JP2009064585A - Manufacturing method of transition metal based compound for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a transition metal based compound for a lithium secondary battery positive electrode material in a short time and efficiently. <P>SOLUTION: A temperature raising speed in a raising temperature process at the time of calcination is 2°C/min. or less and calcination can be done at a high temperature and in a short time without making sintered lumps and without impairing physical properties and characteristics of a transition metal based compound to be obtained. It is desirable that a holding time for calcination is 30 minutes or longer and 20 hours or shorter, and a holding temperature is 800°C or higher and 1100°C or lower. By slowing down the temperature raising speed in the temperature raising process at calcination, a production yield of sieving after calcination even if the holding temperature is raised and the physical properties and characteristics of the transition metal based compound to be obtained are not impaired, and the transition metal based compound can be manufactured by calcination at a high temperature and in a shorter time and efficiently as compared with a conventional method. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a transition metal compound for a lithium secondary battery, and in particular, as a positive electrode active material for a lithium secondary battery without impairing physical properties or characteristics of the obtained transition metal compound for a lithium secondary battery. The present invention relates to a method for improving production efficiency of useful transition metal compounds.

  In recent years, with the reduction in size and weight of portable electronic devices and communication devices, lithium secondary batteries having high output and high energy density have attracted attention as power sources and automobile power sources.

As a positive electrode active material of a lithium secondary battery, it is known that a lithium transition metal composite oxide whose standard composition is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like is preferable.

Furthermore, from the viewpoint of safety and raw material costs, LiNi _1-p Mn _p O _{2 in} which a part of the transition metal of these lithium transition metal composite oxides is substituted with another transition metal (where p is 0 <p <Representing a number satisfying 1), LiNi _1- pq Mn _p Co _q O ₂ (where p and q are 0 <p <1, 0 <q <1 and 0 <p + q <, respectively) A lithium transition metal composite oxide having the same layered structure as LiCoO ₂ or LiNiO ₂ has been attracting attention.

There are many known methods for producing these lithium transition metal composite oxides, including, for example, transition metal-based materials such as nickel raw materials, cobalt raw materials, and manganese raw materials, and a smaller amount of lithium raw materials as desired. The slurry is spray-dried to form granulated particles, and a method in which lithium raw materials are further dry-mixed so as to have a desired composition ratio and then fired (Patent Document 1), nickel, cobalt, and manganese as, for example, carbonates The composite carbonate obtained by coprecipitation is calcined and decarboxylated, and the resulting granulated particles and lithium raw material are dry mixed and then calcined (Patent Document 2), and cobalt, nickel and lithium are coprecipitated How to increase the reactivity by rapidly raising the temperature of the resulting mixture to 750 ° C. at a rate of 3 ° C./min or more and firing to prevent carbonation of lithium hydroxide used as a raw material Etc. (Patent Document 3) it is used.
JP 2003-267732 A Japanese Patent Laid-Open No. 10-134811 JP-A-8-319120

  When producing a lithium transition metal composite oxide by firing a firing precursor, shortening the firing time is extremely important for shortening the residence time of an expensive firing furnace to increase productivity and reduce manufacturing costs. However, for example, in the conventional manufacturing methods described in Patent Documents 1 and 2, the lithium transition obtained when the firing time is shortened by increasing the holding temperature during firing in consideration of productivity. The metal composite oxide has a problem that a sintered lump is formed and the yield in the sieving operation after firing is reduced. Further, in the conventional method described in Patent Document 3, since the firing is performed at a temperature rising rate of 3 ° C./min or more during firing, the firing time is shortened at a high temperature. There are problems similar to the conventional manufacturing methods described in Patent Documents 1 and 2.

  The present invention was devised in view of such problems, and shortens the time required for firing without causing sintered ingots and without impairing the physical properties and characteristics of the obtained transition metal compound. It aims at providing the method of manufacturing the transition metal type compound for lithium secondary batteries efficiently in a short time.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has formed a sintered ingot even when the holding temperature is high by controlling the temperature rising rate in the temperature rising process of the transition metal compound firing step. In other words, by lowering the rate of temperature rise in the temperature raising process during firing, the yield of the sieve after firing can be improved even if the holding temperature is increased, It has been found that the characteristics are not impaired. This makes it possible to produce a transition metal compound more efficiently in a shorter time than in the past by firing at a high temperature for a short time, and the present invention has been completed.

  That is, the gist of the present invention is that in the method for producing a transition metal compound for a lithium secondary battery by calcining a calcined precursor, the rate of temperature rise during the calcining is 2 ° C./min or less. The present invention resides in a method for producing a transition metal compound for a lithium secondary battery (claim 1).

Another aspect of the present invention is a method for producing a transition metal compound for a lithium secondary battery by calcining a calcined precursor, and a holding time during calcining and a temperature rising time during a calcining process are as follows: It exists in the manufacturing method (Claim 2) of the transition metal type compound for lithium secondary batteries characterized by satisfying Formula (1).
Holding time at firing / Temperature raising time in firing process ≦ 1.5 (1)

Further, in the above production method, the holding time at the time of firing is preferably 30 minutes or longer and 20 hours or shorter (claim 3).
Further, in the above production method, the holding temperature at the time of firing is preferably 800 ° C. or higher and 1100 ° C. or lower (claim 4).
Furthermore, it is preferable that the calcined precursor contains granulated particles containing a transition metal and particles of a lithium raw material (Claim 5).
Furthermore, it is preferable that the composition of the obtained transition metal compound for a lithium secondary battery is represented by the following formula (2).
_{Li 1 + x Ni a Mn b} Co c M d O 2-δ (2)
(In formula (2), M represents a metal element that substitutes a part of the sites of Ni and Mn.
a, b, c, and d are numbers satisfying 0.2 ≦ a ≦ 0.85, 0 ≦ b ≦ 0.8, 0 ≦ c ≦ 0.8, 0 ≦ d ≦ 0.4, and a + b + c + d = 1. Represents.
x represents a number satisfying −0.3 ≦ x ≦ 0.3, and δ represents a number satisfying −0.1 <δ <0.1. )

According to the method for producing a transition metal compound for a lithium secondary battery of the present invention, sintering can be performed at a high temperature for a short time without forming a sintered mass and without impairing the physical properties and characteristics of the obtained transition metal compound. It becomes possible.
For this reason, according to this invention, it becomes possible to manufacture the positive electrode active material for lithium secondary batteries efficiently in a shorter time than before.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention. .

