WO2001077023A1

WO2001077023A1 - Lithium/manganese complex oxide and method for producing the same, and lithium cell using the same

Info

Publication number: WO2001077023A1
Application number: PCT/JP2001/002952
Authority: WO
Inventors: Tokuo Suita; Hiromitu Miyazaki; Kenji Kataoka
Original assignee: Ishihara Sangyo Kaisha, Ltd.
Priority date: 2000-04-07
Filing date: 2001-04-05
Publication date: 2001-10-18
Also published as: TW528733B; AU4684001A

Abstract

A lithium/manganese complex oxide having a coating layer on the surface thereof, characterized in that the coating layer comprises Mn and at least one metal element selected from the group consisting of Co, Fe and Ni, and has a crystal structure of the same crystal form as that of the crystal contained in the lithium/manganese complex oxide.

Description

Description Lithium-manganese composite oxide, method for producing the same, and lithium battery using the same

The present invention relates to a lithium-manganese composite oxide, which is a compound useful as a positive electrode material of a lithium battery, a method for producing the same, and a lithium battery using the same.

Background art

Lithium secondary batteries have been rapidly spreading in recent years because of their high voltage, excellent charge / discharge cycle characteristics, light weight, and small size. In particular, batteries with a high electromotive force of 4 V class are required. As such a lithium secondary battery, one using a composite oxide of cobalt or nickel ^ / and lithium as a positive electrode active material is known. However, cobalt and nickel are expensive, and future resources Is a problem.

Useful as a positive electrode active material of a 4 V-class lithium secondary batteries; a composite oxide formula L i M n ₂ 0 ₄ lithium manganate having a spinel type crystal structure which you express the like of manganese to lithium In addition, since manganese as a raw material is inexpensive and abundant in resources, it is a promising alternative to lithium cobaltate and lithium nickelate.

The lithium manganate represented by the above chemical formula has a stoichiometric composition, and a 4 V class lithium battery using this as a positive electrode active material has a theoretical capacity of 148 mAhZg. However, lithium secondary batteries using such lithium manganate do not have sufficient cycle characteristics and storage characteristics especially at high temperatures. For example, at 50 ° C or higher, the battery capacity increases when charging and discharging are repeated. Therefore, lithium manganate having excellent characteristics at high temperatures has been demanded.

Conventionally, there has been known a method of improving the cycle characteristics and the storage characteristics by applying a different kind of metal compound to the surface of lithium manganate particles, which is disclosed in Japanese Patent Application Laid-Open No. H10-116166. Adjusts the pH to 9 to reduce the transition metal compound in aqueous solution. A method is disclosed in which a precipitate is deposited on a titanium manganese oxide, dried at 150 ° C. or lower in a vacuum, and dehydrated. However, in this method, the adhesion of the transition metal compound to the surface of the lithium manganese oxide was poor, and the effect of improving the high-temperature characteristics was insufficient. Japanese Patent Application Laid-Open No. 2000-169,152 discloses that lithium and manganese composite oxide particles and a cobalt compound are oxidized in an alkaline aqueous solution at 20 to 100 ° C. A cobalt-adhered lithium-manganese composite oxide in which a cobalt oxide is epitaxially grown on a cobalt-manganese composite oxide is disclosed, but there is a problem that the charge / discharge capacity is reduced.

Disclosure of the invention

The present invention overcomes the above-described problems of the prior art, and provides a deposited lithium-manganese composite oxide having excellent high-temperature characteristics and high charge / discharge capacity suitable for a lithium battery, and an industrial and economical method for producing the same. It is intended to provide a method for producing in an advantageous manner. As a result of intensive studies, the present inventors have applied a crystalline coating layer having the same crystal structure to the surface of the lithium-manganese composite oxide, and this coating layer has at least a specific element. It has been found that if manganese is contained, not only at room temperature but also at high temperature, the properties are excellent in storage properties and storage stability, and the charge / discharge capacity does not decrease. That is, the present invention relates to a lithium-manganese composite oxide having a coating layer on the surface, wherein the coating layer comprises at least one metal element selected from the group consisting of Co, Fe and Ni and Mn. Lithium-manganese composite oxide characterized by having the same crystal structure as the crystal contained in the lithium-manganese composite acid, a method for producing the same, and a lithium-manganese composite using the same The present invention relates to a lithium battery using an oxide.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an X-ray chart of Sample B and Sample H.

