JPH10324521A - Lithium-manganese multiple oxide, its production and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain lithium-manganese multiple oxide ensuring a higher capacity even at the time of discharge at high current density and having satisfactory cycle characteristics as a positive electrode material for a lithium secondary battery by specifying the ratio of particle diameter to crystallite diameter and imparting a spinel structure. SOLUTION: A lithium compd. and a manganese compd. are fired in the presence of an inert flux preferably contg. one or more among halides, sulfates and molybdates of potassium and barium or sulfate and molybdate of lithium and their hydrates to obtain the objective lithium-manganese multiple oxide. The ratio (DBET/DX) of the particle diameter DBET of the multiple oxide calculated from the BET specific surface area to the crystallite diameter DX calculated using the Scherrer's expression from the measurement of X-ray diffraction is <=5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium manganese composite oxide used as a positive electrode active material for a lithium secondary battery having excellent cycle characteristics, a method for producing the same, and uses thereof.

[0002]

2. Description of the Related Art In recent years, the performance of portable devices such as notebook personal computers and mobile phones has been remarkably advanced.
With the promotion of miniaturization, lightening and high performance, batteries used as power supplies for these devices also need to be small, lightweight, and high performance secondary batteries with little deterioration in charge / discharge cycles. Batteries have been put into practical use.
However, L used as a positive electrode active material of this battery
Since iCoO ₂ uses expensive cobalt as a raw material, attention has been paid to spinel-type LiMn ₂ O ₄ , a composite oxide of lithium and manganese, which is made of inexpensive manganese as a raw material in order to reduce manufacturing costs. It is being actively promoted.

Conventionally, spinel-type LiMn ₂ O of high crystallinity has been used.
₄ , for example, converts Mn ₂ O ₃ and Li ₂ CO ₃ into Mn: Li
= 2: 1 (molar ratio) and mixed at 650 ° C. for 6 hours, 85
It is obtained by calcination in air at 0 ° C. for 14 hours (JP-A-63-187569). However, when such a high-temperature treatment is performed, the sintering reaction between the particles proceeds due to the promotion of the solid-phase reaction. Since LiMn ₂ O ₄ has a lower Li ion conductivity than LiCoO ₂ , as the sintering of particles progresses, the desorption and insertion reaction of Li ions at a higher current density becomes more difficult, and a sufficient discharge capacity is obtained. Not only can it not be obtained, but also the cycle characteristics are poor. On the other hand, low-crystal spinel-type LiMn ₂ O ₄ obtained by low-temperature sintering has almost no sintering among particles, but has a low discharge capacity and poor cycle characteristics.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium secondary battery having a spinel structure having a larger capacity and a good cycle characteristic even when discharged at a high current density. It is an object of the present invention to provide a manganese composite oxide and a method for producing the same, and to provide a lithium secondary battery with high output and high energy density using this lithium manganese composite oxide as a positive electrode.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found a lithium manganese composite oxide having a spinel structure having a high discharge capacity and excellent cycle stability. The present invention is based on the particle diameter _DBET calculated from the specific surface area measured by the BET method and the result of X-ray diffraction measurement.
Ratio D to crystallite diameter D _X calculated using Scherrer's equation
_The present invention relates to a lithium manganese composite oxide having a spinel structure, wherein _BET / D _X is 5 or less. The present invention also relates to a method for producing a lithium manganese composite oxide having a spinel structure, which comprises sintering a lithium compound and a manganese compound in the presence of an inert flux. Further, the present invention relates to a lithium secondary battery using the lithium manganese composite oxide having the spinel structure as a positive electrode material.