The method for producing a transition metal compound for a lithium secondary battery of the present invention (hereinafter referred to as “the production method of the present invention” as appropriate) is a method for producing a transition metal compound for a lithium secondary battery by firing a firing precursor. In the above, the following conditions (i) and / or (ii) are satisfied. Specifically, the raw material of the transition metal compound is mixed, pulverized and granulated to obtain a calcined precursor ( Hereinafter referred to as “firing precursor manufacturing step”) and a step of firing the obtained calcining precursor (hereinafter referred to as “firing step” as appropriate).
(i) The heating rate during the heating process during firing is set to 2 ° C./min or less.
(ii) The holding time during firing and the heating time during the heating process during firing satisfy the following formula (1).
Holding time at firing / Temperature raising time in firing process ≦ 1.5 (1)

In the present invention, the “temperature increase rate in the temperature raising process during firing” is the temperature increase rate in the temperature raising process until reaching the holding temperature during firing, the holding temperature during firing and the start of temperature rise. It is obtained as a value obtained by dividing the difference from the temperature by the time from the start of raising the temperature until reaching the holding temperature. Further, the time from the start of the temperature increase to the holding temperature is the “temperature increase time during the temperature increase process during firing”.
The “holding temperature during firing” is the maximum temperature that is maintained for a predetermined time during firing. However, this maximum temperature does not necessarily have to be constant, and may have a range of about ± 10 ° C. The holding temperature is a temperature that is held with a fluctuation width within a temperature of ± 10 ° C. for the purpose of holding the temperature during firing, and the time that is held at this holding temperature is the “holding time during firing”.

  In addition, the yield when the transition metal compound after calcination is classified with a sieve having an opening of 1 mm means that the transition metal compound obtained by firing is not treated at all and has an opening of 1 mm. This is the ratio of the baked product passed through the sieve when classified by the sieve.

[Transition metal compounds]
Prior to explaining the production method of the present invention, the transition metal compound produced by the present invention will be explained.

<Composition>
There is no particular limitation on the transition metal compound produced by the production method of the present invention (hereinafter referred to as “transition metal compound of the present invention” as appropriate), and any compound is produced as long as the effects of the present invention are not significantly impaired. be able to.

The transition metal compound for lithium ion secondary battery of the present invention is a compound having a structure capable of desorbing and inserting Li ions, such as sulfides, phosphate compounds, and lithium transition metal composite oxidation. Such as things. Examples of sulfides include compounds having a two-dimensional layered structure such as TiS ₂ and MoS ₂ , and strong compounds represented by the general formula Me _x Mo ₆ S ₈ (Me is various transition metals including Pb, Ag, and Cu). Examples thereof include a sugar compound having a three-dimensional skeleton structure. Examples of the phosphate compound include those belonging to the olivine structure, and are generally represented by LiMePO ₄ (Me is at least one or more transition metals), specifically LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , Examples include LiMnPO ₄ .

Examples of the lithium transition metal composite oxide include spinel structures capable of three-dimensional diffusion and those belonging to a layered structure capable of two-dimensional diffusion of lithium ions. Those having a spinel structure are generally expressed as LiMe ₂ O ₄ (Me is at least one transition metal), specifically, LiMn ₂ O ₄ , LiCoMnO ₄ , LiNi _0.5 Mn _1.5 O. ₄ and CoLiVO ₄ . Those having a layered structure are generally expressed as LiMeO ₂ (Me is at least one or more transition metals), specifically, LiCoO ₂ , LiNiO ₂ , LiNi _1-x Co _x O ₂ , LiNi _{1-x. -y Co x Mn y O 2,} LiNi 0.5 Mn 0.5 O 2, Li 1.2 Cr 0.4 Mn 0.4 O 2, Li 1.2 Cr 0.4 Ti 0.4 O 2, Examples include LiMnO ₂ .

Among these, a lithium transition metal composite oxide having a hexagonal layered rock salt structure (ideal formula: LiMeO ₂ , Me contains at least one transition metal) that is effective as a positive electrode active material of a lithium secondary battery, In particular, a lithium transition metal composite oxide represented by the following formula (2) is preferable.

_{Li 1 + x Ni a Mn b} Co c M d O 2-δ (2)
In formula (2), M represents a metal element capable of substituting a part of Ni, Mn, and Co sites with at least one metal element other than Li.
a, b, c, and d are numbers satisfying 0.2 ≦ a ≦ 0.85, 0 ≦ b ≦ 0.8, 0 ≦ c ≦ 0.8, 0 ≦ d ≦ 0.4, and a + b + c + d = 1. Represents.
x is a molar amount of Li in excess of the stoichiometric ratio represented by Li / (Ni + Mn + Co) -1, and represents a number satisfying −0.3 ≦ x ≦ 0.3. This excess Li content may exist outside the layered structure, but may replace the inside of the layered structure (part of the transition metal site).

In the formula (2), x is usually −0.3 or more, preferably 0 or more, more preferably 0.05 or more, and usually 0.3 or less, preferably 0.2 or less, more preferably 0. .15 or less. If x is outside this range, the crystal structure of the lithium transition metal composite oxide may become unstable, or the performance of the lithium secondary battery using the lithium transition metal composite oxide may be degraded.
In the formula (2), a is usually 0.2 or more, preferably 0.25 or more, more preferably 0.3 or more, and usually 0.85 or less, preferably 0.7 or less, more The number is preferably 0.5 or less.
Further, in the formula (2), b is usually 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.8 or less, preferably 0.7 or less, more preferably The number is 0.5 or less.
In the formula (2), c is usually 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.8 or less, preferably 0.5 or less, more preferably The number is 0.4 or less.
In the formula (2), d is usually 0 or more, preferably 0.02 or more, more preferably 0.04 or more, and usually 0.4 or less, preferably 0.2 or less, more preferably The number is 0.1 or less.
δ is a deficiency or excess of oxygen deviating from an ideal stoichiometric ratio of 2, and represents a number satisfying −0.1 <δ <0.1. This analysis for δ is obtained by oxidation-reduction titration such as iodometry, but is not carried out in the present invention because it does not require strictness.

  In the present invention, these composition formulas were confirmed to be hexagonal layered rock salt compounds by X-ray analysis, and the composition coefficients x, a, b and c were confirmed by elemental analysis by ICP measurement.

  In the formula (2), M is a substituted or added element that may be introduced into the structure of the lithium transition metal composite oxide, and Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb , Zr, Mo, W, Sn, B are selected from one or more.

Among lithium transition metal complex oxides represented by the above formula (2), nickel, manganese, and cobalt represented by the following formula (3) corresponding to the case of d = 0 in the formula (2) A lithium transition metal composite oxide containing, or a lithium transition metal composite oxide containing nickel, cobalt, and aluminum represented by the following formula (4) is preferable.
Li _{1 + x} (Ni _a Mn _b Co _c ) O _2-δ (3)

  In the formula (3), x represents a molar excess amount of Li that is equal to or higher than the stoichiometric ratio, and is usually −0.3 or more, preferably 0 or more, more preferably 0.05 or more, and usually 0.3 The number is preferably 0.2 or less, more preferably 0.15 or less. If x is outside this range, the crystal structure of the lithium transition metal composite oxide may become unstable, or the performance of the lithium secondary battery using the lithium transition metal composite oxide may be degraded.

In the formula (3), a is usually 0.2 or more, preferably 0.25 or more, more preferably 0.3 or more, and usually 0.85 or less, preferably 0.7 or less, more The number is preferably 0.5 or less.
Further, in the formula (3), b is usually 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.8 or less, preferably 0.7 or less, more preferably The number is 0.5 or less.

