JP3798923B2 - Method for producing positive electrode active material for lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel positive electrode active material for a lithium secondary battery comprising a lithium-containing composite oxide and a method for producing the same.
[0002]
[Prior art]
In recent years, as devices become portable and cordless, expectations for non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, that are small, lightweight, and have high energy density are increasing. Known positive electrode active materials for lithium secondary batteries include composite oxides of lithium and transition metals, such as LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn ₂ O ₄ , and LiMnO ₂ . A lithium secondary battery using a rock salt layered composite oxide in which cobalt or nickel is dissolved as LiNi _0.8 Co _0.2 O ₂ as a positive electrode active material can achieve a relatively high capacity density of 180 to 190 mAh / g. Good reversibility is exhibited in a high voltage range of 2.7 to 4.3 V.
[0003]
Particularly recently, the adoption of lithium-nickel-cobalt composite oxides typified by LiNi _0.8 Co _0.2 O ₂ has begun as a material capable of developing a high capacity. Commercialization of lithium secondary batteries with high voltage and high energy density has been promoted by using these as positive electrode active materials and using carbon materials or the like that can occlude and release lithium as negative electrode active materials.
[0004]
Conventionally, as a method for producing a rock salt layered composite oxide in which cobalt or nickel is dissolved, such as LiNi _0.8 Co _0.2 O ₂ , a nickel-cobalt coprecipitate is mixed with a lithium compound, and is 920 ° C. in air in a stationary furnace. After heating for 3 hours (JP-A-1-129364), mixing nickel-cobalt coprecipitate with lithium compound, heating at a rate of 330 ° C./min using a rotary kiln, and pre-baking The method of lowering the temperature and further performing the main firing at 750 ° C. for 4 to 20 hours in an oxygen atmosphere in a stationary furnace (Japanese Patent Laid-Open No. 11-111290), mixing the nickel-cobalt coprecipitate with a lithium compound, A method of pre-baking at 500 ° C. for 5 hours and then lowering the temperature and further performing main baking at 720 ° C. for 10 hours in an oxygen atmosphere in a stationary furnace (Japanese Patent Laid-Open No. 10-214624) There has been proposed.
[0005]
However, in the method of performing pre-firing or main-firing using a rotary kiln, since solid powder flows in the rotary kiln, contamination of impurities such as alumina as the inner wall material is unavoidable due to wear of the rotary kiln. There are problems such as poor charge / discharge cycle durability of lithium secondary batteries using as active materials and high temperature deterioration of inner wall materials such as alumina of rotary kilns.
[0006]
In addition, when pre-firing or main-firing is performed in a stationary furnace, in industrial scale production that requires a large amount of firing at one time to improve productivity, avoid temperature fluctuations within the lot when solid powder is heated and cooled. Therefore, it is necessary to decrease the temperature increase or decrease rate in order to reduce the problem that it is difficult to produce a lithium-containing composite oxide with good characteristics and temperature variations. As a result, there is a problem that the temperature rise / fall time becomes long and the productivity is remarkably lowered.
[0007]
Moreover, the half width of the diffraction peak based on the (003) plane in X-ray diffraction obtained by mixing and heat-treating an alkali coprecipitated hydroxide of nickel salt and cobalt salt and lithium hydroxide is 0.01 to 0.1 °. There is also a proposal that this lithium-containing composite oxide has a high capacity and excellent thermal stability (Japanese Patent Laid-Open No. 9-129231). However, even if it is a lithium-containing composite oxide obtained by the production method described in this publication and having a half-value width of the diffraction peak based on the (003) plane within the above range, capacity, discharge average voltage, charge / discharge cycle durability And the safety was still unsatisfactory.
[0008]
[Problems to be solved by the invention]
As described above, the lithium-containing composite oxide produced by the conventional method includes the initial capacity of the battery, the initial discharge average voltage, the charge / discharge cycle durability, the safety and the positive electrode active material for the lithium secondary battery. We needed further improvements in productivity.
[0009]
The present invention provides a novel positive electrode active material for a lithium secondary battery having a large battery capacity, high discharge average voltage, excellent charge / discharge cycle durability, and high safety, and comprising a lithium-containing composite oxide, and its production It aims to provide a method.
[0010]
[Means for Solving the Problems]
The inventor of the present invention has a specific value in a half-value width of a diffraction peak represented by a specific general formula and based on the (110) plane at 2θ = 65 ± 1 ° in powder X-ray diffraction using CuKα rays. It has been found that the lithium-containing composite oxide satisfies all of high initial battery capacity, high discharge average voltage, excellent charge / discharge cycle durability and high safety as a positive electrode active material of a lithium secondary battery.
