JPH04206354A - Lithium manganese composite oxide, and manufacture and use of the same - Google Patents

Abstract

PURPOSE:To constitute an nonaqueous lithium secondary battery having a large cycle discharge capacity by using, as a positive electrode, LiMn2O4 consisting of needle particles having corresponding diameters in which the short axis diameter, long axis diameter and height are specified. CONSTITUTION:LiMn2O4 consisting of needle particles having corresponding diameters of a short axis diameter not more than 5mum, a long axis diameter not more than 10mum, and a height not more than 5mum is mixed in a mortar, and the temperature is raised to bake it under air atmosphere. The obtained LiMn2O4, carbon powder of a conductive material, and polytetrafluoroethylene powder of a binder are mixed together, molded into a pellet, and used as a positive electrode. As a negative elellctrode 5, a lithium piece is used, and an electrolyte obtained by dissolving lithium perchlorate into a mixture of propylene carbonate and 1, 2-dimethoxyethane is impregnated in a separator 4 and used. Thus, a nonaqueous lithium secondary battery having a high cycle discharge capacity can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel LiM n 2O4.
The present invention relates to L I M n 2O4 consisting of acicular particles having an equivalent diameter of 5 μm or less and a height of 5 μm or less, a method for producing the same, and uses thereof.

In recent years, LiM n 2O4 has attracted attention as a positive electrode material for lithium secondary batteries.

[Prior Art] Manganese dioxide having a spinel skeleton structure has a three-dimensional series of passages through which lithium ions can enter octahedral and tetrahedral positions, and through which lithium ions can move. Therefore, LiM with a spinel skeleton structure,
n2O4 can be doped or dedoped with lithium ions into the crystal structure.

Because of this property, L L M n 2O4 has recently attracted attention as a positive electrode material for lithium secondary batteries.

When LiM n 2O4 is used as the positive electrode of a lithium secondary battery, electrochemical redox is performed, so lithium ions are doped into the crystal lattice to compensate for the charge at that time.
Although it is dedoped, the structure of the crystal lattice is not destroyed at that time. Therefore, since this reaction can be carried out repeatedly and stably, LiMn2O4 is promising as a positive electrode material for secondary batteries, and its practical application is being studied.

For example, in JP-A-63-187569, Mn2O
I Ni n 2 O4 was obtained by mixing 3 and L l 2 CO3 at a Li:Mn=1:2 (molar ratio) and calcining the mixture in air at 650°C for 6 hours and at 850°C for 14 hours.
According to the studies conducted by the present inventors, sufficient positive electrode performance has not been obtained. This is because the sintering reaction of the particles progresses as the firing is carried out at high temperatures for a long period of time, which causes the particle size to grow, resulting in a decrease in surface area and a decrease in battery energy usage efficiency.

Several methods have been proposed to solve this problem.

In JP-A No. 63-218156, the above-mentioned JP-A-63-218156
It is proposed that LiMn2O4 be rapidly cooled in water immediately after calcination using the method disclosed in Japanese Patent No. 187569 to pulverize the crystal particles to increase the surface area and improve utilization efficiency.

- However, in this method, the spinel structure, which facilitates the diffusion of LL ions, is distorted and water is mixed in, which causes problems in terms of performance and storage stability.

On the other hand, Japanese Patent Application Laid-Open No. 2-139860 proposes a method of firing at a low temperature of 430°C to 510°C in a short time using Ll ions or easily diffusible γ-type manganese dioxide as the starting manganese species. There is. This proposal is
By firing at a low temperature for a short period of time, the aim is to suppress particle growth and suppress the decrease in surface area. However, according to the studies of the present inventors, LiMn2O obtained at this firing temperature
4, although the decrease in surface area is suppressed, the crystal lattice becomes smaller, and as a result, the three-dimensional channel through which 1 ions diffuse becomes narrower. Therefore, there is a problem that when used as a battery positive electrode, overvoltage increases and battery energy utilization rate decreases.

[Problems to be solved by the invention] The L L M n 2O4 proposed so far has insufficient electrochemical activity, and when used as a positive electrode, a non-aqueous lithium secondary with excellent cycle characteristics Constructing batteries is difficult.

