JP3461800B2 - Lithium manganese nickel composite oxide and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium manganese nickel composite oxide having excellent characteristics and useful as a positive electrode active material for a lithium ion secondary battery, and a method for producing the same. Further, the present invention relates to a lithium ion secondary battery using the same. [0002] LiMn ₂ O ₄ having a spinel structure is
Because of its low cost and low toxicity, it has attracted attention as a positive electrode active material for lithium ion secondary batteries. Further, Mn in which a part of Mn is replaced by another 3d transition metal such as Ni has been actively studied for the purpose of improving performance such as cycle characteristics. In particular, Li [Mn _3/2 M _1/2 ] O _4, where the atomic ratio of manganese to other metal is substantially 3: 1 recently (where M
Is known to have a redox potential of about 5 V as well as a potential of about 4 V for the compound represented by Cr, Fe, Co, Ni, Cu, etc. It is also expected to be used as a positive electrode active material (eg, Material Integration,
Vol. 12, No. 3 (1999)). In order to apply the 5V-class positive electrode active material, which is a characteristic of such a composite oxide, to a lithium ion secondary battery, those having various desirable characteristics such as charge / discharge characteristics are strongly demanded. [0003] The present inventor has made intensive studies to solve the above-mentioned demands, and by using the manufacturing method described below, the atomic ratio of manganese to nickel as a 5V-class positive electrode active material is reduced. Li [Mn _3/2 which is substantially 3: 1
It has been found that those having a composition of [Ni _1/2 ] O ₄ have various characteristics desired for application to a lithium ion secondary battery. Furthermore, they have found that a lithium ion secondary battery having excellent characteristics using the lithium manganese nickel composite oxide according to the present invention can be obtained, and have completed the present invention. That is, the lithium manganese nickel composite oxide according to the present invention has Li [Mn _3/2 Ni _1/2 ] O _{4 in which} the atomic ratio of manganese to nickel is substantially 3: 1.
It is represented by the following compositional formula: the crystal structure is a highly crystalline spinel structure (space group, Fd3m), the lattice constant of which is 8.18 ° or more, and the infrared absorption spectrum is 400 It has a characteristic microstructure of about 800 cm ^-1 . Further, the particles of the lithium manganese nickel composite oxide according to the present invention have a specific surface area of not more than 1.0 m ² / g. Furthermore, the lithium manganese nickel composite oxide according to the present invention exhibits a charge / discharge curve characterized by extremely flat and low polarization. Further, the present invention is characterized in that the discharge capacity ratio at the coexisting 4V class potential and 5V class potential can be controlled over a wide range by the manufacturing method according to the present invention described below. [0006] The present invention also provides a method for producing a lithium manganese nickel composite oxide having the above-described characteristics. That is, as a first step for obtaining a manganese-nickel composite hydroxide and / or a manganese nickel composite oxide in which the atomic ratio of manganese to nickel as the raw material is substantially 3: 1, the complex is prepared in an aqueous solution of pH 9 to 13. Reacting and co-precipitating a mixed aqueous solution of a manganese salt and a nickel salt having an atomic ratio of manganese and nickel of substantially 3: 1 with an alkaline solution in the presence of an agent; Baking the mixture of the hydroxide and / or oxide and the lithium compound obtained in the above step 1 at 850 ° C. or more so that the atomic ratio of lithium to the atomic ratio of lithium is substantially 2: 1; And b. Annealing (annealing and reoxidizing) the mixture after firing obtained in 2 at 650 to 800 ° C. The present invention further provides a lithium ion secondary battery comprising the above-described lithium manganese nickel composite oxide according to the present invention as a positive electrode active substance component. Such batteries have charge and discharge characteristics characterized by extremely flat and low polarization.
In addition, those which show a 4V-class potential having a predetermined discharge capacity in addition to the 5V-class discharge potential are also included. Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION A method for producing a lithium manganese nickel composite oxide according to the present invention is characterized by comprising the following three steps. (Step 1) Production of Raw Material In order to obtain a raw material that is a manganese nickel composite hydroxide and / or a manganese nickel composite oxide having an atomic ratio of manganese to nickel of substantially 3: 1, a pH of 9 to 13 is obtained.
