JPH1067520A - Lithium iron oxide powder and production of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce lithium iron oxide powder having high electrode reaction rate when used as a positive electrode active material in lithium battery. SOLUTION: This lithium iron oxide powder having high electrode reaction rate comprises Lix (Fe, M)O2 (0<x<=1, M is one or two or more kinds of metals selected from Co, Ni and Mn) having a zigzag layer structure and the content of each of Co, Ni and Mn is 0.5-10.0mol% in terms of the total.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to Li _x (Fe, M) having a zigzag layered structure which is suitable as a material for a positive electrode active material of a lithium battery because of a high electrode reaction rate when used as a positive electrode active material. O ₂ (0 <x ≦ 1, M = Co, N
and at least one metal selected from i and Mn) and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices such as personal computers and mobile phones, demand for batteries as power sources has been increasing. In particular, lithium batteries have a low atomic weight and high ionization energy, and as a result, batteries with high electromotive force and high energy density can be expected. Has been done.

[0003] There is no end to the demand for higher performance of lithium batteries, and it is strongly demanded that the electrode reaction rate be as high as possible as a positive electrode active material used in lithium batteries.

In recent years, as a material for a positive electrode active material used in a lithium battery, Li which can generate a high voltage is used.
_x CoO ₂ and Li _x NiO ₂ are known.
_x CoO ₂ has already been put to practical use.

[0005]

The above-mentioned known Li _x CoO ₂ and Li _x NiO which are known as a cathode active material.
₂ has a layered rock salt type (α-NaFeO ₂ type) crystal structure.

On the other hand, lithium iron compound powder is expected to be used as an inexpensive material for a positive electrode active material, but lithium iron compound powder having a layered rock salt type crystal structure is not known.

That is, the lithium iron compound powder is obtained by firing a mixed powder of an iron oxide and a lithium compound at about 800 ° C., that is, in the case of so-called high-temperature synthesis, having a tetragonal rock salt type crystal structure having an irregular arrangement. Is obtained, and the mixed powder is
In the case of firing at about 0 to 500 ° C., that is, by so-called low-temperature synthesis, a regular array of tetragonal crystals was obtained, and in each case, it did not act as a positive electrode active material of a lithium battery.

The present inventors have conducted intensive studies in order to obtain a lithium iron oxide powder acting as a positive electrode active material of a lithium battery, and have found that lithium having a zigzag layer structure similar to the well-known crystal structure of Li _x MnO _2. Iron oxide Li _x Fe
O ₂ powder has already been obtained (Japanese Patent Application No. 8-38283).

However, the Li _x FeO ₂ powder having a zigzag layered structure has low electron conductivity and slow diffusion of lithium ions between layers, and when used as an electrode material of a lithium battery, The reaction rate was low, and the operating current of the battery was low.

Accordingly, an object of the present invention is to obtain a lithium iron oxide powder having an electrode reaction rate as high as possible when used as a positive electrode active material of a lithium battery.

[0011]

The above technical problems can be achieved by the present invention as described below.

That is, according to the present invention, one or more metals selected from cobalt, nickel and manganese are used as Co,
0.5 to 10.0 mol in total of each conversion of Ni and Mn
% And having a zigzag layered structure
_This is a lithium iron oxide powder comprising _x (Fe, M) O ₂ (0 <x ≦ 1, M = one or two or more metals selected from Co, Ni and Mn).

Further, the present invention provides a method for preparing a mixed powder of a levidrosite particle powder containing at least one metal selected from cobalt, nickel and manganese and a lithium compound powder in a temperature range of 100 to 150 ° C. And a method for producing the lithium iron oxide powder.

Next, the configuration of the present invention will be described in detail.
It is as follows.

First, the lithium iron oxide powder according to the present invention will be described.

In the lithium iron oxide powder according to the present invention, one or more metals selected from cobalt, nickel and manganese are used in an amount of 0.5 to 10.0 mol in terms of the total of each of Co, Ni and Mn. %. 0.5mol
%, The lithium iron oxide powder that generates a high electromotive force as the object of the present invention cannot be obtained.
When the content exceeds 10.0 mol%, a lithium iron oxide powder that generates a high electromotive force can be obtained, but it is meaningless to include more than necessary in consideration of economic efficiency.

