JP2003081637A - Lithium - manganese compound oxide for secondary battery, production method therefor and nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spinel type lithium - manganese compound oxide which is suitable as the positive pole material of a high energy density secondary battery, and is usable as a practical battery, and to provide an effective method for producing the oxide. SOLUTION: The lithium - manganese compound oxide for a secondary battery is expressed by the general formula of Lix My Mn2-y O4+δ(M is one or more kinds of transition metals selected from Ni, Co, Cr, Fe and Cu, and 0.9<=x<=1.2, 0.2<=y<=1.0, and 0<; δ<=0.5 are satisfied), and has a structure of a low-crystalline spinel single phase in which the half width of the (111) face in X-ray diffraction is >=0.8 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium-manganese composite oxide for a secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery, and particularly to a high energy suitable for use as a positive electrode material for a secondary battery. This is a proposal for a low-crystallinity 5V class lithium manganese oxide for spinel secondary batteries and a manufacturing method thereof.

[0002]

2. Description of the Related Art Lithium secondary batteries are used as power sources for portable electronic devices such as personal computers and mobile phones because of their small size, light weight and high energy density.

At present, LiCoO ₂ having a high voltage and a high energy density is widely used as a positive electrode material of a lithium secondary battery, but recently, a spinel type lithium manganese composite which has been developed aiming at a higher energy density. Research on oxides (LiMn ₂ O ₄ ) is active. In particular, much research has been done on a positive electrode material for a 5V class spinel type lithium secondary battery in which a part of Mn of this oxide is replaced with a transition metal. The lithium manganese oxide is rich in the amount of manganese, which is the main raw material, and is expected as an excellent material in terms of economy.

Such a spinel type lithium manganese composite oxide has a flat charge / discharge plateau at about 5 V when Li located at the 8a site in the spinel structure of this oxide is removed / inserted using a redox of a substituted transition metal. It comes to function as a positive electrode material. On the other hand, the 16c site, which is an empty site in the spinel structure, is converted into Li using the Mn redox.
By removing / doping (doping), it can also function as a 3V class positive electrode material having a flat charge / discharge plateau at about 3V, which has the advantage of expanding the applicable range.

As described above, in the conventional spinel type lithium manganese composite oxide, desorption of Li into the spinel structure
By inserting, it is possible to cover both 5V and 3V regions, and it is useful as a positive electrode material having a large battery capacity. However, in the 5V region and the 3V region, there is a potential difference of about 2V between the charge and discharge plateaus, which is very inconvenient when considering an actual battery.

[0006]

Therefore, an object of the present invention is a spinel type lithium manganese composite oxide suitable as a positive electrode material of a high energy density secondary battery and usable as a practical battery, and an effective production method thereof. And to provide a non-aqueous electrolyte secondary battery.

[0007]

[Means for Solving the Problems] The inventors of the present invention have conducted earnest research to realize the above-mentioned object. As a result, 5V and
We thought that if the flat charge / discharge plateau at 3V was broken and the charge / discharge plateau gap could be made smaller by providing a gentle slope, the above-mentioned problems of the conventional technology could be overcome.

Normally, the charge / discharge plateau of spinel type lithium manganese composite oxide becomes flat when the crystallinity is high,
If it is low, it will have a slope. This crystallinity can be controlled by the firing temperature at the time of synthesis. The higher the firing temperature, the higher the crystallinity, and the lower the firing temperature, the lower the crystallinity. Therefore, the inventors synthesized a lithium manganese composite oxide at a low temperature, provided a charge / discharge plateau with an inclination, and then baked it at a high temperature, thereby producing a spinel-type lithium manganese composite oxide having a low crystalline 5V class battery capacity. The inventors have found that a single phase of a product can be synthesized, and have conceived the present invention.

The present invention has a general formula of Li _x M _y Mn _2-y O _{4 + δ} (M
Is any one or two or more kinds of transition metals selected from Ni, Co, Cr, Fe and Cu, 0.9 ≦ x ≦ 1.2, 0.2 ≦ y
≦ 1.0, 0 <δ ≦ 0.5) and (111) in X-ray diffraction
A lithium-manganese composite oxide for a secondary battery, which is a low crystalline spinel type single phase having a half-value width of 0.8 ° or more.

In the present invention, the general formula is Li _x M _y Mn _2-y O
_{4 + δ} (M is any one or two or more transition metals selected from Ni, Co, Cr, Fe and Cu, 0.9 ≤ x ≤ 1.
2, 0.2 ≦ y ≦ 1.0, 0 <δ ≦ 0.5), and the discharge capacity is
A lithium-manganese composite oxide for a secondary battery, which is 200 mAh / g or more in a potential range of 2.5 to 5.0 V.

