JPH10310433A - Production of nickel hydroxide, nickel oxide and positive electrode active material for lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nickel multiple oxide with which a positive electrode active material for a lithium secondary cell can be produced to improve cell characteristics such as discharge capacity by using a hydroxide essentially comprising nickel which has a specified range of halfwidth of the peak near a specified angle in the X-ray diffraction profile using CuKα line. SOLUTION: The hydroxide essentially consists of nickel and has 0.1 to 0.60 deg. halfwidth of the peak near 19 deg. angle, 0.1 to 0.50 deg. halfwidth of the peak near 38 deg., and 0.1 to 0.65 deg. halfwidth of the peak near 52 deg. in the X-ray diffraction profile using CuKα line. The compsn. of the hydroxide is preferably expressed by Ni1-x Mx O2-y H2-z (0.01<=x<=0.5; 0<=y<=0.5; 0<=z<=1.5; M is Co, Mn, Al, Fe). The hydroxide is preferably produced by crystallizing method and is obtd. by continuously dropping a metal salt soln. and an alkali hydroxide soln. in pH 8 to 13 range at >=0 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a positive electrode active material for a lithium secondary battery with the aim of improving characteristics, and more particularly to a raw material for a positive electrode active material.

[0002]

2. Description of the Related Art Lithium-ion batteries have attracted attention in recent years with demands for higher capacity and higher energy density of secondary batteries. L as a positive electrode active material of a lithium ion battery
A lithium composite oxide represented by iCoO ₂ is mainly used. Powders of Co (OH) ₂ , Co ₃ O ₄ , metal Co and CoCO ₃ are used as raw materials used as a cobalt source of LiCoO ₂ , and a lithium composite oxide produced from these raw materials has a relatively low crystal structure. It is a positive electrode active material that is stable and exhibits good reversible characteristics.

However, Co contained in LiCoO ₂ is a rare metal and is very expensive.
CoO ₂ has a problem in that there is a limit to the increase in capacity since there is a limit on the amount of Li inserted and removed. For this reason, various lithium composite oxides containing a metal other than Co as a main component have been studied, for example, Li _1-x NiO ₂ (US Pat. No. 4,302,518), Li _x Ni _2-x O ₂ and L
iNi _1-x Co _x O ₂ (JP-A-2-40861) and L
i _y Ni _1-x Co _x O ₂ (Japanese Unexamined Patent Publication No.
No.) has been proposed. These relatively inexpensive LiNiO ₂ -based composite oxides containing Ni as a main component have been energetically developed.

However, it is difficult to produce LiNiO ₂ , and a slight shift in the production conditions causes a rock salt type structural phase to be mixed in, resulting in an extremely low discharge capacity. In addition, the crystal structure is easily broken during charge and discharge, and the cycle characteristics are not good. further,
It is hygroscopic. Attempts have been made to replace part of Ni with another element in order to alleviate such a problem. Although replacement of various elements has been studied, the cycle characteristics are improved, but the capacity is often reduced. It has been clarified that LiNi _1-x Co _x O _{2 in} which a part of Ni is replaced by Co has a small characteristic deterioration due to a charge / discharge cycle and a small capacity decrease.

[0005] As a main means for producing LiNi _1-x Co _x O ₂ , a method of mixing three kinds of raw materials of a nickel compound, a cobalt compound and a lithium compound at a predetermined ratio and firing the mixture is generally performed. It seems. According to such a method, it is difficult to produce a composite oxide in which Ni and Co are in a solid solution state in which a part of the atomic positions of Ni in the crystal structure is substituted with Co. By making the firing temperature relatively high, solid solution is likely to be possible, but a rock salt type structural layer is often mixed.
In order to avoid this problem, a method of mixing an organic acid salt, nitrate, hydroxide or the like co-precipitated from an aqueous solution in which a Ni salt and a Co salt are mixed with a lithium compound and firing the mixture is used. According to this method, Ni and Co form a solid solution in the coprecipitate, and a composite oxide in which Ni and Co form a solid solution can be obtained relatively easily. Method of coprecipitating hydroxide (Japanese Patent Laid-Open No. 8-3)
No. 99806) discloses that a composite oxide having complete substitution and solid solution can be synthesized, and a positive electrode active material having high capacity and excellent cycle characteristics can be produced.
When replacing Ni with an element other than Co, it is better to use hydroxide or the like coprecipitated with nickel as a raw material.
High-performance composite oxides are often obtained.

