JP2009259698A - Method of manufacturing positive electrode active material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing positive electrode active material particles, in which the positive electrode active material particles are prevented from being mutually bonded, and conductive aid particles are arranged on the surface. <P>SOLUTION: This invention relates to the method of manufacturing the positive electrode active material particles 10 in which the conductive aid particles 20 are arranged on the surface. The method of manufacturing a positive electrode active material includes: a step of preparing a dispersion liquid in which particles composed of the positive electrode active material and the particles 20 composed of the conductive aid are dispersed in a solvent; a step of forming droplets containing the positive electrode active material particles 10 and the conductive aid particles 20 by spraying the dispersion liquid into a reaction container in a mist state; and a step of arranging the conductive aid particles 20 on the surface of the positive electrode active material particles 10 by drying the sprayed droplets. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode active material for a battery, in particular, positive electrode active material particles having conductive auxiliary particles arranged on the surface.

  In recent years, lithium-ion batteries, nickel-metal hydride batteries, and other secondary batteries have become increasingly important as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion battery that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle. One typical configuration of this type of lithium ion secondary battery includes a positive electrode having a configuration in which a positive electrode active material capable of reversibly inserting and extracting lithium ions is formed on a positive electrode current collector. For example, a lithium ion secondary battery using a positive electrode active material made of an olivine-based material (olivine-type lithium phosphate compound) is an example of such a battery.

Since the positive electrode active material made of such an olivine-based material (olivine-type lithium phosphate compound) generally has low conductivity (for example, in the case of LiFePO ₄ , about 1 × 10 ⁻⁹ S / cm), In many cases, a conductive additive (for example, a carbon-based material) is mixed and used. In order to further improve the conductivity of the olivine-based positive electrode active material, a technique for forming composite particles for an electrode including a positive electrode active material, a conductive auxiliary agent, and a binder has been proposed.

For example, Patent Document 1 discloses a technique in which a conductive additive and a binder are brought into close contact with particles made of a positive electrode active material and integrated. Specifically, the formation of the composite particles for electrodes is performed using a fluidized tank. That is, an air stream is generated in the fluidized tank, and particles made of the positive electrode active material are introduced into the air stream, whereby the particles made of the positive electrode active material are fluidized. Next, a raw material liquid in which the conductive auxiliary agent and the binder are dispersed is prepared, and droplets of the raw material liquid are sprayed in the fluid tank. As a result, as schematically shown in FIG. 7, the droplet 84 of the raw material liquid is attached to the particles 82 made of the positive electrode active material that has been fluidized, and simultaneously dried in the fluidized tank 80, so that the positive electrode active material The solvent is removed from the droplet 84 of the raw material liquid adhering to the surface of the particles 82, and the particles 82 made of the positive electrode active material and the particles made of the conductive auxiliary agent are brought into close contact with the binder to obtain composite particles 86.
Japanese Patent No. 3785407 JP 2001-110414 A JP 2003-203628 A JP 2007-35358 A

  However, in the technique of Patent Document 1, an air stream is generated in the fluidized tank, and the particles 82 made of the positive electrode active material are introduced into the air stream. Therefore, not only the conductive assistant but also the particles 82 made of the positive electrode active material. They are bound together. That is, as shown in FIG. 7, the particles obtained by the above method become composite particles 86 in which particles 82 made of the positive electrode active material are bound together. As shown in FIG. 7, when the particles 82 made of the positive electrode active material are bound together without using the conductive auxiliary agent 84, the interfacial resistance increases at the bound portion, which adversely affects battery performance (for example, high rate characteristics). It may cause.

  The present invention has been made in view of the above points, and its main purpose is to avoid the situation where the positive electrode active material particles are bound to each other, and the positive electrode active material particles having the conductive auxiliary agent particles arranged on the surface. It is to provide a method of manufacturing.

  The method for producing a positive electrode active material provided by the present invention is a method for producing positive electrode active material particles having conductive auxiliary particles arranged on the surface. Such a production method includes a step of preparing a dispersion liquid in which particles made of the positive electrode active material and particles made of the conductive auxiliary agent are dispersed in a suitable solvent, and the dispersion liquid is sprayed into a predetermined reaction vessel. By spraying in the form of droplets, the step of forming droplets containing the positive electrode active material particles and the conductive auxiliary agent particles, and drying the sprayed droplets, the conductive material on the surface of the positive electrode active material particles. Arranging the auxiliary particles.

