JP2014139926A - Method for manufacturing positive electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a positive electrode for a lithium secondary battery, by which both high energy density and high output characteristics can be achieved.SOLUTION: The method for manufacturing a positive electrode for a lithium secondary battery includes the steps of: preparing positive electrode active material powder that comprises a plurality of primary particles comprising a positive electrode active material having a layered rock salt structure, and includes oriented secondary particles comprising the plurality of primary particles having been oriented; mixing the positive electrode active material powder with a conductive assistant, a binder and a solvent to obtain a positive electrode mixture paste; coating the positive electrode mixture paste on a collector to form a positive electrode layer; and subjecting the positive electrode layer to a press work against the collector, the press-working being performed such that D/D, a ratio of a packing density Dof the positive electrode active material powder in the positive electrode layer relative to a tap density Dof the positive electrode active material powder after the press-working, is 1.15 or more.

Description

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

  With the reduction in size and weight of mobile phones and personal computers, there are increasing demands for higher energy density and higher output in lithium ion batteries used for these. Various positive electrodes have been proposed to satisfy these requirements.

For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2011-70994) discloses a positive electrode active material having a tap density of 0.8 to 3.0 g / cm ³ composed of particles having an average particle diameter of 0.05 μm or more and 1 μm or less. A non-aqueous electrolyte secondary battery containing a powder and further containing 0.5 to 20 parts by weight of a conductive agent, 0.5 to 10 parts by weight of a binder, and 10 to 120 parts by weight of a solvent with respect to 100 parts by weight of the positive electrode active material powder A positive electrode mixture is disclosed. Thus, by using the fine particles as the positive electrode active material powder, the specific surface area corresponding to the reaction area with the electrolytic solution can be increased to improve the output characteristics. However, since it is necessary to add a conductive additive in proportion to the specific surface area to ensure conductivity, it is considered that the energy density decreases accordingly.

Further, Patent Document 2 in the (JP 2012-146590 JP), the average particle diameter _(D 50) fine and average particle diameter of 18~25μm _(D 50) 3~7μm of coarse and a 9: 1 to 6 A positive electrode using a positive electrode active material contained in a mixing ratio of 4: 4 is disclosed. In this positive electrode, high energy density is realized by mixing fine particles and coarse particles. However, it is considered that since the ratio of coarse particles in the positive electrode material is high, the specific surface area is reduced, and the output characteristics are reduced accordingly.

  By the way, a positive electrode active material for a lithium ion battery comprising secondary particles composed of a plurality of oriented primary particles is also known. For example, Patent Document 3 (International Publication No. 2012/137534) includes a plurality of primary particles composed of a positive electrode active material having a layered rock salt structure, and the plurality of primary particles are oriented. A positive electrode active material powder comprising is disclosed.

JP 2011-70994 A JP 2012-146590 A International Publication No. 2012/137534

  The present inventors have recently used a positive electrode active material powder containing oriented secondary particles in which a plurality of primary particles having a layered rock salt structure are oriented, and after forming the positive electrode layer, the particles are cracked or crushed by a pressing process. It has been found that by increasing the density of the electrode, an electrode having both high energy density and high output characteristics can be produced.

  Accordingly, it is an object of the present invention to provide a method for producing a positive electrode for a lithium secondary battery that achieves both high energy density and high output characteristics.

According to one aspect of the present invention, a positive electrode active material powder comprising a plurality of primary particles composed of a positive electrode active material having a layered rock salt structure and including oriented secondary particles in which the plurality of primary particles are oriented is prepared. And a process of
Mixing the positive electrode active material powder with a conductive additive, a binder and a solvent to obtain a positive electrode mixture paste;
Applying the positive electrode mixture paste on a current collector to form a positive electrode layer;
The positive electrode layer is pressed toward the current collector, and at this time, the ratio D ₂ of the packing density D ₂ of the positive electrode active material powder in the positive electrode layer after the pressing to the tap density D ₁ of the positive electrode active material powder. / a _{step D 1} is made the press working so as to at least 1.15,
The manufacturing method of the positive electrode for lithium secondary batteries containing is provided.

It is a conceptual diagram for demonstrating the orientation secondary particle used as a positive electrode active material powder in this invention. It is a SEM image which image | photographed the cross section of the electrode obtained in Example 1 (comparison). 6 is a SEM image obtained by photographing a cross section of an electrode obtained in Example 4. 10 is an enlarged view of an SEM image obtained by photographing a cross section of an electrode obtained in Example 4. FIG. It is a graph which shows the relationship between the resistance value measured in Examples 1-19, and the ratio of an orientation secondary particle. It is a conceptual diagram for demonstrating the non-oriented secondary particle used as a positive electrode active material powder in a prior art.

TECHNICAL FIELD The present invention of a positive electrode for a lithium secondary battery, a process for producing a positive electrode for a lithium secondary battery. In this specification, the lithium secondary battery is a term including various secondary batteries that can be charged and discharged by insertion / extraction of lithium ions, such as a lithium ion secondary battery and a metal lithium secondary battery. Typically, it is a lithium ion secondary battery.

  In the method of the present invention, firstly, a positive electrode active material powder comprising a plurality of primary particles composed of a positive electrode active material having a layered rock salt structure and including oriented secondary particles in which the plurality of primary particles are oriented is prepared. To do. The structure of such a positive electrode active material powder is conceptually shown in FIG. As shown in FIG. 1, the positive electrode active material powder 10 includes oriented secondary particles 14 composed of a plurality of primary particles 12, and the primary particles 12 are single crystal particles having a layered rock salt structure. Due to the layered rock salt structure, the primary particles 12 have a (003) plane that is difficult for lithium ions and electrons to enter and exit, and a plane that is easy for lithium ions and electrons to enter and exit (that is, a plane other than the (003) plane. ) And exist. For this reason, as indicated by arrows in FIG. 1, the plurality of primary particles 12 are oriented so that the surfaces on which lithium ions easily enter and exit are aligned in a substantially uniaxial direction. The contact between the surfaces where lithium ions and electrons are likely to enter and exit between 12 (that is, surfaces other than the (003) surface) is sufficiently ensured, and lithium ion conductivity and electron conductivity are ensured satisfactorily. Yes. The positive electrode active material comprising such oriented secondary particles is a known material as disclosed in Patent Document 3.