BEST MODE FOR CARRYING OUT THE INVENTION

The lithium-manganese composite oxide of the present invention has a surface on which a coating layer containing at least one metal element selected from the group consisting of Co, Fe and Ni and at least Mn is adhered. This coating layer is crystalline and has the same crystal form as the lithium-manganese composite acid. It not only has excellent high temperature properties, but also has Has almost no decrease and has good battery characteristics inherent to lithium-manganese composite oxide. The reason for this is not always clear, but generally the cycle and storage characteristics are degraded because manganese ions elute from the contact interface between the lithium-manganese composite oxide and the electrolyte. It is said that this phenomenon becomes significant especially at high temperatures. In the present invention, there is almost no difference in the lattice constant between the coating layer and the lithium-manganese composite oxide, and since these are crystals having a continuous structure, the adhesion is excellent, and the surface of the lithium-manganese composite oxide is excellent. It is considered well protected. On the other hand, even if the surface is covered by the coating layer, the inclusion and desorption of lithium ions is hardly inhibited by the inclusion of the metal element and Mn in the coating layer, and the charge / discharge capacity is not reduced. It is guessed.

In the present invention, the composition of the coating layer does not need to be uniform. For example, Mn in the coating layer may have a concentration gradient or Mn may exist randomly. The metal element may be contained in the coating layer as a compound such as an oxide, and Mn may be contained as a single compound such as an oxide or a compound compound such as a composite oxide with the metal element. Is good and there is no particular limitation. The crystal form of the coating layer is not particularly limited as long as it is the same form as the lithium-manganese composite oxide, but as described later, the lithium-manganese composite oxide is preferably a spinel type, and thus has the same spinel type. Is preferred. In addition, as long as the object of the present invention is not impaired, a portion having a different amorphous or crystalline form may be contained as a production impurity in a small amount, preferably 5% or less. The Chakuryou metal element contained in the coating layer is a 0.05 to 20 atomic ^_0/0 relative to the total amount of the M n of the lithium-manganese composite oxide及Pi coating layer, the deposition amount of 0.05 atoms ⁰ / lower the desired effect can not be obtained from _0, more preferably in the range of 0.1 to 10 atomic% Deari, more preferably from 1 to 5 atomic% 0.1. Further, the amount of Mn contained in the coating layer is a C o, F e, 0. 1~50 atomic with respect to the total amount of the N i ^_0/0. As described above, at least one of Co, Fe, and Ni may be used, and two or three of them may be used in combination. Among them, Co is particularly effective. Elements other than Co, Fe, Ni, and Mn can be appropriately included in the coating layer for various purposes. Examples of such elements include Mg, Ca, V, Cu, Zn, and Li.The amount of these elements contained in the coating layer is, for example, based on the total amount of Co, Fe, and Ni. 0. 0 to 50 atoms ⁰ / o.

Such a coating layer may be applied to the lithium-manganese composite oxide by reacting the compound containing the metal element and the compound containing Mn with a basic compound. However, in the production method of the present invention, the coating layer is applied under a strong alkaline condition in which free monohydric ion is 0.001 mol Z liter or more. Further, in the production method of the present invention, the compound containing at least one metal element selected from the group consisting of Co, Fe and Ni in the slurry containing the lithium-manganese composite oxide, and a basic compound Is added so that the concentration of free monohydric acid becomes 0.001 mol Z liter or more, and contains at least one kind of the metal element, and preferably contains at least one kind of the metal element. A coating layer containing Mn is applied. In any method, first, the lithium-manganese composite oxide is uniformly dispersed in a medium such as an organic solvent, preferably in water, to prepare a slurry containing the same. Depending on the degree of sintering or agglomeration of the lithium-manganese composite particles, wet pulverization or sizing may be appropriately performed by a known method using a disperser such as a line mill, a sand mill, or a pole mill.

