JPH11265717A - Spinel type lithium manganese oxide for secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium manganese oxide for secondary battery superior in both of a capacity maintaining rate and high temperature characteristics without largely deteriorating the initial discharge capacity. SOLUTION: This lithium manganese oxide for secondary battery is expresses by a formula LiMnx-y My O4 (where, (x) is 1.8 to 2.1, (y) is 0.01 to 0.1, and M is transition metal except A1 or Mn). A peak intensity ratio in X-ray diffraction is a 311 face <400 face and a lattice constant is 8.200 to 8.250. The metal is any at least one kind selected among Fe, Cr and Al.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spinel-type lithium manganese oxide which is advantageous for use as a positive electrode material for a lithium secondary battery and a method for synthesizing the same.

[0002]

2. Description of the Related Art Lithium manganese oxide is made from a manganese compound, which has abundant resources and is advantageous in terms of price, so that LiCoO ₂ , which is a positive electrode material for lithium secondary batteries of high voltage and high energy density, is used. As an alternative material, it has recently attracted attention.

Conventionally, a lithium manganese oxide has been dry-mixed with a lithium salt and a manganese salt, for example, lithium carbonate and Mn ₂ O ₃ or lithium carbonate and manganese carbonate at an atomic ratio of 1: 2, and the resulting mixed powder is obtained. It was synthesized by firing in an oxidizing atmosphere. However, the conventional process for producing a lithium manganese oxide in this way has the following problems, and the lithium manganese oxide obtained by such a process has sufficient charge / discharge cycle characteristics as a cathode material of a secondary battery. Did not have. "Since the above-mentioned dry mixing is a solid-solid mixing and it is impossible to perform microscopic uniform mixing at the atomic or molecular level, the crystal structure of the lithium manganese oxide obtained by this method tends to have defects."

[0004] In order to solve the above-mentioned problems of the conventional lithium manganese oxide, the present inventors first disclosed in Japanese Patent Laid-Open No.
The invention described in -208231 was proposed. The proposed method uses a water-soluble lithium salt, manganese nitrate (Mn (NO ₃ ) ₂ )
To the resulting mixed aqueous solution, a water-soluble polymer containing no metal ions is added as a cation carrier, and then the water content of the mixed aqueous solution is removed by heating to obtain a spinel-type lithium manganese oxide. It is a method of manufacturing.

According to this method, it is possible to synthesize a spinel-type lithium manganese oxide at a lower temperature than before, and to produce a crystalline spinel-type lithium manganese oxide stably without causing defects. can do. Therefore, the obtained spinel-type lithium manganese oxide can be used as a cathode material for a lithium secondary battery, a base material for a lithium adsorbent, or the like having sufficient charge / discharge cycle characteristics.

[0006] However, when the lithium manganese oxide obtained by the above method is used as a cathode material of a battery, a cathode material having an initial discharge capacity of 130 mAh / g and a high capacity and excellent cycle characteristics can be obtained. The cycle characteristics at the time were not enough. Therefore, recently, development of a spinel-type lithium manganese oxide having excellent high-temperature characteristics has been demanded.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to meet the above-mentioned demands, and its main objects are as follows.
An object of the present invention is to provide a lithium manganese oxide for a secondary battery having excellent high-temperature characteristics without significantly lowering the initial discharge capacity.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies for realizing the above-mentioned object, and as a result, have a higher lattice energy in lithium manganese oxide than Mn (a strong force for stabilizing the crystal lattice). It has been found that by coordinating a small amount of an element, that is, a transition metal other than Al or Mn, it is possible to improve both the capacity retention ratio and the high-temperature cycle characteristics without greatly reducing the initial discharge capacity.
The present invention has been conceived of the invention having the following contents as its gist.

That is, the spinel-type lithium manganese oxide for a secondary battery of the present invention is a spinel-type lithium manganese oxide for a secondary battery represented by the following general formula, and has a peak intensity ratio in X-ray diffraction of 311 planes. <400 planes and a lattice constant of 8.200 to 8.250 °. General _{formula: LiMn xy M y O 4 x} : 1.8 ~2.1 y: 0.01~0.1 M: Al or a transition metal other than Mn Incidentally, the metal M is either at least one member selected from among Fe, Cr and Al, Preferably it is a seed.

