is Al
In a positive electrode obtained by applying and pressing a current collector such as a foil, the (003) plane of the positive electrode particles is also likely to be oriented in parallel with the electrode surface. For this reason, even in the method described in JP-A-2001-23639, the output of the battery cannot be obtained at the time of large current discharge.

An object of the present invention is to control the crystal orientation of the positive electrode active material when the positive electrode active material is applied and pressed on the electrode, so as to reduce the diffusion rate of Li ions in the positive electrode active material during discharge. It is an object of the present invention to provide a positive electrode active material and a battery which are capable of reducing the internal resistance of the battery and having excellent output characteristics with a small voltage drop even when discharging a large current.

[0007]

First, it is important that the positive electrode active material of the present invention is a secondary particle obtained by agglomerating primary particles having an α-NaFeO ₂ structure as shown in FIG. one of. Then, in the present invention, the (110) / X-ray diffraction of the positive electrode active material obtained from the plane coated and pressed (pressed at a pressure of about 1.5 ton / cm ² ) on the electrode is obtained.
The peak intensity ratio of (003) is 0.1 or more.

That is, the present invention provides a composite oxide powder of lithium and a transition metal having an α-NaFeO ₂ structure, in which the primary particles are formed into spherical secondary particles to form secondary particles.
It was applied on an electrode and pressed.
(0) / (003) is a positive electrode active material for a non-aqueous lithium secondary battery, wherein the peak intensity ratio is 0.1 or more.

Further, the present invention relates to an L-form having an α-NaFeO ₂ structure.
In the iCoO ₂ powder, the primary particles are made into secondary particles obtained by agglomerating into spherical particles, and the peak intensity ratio of (110) / (003) in X-ray diffraction when the particles are applied and pressed on an electrode. Is not less than 0.1, which is a positive electrode active material for a non-aqueous lithium secondary battery.

The positive electrode material synthesized according to the present invention comprises:
Since the primary particles having an α-NaFeO ₂ structure are secondary particles obtained by aggregating the particles in a spherical shape, the (003) plane of the particles when pressed as shown in FIG. The diffusion rate of Li ions in the positive electrode active material at the time is improved, and thus a positive electrode active material suitable for large-current discharge and a nonaqueous lithium secondary battery using the same can be provided.

[0011]

DETAILED DESCRIPTION OF THE INVENTION α-NaFeO in the present invention_TwoStructure
Has a non-aqueous lithium secondary metal oxide
It is useful as a positive electrode active material for ponds, and it is used as a positive electrode
The charge / discharge characteristics of the used secondary battery become particularly large. Departure
According to Ming, the positive electrode active material for non-aqueous lithium secondary batteries is shown in FIG.
It is manufactured according to the flowchart of FIG. First, in step 1
As a material, a transition metal which becomes an oxide upon firing, for example,
Compounds of cobalt, nickel, manganese (eg Co_ThreeO
_Four, CoO, Mn _ThreeO_Four, MnCO_Three) And baking to form an oxide
Lithium compounds (eg Li_TwoCO_Three, LiOH) and a predetermined ratio
Mix with. Add water to these powders in step 2
Pulverize and mix in a mill or the like for about 50 hours to form a slurry.
You. In step 3, the slurry is dried using a slurry dryer or the like.
You. Firing is step 4, and the raw materials used in this firing are
Becomes an oxide, α-NaFeO_TwoLithium with structure
It becomes a transfer metal oxide. Firing in air or oxygen 800 ℃ ~ 105
Perform at 0 ° C. for several hours to 10 hours. Next, calcinate α-NaF
eO_TwoPowder having a structure of lithium transition metal oxide
Then, in step 5, a predetermined amount of pure water or the like is added, and the ball mill is used again.
Pulverize to an average particle size of about 1 μm or less to form a slurry.
You. In step 6, the PVA solution is converted to a solid content in this slurry.
And add about 1 wt%, and then spray the particles with a spray dryer.
Spheroidization is performed so that the diameter is about 1 to 30 μm. Next
Calcination in air or oxygen at 800 ℃ ～ 1050 ℃ for several hours
Perform for 10 hours. After firing, pulverize with a vibration mill etc. in step 8
And sieved.