Characterized in that a mixed aqueous solution of a manganese salt and a nickel salt having an atomic ratio of manganese and nickel of substantially 3: 1 is reacted with an alkali solution in the presence of a complexing agent in the presence of a complexing agent to cause coprecipitation. By such a coprecipitation method, uniformly mixed particles having an atomic ratio of manganese to nickel of substantially 3: 1 can be obtained. Here, the usable manganese salt is not particularly limited as long as manganese ions generated in an aqueous solution can form a complex with a complexing agent. Specific examples include manganese sulfate, manganese nitrate, and manganese chloride. Similarly, usable nickel salts are not particularly limited as long as nickel ions generated in an aqueous solution can form a complex with a complexing agent. Specific examples include nickel sulfate, nickel nitrate, and nickel chloride. In the present invention, the fact that the atomic ratio of manganese to nickel is substantially 3: 1 is included as long as the range is approximately ± 10%. This value can be accurately measured by various metal analysis methods (for example, an atomic absorption method). The pH value of the aqueous solution is preferably in the range of 9 to 13, and can be maintained in this range by adding an alkali metal hydroxide (eg, sodium hydroxide or potassium hydroxide) if necessary during the reaction. . The complexing agent is capable of forming a complex with manganese ions and nickel ions in an aqueous solution. Examples thereof include ammonium ion donors (ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediaminetetraacetic acid, and nitrite. Triacetic acid, uracil diacetate, and glycine. (Step 2) The firing in the firing step 2 is performed so that the total atomic ratio of manganese and nickel and the atomic ratio of lithium to the raw material obtained in step 1 are substantially 2: 1. Then, the mixture is mixed with a lithium compound, and the resulting mixture is calcined and heated at a temperature of at least 850 ° C. in an air stream. The usable lithium compound is not particularly limited, and examples thereof include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxide. The molar ratio between the manganese nickel composite oxide and the lithium compound is substantially 2: 1. Here, the fact that the molar ratio of the manganese nickel composite oxide to the lithium compound is substantially 2: 1 is included as long as the range is approximately ± 10%. Further, these values can be accurately measured by various metal analysis methods (for example, atomic absorption method). It is preferable that these are sufficiently mixed before firing. For sintering, ordinary LiMn ₂ O ₄ or LiNi
A firing apparatus used for the synthesis of O ₂ can be preferably used. The atmosphere at the time of firing is preferably an ordinary air atmosphere.
In particular, in the production method of the present invention, it is important that calcination is performed at a preferable temperature. The difference in crystallinity of the lithium manganese nickel composite oxide obtained by firing at various firing temperatures can be measured by an X-ray diffraction method. FIG. 1 (a),
(b), (c), (d) and (e) show various firing temperatures (550, 650, 7) when the firing time is fixed at 15 hours.
The crystallinity of the lithium manganese nickel composite oxide obtained at 50, 850 and 1000 ° C.) was shown by X-ray diffraction. FIG. 1 shows that the lithium manganese nickel composite oxide obtained at this firing temperature range has a spinel structure. As a further characteristic, when firing at a higher temperature, the peak of the X-ray diffraction becomes sharper, indicating that it has higher crystallinity. It is also apparent that no thermal decomposition or the like of the material is observed even under the firing condition at a high temperature of 1000 ° C. FIG. 2 shows the relationship between the firing temperature and the lattice constant obtained when the space group is Fd3m. It is apparent from the figure that when the firing temperature is about 800 ° C. or higher, the lattice constant increases as the temperature increases. For the production of the lithium manganese nickel composite oxide exhibiting these high crystallinity and other desirable characteristics described below, the firing temperature is 850 ° C. or higher, preferably 950 ° C. or higher. (Step 3) Firing (Reoxidation, Annealing) Step 3 is a feature of the production method of the present invention.
The lithium manganese nickel composite oxide fired in the above is further fired (reoxidized or annealed) at a specific temperature. By such calcination, a material having excellent charge / discharge characteristics desired when applied to a lithium ion secondary battery as a 5 V class positive electrode active material is obtained. The reason that Step 3 is required is that high temperature (85
It is conceivable that a certain amount of oxygen is reversibly lost due to firing at about 0 to 1000 ° C.). In FIG.
