JP2007238437A - Method for producing lithium nickel manganese complex oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a lithium nickel manganese complex oxide which exhibits good cell characteristics when used as an active substance for a positive electrode of a lithium secondary cell. <P>SOLUTION: When a mixture including a nickel source, a manganese source, and a lithium source is fired to form a lithium nickel manganese complex oxide, one obtained by spray drying a slurry containing at least a nickel source and a manganese source and having a solid substance with an average particle diameter of not more than 2 μm, is used. The lithium source may be mixed into the slurry or may be added to the spray-dried product. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a lithium nickel manganese composite oxide and a secondary battery using the lithium nickel manganese composite oxide obtained by this production method.

As a positive electrode active material for a lithium secondary battery, a lithium transition metal composite oxide is considered promising. In particular, it is known that a high-performance battery can be obtained by using a compound whose transition metal is cobalt, nickel or manganese, that is, lithium cobalt oxide, lithium nickel oxide, or lithium manganese oxide as a positive electrode active material. Yes. Furthermore, in order to stabilize lithium transition metal composite oxides, increase battery capacity, improve safety, and improve battery characteristics at high temperatures, some transition metals may be replaced with other metal elements (hereinafter referred to as such transition elements). It is also known to use a lithium transition metal composite oxide in which a metal element for metal replacement is sometimes referred to as a “substitution metal element”. For example, in the case of spinel type lithium manganese oxide LiMn ₂ O ₄ which is one kind of lithium transition metal composite oxide, the Mn valence is formally 3.5, and both trivalent and tetravalent are mixed in half. In this state, by substituting a part of Mn with another transition metal having a valence smaller than this Mn valence, the Mn trivalence having a yarn teller distortion is reduced, and the crystal structure is stabilized, and finally the battery Characteristics can be improved.

Further, since cobalt is rare and expensive, it is conceivable to introduce a substitution metal element in order to reduce the production cost of lithium cobalt oxide. For example, a lithium cobalt composite oxide such as LiCo _1-x Ni _x O ₂ (0 <x <1) is conceivable. In order to reduce the ratio of expensive Co, x is increased and the performance as a positive electrode active material is improved. Research has been done.
Similarly, when Ni and Mn are compared, since Ni is more expensive, a lithium nickel composite oxide such as LiNi _1-x Mn _x O ₂ (0 <x <1) is also conceivable. Such a lithium nickel manganese composite oxide containing nickel and manganese has remarkable points in terms of battery performance and is a very promising material. However, Solid State Ionics 311-318 (1992) and J. Org. Mater. Chem. 1149-1155 (1996) and J.A. Power Sources 629-633 (1997); In Power Sources 46-53 (1998), the synthesizable range is 0 ≦ x ≦ 0.5, and when x becomes larger than that, a single phase cannot be obtained.

  On the other hand, at the 41st Battery Discussion 2D20 (2000), a single phase with high crystallinity having a layered structure of Ni: Mn = 1: 1 corresponding to x = 0.5 was synthesized by a coprecipitation method. There is a report. According to this, in this lithium nickel manganese composite oxide, nickel and manganese are uniformly present in a single-phase crystal. And in order to make nickel and manganese exist uniformly, it is necessary to disperse | distribute the nickel compound and manganese compound of a raw material uniformly on an atomic level, For that purpose, the coprecipitation method is considered preferable.

However, the coprecipitation method is limited in raw materials and is not necessarily suitable for implementation on an industrial scale. In addition, when the coprecipitate is used as a raw material, the resulting composite oxide becomes irregularly shaped particles, so that there is a problem that the powder packing density when forming the positive electrode is reduced. Further, in order to uniformly react nickel and manganese at an atomic level, both are preferably divalent ions, but divalent manganese is easily oxidized in an aqueous solution and easily becomes trivalent. In order to prevent oxidation, treatment such as removal of dissolved oxygen is necessary, and the operation is complicated. Therefore, the present invention intends to provide a method for producing a lithium nickel manganese composite oxide without using the coprecipitation method.

  According to the present invention, in a method for producing a lithium nickel manganese composite oxide by firing a mixture containing a nickel source, a manganese source and a lithium source, a slurry containing at least the nickel source and the manganese source, By using a product obtained by spray-drying a solid having an average particle size of 2 μm or less, a good single-phase product can be easily produced.

In the present invention, a nickel source and a manganese source are obtained by spray-drying a slurry containing both. The lithium source may be contained in the slurry, or may be added later to the mixture of nickel source and manganese source obtained by spray drying.
As the lithium source, various lithium compounds such as Li ₂ CO ₃ , LiNO ₃ , LiOH, LiOH · H ₂ O, organolithium compounds such as alkyl lithium and lithium acetate, lithium halides such as LiCl and LiI, etc. are used. be able to. Of these, Li ₂ CO ₃ , LiNO ₃ , LiOH · H ₂ O, lithium acetate, and the like are preferably used. The most preferred lithium source is usually LiOH.H ₂ O. This easily reacts with a nickel source and a manganese source upon firing to give a lithium nickel manganese composite oxide.