[0006]

As described above, as described above, LiN
When producing i _1-x Co _x O ₂ , if a hydroxide obtained by co-precipitating nickel and cobalt is used as a raw material, a relatively high capacity can be obtained. I can't say I have it. Furthermore, although the characteristics of the lithium composite oxide are greatly affected by the properties and shape of the metal salt used as the raw material, even when a hydroxide raw material is used, at present, any suitable property and shape of the hydroxide are appropriate. It is not clear. An object of the present invention is to provide a raw material for a nickel-based composite oxide that can be used for a positive electrode active material for a lithium ion battery that can improve battery characteristics such as discharge capacity.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, in the X-ray diffraction profile of hydroxide as a raw material, the half width of a specific diffraction It has been found that when in a certain specific range, a lithium composite oxide produced using this raw material exhibits excellent characteristics. That is, according to the present invention, in the X-ray diffraction profile using CuKα ray, the half width of the peak near 19 ° is 0.1 ° to 0.60 °, and the half width of the peak near 38 ° is 0.1 °. Lithium including nickel used as a positive electrode active material of a lithium secondary battery, wherein the half-width of a peak around 0.5 ° to 0.50 ° is in the range of 0.1 ° to 0.65 °. An object of the present invention is to provide a hydroxide mainly composed of nickel, which is a raw material of a composite oxide.

Here, the diffraction peaks around 19 °, 38 ° and 52 ° are (001), (101) and (1), respectively.
02) means diffraction on a surface that can be indexed. 19 °
When the half value width of the peak near 0.60 °, the half value width of the peak near 38 ° is 0.50 °, and the half value width of the peak near 52 ° is larger than 0.65 °, and the hydroxide is used as a raw material, The discharge capacity of the lithium composite oxide decreases. Of the above three peaks, one having a half width of less than 0.1 ° is extremely difficult to produce by crystallization or coprecipitation, and is not realistic in terms of low cost and mass production. More preferably, the half width of the peak around 19 ° is 0.1 ° to 0.55 °, the half width of the peak around 38 ° is 0.1 ° to 0.45 °, and the half width of the peak around 52 ° is 0.1 ° to 0.62 °.

In the present invention, the composition formula of the hydroxide or oxide used as the raw material of the lithium composite oxide containing Ni is N
i _1-x M _x O _2-y H _2-z (0.01 ≦ x ≦ 0.5, 0 ≦
y ≦ 0.5, 0 ≦ z ≦ 1.5, where M is Co,
It represents at least one element selected from the group consisting of Mn, Al and Fe. ) Is preferable. N
The ratio between i and M can be varied according to the required battery performance. In the substance, it is preferable that M and Ni form a solid solution, and M substitutes for Ni. In the composition formula, the values of y and z change according to the valence numbers of Ni and M, and may be in a state close to not only a hydroxide but also an oxyhydroxide.
Further, M is preferably Co which has a wide solid solution range and is easy to produce.

The hydroxide or oxide containing Ni of the present invention is in the form of a powder, and the powder preferably has a spherical or spherical-like aggregated appearance. In the case of powder having an irregular shape other than a spherical shape or a shape similar to a sphere, problems such as a decrease in packing density when firing into a lithium composite oxide occur. The hydroxide or oxide of the present invention preferably has a tap density of 1.9 g / ml or more.