  According to the method for producing a positive electrode active material of the present invention having such a configuration, first, a droplet containing an appropriate amount of positive electrode active material particles and conductive auxiliary agent particles is prepared, and then the droplet is dried, Since the conductive auxiliary agent particles are disposed (attached) on the surface of the active material particles, it is possible to avoid a situation in which the positive electrode active material particles are brought into contact with each other and bound (granulated). This can suppress an increase in interface resistance due to binding between the positive electrode active material particles. As a result, the internal resistance of the battery can be reduced, and a battery excellent in battery performance (for example, high rate characteristics) can be provided.

  In a preferred embodiment of the production method disclosed herein, the droplets are dried by bringing the droplets into contact with hot air. According to this method, since the dispersion solvent (for example, an organic solvent such as N-methylpyrrolidone) contained in the droplets can be quickly removed by hot air, the sprayed droplets can be dried instantaneously. . Therefore, it is possible to quickly dispose the conductive assistant particles on the surface of the positive electrode active material particles while suppressing the binding (granulation) between the positive electrode active material particles, and the positive electrode active material particles suitable for the purpose of the present invention. Can be manufactured easily and stably.

  In a preferred embodiment of the production method disclosed herein, the obtained positive electrode active material particles (that is, positive electrode active material particles having conductive auxiliary agent particles disposed on the surface) are heated by the hot air to the reaction vessel (typically It is characterized in that hot air is discharged to the outside of the drying tank that can supply the inside. According to this method, the positive electrode active material particles obtained above can be quickly discharged to the outside of the reaction vessel (drying tank) without being kept in one place (that is, in the reaction vessel). Bonding (granulation) between particles can be effectively suppressed.

  In a preferred embodiment of the production method disclosed herein, the dispersion is sprayed using a four-fluid nozzle. Here, the “four-fluid nozzle” refers to a nozzle having two liquid supply (injection) ports and two gas supply (injection) ports.

  By using the four-fluid nozzle in this way, the size of the sprayed droplets can be reduced to, for example, about 5 μm to 15 μm (particularly preferably 5 μm to 10 μm), whereby an appropriate amount of positive electrode active material particles can be contained in the droplets. In addition, the conductive auxiliary particles can be held.

  In a preferred embodiment of the production method disclosed herein, the positive electrode active material is an olivine-based positive electrode active material (olivine-type lithium phosphate compound). The olivine-based positive electrode active material has various characteristics preferable as the positive electrode active material because of its large battery theoretical capacity and high safety, while its low conductivity tends to increase the interface resistance due to binding between the positive electrode active material particles. Becomes prominent. Therefore, when the positive electrode active material particles are made of an olivine-based positive electrode material, the dispersion of the positive electrode active material particles and the conductive auxiliary agent is sprayed into droplets and dried. The effect by adopting can be exhibited particularly well.

  In a preferred embodiment of the production method disclosed herein, the dispersion contains a binder capable of binding the positive electrode active material particles and the conductive auxiliary particles. According to this method, the conductive auxiliary agent particles can be easily attached to the surface of the positive electrode active material particles, and the positive electrode active material particles and the conductive auxiliary agent particles can be firmly integrated.

  Moreover, this invention provides the manufacturing method of the positive electrode for batteries using the positive electrode active material obtained by the said manufacturing method. Such a manufacturing method includes a step of preparing a positive electrode mixture paste containing the positive electrode active material, and forming a positive electrode mixture layer by applying the prepared positive electrode mixture paste onto a positive electrode current collector and drying the paste. Including the step of. According to the method for producing a positive electrode for a battery of the present invention, a positive electrode for a battery having excellent current collecting performance capable of reducing the internal resistance of the battery can be stably produced (with high quality stability).

  In a preferred embodiment of the production method disclosed herein, the positive electrode mixture paste is prepared by dispersing the positive electrode active material in a dispersion solvent using a thin film swirl mixer. The positive electrode active material particles that can be produced by the spraying / drying process become fine powders, so that the wettability may be deteriorated, but by dispersing in the dispersion medium using the thin film swirl mixer as described above. The positive electrode mixture paste is easy to become familiar with the surface of the positive electrode current collector. Therefore, it is possible to avoid a situation in which the positive electrode mixture layer obtained after drying is lifted from the positive electrode current collector or peeled off. Therefore, it is possible to stably produce a positive electrode for a battery excellent in battery performance (with high quality stability).

  Moreover, the battery using the positive electrode active material obtained by the said manufacturing method or the positive electrode for batteries obtained by the said manufacturing method is provided by this invention. Since such a battery is constructed using the positive electrode active material or the positive electrode for a battery, it can exhibit better battery performance (for example, good high rate characteristics).