The results of thermogravimetric analysis (TG) when the lithium manganese nickel composite oxide fired at 0 ° C. is heated to 1000 ° C. at a rate of 5 ° C./minute, and then cooled to 100 ° C. It is apparent from FIG. 3 that the weight loss starts at about 750 ° C. due to the loss of oxygen. Also, it can be seen that the weight has recovered when the temperature is lowered. Therefore, in the production method of the present invention, after firing at a high temperature in order to produce a lithium manganese nickel composite oxide having high crystallinity in step 2,
600-800 ° C in order to sufficiently return the oxygen lost in
, It is necessary to perform re-oxidation. For the purpose of this re-oxidation, it is preferable to carry out the atmosphere in a normal atmosphere. The manganese-nickel composite oxide scanning electron microscope of a method of manufacturing manganese-nickel composite oxide is a raw material obtained by the process 1 of the present invention (hereinafter SE
It is called M. 4) A photograph is shown in FIG. The photograph shows that the raw material particles are substantially spherical. In addition, it can be seen that the surface of the particles has unevenness having a fold-like shape uniformly, and that the particles are porous. Table 1 shows the elemental analysis values and other physical properties of the composite oxide. Table 1 Composition Ni (%) 18.1 Ni (mol / g) 0.0308 Co (%) 0.060 Fe (%) 0.018 Cu (%) ≤ 0.001 Mn (%) 50.4 Mn (mol / g) 0.00917 Na (%) 0.11 Cl (%) ≤ 0.05 SO4 (%) 0.51 Tap density (g / cc) 1.42 Bulk density ( g / cc) 1.03 Particle size (μm) 12.0 Specific surface area (m ² / g) 24.0 Mn: Ni 2.99: 1.01 Lithium manganese nickel composite before reoxidation
Oxide The results of observing the shape of the lithium manganese nickel composite oxide obtained by the production method of the present invention with SEM are shown in FIGS.
6 is shown. FIG. 5 is an SEM (scanning electron microscope) photograph of the lithium manganese nickel composite oxide obtained when the firing temperature in step 2 is 550 ° C., and FIG.
3 shows an SEM photograph of a lithium manganese nickel composite oxide obtained when calcined at 0 ° C. The magnifications of these photographs are 2000, 5000, 20,000 and 50,000 times. From these figures, it is apparent that firing at a high temperature promotes crystal growth and recrystallization, resulting in a smooth particle surface. Actually, as shown in Table 2, the specific surface area (BE) of the lithium manganese nickel composite oxide obtained when calcined at 550 ° C. and 1000 ° C.
It can be seen that T) is significantly different. Because of this feature,
It is considered that when used as a positive electrode active material, the insertion reaction proceeds smoothly, so that the effect of suppressing polarization is exhibited. [0021] [Table 2] Table 2 550 ° C. calcination 1000 ° C. calcination specific surface area (m ² / g) 8.5 0.40 [0022] Lithium manganese-nickel composite after reoxidation
Oxide FIG. 7 shows an X-ray diffraction diagram of the lithium manganese nickel composite oxide according to the present invention obtained after calcining at 1000 ° C. in step 2 and re-oxidizing at 700 ° C. in step 3. 8 and 9 show a SEM photograph and an infrared absorption spectrum thereof. FIG. 7 shows that the lithium manganese nickel composite oxide obtained by the production method of the present invention has a spinel structure having high crystallinity. Further, it is apparent from FIG. 8 that the recrystallization proceeds in the process of absorbing oxygen by reoxidation at a low temperature. In particular, a clear microstructure is seen on the crystal surface obtained. Further, from FIG. 9, by reoxidation, to appear a characteristic microstructure in the area of 400～800Cm ^-1 lithium-manganese-nickel composite oxide (around 600 cm ^-1 and 450 cm ^-1 are particularly peak) I understand. It is considered to indicate that re-oxidation results in higher crystallinity.
Further, the specific surface area is changed by re-oxidation (0.5).
2 m ² / g). Lithium-ion secondary battery The lithium-ion secondary battery of the present invention is a lithium-ion secondary battery comprising the lithium-manganese-nickel composite oxide as a positive electrode active substance component.