  And after apply | coating the positive mix paste containing this positive electrode active material powder on a collector and forming a positive electrode layer, a positive electrode layer is pressed toward a collector. Pressing the positive electrode mixture layer with a roller or the like to increase the density is a conventional method as described in Patent Document 2, but as far as the present inventors know, the positive electrode active material It has been believed that pressing so hard that the secondary particles break or collapse should be avoided. As specified in Patent Document 2, in order to increase the density of the positive electrode active material particles, when trying to roll the positive electrode mixture layer at a high pressure when rolling the positive electrode mixture, This is because there is a concern that the positive electrode active material particles are cracked, the conductivity is lowered, and the cycle characteristics or output characteristics are lowered. This is widely used in the past, as shown in FIG. 6, which is made up of secondary particles 24 (hereinafter sometimes referred to as non-oriented secondary particles) in which innumerable primary particles 22 are aggregated non-oriented. This is especially true for the positive electrode active material powder 20. This is because, in such non-oriented secondary particles 24, the surfaces where lithium ions and electrons easily enter and exit between the adjacent primary particles 22 and 22 are directed in different directions, so that the electron conduction at the contact point is originally slow, In addition, the electron conduction path passing through the contact point is divided by the grain boundary crack C, and the electron conduction is inhibited.

On the other hand, in the method of the present invention using the positive active material powder of a very special form called oriented secondary particles, the press working has a packing density D ₂ of the positive active material powder in the positive electrode layer after the press working, The ratio D ₂ / D ₁ to the tap density D ₁ of the positive electrode active material powder is 1.15 or more. This ratio means that the at least part of the oriented secondary particles is intensively pressed to such an extent that it is broken or crushed, and by doing so, a positive electrode that achieves both high energy density and high output characteristics. Can be manufactured. That is, the high energy density is realized by being able to fill the active material in the positive electrode at a very high density by compacting the particles so that the particles are broken or crushed in the pressing process. In particular, in the method of the present invention, since the specific surface area of the positive electrode active material can be increased by cracking or crushing the particles in the pressing step, it is possible to use a positive electrode active material having a large particle size, thereby easily realizing a high energy density. . On the other hand, the high output characteristics include an increase in specific surface area (ie, an increase in the reaction area with the electrolyte) due to cracking or crushing of the oriented secondary particles in the pressing process, and sufficient electron conductivity even after deformation by pressing. This is realized by the properties unique to the oriented secondary particles. In particular, the latter is an unexpected property due to the use of oriented secondary particles as a positive electrode active material, and is a property that is not found in non-oriented secondary particles. That is, as shown in FIG. 1, in the positive electrode active material 10 composed of secondary particles 14 in which innumerable primary particles 12 are aligned, lithium ions and electrons easily enter and exit between adjacent primary particles 12 and 12. Since the plane is oriented (preferably in a substantially uniaxial direction), electron conduction at the contact point is inherently fast. And even if a part of the contact point is divided by the grain boundary crack C, it is originally oriented (preferably in a substantially uniaxial direction), so the contact point remaining after being broken or crushed and / or newly adjacent This is considered to be because an electron conduction path that provides sufficient electron conductivity is secured through contact points formed between the primary particles. This has the unique property that the surface where lithium ions and electrons easily enter and exit the oriented secondary particles having a layered rock salt structure has an electron conductivity that is three orders of magnitude greater than the surface where lithium ions and electrons do not easily enter and exit. Therefore, it is considered that sufficient electronic conductivity can be realized as long as contact between primary particles is not sufficiently ensured.

  Hereafter, each process of the method of this invention is demonstrated concretely.

(1) Preparation of positive electrode active material powder A positive electrode active material powder comprising a plurality of primary particles composed of a positive electrode active material having a layered rock salt structure and including oriented secondary particles in which the plurality of primary particles are oriented is prepared. To do. Here, the “layered rock salt structure” means a crystal structure in which transition metal layers other than lithium and lithium layers are alternately stacked with an oxygen atom layer interposed therebetween, that is, an ion layer of transition metal other than lithium and lithium ions. Crystal structure in which layers are alternately stacked with oxide ions in between (typically α-NaFeO ₂ type structure: structure in which transition metal and lithium are regularly arranged in the [111] axis direction of cubic rock salt type structure ).

Typically, lithium cobalt oxide (LiCoO ₂ ) can be used as the lithium composite oxide having a layered rock salt structure. However, it is also possible to use a solid solution containing nickel, manganese or the like in addition to cobalt as a lithium composite oxide constituting the positive electrode active material. Specifically, lithium nickel oxide, lithium manganate, nickel / lithium manganate, nickel / lithium cobaltate, cobalt / nickel / lithium manganate, cobalt / lithium manganate, etc. It can be used as a product. 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.

A preferred positive electrode active material is the following composition formula (1):
Li _p MeO ₂ (1)
(Wherein 0.9 ≦ p ≦ 1.3. Me is selected from the group consisting of Mn, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Mg, Zr, B, and Mo. At least one metal element) or the following compositional formula (2):
_{xLi 2 MO 3 - (1-} x) Li p MeO 2 (2)
(Where 0 <x <1 and 0.9 ≦ p ≦ 1.3, and M and Me are each independently Mn, Ti, V, Cr, Fe, Co, Ni, Cu, Al, It is a composition represented by at least one metal element selected from the group consisting of Mg, Zr, B, and Mo.

  “Me” in the above composition formulas (1) and (2) may be at least one metal element having an average oxidation state of “+3”, and is selected from the group consisting of Mn, Ni, Co, and Fe. It is preferable that the metal element is at least one kind. Further, “M” in the above composition formula (2) may be at least one metal element having an average oxidation state of “+4”, and is at least one selected from the group consisting of Mn, Zr and Ti. It is preferable that the metal element.

Particularly preferred positive electrode active material is the following composition formula (3):
_{Li p (Ni x, Co y} , Al z) O 2 (3)
(Where 0.9 ≦ p ≦ 1.3, 0.6 <x ≦ 0.9, 0.05 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.2, and x + y + z = 1). It is a nickel-cobalt-aluminum system having the composition shown.

  In the general formula (3), a preferable range of p is 0.9 ≦ p ≦ 1.3, and a more preferable range is 1.0 ≦ p ≦ 1.1. While ensuring a high discharge capacity, gas generation inside the battery during charging can be suppressed. The preferable range of x is 0.6 <x ≦ 0.9, more preferably 0.7 to 0.85, and within such a range, a high discharge capacity and high stability are ensured. Can do. A preferable range of y is 0.05 ≦ y ≦ 0.25, more preferably 0.10 to 0.20. Within such a range, the crystal structure becomes stable and a high discharge capacity is obtained. Can be secured. A preferable range of z is 0 ≦ z ≦ 0.2, and more preferably 0.02 to 0.1. A high discharge capacity can be ensured within such a range.