The present invention also provides a method for producing the above spinel-type lithium manganese oxide, which comprises an aqueous solution of a water-soluble lithium salt, an aqueous solution of manganese nitrate (Mn (NO ₃ ) ₂ ), an aqueous solution of aluminum nitrate or a transition metal other than manganese. A nitrate aqueous solution is mixed, and then, to the obtained mixed aqueous solution, a water-soluble polymer containing no metal ion is added as a cation carrier, and thereafter, the water content of the mixed aqueous solution is removed by heating.
A method characterized by reacting is proposed. The aqueous aluminum nitrate solution or the aqueous transition metal nitrate solution excluding manganese preferably has an amount of metal of 0.5 to 5.5 mol% with respect to the pure Mn content of the aqueous manganese nitrate solution. As an aqueous solution or an aqueous solution of a nitrate of a transition metal excluding manganese, Fe,
It is preferable to use at least one kind of aqueous solution of nitrate selected from Cr and Al.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium manganese oxide for a secondary battery according to the present invention is obtained by uniformly coordinating a specific amount of a transition metal other than aluminum or manganese in the crystal structure of the lithium manganese oxide. It is characterized in that its crystal structure is further stabilized. Specifically, the general _{formula: LiMn xy M y O 4 (} x: 1.8 ~2.1, y: 0.01
, 0.1; M; a transition metal other than Al or Mn), the peak intensity ratio in X-ray diffraction is 311 <400, and the lattice constant is 8.200 to 8.250 °.

According to the lithium manganese oxide of the present invention, When the peak intensity ratio is 311 plane <400 plane, lithium and manganese and other metals are coordinated without defects in the spinel lattice, and. In addition, since the lattice constant is within the range of 8.200 to 8.250 て も, even if elements other than lithium and manganese are added and coordinated, the lattice constant is very close to the basic lattice constant of the lithium manganese spinel structure (8.240Å). Since it has a constant value, there are no basic lattice defects. In addition, the added element _{M, Mn x (x: 1.8} ~2.1)
When the lithium manganese oxide having such a structure is used as a positive electrode material of a secondary battery, the capacity retention ratio and the high temperature can be reduced without significantly lowering the initial discharge capacity. Stability can be improved. That is, the conventional lithium manganese oxide is
It was generally said that the coordination of elements other than Li and Mn greatly reduced the initial discharge capacity as a lithium electrode material.However, according to the lithium manganese oxide of the present invention, the initial discharge capacity was greatly reduced. Thus, the capacity retention and the high-temperature characteristics can be improved without the need.

In the lithium manganese oxide of the present invention, any transition metal other than Mn may be used as long as it is a transition metal such as Co or Mo. In particular, in the present invention, at least one selected from Fe, Cr and Al is an element having substantially the same ionic radius as that of Mn to be substituted, and is preferably in the range of the above-mentioned lattice constant. The method is most suitable as the selected element because the method can take trivalent nitrate in a stable form.

In the present invention, the additive element M is
Mn x: is to replace a proportion of 0.01 to 0.1 with respect to _(x 1.8 to 2.1), it showed no improvement in capacity retention ratio and high temperature properties that it is less than 0.01, whereas, the initial discharge capacity exceeding 0.1 This is because the reduction is so large that it is not practical.

The method for producing a lithium manganese oxide according to the present invention comprises mixing an aqueous solution of a water-soluble lithium salt, an aqueous solution of manganese nitrate (Mn (NO ₃ ) ₂ ) and an aqueous solution of aluminum nitrate or an aqueous solution of a transition metal nitrate other than manganese. And
Then, to the obtained mixed aqueous solution, a water-soluble polymer containing no metal ion was added as a cation carrier, and then,
It is characterized in that the water content of the mixed aqueous solution is preferably removed by heating at a temperature of 100 ° C. or higher to cause a reaction.

Thus, Li ions and Mn in the mixed aqueous solution
Both the ions and the other metal ions are fixed to the cation carrier as water evaporates, resulting in a uniform state in which the ions easily react. On the other hand, nitrate ions react with the cation carrier by heating to generate nitro compounds. As a result, if the heating is continued, the nitro compound decomposes and burns, and its thermal energy causes the reaction of Li ions, Mn ions and other metal ions, and the crystallinity in which metals other than Li and Mn are regularly coordinated. Spinel-type lithium manganese oxide can be easily synthesized. In the present invention, the decrease in the initial discharge capacity due to the substitution of elements other than Li and Mn is suppressed by adding a small amount. However, since a special liquid phase synthesis method as described above is employed, even a small amount of substitution is required. Coordination is uniform, and the effect of crystal stabilization is increased.

