JP2003112924A - Method for producing lithium - manganese based composite oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a lithium - nickel - manganese composite oxide by using hydrothermal reaction. SOLUTION: Na type birnessite is treated with a dilute acid and Na ions are substituted with H ions. Next, the birnessite is contacted with an organic amine compound, and organic amine ions and organic amine molecules are introduced into the spaces among the layers of the birnessite, and peeling is perfomred per layer to form nanosheets. The peeled nanosheets are contacted with Ni ions, and are cured in an autoclave into the precursor of a lithium - nickel - manganese composite oxide. The precursor is reacted with Li ions in an autoclave to prepare a lithium - nickel - manganese composite oxide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the production of a composite oxide such as lithium manganese nickel having a layered structure, which is used as a positive electrode material for lithium ion secondary batteries.

[0002]

2. Description of the Related Art Lithium-ion secondary batteries are used for mobile phones, portable personal computers, video cameras, etc. as small batteries having high voltage and high energy density. It is also expected as a power source. As a positive electrode active material for a lithium-ion secondary battery, lithium cobalt oxide Li, which is a layered composite oxide, is used.
CoO ₂ has been put to practical use because it can obtain a high voltage of 4 V class and has a high energy density. However, the raw material cobalt is scarce in resources and expensive, and in view of future expansion of demand, there is concern in terms of raw material supply, and a cathode material that can replace cobalt is desired.

LiNiO ₂ , which has the same layered structure as LiCoO ₂ ,
Nickel, which is a raw material, is cheaper than cobalt and has a high energy density in terms of battery performance as well as LiCoO ₂ . However, there is a problem in terms of safety such that the battery may explode due to decomposition and heat generation when overcharged. In addition, spinel-type manganese-based composite oxide LiMn ₂ O _{4, which} is made from manganese, which is cheaper than nickel, is considered to be used as a positive electrode material because of its excellent safety in overcharge. Is lower than that of LiCoO ₂ and LiNiO _2, and there is a problem that the capacity deterioration after repeated charging and discharging, especially the capacity deterioration at a high temperature of 50 to 60 ° C. is large.

Therefore, it has been proposed to improve the capacity and the cycle characteristics by mixing the lithium manganese composite oxide such as LiMn ₂ O ₄ with the above-mentioned lithium cobalt composite oxide or lithium nickel composite oxide. . Kohei
In JP-A 5-82131 and JP-A-8-45498, while the crystal structure of spinel type lithium manganate expands during charging, Li _1-x CoO ₂ (0 ≦ x ≦ 1) or LiNi _y Co _{1 -y} O ₂ (0.3 ≦ y ≦
1.0) focuses on the shrinkage of the crystal structure. The reverse is true during discharge. Then, by mixing both components at a constant ratio, it is possible to suppress the volume change at the time of charging / discharging, suppress the separation of the positive electrode active material from the conductive agent or the current collector, and propose to improve the cycle characteristics. There is.

Further, in Japanese Patent Laid-Open No. 7-235291, a spinel type lithium manganese composite oxide is added to Li _x Co _1-y Ni _y O ₂ (0 <
There has been proposed a method of improving the cycle characteristics by mixing a predetermined amount of x <1,0 ≤ y ≤ 1) to improve the ionic conductivity of the positive electrode active material in a charged state. Further, in Japanese Patent Application Laid-Open No. 10-92430, the battery capacity and the stability against overcharge are improved by mixing a composite oxide mainly composed of lithium and manganese having a spinel structure with a composite oxide mainly composed of Ni. The method of making it proposed is proposed.

Further, in JP-A-10-112318, LiMn ₂ O ₄ is disclosed.
By mixing lithium manganese composite oxide such as and lithium nickel composite oxide such as LiNiO ₂ in a predetermined ratio,
A method of compensating for the irreversible capacity of the negative electrode active material to improve capacity utilization efficiency has been proposed. Furthermore, Japanese Patent Laid-Open No. 2001-151
In JP-A-08, a method has been proposed in which the lithium manganese composite oxide and the lithium nickel composite oxide are not simply mixed but are contained in the same particle to improve the energy density per unit volume.