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. In addition, this invention is not limited to the following embodiment. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, a method of manufacturing a positive electrode current collector, a configuration and a manufacturing method of a separator and an electrolyte, a lithium secondary battery, etc. The general technology related to the construction of the battery of the present invention can be grasped as a design matter of those skilled in the art based on the prior art in the field.

  Although not intended to be particularly limited, the positive electrode active material according to the present embodiment will be mainly described below by taking a positive electrode including a positive electrode active material mainly for a lithium secondary battery (typically a lithium ion battery) as an example. The positive electrode will be described.

  As shown in FIG. 1, the positive electrode according to the present embodiment is formed by laminating a positive electrode mixture 30 including a positive electrode active material 10 on a positive electrode current collector (not shown) (that is, a positive electrode mixture). Layer is formed.). The positive electrode current collector may be the same as that used for a typical lithium ion secondary battery, for example, an aluminum foil. The positive electrode mixture 30 includes particles 10 made of a positive electrode active material and particles 20 and 22 made of a conductive additive. The positive electrode mixture 30 may include other positive electrode mixture layer forming components (for example, a binder such as PVDF) used as necessary.

The material constituting the positive electrode active material particles 10 may be any positive electrode material that can hold lithium ions (can absorb and release lithium ions electrochemically), and in this example, is an olivine-based positive electrode material. A typical example of the olivine-based positive electrode material is a general formula Li _1-x Fe _{1- y My} PO ₄ (−0.2 ≦ x ≦ 0.2, 0 ≦ x ≦ 0.5, M: Li, Ni, Co , Mn, Mg, Al, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y), for example, LiFePO ₄ . The particle diameter of the positive electrode active material particles 10 is not particularly limited, but the average particle diameter is preferably in the range of 50 nm to 500 nm, for example, about 100 nm.

  The material constituting the conductive auxiliary particles 20 and 22 may be the same as that which can be used in a typical lithium secondary battery, for example, a carbon-based material. Preferred examples of the carbon-based material include acetylene black (AB), carbon black, and ketjen black. Thus, by mixing the conductive additive particles 20 and 22 in the positive electrode mixture 30, the conductivity of the positive electrode mixture 30 (positive electrode mixture layer) can be improved, and battery performance (for example, discharge performance) is achieved. Can be improved.

  Part of the conductive additive particles included in the positive electrode mixture 30 constituting the positive electrode mixture layer is disposed on the surface of the positive electrode active material particles 10. In the illustrated example, a plurality of conductive assistant particles 20 are attached to the peripheral portion of the positive electrode active material particles 10, thereby forming a surface coating made of the conductive assistant. Thus, by arranging the conductive auxiliary agent particles 20 on the surface of the positive electrode active material particles 10 (here, attached), the conductivity of the positive electrode mixture 30 (positive electrode mixture layer) can be effectively increased, Battery performance (for example, discharge performance) can be further improved. The particle diameter of the conductive auxiliary agent particles 20 disposed on the surface of the positive electrode active material particles 10 is not particularly limited, but the average particle diameter is preferably in the range of 5 nm to 100 nm, particularly preferably in the range of 10 nm to 50 nm. It is about 30 nm.

  Further, the conductive additive particles contained in the positive electrode mixture 30 are arranged not only on the surface of the positive electrode active material particles 10 but also between the adjacent positive electrode active material particles 10. In the illustrated example, the conductive auxiliary agent particles 22 are not directly in contact with the positive electrode active material particles 10 but are interposed in the gaps between the adjacent positive electrode active material particles 10. The conductive auxiliary agent particles 20 arranged on the surface of the positive electrode active material particles 10 and the conductive auxiliary agent particles 22 arranged between the adjacent positive electrode active material particles 10 may be the same material or different materials. It may be. In this example, the conductive auxiliary agent particles 20 arranged on the surface of the positive electrode active material particles 10 are, for example, acetylene black (AB), and the conductive auxiliary agent particles 22 arranged between the adjacent positive electrode active material particles 10 are For example, other carbon particles (for example, carbon black particles) can be used.

  Next, a method for producing the positive electrode active material particles 10 in which the conductive auxiliary agent particles 20 are arranged on the surface described above will be described with reference to FIG. FIG. 2 is a diagram showing a manufacturing flow of the positive electrode active material 10 according to this embodiment.

