JP2016004703A - Method for manufacturing positive electrode active material plate for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material plate excellent in compactness and flatness and also capable of exhibiting excellent battery characteristics in a lithium secondary battery.SOLUTION: In a method for manufacturing a positive electrode active material plate for a lithium secondary battery, hydroxide raw material powder is prepared, the hydroxide raw material powder comprising plate-like primary particles of nickel-cobalt-manganese composite hydroxide arranged substantially radially from the center of a secondary particle toward the outer direction, powder obtained by mixing a lithium compound to the hydroxide raw material powder is calcined to synthesize lithium transition metal composite oxide and/or a precursor thereof, the lithium transition metal composite oxide and/or the precursor thereof is molded in a sheet to prepare a molded body sheet, and then an excessive amount of lithium carbonate is placed on the molded body sheet and the molded body sheet is fired at a temperature of 850°C or above to form a positive electrode active material plate for a lithium secondary battery.

Description

  The present invention relates to a method for producing a positive electrode active material plate for a lithium secondary battery.

  As a positive electrode active material in a lithium secondary battery (sometimes called a lithium ion secondary battery), a material using a lithium composite oxide (lithium transition metal oxide) having a layered rock salt structure is widely known. (For example, see Patent Document 1 (Japanese Patent Laid-Open No. 5-226004) and Patent Document 2 (Japanese Patent Laid-Open No. 2003-132877)).

In this type of positive electrode active material, the diffusion of lithium ions (Li ⁺ ) therein is performed in the in-plane direction of the (003) plane (that is, any direction in a plane parallel to the (003) plane). It is known that lithium ions enter and exit from crystal planes other than the (003) plane (for example, the (101) plane or the (104) plane).

Therefore, in this type of positive electrode active material, the crystal plane (surface other than the (003) plane, for example, the (101) plane or the (104) plane) on which lithium ions can be satisfactorily entered and exited, is brought into contact with the electrolyte. Attempts have been made to improve the battery characteristics of lithium secondary batteries by exposing them. For example, Patent Document 3 (see WO _{2010/074313), Li p (Co x} , Ni y, Mn z) in _{O 2} (wherein, 0.97 ≦ p ≦ 1.07,0.1 < x ≦ 0.4, 0.3 <y ≦ 0.5, 0.1 <z ≦ 0.5, x + y + z = 1), and a positive electrode active material film of a lithium secondary battery having a layered rock salt structure. It is disclosed that the (003) plane is oriented so as to intersect the film plane.

In Patent Document 4 (International Publication No. 2014/061579) and Patent Document 5 (International Publication No. 2014/061580), at least a part of the primary particles is radially outward from the center of the secondary particles. A method for producing a positive electrode active material for a lithium secondary battery having a layered rock salt structure using a hydroxide raw material powder arranged side by side is disclosed. In these patent documents, Li _x Ni _1-z M _z O ₂ (wherein 0.96 ≦ x ≦ 1.09, 0 <z ≦ 0.5) is used as a lithium composite oxide constituting the positive electrode active material. , M is preferably represented by Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga), and particularly preferred combinations of metal elements M Is Co and Al, or Co and Mn.

JP-A-5-226004 JP 2003-132877 A International Publication No. 2010/074333 International Publication No. 2014/061579 International Publication No. 2014/061580

  The positive electrode active material made of lithium-nickel-cobalt-manganese composite oxide (often abbreviated as NCM) as disclosed in Patent Documents 3 to 5 has good battery characteristics (for example, capacity, rate characteristics, and durability). In addition, there is an advantage that expansion and contraction associated with the entry and exit of lithium during charging and discharging are small. Therefore, if a positive electrode active material plate made of a lithium / nickel / cobalt / manganese composite oxide can be successfully produced, it will be extremely useful in a lithium secondary battery, and it is also suitable for an all solid state battery in terms of small expansion and contraction. It will be. In this regard, according to the method described in Patent Document 3, by producing oriented plate-like particles having a (104) plane exposed on the surface, a positive electrode active having excellent battery characteristics (for example, capacity, rate characteristics, and durability). It is possible to obtain a material free-standing film. However, since the positive electrode plate produced by the technique disclosed in Patent Document 3 is obtained by promoting grain growth, the flatness tends to deteriorate at the grain boundary portion on the surface of the positive electrode plate, and warpage is also caused. It tends to occur. For this reason, further improvement is desired when applying to a positive electrode active material plate having a large area (for example, 10 mm × 10 mm square or more) in which warpage is easily emphasized.

