JP2010251194A - Positive electrode for battery and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a battery including a positive electrode active material having a particulate conductive material on its surface, which can avoid such an event that the particulate conductive material exfoliates from the surface of the positive electrode active material and which is superior in quality stability. <P>SOLUTION: The positive electrode for the battery includes a positive current collector and the positive electrode active material 12, wherein the positive electrode active material 12 has the particulate conductive material 14 on its surface 15, at least the surface part 15 of the positive electrode active material 12 is a porous structure formed with pores 16, and the particulate conductive material 14 is retained on the surface 15 of the positive electrode active material 12 with a portion of it being buried in the pores 16. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode for a battery and a method for producing the same. Specifically, the present invention relates to a positive electrode for a battery including a positive electrode active material having a granular conductive material on its surface and a method for manufacturing the same.

  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, as one of the electrode active materials (positive electrode active materials) used for the positive electrode, an oxide (lithium transition metal composite oxide) containing lithium and one or more transition metal elements as constituent metal elements can be given.

  When a lithium transition metal composite oxide is used as the positive electrode active material, the lithium transition metal composite oxide has a low electronic conductivity, and therefore a conductive material is mixed and used. For example, in one typical configuration of this type of lithium secondary battery, a carbon-based material (such as carbon black) as a conductive material is mixed with a lithium transition metal composite oxide that is a positive electrode active material, and this is mixed with a binder. The positive electrode comprised by having been attached by is provided. Further, since the contact between the positive electrode active material and the conductive material is insufficient only by mixing the conductive material with the positive electrode active material, it has been studied to attach the conductive material to the surface of the positive electrode active material. For example, Patent Document 1 discloses a technique in which a conductive material in the form of a thin film is attached to the surface of positive electrode material particles by sputtering. As another conventional technique for attaching a conductive material to the surface of the positive electrode active material, for example, Patent Document 2 can be cited.

Japanese Patent Laid-Open No. 11-307083 JP 2001-328813 A

  However, in the conventional adhesion methods such as Patent Documents 1 and 2, since the adhesion force of the conductive material to the surface of the positive electrode active material is small, the conductive material is caused by expansion / contraction of the positive electrode active material during repeated charge / discharge. May peel off from the surface of the positive electrode active material, and battery characteristics may deteriorate.

  This invention is made | formed in view of this point, The main objective is the positive electrode for batteries provided with the positive electrode active material which has a granular conductive material on the surface, A granular conductive material is from the surface of a positive electrode active material. An object of the present invention is to provide a positive electrode for a battery that can avoid the phenomenon of peeling and has excellent quality stability. Moreover, the other objective is to provide the suitable manufacturing method of the positive electrode for batteries which has such performance.

  The positive electrode for a battery provided by the present invention is a positive electrode for a battery including a positive electrode current collector and a positive electrode active material. The positive electrode active material has a granular conductive material on its surface. In addition, at least a surface portion of the positive electrode active material has a porous structure in which pores are formed, and the particulate conductive material has the positive electrode in a state where a part thereof is embedded in the pores. It is held on the surface of the active material.

  According to the positive electrode for a battery of the present invention, a part of the granular conductive material is held on the surface of the positive electrode active material in a state of being embedded in the pores. This can increase the adhesion of the particulate conductive material, thereby preventing the granular conductive material from floating or peeling off from the surface of the positive electrode active material. Therefore, according to the present invention, it is possible to avoid an event in which the granular conductive material is peeled off from the surface of the positive electrode active material, and it is possible to provide a positive electrode for a battery having excellent quality stability. According to such a positive electrode, a battery with more stable performance can be constructed.

  In one aspect of the positive electrode for a battery disclosed herein, the volume of the portion exposed to the outside of the pores of the whole of the granular conductive material held on the surface of the positive electrode active material is small. The volume is preferably larger than the volume of the portion embedded in the hole. According to such a configuration, 1/2 or more of the granular conductive material held on the surface of the positive electrode active material is exposed to the outside of the pores, so that it is easy to secure a conductive path on the surface of the positive electrode active material.

  In one embodiment of the positive electrode for a battery disclosed herein, the average pore diameter of the pores opened on the surface of the positive electrode active material is preferably 5 nm or more, for example, in the range of 5 nm to 500 nm. If the average pore diameter of the pores is too small, the volume of the particulate conductive material embedded in the pores also becomes small. Therefore, by embedding a part of the granular conductive material in the pores, This is because the effect of the present invention to increase the adhesion between the positive electrode active material is reduced. The average pore diameter of the pores can be obtained, for example, by measurement based on a gas adsorption method.