In the present invention, the general formula is Li _x M _y Mn _2-y O
_{4 + δ} (M is any one or two or more transition metals selected from Ni, Co, Cr, Fe and Cu, 0.9 ≤ x ≤ 1.
2, 0.2 ≦ y ≦ 1.0, 0 <δ ≦ 0.5), a low crystalline spinel type single phase with a (111) plane half width of 0.8 ° or more in X-ray diffraction, and 2.5 to 200mA in 5.0V potential range
A lithium-manganese composite oxide for a secondary battery, which has a discharge capacity of h / g or more.

Further, in the present invention, in producing the lithium manganese composite oxide according to any one of the above items 1 to 3, Li nitrate, Mn nitrate, and M metal (N
i, Co, Cr, Fe and Cu, any one kind or two or more kinds of transition metals) in a mixed aqueous solution with nitrate,
Add a nonionic water-soluble polymer as a cation carrier,
Thereafter, the mixed aqueous solution is heated at 80 to 300 ° C. to cause a self-reaction to synthesize the lithium-manganese composite oxide.

Then, in the present invention, in producing the lithium-manganese composite oxide according to any one of the above items 1 to 3, Li nitrate, Mn nitrate, and M metal (N
i, Co, Cr, Fe and Cu any one kind or two or more kinds of transition metals selected from among) a mixed aqueous solution with a nitrate, a nonionic water-soluble polymer is added as a cation carrier, and then, The method for producing a lithium manganese composite oxide is characterized in that a self-reaction is caused by heating the obtained mixed aqueous solution at 80 to 300 ° C., and then the mixture is baked at 200 to 500 ° C. to synthesize.

Further, according to the present invention, a secondary battery comprises a positive electrode using the lithium manganese composite oxide as an active material, a negative electrode using a carbonaceous material or a lithium storage material as an active material, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery is proposed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION First, a method for producing a lithium manganese composite oxide according to the present invention will be described below. The characteristic of this manufacturing method is that it is synthesized by a low temperature self-reaction method (a method of reacting lithium ions and manganese ions in a liquid-liquid homogeneous mixture system, which is disclosed in Japanese Patent No. 2977909). That is, this synthetic method, Li nitrate, Mn nitrate and a mixed aqueous solution of the transition metal nitrate as a Mn substitution element, a nonionic water-soluble polymer containing no metal ion is added as a cation carrier, 100-200
In this method, the water content of the mixed aqueous solution is removed by heating at a low temperature of ° C to cause a self reaction.

Lithium nitrate (LiNO ₃ ) is used as the Li nitrate in the mixed aqueous solution. The reason for this is that nitrate ions are decomposed at a low temperature, so that they are easier to remove than other anions (sulfate ions, chlorine ions, etc.) and do not remain in the baked product.

As the Mn nitrate, manganese nitrate (Mn (N
O ₃ ) ₂ ) is used. The reason for this is that the nitrate ion of manganese nitrate reacts with the water-soluble polymer that is the cation carrier,
This is because a nitro compound is easily produced.

Further, as a starting material, a nitrate of an Mn-substituting element composed of one or more transition metals selected from Ni, Co, Cr, Fe and Cu is used. When these transition metals are uniformly coordinated in the crystal structure of the lithium-manganese composite oxide, they have a function of stabilizing the crystal structure. Note that these transition metals are elements having almost the same ionic radius as Mn to be substituted, and they are desirable because they can take a trivalent nitrate in a stable form in the synthesis process. As a result, it becomes possible to synthesize a spinel-type lithium manganese composite oxide having a large capacity of 5 V class, and by synthesizing at low temperature, the charge-discharge plateau gap can be reduced.

In the above manufacturing method, the reason why the cation carrier made of a nonionic water-soluble polymer containing no metal ion is used is that if the cation carrier is not added, the water content in the mixed aqueous solution is evaporated by heating. This is because nitrates of each element are separated and deposited due to the difference in solubility. As the cation carrier, any substance having a function of supporting and fixing cations may be used, and examples thereof include starchy substances such as wheat starch, seaweeds such as mannan (konjac and the like) and agar (agar), Trolooi and gum arabic. Such as plant mucilages, microbial mucilages such as dextran, natural polymers represented by proteins such as glue and gelatin, cellulosics such as viscose and methylcellulose (MC), and starches such as soluble starch and dialdehyde starch. There are representative semi-synthetic products and synthetic products such as polyvinyl alcohol (PVA). Among them, it is preferable to use one or more selected from PVA, MC, agar, etc., which are organic substances that are easily metal-nitrated and have an OH group.