  From the viewpoint of increasing the volume energy density, the positive electrode active material plate is desirably a dense plate. In general, although a dense plate can be produced by baking and solidifying the powder of the positive electrode active material at a high temperature, the composition deviation in the positive electrode active material plate may increase due to decomposition or lithium volatilization. The desired characteristics cannot be fully exhibited. Therefore, a technique capable of densifying the positive electrode active material plate without deteriorating battery characteristics is desired.

  The present inventors recently synthesized lithium transition metal composite oxide (NCM) using a hydroxide raw material powder having a radial orientation, and an excessive amount of NCM sheet formed of this lithium transition metal composite oxide. The knowledge that a positive electrode active material plate that is excellent in denseness and flatness and that can exhibit excellent battery characteristics in a lithium secondary battery can be produced by placing and firing lithium carbonate. Obtained.

  Accordingly, an object of the present invention is to provide a positive electrode active material plate that is excellent in denseness and flatness and that can exhibit excellent battery characteristics in a lithium secondary battery.

According to one aspect of the present invention, there is provided a method for producing a positive electrode active material plate for a lithium secondary battery,
(A) It consists of secondary particles in which plate-like primary particles of nickel / cobalt / manganese composite hydroxide are agglomerated, and the plate-like primary particles are arranged almost radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder;
(B) A step of mixing a predetermined amount of a lithium compound with the hydroxide raw material powder to obtain a mixed powder, wherein the predetermined amount is relative to the total amount of Ni + Co + Nn contained in the hydroxide raw material powder. A molar ratio of the Li content contained in the lithium compound, that is, a step in which Li / (Ni + Co + Mn) is an amount that is 1.00 or more;
(C) calcining the mixed powder to synthesize a lithium transition metal composite oxide and / or precursor thereof;
(D) forming the molded body sheet by molding the lithium transition metal composite oxide and / or its precursor into a sheet;
(E) A step of placing a predetermined amount of lithium carbonate on the molded body sheet, wherein the predetermined amount is a lithium carbonate placed as described above with respect to a total amount of Ni + Co + Mn contained in the molded body sheet A molar ratio of the Li content contained, that is, a step in which Li / (Ni + Co + Mn) is 0.7 or more,
(F) firing the molded sheet on which the lithium carbonate is placed at a temperature of 850 ° C. or higher to form a positive electrode active material plate;
A method is provided comprising.

It is a schematic cross section which shows the radially oriented hydroxide raw material powder used for the method of this invention. In the method of this invention, it is a figure which shows typically a series of processes until radial alignment hydroxide raw material powder is processed into a positive electrode active material board. 6 is a photograph of the positive electrode active material plate produced in Example 5 taken from above. 7 is a photograph of the positive electrode active material plate produced in Example 5 taken from the side. 6 is a SEM image of a cross section of the positive electrode active material plate produced in Example 5. It is the photograph which image | photographed the positive electrode active material board produced in Example 10 (comparison) from the top. It is the photograph which image | photographed the positive electrode active material board produced in Example 10 (comparison) from the side. It is a SEM photograph of the section of the cathode active material board produced in Example 10 (comparison).

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material plate for a lithium secondary battery. The positive electrode active material plate produced according to the present invention is made of a lithium-nickel-cobalt-manganese composite oxide (hereinafter referred to as NCM) which is a positive electrode active material. A typical NCM is Li _p (Ni _x , Co _y , Mn _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0.7 and x + y + z = 1, preferably 0.95 ≦ p ≦ 1.1, 0.1 ≦ x <0.7, 0.1 ≦ y <0.9, 0 ≦ z ≦ 0. 6, x + y + z = 1). However, the positive electrode active material plate is within the scope of the present invention, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb. , Mo, Ag, Sn, Sb, Te, Ba, Bi, etc. are added in a trace amount in the form of doping or equivalent (for example, partial solid solution or segregation of crystal grains on the surface layer). Also good. In any case, the positive electrode active material having the NCM composition has a layered rock salt structure. “Layered rock salt structure” means a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers in between (typically α-NaFeO ₂ type structure: cubic rock salt type structure) [111] A structure in which transition metals and lithium are regularly arranged in the axial direction. In this respect, the positive electrode active material plate according to the present invention uses a hydroxide raw material powder in which plate-like primary particles 1 a as shown in FIG. 1 are arranged radially outward from the center of the secondary particles 1. The positive electrode active material plate can take over the orientation derived from the radial orientation of the raw material powder significantly or to some extent. In particular, the individual plate-like primary particles arranged in a radial manner have a (003) plane (lithium moves in the in-plane direction), and therefore the plate-like primary particles are generally arranged in a radial manner. Further, the surface of the secondary particles and the surface of the positive electrode active material plate formed by sintering such secondary particles have a crystal plane (for example, (101) plane ( 104) surface)) is exposed, and lithium ions can easily enter and exit on the surface. That is, as a result of the smooth movement of lithium ions over the surface of the positive electrode active material plate and the inside thereof (a large number of secondary particles are sintered), battery characteristics (for example, capacity and rate characteristics) are improved. Can do.