If the heating temperature is lower than 100 ° C., decomposition and combustion of the nitro compound do not occur, and lithium manganese oxide cannot be synthesized.

In the method of the present invention, lithium nitrate, lithium sulfate, lithium chloride and the like can be used as the water-soluble lithium salt, and lithium nitrate (LiNO ₃ ) is preferably used. The reason for this is that nitrate ions are decomposed at low temperatures, causing other anions (sulfate,
(E.g., chlorine ions), because they are easier to remove and do not remain in the fired product.

In the method of the present invention, it is necessary to use manganese nitrate (Mn (NO ₃ ) ₂ ) as a Mn source because nitrate ions of manganese nitrate react with a water-soluble polymer as a cation carrier. This is because a nitro compound is easily generated.

In the method of the present invention, the reason why an aqueous nitrate solution thereof is used as a transition metal other than aluminum or manganese is to uniformly mix with the above-mentioned lithium salt or manganese salt. It may be in the form of a metal salt, for example a salt such as cobalt sulfate, but preferably a trivalent metal nitrate. In particular, in the present invention, it is preferable to use at least one selected from Fe, Cr and Al having substantially the same lattice constant as Mn as such a trivalent metal.

In the method of the present invention, the aqueous solution of aluminum nitrate or the aqueous solution of nitrate of a transition metal other than manganese is used when the amount of the metal is less than that of the aqueous solution of manganese nitrate.
It is desirable that the content is 0.5 to 5.5 mol% based on the pure Mn content.
The reason for this is that when less than 0.5 mol%, the capacity retention ratio and the high temperature characteristics are not improved, while when it exceeds 5.5 mol%, the initial discharge capacity is greatly reduced.

The reason for using a cation carrier in the method of the present invention is that, unless a cation carrier is added, Li salt and manganese nitrate are separated and precipitated due to a difference in solubility due to the evaporation of water in the mixed aqueous solution by heating. It is because. This cation carrier is a substance having a function of supporting and fixing metal ions such as Li ions and Mn ions, and may be any water-soluble polymer containing no metal ions, for example, starch such as wheat starch, Seaweeds such as mannan (konjac), agar (agar), plant mucilage such as trolley mallow and arabic gum, mucous microbes such as dextran, natural polymers represented by proteins such as glue and gelatin, viscose and There are cellulosic products such as methylcellulose (MC), semi-synthetic products such as starches such as soluble starch and dialdehyde starch, and synthetic products such as polyvinyl alcohol (PVA). Among them, it is preferable to use at least one selected from the group consisting of PVA, MC, agar and the like, which is an organic substance which is easily nitrated and has an OH group. The reason why a water-soluble polymer containing no metal ion is used is that if metal ions such as potassium and sodium remain, compounds other than lithium manganese oxide are synthesized.

In the method of the present invention, the crystalline spinel-type lithium manganese oxide is considered to be synthesized by the following reaction mechanism. That is,. First, a water-soluble lithium salt and manganese nitrate (Mn (N
The Li ions and Mn ions in the mixed aqueous solution of O ₃ ) ₂ ) gradually become supported on the cation carrier as water evaporates due to heating.
It is fixed and becomes a uniform state that is easy to react. . On the other hand, nitrate ions in the mixed aqueous solution react with the cation carrier by heating to generate a nitro compound. . The nitro compound carrying the above cations is decomposed and burned by heating at 100 ° C. or more to generate heat, and the heat energy from the decomposition and combustion causes Li ions and Mn ions to react to form lithium manganese oxide. It can be easily synthesized.

The spinel-type lithium manganese oxide of the present invention thus synthesized is then further heated to 750 ° C.
It is fired under conditions of about × 5 hrs to form a complete spinel form, and then pulverized, and used as a positive electrode material for a secondary battery.

[0025]

EXAMPLES (Example 1) in _{LiMn 2-y M y O 4} , the substitution amount y of substituting element M (Fe, Cr, Al) are respectively 0.
First, LiNO ₃ , Mn (NO ₃ ) ₂・ 6H ₂ O
If, Fe, Cr or trivalent nitrate (Fe (NO ₃ of Al,) ₃ · 6H ₂ O
_{, Cr (NO 3) 3 ·} 9H 2 O, Al a _{(NO 3) 3 · 9H 2} O) were mixed, and the mixed aqueous solution. Next, this mixed aqueous solution was heated, and 8 g of PVA was added as a cation carrier. Thereafter, the heating was continued to evaporate a certain amount of water, and the mixture was transferred to a dryer at 150 ° C. and reacted to obtain a reaction product as a black powder.

