JP2010219068A - Manufacturing method of sheet-shaped particles for cathode active material of lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of stably manufacturing sheet-shaped particles for a cathode active material of a lithium secondary battery, which improves battery characteristics such as capacity of a lithium secondary battery. <P>SOLUTION: The manufacturing method of sheet-shaped particles for the cathode active material of the lithium secondary battery includes the following processes: (1) a slurry containing raw material particles is prepared; (2) the prepared slurry is molded into an independent molded body while a magnetic field is being impressed; (3) the sheet-shaped molded body is calcined; and (4) lithium is introduced into the calcined body. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing plate-like particles for a positive electrode active material of a lithium secondary battery (hereinafter simply referred to as “positive electrode active material plate-like particles”).

As a positive electrode active material of a lithium secondary battery (sometimes called a lithium ion secondary battery), a material having a so-called α-NaFeO ₂ type layered rock salt structure is widely used (for example, special (See Japanese Unexamined Patent Publication No. 2003-132877). In such a positive electrode active material having a layered rock salt structure, lithium ions (Li ⁺ ) are present on crystal planes other than the (003) plane (lithium ion entry / exit planes: for example, (101) plane or (104) plane). In and out. The charging / discharging operation is performed by the entry and exit of the lithium ions.

Here, the “layered rock salt structure” is a crystal structure in which a lithium layer and a transition metal layer other than lithium are alternately stacked with an oxygen layer interposed therebetween, that is, a transition metal ion layer and a lithium through an oxide ion. It refers to a crystal structure in which single layers are alternately stacked (typically an α-NaFeO ₂ type structure: a structure in which transition metals and lithium are regularly arranged in the [111] axis direction of a cubic rock salt type structure).

  In the positive electrode active material of this type of battery, more lithium ion entry / exit surfaces are exposed to the electrolyte, thereby improving battery characteristics such as capacity. The present invention has been made to solve such problems. That is, an object of the present invention is to provide a method for more stably producing the positive electrode active material plate-like particles capable of improving battery characteristics such as capacity in a lithium secondary battery than before.

The characteristic of this invention is that the manufacturing method of the said positive electrode active material plate-like particle includes the following processes.
-Prepare slurry containing raw material particles-Slurry preparation step-Form the slurry into a self-supporting sheet-like molded body while applying a magnetic field, Sheet molding step-Firing the molded body, Firing step- Lithium introduction process for introducing lithium into the fired body obtained by the firing process

The positive electrode active material plate-like particle manufacturing method of the present invention may further include the following steps.
-Crushing process which crushes the sheet-like sintered body obtained by the said baking process In this case, in the said lithium introduction | transduction process, lithium is introduce | transduced into the pulverized particle obtained by the said crushing process.

  In the slurry preparation step, it is preferable that the viscosity of the slurry is adjusted to 30 to 300 cP.

The magnetic field application conditions in the sheet forming step are preferably as follows.
Magnetic flux density: 1 Tesla or higher Magnetic field application direction: 20 ° ≦ θ ≦ 70 °
(Θ is an angle formed by the direction in which the magnetic field is applied and the normal of the compact)

  “Plate-like particles” refer to particles whose outer shape is plate-like. The concept of “plate-like” is clear from a social wisdom without any special explanation in the present specification, but can be defined as follows, for example.

  “Plate-like” means that particles are placed on a horizontal plane (a plane perpendicular to the vertical direction, which is the direction in which gravity acts), stably (external impact (the particles are flying from the horizontal plane). The first plane and the second plane orthogonal to the horizontal plane (the first plane and the second plane) in a state of being placed (in a manner that will not fall down even if subjected to impact) When the cross section of the particle is observed by crossing the plane and typically orthogonal, the angle along the horizontal plane (parallel to or parallel to the horizontal plane) The dimension in the width direction which is the α degree (0 <α <45) direction (the dimension is referred to as the “width” or “diameter” of the particle) is the direction perpendicular to the width direction. Dimension in a certain thickness direction (the dimension is the "thickness of the particle It is referred to as a larger state. The above-mentioned “thickness” does not include a void portion between the horizontal plane and the particle.

  That is, when the “aspect ratio” is defined as a value obtained by dividing the particle “width”, that is, the maximum diameter in the direction perpendicular to the thickness direction of the particle by the thickness of the particle, the “plate-like” particle is an aspect ratio. Refers to particles having a value exceeding 1 (typically 2 or more). In addition, as described later, the positive electrode active material plate-like particles according to the present invention preferably have an aspect ratio of 4 to 20.

  The positive electrode active material plate-like particles according to the present invention are usually formed in a flat plate shape. Here, “flat plate” refers to a state in which the particle is stably placed on a horizontal plane, and the height of the void formed between the horizontal plane and the particle is smaller than the thickness of the particle. It shall be said. Since what is bent more than this usually does not occur in this type of plate-like particles, the above definition is appropriate for the positive electrode active material plate-like particles according to the present invention.

  In a state where particles are stably placed on a horizontal plane, the thickness direction is not necessarily parallel to the vertical direction. For example, in a state where the particles are stably placed on a horizontal plane, the cross-sectional shape of the particles by the first plane or the second plane is (a) a rectangle, (b) a rhombus, (c) an ellipse. A case is assumed in which the most approximate shape is classified. When this particle cross-sectional shape approximates (a) a rectangle, the width direction is a direction parallel to the horizontal plane in the above state, and the thickness direction is a direction parallel to the vertical direction in the above state.