The hydroxide which can be used as a raw material of the lithium composite oxide of the present invention is preferably produced by a crystallization method. That is, the metal salt solution and the alkali hydroxide solution can be obtained by continuously dropping the solution in a pH range of 8 to 13 at a temperature of 0 ° C. or higher. Depending on the conditions, a complex-forming agent such as ammonia or ethylenediamine may be used. As the metal salt, any of salts such as sulfate, nitrate, chloride, and organic acid salt, and a mixture of two or more kinds may be used.As the alkali hydroxide solution, sodium hydroxide, potassium hydroxide, and lithium hydroxide may be used. Can be used. Crystallization conditions vary depending on the type of metal salt or alkali solution used.

In the present invention, as a method for producing a positive electrode active material for a lithium ion secondary battery, a hydroxide mainly containing nickel of the present invention and a lithium compound are mixed, and this mixture is subjected to a pressure of 0.2 atm or more. 600-900 under oxygen partial pressure
Heat treatment is performed in a temperature range of ° C. When calcination is performed in an atmosphere in which the oxygen partial pressure is lower than 0.2 atm, a different phase such as a rock salt structural phase is mixed and the active material characteristics are reduced. The upper limit of the oxygen partial pressure is not particularly limited, but in order to make the oxygen partial pressure higher than normal pressure, a pressurizing device or the like must be used to increase the total pressure. Not preferred. A more preferable range of the oxygen partial pressure is 0.9 atm or more. The appropriate value of the heat treatment temperature differs depending on the oxygen partial pressure. However, even if the heat treatment temperature is less than 600 ° or more than 900 °, the heterogeneous phases are mixed together, so that the characteristics as the active material deteriorate.

When producing a lithium composite oxide containing Ni used as a positive electrode active material for a lithium ion secondary battery, a heat treatment is carried out after mixing a hydroxide mainly composed of nickel of the present invention with a lithium compound. It is also possible, and after mixing the hydroxide mainly composed of nickel of the present invention into an oxide or the like by heating or the like, mixing a lithium compound,
Heat treatment can also be performed. These methods can be properly used depending on the heat treatment apparatus to be used and the properties of the lithium compound to be mixed. The hydroxide of the present invention that has been subjected to treatment such as heating is preferably

An oxide represented by the following formula: Since the oxygen content varies depending on the average valence number of the metal element, δ is −
The value is in the range of 0.5 to 1.0.

By using the hydroxide or oxide of the present invention,
When preparing a lithium composite oxide containing i, there is no particular limitation on a lithium compound serving as a lithium source, and for example, lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, lithium phosphate, and the like can be used.

[0015]

The hydroxide mainly composed of nickel, which is the raw material of the lithium composite oxide of the present invention, has a small peak half width in the X-ray diffraction profile, particularly around 19 °, 38 °, 52 °. The half width at the vicinity is small. This half width reflects the size and crystallinity of the crystallite. Generally, the smaller the half width, the larger the crystallite and the better the crystallinity. Details are not clear,
It is presumed that when the raw material of the present invention is used, the characteristics of the lithium composite oxide improve due to the following.

The properties of lithium composite oxides are likely to be greatly affected by the properties and shapes of the metal compounds used as raw materials. For this reason, it is considered that the structure of the metal compound such as a hydroxide also affects the lithium composite oxide after firing. The hydroxide of the present invention is considered to have a more uniform solid solution of Ni and other elements because of the narrow half-width of X-ray diffraction. That is, it is considered that there is little variation in element concentration within one grain, and there is little variation in concentration in each grain. For this reason, it is considered that even after firing to the lithium composite oxide, variation in element concentration is small and variation in micro-capacity is also reduced, and a lithium composite oxide having high capacity and high characteristics can be obtained.

Furthermore, the characteristics of the composite oxide greatly depend on the half-width of the diffraction plane containing the component in the c-axis direction of the crystal, that is, the half-width of the diffraction plane expressed by (hk0) Since the dependence is not large, it is suggested that the hydroxide of the present invention grows sufficiently in the c-axis direction of the crystal and that stacking faults in the c-axis direction are small. The hydroxide mainly composed of nickel is hexagonal, and has a structure in which a metal atomic layer composed of nickel and its substituting element and an OH layer are laminated and stacked. Therefore, during precipitation by crystallization, etc.,
Grains grow preferentially in the direction parallel to the layer, that is, in the plane direction perpendicular to the c-axis of the crystal, forming a flat crystallite.