The lithium iron oxide powder according to the present invention has a zigzag layered structure, and particularly exhibits an electrochemical reversible reaction of lithium ions.

The lithium iron oxide powder according to the present invention is obtained by an ion exchange reaction between protons contained between layers of a zigzag layered structure of lepidocrocite and lithium ions contained in a lithium compound. ,
Its composition is Li _x (Fe, M) O ₂ (0 <x ≦ 1, M
= One or more metals selected from Co, Ni and Mn). The lithium ion conductive electrolyte has a composition of Li _x (Fe, M) O ₂ (0 <x ≦ 2) because lithium ions enter and exit.

The size of the lithium iron oxide powder according to the present invention is substantially the same as the particle size of lepidocrocite powder, which is an iron raw material, and has an average particle size of about 0.01 to 1.0 μm.

Next, a method for producing the lithium iron oxide powder according to the present invention will be described.

The lepidocrocite powder containing one or more metals M selected from cobalt, nickel and manganese according to the present invention is represented by γ- (Fe, M) OOH, and comprises cobalt, nickel and manganese. Particles having an average particle size of 0.01 to 1.0 μm containing one or two or more metals selected from the group consisting of Co, Ni and Mn in a total of 0.5 to 10.0 mol% in terms of respective conversions are preferred.

In the lepidocrocite particles according to the present invention, the content of one or more metals selected from cobalt, nickel and manganese is Co, Ni and Mn.
If the total of the conversions is less than 0.5 mol%, it is difficult to obtain a lithium iron oxide powder having a high lithium ion diffusion rate, which is the object of the present invention. One or more metals selected from cobalt, nickel and manganese are used in the reaction for forming lepidocrocite powder to be described later.
When an amount exceeding 10.0 mol% in total in terms of each of Mn and Mn is added, spinel ferrite powder is formed and mixed in addition to the lepidocrocite particles, and one of metals selected from cobalt, nickel and manganese is added. Alternatively, it is difficult to obtain only the lepidocrocite particle powder containing two or more kinds.

The lepidocrocite particles containing one or more metals selected from the group consisting of cobalt, nickel and manganese according to the present invention can be prepared by adding a cobalt compound to a reaction system in a known method for producing lepidocrocite particles. ,
It can be obtained by the presence of one or more compounds of metals selected from nickel compounds and manganese compounds.

The most typical method for producing lepidocrocite powder is a method in which an oxygen-containing gas such as air is passed through an acidic or neutral suspension containing ferrous hydroxide to oxidize the suspension.

As the lithium compound powder in the present invention, Li ₂ O, LiOH, LiOH.H ₂ O and the like can be used. The formation of α-LiFeO _{2 having} an irregular arrangement is suppressed, and Li _x (Fe, M) O _{2 which} is the object of the present invention is obtained.
(0 <x ≦ 1, M = one or more of metals selected from Co, Ni and Mn) In order to produce only powder, it is preferable to use an anhydride of a lithium compound.

In the present invention, the mixing ratio of the lepidocrocite powder containing one or two or more metals selected from cobalt, nickel and manganese to the lithium compound powder is such that lithium and iron have a molar ratio of Li / Fe It is preferable that the range is ≧ 1.2. More preferably Li / F
e ≧ 1.4. When the molar ratio of lithium to iron is less than 1.2, Li _x (Fe, M) O _{2 which} is the object of the present invention is used.
(0 <x ≦ 1, M = one or two or more metals selected from Co, Ni and Mn), thereby producing an irregular spinel β-Li (Fe, M) ₅ O ₈ powder having a smaller amount of lithium. Easier to do.

When the amount of the lithium compound greatly exceeds the stoichiometric composition, unreacted lithium compound powder such as lithium hydroxide remains as it is, and Li _x (Fe, M) O ₂ (0 <x
≦ 1, M = one or two or more metals selected from Co, Ni and Mn) powder mixed with a lithium compound powder such as lithium hydroxide.

In the present invention, the heating temperature of the mixed powder is 1
It is in the range of 00 to 150 ° C. If the temperature is lower than 100 ° C., the reaction rate of the ion exchange reaction becomes slow, and the ion exchange reaction takes a long time. When the temperature exceeds 150 ° C., α-Li (Fe,
M) The amount of generated O ₂ increases.