  On the other hand, in the case of (b) rhombus or (c) ellipse, the width direction makes a slight angle (45 degrees or less: typically about several to 20 degrees) with the horizontal plane in the above state. . In this case, the width direction is a direction connecting two points on the outline of the cross section that have the longest distance from each other (this definition is a diagonal line in the case of the above-described (a) rectangle) Is not appropriate to end up).

  In addition, the “plate surface” of the particle is a surface facing the horizontal plane in a state where the particle is stably placed on the horizontal plane, or is positioned above the particle and parallel to the horizontal plane when viewed from the horizontal plane. A surface that faces a virtual plane. The “plate surface” of the particle is sometimes referred to as the “principal surface” because it is the widest surface of the plate-like particle. The plane intersecting (typically orthogonal) the plate surface (main surface), that is, the surface intersecting the plate surface direction (or in-plane direction) that is perpendicular to the thickness direction is a particle. From the edge of the particle in a state where the particle is stably placed on the horizontal plane (when viewed from above in the vertical direction with the particle stably placed on the horizontal surface) , Referred to as “end face”.

  However, the positive electrode active material plate-like particles according to the present invention often have a particle cross-sectional shape that approximates the above-mentioned (a) rectangle. For this reason, in the positive electrode active material plate-like particle according to the present invention, the thickness direction may be a direction parallel to the vertical direction in a state where the particle is stably placed on a horizontal plane. Similarly, in the positive electrode active material plate-like particle according to the present invention, the “plate surface” of the particle may be a surface orthogonal to the thickness direction of the particle.

  A “self-supporting” sheet-like molded body refers to a sheet-like molded body that can be handled as a single unit independently of other supports, and typically, as a single sheet-like molded body. The shape can be maintained.

  In the manufacturing method of the present invention, by applying a magnetic field in the predetermined manner as described above in the sheet forming step, a self-supporting sheet-like formed body is formed in a state where the raw material particles are well oriented. The

Specifically, for example, when the raw material particles are Co ₃ O ₄ , when a magnetic field is applied, the (111) surface (the surface corresponding to the (003) surface in the LiCoO ₂ particles after firing and lithium introduction). ) Are oriented so that) is perpendicular to the magnetic field application direction. Therefore, by inclining the magnetic field application direction with respect to the thickness direction of the molded body, the surface corresponding to the lithium ion entrance / exit surface after firing and lithium introduction is satisfactorily exposed on the plate surface of the molded body. To do.

  Therefore, according to the present invention, it is possible to more stably manufacture the positive electrode active material plate-like particles having more lithium ion entrance / exit surfaces exposed on the surface by a simple manufacturing process. Specifically, for example, the positive electrode active material plate-like particles (more specifically, for example, in X-ray diffraction, (003) plane in which lithium ions cannot enter and exit are aligned so as to intersect the plate surface. 104) The ratio [003] / [104] of the diffraction intensity by the (003) plane to the diffraction intensity by the plane is in the range of 0.005 to 1.0) by the production method of the present invention. It can be manufactured stably.

  As the degree of orientation, when the peak intensity ratio [003] / [104] is 1.0 or less, lithium ions can be easily taken out, and the charge / discharge characteristics are significantly improved. However, when the peak intensity ratio [003] / [104] is less than 0.005, the cycle characteristics deteriorate. This is considered to be because if the degree of orientation is too high (that is, the orientation of the crystals is too uniform), the particles are easily broken by the volume change of the crystals accompanying the entry and exit of lithium ions (this cycle characteristic deterioration) The details of the reason are not clear.)

  In this regard, if the slurry viscosity is too low, it is difficult to maintain the orientation state of the raw material particles after application of the magnetic field. On the other hand, if the slurry viscosity is too high, the raw material particles are hardly oriented well even when a magnetic field is applied. For this reason, even if the slurry viscosity is too high or too low, it becomes difficult to obtain the positive electrode active material plate-like particles in a good orientation state.

  On the other hand, if θ is too small (that is, if the magnetic field application direction is too close to the thickness direction of the molded body), the degree of exposure of the lithium ion entrance / exit surface to the plate surface becomes small, and the rate characteristics deteriorate. On the other hand, if θ is too large (that is, if the magnetic field application direction is too close to the plate surface direction of the molded body), the (003) plane is arranged in a stacked manner along the plate surface direction, so that the particle strength decreases. , Durability decreases.

  As described above, according to the present invention, it is possible to more stably produce the positive electrode active material plate-like particles that can improve battery characteristics such as capacity in a lithium secondary battery as compared with the related art.

It is sectional drawing which shows an example of schematic structure of a lithium secondary battery. It is an expanded sectional view of the positive electrode shown by FIG. 1A. It is an expansion perspective view of the plate-like particle for positive electrode active materials shown in FIG. It is an expansion perspective view of the positive electrode active material particle of a comparative example. It is an expansion perspective view of the positive electrode active material particle of a comparative example. It is a figure which shows schematic structure of the sheet forming apparatus which is an example of the apparatus used for the sheet forming process which concerns on the manufacturing method of this invention. It is a figure which shows schematic structure of the magnetic field application part shown by FIG. 3A. It is sectional drawing which shows the structure of the modification of the positive electrode shown by FIG. 1B.

  Embodiments of the present invention will be described below with reference to the drawings. It should be noted that various modifications that can be made to the present embodiment are described at the end of the description because if they are inserted during the description of the embodiment, the understanding of the consistent description of the embodiment is hindered. ing.