Since the hydroxide of the present invention is considered to have grown in the c-axis direction, the crystallite is considered to be relatively isotropic. For this reason, it is considered that the distribution of lithium in the grains of the composite oxide becomes more uniform when mixed with a lithium compound and subjected to heat treatment. Furthermore, since the crystallites of the composite oxide are also expected to be relatively isotropic, it is presumed that lithium can be inserted and removed more smoothly during charge and discharge when used as a positive electrode active material. .

Further, in the present invention, a hydroxide mainly composed of nickel and a lithium compound are mixed and heat-treated in an atmosphere having a high oxygen partial pressure. The reason is that if the oxygen partial pressure is high, the formation temperature range of the target lithium composite oxide is widened, and the reaction proceeds sufficiently because the atom diffusion during the reaction is driven at a somewhat lower temperature. Conceivable.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) A nickel sulfate solution and a cobalt sulfate solution were
An aqueous solution with a metal component concentration of 0.8 mol / liter was prepared by mixing i: Co at a molar ratio of 8: 2. The mixture was heated to 50 ° C., and the above-described metal salt solution and aqueous ammonia were added dropwise to a tank whose pH was adjusted to 9.7, 10.3, 10.6, and 11.0 by dropwise addition of an aqueous sodium hydroxide solution. A slurry containing four kinds of hydroxides was obtained.
These slurries were filtered, immersed in an aqueous sodium hydroxide solution to remove SO ₄ , filtered again, and dried at 90 ° C. in the atmosphere to obtain four kinds of hydroxide powders.

With respect to these hydroxides, the divergence slit was reduced to 1/2 at 40 KV and 250 mA using a CuKα radiation source.
°, scattering slit 1.2 °, receiving slit 0.15
mm, the sampling time was set to 1.00 seconds, and the step width was set to 0.01 °, and an X-ray diffraction profile was obtained using a rotating sample stage. Judging from the profiles, all materials were single-phase. Taken together, the results of elemental analysis, the resulting material is equivalent to a composition formula _{Ni 0. 8 Co 0.2 (OH)} 2. The diffraction profiles of these samples at 19 °, 33 °
°, 38 °, 52 °, and 59 °, that is, (001), (101), (100), (102),
When the half width was calculated for the peak indexable as (110), it was as shown in FIG. The half width was calculated by smoothing, background removal, and Kα2 removal. In addition, scanning electron microscope observation revealed that the particles of the raw material powder were spherical or nearly spherical in all samples.

These samples were weighed and mixed with lithium hydroxide so that the molar ratio of Ni + Co: Li was 1: 1.003, and then mixed in an oxygen stream at 400 ° C. for 1 hour and 70 hours.
Heat treatment was performed at 0 ° C. for 10 hours to obtain a lithium composite oxide powder. The oxygen partial pressure during heating at 700 ° C. was 0.99 atm. As a result of the same X-ray diffraction as described above, the obtained oxide was in a single phase, and it was determined that a composite oxide represented by LiNi _0.8 Co _0.2 O ₂ was synthesized. This oxide powder was mixed with acetylene black and polytetrafluoroethylene, and the mixture was pressurized at ² ton / cm ² to have a diameter of 20 mm.
To form a positive electrode. Lithium rolled plate with diameter 2
Punched into 0 mm to form a negative electrode, lithium perchlorate was dissolved at a concentration of 1 mol / l in a mixture of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 to form an electrolyte, and a polypropylene film was used as a separator. A test battery as shown in FIG. 2 was prepared by using and sealing in a stainless steel container.

(Comparative Example 1) The pH of an aqueous reaction solution was 11.3,
A hydroxide was prepared under substantially the same conditions as in Example 1 except that it was 11.6, and a test battery was prepared in the same manner as in Example 1 except that the half widths of the five X-ray diffraction peaks were as shown in Table 1. Produced. For the batteries prepared in Example 1 and Comparative Example 1, the charging current was 1
A charge / discharge test was performed in which constant current charging was performed at a mA of 4.2 V and a constant current of 3.2 mA, and constant current discharging was performed at a discharge current of 3 mA and a final voltage of 3.0 V.