  In the formula (3), c is usually 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.8 or less, preferably 0.5 or less, more preferably The number is 0.4 or less.

  Further, in the formula (3), δ represents a deficiency or excess of oxygen deviating from the ideal stoichiometric ratio 2 as in the formula (2), and is usually larger than −0.1 and usually 0. . Represents a number less than 1.

Li _{1 + y} Ni _1-ef Co _e Al _f O _2-δ (4)

  In the formula (4), y represents a molar excess amount of Li equal to or higher than the stoichiometric ratio, and is usually 0.01 or more, preferably 0.02 or more, and usually 0.2 or less, preferably 0.15 or less, More preferably, the number is 0.10 or less. If y is outside this range, the lithium transition metal composite oxide crystal structure may become unstable, or the performance of a lithium secondary battery using the lithium transition metal may deteriorate.

In the formula (4), e is usually larger than 0, preferably 0.05 or more, more preferably 0.1 or more, and usually 0.4 or less, preferably 0.3 or less, more preferably Is a number of 0.2 or less.
Further, in the formula (4), f is usually 0 or more, preferably 0.02 or more, more preferably 0.04 or more, and usually 0.3 or less, preferably 0.25 or less, more preferably The number is 0.2 or less.
If e and f are too small, the chemical stability of this lithium transition metal composite oxide may be insufficient. If e is too large, the cost will increase. If f is too large, this lithium transition metal composite oxidation will occur. There is a risk that the capacity of the lithium secondary battery using the product will be reduced.
Further, in Expression (4), δ represents the same value as in Expression (3).

<Particle size>
The particle size of the transition metal compound produced in the present invention is not limited, but in applications as a positive electrode active material, the transition metal compound is a particle size distribution obtained by laser diffraction method for a sample that is not subjected to dispersion treatment by an ultrasonic oscillator. The median diameter when measuring is usually 20 μm or less, preferably 15 μm or less. When the median diameter exceeds this upper limit, when producing a positive electrode plate using the transition metal compound as a positive electrode active material, there is a risk of causing streaks in the coating process, and the composition may be segregated.
On the other hand, the lower limit of the median diameter is usually 1 μm or more, preferably 3 μm or more. If the median diameter is below the lower limit, fine powder may increase and the particles of the transition metal compound may aggregate.

  In addition, the value measured by the well-known laser diffraction / scattering type particle size distribution measuring apparatus based on JISZ8825-1 can be employ | adopted for the median diameter of a transition metal type compound. Moreover, as a dispersion medium used in the measurement, a 0.1% by weight sodium hexametaphosphate aqueous solution is used. Furthermore, the refractive index used at the time of measurement is 1.60a010i (real part 1.60, imaginary part 0.10).

[Production of transition metal compounds]
The production method of the present invention will be described below by exemplifying the case of producing a lithium nickel manganese cobalt-based composite oxide. However, the method of the present invention is not limited to the lithium nickel manganese cobalt-based composite oxide, but as described above. It is effective for the production of various lithium transition metal composite oxides and other transition metal compounds.

<Baking precursor manufacturing process>
The method for producing the calcined precursor of the lithium nickel manganese cobalt based composite oxide is not particularly limited, but most generally, a slurry in which a lithium compound, a nickel compound, a manganese compound, and a cobalt compound are dispersed in a liquid medium. And a method of obtaining granulated particles by spray drying. In addition, about a lithium compound, a nickel compound, a manganese compound, and the slurry which disperse | distributed the cobalt compound in the liquid medium can also be used by mixing with the obtained spray-dried body after spray-drying. When manufacturing conditions are constant, the mixing ratio of each compound when preparing a slurry in which a lithium compound, a nickel compound, a manganese compound, and a cobalt compound are dispersed in a liquid medium, a nickel compound, a manganese compound, and By adjusting the mixing ratio of each compound when preparing a slurry in which a cobalt compound is dispersed in a liquid medium and the mixing ratio of the spray-dried product and the lithium compound after spray drying, the target lithium nickel manganese cobalt system The molar ratio of Li / Ni / Mn / M of the composite oxide can be controlled.

(material)
Among the raw material compounds used for the preparation of the slurry, the lithium compounds include Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH.H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ OOLi, Li _2. O, Li ₂ SO ₄ , Licarboxylic acid Li, Citric acid Li, Fatty acid Li, Alkyl lithium and the like can be mentioned. Among these lithium compounds, lithium compounds containing no nitrogen atom, sulfur atom, or halogen atom are preferable because they do not generate harmful substances such as SO _x and NO _x during the firing treatment. It is a compound that tends to form voids by generating cracked gas in the secondary particles of the spray-dried powder by generating cracked gas. Taking these points into consideration, Li ₂ CO ₃ , LiOH in particular , LiOH · _{H 2} O is, inter alia easy to handle, preferably _Li 2 CO ₃ because it is relatively inexpensive. These lithium compounds may be used individually by 1 type, and may use 2 or more types together.

Moreover, as a nickel compound, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , 2NiCO ₃ .3Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O, nickel fatty acid, nickel halide and the like. Among these, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , 2NiCO ₃ .3Ni (OH) ₂ .4H ₂ O, NiC are used in that no harmful substances such as SO _x and NO _X are generated during the firing process. Nickel compounds such as ₂ O ₄ .2H ₂ O are preferred. Further, from the viewpoint that it can be obtained as an industrial raw material at a low cost and from the viewpoint of high reactivity, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , and further, a decomposition gas is generated at the time of firing. Ni (OH) ₂ , NiOOH, and NiCO ₃ are particularly preferable from the viewpoint of easily forming voids in the secondary particles. These nickel compounds may be used individually by 1 type, and may use 2 or more types together.

In addition, manganese compounds such as Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , manganese oxide, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, fatty acid manganese And manganese salts such as oxyhydroxide, manganese chloride and the like. Among these manganese compounds, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCO ₃ do not generate gases such as SO _x and NO _x during firing, and can be obtained at low cost as industrial raw materials. Therefore, it is preferable. These manganese compounds may be used individually by 1 type, and may use 2 or more types together.

Further, as the cobalt compound, Co (OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (OCOCH ₃ ) ₂ .4H ₂ O, CoCl ₂ , Co (NO ₃ ) ₂ .6H ₂ O, Co (SO ₄ ) ₂ · 7H ₂ O, CoCO _{3 and the} like. Among them, Co (OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , Co ₃ O ₄ , and CoCO ₃ are preferable in terms of not generating harmful substances such as SO _x and NOX during the firing step, more preferably Co (OH) ₂ and CoOOH are industrially inexpensively available and highly reactive. In addition, Co (OH) ₂ , CoOOH, and CoCO ₃ are particularly preferable from the viewpoint of easily forming voids in the secondary particles of the spray-dried powder due to generation of decomposition gas during firing. These cobalt compounds may be used individually by 1 type, and may use 2 or more types together.