  The oriented secondary particles 14 contained in the positive electrode active material powder 10 preferably have a high (003) plane uniaxial orientation. “Orientation ratio of (003) plane” refers to the percentage of orientation ratio of (003) plane in secondary particles. That is, the orientation ratio of the (003) plane in the secondary particles is 60%, which means that among the many (003) planes ((003) plane in the layered rock salt structure) included in the secondary particles. This corresponds to the fact that the splits are parallel to each other. Therefore, the higher this value, the higher the degree of orientation of the (003) plane in the secondary particles (specifically, the primary particles of a large number of single crystals constituting the secondary particles have their (003) planes It is said that they are provided in parallel to each other as much as possible. On the other hand, the lower this value, the lower the degree of orientation of the (003) plane in the secondary particles (specifically, the primary particles of a large number of single crystals constituting the secondary particles have their (003) planes It is said that it is provided so as to face in a “separate” direction. The secondary particles contain a large number of primary particles as described above. Since the primary particles are single crystals, the orientation rate of the primary particles is not a problem. Therefore, from the viewpoint of capturing the orientation state of a large number of primary particles in the secondary particles as the orientation state of the (003) plane as the whole secondary particles, the orientation ratio of the (003) plane in the secondary particles is In other words, “the orientation ratio of the (003) plane of the primary particles in the secondary particles”. The orientation ratio of the (003) plane is determined by, for example, electron backscatter diffraction imaging (EBSD) or transmission electron microscope (TEM) on the plate surface or cross section of secondary particles (processed by a cross section polisher, a focused ion beam, or the like). ) Etc. are used to specify the orientation of the (003) plane of each primary particle in the secondary particle, and the ratio of the number of primary particles with the same orientation (within ± 10 degrees) to the total number of primary particles is calculated. It can be obtained by doing.

  In the oriented secondary particles 14, the numerous primary particles 12 constituting the same are aligned so that the orientations of the (003) planes are aligned with each other (so that the (003) planes are as parallel as possible). Preferably it is provided. Specifically, the orientation of the (003) plane is the same as the total number of the plurality of primary particles 12 contained in the positive electrode active material powder 10 so that the orientation ratio of the (003) plane is 50% or more. Positive electrode active material particles 10 are formed so that the ratio of primary particles 12 to 50% or more. The orientation ratio of the (003) plane is more preferably 70% or more, and particularly preferably 90%. The higher the orientation ratio, the more in-plane directions of the (003) plane are parallel to each other in the primary ion 12 contained in the positive electrode active material powder 10 in which lithium ion diffusion and electron conduction are favorably performed. It can be said that the ratio will increase. For this reason, the higher the orientation ratio, the shorter the lithium ion diffusion and electron conduction distance and the lower the lithium ion diffusion resistance and electronic resistance as described above. Remarkably improved. Therefore, for example, when the positive electrode active material powder 10 is used as a positive electrode material of a liquid lithium secondary battery, the positive electrode active material is used for the purpose of improving durability, increasing capacity, and improving safety. Even when the average particle diameter of the powder 10 is increased, it is possible to maintain high rate characteristics by increasing the orientation ratio.

  The average particle diameter of the primary particles 12 is preferably from 0.01 μm to 5 μm, more preferably from 0.01 μm to 3 μm, and still more preferably from 0.01 μm to 1.5 μm. Here, the “average particle diameter” is an average value of particle diameters. The “diameter” is typically a diameter of the sphere when the particle is assumed to be a sphere having the same volume or the same cross-sectional area. The “average value” is preferably calculated on the basis of the number. The average particle diameter of the primary particles can be determined, for example, by observing the surface or cross section of the secondary particles with a scanning electron microscope (SEM). By setting the average particle diameter of the primary particles 12 within the above range, the crystallinity of the primary particles 12 is ensured. In this regard, if the average particle diameter of the primary particles 12 is less than 0.1 μm, the crystallinity of the primary particles 12 may be reduced, and the output characteristics and rate characteristics of the lithium secondary battery may be deteriorated. However, in the positive electrode active material powder 10 composed of the oriented secondary particles 14, even if the average particle diameter of the primary particles 12 is 0.1 to 0.01 μm, no significant reduction in output characteristics or rate characteristics is observed.

  The average particle diameter of the oriented secondary particles 14 is 1 μm or more and 100 μm or less, preferably 2 μm or more and 70 μm or less, and more preferably 3 μm or more and 50 μm or less. The average particle diameter of the secondary particles is evaluated by a volume-based D50 average particle diameter (median diameter) measured using water as a dispersion medium using a commercially available laser diffraction / scattering particle size distribution analyzer. By setting the average particle diameter of the oriented secondary particles 14 within this range, the filling property of the positive electrode active material in the electrode is ensured (the filling rate is improved). In addition, a flat electrode surface can be formed while maintaining the output characteristics and rate characteristics of the lithium secondary battery. On the other hand, when the average particle diameter of the oriented secondary particles 14 is within the above range, the filling rate of the positive electrode active material can be increased, the output characteristics and rate characteristics of the lithium secondary battery are deteriorated, and the electrode surface is flat. The fall of property can be prevented. The distribution of the average particle diameter of the oriented secondary particles 14 may be sharp, broad, or have a plurality of peaks. For example, when the distribution of the average particle size of the oriented secondary particles 14 is not sharp, the packing density of the positive electrode active material in the positive electrode active material layer is increased, or the adhesion between the positive electrode active material layer and the positive electrode current collector is increased. Can be. Thereby, charge / discharge characteristics can be further improved.

  The aspect ratio of the oriented secondary particles 14 is preferably 1.0 or more and less than 3.0, more preferably 1.0 or more and less than 2.0, and even more preferably 1.1 or more and less than 1.5. is there. By setting the aspect ratio within this range, even when the packing density of the positive electrode active material in the positive electrode layer is increased, lithium ions in the electrolyte impregnated in the positive electrode layer are in the thickness direction of the positive electrode layer. It is possible to form an appropriate gap between the positive electrode active material particles so as to ensure a diffusion path. Thereby, the output characteristics and rate characteristics of the lithium secondary battery can be further improved. That is, when the aspect ratio is within this range, the positive electrode active material particles are filled in a state in which the plate surface direction of the positive electrode current collector and the major axis direction of the particles are parallel when the positive electrode layer is formed. Therefore, it is possible to avoid an increase in the diffusion path in the thickness direction of the positive electrode layer of lithium ions in the electrolyte solution impregnated in the positive electrode layer. For this reason, the fall of the output characteristic and rate characteristic of a lithium secondary battery can be suppressed. The aspect ratio of the single crystal primary particles 12 is also preferably 1.0 or more and less than 2.0, and more preferably 1.1 or more and less than 1.5. By setting the aspect ratio of the primary particles 12 within this range, good lithium ion conductivity and electronic conductivity can be secured.