[0011]
Thus, the present invention has the general formula LiNi _x Co _y M _z O ₂ (where M is at least one element selected from Al, Mn, Ti, Mg and Cr, 0.95 ≦ x + y + z ≦ 1.05). 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.2) and 2θ = 65 ± of powder X-ray diffraction using CuKα ray. A method for producing a positive electrode active material for a lithium secondary battery comprising a lithium-containing composite oxide having a half-width of a diffraction peak based on a (110) plane at 1 ° of 0.13 to 0.20 °, comprising: A pre-firing of a salt or coprecipitate containing cobalt, a mixture of a salt or coprecipitate containing nickel, cobalt, and element M and a lithium compound, or a mixture of a lithium compound and a compound containing element M is performed at a firing temperature 430. ~ 530 ° C , temperature drop rate 20 Lithium characterized in that it is carried out at 0 to 600 ° C./hour , followed by post- stage calcination at a calcination temperature of 700 to 850 ° C. and a temperature drop rate of 100 to 500 ° C./hour , and at least the post-stage calcination performed at a roller hearth kiln It exists in the manufacturing method of the positive electrode active material for secondary batteries.
[0012]
Hereinafter, the present invention will be described in more detail.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, lithium-containing composite oxide constituting the positive electrode active material of a lithium secondary battery, the general formula is represented by _{LiNi x Co y M z O 2} . Here, M is at least one element selected from Al, Mn, Ti, Cr and Mg. x, y, and z are 0.95 ≦ x + y + z ≦ 1.05, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, and 0 ≦ z ≦ 0.2, respectively. Chosen to satisfy.
[0014]
In the above, even when z = 0 and M is not included, the initial capacity of the battery is high and the charge / discharge cycle stability is also high. In the case where z is not 0 and M is Al, the charge / discharge cycle stability of the battery is further higher than that in the case where M is not added (z = 0), the capacity decrease during rapid charge / discharge is small, the heat generation temperature is high, Safety is even higher. When z is not 0 and M is Mn, the heat generation temperature of the battery is higher and the safety is higher than when M is not added. Furthermore, when z is not 0 and M is Ti, Cr, or Mg, the charge / discharge cycle stability of the battery is high and the discharge voltage is high as compared with the case where they are not added. In particular, in the present invention, M is preferably at least one element of Al and Mn.
[0015]
In the above, when x is less than 0.5 for x, y, and z, the initial capacity of the battery decreases. When it exceeds 0.9, the thermal stability of the battery is lowered or the charge / discharge cycle durability is lowered. Preferably, 0.60 ≦ x ≦ 0.85. It is not preferred that y is less than 0.05 because the thermal stability of the battery is lowered or the charge / discharge cycle durability is lowered. If it exceeds 0.3, the initial capacity of the battery is lowered. Preferably, 0.10 ≦ y ≦ 0.20. Further, z is preferably 0.005 ≦ z ≦ 0.10 although it depends on the additive element.
[0016]
In addition, the lithium-containing composite oxide that is the positive electrode active material of the present invention has a half-value width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° in powder X-ray diffraction using CuKα rays is 0. .13 to 0.20 °. The half width of the diffraction peak based on the (110) plane reflects the crystallite diameter of the lithium-containing composite oxide, and it seems that the larger the half width, the smaller the crystallite diameter. When the half width of the diffraction peak based on the (110) plane is less than 0.13 °, the charge / discharge cycle durability, initial capacity, average discharge voltage, or safety of the battery used as the positive electrode active material is lowered. On the other hand, when the half width of the diffraction peak based on the (110) plane exceeds 0.20 °, the initial capacity and safety of the battery are lowered. A preferred half width is 0.14 to 0.17 °.
[0017]
In the present invention, the lithium-containing composite oxide having the specific formula and the half-value width of the specific X-ray diffraction peak is manufactured as follows . That is, a salt or coprecipitate containing nickel and cobalt, a mixture of a salt or coprecipitate containing nickel, cobalt and element M and a lithium compound, or a mixture of a compound containing lithium compound and element M Pre-stage baking is performed at ˜530 ° C., and then post-stage baking is performed at 700 to 850 ° C. In the above, when the element M is not included in the lithium composite oxide (when z = 0), a mixture of a salt or coprecipitate containing nickel and cobalt and a lithium compound is fired.
