JP2013082581A - Lithium-containing composite oxide powder and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium-containing composite oxide powder which contains a lithium manganese nickel-based oxide belonging to the spinel structure and which, when used as a positive electrode active material of a non-aqueous electrolyte secondary battery, enables the secondary battery to be stably used even performing charging and discharging upto a high votage, and to provide a method for producing the lithium-containing composite oxide powder.SOLUTION: The lithium-containing composite oxide powder contains primary particles of single crystal comprising a lithium manganese nickel-based oxide which contains at least lithium, manganese and nickel and has a crystal structure belonging to the spinel structure, wherein an average primary particle diameter of the powder which is an average particle diameter of the primary particles is 1-50 μm. The lithium-containing composite oxide powder is obtained by heating metal-containing raw materials and lithium hydroxide at ≥900°C.

Description

  The present invention relates to a composite oxide powder mainly used as a positive electrode active material of a lithium ion secondary battery and a secondary battery using the composite oxide powder.

  In recent years, along with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, secondary batteries with small and light weight and high capacity are required. For example, a lithium ion secondary battery has an active material capable of inserting and removing lithium (Li) in each of a positive electrode and a negative electrode. And it operate | moves because Li ion moves in the electrolyte solution provided between both electrodes.

The performance of the secondary battery depends on the materials of the positive electrode, the negative electrode, and the electrolyte constituting the secondary battery. Among them, active research and development of active material forming active material is being actively conducted. For example, as the positive electrode active material of the secondary battery, a lithium manganese nickel-based oxide having a spinel structure such as LiNi _0.5 Mn _1.5 O ₄ can be given. LiNi _0.5 Mn _1.5 O ₄ is charged and discharged at around 4.8 V on the basis of metallic lithium. Therefore, theoretically, the energy density is increased by charging to a high voltage of about 5.0V.

For example, in Patent Document 1, single crystal lithium manganese nickel oxide having a high practical value is synthesized as a material constituting a lithium battery using a lithium manganese nickel oxide that is expected to have a potential of 5 V class. In Example 3, after mixing LiCl powder, NiCl ₂ powder, and MnCl ₂ powder at a molar ratio of 120: 1: 3, this mixed powder was heated at 750 ° C. for 60 hours to obtain LiNi _0.5 Mn _1.5 A single crystal having a basic composition of O ₄ is grown. It is described that the obtained single crystal has a regular octahedral shape of about 200 μm square at the maximum.

In Patent Document 2, it has an average particle size of LiMn ₂ O ₄ which is used as a positive electrode active material 5μm or less and still more by a 1μm or less, to improve the output of the secondary battery. The LiMn ₂ O ₄ used is synthesized by a “solid phase method” in which LiOH and MnO ₂ are mixed so that Li: Mn is an atomic ratio of 1: 2, and fired at 700 to 900 ° C. in the atmosphere. .

JP 2004-196579 A JP-A-2005-116304

Although not specified in Patent Document 1, it is known that when a lithium ion secondary battery is charged and discharged at a high voltage, a general organic electrolyte used in the secondary battery is decomposed. Decomposition of the organic electrolyte leads to deterioration of battery characteristics such as cycle characteristics. Therefore, LiNi _0.5 Mn _1.5 O ₄ is difficult to use efficiently in the current battery system, and there are many problems to be improved.

Patent Document 1 describes that a potential of 5V class is expected because the concentration distribution of constituent elements in a single crystal having a basic composition of LiNi _0.5 Mn _1.5 O ₄ is uniform. . Indeed, in Patent Document 1, in Example 3, a coarse single crystal lithium manganese nickel oxide was successfully synthesized. However, the initial capacity and cycle characteristics of the lithium manganese nickel oxide synthesized in Example 3 when used as a positive electrode active material for a secondary battery are not clarified. Furthermore, it is unclear whether or not this oxide performs sufficient charge and discharge as a secondary battery.

Patent Document 2 describes that LiMn ₂ O ₄ having an average particle diameter of 5 μm or less, further 1 μm or less is used as a positive electrode active material. Furthermore, it is described that the particle structure of LiMn ₂ O ₄ is preferably a single crystal. However, each example does not describe whether the LiMn ₂ O ₄ particles are single crystals, and the average particle size is also the average primary particle size of single crystal particles, polycrystalline particles or single crystals. It is unclear whether the average particle size of the aggregate of crystal particles. Further, in the solid phase method described in the examples, it is estimated that single particles close to polycrystals in which a plurality of fine single crystal particles less than 1 μm are aggregated are synthesized in view of the firing temperature (around 800 ° C.). The Therefore, even if Patent Document 2 shows the relationship between the average particle size of the secondary particles and the output of the secondary battery, single-crystal LiMn ₂ O ₄ having a specific particle size is used as the positive electrode active material of the secondary battery. The battery characteristics when used for the above have not been evaluated.

  The present invention includes a lithium manganese nickel-based oxide belonging to a spinel structure and stably uses a secondary battery even when charged and discharged to a high voltage when used as a positive electrode active material of a non-aqueous electrolyte secondary battery. Provided is a lithium-containing composite oxide powder and a method for producing the same.

  The present inventors use lithium hydroxide as a lithium supply source, and heat the raw material containing manganese and nickel and lithium hydroxide at a temperature near or near the decomposition temperature of the lithium hydroxide, It was newly found that a lithium manganese nickel-based oxide suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery used at high voltage can be synthesized. And since the lithium manganese nickel-type oxide obtained by such a method has a particle structure advantageous for use at a high voltage, it came to this invention.

  That is, the lithium-containing composite oxide powder of the present invention includes primary particles of single crystals composed of a lithium manganese nickel-based oxide containing at least lithium, manganese and nickel and having a crystal structure belonging to a spinel structure, and the average particle size of the primary particles The average primary particle size as a diameter is 1 μm or more and 50 μm or less.

  The lithium-containing composite oxide powder of the present invention contains primary particles of single crystals and has an average primary particle size of 1 μm or more and 50 μm or less. There is a polycrystal as an expression in contrast to a single crystal. There are crystal grain boundaries in the polycrystalline particles. Therefore, when a secondary battery using a lithium-containing composite oxide powder containing polycrystalline particles as a positive electrode active material of a non-aqueous electrolyte secondary battery is charged and discharged, it tends to collapse starting from a grain boundary. In addition, a compound (impurity) having a composition different from that of the target lithium manganese nickel-based oxide tends to exist in the crystal grain boundary. Therefore, the crystal grain boundary is likely to be an active point for electrolytic solution decomposition. Lithium-containing composite oxides containing primary particles of single crystals and having an average primary particle size of 1 μm or more and 50 μm or less have a relatively large single crystal particle size on the order of microns. Even if there are grain boundaries, the amount is relatively small. In addition, if the single crystal particles are relatively large, the area in contact with the electrolytic solution is reduced, so that the region where the electrolytic solution is decomposed decreases. As a result, the collapse of the active material particles and the decomposition of the electrolytic solution accompanying charging / discharging of the secondary battery are suppressed, and a secondary battery excellent in battery characteristics, particularly cycle characteristics, is obtained. Such an effect is remarkable in a non-aqueous electrolyte secondary battery that is charged to a high voltage of 4.3 V or higher with respect to metallic lithium.