  In a preferred embodiment of the positive electrode for a battery disclosed herein, the positive electrode active material is formed into particles having a porous structure. In this case, the granular conductive material is embedded on the surface of the positive electrode active material particles in a state where a part thereof is embedded in the pores of the surface of the particles made of the positive electrode active material (hereinafter also referred to as positive electrode active material particles). Is retained. According to such a configuration, since a part of the granular conductive material is held on the surface of the positive electrode active material particles in a state of being embedded in the pores, an attachment between the granular conductive material and the positive electrode active material particles is performed. Adhesive force is increased, which can prevent the granular conductive material from floating or peeling off from the surface of the positive electrode active material particles.

  In a preferable aspect of the battery positive electrode disclosed herein, the positive electrode active material is disposed in a thin film on the positive electrode current collector. In this case, the surface of the positive electrode active material film is partially embedded in the pores of the surface of the thin film (hereinafter also referred to as the positive electrode active material film) made of the positive electrode active material. Is held in. According to such a configuration, since a part of the granular conductive material is held on the surface of the positive electrode active material film in a state of being embedded in the pores, the attachment between the granular conductive material and the positive electrode active material film is performed. The adhesion is increased, and this prevents the granular conductive material from floating or peeling off the surface of the positive electrode active material film.

  In a preferred embodiment of the positive electrode for a battery disclosed herein, indium tin oxide is used as the granular conductive material. Indium tin oxide is excellent in electronic conductivity and is an electrochemically inactive material, and therefore can be preferably used as a granular conductive material suitable for the purpose of the present invention.

  In a preferred embodiment of the battery positive electrode disclosed herein, lithium manganese phosphate is used as the positive electrode active material. Lithium manganese phosphate has a property that it has a high theoretical capacity and is excellent in safety, and thus has a preferable performance as a positive electrode active material, while it has a property of low electronic conductivity as compared with other olivine-type phosphate compounds. Therefore, when the positive electrode active material is lithium manganese phosphate, the effect of the present invention of supplementing the low electron conductivity of the positive electrode active material by attaching the granular conductive material to the surface of the positive electrode active material is particularly well exhibited.

  In addition, according to the present invention, a method for producing any of the positive electrodes for batteries disclosed herein is provided. That is, a method for producing a positive electrode for a battery comprising a positive electrode current collector and a positive electrode active material, the step of preparing a positive electrode active material having a porous structure in which at least a surface portion is formed with pores And a step of applying a granular conductive material to the surface of the positive electrode active material. In the granular conductive material application step, the granular conductive material is held on the surface of the positive electrode active material such that a part of the granular conductive material is embedded in the pores.

  According to the manufacturing method of the present invention, the granular conductive material is held on the surface of the positive electrode active material so that a part of the granular conductive material is embedded in the pores. The phenomenon of peeling from the surface of the substance can be avoided, and a positive electrode for a battery having excellent quality stability can be manufactured.

  In a preferred embodiment of the positive electrode manufacturing method disclosed herein, a positive electrode active material prepared in a particulate form having a porous structure by a sol-gel method is used as the positive electrode active material. According to this method, it is possible to manufacture a battery positive electrode that is held on the surface of the positive electrode active material particles in a state in which a part of the granular conductive material is embedded in the pores. Further, by using the sol-gel method, positive electrode active material particles having a porous structure with good uniformity can be obtained.

  In a preferred embodiment of the positive electrode manufacturing method disclosed herein, a thin film made of the positive electrode active material is formed on the positive electrode current collector. And the said granular conductive material is provided with respect to the surface of the thin film which consists of this positive electrode active material. In this case, the pores on the surface of the thin film made of the positive electrode active material are preferably formed by subjecting the surface of the thin film to dry etching. According to this method, it is possible to manufacture a battery positive electrode that is held on the surface of the positive electrode active material film in a state in which a part of the granular conductive material is embedded in the pores.

  In a preferred embodiment of the positive electrode manufacturing method disclosed herein, in the step of applying the granular conductive material, a part of the granular conductive material is contained in the pores by sputtering using the granular conductive material as a target. The granular conductive material is held on the surface of the positive electrode active material so as to be embedded in the surface. By performing sputtering using the granular conductive material as a target, the granular conductive material can be appropriately embedded in the pores.