  When the oriented secondary particles 14 are densely formed (that is, in a state where a large number of primary particles 12 are densely packed without gaps), the packing density of the positive electrode active material in the positive electrode layer can be increased, which is advantageous for increasing the capacity. is there. On the other hand, by introducing voids partially into densely oriented secondary particles, electrolytes and conductive materials can be contained in the voids, thereby improving rate characteristics while maintaining high capacity. can do. Moreover, the stress at the time of charging / discharging can also be relieved and the capacity deterioration (cycle characteristic) by repetition of charging / discharging can also be improved.

  The positive electrode active material powder composed of such oriented secondary particles is a known substance and can be produced based on the method described in Patent Document 3. For example, (1) a step of preparing a raw material slurry containing raw material powder, (2) a step of forming and drying the raw material slurry to obtain a sheet-like formed body, and (3) pulverizing and disassembling the sheet-like formed body. A step of obtaining a crushed powder, a step of (4) mixing a lithium compound with the crushed powder to obtain a lithium mixed powder, and a step of (5) firing the lithium mixed powder and reacting the crushed powder with the lithium compound. Thus, a positive electrode active material powder can be produced. Preferable examples of the method for forming the sheet include a doctor blade method and a technique using a drum dryer. Examples of crushing methods include a method of pressing on a mesh with a spatula; a method of crushing with a crusher with weak crushing force such as a pin mill; a method of causing sheet pieces to collide with each other in an air current (specifically, an air classifier) Slewing jet mill; pot crushing; barrel polishing; and the like. In addition, a process for spheroidizing the crushed material may be performed. As an example of the spheroidizing process, a method of taking an “angle” of the crushed material particles by colliding the crushed material particles with each other in an air current (air current Classification, hybridization, etc.); Method to take “corner” of crushed particles by colliding crushed particles in container (method using hybrid mixer, high-speed stirrer / mixer, barrel polishing, etc.); mechano Chemical method; a method of melting the surface of the crushed particles with hot air. The spheronization treatment and crushing may be performed separately, but may be performed simultaneously. That is, for example, by using an airflow classifier, crushing and spheronization can be performed simultaneously. In order to facilitate crushing and spheronization, the molded body may be degreased or heat treated (fired or temporarily fired) in advance.

Alternatively, the production of the positive electrode active material powder composed of oriented secondary particles may be started from the preparation of the hydroxide raw material powder. For example, (1) having a predetermined composition (for example, (Ni _0.844 Co _0.156 ) (OH) ₂ ), the secondary particles are almost spherical, and a part of the primary particles is outward from the center of the secondary particles. (2) A predetermined molar ratio (for example, Ni: Co: Al: Li = 81: to the obtained hydroxide raw material powder) 15: 4: 20) After adding the Al raw material (for example, boehmite) and the Li raw material (for example, LiOH.H ₂ O powder), lightly pulverize and mix with a dispersion medium (for example, pure water) in a bead mill, A step of preparing a slurry having a desired viscosity (for example, 0.5 Pa · s) and a desired solid content concentration (for example, 20% by mass) through stirring (defoaming) and addition of pure water, and (3) Use a drum dryer to remove the slurry.燥後, a step and then disintegrated to prepare a plate-like secondary particle granulated powder with a pin mill, (4) the resultant powder and LiOH · _{H 2} O powder and a predetermined mol ratio (e.g. Li / (Ni _0.81 Co _0.15 Al _0.04 ) = 1.04), (5) The mixed powder is put into a crucible made of high-purity alumina, and in an oxygen atmosphere (for example, 0.1 MPa ) At a predetermined temperature increase rate (for example, 50 ° C./h), and a baking step (lithium introduction step) in which heat treatment is performed at the predetermined temperature for a predetermined time (for example, 765 ° C. for 24 hours). An active material powder (for example, Li (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ powder) can be produced. The nickel / cobalt composite hydroxide powder in the step (1) can be produced according to a known technique, and can be produced, for example, as follows. That is, a mixed aqueous solution of nickel sulfate and cobalt sulfate having a molar ratio of Ni: Co = 84.4: 15.6 in a molar ratio of 1 mol / L to a reaction vessel containing 20 L of pure water at a charging rate of 50 ml / min. Ammonium sulfate having a concentration of 3 mol / L is continuously charged at a charging rate of 10 ml / min. On the other hand, an aqueous sodium hydroxide solution having a concentration of 10 mol / L is added so that the pH in the reaction vessel is automatically maintained at 11.0. The temperature in the reaction vessel is maintained at 50 ° C. and is always stirred with a stirrer. The produced nickel-cobalt composite hydroxide is overflowed from the overflow pipe, taken out, washed with water, dehydrated and dried.

  In addition, post-heat treatment may be performed at 100 to 400 ° C. in the positive electrode active material after firing or after being crushed or classified. By performing such a post heat treatment step, the surface layer of the primary particles can be modified, thereby improving the rate characteristics and output characteristics. In addition, the positive electrode active material may be subjected to a water washing treatment after firing or after being crushed or classified. By performing this water washing treatment step, the unreacted lithium raw material remaining on the surface of the positive electrode active material powder or the lithium carbonate produced by the adsorption of moisture and carbon dioxide in the atmosphere on the surface of the positive electrode active material powder is removed. Thereby, the high-temperature storage characteristics (especially gas generation suppression) are improved.

  Moreover, what is necessary is just to mix | blend the space | gap formation material as an additive with a raw material, when forming a space | gap in an orientation secondary particle. As such a void forming material, a particulate or fibrous substance that is decomposed (evaporated or carbonized) in the pre-baking step can be suitably used. Specifically, particulate or fibrous materials of organic synthetic resins such as theobromine, nylon, graphite, phenol resin, polymethyl methacrylate, polyethylene, polyethylene terephthalate, and foamable resin can be suitably used. Of course, without using such a void-forming material, the above-mentioned oriented secondary particles having the desired voids can be appropriately adjusted by adjusting the particle size of the raw material particles, the firing temperature in the temporary firing (heat treatment) step, and the like. Can be formed.

  A compound containing a metal element not included in the active material on the surface (including the pore inner wall) of the positive electrode active material, for example, a compound containing a transition metal capable of taking an expensive number such as W, Mo, Nb, Ta, Re, etc. May be present. Such a compound may be a compound of a transition metal capable of taking an expensive number such as W, Mo, Nb, Ta, and Re and Li. The compound containing a metal element may be dissolved in the positive electrode active material or may exist as the second phase. By doing so, it is considered that the interface between the positive electrode active material and the non-aqueous electrolyte is modified, the charge transfer reaction is promoted, and the output characteristics and rate characteristics are improved.