In the present invention, the reason why the nonionic water-soluble polymer containing no metal ion is used is that if a metal ion such as potassium or sodium remains, the metal ion is incorporated into the crystal structure of the complex oxide or is newly added. This is because various compounds are produced.

When the heating temperature is lower than 80 ° C., decomposition or combustion of the nitro compound does not occur and the composite oxide cannot be synthesized. Therefore, it is desirable to set the heating temperature to 80 ° C. or higher.
On the other hand, the upper limit of the temperature may be a temperature at which water evaporates and the nitro compound decomposes, and therefore, it is desirable to set the temperature in the range of 300 ° C. or lower depending on the type of the water-soluble polymer used. More preferably, the temperature range is 100 ° C to 200 ° C.

By heating in the above-mentioned temperature range, two or more kinds of cations in the mixed aqueous solution are fixed in a state of being uniformly mixed with the cation carrier as the water vaporizes. On the other hand, nitrate ions react with the cation carrier by heating to produce a nitro compound. As a result, when the heating is continued, the nitro compound decomposes and burns, and the thermal energy causes cations to easily react with each other to synthesize a composite oxide.

Furthermore, the present invention is characterized in that, in addition to the above-mentioned process of synthesizing the composite oxide, a reheating treatment (baking) is further performed at a temperature of 200 to 500 ° C. In the above-mentioned synthetic process, nitric acid and organic substances added as a cation carrier may remain in the synthetic product powder unreacted, and the presence of these impurities affects the battery characteristics. It is desirable to perform a spinelization to completely form a single phase of the lithium-manganese composite oxide.

The limit for the reheat treatment temperature is 20.
This is because if the temperature is lower than 0 ° C., unreacted substances remain in the synthetic powder as described above, and if the temperature is 500 ° C. or higher, the crystallinity becomes high and the charge / discharge plateau gap becomes large.

The first lithium manganese composite oxide according to the present invention obtained by adopting the above-mentioned method is
The general formula is Li _x M _y Mn _2-y O _{4 + δ} (where M is Ni, Co, C
Any one or two selected from r, Fe and Cu
More than one kind of transition metal, 0.9 ≦ x ≦ 1.2, 0.2 ≦ y ≦ 1.0, 0 <δ ≦
0.5). This oxide is characterized by a low crystalline spinel single phase having a (111) plane full width at half maximum of 0.8 ° or more in X-ray diffraction. In the above general formula, the reason for limiting x, y, and δ as described above is that for x, a spinel single phase cannot be obtained at 0.9 or less, and a capacity decrease becomes large at 1.2 or more. , Y is 0.2 or less, the capacity in the 5V region is small, and 1.0 or more, a spinel single phase cannot be obtained, and δ is 0.
This is because the plateaus in the 5V region and the 3V region are flat and the potential gap becomes large below, and the capacitance decrease in the 5V region becomes large at 0.5 or more.

In the present invention, the full width at half maximum showing crystallinity is specified as a broad half having a full width at half maximum of 0.8 ° or more at the peak of the (111) plane in X-ray diffraction. The reason for this is that at 0.8 ° or less, the crystallinity becomes high, the plateaus in the 5V region and 3V region become flat, and the potential gap becomes large.

The second lithium manganese composite oxide according to the present invention has a structure represented by the above general formula, and further has a discharge capacity of 200 mAh / g or more in a potential range of 2.5 to 5.0 V. An oxide, the third one of the lithium-manganese composite oxide according to the present invention is (111) in X-ray diffraction.
An oxide in which the full width at half maximum and the discharge capacity both satisfy the first and second conditions described above.

By using the above-mentioned lithium manganese composite oxide according to the present invention as a positive electrode active material, high density,
A secondary battery having a high energy density and suitable as a practical battery can be provided. At that time, in the negative electrode active material,
A carbonaceous material or a lithium occlusion substance is used, and a nonaqueous electrolytic solution is used as the electrolytic solution. The non-aqueous electrolyte is generally prepared by dissolving a lithium salt as an electrolyte and dissolving this in an organic solvent. In the present invention, lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolyte, and a mixed solution of ethylene carbonate and dimethyl carbonate is used as the organic solvent. Other electrolytes include LiClO ₄ , LiAsF ₆ , LiBF ₄ , and LiS.
O ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ or the like or a mixture thereof is used. Further, as the organic solvent, diethyl carbonate,
Propylene carbonate and a mixture thereof can be used.