Equipment using a lithium-ion secondary battery is aimed at further miniaturization and higher performance, and there is an increasing demand for size reduction of the lithium-ion secondary battery. However, the positive electrode material as a substitute for lithium cobalt oxide does not have a sufficient energy density per unit volume, and a positive electrode material having a higher energy density is required.

[0008] Journal of The Electrochemical Societ
y, 145 (12), 4160-4168 (1998), or Journal of Th
e Electrochemical Society, 147 (3), 861-868 (2000)
, Journal of The Electrochemical Society, 147 (7),
2478-2485 (2000) and the like report that a lithium manganese-based composite oxide having a layered structure is used as a positive electrode material. This material is promising in that a high voltage can be obtained and that it has a high energy density. In the method for producing a lithium-manganese-based composite oxide, for example, a solid-phase method in which manganese oxide and nickel oxide, and a lithium compound are mixed and baked, or a lithium compound is added to a coprecipitate from a mixed solution of manganese salt and nickel salt. There is a coprecipitation method of mixing and firing.
In these methods, in order to obtain a lithium manganese-based composite oxide, calcination at a temperature exceeding 1000 ° C. is required,
It is difficult to have a uniform composition due to segregation of each element, and it is also difficult to have a uniform particle shape.

[0009]

An object of the present invention is to provide a new method for producing a lithium manganese-based composite oxide (claims 1 to 6).

[0010]

According to the present invention, an Mn compound having a layered structure and containing oxygen is contacted with an ion of at least one member of a group consisting of Ni ion, Co ion and Fe ion in an aqueous solvent. To prepare a precursor compound in which at least one member of Ni ion, Co ion, and Fe ion is introduced between the layers, and then the precursor compound is reacted with Li ion under hydrothermal conditions to give a composition formula (1 The method for producing a lithium-manganese-based composite oxide according to (4). Li _y Me _x Mn _1-x O _2-δ (1) (In the formula, Me represents an element of at least one member of the group consisting of Mi, Co, Fe, and 0.8 ≦ y ≦ 1.2, 0.2 ≦ x ≦ 0.6, and δ is The non-stoichiometric parameter is about ± 0.1 or less.) Although the solvent used in the reaction is an aqueous solvent such as water, it does not exclude an aqueous mixed solvent such as water-ethanol. Hydrothermal conditions at the time of introducing lithium ions are, for example, 150 ° C. to 2
At 50 ° C, 4 hours to 3 weeks. Preferably, the
Ions of at least one member of the group consisting of Ni, Co, and Fe are Ni
It is an ion (claim 2).

Preferably, the Mn compound having the layered structure and containing oxygen is birnessite (A).
^{+ p} _q Mn ₁₄ O _28-z · nH ₂ O, A is metal or hydrogen, p is the number of charges of the A element, p × q is 2 to 7, and n is a positive number) (claim) 3). The A element is, for example, Na, but the same applies to other alkali metals or alkaline earth metals. The value of p × q indicating the content of the A element is, for example, 2 to 7 per Mn14 atom, and z
Is 0 to 3, and in the case of hydrogen-type bournesite in which Na or the like is replaced with H, it may be treated with a dilute acid such as dilute nitric acid. The method for producing banesite is known, and for example, Chemistry of
The method described in Materials, 1995, (7), P.1722 may be used. Note that the compound containing Mn and oxygen having a layered structure is not limited to vernesite.

Particularly preferably, for example, alkali-type vernesite is treated with a dilute acid such as dilute nitric acid to produce hydrogen-type vernesite (H _{2 to 7} Mn ₁₄ O ₂₈ -z.nH ₂ O, z is 0 to 3). ). Next, the hydrogen-type vernesite is brought into contact with a nitrogen-containing organic substance such as an amine compound. Then, an organic cation such as an amine ion is replaced with a hydrogen ion in the banesite, or an amine compound or the like is added to the hydrogen ion, so that an organic substance is introduced between the layers of the banesite. Since the molecular radius and ionic radius of the introduced organic substance are generally larger than the ionic radius of hydrogen ions, the vernesite layer is exfoliated to form a nanosheet. Here, the nanosheet is a layer having a thickness of about nm, in which a small number of layers such as one layer of vernesite are separated. The type of nitrogen-containing organic compound is arbitrary, but the tetraalkylammonium compound is strongly alkaline, easily dissociated into cations, and can be obtained at a low cost (claim 5).

