JP6872816B2 - Nickel-manganese-based composite oxide and its manufacturing method - Google Patents

Description

The present invention relates to a nickel-containing lithium manganese composite oxide and a method for producing the same.

Lithium-ion secondary batteries, which are used as power sources for notebook computers, mobile phones, smartphones, etc. (for small consumers) in Japan, are widely used as batteries with extremely high battery size and electrical energy per weight (energy density). It is being utilized. More recently, it is a promising battery system that has begun to be used in large systems such as electric vehicles, plug-in hybrid vehicles, houses and power plants.

In a lithium ion secondary battery, the material used for the positive electrode determines the battery capacity and voltage. Most of these are lithium-containing transition metal oxides, and lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc. have been put into practical use. Price instability due to resource scarcity, low chemical stability during charging, low charge / discharge capacity, etc. have been pointed out, and there is an urgent need to secure further material candidates.

_{Lithium nickel manganate (LiNi 1/2} Mn _1/2 O ₂ ) has been proposed by Non-Patent Document 1 as such a material candidate, and has been studied as a promising material for a positive electrode. However, lithium nickel manganate has a problem that it is not easy to synthesize. For example, it has been found that lithium nickel manganate can be obtained by the coprecipitation-hydrothermal-calcination method (Patent Document 1), but there is a problem that the synthesis method is complicated and cannot be directly applied to the practical manufacturing process. .. Therefore, recently, it has been changed to _{lithium nickel-cobalt manganate (LiNi 1/3} Co _1/3 Mn _1/3 O ₂ ), which is called a ternary system that is easier to synthesize.

However, since a battery using lithium nickel cobalt manganate has cobalt, there is a problem in low chemical stability during charging, and such low chemical stability is due to the safety of the battery and the setting of a high upper limit potential. It may cause problems with the cycle characteristics (for example, 4.5V or higher). Therefore, it can be said that it is still meaningful to develop an easy method for synthesizing a battery using lithium nickel manganate, which is excellent in terms of battery safety and cycle characteristics.

Although the reason why Co substitution has been performed in the first place is to facilitate synthesis and reduce the amount of transition metal ions in the Li layer, the cobalt-containing material has the above-mentioned problems. Therefore, if a material that does not contain cobalt and has a small amount of transition metal ions in the Li layer can be obtained, it is considered to be extremely useful in industry.

Therefore, there has been a demand for a nickel-manganese-based positive electrode material having a small amount of transition metal ions in the Li layer, which has excellent cycle characteristics and can be used in a lithium secondary ion battery.

Electrochem. Solid-State Lett., 4, A191-A194, (2001). Electrochemistry, 84, 789-792, (2016).

Japanese Unexamined Patent Publication No. 2008-127233

In view of the above circumstances, an object of the present invention is a nickel-containing lithium-manganese composite having a small amount of transition metal ions in the Li layer and excellent cycle characteristics, which can be suitably used for a lithium secondary ion battery. To provide oxides.

As a result of diligent research to achieve the above object, the present inventors have obtained a nickel-containing lithium manganese composite oxide having a predetermined chemical formula including a layered rock salt type crystal phase, and further, the nickel-containing lithium manganese composite oxide. It has been found that a lithium ion secondary battery having excellent cycle characteristics can be obtained by using it. The present inventors have further studied based on such findings, and have completed the present invention.

That is, the present invention provides the following nickel-manganese-based composite oxide and a method for producing the same.
Item 1.
General formula (1):
_{Li 1 + x (Ni y Mn} 1-y) 1-x O 2 (1)
[In the formula, x and y indicate 0.0 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by, containing a layered rock salt type crystalline phase,
The lattice constant a is 2.870 Å or less, and the lattice volume is 102.0 Å ³ or less.
Nickel-containing lithium-manganese composite oxide.
Item 2.
Item 2. The nickel-containing lithium-manganese composite oxide according to Item 1, wherein the amount of the transition metal contained in the lithium layer in the layered rock salt type crystal phase is 5% or less.
Item 3.
Item 2. The nickel-containing lithium-manganese composite oxide according to Item 1 or 2, wherein the amount of the transition metal contained in the transition metal layer in the layered rock salt type crystal phase is 88% or less.
Item 4.
Item 2. The nickel-containing lithium-manganese composite oxide according to any one of Items 1 to 3, wherein the average valence of nickel ions is 2.5 or more.
Item 5.
Item 2. The nickel-containing lithium-manganese composite oxide according to any one of Items 1 to 4, wherein the O / (Ni + Mn) atomic ratio is 2.3 or more.
Item 6.
A lithium ion secondary battery containing the nickel-containing lithium manganese composite oxide according to any one of Items 1 to 5 as a cathode active material.
Item 7.
Step 1 of forming a precipitate from a mixed aqueous solution containing a manganese compound and a nickel compound under alkaline conditions of 20 ° C. or lower.
Step 2 of performing a wet oxidation treatment on the precipitate
And has a step 3 of heat treatment in an oxidizing atmosphere in the presence of a lithium salt.
Item 8. The method for producing a nickel-containing lithium-manganese composite oxide according to any one of Items 1 to 5.

The nickel-containing lithium-manganese composite oxide according to the present invention can be suitably used for a lithium ion secondary battery in which the amount of transition metal ions in the Li layer is small and the cycle characteristics are excellent.

It is a figure which shows the X-ray diffraction pattern of the sample of Example 1. FIG. It is a figure which shows the X-ray diffraction pattern of the sample of the comparative example 1. FIG. It is a figure which shows the X-ray absorption spectrum (XANES) near the K end of Mn and Ni of Example 1, Comparative Example 1 and the valence standard data (Li ₂ MnO ₃ , NiO and LiNiO _2). It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of Example 1. FIG. It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of the comparative example 1. FIG. It is a figure which shows the X-ray diffraction pattern of the sample of Example 2. It is a figure which shows the X-ray diffraction pattern of the sample of the comparative example 2. It is a figure which shows the X-ray absorption spectrum (XANES) near the K end of Mn and Ni of Example 2, Comparative Example 2 and the valence standard data (Li ₂ MnO ₃ , NiO and LiNiO _2). It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of Example 2. It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of the comparative example 2. It is a figure which shows the X-ray diffraction pattern of the sample of Example 3. FIG. It is a figure which shows the X-ray diffraction pattern of the sample of the comparative example 3. It is a figure which shows the X-ray absorption spectrum (XANES) near the K end of Mn and Ni of Example 3, Comparative Example 3 and the valence standard data (Li ₂ MnO ₃ , NiO and LiNiO _2). It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of Example 3. FIG. It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of the comparative example 3. FIG. It is a figure which shows the X-ray diffraction pattern of the sample of Example 4. FIG. It is a figure which shows the X-ray absorption spectrum (XANES) near the K end of Mn and Ni of Example 4, Comparative Example 4 and the valence standard data (Li ₂ MnO ₃ , NiO and LiNiO _2). It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of Example 4. It is a figure which shows the X-ray diffraction pattern of the sample of Example 5. It is a figure which shows the charge / discharge characteristic evaluation test result of the lithium ion secondary battery of Example 5.