  In a preferred embodiment of the positive electrode manufacturing method disclosed herein, in the granular conductive material application step, the whole of the granular conductive material held on the surface of the positive electrode active material is exposed outside the pores. The granular conductive material is held on the surface of the positive electrode active material such that the volume of the portion being made is larger than the volume of the portion embedded in the pores. As a result, a volume of 1/2 or more of the granular conductive material is exposed to the outside of the pores (the surface of the positive electrode active material), so that the function as the granular conductive material can be appropriately exhibited.

  Further, according to the present invention, there is provided a lithium secondary battery (typically a lithium ion secondary battery) comprising any of the battery positive electrodes disclosed herein or a battery positive electrode produced by any method. The Such a lithium secondary battery is built using the positive electrode for a battery, and thus has excellent quality stability and better battery performance (for example, excellent charge / discharge cycle characteristics, low internal resistance of the battery, The battery has good durability).

  Such a lithium secondary battery is suitable as a lithium secondary battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including the lithium secondary battery disclosed herein (which may be in the form of an assembled battery to which a plurality of lithium secondary batteries are connected). In particular, since it is lightweight and provides high output, a vehicle (for example, an automobile) including the lithium secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

Sectional drawing which shows typically the positive electrode which concerns on one Embodiment of invention. Sectional drawing which shows typically the positive electrode active material particle which concerns on one Embodiment of this invention. The figure which shows typically the principal part of the positive electrode active material particle which concerns on one Embodiment of this invention. Process sectional drawing which shows typically the positive electrode active material particle which concerns on one Embodiment of this invention. Sectional drawing which shows typically the positive electrode which concerns on one Embodiment of this invention. Process sectional drawing which shows the positive electrode which concerns on one Embodiment of this invention typically. Process sectional drawing which shows the positive electrode which concerns on one Embodiment of this invention typically. Process sectional drawing which shows the positive electrode which concerns on one Embodiment of this invention typically. The figure which shows typically the lithium secondary battery which concerns on one Embodiment of this invention. The side view which shows typically the vehicle carrying the lithium secondary battery which concerns on one Embodiment of this invention.

  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. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, The battery and other general technologies related to the construction of the battery, etc.) 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, in the following, for a lithium secondary battery (typically a lithium ion battery) having a positive electrode current collector made mainly of aluminum and a positive electrode active material made of lithium manganese phosphate. The positive electrode for a battery according to the present embodiment will be described by taking the positive electrode as an example.

<First Embodiment>
The battery positive electrode 10 according to the present embodiment will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the battery positive electrode 10 according to the present embodiment includes a positive electrode current collector 20 and a positive electrode active material layer (positive electrode active material 12 (FIG. 2)) held on the positive electrode current collector 20. A layer 22). As the positive electrode current collector 20, one made of aluminum or an aluminum alloy, which is excellent in conductivity and can be easily processed into a thin film (sheet), can be used. In this embodiment, the positive electrode current collector 20 is an aluminum foil having a thickness of about 10 μm to 30 μm. The positive electrode active material layer 22 may be a layer containing a positive electrode active material for a lithium secondary battery. For example, the positive electrode active material and other positive electrode active material layer forming components (for example, a conductive assistant) used as necessary. Agent and binder). In this embodiment, as shown in FIG. 2, the positive electrode active material 12 is formed in the form of particles, and particles made of the positive electrode active material (hereinafter referred to as “positive electrode active material particles”) 12 are bound to a binder ( The positive electrode active material layer 22 including the positive electrode active material particles 12 is formed by fixing a layer on the positive electrode current collector 20 using a resin component typically.

  The positive electrode active material 12 is formed in a particle shape having a porous structure, and pores 16 are formed on at least the surface portion 15 of the positive electrode active material particle 12. The positive electrode active material particles 12 have a granular conductive material 14 on the surface 15 thereof. The granular conductive material 14 has a function of supplementing the electron conductivity of the positive electrode active material particles 12 and improving the electron transfer between the positive electrode active material particles 12. The particulate conductive material 14 is held on the surface 15 of the positive electrode active material particles 12 with a part thereof embedded in the pores 16. That is, the granular conductive material 14 is not simply attached to the surface 15 of the positive electrode active material particles 12 but is held in a state of being embedded in the pores 16 opened in the surface 15 of the positive electrode active material particles 12. ing.

  In this way, the granular conductive material 14 is held on the surface 15 of the positive electrode active material particles 12 such that a part of the granular conductive material 14 is embedded in the pores 16, thereby causing the granular conductive material 14 to be retained. A large adhesive force is generated between the positive electrode active material particles 12 and the positive electrode active material particles 12. This adhesion force can prevent the granular conductive material 14 from floating or peeling off from the surface 15 of the positive electrode active material particles 12. Therefore, according to the present embodiment, it is possible to avoid the phenomenon that the granular conductive material 14 is peeled off from the positive electrode active material particles 12, and it is possible to provide the positive electrode 10 for a lithium secondary battery excellent in quality stability. According to such a positive electrode 10, a lithium secondary battery with more stable performance can be constructed.