  This manufacturing method will be briefly described. First, a step of preparing a dispersion liquid in which particles 10 made of a positive electrode active material and particles 20 made of a conductive additive are dispersed in a suitable solvent (Step S10), A step of forming a droplet containing the positive electrode active material particles 10 and the conductive auxiliary agent particles 20 by spraying the dispersion liquid in a predetermined reaction container in a mist form (step S20), and the sprayed droplets And the step of arranging the conductive auxiliary agent particles 20 on the surface of the positive electrode active material particles 10 by drying (Steps S30 and S40). This will be described below.

First, in Step S10, a dispersion liquid is prepared by dispersing the particles 10 made of the positive electrode active material and the particles 20 made of the conductive auxiliary agent in a suitable solvent. In this embodiment, the dispersion is prepared by mixing LiFePO ₄ powder as the positive electrode active material particles 10 and acetylene black powder as the conductive auxiliary particles 20 in a suitable solvent (here, N-methylpyrrolidone). Is dispersed by using a homogenizer. By dispersing in this way, the positive electrode active material particles 10 and the conductive auxiliary agent particles 20 can be stably dispersed (uniformly dispersed) in the dispersion.

  In addition, it is preferable to add a binder capable of binding the positive electrode active material particles 10 and the conductive additive particles 20 to the solvent used for the dispersion (N-methylpyrrolidone in this case). According to this aspect, the conductive auxiliary agent particles 20 can be easily attached (adhered) to the surface of the positive electrode active material particles 10, and therefore the positive electrode active material particles 10 and the conductive auxiliary agent particles 20 are firmly integrated. can do. An example of such a binder is PVDF (polyvinylidene fluoride).

  Next, in step S20, the dispersion liquid is sprayed in the form of a mist into a predetermined reaction vessel 66 (typically a drying tank capable of supplying hot air to the inside), whereby the positive electrode active material particles 10 and the conductive material are sprayed. A droplet 40 containing the auxiliary particles 20 is formed. In this embodiment, the dispersion is sprayed using a four-fluid nozzle 60. That is, as shown in FIGS. 3A and 3B, the four-fluid nozzle 60 includes two liquid supply ports 62a and 62b and two gas supply ports 64a and 64b. Then, the dispersion liquid supplied from the liquid supply ports 62a and 62b and the gas (typically air) supplied from the gas supply ports 64a and 64b are mixed and sprayed in the reaction container 66 in the form of a mist. It has become. In the example of FIG. 3B, the four-fluid nozzle 60 is installed at the upper part of the reaction vessel 66 and sprays the dispersion liquid downward in the reaction vessel 66.

  Thereby, the droplet 40 containing the appropriate amount of the positive electrode active material particles 10 and the conductive auxiliary agent particles 20 can be formed. The size of the droplet that can be formed may be any size that can hold the positive electrode active material particles 10 and the conductive additive particles 20, and is, for example, about 5 μm to 15 μm, and particularly preferably 5 μm to 10 μm. The size of such droplets can be easily controlled by appropriately adjusting the liquid supply amount and gas supply amount of the four-fluid nozzle 60, for example. The size of the droplets that can be formed can be appropriately adjusted according to the particle diameters of the positive electrode active material particles and the conductive additive particles. Further, depending on the required droplet size, a two-fluid nozzle or a three-fluid nozzle may be used instead of the four-fluid nozzle.

  Next, in step S <b> 30, the sprayed droplets 40 are dried to place the conductive auxiliary agent particles 20 on the surfaces of the positive electrode active material particles 10. In this embodiment, drying of the droplet 40 is performed by bringing the sprayed droplet 40 into contact with hot air. That is, a hot air inlet (not shown) is provided in the reaction container 66 shown in FIG. 3B (for example, provided on the upper surface side of the container 66), and hot air is introduced into the reaction container 66 from the hot air inlet. Alternatively, the discharge path 68 shown in the figure may be used as a hot air introduction path. In this case, since the hot air can be brought into contact with the droplets 40 falling in the container from below, the dropping speed of the droplets 40 (that is, the contact time with the hot air) can be appropriately adjusted.

  According to the said aspect, the solvent (N-methylpyrrolidone here) contained in the droplet 40 can be rapidly removed with hot air, and the sprayed droplet can be dried instantaneously. Thereby, the conductive auxiliary agent particles 20 can be quickly arranged on the surface of the positive electrode active material particles 10. In this embodiment, since the binder (in this case, PVDF) is added to the solvent, the conductive auxiliary agent particles 20 are easily attached to the positive electrode active material particles 10 to be electrically connected to the positive electrode active material particles 10. The auxiliary particles 20 can be firmly integrated with the binder.