1. 1. Nickel-containing lithium manganese composite oxide The nickel-containing lithium manganese composite oxide of the present invention has the general formula (1):
_{Li 1 + x (Ni y Mn} 1-y) 1-x O 2 (1)
[In the formula, x and y indicate 0.0 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by, containing a layered rock salt type crystalline phase,
The lattice constant a is 2.870 Å or less, and the lattice volume is 102.0 Å ³ or less.

In the above general formula (1), x is 0.0 ≦ x <1/3, and more preferably 0.05 ≦ x ≦ 0.25. When x is less than 1/3, it is possible to suppress the generation of excess lithium as an impurity, and as a result, excellent cycle characteristics of the battery can be obtained.

In the above general formula (1), the nickel content y is 0.3 ≦ y ≦ 0.6, and more preferably 0.3 ≦ y ≦ 0.5. When y is 0.3 or more, it is possible to suppress the occurrence of a decrease in battery voltage. Further, when y is 0.6 or less, the structural stability of the nickel-containing lithium-manganese composite oxide can be well maintained even during charging.

Further, the nickel-containing lithium-manganese composite oxide of the present invention contains a layered rock salt type crystal phase. The layered rock salt type crystal structure constituting the layered rock salt type crystal phase is _{a crystal that frequently appears in ABO type 2} (A is an alkali metal and B is a transition metal) inorganic compound possessed by lithium cobaltate or lithium nickelate. It is a structure. It has a crystal structure in which transition metal layers and lithium layers are alternately laminated via oxide ions, and it is said that the desorption / insertion reaction of lithium ions is easy with charging and discharging.

Furthermore, the layered rock salt type crystal phase is a space group:

Hexagonal layered rock salt type crystal phase or space group belonging to:

It is preferable to include a crystal phase of a monoclinic layered rock salt type structure attributed to. The nickel-containing lithium-manganese composite oxide of the present invention preferably contains the above-mentioned crystal phase of hexagonal layered rock salt type structure or monoclinic layered rock salt type structure, and crystal phase of other rock salt type structure (for example). , Cubic rock salt type structure, etc.). In the case of a mixed phase, the ratio of the crystal phase of the hexagonal layered rock salt type structure or the crystal phase of the monoclinic layered rock salt type structure is preferably 50 to 90% by mass with respect to the entire mixed phase. Further, the nickel-containing lithium-manganese composite oxide of the present invention may consist only of the crystal phase of the hexagonal layered rock salt type structure or the crystal phase of the monoclinic layered rock salt type structure.

The lattice constant a in the layered rock salt type crystal structure of the nickel-containing lithium manganese composite oxide of the present invention is calculated as the a-axis value in the hexagonal layered rock salt type lattice corresponding to the distance between transition metal ions and is 2.870 Å or less. It is more preferably 2.86 Å or less, and further preferably 2.860 Å or less. Further, the lower limit of the lattice constant a is preferably 2.850 Å or more from the viewpoint of securing a certain amount of trivalent nickel. ^{Similarly, the lattice volume is 102.0 Å 3} or less, and more preferably ^{101.0 Å 3} or less, calculated assuming a hexagonal layered rock salt type lattice. On the other hand, the lower limit of the lattice volume is preferably ^{100.0 Å 3 or more from the viewpoint of ensuring the transition metal regular structure.} The lattice constant a and the lattice volume in the present specification mean values calculated assuming a hexagonal layered rock salt type lattice.

By having the above configuration with respect to the lattice constant a and the lattice volume, more than half of the nickel ions contained in the nickel-containing lithium manganese composite oxide are trivalently oxidized. The manganese ion valence remains tetravalent regardless of the production method, but the average valence of nickel ions can vary from divalent to trivalent. If the reactivity with lithium ion is high, it tends to become trivalent. If the reactivity with lithium ions is low, it tends to remain divalent.

The average valence of nickel ions in the nickel-containing lithium-manganese composite oxide of the present invention is preferably 2.5 valence or higher, and more preferably 2.6 valence or higher. By having such a configuration, it is possible to improve the charge / discharge characteristics of a lithium ion secondary battery manufactured by using the nickel-containing lithium manganese composite oxide as a positive electrode material. Average valence of nickel ions, for example, by X-ray absorption (Ni-K XANES) spectrum of nickel K-edge near which will be described later, LiNiO ₂ trivalent, the 1s → 4p transition of each sample of NiO as divalent standard The position of the corresponding peak top can be determined by comparing it with that of the standard material. On the other hand, the upper limit of the average valence of nickel ions in the nickel-containing lithium-manganese composite oxide is trivalent from the viewpoint of securing as much trivalent nickel ions as possible as a result of incorporating a large amount of Li ions. preferable.

Further, the nickel-containing lithium-manganese composite oxide of the present invention, it is also preferred oxygen content (O / (Ni + Mn) molar ratio) is large relative to the transition metal, the composition _{formula: Li 1 + x (Ni y} Mn 1-y) 1-x In _{the y = 0.5 composition in O 2} , assuming that Ni is divalent, the composition formula is LiNi _1/2 Mn _1/2 O ₂ , and (O / (Ni + Mn) molar ratio) is 2. On the other hand, when Ni is trivalent, the composition formula is Li _1.2 Ni _0.4 Mn _0.4 O ₂ , and the (O / (Ni + Mn) molar ratio) is 2.5. Since the substance of the present invention has an average Ni valence of 2.5 or more, the lower limit of the above values is 2.3, but from the viewpoint of constructing a battery having excellent discharge capacity and cycle characteristics, the lower limit is set. Is preferably 2.4. On the other hand, since the average Ni valence of the substance of the present invention is preferably close to trivalent as described above, the upper limit of the above value is preferably 3. (O / (Ni + Mn) molar ratio) can be determined by quantifying the amount of transition metal ions and the amount of oxygen in the sample with a fluorescent X-ray analyzer.