  In addition to the above Li, Ni, Mn, and Co raw material compounds, other elements are substituted to introduce the above-mentioned foreign elements, and voids in secondary particles formed by spray drying described later are efficiently formed. It is possible to use a group of compounds intended to be used. In addition, the addition stage of the compound used for the purpose of efficiently forming the voids of the secondary particles used here can be selected either before or after mixing the raw materials depending on the property. It is. In particular, it is preferable to add a compound that is easily decomposed due to mechanical shear stress applied by the mixing step after the mixing step.

(Mixing process)
The method for mixing the raw materials is not particularly limited, and may be wet or dry. For example, a method using an apparatus such as a ball mill, a vibration mill, or a bead mill can be used. Wet mixing in which the raw material compound is mixed in a liquid medium such as water or alcohol is preferable because more uniform mixing is possible and the reactivity of the mixture can be increased in the firing step.
The mixing time varies depending on the mixing method, but it is sufficient that the raw materials are uniformly mixed at the particle level. For example, in a ball mill (wet or dry type), usually about 1 to 2 days, and in a bead mill (wet continuous method), a residence time. Is usually about 0.1 to 6 hours.

  In the raw material mixing stage, it is preferable that the raw material is pulverized in parallel. As the degree of pulverization, the particle diameter of the raw material particles after pulverization is an index, but the average particle diameter (median diameter) is usually 1.0 μm or less, preferably 0.6 μm or less, and most preferably 0.4 μm or less. . If the average particle size of the pulverized raw material particles is too large, the reactivity in the firing process is lowered, and the composition is difficult to homogenize. However, making particles smaller than necessary leads to an increase in the cost of pulverization, so that the average particle size is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.05 μm or more. It ’s fine. A means for realizing such a degree of pulverization is not particularly limited, but a wet pulverization method is preferable. Specific examples include dyno mill.

  The median diameter of the pulverized particles in the slurry described in the examples of the present invention is set to a refractive index of 1.24 by a known laser diffraction / scattering particle size distribution measuring apparatus, and the particle diameter reference is set to the volume reference. Measured. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz). The median diameter of the spray-dried powder (granulated particles) described below is the same as that except that measurement was performed after ultrasonic dispersion for 5 minutes.

(Spray drying process)
After the wet mixing, it is then usually subjected to a drying process. The drying method is not particularly limited, but the spray drying method is preferable from the viewpoints of uniformity of generated particles, powder flowability, powder handling performance, and efficient production of dry particles. In the spray drying method, the obtained slurry is dried to obtain granulated particles (spray dried particles).

Spray drying may be performed by a known method. For example, it is possible to use a method in which a gas flow and slurry are caused to flow into the tip of the nozzle so that the slurry is ejected as droplets from the nozzle and brought into contact with a drying gas to quickly dry the droplets.
The concentration of the slurry to be subjected to spray drying is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired, but usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, particularly Preferably it is 15 weight% or more. This is because if the slurry concentration is too low, productivity is significantly impaired. The upper limit of the slurry concentration is usually 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less. If the slurry concentration is too high, the viscosity of the slurry becomes high, and there is a possibility that it cannot be sprayed with a nozzle in the spraying process.

Further, the viscosity of the slurry is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. Usually, it is 100 mPs · s or more, preferably 200 mPs · s or more, and usually 3000 mPs · s or less, preferably 2000 mPs. -S or less. When the viscosity of the slurry is too low, it becomes difficult to form clean spherical particles when sprayed in the spraying process, and when the viscosity is too high, there is a possibility that the nozzle cannot be sprayed.
There is no restriction | limiting in the conditions of spray-drying, as long as the effect of this invention is not impaired remarkably. For example, the dry atmosphere is usually air, but may be an inert atmosphere such as nitrogen. Moreover, although the temperature of the drying gas is also arbitrary, it is usually preferable to introduce into the spraying device at 80 to 300 ° C and to discharge from the device at 45 to 250 ° C.

  By such spray drying, a powder obtained by agglomerating primary particles to form secondary particles can be obtained. The shape of the spray-dried powder formed by agglomerating primary particles to form secondary particles can be confirmed by, for example, SEM observation or cross-sectional SEM observation.

  The median diameter of the spray-dried powder obtained by spray drying is usually 18 μm or less, more preferably 15 μm or less, still more preferably 12 μm or less, and most preferably 9 μm or less. However, since it tends to be difficult to obtain a too small particle size, it is usually 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more. The particle size of the spray-dried particles can be controlled by appropriately selecting the spray format, pressurized gas flow supply rate, slurry supply rate, drying temperature, and the like.

  The bulk density of the spray-dried powder is usually 0.1 g / cc or more, preferably 0.3 g / cc or more, more preferably 0.5 g / cc or more, and most preferably 0.7 g / cc or more. Below this lower limit, there is a possibility of adversely affecting powder filling properties and powder handling, and is usually 1.7 g / cc or less, preferably 1.6 g / cc or less, more preferably 1.5 g / cc. Hereinafter, it is most preferably 1.4 g / cc or less. The bulk density exceeding this upper limit is preferable for powder filling properties and powder handling, but the specific surface area may be too low, and the reactivity in the firing step may be reduced.

In addition, if the powder obtained by spray drying has a small specific surface area, the reactivity between the raw material compounds is reduced in the next firing step, so as described above, the starting material is pulverized before spray drying, etc. It is preferable that the specific surface area be increased as much as possible by the above means. On the other hand, if the specific surface area is excessively increased, not only is industrial disadvantageous, but a lithium nickel manganese cobalt based composite oxide may not be obtained. Accordingly, the spray-dried particles thus obtained have a BET specific surface area of usually 10 m ² / g or more, preferably 20 m ² / g or more, more preferably 30 m ² / g or more, most preferably 35 m ² / g or more. Usually, it is preferably 70 m ² / g or less, preferably 65 m ² / g or less, and most preferably 60 m ² / g or less.

<Manufacture of a firing precursor in which lithium raw materials are separately mixed>
As a method for producing a firing precursor suitable for the present invention, a slurry in which a nickel compound, a manganese compound, and a cobalt compound are dispersed in a liquid medium is spray-dried and / or pyrolyzed, and then mixed with a lithium compound and fired. A method for producing the precursor will be described.

  In this case, the same nickel compound, manganese compound, and cobalt compound as those described above can be used, and the mixing method is also the same.

  In this method, after the wet mixing of the nickel compound, manganese compound and cobalt compound, it is then usually subjected to a drying and / or pyrolysis step. The drying method is not particularly limited, but the spray drying method is preferable for the same reason as described above.