<Schematic configuration of lithium secondary battery>
FIG. 1A is a cross-sectional view showing a schematic configuration of a lithium secondary battery 10 to which an embodiment of the present invention is applied.

  Referring to FIG. 1A, the lithium secondary battery 10 of the present embodiment is a so-called liquid type, and includes a battery case 11, a separator 12, an electrolyte 13, a negative electrode 14, and a positive electrode 15.

  The separator 12 is provided so as to bisect the inside of the battery case 11. In the battery case 11, a liquid electrolyte 13 is accommodated, and a negative electrode 14 and a positive electrode 15 are provided so as to face each other with the separator 12 therebetween.

  As the electrolyte 13, for example, a non-aqueous solvent based electrolyte in which an electrolyte salt such as a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent is preferably used because of its electrical characteristics and ease of handling. Examples of the solvent for the nonaqueous electrolytic solution include chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propion carbonate; cyclic esters having high dielectric constant such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; A mixed solvent of a chain ester and a cyclic ester can be used, and a mixed solvent with a cyclic ester having a chain ester as a main solvent is particularly suitable.

As the electrolyte salt to be dissolved in the solvent described above when the preparation of the non-aqueous electrolyte, 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 (RfSO ₂ ) (Rf′SO ₂ ), LiC (RfSO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [wherein Rf and Rf ′ are fluoroalkyl groups], etc. can be used. These may be used alone or in combination of two or more. Among the above electrolyte salts, a fluorine-containing organic lithium salt having 2 or more carbon atoms is particularly preferable. This is because this fluorine-containing organolithium salt has a large anionic property and is easily ion-separated, so that it is easily dissolved in the above-mentioned solvent. The concentration of the electrolyte salt in the nonaqueous electrolytic solution is not particularly limited, but is, for example, 0.3 mol / l or more, more preferably 0.4 mol / l or more, and 1.7 mol / l or less, more preferably 1. .5 mol / l or less.

The negative electrode active material according to the negative electrode 14 may be any material as long as it can occlude and release lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, mesocarbon micro Carbonaceous materials such as beads, carbon fibers, activated carbon and the like are used. In addition, metallic lithium, alloys containing silicon, tin, indium, etc., oxides of silicon, tin, etc. that can be charged and discharged at a low potential close to lithium, and nitriding of lithium and cobalt such as Li _2.6 Co _0.4 N Lithium storage materials such as materials can also be used as the negative electrode active material. Furthermore, a part of graphite can be replaced with a metal, oxide, or the like that can be alloyed with lithium. When graphite is used as the negative electrode active material, the voltage at the time of full charge can be regarded as about 0.1 V on the basis of lithium, so the potential of the positive electrode 15 is calculated for convenience by adding 0.1 V to the battery voltage. Therefore, it is preferable that the charging potential of the positive electrode 15 is easy to control.

  FIG. 1B is an enlarged cross-sectional view of the positive electrode 15 shown in FIG. 1A. Referring to FIG. 1B, the positive electrode 15 includes a positive electrode current collector 15a and a positive electrode active material layer 15b. The positive electrode active material layer 15b is composed of a binder 15b1 and plate particles 15b2 for positive electrode active material.

  The basic configuration of the lithium secondary battery 10 and the positive electrode 15 shown in FIGS. 1A and 1B (battery case 11, separator 12, electrolyte 13, negative electrode 14, positive electrode current collector 15a, and binder 15b1. Is included in the present specification, and a detailed description thereof is omitted.

  The positive electrode active material plate-like particle 15b2 according to an embodiment of the present invention is a particle containing lithium and having a layered rock salt structure, and is formed in a plate shape having a thickness of about 2 to 100 μm.

  2A is an enlarged perspective view of the plate-like particles 15b2 for positive electrode active material shown in FIG. 2B and 2C are enlarged perspective views of positive electrode active material particles of a comparative example.

  As shown in FIG. 2A, the plate-like particles 15b2 for the positive electrode active material are plate surfaces (upper surface A and lower surface B: hereinafter “upper surface”) that are surfaces orthogonal to the thickness direction (vertical direction in the figure). Surfaces other than (003) (for example, (101) surface and (104) surface) are exposed on “surface A” and “lower surface B” respectively referred to as “plate surface A” and “plate surface B”. Is formed.

  That is, the plate-like particles 15b2 for the positive electrode active material are formed so that surfaces other than (003) (for example, (104) surface) are parallel to the plate surfaces A and B of the particles. It should be noted that the (003) plane (surface painted in black in the drawing) may be exposed at the end surface C that intersects the plate surface direction (in-plane direction) of the particles.

  In contrast, the particles of the comparative example shown in FIG. 2B are formed in an isotropic shape instead of a thin plate shape. Moreover, although the particle of the comparative example shown by FIG. 2C is thin plate shape, it is formed so that (003) may be exposed to both surfaces (plate surface A and B) in the thickness direction of particle | grains. The particles of these comparative examples are produced by a conventional production method.

  In addition, the thickness of the plate-like particle 15b2 for the positive electrode active material is 2 to 100 μm, more preferably 5 to 50 μm, and still more preferably 5 to 20 μm. When the thickness is more than 100 μm, the diffusion distance of lithium at the time of introduction of lithium is increased, so that the rate characteristics are lowered and the sheet formability is deteriorated. In addition, the thickness of the positive electrode active material plate-like particles 15b2 is desirably 2 μm or more. If it is thinner than 2 μm, the effect of increasing the filling rate is reduced.

