JP3344853B2 - Positive active material for non-aqueous lithium secondary battery and lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention includes a valid LiNiO ₂ particles as a positive electrode active material for non-aqueous lithium secondary battery, the charge and discharge using the positive electrode plate and high capacity load characteristics composed mainly of particles The present invention relates to an improved lithium secondary battery.

[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 calcined at a temperature of about 750 ° C. for 15 hours in an oxygen stream to synthesize a desired LiNiO ₂ . However, there has been known a method of developing a Li-intercalation type crystal structure, facilitating the movement of lithium ions, and increasing the battery capacity.

However, in such a conventional technique, conditions (eg, starting materials and firing conditions) for obtaining an initial crystal structure for increasing the capacity have been studied, but the reproducibility of the capacity is low. Also, there are problems such as low load characteristics of the secondary battery.

[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 was desired to ensure reproducibility of the initial capacity and to develop a new positive electrode active material having high load characteristics.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, a conventionally known LiN
Even with iO ₂ powder, it was found that the load characteristics were improved if the pore volume was within a certain range, and the present invention could be provided.

That is, a first aspect of the present invention is a LiNiO ₂ particle having a pore volume in the range of 0.01 to 0.04 ml / g produced using nickel hydroxide having a particle size of 3 μm or more as a nickel source. A second active material is a positive electrode active material for a non-aqueous lithium secondary battery characterized by comprising nickel hydroxide having a specific surface area of 50 m ² / g or more and a particle size of 3 μm or more as a nickel source. Pore volume is 0.01 ~
A positive electrode active material for a non-aqueous lithium secondary battery, comprising LiNiO ₂ particles in the range of 0.04 ml / g.
A lithium secondary battery characterized in that a molded body formed by kneading _two 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 escapes from the positive electrode active material during charging and deposits on the negative electrode through the electrolyte or the electrolyte. At the time of discharge, the reverse change occurs. At these times, lithium is considered to move in a state of a compound such as an ion or a complex.

[0008] The LiNiO ₂ active material powder has a structure of secondary particles in which primary particles are gathered, and the primary particles are considered to be imperfect but one LiNiO ₂ crystal particles, and are used for charging and discharging. The lithium in the primary particles migrates through the intercalated layer of the crystal lattice in the state of ions by solid diffusion.

In this case, since there is some space between the primary particles and the electrolyte or the electrolyte is held, it is considered that the pores are filled with the solution. The positive electrode is considered to have a tertiary structure including the active material, the conductive agent, the binder, and the electrolyte. In general, the quality of the transfer between the primary particles and the inside and outside of the tertiary particles is examined.

Since the movement of lithium during charge and discharge involves liquid diffusion in the space in the secondary particles, it can be easily estimated that the pore volume has a large effect. In this case, the pore volume becomes large. As the amount of electrolyte increases, mass transfer is promoted.

However, if the volume becomes larger,
Since the filling of the primary particles is sparse, the amount of energy per volume is reduced, so an upper limit is naturally determined. If the pore volume is 0.04 ml / g or more, the density of the secondary particles themselves decreases by 20% or more. Therefore, the range of the appropriate pore volume empirically obtained in the present invention is 0.01%. ~ 0.0
4 ml / g, more preferably 0.015 to 0.03 ml
/ g.

In this case, the pore volume is desirably determined by the adsorption / desorption isotherm of the gas adsorption method. In the conventional mercury intrusion method, the space between the powders is measured at the time of measurement, so that the space between the powders is not measured. It is difficult to measure and evaluate accurately.

The production method of the present invention will be described in comparison with a conventional method. Generally, in the production of LiNiO ₂ ,
The nickel raw material component and the lithium raw material component are mixed and reacted by heating, and pulverization is performed if necessary. In this case, hydroxides, basic carbonates, oxyhydroxides, and oxides can be used as nickel raw materials, and hydroxides are typical as lithium raw materials.

In order to further enhance the reactivity during firing and to make the resulting LiNiO ₂ powder a good crystalline phase as a battery active material, it is desirable that the components of nickel and lithium be finely and homogeneously dispersed in each other. It is believed that.

Therefore, according to 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. , And compaction molding, but the firing temperature of LiNiO ₂ is often around 750 ° C.

As described above, the volume of a prototype under known conditions using nickel hydroxide and lithium hydroxide is 0.005.
It was about ml / g, and such LiNiO ₂ had a small amount of electrolyte in the secondary particles and was inferior in load characteristics.

As a countermeasure to this, it is conceivable to reduce the secondary particle diameter, but as a result, the filling property is reduced, and the capacity of the battery is reduced.

The lithium raw material used in the method of the present invention may be a known salt, but lithium hydroxide is sufficient.
NiO ₂ grows from the nickel raw material by firing. Therefore, to control the pores, the characteristics of the Ni raw material are important.

In this case, nickel hydroxide has a specific surface area of 50.
m ² / g or more with a particle size of 3 μm or more,
It is effective to use the mixture with the i raw material.