The reaction product of the black powder was heated at 750 ° C. for 5 hours.
When calcined and identified by X-ray diffraction, it was confirmed that it was a LiMn ₂ O ₄ spinel single phase having a component composition and a lattice constant shown in Table 1. In addition, as is clear from the X-ray diffraction chart of the reactant shown in FIG. 1, the spinel-type lithium manganese oxide of the present invention has a peak intensity ratio of 311 planes <
It can be seen that there are 400 surfaces.

(Example 2) The product powder (calcined and crushed product) of the spinel-type lithium manganese oxide having the physical properties shown in Table 1 obtained in Example 1 was mixed with a conductive material and a binder, kneaded, and then sheeted. And sandwiched between SUS meshes to obtain a positive electrode material. Next, this positive electrode material was housed in a three-electrode glass cell, and Li foil was used as a counter electrode (reference electrode).
Charge and discharge were repeated using M LiClO ₄ as an electrolyte. The charge / discharge voltage is 3 to 4.4 V, and the discharge rate is
0.5C. The high-temperature cycle test was performed at 60 ° C. using a commercially available closed cell.

As a result, the initial discharge capacity at 25 ° C.
Table 2 shows the discharge capacities after 30 and 100 repetitions. As is clear from the results shown in this table, the comparative example (an example using a spinel-type lithium manganese oxide manufactured by the same method as in the example except that the additional elements Fe, Cr, and Al were not added) was used. It can be seen that the capacity maintenance ratio is improved as compared with the capacity maintenance ratio. The initial discharge capacity is
Although there are some cases where the content is slightly lower than that of the comparative example, it is the same, and it has been conventionally said that the capacity is greatly reduced when the additive is added. However, in the present invention, the capacity was not significantly reduced. Table 2 also shows the measured values of the discharge capacity and the capacity retention at 60 ° C. as the high-temperature characteristics. As is clear from the results shown in this table, a significant improvement was observed as compared with the conventional product.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As described above, according to the present invention, it is possible to provide a lithium manganese oxide for a secondary battery having both excellent capacity retention ratio and high temperature characteristics without significantly lowering the initial discharge capacity. .

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of a spinel-type lithium manganese oxide (substituted with Cr 0.1) obtained in Example 1.

Continued on the front page (72) Inventor Takumi Murai 1-1-1 Yoshihisa, Takaoka City, Toyama Prefecture Nippon Heavy Chemical Industry Co., Ltd. Takaoka Office (72) Inventor Kenya 1-1-1 Yoshihisa, Takaoka City, Toyama Prefecture Nippon Heavy Chemical Industrial Co., Ltd. Inside Takaoka Office

Claims (5)

[Claims] 1. A spinel-type lithium manganese oxide for a secondary battery represented by the following general formula, wherein the peak intensity ratio in X-ray diffraction is 311 <400, and the lattice constant is 8.200 to 8.250 °. A spinel-type lithium manganese oxide for a secondary battery. General _{formula: LiMn xy M y O 4 x} : 1.8 ~2.1 y: 0.01~0.1 M: Al or a transition metal other than Mn, 2. The spinel-type lithium manganese oxide for a secondary battery according to claim 1, wherein the metal M is at least one selected from the group consisting of Fe, Cr and Al. 3. An aqueous solution of a water-soluble lithium salt, an aqueous solution of manganese nitrate (Mn (NO ₃ ) ₂ ) and an aqueous solution of aluminum nitrate or an aqueous solution of a transition metal except for manganese are mixed.
Then, to the obtained mixed aqueous solution, a water-soluble polymer containing no metal ion was added as a cation carrier, and then,
A method for producing a spinel-type lithium manganese oxide for a secondary battery, wherein a water content of the mixed aqueous solution is removed by heating. 4. The aqueous nitrate solution of aluminum or the aqueous nitrate solution of a transition metal other than manganese has a metal content of 0.5 to 0.5% based on the pure Mn content of the aqueous manganese nitrate solution.
The method according to claim 3, wherein the amount is 5.5 mol%. 5. An aqueous nitrate solution of aluminum or an aqueous nitrate solution of a transition metal other than manganese, wherein Fe or Cr is used.
5. An aqueous solution of at least one nitrate selected from the group consisting of Al and Al.
The production method described in 1.