[0029]

EXAMPLES (Example 1) LiNO _3: 0.1 mol of _{Mn (NO 3) 2 · 6H} 2
O: 0.15 mol and _{Ni (NO 3) 2 · 6H} 2 O: 0.05 mol of pure water 30ml
To obtain a mixed aqueous solution. To this mixed aqueous solution, 33 g of 20% PVA solution as a cation carrier was added, mixed well, transferred to a dryer and heated at 150 ° C. for 2 hours and dried to cause a self-reaction to obtain a blackish brown powder. . Furthermore, 300 ℃
The powder was baked for 5 hours to obtain a synthetic powder. When this synthetic powder was identified by X-ray diffraction, it was confirmed to be a low crystalline spinel type single phase. The full width at half maximum of the (111) plane is
It was 1.09 °.

[0030] (Example 2) LiNO _3: 0.1 mol of Mn (NO _{3) 2} · 6H
₂ O: 0.15 mol and Ni (NO ₃ ) ₂ .6H ₂ O: 0.05 mol, pure water 30 m
It was dissolved in 1 to obtain a mixed aqueous solution. 33 g of a 20% solution of PVA as a cation carrier was added to this mixed aqueous solution, mixed well, transferred to a dryer and heated at 150 ° C. for 2 hours and dried to cause a self reaction to obtain a blackish brown powder. Furthermore, 400 ℃
It was baked for 5 hours to obtain a synthetic powder. When this synthetic powder was identified by X-ray diffraction, it was confirmed to be a low crystalline spinel type single phase. The full width at half maximum of the (111) plane is
It was 1.06 °.

[0031] (Example ₃₎ LiNO 3: 0.1 mol of Mn (NO _{3) 2} · 6H
₂ O: 0.15 mol and Ni (NO ₃ ) ₂ .6H ₂ O: 0.05 mol, pure water 30 m
It was dissolved in 1 to obtain a mixed aqueous solution. 33 g of a 20% solution of PVA as a cation carrier was added to this mixed aqueous solution, mixed well, transferred to a dryer and heated at 150 ° C. for 2 hours and dried to cause a self reaction to obtain a blackish brown powder. Furthermore, 500 ℃
It was baked for 5 hours to obtain a synthetic powder. When this synthetic powder was identified by X-ray diffraction, it was confirmed to be a low crystalline spinel type single phase. The full width at half maximum of the (111) plane is
It was 0.87 °.

Comparative Example LiNO ₃ : 0.1 mol and Mn (NO ₃ ) ₂ .6H ₂
O: 0.15 mol and _{Ni (NO 3) 2 · 6H} 2 O: 0.05 mol of pure water 30ml
To obtain a mixed aqueous solution. 33 g of a 20% PVA solution as a cation carrier was added to this mixed aqueous solution, mixed well, transferred to a drier and dried by heating at 150 ° C. for 2 hours to cause a self-reaction to obtain a blackish brown powder. Further, it was baked at 700 ° C. for 5 hours to obtain a synthetic powder. When this synthetic powder was identified by X-ray diffraction, it was confirmed to be a low crystalline spinel type single phase. The full width at half maximum of the (111) plane is 0.19.
It was °.

The powder synthesized in each of the above Examples and Comparative Examples was used as a positive electrode active material, and an electrochemical measurement was performed by setting up a three-electrode type glass type test cell.

FIG. 1 shows an X-ray diffraction pattern of the powders synthesized in each Example and Comparative Example. The powders synthesized in each of the examples and the comparative examples all have a single phase of spinel type structure, but the peaks of each example are broad and it is understood that the crystallinity is low.

Table 1 shows the initial discharge capacities and energy densities of the samples obtained in the respective examples and comparative examples.
In this measurement, metallic Li was used as the counter electrode. Each of the synthetic powders has a large discharge capacity of 200 mAh / g or more and an energy density of 700 Wh / g in the potential range of 2.5 V to 4.9 V.
It showed a high value of kg.

[0036]

[Table 1]

FIG. 2 shows initial discharge curves of the samples obtained in the respective examples and comparative examples. In the example, the discharge plateau in the 5V range is broken, and a gentle curve is drawn with the discharge plateau in the 3V range. That is, it can be seen that the gap between the discharge plateaus in the 5V region and the 3V region is small. on the other hand,
In the comparative example, it can be seen that the discharge plateaus in the 5V region and the 3V region are flat and have a large gap.