Further, since the lithium manganese nickel composite oxide according to the present invention is contained as a positive electrode active material component, such a battery has a charge / discharge characteristic characterized by extremely flat and low polarization around 5 V as shown in FIG. Have. Also 5
In addition to V-class discharge potentials, those exhibiting a 4V-class potential having a predetermined discharge capacity are included. Therefore, at the time of discharge, 5
Using the fact that the discharge potential near V changes to 4 V, the charging timing can be detected. [0025] Water was placed 13L cylindrical reactor 15L with Example stirrer and an overflow pipe, 30% sodium hydroxide solution until the pH was 11.6 was added, keeping the temperature at 50 ° C. Stirring was performed at a constant speed. Next, Mn / (Mn +
Ni) is added to a mixture of a 20 wt% manganese sulfate aqueous solution and a 20 wt% nickel sulfate solution so that the atomic ratio of Ni) becomes 0.33.
A 10% (v / v) aqueous solution of wt% ammonium sulfate was added to the reaction tank at a flow rate of 10 cc / min. Further, 30% sodium hydroxide was intermittently added so that the solution in the reaction tank had a pH of 11.2, to form manganese nickel composite oxide particles. After 120 hours when the inside of the reaction tank was in a steady state, manganese nickel composite oxide particles were continuously collected from the overflow pipe for 24 hours, washed with water, filtered, dried at 100 ° C. for 15 hours, and further dried for 2 hours.
After drying at 50 ° C. for 15 hours, a manganese nickel composite oxide as a dry powder was obtained. 2.6776 g of the obtained manganese nickel composite oxide and 0.7088 g of lithium hydroxide monohydrate
Was sufficiently mixed and pressed at a pressure of 1 t / cm ² using a pellet molding machine. This was put on an alumina boat, transferred to the center of the flow of the electric furnace, fired at 550 ° C. for 15 hours in an air atmosphere, and then pulverized to obtain a sample A made of lithium manganese nickel composite oxide. The firing temperatures were 650 ° C., 750 ° C., 850 ° C., 950 ° C., 10
Except that the temperature was set to 00 ° C., samples B, C, D, E, and
F was produced. The sample F was pressed again using a pellet molding machine at a pressure of 1 t / cm ² , calcined at 700 ° C. for 15 hours in an air atmosphere, and pulverized to obtain a sample G made of lithium manganese nickel composite oxide. Obtained. The electrochemical characteristics of the obtained lithium manganese nickel composite oxide were evaluated by preparing a coin-type battery. Samples A, B, C, D, E, and G obtained under the respective firing conditions, acetylene black as a conductive agent, and polyvinylidene fluoride resin (P
VDF) in a ratio of 80:10:10 by weight,
A sheet-like molded product was obtained. Then, the molded product is punched into a disk shape and dried at 80 ° C. for about 15 hours in a vacuum.
A positive electrode was obtained. In addition, a sheet-shaped lithium metal was punched into a disk to form a negative electrode. A polyethylene microporous membrane is used as the separator, and the electrolytic solution is ethylene carbonate (EC): diethyl carbonate (DEC).
A non-aqueous electrolyte obtained by adding 1 mol of LiPF ₆ to a mixed solvent of = 1: 1 (volume ratio) was used. The test cell was repeatedly charged and discharged between 3.0 and 4.7 V at a constant current value corresponding to a 10-hour rate. The charge / discharge curves at this time are shown in FIGS. Figures 10-14
Are for samples A, B, C, D, E and G, respectively. Low temperature (FIGS. 10 and 11, 650 ° C. and 750
C), the shape of the charge-discharge curve was smooth and flat, but showed large polarization. On the other hand, it was found that those fired at a high temperature (FIGS. 12 to 13, 850 to 950 ° C.) had small polarization, but poor flatness of the charge / discharge curve. On the other hand, as shown in FIG. 14, the sample F fired at 1000 ° C. and then re-oxidized at 700 ° C.
It was found that the charge-discharge curve was sufficiently flat and showed extremely small polarization. This characteristic indicates that the lithium manganese nickel composite oxide of the present invention is a superior positive electrode material for lithium ion secondary batteries of the 5V class. Further, from FIG. 14, since the voltage suddenly changes from 5 V to 4 V at the time of discharging, such a change in the discharge potential can be used for the purpose of detecting when the battery is charged. According to the production method of the present invention, a lithium manganese nickel composite oxide having a highly crystalline spinel structure, wherein the atomic ratio of manganese to nickel is substantially 3: 1. Having a lattice constant of at least 8.18 ° and an infrared absorption spectrum of 400 to 800 cm.