  As used herein, “primary particles” include single particles (single particles), or particles of a minimum unit constituting a polycrystal or aggregate. Therefore, aggregates and polycrystals are treated as “secondary particles”. Coarse particles formed by sintering and bonding a plurality of particles, which are difficult to distinguish from aggregates and polycrystals, are also in the category of secondary particles. The “average primary particle diameter” refers to the diameter of a single particle, or the diameter of a minimum unit particle constituting a polycrystal, aggregate or coarse particle, that is, the diameter of a primary particle.

  The lithium-containing composite oxide powder of the present invention preferably contains single particles of single crystal particles and / or aggregates of single crystal particles. In theory, there is no grain boundary in single-crystal particles and single-crystal particle aggregates. Therefore, such lithium-containing composite oxides are used as positive electrode active materials for non-aqueous electrolyte secondary batteries. The rechargeable battery had excellent cycle characteristics.

  Furthermore, since the lithium-containing composite oxide powder of the present invention comprises single crystal particles having a relatively large size, it can be uniformly and densely filled in the active material layer of the positive electrode. As a result, a non-aqueous electrolyte secondary battery having excellent cycle characteristics and high capacity can be obtained using the lithium-containing composite oxide powder of the present invention.

Further, the present invention is a method for producing the lithium-containing composite oxide powder of the present invention,
A metal-containing raw material containing at least manganese and nickel and a lithium hydroxide, wherein an atomic ratio of lithium contained in the lithium hydroxide to a metal element contained in the metal-containing raw material is a metal of the lithium manganese nickel-based oxide It includes a heating reaction step in which a reaction raw material prepared so as to be more than 1.0 times and less than 1.1 times the stoichiometric ratio of lithium to element is heated at 900 ° C. or higher.

  A lithium hydroxide is used as a lithium supply source, and the crystal structure belongs to the spinel structure by heating the above metal-containing raw material and lithium hydroxide at a temperature near or higher than the decomposition temperature of the lithium hydroxide. A lithium-containing composite oxide powder containing single crystal particles made of lithium manganese nickel-based oxide and having an average primary particle size of 1 μm or more and 50 μm or less can be easily obtained.

Further, the method for producing a lithium-containing composite oxide powder of the present invention is the above production method,
The heating reaction step is a step in which lithium chloride is further added to the reaction raw material, and the metal-containing raw material is reacted in a molten salt of lithium hydroxide and lithium chloride,
Furthermore, a cooling step for cooling the molten salt after the heating reaction step and a recovery step for recovering the generated lithium manganese nickel-based oxide from the solid after cooling may be included.

  That is, the lithium-containing composite oxide powder of the present invention can be synthesized by a molten salt method. Although the added lithium chloride is considered to act as a flux and not contribute to the reaction, it can suppress aggregation of single crystal particles synthesized in the heating reaction step.

  The lithium-containing composite oxide powder of the present invention can be used as a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. That is, the present invention can also be regarded as a positive electrode active material characterized by including the lithium-containing composite oxide powder of the present invention.

  When the lithium-containing composite oxide powder of the present invention is used as a positive electrode active material of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, battery characteristics such as cycle characteristics are improved.

Lithium-containing composite oxide powder of the present invention: a drawing-substitute photograph showing a result of observation of the _{(LiNi 0.5 Mn} 1.5 _{O 4} powder Example 1) by a scanning electron microscope (SEM). _LiNi 0.5 _Mn 1.5 _{O 4} powder synthesized by the conventional method (Comparative Example 1-1) is a drawing-substitute photograph showing a result of observation by SEM. Conventional of _LiNi 0.5 _Mn 1.5 _{O 4} powder synthesized by the method (Comparative Example 1-2) is a drawing-substitute photograph showing a result of observation by SEM. Lithium-containing composite oxide powder of the present invention synthesized using lithium chloride: is a photograph substituted for a drawing, showing the _{(LiNi 0.5 Mn} 1.5 _{O 4} powder Example 2) As a result of observation by SEM and. Lithium-containing composite oxide powder of the comparative example were synthesized using sodium chloride is a photograph substituted for a drawing, showing the _{(LiNi 0.5 Mn} 1.5 _{O 4} powder Comparative Example 2) As a result of observation by SEM and. The present invention and the conventional lithium-containing composite oxide powder _{(LiNi 0.5 Mn} 1.5 _{O 4} powder) is a graph showing the charge-discharge characteristics of the secondary battery using as the positive electrode active material. The present invention and the conventional lithium-containing composite oxide powder _{(LiNi 0.5 Mn} 1.5 _{O 4} powder) is a graph showing the cycle characteristics of the secondary battery using as the positive electrode active material.

  Below, the form for implementing the manufacturing method of the lithium containing complex oxide powder of this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples.

<Lithium-containing composite oxide powder>
The lithium-containing composite oxide powder of the present invention includes particles composed of a lithium manganese nickel-based oxide containing at least lithium, manganese, and nickel and having a crystal structure belonging to a spinel structure. Lithium manganese nickel-based oxides have high energy density and increased capacity when used as a positive electrode active material for secondary batteries at high cut-off voltages (for example, charging up to 4.8 V or more based on Li). Is an expected compound.

If a lithium manganese nickel-based oxide having a crystal structure belonging to the spinel structure is expressed by a composition formula, Li _{1 + x} (Ni _0.5 Mn _1.5 ) _1-xy Me _y O ₄ (0 ≦ x ≦ 0) 0.5, 0 ≦ y ≦ 0.5, (x + y) <1, Me is one or more of Al, Mg, Ca, and Co). In addition, a part of Li may be substituted with H, and 60% or less, or 45% or less of Li in atomic ratio may be substituted with H. LiNi _0.5 Mn _1.5 O ₄ is particularly preferable. The lithium manganese nickel-based oxide is based on the above composition formula or LiNi _0.5 Mn _1.5 O ₄ , and needless to say, defects of Li, Ni, Mn, Me, or O that are inevitably generated, etc. Thus, a composite oxide slightly deviating from the above composition formula is also included. The crystal structure and composition of the lithium manganese nickel-based oxide can be identified by X-ray diffraction (XRD), electron diffraction, emission spectroscopic analysis (ICP), and the like.

  The lithium-containing composite oxide powder of the present invention has an average primary particle size of 1 μm or more and 50 μm or less. The average primary particle size is measured by measuring the maximum diameter of a plurality of primary particles (maximum value of the interval between parallel lines when the particles are sandwiched between two parallel lines) from a micrograph such as SEM. Average value. If the average primary particle size is in the above range, the secondary battery is excellent in battery characteristics, in particular, cycle characteristics, by suppressing the collapse of the active material particles and the decomposition of the electrolyte accompanying the charging / discharging of the secondary battery. Is as described above.

  A powder having an average primary particle size of 1 μm or more is industrially easy to handle. Specifically, aggregation of particles is suppressed during the production of the electrode, and it is easy to uniformly disperse in the active material layer. Moreover, since crystallinity is high, it is excellent in characteristics, such as a filling property in an active material layer, and heat stability. Preferably it is 1.1 micrometers or more, 1.2 micrometers or more, More preferably, it is 1.3 micrometers or more. On the other hand, when the average primary particle size is too large, the surface that comes into contact with the electrolytic solution and contributes to the battery reaction decreases. However, the average primary particle size of 50 μm or less is sufficient in terms of capacity and rate characteristics. Battery characteristics are obtained. On the other hand, when the average primary particle size exceeds 50 μm, it is not practical even if the thickness of the positive electrode active material layer formed on the current collector (usually about 30 to 100 μm) is taken into consideration. A preferable average primary particle size is 30 μm or less, 25 μm or less, more preferably 10 μm or less.