Next, a solution of a compound containing one kind of metal element selected from the group consisting of Co, Fe and Ni and a basic compound are added to the slurry to form a mixture of free hydroxide in the slurry. When added and reacted so that the concentration becomes 0.0001 mol Z liter or more, the above-mentioned coating layer is adhered to the surface. Examples of the metal element compound to be added include salts such as chlorides, sulfates, nitrates, acetates, and carbonates, and hydroxides, oxyhydroxides, and oxides. Oxides and carbonates can be used. As a method of adding these compounds, a method of adding a basic compound first and then simultaneously adding a solution of a metal compound is preferable because both are uniformly coated.

The salt of Co, Fe, and Ni reacts with the basic compound to precipitate as a hydroxide, an oxyhydroxide or an oxide, and has a free hydroxyl ion concentration of 0.000. When it exceeds 0 mol / liter, complexation of these compounds proceeds. Alternatively, when a hydroxide, an oxyhydroxide, or an oxide of the metal element is added to the slurry, a complex is formed in the presence of 0.0001 mol / liter or more of free hydroxyl ions. . From the above, this method (1) forming a crystalline coating layer on the surface while the complex reacts with a part of manganese in the lithium-manganese composite oxide; (2) After the complex forms a crystalline coating layer, part of the manganese in the lithium-manganese composite oxide diffuses into the coating layer. (3) Part of manganese from the lithium-manganese composite oxide under strong alkalinity Is eluted, and manganese and the complex react to form a further complex to form a crystalline coating layer. Therefore, a complexing agent such as ammonia or EDTA may be added during the deposition process. The deposition treatment can be usually performed at a temperature of 25 to 200 ° C. for 0.5 to 20 hours, and can be appropriately set depending on reaction conditions such as a free hydroxyl ion concentration. The atmosphere for the deposition treatment is not particularly limited. However, when the deposition is performed in a non-oxidizing atmosphere by blowing an inert gas such as nitrogen into the slurry, the compound of the added metal element reacts. This is preferable because the reaction is not easily performed before the reaction and the reaction easily proceeds.

In addition, the free hydroxyl ion referred to in the present invention refers to a hydroxyl ion present in a slurry after a predetermined amount of a metal compound and a basic compound have been added. If the free hydroxyl ion concentration is lower than 0.001 mol Z liter, the formation of a coating layer of a metal compound is not sufficient, and good high-temperature characteristics cannot be obtained. When the concentration of free hydroxyl ions is increased, the coating layer aimed at by the present invention can be formed in a short time, but the effect is saturated when the concentration is 5 mol Z liter or more, which is not industrially advantageous. The range of the free hydroxyl ion concentration is 0.001 to 5 mol / L, preferably 0.001 to 3 mol / L, and more preferably 0.01 to 2 mol / L. When the deposition treatment is performed by this method, the lithium manganese composite acid may be partially reduced, which is not preferable in terms of battery characteristics. Therefore, after the deposition, the deposition is performed in a slurry or in the air. It is preferable to oxidize. Thereafter, filtration and washing are appropriately performed, and drying is performed at 50 to 200 ° C, preferably 90 to 150 ° C. Drying may be performed in an oxidizing atmosphere such as the air or a non-oxidizing atmosphere such as nitrogen. If the temperature is lower than 50 ° C., the drying rate is low, which is not industrially advantageous. If the temperature is higher than 200 ° C., the structure of the coating layer changes, and the coating layer of the present invention cannot be obtained. The dried lithium manganese composite oxide that has been subjected to the deposition treatment after drying may be subjected to a powder frame depending on its aggregation state.

Lithium 'manganese Sani匕物used in the present invention has the general formula L i _x M n _y 0 ₄ or Chopsticks _{_{_{i 1 + x M y Mn 2}}} -x-y0 4 was (M is F e, C r, Co, Ni, A 1, Mg, Ca, B, Zn, V, Nb, Mo, T i, Z r, at least one metal element selected from the group consisting of Ga and In) wherein X and Y in the formula are (1 + X) / (2-XY) Expressed in the range of 0.3 to 1.5 is a preferred composition. In particular or general formula L iMn ₂ 0 _4, preferably has a _{_{L i 4/3 Mn 5/3 0}} 4 spinel crystal structure which is Ru represented by like, a single phase of the lithium-manganese composite oxide Alternatively, a mixture of a lithium * manganese composite oxide and a manganese oxide may be used.