^-1 with characteristic microstructure, specific surface area is 1.0m ²
/ G or less, exhibiting high flatness and low polarization charge / discharge characteristics, whereby a positive electrode active material for nonaqueous electrolyte batteries can be obtained. Further, an excellent lithium ion secondary battery characterized by containing such a lithium manganese nickel composite oxide as a positive electrode active substance component can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an X-ray diffraction diagram of a lithium manganese nickel composite oxide obtained when calcined at various temperatures. FIG. 2 shows lattice constants of a lithium manganese nickel composite oxide obtained when firing at each temperature. FIG. 3 shows the results of thermogravimetric analysis of a lithium manganese nickel composite oxide synthesized at a firing temperature of 650 ° C. FIG. 4 shows an SEM photograph of a manganese nickel composite oxide. FIG. 5 shows an SEM photograph of a lithium manganese nickel composite oxide synthesized at a firing temperature of 550 ° C. Where (a)
~ (D) are 2000 times, 5000 times, and 20000 times, respectively.
The photograph is shown at a magnification of × 5, 50,000. FIG. 6 shows an SEM photograph of a lithium manganese nickel composite oxide synthesized at a firing temperature of 1000 ° C. here
(a) to (d) are 2000 times, 5000 times, and 200 times, respectively.
Photographs at magnifications of 00 and 50,000 are shown. FIG. 7 shows an X-ray diffraction diagram of a lithium manganese nickel composite oxide synthesized at a firing temperature of 1000 ° C. and then reoxidized at 700 ° C. FIG. 8 shows an SEM photograph of a lithium manganese nickel composite oxide synthesized at a firing temperature of 1000 ° C. and reoxidized at 700 ° C. Here, (a) to (d) are 2000 times, 5
Photographs at 000, 20,000 and 50,000 magnifications are shown. FIG. 9 shows infrared absorption spectra of lithium manganese nickel composite oxide synthesized under each firing condition. FIG. 10 shows a charge-discharge curve of a coin-type battery using a lithium manganese nickel composite oxide synthesized at a firing temperature of 650 ° C. as a positive electrode active material. FIG. 11 shows a charge / discharge curve of a coin-type battery using a lithium manganese nickel composite oxide synthesized at a firing temperature of 750 ° C. as a positive electrode active material. FIG. 12 shows a charge / discharge curve of a coin-type battery using a lithium manganese nickel composite oxide synthesized at a firing temperature of 850 ° C. as a positive electrode active material. FIG. 13 shows a charge / discharge curve of a coin-type battery using a lithium manganese nickel composite oxide synthesized at a firing temperature of 950 ° C. as a positive electrode active material. FIG. 14 shows a charge / discharge curve of a coin-type battery using a lithium manganese nickel composite oxide synthesized at a firing temperature of 1000 ° C. and then reoxidized at 700 ° C. as a positive electrode active material.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Tokuyoshi Iida 45-10, Sakahama-wari, 45, Shirakata-cho, Fukui-shi, Fukui In Tanaka Chemical Laboratory Co., Ltd. (56) References JP-A-2001-143704 (JP, A JP-A-8-298115 (JP, A) JP-A-10-172568 (JP, A) JP-A-7-6761 (JP, A) JP-A-2001-185145 (JP, A) JP-A 2002-63904 (JP, A) JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 C01G 53/00 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claim 1] A lithium manganese nickel composite oxide having a highly crystalline spinel structure, wherein the atomic ratio of manganese to nickel is substantially 3: 1; A non-aqueous electrolyte battery positive electrode characterized by having a specific surface area of not less than 8.18 °, a specific surface area of not more than 1.0 m ² / g, and exhibiting charge / discharge characteristics of high flatness and low polarization of 5V class. A method for producing an active material, comprising: mixing a mixed aqueous solution of a manganese salt and a nickel salt having an atomic ratio of manganese and nickel of substantially 3: 1 with an alkaline solution in the presence of a complexing agent in an aqueous solution having a pH of 9 to 13. Reacting and co-precipitating to obtain a manganese-nickel composite hydroxide and / or manganese-nickel composite oxide having an atomic ratio of manganese and nickel of substantially 3: 1, and a total atomic ratio of manganese and nickel; Lichi And baking the mixture of the hydroxide and / or oxide and the lithium compound at a temperature of 850 ° C. or more so that the atomic ratio of aluminum is substantially 2: 1. And b. Further baking the mixture at 650-800 ° C.