Regarding the distribution of transition metal ions in the hexagonal layered rock salt type lattice, tetravalent Mn ions and trivalent Ni ions are mainly distributed at the 3b position (001/2) in the transition metal layer, but divalent Ni. Ions or Mn ions of trivalent or less are mainly present at the 3a position (000) in the Li layer. In the nickel-containing lithium-manganese composite oxide of the present invention, the amount of transition metal in the Li layer is preferably 7% or less, preferably 5% or less, based on 100% of the total amount of transition metals in the hexagonal layered rock salt type lattice. It is more preferable to do so. The amount of transition metal contained in the transition metal layer is preferably 88% or less, more preferably 82% or less, and more preferably 80% or less, based on 100% of the total amount of transition metal in the hexagonal layered rock salt lattice. It is more preferably% or less. By having such a transition metal distribution, not only the amount of tetravalent Mn ions and trivalent Ni ions increases, but also the diffusion of Li ions in the layered rock salt type structure becomes faster, so that the charge / discharge characteristics can be improved. You can expect it. Further, when the total amount of transition metals per composition formula is reduced, more Li ions can be incorporated into the transition metal layer, and the Li can move into the Li layer during charging. It suppresses the deterioration of characteristics due to the repulsion between oxide ions and the like, and as a result contributes to the improvement of the chemical stability of the positive electrode active material during charging. On the other hand, the amount of transition metal in the Li layer of the nickel-containing lithium-manganese composite oxide of the present invention is preferably 0.01% or more. Similarly, the amount of the transition metal contained in the transition metal layer is preferably 50% or more.

In the prior art, the amount of transition metal ions in the Li layer was reduced by adding Co, but adding Co reduces the cycle characteristics during high-potential charging and the thermal stability of the positive electrode after charging. Is known, and the substance of the present invention is characterized in that a substance having a low amount of transition metal in the Li layer was obtained without adding Co.

2. Positive Electrode Material for Lithium Ion Secondary Battery and Lithium Ion Secondary Battery The nickel-containing lithium manganese composite oxide described above can be used as the positive electrode material for lithium ion secondary battery. A positive electrode can be manufactured by supporting a positive electrode mixture prepared by mixing a known conductive agent and a binder on such a positive electrode material on a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth. As the conductive agent, for example, a carbon material such as graphite, coke, carbon black, or acicular carbon can be used. The negative electrode material is also not particularly limited, and examples thereof include metallic lithium, graphite, Si—SiO-based negative electrode, and LTO (Li ₄ Ti ₅ O ₁₂ ) -based negative electrode. As for these negative electrode materials, if necessary, a negative electrode may be manufactured by supporting them on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon or the like using a conductive agent, a binder or the like. The electrolyte is not particularly limited, _{and an organic electrolyte solution in which LiPF 6} or the like is used as an electrolyte salt and dissolved in various solvents such as ethyl carbonate (EC) and dimethyl carbonate (DMC), Li ₂ SP ₂ S ₅ , Li Examples thereof include inorganic sulfide-based solid electrolytes such as ₂ S-GeS _2- P ₂ S ₅ , Li ₂ S-SiS _{2 -Li 3} PO _{4, and high molecular weight polymers having lithium ion conductivity.} The separator is not particularly limited, and examples thereof include polyethylene and polypropylene.

3. 3. Method for Producing Nickel-Containing Lithium-Manganese Composite Oxide The present invention further includes the above-mentioned method for producing a nickel-containing lithium-manganese composite oxide. The method for producing a nickel-containing lithium manganese composite oxide of the present invention is
Step 1 of forming a precipitate from a mixed aqueous solution containing a manganese compound and a nickel compound under alkaline conditions of 20 ° C. or lower.
Step 2 of performing a wet oxidation treatment on the precipitate
It also has a step 3 of heat treatment in an oxidizing atmosphere in the presence of a lithium salt.

3.1. Process 1
The manganese compound used is not particularly limited, and is limited to manganese chloride (II), manganese sulfate (II), manganese acetate (II), manganese acetate (III), manganese nitrate (II), acetyl manganese acetate (II), and acetyl. Known compounds can be widely used, including hydrates such as manganese acetate (III) and potassium permanganate (VII). In addition, manganese oxide and metallic manganese can also be used as water-soluble salts by dissolving them with an appropriate acid.

The nickel compound to be used is not particularly limited, and known compounds including hydrates such as nickel nitrate (II), nickel acetate (II), nickel chloride (II) and nickel sulfate (II) can be widely used. it can. Nickel oxide and metallic nickel can also be used as water-soluble salts by dissolving them with an appropriate acid.

The alkaline source used for making alkaline conditions is not particularly limited, and known sources such as sodium hydroxide, lithium hydroxide (including its hydrate), aqueous ammonia, potassium hydroxide, etc. can be widely used. Is.

The alkaline source is added to a mixed aqueous solution obtained by mixing the manganese compound and the nickel compound to obtain alkaline conditions. As the mixing method at this time, a known mixing method can be widely adopted, and there is no particular limitation. Further, as the solvent of the mixed aqueous solution, water is usually used, but the solvent is not necessarily limited to this, and alcohols such as ethanol and methanol may be used. These solvents may be used alone or in combination of two or more. Alcohols can also be used as a precipitating material when potassium permanganate is used as a manganese source, and can also be used as an antifreeze solution when dropped at a low temperature of 0 ° C. or lower as described later.

Further, in step 1, a precipitate is formed in a known container such as a constant temperature bath, which can adjust and maintain the temperature of the mixed aqueous solution. At this time, the temperature of the mixed aqueous solution needs to be set to 20 ° C. or lower. If the temperature is higher than this, the primary particle size of the precipitate becomes large, and the reactivity with lithium tends to decrease. From the same viewpoint, the upper limit of the set temperature of the mixed aqueous solution in step 1 is more preferably 25 ° C. or lower, further preferably 20 ° C. or lower. On the other hand, the lower limit of the set temperature is preferably −10 ° C. or higher, more preferably 0 ° C. or higher, from the viewpoint of ease of manufacture. Here, when the set temperature is set to 0 ° C. or lower, it is preferable to put ethanol as an antifreeze on the alkaline side. Further, the alkali concentration may be strongly alkaline (pH 11 or higher) at the end of the precipitation preparation in step 1.

3.2. Step 2
In step 2, the precipitate obtained in step 1 is subjected to a wet oxidation treatment. In step 2, the precipitate is oxidatively aged by blowing (babbling) an oxidizing gas such as air or oxygen gas into an alkaline aqueous solution containing the precipitate to produce a precursor having high reactivity with lithium. The gas to be blown may be oxygen gas (for example, air), and is not particularly limited, but oxygen gas is preferable from the viewpoint of shortening the oxidation time. In the case of oxygen gas, not only a normally used cylinder but also an industrial oxygen generator may be used. The temperature of wet oxidation is also not particularly limited, and may be, for example, around room temperature. The wet oxidation time is preferably longer, but more preferably 1 hour or longer, more preferably 24 hours or longer, still more preferably 48 hours or longer, from the viewpoint of sufficiently advancing the reaction.