Nitrogen-containing organic matter is present on the surface of the nanosheet by ion exchange or addition, and when it is brought into contact with at least one member of the group consisting of Ni ion, Co ion, and Fe ion, the layer of the ion is formed. As a result, a precursor compound in which nanosheets are laminated on each other is obtained. In this compound, at least one member of Ni ions, Co ions, and Fe ions is introduced between layers, and when Li ions are introduced into this under hydrothermal conditions, the target lithium manganese-based composite oxide is obtained. 4). A characteristic of the production method using the nanosheet is that the Ni content can be increased, which leads to the production of a positive electrode active material having a high energy density.

Further, preferably, the above-mentioned bournesite is Ni
The precursor compound is prepared by bringing the precursor compound into contact with at least one member of the group consisting of ions, Co ions, and Fe ions, and introducing the ions between the layers of the vernasite by intercalation (claim 6). In this method, ions such as Ni are introduced through intercalation between the layers of bournesite. The problem with this method is that the amount of Ni ions introduced is smaller than when nanosheets are used, and the value of x is 0.2 to 0.4, for example.

[0015]

EXAMPLE A first example will be described with reference to FIGS.
To do. Na-type barnesite, here Na_FourMn₁₄O₂₇・ 9H
₂O is prepared according to a known method (step 1). In addition,
-In neesite, the number of atoms such as Na and the number of oxygen atoms are
There is fluctuation, Na_FourMn₁₄O₂₇・ 9H ₂O is not always a precise composition
There is no. The X-ray diffraction pattern of this compound is shown in Figure 2A.
However, the distance between the layers of bournesite from the diffraction pattern is 0.72.
nm. Dilute this barnesite (4.75g) with
Is a concentration of 0.1 mol / dm³Treated with dilute nitric acid to remove Na ions from hydrogen ion.
Replace by turning on (step 2). The type of dilute acid is optional,
The concentration is 0.01-1 mol / dm³Is preferred. The resulting hydrogen type bar
-The X-ray diffraction pattern of neesite is shown in Fig. 2B.
The separation was 0.74 nm.

The vernasite is brought into contact with an organic amine to replace the hydrogen ion of the vernasite with a cation of the organic amine, or add an organic amine molecule to the hydrogen ion. As a result, the distance between the layers of the bournesite increases, the bond between the layers weakens, and the layers are separated into nanosheets (step 3). Here, using an ion of tetramethylammonium hydroxide, which is an inexpensive strong alkali, the hydrogen-type bournesite prepared as described above is dispersed in 2500 ml of water,
15 wt% concentration tetramethylammonium hydroxide aqueous solution
120 ml was added to make a nanosheet colloidal suspension. The type of the alkyl group is not limited to the methyl group, and any organic amine may be used as long as the organic amine is soluble in water. The amine is not limited to the quaternary amine and may be a primary, secondary, or tertiary amine. For example, a lithium manganese nickel composite oxide could be similarly prepared by using monopropylamine instead of tetramethylammonium hydroxide. In the case of monopropylamine, it is considered that the monopropylammonium ion generated by dissociation replaces the hydrogen ion of the branesite, or the monopropylamine molecule adds to the hydrogen of the banesite.

When a tetraalkylammonium compound is used, the alkyl group preferably has 1 to 3 carbon atoms.
Examples of nitrogen-containing organic substances include guanidine (NH ₂ —C═NH—N
H ₂ ) and piperidine (secondary cyclic amine of (CH ₂ ) ₅ —NH) can also be used. An X-ray diffraction pattern when the nanosheet suspension was dried is shown in FIG. 2C, and the interlayer distance was increased to 0.96 nm. The dried suspension was easily decomposed into nanosheets when dispersed in water.

