JP3863604B2 - Method for producing lithium composite oxide - Google Patents

Description

【００４０】
【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。[0001]
BACKGROUND OF THE INVENTION
The present invention, Ru der relates to a process for the preparation of a lithium composite oxide.
[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.
They are, for example, Li _1-X Ni O ₂ (where 0 ≦ x ≦ 1) (US Pat. No. 4,302,518), Li Ni _2-Y O ₂ (Japanese Patent Laid-Open No. 2-40861), Li _Y Ni. _x Co _1-x O ₂ (where 0 <x ≦ 0.75, y ≦ 1) (Japanese Patent Laid-Open No. 63-299056) is a typical example of a composite oxide mainly composed of lithium and a transition metal. It is done.
[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, LiNiO ₂ has the advantage that it is cheaper than cobalt, but it is likely to cause defects during use as a positive electrode material of a battery, so that the capacity characteristics are inferior to that of Co, such as lack of battery stability. It was done. For this reason, lithium composite oxides in which a part of LiNiO ₂ and nickel (Ni), which are as close to the stoichiometric ratio as possible, are substituted with other transition metals and their synthesis methods are being 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 manufacturing method of the initial discharge capacity and excellent discharge retention rate providing a high energy density lithium secondary battery positive electrode active substance.
[0006]
[Means for Solving the Problems]
Under such circumstances, the present inventors have conducted extensive 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 lithium composite oxide in which the ratio of the constant to the theoretical lattice constant is in the range of 0.990 and less than 1.010 and the increase in moisture absorption is 5% or less is used as the positive electrode active material of the lithium secondary battery In this case, the inventors have found that a high energy density excellent in initial discharge capacity and discharge retention is obtained, and have completed the present invention.
[0007]
That is, the present invention relates to Ni salt crystal particles or Ni—Co salt crystal particles formed by solid solution and / or coprecipitation of Ni and Co, and lithium hydroxide having a particle diameter of 350 μm or less of 80% or more. After mixing and then firing at 200 to 400 ° C., further performing multi-stage firing in which firing is further performed at 750 to 900 ° C. The following general formula (1)
Li _x Ni _1-y Co _y O ₂ (1)
The present invention provides a method for producing a lithium composite oxide represented by the formula (where 0 <x <1.1 and 0 ≦ y ≦ 0.4).
Further, the present invention includes a crystal grain of N i N i -Co salt formed in a solid solution and / or co-precipitation of the crystal grains or N i and Co salts, water particle size not greater than 150μm is less than 90% Lithium oxide is mixed, then fired at 200 to 400 ° C., and then subjected to multi-stage firing in which firing is further performed at 750 to 900 ° C. The following general formula (1)
_{Li X N i 1-y Co} y O 2 (1)
The present invention provides a method for producing a lithium composite oxide represented by the formula (where 0 <x <1.1 and 0 ≦ y ≦ 0.4).
Further, the present invention includes a crystal grain of N i N i -Co salt formed in a solid solution and / or co-precipitation of the crystal grains or N i and Co salts, water particle size not greater than 50μm is 70% or more Lithium oxide is mixed, then fired at 200 to 400 ° C., and then subjected to multi-stage firing in which firing is further performed at 750 to 900 ° C. The following general formula (1)
_{Li X N i 1-y Co} y O 2 (1)
The present invention provides a method for producing a lithium composite oxide represented by the formula (where 0 <x <1.1 and 0 ≦ y ≦ 0.4).
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The above equation (2) is said to be Vergard's law ("Material analysis by powder X-ray diffraction" Kodansha Scientific, 88-90, issued on June 1, 1993). Using the difference in radius, the solid solubility (y) of both ions is obtained from the lattice constant.
That is, the ion radius of the solid solution ions of the solid solution affects the inter-ion distance, that is, the lattice constant. If the lattice constants of the crystal ions at both ends of the solid solution Ni ion and Co ion are aNi and aCo, The lattice constant of the composition is the above equation (2). The above formula (2) indicates that the lattice constant of the solid solution is proportional to the solute ion concentration based on the linearity of the volume change.
[0011]
This lattice constant is obtained by measurement by X-ray diffraction, and can be carried out by preparing a calibration curve using the lattice constants of both end components of the solid solution and comparing it. The lithium composite oxide of the present invention has a lattice constant ratio d value in the range of more than 0.990 and less than 1.010, preferably in the range of more than 0.999 and less than 1.005. When the d value is out of the above range, a favorable result as battery characteristics cannot be obtained. Further, the increase in the moisture absorption rate of such a compound is 5% or less, preferably 2% or less, based on the dry weight standard.
[0012]
In the present invention, in order to determine the moisture absorption rate of the lithium composite oxide, first, the lithium composite oxide is left in a vacuum dryer at 100 ° C. for 24 hours, and this is accurately weighed in a weighing bottle. Next, the sample is placed in a thermo-hygrostat kept at 30 ° C. and a relative humidity of 80% and left for 72 hours, and the weight of the sample after moisture absorption is measured to determine the moisture absorption rate. Usually, lithium nickelate has high hygroscopicity, and elution of lithium occurs with a slight amount of water, resulting in a change in composition. However, in the present invention, when the increase in moisture absorption exceeds 5%, the composition change increases, and the battery The result is an undesirable result.
[0013]
The compositional feature of the lithium composite oxide in the present invention is represented by the general formula (1), and the compounding ratio is such that the atomic ratios of Li, Ni and Co are x (Li) and 1-y (Ni), respectively. And y (Co) (where 0 <x <1.1, 0 ≦ y ≦ 0.4 is shown). For example, the blending ratio is preferably set to around 1 as the Li / (Ni content alone or Ni and Co content) ratio, 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]
Further, the atomic ratio of Ni and Co (Ni: Co) is 1: 0-0.6: shall be the range of 0.4. 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, and the solid-soluble compound contains lithium ions. The intercalation and deintercalation reactions can be carried out more smoothly and in a higher potential range, and is highly practical as a positive electrode material for batteries.
[0015]
Next, the manufacturing method of the lithium composite compound of this invention is demonstrated.
The production method of the present invention is characterized in that a Ni salt or Ni-Co salt solid solution and / or coprecipitate is mixed with a lithium salt and then calcined.
[0016]
The Ni salt or Ni-Co-based salt used as the starting material has a Ni / Co atomic ratio (Ni / Co) in the range of 1: 0 to 0.6: 0.4. In the case of a base salt, a predetermined amount of Ni and Co salts are not mixed, but a solid solution in which nickel ions are partially substituted with cobalt ions, or nickel salts and cobalt salts are coprecipitated or occluded. Must be what you are doing.
[0017]
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.
[0018]