[0018]
In the salt or coprecipitate containing nickel and cobalt, or the salt or coprecipitate containing nickel, cobalt, and element M, when nickel, cobalt, and element M are contained, nickel, cobalt, and element M are uniform. Are preferably distributed. In addition, in the salt containing nickel and cobalt and the salt containing nickel, cobalt and element M, carbonate, sulfate, nitrate, complex salt and the like are preferably used.
[0019]
The salt or coprecipitate containing nickel and cobalt, or the salt or coprecipitate containing nickel, cobalt and element M is preferably produced by the following method. For example, when nickel chloride, cobalt chloride, and the element M are contained, the respective chlorides of the element M are dissolved in an aqueous solution saturated with carbon dioxide gas, and a sodium hydrogen carbonate solution is added to cause coprecipitation, followed by drying. Method, when nickel, cobalt, and element M are the same as above, alkali is added to an aqueous solution containing the respective chlorides of element M and coprecipitated and dried, nickel, cobalt, and if necessary Then, an ammine complex mixed aqueous solution containing the element M is heated to 100 to 150 ° C. at a pressure of 1 to 5 atm and dried.
[0020]
In the case where the element M is included in the lithium-containing composite oxide and the salt or coprecipitate containing nickel, cobalt, and the element M is not used, the salt or coprecipitate containing nickel and cobalt, and the element M A method of mixing an aqueous solution containing the above compound, further mixing a lithium compound, and drying is preferably employed. Even when a salt or coprecipitate containing nickel, cobalt and element M is used, element M may be replenished by further mixing with an aqueous solution containing a compound of element M. As the lithium compound mixed with the salt or coprecipitate containing nickel, cobalt, and element M contained as necessary, lithium hydroxide, lithium carbonate, lithium oxide and the like are preferably used.
[0021]
In the present invention, a mixture of a salt or coprecipitate containing nickel, cobalt and optionally the element M and a lithium compound is then fired. Firing is required to be performed by pre-stage firing and post-stage firing in each of the specific temperature ranges described above. The firing in the former stage and the latter stage may be two or more, respectively. When any one-stage firing is performed instead of the above-mentioned two-stage firing of the former stage and the latter stage, characteristics of the obtained lithium-containing composite oxide as a positive electrode active material, specifically, an initial capacity of the battery, Charge / discharge cycle durability, safety, average discharge voltage, etc. are reduced. Even in the two-stage firing, when the temperature of the first-stage firing was less than 430 ° C. or over 530 ° C., or the temperature of the second-stage firing was less than 700 ° C. or over 850 ° C., it was obtained in the same manner as above. The characteristics of the lithium-containing composite oxide as the positive electrode active material, that is, the initial capacity, the charge / discharge cycle durability, the safety, the average discharge voltage, the rapid charge / discharge characteristics and the like are deteriorated.
[0022]
In the present invention, in the pre-stage firing, the holding time at the firing temperature is preferably 0.3 to 3 hours, and particularly 0.5 to 2 hours is appropriate. Further, the rate of temperature decrease in the pre-stage firing (rate at which the furnace temperature falls from the firing temperature to 200 ° C.) is 200 to 600 ° C./hour , preferably 300 to 500 ° C./hour. When the pre-stage firing time is less than 0.3 hours, the reaction between the powder mainly composed of nickel and cobalt and the lithium compound is insufficient, and the lithium secondary oxide using the obtained lithium-containing composite oxide as the positive electrode active material This is not preferable because the initial capacity of the battery is reduced. On the other hand, if the firing time exceeds 3 hours, the productivity of the battery decreases, which is not preferable. In the pre-stage firing, the rate of temperature increase has little effect, but if the rate of temperature decrease is less than 200 ° C./hour, the crystal diameter of the lithium-containing composite oxide becomes unfavorable. On the other hand, if the rate of temperature decrease exceeds 600 ° C./hour, rapid cooling equipment is required in large-scale production, which increases equipment costs and running costs. Further, in the present invention, the post-stage baking is preferably performed for 1 to 4 hours at the above-mentioned baking temperature, and in particular, 1 to 2.5 hours is appropriate. Moreover, the temperature-fall rate (speed at which the furnace temperature falls from the firing temperature to 200 ° C.) in the latter-stage firing is 100 to 500 ° C./hour , and preferably 200 to 400 ° C./hour. When the firing time is less than 1 hour, the conversion reaction of a powder mainly composed of nickel and cobalt and a lithium compound into a layered structure containing lithium is not preferable. On the other hand, when the calcination time exceeds 4 hours, as a result of crystal growth, the performance of the obtained lithium-containing composite oxide as a positive electrode active material decreases, and the productivity of the lithium-containing composite oxide decreases. Therefore, it is not preferable. Even in the post-stage firing, the rate of temperature rise has little effect, whereas when the rate of temperature drop is less than 100 ° C./hour, the crystal diameter of the lithium-containing composite oxide increases. On the other hand, if the temperature lowering rate exceeds 300 ° C./hour or more, rapid cooling equipment is required in large-scale production, which is not preferable because equipment costs and running costs increase.