Ni ions are adsorbed on the surface of the nanosheet,
A precursor compound in which Ni ions are introduced into the surface of the banesite or between the layers is prepared (step 4). Organic cations are adsorbed on the surface of the nanosheet and are alkaline. When Ni ions are contacted here, the Ni ions are hydrolyzed, and a layer having a composition of almost nickel hydroxide (Ni (OH) ₂ ) is formed between the layers of the nanosheets, and the nanosheets are laminated again through this layer. . For example, an aqueous solution of nickel nitrate (0.037 mol) so that the atomic ratio of Ni / Mn in the target compound is 1: 1.
/ dm ³ × 1000 ml) was added to the nanosheet suspension with stirring, and the mixture was aged in an autoclave at 150 ° C. for 3 days. Instead of aging in an autoclave, aging may be performed at about 80 ° C. The aging temperature is, for example, 60 to 250 ° C, and the aging period is 4
Time to 3 weeks. FIG. 2D shows the X-ray diffraction pattern after the introduction of nickel nitrate and before aging, and FIG. 2 shows the pattern after aging.
Shown in E. The target composition of the substance after aging is Ni ₁₄ Mn ₁₄ O _27-x (O
H) _{24 + 2x} · nH ₂ O (x is 0 to 2, n is a positive number). Upon contact with Ni ions, a layer of Ni ions is formed between the layers of the exfoliated nanosheets, and the nanosheets are re-laminated through this layer and converted into a precursor compound that precipitates and is aged in an autoclave to crystallize. Sex increases. In the X-ray diffraction pattern before aging, there was a broad peak near 0.48 nm, and this peak shifted to around 0.46 nm for growth.

The obtained precipitate is reacted with a solution of Li ions under hydrothermal conditions (step 5). For example, the above-mentioned precipitate (precursor compound), LiOH.H ₂ O and water are mixed in a weight ratio of 1:10:
The mixture was mixed with 10 parts and the like and reacted in an autoclave at 200 ° C. for 3 days. The reaction temperature is preferably 150 to 250 ° C., and the reaction time is preferably 4 hours to 3 weeks. This gives Li _0.9 Ni _0
.47 Mn _0.53 O ₂ (chemical analysis value) was obtained. The X-ray diffraction pattern of the product is shown in Figure 2F. By adjusting the concentration of Li ions and the amount and concentration of Ni ions, Li _y Ni _x Mn
When described as _1-x O _2-δ , the Li amount y is 0.8 ≦ y ≦ 1.2, and x, which represents the Ni / Mn ratio, is 0.2 ≦ x ≦ 0.6,
The non-stoichiometric parameter δ is about ± 0.1.

In the examples, at this stage, a layered lithium manganese nickel ternary composite oxide having no segregation of each element of Li, Ni and Mn was obtained, which was calcined at an appropriate temperature to obtain a desired average grain size. A positive electrode active material having a diameter and particle size distribution is obtained (step 6). As is clear from the fact that the reaction in solution is used, the product has no segregation, and the shape of the product particles is almost uniform. On the other hand, in the solid phase method or the coprecipitation method, the firing temperature is 1000 ° C in order to eliminate the segregation between the constituent elements.
It is difficult to optimize the charge capacity and the discharge capacity of the active material, because the temperature is limited to ℃ or higher.

[0021]

Comparative Example A caustic soda solution was added to a mixed aqueous solution of manganese nitrate and nickel nitrate in which the ratio of Ni / Mn was adjusted, coprecipitated, filtered, washed and dried to obtain a solid. A predetermined amount of lithium hydroxide was added to this solid substance, and the mixture was thoroughly mixed in a mortar and then baked at 1050 ° C. for 10 hours to obtain a solid substance. The composition of this solid was Li _0.92 Ni _0.48 Mn _{0.520 2} .