The evaluation of the characteristics of the positive electrode active material according to the present invention was performed according to the following procedure. First, the positive electrode material, conductive auxiliary material (carbon powder),
A binder (8 wt% PVdF / NMP) was kneaded at a weight ratio of 85: 10: 5 in an agate bowl to form a slurry-like mixture. The obtained mixture was applied to a thickness of about 200 μm on a current collector (Al foil) having a thickness of 20 μm. After the applied mixture has dried,
mm, length is about 50mm) and cut using a mold to 1.5t
Pressing was performed at a pressure of on / cm ² . The obtained positive electrode was sufficiently filled with an electrolytic solution (ethylene carbonate: dimethyl carbonate =
1: 2, electrolyte 1M-LiPF ₆ )
5 mm thick polyethylene), a metal lithium counter electrode, and a test battery. After the cell was left for several hours so as to be electrochemically equilibrated, it was connected to a charge / discharge measurement device to measure the battery capacity. The measurement of X-ray diffraction was performed in the form as shown in FIG. Using a Cu-Kα ray, a wide-angle goniometer was used. The scanning method used was continuous scanning, with a scan speed of 2 degrees / minute and a sampling interval of 0.006 degrees. The scanning range was 15 to 100 degrees in 2θ value.

Hereinafter, embodiments showing the effects of the present invention will be described. (Comparative Example 1) Lithium carbonate and cobalt oxide were weighed so that Li: Co = 1: 1, pure water was added, and the mixture was subjected to ball milling.
The mixture was mixed for a time to form a slurry. Next, the slurry is
After drying in a dryer (120 ° C.), the mixture was filled in an alumina crucible and fired in an electric furnace at 950 ° C. for 10 hours in the atmosphere. The fired powder is pulverized with a raikai machine and
To obtain a powder having a particle size of about 10 μm.

Example 1 Lithium carbonate and cobalt oxide were weighed so that Li: Co = 1: 1, and pure water was added.
The mixture was mixed with a mill for 24 hours to form a slurry. Next, the slurry was dried with a slurry drier (120 ° C.), filled in an alumina crucible, and fired in an electric furnace at 950 ° C. for 10 hours in the atmosphere. The fired powder was pulverized by a raikai machine and passed through a 45 μm sieve to obtain a powder having a particle size of about 10 μm. Next, pure water was added to the fired powder again, and the powder was pulverized to a particle diameter of about 1 μm using a ball mill or the like to obtain a slurry.
Next, the PVA solution was added to the slurry at a solid content of 1 wt%.
After the addition before and after, the particle diameter is 1 to 30 with a spray dryer or the like.
Perform spheroidization so as to have a thickness of about μm. Next, baking was performed at 800 ° C. for 10 hours in the air. After firing, the mixture was crushed with a vibration mill or the like, and sieved with a 45 μm mesh.

Example 2 The same operation as in Example 1 was carried out to form a spherical agglomerate having a particle diameter of about 1 to 30 μm using a spray dryer or the like, and then firing was performed at 900 ° C. in the air for 10 hours. Was. After firing, pulverize with a vibration mill
The mesh was sieved with a mesh of m. Example 3 The same operation as in Example 1 was performed to form a spherical aggregate having a particle diameter of about 1 to 30 μm using a spray dryer or the like, and then firing was performed at 1,000 ° C. in the air for 10 hours. After firing, the mixture was crushed with a vibration mill or the like, and sieved with a 45 μm mesh. Example 4 The same operation as in Example 1 was performed to form a spherical aggregate having a particle diameter of about 1 to 30 μm using a spray dryer or the like, and then firing was performed at 1050 ° C. in the air for 10 hours. After firing, the mixture was crushed with a vibration mill or the like, and sieved with a 45 μm mesh. Table 1 shows the evaluation results.