[0023]
The above-mentioned pre-stage baking and post-stage baking are preferably carried out in an oxygen-containing gas, and the oxygen concentration in the pre-stage baking is not particularly problematic, but is suitably carried out in the atmosphere. On the other hand, the post-stage firing is preferably performed in an oxygen-containing gas having a high oxygen concentration. The oxygen concentration in the subsequent firing is preferably 19 to 100% by volume, and particularly preferably 25 to 50% by volume. If the oxygen concentration in the subsequent firing is low, the performance of the obtained lithium-containing composite oxide as a positive electrode active material is undesirably lowered.
[0024]
Examples of means for carrying out the above pre-stage baking and post-stage baking of the present invention on an industrial scale include a rotary kiln, a tunnel furnace, a roller hearth kiln, and the like. The durability of the inner wall is poor, and in the case of rapid firing, there is a problem of dust treatment at the outlet, which is not preferable. The tunnel furnace is not preferable when processing a large amount of powder on an industrial scale, because it is difficult to make the temperature distribution uniform, and as a result, the performance of the obtained lithium-containing composite oxide as a positive electrode active material is inferior.
[0025]
On the other hand, a roller hearth kiln is filled with powder to be fired in a sheath box made of refractory, and continuously fired by moving the sheath box over the rotating roller by putting the sheath box into a tunnel-shaped furnace. Device. Roller hearth kiln, also in the rapid temperature rise or rapid cooling, the positive electrode active properties as materials are particularly good, and the productivity of the lithium-containing composite oxide obtained since the temperature distribution can be made uniform in the sheath boxes It is preferable because it is high. This is because the average crystallite diameter can be controlled because the temperature distribution is uniform. Pre-stage calcination and subsequent firing, which both are suitable to be implemented in a roller hearth kiln, in the present invention, it performs at least subsequent firing in a roller hearth kiln.
[0026]
In the present invention, the positive electrode used as the positive electrode active material of the lithium-containing composite oxide is preferably produced as follows. That is, a positive electrode mixture is formed by mixing the lithium-containing composite oxide powder with a carbon-based conductive material such as acetylene black, graphite, and ketjen black and a binder.
[0027]
A slurry or kneaded material comprising the above-mentioned positive electrode mixture and a solvent or dispersion medium of the binder in the positive electrode mixture is applied to and / or supported on a positive electrode current collector such as an aluminum foil or a stainless steel foil, and the positive electrode A board. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is used. A porous polyethylene, a porous polypropylene film, etc. are used for a separator.
[0028]
As the solvent of the electrolyte solution used in the lithium secondary battery using the lithium-containing composite oxide of the present invention as the positive electrode active material, carbonate is preferable. The carbonate ester can be either cyclic or chain. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate (hereinafter referred to as EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (hereinafter referred to as DEC), ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and the like.
[0029]
In this invention, the said carbonate ester can be used individually or in mixture of 2 or more types. Moreover, you may mix and use with another solvent. Moreover, depending on the material of the negative electrode active material, when a chain carbonate ester and a cyclic carbonate ester are used in combination, discharge characteristics, cycle durability, and charge / discharge efficiency may be improved. Further, vinylidene fluoride-hexafluoropropylene copolymer (for example, “Kyner” Atchem Co., Ltd. trade name), vinylidene fluoride-perfluoro (propyl vinyl ether) disclosed in JP-A-10-294131 is used as these organic solvents. It is good also as a gel polymer electrolyte by adding a copolymer and adding the solute mentioned later.