In this method, a powder obtained by pulverizing to an average particle size of 0.4 μm or less by wet pulverization and then agglomerating primary particles to form solid secondary particles by spray drying and / or thermal decomposition. It is preferable to obtain The shape characteristics of the powder formed by agglomeration of primary particles to form solid secondary particles is basically lithium nickel manganese obtained by further mixing and firing with lithium raw material, although the particle size varies. This is also reflected in the cobalt-based composite oxide powder. Examples of the shape confirmation method include SEM observation and cross-sectional SEM observation.
The average particle size of the powder obtained by spray drying and / or thermal decomposition is usually 50 μm or less, more preferably 40 μm or less, and most preferably 30 μm or less. However, since it tends to be difficult to obtain a too small particle size, it is usually 3 μm or more, preferably 5 μm or more, more preferably 6 μm or more. As described above, the particle size of the spray-dried particles can be controlled by appropriately selecting the spray type, the pressurized gas flow supply rate, the slurry supply rate, the drying temperature, and the like.

Further, when the particulate matter obtained by spray drying and / or thermal decomposition has a small specific surface area, a lithium nickel manganese cobalt based composite oxide is produced by a firing reaction with a lithium compound in the next step. As described above, it is preferable that the specific surface area be increased as much as possible by means such as pulverizing the starting material before spray drying and / or thermal decomposition. On the other hand, excessively high specific surface area is industrially disadvantageous. Therefore, the powder particles obtained by spray drying and / or pyrolysis are usually 20 m ² / g or more, preferably 30 m ² / g or more, more preferably 40 m ² / g or more, and more preferably in terms of BET specific surface area. It is preferably 50 m ² / g or more, most preferably 60 m ² / g or more, and usually 200 m ² / g or less, preferably 150 m ² / g or less.

Examples of the lithium compound mixed with the granulated particles obtained by spray drying and / or thermal decomposition include Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH · H ₂ O, LiH, LiF, LiCl, LiBr, LiI. , CH ₃ OOLi, Li ₂ O, Li ₂ SO ₄ , dicarboxylic acid Li, citrate Li, fatty acid Li, alkyllithium and the like. Among these lithium compounds, lithium compounds that do not contain nitrogen atoms or sulfur atoms are preferred because they do not generate harmful substances such as SO _x and NO _x during the firing treatment. In view of reducing the carbon concentration C as much as possible, it is a compound that does not contain a carbon atom. Taking these points into consideration, LiOH and LiOH.H ₂ O are particularly preferable. These lithium compounds are used alone. Two or more kinds may be used in combination.

  As the particle size of such a lithium compound, the average particle size is usually 500 μm or less, preferably in order to improve the mixing performance with a mixture containing a nickel raw material, a manganese raw material, and a cobalt raw material, and to improve battery performance. Is 100 μm or less, more preferably 50 μm or less, still more preferably 20 μm or less, and most preferably 10 μm or less. On the other hand, those having a too small particle size have a mean particle size of usually 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.2 μm or more, and most preferably 0 because the stability in the air is low. .5 μm or more. The median diameter as the average particle diameter of lithium hydroxide used as a raw material in the examples described later is set to a refractive index of 1.14 using a known laser diffraction / scattering particle size distribution measuring device, and the particle diameter standard is Measured as a volume reference. In this measurement, ethyl alcohol was used as a dispersion medium used in the measurement to obtain a saturated lithium hydroxide solution, and the measurement was performed after ultrasonic dispersion for 5 minutes.

  It is important to sufficiently mix the powder obtained by spray drying and / or pyrolysis with the lithium compound. The mixing method is not particularly limited as long as it can be sufficiently mixed, but it is preferable to use a powder mixing apparatus generally used for industrial purposes.

[Baking process]
The fired precursor thus obtained is then fired. Here, the “firing precursor” in the present invention means a lithium transition metal-based compound precursor before firing obtained by treating a spray-dried body, and for example, generates or sublimates decomposition gas during the aforementioned firing. Then, a compound that forms voids in the secondary particles may be contained in the spray-dried body to form a calcined precursor.

  For firing, for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like can be used. The firing process is usually divided into three parts: temperature increase, maximum temperature retention, and temperature decrease. The second maximum temperature holding portion is not necessarily limited to one time, and may include two or more stages depending on the purpose, which means that aggregation is eliminated to the extent that secondary particles are not destroyed. The temperature raising, maximum temperature holding, and temperature lowering steps may be repeated twice or more with a crushing step or a pulverization step which means crushing to primary particles or even fine powder. Even when the temperature raising / maximum temperature holding / temperature lowering process is repeated twice or more, each of the conditions (i) and (ii) is satisfied at each time.

  In the present invention, the amount (kg) of charging the raw material of the lithium transition metal compound described above into the firing container with respect to the volume (L) of the firing container during firing is not particularly limited, but is usually 0. 25 kg / L or more, preferably 0.30 kg / L or more, more preferably 0.35 kg / L or more, particularly preferably 0.40 kg / L or more, usually 0.75 kg / L or less, preferably 0.70 kg / L. Hereinafter, it is more preferably 0.65 kg / L or less, particularly preferably 0.60 kg / L or less. If this upper limit is exceeded, abnormal sintering may occur. Further, when the lower limit is not reached, productivity may not increase.

  Further, in the present invention, it is desirable to cover the firing container for the purpose of preventing foreign matters from being mixed into the powder being fired. In that case, since the air necessary for the reaction is prevented from being supplied to the powder being fired by covering, it is desirable to provide an opening in the firing container. The ratio of the opening is not particularly limited. Usually, when the area S1 of the opening of the container when the lid is not covered and the area of the opening when the lid is closed is S2, the value obtained by dividing S2 by S1 is 0. 02 or more, preferably 0.03 or more, more preferably 0.04 or more, particularly preferably 0.05 or more, usually 0.40 or less, preferably 0.30 or less, more preferably 0.20 or less, particularly preferably 0.10 or less. When this upper limit is exceeded, the opening is too large and foreign matter may be mixed during firing. Moreover, when less than this lower limit, there exists a possibility that air required for reaction may not fully be supplied.

In the production method of the present invention, in the temperature raising process, the temperature in the furnace is usually raised at a temperature raising rate of 2 ° C./min or less. If the heating rate is too high, a large amount of sintered ingots are produced when the holding temperature is increased to shorten the holding time, and the yield of the sieve is lowered when classification is performed after sintering. The baking is carried out at a rate of temperature rise of preferably 1.9 ° C./min or less, more preferably 1.8 ° C./min or less, and most preferably 1.7 ° C. or less.
The lower limit value of the heating rate in the heating process is not particularly limited in order to exhibit the effect of the present invention, but is preferably 0.6 ° C./min or more, more preferably 0.7 ° C. from the viewpoint of productivity. / Min or more, most preferably 0.8 ° C./min or more.

  In the present invention, the temperature rise start temperature during firing is not particularly limited, but is usually 300 ° C. or higher, preferably 325 ° C. or higher, more preferably 350 ° C. or higher, particularly preferably 375 ° C. or higher, usually 600 ° C. or lower, preferably It is 575 ° C. or lower, more preferably 550 ° C. or lower, particularly preferably 525 ° C. or lower. If this upper limit is exceeded, firing may be started at the temperature rise start temperature, which may cause sintering. When the lower limit value is not reached, it may take time to raise the temperature from the temperature rise start temperature to the holding temperature.

