JPH07235306A - Manufacture of positive electrode active material for nonaqueous lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide a lithium secondary battery having high discharge capacity and a high filling characteristic by using a nickel compound in which a particle diame ter of a secondary particle is limited to a range of 5mum to 100mum, obtaining LiNiO2 powder, and using this as a positive electrode active material. CONSTITUTION:Lithium hydroxide LiOH and nickel hydroxide Ni(OH)2 having an average diameter of 20i m are weighed so as to become Li/Ni=1/1 in a mole ratio, and after these powders are thrown in the water, citric acid is added, and it is dried. Afterwards, heat treatment is performed in an oxygen air current, and powder having an average diameter of 1.6mum is obtained. This is used as a positive electrode active material, and after a conductive agent and a binding agent are added, and a positive electrode plate is obtained by pressurizing molding. This positive electrode plate is used as a positive electrode 4 of a test cell of a lithium secondary battery, on the one hand, in a negative electrode 7, a lithium metal plate is used as a negative electrode plate. Polypropylene is used as a separator 5. A separator fixing spacer is 6, and a negative electrode current collecting body is 8, and a cell fixing machine screw is 9, and an electrolyte injecting plug is 10, and a negative electrode lead wire is 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to Li as a positive electrode active material.
The present invention relates to increasing the charge / discharge capacity of a non-aqueous lithium secondary battery using NiO ₂ , and more particularly to a method for producing a positive electrode active material for a non-aqueous lithium secondary battery, which increases the capacity.

[0002]

_2. Description of the Related Art The following techniques have been conventionally used to produce a LiNiO ₂ positive electrode active material. That is,
Lithium salt and nickel salt raw materials are finely pulverized and mixed in an organic solvent, then dried and molded, and baked in an oxygen stream at a temperature of about 750 ° C. for 24 hours to synthesize LiNiO ₂ ,
Its crystal structure was developed to facilitate the migration of lithium ions and increase their capacity.

In such conventional techniques, in order to develop a desired crystal structure, it was considered desirable to make the grain size of the starting material as fine as possible and promote the reaction by firing.

[0004]

However, in an actual battery, it is also required to increase the packing density of the LiNiO ₂ powder as a means for increasing the capacity. In order to increase the packing density, it is required that the LiNiO ₂ powder has a proper particle size distribution and that each particle has a high density.
However, if the raw material particle size is too large at the firing temperature adopted in the conventional technique, the synthesis of the LiNiO ₂ crystal phase becomes insufficient, so the raw material particle size is made fine. As a result, there is a problem that the density of the LiNiO ₂ particles obtained by firing becomes low because the filling of the raw material powder becomes low.

The problem to be solved by the present invention is that LiN
In order to increase the charge / discharge capacity per volume in a non-aqueous lithium secondary battery using iO ₂ as a positive electrode active material, a method for producing LiNiO ₂ powder having a high packing density is being developed.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have defined the particle size of nickel powder as a starting material, and determined the lithium component by water and an organic acid. It was found that by mixing, a LiNiO ₂ powder having a high charge / discharge capacity and a high packing density can be obtained.

That is, according to the present invention, firstly, the average particle size is 10
A nickel compound composed of secondary or more agglomerated particles having a diameter of not more than 0 μm and not less than 5 μm is suspended in an aqueous solution containing lithium ions and an organic acid and then dried, and the dried product is subjected to an oxidizing atmosphere. Li characterized by firing in
A NiO ₂ positive electrode active material and a method for producing the same are provided. Secondly,
A LiNiO ₂ positive electrode active material using one or more nickel compounds selected from the group consisting of nickel hydroxide, nickel oxide, nickel oxyhydroxide, and nickel carbonate as the nickel compound, and a method for producing the same.

[0008]

In general, nickel salt and lithium salt are used as raw materials for producing LiNiO _2. However, since these are produced in industrial quantities, the raw material cost can be kept low, and thus they have been conventionally used. It was Among nickel raw materials, nickel hydroxide is most often produced.
In addition, nickel oxide obtained by heat-treating nickel hydroxide and subjecting it to dehydration and nickel oxyhydroxide are also used, but the production amount of these is smaller than that of nickel hydroxide.