[0030]
Solutes constituting the electrolyte solution used in the present invention include ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ CO ₂ ⁻ , (CF ₃ SO ₂ ) It is preferable to use any one or more of lithium salts having ₂ N ⁻ or the like as an anion. In the above electrolyte solution or polymer electrolyte, an electrolyte comprising a lithium salt is preferably added to the solvent or solvent-containing polymer at a concentration of 0.2 to 2.0 mol / liter. If it deviates from this range, the ionic conductivity is lowered, and the electrical conductivity of the electrolyte solution is lowered. Particularly preferably, 0.5 to 1.5 mol / liter is selected.
[0031]
The negative electrode active material in the lithium secondary battery of the present invention is a material that can occlude and release lithium ions. Although the material which forms these negative electrode active materials is not specifically limited, For example, a lithium metal, a lithium alloy, a carbon material, an oxide mainly composed of a metal of group 14 or 15 of the periodic table, a silicon carbide compound, a boron carbide compound, etc. Carbon compounds, silicon oxide compounds, titanium sulfide, and the like. As the carbon material, pyrolyzate of organic matter, artificial graphite, natural graphite, earth graphite, expanded graphite, scale-like graphite and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used. As the negative electrode current collector, a copper foil, a nickel foil or the like is used.
[0032]
When the active material is a carbon material or the like, the negative electrode used in the present invention can be produced by kneading with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector, drying, or pressing. preferable. There are no particular restrictions on the shape of the lithium battery. A sheet shape (so-called film shape), a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.
[0033]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Examples 6 to 8 are comparative examples of the present invention.
[Example 1]
Each of the nickel and cobalt ammine complexes is mixed and heated to 100 to 150 ° C. under a pressure of 1 to 5 atm. A salt containing nickel and cobalt (Ni: Co atomic ratio 0.8: 0.2) and lithium hydroxide monohydrate powder were mixed and filled into a sheath box (external dimensions, length 300 mm × width 300 mm × height 80 mm) made of mullite-cordierite refractory. The above-mentioned sheath box filled with the raw material powder is continuously supplied to a roller hearth kiln (full length 15m, height 1.8m, width 1.8m) and held at 515 ° C for 30 minutes for pre-stage firing. It was. The temperature increase rate from room temperature to 515 ° C. was 100 ° C./hour, and the temperature decrease time from 515 ° C. to 200 ° C. was 40 minutes (temperature decrease rate 470 ° C./hour).
[0034]
After the pre-stage firing, the powder was taken out from the sheath box, remixed, and again filled with the powder after the pre-stage firing. Using the same roller hearth kiln as above, changing the temperature distribution setting from the inlet to the outlet and the supply speed of the sheath box, continuously supplying the sheath box, under an oxygen-nitrogen stream containing 40% by volume of oxygen, 770 Subsequent firing was performed by holding at 1.5 ° C. for 1.5 hours. The temperature increase rate from room temperature to 770 ° C. was 400 ° C./hour, and the temperature decrease rate from 770 ° C. to 200 ° C. was 350 ° C./hour.
[0035]
The LiNi _0.80 Co _0.20 O ₂ powder thus obtained was measured for X-ray diffraction with CuKα using a RINT2100 type X-ray diffractometer manufactured by Rigaku Corporation. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.148 °.
[0036]
The above LiNi _0.80 Co _0.20 O ₂ powder, acetylene black, and polytetrafluoroethylene powder are mixed at a weight ratio of 80/16/4, and kneaded, molded, and dried while adding toluene to form a positive electrode plate having a thickness of 150 μm. Produced. Aluminum foil with a thickness of 20 μm is used as a positive electrode current collector, porous polypropylene with a thickness of 25 μm is used as a separator, a metal lithium foil with a thickness of 500 μm is used as a negative electrode, and a nickel foil with a thickness of 20 μm is used as a negative electrode current collector. Then, a stainless steel simple sealed cell (battery) was assembled in an argon glove box using a solution containing LiPF ₆ at a concentration of 1 mol in a 1: 1 mixed solvent of EC and DEC.
[0037]
The cell is charged to 4.3 V at a constant current of 0.2 mA per 1 cm ^{2 of} the positive electrode area, and then discharged to 2.5 V at a constant current of 0.2 mA to obtain an initial discharge capacity and a charge / discharge cycle test Was performed 20 times. The initial discharge capacity at 2.5 to 4.3 V was 198 mAh / g, the initial discharge average voltage was 3.777 V, and the capacity after 20 charge / discharge cycles was 198 mAh / g. Similarly, a stainless steel simple sealed cell is charged to 4.3 V at a constant current of 0.2 mA per 1 cm ^{2 of the} positive electrode area, disassembled in an argon glove box, and the positive electrode sheet after charging is taken out. After washing, punched out to a diameter of 3 mm, sealed in an aluminum capsule together with EC, and heated at a rate of 5 ° C./min with a scanning differential calorimeter to measure the heat generation start temperature. As a result, the heat generation start temperature was 186 ° C.