  Production of a positive electrode active material plate for a lithium secondary battery according to the method of the present invention is as follows. (A) Nickel / cobalt / manganese composite hydroxide raw material powder having such a radial orientation as shown in FIG. (B) A predetermined amount of a lithium compound is mixed with this raw material powder, (c) the obtained mixed powder is calcined to synthesize a lithium transition metal composite oxide and / or its precursor, d) This is formed into a sheet, (e) an excess amount of lithium carbonate (melting point: 730 ° C.) is placed on the resulting molded sheet, and (f) a positive electrode is fired at a temperature of 850 ° C. or higher. This is done by forming an active material plate. And the positive electrode active material board manufactured in this way is excellent in denseness and flatness, and can exhibit the outstanding battery characteristic in a lithium secondary battery. With regard to this point and excellent battery characteristics, as described above, by using a hydroxide raw material powder (NCM hydroxide) having a radial orientation, plate-like primary particles (crystal particles) in the positive electrode active material plate are used. ) In a radial direction (that is, an orientation state in which the (003) plane does not appear on the surfaces of the secondary particles and the positive electrode active material plate). On the other hand, the point that it is excellent in denseness and flatness was actually unexpected, but the excellent flatness reduces unnecessary reaction during firing by lithium synthesis (calcination) of raw material powder in advance. As a result, it is presumed that warpage was suppressed. Moreover, it is surmised that the excellent denseness is because the densification was promoted by excessive supply of lithium from the outside of the sheet during firing.

  According to the present invention, the following advantages can be brought about. First, since a dense and flat plate-shaped positive electrode active material plate is obtained, it can be preferably applied to a thin battery or the like. In addition, unlike the positive electrode active material in powder form, it does not need to be mixed with a binder or conductive additive, and there is almost no or little space due to pores, so that the active material density is maximized when used as a positive electrode active material plate for a battery. The battery capacity can be increased by increasing the limit. In that sense, it can be said that the positive electrode active material plate according to the present invention preferably does not contain a binder and a conductive additive. Second, by radially sintering the crystal grains that are radially oriented, the surface of the positive electrode active material plate has a crystal plane other than the lithium in / out plane (that is, a (003) plane (for example, (101) plane or (104) Surface)) exposed structure can be made. As a result, it is possible to manufacture a positive electrode active material plate (that is, a positive electrode active material plate having a high charge / discharge rate when used as a battery) that can efficiently move lithium ions on the surface. Third, since there is no anisotropy in the expansion and contraction of the positive electrode active material plate during charge / discharge, there is little deterioration (for example, internal cracks) due to repeated use (that is, deterioration is small even after repeated charge / discharge). A board can be manufactured.

  Hereinafter, the detail of each process of the manufacturing method of this invention is demonstrated.

(A) Preparation of hydroxide raw material powder In this step (a), as schematically shown in FIG. 1, secondary particles 1 in which plate-like primary particles 1a of nickel / cobalt / manganese composite hydroxide are aggregated are aggregated. A hydroxide raw material powder is prepared, in which the plate-like primary particles 1a are arranged in a generally radial manner from the center of the secondary particles 1 outward. Such hydroxide powders having a radial orientation are known together with their production methods. The nickel-cobalt-manganese composite hydroxide is typically (Ni _x , Co _y , Mn _z ) (OH) ₂ (where 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0.7, x + y + z = 1), preferably 0.95 ≦ p ≦ 1.1, 0.1 ≦ x <0.7, 0.1 ≦ y <0.9, 0 ≦ z ≦ 0.6 and x + y + z = 1. This hydroxide raw material powder may contain other trace additive elements (for example, Al, Mg, Ti, Fe, Cr, Zn, Ga, etc.) without departing from the spirit of the present invention. A small amount of an additive element may be appropriately added in the subsequent step.

  The hydroxide raw material powder preferably has a volume-based median diameter D50 of 2 to 10 μm as a secondary particle diameter, more preferably 2 to 7 μm, and further preferably 3 to 5 μm. Usually, when the hydroxide raw material powder has a particle diameter in such a range, pores are likely to remain, and it is difficult to densify the positive electrode active material plate. However, according to the method of the present invention, densification can be promoted. .