3.3. Process 3
In step 3, the aged product obtained in step 2 is heat-treated in the presence of a lithium salt. Here, from the viewpoint of reducing impurities derived from the water-soluble salts, the aged product obtained in the above step 2 is washed with distilled water or the like to remove the salts before performing the heat treatment in the presence of the lithium salt. After filtering and adding a lithium salt, it is preferable to heat-treat in an oxidizing atmosphere in the presence of a lithium salt as a raw material for heat treatment, but of course, the reaction product obtained in the above step 2 is used as it is as a raw material for heat treatment in step 3. , The heat treatment may be performed in an oxidizing atmosphere in the presence of a lithium salt.

As a specific method for coexisting the heat treatment raw material and the lithium salt in the heat treatment, a known method can be used, and there is no particular limitation, but for example, the reaction product obtained in the above step 2 and lithium. A method of mixing with a salt can be mentioned. More specifically, if the lithium salt is insoluble in water, dry-mix it and then grind it well with a vibration mill or the like. If it is water-soluble, sufficiently disperse the precipitate in an aqueous solution containing the lithium salt and then mix it uniformly with a mixer. It is desirable to prepare a good slurry. The slurry or the like may be dried by a dryer and pulverized again if necessary.

Further, as the heat treatment raw material, a dried material may be used. When a dried product is used, it is preferably mixed with the lithium salt before drying from the viewpoint of avoiding consolidation with the residual alkali during drying and difficulty in uniform mixing with the lithium salt.

As the lithium salt, a known lithium salt can be widely used, and there is no particular limitation. Specifically, in addition to inexpensive lithium carbonate and lithium hydroxide having high reactivity with precipitation, lithium acetate, lithium nitrate, lithium chloride and the like can be used. In addition to the above lithium salt, lithium perchlorate and its hydrate can also be used as an oxidizing agent.

The amount of lithium salt added to the heat treatment raw material should be adjusted according to the assumed average nickel valence of the lithium molar amount (Li / (Ni + Mn) ratio) with respect to the molar number of nickel and manganese in the heat treatment raw material. preferable. That is, as described above, since the nickel-containing lithium manganese composite oxide of the present invention has a Mn valence of tetravalent and an average Ni valence of 2.5 valence or more, the y value in the composition formula is 0.4 to 0.4 to In the case of 0.6, the Li / (Ni + Mn) ratio is preferably 1.25 or more, and more preferably 1.5 or more. There is no particular upper limit of the Li / (Ni + Mn) ratio, but since an expensive lithium source is used, it is preferably 2.5 or less from the viewpoint of economy. The Li / (Ni + Mn) ratio can be set within the above range depending on the average valence of the constituent Mn and Ni, but the (Li / (Ni + Mn) ratio) should be 1.25 or more (Li excess composition). Is preferable. By making the Li excess composition, it is possible _{to suppress the formation of impurity phases such as LiMn 2} O ₄ spinel, which has a small amount of lithium, in the sample, stabilize a large number of trivalent nickel ions during high-temperature heat treatment, and due to the flux effect. Contributes to improving the primary and secondary particle size of the heat-treated product.

Here, if the lithium salt is insoluble in water, dry-mix it and then pulverize it well with a vibration mill or the like. If it is water-soluble, sufficiently disperse the precipitate in an aqueous solution containing the lithium salt, and then mix it with a mixer to obtain a uniform slurry. It is desirable to make it. The slurry or the like may be dried by a dryer and pulverized again if necessary. The drying temperature is preferably 100 ° C. or lower, more preferably 60 ° C. or lower. When dried under a temperature condition exceeding 100 ° C., the viscosity of the slurry decreases due to the high temperature, and the precipitate easily separates from the lithium salt. On the other hand, if the drying temperature is too low, it will not dry, so vacuum or freeze-drying may be used.

The heat treatment is not particularly limited as long as it is a process of applying heat, and a known method can be widely adopted. Above all, it is preferable to perform the firing treatment from the viewpoint that the heat treatment can be easily performed. The firing treatment is performed in an oxidizing atmosphere. In the present specification, firing in an oxidizing atmosphere means firing in the atmosphere or an oxygen stream. By performing the firing treatment in an oxidizing atmosphere, the lattice constant a and the lattice volume in the composite oxide of the present invention can be set in the above-mentioned numerical ranges, and eventually the nickel-containing lithium-manganese composite oxidation finally obtained can be obtained. It is possible to increase the average valence of nickel ions in a product. As described above, a lithium ion secondary battery using a nickel-containing lithium manganese composite oxide having a high average valence of nickel ions contained as a positive electrode material is excellent in charge / discharge characteristics.

The firing temperature is generally preferably 750 ° C. to 1000 ° C., although it depends on the composition of the raw material for heat treatment. By firing at a temperature of 750 ° C. or higher, the particle size of the obtained nickel-containing lithium-manganese composite oxide becomes a predetermined size or larger. As a result, the reactivity with the electrolytic solution does not become excessive, and a sample having excellent cycle characteristics can be obtained. On the other hand, by setting the firing temperature to 1000 ° C. or lower, it is possible to prevent the particle size of the obtained nickel-containing lithium manganese composite oxide from becoming excessive. This makes it possible to secure a constant exchange of lithium ions with the electrolytic solution and obtain a sample having excellent discharge rate characteristics. Further, by setting the firing temperature to 1000 ° C. or lower, it is possible to suppress volatilization of the Li source and prevent cost loss.

From the viewpoint of performing a sufficient reaction, the firing time is preferably 30 minutes or more while being maintained at a temperature within the above firing temperature range, and more preferably 3 hours or more. The upper limit of the firing time is not particularly limited, but is preferably 30 hours or less from the viewpoint of suppressing an increase in manufacturing cost.

After the heat treatment, if necessary, the excess lithium salt may be removed by washing with water, and the mixture may be filtered and dried. Further, if necessary, step 3 may be repeated a plurality of times in order to obtain a nickel-containing lithium-manganese composite oxide having more excellent charge / discharge property. The number of repetitions is preferably 2 to 3 times from the viewpoint of simplifying the process and ensuring uniformity.

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail based on Examples, but the present invention is not limited thereto.

(Example 1)
Weigh 36.35 g of nickel (II) nitrate hexahydrate and 24.74 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 1: 1) and put them in 500 ml of distilled water. Completely dissolved. 50 g of sodium hydroxide was placed in another titanium beaker, and 500 ml of distilled water was added to completely dissolve the sodium hydroxide. The aqueous sodium hydroxide solution was fixed in a constant temperature bath kept at 20 ° C., and the solution was kept stirred until the temperature became the same. A liquid feed pump was set in the metal salt solution, and the metal salt solution was gradually added to the alkaline solution over 3 hours to form a precipitate. It was confirmed that the pH of the alkaline solution was 11 or more even after the completion of precipitation preparation. After the preparation of the precipitate was completed, the beaker was taken out from a constant temperature bath, and while stirring at room temperature, wet oxidation and aging were carried out for two days while blowing oxygen into the precipitate using an oxygen gas generator. After aging, the precipitate was washed with distilled water to remove alkalis or salts, and then filtered. After filtration, 0.25 mol (18.47 g) of lithium carbonate was added to the precipitate and mixed with 200 ml of distilled water in a mixer to prepare a slurry. The slurry was transferred to a polytetrafluoroethylene charley and dried at 50 ° C. for 2 days to prepare a raw material for firing. The raw material was crushed by a vibration mill, spread thinly on an alumina crucible lid, first fired in the air at 650 ° C. for 5 hours, and then cooled in a furnace. The raw material after firing was pulverized again with a vibration mill and secondarily fired in the atmosphere at 850 ° C. for 5 hours. After cooling in a furnace, the sample was taken out, washed with distilled water, filtered and dried to obtain the desired composite oxide.