  Thereafter, the obtained positive electrode active material particles (that is, positive electrode active material particles having conductive auxiliary particles arranged on the surface) 10 are discharged to the outside of the reaction vessel 66 by the hot air. In this embodiment, a discharge path 68 is connected to the lower part of the reaction vessel 66. The obtained positive electrode active material particles 10 are guided to the discharge path 68 by the hot air, and discharged to the outside of the reaction vessel 66 through the discharge path 68. In addition, when discharging to the outside of the reaction vessel 66 by the hot air (for example, while passing through the discharge path 68), the positive electrode active material particles may be further dried. Thus, in step S40, the positive electrode active material particles 10 having the conductive auxiliary agent particles 20 disposed on the surface can be obtained.

  According to the positive electrode active material manufacturing method of the present embodiment, first, a droplet 40 including an appropriate amount of the positive electrode active material particle 10 and the conductive auxiliary agent particle 20 is produced, and then the droplet 40 is dried. Since the conductive auxiliary agent particles 20 are arranged (attached) on the surface of the positive electrode active material particles 10, it is possible to avoid a situation where the positive electrode active material particles 10 are brought into contact with each other and bound (granulated). Thereby, an increase in interface resistance due to binding between the positive electrode active material particles 10 can be suppressed. As a result, the internal resistance of the battery can be reduced, and a battery excellent in battery performance (for example, high rate characteristics) can be provided.

  In this embodiment, the droplet 40 is dried by bringing hot air into contact with the droplet 40. According to such a method, since the dispersion solvent (for example, an organic solvent such as N-methylpyrrolidone) contained in the droplet 40 can be quickly removed by hot air, the sprayed droplet 40 can be dried instantaneously. Can do. Therefore, it is possible to quickly dispose the conductive auxiliary particles on the surface of the positive electrode active material particles while suppressing the binding (growth) between the positive electrode active material particles 10, and the positive electrode active material suitable for the purpose of the present invention. The particles 10 can be manufactured easily and stably. Note that a drying process other than hot air (for example, a heating process using a heater or the like, or a drying process that blows air at room temperature or lower) may be performed.

  Furthermore, in this embodiment, the obtained positive electrode active material particles 10 (that is, positive electrode active material particles having conductive auxiliary agent particles arranged on the surface) are mixed with the hot air into the reaction vessel 66 (typically hot air inside). It is discharged outside the drying tank that can be supplied. According to such a method, since the obtained positive electrode active material particles 10 can be quickly discharged to the outside of the reaction vessel 66 (drying tank) without being kept in one place (that is, in the reaction vessel 66), Binding (granulation) between the positive electrode active material particles 10 can be effectively suppressed.

  An example of the manufacturing conditions of the above-described positive electrode active material particles (that is, positive electrode active material particles having conductive auxiliary particles arranged on the surface) 10 is as follows. The temperature of the hot air may be a temperature at which the solvent (N-methylpyrrolidone here) can be removed, and may be in the range of 80 ° C. to 250 ° C., for example, 120 ° C. in this example. The liquid supply amount of the four-fluid nozzle 60 is in the range of 1 ml / min to 50 ml / min, for example 10 ml / min. The gas supply amount of the four-fluid nozzle 60 is in the range of 1 NL / min to 100 NL / min, for example 50 NL / min.

  The solid content concentration in the dispersion (that is, the concentration of the positive electrode active material and the conductive additive) is preferably in the range of 1% by mass to 20% by mass, particularly preferably 2% by mass to 10% by mass. By setting the solid content concentration in the above range, the positive electrode active material particles 10 and the conductive additive 20 can be stably dispersed (uniformly dispersed) in the dispersion, and the droplets sprayed using a four-fluid nozzle are used. Appropriate amounts of the positive electrode active material particles 10 and the conductive auxiliary agent particles 20 are easily retained.

  The mass ratio of the conductive auxiliary agent contained in the dispersion to the positive electrode active material (conductive auxiliary agent mass / positive electrode active material amount) is preferably in the range of 0.005 to 0.2. 0.01 to 0.04 is particularly preferable. By setting the mass ratio of the conductive additive contained in the dispersion to the positive electrode active material in the above range, the conductive auxiliary particles 20 can be easily arranged uniformly on the surface of the positive electrode active material particles 10. Therefore, for example, the surfaces of the positive electrode active material particles 10 can be uniformly coated (coated) with the conductive auxiliary agent particles 20.