  The aspect ratio (value obtained by dividing the maximum diameter in the direction orthogonal to the thickness direction of the particle by the thickness of the particle) of the plate-like particle 15b2 for the positive electrode active material is preferably 4 to 20. When the aspect ratio is smaller than 4, the effect of expanding the lithium ion entrance / exit surface by orientation becomes small. On the other hand, if the aspect ratio is greater than 20, the positive electrode active material plate particles 15b2 are filled so that the plate surface of the positive electrode active material plate particles 15b2 is parallel to the in-plane direction of the positive electrode active material layer 15b. In this case, the rate characteristic is deteriorated because the lithium ion diffusion path in the thickness direction of the positive electrode active material layer 15b becomes longer.

<Outline of production method of plate-like particles for positive electrode active material>
The plate-like particle for positive electrode active material 15b2 having the configuration shown in FIG. 2A is stably (easy and reliable) formed by a manufacturing method including the following steps.
(1) Slurry preparation step: A slurry containing raw material particles is prepared with a predetermined viscosity (30 to 300 cP).
(2) Sheet forming step: The prepared slurry is formed into a self-supporting sheet-like formed body (green sheet) while applying a magnetic field. At this time, the application conditions of the magnetic field are as follows.
・ Magnetic flux density: 1 Tesla or more ・ Magnetic field application direction: 20 ° <θ <70 °
(Θ is the angle between the magnetic field application direction and the green sheet thickness direction (normal direction of the plate surface))
(3) Firing step: firing the green sheet.
(4) Crushing step: The fired body sheet obtained by the firing step is crushed.
(5) Lithium introduction step: Lithium is introduced into the fired particles obtained in the crushing step.

As the raw material particles, powders of transition metal compounds that do not contain lithium compounds, such as Co ₃ O ₄ , (Ni, Co) (Co, Al) ₂ O ₄ , (Ni, Co, Al) O, are used. For the purpose of promoting grain growth, an appropriate amount of additives (for example, low melting point oxide such as bismuth oxide, low melting point glass such as borosilicate glass) can be added. In addition, the slurry is preferably degassed by reducing the pressure.

  For example, a doctor blade method is used as a method for forming a “self-supporting” sheet-like formed body, that is, a green sheet. As described above, the thickness of the sheet molding is set to 100 μm or less. Further, when the thickness of the sheet molding is 2 μm or more, it becomes easy to form a “self-supporting” sheet-like molded body, that is, a green sheet. The thickness of the sheet molding (the thickness of the green sheet) is almost the same as the thickness of the plate particles 15b2 for the positive electrode active material, and is appropriately set according to the use of the plate particles 15b2 for the positive electrode active material. .

  FIG. 3A is a diagram illustrating a schematic configuration of a sheet forming apparatus 20 which is an example of an apparatus used in the sheet forming process according to the manufacturing method of the present invention. The sheet molding apparatus 20 according to the present embodiment is configured to feed a long belt-like base film BF made of a synthetic resin such as polyethylene terephthalate (PET) or a metal thin plate such as stainless steel at a constant speed in a predetermined direction (y-axis positive direction in the figure). The green sheet GS is formed on the base film BF while being conveyed.

  Specifically, referring to FIG. 3A, the sheet forming apparatus 20 includes a coating unit 21, a magnetic field application unit 22, and a drying unit 23. The coating unit 21 is a so-called doctor blade type coating machine, and is configured to continuously apply the slurry S onto the base film BF with a predetermined thickness. The magnetic field application unit 22 is configured to orient the raw material particles by applying a magnetic field to the coating film CF formed on the base film BF by the coating unit 21. The drying unit 23 is configured to form the green sheet GS by drying the coating film CF subjected to the alignment treatment by the magnetic field application unit 22.

  FIG. 3B is a diagram showing a schematic configuration of the magnetic field application unit 22 shown in FIG. 3A. The magnetic field application unit 22 includes electromagnets 221 and 222 arranged to face each other with the base film BF interposed therebetween. The electromagnets 221 and 222 are provided so as to apply a magnetic field to the coating film CF before drying in a direction that forms a predetermined angle θ with the sheet thickness direction (z direction in the drawing). That is, the magnetic field application unit 22 is configured so that the magnetic field application direction with respect to the coating film CF is orthogonal to the sheet conveyance direction (y direction in the figure) and is inclined with respect to the sheet thickness direction.

  The obtained fired body sheet is in a state of being easily crushed at the grain boundary part. Therefore, the fired body sheet is placed on a mesh having a predetermined opening diameter and pressed with a spatula from above to break the fired body sheet into a large number of plate-like particles (fired body particles). In this crushing step, the aspect ratio of the sintered plate-like particles after crushing (that is, the aspect ratio of the plate-like particles for positive electrode active material 15b2 obtained after lithium introduction) is 4 to 20, Crushing conditions (such as mesh opening diameter) of the fired body sheet are set.

  Lithium compound such as lithium nitrate is added to the obtained fired particles, and the molar ratio Li / M between lithium (Li) and other transition metal (M) (when there are a plurality of types M, M = M1 + M2...) Is introduced so as to be 1 or more and heat treatment is performed. Here, the heat treatment temperature is preferably 750 ° C to 900 ° C. At a temperature lower than 750 ° C., the reaction does not proceed sufficiently. On the other hand, when the temperature is higher than 900 ° C., the orientation is remarkably lowered.