[Table 1]

Example 2 A nickel sulfate solution, a cobalt sulfate solution and aluminum sulfate were mixed so that the molar ratio of Ni: Co: Al was 85: 13: 2, and the metal component concentration was 0.8 mol / liter. An aqueous solution was prepared. 5
The slurry was heated to 0 ° C., and a slurry containing hydroxide was obtained by dropping the above-mentioned metal salt solution and aqueous ammonia into a tank whose pH was adjusted to 10.6 by dropping a sodium hydroxide solution. These slurries were filtered, immersed in a sodium hydroxide solution to remove SO ₄ , filtered again, and dried in air at 90 ° C. to obtain a hydroxide powder.

With respect to these hydroxides, the divergence slit was reduced to 1/2 at 40 KV and 250 mA using a CuKα radiation source.
°, scattering slit 1.2 °, receiving slit 0.15
mm, the sampling time was set to 1.00 seconds, and the step width was set to 0.01 °, and an X-ray diffraction profile was obtained using a rotating sample stage. Judging from the profile, it was single phase. The diffraction profiles of these samples at 19 °, 33 °
°, 38 °, 52 °, and 59 °, that is, (001), (101), (100), (102),
Table 2 shows the half value width of the peak indexable as (110). In addition, smoothing, background removal, and Kα2 removal were performed for the calculation of the half width. In addition, scanning electron microscope observation revealed that the particles of the raw material powder had a spherical shape or a shape close to a sphere. This sample was prepared at a molar ratio of Ni + Co + Al: Li of 1: 1.0.
After weighing and mixing lithium hydroxide so as to be 03, heat treatment was performed in an oxygen stream at 400 ° C. for 1 hour and at 700 ° C. for 10 hours to obtain a lithium composite oxide powder. 7
The oxygen partial pressure during heating at 00 ° C. was 0.99 atm.

[0026] obtained for the oxide described above and similar X-ray diffraction result, a single-phase, LiNi _0.85 Co _0.13 Al
It was determined that a composite oxide considered to be represented by _0.02 O ₂ was synthesized. This oxide powder was mixed with acetylene black and polytetrafluoroethylene, and 2 ton /
It was pressurized at ² cm ² and formed into a disc having a diameter of 20 mm to obtain a positive electrode. A lithium rolled plate was punched out to a diameter of 20 mm to form a negative electrode. Lithium perchlorate was mixed with 1 m of a mixture of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1.
A test battery as shown in FIG. 2 was prepared by dissolving at a concentration of ol / liter to make an electrolyte, using a polypropylene film as a separator, and enclosing in a stainless steel container.

Comparative Example 2 A hydroxide was prepared under substantially the same conditions as in Example 2 except that the pH of the reaction solution was changed to 11.3.
A test battery was prepared in the same manner as in Example 1, except that the half-widths of the five X-ray diffraction peaks were as shown in Table 1. The batteries prepared in Example 2 and Comparative Example 2 were subjected to a charge / discharge test in which constant current charging was performed at a charging current of 1 mA and a final voltage of 4.2 V, and constant current discharging was performed at a discharge current of 3 mA and a final voltage of 3.0 V. Was. Table 2 shows the relationship between the half width of the five peaks and the discharge capacity at the tenth cycle. (001), (101), (10
The sample having a small half width in 2) has a large discharge capacity. Further, it can be seen that the (100) and (110) peaks have little correlation between the half width and the characteristics.