  In this embodiment, the positive electrode active material particles are made of an olivine-based positive electrode material. The olivine-based positive electrode active material has various characteristics preferable as the positive electrode active material because of its large battery theoretical capacity and high safety, while its low conductivity tends to increase the interface resistance due to binding between the positive electrode active material particles. Becomes prominent. Therefore, when the positive electrode active material particles are made of an olivine-based positive electrode material, the dispersion containing the positive electrode active material particles 10 and the conductive additive 20 is sprayed in the form of droplets and dried. The effect by employ | adopting an aspect can be exhibited especially well.

  Subsequently, returning to FIG. 2, a process of manufacturing a positive electrode using the positive electrode active material particles 10 obtained in Step S40 will be described. This manufacturing method will be briefly described. A step of preparing a positive electrode mixture paste containing the positive electrode active material particles 10 obtained by the above-described manufacturing method (that is, positive electrode active material particles having conductive auxiliary particles arranged on the surface). (Step S50) and a step of forming the positive electrode mixture layer by applying the prepared positive electrode mixture paste on the positive electrode current collector and drying it (Step S60). This will be described below.

First, in step S50, a positive electrode mixture paste containing the above-obtained positive electrode active material particles 10 (that is, positive electrode active material particles having conductive auxiliary particles arranged on the surface) is prepared. In this embodiment, the preparation of the positive electrode mixture paste is performed by using the positive electrode active material particles 10 obtained above,
Carbon powder as the conductive auxiliary agent particles 22 (that is, the conductive auxiliary agent disposed between the adjacent positive electrode active material particles 10 shown in FIG. 1), and other positive electrode mixture layer forming components used as necessary (In this case, PVDF as a binder) is dispersed in a suitable solvent (N-methylpyrrolidone in this case) using a planetary mixer and kneaded. The dispersion medium may be a non-aqueous medium organic medium (for example, N-methylpyrrolidone), or water or a mixed solvent mainly composed of water.

  Further, the dispersion and kneading of the positive electrode mixture paste may be performed using a thin film swirl mixer (thin film swirl mixer, for example, TK Fillmix (registered trademark: product of Primics)). The positive electrode active material particles produced using the reaction container 66 shown in FIG. 3B (for example, a spray dryer apparatus) may be fine powder and may have poor wettability. By dispersing in a dispersion medium using a swirling mixer, the positive electrode mixture paste becomes easy to conform to the surface of the positive electrode current collector. Therefore, it is possible to avoid a situation in which the positive electrode mixture layer obtained after drying is lifted from the positive electrode current collector or peeled off. Therefore, it is possible to stably produce a positive electrode for a battery excellent in battery performance (with high quality stability).

  Next, in step S60, the prepared positive electrode mixture paste is applied on the positive electrode current collector and dried to form a positive electrode mixture layer. In this embodiment, the application (typically application) of the positive electrode mixture paste is performed from above the positive electrode current collector using, for example, an appropriate application device (slit coater, die coater, comma coater, etc.). It is performed by coating a predetermined amount of positive electrode mixture paste to a uniform thickness. Then, the dispersion medium in the positive electrode mixture paste can be removed by drying (typically 70 to 200 ° C.) the positive electrode mixture paste by an appropriate drying means. A positive electrode mixture layer 30 including the positive electrode active material particles 10 on which the particles 20 are arranged is formed.

  Thus, in step S70, a positive electrode sheet (positive electrode) on which the positive electrode mixture layer 30 including the positive electrode active material particles 10 on the surface of which the conductive auxiliary agent particles 20 are disposed can be obtained. In addition, after drying, the thickness and the density of the positive electrode mixture layer 30 can be appropriately adjusted by performing an appropriate press process (for example, a roll press process) as necessary.

  According to the battery positive electrode manufacturing method of the present embodiment, a battery positive electrode excellent in current collecting performance that can reduce the internal resistance of the battery can be manufactured stably (with high quality stability). For example, a positive electrode including any positive electrode active material disclosed herein, a negative electrode, an electrolyte disposed between the positive and negative electrodes, and a separator (solid or It can be omitted in a battery using a gel electrolyte.) And can be preferably used as a component of a lithium secondary battery. Especially about the structure (for example, a metal housing or laminate film structure) and size of an outer container constituting such a battery, or the structure of an electrode body (for example, a wound structure or a laminated structure) mainly composed of positive and negative electrodes There is no limit.