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventors succeeded in producing L I M n 2O4 by firing a mixture of manganese oxide and lithium material. In the method, acicular hydrated manganese oxide or acicular β-manganese dioxide having an equivalent diameter of 1 μm or less in short axis diameter, 5 μm or less in major axis diameter, and 1 μm or less in height is used in manganese oxide to form a lithium material. By performing calcination, particle growth is suppressed, the minor axis diameter is 5 μm or less, and the major axis diameter is I Q lt m
Hereinafter, LiM n is composed of acicular particles with an equivalent diameter of 5 μm or less in height, has a high surface area, and has high electrochemical activity.
We have discovered that 2O4 (hereinafter abbreviated as acicular LIMn2O4) can be synthesized. Furthermore, it was discovered that a lithium secondary battery with high cycle discharge capacity could be constructed by using this as the positive electrode of a nonaqueous lithium secondary battery that uses lithium or a lithium alloy as the negative electrode and a nonaqueous electrolyte as the electrolyte, and the present invention. I was able to complete it.

Note that the equivalent diameter used by the present inventors here refers to the shape of a single particle that is stably placed on a horizontal surface and the shape of the particle is expressed by the length of the axes in three mutually orthogonal directions. w o
This is based on the definition of od (see Yasuo Arai, Powder Materials Chemistry, Baifukan).

The present invention will be specifically explained below.

[Working L to calcinate the mixture of comanganese oxide and lithium material
1. In the method for producing M n 2O4, particle growth is significantly suppressed by using acicular hydrated manganese oxide or acicular β-manganese dioxide. Although this mechanism is not clear, it is thought to be as follows.

The acicular hydrated manganese oxide used in the present invention easily transforms into β-type manganese dioxide having a rutile crystal structure at a temperature of 300° C. or higher in the presence of oxygen. Since this transition occurs easily and quickly, the particle shape remains acicular. Therefore, the obtained manganese dioxide becomes β-type manganese dioxide with a high surface area, and the reactivity when reacting with a lithium compound becomes high. Furthermore, manganese dioxide, which has a β-type crystal structure, has an (IXI) channel structure, which ensures a diffusion path for lithium into the crystal, so when it is reacted with a lithium compound, the reaction is easy. As the process progresses, LiNi n 2O4 having a uniform composition is easily generated. Regarding the thermal phase transition of manganese oxide that occurs during firing, M. M. Thackera et al.
It has been reported by y et al.
Chimi e M i n e r a l e
2 U., 55 (1984)), and from this fact it is thought that the calcination reaction proceeds easily. Therefore, due to the synergistic effect of the above, the reaction proceeds without excess lithium remaining on the surface of the manganese dioxide particles, resulting in a uniform composition of L.
iMn2O4 is generated, and the surface contains lithium or a composite oxide of excess lithium and manganese dioxide, such as LiMn
Composite oxides with low battery activity such as O3 are not generated.

Furthermore, under conditions where the lithium concentration on the manganese dioxide surface and inside the manganese dioxide is uniform, as in the present invention, particle growth due to excess lithium is suppressed, and the starting manganese seeds have a high surface area that maintains the acicular particle shape and are electrochemically highly active L I
It is believed that M n 2O4 is obtained.

Even when the starting manganese species is fused into acicular β-manganese dioxide, the same effect as in the case where the acicular hydrated manganese oxide is used appears.

The acicular hydrated manganese oxide used in the present invention is, for example, Ow
The method reported by En Br1cker, that is, the method of oxidizing manganese hydroxide (M n (OH) 2 ) with hydrogen peroxide (H2O2) (The Amer
ican mineralogist vol.
50, 1296P (1965)) and K. Matsuk.
i et al. reported, that is, a method of adding ammonia (NH40H) to a mixture of manganese sulfate (MnS04) and hydrogen peroxide at a temperature of 20°C or less (E lec
troch 1m1ca Acta vol
, 31. 13P (1986)).

The acicular β-manganese dioxide used in the present invention is
It can be manufactured using the method disclosed in Japanese Patent No. 30323.

The lithium material used in the production of L IM n 2O4 of the present invention is not particularly limited, and any lithium metal and/or lithium compound may be used. Examples include lithium metal, lithium hydroxide, lithium oxide, lithium carbonate, lithium iodide, lithium nitrate, lithium oxalate, and alkyl lithium.

The method of mixing the lithium material and manganese oxide is not particularly limited, and the mixing may be performed in a solid phase and/or liquid phase. For example, methods include dry and/or wet mixing of lithium material and manganese oxide powder, methods of mixing by adding manganese oxide to a solution in which lithium material is dissolved and/or suspended, and stirring. is exemplified.

In the present invention, it is necessary to perform firing at a temperature of 650° C. or higher. Below this temperature, the reaction does not proceed sufficiently, making it impossible to obtain L i M n 2O4 with a uniform composition.

In addition, when using hydrated manganese oxide in firing,
Firing must be performed in the presence of oxygen. Hydrated manganese oxide undergoes a thermal phase transition to β-type manganese dioxide at temperatures above 300°C in the presence of oxygen, but in an inert gas atmosphere Mn508
Because of the transition of Mn and Mn 304 to manganese oxide in a low oxidation state, it becomes difficult to obtain the desired L I M n 2O4.