There is no particular limitation on the method for producing such a lithium-manganese composite oxide, and even if manganese oxide and a lithium compound are mixed and then heated and baked, the manganese oxide reacted with a manganese oxide or acid can be used. One of arsenic or manganic acid and a lithium compound may be reacted in a medium such as water, and the resulting precursor of the lithium-manganese composite oxide may be heated and fired. However, the latter method is preferable because a lithium-manganese composite oxide having excellent crystallinity can be obtained.Manganese oxide or manganic acid which has been previously reacted with an acid has good reactivity with a lithium compound. It is more preferable to use this. In addition, if a large particle diameter having an average particle diameter of 0.1 to 50 / xm is used, the finally obtained lithium-manganese composite oxide that has been subjected to the deposition treatment has excellent filling properties as a positive electrode active material. Is preferred. In the case of such a large particle diameter, for example, lithium-manganese composite acid may be sintered to grow the particles, but manganese oxide is used as a seed (a nucleus or a seed crystal is hereinafter referred to as a seed). It is preferred that the particles be grown in a medium and then reacted with a lithium compound, since a crystal having good crystallinity and a uniform particle size / size distribution can be obtained.

Next, the present invention is a lithium battery using the above-described lithium-manganese composite oxide as a positive electrode active material. A lithium battery as referred to in the present invention is a primary battery using lithium metal for the negative electrode, a rechargeable battery using lithium metal for the negative electrode, a charging using a carbon material, a tin compound, lithium titanate, or the like for the negative electrode. A possible lithium ion secondary battery. Since the lithium-manganese composite oxide of the present invention has a specific coating layer adhered to the surface, if it is used as a positive electrode active material of a lithium secondary battery, it can be used at high temperatures such as 50 ° C. Release of manganese ions during charging and discharging Not only is it hard to scrape, it has excellent cycle characteristics and storage characteristics, but also has a large charge / discharge capacity.

When the positive electrode for a lithium battery is to be used for a coin-type battery, the lithium-manganese composite acid powder of the present invention may be added to a carbon-based conductive agent such as acetylene black, carbon, or graphite powder, or a polycondensate. It can be obtained by adding, kneading, and molding a binder such as tetrafluoroethylene resin or polyvinylidene fluoride resin. Further, when the battery is used for a cylindrical or prismatic battery, an organic solvent such as N-methylpyrrolidone is added to the lithium and manganese composite oxide powder of the present invention in addition to these additives, and the mixture is kneaded. Into a paste, applied to a metal current collector such as an aluminum foil, and dried.

Lithium ion is dissolved in the electrolyte of a lithium battery in a polar organic solvent that is electrochemically stable, that is, is not oxidized or reduced in a wider range than the potential range that operates as a lithium ion battery. Things can be used. As the polar organic solvent, propylene carbonate, ethylene carbonate, getylcaponate, dimethoxetane, tetrahydrofuran, γ-butyltyl lactone, or a mixture thereof can be used. As a solute serving as a lithium ion source, lithium perchlorate / lithium hexafluorophosphate, lithium tetrafluoroborate, or the like can be used. In addition, a porous polypropylene film / polyethylene film is disposed as a separator between the electrodes.

Battery types include a separator between the positive and negative electrodes in the form of pellets, pressure bonding to a sealed can with a polypropylene gasket, injection of electrolyte, and a sealed coin-type battery. The negative electrode material is coated on a metal current collector, the separator is sandwiched and wound, inserted into a battery can with a gasket, injected with an electrolyte, and sealed. There are also three-electrode batteries specifically for measuring electrochemical properties. This battery evaluates the electrochemical characteristics of each electrode by arranging a reference electrode in addition to the positive electrode and the negative electrode, and controlling the potential of other electrodes with respect to the reference electrode.

Regarding the performance of the lithium-manganese composite oxide as a positive electrode material, a secondary battery is constructed using metal lithium or the like as the negative electrode, and charged and discharged at an appropriate voltage range with constant current. Thus, the capacity can be measured. Further, by repeating charge and discharge, it is possible to judge the quality of the cycle characteristics from the change in the capacity.