The nickel raw material is generally supplied as a powder composed of secondary particles in which very fine primary particles are aggregated. The size of the primary particles is about 0.1 μm, and the size of the secondary particles is 1 mm or more when the size is extremely large, and conversely, the size of the small particles is about 10 times the size of the primary particles, 1 μm.
It is a degree. The filling of the primary particles in the secondary particles is often 50% or more.

In the conventional method, the nickel raw material and the lithium raw material were mixed in an organic solvent. However, since it was considered desirable that the particle diameters of these raw materials be 1 μm or less, pulverization was performed at the same time as mixing. It was The purpose is to enhance the reactivity during firing by finely and uniformly dispersing and mixing both nickel and lithium components,
This was to ensure that the resulting LiNiO ₂ powder had a homogeneous crystal structure.

However, as a result of the pulverization process, the raw material mixed powder of nickel and lithium has a drawback that the density is extremely low. For example, the density at the time of pulverization was about 0.3 g / cc, and even after the pressure treatment, it was only about 1.0 g / cc.

Even if these pulverized raw materials were used and fired at a normal firing temperature of 750 ° C., they could not be sintered at a high density in this temperature range, so that the low density before sintering was maintained as it was. .

The present invention solves the above-mentioned drawbacks of the prior art, and increases the packing density regardless of the firing conditions.
A nickel raw material having a coarse secondary particle diameter was used, and the particle diameter was maintained in the subsequent steps. On the other hand, if the particle size is large, the reactivity with the lithium component decreases, so an effective mixing method for preventing this has been devised as shown below.

In the method of the present invention, the starting material used is secondary particles of a nickel compound, the average particle size of which is 100 μm.
It is preferably in the range of 5 μm or more without exceeding m. This can be obtained by classifying a commercially available reagent with a screen finer than 150 mesh. As the lithium raw material, lithium hydroxide is sufficient in view of cost and the like, but lithium carbonate or a lithium salt of an organic acid can also be used.

Nickel raw material particles having an average particle diameter within the above range are suspended in an aqueous solution of lithium hydroxide and an organic acid typified by citric acid while stirring with a stirrer. At this time, as in the conventional method. The use of media should be avoided. Next, the suspension is concentrated or dried by heating or reducing the pressure. In the conventional method, an organic solvent was used to prevent the dissolution or segregation of the lithium salt, but in this method, an aqueous solution of an organic acid is used, so it is not necessary to take explosion-proof or toxicity measures, and is suitable for industrial production.

Concentrating and drying a plurality of elements using water and an organic acid is known as a complex polymerization method or an organic acid gelation method. This is because the starting materials are all dissolved in water with a large excess of organic acid represented by carboxylic acid, and after passing through the state of an aqueous solution of the raw material element, the organic acid is polymerized and gelled, and the reaction between the polymer and the raw material element Is the way. as a result,
It is said that the raw material elements are incorporated in the structure of the organic polymer in the form of ions, so that the plurality of elements are homogeneously dispersed and fine powder is obtained, which is effective for the substance synthesis.

The point that the method of the present invention is fundamentally different from the above method is that one of the two or more raw materials must not be dissolved in water. The term "one kind" as used herein refers to a nickel raw material, and since it is necessary to maintain the particle morphology in the subsequent steps, a water-soluble nickel raw material cannot be used as a raw material. Further, the nickel raw material cannot be dissolved by making the aqueous solution strongly acidic with a large excess of organic acid.

The purpose of using the organic acid in the method of the present invention is as follows. Generally, in the method of mixing with lithium in water, a highly soluble lithium salt segregates during the drying and coarsely grows, so that a desirable crystal structure cannot be naturally obtained. On the other hand, the organic acid increases the viscosity of the aqueous solution as the water content decreases due to drying, and also prevents the segregation and growth by forming a lithium salt. It has a function of mechanically protecting the nickel raw material particles and preventing the fineness of the particles until the organic matter is decomposed on the way.

