JPH087894A - Positive active material for nonaqueous lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

PURPOSE:To ensure reproducibility of initial capacity and suppress drop in capacity attendant on cycles by using LiNiO2 particles having specified pore volume, specified average pore radius, and secondary particle diameter existing in a specified range. CONSTITUTION:A molding obtained by kneading LiNiO2 particles with a conductor and a binder, then molding is used as a positive electrode plate. In a nonaqueous secondary battery, on charging, lithium is released from a positive active material and deposited on a negative electrode through an electrolyte, and on discharge, opposite change occurs. LiNiO2 particles in which secondary particle diameter is 3-30mum, 80% or more of pore volume has pore radius of 50nm or less, and average pore radius is 3-10nm is used. Discharge capacity is increased, and cycle life is lengthened.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses LiNiO ₂ particles effective as a positive electrode active material of a non-aqueous lithium secondary battery and a positive electrode plate containing the particles as a main component to increase the charge / discharge capacity and cycle the cycle. TECHNICAL FIELD The present invention relates to a lithium secondary battery with improved properties.

[0002]

_2. Description of the Related Art Conventionally, as a typical technique for producing LiNiO ₂ , a mixture of a lithium compound and a nickel compound is baked at a temperature of about 750 ° C. for 15 hours in an oxygen stream to synthesize desired LiNiO ₂ . However, a Li intercalation type crystal structure was developed to facilitate the movement of lithium ions and increase the battery capacity.

However, in such a conventional technique, although the conditions for obtaining the crystal structure for the initial high capacity (for example, starting materials and firing conditions) have been studied, the reproducibility of the capacity is not improved. Although it is low, and it is necessary to suppress the other characteristics of the secondary battery, specifically, the capacity decrease due to repeated charging / discharging (hereinafter referred to as cycle), there is no effective measure.

[0004]

As described above, the positive electrode active material obtained by the conventional manufacturing method has problems such as poor reproducibility of the initial capacity of the obtained material.
_{In a} non-aqueous lithium secondary battery using ₂ as a positive electrode active material, it has been desired to secure reproducibility of initial capacity and to develop a new positive electrode active material that suppresses capacity reduction due to cycling.

[0005]

[Means for Solving the Problems] The present applicants have conducted diligent research in order to solve the above problems, and found that a conventionally known Li
It was found that even the NiO ₂ powder can solve the conventional problems by using a powder in a specific range as the positive electrode active material, and the present invention could be submitted.

That is, according to one aspect of the present invention, in a LiNiO ₂ powder having a secondary particle diameter within the range of 3 to 30 μm, 80% or more of the pore volume has a pore radius of 50 nm or less, and the average. A positive electrode active material for a non-aqueous lithium secondary battery, comprising LiNiO ₂ particles having a pore radius in the range of 3 to 10 nm.
The present invention relates to a lithium secondary battery, wherein a molded body formed by kneading iNiO ₂ particles with a conductive agent and a binder is used as a positive electrode plate.

[0007]

[Function] Looking at the movement of lithium in the battery as a model,
In the case of a non-aqueous secondary battery, lithium is extracted from the positive electrode active material at the time of charging and is deposited on the negative electrode through the electrolytic solution or electrolyte. The opposite change occurs at the time of discharge, and at these times, lithium is considered to move in the state of a compound such as an ion or a complex.

Although the primary particles of LiNiO ₂ are incomplete, it is considered to be one LiNiO ₂ crystal particle, and the lithium in the primary particle due to charge and discharge is in an ionic state in the intercalated layer of the crystal lattice. Move by solid diffusion.

Further, the LiNiO ₂ active material powder has a secondary structure in which primary particles are gathered, and a space between these primary particles holds an electrolytic solution or an electrolyte to some extent. The positive electrode is composed of a tertiary structure containing the active material, conductive agent, binder and electrolyte.

[0010] Generally, the quality of the characteristics of the movement of lithium in and out of the primary particles and the tertiary structure has been examined, but the movement of lithium in the secondary structure has not been examined at present. However, the size of the passages in the primary particles is on the order of Angstroms, while
Since the size of the passages in the tertiary structure is on the order of μm, it is obvious that the passages in the secondary structure are particularly important during discharge.

The migration of lithium in the secondary structure is presumed to be liquid diffusion through the electrolytic solution, and the space between the primary particles is considered to be a thin tube filled with the electrolytic solution. Is shown by the average value and distribution of the pore radius.

The apparent capacity of the battery is determined by the amount of the active material packed into a fixed volume, and when charging and discharging are repeated, the volume change of the primary particles is repeated with the change of the crystal structure. In this case, since it is possible to extend the cycle life by suppressing the volume change, it is considered that dense packing of the primary particles is desirable, and as a result, the diameter of the thin tube is thin.