Example

Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1

1. Synthesis of manganese hydroxide

8. A 0.63 liter solution of 37 mol / liter sodium hydroxide and 0.419 liters of water were charged into a stainless steel reaction vessel. While blowing therein a nitrogen gas 2. 5 l Z min, rapidly stirring a solution of (88.06% content as Mn S_〇 ₄₎ 0. 937 kg manganese sulphate in water 3. 75 kg And neutralized at 70 ° C. Thereafter, the mixture was aged at 70 ° C. for 3 hours to obtain a manganese hydroxide.

2. Synthesis of manganese oxide seed

While stirring the obtained solution containing the manganese hydroxide, air was blown in at a rate of 2.5 l / min, and the mixture was oxidized at a temperature of 70 ° C .; when the pH reached 6.4, The oxidation was terminated, and a manganese oxide seed was obtained.

3. Manganese oxide seed growth

The solution was maintained at 7 0 ° C containing manganese oxide seed described above, was added an aqueous solution prepared by dissolve the 88.06% containing) 5. 618 kg as manganese sulfate 30 ₄ in water 21. 28 kg, stirring 8.37 monoles / liter sodium hydroxide 4.567 liters were added over 64 hours while blowing a mixed gas of air Z nitrogen = 1/1 at 2.5 liters / minute, neutralizing and oxidizing. After growing the manganese oxide seed by filtration, filtration and washing were performed to obtain a manganese oxide.

4. Reaction between manganese oxide and acid

A slurry in which manganese oxide (1200 g in terms of Mn) was dispersed in water was charged into a stainless steel reaction vessel, and the temperature was raised to 60 ° C. To this slurry was added 3.55 liters of 1 mol of sulfuric acid over 1 hour while stirring, and after reacting for 2 hours, washed with filtered water to obtain a manganese oxide reacted with an acid. 5. Synthesis of precursor for lithium'manganese complex

5.234 mol of hydrium lithium monohydrate was added to a slurry prepared by dispersing a manganese oxidant (500 g in terms of Mn) reacted with an acid and dissolved in water. The mixture was made into 1 1 liter and charged in a glass reaction vessel. Air was blown into the slurry at 1.5 liters, the temperature was raised to 90 ° C with stirring, and the reaction was allowed to proceed for 14 hours.The temperature was cooled to 60 ° C, filtered, and then 0.05 mole Z liter. The solution was washed with an aqueous solution of lithium hydroxide and a precursor of a lithium-manganese composite oxide was obtained.

6. Sintering of precursor of lithium'manganese complex

The precursor of the lithium-manganese composite oxide was dried at 110 ° C for 12 hours, and then calcined in air at 750 for 3 hours to obtain a lithium-manganese composite oxide. The specific surface area of the lithium-manganese composite acid was 0.94 m 2 / g.

7. Coating of Co, Mn containing coating layer

Lithium-manganese composite acid (200 g in terms of Mn) was dispersed in water with a mixer to form a slurry, and then charged into a reaction vessel. Next, 95.2 milliliters of a 4.5 molar Z liter aqueous lithium hydroxide solution was added to adjust the liquid volume to 1.00 liter. After nitrogen gas was blown into the slurry and the temperature was raised to 60 ° C., 128.5 milliliters of a 50 g / litre aqueous solution of sodium salt as a copart was added over 1 hour, reacted for 5 hours, and cooled. The amount of lithium hydroxide added was set such that the free hydroxyl ion concentration after the reaction with cobalt chloride was 0.20 mol Z liter. After cooling, the mixture was filtered and washed, and dried at 110 ° C. for 12 hours to obtain a lithium-manganese composite oxide coated with the coating layer of the present invention containing Co and Mn. (Sample A)

Example 2

1. Synthesis of precursor of lithium'manganese composite oxide

Using the manganese acid product reacted with the acid obtained in the fourth step of Example 1, except that the addition amount of lithium hydroxide monohydrate was 5.190 mol and the reaction time was 16 hours In the same manner as in the fifth step of Example 1, a precursor of a lithium-manganese composite oxide was obtained.

2. Sintering of precursor of lithium-manganese composite oxide The lithium-manganese composite oxide precursor was heated and calcined in the same manner as in the sixth step of Example 1 to obtain a lithium-manganese composite oxide. The specific surface area of this lithium-manganese composite oxide was 1.01 m ² Zg.