It is known that the heat treatment is carried out in an oxidizing atmosphere, preferably in an oxygen gas stream, at a temperature of about 750 ° C. and a holding time of 10 to 20 hours as a firing condition. It could be fired. However, if the pore volume is in the range of 0.01 to 0.04 ml / g, it is possible to perform firing at a temperature other than the above.

[0021] Lithium in the raw material is reduced to 0.1 by firing.
Since about 5% is volatilized, if necessary, it is advisable to measure this amount in advance. The appearance after firing becomes a black mass, but this mass is crushed and classified for use as a positive electrode active material.

Generally, as a positive electrode active material powder for a battery,
Empirically, from the molding method and conditions, and from the reason of preventing short-circuiting and discharge during storage, the particle size is from 1 μm to 100 μm.
Those within the range of m or less are considered appropriate. still,
A common device can be used for crushing and classifying the above-mentioned mass.

When 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 / Ni
When Ni is within the range of 1 ± 0.05 / 1, the same result is obtained in the battery characteristics. Even when a small amount of additive is used, the result is the same as the effect of the present invention. If present, it is included in the scope of the present invention.

The thus obtained LiNiO ₂ was used as a positive electrode active material, Ketjen black was used as a conductive agent, and polytetrafluoroethylene (P) was used as a binder.
TFE) was added at a weight ratio of 87: 8: 5, kneaded, and pressed into a disk having a diameter of 18 mm at a pressure of ² ton / cm ² .

This pressed product was used as the positive electrode 2 in the test cell shown in FIG. 1, and the negative electrode 4 was made by cutting out a 0.7 mm thick lithium metal. Separator 3 in the figure
A polypropylene film cut out is used as the electrolyte, and a mixture of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1 is used as an electrolyte. LiPF ₆ ) 1mo
A solution dissolved at a concentration of l / l was used. In this case, another solvent may be used as the electrolytic solution.

In the lithium secondary battery of the present invention, the upper limit of the charging voltage is set to 4.2 V, and in the measurement of the charging and discharging capacity, the charging and discharging capacity up to the second time is low in reproducibility. After that, the capacity was measured in the third charge / discharge, and the quality was compared by the ratio of the discharge capacity to the charge capacity. The higher this ratio, the higher the load characteristics. In Examples 1 to 4, the third 0.2
The discharge capacity at C is 170 to 18 which is about 10% higher than that of the comparative example.
It was found to be 0 mAH / g.

Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

[0028]

EXAMPLE 1 LiOH having an average particle size of 1.5 μm as a raw material
-H ₂ O, and as shown in Table 1, the average particle size is 0.8;
Nickel hydroxide consisting of four types of 5, 5.2, and 7.2 is weighed so that the molar ratio of Li / Ni is 1.005 / 1, and these powders are mixed in a liquid, and sprayed with a spray drier. The mixture was dried, granulated, and sieved to obtain a mixed powder of about 27 μm (first step).

[0029]

[Table 1]

Next, these mixed powders were placed in an oxygen stream at 76.degree.
Heat treatment was performed at 5 ° C. for 6 hours to obtain a fired product.

Next, the obtained calcined product was pulverized in a mortar to form a powder of LiNiO _2. The powder was classified and found to have the pore volume shown in Table 1. When the obtained powders were subjected to XRD measurement, the same pattern as previously reported was obtained.
No phases other than iO ₂ were identified (not shown).

The thus obtained LiNiO ₂ is used as a positive electrode active material, and Ketjen black as a conductive agent and polytetrafluoroethylene as a binder are kneaded at a ratio of 87: 8: 5 by weight. Then, pressure molding was performed at a pressure of ² ton / cm ² into a disk having a diameter of 18 mm.

This pressed product was used as a positive electrode in the test cell shown in FIG. 1, a negative electrode 4 was obtained by cutting out a 0.7 mm thick lithium metal, and a separator 3 was used as a separator 3.
The polypropylene film was cut out, and lithium hexafluorophosphate (LiPF ₆ ) was used as an electrolyte in a mixed solution of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1. A solution dissolved at a concentration of 1.0 mol / l was used.

Using the LiNiO ₂ powders shown in Table 1, separate positive electrodes were prepared and assembled into the test cell shown in FIG. 1 and subjected to a charge / discharge test. The efficiency of the obtained (1C) and (2C) was obtained. And the results are shown in Table 1.

As a result, the pore volume is 0.01 to 0.04
Included in the range of ml / g (No. 2 to No. 4)
However, both 1C and 2C showed an efficiency of 72% or more.

[0036]

EXAMPLE 2 Li / Ni = 1.00 in molar ratio between lithium hydroxide and nickel hydroxide having an average particle size shown in Table 2.
It was weighed to be 5/1. Next, these powders were added to a liquid in which citric acid was adjusted to 35% by weight with respect to nickel hydroxide, mixed, and dried at 60 ° C. with stirring.

Then, the obtained dried product was formed into a lump of about 2 cm, and calcined at 350 ° C. for 3 hours in an air stream to form a lump of 60 cm.
The mixture is crushed into a mesh pass, and the crushed material is placed in an oxygen stream at 720 ° C.
, And then heat-treated at 770 ° C. for 5 hours.