Various nickel compounds can also be used as the nickel source. Some examples are Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O. Organic nickel compounds such as fatty acid nickel and nickel oxalate, and nickel halides. Preferably, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O, etc. that do not generate harmful substances such as NOx and SOx during firing Use. Of these, Ni (OH) ₂ , NiO, NiOOH, and the like are preferably used because they are available as industrial raw materials at low cost and are easily wet pulverized.

As a manganese source, Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , MnOOH, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , an organic manganese compound, manganese hydroxide, manganese halide, etc. should be used. Can do. Among these manganese sources, Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ are preferable because they have a valence close to the manganese oxidation number of the composite oxide that is the final target product. Further, Mn ₂ O ₃ is particularly preferable because it is available as an industrial raw material at a low cost and is easy to wet pulverize.

  In the present invention, another metal source can be further contained in the slurry, whereby these metals can be contained in the lithium nickel manganese composite oxide finally obtained. Examples of such metal elements include aluminum, cobalt, iron, magnesium, and calcium. Among these, aluminum, cobalt, and magnesium are preferable, and aluminum and cobalt are more preferable. Aluminum, cobalt, and magnesium have the advantage that they can be easily dissolved in a lithium nickel manganese composite oxide to obtain a single phase, and aluminum and cobalt can be used as a lithium secondary battery. When used as a positive electrode active material, there is an advantage that high performance battery characteristics, in particular, good performance with respect to the discharge capacity retention rate when repeatedly charged and discharged. A plurality of these metal elements may be contained in the composite oxide.

These metal element sources include oxyhydroxides, oxides, hydroxides, halides, inorganic acid salts such as carbonates, nitrates and sulfates, and organic acid salts such as acetates and oxalates. Can be mentioned.
Various aluminum compounds such as AlOOH, Al ₂ O ₃ , Al (OH) ₃ , AlCl ₃ , Al (NO ₃ ) ₃ .9H ₂ O, organoaluminum compounds and Al ₂ (SO ₄ ) ₃ are used as the aluminum source. Can be mentioned. Preferably, AlOOH, Al ₂ O ₃ or Al (OH) ₃ is used. AlOOH is most preferably used because it can be obtained industrially at low cost and has high reactivity.

Cobalt sources include Co (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , organic cobalt compounds such as cobalt acetate, CoCl ₂ , Co (NO ₃ ) ₂ .6H ₂ O, and Co (SO ₄ ) · 7H ₂ various cobalt compounds of O, and the like. Preferably Co (O
H) ₂ , CoO, Co ₂ O ₃ , or Co ₃ O ₄ is used. It is most preferable to use Co (OH) ₂ because it can be obtained industrially at low cost and has high reactivity.

Examples of iron sources include FeO (OH), Fe ₂ O ₃ , Fe ₃ O ₄ , FeCl ₂ , FeCl ₃ , Fe (NO ₃ ) ₃ · 9H ₂ O, iron oxalate and other organic iron compounds, FeSO ₄ · 7H Examples include various iron compounds such as ₂ O and Fe ₂ (SO ₄ ) ₃ .nH ₂ O. Among them, it is preferable to use FeO (OH), Fe ₂ O ₃ or Fe ₃ O ₄ , and most preferable is FeO (OH) and Fe ₂ O in that they are industrially available at low cost and have high reactivity. ₃ .

Examples of magnesium sources include organic magnesium compounds such as Mg (OH) ₂ , MgO, magnesium oxalate, and magnesium acetate, and various magnesium compounds such as MgCl ₂ , Mg (NO ₃ ) ₂ .6H ₂ O, and MgSO _4. be able to. Of these, Mg (OH) ₂ or MgO, particularly Mg (OH) ₂ is preferably used.
The calcium _{source, Ca (OH) 2, CaO} , organic calcium compounds such as calcium and calcium oxalate _{acid, CaCO 3, CaC 2, CaCl} 2, CaWO 4, Ca (NO 3) 2 · 4H 2 O, and CaSO ₄ · 2H ₂ various calcium compounds of O, and the like. Of these, Ca (OH) ₂ , CaO or CaCO ₃ is preferably used. Most preferred is Ca (OH) ₂ which is industrially available at low cost and has high reactivity.

The atomic ratio of lithium, nickel, manganese, and substituted metal elements such as aluminum and cobalt used as necessary in preparing the slurry is appropriately adjusted according to the composition of the target lithium nickel manganese composite oxide. For example, the atomic ratio (Ni / Mn) of nickel and manganese is adjusted in the range of 0.7 ≦ Ni / Mn ≦ 9 according to the desired composition of the composite oxide. The ratio of the total number of substituted metal elements such as aluminum to the total number of atoms of nickel and manganese (substituted metal element / Ni + Mn) is in the range of 0 to 1.0 depending on the desired composition of the composite oxide. Adjust the ratio. Note that lithium does not necessarily need to be contained in the slurry. The lithium source is mixed with a powder obtained by spray-drying a slurry containing a substitution metal element such as nickel, manganese, and aluminum, and fired. Even in this case, a composite oxide having a desired composition can be obtained. That is, unlike substituted metal elements such as nickel, manganese, and aluminum, lithium is likely to move during the solid-phase reaction of firing, and thus does not need to be uniformly mixed with other elements in advance. In addition, since lithium is easily volatilized during firing, it is preferably used in a larger amount than the desired composition for the composite oxide. Further, when the lithium source is mixed with the slurry obtained by spray-drying the slurry containing the nickel source and the manganese source, the lithium source is preferably mixed as a fine powder having a maximum particle size of 100 μm or less, particularly 50 μm or less. . However, considering the relationship between the cost of making fine powder and the effect of using fine powder, the average particle size of fine powder is usually measured by the same method as the average particle size of solid content in the slurry to 0.1 μm. In many cases, it is sufficient to have an average particle size of up to 0.5 μm.