[0006]

Hereinafter, the present invention will be described in more detail. The lithium manganese composite oxide of the present invention has a cubic spinel-type crystal structure and an X-ray diffraction pattern of JCPDS: N
o. This shows a pattern similar to that of LiMn ₂ O _{4 of} No. 35-782. Further, the lithium manganese composite oxide of the present invention, the particle being the diameter D _BET and X-ray diffraction measurement results calculated from the measured specific surface area by the BET method of the crystallite diameter D _X to be calculated using the Scherrer equation the ratio D _BET / D _X is 5 or less. When the ratio D _BET / D _X exceeds 5, sintering between particles proceeds too much, and the ratio of the grain boundary portion which becomes the resistance of the diffusion of Li ions and electrons on the surface of the crystallite becomes large, and at a high current density, This is because there is a possibility that a sufficient discharge capacity cannot be obtained when the discharge is performed, or the structure may be destroyed, thereby deteriorating the battery performance. The particle diameter _DBET of the lithium manganese composite oxide of the present invention is a spherical particle having a constant diameter _DBET , based on the specific surface area S measured by the BET method and the theoretical density ρ calculated from the cubic lattice constant. Particles, and D _BET = 6 / (ρ ·
It is calculated by S). Further, the crystallite diameter D _X is below the peak indicating the maximum intensity of X-ray diffraction pattern Sc
It was calculated from herrer's formula. D _X = (K · λ) · (β · cos θ) (where K = 1, β: half-width of the peak corrected for the spread peculiar to the diffraction system, 2θ: diffraction angle)

Hereinafter, a method for producing the lithium manganese composite oxide of the present invention will be described. The raw materials are a lithium compound serving as a lithium source of the lithium manganese composite oxide, a manganese compound serving as a manganese source of the lithium manganese composite oxide, and an inert flux that does not react with the lithium manganese composite oxide of these raw materials and products. It is.
The lithium compound serving as a lithium source is not particularly limited as long as it becomes an oxide during heat treatment, but lithium oxide, lithium carbonate, lithium hydroxide, lithium nitrate,
Lithium chloride, lithium acetate and the like can be mentioned. The manganese compound serving as a manganese source is not particularly limited as long as it becomes an oxide during heat treatment, but MnO, Mn ₃ O
₄ , manganese oxides such as Mn ₂ O ₃ and MnO ₂ , manganese carbonate, manganese hydroxide, manganese nitrate, manganese acetate and the like.

[0008] The inert melting agent is not particularly limited as long as it does not decompose at the firing temperature and does not react with the lithium manganese composite oxide as a raw material and a product, and lithium ion (ionic radius: 0.68 Å, Ahr
en) and manganese ions (ionic radius: Mn ³⁺ ;
Potassium ion (ion radius: 1.6 Angstrom, Mn ⁴⁺ ; 0.60 Angstrom, according to Ahren) having a size about twice as large as the ion radius.
33 Å, according to Ahren) and barium ions (ion radius: 1.34 Å, Ah
a) a spinel-type lithium manganese composite comprising at least one of halides, sulfates, molybdates having a cation as a cation or sulfates, molybdates having a lithium ion as a cation, and hydrates thereof. It is particularly preferred as an inert flux because it is not incorporated into the oxide structure. In the production of the lithium manganese composite oxide, first, these raw materials are mixed, but the mixing method is not particularly limited, and a dry method of mixing using a mortar, a mixer, a ball mill, or the like, water, ethanol, or the like. Any method can be used as long as it can be uniformly mixed such as a wet mixing method used.

In the production of the lithium-manganese composite oxide of the present invention, the above-mentioned lithium source, manganese source and inert flux are mixed and heat-treated at 500 ° C. to 900 ° C. for 1 hour or more. Since the liquid phase created by the inert flux facilitates the transfer of lithium and manganese sources, it is necessary to generate lithium oxide, manganese oxide, and lithium manganese composite oxide other than the lithium manganese composite oxide having a spinel structure. Further, it is considered that the liquid phase exists around the generated lithium manganese composite oxide crystal having the spinel structure, so that sintering of the crystal grains hardly occurs. The addition amount of the inert melting agent varies depending on the type of the melting agent used, but may be any amount as long as a liquid amount sufficient to suppress sintering between crystal particles is secured. It is preferably at least 0.1 times, more preferably at least 0.5 times the weight of the lithium compound and the manganese compound as the manganese source in terms of oxide. After the heat treatment, the resultant is washed with water to remove the melting agent, filtered, and dried to produce a lithium manganese composite oxide.