The constituent material of the positive electrode active material particles 12 is not particularly limited as long as it is the same as that of a typical positive electrode active material for a lithium secondary battery. For example, the main component is an olivine-type phosphate compound containing lithium. Is preferably used. Preferable examples include lithium iron phosphate (such as LiFePO ₄ ) and lithium manganese phosphate (such as LiMnPO ₄ ). Alternatively, an oxide (lithium transition metal composite oxide) containing lithium and one or more transition metal elements as constituent metal elements may be used as the positive electrode active material. Typical examples include lithium nickel-based composite oxides (for example, LiNiO ₂ ), lithium cobalt-based composite oxides (for example, LiCoO ₂ ), and the like.

  In a preferred embodiment of the battery positive electrode disclosed herein, lithium manganese phosphate is used as the positive electrode active material. Lithium manganese phosphate has a property that it has a high theoretical capacity and is excellent in safety, and thus has a preferable performance as a positive electrode active material, while it has a property of low electronic conductivity as compared with other olivine-type phosphate compounds. Therefore, in the case where the positive electrode active material is lithium manganese phosphate, the effect of the present embodiment of compensating the low electronic conductivity of the positive electrode active material particles 12 by adhering the granular conductive material 14 to the surface 15 of the positive electrode active material particles 12. Is particularly well demonstrated.

  The positive electrode active material particles 12 shown in FIG. 2 are so-called primary particles. In the actual positive electrode active material layer 22, a large number of positive electrode active material particles 12 aggregate to form secondary particles (not shown). ing. In this embodiment, primary particles (positive electrode active material particles) 12 constituting secondary particles are formed into particles having a porous structure, and fine particles on the surface portion 15 of the primary particles (positive electrode active material particles) 12 are formed. The granular conductive material 14 is held on the surface 15 of the positive electrode active material particles 12 so that a part of the granular conductive material 14 is embedded in the holes 16. The average particle diameter of the positive electrode active material particles 12 is not particularly limited, but may be, for example, in the range of 30 nm to 100 nm.

As the granular conductive material 14 to be attached to the surface of the positive electrode active material particles 12, a material having high electron conductivity can be used. The electrical resistivity of the granular conductive material may be approximately 10 ⁻¹ Ωcm or less, and preferably 10 ⁻⁴ Ωcm to 10 ⁻¹ Ωcm. Moreover, it is preferable to use an electrochemically inactive material as the granular conductive material. By attaching an electrochemically inactive material to the surface of the positive electrode active material particles, reaction at the interface between the electrolytic solution and the positive electrode active material can be suppressed, and durability can be improved. Specifically, an oxide ceramic material such as indium tin oxide, platinum oxide, ruthenium oxide, or zirconia is preferably used.

In a preferred embodiment of the positive electrode for a battery disclosed herein, indium tin oxide is used as the granular conductive material. Indium tin oxide is excellent in electronic conductivity and is an electrochemically inactive material, so that it can be preferably used as a granular conductive material suitable for the purpose of this embodiment. Here, indium tin oxide is obtained by adding tin oxide (SnO ₂ ) to indium oxide (In ₂ O ₃ ). The amount of SnO ₂ added is not particularly limited. For example, it is preferably added so that the atomic composition percentage of Sn in indium tin oxide is Sn / (In + Sn) = 0.1 at% to 10 at%. If the amount of the SnO ₂ is too small, while the effect due to the addition of SnO ₂ is decreased, the amount of SnO ₂ is too large, the positive electrode active material particle indium tin oxide electrical resistivity is increased It is because the merit by making it adhere to becomes small.

  The size of the pores 16 opening on the surface of the positive electrode active material is not particularly limited. However, if the size of the pores 16 is too small, the volume of the granular conductive material 14 embedded in the pores 16 is also small. By embedding a part of the granular conductive material 14 in the pores 16, the effect of increasing the adhesion between the granular conductive material 14 and the positive electrode active material 12 may be reduced. Therefore, the average pore diameter of the pores 16 is preferably in the range of 1 nm to 100 nm, for example.