  Since the battery constructed in this manner is constructed using the positive electrode active material particles 10 having the conductive assistant particles 20 arranged on the surface as described above, the battery exhibits better battery performance. . For example, by constructing a battery using positive electrode active material particles having conductive auxiliary agent particles 20 disposed on the surface, a battery having excellent high-rate discharge characteristics (decrease in discharge characteristics even when rapidly discharged with a large current) A small battery).

  In order to confirm that a lithium ion secondary battery can be constructed using the positive electrode active material according to the present invention to construct a battery having excellent high rate characteristics, the following experiment was conducted as an example. This will be described below.

First, 87% by mass of LiFePO ₄ powder as a positive electrode active material is appropriately combined with 2% by mass of acetylene black (AB) powder as a conductive additive and 1.5% by mass of PTFE (solid content) as a positive electrode binder. The mixture was dispersed using a homogenizer in an appropriate solvent (N-methylpyrrolidone). At this time, the solid content concentration in the dispersion was adjusted to 5% by mass. Here, the mass% of the electrode material represents the mass% of the finally produced positive electrode, and therefore the total is not 100%. Subsequently, the prepared dispersion liquid was sprayed in the form of a mist and dried to prepare positive electrode active material particles having conductive auxiliary particles arranged on the surface. This spraying / drying treatment was performed using a commercially available micro mist dryer apparatus (manufactured by Fujisaki Electric). As the spray treatment conditions, a four-fluid nozzle was used, the liquid supply amount was 10 ml / min, and the gas supply amount was 50 NL / min. Moreover, as drying process conditions, the inlet temperature of the hot air for drying was about 220 degreeC.

  Next, 90.5% by mass of the positive electrode active material particles (positive electrode active material particles having the conductive assistant particles 20 disposed on the surface) obtained as described above was mixed with 8% by mass of carbon as a positive electrode conductive auxiliary agent and positive electrode particles. A positive electrode mixture paste was prepared by dispersing and kneading PTFE (solid content) 1.5% by mass in a suitable solvent (N-methylpyrrolidone) using a primary mixer. The solid content concentration in the positive electrode mixture paste was adjusted to 40% by mass. Next, this paste was applied to a positive electrode current collector (aluminum foil) and pressed to volatilize the solvent at 120 ° C., thereby producing a positive electrode sheet in which a positive electrode mixture layer was provided on both surfaces of the positive electrode current collector. In addition, application | coating of the positive mix paste was performed using the coater, and the positive mix paste was pressed using the roll press machine.

  On the other hand, 95% by mass of graphite as a negative electrode active material was dispersed in an appropriate solvent (N-methylpyrrolidone) together with 5% by mass of PVDF as a negative electrode binder to prepare a negative electrode mixture paste. This paste was applied to a negative electrode current collector (copper foil) and pressed to volatilize the solvent, thereby preparing a negative electrode sheet in which a negative electrode mixture layer was provided on both surfaces of the negative electrode current collector. In addition, application | coating of the negative mix paste was performed using the coater, and the negative mix paste was pressed using the roll press machine.

Then, these positive electrode sheet and negative electrode sheet were laminated via two separator sheets made of fine porous polyethylene having a thickness of 25 μm, and the laminated body was wound to produce a wound electrode body. The wound electrode body thus obtained was accommodated in a coin-type battery case. In addition, as an electrolytic solution, a solution obtained by dissolving about 1 mol / liter of LiPF ₆ in a 3: 7 (mass ratio) mixed solvent of ethylene carbonate and diethyl carbonate was used. In this way, a test lithium ion secondary battery was produced.

Moreover, the positive electrode sheet was produced as a comparative example using the positive electrode active material particle in which the conductive support agent particle | grains are not arrange | positioned on the surface. Specifically, 87% by mass of LiFePO ₄ powder as the positive electrode active material on which no conductive auxiliary agent particles are arranged on the surface, 10% by mass of carbon as the positive electrode conductive agent, and PTFE (solid content) 3 as the positive electrode binder. A positive electrode mixture paste was prepared by dispersing it in an appropriate solvent (N-methylpyrrolidone) using a primary mixer together with the mass%, and a lithium ion secondary battery was constructed using this. A battery was produced under the same conditions as in the above-described example except that positive electrode active material particles having no conductive auxiliary agent particles arranged on the surface were used.

  Discharge characteristic tests were performed on the test batteries of Examples and Comparative Examples manufactured as described above, and their discharge rate characteristics were evaluated. The test conditions for the discharge characteristics were a measurement temperature of 25 ° C., an upper limit voltage of 4.1 V, a lower limit voltage of 2.5 V, and the measurement was performed twice for each discharge rate. The results are shown in FIGS. 4 and 5, the horizontal axis represents capacity density, and the vertical axis represents voltage.