The other raw material, lithium hydroxide, has a particle size of 350 μm or less of 80% or more, a particle size of 150 μm or less of 90% or more, or a particle size of 50 μm or less of 70% or more. Lithium hydroxide with a small diameter and a sharp particle size distribution . Also, when using a lithium hydroxide of the particle size range, mixer - mixing becomes possible by a simple mixer such as a few minutes lithium and Ni salt or Ni -Co salt hydroxide with a mixing time of uniform and Thoroughly mixed. When the particle size is outside the above range, uniform mixing is not possible, and the product obtained after firing can be made of a large amount of Li, Ni, or Co oxides, which reduces the purity of the lithium composite oxide. Absent.
[0019]
The lithium composite oxide of the present invention can be obtained by mixing a predetermined amount of Ni salt or Ni-Co salt having a specific structure and lithium hydroxide , and then firing the mixture. 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 rate should be fast, but usually it should be 1 ° C./min or more . Baked formed, after slowly fired in the range of about 200 to 400 ° C. to moisture contained in the starting material disappeared, it row by multistage firing rapidly heated firing to around further 750 to 900 ° C..
[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]
The lithium composite oxide produced by the above method has a uniform particle diameter, and a coating film can be uniformly applied to the sheet when a positive electrode plate of a lithium secondary battery is produced.
[0022]
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 for a lithium secondary battery. A positive electrode plate can be obtained, and a lithium secondary battery using the positive electrode plate can be provided.
[0023]
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.
[0024]
【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 obtained by solid solution and / or coprecipitation with an Ni / Co atomic ratio of 7: 3, lithium hydroxide with a particle size of 50 μm or less occupying 70% or more, lithium and a transition metal (Ni And Co content) were weighed so that the atomic ratio was 1, and mixed uniformly. This mixture was calcined at 350 ° C., then heated to 730 ° 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.
[0025]
Reference example 1
Lithium carbonate and lithium nitrate, in which 150 μm or less occupies 90%, are mixed at a molar ratio of 8: 2. The substantially spherical Ni-Co hydroxide obtained by this solution and a solid solution and / or coprecipitation with a Ni: Co atomic ratio of 7: 3 is converted into atoms of lithium and transition metal (content of Ni and Co). They were weighed so that the ratio was 1 and mixed uniformly. The mixture was calcined at 350 ° C. and then heated to 730 ° 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.
[0026]
Example 2
Lithium hydroxide is a substantially spherical Ni-Co hydroxide obtained by solid solution and / or coprecipitation with an atomic ratio of Ni and Co of 8: 2, and lithium hydroxide occupying 90% or more with a particle size of 150 μm or less. And transition metal (content of Ni and Co) were weighed so that the atomic ratio 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.
[0027]
Example 3
Lithium hydroxide is a substantially spherical Ni—Co hydroxide obtained by solid solution and / or coprecipitation with an atomic ratio of Ni and Co of 6: 4, and lithium hydroxide occupying 90% or more with a particle size of 150 μm or less. And transition metal (content of Ni and Co) were weighed so that the atomic ratio was 1, and mixed uniformly. The mixture was calcined at 350 ° C. and then heated to 750 ° C. at 4 ° C./min, then heated to 800 ° 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.
[0028]
Example 4
Lithium hydroxide is a substantially spherical Ni-Co hydroxide obtained by solid solution and / or coprecipitation with an atomic ratio of Ni and Co of 9: 1 and lithium hydroxide with a particle size of 150 μm or less accounting for 90% or more. And transition metal (content of Ni and Co) were weighed so that the atomic ratio was 1, and mixed uniformly. This mixture was pressed and pelletized. The pellets were calcined at 350 ° C., 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.
[0029]
Example 5
A substantially spherical Ni—Co hydroxide obtained by solid solution and / or coprecipitation with an atomic ratio of Ni and Co of 9: 1 was baked at 250 ° C. for 3 hours to obtain Ni—Co oxide. This oxide and lithium hydroxide in which the particle diameter was 350 μm or less accounted for 80% or more were weighed so that the atomic ratio of lithium and transition 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 12 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.
[0030]
Comparative Example 1
Nickel hydroxide and cobalt hydroxide are uniformly mixed so that the atomic ratio of Ni and Co is 7: 3. Lithium hydroxide is mixed with lithium hydroxide and the transition metal (Ni and Co content) atomic ratio is 1. It weighed so that it might become and dry-mixed. This mixture was held at 780 ° C. 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.
[0031]
Comparative Example 2
Nickel hydroxide and cobalt hydroxide are uniformly mixed so that the atomic ratio of Ni and Co is 8: 2, and lithium hydroxide is mixed with lithium and transition metal (Ni and Co content) atomic ratio of 1. Were weighed and mixed uniformly. 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.
[0032]
Comparative Example 3
Nickel hydroxide and cobalt hydroxide are uniformly mixed so that the atomic ratio of Ni and Co is 6: 4, and lithium hydroxide is mixed with lithium and transition metal (Ni and Co content) atomic ratio of 1. Were weighed and mixed uniformly. The mixture was heated to 790 ° 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.
[0033]
Comparative Example 4
Nickel hydroxide and cobalt hydroxide are uniformly mixed so that the atomic ratio of Ni and Co is 9: 1. Lithium hydroxide is mixed with lithium hydroxide and the transition metal (Ni and Co content) atomic ratio is 1. Were weighed and mixed uniformly. The mixture was heated to 800 ° C. at 4 ° C./min, then heated to 850 ° C. at 1 ° C./min and held for 12 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.
[0034]
(I) Measurement of moisture absorption The moisture absorption of the lithium composite oxides obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured by the above method. The results are shown in Table 1.
(II) Method for calculating lattice constant Lithium hydroxide and nickel hydroxide having a lattice constant of 60 μm or less of 70% or more were weighed so that the atomic ratio of Li and Ni was 1, and mixed uniformly. After calcining this compound for 2 hours at 350, the temperature was raised to 700 ° C. at 4 ° C./min in an oxygen atmosphere, then to 750 ° C. at 1 ° C./min and maintained for 7 hours to obtain Li Ni O ₂ . Synthesized. Further, lithium carbonate and cobalt oxide were weighed so that the atomic ratio of Li and Co was 1: 1 and mixed uniformly. This compound was calcined at 1000 ° C. for 3 hours to obtain LiCoO ₂ . The resulting Li Ni O ₂ and the lattice constant of LiCoO ₂ was measured by X-ray diffractometry, aNi O = 2.8783, was obtained Acoo = 2.8152. Similarly, the lattice constants of the products of Examples 1 to 6 and Comparative Examples 1 to 4 obtained by the above method were measured. The results are shown in Table 1.
[0035]
(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, 1M-Li ClO ₄ / EC + DEC was used as the electrolyte, and Li metal was used as the negative electrode, and the respective members were stacked as shown in FIG. 1 to produce a lithium secondary battery.
[0036]
(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.
[0037]
(Capacity retention)
The capacity retention rate was calculated by the following equation from the result of repeating the above charge and discharge.
[0038]
Volume retention (%) = (discharge capacity at the 10th cycle) × 100 / (discharge capacity at the first cycle)
[0039]
[Table 1]