  Examples of the lithium source at the time of introducing lithium include various lithium salts such as lithium carbonate, lithium nitrate, lithium acetate, lithium chloride, lithium oxalate and lithium citrate, and lithium such as lithium methoxide and lithium ethoxide. Alkoxides can be used.

<Specific example>
Hereinafter, specific examples of the above-described manufacturing method and evaluation results of particles manufactured by the specific examples will be described in detail.

Specific example 1: Cobalt-nickel system <Production method>
<< Slurry Preparation >>
First, a slurry was prepared by the following method.

NiO powder (particle size 1-10 μm, manufactured by Shodo Chemical Industry Co., Ltd.) 75.1 parts by weight, Co ₃ O ₄ powder (particle size 1-5 μm, manufactured by Shodo Chemical Industry Co., Ltd.) 21.5 parts by weight, Al By mixing and pulverizing 3.4 parts by weight of ₂ O ₃ powder (particle size: 1-10 μm, manufactured by Showa Denko KK) and heat-treating at 1300 ° C. for 5 hours in the atmosphere (Ni, Co, Al) O powder was synthesized.

  100 parts by weight of (Ni, Co, Al) O raw material particles (particle size 0.3 μm) obtained by grinding this powder for 16 hours in a pot mill, and 150 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1) And 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) and 4 parts by weight of a plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) 2 parts by weight of an agent (product name: Leodole SP-O30, manufactured by Kao Corporation) was mixed. The mixture was defoamed by stirring under reduced pressure, and the viscosity was adjusted to 150 cP by appropriately adding a dispersion medium (the viscosity was measured with an LVT viscometer manufactured by Brookfield. The same applies hereinafter. .)

<< Sheet molding >>
The slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 10 μm. A green sheet in which raw material particles were oriented was obtained by applying a magnetic field to the sheet-like molded body (coating film) under the conditions of magnetic flux density B = 7 [T] and θ = 40 ° and then drying.

<< Baking >>
The green sheet peeled off from the PET film was cut into a 50 mm square with a cutter and placed in the center of a zirconia setter (dimension 90 mm square, height 1 mm) with an embossed projection of 300 μm in air. After heat treatment at 1000 ° C. for 10 hours, the portion not welded to the setter was taken out.

<< Disintegration >>
The (Ni, Co, Al) O fired body sheet thus obtained was placed on a sieve (mesh) having an opening diameter of 100 μm, and crushed by passing through the mesh while lightly pressing with a spatula.

<< Lithium introduction >>
The (Ni, Co, Al) O fired body powder obtained by crushing the fired body sheet and the LiNO ₃ powder (manufactured by Kanto Chemical Co., Ltd.) have a molar ratio of Li / NiCoAl) = 1.2. The mixture was heat-treated at 750 ° C. for 5 hours in an oxygen atmosphere (0.1 MPa) to obtain powdered Li (Ni, Co, Al) O ₂ plate-like particles.

<Evaluation method>
<< XRD evaluation >>
XRD (X-ray diffraction) measurement was performed by the following method: 2 g of ethanol plus 0.1 g of plate-like particles was dispersed for 30 minutes with an ultrasonic disperser (ultrasonic cleaner), and this was 25 mm. It spin-coated at 2000 rpm on the glass substrate of * 50mm, and it has arrange | positioned in the state with which a crystal plane and a glass substrate surface became parallel so that plate-shaped particle | grains may not overlap as much as possible. Using an XRD apparatus (Rigaku Co., Ltd., Geiger Flex RAD-IB), the XRD profile when the surface of the plate-like particle is irradiated with X-rays is measured, and the diffraction intensity (peak height) by the (104) plane is measured. The ratio [003] / [104] of the diffraction intensity (peak height) by the (003) plane was determined. In the above method, the plate surface of the plate-like particles is in surface contact with the glass substrate surface, and the particle plate surface and the glass substrate surface are parallel to each other. For this reason, according to the above method, a diffraction profile is obtained by a crystal plane that is parallel to the crystal plane of the grain plate surface, that is, a crystal plane that is oriented in the grain plane direction of the grain.

<< Battery evaluation >>
In order to evaluate the battery characteristics, a battery was prepared as follows.

The obtained Li (Ni, Co, Al) O ₂ plate-like particles, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 75: 20: 5 to prepare a positive electrode material. . A positive electrode active material layer was produced by press-forming 0.02 g of the prepared positive electrode material into a disk shape having a diameter of 20 mm at a pressure of 300 kg / cm ² .

The prepared positive electrode active material layer, the negative electrode made of a lithium metal plate, the stainless steel current collector plate, and the separator are arranged in the order of current collector plate-positive electrode active material layer-separator-negative electrode-current collector plate, and this aggregate is used as an electrolyte. The coin cell was produced by filling with. The electrolytic solution was prepared by dissolving LiPF ₆ in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an equal volume ratio so as to have a concentration of 1 mol / L.

  Using the battery (coin cell) produced as described above, the battery capacity (discharge capacity) and capacity retention rate were evaluated.

  Charge at a constant current until the battery voltage reaches 4.2 V at a current value of 0.1 C rate, and then charge at a constant voltage until the current value drops to 1/20 under the current condition of maintaining the battery voltage at 4.2 V. Charge / discharge operation of 10 minutes after that, followed by constant current discharge at a current value of 1 C rate until the battery voltage reaches 3.0 V, and then pause for 10 minutes. Three cycles were repeated, and the discharge capacity at the third cycle was measured.

