JP3770569B2 - Lithium composite oxide, method for producing the same, and positive electrode active material for lithium secondary battery - Google Patents

Description

【００３５】
【表２】
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回折装置 ＲＩＮＴー２４００（理学電機社製）
Ｘ線管球 Ｃｕ
管電圧・管電流 ５０ｋＶ，２００ｍＡ
スリット ＤＳーＳＳ：１度，ＲＳ：０．１５ｍｍ
モノクロメータ グラファイト
測定間隔 ０．０２度
計数方法 定時計数法
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【００３６】
【発明の効果】
本発明のリチウム複合酸化物をリチウム二次電池用正極活物質として正極板に用いることにより、初期放電容量および放電保持率に優れ、高エネルギー密度を与えるリチウム二次電池を得ることができる。
また、本発明のリチウム複合酸化物の製造方法は、簡易な方法であるため工業的にも有利である。
【図面の簡単な説明】
【図１】本発明の実施例１におけるリチウム複合酸化物のＸ線回折パターンを示す図である。
【図２】本発明の実施例２におけるリチウム複合酸化物のＸ線回折パターンを示す図である。
【図３】図２のＸ線回折におけるｈｋｌ（１，０，８）及びｈｋｌ（１，１，０）部分の拡大図である。
【図４】本発明の実施例４におけるリチウム複合酸化物のＸ線回折パターンを示す図である。
【図５】従来（比較例１）のリチウム複合酸化物のＸ線回折パターンを示す図である。
【図６】本発明のリチウム二次電池を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium composite oxide and a method for producing the same, and further relates to a positive electrode active material for a lithium secondary battery, a lithium secondary battery positive electrode plate, and a lithium secondary battery having excellent energy density.
[0002]
[Prior art]
2. Description of the Related Art In recent years, lithium secondary batteries have been put into practical use as power sources for small electronic devices as consumer electronic devices have become increasingly portable and cordless. Regarding this lithium secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium secondary batteries ["Material Research Brain" vol 115, P783-789 (1980)]. Since then, research and development on lithium (Li) -based composite oxides has been actively encouraged, and many proposals have been made so far.
For example, Li _1-x Ni O ₂ (where 0 ≦ x ≦ 1) (US Pat. No. 4,302,518), Li _y Ni _2-y O ₂ (Japanese Patent Laid-Open No. 2-40861), Li _y A composite oxide mainly composed of lithium and a transition metal such as Ni _x Co _1-x O ₂ (where 0 <x ≦ 0.75, y ≦ 1) (Japanese Patent Laid-Open No. 63-299056) is typically used. Can be mentioned.
[0003]
[Problems to be solved by the invention]
In the above compounds, lithium cobaltate is relatively easy to synthesize and has excellent electrical characteristics, so it has been studied as a positive electrode material for lithium secondary batteries from the earliest, but the raw material cobalt (Co) is rarely produced. In addition to being expensive, there is a drawback that charging of 0.7 electrons or more causes a decrease in crystallinity and decomposition of the electrolytic solution, which is not suitable for increasing the capacity.
On the other hand, Li Ni O ₂ has an advantage that it is cheaper than cobalt, but it tends to cause defects during use as a positive electrode material of a battery, and therefore the capacity characteristics are inferior to that of Co, such as lack of battery stability. It was thought. Therefore, as much as possible stoichiometric lithium composite oxide a portion near Li Ni O _2, and nickel (Ni) to the ratio obtained by substituting other transition metals and their synthesis have been studied.
[0004]
However, the present invention has not yet found an industrial production method as well as a material that can be satisfactorily applied as a positive electrode material of a lithium secondary battery.
[0005]
Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery that is excellent in initial discharge capacity and discharge retention rate and provides a high energy density, and a method for producing the same.