  The application of the granular conductive material 14 to the surface 15 of the positive electrode active material particles 12 may be performed, for example, by sputtering using the granular conductive material as a target. When sputtering is performed using a granular conductive material as a target, sputtered particles made of the granular conductive material are selectively deposited in the pores 16 opened on the positive electrode active material surface 15. Therefore, the granular conductive material 14 grows so as to be embedded in the pores 16, and finally the positive electrode active material particles 12 of the positive electrode active material particles 12 in a state where a part of the granular conductive material 14 is embedded in the pores 16. It is held on the surface 15.

  Here, if the volume of the part exposed to the outside of the pores 16 in the whole of the granular conductive material 14 held on the surface 15 of the positive electrode active material particles 12 is too small, the granular conductive material 14 (That is, the function of supplementing the electron conductivity of the positive electrode active material particles 12 by adhering to the surface 15 of the positive electrode active material particles 12) may not be exhibited properly. Therefore, as shown in FIG. 3, the volume V1 of the portion exposed to the outside of the pores 16 in the whole of the granular conductive material 14 held on the surface 15 of the positive electrode active material particles 12 is the pores. The granular conductive material 14 is preferably held on the surface 15 of the positive electrode active material particles 12 so as to be larger than the volume V2 of the portion embedded in the positive electrode 16. According to such a configuration, 1/2 or more of the granular conductive material 14 held on the surface 15 of the positive electrode active material particles 12 is exposed to the outside of the pores 16, so that the surface 15 of the positive electrode active material particles 12 is electrically conductive. It is easier to secure a pass. Note that the volumes V1 and V2 of the exposed portion and the embedded portion of the granular conductive material can be obtained by, for example, analyzing a scanning electron microscope (SEM) image.

  In the illustrated example, the region (range) of the surface 15 of the positive electrode active material particles 12 to which the granular conductive material 14 is attached is limited to the inside of the pores 16, but is not limited thereto. For example, in some cases, the particulate conductive material 14 may be attached not only in the pores 16 but also to a region of the surface 15 of the positive electrode active material particles 12 where the pores 16 are not formed.

  Then, the manufacturing process of the positive electrode 10 which concerns on this embodiment is demonstrated. The positive electrode manufacturing method according to this embodiment includes a positive electrode current collector 20 and a positive electrode 10 for a battery including a positive electrode active material layer (a layer including the positive electrode active material particles 12) 22 held on the positive electrode current collector 20. It is a manufacturing method. This method includes a step of preparing positive electrode active material particles 12 having a porous structure in which at least surface portions 15 are formed with pores 16 (positive electrode active material preparation step), and a surface of positive electrode active material particles 12 A step of applying the granular conductive material 14 to 15 (a granular conductive material applying step). In the granular conductive material application step, the granular conductive material 14 is held on the surface 15 of the positive electrode active material particles 12 such that a part of the granular conductive material 14 is embedded in the pores 16.

Hereinafter, although not intended to be particularly limited, a case where a positive electrode 10 for a lithium secondary battery having a positive electrode current collector 20 made of aluminum and positive electrode active material particles 12 made of LiMnPO ₄ is manufactured is taken as an example. Each step will be described.

First, in the positive electrode active material preparation step, as shown in FIG. 4, LiMnPO ₄ particles 12 having a porous structure in which at least the surface portion 15 is formed with pores 16 are prepared (for example, purchase, synthesis, etc.) To do. In this embodiment, LiMnPO ₄ particles 12 prepared as particles having a porous structure by a sol-gel method are used as the positive electrode active material particles 12. The LiMnPO ₄ particles 12 having a porous structure by the sol-gel method may be prepared as follows.

  First, starting materials including a lithium source, a manganese source, and a phosphoric acid source are weighed so as to have a predetermined mixing ratio, and an organic additive such as citric acid is added to this and dissolved in an appropriate solvent, and then the raw materials are mixed. Prepare the solution. As a starting material including a lithium source, a manganese source, and a phosphate source, one or more compounds including a lithium source, a manganese source, and a phosphate source may be appropriately used. As the solvent, water or a mixed solvent mainly composed of water is preferably used. As a solvent component other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

If the said raw material mixed solution is prepared, next, a raw material mixed liquid will be gelatinized and a gel-like composition will be obtained. The gelation treatment is not particularly limited. For example, the raw material mixture is heated to a temperature at which the solvent can volatilize (for example, approximately 60 ° C. when the solvent is water), and a part of the solvent is volatilized from the raw material mixture. You can do it. When a part of the solvent is volatilized from the raw material mixture, a LiMnPO ₄ precursor precipitate is generated, and when the solvent is further volatilized, it changes to a gel composition that loses fluidity. In order to further promote gelation, a gelling agent (for example, glycolic acid) can be added to the raw material mixture.