  With respect to the produced battery, the test temperature was set to 25 ° C., and (1) 1C rate constant current-constant voltage charging to 4.2V and (2) 1C rate constant current discharging to 3.0V were repeated. Cycle charge / discharge was performed. The value obtained by dividing the discharge capacity of the battery after the end of 100 cycles of charge / discharge by the discharge capacity of the first battery was taken as the capacity retention rate (%).

<Evaluation results>
Sixteen production examples (Experimental Examples 1 to 9 and Comparative Example 1) in which the degree of orientation was changed by changing the conditions of slurry viscosity (η), magnetic flux density (B), and magnetic field application direction (θ) in the production method described above. The evaluation results of (7) to (7) are shown in the following Table 1 (those that match the conditions in the above production method are Experimental Example 2).

  As is apparent from the results in Table 1, in Examples 1 to 9 in which the slurry viscosity is 30 to 300 cP, the magnetic flux density is 1 Tesla or more, and the magnetic field application direction is 20 to 70 °, good discharge capacity and capacity retention rate are obtained. It was. In contrast, Comparative Examples 1 and 2 in which the slurry viscosity was out of the predetermined range, Comparative Example 3 in which the magnetic flux density in the applied magnetic field was small, and Comparative Examples 4 to 7 in which the magnetic field application direction θ was out of the predetermined range were good. The degree of orientation was not obtained, and the discharge capacity was low.

Specific Example 2: Cobalt-nickel-manganese ternary system <Production method>
<< Slurry Preparation >>
First, a slurry was prepared by the following method.

30.9 parts by weight of NiO powder (particle size 1-10 μm, manufactured by Shodo Chemical Co., Ltd.), 35.9 parts by weight of MnCO ₃ powder (particle size 1-10 μm, manufactured by Tosoh Corporation), Co ₃ O ₄ powder ( (Ni, Co) (Co, Al) by mixing and pulverizing 33.2 parts by weight (particle size 1-5 μm, manufactured by Shodo Chemical Co., Ltd.) and heat-treating at 850 ° C. for 5 hours in an air atmosphere. ₂ O ₄ powder was synthesized.

(Ni, Co) (Co, Al) ₂ O ₄ raw material particles (particle size: 0.3 μm) obtained by pulverizing this powder for 16 hours in a pot mill, and a dispersion medium (toluene: isopropanol = 1: 1) 150 parts by weight, 10 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) and plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) 4 Part by weight and 2 parts by weight of a dispersant (product name Leodol SP-O30, manufactured by Kao Corporation) were mixed. The mixture was degassed by stirring under reduced pressure, and the viscosity was adjusted to 150 cP.

<< Sheet molding >>
The slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 10 μm. A green sheet with oriented raw material particles was obtained by applying a magnetic field to the sheet-like molded body under the conditions of magnetic flux density B = 7 [T] and θ = 40 ° and then drying.

<< Baking >>
The green sheet peeled off from the PET film was cut into 30mm squares with a cutter and placed in the center of a zirconia setter (dimensions 90mm square, 1mm height) with a protrusion size of 300μm in the atmosphere. After the heat treatment at 900 ° C. for 10 hours, the portion not welded to the setter was taken out.

<< Disintegration >>
The (Ni, Co) (Co, Al) ₂ O ₄ fired body sheet thus obtained is placed on a sieve (mesh) having an opening diameter of 100 μm, and is crushed by allowing the mesh to pass while pressing lightly with a spatula. did.

<< Lithium introduction >>
(Ni, Co) (Co, Al) ₂ O ₄ powder obtained by crushing the fired body sheet and Li ₂ CO ₃ powder (manufactured by Kanto Chemical Co., Ltd.), Li / (Ni, Co) The mixture was mixed so that (Co, Al) ₂ O ₄ = 1.2, and heat-treated in a crucible at 900 ° C. for 12 hours to obtain powdered Li (NiCoMn) O ₂ plate-like particles.

<Evaluation>
In the same manner as in the specific example 1 (cobalt-nickel system) described above, 16 production examples in which the degree of orientation was changed by changing the conditions of slurry viscosity (η), magnetic flux density (B), and magnetic field application direction (θ) ( Comparative Examples 8 to 14 and Experimental Examples 10 to 18) were evaluated (Experimental Example 11 is the one that matches the conditions in the above manufacturing method). As is clear from the evaluation results shown in Table 2 below, also in this specific example (cobalt-nickel-manganese ternary system), the same result as in the above-described specific example 1 (cobalt-nickel system) was obtained.

Example 3: Cobalt-based <Production method>
<< Slurry Preparation >>
First, a slurry was prepared by the following method.

Co ₃ O ₄ powder (particle size: 1-5 μm, manufactured by Shodo Chemical Industry Co., Ltd.) was pulverized to produce Co ₃ O ₄ raw material particles (particle size: 0.3 μm) at a rate of 20 wt% Bi ₂ O ₃ ( 100 parts by weight with a particle size of 0.3 μm added by Taiyo Mining Co., Ltd., 150 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), and a binder (polyvinyl butyral: product number BM-2, Sekisui Chemical) 10 parts by weight of Kogyo Co., Ltd., 4 parts by weight of plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) and a dispersant (product name: Leodoll SP-O30, manufactured by Kao Corporation) 2 parts by weight were mixed. The mixture was degassed by stirring under reduced pressure, and the viscosity was adjusted to 150 cP.