3. Deposition of coating layer containing Co and Mn

Lithium coated with a coating layer compound containing Co and Mn in the same manner as in the seventh step of Example 1, except that the reaction time between the salt and the lithium hydroxide was 12 hours. A manganese composite oxide was obtained. (Sample B)

Example 3

1. Deposition of coating layer containing Fe and Mn

Lithium manganese composite oxide obtained in the second step of Example 2 (converted to Mn)

200 g) was dispersed in water with a mixer to form a slurry, and then charged into a reaction vessel. Then, 94.8 ml of a 4.5 mol aqueous solution of lithium hydroxide was added to adjust the liquid volume to 1.00 liter. Nitrogen gas was blown into this slurry, and the temperature was raised to 60 ° C. Then, 50 g / liter of ferrous sulfate aqueous solution of 122.0 milliliters was added as iron over 1 hour, reacted for 12 hours, and then cooled. Was. The amount of lithium hydroxide added was set so that the free hydroxyl ion concentration after the reaction with ferrous sulfate was 0.20 mol mol. After cooling, the mixture was filtered and washed, and dried in air at 110 ° C. for 12 hours to obtain a lithium-manganese composite oxide coated with a coating layer compound containing Fe and Mn. (Sample C)

Example 4

1. Deposition of coating layer containing Co and Mn

Co and Co were prepared in the same manner as in the third step of Example 2 except that the lithium manganese composite oxide obtained in the second step of Example 2 was used, and the addition amount of the lithium hydroxide aqueous solution was 233.8 milliliters. A lithium manganese composite oxide treated with a coating layer compound containing Mn was obtained. (Trial D) The addition amount of lithium hydroxide was set so that the concentration of free monohydric ion after reaction with cobalt salt was 0.80 mol.

Example 5

1. Coating of Co and Mn Third step of Example 2 except that the reaction temperature of cobalt chloride and lithium hydroxide was 90 ° C using the lithium-manganese composite oxide obtained in the second step of Example 2 In the same manner as in the above, a lithium-manganese composite oxide treated with a coating layer compound containing Co and Mn was obtained. (Sample E)

Example 6

1. Coating of Co and Mn

Using the lithium 'manganese composite oxide obtained in the second step of Example 2, after reacting salt sodium hydroxide and lithium hydroxide, air was passed through the slurry at 1 liter / min for 3 hours. A lithium-manganese composite oxide treated with a coating layer compound containing Co and Mn was obtained in the same manner as in the third step of Example 2 except that the oxidation was performed.

(Sample F)

Comparative Example 1

A lithium / manganese composite acid product was obtained in the same manner as in Example 1 except that the coating treatment of the coating layer containing Co and Mn in the seventh step was not performed. (Sample G) Comparative Example 2

A lithium-manganese composite oxide was obtained in the same manner as in Example 2, except that the coating treatment including the Co and Mn in the third step was not performed. (Sample H) Comparative Example 3

1. Co deposition process

The lithium-manganese composite oxide (200 g in terms of Mn) obtained in the second step of Example 2 was dispersed in water with a mixer to form a slurry, and then charged into a reaction vessel. Next, 4.51 milliliters of an aqueous lithium hydroxide solution (26.1 milliliters) was added to adjust the liquid volume to 1.0 liters. While blowing nitrogen gas into this slurry, 50 g Z liters of a salt solution of 93.3 milliliters of an aqueous solution of cobalt were added as a co-part, and then 90. The temperature was raised to C, and the nitrogen gas was stopped after the temperature was raised. Subsequently, air was circulated for 3 hours at a volume of 3 liters Z to oxidize. After cooling, filtration,? Pre-cleaning was performed and dried in air at 110 ° C. for 12 hours to obtain a lithium-manganese composite oxidized product to which a C 0 compound was applied. (Sample I)

Rating 1 Sample B obtained in Example 2, the sample H obtained in及Pi Comparative Example 2, Ite use high deca 0 11 1 ^ _(¾ line of tube voltage 5 0 KV, tube current 2 0 0 111 Powder diffraction was measured.