The dried product obtained in the present invention is in the form of mortar or resin, and these are then heated in an oxidizing atmosphere, preferably in an oxygen stream, under known firing conditions (firing temperature 750).
Heat treatment is carried out at a temperature of about 10 to 30 hours) to obtain a lump having a black appearance.

A differential thermal analysis of the mixed powder in the above-mentioned step shows that the endothermic peak is observed at around 700 ° C., although the value does not become constant depending on the type of raw material used and the process conditions. When the temperature is lower than this temperature, the deterioration of the cycle characteristics is remarkably observed, which is considered to be due to the undeveloped suitable crystal structure.

From these facts, it is preferable that the heat treatment is performed at a temperature higher than the temperature at which the above endothermic peak appears.
It is considered that the proper heat treatment temperature is not lower than the temperature of the endothermic peak of the thermal analysis result and not higher than about 750 ° C.

Next, the lumps are crushed and classified to obtain a positive electrode active material. Generally, the active material powder for a positive electrode material for a battery is empirically used in terms of filling property and discharge prevention property during storage. It is said that the average particle size of the particles is preferably 50 μm or less and 5 μm or more. Therefore, in the present invention, LiNiO
_{Even in} the production of ₂ powders, the maximum shrinkage rate due to firing (must be expected regardless of the quantity) is 50%
If so, the average diameter of the starting nickel compound is 10 at maximum.
It should be 0 μm, on the contrary, if there is no firing shrinkage, at least 5
The average particle size is preferably 10 to 30 μm.

In place of the above firing, a pulverized product of the dried product or a powder calcined at a temperature lower than the firing temperature may be pressure-molded and then fired. However, even in that case, pulverizing the particles of the nickel raw material into fine particles makes the purpose of the present invention meaningless.

In the firing temperature range suitable for ensuring the battery capacity,
LiNiO ₂ has an insufficient degree of sintering for increasing the density, which means that the degree of bonding between the LiNiO ₂ particles is low. Therefore, the crushing is easy, and it is possible to prevent the LiNiO ₂ particles based on the nickel raw material particles from becoming fine in the final stage and lowering the packing property, and at the same time, suppressing the reduction in shrinkage due to classification.

In addition, it is also considered to improve the battery characteristics by slightly changing the component ratio of nickel and lithium. Even if the molar ratio of the lithium raw material to the nickel raw material is not exactly Li / Ni = 1/1, if Li / Ni = 1 ± 0.05 / 1, the Li / Ni battery characteristics It is known that the same effect as that of = 1/1 can be obtained.

The capacity of the battery in the present invention was evaluated by the following method. The LiNiO ₂ powder obtained by the above method was used as a positive electrode active material, Ketjen black as a conductive agent, and polytetrafluoroethylene (PTFE) as a binder in a weight ratio of 8: 1. The mixture was kneaded at a ratio of 1: 1, and pressure-molded at a rate of 2 t / cm ² into a disk having a diameter of 37 mm. The obtained molded body was formed into the positive electrode body 4 of the test cell shown in FIG. 1, while the negative electrode 7 in the figure was prepared by cutting out a lithium metal plate (thickness 0.7 mm).
Propylene carbonate (PC) and 1, 2 as electrolyte
-0.5 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solution of dimethoxyethane (DME) at a volume ratio of 1: 1.
l The one dissolved at a concentration was used.

The discharge capacity was determined using the secondary battery shown in FIG. 1, and the value obtained by this is the capacity per weight, and the capacity per capacity is shown in consideration of the filling property. There is a need. The filling property is evaluated by using the tap bulk density, which is a general evaluation method of powder properties, and the capacity per volume is determined by using the product of the tap bulk density and the capacity obtained by the above method as an index. Further, the decrease in discharge capacity due to repetition was also described, and the durability as a secondary battery was relatively evaluated.