<< Sheet molding >>
The slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 10 μm. A green sheet with oriented raw material particles was obtained by applying a magnetic field to the sheet-like molded body under the conditions of magnetic flux density B = 7 [T] and θ = 40 ° and then drying.

<< Baking >>
The green sheet peeled off from the PET film is cut into a 70 mm square with a cutter and placed in the center of a zirconia setter (dimension 90 mm square, height 1 mm) with a protrusion size of 300 μm. After that (the conditions for firing and temperature lowering will be described later), a portion not welded to the setter was taken out.

<< Disintegration >>
The Co ₃ O ₄ fired body sheet thus obtained was placed on a sieve (mesh) having an opening diameter of 100 μm, and crushed by passing through the mesh while lightly pressing with a spatula.

<< Lithium introduction >>
Co ₃ O ₄ powder obtained by pulverizing the fired body sheet and Li ₂ CO ₃ powder (manufactured by Kanto Chemical Co., Inc.) were mixed so that Li / Co = 1.0, and in the crucible Was subjected to heat treatment at 750 ° C. for 3 hours to obtain powdered LiCoO ₂ plate-like particles.

<Evaluation>
Three production examples (Comparative Examples 15 and 16 and Experimental Example 19) in which the degree of orientation was changed by changing the magnetic field application direction (θ) were evaluated by the same method as in Specific Examples 1 and 2 described above ( The example that matches the conditions in the above manufacturing method is Experimental Example 19). As is clear from the evaluation results shown in Table 3 below, in this specific example (cobalt type), the same results as those of the specific examples described above were obtained.

<Effect by embodiment>
Thus, in the positive electrode active material plate-like particle 15b2 produced by the production method of the present invention (the above specific example), the lithium ion entrance / exit surface is oriented so as to be parallel to the plate surface of the particle, and the plate Most of the surface of the particle-like particle is exposed. On the other hand, the (003) plane where lithium ions cannot enter and exit is only slightly exposed at the end faces of the plate-like particles (see FIG. 2A).

  That is, in the positive electrode active material plate-like particles 15b2 produced by the production method of the present invention, the exposure of the lithium ion entrance / exit surfaces to the electrolyte 13 (including those permeating the binder 15b1) is more. In addition, the exposure ratio of the surface where lithium ions cannot enter and exit is extremely low. In the example of FIG. 2A, the (003) plane is exposed as a plane at the end face C, but other structures can also be realized. For example, a structure (see FIG. 3C) in which the (003) plane and another plane (such as the (104) plane) form steps can be formed.

  By the way, in the normal positive electrode active material plate-like particles (as shown in FIG. 2B and FIG. 2C), when the particle diameter is reduced, the specific surface area is increased and the rate characteristics are increased. However, since the durability is lowered, the capacity is reduced because the ratio of the binder is increased. As described above, in the normal (conventional) plate-like particles for the positive electrode active material, the rate characteristics, the durability and the capacity are in a trade-off relationship.

  In contrast, in the plate-like particles for the positive electrode active material produced by the production method of the present invention, when the particle diameter is increased to improve the durability and capacity, the total area of the lithium ion entry / exit surface is also increased, High rate characteristics can be obtained. Therefore, according to the present invention, capacity, durability, and rate characteristics can be improved as compared with the conventional case.

  In particular, a lithium-ion secondary battery for mobile devices mounted on a mobile phone, a notebook PC, or the like requires a high-capacity battery that can be used for a long time. In order to increase the capacity, it is effective to improve the filling rate of the active material powder, and it is preferable to use large particles having a particle size of 10 μm or more with good filling properties.

  In this regard, in the prior art, when the particle diameter is increased to 10 μm or more, the surface (003) where the lithium ions and electrons cannot enter and exit from the crystal structure becomes plate-like particles that are widely exposed on the surface (see FIG. 2C). ), The output characteristics may be adversely affected.

  On the other hand, in the plate-like particles for the positive electrode active material produced by the production method of the present invention, the conductive surfaces of lithium ions and electrons are widely exposed on the surface. For this reason, according to this invention, the plate-like particle for positive electrode active materials can be enlarged without adversely affecting the output characteristics. Therefore, according to the present invention, it is possible to provide a high-capacity positive electrode active material layer that is filled more than before.

<List of examples of modification>
It should be noted that the above-described embodiments and specific examples are merely examples of realization of the present invention that the applicant has considered to be the best at the time of filing of the present application, and the present invention is not limited to the above. It should not be limited at all by the embodiments and specific examples. Therefore, it goes without saying that various modifications can be made to the above-described embodiments and specific examples without departing from the essential part of the present invention.

  Hereinafter, some modifications will be exemplified. In the following description of the modification, components having the same configurations and functions as the components in the above-described embodiment are given the same name and the same reference numerals in this modification. And about description of the said component, description in the above-mentioned embodiment shall be used suitably in the range which is not inconsistent.

  However, it goes without saying that the modified examples are not limited to the following. The limited interpretation of the present invention based on the description of the above-described embodiment and the following modifications unfairly harms the interests of the applicant (especially rushing the application under the principle of prior application), but improperly imitates the imitator. It is beneficial and not allowed.

  It goes without saying that the configuration of the above-described embodiment and the configuration described in each of the following modifications can be combined in an appropriate manner within a technically consistent range.