  The positive electrode active material powder preferably contains oriented secondary particles in an amount of 10 to 100% by mass, more preferably 15 to 100% by mass, and still more preferably 20 to 100% by mass with respect to the total amount of the positive electrode active material powder. . That is, the positive electrode active material powder may be composed of oriented secondary particles, or may contain oriented secondary particles and other particles. In the latter case, the positive electrode active material powder is preferably a mixed powder composed of oriented secondary particles and non-oriented secondary particles having a substantially smaller particle diameter. This is because positive stress is caused by stress concentration on the large secondary particle during the positive electrode layer press process and is easily cracked. Therefore, the positive electrode is a mixture of large-sized oriented secondary particles and small-sized non-oriented secondary particles. This is because, in the active material powder, secondary particles that are broken or crushed during press processing are mainly oriented secondary particles. That is, as described above, the oriented secondary particles are cracked or crushed and contribute to high energy density and high output characteristics. Therefore, both the high energy density and high output characteristics can be achieved by using the mixed powder. Therefore, the positive electrode active material powder includes oriented secondary particles and non-oriented secondary particles, and the volume-based D50 average particle size of the oriented secondary particles is larger than the volume-based D50 average particle size of the non-oriented secondary particles. Is preferred. The volume-based D50 average particle diameter of the oriented secondary particles is preferably 1.5 times or more, more preferably 1.8 times or more, more preferably the volume-based D50 average particle diameter of the non-oriented secondary particles. Is 2.0 times or more. When such a mixed powder is used, non-oriented secondary particles are prepared by a known method so as to be substantially smaller than the oriented secondary particles, and then mixed with the oriented secondary particles. Alternatively, the mixed secondary particle precursor and the non-oriented secondary particle precursor before being subjected to the mixing step and the baking step (lithium introduction step) with the lithium compound are mixed, and then the mixing step and the baking step with the lithium compound. You may attach | subject (lithium introduction process). The conditions and preferred form of the non-oriented secondary particles are the same as the above-mentioned oriented secondary particles except that there is no orientation and that the particle size is generally smaller than the oriented secondary particles. The above description referring to the oriented secondary particles within the range is directly applicable to the non-oriented secondary particles.

(2) Preparation of positive electrode mixture paste The positive electrode active material powder is mixed with a conductive additive, a binder and a solvent to form a positive electrode mixture paste. There are no particular limitations on the type, blending amount, and mixing method of the solvent for these components, and known production conditions for the positive electrode may be employed as appropriate.

  A preferred conductive aid is a carbon material, more preferably a graphite or non-graphite carbon material. Examples of graphite include commonly used graphite such as natural graphite and artificial graphite. Examples of non-graphitic carbon materials include carbon black and acetylene black. Moreover, fibrous carbon materials, such as graphitized carbon fiber and a carbon nanotube, can also be used.

  A preferred binder is a thermoplastic resin. Examples of thermoplastic resins include polyvinylidene fluoride (also referred to as PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, propylene hexafluoride / fluoride Fluorine resins such as vinylidene copolymers and tetrafluoroethylene / perfluorovinyl ether copolymers, polyolefin resins such as polyethylene and polypropylene, and the like, particularly preferably polyvinylidene fluoride.

Examples of preferred solvents include ether solvents such as N, N-dimethylaminopropylamine, diethylenetriamine, amine solvents such as N, N-dimethylformamide (hereinafter also referred to as DMF), tetrahydrofuran, and ketone solvents such as methyl ethyl ketone. Examples thereof include solvents, ester solvents such as methyl acetate, amide solvents such as dimethylacetamide and 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), dimethyl sulfoxide (hereinafter referred to as DMSO), and the like. A solvent having a specific gravity in the range of 0.935 to 1.200 g / cm ³ is preferable from the viewpoint of operability. Examples of such a solvent include diethylenetriamine (bp is 199-209 ° C., Fp is 94 ° C., d is 0 N, N-dimethylformamide (bp is 153 ° C., Fp is 57 ° C., d is 0.944), dimethylacetamide (bp is 164.5-166 ° C., Fp is 70 ° C., d Is 0.937), 1-methyl-2-pyrrolidone (bp is 204 ° C., Fp is 86 ° C., d is 1.028), and dimethyl sulfoxide (bp is 189 ° C., Fp is 85 ° C., d Is 1.101). Here, bp represents the boiling point, Fp represents the flash point, and d represents the specific gravity (g / cm ³ ).

  The ratio of the positive electrode active material to the total amount of 100 parts by mass of the positive electrode active material powder, the conductive additive, and the binder is preferably as high as 85 to 98 parts by mass, and more preferably 90 to 96 parts by mass. This is because the positive electrode layer is excessively consolidated in the subsequent pressing step, so that even if the amount of the conductive additive is reduced, sufficient conductivity and resulting high output characteristics can be obtained, and the energy density can be increased. . Further, the proportion of the conductive auxiliary agent in the total amount of 100 parts by mass of the positive electrode active material powder, the conductive auxiliary agent and the binder is preferably 1 to 10 parts by mass, more preferably 2 to 5 parts by mass, and the ratio of the binder is 1-10 mass parts is preferable, More preferably, it is 2-5 mass parts. A positive electrode mixture paste is obtained by mixing and kneading these components together with a solvent by an arbitrary technique.

(3) Formation of positive electrode layer A positive electrode mixture paste is applied on a current collector to form a positive electrode layer. Examples of the current collector include metals such as Al, Ni, and stainless steel, and Al is preferable because it is easy to process into a thin film and is inexpensive. The current collector may be in any form such as a plate, foil, or film. Examples of the method for applying the positive electrode mixture to the current collector include a die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. The positive electrode layer is preferably dried before subsequent pressing.

(4) Press processing The positive electrode layer is pressed toward the current collector to obtain a positive electrode for a lithium secondary battery. In this pressing, the ratio D ₂ / D ₁ of the packing density D ₂ of the positive electrode active material powder in the positive electrode layer after the pressing to the tap density D ₁ of the positive electrode active material powder is 1.15 or more, preferably 1.15. To 1.35, more preferably 1.15 to 1.30. The pressure value of such press working is not particularly limited as long as it is appropriately selected so as to realize the above ratio, but is typically a pressure within a range of 2000 to 10000 kgf / cm ² , and more typically 3000. ˜8000 kgf / cm ² . The method of press working is not particularly limited, but it is preferable to use compression using a single-screw press, rolling using a roller, or the like.

The tap density D ₁ of the positive electrode active material powder is determined by D ₁ = m / V (in the formula, m) after tapping a measuring cylinder containing a powder sample of the positive electrode active material particles 200 times using a commercially available tap density measuring device. Can be calculated based on the formula of the weight of the powder and V the bulk volume of the powder after tapping. This measurement can be performed according to JIS R 1628 (1997). The positive electrode active material powder preferably has a tap density of 2.4 to 3.4 g / cc, more preferably 2.6 to 3.1 g / cc.