However, the ionic radius of lithium is 0.7.
Since it is angstrom and the size of the lithium complex or compound is larger than this, if the thin tube becomes thin relative to the size of the transfer material, physical resistance against mass transfer works, so the tube is thick, that is, the primary It is desirable that the packing of particles be sparse. Therefore, the lower limit of the thin tube diameter is naturally limited.

On the other hand, if the diameter of the thin tube is too large, the cycleability is lowered. This is due to the wettability of the electrolytic solution or the capillary phenomenon, and it is difficult for the electrolytic solution to permeate into the space of the secondary structure, or because the electrolytic solution components are selectively absorbed, the thin tube is deteriorated. It is presumed that the cause may be a change in the electrochemical balance between the active material and the electrolyte in the tertiary structure.

Further, it is known that the particle size of the active material powder is related to the migration distance of lithium, and the active material powder having a large particle size exhibits resistance to the migration of lithium.

Empirically obtaining the appropriate range of the pore radius in consideration of the above, 80% or more of the pore volume has a pore radius of 50 nm or less, and the average pore radius is 3 to. It has been found that an active material powder of 10 nm is optimal.

In this case, it is desirable that the distribution and average value of the pore radii be obtained by the adsorption / desorption isotherm of the gas adsorption method, and the BJH method is sufficient for the analysis.

This is for the following reason. That is, in the mercury injection method, the space between powders is also measured at the time of measurement, so that it is difficult to measure and evaluate the inside of powder particles. Further, even in the gas adsorption method, the MP method is used to analyze the results. No need. This is because pores of 7 angstroms or less are unknown by the current measurement method. Furthermore, within the secondary structure, the migration of lithium is considered to occur in a larger form, not as an ion.

The manufacturing method of the present invention will be described in comparison with the conventional method. Generally in the production of LiNiO ₂ ,
The nickel raw material component and the lithium component are mixed and the reaction is carried out by heating, but if necessary, pulverization is also carried out. In this case, hydroxide, basic carbonate, oxyhydroxide, and oxide can be used as the nickel raw material, and hydroxide is typical as the lithium raw material.

It is desirable that the nickel and lithium components be finely and uniformly dispersed in each other in order to further enhance the reactivity during firing and to make the resulting LiNiO ₂ powder into a good crystal phase as an active material for batteries. It is believed that.

Therefore, in the conventional method, a nickel raw material and a lithium raw material are finely pulverized and mixed in an organic solvent to obtain a mixed raw material having an average particle size of about 1 μm, which is dried at about 500 ° C. It is calcined at a temperature, compacted, and fired, but the firing temperature of LiNiO ₂ is often around 750 ° C.

By this firing, it seems that lithium is diffused with the nickel raw material as the mother to form LiNiO ₂ . In this process, LiNiO ₂ grows to a particle size of about ₂ to 3 μm, but it can be seen by observation with a microscope that the secondary particles are sparse.

Further, the prototype of nickel hydroxide and lithium hydroxide under known conditions has a pore radius of about 2 nm, and the measured values are not stable when the capacity and cycle characteristics of each production lot are measured. Such LiNiO ₂ powder is far from a practical level.

The method of the present invention is intended to improve the characteristics as an active material by controlling the above-mentioned drawbacks of the conventional method.

The lithium raw material used in the method of the present invention is a known salt, but lithium hydroxide is sufficient, and Li
NiO ₂ grows with a nickel raw material as a mother by firing. Therefore, in order to control the average diameter and pores of the LiNiO ₂ powder, the form of the nickel raw material before firing is important.

In such a case, nickel hydroxide having a specific surface area of 100 m ³ / g or less is 45 μm.
It is desirable to use particles having a particle size of m or less from the viewpoint of reaction, but the processing conditions are slightly different depending on the type of raw material.

As firing conditions, it is known that heat treatment is carried out at a temperature of about 750 ° C. and a holding time of 10 to 20 hours in an oxidizing atmosphere, preferably in an oxygen stream. It is not necessary to treat at temperature.

When the mixed powder was subjected to differential thermal analysis, an endothermic peak was observed at around 700 ° C., although the value was not constant depending on the type of raw materials used and the conditions of the combination process. The heat treatment at a temperature lower than this temperature shows a deterioration in the high temperature retention property, so it is desirable to perform the heat treatment at a temperature higher than the temperature indicated by this endothermic peak.

In this case, about 0.5% of lithium is volatilized by firing, so if necessary, it is advisable to measure a large amount of this in advance. The appearance after firing becomes a black lump, but for use as a positive electrode active material, this lump is disintegrated and classified.

Generally, as an active material powder for a positive electrode material for a battery, empirically, its particle size is 1 μm or more and 10 because of its molding method and conditions, and for the purpose of preventing short circuit and discharge during storage.
Those within the range of 0 μm or less are considered to be suitable.
In the present invention, similar results were obtained with an average diameter of 3 to 30 μm, but it was found that an average diameter of 7 to 15 μm and a pore radius of 4 to 8 nm are preferable.