If the said gel-like composition is obtained, next, a gel-like composition will be baked at predetermined temperature. The firing temperature is not particularly limited as long as LiMnPO ₄ can be synthesized, but firing is preferably performed at a temperature not exceeding 900 ° C. This is because when the firing temperature is too high, LiMnPO ₄ phase separation occurs and impurities are generated. By such firing treatment, the gel composition becomes LiMnPO ₄ particles having an olivine structure. In addition, when the organic additive such as citric acid is released from the fired product as a gas such as carbon dioxide during firing, the LiMnPO ₄ particles are made porous. In this way, LiMnPO ₄ particles 12 prepared in the form of particles having a porous structure by the sol-gel method are obtained.

The method for synthesizing LiMnPO ₄ particles is not limited to the sol-gel method. For example, LiMnPO ₄ particles may be synthesized by a solid phase reaction method. Even in such a case, by mixing an organic additive such as citric acid at the time of firing, the LiMnPO ₄ particles 12 prepared in the form of particles having a porous structure can be obtained.

Next, in the granular conductive material application step, as shown in FIG. 2, the granular conductive material 14 is applied to the surface 15 of the LiMnPO ₄ particles 12 having the prepared porous structure. A method for applying the granular conductive material 14 is not particularly limited, but a general film forming process, for example, a physical vapor deposition method (PVD method, for example, sputtering method) or a chemical vapor deposition method (CVD method, for example, plasma CVD method) is preferably used. It is done. The application of the granular conductive material 14 by the film forming process is typically performed under reduced pressure conditions (for example, in an inert gas atmosphere having a pressure of about 0.01 Pa to 100 Pa).

In the technique disclosed herein, as a method of applying the granular conductive material 14 to the surface 15 of the LiMnPO ₄ particles 12, for example, a sputtering method using a granular conductive material as a target is preferably used. Sputtering particles (granular conductive material) can be efficiently deposited on the surface 15 of the LiMnPO ₄ particles 12 by performing sputtering using the granular conductive material as a target. Further, by performing sputtering using a granular conductive material as a target, sputtered particles (particulate conductive material) are selectively deposited in the pores 16 of the LiMnPO ₄ particles 12. Therefore, the sputtered particles (granular conductive material) grow so as to be embedded in the pores 16, and thus LiMnPO ₄ particles in a state where a part of the granular conductive material 14 is embedded in the pores 16. 12 surfaces 15 are held.

In such a granular conductive material application step, as shown in FIG. 3, the portion of the entire granular conductive material 14 held on the surface 15 of the LiMnPO ₄ particles 12 is exposed to the outside of the pores 16. It is desirable to hold the granular conductive material 14 on the surface 15 of the LiMnPO ₄ particles 12 so that the volume V 1 is larger than the volume V 2 of the portion embedded in the pores 15. Such control of the adhesion amount of the granular conductive material 14 can be performed by appropriately adjusting the above-described sputter deposition conditions (sputtering time, etc.).

  Thus, the positive electrode active material particles 12 held on the surface 15 of the positive electrode active material particles 12 in a state where a part of the granular conductive material 14 is embedded in the pores 16 can be obtained. Therefore, the above steps can be grasped as a method for producing a positive electrode active material or a process for preparing (manufacturing) a positive electrode active material.

  Note that the method of applying the granular conductive material 14 to the surface of the positive electrode active material particles 12 is not limited to the film forming process such as sputtering. For example, the granular conductive material 14 can be attached to the surface of the positive electrode active material particles 12 by a sol-gel method. In this case, the raw material mixture used when synthesizing the positive electrode active material particles 12 (in the above-described example, the starting raw materials including the lithium source, the manganese source, and the phosphoric acid source are weighed so as to have a predetermined mixing ratio, A granular conductive substance may be added and dispersed in advance in a raw material mixture obtained by dissolving an organic additive such as citric acid in an appropriate solvent. Thereby, the positive electrode active material particle which has a granular conductive material on the surface is obtained. According to this method, the synthesis of the positive electrode active material particles and the application of the granular conductive material can be performed in the same process, and the manufacturing process can be simplified.

Subsequently, a process of manufacturing the positive electrode 10 using the LiMnPO ₄ particles 12 obtained by the above method will be described.