Figure 1 shows the powder X-ray diffraction patterns of Samples B and H, and Table 1 shows the results. None of the samples showed a diffraction peak of spinel alone and no power was recognized. By applying the coating layer of the present invention to the surface, the diffraction angle shifts to the lower angle side, and the half width tends to increase. Regarding the peak area, some peaks, such as the main peak, show a decreasing trend, while others show an increasing trend. In particular, the diffraction peak of the plane index (220) showed the largest increasing tendency. From these results, it was found that a surface coating layer composed of a substance having a (220) diffraction intensity was formed, which had the same crystal form as that of the lithium-manganese composite oxide, had a rather large lattice constant, and had a high diffraction intensity of (220). it is conceivable that. As a such compounds are considered if M n C o ₂ 0 ₄ samples B, C o ₃ 0 ₄ of such small cobalt alone spinels lattice constants such considered les. However, the actual composition of the coating layer is not always a stoichiometric composition as in the above formula, and a spinelidized product having a wider composition containing manganese and cobalt / reto, and in some cases containing lithium may be formed. It is thought that it is. In addition, EDX analysis was performed on Sample B inside a few nm from the outermost surface of the particles, that is, a portion corresponding to the coating layer. Table 2 shows the results. EDX analysis also shows that Co and Mn exist in the coating layer.

table 1

Sample B Sample H

Plane index Diffraction angle Peak area FWHM Diffraction angle Peak area FWHM

(Degree) (arb. Unit) (degree) (degree) (arb. Unit) (degree)

(111) 18.584 74634 0.149 18.587 82400 0.143

(220) 30.638 712 0.177 30.658 588 0.133

(311) 36.079 37228 0.144 36.090.37811 0.151

(222) 37.753 7088 0.129 37.766 7319 0.134

(400) 43.881 38534 0.170 43.892 44176 0.148

(331) 48.069 7299 0.151 48.078 7432 0.140

(511) 58.107 15267 0.185 58.115 147860.149

(440) 63.835 23696 0.159 63.851 23667 0.151 Table 2

Rating 2

Charge and discharge characteristics and cycle characteristics of lithium secondary batteries using lithium manganese composite oxides (Samples A to I) obtained in Examples 1 to 6 and Comparative Examples 1 to 3 as positive electrode active materials. Was evaluated. The form of the battery and the measurement conditions will be described.

Each of the above samples, graphite powder as a conductive agent, and polytetrafluoroethylene resin as a binder were mixed at a weight ratio of 70: 24: 6, kneaded in a mortar, and molded into a circular shape with a diameter of 1 Omm. To make a pellet. The pellet weighed 4 Omg. A metal titanium mesh cut into a circle having a diameter of 1 Omm was superimposed on the pellet, and pressed at 14.7 MPa to obtain a positive electrode.

The positive electrode was vacuum-dried at 120 ° C for 4 hours, and then incorporated into a sealable coin-type evaluation cell in a glove box with a dew point of 70 ° C or less. The evaluation cell used was made of stainless steel (SUS 316) and had an outer diameter of 20 mm and a height of 1.6 mm. The negative electrode used was 0.5 mm thick metallic lithium molded into a 14 mm diameter circle. As a non-aqueous electrolyte, at a concentration of 1 mol Z liter

(Volume ratio 1: 2 mixed) L i PF ₆ dissolved ethylene carbonate and a mixed solution of dimethyl carbonate was used.

The positive electrode was placed in the lower can of the evaluation cell, a porous propylene film was placed thereon as a separator, and seven drops of a non-aqueous electrolyte were dropped from above with a dropper. The negative electrode was placed on top of it, and an upper can with a gasket made of polypropylene was covered, and the outer peripheral edge was crimped and sealed. In order to adjust the thickness, a hydrophilic non-woven polypropylene nonwoven fabric was placed above and below the separator as necessary.

The coin-type evaluation cell thus fabricated was set in a special battery holder, and the battery characteristics were measured with a load of 5 kg applied. The charge / discharge capacity was measured at a constant current with the voltage range set from 4.3 V to 3.5 V and the charge / discharge current set at 0.84 mA (about 3 cycles / day). The values measured in the second cycle at 25 ° C are used as initial charge / discharge characteristics. did. The cycle characteristics were measured at 25 ° C. and 50 ° C., and represented by the respective capacity retention rates% {(30th discharge capacity Z 5th discharge capacity) × 100}.