Packing density D ₂ of the positive electrode active material powder in the positive electrode layer is the density of the positive electrode active material powder occupying the positive electrode layer and is calculated by the following equation.
D ₂ = [Positive electrode layer density (g / cc)] × [Positive electrode active material powder blending ratio (wt%)] / 100
= [Weight of positive electrode layer (g)] / [Volume of positive electrode layer (cc)]
× [Composition ratio of positive electrode active material powder (wt%)] / 100
Since the positive electrode layer is a portion occupied by the positive electrode mixture in the positive electrode, the above equation can also be expressed by the following equation.
D ₂ = ([positive electrode weight] − [current collector weight]) / {positive electrode area × ([positive electrode thickness] − [current collector thickness])}
× [Composition ratio of positive electrode active material powder (wt%)] / 100

  The packing density of the positive electrode active material powder in the positive electrode layer after press working is preferably 2.8 to 4.6 g / cc, more preferably 3.0 to 4.4 g / cc.

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

Examples 1, 4 and 9 : Example of single use of oriented secondary particles (1) Preparation of oriented secondary particles (1a) Preparation of raw material particles and slurry First, the molar ratio of Ni, Co and Al in the mixture was 80: 15: so that 5, Ni _(OH) (manufactured by Kojundo Chemical Laboratory Co., Ltd.) ₂ powder, Co _(OH) (manufactured by Kojundo Chemical Laboratory Co., Ltd.) ₂ powder, and _Al 2 _O 3 · _{H 2} O (manufactured by SASOL) was weighed. Next, a pore former (spherical, Bell Pearl R100, manufactured by Air Water Co., Ltd.) was added to the weighed product. The pore former was weighed so that the ratio to the total powder weight after addition was 2% by mass. And the powder of raw material particle | grains was prepared by grind | pulverizing and mixing the mixed powder after pore former addition for 24 hours with a ball mill.

  100 parts by weight of the powder of the prepared raw material particles, 400 parts by weight of pure water as a dispersion medium, 1 part by weight of a binder (polyvinyl alcohol, product number VP-18, manufactured by Nippon Vinegar Poval Co., Ltd.), and a dispersant (Marialim 1 part by mass of KM-0521 (manufactured by NOF Corporation) and 0.5 part by mass of an antifoaming agent (1-octanol, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed. Further, the mixture was defoamed by stirring under reduced pressure, and a slurry was prepared by adjusting the viscosity to 0.5 Pa · s (measured using a Brookfield LVT viscometer).

(1b) Molding of raw material particles and heat treatment (temporary firing)
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 25 μm. The sheet-like molded body peeled off from the PET film after drying is placed in the center of a zirconia setter, heated at 200 ° C./h in the atmosphere, and heated at 900 ° C. for 3 hours to form a sheet. (Ni _0.8 Co _0.15 Al _0.05 ) O ceramic sheet was obtained.

(1c) Crushing the molded body The ceramic sheet obtained by heat treatment (preliminary firing) is placed on a sieve (mesh) having an opening diameter of 30 μm, and is crushed by passing through the mesh while lightly pressing with a spatula. A substantially spherical (Ni _0.8 Co _0.15 Al _0.05 ) O powder was obtained.

(1d) Spheronization treatment and classification of pulverized product (Ni _0.8 Co _0.15 Al _0.05 ) O powder obtained by pulverization was converted into an air classifier (Turbo Classifier TC-15, Nisshin Engineering Co., Ltd.) Manufactured, exhausted air volume: 1.7 m ³ / min, classification rotor rotation speed: 10000 rpm) at a speed of 20 g / min, and the coarse powder side of the obtained powder was recovered. This spheronization treatment (at the same time classification by fine powder removal) was repeated 5 times.

(1e) Mixing with lithium compound (Ni _0.8 Co _0.15 Al _0.05 ) O powder after fine powder removal and LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) And mixed so that Li / (Ni _0.8 Co _0.15 Al _0.05 ) = 1.05.

(1f) Firing step (lithium introduction step)
The above mixed powder is put into a crucible made of high-purity alumina and heat-treated in an oxygen atmosphere (0.1 MPa) at 775 ° C. for 24 hours, whereby Li (Ni _0.8 Co _0.15 Al _{0 .05} ) O ₂ powder was obtained as a positive electrode active material powder.

(2) Various measurements Various characteristics of the obtained positive electrode active material powder were measured. The tap density was 2.9 g / cc, the primary particles had an average particle diameter of 0.1 μm, and the secondary particles were 20 μm. And the orientation ratio of the (003) plane of the primary particles in the secondary particles was 90% or more. The measuring method of these characteristics was as follows.
[Tap density]
After tapping a graduated cylinder containing a powder sample of positive electrode active material particles 200 times using a commercially available tap density measuring device, D ₁ = m / V (where m is the weight of the powder and V is the powder after tapping. It was calculated tap density D ₁ on the basis of the equation of the bulk volume). This measurement is based on JIS R 1628 (1997).
[Secondary particle size (μm)]
Using a laser diffraction / scattering type particle size distribution analyzer (model number “LA-750” manufactured by Horiba, Ltd.), the median diameter (D50) of secondary particles is measured using water as a dispersion medium, and this value is determined as a secondary value. The particle diameter was taken.
[Primary particle size (μm)]
Using a FE-SEM (field emission scanning electron microscope: product name “JSM-7000F” manufactured by JEOL Ltd.), a magnification at which 10 or more primary particles enter the field of view was selected, and an SEM image was taken. . In this SEM image, for each of the ten primary particles, the diameter of the inscribed circle when the inscribed circle was drawn was determined. And the average value of the obtained 10 diameter was made into the primary particle diameter.
[aspect ratio]
Using the above-mentioned FE-SEM, SEM images were taken by selecting a magnification at which 10 or more secondary particles were in the field of view. In this SEM image, the major axis diameter and the minor axis diameter were determined for each of the ten secondary particles, and then the value obtained by dividing the major axis diameter by the minor axis diameter was determined. The average value of the 10 values obtained was taken as the aspect ratio. The aspect ratio of primary particles was determined in the same manner.
[Orientation rate (%)]
Secondary particle powder was arranged on a glass substrate so that secondary particles might not overlap as much as possible. A sample for observation was prepared by polishing a powder obtained by copying this powder onto an adhesive tape and embedding it in a synthetic resin so that the plate surface or cross-section polished surface of the secondary particles can be observed. In the case of plate surface observation, as a final polishing, polishing was performed with a vibration type rotary polishing machine using colloidal silica (0.05 μm) as an abrasive. On the other hand, in the case of cross-sectional observation, polishing was performed with a cross section polisher (CP). With respect to the sample thus prepared, in a field where 10 or more primary particles are seen in one secondary particle, EBSD (Electron Backscattering Diffraction Image Method: Measurement Software “OIM Data Collection”) and Analysis Software “OIM Analysis” "" Was made by TSL Solutions Co., Ltd.), and the crystal orientation analysis of each secondary particle was performed with a pixel resolution of measurement of 0.1 μm. Thereby, the inclination angle with respect to the measurement surface (polished surface) was determined for the (003) surface of each primary particle. A histogram (angle distribution) of the number of particles with respect to the angle is output, and the angle at which the number of primary particles is maximum (peak value) is defined as the (003) plane inclination angle θ with respect to the measurement surface of the secondary particles. With respect to the tilt angle θ, the number of primary particles having a (003) plane within θ ± 10 degrees was calculated for the measured secondary particles. By dividing the determined number of primary particles by the total number of primary particles, the orientation ratio of the (003) plane in the measured secondary particles was calculated. This was performed for 10 different secondary particles, and the average value was defined as the orientation ratio of the (003) plane.