  The hydroxide raw material powder having such a radial orientation can be produced according to a known technique (see, for example, Patent Documents 4 and 5). For example, in a tank whose pH and temperature are appropriately adjusted, a nickel salt aqueous solution (for example, nickel sulfate aqueous solution), a cobalt salt aqueous solution (for example, cobalt sulfate aqueous solution), a manganese salt aqueous solution (for example, manganese sulfate aqueous solution), or a caustic alkaline aqueous solution (for example, hydroxylated) Sodium aqueous solution), and an ammonium ion supplier (for example, ammonium sulfate aqueous solution) are continuously supplied and collected while controlling the concentration and flow rate. At this time, it is preferable that pH in a tank shall be 10.0-13.0, and temperature shall be 40-80 degreeC. The nickel-cobalt-manganese composite hydroxide thus produced is preferably subjected to water washing, dehydration, and drying treatment. In addition, it is preferable that all of a series of steps (that is, a series of steps excluding water washing, dehydration, and drying treatment) from the introduction of each compound into the reaction vessel to the removal of the hydroxide are performed in an inert atmosphere. .

(B) Mixing with lithium compound In this step (b), a predetermined amount of lithium compound is mixed with the hydroxide raw material powder to obtain a mixed powder. At this time, the amount of the lithium compound is such that the molar ratio of the Li content contained in the lithium compound to the total amount of Ni + Co + Nn contained in the hydroxide raw material powder, that is, Li / (Ni + Co + Mn) is 1.00 or more, preferably 1 .0000 to 1.20, more preferably 1.02 to 1.10. Thus NCM composition (i.e. _{Li p (Ni x, Co y} , Mn z) O 2) by equal or more lithium compound amount relative to a subsequent calcining step at the time of (c) The synthesis reaction with lithium can be promoted while compensating for lithium loss due to volatilization. Lithium compound composition of the positive electrode active material plate (i.e. _{Li p (Ni x, Co y} , Mn z) O 2) to be any lithium-containing compound capable of providing ultimately be used, carbonate Preferred examples Lithium, lithium hydroxide, and hydrates thereof, and any combination thereof may be mentioned. Prior to the reaction, the hydroxide raw material powder is preferably mixed with the lithium compound by a method such as dry mixing or wet mixing. The average particle size of the lithium compound is not particularly limited, but is preferably 0.1 to 5 μm from the viewpoint of ease of handling and reactivity from the viewpoint of hygroscopicity. Further, as described above, a trace amount of added elements (for example, Al, Mg, Ti, Fe, Cr, Zn, Ga, etc.) may be added in this step (b) within the range not departing from the gist of the present invention.

(C) Calcination (lithium synthesis)
In this step (c), the mixed powder is calcined to synthesize a lithium transition metal composite oxide and / or a precursor thereof (hereinafter collectively referred to as a lithium transition metal composite oxide or the like). At this time, it is desirable that the lithium transition metal composite oxide is synthesized. However, since it is sufficient that the lithium transition metal composite oxide can be synthesized in the final firing step (f), a precursor of the lithium transition metal composite oxide (for example, It may be synthesized in a form including those that are not completely synthesized with lithium and those that are not completely oxides. The calcination in this step is preferably performed at a temperature of 500 to 900 ° C, more preferably 600 to 800 ° C, and still more preferably 700 to 800 ° C. Within this range, grain growth is sufficient, and it becomes easy to achieve a desired composition by suppressing decomposition of lithium transition metal composite oxide and the like and volatilization of lithium. The calcining time is not particularly limited, but is preferably 1 to 50 hours, and more preferably 5 to 30 hours. This calcination is preferably performed in an oxidizing atmosphere such as an air atmosphere by putting the mixed powder in a sheath (preferably made of alumina).

  The calcination atmosphere is desirably set as appropriate so that decomposition does not proceed during calcination. When the volatilization of lithium proceeds, it is preferable to arrange lithium carbonate or the like in the same sheath to create a lithium atmosphere. When oxygen release or further reduction proceeds during calcination, firing is preferably performed in an atmosphere having a high oxygen partial pressure. In addition, after calcination, for the purpose of releasing the adhesion and aggregation between the positive electrode active material particles or adjusting the average particle diameter of the lithium transition metal composite oxide, etc., it may be appropriately crushed or classified. Good.