(Comparative Example 1)
A sample was prepared in the same manner as in Example 1 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 1)
The measured (+) of the sample of Example 1 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 1, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.86194 (7) Å, c = 14.2321 (3) Å and lattice volume V = 100.953 (4) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer is 4.75 (6)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer is 81.14 (16). %Met. The sum of the two was the amount of transition metal per composition formula, and the value was 85.9 (2)% (0.859 (2)).

Evaluation by X-ray diffraction (Comparative Example 1)
The measured (+) of the sample of Comparative Example 1 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 2, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.88374 (8) Å, c = 14.2758 (3) Å and lattice volume V = 102.812 (4) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer is 8.79 (6)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer is 87.09 (15). %Met. The sum of the two was the amount of transition metal per composition formula, and the value was 95.9 (2)% (0.959 (2)).

Chemical analysis (Example 1)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Example 1 was estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.30. It was (1). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.48 (1) and 2.62 (5), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was 0.130 (5).
On the other hand, the y value was 0.48 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative example 1)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Comparative Example 1 was estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 0.98. It was (1). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.50 (1) and 2.11 (6), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was -0.01 (1).
On the other hand, the y value was 0.50 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Phylogenetic Analysis of Mn Ions and Ni Ions Figures 3 (a) and 3 (b) show X-ray absorption spectra (XANES) near the K-end of Mn and Ni in the samples of Example 1 and Comparative Example 1, respectively. As the standard substances of tetravalent Mn, divalent Ni and trivalent Ni, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used, respectively.
At the MnK end, there is no difference in the spectra of Example 1 and Comparative Example 1, and _{since they almost overlap with the XANES data of Li 2} MnO ₃ which is a standard substance of tetravalent Mn, the Comparative Example 1 sample is the Example 1 sample. Similarly, there is no difference in the Mn valence and it can be judged to be tetravalent. On the other hand, it can be seen that the peak top positions corresponding to the 1s → 4p transitions of the XANES data at the NiK end are significantly different between Example 1 and Comparative Example 1. The sample of Example 1 is shifted to the higher energy side than the sample of Comparative Example 1, reflecting the higher Ni ion valence. Therefore, the average Ni valence was estimated using the following formula.
Ni average valence = 2 + {(peak top energy value of example sample)-(peak top energy value of NiO)}
÷ {( _{Peak top energy value of LiNiO 2} sample)-(Peak top energy value of NiO)}
(Example 1)
The energy values of NiO and LiNiO ₂ were 8349.3 and 8351.3 eV, respectively, and the energy value of the example sample was estimated to be 8351 eV, so the average valence of the obtained nickel ions was calculated to be 2.85 valence. Was done.
(Comparative Example 1)
The energy values of NiO and LiNiO ₂ were 8349.3 and 8351.3 eV, respectively, and the energy value of the comparative example sample was estimated to be 8350 eV, so the average valence of the obtained nickel ions was calculated to be 2.35 valence. Was done.

Evaluation of Charge / Discharge Characteristics 20 mg of the obtained powder of Example 1 was mixed well with 5 mg of acetylene black, and then a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. After vacuum drying at 120 ° C., the negative electrode is dissolved in metallic lithium and the electrolytic solution is _{a supporting salt equivalent to 1M-LiPF 6} dissolved in a mixed solvent of EC (ethylene carbonate) + DMC (dimethyl carbonate) (volume ratio 3: 7). As an electrolytic solution, a lithium semi-battery was assembled, and a charge / discharge test for starting charging was performed at 30 ° C. The potential range was 2.0-4.6V. Up to 1-4 cycles, the charge capacity is limited to 80 mAh / g in the first cycle as a preliminary charge / discharge, and after discharge, the charge capacity is restricted to 120 mAh / g, which is 40 mAh / g higher in the second cycle, and then 4 Charging and discharging were performed while increasing the charging capacity by 40 mAh / g until the cycle, and the battery was charged to 4.8 V in the fifth cycle and then discharged. After that, 29 cycles of charging and discharging were performed in the set potential range. For the Comparative Example 1 sample, a battery was prepared under the same conditions, and the same charge / discharge characteristic evaluation test was carried out.
(Example 1)
FIG. 4 shows a charge / discharge curve of a lithium secondary battery using the sample of Example 1 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). The number indicates the number of cycles. From FIG. 4, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 226 mAh / g and 205 mAh / g, respectively, and the charge / discharge efficiency was 93%. In addition, the average voltage at the time of discharging in the 5th cycle is 3.69V, and the energy density corresponding to the product of the discharging capacity is 757mWh / g, which not only has sufficient initial characteristics as a high-capacity positive electrode, but also after 34 cycles (activation). The discharge capacity (corresponding to the latter 30 cycles) was also high at 189 mAh / g, and the discharge capacity retention rate at 30 cycles with respect to 5 cycles was high at 92%. It was also found that there was almost no decrease in potential and capacity from the 24th cycle onward, and it was confirmed that the material had excellent characteristics as a positive electrode material for a lithium ion secondary battery.
(Comparative Example 1)
Further, FIG. 5 shows a charge / discharge curve of a lithium secondary battery using the sample of Comparative Example 1 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). From FIG. 5, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 218 mAh / g and 205 mAh / g, respectively, and the charge / discharge efficiency was 93%. The average voltage at the time of discharging in the 5th cycle is 3.78V, and the energy density corresponding to the product of the discharging capacity is 773mWh / g, which is sufficient initial characteristics as a high-capacity positive electrode, but after 34 cycles (30 after activation). The discharge capacity (corresponding to a cycle) was as low as 30 mAh / g, and the discharge capacity retention rate at 30 cycles with respect to 5 cycles was as low as 14%. That is, the comparative example sample did not have sufficient cycle characteristics as a positive electrode material for a lithium ion secondary battery.

(Example 2)
Weigh 29.08 g of nickel (II) nitrate hexahydrate and 29.69 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 4: 6) and completely in 500 ml of distilled water. It was dissolved. The aqueous sodium hydroxide solution was fixed in a constant temperature bath kept at + 5 ° C., and the solution was kept stirred until the temperature became the same. After that, a sample was prepared by the same process as in Example 1 to obtain the desired composite oxide.