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

[0029]

[Example 1] Lithium hydroxide LiOH and average diameter 20 μm
Nickel hydroxide Ni (OH) ₂ in a molar ratio of Li / Ni
= 1/1, put these powders in water, and then add 5 parts of citric acid to nickel hydroxide.
0 wt% was added, and the mixture was dried at 60 ° C with stirring. Next, the dried product was lumped to a size of about 2 cm, heat-treated in an oxygen stream at 740 ° C. for 20 hours, and the calcined product was crushed in a mortar to obtain a powder of 150 mesh or less. The average diameter was 16 μm.

When the obtained powder was subjected to XRD measurement, a pattern having the same shape as that of LiNiO ₂ reported hitherto was obtained as shown in FIG. The bulk density of this powder is 2.53.
It was g / cc and was 51% with respect to the theoretical density of 5 g / cc. Generally, the relative density increases as the average particle size increases, but rarely exceeds 70%, and it was confirmed that the LiNiO ₂ powder obtained in this example has the same tendency.

The LiNiO ₂ powder obtained by the above method was used as a positive electrode active material, and Ketjen black as a conductive agent and polytetrafluoroethylene (PTFE) as a binder were added thereto in a weight ratio. The mixture was added at a ratio of 8: 1: 1, kneaded, and subjected to a pressure of ² t / cm ² to form a disk-shaped pressure-molded body having a diameter of 37 mm to obtain a positive electrode plate.

Next, the positive electrode plate was used as the positive electrode 4 of the test cell which is the lithium secondary battery shown in FIG.
A disk formed by cutting out a lithium metal plate (thickness 0.7 mm) was used as the negative electrode plate. For the separator 5, a polypropylene film cut out is used, and the electrolyte solution is propylene carbonate (PC).
1,2-dimethoxyethane (DME) in a volume ratio of 1: 1
Lithium hexafluorophosphate (LiPF
₆ ) was dissolved at a concentration of 0.5 mol / l was used. still,
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, 8 is a negative electrode current collector,
Reference numeral 9 represents a cell fixing screw, 10 represents an electrolytic solution injection plug, and 11 represents a negative electrode lead wire.

Next, as a result of assembling these as the test cell of FIG. 1 and conducting a charge / discharge test, as shown in FIG. 3, the most excellent charge capacity value of the secondary battery reported in the prior art of 190 mAh / g was obtained.

Similarly, nickel hydroxide as a starting material having an average particle size of the values shown in Table 1 was used to form a positive electrode active material by the above-mentioned production method, and the discharge capacity, bulk density and product of each were obtained. The index and the capacity decrease due to repetition were determined, and the results are also shown in Table 1. From these results, the average particle size of the secondary aggregate as the starting material is 100 μm.
It has been found that those having a thickness of 5 μm or less do not exceed the object of the present invention.

[0035]

[Table 1]

An SEM photograph showing the particle structure when a nickel hydroxide raw material having a particle size of 42 μm is used is shown in FIG. 4, and an SEM photograph showing the particle structure of the LiNiO ₂ powder thus obtained is shown. 5 shows.

[0037]

Example 2 Lithium hydroxide monohydrate LiOH.H ₂ O
And nickel oxide (NiO) having an average particle size of 30 μm obtained by heat-treating nickel hydroxide at 300 ° C., in a molar ratio, Li / Ni = 0.97 / 1 and Li / Ni = 1.0
Each of them was weighed so as to be 3/1, 60% by weight of citric acid was added to the total amount of lithium and nickel, and the mixture was mixed in water at 90 ° C. for 4 hours and then cooled.

Then, the cooled product was taken out of the stirring container, crushed to 10 mm or less, sufficiently dried, and then dried in an oxygen stream to 7 mm.
Heat treatment was performed at 30 ° C. for 15 hours to obtain LiNiO ₂ powder having an average particle size of 17 μm.

XRD measurement of the obtained LiNiO ₂ powder gave the same XRD pattern as that of FIG. 2 shown in Example 1. In addition, each of the above starting composition ratios of LiNiO
_Two powders were used to form a positive electrode molded body by the means shown in Example 1, and the mixture was incorporated into the test cell shown in FIG. As a result, it was found that the discharge capacity was almost the same as that of the conventional product.