(D) Production of molded body sheet In this step (d), a lithium transition metal composite oxide or the like is molded into a sheet shape to produce a molded body sheet. The method for forming the sheet is not particularly limited as long as it is performed according to a known method, but it is preferably performed by slurrying a lithium transition metal composite oxide or the like and subjecting it to tape forming. A typical example of the tape forming method is a doctor blade method. When using a tape molding method such as the doctor blade method, the slurry is applied to a flexible plate (for example, an organic polymer plate such as a PET film), and the applied slurry is dried and solidified to form a molded body sheet. The body sheet may be peeled from the plate to form a self-supporting molded body sheet. When preparing a slurry or clay before molding, a lithium transition metal composite oxide or the like may be dispersed in a dispersion medium, and a binder, a plasticizer, or the like may be appropriately added. Moreover, it is preferable to prepare the slurry so that the viscosity is 500 to 4000 cP, and it is preferable to defoam by decompression. The thickness of the molded sheet is preferably 5 to 80 μm, more preferably 10 to 60 μm, still more preferably 20 to 50 μm, and particularly preferably 20 to 40 μm. When the thickness is within this range, a positive electrode active material plate excellent in denseness and flatness can be obtained even though the plate is relatively thick.

  In addition, as another method for forming a sheet, a method using a drum dryer (for example, a slurry containing a lithium transition metal composite oxide or the like is applied onto a heated drum and the dried one is scraped with a scraper) , A technique using a disk dryer (for example, applying a slurry containing lithium transition metal composite oxide etc. to a heated disk surface, drying it and scraping it with a scraper), and an extrusion method (for example, lithium transition metal composite And extruding clay containing oxides and the like into a sheet).

  The molded body sheet obtained in this step (d) is typically a “self-supported molded body” that can maintain the shape of the sheet-shaped molded body by itself. In addition, even if it cannot maintain the shape of the sheet-like molded body by itself, it can be attached to a substrate or formed into a film and peeled off from the substrate before or after firing. Included in "body". Prior to the subsequent step, the molded body sheet may be appropriately cut to a desired size. However, it goes without saying that it may be subjected to subsequent steps in the form of a sheet as it is formed.

(E) Placement of lithium carbonate In this step (e), a predetermined amount of lithium carbonate is placed on the compact sheet. At this time, the molar ratio of the Li content contained in the lithium carbonate to be placed with respect to the total amount of Ni + Co + Mn contained in the molded body sheet, that is, Li / (Ni + Co + Mn) is 0.7 or more, preferably Is 0.7 to 2.0, more preferably 1.0 to 1.8, and still more preferably 1.1 to 1.5. That is, since the molded body sheet contains lithium transition metal composite oxide and the like, in this step (e), lithium carbonate is further placed thereon as an excessive amount of lithium compound. Most or all of the excess amount of the lithium compound disappears in the subsequent firing step (f), but it is unexpected because the excess amount of lithium carbonate is present on the molded body sheet during the firing. Thus, a positive electrode active material plate excellent in denseness and flatness can be obtained.

  The placement of lithium carbonate is particularly preferably carried out by placing it on a molded body sheet in the form of a lithium-containing sheet comprising lithium carbonate. The lithium-containing sheet is preferably obtained by slurrying lithium carbonate and subjecting it to tape molding, and the tape molding method is the same as the method described in the step (d) described above. Good. The thickness of the lithium-containing sheet may be appropriately determined so as to give an amount of lithium carbonate such that the Li / (Ni + Co + Mn) ratio is a desired value, and is, for example, 20 to 60 μm.

Moreover, the molded sheet is, compositions generally corresponding to the composition of the positive electrode active material plate, typically _{Li p (Ni x, Co y} , Mn z) in _{O 2} (wherein, 0.9 ≦ p ≦ 1.3 , 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0.7, x + y + z = 1) is preferably placed on the base layer laid down with a powder. This powder may be produced by any known method as long as it has the above composition. In any case, a high-quality positive electrode active material plate having a more uniform composition can be produced by interposing this base layer (laying powder). This underlayer (laying powder) is preferably formed on a setter (preferably made of alumina).

(F) Firing In this step (f), the formed body sheet on which lithium carbonate is placed is fired to form a positive electrode active material plate. A calcination temperature is 850 degreeC or more, Preferably it is 850-960 degreeC, More preferably, it is 880-940 degreeC, More preferably, it is 880-920 degreeC. Although baking time is not specifically limited, Preferably it is 1 to 50 hours, More preferably, it is 10 to 30 hours. This firing is preferably performed in an oxidizing atmosphere such as an air atmosphere by placing a setter (preferably made of alumina) on which a molded body sheet on which lithium carbonate is placed is placed in a sheath (preferably made of alumina). Lithium carbonate placed on the molded sheet is not absorbed by the positive electrode active material plate, but is volatilized or absorbed by the setter. You may remove by heat processing, a water washing process, etc.