On the other hand, when using β-manganese dioxide, the firing atmosphere is not particularly limited.

As the negative electrode of the non-aqueous lithium secondary battery of the present invention, lithium metal or lithium alloy can be used. Examples of lithium alloys include lithium/tin alloys and lithium/tin alloys.
Examples include lead alloys.

Further, the electrolyte of the non-aqueous lithium secondary battery of the present invention is not particularly limited, but examples include those in which a lithium salt is dissolved in an organic solvent such as carbonates, sulfolanes, lactones, and ethers, and electrolytes with lithium ion conductivity. solid electrolyte can be used.

A battery shown in FIG. 1 was constructed using L I M n 2O4 obtained in the present invention. In the figure, 1: positive electrode lead wire, 2: positive electrode current collection mesh, 3: positive electrode 4: separator, 5: negative electrode, 6: negative electrode current collection mesh, 7: negative electrode lead wire, 8: container shows.

[Examples] Examples will be described below, but the present invention is not limited thereto.

Example 1 [Preparation of L iM n 2O4] As Example 1, L L Fvl n 2O4 was manufactured as follows.

Commercially available acicular hydrated manganese oxide (
After mixing 44 g (manufactured by Tosoh Co., Ltd., hereinafter abbreviated as acicular water-use manganese oxide manufactured by Bunsaw +-J) and 3.75 g of lithium oxide in a mortar, the mixture was heated from room temperature to 850°C at a rate of 10°C/min in an air atmosphere. The temperature was raised and firing was performed. Second
From the results of X-ray diffraction and chemical composition analysis of the obtained compound shown in the figure and Table 1, this compound is L IMn 2O
It was identified as 4. Also, the SEM shown in Figure 3(A)
As a result of the observation, the particle shape is likely to be acicular particles with equivalent diameters of a short axis diameter of 5 μm or less, a long axis diameter of 10 μm or less, and a height of 5 μm or less.

[Constitution of Battery] The obtained LIMn2o4, carbon powder as a conductive material, and polytetrafluoroethylene powder f-jl as a binder were mixed in a ratio of 88:9:3. 75 mg of this mixture at a pressure of 5 ton/cm2
It was molded into a mmφ pellet. This is used as the positive electrode in N1 Figure 3, and the negative electrode in Figure 1 is a lithium foil (thickness 0.2
Using a lithium piece cut out from mm), the electrolyte was
An electrolytic solution prepared by dissolving lithium perchlorate at a concentration of 1 mo1/dm3 in a mixture of propylene carbonate and 1゜2 dimethoxyethane at a volume ratio of 1:1 is used in Figure 1.4.
A battery having a cross-sectional area of 0.5 cm 2 as shown in FIG. 1 was constructed by impregnating a separator with the same.

[Battery Performance Evaluation] Using the battery prepared by the above method, charging and discharging were repeated at a constant current of 5 mA at a battery voltage in the range of 2V to 4V.

The results are shown in Figure 4. The discharge capacity at the 5th cycle was approximately 90% of the discharge capacity at the 1st cycle.

Example 2 As the starting manganese seed in Example 2, acicular β-manganese dioxide having an equivalent diameter of 1 μm or less in minor axis diameter, 5 μm or less in major axis diameter, and 1 μm or less in height was used.

The acicular β-manganese dioxide was produced by the following method. 100g of commercially available acicular hydrated manganese oxide (Eiwa manganese oxide manufactured by Tosoh Corporation) and 10mJ of concentrated nitric acid (specific gravity 1.3)! were mixed and heat treated at a temperature of 200°C for 8 hours. The product was crushed in a mortar and washed with hot water.

From the X-ray diffraction shown in FIG. 5, this product was identified as β-manganese dioxide. Furthermore, S shown in Figure 6
From the results of EM observation, the particle shape of the product has a minor axis diameter of 1μ.
The particles were acicular particles having an equivalent diameter of 1 μm or less, a major axis diameter of 5 μm or less, and a height of 1 μm or less.

Next, L h M n 2O4 was prepared in the same manner as in Example 1 except that 43.5 g of the obtained acicular β manganese dioxide was used. From the results of X-ray diffraction and chemical composition analysis shown in FIG. 2 and Table 1, the obtained compound was identified as LIM n 2O4. In addition, S E M shown in Fig. 3 (B)
From the observation results, the particle shape of the obtained LiMn2O4 has a minor axis diameter of 5 μm or less, a major axis diameter of 10 μm or less, and a height of 5 μm.
They were acicular particles with an equivalent diameter of μm or less. moreover,
A battery shown in FIG. 1 was produced in the same manner as in Example 1 except that this was used as the positive electrode in FIG. 1. As a result of the battery characteristic evaluation shown in FIG. 4, the discharge capacity at the 50th cycle maintained a capacity of about 8026 compared to the discharge capacity at the 1st cycle.