[0006]
[Means for Solving the Problems]
Under such circumstances, the present inventors have conducted intensive research on a lithium composite oxide that is stable as a positive electrode material that does not cause crystal defects in the compound and a method for producing the same. The half width of the diffraction peak of (0, 0, 3) is 0.3 or less, and the height b of the diffraction peak of hkl (1, 1, 0), hkl (1, 0, 8) and hkl (1 , 1, 0) The lithium composite oxide having a ratio c of the distance a from the base where the diffraction peaks intersect with each other is 2 or less is used as a positive electrode active material of a lithium secondary battery. The present inventors have found that a high energy density with excellent retention is provided, and have completed the present invention.
[0007]
That is, the present invention provides the following general formula (1):
Li _x Ni _1-y Co _y O ₂ (1)
(Where 0 <x <1.1 and 0 ≦ y ≦ 1)
The half-width of the diffraction peak of hkl (0,0,3) by X-ray diffraction is 0.3 or less and the diffraction peak of hkl (1,1,0) The ratio c between the height b of h and the distance a from the base at which the diffraction peaks of hkl (1, 0, 8) and hkl (1, 1, 0) intersect is c = b / a ≧ 2 (2)
A lithium composite oxide is provided.
[0008]
The present invention also provides a lithium composite oxide having an oxygen occupancy ratio of 95% or more by Rietveld analysis by powder X-ray diffraction.
[0009]
Further, the present invention is characterized in that Ni salt crystal particles or Ni-Co salt crystal particles of Ni and Co are mixed with Li salt having a particle size of 350 μm or less of 80% or more, and then calcined. General formula (1)
Li _x Ni _1-y Co _y O ₂ (1)
(Where 0 <x <1.1 and 0 ≦ y ≦ 1)
The manufacturing method of the lithium composite oxide represented by these is provided.
[0010]
Furthermore, the present invention provides a positive electrode active material for a lithium secondary battery comprising the above lithium composite oxide as a main material, a positive electrode plate for a lithium secondary battery comprising the positive electrode material, and a lithium secondary battery using the same. It is to provide.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The lithium composite oxide represented by the general formula (1) of the present invention is characterized by a peak obtained from a chart measured by X-ray diffraction. That is, the characteristics are the half width of the diffraction peak of hkl (0,0,3), the height b of the diffraction peak of hkl (1,1,0), hkl (1,0,8) and hkl (1 , 1, 0) is a ratio c to a distance a from the base at which the diffraction peaks intersect.
Regarding the half width and the c value of the above formula (2), such a numerical range is necessary from the viewpoint of the crystal structure, particularly the solid solution state of Li, Ni, and Co. 02 to 0.25, and the preferred range of the c value is 2 to 6.
[0012]
Further, the lithium composite oxide of the present invention has an oxygen occupancy ratio of 95% or more by a Rietveld analysis method by powder X-ray diffraction.
The Rietveld analysis method by X-ray diffraction is a method described in the document “Material analysis by powder X-ray diffraction” (pages 108 to 122, June 1, 1993, issued by Kodansha Scientific), etc. The functions such as lattice constants and structural parameters of all pattern data of powder X-ray diffraction are refined and analyzed. The oxygen occupancy is the occupancy at the 6c site of the lithium composite oxide represented by the general formula (1) belonging to the R-3m space group. The procedure of the Rietveld analysis method is as shown in the evaluation method described later. When the battery characteristics of the lithium composite oxide were evaluated by this Rietveld analysis method, a correlation was found between the value of the oxygen occupancy by the Rietveld analysis and the initial discharge rate. When the oxygen content was less than 95%, The initial discharge capacity is significantly adversely affected.
[0013]
The compositional characteristic of the lithium composite oxide in the present invention is represented by the above general formula (1), and the compounding ratio is such that the atomic ratio of Li, Ni, and Co is x (Li), 1-y (Ni), respectively. ) And y (Co) (where 0 <x <1.1, 0 ≦ y ≦ 1). For example, the blending ratio is preferably set to around 1 as the ratio Li / (Ni alone or Ni and Co content), but it may have some width around the blending ratio of 1 depending on raw material properties and firing conditions. Specifically, it is preferably in the range of 0.99 to 1.10.