  The holding temperature at the time of firing, that is, the maximum temperature depends on the composition and the lithium compound raw material used, but as a tendency, if the firing temperature is too high, the primary particles grow too much, and conversely, if the firing temperature is too low, the crystal structure is not sufficient. Development and specific surface area become too large. The firing temperature is usually 800 ° C. or higher, preferably 850 ° C. or higher, more preferably 900 ° C. or higher, most preferably 950 ° C. or higher, and usually 1100 ° C. or lower, preferably 1075 ° C. or lower, more preferably 1050 ° C. or lower, Most preferably, it is 1025 degrees C or less.

  The holding time in this maximum temperature holding step, that is, the holding time at the time of firing varies depending on the holding temperature, but is usually 30 minutes or more, preferably 3 hours or more, more preferably 5 hours or more within the above temperature range. Most preferably, it is 6 hours or more, 20 hours or less, preferably 18 hours or less, more preferably 16 hours or less, and most preferably 15 hours or less. If the holding time is too short, it is difficult to obtain a lithium nickel manganese cobalt based composite oxide powder with good crystallinity, and it is not practical to have a too long holding time. If the firing time is too long, productivity is significantly impaired, which is disadvantageous.

In the present invention, in particular, since the holding temperature is increased to shorten the holding time, and the rate of temperature rise is slowed to prevent the formation of sintered ingots in this case, the holding time during firing and the temperature rise during firing The heating time of the process is set to satisfy the following formula (1).
Holding time at firing / Temperature raising time in firing process ≦ 1.5 (1)
If the holding time at the time of firing is longer than 1.5 times the temperature raising time, the effect of shortening the firing time according to the present invention is insufficient. In particular, the holding time during firing / temperature raising time during the temperature raising process during firing is preferably 1.4 or less, and particularly preferably 1.3 or less. In addition, although there is no restriction | limiting in particular about the holding time at the time of baking / the temperature rising time of the temperature rising process at the time of baking, Preferably it is 0.3 or more, Most preferably, it is 0.5 or more.

  In the temperature lowering step after the holding step, the temperature in the furnace is usually decreased at a temperature lowering rate of 0.1 ° C./min to 10 ° C./min. If the temperature lowering rate is too slow, it takes time and is industrially disadvantageous. However, if it is too fast, the uniformity of the target object tends to be lost or the deterioration of the container tends to be accelerated. The temperature lowering rate is preferably 1 ° C./min or more, more preferably 3 ° C./min or more, preferably 7 ° C./min or less, more preferably 5 ° C./min or less.

  As an atmosphere during firing, an oxygen-containing gas atmosphere such as air can be used. Usually, the atmosphere has an oxygen concentration of 1% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and 100% by volume or less, preferably 50% by volume or less, more preferably 25% by volume or less.

In the present invention, firing can be performed while forcibly aeration of air through a firing furnace using a blower or the like. The amount of aeration is not particularly limited, but usually the value obtained by dividing B by A when the amount of calcined powder recovered from the furnace per unit time is A kg / hr and the amount of aeration is Bm ³ / hr is 1 .0m ³ / kg or more, preferably 2.0 m ³ / kg or more, more preferably 3.0 m ³ / kg or more, particularly preferably 4.0 m ³ / kg or more, usually 9.0 m ³ / kg or less, preferably It is 8.0 m ³ / kg or less, more preferably 7.0 m ³ / kg or less, and particularly preferably 6.0 m ³ / kg or less. When this upper limit is exceeded, temperature control may be difficult due to the air that is ventilated. When the lower limit is not reached, sufficient oxygen required for firing may not be distributed, and abnormal sintering may occur.

  According to the present invention, although the temperature raising time is prolonged by slowing the temperature raising rate in the temperature raising process, a series of firing of temperature raising, maximum temperature holding, and temperature lowering by conventional methods by high temperature and short time baking. While the process required 20 to 25 hours, this series of baking steps can be shortened to 0.6 to 0.9 times, 15 to 18 hours.

[Sieving process after firing]
Although the target lithium transition metal composite oxide can be obtained by performing the above-mentioned firing step, the production method of the present invention is fired because there is no problem of formation of a sintered mass in the firing step. When the lithium transition metal composite oxide after being classified with a sieve having an opening of 1 mm without any treatment, the lithium transition metal composite oxide can be obtained in high yield.
The yield is usually 90% or more, preferably 94% or more, and more preferably 98% or more. When less than this lower limit, the amount that can be used as the battery material is small, the raw material loss is large, and the productivity is poor.

There is no restriction | limiting in the sieving system in this sieving process, as long as the effect of this invention is not impaired remarkably. For example, it can be sieved by a vibrating sieve (with or without balls), manual sieving, or the like.
Moreover, there is no restriction | limiting also in the strength of a sieve, and it is arbitrary in the range which does not impair the effect of this invention remarkably. Further, there is no limit to the time for sieving.

In addition, as described above, after classification with the sieve having a mesh opening of 1 mm, for the purpose of preventing streaking when producing a positive electrode plate using a lithium transition metal composite oxide as a positive electrode active material, finer mesh openings Classification may be performed with a sieve. There is no restriction | limiting in the sieving system, and it is arbitrary unless the effect of this invention is impaired remarkably. For example, it can be sieved by a vibrating sieve (with or without balls), a classifier of a type that presses powder against a cylindrical mesh screen with a blade rotating at high speed, and a manual sieve.
Moreover, there is no restriction | limiting also in the strength of a sieve, and it is arbitrary in the range which does not impair the effect of this invention remarkably. Further, there is no limit to the time for sieving.

[Other processes]
In the production method of the present invention, steps other than the sieving step and the firing step may be performed as long as the effects of the present invention are not significantly impaired.
For example, a pulverization step of pulverizing the lithium transition metal composite oxide obtained by firing, a classification step of sieving the obtained lithium transition metal composite oxide, or the like may be performed.
When the lithium transition metal composite oxide of the present invention is used as a positive electrode active material of a lithium secondary battery, it is usually used as a positive electrode active material after performing these pulverization steps and classification steps.

Further, for example, a part of the raw material may be added to or removed from the firing precursor in order to adjust the ratio of the contained elements.
Further, for example, in order to keep the median diameter and maximum particle diameter of the firing precursor within the above-described range, pulverization or the like may be performed as appropriate.

  EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples unless it exceeds the gist.

[Production of lithium transition metal composite oxide]
<Example 1>
LiOH.H ₂ O, NiO, CoOOH, and Mn ₃ O ₄ were mixed at a molar ratio of Li: Ni: Co: Mn = 0.05: 0.33: 0.33: 0.33. Water was added to the slurry to prepare a slurry having a solid content concentration of 20% by weight. While stirring this slurry, it was pulverized using a circulating medium agitation type wet pulverizer until the average particle size of the solids in the slurry was 0.4 μm or less and the viscosity of the slurry was 200 cP. This slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 7 μm. Air was used as the drying gas during spray drying, and the drying gas inlet temperature was 140 ° C.