Thus obtained positive electrode active material plate is composed of a lithium-nickel-cobalt-manganese composite oxide (NCM), typically _{Li p (Ni x, Co y} , Mn z) in _{O 2} (wherein, 0.9 ≦ p ≦ 1.3, 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0.7, x + y + z = 1, preferably 0.95 ≦ p ≦ 1.1, 0.1 ≦ x <0.7, 0.1 ≦ y <0.9, 0 ≦ z ≦ 0.6, and x + y + z = 1). Further, as described above, the positive electrode active material plate can inherit the orientation derived from the radial orientation of the raw material powder significantly or to some extent, so that the positive electrode active material plate is made thicker than the non-oriented positive electrode active material plate. Is suitable. This is because the lithium ions can move more smoothly in the thickness direction due to the orientation. The thickness of the positive electrode active material plate is preferably 5 to 75 μm, more preferably 10 to 60 μm, still more preferably 20 to 50 μm, and particularly preferably 20 to 40 μm. Further, the size of the positive electrode active material plate is preferably 5 mm × 5 mm square or more, more preferably 10 mm × 10 mm to 100 mm × 100 mm square, and further preferably 10 mm × 10 mm to 50 mm × 50 mm square. if, preferably 25 mm ² or more, more preferably 100～10000Mm ^2, more preferably from 100~2500mm ^2.

  The present invention is more specifically described by the following examples.

  In addition, the evaluation method of various characteristics regarding the positive electrode active material plate and the battery including the same in the following examples was as follows.

<Dense>
The positive electrode active material plate was subjected to cross-sectional polishing with a CP polishing machine (IB-09010CP, manufactured by JEOL Ltd.). The polished cross section was observed with an SEM to confirm the presence or absence of voids and pores. The obtained SEM image was subjected to image processing to calculate the pore ratio. A sample having a porosity ratio of 5% or less was evaluated as “A” (that is, a non-defective product), and a sample having a porosity of less than 5% was evaluated as “B”.

<Flatness>
For the positive electrode active material plate, one line of the contour curve (specifically waviness profile) near the center of the sample is measured with a laser three-dimensional surface shape measuring instrument (LEXT OLS4100, manufactured by Olympus), and the maximum height is measured. Swell Wz was measured. The obtained sample with the maximum height waviness Wz of 10 μm or less was designated as “A”, the sample with Wz exceeding 10 μm and 20 μm or less was designated as “B”, and the sample with Wz exceeding 20 μm was designated as “C”. “A” and “B” were evaluated as good. The maximum height waviness Wz is the maximum height of the contour curve defined in JIS B0601-2001, and the maximum value and valley depth of the peak height Zp of the contour curve (specifically the waviness curve) at the reference length. This corresponds to the sum of the maximum values of Zv. Therefore, it means that it is so flat that this value is low.

<Battery characteristics>
The positive electrode active material plate was divided into sample pieces of about 5 mm square. A positive electrode plate was obtained by sputtering an Au film having a thickness of 1000 mm on one side of the sample piece as a current collecting layer. A positive electrode plate, a negative electrode made of lithium metal, a stainless steel current collector plate, and a separator are arranged in the order of current collector plate-positive electrode plate-separator-negative electrode-current collector plate, and this integrated body is filled with an electrolyte solution, whereby a coin cell is formed. Produced. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ in an organic solvent in which ethylene carbonate and diethyl carbonate were mixed at an equal volume ratio to a concentration of 1 mol / L was used. The battery capacity (discharge capacity) was evaluated for the coin cell. Charge at constant current until the battery voltage reaches 4.2 V at a current value of 0.1 C rate, and then charge at constant voltage until the current value drops to 1/20 under the current condition of maintaining the battery voltage at 4.2 V. did. The operation of resting for 10 minutes, then discharging at constant current until the battery voltage reaches 3.0 V at a current value of 0.1 C rate, and then resting for 10 minutes is defined as one cycle, and the second cycle at 25 ° C. The discharge capacity was measured. A sample having a discharge capacity of 95% or more of the theoretical capacity (NCM: 160 mAh / g) was evaluated as “A” (that is, a non-defective product), and a sample having a discharge capacity of less than 95% was evaluated as “B”.