  The battery of the example shown in FIG. 4 shows a capacity density of about 140 mAh / g at a discharge rate of 1 C, shows about 117 mAh / g at a discharge rate of 5 C, and maintains a capacity of about 100 mAh / g even at a higher discharge rate of 10 C. I understood that I could do it. On the other hand, the battery of the comparative example shown in FIG. 5 was almost the same as the battery of the example at a low discharge rate (for example, 1C, 1 / 3C), but the capacity decreased to about 102 mAh / g at the discharge rate of 5C. It can be seen that at a higher discharge rate of 10 C, the voltage suddenly drops to about 6102 mAh / g immediately after the start of discharge, and a large voltage drop occurs.

  From these results, a battery with excellent high-rate discharge characteristics was constructed by constructing a lithium ion secondary battery using positive electrode active material particles having conductive auxiliary particles arranged on the surface by the production method of the present invention. Confirmed to get.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, the type of the battery is not limited to the above-described lithium ion secondary battery, but may be a battery having various contents with different electrode body constituent materials and electrolytes, such as a nickel hydrogen battery and a nickel cadmium battery.

  In addition, since the battery provided with the positive electrode using the positive electrode active material according to the present embodiment has excellent high rate characteristics as described above, it is particularly suitable as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Can be used. That is, a battery (typically an automobile, in particular a hybrid), in which the battery is arranged as a single battery in a predetermined direction, an assembled battery is constructed by restraining the single battery in the arrangement direction, and the assembled battery is used as a power source. An automobile equipped with an electric motor such as an automobile, an electric automobile, and a fuel cell automobile) can be provided.

The figure which shows typically the positive mix layer containing the positive electrode active material which concerns on one Embodiment of this invention. The figure which shows the manufacture flow of the positive electrode active material which concerns on one Embodiment of this invention. The figure which shows typically the four fluid nozzle which concerns on one Embodiment of this invention. The figure which shows typically the reaction container which concerns on one Embodiment of this invention. The discharge rate characteristic figure which concerns on the Example of this invention. The discharge rate characteristic view concerning the comparative example of the present invention. The graph which shows the rate characteristic which concerns on an Example and a comparative example. The figure for demonstrating the conventional composite particle which the particle | grains which consist of a positive electrode active material bound.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Positive electrode active material particle 20 Conductive auxiliary agent particle 22 Conductive auxiliary agent particle 30 Positive electrode compound material 40 Droplet 60 Four-fluid nozzle 62a Liquid supply port 64a Gas supply port 66 Reaction container 68 Discharge route

Claims (9)

A method for producing a positive electrode active material having conductive auxiliary particles disposed on a surface,
Preparing a dispersion obtained by dispersing particles composed of the positive electrode active material and particles composed of the conductive additive in a solvent;
Forming a droplet containing the positive electrode active material particles and the conductive auxiliary particles by spraying the dispersion liquid in a mist in a reaction vessel;
Arranging the conductive auxiliary agent particles on the surface of the positive electrode active material particles by drying the sprayed droplets;
A method for producing a positive electrode active material, comprising:   The manufacturing method according to claim 1, wherein drying of the droplets is performed by bringing hot air into contact with the droplets.   The manufacturing method according to claim 2, wherein the positive electrode active material particles having conductive auxiliary agent particles arranged on the obtained surface are discharged to the outside of the reaction vessel by the hot air.   The manufacturing method according to claim 1, wherein the spraying of the dispersion liquid is performed using a four-fluid nozzle.   The said positive electrode active material is a manufacturing method as described in any one of Claim 1 to 4 which is an olivine type | system | group positive electrode active material.   The manufacturing method according to claim 1, wherein the dispersion liquid includes a binder capable of binding the positive electrode active material particles and the conductive additive particles. Preparing a positive electrode mixture paste containing a positive electrode active material obtained by the method according to any one of claims 1 to 6;
Forming the positive electrode mixture layer by applying and drying the prepared positive electrode mixture paste on the positive electrode current collector; and
The manufacturing method of the positive electrode for batteries containing this.   The manufacturing method according to claim 7, wherein the positive electrode mixture paste is prepared by dispersing the positive electrode active material in a dispersion solvent using a thin-film swirling mixer. A battery comprising a positive electrode active material obtained by the method according to any one of claims 1 to 6 or a positive electrode for a battery obtained by the method of claim 7 or 8.

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