[Example 2]
After mixing each ammine complex of nickel and cobalt and mixing the salt containing nickel and cobalt obtained by heating this to 100 to 150 ° C. under a pressure of 1 to 5 atm, and an aluminum nitrate aqueous solution The powder was obtained by drying and baking at 300 ° C. for 5 hours. The powder and lithium hydroxide monohydrate powder are mixed, and the sheath box filled with the raw material powder is continuously supplied to the same roller hearth kiln as in Example 1, and the pre-stage firing is performed under the same conditions as in Example 1. Subsequent firing was performed.
[0038]
In the same manner as in Example 1, an X-ray diffraction chart of the obtained LiNi _0.8 Co _0.17 Al _0.03 O ₂ powder was measured. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane near 2θ = 65 ± 1 ° was 0.168 °.
[0039]
Using the LiNi _0.8 Co _0.17 Al _0.03 O ₂ powder, the battery performance was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity at 2.5 to 4.3 V was 188 mAh / g, the initial discharge average voltage was 3.770 V, and the capacity after 20 charge / discharge cycles was 185 mAh / g. Further, in the same manner as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 192 ° C.
[Example 3]
A nickel-cobalt coprecipitation hydroxide obtained by heating a coprecipitate obtained by coprecipitation of an aqueous solution containing chlorides of nickel and cobalt with an alkali and a manganese nitrate aqueous solution were mixed and dried, and the mixture was dried at 300 ° C. for 5 hours. Powder was obtained by firing for a period of time.
[0040]
The powder and lithium hydroxide monohydrate powder are mixed, and the sheath box filled with the raw material powder is continuously supplied to the same roller hearth kiln as in Example 1, and the pre-stage firing is performed under the same conditions as in Example 1. Subsequent firing was performed. For the obtained LiNi _0.76 Co _0.18 Mn _0.06 O ₂ powder, X-ray diffraction was measured in the same manner as in Example 1 using CuKα rays. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.161 °.
[0041]
Battery performance was evaluated in the same manner as in Example 1 using the above LiNi _0.76 Co _0.18 Mn _0.06 O ₂ powder. As a result, the initial discharge capacity at 2.5 to 4.3 V was 183 mAh / g, the initial discharge average voltage was 3.767 V, and the capacity after 20 charge / discharge cycles was 183 mAh / g. Further, in the same manner as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation starting temperature was 188 ° C.
[Example 4]
A nickel-cobalt coprecipitation hydroxide obtained by heating a coprecipitate obtained by coprecipitation of an aqueous solution containing chlorides of nickel and cobalt with an alkali and a titanium nitrate aqueous solution were mixed and then dried, and the mixture was dried at 300 ° C. for 5 hours. Powder was obtained by firing for a period of time.
[0042]
The powder and lithium hydroxide monohydrate powder are mixed, and the sheath box filled with the raw material powder is continuously supplied to the same roller hearth kiln as in Example 1, and the pre-stage firing is performed under the same conditions as in Example 1. Subsequent firing was performed. The obtained LiNi _0.75 Co _0.22 Ti _0.03 O ₂ powder was used in the same manner as in Example 1. X-ray diffraction was measured using CuKα rays. In this X-ray diffraction, the half-value width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.162 °.
[0043]
Using the LiNi _0.75 Co _0.22 Ti _0.03 O ₂ powder, the battery performance was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity at 2.5 to 4.3 V was 187 mAh / g, the initial discharge average voltage was 3.795 V, and the capacity after 20 charge / discharge cycles was 187 mAh / g. Further, in the same manner as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 195 ° C. In addition, LiNi _0.75 Co _0.22 Mg _0.03 O ₂ and LiNi _0.75 Co _0.22 Cr _0.03 O ₂ using magnesium nitrate or chromium nitrate instead of titanium nitrate can obtain the same half-width of the diffraction peak, and have excellent battery characteristics. Obtained.