As the dispersion medium used in the slurry, various organic solvents and aqueous solvents can be used, but water is preferred.
The total weight ratio of raw materials such as a lithium source, a nickel source, and a manganese source to the weight of the entire slurry is usually 10% by weight or more, preferably 12.5% by weight or more. When the slurry concentration is dilute, the particles obtained by spray drying may be reduced in size, or voids may be generated inside the particles and easily broken. On the other hand, if the concentration is too high, it becomes difficult to maintain the uniformity of the slurry. Therefore, the slurry concentration is preferably 50% by weight or less, and particularly preferably 35% by weight or less.

  The average particle size of the solids in the slurry must be 2 μm or less. The average particle size is preferably 1 μm or less, and more preferably 0.5 μm or less. If the average particle size of the solids in the slurry is too large, not only will the reactivity in the firing step be reduced, but the sphericity of the granulated product obtained by spray drying will be reduced, and the composite oxide finally obtained will be reduced. The powder packing density tends to be low. This tendency is particularly remarkable when a granulated product having an average particle diameter of 50 μm or less is to be produced. However, it is not necessary to reduce the average particle size of the solid material to 0.01 μm or less because reducing the particle size of the solid material in the slurry more than necessary increases the cost. Considering the cost of grinding and the advantages obtained by grinding, it is preferred that the grinding should be such that the average particle size does not fall below 0.05 μm, in particular 0.1 μm.

  In the present invention, when preparing a slurry by mixing a lithium source, a nickel source, a manganese source and the like in a dispersion medium, it is preferable to perform wet pulverization by vigorously stirring using a medium stirring type pulverizer or the like. . Thereby, the uniformity of the metal element in a slurry can be improved, and the reactivity in a baking process can be improved. Examples of wet pulverizers used for wet pulverization include homogenizers, homomixers and the like mainly for the purpose of dispersion crushing, beads mills, ball mills, vibration mills and the like mainly for the purpose of pulverization, etc. Since the latter pulverizer has a very high pulverization efficiency of the slurry solid content, it is preferable to use the pulverizer to pulverize the solid content in the slurry to a desired small particle size. Particularly preferred is wet grinding with a bead mill.

  In the present invention, the average particle size of the solid content in the slurry, the average particle size of the granulated product obtained by spray drying, and the average particle size of the lithium nickel manganese composite oxide are all known laser diffraction. / Measured with a scattering type particle size distribution analyzer. The measurement principle of this method is as follows. That is, a slurry or powder dispersed in a dispersion medium is irradiated with laser light, and scattered light that is incident on the particles and scattered (diffracted) is detected by a detector. The scattering angle θ (angle between the incident direction and the scattering direction) of the detected scattered light is forward scattering (0 <θ <90 °) for large particles, and side scattering or backscattering (90 for small particles). ° <θ <180 °). From the measured angular distribution value, the particle size distribution is calculated using information such as the incident light wavelength and the refractive index of the particles. Further, the average particle size is calculated from the obtained particle size distribution. As a dispersion medium used in the measurement, for example, a 0.1% by weight sodium hexametaphosphate aqueous solution is used.

Further, the viscosity of the slurry is usually 50 mPa · s or more. It is preferably 100 mPa · s or more, particularly 200 mPa · s or more. When the viscosity is not more than the above range, a large burden is imposed on the spray drying, or the granulated product obtained by the spray drying becomes small or easily damaged. On the other hand, if the viscosity is too large, it becomes difficult to transport the slurry by the pump. Therefore, the viscosity should usually be 3000 mPa · s or less. It is preferably 2000 mPa · s or less, particularly 1600 mPa · s or less. The viscosity of the slurry is measured using a known BM type viscometer. The BM viscometer is a measurement method that employs a method of rotating a predetermined metal rotor in the room temperature atmosphere. The viscosity of the slurry is calculated from the resistance force (twisting force) applied to the rotating shaft when the rotor is rotated with the rotor immersed in the slurry. However, the room temperature atmosphere means a normal laboratory environment at a temperature of 10 ° C. to 35 ° C. and a relative humidity of 20% RH to 80% RH.

  Spray drying may be performed by a conventional method. For example, it is possible to use a method in which a gas flow and slurry are caused to flow into the tip of the nozzle so that the slurry is ejected as droplets from the nozzle and brought into contact with a drying gas to quickly dry the droplets. As the dry gas, air, nitrogen, or the like can be used, but air is usually used. These are preferably used under pressure. The gas flow from the nozzle is ejected at a gas linear velocity of usually 100 m / s or more, preferably 200 m / s or more, more preferably 300 m / s or more. If the gas linear velocity is too low, it is difficult to form appropriate droplets. However, since it is difficult to obtain a linear velocity that is too high, the normal injection speed is 1000 m / s or less. The shape of the nozzle is not particularly limited as long as it can eject minute droplets, and a conventionally known one, for example, a nozzle described in Japanese Patent No. 2797080 can also be used. The droplets are preferably sprayed in an annular shape from the viewpoint of improving productivity.