(3) Production of electrode and coin cell LiNi _0.8 Co _0.15 Al _0.05 O ₂ oriented secondary particle powder having a tap density of 2.9 g / cc obtained by the above process, acetylene black (DENKA BLACK HS100, Electric Chemical Industry Co., Ltd.) and polyvinylidene fluoride (PVDF) (KF Polymer # 1120, Kureha Co., Ltd.) were mixed so that the mass ratio was 94: 3: 3, and N-methyl-2-pyrrolidone ( A positive electrode active material paste was prepared by dispersing in Wako Pure Chemical Industries, Ltd.). This paste was applied on a 20 μm-thick aluminum foil as a positive electrode current collector so as to have a uniform thickness (thickness after drying: 90 μm) and dried. The positive electrode active material having a packing density (hereinafter referred to as positive electrode packing density) D ₂ of the positive electrode active material powder in the positive electrode layer after press working is obtained by punching the obtained dried sheet into a disk shape having a diameter of 14 mm. A positive electrode was obtained by pressing at 6600 kgf / cm ² using a uniaxial press so that the ratio of the powder to the tap density D ₁ (hereinafter referred to as D ₂ / D ₁ ratio) was 1.15 or more. The electrode density, positive electrode packing density D ₂ and D ₂ / D ₁ ratio were as shown in Table 1.

A coin cell was produced using the positive electrode plate thus obtained. The electrolytic solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an equal volume ratio. Moreover, a metal lithium foil was used as the negative electrode.

(4) Electrochemical measurement Using the battery for characteristic evaluation (coin cell) produced as described above, the discharge capacity and the internal resistance were evaluated by performing a charge / discharge operation as follows. Specifically, constant current charging was performed until the battery voltage reached 4.3 V at a current value of 0.1 C rate. Thereafter, constant voltage charging was performed until the current value decreased to 1/20 under the current condition of maintaining the battery voltage at 4.3V. After resting for 10 minutes, the battery was discharged at a constant current at a current value of 5C until the battery voltage reached 2.5 V, and then rested for 10 minutes. These charging / discharging operations were defined as one cycle, and a total of two cycles were repeated under the condition of 25 ° C., and the energy density was calculated from the obtained discharge capacity and mixture density. In addition, the battery is charged up to 50% (SOC 50%: SOC is an abbreviation of “State of Charge”, meaning a charged state) when the discharge capacity at the second cycle is 100%, and the open circuit voltage at that time (OCV: an abbreviation of “Open-CircuitVoltage”, which means the battery voltage when no current flows). Thereafter, the voltage drop 10 seconds after the discharge at 0.5 C equivalent was read. Further, discharging was performed while changing the discharge current to 1C or 2C, and the voltage drop at each discharge current was read. These discharge currents and voltage drops were plotted, and the value of the internal resistance calculated from the slope was used as an index of output characteristics. The lower this value, the higher the output characteristics. The evaluation results are as shown in Table 1. The obtained battery had high energy density and low internal resistance.

(5) Electrode structure evaluation (cross-sectional observation)
About the electrode of Example 1 obtained by said method, it grind | polished so that the cross-section grinding | polishing surface of an electrode can be observed with a cross section polisher (CP), and using a scanning type | mold microscope (JEOL JSM-6390), FIG. The cross-sectional image shown in 2 was obtained. Moreover, when the cross section of the electrode obtained in Example 4 was observed using a scanning child microscope (JSM-6390, manufactured by JEOL) in the same manner as described above, the cross-sectional images shown in FIGS. 3 and 4 were obtained. FIG. 4 is an enlarged view of FIG.

Examples 2, 5 to 7 and 10 to 12 : Combined example of oriented secondary particles and small particle size non-oriented secondary particles A slurry prepared in the same manner as in Example 1 (1a) was spray-dried (Okawara Kako Co., Ltd.) , Model “OC-16”, hot air inlet temperature 120 ° C., sprayed at 0.15 MPa with a twin jet nozzle) and granulated to obtain a substantially spherical shape (Ni _0.8 Co _0.15 Al _{0. 05} ) O powder was obtained as non-oriented secondary particles with small particle size. The D50 particle size after drying of the substantially spherical small particle size non-oriented secondary particles was 12 μm. The substantially spherical small particle size non-oriented secondary particles obtained in this way and the oriented secondary particles obtained in (1d) of Example 1 were mixed at the blending ratio shown in Table 1, and then ( 1e) A step of mixing with a lithium compound and (1f) a step similar to the firing step (lithium introduction step) were performed to prepare a positive electrode active material. The positive electrode active material thus obtained contains both oriented secondary particles and small-size non-oriented secondary particles, and is the same as in Examples 1 (2) to (4) and according to the conditions shown in Table 1. When various measurements were performed, the results shown in Table 1 were obtained.

Examples 3, 8 and 13 : Example of single use of non-oriented secondary particles having small particle diameters A slurry prepared in the same manner as in (1a) of Example 1 was spray-dried (Okawara Chemical Co., Ltd., model “OC-16”, Drying and granulating at a hot air inlet temperature of 120 ° C. and spraying at 0.15 MPa with a twin jet nozzle) yields a substantially spherical (Ni _0.8 Co _0.15 Al _0.05 ) O powder with a small particle size Obtained as non-oriented secondary particles. The D50 particle size after drying of the substantially spherical small particle size non-oriented secondary particles was 12 μm. The substantially spherical small particle size non-oriented secondary particles thus obtained were subjected to the same steps as the mixing step (1e) with the lithium compound and the (1f) firing step (lithium introduction step) in Example 1 to obtain a positive electrode active material Was made. The positive electrode active material powder obtained after the firing step had a D50 particle size of 9 μm and a tap density of 2.4 g / cc. The positive electrode active material thus obtained contains small non-oriented secondary particles alone (that is, does not contain oriented secondary particles), and is the same as in Examples 1 (2) to (4). When various measurements were performed according to the various conditions shown in Table 1, the results shown in Table 1 were obtained.