[0014]
Furthermore, the atomic ratio of Ni to Co (Ni: Co) is in the range of 0: 1 to 1: 0, but considering the economics, the amount of Co is better and 1: 0 to The range of 0.6: 0.4 is preferable. Such a Li-Ni-Co-based composite oxide is not a mixture of the metals but a solid-soluble compound in which a part of nickel in the crystal structure of lithium nickelate is substituted with cobalt. Have. The solid-soluble compound can perform intercalation and deintercalation reactions of lithium ions more smoothly and in a higher potential range, and is highly practical as a positive electrode material for a battery.
[0015]
Next, the manufacturing method of the lithium composite compound of this invention is demonstrated.
The Ni salt or Ni-Co-based salt used as a starting material has an Ni / Co atomic ratio (Ni / Co) in the range of 0: 1 to 1: 0, but the Ni salt or Ni-Co salt. Is simply mixed in a predetermined amount, but Ni and Co solid phase and / or coprecipitation is particularly preferable.
[0016]
Such Ni salt or Ni-Co-based salt is a so-called precursor compound that becomes a metal oxide when heated, and is, for example, an organic acid such as hydroxide, carbonate, oxide, oxalate, and acetate. Examples thereof include salts, and among these, hydroxides are preferable.
[0017]
Further, the Li salt as the other raw material needs to have a particle size of 350 μm or less and 80% or more. Examples of the lithium salt include lithium oxide, lithium hydroxide, lithium carbonate, lithium nitrate, acetic acid. Examples thereof include lithium, lithium peroxide, and lithium sulfate. In the present invention, when a part of lithium nitrate is used as the lithium salt, the reaction is accelerated.
[0018]
In the production method of the present invention, a predetermined amount of the above raw materials are mixed and then baked. The heating rate of the calcination should be fast, but it is usually 1 ° C./min or more.
The firing atmosphere is not particularly limited and may be in the air or in an oxygen atmosphere, but is preferably in an oxygen atmosphere. . The firing is preferably performed by multi-stage firing. After firing slowly in the range of about 200 to 400 ° C. where water contained in the raw material disappears, the rate of temperature increase is further 4 ° C./min to around 700 to 900 ° C. It is preferable that the temperature is rapidly raised and fired.
[0019]
Further, the larger the value of y in the above general formula (1), the more it is necessary to fire at a lower temperature. However, if the mixing of Ni and Co is insufficient, for example, a lithium composite oxide with y = 0.5 will be synthesized. However, since lithium oxides having different compositions are obtained, it is necessary to sufficiently mix the raw materials.
[0020]
The cooling method after completion of firing is not particularly limited and may be gradually cooled in the furnace, but is preferably cooled in the atmosphere.
[0021]
In addition, the lithium composite oxide of the present invention obtained by the above method is useful as a positive electrode active material for a lithium secondary battery containing this as a main component because of its excellent electronic properties, and thus a conductive substrate. Can be obtained, and a lithium secondary battery using the positive electrode plate can be provided.
[0022]
The configuration of the lithium secondary battery in the present invention is not particularly limited. For example, the lithium secondary oxide produced by the above method is a main component, and graphite powder, polyvinylidene fluoride, and the like are mixed and processed into a positive electrode material ( A lithium secondary battery positive electrode active material) is dispersed in an organic solvent to prepare a kneaded paste. The kneaded paste is applied to a conductive substrate such as an aluminum foil, dried, pressed and cut into an appropriate shape to obtain a positive electrode plate.
What is necessary is just to manufacture a lithium secondary battery by laminating | stacking each member which comprises a lithium secondary battery using this positive electrode plate.
[0023]
【Example】
EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, this is merely an example and does not limit the present invention.
Example 1
Ni—Co hydroxide having an atomic ratio of Ni and Co of 7: 3 and lithium hydroxide having an atomic ratio of 350 μm or less of 80% so that the atomic ratio of lithium and transition metal (content of Ni and Co) is 1. And weighed uniformly.