  The present invention is not limited to the configurations and manufacturing methods specifically disclosed in the above-described embodiments. For example, the application target of the plate-like particles for the positive electrode active material of the present invention is not limited to a liquid type like the lithium secondary battery 10 shown in FIG. 1A. Specifically, as the electrolyte, an inorganic solid, an organic polymer, or a gel-like one in which an electrolytic solution is impregnated into an organic polymer, or the like can be used.

  Further, as shown in FIG. 4, in the positive electrode active material layer 15b, plate-like particles 15b2 for the positive electrode active material produced by the production method of the present invention and conventional equiaxed particles 15b3, They may be mixed at an appropriate mixing ratio. Specifically, for example, the particles are arranged efficiently by mixing equiaxed particles and the plate-like particles 15b2 for the positive electrode active material having the same thickness as the particle size at an appropriate mixing ratio. The filling rate can be increased.

  The crushing step may be performed after the lithium introduction step. That is, a manufacturing method in which a positive electrode active material sheet is formed by performing a lithium introduction step after the firing step, and plate-like particles for the positive electrode active material are obtained by pulverizing the positive electrode active material sheet, Within the scope of the invention.

  In the sheet forming step, methods other than the doctor blade method are also used favorably. For example, in the sheet forming step, a drum dryer method can be used in which a slurry containing raw materials is applied onto a heated drum and the dried material is scraped off with a scraper. Further, in the sheet forming step, a disk dryer method can be used in which slurry is applied to a heated disk surface, dried and scraped with a scraper. Furthermore, an extrusion method using a clay containing raw material particles can also be used in the sheet forming step.

  The plate-like particle for positive electrode active material according to the present invention is not limited to the specific composition shown in the above specific examples as long as it has a layered rock salt structure. For example, the plate-like particles for a positive electrode active material may be made of a solid solution containing nickel, manganese or the like in addition to cobalt. Specific examples include lithium nickelate, lithium manganate, nickel / lithium manganate, nickel / lithium cobaltate, cobalt / nickel / lithium manganate, cobalt / lithium manganate, and the like. Further, these materials include Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba. One or more elements such as Bi and Bi may be contained.

Note that in the olivine-structured positive electrode active material typified by LiFePO ₄ , the lithium ion conduction direction is the b-axis direction ([010] direction). Therefore, plate-like particles for a positive electrode active material having good performance can be obtained by using plate-like particles oriented so that the ac plane (for example, (010) plane) is parallel to the plate surface.

  The raw material particles may partially contain a lithium compound.

Instead of simply mixing (h00) oriented Co ₃ O ₄ particles and Li ₂ CO ₃ in the lithium introduction step and heating them for a predetermined time, they are mixed with sodium chloride (melting point 800 ° C.) or potassium chloride (melting point 770 ° C.). It may be mixed and heated in a flux such as.

  Other modifications not specifically mentioned are naturally included in the technical scope of the present invention without departing from the essential part of the present invention.

  In addition, in each element constituting the means for solving the problems of the present invention, the elements expressed in terms of operation and function are the specific structures disclosed in the above-described embodiments and modifications, It includes any structure that can realize this action / function. Furthermore, the contents of the prior application and each publication (including the specification and the drawings) cited in the present specification may be incorporated as appropriate as part of the present specification.

DESCRIPTION OF SYMBOLS 10 ... Lithium secondary battery 11 ... Battery case 12 ... Separator 13 ... Electrolyte 14 ... Negative electrode 15 ... Positive electrode 15a ... Positive electrode collector 15b ... Positive electrode active material layer 15b1 ... Binder 15b2 ... Plate-like particle 20 for positive electrode active materials ... Sheet forming apparatus 21 ... coating unit 22 ... magnetic field application unit 221 ... electromagnet 222 ... electromagnet 23 ... drying unit A ... plate surface (upper surface) B ... plate surface (lower surface) C ... end surface BF ... base film CF ... coating Film GS ... Green sheet S ... Slurry

Japanese Patent Laid-Open No. 9-22893 JP 2003-132877 A JP 2003-346809 A

Claims (4)

A slurry preparation step of preparing a slurry containing raw material particles;
The slurry is formed into a self-supporting sheet-like molded body while applying a magnetic field, and a sheet forming step,
Firing the molded body, and a firing step;
Introducing lithium into the fired body obtained by the firing step, a lithium introduction step;
The manufacturing method of the plate-shaped particle for positive electrode active materials of a lithium secondary battery characterized by including these. In the manufacturing method of the plate-shaped particle for positive electrode active materials of a lithium secondary battery of Claim 1,
Crushing the sheet-like fired body obtained by the firing step, further comprising a crushing step,
The method for producing plate-like particles for a positive electrode active material of a lithium secondary battery, wherein the lithium introduction step introduces lithium into the crushed particles obtained by the pulverization step. A method for producing plate-like particles for a positive electrode active material of a lithium secondary battery according to claim 1 or 2,
In the slurry preparation step, the viscosity of the slurry is adjusted to 30 to 300 cP. A method for producing plate-like particles for a positive electrode active material of a lithium secondary battery. A method for producing plate-like particles for a positive electrode active material of a lithium secondary battery according to any one of claims 1 to 3,
The sheet forming step has a magnetic flux density of 1 Tesla or more and 20 ° ≦ θ ≦ 70 ° (θ is an angle formed between the magnetic field application direction and the normal of the molded body)
A method for producing plate-like particles for a positive electrode active material of a lithium secondary battery, wherein the compact is molded while applying a magnetic field.

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