Next, the lithium secondary battery of the present invention will be described in detail. The positive electrode of the lithium secondary battery of the present invention,
It contains the above-mentioned lithium manganese composite oxide as an active material. Specifically, the positive electrode is composed of the lithium-manganese composite oxide, a conductive agent, and a binder. Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, and coke. Vinylidene, polytetrafluoroethylene, polyethylene,
Thermoplastic resins such as polypropylene are exemplified. As the negative electrode of the lithium secondary battery of the present invention, lithium metal,
A lithium alloy or a material capable of inserting and extracting lithium ions is used. A material capable of inserting and extracting lithium ions is used. Materials capable of occluding and releasing lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, and carbon fibers.

As the electrolyte of the lithium secondary battery of the present invention, a known electrolyte selected from a nonaqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent and a solid electrolyte is used. LiClO ₄ , Li
PF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃
One or a mixture of two or more of these.

Examples of the organic solvent include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane and tetrahydrofuran; methyl formate, methyl acetate, γ Esters such as -butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide; and sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone. Two or more of these are used as a mixture.

As the solid electrolyte, polyerylene oxa
Id derivative or polymer containing the derivative, polypropylene
Oxide derivatives or polymers containing the derivatives
Organic solid electrolyte, Li_ThreeN, LiI, Li_ThreeN-Li
I-LiOH, Li_FourSiO _Four, Li_FourSiO_Four−Li
_ThreePO_FourAnd other inorganic solid electrolytes. Also high
Using a gel-like material that holds a non-aqueous electrolyte solution in the molecule
You can also. The shape of the lithium secondary battery of the present invention is
Not limited to paper type, coin type, cylindrical type, square type
Any one may be used.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. Example 1 10.32 g of Li ₂ CO ₃ and Mn ₃ O ₄ ; 42.6
41. 2 g (Li / Mn = 0.5, molar ratio) and KCl;
After well mixing 43 g in a mortar, the temperature was raised to 800 ° C. in the air in 2 hours, and kept at 800 ° C. for 1 hour. The reaction product was washed with hot water repeatedly to remove the inert flux, then filtered and dried to produce a lithium manganese composite oxide. As a result of the X-ray diffraction measurement, the obtained lithium manganese composite oxide was JCPDS: No. L of 35-782
It was found that the crystal had a spinel-type crystal structure showing a pattern similar to that of iMn ₂ O _4, and no other crystal phase peak was detected. Further, as a result of composition analysis by ICP spectroscopy, the molar ratio was Li / Mn = 0.5, almost as charged. Furthermore, as a result of analyzing the K ion by flameless atomic absorption spectrometry and the chloride ion by ion chromatography, it was not detected.

Example 2 Li ₂ SO ₄ .H ₂ O instead of KCl as a melting agent;
A lithium manganese composite oxide was produced in the same manner as in Example 1 except that 17.87 g was used. When the obtained lithium manganese composite oxide was analyzed by the X-ray diffraction and the like, the result was the same as in Example 1.

Example 3 Li ₂ MoO ₄ instead of KCl as a melting agent;
Lithium manganese composite oxide was produced in the same manner as in Example 1 except that 04 g was used and the firing temperature was 750 ° C. When the obtained lithium manganese composite oxide was analyzed by the X-ray diffraction and the like, the result was the same as in Example 1.

Example 4 26.19 g of KCl as a melting agent and Li ₂ SO _4.
A lithium manganese composite oxide was produced in the same manner as in Example 1 except that 48.89 g of H ₂ O was used. When the obtained lithium manganese composite oxide was analyzed by the X-ray diffraction and the like, the result was the same as in Example 1.

Example 5 A lithium manganese composite oxide was prepared in the same manner as in Example 1 except that 33.80 g of BaCl ₂ .2H ₂ O was used as a melting agent. When the obtained lithium manganese composite oxide was analyzed by the X-ray diffraction and the like, the result was the same as in Example 1.