[0038]

As described above, according to the present invention,
It is possible to manufacture a spinel type lithium manganese composite oxide having a large discharge capacity and energy density. Therefore, by using the lithium manganese composite oxide as a positive electrode material, it is possible to provide a lithium secondary battery having a high energy density that can be used as a practical battery.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of spinel type lithium manganese composite oxides obtained in Examples of the present invention and Comparative Examples.

FIG. 2 is an initial discharge curve of a spinal type lithium manganese composite oxide obtained in Examples and Comparative Examples of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Endo             5-9-6 Tokodai, Tsukuba-shi, Ibaraki             Inside the Tsukuba Research Laboratory, Honju Chemical Industry Co., Ltd. (72) Inventor Hiroki Hashiba             1-1-1 Yoshihisa, Takaoka City, Toyama Prefecture             Takaoka Industrial Co., Ltd. (72) Inventor Takehiro Noguchi             5-7 Shiba 5-1, Minato-ku, Tokyo NEC Corporation             Inside the company (72) Inventor Tatsuharu Numata             5-7 Shiba 5-1, Minato-ku, Tokyo NEC Corporation             Inside the company (72) Inventor Masato Shirokata             5-7 Shiba 5-1, Minato-ku, Tokyo NEC Corporation             Inside the company F-term (reference) 4G048 AA04 AB02 AB05 AC06 AD06                       AE05                 5H029 AJ03 AK03 AL06 AM03 AM05                       AM07 CJ02 CJ08 DJ17 HJ02                       HJ13 HJ18 HJ19                 5H050 AA08 BA17 CA09 CB07 FA19                       GA02 GA10 HA02 HA13 HA18                       HA19

Claims (6)

[Claims] 1. The general formula is Li _x M _y Mn _2-y O _{4 + δ} (M is Ni, C
o, Cr, Fe, and any one or more transition metals selected from Cu, 0.9 ≦ x ≦ 1.2, 0.2 ≦ y ≦ 1.0, 0 <
Lithium-manganese composite oxide for secondary batteries characterized by δ ≦ 0.5) and a low crystalline spinel type single phase having a (111) plane half width of 0.8 ° or more in X-ray diffraction. . 2. The general formula is Li _x M _y Mn _2-y O _{4 + δ} (M is Ni, C
o, Cr, Fe, and any one or more transition metals selected from Cu, 0.9 ≦ x ≦ 1.2, 0.2 ≦ y ≦ 1.0, 0 <
A lithium manganese composite oxide for a secondary battery, which is represented by δ ≦ 0.5) and has a discharge capacity of 200 mAh / g or more in a potential range of 2.5 to 5.0 V. 3. The general formula is Li _x M _y Mn _2-y O _{4 + δ} (M is Ni, C
o, Cr, Fe, and any one or more transition metals selected from Cu, 0.9 ≦ x ≦ 1.2, 0.2 ≦ y ≦ 1.0, 0 <
δ ≦ 0.5), a low crystalline spinel type single phase with a (111) plane half-value width of 0.8 ° or more in X-ray diffraction, and 200 mAh / g or more in the potential range of 2.5 to 5.0 V. A lithium-manganese composite oxide for a secondary battery, which has a discharge capacity of 4. In producing the lithium-manganese composite oxide according to claim 1, Li nitrate and Mn nitrate, and M metal (Ni, Co, Cr, Fe, and Cu A nonionic water-soluble polymer as a cation carrier is added to a mixed aqueous solution of one or more transition metal) nitrates selected from among them, and then these mixed aqueous solutions are heated at 80 to 300 ° C. Then, a method for producing a lithium-manganese composite oxide is characterized in that it is synthesized by causing a self-reaction. 5. In producing the lithium manganese composite oxide according to claim 1, Li nitrate and Mn nitrate, and M metal (Ni, Co, Cr, Fe, and Cu One or two or more transition metals selected from among them) In a mixed aqueous solution with a nitrate, a nonionic water-soluble polymer is added as a cation carrier, and then the resulting mixed aqueous solution is heated at 80 to 300 ° C. A method for producing a lithium-manganese composite oxide, characterized in that the lithium-manganese composite oxide is synthesized by heating at 200 ° C. to cause a self-reaction and then firing at 200 to 500 ° C. 6. A secondary battery, a positive electrode using the lithium manganese composite oxide according to any one of claims 1 to 3 as an active material, and a negative electrode using a carbonaceous office or a lithium storage material as an active material. And a non-aqueous electrolyte solution.