In the present invention, as described above, Li _x (Fe, M) O ₂ , which is the object of the present invention, depends on the reaction conditions.
(0 <x ≦ 1, M = one or two or more metals selected from Co, Ni and Mn) In addition to powder, unreacted lithium compound powder may be mixed.

L containing unreacted lithium compound powder
_{i x (Fe, M) O} 2 (0 <x ≦ 1, M = Co, 1 or two or more metals selected from Ni and Mn) if powder to constitute a lithium battery as cathode active material for a material However, since the unreacted lithium does not show a reversible electrode reaction, the capacity of the battery becomes low, and the electrochemical reversible reaction rate decreases. Therefore, it is important to remove unreacted lithium compound powder. In order to remove the mixed unreacted lithium compound powder, the reaction product powder is suspended in water at a temperature as low as possible, in particular, at 30 ° C. or lower, and then filtered and dried in a time as short as possible. Is preferred.

The reaction product powder is preferably suspended in water so as to have a concentration of 10 to 50% by weight. Underwater, L
_{i x (Fe, M) O} 2 (0 <x ≦ 1, M = Co, 1 or two or more metals selected from Ni and Mn) and decomposed lepidocrocite γ- (Fe, M) OOH is easily generated. For this reason, when suspending the reaction product powder in water, the produced Li _x (Fe, M) O ₂ (0
<X ≦ 1, M = one or two or more metals selected from Co, Ni and Mn) are not decomposed and are suspended in cold water at a temperature as low as possible, especially at a temperature of 30 ° C. or less, and as short as possible. And filtered to obtain Li _x (Fe, M) O ₂ (0 <x ≦
1, M = one or two or more metals selected from Co, Ni and Mn) is preferably suppressed as much as possible.

The reaction product powder is suspended in water and LiOH
Drying of the precipitate after washing and removing unreacted lithium compound powder such as the above is preferably carried out at a temperature as low as possible, particularly at 40 ° C. or lower, and if necessary, preferably under reduced pressure. When the temperature exceeds 40 ° C., the obtained Li _x (Fe,
M) O ₂ (0 <x ≦ 1, M = one or two or more metals selected from Co, Ni and Mn) is decomposed and lepidocrosite γ- (Fe, M) OOH is easily produced. Become.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The identification of the reaction product powder, its crystal structure and the degree of crystallinity were determined by X-ray diffraction (manufactured by RIGAKU, X-ray used: Mn-filtered Fe-Kα ray, tube voltage: 40 kV, tube current: 20 mA). ).

The crystal structure was confirmed by comparison with orthorhombic LiMnO ₂ , which has a zigzag layer structure.

Co, contained in the lithium iron oxide powder,
The amounts of Ni and Mn were determined by dissolving a lithium iron oxide powder in concentrated hydrochloric acid and using an inductively coupled plasma emission spectrometer (ICA).
P-575, manufactured by Nippon Jarrell Ash Co.). From the results of the above-mentioned plasma emission spectroscopy, only lithium, iron, cobalt, nickel, and manganese were determined, and oxygen contained two atoms per (Fe, M).

As an electrode active material of lithium iron oxide, its electrochemical characteristics were evaluated by a potential sweep method.

First, lithium iron oxide as a working electrode for measurement, polytetrafluoroethylene as a binder, and graphite as a conductive agent were mixed at a weight ratio of 10%, and 30 mg of this mixture was weighed and collected. A stainless steel mesh was filled as a body to obtain a working electrode.

A lead terminal made of a stainless steel wire was spot-welded to the working electrode thus obtained. As a counter electrode, a lithium metal foil was filled in a stainless steel mesh, and the lead terminals were similarly spot-welded.
The reference electrode was similarly configured using lithium metal.

As the electrolyte, lithium perchlorate (LiC
1O ₄ ) was dissolved at a concentration of 1 mol in a solvent in which propylene carbonate and dimethoxyethane were mixed at a volume ratio of 1: 1.

The working electrode, counter electrode and reference electrode thus prepared were immersed in an electrolyte to form an electrochemical cell. Using this electrochemical cell, a potential sweep was performed at a sweep rate of 10 mV / sec in a potential range of 1.5 V to 3.5 V with respect to a metal lithium electrode, and the current change observed at that time was examined. Preparation and measurement of these electrochemical measurement cells were performed in a dry box filled with argon.