Examples 14 to 16 : Combination examples of blended secondary particles and non-oriented secondary particles with large particle size Slurry prepared in the same manner as in (1a) of Example 1 was spray-dried (Okawara Koki Co., Ltd., model “FOC-16” ”By drying and granulating at a hot air inlet temperature of 120 ° C. and an atomizer speed of 20000 rpm, a substantially spherical (Ni _0.8 Co _0.15 Al _0.05 ) O powder is non-oriented with a large spherical particle size. Obtained as secondary particles. The D50 particle size after drying was 25 μm. The substantially spherical large-diameter non-oriented secondary particles thus obtained and the oriented secondary particles obtained in (1d) of Example 1 were mixed at the blending ratio shown in Table 1, and then ( 1e) A step of mixing with a lithium compound and (1f) a step similar to the firing step (lithium introduction step) were performed to prepare a positive electrode active material. The positive electrode active material thus obtained contains both oriented secondary particles and large-size non-oriented secondary particles, in the same manner as in Examples 1 (2) to (4) and according to the conditions shown in Table 1. When various measurements were performed, the results shown in Table 1 were obtained.

Examples 17 to 19 : Example of single use of non-oriented secondary particles having large particle diameters Slurry prepared in the same manner as in (1a) of Example 1 was spray-dried (Okawara Kako Co., Ltd., model “FOC-16”, hot air inlet By drying and granulating at a temperature of 120 ° C. and an atomizer rotational speed of 20000 rpm, a substantially spherical (Ni _0.8 Co _0.15 Al _0.05 ) O powder is obtained as a substantially spherical large particle size non-oriented secondary particle. Obtained. The D50 particle size after drying was 25 μm. The substantially spherical large particle size non-oriented secondary particles thus obtained were subjected to the same steps as in Example 1 (1e) mixing step with lithium compound and (1f) firing step (lithium introduction step) to obtain a positive electrode active material Was made. The particle size of the powder obtained after the firing step was 20 μm, and the tap density was 2.9 g / cc. The positive electrode active material obtained in this way contains large-size non-oriented secondary particles alone (that is, does not contain oriented secondary particles), and is the same as in Examples 1 (2) to (4). When various measurements were performed according to the various conditions shown in Table 1, the results shown in Table 1 were obtained.

  From the results in Table 1, the following can be understood. Examples 1 to 3 are comparative examples relating to the press electrode to the extent that the secondary particles do not break, and it can be seen that even when non-oriented secondary particles having a small particle size are blended, the energy density does not increase, but the resistance is low. Examples 4 to 8 are examples relating to electrodes pressed to such an extent that the secondary particles start to crack, and it is understood that the resistance value of the electrodes mixed with the oriented secondary particles is hardly deteriorated. Examples 9 to 13 are examples relating to electrodes in which the oriented secondary particles are broken to further increase the electrode density, and it is understood that the resistance value of the electrode mixed with the oriented secondary particles is small. Examples 14 to 19 are examples relating to electrodes using non-oriented secondary particles having a large particle size, and are not non-oriented secondary particles having a particle size smaller than that of the aligned secondary particles. It turns out that an effect is not acquired.

  Moreover, the graph which shows the relationship between the resistance value measured in Examples 1-19 and the ratio of the orientation secondary particle in FIG. 5 is shown. From the results shown in FIG. 5, it can be seen that the resistivity is significantly reduced when the positive electrode active material contains 10 to 100 mass% of oriented secondary particles (relative to the total amount of the positive electrode active material powder).

DESCRIPTION OF SYMBOLS 10 Positive electrode active material powder 12 Primary particle 14 Oriented secondary particle 20 Positive electrode active material powder 22 Primary particle 24 Unoriented secondary particle

Claims (9)

A step of preparing a positive electrode active material powder comprising a plurality of primary particles composed of a positive electrode active material having a layered rock salt structure, and comprising oriented secondary particles in which the plurality of primary particles are oriented;
Mixing the positive electrode active material powder with a conductive additive, a binder and a solvent to obtain a positive electrode mixture paste;
Applying the positive electrode mixture paste on a current collector to form a positive electrode layer;
The positive electrode layer is pressed toward the current collector, and at this time, the ratio D ₂ of the packing density D ₂ of the positive electrode active material powder in the positive electrode layer after the pressing to the tap density D ₁ of the positive electrode active material powder. / a _{step D 1} is made the press working so as to at least 1.15,
The manufacturing method of the positive electrode for lithium secondary batteries containing.   The method according to claim 1, wherein the pressing is performed such that at least a part of the oriented secondary particles is cracked or crushed.   The method according to claim 1, wherein the plurality of primary particles are oriented in a substantially uniaxial direction.   The primary particles have an average particle diameter of 0.01 to 5 μm, the oriented secondary particles have an average particle diameter of 1 to 100 μm, and the (003) plane orientation of the primary particles in the oriented secondary particles The method according to any one of claims 1 to 3, wherein the rate is 50% or more. The positive electrode active material has the following composition formula (1):
Li _p MeO ₂ (1)
(Wherein 0.9 ≦ p ≦ 1.3. Me is selected from the group consisting of Mn, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Mg, Zr, B, and Mo. At least one metal element) or the following compositional formula (2):
_{xLi 2 MO 3 - (1-} x) Li p MeO 2 (2)
(Where 0 <x <1 and 0.9 ≦ p ≦ 1.3, and M and Me are each independently Mn, Ti, V, Cr, Fe, Co, Ni, Cu, Al, The method according to claim 1, which has a composition represented by (at least one metal element selected from the group consisting of Mg, Zr, B, and Mo). The positive electrode active material has the following composition formula (3):
_{Li p (Ni x, Co y} , Al z) O 2 (3)
(Where 0.9 ≦ p ≦ 1.3, 0.6 <x ≦ 0.9, 0.05 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.2, and x + y + z = 1). 6. A method according to any one of claims 1 to 5 having the composition represented.   The method as described in any one of Claims 1-6 in which the said positive electrode active material powder contains 10-100 mass% of said orientation secondary particles with respect to the total amount of the said positive electrode active material powder.   The positive electrode active material powder includes the oriented secondary particles and non-oriented secondary particles, and the volume-based D50 average particle size of the oriented secondary particles is larger than the volume-based D50 average particle size of the non-oriented secondary particles. The method according to any one of claims 1 to 7.   The method according to claim 8, wherein the volume-based D50 average particle diameter of the oriented secondary particles is 1.5 times or more the volume-based D50 average particle diameter of the non-oriented secondary particles.