[0022]

[Measurement of battery characteristics] The solid matter prepared in the example was subjected to 1 at 900 ° C.
After firing for 0 hours, the fired product and the solid substance prepared in Comparative Example were used as a positive electrode active material, and the battery characteristics thereof were measured under the following conditions. The charge / discharge characteristics are shown in Table 1. Charging / discharging characteristics measurement conditions: positive electrode composition; active material / acetylene black / Teflon (registered trademark) = 70: 20: 10 negative electrode material; lithium metal charging; charging / discharging up to 4.3 V at 0.1 mA / cm ² ; 0.1 mA / cm Discharge electrolyte up to 2.5 V at ² ; 1 mol / dm ³ LiClO ₄ / PC: DME (1: 1) ambient temperature; 25 ° C initial charge / discharge capacity (mAh / g)

[0023]

[Table 1] Charging / discharging characteristics Active material composition First charge capacity (mAh / g) First discharge capacity (mAh / g) Example Li _0.90 Ni _0.47 Mn _0.53 0 ₂ 164 146 Comparative example Li _0.92 Ni _0.48 Mn _0.52 0 ₂ 155 135

[0024]

[Example 2] The Na ion of the vernasite was replaced with the Ni ion, and the Ni ion was introduced between the layers by intercalation,
An example is shown in which the reaction with Li ions is performed under hydrothermal conditions. An outline of the example is shown in FIG. 3, and an X-ray diffraction pattern of each sample is shown in FIG. Vernesite having a layered structure (Na ₄ Mn
₁₄ O ₂₇ · 9H ₂ O) is prepared according to a known method (step 1
1). The X-ray diffraction pattern of vernesite is shown in FIG. 4A. Then, it is treated in a 1 mol / dm ³ Ni (NO ₃ ) ₂ aqueous solution, and treated with Na
Ions are exchanged with Ni ions, and Ni birnessite (Ni ₂
Convert to 1.6 g of Mn ₁₄ O ₂₇ · nH ₂ O (step 12). Ni
The X-ray diffraction pattern of vernesite is shown in FIG. 4B. Add Ni (OH) ₂ 0.42g to the Ni / Mn molar ratio of 1: 2.
Was further added, and 30 g of water was further added, followed by hydrothermal treatment at 200 ° C. for 3 days (step 13). After this, filtration and washing were performed to obtain a solid. The conditions of the hydrothermal treatment are 150 to 250 ° C. for 4 hours to 3 weeks, during which intercalation causes Ni ions to infiltrate between the layers of the birnessite to obtain a precursor compound.
The X-ray diffraction pattern before hydrothermal treatment is shown in FIG. 4C, and the pattern after hydrothermal treatment is shown in FIG. 4D. The pattern of nickel hydroxide is seen before the hydrothermal treatment, but this pattern disappears by the hydrothermal treatment, and the Ni (OH) ₂ layer is sandwiched.

The solid obtained was placed in a LiOH solution (LiOH.H ₂ O
/ H ₂ O in a mass ratio of 1: 2) and hydrothermally treated at 200 ° C. for 3 days (step 14). Similarly, the hydrothermal treatment conditions are 150 to 250 ° C. for 4 hours to 3 weeks. The product after the hydrothermal treatment was filtered, washed and dried to obtain a solid. This solid had a layered structure by XRD analysis, and had a composition of Li _0.95 Ni _0.32 Mn _0.68 0 ₂ as a result of chemical analysis. Adjusting the concentration of Li ions and the amount and concentration of Ni ions, using the general formula
When described as Li _y Ni _x Mn _1-x O _2-δ , the Li amount y is 0.8 ≦
y ≦ 1.2 and x, which represents the Ni / Mn ratio, is 0.2 ≦ x ≦ 0.4
Becomes The non-stoichiometric parameter δ is about ± 0.1. The reason why the upper limit of the Ni content is lower than that when the nanosheet is used is that it is more difficult to introduce Ni ions by intercalation than to adsorb Ni ions to the nanosheets. Then, by baking this solid at an appropriate temperature, a positive electrode active material is obtained (step 15).