[0040]

[Table 2]

[0041]

Example 3 Similarly, LiOH and basic nickel carbonate having an average particle size of 15 μm were weighed so that the molar ratio was Li / Ni = 1/1, and dried under the same conditions as in Example 1. Then, the obtained mass was calcined in the air at 450 ° C., cooled, and then cooled to 0.
After press-molding at a pressure of 5 ton / cm ² into a disk-shaped molded body having a diameter of 20 mm and a thickness of 2 mm, the molded body was fired in an oxygen stream atmosphere at 750 ° C. for 15 hours in a firing furnace.
The disc was crushed to obtain a powder having an average diameter of 9 μm. When the obtained LiNiO ₂ powder was measured by XRD, the same XRD pattern as that of FIG. 2 shown in Example 1 was 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. As a result, as shown in FIG. 6, the charge capacity at the first cycle was 206 mAh / g.
The discharge capacity was 196 mAh / g, and the charge / discharge capacity was around 180 mAh / g after the second cycle. The bulk density was 2.11 g / cc, the product was 413, and the capacity loss due to repetition was 26% after 10 times.

[0042]

Comparative Example 1 Similar to 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 and mixed in ethanol for 50 hours to obtain a powder having an average particle size of about 2 μm. The pulverized product was heat-treated in an oxygen stream at 750 ° C. for 24 hours to obtain LiNiO ₂ powder.

XRD measurement of the obtained LiNiO ₂ powder showed the same results as in FIG. 2 in Example 1. However, when the powder was observed by SEM photograph, as shown in FIG. It was only about 1 μm.

Using this powder, a test cell shown in FIG. 1 was prepared in the same manner as in Example 1, and the charge / discharge amount was measured. As a result, as shown in FIG. 8, only 146 mAh / g was obtained. Also, the bulk density is 1.20 g / cc, the product index is 175,
The capacity loss due to repetition was 66% after 10 times.

[0045]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, an ideal LiNiO ₂ powder is obtained by using a nickel compound in which the particle size of the secondary particles is limited to the range of 5 μm or more without exceeding 100 μm as a starting material. By using it as a positive electrode active material, it has become possible to manufacture a lithium secondary battery having a high discharge capacity and a high filling property.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a test cell used for a performance measurement test of a positive electrode active material or a positive electrode plate according to the present invention.

_{2 is} the XR of LiNiO ₂ prepared in Example 1. FIG.
It is D (X-ray diffraction pattern).

3 is a charge / discharge curve of the test cell manufactured in Example 1. FIG.

FIG. 4 is an SEM photograph showing a particle structure of Ni (OH) ₂ used in Example 1.

5 is an SEM photograph showing the particle structure of LiNiO ₂ obtained in Example 1. FIG.

6 is a charge / discharge curve of the test cell manufactured in Example 3. FIG.

FIG. 7 is an SEM photograph showing a particle structure of LiNiO ₂ obtained in Comparative Example 1.

8 is a charge / discharge curve of the test cell manufactured in Comparative Example 1. FIG.

[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

Front Page Continuation (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 Dowa Mining Co., Ltd. In-house (72) Inventor Katsuaki Okabe 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (2)

[Claims] 1. LiN using a lithium compound as a lithium raw material and a nickel compound as a nickel raw material
In the method for producing the iO ₂ powder, the secondary particles of the nickel compound, which is one of the starting materials, has an average diameter of 10 or more.
The nickel compound was adjusted to have a size in the range of 5 μm or more without exceeding 0 μm, the nickel compound was suspended and stirred in an aqueous solution containing lithium ions and an organic acid, and then the dried product was oxidized. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, which comprises forming a LiNiO ₂ powder by firing in a neutral atmosphere. 2. The nickel compound is nickel hydroxide,
The method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to claim 1, which is at least one nickel compound selected from the group consisting of nickel oxide, nickel oxyhydroxide, and nickel carbonate.