[Example 5]
As in Example 1, each of the ammine complexes of nickel and cobalt was mixed and heated to 100 to 150 ° C. under a pressure of 1 to 5 atm. 8: 0.2) and lithium hydroxide monohydrate powder were mixed and filled into a sheath box made of mullite-corgerite refractory. The above-mentioned sheath box filled with the raw material powder was continuously supplied to the same roller hearth kiln as in Example 1 and held at 490 ° C. for 1 hour for pre-stage firing. The rate of temperature increase from room temperature to 490 ° C. was 100 ° C./hour, and the rate of temperature decrease from 490 ° C. to 200 ° C. was 400 ° C./hour.
[0044]
After the powder was taken out from the sheath box after the pre-stage firing and remixed, the sheath box was again filled with the powder after the pre-stage firing. Using the same roller hearth kiln as in Example 1, changing the temperature distribution setting from the inlet to the outlet and changing the feeding speed of the sheath box, the sheath box was continuously fed, and under the oxygen-nitrogen flow of 40 vol% oxygen, 790 Subsequent firing was performed by holding at 2 ° C. for 2 hours. The rate of temperature increase from room temperature to 790 ° C. was 200 ° C./hour, and the rate of temperature decrease from 790 ° C. to 200 ° C. was 150 ° C./hour. In the same manner as in Example 1, X-ray diffraction using CuKα rays was measured for LiNi _0.80 Co _0.20 O ₂ powder. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.142 °.
[0045]
As a result of evaluating battery performance in the same manner as in Example 1 using the above LiNi _0.80 Co _0.20 O ₂ powder, the initial discharge capacity at 2.5 to 4.3 V was 198 mAh / g, and the initial discharge average voltage was 3.760 V. The capacity after 20 charge / discharge cycles was 197 mAh / g. Further, as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 183 ° C.
[Example 6]
As in Example 1, each ammine complex of nickel and cobalt was mixed and heated to 100 to 150 ° C. under a pressure of 1 to 5 atmospheres (the atomic ratio of Ni: Co was 0 .8: 0.2) and lithium hydroxide monohydrate powder were mixed and filled into a sheath box made of mullite-cordierite refractory. The above-mentioned sheath box filled with the raw material powder was laminated in a static furnace having a height of 2.8 m, a width of 2.8 m, and a depth of 2.8 m, and pre-baking was performed by holding at 515 ° C. for 18 hours. The temperature increase rate from room temperature to 515 ° C. was 30 ° C./hour, and the temperature decrease time from 515 ° C. to 200 ° C. was 5 hours (temperature decrease rate 63 ° C./hour).
[0046]
After the powder was taken out from the sheath box after the pre-stage firing and remixed, the sheath box was again filled with the powder after the pre-stage firing. Using the same static furnace as described above, the sheath box was laminated, and the subsequent firing was performed by holding at 770 ° C. for 35 hours under an oxygen-nitrogen stream containing 40% by volume of oxygen. The rate of temperature increase from room temperature to 770 ° C. was 70 ° C./hour, and the rate of temperature decrease from 770 ° C. to 200 ° C. was 60 ° C./hour.
[0047]
The obtained LiNi _0.80 Co _0.20 O ₂ powder was measured for X-ray diffraction using CuKα rays in the same manner as in Example 1. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.125 °.
[0048]
As a result of evaluating the battery performance using the above LiNi _0.80 Co _0.20 O ₂ powder in the same manner as in Example 1, the initial discharge capacity at 2.5 to 4.3 V was 187 mAh / g, and the initial discharge average voltage was 3.730 V. The capacity after 20 charge / discharge cycles was 182 mAh / g. Further, as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 176 ° C.
[Example 7]
Nickel-cobalt hydroxide obtained by heating the coprecipitate obtained by mixing each ammine complex of nickel and cobalt and coprecipitating with carbon dioxide gas (atomic ratio of Ni: Co is 0.8: 0. 2) and lithium hydroxide monohydrate powder were mixed and filled into a sheath box made of mullite-corgerite refractory. The above-mentioned sheath box filled with the raw material powder was continuously supplied to the same roller hearth kiln as in Example 1 and held at 515 ° C. for 5 hours for pre-stage baking. The temperature increase rate from room temperature to 515 ° C. was 50 ° C./hour, and the temperature decrease time from 515 ° C. to 200 ° C. was 5 hours (temperature decrease rate 63 ° C./hour).
[0049]
After the powder was taken out from the sheath box after the pre-stage firing and remixed, the sheath box was again filled with the powder after the pre-stage firing.