(Comparative Example 2)
A sample was prepared in the same manner as in Example 2 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 2)
The measured (+) of the sample of Example 2 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (the space group) are shown in FIG.

The residuals are shown below the pattern. Around 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks around 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 6, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.85599 (8) Å, c = 14.2254 (3) Å, lattice volume V = 100.487 (5) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer was 4.03 (8)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer was 76.6 (2)%. .. The sum of the two is the amount of transition metal per composition formula, and the value was 80.6 (3)% (0.806 (3)).

Evaluation by X-ray diffraction (Comparative Example 2)
The measured (+) of the sample of Comparative Example 2 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 7, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.87164 (10) Å, c = 14.2729 (4) Å, lattice volume V = 101.930 (5) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer was 6.41 (6)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer was 82.20 (17)%. .. The sum of the two is the amount of transition metal per composition formula, and the value was 88.6 (2)% (0.886 (2)).

Chemical analysis (Example 2)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Example 2 was estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.361. It was (8). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.398 (1) and 2.43 (3), respectively. The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was 0.153 (4).
On the other hand, the y value was 0.398 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative example 2)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Comparative Example 2 by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.20 (1). )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.398 (1) and 2.36 (5), respectively. The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value is 0.090 (6).
On the other hand, the y value was 0.398 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Phylogenetic Analysis of Mn Ions and Ni Ions Figures 8 (a) and 8 (b) show X-ray absorption spectra (XANES) near the K-end of Mn and Ni in the samples of Example 2 and Comparative Example 2, respectively. As the standard substances of tetravalent Mn, divalent Ni and trivalent Ni, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used, respectively.
At the MnK end, there is no difference in the spectra of Example 2 and Comparative Example 2, and _{the XANES data of Li 2} MnO ₃ , which is a standard substance of tetravalent Mn, almost overlaps. Therefore, the Comparative Example 2 sample is the Example 2 sample. Similarly, there is no difference in the Mn valence and it can be judged to be tetravalent. On the other hand, as for the XANES data at the NiK end, it can be seen that the peak top position corresponding to the 1s → 4p transition is significantly different between Example 2 and Comparative Example 2. The sample of Example 2 is shifted to the higher energy side than the sample of Comparative Example 2, reflecting the higher Ni ion valence. Therefore, the average Ni valence was estimated using the following formula.
Ni average valence = 2 + {(peak top energy value of example sample)-(peak top energy value of NiO)} ÷ {( _{peak top energy value of LiNiO 2} sample)-(peak top energy value of NiO)}
(Example 2)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the peak top energy value of the example sample was estimated to be 8348.5 eV, so the average valence of the obtained nickel ions was calculated to be 2.86 valence. ..
(Comparative Example 2)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the energy value of the comparative example sample was estimated to be 8347.6 eV, so the average valence of the obtained nickel ions was calculated to be 2.43 valence.

Evaluation of Charge / Discharge Characteristics A lithium half-cell was assembled in the same manner as in Example 1 using the powder of the obtained Example 2 sample as a positive electrode active material, and a charge / discharge test for starting charging was performed at 30 ° C. The charge / discharge test conditions are also the same as in Example 1. For the Comparative Example 2 sample, a battery was prepared under the same conditions, and the same charge / discharge characteristic evaluation test was carried out.
(Example 2)
FIG. 9 shows a charge / discharge curve of a lithium secondary battery using the sample of Example 2 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). The number indicates the number of cycles. From FIG. 9, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 217 mAh / g and 209 mAh / g, respectively, and the charge / discharge efficiency was 96%. In addition, the average voltage at the time of discharging in the 5th cycle is 3.58V, and the energy density corresponding to the product of the discharging capacity is 749mWh / g, which not only has sufficient initial characteristics as a high-capacity positive electrode, but also after 34 cycles (after activation). The discharge capacity (corresponding to 30 cycles) was also high at 206 mAh / g, and the discharge capacity retention rate after 30 cycles was as high as 99% with respect to 5 cycles. It was also found that there was almost no decrease in potential and capacity from the 14th cycle onward, and it was confirmed that the material had excellent characteristics as a positive electrode material for lithium ion secondary batteries.
(Comparative Example 2)
Further, FIG. 10 shows a charge / discharge curve of a lithium secondary battery using the sample of Comparative Example 2 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). From FIG. 10, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 218 mAh / g and 206 mAh / g, respectively, and the charge / discharge efficiency was 94%. The average voltage at the time of discharging in the 5th cycle is 3.65V, and the energy density corresponding to the product of the discharging capacity is 749mWh / g, which is sufficient initial characteristics as a high-capacity positive electrode, but after 34 cycles (30 cycles after activation). The discharge capacity of (corresponding to) was as low as 126 mAh / g, and the discharge capacity retention rate after 30 cycles was as low as 61% with respect to 5 cycles. That is, the comparative example sample did not have sufficient cycle characteristics as a positive electrode material for a lithium ion secondary battery.

(Example 3)
Weigh 43.62 g of nickel (II) nitrate hexahydrate and 19.79 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 6: 4) and completely in 500 ml of distilled water. It was dissolved. The aqueous sodium hydroxide solution was fixed in a constant temperature bath kept at 5 ° C., and the solution was kept stirred until the temperature became the same. After that, a sample was prepared by the same process as in Example 1 to obtain the desired composite oxide.
(Comparative Example 3)
Samples were prepared in the same manner as in Example 3 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 3)
The measured (+) of the sample of Example 3 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (the above space group) that cannot be fitted by this model ) Was confirmed.

From FIG. 11, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.86563 (6) Å, c = 14.2291 (2) Å, lattice volume V = 101.192 (3) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer was 4.17 (5)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer was 84.72 (15)%. .. The sum of the two is the amount of transition metal per composition formula, and the value was 88.9 (2)% (0.889 (2)).

Evaluation by X-ray diffraction (Comparative Example 3)
The measured (+) of the sample of Comparative Example 3 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 12, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the above space group) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.89131 (5) Å, c = 14.2840 (2) Å, lattice volume V = 103.412 (3) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer was 11.11 (5)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer was 90.32 (14)%. .. The sum of the two is the amount of transition metal per composition formula, and the value was 101.43 (19)% (1.0143 (19)).