Table 1. Chemical Composition Analysis Value Comparative Example 1 As Comparative Example 1, 43.5 g of commercially available electrolytic manganese dioxide (spherical particles, γ-type crystal structure) and 3.75 g of lithium oxide were mixed in a mortar with manganese dioxide. This mixture was fired at 850° C. for 20 hours in an oxygen atmosphere. Based on the results of X-ray diffraction, this compound was identified as L IM n 2O4. Further, SEM observation revealed that the particles were spherical in shape and had a particle size of about 50 μm. In addition, this was used as the positive electrode in Figure 1 and 3 to construct a battery in Figure 1 similar to that in Example 1, and the battery characteristics were evaluated. As a result, the discharge capacity at the 50th cycle was as shown in Figure 4. , only about 30% of the discharge capacity at the first cycle was retained.

[Effects of the Invention] As described above, the method of the present invention suppresses particle growth and produces acicular particles having an equivalent diameter of 5 μm or less in short axis diameter, 10 μm or less in major axis diameter, and 5 μm or less in height. By using this as the positive electrode of a nonaqueous lithium secondary battery that uses lithium or lithium alloy for the negative electrode and a nonaqueous electrolyte for the electrolyte, the cycle discharge capacity can be increased. It becomes possible to construct a non-aqueous lithium secondary battery with a large capacity.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing embodiments of batteries prepared in Example 1, Example 2, and Comparative Example 1. In the figure, 1: positive electrode lead wire, 2. Positive electrode current collection mesh 3: Positive electrode 4: Separator 5: Negative electrode 6
: Negative electrode current collection mesh 7: Negative electrode lead wire 8: Indicates a container. Figure 2 shows the L used for the positive electrode in Example 1 and Example 2.
An X-ray diffraction diagram of iM n 2O4 is shown. FIG. 3 shows Example 1 (A) and Example 2 (B). FIG. 4 shows the battery characteristic evaluation results of the batteries prepared in Example 1, Example 2, and Comparative Example 1. FIG. 5 shows an X-ray diffraction pattern of the acicular β-manganese dioxide prepared in Example 2. FIG. 6 shows a SEM observation diagram of the acicular β-manganese dioxide prepared in Example 2. Patent applicant: Tosoh Corporation Figure 2 2O force eg (Cu) Figure 3 (A) (B) Figure 4 Number of cycles Figure 5 2O/deg (C:u) Figure 6 Procedure correction writing method) % formula % 1 Display of the case 1990 Patent Application No. 329943 2 Name of the invention Lithium mankan complex oxide, its manufacturing method, and its uses 3 Person making the amendment Relationship to the case Patent applicant Kaisei-cho, Shinnanyo City, Yamaro Prefecture, 746 Address 4560 4 Draft date of amendment order February 25, 1991 5 Column for brief explanation of the drawings in the amended eight-part specification 6 Contents of the amendment (1) Second line from the bottom of page 17 of the specification, rSEM observation drawing (2) Specification] Page 8, line 5, change rsEMli observation diagram to "Particle structure 1."

Claims (4)

[Claims] (1) LiM consisting of acicular particles with an equivalent diameter of 5 μm or less in short axis diameter, 10 μm or less in major axis diameter, and 5 μm or less in height
n_2O_4. (2) In a method for producing LiMn_2O_4 by firing a mixture of manganese oxide and lithium material, the manganese oxide has a minor axis diameter of 1 μm or less and a major axis diameter of 5 μm.
characterized by using acicular hydrated manganese oxide (MnOOH) having an equivalent diameter of 1 μm or less and a height of 1 μm or less,
A method for producing LiMn_2O_4 according to claim 1. (3) In a method for producing LiMn_2O_4 by firing a mixture of manganese oxide and lithium material, the manganese oxide has a minor axis diameter of 1 μm or less and a major axis diameter of 5 μm.
The method for producing LiMn_2O_4 according to claim 1, characterized in that acicular β-manganese dioxide having an equivalent diameter of 1 μm or less and a height of 1 μm or less is used. (4) In a non-aqueous lithium secondary battery using lithium or a lithium alloy for the negative electrode and a non-aqueous electrolyte for the electrolyte, the positive electrode is LiMn_2O_ as described in claim 1.
A non-aqueous lithium secondary battery characterized by using 4.