A general apparatus can be used for crushing and classifying the lumps.

The component ratio of the lithium raw material and the nickel raw material is
Even if the molar ratio is not Li / Ni = 1/1, Li
Within the range of /Ni=(1±0.05)/1, similar results can be obtained in the battery characteristics, and even when a small amount of additive is used, the result is the effect of the present invention. The same as above is included in the scope of the present invention.

The LiNiO ₂ thus obtained was used as a positive electrode active material, to which Ketjen black as a conductive agent and polytetrafluoroethylene (PTFE) as a binder were mixed in a weight ratio. At a ratio of 8: 1: 1 and kneaded, and pressure-molded at a pressure of ² ton / cm ² into a disk having a diameter of 37 mm.

This pressure-molded body was used as the positive electrode 4 in the test cell shown in FIG. 1, and the negative electrode 7 was a lithium metal having a thickness of 0.7 mm cut out. As the separator 5 in the figure, a polypropylene film cut out is used, and the electrolyte solution is a mixture of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1 and 6 foot. Lithium phosphate (LiPF ₆ ) was added to
What was dissolved at a concentration of 5 mol / l was used.

Further, in the present invention, the decrease in discharge capacity due to repetition is also described, and the durability as a secondary battery is relatively evaluated.

The present invention will be described in detail below with reference to examples.

[0037]

Example 1 Lithium hydroxide having an average diameter of 1 μm and nickel hydroxide having an average diameter shown in Table 1 were used in a molar ratio of Li / Ni =
The powders were weighed so as to be 1.01 / 1, and these powders were mixed without using water or a solvent and dried at 200 ° C.

Next, 1 kg / cm ^{2 of} these mixed powders was added.
With a pressure of 25 mm and a thickness of 2 mm, and heat-treated in an oxygen stream at 740 ° C. for 10 hours, and the fired product was crushed in a mortar to obtain LiNiO ₂ powder shown in Table 1. As a result, it was found that the average diameter of LiNiO ₂ contracted about 20% with respect to nickel hydroxide.

When the obtained powder was subjected to XRD measurement, as shown in FIG. 2, a pattern having the same shape as that of LiNiO ₂ reported previously was obtained.

50n only when the average diameter is 38 μm.
The number of pores of m or more was 27%.

In FIG. 1, 1 is a positive electrode lead wire, 2 is a cell fixing nut, 3 is a positive electrode current collector, 4 is a positive electrode, 5 is a separator, 6 is a separator fixing spacer, 7 is a negative electrode, Reference numeral 8 represents a negative electrode current collector, 9 represents a cell fixing screw, 10 represents an electrolytic solution injection plug, and 11 represents a negative electrode lead wire.

Next, these were assembled into a test cell shown in FIG. 1 and a charge / discharge test result was shown in Table 1. From these results, it was found that when the average pore radius is in the range of 3 to 10 nm, the decrease in discharge capacity due to repetition is small.

[0043]

[Table 1]

[0044]

Example 2 Li / Ni = 1.01 / in molar ratio of lithium hydroxide and nickel hydroxide having an average diameter shown in Table 2.
The powders were weighed so as to be 1, the powders were put into water, 50% by weight of citric acid was added to nickel hydroxide, and the mixture was dried at 60 ° C. with stirring.

Next, the dried product was lumped to a diameter of about 2 cm and heat-treated at 740 ° C. in an oxygen stream, and the obtained baked product was crushed in a mortar to obtain a 150 mesh powder.
A charge / discharge test was performed according to the procedure shown in Example 1. The results are also shown in Table 2.

From Table 2, it was found that, as in Example 1, when the average pore diameter was in the range of 3 to 10 nm, the decrease in discharge capacity due to repetition was small.

[0047]

[Table 2]

[0048]

Example 3 Lithium hydroxide monohydrate (LiOH.H ₂
O) and nickel hydroxide are heat treated at 300 ° C. to obtain nickel oxide (NiO) in a molar ratio of Li / Ni = 0.
97/1 and Li / Ni = 1.04 / 1 were weighed, citric acid was added in an amount of 60% by weight based on the total amount of lithium and nickel, and the mixture was mixed in water at 90 ° C for 4 hours. Cooled.

Next, the mixture was taken out of the stirring container, crushed to a size of 10 mm or less, sufficiently dried, and heat-treated in an oxygen stream at 730 ° C. for 15 hours, and the fired product was crushed in a mortar. The average diameter was 14 μm, and the average diameter of the obtained LiNiO ₂ was 11 μm.

When the powder after the heat treatment was measured by XRD,
A pattern having the same shape as that of FIG. 2 shown in Example 1 was obtained.