  The lithium-containing composite oxide powder of the present invention may include polycrystalline particles or coarse particles formed by sintering and bonding a plurality of particles as long as the primary crystal particle size is in the above range. It is preferable to include single particles of crystal particles and / or aggregates of single crystal particles. In the present specification, the term “single particle” refers to a particle composed of a single particle that does not include a crystal grain boundary, unlike a polycrystalline particle composed of a plurality of crystal grains or a secondary particle composed of a plurality of fine particles aggregated. The fact that the single particle is a single crystal can be known, for example, by analyzing an electron beam diffraction image using a transmission electron microscope.

If the lithium-containing composite oxide powder of the present invention is defined by the specific surface area, it is preferably 0.01 m ² / g or more and 2.0 m ² / g or less. If the specific surface area is in the above range, an appropriate contact area with the electrolytic solution is ensured. A further preferred specific surface area of the ^{powder, 0.05~1.5m 2 /g,0.1~1.3m} 2 / g even at 0.5~0.8m ² / g. In the present specification, the specific surface area employs a value obtained by measuring the lithium-containing composite oxide powder by the BET method.

<Method for producing lithium-containing composite oxide powder>
Next, each process is demonstrated about the manufacturing method of the lithium containing complex oxide powder of the said invention. The method for producing a lithium-containing oxide powder mainly includes a heating reaction step.

  In the heating reaction step, first, a raw material preparation step for preparing a reaction raw material including a supply source of Li, Ni, and Mn may be performed. Lithium hydroxide is used as the Li supply source. As a supply source of metal elements such as Ni and Mn, a metal-containing raw material containing at least them is used. Any of them is preferably used in a powder form, and the particle size is not particularly limited, but it is desirable to remove coarse particles by sieving to 100 μm or less, further 50 μm or less. When performing a raw material preparation process, it is good to mix a metal containing raw material and lithium hydroxide uniformly, and to obtain a raw material mixture.

The lithium hydroxide may be anhydrous lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH.H ₂ O).

The metal-containing raw material is not particularly limited as long as it is a material containing at least Ni and Mn and, if necessary, one or more of additive metals (Me) such as Al, Mg, Ca and Co. Each single metal, Mn compound, Ni compound, and compound of added metal (Me) may be used in combination according to the composition of the target lithium-containing composite oxide powder. Particularly preferred are metal oxides, metal hydroxides, and other metal salts containing at least one of Ni, Mn and Me. Specifically, if it is a Mn supply source, manganese dioxide (MnO ₂ ), dimanganese trioxide (Mn ₂ O ₃ ), manganese monoxide (MnO), trimanganese tetroxide (Mn ₃ O ₄ ), hydroxide Manganese (Mn (OH) ₂ ), manganese oxyhydroxide (MnOOH), and the like can be given. If it is Ni supply source, nickel oxide (NiO), nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O), nickel sulfate (NiSO ₄ .6H ₂ O), nickel chloride (NiCl ₂ .6H ₂ O), Etc. As the added source of metal (Me), aluminum hydroxide (Al _(OH) 3), aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O), magnesium hydroxide (Mg _(OH) 2), Magnesium nitrate (Mg (NO ₃ ) ₂ .6H ₂ O), calcium hydroxide (Ca (OH) ₂ ), cobalt oxide (CoO, Co ₃ O ₄ ), cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O ), Cobalt hydroxide (Co (OH) ₂ ), cobalt chloride (CoCl ₂ .6H ₂ O), cobalt sulfate (Co (SO ₄ ) · 7H ₂ O), and the like. A metal compound in which a part of a metal element contained in these oxides, hydroxides, or metal salts is substituted with another metal element may be used.

Among the above metal compounds, MnO ₂ , Mn ₂ O ₃ and Mn ₃ O ₄ are preferable for the Mn supply source, and Ni (OH) ₂ is preferable for the Ni supply source. High purity is easy to obtain.

  In addition, the metal-containing raw material may be obtained as a precipitate (precursor) by performing a metal-containing raw material synthesis step before the heating reaction step to make an aqueous solution containing at least manganese ions and nickel ions alkaline. As an aqueous solution, a water-soluble inorganic salt, specifically, a nitrate, sulfate, or chloride salt of a metal element is dissolved in water, and the aqueous solution is made alkaline with an alkali metal hydroxide, aqueous ammonia, etc. Is produced as a precipitate. Adopting a production method using a precursor is preferable because generation of by-products (NiO) that are difficult to remove is suppressed. The obtained precipitate may be used as it is as a metal-containing raw material after being dried. Alternatively, the obtained precipitate may be heat-treated in an oxygen-containing atmosphere so that the precipitate is converted from a metal hydroxide to a metal oxide and then used as a metal-containing raw material.

  The compounding ratio of the metal-containing raw material and the lithium hydroxide is such that the atomic ratio of Li contained in the lithium hydroxide to the metal element (Ni and Mn as required Me) contained in the metal-containing raw material is the target lithium manganese It is prepared so as to be more than 1.0 times and less than 1.1 times the stoichiometric ratio of Li to the metal element (excluding Li) of the nickel-based oxide. More preferably, it is 1.03 times or more and 1.1 times or less, and further 1.05 times or more and 1.1 times or less. Therefore, this production method differs from the molten salt method using lithium chloride described later in the amount of lithium present in the reaction.

  A heating reaction process is a process of heating the prepared reaction raw material at 900 degreeC or more. Since the decomposition temperature of lithium hydroxide is 925 ° C., the heating reaction step is preferably performed at 900 ° C. or higher, further 930 ° C. or higher and 1300 ° C. or lower. When the heating temperature is low, coarse polycrystalline particles are easily formed. By increasing the heating temperature, single crystal particles are likely to be formed, but if the temperature is less than 900 ° C., only fine single crystal particles having an average primary particle size of less than 1 μm can be obtained.

  Prior to the heating reaction step (main baking), preliminary baking (temporary baking) may be performed. That is, two-stage baking, that is, a first heating reaction process for performing preliminary baking and a second heating reaction process (that is, the above-described heating reaction process) that is an essential baking process may be performed. Of the two-stage firing, the former is a process in which Ni, Mn, etc. are mainly reacted with Li to synthesize a composite oxide having a desired composition, and the latter is mainly used to grow particles to obtain a desired particle structure. It is a process. The first heating reaction step is desirably a step of heating the prepared reaction raw material at 450 to 700 ° C, further 600 to 700 ° C. The heating time is not particularly limited, but is preferably 1 to 24 hours, and more preferably 5 to 14 hours. The second heating reaction step is a step of further firing the powder after the first heating reaction step, and is preferably performed at 900 ° C. or higher, more preferably 930 ° C. or higher and 1300 ° C. or lower. The heating time is not particularly limited, but is preferably 1 to 24 hours, and more preferably 5 to 14 hours. In the case where only the second heating reaction step (that is, only the heating reaction step described above) is performed without performing the first heating reaction step, the reaction and crystal growth of Ni, Mn, etc. with Li in the second heating reaction step Proceed in order.