[Table 2]

(Example 3) The oxide (Ni _0.8 Co _0.2 ) ₃ O _{4- of} the hydroxide mainly composed of Ni of the sample 2 of Example 1 was heated at 400 ° C. for 10 hours in the air. δ
Was prepared. The oxide powder thus obtained was converted to Ni +
Lithium carbonate was weighed and mixed so that the molar ratio of Co: Li became 1: 1.003, and then mixed at 400 ° C. in a carbon dioxide stream.
For 1 hour and at 700 ° C. for 10 hours to obtain a lithium composite oxide powder. The oxygen partial pressure during heating at 700 ° C. was 0.99 atm. The obtained oxide was in a single phase as a result of the same X-ray diffraction as described above, and was LiNi _0.8 Co _0.2 O
It was determined that the composite oxide represented by ₂ was synthesized.
When a battery was prepared and measured for this composite oxide in the same manner as in Example 1, the discharge capacity was 178 mAh / g.

(Comparative Example 3) The hydroxide mainly composed of Ni of Sample 6 of Comparative Example 1 was heated in the air at 400 ° C. for 10 hours to form an oxide (Ni _0.8 Co _0.2 ) ₃ O _4- δ
Was prepared. The oxide powder thus obtained was converted to Ni +
Lithium carbonate was weighed and mixed so that the molar ratio of Co: Li was 1: 1.003, and then 400 ° C. in an oxygen stream.
For 1 hour and at 700 ° C. for 10 hours to obtain a lithium composite oxide powder. The oxygen partial pressure during heating at 700 ° C. was 0.99 atm. When a battery was prepared and measured for this composite oxide in the same manner as in Example 1, the discharge capacity was 15
It was 5 mAh / g. From the above, it can be seen that even when the heating step is changed, a higher discharge capacity can be obtained by using a hydroxide having a smaller half-value width of X-ray diffraction as a raw material hydroxide.

[0030]

As described above, the discharge capacity of the lithium composite oxide depends on the half width of the peak of the specific X-ray diffraction profile of the raw material hydroxide. By using, as a raw material, a hydroxide mainly composed of nickel having a half value width in a relatively low range of the present invention, a high capacity lithium composite oxide for a positive electrode active material can be obtained.

[0031]

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a half width of five X-ray diffraction peaks and a discharge capacity.

FIG. 2 is a sectional view of a test battery used in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sealing can 2 Lithium negative electrode 3 Insulation packing 4 Positive electrode can 5 Positive electrode pellet 6 Separator

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takao Yaginuma 4017 Ushigome, Shirako-cho, Nagao-gun, Chiba Prefecture Inside Ise Chemical Industry Co., Ltd.

Claims (8)

[Claims] In an X-ray diffraction profile using CuKα radiation, the half width of a peak near 19 ° is 0.1 ° to 0.60 °, and the half width of a peak near 38 ° is 0.1 ° to 0.1 °. Nickel for a lithium composite oxide, which is a positive electrode active material of a lithium secondary battery, wherein the half width of a peak near 0.50 ° and 52 ° is in the range of 0.1 ° to 0.65 °. A hydroxide mainly composed of. 2. An oxide obtained by heating the hydroxide of claim 1. 3. The composition formula is Ni _1-x M _x O _2-y H _2-z
(0.01 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦
2. The method according to claim 1, wherein 1.5 M is one or more elements selected from Co, Mn, Al and Fe.
Hydroxide mainly composed of nickel. 4. A composition obtained by subjecting the hydroxide of claim 1 to a heat treatment is represented by the following formula: An oxide represented by the formula: 5. A mixture of a hydroxide mainly composed of nickel according to claim 1 or 3 and a lithium compound, and heat treating the mixture at a partial pressure of oxygen of 0.2 atm or more at a temperature of 600 to 900 ° C. A method for producing a positive electrode active material for a lithium ion battery. 6. The oxide according to claim 2 or 4, wherein the oxide mainly comprising nickel and a lithium compound are mixed, and this mixture is heat-treated at a partial pressure of oxygen of 0.2 atm or more in a temperature range of 600 to 900 ° C. A method for producing a positive electrode active material for a lithium ion battery. 7. A lithium ion battery comprising the positive electrode active material obtained by the method according to claim 5. 8. A method for producing nickel hydroxide, comprising continuously dropping a metal salt solution and an alkali hydroxide solution at a pH of 8 to 13 in a temperature range of 0 ° C. or higher.