The granulated particles obtained by spray drying and an anhydrous LiOH pulverized product (median diameter of about 15 μm) are weighed so that the molar ratio is anhydrous LiOH: (Ni + Co + Mn) = 1: 1, and is mixed with a mixer-type mixer. Mixing was performed to obtain a calcined precursor as a mixed powder. The mixture, including LiOH · _{H 2} O was added in the preceding grinding, Li, Ni, Co, the molar ratio of Mn Li: (Ni + Co + Mn) = 1.05: was 1.00.

This firing precursor is filled in a 3.7L ceramic firing container at a rate of 1.5kg per container (amount of charge per container 0.4kg / L), and four containers are continuously fired. The furnace was charged and heated in an air atmosphere from a temperature increase start temperature of 378 ° C. to 975 ° C. at a temperature increase rate of 1.75 ° C./min (temperature increase time 6.38 hours), and then 975 ° C. And calcined for 7.5 hours, and then cooled to 3.35 ° C./min to obtain a calcined powder. At this time, for the purpose of preventing foreign matter from being mixed during firing, the firing container was covered and an opening was provided in the firing container for the purpose of spreading air over the firing precursor even in the covered state. The opening was designed so that the value obtained by dividing S2 by S1 is 0.056, where S1 is the area S1 of the opening of the container when the lid is not covered, and S2 is the area of the opening when the lid is closed. Further, forced aeration with a blower was performed in the firing furnace during firing. The air flow rate is 2.4 m ³ / kg when B is divided by A when the amount of calcined powder recovered from the furnace per unit time is A kg / hr and the air flow rate is Bm ³ / hr. Was set as follows.

The fired powder was passed through a sieve having an opening of 1 mm and further passed through a sieve having an opening of 45 μm to obtain a lithium transition metal composite oxide as a positive electrode active material for a lithium secondary battery.

  When the obtained lithium transition metal complex oxide was subjected to X-ray structural analysis, it was a hexagonal layered rock salt type single-phase compound. Further, elemental analysis by ICP was performed, and it was Li: Ni: Co: Mn = 1.04: 0.33: 0.33: 0.33.

<Comparative Example 1>
The firing precursor was heated from a temperature increase start temperature of 378 ° C. to 945 ° C. at a temperature increase rate of 2.50 ° C./min in an air atmosphere (temperature increase time 4.76 hours), and then at 945 ° C. for 15 hours. A lithium transition metal composite oxide was obtained as a positive electrode active material for a lithium secondary battery in the same manner as in Example 1 except that firing was performed.

<Comparative example 2>
The firing precursor was heated from a temperature increase start temperature of 378 ° C. to 975 ° C. at a temperature increase rate of 2.50 ° C./min in an air atmosphere (temperature increase time 4.76 hours), and then 7 minutes at 975 ° C. A lithium transition metal composite oxide was obtained as a positive electrode active material for a lithium secondary battery in the same manner as in Example 1 except that firing was performed for 5 hours.

<Comparative Example 3>
The calcined precursor was heated from a temperature increase start temperature of 378 ° C. to 975 ° C. at a temperature increase rate of 6.1 ° C./min in an air atmosphere (temperature increase time 1.94 hours), and then at 975 ° C. 7. A lithium transition metal composite oxide was obtained as a positive electrode active material for a lithium secondary battery in the same manner as in Example 1 except that baking was performed for 5 hours.

<Example 2>
Li ₂ CO ₃ , Ni (OH) ₂ , CoOOH, and Mn ₃ O ₄ are mixed at a molar ratio of Li: Ni: Co: Mn = 1.095: 0.33: 0.33: 0.33 Then, water was added thereto to prepare a slurry having a solid content concentration of 20% by weight. While this slurry was stirred, it was pulverized using a circulating medium agitation type wet pulverizer until the average particle size of the solid content in the slurry was 0.4 μm or less and the viscosity of the slurry was 2000 cP. This slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 10 μm. Air was used as the drying gas during spray drying, and the drying gas inlet temperature was 200 ° C.

This spray-dried powder is filled in a ceramic firing container with a capacity of 3.7 L at a rate of 1.8 kg per container (a charged amount per container is 0.49 kg / L), and four containers are continuously fired. The furnace was charged and heated in an air atmosphere from a temperature rise start temperature of 350 ° C. to a temperature of 1007 ° C. at a temperature rise rate of 1.25 ° C./min (temperature rise time: 7.3 hours). Was calcined for 3.8 hours and then cooled to 1.95 ° C./min to obtain a calcined powder. At this time, for the purpose of preventing foreign matter from being mixed during firing, the firing container was covered and an opening was provided in the firing container for the purpose of spreading air over the firing precursor even in the covered state. The opening was designed so that the value obtained by dividing S2 by S1 is 0.056, where S1 is the area S1 of the opening of the container when the lid is not covered, and S2 is the area of the opening when the lid is closed. Further, forced aeration with a blower was performed in the firing furnace during firing. The air flow rate is 4.1 m ³ / kg when B is divided by A when the amount of calcined powder recovered from the furnace per unit time is A kg / hr and the air flow rate is Bm ³ / hr. Was set as follows.

  The fired powder was passed through a sieve having an opening of 1 mm and further passed through a sieve having an opening of 45 μm to obtain a lithium transition metal composite oxide as a positive electrode active material for a lithium secondary battery.

[Evaluation of productivity and yield under sieve]
For each of the fired powders obtained in Examples 1 and 2 and Comparative Examples 1 to 3, the yield and productivity of the 1 mm sieve after firing (when the firing precursor is fired by the method as in Example 1) The weight of the calcined powder collected per unit time) was compared, and the results are shown in Table 1.

From Table 1, when the holding temperature is raised to shorten the holding time, the productivity is improved, but at the same heating rate as the normal baking, the yield of 1 mm sieve after baking is reduced due to abnormal sintering. It was found that the loss increased (Comparison between Comparative Example 1 and Comparative Example 2).
Further, it was found that when the heating rate in the heating process was increased in order to further shorten the firing time from Comparative Example 2, the yield reduction of the 1 mm sieve became more remarkable and the loss increased (Comparative Examples 1 to 1). 3 contrast).
However, it has been found that productivity can be improved with little loss due to 1 mm sieve after firing even if firing is carried out under the conditions of raising the holding temperature and shortening the holding time by lowering the heating rate (Example 1 and Comparison with Comparative Example 1).
Further, in Example 1, since the time required for raising the temperature is long, the total firing time is long. Therefore, when Example 1 is compared with Comparative Example 2 and Comparative Example 3, the productivity of Example 1 is Looks like it's going down. However, in Comparative Example 2 and Comparative Example 3, abnormal sintering was caused and a sintered lump was formed, so that the yield under the 1 mm sieve was low and the loss of raw material was high (Example) 1 and Comparative Example 2 and Comparative Example 3).
Based on the knowledge obtained in Example 1 and Comparative Examples 1 to 3, Example 2 obtained a good result by applying it to a system in which the raw material compound and the production process were changed.