Comparative Example 1 A lithium-manganese composite oxide was prepared in the same manner as in Example 1 except that no melting agent was used. As a result of the X-ray diffraction measurement, the obtained lithium manganese composite oxide was JCPD
S: No. It was found that the crystal had a spinel-type crystal structure showing a pattern similar to that of LiMn ₂ O _{4 of} No. 35-782, and no other crystal phase peak was detected.
As a result of composition analysis by ICP spectroscopy, Li / Mn
= 0.5, which was almost the same as the charged molar ratio.

[Evaluation of Sinterability between Crystallites]
5 and the particle diameter D _BET calculated from the specific surface area measured by the BET method of the lithium manganese composite oxide powder obtained in Comparative Example 1, and the crystallite diameter calculated from the X-ray diffraction measurement result using the Scherrer equation D _X, and the ratio D _BET / D _X shown in Table 1. While the ratio D _BET / D _X was about 9 in the conventional method, the lithium manganese composite oxide obtained in the example of the present invention showed a value smaller than 5, indicating that the sintering of crystallites was compared. It can be seen that the size is kept very small.

[Evaluation of charge / discharge characteristics] Examples 1 to 5 and ratio
The lithium manganese composite oxide obtained in Comparative Example was used as the positive electrode active material.
Using a three-electrode electrochemical cell as follows
And the charge / discharge characteristics were measured. Lithium man obtained
Acetylene black and polyethylene
Mixture of trafluoroethylene (trade name: TAB-2)
Are mixed at a ratio of 2: 1 by weight, and 30 mg of the mixture is mixed with S
SUS31 with US316 lead terminal spot welded
6 mesh (1.9cm^Two) Pressurized, filled and test electrode
And In addition, metal lithium foil is used for SUS316 lead.
The terminal is added to the SUS316 mesh spot-welded.
Pressure, filling, and the counter and reference electrodes were constructed. As electrolyte
Is LiPF ₆The ethylene carbonate and dimethyl carbonate
1: 1 in a solvent in which the carbonate is mixed at a volume ratio of 1: 2.
M dissolved at a concentration of M was used. Gain in this way
The test electrode, the counter electrode, and the reference electrode are immersed in the electrolyte,
An electrochemical cell was constructed. Using this electrochemical cell, 1
mA / cm^TwoTest for reference electrode at constant current density
Charge and discharge when the electrode potential of the pole is in the range of 3.5V to 4.3V
went. When the discharge capacity at the first cycle is 100
Table 2 shows the discharge capacity retention ratio at the 50th cycle. Conventional method
, The discharge capacity retention rate is 84%,
In all of the clear examples, a high retention rate of 90% or more was shown.
Was.

[0022]

According to the present invention, as a positive electrode material for a lithium secondary battery, a lithium manganese composite oxide having a spinel structure having a higher capacity even at high current density discharge and excellent cycle characteristics, and A manufacturing method can be provided, and a high-output, high-energy-density lithium secondary battery can be formed using the lithium-manganese composite oxide as a positive electrode.

[0023]

[Table 1]

[0024]

[Table 2]

Claims (7)

[Claims] 1. A Scherrer from the particle diameter D _{BE T} and X-ray diffraction measurement results calculated from the specific surface area measured by the BET method
The ratio D _BET / D with crystallite size D _X to be calculated using the formula
_A lithium manganese composite oxide having a spinel structure, wherein _X is 5 or less. 2. The lithium manganese composite oxide having a spinel structure according to claim 1, which is obtained by calcining a lithium compound and a manganese compound in the presence of an inert flux. 3. The lithium manganese composite having a spinel structure according to claim 2, wherein the inert flux is a potassium salt, a sulfate and a molybdate of another metal, or a mixture thereof. Oxides. 4. A method for producing a lithium manganese composite oxide having a spinel structure, comprising firing a lithium compound and a manganese compound in the presence of an inert flux. 5. The method for producing a lithium-manganese composite oxide according to claim 1, wherein the lithium compound and the manganese compound are calcined in the presence of an inert flux. 6. The lithium manganese composite oxide according to claim 4, wherein the inert flux is a potassium salt, a sulfate and a molybdate of another metal, or a mixture thereof. Manufacturing method. 7. A lithium secondary battery comprising the lithium manganese composite oxide according to claim 1 as a positive electrode material.