Chemical analysis (Example 3)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Example 3 by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.119 (18). )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.596 (1) and 2.40 (10), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was 0.056 (9).
On the other hand, the y value was 0.596 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative example 3)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Comparative Example 3 by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 0.906 (2). )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.595 (1) and 2.20 (2), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value is -0.0493 (10). This x value became a negative value.
On the other hand, the y value was 0.595 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Phylogenetic Analysis of Mn Ions and Ni Ions Figures 13 (a) and 13 (b) show X-ray absorption spectra (XANES) near the K-end of Mn and Ni in the samples of Example 3 and Comparative Example 3, respectively. As the standard substances of tetravalent Mn, divalent Ni and trivalent Ni, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used, respectively.
At the MnK end, there is no difference in the spectra of Example 3 and Comparative Example 3, and _{it almost overlaps with the XANES data of Li 2} MnO ₃ which is a standard substance of tetravalent Mn. Therefore, the Comparative Example 3 sample is the Example 3 sample. Similarly, there is no difference in the Mn valence and it can be judged to be tetravalent. On the other hand, as for the XANES data at the NiK end, it can be seen that the peak top position corresponding to the 1s → 4p transition is significantly different between Example 3 and Comparative Example 3. The sample of Example 3 is shifted to the higher energy side than the sample of Comparative Example 3, reflecting the higher Ni ion valence. Therefore, the average Ni valence was estimated using the following formula.
Ni average valence = 2 + {(peak top energy value of example sample)-(peak top energy value of NiO)} ÷ {( _{peak top energy value of LiNiO 2} sample)-(peak top energy value of NiO)}
(Example 3)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the peak top energy value of the example sample was estimated to be 8348.2 V, so the average valence of the obtained nickel ions was calculated to be 2.71 valence. ..
(Comparative Example 3)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the energy value of the comparative example sample was estimated to be 8347.2 eV, so the average valence of the obtained nickel ions was calculated to be 2.24 valence.

Evaluation of Charge / Discharge Characteristics A lithium half-cell was assembled in the same manner as in Example 1 using the powder of the obtained Example 3 sample as a positive electrode active material, and a charge / discharge test for starting charging was performed at 30 ° C. The charge / discharge test conditions are also the same as in Example 1. For the Comparative Example 3 sample, a battery was prepared under the same conditions, and the same charge / discharge characteristic evaluation test was carried out.

(Example 3)
FIG. 14 shows a charge / discharge curve of a lithium secondary battery using the sample of Example 3 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). The number indicates the number of cycles. From FIG. 14, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 164 mAh / g and 156 mAh / g, respectively, and the charge / discharge efficiency was 95%. In addition, the average voltage at the time of discharging in the 5th cycle is 3.80V, and the energy density corresponding to the product of the discharging capacity is 592mWh / g, which not only has sufficient initial characteristics as a high-capacity positive electrode, but also after 34 cycles (after activation). The discharge capacity (corresponding to 30 cycles) was also high at 142 mAh / g, and the discharge capacity retention rate after 30 cycles was as high as 91% with respect to 5 cycles. It was also found that the decrease in potential and capacity from the 14th cycle onward was small, and it was confirmed that the material had excellent characteristics as a positive electrode material for lithium ion secondary batteries.
(Comparative Example 3)
Further, FIG. 15 shows a charge / discharge curve of a lithium secondary battery using the sample of Comparative Example 3 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). From FIG. 15, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 175 mAh / g and 169 mAh / g, respectively, and the charge / discharge efficiency was 97%. The average voltage at the time of discharge in the 5th cycle is 3.83, and the energy density corresponding to the product of the discharge capacity is 647 mWh / g, which has sufficient initial characteristics as a high-capacity positive electrode, but after 34 cycles (equivalent to 30 cycles after activation). The discharge capacity was as low as 105 mAh / g, and the discharge capacity retention rate after 30 cycles was as low as 62% with respect to 5 cycles. That is, the comparative example sample did not have sufficient cycle characteristics as a positive electrode material for a lithium ion secondary battery.

(Example 4)
Weighed 29.08 g of nickel (II) nitrate hexahydrate and 29.69 g (0.25 mol / batch, Ni: Mn molar ratio of 4: 6) of manganese (II) chloride tetrahydrate and put them in 500 ml of distilled water. Completely dissolved. 50 g of sodium hydroxide was placed in another titanium beaker, and 500 ml of distilled water was added to completely dissolve the sodium hydroxide. Then, 200 ml of ethanol was added as an antifreeze solution, and the mixture was stirred well. The sodium hydroxide solution was fixed in a constant temperature bath kept at −10 ° C. and kept stirred until the solution reached the same temperature. A liquid feed pump was set in the metal salt solution, and the metal salt solution was gradually added to the alkaline solution over 3 hours to form a precipitate. It was confirmed that the pH of the alkaline solution was 11 or more even after the completion of precipitation preparation. After the preparation of the precipitate was completed, the beaker was taken out from a constant temperature bath, and while stirring at room temperature, wet oxidation and aging were carried out for two days while blowing oxygen into the precipitate using an oxygen gas generator. After aging, the precipitate was washed with distilled water to remove alkalis or salts, and then filtered. After filtration, 0.5 mol (20.98 g) of lithium hydroxide monohydrate was added to the precipitate, dissolved in 200 ml of distilled water, and mixed with the aged precipitate with a mixer to prepare a slurry. The slurry was transferred to a polytetrafluoroethylene charley and dried at 50 ° C. for 2 days to prepare a raw material for firing. The raw material was crushed by a vibration mill, spread thinly on an alumina crucible lid, first fired in an oxygen stream at 500 ° C. for 20 hours, and then cooled in a furnace. The raw material after firing was pulverized again with a vibration mill and secondarily fired in nitrogen at 850 ° C. for 5 hours. After cooling in a furnace, the sample was taken out, washed with distilled water, filtered and dried to obtain the desired composite oxide.

Evaluation by X-ray diffraction (Example 4)
The measured (+) of the sample of Example 4 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 16, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.86135 (8) Å, c = 14.2379 (3) Å and lattice volume V = 100.953 (4) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer is 4.85 (6)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer is 79.78 (17). %Met. The sum of the two was the amount of transition metal per composition formula, and the value was 84.6 (2)% (0.846 (2)).

Chemical analysis (Example 4)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Example 4 was estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.32. It was (5). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.395 (10) and 2.7 (2), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was 0.14 (2).
On the other hand, the y value was 0.395 (10) because it was the Ni / (Ni + Mn) molar ratio itself.