That is, as shown in FIG. 1, the positive electrode active material layer 22 including the LiMnPO ₄ particles 12 obtained as described above is formed on the positive electrode current collector 20. Specifically, a positive electrode active material layer forming paste containing LiMnPO ₄ particles 12 obtained as described above and a suitable residual medium is applied (typically applied) on the positive electrode current collector 20. The negative electrode active material layer forming paste can be prepared by mixing the positive electrode active material particles 12 as described above and other positive electrode active material layer forming components used as necessary in a suitable dispersion medium. . Thereby, the positive electrode active material layer forming paste in which the positive electrode active material particles are dispersed in the dispersion medium containing other positive electrode mixture layer forming components used as necessary is obtained. Examples of the dispersion medium include water or a mixed solvent mainly composed of water (aqueous solvent). As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. It is not limited to an aqueous solvent, and may be a non-aqueous solvent. As the non-aqueous solvent, an organic solvent such as N-methylpyrrolidone (NMP) can be used.

The positive electrode active material layer forming paste may contain, in addition to the LiMnPO ₄ particles 12 and the dispersion medium, materials used for the positive electrode active material layer forming paste in the production of a general positive electrode as necessary. . Typical examples of such materials include conductive materials and binders. The conductive material may be the same as the granular conductive material 14 attached to the surface 15 of the LiMnPO ₄ particles 12, or may be of a different type (for example, carbon powder such as carbon black and graphite, nickel powder, etc. A conductive metal powder or the like. As the binder, a water-soluble or water-dispersible polymer such as polyvinylidene fluoride (PVDF) can be used.

The operation of applying (typically applying) such a positive electrode active material layer forming paste to the positive electrode current collector is such that a part of the granular conductive material 14 as the LiMnPO ₄ particles 12 has pores 16 as described above. A conventional general positive electrode for a lithium secondary battery can be produced in the same manner except that a material held on the surface 15 of the LiMnPO ₄ particles 12 in an embedded state is used. For example, it can be produced by applying a predetermined amount of a positive electrode active material layer forming paste to a positive electrode current collector in a layer form using a suitable coating device (die coater or the like). After coating, the coated product is dried (typically 70 to 200 ° C.) by a suitable drying means, whereby the positive electrode 10 in which the positive electrode active material layer 22 is held on the positive electrode current collector 20 is obtained.

<Second Embodiment>
Subsequently, another embodiment of the present invention will be described. In this embodiment, the positive electrode active material is not formed in the form of particles having a porous structure, but is arranged in a thin film on the positive electrode current collector. Is different. The structure of the positive electrode according to the second embodiment is schematically shown in FIG. In addition, since each material which comprises a positive electrode can use the same thing as 1st Embodiment mentioned above, the overlapping description is abbreviate | omitted here.

  As shown in FIG. 5, the positive electrode active material 112 is disposed on the positive electrode current collector 120 in a thin film shape, and at least a thin film (hereinafter referred to as “positive electrode active material film”) 112 made of the positive electrode active material. A pore 116 is formed in the surface portion 115. The positive electrode active material film 112 has a granular conductive material 114 on the surface 115 thereof. The granular conductive material 114 is held on the surface 115 of the positive electrode active material film 112 in a state where a part thereof is embedded in the pores 116. That is, the granular conductive material 114 is not simply attached to the surface 115 of the positive electrode active material film 112 but is held in a state of being embedded in the pores 116 opened in the surface 115 of the positive electrode active material film 112. ing.

  As described above, the granular conductive material 114 is held on the surface 115 of the positive electrode active material film 112 such that a part of the granular conductive material 114 is embedded in the pores 116, thereby allowing the granular conductive material 114 to be retained. A large adhesive force is generated between the positive electrode active material film 112 and the positive electrode active material film 112. This adhesion force can prevent the granular conductive material 114 from floating or peeling off from the surface 115 of the positive electrode active material film 112. Therefore, according to the present embodiment, it is possible to avoid the phenomenon that the granular conductive material 114 peels from the positive electrode active material film 112, and it is possible to provide the positive electrode 110 for a lithium secondary battery excellent in quality stability. According to such a positive electrode 110, a lithium secondary battery with more stable performance can be constructed.

  The film thickness of the positive electrode active material film 112 is not particularly limited. However, if the film thickness of the positive electrode active material film 112 is too small, the battery capacity tends to decrease, but the film thickness of the positive electrode active material film 112 is too large. The positive electrode active material film 112 may be easily peeled off from the positive electrode current collector 120 due to a difference in thermal expansion coefficient between the positive electrode active material and aluminum constituting the positive electrode current collector 120. Therefore, the thickness of the positive electrode active material film 112 is preferably in the range of 1 μm to 10 μm, for example.