  The drying gas is preferably introduced in a down flow from the upper part to the lower part. By adopting such a structure, the throughput per unit volume of the tower can be greatly improved. In addition, when spraying droplets in a substantially horizontal direction, it is possible to greatly reduce the diameter of the drying tower by suppressing the droplets sprayed in the horizontal direction with a downflow gas, which makes it possible to produce granulated materials at low cost and in large quantities. Can be manufactured. The drying gas temperature is usually 50 ° C. or higher, preferably 70 ° C. or higher, and usually 120 ° C. or lower, preferably 100 ° C. or lower. If the temperature is too high, the resulting granulated particles have a lot of hollow structure, and the powder packing density tends to decrease. On the other hand, if the temperature is too low, problems such as powder sticking and blockage due to condensation may occur. There is sex.

  The spray drying is preferably performed so that the average particle diameter of the granulated product is 50 μm or less, particularly 30 μm or less. However, since it is difficult to produce a granulated product having a too small particle size, the average particle size is usually 4 μm or more, preferably 5 μm or more. The particle diameter of the granulated product can be controlled by appropriately selecting the spray format, pressurized gas flow supply rate, slurry supply rate, drying temperature, and the like.

The granulated product is calcined as it is or after being mixed with a powdered lithium source to obtain a target lithium nickel manganese composite oxide. What is necessary is just to perform mixing with a lithium source using a usual mixing apparatus. In mixing, it is preferable that the granulated material is not crushed, that is, the granulated material substantially retains its shape.
The firing temperature varies depending on the kind of lithium source, nickel source, manganese source and the like used as raw materials and the atomic ratio, but is usually 700 ° C. or higher, preferably 750 ° C. or higher, more preferably 800 ° C. or higher. The temperature is usually 1050 ° C or lower, preferably 950 ° C or lower. If the temperature is too low, a long firing time is required to obtain a lithium nickel manganese composite oxide with good crystallinity. On the other hand, if the temperature is too high, a crystal phase other than the target lithium nickel manganese composite oxide is generated, or a lithium nickel manganese composite oxide with many defects is generated. A lithium secondary battery using such a lithium nickel manganese composite oxide as a positive electrode active material may have a reduced battery capacity or a deterioration due to a collapse of a crystal structure due to charge / discharge.

Although the firing time varies depending on the temperature, it is usually 30 minutes or more and 50 hours or less in the above-mentioned temperature range. If the firing time is too short, it is difficult to obtain a layered lithium nickel manganese composite oxide with good crystallinity.
In order to obtain a lithium nickel manganese composite oxide with few crystal defects, it is preferable to cool slowly after firing, for example, to cool slowly at a cooling rate of 5 ° C./min or less.

The atmosphere during firing is usually an oxygen-containing gas such as air.
As the baking apparatus, a conventional apparatus may be used. For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, or the like can be used.
The lithium nickel manganese composite oxide produced in the present invention is represented by the following general formula (I) and has a layered structure.

  In the formula (I), X represents a number in the range of 0 <X ≦ 1.2, preferably 0 <X ≦ 1.1. If X is too large, the crystal structure may become unstable, or the battery capacity of a lithium secondary battery using this may be reduced. Y and Z represent numbers in the range of 0.5 ≦ Y + Z ≦ 1 and 0.7 ≦ Y / Z ≦ 9. When the proportion of manganese becomes relatively large, it becomes difficult to synthesize a single-phase lithium nickel manganese composite oxide.

  Note that the atomic ratio (Y / Z) of nickel and manganese greatly affects the characteristics of the composite oxide as a positive electrode active material. For example, when it is desired to increase the amount of manganese to be inexpensive and have a high discharge voltage, it is preferable that 0.8 ≦ Y / Z ≦ 1.2, particularly 0.9 ≦ Y / Z ≦ 1.1. On the contrary, even if the amount of nickel is large and the cost is high, it is preferable to satisfy 1 ≦ Y / Z ≦ 7, particularly 1.5 ≦ Y / Z ≦ 5 when a battery having a large capacity is desired. Further, the total of nickel and manganese, that is, Y + Z is preferably Y + Z ≧ 0.65, and more preferably Y + Z ≧ 0.75. When Y + Z is small, the capacity of a battery using this as a positive electrode active material may be greatly reduced.

Q represents at least one selected from the group consisting of Al, Co, Fe, Mg, and Ca. Among these, Al, Co, and Mg are preferable, and Al and Co are more preferable. Al, Co, and Mg can easily form a solid solution with LiNi _1-x Mn _x O ₂ (0.7 ≦ Ni / Mn ≦ 9) to form a single-phase lithium nickel manganese composite oxide. it can. Furthermore, with regard to Al and Co, the lithium secondary battery using the obtained lithium nickel manganese composite oxide as the positive electrode active material has high performance battery characteristics, particularly good discharge capacity maintenance rate when repeatedly charged and discharged. Show performance. In the composition of the general formula (I), the amount of oxygen may have some non-stoichiometry.