Phylogenetic analysis of Mn and Ni ions Figures 17 (a) and 17 (b) show the X-ray absorption spectra (XANES) near the K-end of Mn and Ni in the sample of Example 4. As the standard substances of tetravalent Mn, divalent Ni and trivalent Ni, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used, respectively.
At the MnK end, the spectrum of the sample of Example 4 _{almost overlaps with the XANES data of Li 2} MnO ₃ which is a standard substance of tetravalent Mn, so that the Mn valence can be judged to be tetravalent. On the other hand, the peak top value associated with the 1s → 4p transition of the XANES data at the NiK end of the Example 4 sample was present at a position approximately intermediate between the two standard substances having known valences. Therefore, the average Ni valence was estimated using the following formula.
Ni average valence = 2 + {(peak top energy value of example sample)-(peak top energy value of NiO)}
÷ {( _{Peak top energy value of LiNiO 2} sample)-(Peak top energy value of NiO)}
The energy values of NiO and LiNiO ₂ were 8346.3 and 8348.4 eV, respectively, and the energy values of the sample of Example 4 were estimated to be 8347.5 eV, so the average valence of the obtained nickel ions was calculated to be 2.57 valence. From the above, it is shown that if an oxidizing atmosphere is selected as the primary firing, the target substance can be obtained even if an inert gas atmosphere such as in a nitrogen stream is selected during the secondary firing.

Evaluation of Charge / Discharge Characteristics 20 mg of the obtained powder of Example 4 was mixed well with 5 mg of acetylene black, and then a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. After that, a battery was prepared under the same conditions as in Example 1, and a charge / discharge characteristic evaluation test was carried out under the same test conditions.
FIG. 18 shows a charge / discharge curve of a lithium secondary battery using the sample of Example 4 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). The number indicates the number of cycles. From FIG. 18, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 240 mAh / g and 228 mAh / g, respectively, and the charge / discharge efficiency was 95%. In addition, the average voltage at the time of discharging in the 5th cycle is 3.67V, and the energy density corresponding to the product of the discharging capacity is 838mWh / g, which not only has sufficient initial characteristics as a high-capacity positive electrode, but also after 34 cycles (after activation). The discharge capacity (equivalent to 30 cycles) was also high at 218 mAh / g, and the discharge capacity retention rate at 34 cycles with respect to 5 cycles was high at 96%. In addition, there is almost no decrease in capacity from the 14th cycle onward, and although a slight potential decrease occurs around 3.5-3.0V during discharge as the cycle elapses after the 14th cycle, it has excellent characteristics as a positive electrode material for lithium-ion secondary batteries. It was confirmed that it had.

(Example 5)
A sample was prepared in the same manner as in Example 4 except that the secondary firing atmosphere was changed from nitrogen to the atmosphere.

Evaluation by X-ray diffraction (Example 5)
The measured (+) of the sample of Example 5 obtained above and the calculated (curve) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (space group below) are shown in FIG.

The residuals are shown below the pattern. In the vicinity of 2θ = 20-25 °, superlattice peaks (2θ = 20.5 ° and broad peaks in the vicinity of 21.5 °) derived from monoclinic layered rock salt type unit cells (space group below) that cannot be fitted by this model ) Was confirmed.

From FIG. 19, the obtained XRD pattern could basically be assigned to the monoclinic Li ₂ MnO _{type 3} structure (space group below) phase having a hexagonal network regular arrangement in the transition metal layer.

しかしながら今回フィットは、より単純な超格子のないα−ＮａＦｅＯ_２型構造と呼ばれる六方晶層状岩塩型結晶相（下記空間群）に帰属して解析した。

However, this time, the fit was analyzed by belonging to the hexagonal layered rock salt type crystal phase (the space group below) called the _{α-NaFeO type 2 structure without a simpler superlattice.}

From X-ray Rietveld analysis (using analysis program RIETAN-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), Lattice constant a = 2.85259 (9) Å, c = 14.2235 (4) Å, lattice volume V = 100.234 (5) Å ³ .
As for the occupancy rate at each lattice position, the occupancy rate of the transition metal (3a) position in the Li layer was 3.65 (8)%, and the occupancy rate of the transition metal (3b) position in the transition metal layer was 77.7 (2)%. .. The sum of the two is the amount of transition metal per composition formula, and the value was 81.4 (3)% (0.814 (3)).

Chemical analysis (Example 5)
When the amount of Li was estimated by ICP emission spectrometry and the amount of Mn, Ni and O of the sample of Example 5 was estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.37 (5). )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.400 (5) and 2.64 (9), respectively.
The x value is calculated by the following formula from the correspondence with the composition formula.
x = (Li / (Ni + Mn) molar ratio -1) ÷ (Li / (Ni + Mn) molar ratio +1)
Therefore, the x value was 0.16 (2).
On the other hand, the y value was 0.400 (5) because it was the Ni / (Ni + Mn) molar ratio itself.

Evaluation of Charge / Discharge Characteristics 20 mg of the obtained powder of Example 5 was mixed well with 5 mg of acetylene black, and then a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. After that, a battery was prepared under the same conditions as in Example 1, and a charge / discharge characteristic evaluation test was carried out under the same test conditions.
FIG. 20 shows a charge / discharge curve of a lithium secondary battery using the sample of Example 5 as a positive electrode at 30 ° C. The upward-sloping curve corresponds to charging (c), and the downward-sloping curve corresponds to discharging (d). The number indicates the number of cycles. From FIG. 20, the charge capacity and the discharge capacity in the 5th cycle (corresponding to the initial stage after activation) were 231 mAh / g and 222 mAh / g, respectively, and the charge / discharge efficiency was 96%. In addition, the average voltage at the time of discharging in the 5th cycle is 3.50V, and the energy density corresponding to the product of the discharging capacity is 778mWh / g, which not only has sufficient initial characteristics as a high-capacity positive electrode, but also after 34 cycles (after activation). The discharge capacity (equivalent to 30 cycles) was also high at 218 mAh / g, and the discharge capacity retention rate at 34 cycles with respect to 5 cycles was high at 98%, confirming that it has excellent characteristics as a positive electrode material for lithium ion secondary batteries.

Claims (7)

General formula (1):
_{Li 1 + x (Ni y Mn} 1-y) 1-x O 2 (1)
[In the formula, x and y indicate 0.05 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by, containing a layered rock salt type crystalline phase,
The lattice constant a is 2.870 Å or less, and the lattice volume is 102.0 Å ³ or less.
Nickel-containing lithium-manganese composite oxide. The nickel-containing lithium-manganese composite oxide according to claim 1, wherein the amount of the transition metal contained in the lithium layer is 5% or less in the layered rock salt type crystal structure. The nickel-containing lithium-manganese composite oxide according to claim 1 or 2, wherein the amount of the transition metal contained in the transition metal layer in the layered rock salt type crystal structure is 88% or less. The nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 3, wherein the nickel ion has a valence of 2.5 or more. The nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 4, wherein the O / (Ni + Mn) atomic ratio is 2.3 or more. A lithium ion secondary battery containing the nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 5 as a cathode active material. Step 1 of forming a precipitate from a mixed aqueous solution containing a manganese compound and a nickel compound under alkaline conditions of 20 ° C. or lower.
Step 2 of performing a wet oxidation treatment on the precipitate
And has a step 3 of heat treatment in an oxidizing atmosphere in the presence of a lithium salt.
The method for producing a nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 5.

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