Examples 1-9
(A) Preparation of hydroxide raw material powder As the hydroxide raw material powder, the composition is (Ni _0.5 Co _0.2 Mn _0.3 ) (OH) ₂ , the secondary particles are almost spherical and the primary particles are A nickel-cobalt-manganese composite hydroxide powder having a volume-based median diameter D50 of 4 μm and arranged radially outward from the center of the secondary particles was prepared. This nickel / cobalt / manganese composite hydroxide powder can be produced according to a known method such as a solution method, and specifically, produced as follows. That is, a mixed aqueous solution of nickel sulfate, cobalt sulfate and manganese sulfate having a concentration of 1 mol / L in a molar ratio of Ni: Co: Mn = 50: 20: 30 is charged into a reaction tank containing 20 L of pure water at a rate of 50 mL / min. In addition, ammonium sulfate having a concentration of 3 mol / L was continuously charged simultaneously at a charging rate of 2 ml / min. On the other hand, an aqueous sodium hydroxide solution having a concentration of 10 mol / L was added so that the pH in the reaction vessel was automatically maintained at 12.5. The temperature in the reaction vessel was maintained at 70 ° C., and was always stirred with a stirrer. The produced nickel-cobalt-manganese composite hydroxide was taken out by overflowing from the overflow tube, washed with water, dehydrated and dried. In addition, all of a series of steps (i.e., a series of steps excluding water washing, dehydration and drying treatment) from the introduction of each compound into the reaction vessel to the removal of the hydroxide was performed in an inert atmosphere.

(B) Mixing with Lithium Compound The obtained hydroxide raw material powder and Li ₂ CO ₃ powder in an amount of 45 wt% with respect to the hydroxide raw material powder are mixed in a hybrid mixer to obtain a mixed powder. It was. The molar ratio of the Li content contained in the mixed amount of Li ₂ CO ₃ powder to the total amount of Ni + Co + Nn contained in the hydroxide raw material powder, that is, Li / (Ni + Co + Mn) was 1.06.

(C) Calcination (lithium synthesis)
The mixed powder was packed in an alumina sheath and heat-treated (calcined) at 700 ° C. for 20 hours in an air atmosphere. The obtained calcined material was crushed in a mortar to obtain lithium-synthesized NCM powder.

(D) Production of molded body sheet 100 parts by weight of a lithium-synthesized NCM powder, 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), binder (polyvinyl butyral: BM-2 manufactured by Sekisui Chemical Co., Ltd.) ) 10 parts by weight, 4 parts by weight of a plasticizer (DOP: manufactured by Kurokin Kasei Co., Ltd.), and 2 parts by weight of a dispersant (Reodol SP-O30 manufactured by Kao Corporation) were mixed. While stirring the obtained mixture under reduced pressure, it deaerated and adjusted to the viscosity of 3000-4000 cP. The obtained slurry was molded into a sheet shape on a PET film using a tape molding machine so that the film thickness after drying was 28 μm, and an NCM sheet was obtained.

(E) Placement of lithium carbonate The NCM sheet was peeled off from the PET film and cut into 10 mm squares. On the setter made of alumina, NCM powder synthesized separately in advance was placed as a spread powder (underlayer), and the NCM sheet cut into 10 mm square was placed on the spread powder (underlayer). The NCM powder separately synthesized in advance was mixed with 45 wt% of Li ₂ CO ₃ in NCM raw material powder (commercially available) having a composition of Ni: Co: Mn = 50: 20: 30 in molar ratio, and 20% at 850 ° C. It was produced by heat treatment for a period of time. In Examples 2 to 9, a Li ₂ CO ₃ sheet having a predetermined thickness obtained by tape molding in the same manner as described above and cut into a 10 mm square was placed on the NCM sheet. The thickness of this Li ₂ CO ₃ sheet is the value that the molar ratio of the Li content contained in the Li ₂ CO ₃ sheet to the total amount of Ni + Co + Mn contained in the NCM sheet, that is, Li / (Ni + Co + Mn) is shown in Table 1. (That is, 14 μm in Example 2, 16 μm in Example 3, 28 μm in Examples 4 to 8, and 42 μm in Example 9). In Example 1, a Li ₂ CO ₃ sheet was not placed for comparison.

(F) Firing A setter on which the NCM powder, NCM sheet and Li ₂ CO ₃ sheet are placed in this order is placed in an alumina sheath, and the lid is closed. Temporal heat treatment (firing) was performed. In this way, a positive electrode active material plate (thickness: 23 μm, size: 8 mm × 8 mm) was obtained. When the surface of the positive electrode active material plate was observed, the Li ₂ CO ₃ sheet placed on the positive electrode active material plate was completely lost by firing.

(G) Various evaluations With respect to the obtained positive electrode active material plate, the density, flatness, and battery characteristics were evaluated by the procedure described above. The results were as shown in Table 1. Moreover, the photograph and cross-sectional SEM image of the positive electrode active material board produced in Example 5 are shown to FIG. As is clear from these drawings, it can be seen that the positive electrode active material plate produced according to the present invention is very flat with little warpage and has high density.