[0050]
Using the same roller hearth kiln as above, changing the temperature distribution setting from the inlet to the outlet and the supply speed of the sheath box, continuously supplying the sheath box filled with the powder after the pre-stage firing, oxygen of 40 vol% oxygen -Post-stage baking was performed at 770 ° C for 8 hours under a nitrogen stream. The temperature increase rate from room temperature to 770 ° C. was 50 ° C./hour, and the temperature decrease rate from 770 ° C. to 200 ° C. was 63 ° C./hour.
[0051]
In the same manner as in Example 1, the obtained LiNi _0.80 Co _0.20 O ₂ powder was measured for X-ray diffraction using CuKα rays. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 64 ± 1 ° was 0.118 °.
[0052]
As a result of evaluating the battery performance using the above LiNi _0.80 Co _0.20 O ₂ powder, the initial discharge capacity at 2.5 to 4.3 V is 182 mAh / g, the initial discharge average voltage is 3.715 V, and charging is performed 20 times. The capacity after the discharge cycle was 175 mAh / g. Further, as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 179 ° C.
[Example 8]
Nickel-cobalt hydroxide obtained by mixing nickel and cobalt ammine complexes and heating the coprecipitate coprecipitated with carbon dioxide (Ni: Co atomic ratio is 0.8: 0.2). ) And lithium hydroxide monohydrate powder were mixed and filled into a sheath box made of mullite-corgerite refractory. The above-mentioned sheath box was continuously supplied to the same roller hearth kiln as in Example 1, and pre-baking was performed by holding at 515 ° C. for 5 hours. The temperature increase rate from room temperature to 515 ° C. was 50 ° C./hour, and the temperature decrease time from 515 ° C. to 200 ° C. was 5 hours (temperature decrease rate 63 ° C./hour).
[0053]
After the powder was taken out from the sheath box after the pre-stage firing and remixed, the sheath box was again filled with the powder after the pre-stage firing. The total time for pre-stage firing was 20 hours. Using the same roller hearth kiln as above, changing the temperature distribution setting from the inlet to the outlet and the supply speed of the sheath box, continuously supplying the sheath box filled with the powder after the pre-stage firing, containing 40% by volume of oxygen Subsequent firing was performed by holding at 750 ° C. for 1 hour under an oxygen-nitrogen stream. The rate of temperature increase from room temperature to 750 ° C. was 50 ° C./hour, and the rate of temperature decrease from 750 ° C. to 200 ° C. was 63 ° C./hour.
[0054]
In the same manner as in Example 1, the obtained LiNi _0.80 Co _0.20 O ₂ powder was measured for an X-ray diffraction spectrum using CuKα rays. In this X-ray diffraction, the half width of the diffraction peak based on the (110) plane at 2θ = 65 ± 1 ° was 0.215 °.
[0055]
As a result of evaluating the battery performance using the above LiNi _0.80 Co _0.20 O ₂ powder, the initial discharge capacity at 2.5 to 4.3 V was 178 mAh / g, the initial discharge average voltage was 3.765 V, and charging was performed 20 times. The capacity after the discharge cycle was 177 mAh / g. Further, as in Example 1, the temperature was increased at a rate of 5 ° C./min with a scanning differential calorimeter, and the heat generation start temperature was measured. As a result, the heat generation start temperature was 179 ° C.
[0056]
【The invention's effect】
According to the present invention, high initial battery capacity, a high average discharge voltage, a lithium-containing composite oxides used as the positive electrode active material of a lithium secondary battery that satisfies both excellent charge and discharge cycle durability and high safety , at low cost, it is provided in an efficient manufacturing process.

Claims (1)

General formula, LiNi _x Co _y M _z O ₂ (where M is at least one element selected from Al, Mn, Ti, Mg and Cr, 0.95 ≦ x + y + z ≦ 1.05, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.2), and X-ray powder diffraction using CuKα ray at 2θ = 65 ± 1 ° (110) A method for producing a positive electrode active material for a lithium secondary battery comprising a lithium-containing composite oxide having a half-value width of a diffraction peak based on a surface of 0.13 to 0.20 °, the method comprising: precipitate, or a salt or co-precipitate containing nickel, cobalt and element M, mixture, or sintering temperature four hundred thirty to five hundred thirty ° C. the pre-stage calcination of the mixture of compounds including lithium compound and element M with the lithium compound, cooling rate 200-600 ℃ / hour Then, post- stage firing is performed at a firing temperature of 700 to 850 ° C. , a temperature drop rate of 100 to 500 ° C./hour , and at least the latter-stage firing is performed in a roller hearth kiln. Manufacturing method.