The obtained lithium nickel manganese composite oxide has an average primary particle size of usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.1 μm or more, and usually 30 μm or less, preferably 5 μm or less. More preferably, it is 2 μm or less. The average secondary particle size is usually 1 μm or more, preferably 4 μm or more, and is usually 50 μm or less, preferably 40 μm or less. Further, the lithium nickel manganese composite oxide has a specific surface area by the BET method of 0.1 m ² / g or more and 8.0 m ² / g or less, preferably 0.2 m ² / g or more and 6.0 m ² / g or less. It is. The size of the primary particles can be controlled by the firing temperature, firing time, etc., and the particle diameter of the primary particles can be increased by increasing the firing temperature or increasing the firing time. . The particle diameter of the secondary particles can be controlled by, for example, spraying conditions such as a gas-liquid ratio in the spray drying process. The specific surface area can be controlled by the primary particle size and the secondary particle size, and decreases by increasing the primary particle size and / or the secondary particle size. In general, if the specific surface area is too small, the primary particles are too large and the battery characteristics are poor. Conversely, if the specific surface area is too large, it becomes difficult to produce an electrode when a lithium secondary battery is produced using the specific surface area. However, the appropriate specific surface area varies depending on the composition ratio of the lithium nickel manganese composite oxide. For example, if in the general formula (I) is nickel and manganese of about the same amount, usually 1 m ² / g or more, preferably 2m ² / g or more, and usually 8.0 m ² / g or less, preferably 6.0 m ² / g or less. Further by introducing cobalt as a substituent metal element, the atomic ratio of Y: Z: (1-Y -Z) = 0.65: 0.15: If you 0.20, usually 0.1 m ² / g or more, It is preferably 0.2 m ² / g or more and usually 1.0 m ² / g or less, preferably 0.8 m ² / g or less. In the case of introducing cobalt as a substitutional metal element, it is preferable that the atomic ratio is approximately as described above. That is, in terms of numerical values, 1 ≦ Y / Z ≦ 7 and 0 <(1-YZ) ≦ 0.3, particularly 2 ≦ Y / Z ≦ 5 and 0.1 ≦ (1-YZ) ≦ 0. 25 is preferred. The powder filling density is a tap density (after 200 taps), and is usually 0.5 g / cc or more, preferably 0.6 g / cc or more, more preferably 0.8 g / cc or more. The higher the powder packing density, the larger the energy density per unit volume of a battery using this as the positive electrode active material, but in reality it is 3.0 g / cc or less, usually 2.5 g. / Cc or less.

  The specific surface area of the lithium nickel manganese composite oxide is measured by a known BET type powder specific surface area measuring device. The measurement method is BET one-point measurement by a continuous flow method, and the adsorption gas and carrier gas used are nitrogen, air, and helium. In the measurement, the powder sample is heated and deaerated with a mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen to adsorb the mixed gas. This is heated with water to desorb the adsorbed nitrogen gas, detected by a thermal conductivity detector, the amount is determined as a desorption peak, and the specific surface area of the sample is calculated therefrom.

  The lithium nickel manganese composite oxide obtained by the method of the present invention is suitable for use as a positive electrode material (active material) of a lithium secondary battery. That is, this lithium nickel manganese composite oxide is mixed with a binder, and if necessary, a conductive material is further mixed, and then a solvent is added to form a uniform coating solution, which is applied onto a current collector and dried. Can be formed.

The positive electrode may further contain an active material that can occlude and release lithium ions other than lithium nickel manganese composite oxide, such as LiFePO ₄ .
As the conductive material, carbon materials such as natural graphite, artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke are usually used. The proportion of the conductive material in the positive electrode is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 40% by weight or less, More preferably, it is 30 weight% or less. If the proportion of the conductive material is too low, the conductivity may be insufficient, and conversely if it is too high, the battery capacity will decrease.

  As binders, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like can be used. The proportion of the binder in the positive electrode is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 50% by weight or less, preferably 30% by weight or less, more preferably 10% by weight or less. If the binder ratio is too low, the active material cannot be sufficiently retained and the positive electrode mechanical strength is insufficient, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, battery capacity and conductivity will be reduced. To do.

As the solvent, organic solvents such as N-methylpyrrolidone, tetrahydrofuran, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran are usually used. However, water can also be used.
A latex of binder resin can also be used.

  Examples of the material for the current collector include aluminum, stainless steel, and nickel-plated steel. Aluminum is preferable. The thickness of the current collector is usually about 1 to 1000 μm, preferably about 5 to 500 μm. The positive electrode is usually compacted by a method such as a roller press after the above-mentioned coating solution is applied on a current collector and dried. On the other hand, as the negative electrode, a material obtained by applying a carbon material such as natural graphite or pyrolytic carbon on a current collector such as copper, a lithium metal foil, a lithium-aluminum alloy, or the like can be used. Preferably, a carbon material is used.