The Ni ion or Li ion may be introduced in any form as long as it does not interfere with the aging or reaction in the autoclave. The Ni ion may be a hydroxide or a salt, and the Li ion may be hydrolyzed under hydrothermal conditions. So long as it is soluble in water. In the examples, the introduction of Ni ions having a high practical value is explained, but when introducing Co ions or Fe ions, for example, by reacting the nanosheet with divalent Co ions or Fe ions in the same manner, and introducing them. Good. With respect to the lithium manganese composite oxide, it is difficult to measure the oxygen content accurately, and some variation in the oxygen content is allowed.

[0027]

According to the present invention, a lithium manganese-based composite oxide having a homogeneous composition and a layered crystal structure can be obtained. When used as a positive electrode active material of a lithium secondary battery, this compound becomes a high energy density active material.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for producing a lithium nickel manganese composite oxide in a first example.

FIG. 2 shows the X-ray diffraction pattern of the preparation of the first example, A being the raw material NaBir pattern, B being the HBir pattern, C being contacted with tetramethylammonium hydroxide and then dried. The pattern of the sample was D, the pattern after contacting with Ni ions and before aging in the autoclave,
Shows a pattern after aging in an autoclave, and F shows a pattern after introducing lithium ions under hydrothermal conditions.

FIG. 3 is a process drawing showing a method for producing a lithium nickel manganese composite oxide in the second embodiment.

Figure 4 shows the X-ray diffraction pattern of the preparation in the second embodiment, A is the pattern of NaBir raw material, B is the pattern of NiBir ion-exchanged with Na ⁺ ions in Ni ²⁺ ions,
C shows the pattern before aging in an autoclave after contact with Ni ions, and D shows the pattern after aging in an autoclave.

Continued front page    F-term (reference) 4G048 AA04 AB02 AB05 AC06 AD04                       AD06 AE05                 5H050 AA19 BA17 CA09 FA19 GA02                       HA02

Claims (6)

[Claims] 1. A Mn compound having a layered structure and containing oxygen is brought into contact with at least one member ion of a group consisting of Ni ion, Co ion and Fe ion in an aqueous solvent to form Ni ion, Co ion between layers. A precursor compound into which at least one member of an ion and an Fe ion is introduced is prepared, and then the precursor compound is reacted with Li ion under hydrothermal conditions to give a lithium manganese-based composite oxide of composition formula (1). And a method for producing a lithium manganese-based composite oxide. Li _y Me _x Mn _1-x O _2-δ (1) (wherein Me represents at least one element of the group consisting of Mi, Co, Fe, and 0.8 ≦ y ≦ 1.2, 0.2 ≦ x ≦ 0.6, and δ is It is a non-stoichiometric parameter.) 2. The method for producing a lithium manganese composite oxide according to claim 1, wherein at least one member ion of the group consisting of Ni, Co, and Fe is a Ni ion. 3. The Mn compound having a layered structure and containing oxygen, is composed of birnessite (A ^{+ p} _q Mn ₁₄ O _28- z.nH ₂ O, A is a metal or hydrogen, and p is the number of charges of the A element. And p × q is 2 ~
7. The method for producing a lithium manganese-based composite oxide according to claim 1, wherein z is 0 to 3 and n is a positive number. 4. The branesite is a hydrogen type banesite (H _{2 to 7} Mn ₁₄ O _28- z.nH ₂ O, z is 0 to 3, n is a positive number), and the banesite is a nitrogen-containing organic substance. By contacting with each other to separate the vernasite between layers to form a nanosheet, and contacting the nanosheet with at least one member of the group consisting of Ni ion, Co ion, and Fe ion,
The method for producing a lithium-manganese-based composite oxide according to claim 3, wherein nanosheets are laminated on each other through the layer of ions to obtain the precursor compound. 5. The method for producing a lithium manganese composite oxide according to claim 4, wherein the organic substance is a tetraalkylamine compound. 6. The precursor compound is brought into contact with at least one member of the group consisting of Ni ion, Co ion, and Fe ion by intercalation to introduce the ion into the interlayer of the vernesite to obtain the precursor compound. The method for producing a lithium-manganese-based composite oxide according to claim 3, which is prepared.