[Performance evaluation as positive electrode active material]
Using the lithium transition metal composite oxides obtained in Examples 1 and 2 and Comparative Example 1 above, coin-type cells were prepared according to the following <Battery Evaluation>, initial discharge capacity evaluation, rate evaluation, and low temperature The characteristics were evaluated and the results are shown in Table 2.
In the following, 1C represents a current value for discharging the reference capacity of the battery in one hour.

<Battery evaluation>
1. Rate evaluation 1-1. Battery preparation 75 parts by weight of lithium transition metal composite oxide (positive electrode active material) obtained in Examples and Comparative Examples, 20 parts by weight of acetylene black, and 5 parts by weight of polytetrafluoroethylene powder are sufficiently mixed in a mortar to form a thin sheet. What was made was punched out to 9 mmφ. This was crimped to Al expanded metal to obtain a positive electrode.
As the negative electrode, lithium metal having a diameter of 12 mm and a thickness of 1 mm was used.
Furthermore, lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a weight ratio of 3: 7 so as to be 1 mol / liter to prepare an electrolytic solution.
After placing the above positive electrode soaked with electrolyte in a positive electrode can and a separator made of porous polyethylene film soaked with electrolyte, a polypropylene gasket was placed and pressed. Furthermore, the above negative electrode and spacer were put, and finally a negative electrode can was covered and sealed to produce a coin-type battery.

1-2. Rate evaluation About the battery produced as mentioned above, charging / discharging was implemented in the voltage range of 3.0V-4.2V as measurement conditions.
Charging time 0.2 mA / cm ^2, the charge and discharge test was performed at a current density during discharge 11 mA / cm ^2, rate evaluated by measuring the initial discharge capacity (mAh / g) of the positive electrode active material per unit weight at that time It was.

2. Resistance evaluation 2-1. Battery preparation 75 parts by weight of lithium transition metal composite oxide (positive electrode active material) obtained in Examples and Comparative Examples, 20 parts by weight of acetylene black, and 5 parts by weight of polytetrafluoroethylene powder are sufficiently mixed in a mortar to form a thin sheet. What was made was punched to 12 mmφ. This was crimped to Al expanded metal to obtain a positive electrode.
Further, 92.5 parts by weight of graphite powder having a particle size of about 8 to 10 μm and 7.5 parts by weight of polyvinylidene fluoride were mixed, and N-methylpyrrolidone was added thereto to form a slurry. This slurry was applied to one side of a copper foil and dried. This was punched out to 12 mmφ, and further pressed at 0.5 ton / cm ² to obtain a negative electrode.
Furthermore, lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a weight ratio of 3: 7 so as to be 1 mol / liter to prepare an electrolytic solution.
After placing the above positive electrode soaked with electrolyte in a positive electrode can and a separator made of porous polyethylene film soaked with electrolyte, a polypropylene gasket was placed and pressed. Furthermore, the negative electrode and the spacer soaked with the electrolytic solution were put, and finally the negative electrode can was covered and sealed to prepare a coin-type battery.

2-2. Evaluation of low-temperature resistance Before and after “2-3. Cyclic load test” described later, the low-temperature resistance described below was evaluated.
The manufactured coin-type battery was charged to 4.1 V with a constant current of 1/3 C, and then charged with a constant current of 1/3 C with a lower limit voltage of 3.0 V to adjust the charging depth to 40%. The coin-type battery was held in a low temperature atmosphere of −30 ° C. for 1 hour, and then discharged at ¼ C for 10 seconds. The current value (I) at the time of discharge, OCV ₁ (Open Circuit Voltage) immediately before discharge, and OCV ₂ after discharge were measured. The difference between OCV ₁ and OCV ₂ was ΔV, and resistance (R) was calculated from the following equation.
R = ΔV / I

As can be seen from Table 2, for the lithium transition metal composite oxides of Examples 1 and 2 and Comparative Example 1, the initial discharge capacity, the discharge capacity at a high current value (mA / cm ² ), and the low temperature resistance value were confirmed. Almost equivalent results were obtained.

In summary, by reducing the heating rate during the heating process during firing and increasing the holding temperature, the yield of the sieve after firing and the battery characteristics as the positive electrode active material are not impaired even if the firing time is shortened. I understand.
Further, if only the holding temperature at the time of firing is increased as in Comparative Example 2 to shorten the firing time, or if the firing time is shortened by increasing the heating rate at the time of firing as in Comparative Example 3, abnormal It turns out that the yield of the sieve after baking falls by sintering.
Therefore, it has been confirmed that the method for producing a positive electrode active material for a lithium secondary battery according to the present invention makes it possible to produce a high-quality positive electrode active material for a lithium secondary battery more efficiently and in a shorter time than before. It was.

  The field of application of the present invention is not particularly limited, and can be used for various known applications. For example, a notebook computer, a pen input personal computer, a mobile personal computer, an electronic book player, a mobile phone, a mobile fax, a mobile copy, a mobile phone Printer, Headphone Stereo, Video Movie, LCD TV, Handy Cleaner, Portable CD, Mini Disc, Walkie Talkie, Electronic Notebook, Calculator, Memory Card, Portable Tape Recorder, Radio, Backup Power Supply, Motor, Lighting Equipment, Toy, Game Equipment, Clock Suitable for use in strobes, cameras, etc.

Claims (6)

  A method for producing a transition metal compound for a lithium secondary battery by firing a firing precursor, wherein the temperature rise rate during the firing is 2 ° C./min or less. For producing a transition metal compound for use. In the method for producing a transition metal compound for a lithium secondary battery by firing a firing precursor, the holding time during firing and the temperature rising time during the firing satisfy the following formula (1): A method for producing a transition metal compound for a lithium secondary battery.
Holding time at firing / Temperature raising time in firing process ≦ 1.5 (1)   The method for producing a transition metal compound for a lithium secondary battery according to claim 1 or 2, wherein a holding time during firing is 30 minutes or longer and 20 hours or shorter.   The method for producing a transition metal compound for a lithium secondary battery according to any one of claims 1 to 3, wherein a holding temperature during firing is 800 ° C or higher and 1100 ° C or lower.   The method for producing a transition metal compound for a lithium secondary battery according to any one of claims 1 to 4, wherein the firing precursor includes granulated particles containing a transition metal and particles of a lithium raw material. . 6. The transition metal compound for a lithium secondary battery according to claim 1, wherein the composition of the obtained transition metal compound for a lithium secondary battery is represented by the following formula (2): 7. Manufacturing method.
_{Li 1 + x Ni a Mn b} Co c M d O 2-δ (2)
(In formula (2), M represents a metal element that substitutes a part of the sites of Ni and Mn.
a, b, c, and d are numbers satisfying 0.2 ≦ a ≦ 0.85, 0 ≦ b ≦ 0.8, 0 ≦ c ≦ 0.8, 0 ≦ d ≦ 0.4, and a + b + c + d = 1. Represents.
x represents a number satisfying −0.3 ≦ x ≦ 0.3, and δ represents a number satisfying −0.1 <δ <0.1. )