Carbon materials are usually graphite, coke, coal-based or petroleum-based pitch carbides, or carbides obtained by oxidizing these pitches, carbides such as needle coke, pitch coke, phenol resin, crystalline cellulose, etc. and some of these. Graphitized carbon materials, furnace black, acetylene black, pitch-based carbon fibers, and the like are used.
As the negative electrode active material, SnO, SnO ₂ , Sn _1-x M _x O (M = Hg, P, BSi, Ge or Sb, where 0 ≦ x <1), Sn ₃ O ₂ (OH), Sn _{3 -x M x O 2 (OH)} 2 (M = Mg, P, B, Si, Ge, Sb or Mn, where 0 ≦ x <3), can also be used LiSiO _2, SiO ₂ or LiSnO ₂ like.

The electrolytic solution used for the lithium secondary battery is a non-aqueous electrolytic solution in which an electrolytic salt is dissolved in a non-aqueous solvent. Examples of the electrolytic salt include lithium salts such as LiCiO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiBr, and LiCF ₃ SO ₃ . Non-aqueous solvents include tetrahydrofuran, 1,4-dioxane, dimethylformamide, acetonitrile, benzonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and other carbonates, ethers, Examples include ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides, and phosphate ester compounds. These electrolytic salts and non-aqueous solvents may be used alone or in combination of two or more. In addition, instead of these electrolytic solutions, conventionally known various solid electrolytes and gel electrolytes can be used.

  As separators used in lithium secondary batteries, polytetrafluoroethylene, polyethylene, polypropylene, polybutene, polyester, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile and other microporous polymer filters, glass fibers, etc. Nonwoven fabric filters, composite nonwoven fabric filters of glass fibers and polymer fibers, and the like can be mentioned. The chemical and electrochemical stability of the separator is an important factor. From this point, a polyolefin-based polymer is preferable, and it is desirable that the separator is made of polyethylene in view of the self-occluding temperature which is one of the purposes of the battery separator.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely using an Example, this invention is not restrict | limited to a following example, unless the summary is exceeded.
Example 1
LiOH.H ₂ O, Ni (OH) ₂ and Mn ₂ O ₃ were mixed so that Li: Ni: Mn = 1.05: 0.50: 0.50 (atomic ratio), and pure water was added thereto. In addition, a slurry having a solid concentration of 12.5% by weight was prepared. While this slurry is stirred, it is pulverized using a circulating medium agitation type wet pulverizer (Shinmaru Enterprises Co., Ltd .: Dynomill KDL-A type) until the average particle size of the solid content in the slurry becomes 0.30 μm. did. A 300 ml pot was used and the grinding time was 6 hours. When the viscosity of this slurry was measured with a BM type viscometer (manufactured by Tokimec), the initial viscosity was 1510 mPa · s.

This slurry was spray-dried using a two-fluid nozzle type spray dryer (Okawara Chemical Industries, Ltd .: L-8 type spray dryer). Air was used as the drying gas, the drying gas introduction amount was 45 m ³ / min, and the drying gas inlet temperature was 90 ° C. And the granulated material obtained by spray-drying was baked in the air at 900 degreeC for 10 hours, and the lithium nickel manganese complex oxide of the substantially prepared atomic ratio composition was obtained.

The obtained lithium nickel manganese composite oxide was particles having an approximately spherical shape with an average secondary particle diameter of 4.9 μm and a maximum particle diameter of 15 μm.
The average particle size of the solid content in the slurry and the average particle size and the maximum particle size of the obtained lithium nickel manganese composite oxide were measured by a laser diffraction / scattering type particle size distribution analyzer (manufactured by Horiba: LA-920 type). It was determined using a particle size distribution measuring device. Specifically, the slurry or calcined powder is dispersed in a 0.1% sodium hexametaphosphate aqueous solution by ultrasonic dispersion and stirring in the air at room temperature, and the transmittance is adjusted between 70% and 95%. The average particle size and the maximum particle size were determined from the particle size distribution.

Further, when the powder X-ray diffraction of the obtained lithium nickel manganese composite oxide was measured, it was confirmed that it had a rhombohedral layered lithium nickel manganese composite oxide structure.
5 g of this composite oxide was put in a 10 ml glass graduated cylinder, and the powder packing density (tap density) after tapping 200 times was measured. As a result, it was 0.9 g / cc.

As a result of measuring the BET specific surface area of this composite oxide, it was 5.0 m ² / g. The specific surface area was measured using a BET type powder specific surface area measuring device (manufactured by Ritsu Okura: AMS8000 type fully automatic powder specific surface area measuring device).
The slurry was prepared (concentration: 12.5% by weight) and spray-dried in the same manner as above except that LiOH.H ₂ O was not contained in the slurry. H ₂ O powder (maximum particle size of 20 μm or less) was added so that Li: Ni: Mn = 1.05: 0.5: 0.5, and mixed well by hand, then in air at 900 ° C. for 10 hours The layered lithium nickel manganese composite oxide having almost the same rhombohedral crystal as that obtained above can be obtained even by firing with the above.