  Moreover, there is no limitation in particular in the atmosphere which performs a heating reaction process, What is necessary is just to carry out in air | atmosphere. A compound having a spinel structure tends to have an oxygen deficient composition at high temperatures. Therefore, the lithium-containing composite oxide powder having a spinel structure is easily obtained in a single phase by performing cooling after the heating reaction step (cooling step) in an oxygen-containing atmosphere such as the air. The oxygen gas concentration in the atmosphere in the heating reaction step and cooling is preferably 50% by volume or less, more preferably 15 to 25% by volume.

  Although there is no particular limitation on the cooling rate after the heating reaction step, it is desirable to gradually cool from the reaction temperature to room temperature from the viewpoint of growing single crystal particles greatly. For example, the furnace may be cooled to room temperature in the furnace used for the heating reaction step. Specifically, a slow cooling rate of 100 ° C./hour or less, further 50 ° C./hour or less is desirable. The lower limit of the cooling rate is not particularly limited, but a very slow cooling rate of, for example, less than 10 ° C./hour is not desirable because production efficiency is not good. After cooling, the powdered lithium-containing composite oxide powder is obtained by lightly pulverizing as necessary.

  Moreover, after synthesizing the lithium-containing composite oxide powder, a proton substitution step of substituting a part of Li with hydrogen (H) may be performed. In the proton substitution step, a part of Li is easily substituted with H by bringing the synthesized lithium-containing composite oxide into contact with a solvent such as diluted acid.

<Method for producing lithium-containing composite oxide powder using lithium chloride>
In the heating reaction step, the reaction raw material may further contain lithium chloride. In this case, since the reaction raw material further contains lithium chloride in the metal-containing raw material and lithium hydroxide in the above blending ratio, in the heating reaction step, the metal-containing raw material is reacted in a molten salt of lithium hydroxide and lithium chloride. I will let you. As a result, the aggregation of the primary particles of the product is suppressed. Hereinafter, although the manufacturing method of the lithium containing complex oxide powder of this invention using lithium chloride is demonstrated, only a different point from the manufacturing method of the lithium containing complex oxide powder which does not use lithium chloride already demonstrated is demonstrated. Matters not specifically mentioned are the same as those described above for the method for producing a lithium-containing composite oxide powder that does not use lithium chloride.

  The mixing ratio of lithium chloride contained in the reaction raw material is not particularly limited, but the atomic ratio of Li contained in lithium chloride to the metal element (Ni and Mn as required Me) contained in the metal-containing raw material is the target lithium. It is desirable that the stoichiometric ratio of Li to the metal element (excluding Li) of the manganese nickel-based oxide is 5 to 15 times, further 10 to 15 times. If it is 5 times or more, there is sufficient molten salt for dispersing the metal-containing raw material, and the aggregation of the product in the molten salt is suppressed. However, if it exceeds 15 times, the amount of the product is less than the amount of the molten salt raw material to be used, which is not desirable in terms of production efficiency.

  When lithium chloride is used, the reaction proceeds in the molten salt. Therefore, the metal-containing raw material, lithium hydroxide, and lithium chloride may contain coarse particles, and the sieving step as described above, the mixing step of uniformly mixing each raw material, and the like may be omitted.

  In the case of using lithium chloride, a drying step of drying at least lithium hydroxide is preferably performed prior to the heating reaction step. The drying step is mainly intended to dehydrate lithium hydroxide monohydrate, but even when anhydrous lithium hydroxide is used, when a highly hygroscopic compound is used as the metal-containing raw material. Is valid. The water present in the molten salt containing lithium hydroxide in the heating reaction step has a very high pH. When the heating reaction step is performed in the presence of water having a high pH, the water may come into contact with the crucible, and depending on the type of the crucible, there is a possibility that the components of the crucible may elute into the molten salt although the amount is small. In the drying process, water in the raw material mixture is removed, which leads to suppression of elution of the crucible components. In addition, by removing moisture from the raw material mixture in the drying step, it is possible to prevent water from boiling and the molten salt from being scattered in the single crystal growing step. If a vacuum dryer is used for a drying process, it is good to vacuum-dry at 80-150 degreeC for 2 to 24 hours.

  A heating reaction process is a process of heating the prepared reaction raw material at 900 degreeC or more. Since the melting point of lithium chloride is 613 ° C., a molten salt of lithium chloride can be obtained at 900 ° C. or higher. The heating reaction step may be performed at 900 ° C. or higher, further 930 ° C. or higher and 1300 ° C. or lower. If it is less than 900 ° C., reduction of nickel by molten lithium chloride may occur, which is not desirable. However, when the temperature exceeds 1300 ° C., lithium chloride evaporates and cannot take a molten salt form. The heating time in the heating reaction step is not particularly limited, but is preferably 30 minutes to 24 hours, and more preferably 5 to 14 hours.

  Although there is no particular limitation on the cooling rate after the heating reaction step, it is desirable to gradually cool from the reaction temperature to room temperature from the viewpoint of growing single crystal particles greatly. For example, the furnace may be cooled in the furnace used for the heating reaction step. Specifically, a slow cooling rate of 100 ° C./hour or less, further 50 ° C./hour or less is desirable. The lower limit of the cooling rate is not particularly limited, but a very slow cooling rate of, for example, less than 10 ° C./hour is not desirable because production efficiency is not good. After the cooling step, the molten salt of lithium chloride solidifies, so that a mixture of the synthesized lithium-containing composite oxide and the molten salt is obtained as a solid.

  In the case of using lithium chloride, a recovery step of recovering the produced target lithium manganese nickel-based oxide from the solid after cooling is necessary. Specifically, it may be a separation and recovery step in which the molten salt solidified in the cooling step is dissolved in a polar protic solvent, and the lithium-containing composite oxide produced in the single crystal growth step is separated from the solidified molten salt. . The polar protic solvent is employed in this step because it can dissolve the solidified molten salt (that is, lithium chloride). Specific examples of the polar protic solvent include pure water such as ion exchange water, alcohols such as ethanol, and the like. One of these may be used alone, or two or more may be used in combination. The solidified molten salt is easily dissolved in the polar protic solvent, and the lithium-containing composite oxide that is difficult to dissolve in the polar protic solvent remains undissolved in the solvent. Therefore, the molten salt and the lithium-containing composite oxide are easily separated. The method for recovering the lithium-containing composite oxide powder is not particularly limited, but it can be recovered by centrifuging or filtering the solution. The recovered lithium-containing composite oxide may be dried. After the collection step, the powdered lithium-containing composite oxide powder is obtained by lightly pulverizing as necessary.

<Secondary battery>
The lithium-containing composite oxide of the present invention can be used as a positive electrode active material for a secondary battery such as a non-aqueous electrolyte secondary battery, for example, a lithium ion secondary battery. Hereinafter, a non-aqueous electrolyte secondary battery using a positive electrode active material containing the composite oxide will be described. The non-aqueous electrolyte secondary battery mainly includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Moreover, the separator pinched | interposed between a positive electrode and a negative electrode is provided similarly to a general nonaqueous electrolyte secondary battery.