As an index of the electrode reaction rate of the lithium iron oxide, a peak value of a reduction current, which appeared in a potential-current curve observed in this potential range, was determined.

<Production of lithium iron oxide> Co was 3.0.
mol% lepidocrocyte γ- (Fe, Co)
24.0 g of OOH powder and 9.0 of LiOH (anhydride) powder
5 g (Li / Fe = 1.4) were mixed, and the mixed powder was placed in a screw-cap pressure-resistant bottle, placed in an electric oven that had been heated to 130 ° C. in advance, and reacted for 1 hour to obtain a reaction product powder. I got

The above reaction product powder is immersed in 200 cc of cold water at a water temperature of about 10 ° C. for 5 minutes, suspended and washed with water,
After the precipitated solid was separated by filtration, the precipitate was dried under reduced pressure at 30 ° C. for 3 days to obtain a tan powder.

As shown in the X-ray diffraction diagram shown in FIG. 1, the obtained tan powder was made of Li _x (F) having a zigzag layered structure.
e, Co) O ₂ powder. In FIG. 1, peak A is L
i _x (Fe, Co) shows the O _2. As a result of the ICAP analysis, Li _0.95 Fe containing 3.0 mol% of Co was used.
_0.97 Co _0.03 O ₂ powder.

The peak value of the reduction current that appeared in the potential sweep performed on the lithium iron oxide was 22.3 mV.

[0048]

The most important point in the present invention is that one of metals selected from cobalt, nickel and manganese is used as an iron raw material.
In the case of using the lepidocrocite particles containing more species or two species, it has a corrugated layer structure that acts as a positive electrode active material, and the electrode reaction rate is high when used as a positive electrode active material Li _x (Fe, M) O ₂ (0 <x ≦
1, M = one or more metals selected from Co, Ni and Mn).

Li _x (Fe, having a zigzag layered structure)
_{M) O 2 (0 <x} ≦ 1, M = Co, 1 or two or more metals selected from Ni and Mn) the reason why the powder is obtained, the present inventors have lepidocrocite .gamma. (Fe ,
M) Since the OOH powder has a crystal structure containing protons between the layers of the zigzag layer structure, when heated together with the lithium compound, an ion exchange reaction occurs, and the protons are released, and at the same time, lithium ions are introduced between the zigzag layers. Believe in things.

Li _x (Fe, having a zigzag layered structure)
(M) O ₂ (0 <x ≦ 1, M = one or two or more metals selected from Co, Ni and Mn) Regarding the reason why the powder acts as the positive electrode active material, the present inventor has proposed that the powder exists between the layers. This is thought to be due to electrochemically entering and exiting lithium ions.

When used as a positive electrode active material, Li _x (Fe, M) O ₂ (0 <x ≦ 1, M = C
The reason why the powder (one or more of the metals selected from o, Ni and Mn) can be obtained is not yet clear, but the present inventor thinks as follows.

That is, lithium iron oxide is a mixed conductor of electrons and lithium ions, and electrons are conducted between iron ions by hopping, and lithium ions are conducted between ion sites between FeO ₂ layers. When electrons are inserted into and desorbed from the iron ions as the electrons move, the energy level of the lithium ion sites in the vicinity also changes, so that the probability that the lithium sites occupy the ion sites also changes. Conducts as if they are coupled in the crystal.

When part of the iron in the lithium iron oxide is replaced by one or more metals selected from cobalt, nickel and manganese, the electronic structure near the Fermi level changes, and the conduction electron It is thought that the number of electrons thermally excited in the band increases. As a result, the number of electrons hopping between iron ions increases, and lithium ions between the layers also conduct with the conduction of the electrons, so that the conductivity of lithium ions also improves. In addition, since the electron conductivity of lithium iron oxide is also high, when used as an electrode active material, the electrode reaction speed is improved.

[0054]

Next, examples, comparative examples, and usage examples will be described.

Examples 1 to 6 and Comparative Examples 1 to 4 Types of lepidocrocite powder, mixing ratio of lepidocrocite powder and lithium compound powder Li / Fe (mol)
The reaction product powder was obtained in the same manner as in the embodiment of the invention except that the ratio) and the heating temperature were variously changed.

Table 1 shows the production conditions, various properties of the reaction product, and properties of the heat-treated product.