Example 2
LiOH.H ₂ O, NiO, Mn ₂ O ₃ , and Co (OH) ₂ should be Li: Ni: Mn: Co = 1.05: 0.65: 0.15: 0.20 (atomic ratio) A lithium manganese nickel composite oxide was obtained in the same manner as in Example 1 except that a slurry was prepared by mixing and firing was performed in air at 850 ° C. for 10 hours.

The initial viscosity of the slurry was 220 mPa · s. The average particle size of the solid content contained in the slurry was 0.3 μm. The obtained composite oxide had an average particle size of 9.8 μm and a maximum particle size of 34 μm, and was a particle having a substantially spherical shape. Further, when the powder X-ray diffraction of the obtained composite oxide was measured, it was confirmed that it had a rhombohedral layered lithium nickel manganese composite oxide structure. 5 g of this composite oxide was put in a 10 ml glass graduated cylinder, and the powder packing density (tap density) after tapping 200 times was measured. As a result, it was 2.0 g / cc. Further, the BET specific surface area of this composite oxide was measured and found to be 0.8 m ² / g.

Example 3
LiOH.H ₂ O, Ni (OH) ₂ , Mn ₂ O ₃ and AlOOH are set to Li: Ni: Mn: Al = 1.05: 0.45: 0.45: 0.10 (atomic ratio). A lithium nickel manganese composite oxide was obtained in the same manner as in Example 1 except that the slurry was prepared by mixing.

The initial viscosity of the slurry was 790 mPa · s. The obtained composite oxide had an average particle size of 5.0 μm and a maximum particle size of 15 μm, and was a particle having a substantially spherical shape. This product was confirmed to have a rhombohedral layered lithium nickel manganese composite oxide structure by powder X-ray diffraction. The powder packing density (tap density) after tapping 200 times was 0.9 g / cc, and the BET specific surface area was 5.7 m ² / g.

Example 4
LiOH.H ₂ O, Ni (OH) ₂ , Mn ₂ O ₃ and Co (OH) ₂ are replaced by Li: Ni: Mn: Co = 1.05: 0.45: 0.45: 0.10 (atomic ratio) A lithium nickel manganese composite oxide was obtained in the same manner as in Example 1 except that the slurry was prepared by mixing so that

The initial viscosity of the slurry was 820 mPa · s. The obtained composite oxide had an average particle size of 5.8 μm and a maximum particle size of 15 μm, and was a particle having a substantially spherical shape. This was confirmed by powder X-ray diffraction to have a rhombohedral layered lithium nickel manganese composite oxide structure. The powder packing density (tap density) after tapping 200 times was 1.0 g / cc, and the BET specific surface area was 3.4 m ² / g.

Example 5
A lithium nickel manganese composite oxide was obtained in the same manner as in Example 1 except that NiO was used as the nickel raw material.
The initial viscosity of the slurry was 190 mPa · s. The obtained composite oxide had an average particle size of 7.1 μm and a maximum particle size of 20 μm, and was a particle having a substantially spherical shape. This product was confirmed to have a rhombohedral layered lithium nickel manganese composite oxide structure by powder X-ray diffraction. The powder packing density (tap density) after tapping 200 times was 1.1 g / cc, and the BET specific surface area was 2.8 m ² / g.

Comparative Example 1
LiOH · H ₂ O having a maximum particle size of 20 μm or less, NiO having an average particle size of 0.55 μm, and Mn ₂ O ₃ having an average particle size of 4.4 μm were combined with Li: Ni: Mn = 1.05: 0.5: 0. 5 (atomic ratio) was mixed, placed in a suitable container, shaken by hand and mixed, and then fired in air at 900 ° C. for 10 hours.

When the powder X-ray diffraction of the obtained lithium nickel manganese composite oxide was measured, it was confirmed that it was not a rhombohedral layered lithium nickel manganese composite oxide single phase.
Comparative Example 2
The same LiOH · H ₂ O, NiO, and Mn ₂ O ₃ as used in Comparative Example 1 and Co (OH) ₂ with an average particle diameter of 7.9 μm were used as Li: Ni: Mn: Co = 1.05: 0. It mixed so that it might become 65: 0.15: 0.20 (atomic ratio), this was put into a suitable container, and it mixed by shaking well by hand, Then, it baked in the air at 850 degreeC for 10 hours.

When the powder X-ray diffraction of the obtained lithium nickel manganese composite oxide was measured, it was confirmed that it was not a rhombohedral layered lithium nickel manganese composite oxide single phase.
Battery evaluation test (1)
The lithium nickel manganese composite oxides obtained in the examples and comparative examples of the present invention were evaluated as positive electrode active materials by the following methods.

A. Preparation of positive electrode 75 parts by weight of lithium nickel manganese composite oxide obtained in Examples and Comparative Examples, 20 parts by weight of acetylene black, and 5 parts by weight of polytetrafluoroethylene powder were sufficiently mixed in a mortar to form a thin sheet. Things were punched out using a 9 mmφ punch. The weight of what was obtained was about 8 mg. This was crimped to an aluminum expanded metal to form a positive electrode.

B. Production and characteristic test of battery with lithium metal as counter electrode Place a positive electrode punched into 9mmφ in a coin-type cell, place a porous polyethylene film (separator) with a thickness of 25μm on it, and further lithium metal (negative electrode) on it I put it on. To this was added a non-aqueous electrolyte (lithium hexafluorophosphate (LiPF ₆ ) dissolved in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1 mol / L), Further, after placing a spacer for adjusting the thickness, a lid was caulked through a polypropylene gasket to obtain a battery.