  The positive electrode includes a positive electrode active material capable of inserting / extracting lithium ions and a binder that binds the positive electrode active material. Further, a conductive aid may be included. The positive electrode active material is used for a general non-aqueous electrolyte secondary battery together with the composite oxide of the present invention, as long as the composite oxide of the present invention is used alone or without adversely affecting the effects obtained by the present invention. One or more other positive electrode active materials may be included.

  Further, the binder and the conductive additive are not particularly limited as long as they can be used in a general non-aqueous electrolyte secondary battery. The conductive aid is for ensuring the electrical conductivity of the electrode, and for example, a mixture of one or more carbon material powders such as carbon black, acetylene black, and graphite may be used. it can. The binder plays a role of connecting the positive electrode active material and the conductive additive, and includes, for example, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene. Can be used.

  The negative electrode opposed to the positive electrode can be formed by forming a sheet of metal lithium, which is a negative electrode active material, or by pressing the sheet into a current collector network such as nickel or stainless steel. A lithium alloy or a lithium compound can also be used in place of metallic lithium. Moreover, you may use the negative electrode which consists of a negative electrode active material and binder which can occlude / desorb lithium ion like a positive electrode. Examples of the negative electrode active material that can be used include a fired organic compound such as natural graphite, artificial graphite, and phenol resin, and a powdery carbon material such as coke. As the binder, as in the positive electrode, a fluorine-containing resin, a thermoplastic resin, or the like can be used.

  The positive electrode and the negative electrode generally have an active material layer formed by binding at least a positive electrode active material or a negative electrode active material with a binder attached to a current collector. Therefore, a positive electrode and a negative electrode are prepared by preparing an electrode mixture layer forming composition containing an active material, a binder, and, if necessary, a conductive additive, and further adding a suitable solvent to make a paste, After coating on the surface of the film, it can be dried and, if necessary, compressed to increase the electrode density.

  A metal mesh or metal foil can be used for the current collector. Examples of the current collector include a porous or non-porous conductive substrate made of a metal material such as stainless steel, titanium, nickel, aluminum, or copper, or a conductive resin. Examples of the porous conductive substrate include a mesh body, a net body, a punching sheet, a lath body, a porous body, a foamed body, a fiber group molded body such as a nonwoven fabric, and the like. Examples of the non-porous conductive substrate include a foil, a sheet, and a film. As a method for applying the composition for forming an electrode mixture layer, a conventionally known method such as a doctor blade or a bar coater may be used.

  As a solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

  As the nonaqueous electrolytic solution, a general organic solvent-based electrolytic solution in which an electrolyte is dissolved in an organic solvent may be used. By using the lithium-containing composite oxide powder of the present invention as the positive electrode active material, decomposition of a general electrolytic solution used in a non-aqueous electrolyte secondary battery is suppressed.

  In general, the organic solvent preferably contains a chain ester from the viewpoint of load characteristics. Examples of such chain esters include chain carbonates typified by dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and organic solvents such as ethyl acetate and methyl propionate. These chain esters may be used alone or in admixture of two or more. Particularly, for improving low-temperature characteristics, the above-mentioned chain esters occupy 50% by volume or more in the total organic solvent. In particular, it is preferable that the chain ester occupies 65% by volume or more of the total organic solvent.

  However, in order to improve the discharge capacity, it is preferable to use an organic solvent in which an ester having a high induction rate (induction rate: 30 or more) is mixed with the chain ester rather than the chain ester alone. Specific examples of such esters include, for example, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, ethylene glycol sulfite, and the like. A cyclic ester such as carbonate is preferred. Such an ester having a high dielectric constant is preferably contained in an amount of 10% by volume or more, particularly 20% by volume or more in the total organic solvent from the viewpoint of discharge capacity. Moreover, from the point of load characteristics, 40 volume% or less is preferable and 30 volume% or less is more preferable.

  Among the above, the electrolyte solution containing ethylene carbonate and ethyl methyl carbonate is widely used, and the use of the lithium-containing composite oxide powder of the present invention is also effective for such an electrolyte solution. .

As an electrolyte to be dissolved in an organic solvent, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 ( SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2) are used alone or in combination. Among these, LiPF ₆ and LiC ₄ F ₉ SO ₃ that can obtain good charge / discharge characteristics are preferably used.

The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm ³ , particularly about 0.4 to 1.5 mol / dm ³ .

  Moreover, in order to improve the safety | security and storage characteristic of a battery, you may make an non-aqueous electrolyte contain an aromatic compound. As the aromatic compound, benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.

  As the separator, a separator having sufficient strength and capable of holding a large amount of electrolyte solution is preferable. From such a viewpoint, the separator is made of polyolefin such as polypropylene, polyethylene, a copolymer of propylene and ethylene, with a thickness of 5 to 50 μm. A microporous film or non-woven fabric is preferably used. In particular, when a thin separator of 5 to 20 μm is used, the characteristics of the battery are likely to deteriorate during charge / discharge cycles, high-temperature storage, and the like, and the safety is also lowered. However, the above composite oxide was used as the positive electrode active material. Since the lithium ion secondary battery is excellent in stability and safety, the battery can function stably even if such a thin separator is used.

  The shape of the non-aqueous electrolyte secondary battery constituted by the above components can be various, such as a cylindrical type, a laminated type, and a coin type. In any case, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. Then, the positive electrode current collector and the negative electrode current collector are connected to the positive electrode terminal and the negative electrode terminal that communicate with the outside with a current collecting lead or the like, and the electrode body is impregnated with the electrolyte solution and sealed in the battery case. An electrolyte secondary battery is completed.

In addition, it is desirable that the cut-off voltage for charging when the secondary battery of the present invention is used is set to 4.3 V or higher, more preferably 4.8 V or higher on the basis of metallic lithium (based on Li / Li ⁺ ). By using the lithium-containing composite oxide powder of the present invention, it is possible to suppress the decomposition of the electrolytic solution that is likely to occur with charge / discharge of 4.3 V or higher. In particular, since the lithium-containing composite oxide powder of the present invention efficiently charges and discharges at around 4.8 V, it is preferable to set the charge cut-off voltage in the range of 4.8 to 5.0 V.

  The secondary battery using the lithium-containing composite oxide powder of the present invention described above can be suitably used not only in the field of communication devices such as mobile phones and personal computers, and information-related devices but also in the field of automobiles. For example, if this secondary battery is mounted on a vehicle, the secondary battery can be used as a power source for an electric vehicle.

  As mentioned above, although embodiment of the lithium containing complex oxide of this invention, its manufacturing method, and a secondary battery was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be specifically described with reference to examples of the lithium-containing composite oxide and the method for producing the same.

<Example 1: High-temperature synthesis of LiNi _0.5 Mn _1.5 O ₄ >
A raw material mixture was prepared by mixing 0.67 mol of anhydrous lithium hydroxide (LiOH, 25.6 g) and a precursor (100 g) as a metal compound raw material. Below, the synthesis | combining procedure of a precursor is demonstrated.