This mixture was calcined at 350 ° C., heated to 750 ° C. at 4 ° C./min, then heated to 780 ° C. at 1 ° C./min and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing. The X-ray diffraction pattern of the obtained compound is shown in FIG.
[0024]
Example 2
The atomic ratio of Ni and transition metal (content of Ni and Co) is 1 for Ni-Co hydroxide having an atomic ratio of Ni and Co of 8: 2 and lithium hydroxide having an atomic ratio of 350 μm or less of 80% or more. And weighed uniformly.
This mixture was calcined at 350 ° C., then heated to 700 ° C. at 4 ° C./min, then heated to 750 ° C. at 1 ° C./min and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing. The X-ray diffraction pattern of the obtained compound is shown in FIG. 2 and its enlarged view is shown in FIG.
[0025]
Example 3
Ni-Co hydroxide having an atomic ratio of Ni and Co of 8: 2, and lithium carbonate and lithium nitrate having a molar ratio of 350: 1 or less so that the molar ratio of lithium carbonate and lithium nitrate is 9: 1. They were weighed so that the atomic ratio of metal (Ni and Co content) was 1, and mixed uniformly.
This mixture was calcined at 350 ° C., then heated to 700 ° C. at 4 ° C./min, then heated to 750 ° C. at 1 ° C./min and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing.
[0026]
Example 4
Ni—Co hydroxide having an atomic ratio of Ni: Co of 9: 1, and lithium carbonate and lithium nitrate having a molar ratio of 350% or less of 80% or less so that the molar ratio of lithium carbonate and lithium nitrate is 9: 1. They were weighed so that the atomic ratio of (Ni and Co contents) was 1, and uniformly mixed and pelletized.
This mixture was calcined at 350 ° C., then heated to 700 ° C. at 4 ° C./min, then heated to 750 ° C. at 1 ° C./min and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing. The X-ray diffraction pattern of the obtained compound is shown in FIG.
[0027]
Comparative Example 1
The atomic ratio of Ni to Co and the transition metal (content of Ni and Co) is 1 with Ni-Co hydroxide so that the atomic ratio of Ni and Co is 7: 3 and lithium hydroxide of 60% at 400 μm or more. And weighed uniformly with a mixer.
The mixture was heated to 780 ° C. and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing. The X-ray diffraction pattern of the obtained compound is shown in FIG. 1 to 5, the horizontal axis represents 2 days, and the vertical axis represents intensity.
[0028]
Comparative Example 2
The atomic ratio of Ni to Co and the transition metal (the content of Ni and Co) is 1 for Ni-Co hydroxide and 60% or more of lithium carbonate so that the atomic ratio of Ni and Co is 8: 2. And weighed uniformly with a mixer.
The mixture was heated to 780 ° C. and held for 7 hours. After the completion of firing, the lithium composite oxide was obtained by taking it out from the furnace, allowing it to cool in the atmosphere and pulverizing.
[0029]
(Ii) Measurement of c value The samples obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were subjected to X-ray diffraction analysis, and the half-value width of the diffraction peak of hkl (0, 0, 3), hkl (1, The distance a from the base where the diffraction peaks of 0,8) and hkl (1,1,0) intersect and the height b of the diffraction peak of hkl (1,1,0) are measured. The c value was determined. The results are shown in Table 1. The measurement conditions are shown in Table 2.
[0030]
(II) Measuring method of oxygen content by Rietveld analysis method The samples obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated by the following methods. The results are shown in Table 1.
(1) Index the peak of the powder X-ray diffraction pattern.
(2) Refine the lattice constant by least square method or Pawley method.
(3) Estimate the approximate atomic arrangement from the crystallographic viewpoint and chemical composition.
(4) The powder X-ray diffraction pattern is simulated based on the structural model constructed in (3).
(5) Refine the 6c site oxygen occupancy in the lithium composite oxide.