Further, using these powders as a positive electrode active material, a charge and discharge test was carried out by the procedure shown in Example 1 to obtain 190 mAh / g and 206 mAh / g, respectively.
It was possible to obtain the same battery characteristics as when Li / Ni = 1/1. The average pore radii are both in the 5 nm range, and the capacity decrease due to repetition is 21% and 17% after 50 times, respectively.
%Met.

[0052]

Example 4 LiOH having an average particle size of 1 μm and an average particle size of 23
μm basic nickel carbonate in molar ratio Li / Ni = 1 /
It was weighed to be 1 and dried under the same conditions as in Example 1.

Then, the obtained lump was baked in the air at 350 ° C., cooled and pressure-molded at a pressure of 0.5 ton / cm ² to obtain a disk-shaped molded body having a diameter of 25 mm and a thickness of 2 mm. This molded body was baked in an oxygen stream at 750 ° C. for 10 hours.

The fired product obtained was crushed in a mortar to obtain a powder having an average diameter of 19 μm. When this powder was measured by XRD, the same results as in FIG. 2 in Example 1 were obtained.

Further, using this powder as a positive electrode active material, a test cell was assembled and a charge / discharge test was conducted in the same manner as in Example 1. The charge capacity and discharge capacity in the first cycle were as follows.
It was 206 mAh / g and 196 mAh / g, respectively.

As the charge and discharge capacity after 50 cycles, a value of around 150 mAh / g was obtained in all cases. In this case, 90% or more of the pore volume of the powder used is 10n
The average pore radius was 4.7 nm.

[0057]

[Example 5] The particle size of nickel hydroxide obtained by treating under the same conditions as in Example 1 except that two kinds of nickel hydroxide in which 5% or 10% of the Ni component was replaced with Co were used Were 18 μm, and the particle size of the obtained LiNiO ₂ was 14 μm.

When a charge / discharge test was conducted using these powders, the initial discharge capacity was 186 mAh / g.
And 174 mAh / g, and the reduction rates after 50 cycles were 22% and 18%, respectively. The average pore radii in this case are 6.3 and 7.2 nm, but it was found that using these powders, the average voltage was increased by about 0.03 V as compared with the case of Example 1.

[0059]

Comparative Example As in Example 1, LiOH.H ₂ O and Ni
(OH) ₂ was weighed so that the molar ratio was Li / Ni = 1/1, and these powders were pulverized in ethanol for 50 hours.
After mixing, heat treatment was performed at 750 ° C. for 15 hours in an oxygen stream. In this case, the average diameter after mixing was 0.8 μm.

When this powder was subjected to XRD measurement, the same results as those in Example 1 (see FIG. 2) were obtained, and when an SEM photograph of this powder was observed, the aggregate particle size was about 10 μm. .

Further, using this powder as a positive electrode active material,
When a test cell was assembled and a charge / discharge test was conducted in the same manner as in Example 1, the discharge capacity was as low as 156 mAh / g. In this case, 95% of the pore volume was 10 nm or less, and the average pore radius was about 2 nm. The rate of decrease in discharge capacity due to repetition was 46% after 50 times.

[0062]

As described above, by using the LiNiO ₂ particles in the specific range shown in the present invention, a positive electrode active material for a lithium secondary battery having a high discharge capacity and a high cycle property was obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of test cells produced in Examples and Comparative Examples.

FIG. 2 XRD of LiNiO ₂ powder obtained in Example 1
It is a diffraction diagram.

[Explanation of symbols]

 1 Positive electrode lead wire 2 Cell fixing nut 3 Positive electrode current collector 4 Positive electrode 5 Separator 6 Separator fixing spacer 7 Negative electrode 8 Negative electrode current collector 9 Cell fixing screw 10 Electrolyte injection plug 11 Negative electrode lead wire

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukio Hiraoka 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Norio Haga 1-2-8, Marunouchi, Chiyoda-ku, Tokyo Within Wa Mining Co., Ltd. (72) Inventor Katsuaki Okabe 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Within Wa Mining Co., Ltd.

Claims (2)

[Claims] 1. A LiNiO ₂ powder having a secondary particle size in the range of 3 to 30 μm, in which 80% or more of the pore volume has a pore radius of 50 nm or less, and the average pore radius is 3 or less.
A positive electrode active material for a non-aqueous lithium secondary battery, which comprises LiNiO ₂ particles within a range of -10 nm. 2. The secondary particle size is in the range of 3 to 30 μm, 80% or more of the pore volume has a pore radius of 50 nm or less, and the average pore radius is in the range of 3 to 10 nm. A lithium secondary battery, wherein a molded body formed by kneading certain LiNiO ₂ particles with a conductive agent and a binder is used as a positive electrode plate.