[0040]
【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.

Claims (3)

Ni salt crystal particles or Ni-Co salt crystal particles formed by solid solution and / or coprecipitation of Ni and Co are mixed with lithium hydroxide having a particle size of 350 μm or less of 80% or more, and then 200 to 200- After firing at 400 ° C., the following general formula (1), characterized by performing multi-stage firing at 750 to 900 ° C.
Li _x Ni _1-y Co _y O ₂ (1)
(Wherein 0 <x <1.1 and 0 ≦ y ≦ 0.4 are satisfied). N i Salt crystal particles or N i N formed by solid solution and / or coprecipitation with Co i -Co salt crystal particles and lithium hydroxide having a particle diameter of 150 μm or less of 90% or more are mixed, then fired at 200 to 400 ° C., and then further fired at 750 to 900 ° C. The following general formula (1)
Li  _X N i _1-y Co _y O ₂ (1)
(Wherein 0 <x <1.1 and 0 ≦ y ≦ 0.4 are satisfied). N i Salt crystal particles or N i N formed by solid solution and / or coprecipitation with Co i -Co salt crystal particles and lithium hydroxide having a particle size of 50 μm or less of 70% or more are mixed, then fired at 200 to 400 ° C., and then further fired at 750 to 900 ° C. The following general formula (1)
Li  _X N i _1-y Co _y O ₂ (1)
(Wherein 0 <x <1.1 and 0 ≦ y ≦ 0.4 are satisfied).