This battery was subjected to constant current charging at 4.2 mA / cm ² to 4.2 V or 4.3 V, and then to 3.0 V at 0.2 mA / cm ² at a constant current discharge. Table 1 shows the ratio (E%) of the discharge capacity to the discharge capacity Qs (mAhr / g) and the charge capacity Qc (mAhr / g) at this time. Further, following this charging / discharging, 4.3V-3.0V constant current charging / discharging is performed at a constant charge of 0.2 mA / cm ² each time, and discharging is performed at 0.5 mA / cm ² , 1 mA / cm ^2. was performed to enhance the ^{3mA / cm 2, 5mA / cm} 2, 7mA / cm 2, 9mA / cm 2 and 11 mA / cm ² and successively the current value for each one. Table 1 shows the discharge capacity Qa (mAhr / g) when the last constant current discharge was performed at 11 mA / cm ² .

Battery evaluation test (2)
A. Production of positive electrode It was produced in the same manner as in the battery evaluation test (1). However, a punch having a diameter of 12 mφ was used. The weight of what was obtained was about 18 mg.
B. Preparation of negative electrode 92.5 parts by weight of graphite powder (d ₀₀₂ = 3.35A) having a particle size of about 8 to 10 μm and 7.5 parts by weight of polyvinylidene fluoride were mixed, and N-methylpyrrolidone was added to the slurry. It was. This slurry was applied to one side of a 20 μm thick copper foil and dried. This was punched with a 12 mmφ punch, and further pressed at 0.5 ton / cm ² to obtain a negative electrode.

C. Production of Battery A battery was produced in the same manner as in the battery evaluation test (1). The weight ratio of the positive electrode active material to the negative electrode active material is such that the negative electrode charge capacity is 1.2 times the positive electrode charge capacity Qs (mAhr / g) measured in the battery evaluation test (1). I did it. The charge capacity of the negative electrode was the same as that in the battery evaluation test (1) using this negative electrode and lithium metal as the counter electrode, and when constant current discharge was performed at 0.2 mA / cm ² up to 0 V. Calculation was based on the initial charge capacity per unit weight of the negative electrode active material.

D. Cycle test At room temperature, charge and discharge was performed for 2 cycles at a constant current of 0.2 C (1 C is a current value for 1 hour and calculated by 1 C (mA) = Qsx positive electrode active material weight). One cycle of charge / discharge was performed with current. Subsequently, one cycle of charge / discharge was performed at a constant current of 0.2 C at 50 ° C., and then 100 cycles of charge / discharge were performed at a constant current of 1 C. The lower limit of charging / discharging was 3.0V, and the upper limit was 4.1V or 4.2V. Table 1 shows the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 100th cycle of charge / discharge of 100 cycles at a constant current of 50 ° C. and 1 C as P (%).

Claims (13)

  In a method for producing a lithium nickel manganese composite oxide by firing a mixture containing a nickel source, a manganese source and a lithium source, at least a nickel source and a manganese source, a slurry containing both of them, and an average particle size of solid matter A method obtained by spray-drying a material having a particle size of 2 μm or less.   The method of claim 1 wherein the slurry also contains a lithium source.   The method according to claim 1, wherein the lithium source is mixed with the product obtained by spray drying and calcined.   The method according to any one of claims 1 to 3, wherein the product obtained by spray drying is subjected to calcination while substantially maintaining its shape.   The method according to any one of claims 1 to 4, wherein the slurry is subjected to a wet pulverization treatment.   6. The method according to claim 1, wherein the Ni / Mn atomic ratio of the slurry is 0.7 ≦ Ni / Mn ≦ 9. Nickel sources used for preparing the slurry are Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO ₄ .6H ₂ O, 7. The method according to claim 1, wherein the method is selected from the group consisting of an organic nickel compound and a nickel halide. Manganese sources used in the preparation of the slurry are Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , MnOOH, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , organic manganese compound, manganese hydroxide and manganese halide. The method according to any one of claims 1 to 7, wherein the method is selected from the group consisting of: 9. The method according to claim 1, wherein the lithium source is selected from the group consisting of LiCO ₃ , LiNO ₃ , LiOH.H ₂ O and Li acetate.   The method according to any one of claims 1 to 9, wherein the slurry contains one selected from the group consisting of an aluminum source, a cobalt source, an iron source, a magnesium source and a calcium source. The method according to any one of claims 1 to 10, wherein the lithium nickel manganese composite oxide produced is represented by the following formula (I).

(In the formula, X represents a number satisfying 0 <X ≦ 1.2. Y and Z represent a number satisfying the expressions 0.7 ≦ Y / Z ≦ 9 and 0.5 ≦ Y + Z ≦ 1.0 at the same time. Q represents one selected from the group consisting of Al, Co, Fe, Mg and Ca.) A lithium nickel manganese composite oxide produced by the method according to claim 1. A lithium secondary battery using the lithium nickel manganese composite oxide according to claim 12 as a positive electrode active material.