0.30 mol of Mn (NO ₃ ) ₂ .6H ₂ O (86.1 g) and 0.10 mol of Ni (NO ₃ ) ₂ .6H ₂ O (29.0 g) were dissolved in 500 mL of distilled water. Thus, an aqueous solution containing a metal salt was prepared. While stirring this aqueous solution with a stirrer in an ice bath, a solution obtained by dissolving 50 g (1.2 mol) of LiOH.H ₂ O in 300 mL of distilled water was dropped over 2 hours to make the aqueous solution alkaline. A metal hydroxide precipitate was deposited. The precipitation solution was aged for one day in an oxygen atmosphere while being kept at 5 ° C. The resulting precipitate was filtered and washed with distilled water to obtain a metal hydroxide containing Ni and Mn at Mn: Ni = 3: 1. This metal hydroxide was calcined at 500 ° C. for 2 hours to obtain a precursor made of a metal oxide.

The obtained precursor was confirmed to be composed of a mixed phase of Mn ₃ O ₄ and NiO by XRD measurement and emission spectroscopic analysis (ICP). Therefore, the total content of Ni and Mn in 100 g of this precursor is 1.28 mol. Therefore, the molar ratio of Li, Mn and Ni contained in the raw material mixture is Li: (Ni + Mn) = 1.05: 2, and the amount of Li is determined by the target LiNi _0.5 Mn _1.5 O ₄ Ni and It was 1.05 times the stoichiometric ratio of Li to Mn (Li: (Ni + Mn) = 1: 2).

Note that LiNi _0.5 Mn _1.5 O ₄ is a composition formula, Li _{1 + x} (Ni _0.5 Mn _1.5 ) _1-xy Me _y O ₄ (0 ≦ x ≦ _0.5, 0 ≦ y ≦ 0.5, (x + y) <1, Me is one or more of Al, Mg, Ca and Co), and corresponds to the case of x = 0 and y = 0.

  The raw material mixture obtained by the above procedure was placed in an alumina crucible and heated in the atmosphere for 6 hours in a muffle furnace heated to 600 ° C. to perform preliminary firing. Thereafter, it was gradually cooled to room temperature in a muffle furnace. The cooled powder was pulverized using a mortar and pestle.

  Next, the powder after the pre-baking was heated in the atmosphere for 6 hours in a muffle furnace heated to 1000 ° C. to perform main baking. Thereafter, it was gradually cooled to room temperature in a muffle furnace. Since it took 24 hours for the whole to reach room temperature (25 ° C.), the cooling rate was 40 ° C./hour. The cooled powder was pulverized using a mortar and pestle.

The obtained powder was subjected to emission spectroscopic analysis (ICP) and average valence analysis of Mn by oxidation-reduction titration. As a result, the composition was confirmed to be LiNi _0.5 Mn _1.5 O ₄ . Further, X-ray diffraction (XRD) measurement using CuKα rays was performed on the obtained powder. According to XRD, the obtained compound was found to have a spinel structure.

In addition, the valence evaluation of Mn was performed as follows. A sample of 0.05 g was placed in an Erlenmeyer flask, 40 mL of an aqueous sodium oxalate solution (1%) was accurately added, and 50 mL of H ₂ SO ₄ was further added to dissolve the sample in a 90 ° C. water bath in a nitrogen gas atmosphere. To this solution, an aqueous potassium permanganate solution (0.1 N) was titrated, and the reaction was performed until the end point (titer: V1) instead of a slight red color. In another flask, 20 mL of an aqueous sodium oxalate solution (1%) was accurately taken, and an aqueous potassium permanganate solution (0.1 N) was titrated to the end point in the same manner as described above (titration: V2). The consumption amount of oxalic acid when an expensive number of Mn was reduced to Mn ²⁺ was calculated as an oxygen amount (active oxygen amount) from V1 and V2 by the following formula.
Active oxygen amount (%) = {(2 × V2−V1) × 0.00080 / sample amount} × 100
In the above formula, the unit of V1 and V2 is mL, and the unit of the sample amount is g. And the average valence of Mn was computed from the amount of Mn in a sample (ICP measured value) and the amount of active oxygen.

<Comparative Example 1-1: Low-temperature synthesis of LiNi _0.5 Mn _1.5 O ₄ by solid phase method I>
Using the raw material mixture prepared in Example 1, LiNi _0.5 Mn _1.5 O ₄ was synthesized at a low temperature.

  The raw material mixture obtained by the above procedure was put into an alumina crucible and heated in the atmosphere for 12 hours in a muffle furnace heated to 700 ° C. to perform preliminary firing. Thereafter, it was gradually cooled to room temperature in a muffle furnace. The cooled powder was pulverized using a mortar and pestle.

  Next, the powder after the preliminary firing was heated in the atmosphere for 6 hours in a muffle furnace heated to 800 ° C. to perform the main firing. Thereafter, it was gradually cooled to room temperature in a muffle furnace. Since it took 24 hours for the whole to reach room temperature (25 ° C.), the cooling rate was 32 ° C./hour. The cooled powder was pulverized using a mortar and pestle.

The obtained powder was subjected to an average valence analysis of Mn by ICP and oxidation-reduction titration. As a result, the composition was confirmed to be LiNi _0.5 Mn _1.5 O ₄ . Further, XRD measurement using CuKα rays was performed on the obtained powder. According to XRD, the obtained compound was found to have a spinel structure.

<Comparative Example 1-2: Low-temperature synthesis of LiNi _0.5 Mn _1.5 O ₄ by solid phase method II>
Using the raw material mixture prepared in Example 1, LiNi _0.5 Mn _1.5 O ₄ was synthesized at a low temperature.

  The raw material mixture obtained by the above procedure was put in an alumina crucible and heated in the atmosphere for 6 hours in a muffle furnace heated to 700 ° C. to perform preliminary firing. Thereafter, it was gradually cooled to room temperature in a muffle furnace. The cooled powder was pulverized using a mortar and pestle.

  Next, the powder after the preliminary firing was heated in the atmosphere for 12 hours in a muffle furnace heated to 650 ° C. to perform the main firing. Thereafter, it was gradually cooled to room temperature in a muffle furnace. Since it took 24 hours for the whole to reach room temperature (25 ° C.), the cooling rate was 26 ° C./hour. The cooled powder was pulverized using a mortar and pestle.

The obtained powder was subjected to an average valence analysis of Mn by ICP and oxidation-reduction titration. As a result, the composition was confirmed to be LiNi _0.5 Mn _1.5 O ₄ . Further, XRD measurement using CuKα rays was performed on the obtained powder. According to XRD, the obtained compound was found to have a spinel structure.

<Example 2: Synthesis of LiNi _0.5 Mn _1.5 O ₄ by the molten salt method using LiCl>
A raw material mixture was prepared by mixing 0.67 mol of anhydrous lithium hydroxide (LiOH, 25.6 g) and a precursor (100 g) as a metal compound raw material. The same precursor as in Example 1 was used as the precursor. Therefore, the molar ratio of Li, Mn and Ni contained in the raw material mixture is Li: (Ni + Mn) = 1.05: 2, and the amount of Li is determined by the target LiNi _0.5 Mn _1.5 O ₄ Ni and It was 1.05 times the stoichiometric ratio of Li to Mn (Li: (Ni + Mn) = 1: 2).