(III) Preparation of lithium secondary battery;
85% by weight of lithium composite oxide, 10% by weight of graphite powder and 5% by weight of polyvinylidene fluoride were mixed to prepare a positive electrode material, which was dispersed in 2-methylpyrrolidone to prepare a kneaded paste. The kneaded paste was applied to an aluminum foil, dried, pressed with a pressure of 2000 kg / cm ² , and punched into a 2 cm square to obtain a positive electrode plate.
Further, by using the _{1M-Li ClO 4 / EC +} DEC in the electrolyte, the negative electrode using Li metal, to produce a lithium secondary battery by stacking the members as shown in FIG.
[0031]
(IV) Battery performance evaluation The fabricated lithium secondary battery was operated, and the initial discharge capacity and capacity retention were measured to evaluate the battery performance. The results are shown in Table 1.
(Measurement of initial discharge capacity)
The initial discharge capacity was measured by charging / discharging the positive electrode to 4.2 V at 0.5 mA / cm ² and then discharging to 2.7 V.
[0032]
(Capacity retention)
The capacity retention rate was calculated by the following equation from the result of repeating the above charge and discharge.
[0033]
Volume retention (%) = (discharge capacity at the 10th cycle) × 100 / (discharge capacity at the first cycle)
[0034]
[Table 1]

[0035]
[Table 2]
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Diffraction device RINT-2400 (manufactured by Rigaku Corporation)
X-ray tube Cu
Tube voltage / tube current 50kV, 200mA
Slit DS-SS: 1 degree, RS: 0.15mm
Monochromator Graphite measurement interval 0.02 degree counting method Constant clock method ──────────────────────────────
[0036]
【The invention's effect】
By using the lithium composite oxide of the present invention for a positive electrode plate as a positive electrode active material for a lithium secondary battery, a lithium secondary battery excellent in initial discharge capacity and discharge retention and giving a high energy density can be obtained.
In addition, the method for producing a lithium composite oxide according to the present invention is a simple method and is industrially advantageous.
[Brief description of the drawings]
FIG. 1 is a diagram showing an X-ray diffraction pattern of a lithium composite oxide in Example 1 of the present invention.
FIG. 2 is a diagram showing an X-ray diffraction pattern of a lithium composite oxide in Example 2 of the present invention.
FIG. 3 is an enlarged view of hkl (1, 0, 8) and hkl (1, 1, 0) portions in the X-ray diffraction of FIG. 2;
FIG. 4 is a diagram showing an X-ray diffraction pattern of a lithium composite oxide in Example 4 of the present invention.
FIG. 5 is a diagram showing an X-ray diffraction pattern of a conventional lithium composite oxide (Comparative Example 1).
FIG. 6 is a view showing a lithium secondary battery of the present invention.

Claims (6)

The following general formula (1)
Li _x Ni _1-y Co _y O ₂ (1)
(Where 0 <x <1.1 and 0 ≦ y ≦ 1)
The half-width of the diffraction peak of hkl (0,0,3) by X-ray diffraction is 0.3 or less and the diffraction peak of hkl (1,1,0) The ratio c between the height b of h and the distance a from the base at which the diffraction peaks of hkl (1, 0, 8) and hkl (1, 1, 0) intersect is c = b / a ≧ 2 (2)
Lithium composite oxide. 2. The lithium composite oxide according to claim 1, wherein the oxygen occupancy by a Rietveld analysis method by powder X-ray diffraction is 95% or more. Ni salt crystal particles or Ni and Co Ni-Co salt crystal particles and a Li salt having a particle size of 350 μm or less of 80% or more are mixed and then fired, and the following general formula (1)
Li _x Ni _1-y Co _y O ₂ (1)
(Where 0 <x <1.1 and 0 ≦ y ≦ 1)
The manufacturing method of lithium complex oxide represented by these. A positive electrode active material for a lithium secondary battery comprising the lithium composite oxide according to claim 1 as a main material. The positive electrode plate for lithium secondary batteries which comprises a positive electrode material with the positive electrode active material for secondary batteries of Claim 4. A lithium secondary battery using the positive electrode plate according to claim 5.

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