Next, the obtained calcined product was pulverized in a mortar to form a LiNiO ₂ powder, which was then sieved to obtain a powder of 150 mesh under.

[0039]

[Table 2]

The thus obtained LiNiO ₂ powder was formed into a positive electrode according to the procedure shown in Example 1, a test cell was prepared, and a charge / discharge test was performed. The results are also shown in Table 2. As in Example 1, the pore volume was in the range of 0.01 to 0.04 ml / g, and the discharge conditions had an efficiency of 72% or more for both 1C and 2C.

[0041]

Example 3 Lithium hydroxide monohydrate (LiOH.H ₂
O) and nickel oxide (NiO) obtained by heat-treating nickel hydroxide at 700 ° C. in a molar ratio of Li / Ni =
0.97 / 1 and Li / Ni = 1.04 / 1 were weighed, citric acid was added at 60% by weight based on the total amount of lithium and nickel, and mixed in water at 90 ° C. for 4 hours. Then, it was cooled.

Next, the mixture was taken out of the stirring vessel, crushed in a mortar to 1 mm or less, and dried sufficiently to form a lump having a diameter of about 2 cm, and heat-treated at 760 ° C. for 10 hours in an oxygen stream. And the obtained fired product was treated in the same manner as in Example 1 to form a positive electrode. A charge / discharge test was performed. The results are shown in Table 3.

[0043]

[Table 3]

From the results shown in Table 3, the LiNiO ₂ powder obtained in this example also has a pore volume of 0.01 to 0.04 ml.
/ g, and the charge / discharge efficiency was 80% or more at 2C, and the characteristics were excellent. The average diameter of the nickel oxide used in this example was about 12 μm,
As a result, it was confirmed that the average diameter of the obtained LiNiO ₂ particles was almost the same.

[0045]

Example 4 LiOH of about 4 μm and nickel hydroxide having an average diameter of about 18 μm to which Co was added by 4% were weighed such that Li / Ni + Co = 1.005 / 1 in a molar ratio, and a small amount of LiOH was weighed. Water was added and mixed to form a lump.

Next, the lump was dried in an air atmosphere at 300 ° C., and then molded under pressure at a pressure of 50 kg / cm ² , crushed in a mortar, and baked with a 100 mesh-passed powder. After 4 hours at 760 ° C. in an air stream, the mixture was mechanically pulverized to obtain a powder having an average diameter of 17 μm.

A positive electrode body was formed using the powder in the same procedure as in Example 1, and a charge / discharge test was conducted. The pore volume was 0.014 ml / g, and the charge / discharge efficiency was 1 C. The efficiency at 85% and 2C was 78%.

[0048]

Comparative Example 1 As in Example 1, LiOH.H ₂ O and Ni
(OH) ₂ was weighed such that Li / Ni = 1.02 / 1 in molar ratio, and these powders were ground and mixed in ethanol for 50 hours to obtain a powder having an average diameter of 1.8 μm. .

The powder was molded at a pressure of 1 ton / cm ² using the powder, and the firing temperature was 700 ° C. and 72
The temperature was changed to 0 ° C. and 750 ° C., followed by heat treatment in an oxygen stream for 12 hours, followed by pulverization to obtain a 7 μm powder.

[0050]

[Table 4]

Next, a positive electrode body was formed using the above powder in the same procedure as in Example 1, and a charge / discharge test was performed. The results are also shown in Table 4.

From Table 4, the pore volume of this comparative example is 0.01 ml / g or less in the range of the present invention, and the discharge efficiency is lower than the lower limit of 72% in 2C of the present invention. Was also inferior.

[0053]

As described above, by using the LiNiO ₂ particles having the specific pore volume range shown in the present invention, a positive electrode active material for a lithium secondary battery having high load characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a test cell manufactured in Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Positive electrode 3 Separator 4 Negative electrode 5 Negative electrode can 6 Insulating packing

Continuing from the front page (72) Inventor Katsuaki Okabe 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Akinobu Iikawa 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Takashi Kobayashi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-6-267539 (JP, A) JP-A-6-111822 (JP, A) JP-A-5-32968 (JP, A) JP-A-1-304663 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (3)

(57) [Claims] 1. A hydroxyl source having a particle size of 3 μm or more as a nickel source.
The pore volume produced using nickel halide is 0.01 to 0.1.
A positive electrode active material for a non-aqueous lithium secondary battery, comprising LiNiO ₂ particles in a range of 04 ml / g. 2. A specific surface area of 50 m ² / g as a nickel source.
And using nickel hydroxide with a particle size of 3 μm or more
A positive electrode active material for a non-aqueous lithium secondary battery, wherein the positive electrode active material comprises LiNiO ₂ particles having a reduced pore volume in the range of 0.01 to 0.04 ml / g. 3. LiNiO _{2 according} to claim 1 or ₂
A lithium secondary battery comprising a molded body formed by kneading particles with a conductive agent and a binder as a positive electrode plate.