To the above raw material mixture, 5.73 mol of lithium chloride (LiCl, 242.95 g) was added. The molar ratio of Li contained in LiCl and Mn and Ni contained in the raw material mixture is Li: (Ni + Mn) = 5: 1. The amount of Li is determined by the target LiNi _0.5 Mn _1.5 O ₄ Ni and It was 10 times the stoichiometric ratio of Li to Mn (Li: (Ni + Mn) = 1: 2).

  This LiCl-containing raw material mixture was put in an alumina crucible and vacuum-dried at 120 ° C. for 12 hours in a vacuum drying container. Thereafter, the dryer was returned to atmospheric pressure, the crucible containing the raw material mixture was taken out, immediately transferred to a 900 ° C. muffle furnace, and heated in the atmosphere at 900 ° C. for 3 hours. At this time, the raw material mixture in the crucible melted into a molten salt, and a black product was precipitated.

  Thereafter, the crucible containing the molten salt was cooled to room temperature in the furnace, and the crucible was taken out from the electric furnace. Since it took 24 hours for the molten salt to solidify to room temperature (25 ° C.), the cooling rate was 36 ° C./hour. After the molten salt was sufficiently cooled and solidified, the crucible was immersed in 200 mL of ion exchange water and stirred to dissolve the solidified molten salt in water. Since the product was insoluble in water, the water became a black suspension. Filtration of the black suspension yielded a clear filtrate and a black solid residue on the filter paper.

  The obtained filtrate was further filtered while thoroughly washing with acetone. The washed black solid was held in a constant temperature bath at 120 ° C. for 12 hours or more and then pulverized using a mortar and pestle to obtain a black powder.

The obtained powder was subjected to an average valence analysis of Mn by ICP and oxidation-reduction titration. As a result, the composition was confirmed to be LiNi _0.5 Mn _1.5 O ₄ . Further, XRD measurement was performed on the obtained powder using CuKα rays. According to XRD, the obtained compound was found to have a spinel structure.

<Comparative Example 2: Synthesis of LiNi _0.5 Mn _1.5 O ₄ by the molten salt method using NaCl>
LiNi _0.5 Mn _1.5 O ₄ was synthesized in the same manner as in Example 2 except that sodium chloride was used without using lithium chloride and the synthesis temperature was changed.

  Specifically, a raw material mixture is prepared by mixing 0.67 mol of anhydrous lithium hydroxide (LiOH, 25.6 g) and a precursor (100 g) as a metal compound raw material, and further, 5.73 mol of chloride. Sodium (NaCl, 335 g) was added. This NaCl-containing raw material mixture was put in an alumina crucible and heated at 1000 ° C. for 12 hours. Other procedures were the same as in Example 2.

The obtained powder was subjected to an average valence analysis of Mn by ICP and oxidation-reduction titration. As a result, the composition was confirmed to be LiNi _0.5 Mn _1.5 O ₄ . Further, XRD measurement using CuKα rays was performed on the obtained powder. According to XRD, the obtained compound was found to have a spinel structure.

<Observation of particles>
The lithium-containing composite oxide powders of Examples and Comparative Examples synthesized by the above procedure were observed using a scanning electron microscope (SEM). The observation results of each lithium-containing composite oxide powder are shown in FIGS.

In Example 1 (FIG. 1), Comparative Example 1-1 (FIG. 2), Example 2 (FIG. 4), and Comparative Example 2 (FIG. 5), characteristic faces and ridges are seen in the single crystal particles. It was found to contain single crystalline primary particles. Moreover, the maximum primary particle diameter was measured from the image of a plurality of particles obtained by SEM observation (in Comparative Example 1-2, TEM observation), and the average primary particle diameter was calculated. The results were as follows.
Example 1: 8 μm
Comparative Example 1-1: 950 nm
Comparative Example 1-2: 80 nm (secondary particles are polycrystalline particles)
Example 2: 1.3 μm
Comparative Example 2: 620 nm

<Measurement of specific surface area>
Using the BET method (adsorbate: nitrogen) by low temperature and low humidity physical adsorption, the specific surface area of the lithium-containing composite oxide powder of each example was measured. The results were as follows.
Example 1: 0.61 m ² / g
Comparative Example 1-1: 1.28 m ² / g
Comparative Example 1-2: 3.23 m ² / g
Example 2: 0.79 m ² / g
Comparative Example 2: 1.59 m ² / g

<Electron diffraction>
The lithium-containing composite oxide powders of Examples 1 and 2 were observed with a transmission electron microscope (TEM), subjected to limited field electron diffraction under conditions of an acceleration voltage of 200 kV, and single crystals were identified and evaluated. In the limited-field electron diffraction pattern in which one entire particle was placed in the limited field, regular diffraction points indicating the characteristics of single crystals were observed regardless of which particle was observed. In addition, diffraction patterns obtained from different positions in the same plane in one particle were observed as diffraction spots having the same plane index. Therefore, it was found that the primary particles are single crystal particles having no grain boundaries.

  On the other hand, when the same TEM observation was performed with respect to Comparative Example 1-2, the limited-field electron diffraction pattern in which one entire particle was placed in the limited field was an irregular diffraction pattern showing the characteristics of polycrystal. Therefore, it was found that Comparative Example 1-2 was composed of single particles of polycrystalline particles.

<Charge / discharge test>
Three types of secondary batteries were produced using the lithium-containing composite oxide powders of Example 1, Comparative Examples 1-1 and 1-2 synthesized by the above procedure as positive electrode active materials, respectively.

  Any of the composite oxides, acetylene black as a conductive additive, and polytetrafluoroethylene (PTFE) as a binder were mixed at a mass ratio of 50:40:10. Subsequently, this mixture was crimped | bonded to the aluminum mesh which is a collector. Then, it vacuum-dried at 120 degreeC for 12 hours or more, and was set as the electrode (positive electrode: (phi) 12mm). The negative electrode facing the positive electrode was metallic lithium (φ14 mm, thickness 30 μm).

A microporous polyethylene film having a thickness of 20 μm was sandwiched between the positive electrode and the negative electrode as a separator to obtain an electrode body battery. This electrode body battery was accommodated in a battery case (CR2032 coin cell manufactured by Hosen Co., Ltd.). In addition, a non-aqueous electrolyte solution in which LiPF ₆ is dissolved at a concentration of 1.0 mol / L is injected into a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2 into the battery case, and lithium ions are added. A secondary battery was obtained.

  A charge / discharge test was conducted at room temperature (25 ° C.) using the produced secondary battery. Charging was performed at a constant current of up to 5.0 V at a rate of 0.2 C, and then charged at a constant voltage up to a current value of 0.02 C. The discharge was performed at a rate of 0.2 C up to 3.5V. The charge / discharge curve at the fifth cycle of each secondary battery is shown in FIG. Moreover, the change of the discharge capacity from the first to the 50th cycle is shown in FIG.