Rating 3

3 g of each of Samples A to I was weighed and placed in a heat-resistant Teflon container with a lid having a capacity of 50 milliliters. These were transferred to a vacuum sample dryer installed in a glove box whose inside was replaced with argon and the dew point was kept below 170 ° C, and dried by heating at 120 ° C for 4 hours.

After vacuum drying at normal pressure was naturally cooled to room temperature and returned to, then 1 mole Z liters and a mixture of Na Ru concentration E Ji Ren carbonate and dimethyl carbonate was dissolved L i PF ₆ (volume ratio 1: 1 15 milliliters were added to each container. Close the lid of each container, hold in a vacuum sample dryer at normal pressure at 60 ° C for 168 hours, cool, open the lid, add 7.5 ml of dimethyl carbonate, take out the solution and remove the PTFE Natural filtration was performed using a filter (pore size 0.2 ^ 111). The filtrate was taken out of the glove box, and the concentration of manganese ions in the filtrate was measured by ICP analysis.

Table 3 shows the initial charge / discharge characteristics, cycle characteristics, and manganese elution amount of Samples A to I. The lithium-manganese composite oxide having a coating layer containing Co or Fe and Mn obtained on the surface thereof obtained by the present invention is subjected to a deposition treatment especially at a high temperature cycle 4. It is superior to non-lithium-manganese composite oxide and has the same initial charge / discharge characteristics. In addition, both the cycle characteristics and the initial charge / discharge characteristics are better than those with the conventional Co coating applied to the surface. Furthermore, from any of the comparative examples

It can be seen that the elution amount is small. Table 3

Industrial applications

The present invention relates to a lithium-manganese composite oxide having a coating layer on its surface,

5 The coating layer contains at least one metal element selected from the group consisting of Co, Fe, and Ni and Mn, and has a crystal structure identical to the crystal contained in the lithium-manganese composite oxide. Is a lithium-manganese composite oxide. The lithium-manganese composite oxidized product of the present invention has high adhesion of the treated coating layer, excellent protection of the particle surface, and is difficult to dissolve manganese ions even when contacted with an electrolytic solution. . As a result, the deterioration of the lithium 10 manganese manganese compound becomes difficult to progress, and the lithium battery using this as a positive electrode active material has a cycle characteristic and a storage characteristic, especially at 50 ° C. Good at high temperatures. In addition, since this coating layer does not easily inhibit the introduction and desorption of lithium ions contained in the lithium-manganese composite oxide, the charge / discharge capacity does not decrease.

Claims

The scope of the claims

1. A lithium-manganese composite oxide having a coating layer on the surface, wherein the coating layer contains at least one metal element selected from the group consisting of Co, Fe and Ni, and Mn, A lithium-manganese composite oxide having the same crystal structure as the crystal contained in the lithium-manganese composite oxide.

2. The lithium / manganese composite oxide according to claim 1, wherein the crystal is of a spinel type.

3. The lithium-manganese composite oxide according to claim 1, wherein the coating layer contains at least Co and Mn.

4. At least one metal element selected from the group consisting of Co, Fe and Ni ίΚ Lithium マンガン 0.05 to 20 atomic% with respect to the total amount of Mn in the manganese composite oxide and the deposited layer. The lithium-manganese composite oxide according to claim 1, which is applied.

The production of the lithium manganese composite oxide according to claim 1, wherein the coating layer is applied in the presence of 5.00.01 mol / liter or more of free monohydric ion. Method.

6. In a slurry containing lithium-manganese composite oxide, a compound containing at least one metal element selected from the group consisting of Co, Fe, and Ni and a basic compound are mixed with a free monohydric ion. A method for producing a lithium-manganese composite oxide having a coating layer containing at least the metal element on the surface, comprising a step of adding and reacting so that the concentration becomes 0.0001 mol Z liter or more.

7. The method for producing a lithium-manganese composite oxide according to claim 5, wherein the amount of free hydroxyl ions is 5 mol liter or less.

8. The method for producing a lithium-manganese composite oxide according to claim 5, wherein the deposition is performed in a non-oxidizing atmosphere.

9. The method for producing a lithium-manganese composite oxide according to claim 5, wherein the oxidizing is performed after the application.

10. Use of the lithium-manganese composite oxide according to claim 1 as a positive electrode active material A lithium battery.