Examples 10 and 11 (Comparison)
A positive electrode active material plate was prepared and evaluated in the same manner as in Example 1 except that the conditions described in Table 1 were used instead of the hydroxide raw material powder using the fine particles produced by the following production method. Incidentally, the production of fine grain, Ni molar ratio: Co: Mn = 50: 20 : so that 30, NiO (manufactured by Seido Chemical Industry), _Co 3 _{O 4} (manufactured by Seido Chemical Industry), MnCO ₃ ( Manufactured by Tosoh Corporation), wet pulverized for 10 hours using ethanol as a solvent in a pot mill, and the pulverized product was taken out of the pot mill and dried. The results were as shown in Table 1. Moreover, the photograph and cross-sectional SEM image of the positive electrode active material board produced in Example 10 are shown to FIG. As can be seen from these figures, the positive electrode active material plate produced by a technique not according to the present invention is warped and inferior in flatness.

1a Plate-like primary particles 1 Hydroxide raw material powder (secondary particles)

Claims (13)

A method for producing a positive electrode active material plate for a lithium secondary battery, comprising:
(A) It consists of secondary particles in which plate-like primary particles of nickel / cobalt / manganese composite hydroxide are agglomerated, and the plate-like primary particles are arranged almost radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder;
(B) A step of mixing a predetermined amount of a lithium compound with the hydroxide raw material powder to obtain a mixed powder, wherein the predetermined amount is relative to the total amount of Ni + Co + Nn contained in the hydroxide raw material powder. A molar ratio of the Li content contained in the lithium compound, that is, a step in which Li / (Ni + Co + Mn) is an amount that is 1.00 or more;
(C) calcining the mixed powder to synthesize a lithium transition metal composite oxide and / or precursor thereof;
(D) forming the molded body sheet by molding the lithium transition metal composite oxide and / or its precursor into a sheet;
(E) A step of placing a predetermined amount of lithium carbonate on the molded body sheet, wherein the predetermined amount is a lithium carbonate placed as described above with respect to a total amount of Ni + Co + Mn contained in the molded body sheet A molar ratio of the Li content contained, that is, a step in which Li / (Ni + Co + Mn) is 0.7 or more,
(F) firing the molded sheet on which the lithium carbonate is placed at a temperature of 850 ° C. or higher to form a positive electrode active material plate;
Comprising a method. The nickel-cobalt-manganese composite hydroxide is (Ni _x , Co _y , Mn _z ) (OH) ₂ (where 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0. 7. The method according to claim 1, wherein the method has a composition represented by x + y + z = 1). The positive electrode active material plate is Li _p (Ni _x , Co _y , Mn _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0 <x <0.8, 0 <y <1, 0 The method according to claim 1, wherein the composition has a composition of ≦ z ≦ 0.7 and x + y + z = 1).   The method according to any one of claims 1 to 3, wherein the molar ratio Li / (Ni + Co + Mn) in the step (e) is 1.0 to 1.8.   The sheet-shaped forming in the step (d) is performed by slurrying the lithium transition metal composite oxide and / or its precursor and subjecting it to tape forming. The method described in 1.   The method as described in any one of Claims 1-5 in which the said molded object sheet in the said (d) process has a thickness of 10-60 micrometers.   The method according to any one of claims 1 to 6, wherein in the step (e), lithium carbonate is placed on the molded sheet in the form of a lithium-containing sheet comprising the lithium compound.   The method according to claim 7, wherein the lithium-containing sheet in the step (e) is obtained by slurrying lithium carbonate and subjecting it to tape molding. Wherein said molded sheet in step (e) is, the positive active generally to the composition of matter plate the corresponding _{Li p (Ni x, Co y} , Mn z) in _{O 2} (wherein, 0.9 ≦ p ≦ 1.3 , 0 <x <0.8, 0 <y <1, 0 ≦ z ≦ 0.7, x + y + z = 1). 9. The method according to any one of items 8.   The method according to any one of claims 1 to 9, wherein in the step (a), the hydroxide raw material powder has a volume-based median diameter D50 of 2 to 10 µm.   The lithium compound used in the step (b) is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, and hydrates thereof. The method described.   The method according to any one of claims 1 to 11, wherein the calcination in the step (c) is performed at a temperature of 500 to 900 ° C.   The method according to any one of claims 1 to 12, wherein the firing in the step (f) is performed at a temperature of 850 to 960 ° C.