<Evaluation results>
1 to 3 are SEM images of LiNi _0.5 Mn _1.5 O ₄ powders having different temperatures for main firing. The firing temperature was 1000 ° C. in FIG. 1 (Example 1), 800 ° C. in FIG. 2 (Comparative Example 1-1), and 650 ° C. in FIG. 3 (Comparative Example 1-2). In Comparative Example 1-2, in which the main firing was performed at a very low temperature, a powder containing coarse particles was synthesized. This particle is a polycrystalline secondary particle composed of very fine single crystal particles. there were. In Comparative Example 1-1 in which the main baking was performed at a temperature higher than that of Comparative Example 1-2, a plurality of fine single crystal primary particles gathered to form secondary particles. It is difficult to determine whether the secondary particles are aggregates of single crystals or coarse particles in which the single crystals are sinter-bonded, but the average particle size of the primary particles constituting the secondary particles is less than 1 μm. It was fine particles. In Example 1 where the main calcination was performed at a higher temperature, a powder composed of single crystal primary particles having a particle size of about 1.2 to 9.5 μm was obtained.

In addition, as shown in FIG. 6, the secondary batteries using the LiNi _0.5 Mn _1.5 O ₄ powders obtained in Example 1 and Comparative Examples 1-1 and 1-2 as positive electrode active materials are all based on Li. Thus, it was confirmed that charging / discharging was efficiently performed at around 4.8V. However, it was found that there was a difference in discharge capacity and its stability due to the difference in particle structure observed by SEM.

From FIG. 6 and FIG. 7, the discharge capacity per second to seventh cycles of the secondary battery using the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Comparative Examples 1-1 and 1-2 is large. There was no difference. However, in terms of cycle characteristics, the secondary battery using the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Comparative Example 1-1 was superior. This is because the powder synthesized in Comparative Example 1-2 contains polycrystalline particles, and the crystal grain boundaries constituting the polycrystalline particles cause the breakdown of the particles accompanying charge and discharge and the decomposition of the electrolyte. This is probably because Since Comparative Example 1-1 is excellent in cycle characteristics, the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Comparative Example 1-1 is an aggregate of single crystal fine particles, and the crystal grain boundaries are It is estimated that there were few impurities. The reason why a high discharge capacity could not be obtained even though the cycle characteristics were good was considered to be that the composition of the NiNi _0.5 Mn _1.5 O ₄ was greatly deviated due to the desorption of oxygen during the synthesis. Furthermore, after 50 cycles, the secondary battery using the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Comparative Example 1-2 was swollen, and this was presumed to be due to the gas generated by charging and discharging. Is done. On the other hand, the secondary battery using the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Example 1 was excellent in cycle characteristics and exhibited a high discharge capacity from the first to the 50th cycle. This is because the primary particles are relatively large single crystal particles, so that there are few crystal grain boundaries that cause deterioration in cycle characteristics and the specific surface area is small. That is, it was found that by using the lithium-containing composite oxide powder of the present invention, a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics can be obtained.

  Note that the solid phase method described in Patent Document 2 uses LiOH as in Comparative Example 1-1, and is fired at the same temperature. Therefore, according to the solid phase method described in Patent Document 2, it is presumed that the fine single crystal fine particle aggregate shown in FIG. 2 can be obtained.

4 and 5 are LiNi _0.5 Mn _1.5 O ₄ powders obtained by the molten salt method using LiCl or NaCl as a flux. The LiNi _0.5 Mn _1.5 O ₄ powder obtained in Example 2 using LiCl was a powder composed of single crystal primary particles having a particle diameter of about 1 to 5 μm. Therefore, the secondary battery including the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Example 2 as the positive electrode active material is also estimated to have excellent cycle characteristics as in Example 1. In addition, in the LiNi _0.5 Mn _1.5 O ₄ powder of Example 1, a portion where single crystal particles are directly adjacent to each other in FIG. 1 was partially observed, but in Example 2, most of the single crystal particles were observed. Were independent single particles. That is, it was found that single crystal particles can be obtained as single particles by using LiCl as a flux. On the other hand, the LiNi _0.5 Mn _1.5 O ₄ powder obtained in Comparative Example 2 using NaCl contained secondary particles composed of very fine particles of less than 1 μm. That is, it can be said that even if NaCl is used as the flux, there is no effect of suppressing the aggregation of the single crystal particles, the primary particles become fine, and the desired LiNi _0.5 Mn _1.5 O ₄ powder cannot be obtained.

Claims (14)

  Including primary particles of a single crystal comprising at least lithium, manganese and nickel and having a crystal structure belonging to a spinel structure and having an average primary particle size of 1 μm to 50 μm. There is a lithium-containing composite oxide powder. ^2. The lithium-containing composite oxide powder according to claim 1, wherein the specific surface area is 0.01 m ² / g or more and 2.0 m ² / g or less. The lithium manganese nickel-based oxide is Li _{1 + x} (Ni _0.5 Mn _1.5 ) _1-xy Me _y O ₄ (0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, (x + y) The lithium-containing composite oxide powder according to claim 1 or 2, wherein <1, Me is one or more of Al, Mg, Ca and Co).   A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the lithium-containing composite oxide powder according to claim 1.   A nonaqueous electrolyte secondary battery comprising at least a positive electrode including the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 4, a negative electrode, and a nonaqueous electrolyte.   The nonaqueous electrolyte secondary battery according to claim 5, wherein the battery is charged up to 4.3 V or more based on metallic lithium.   A vehicle comprising the non-aqueous electrolyte secondary battery according to claim 5. A method for producing a lithium-containing composite oxide powder according to any one of claims 1 to 3,
A metal-containing raw material containing at least manganese and nickel and a lithium hydroxide, wherein an atomic ratio of lithium contained in the lithium hydroxide to a metal element contained in the metal-containing raw material is a metal of the lithium manganese nickel-based oxide A lithium-containing composite oxidation comprising a heating reaction step of heating a reaction raw material prepared so as to be more than 1.0 times and less than 1.1 times the stoichiometric ratio of lithium to an element at 900 ° C. or more A method for producing powder.   The lithium-containing composite oxide powder according to claim 8, further comprising a metal-containing raw material synthesis step in which an aqueous solution containing at least manganese ions and nickel ions is made alkaline before the heating reaction step to obtain the metal-containing raw material as a precipitate. Production method.   The method for producing a lithium-containing composite oxide powder according to claim 8 or 9, wherein the heating reaction step is a step of heating the reaction raw material at 930 ° C or higher and 1300 ° C or lower.   In the heating reaction step, the metal-containing raw material and the lithium hydroxide have an atomic ratio of lithium contained in the lithium hydroxide with respect to a metal element contained in the metal-containing raw material. 11. The method for producing a lithium-containing composite oxide powder according to claim 8, 9 or 10, wherein the lithium-containing composite oxide powder is prepared in such a manner that the stoichiometric ratio of lithium to the metal element is 1.05 to 1.1 times. In the manufacturing method of the lithium containing complex oxide powder in any one of Claims 8-11,
The heating reaction step is a step in which lithium chloride is further added to the reaction raw material, and the metal-containing raw material is reacted in a molten salt of lithium hydroxide and lithium chloride,
Furthermore, a cooling step for cooling the molten salt after the heating reaction step, and a recovery step for recovering the generated lithium manganese nickel-based oxide from the solid after cooling, containing lithium A method for producing a composite oxide powder.   The atomic ratio of lithium contained in lithium chloride to the metal element contained in the metal-containing raw material is not less than 5 times and not more than 15 times the stoichiometric ratio of lithium to the metal element of the lithium manganese nickel-based oxide. 12. The method for producing a lithium-containing composite oxide powder according to 12.   A lithium-containing composite oxide powder obtained by the method according to claim 8.