[0057]

[Table 1]

Each of the lithium iron oxide powders obtained in Examples 1 to 6 has a zigzag layered structure.
_{i x (Fe, M) O} 2 (0 <x ≦ 1, M = Co, 1 or two or more metals selected from Ni and Mn) to be a was observed.

FIG. 2 shows an X-ray diffraction diagram of the lithium iron oxide powder obtained in Example 3.

The powder obtained in Comparative Example 1 was also a Li _0.93 Fe _1.0 O ₂ powder having a zigzag layered structure.

The yellow-brown powder obtained in Comparative Example 2 had a zigzag layered structure as shown in the X-ray diffraction diagram of FIG.
_x was a mixture powder of FeO ₂ , α-LiFeO ₂ and γ-FeOOH.

The yellow-brown powder obtained in Comparative Example 3 was made of Li having a zigzag layered structure as shown in the X-ray diffraction diagram of FIG.
It was a powder mixture of _x FeO ₂ (0 <x ≦ 1) and α-LiFeO ₂ .

The yellow-brown powder obtained in Comparative Example 4 had a zigzag layered structure as shown in the X-ray diffraction diagram of FIG.
_x FeO _2, it was a mixture powder of gamma-FeOOH and β-LiFe ₅ O _8.

Use Examples The lithium iron oxide powder obtained in each of the examples 1 to 6 and the powder obtained in each of the comparative examples 1 to 4 were used for the invention of the present invention. The characteristics were confirmed in the same manner as in the embodiment.

Table 1 shows the reduction current beak values of the lithium iron oxide powders obtained in Examples 1 to 6 in the same manner as in the embodiment of the present invention.

The peak value of the reduction current when the lithium iron oxide obtained in each of Examples 1 to 6 was used was the same as that of Comparative Example 1.
In addition, the value is larger than that of Comparative Example 4, indicating that a lithium iron oxide having a higher electrode reaction rate according to the present invention can be obtained.

In the use example of the present invention, the case where the lithium iron oxide obtained by using anhydrous lithium hydroxide as the lithium compound is used as the material for the positive electrode active material has been described. The same effect is obtained by using hydrates of lithium, lithium oxide, lithium peroxide, or the like.

In the case where a lithium iron oxide containing Co and Ni, Co and Mn, and Co, Ni and Mn as M elements is used as the positive electrode active material, Examples 1 to 6 were also used. It has been confirmed that the electrode reaction rate is high as in the case of.

When the lithium iron oxide powder obtained in Comparative Example 1 was used, electrochemical activity was exhibited, but the electrode reaction rate was low.

When the powders obtained in Comparative Examples 2 to 4 were used, almost no electrochemical activity was exhibited.

[0071]

The lithium iron oxide powder according to the present invention comprises:
Since it acts as a positive electrode active material of a lithium battery and has a high electrode reaction rate, it is suitable as a material for a positive electrode active material of a lithium battery.

The lithium iron oxide powder according to the present invention is inexpensive compared to Li _x CoO ₂ , Li _x NiO _2, etc., and does not require the use of a large amount of expensive Co or Ni. It is industrially and economically advantageous because it can be supplied on an economic scale as a positive electrode active material.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction diagram of lithium iron oxide obtained in an embodiment of the present invention.

FIG. 2 is an X-ray diffraction diagram of the lithium iron oxide obtained in Example 3.

FIG. 3 shows an X-ray diffraction pattern of the powder obtained in Comparative Example 2.

FIG. 4 is an X-ray diffraction diagram of the powder obtained in Comparative Example 3.

FIG. 5 is an X-ray diffraction diagram of the powder obtained in Comparative Example 4.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01M 10/40 H01M 10/40 Z

Claims (2)

[Claims] 1. A metal containing one or more metals selected from cobalt, nickel and manganese in a total amount of 0.5 to 10.0 mol% in terms of Co, Ni and Mn, and zigzag. Li _x (Fe,
M) Lithium iron oxide powder comprising O ₂ (0 <x ≦ 1, M = one or more metals selected from Co, Ni and Mn). 2. A mixed powder of a levidrosite particle powder and a lithium compound powder containing one or two or more metals selected from cobalt, nickel and manganese.
The method for producing a lithium iron oxide powder according to claim 1, wherein the heating is performed in a temperature range of 0 to 150 ° C.