[0016]

[Table 1]

In Comparative Example 1, LiCoO synthesized by a usual method was used._Twoso
is there. FIG. 8A shows an SEM photograph of the grain morphology at this time.
You. Flat particles are seen. Discharge current density I = 0.5mA / cm
^TwoCapacity per weight at 155mAh / g is a practical value
But discharge current density I = 6.0mA / cm ^TwoPer weight obtained in
Capacity is 130mAh / g and I = 0.5mA / cm^Two84% of the value at
It is about. At this time, the positive electrode material is applied and pressed.
FIG. 9A shows the result of measuring the X-ray diffraction of the pole face. This
From this, the intensity ratio of the (110) / (003) plane is about 0.05.
You. This allows, as explained above, the electrode surface
The (003) plane of the positive electrode particles is
Measured. Therefore, the diffraction intensity of (003) is perpendicular to it.
Larger than the diffraction of the (110) plane
The intensity ratio of (110) / (003) is small.

On the other hand, the positive electrode material of the present invention shown in the examples is obtained by baking and crushing primary particles obtained by baking and pulverizing, and baking them again as aggregates. ) Is difficult to orient, and the peak of (110) / (003)
The crack strength is higher than that of the comparative example. This means
When the firing temperature after the spheroidization is increased, it appears more remarkably. This is probably because the higher the sintering temperature, the stronger the agglomeration becomes less likely to collapse. FIG. 8B,
FIG. 9B shows the SEM of the grain morphology of Example 4 as the material of the present invention.
A photograph and an X-ray diffraction pattern are shown. The results of these grain morphologies and diffraction intensity ratios support the effects of the present invention.
Then, in this example, when the (110) / (003) ratio is 0.10 or more, I
The capacity at 6.0 mA / cm ² was 142 mAh / g or more, which was a practical level. It is to be noted that firing at 1100 ° C. or more is not preferable because it is close to the melting point of the positive electrode material and may change the crystal structure.

[0019]

As described above, according to the present invention, the diffusion rate of Li ions in the positive electrode active material at the time of charging and discharging is improved, and the positive electrode active material suitable for large current discharge and the non- An aqueous lithium secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a unit cell having an α-NaFeO ₂ structure and a diffusion path of Li ions.

FIG. 2 is an explanatory view showing cleavage of an α-NaFeO ₂ structure.

FIG. 3 is a schematic diagram showing a state of orientation of a LiCoO 2 active material on an electrode.

FIG. 4 is a schematic diagram showing secondary particles obtained by aggregating primary particles into a spherical shape in the positive electrode active material of the present invention.

5 is a schematic view showing a case where the positive electrode active material of the present invention shown in FIG. 4 is applied on an electrode.

FIG. 6 shows a flowchart for preparing a positive electrode active material according to the present invention.

FIG. 7 is a view showing a measuring method of X-ray diffraction.

FIGS. 8A and 8B show scanning electron micrographs (1000 × magnification) of (a) Comparative Example 1 and (b) Example 4.

9 (a) shows diffraction patterns of X-ray diffraction of Comparative Example 1 and (b) of Example 4. FIG.

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Claims (3)

[Claims] 1. In a composite oxide powder of lithium and a transition metal having an α-NaFeO ₂ structure, the primary particles are formed into secondary particles obtained by agglomerating into spherical particles, so that the particles are applied and pressed on an electrode. X-ray diffraction (110) / (00)
3) The positive electrode active material for a non-aqueous lithium secondary battery, wherein the peak intensity ratio is 0.1 or more. 2. In LiCoO ₂ powder having an α-NaFeO ₂ structure, by forming primary particles into secondary particles that are aggregated into a sphere, X-ray diffraction at the time of applying and pressing it on an electrode is described. 110) / (003) peak intensity ratio of 0.1
A positive electrode active material for a non-aqueous lithium secondary battery, characterized in that: 3. A non-aqueous lithium secondary battery using the positive electrode active material according to claim 1 or 2.