  The size of the pores 116 that open to the surface 115 of the positive electrode active material film 112 is not particularly limited. However, if the size of the pores 116 is too small, the adhesion of the granular conductive material 114 embedded in the pores 116. On the other hand, if the size of the pores 116 is too large, it may take a long time to form the pores 116 and the productivity may decrease. Therefore, the average pore diameter of the pores 116 is preferably in the range of 5 nm to 500 nm, for example.

  Then, the manufacturing process of the positive electrode 110 which concerns on this embodiment is demonstrated. The positive electrode manufacturing method according to the present embodiment is a method for manufacturing a positive electrode 110 for a battery that includes a positive electrode current collector 120 and a positive electrode active material film 112 held on the positive electrode current collector 120. This method includes a step of preparing a positive electrode active material film 112 having a porous structure in which at least a surface portion 115 is formed with pores 116 (positive electrode active material preparation step), and a surface of the positive electrode active material film 112. A step of applying a granular conductive material 114 to 115 (a granular conductive material applying step). Then, in the granular conductive material application step, the granular conductive material 114 is held on the surface 115 of the positive electrode active material film 112 so that a part of the granular conductive material 114 is embedded in the pores 116.

Hereinafter, although not intended to be particularly limited, a case where a positive electrode 110 for a lithium secondary battery having a positive electrode current collector 120 made of aluminum and a positive electrode active material film 112 made of LiMnPO ₄ is manufactured is taken as an example. Each step will be described.

First, in the positive electrode active material preparation step, as shown in FIG. 6B, a LiMnPO ₄ film 112 having a porous structure in which at least the surface portion 115 is formed with pores 116 is prepared (for example, purchase, synthesis, etc.) To do. In this embodiment, a LiMnPO ₄ film 112 in which the average pore diameter of the pores 116 opening on the surface 115 is in the range of 5 nm to 500 nm is used as the positive electrode active material film 112. The LiMnPO ₄ film 112 having such pores 116 can be formed as follows.

First, as shown in FIG. 6A, a thin film 112 made of LiMnPO ₄ is formed on the positive electrode current collector 120. The formation method of the LiMnPO ₄ film 112 is not particularly limited, but, for example, a general film formation process, for example, a physical vapor deposition method (PVD method, for example, sputtering method), a chemical vapor deposition method (CVD method, for example, plasma CVD method) or the like is preferable. Used. As a method for forming the LiMnPO ₄ film 112 on the positive electrode current collector 120 in the technique disclosed herein, for example, a sputtering method using LiMnPO ₄ as a target can be preferably employed. Sputtering particles (LiMnPO ₄ particles) can be efficiently deposited on the surface of the positive electrode current collector 120 by performing sputtering using LiMnPO ₄ as a target.

Once the LiMnPO ₄ film 112 is formed, next, pores 116 are formed on the surface 115 of the LiMnPO ₄ film 112 as shown in FIG. 6B. LiMnPO pores 116 of surface 115 of the ₄ film 112, for example, it may be formed by performing dry etching with respect to the surface 115 of the LiMnPO ₄ film 112. In this embodiment, by performing Ar etching process on the surface 115 of the LiMnPO ₄ film 112, an average pore diameter of the surface 115 of the LiMnPO ₄ film 112 to form pores 116 nano-order of about 5 nm to 500 nm. In this way, the LiMnPO ₄ film 112 having the desired pores 116 is obtained.

Next, in the granular conductive material application step, the granular conductive material 14 is applied to the surface 15 of the LiMnPO ₄ film 112 prepared as shown in FIG. 6C. A method for applying the granular conductive material 14 is not particularly limited, but a general film forming process, for example, a physical vapor deposition method (PVD method, for example, sputtering method) or a chemical vapor deposition method (CVD method, for example, plasma CVD method) is preferably used. It is done. The application of the granular conductive material 14 by the film forming process is typically performed under reduced pressure conditions (for example, in an inert gas atmosphere having a pressure of about 0.01 Pa to 100 Pa).

In the technique disclosed herein, as a method for applying the granular conductive material 114 to the surface 115 of the LiMnPO ₄ film 112, for example, a sputtering method using a granular conductive material as a target is preferably used. Sputtering particles (granular conductive material) can be efficiently deposited on the surface 115 of the LiMnPO ₄ film 112 by performing sputtering using the granular conductive material as a target. Further, by performing sputtering using a granular conductive material as a target, sputtered particles (particulate conductive material) are selectively deposited in the pores 116 of the LiMnPO ₄ film 112. Therefore, the LiMnPO ₄ film grows while sputtered particles (granular conductive material) are embedded in the pores 116, and in this way, a part of the granular conductive material 114 is embedded in the pores 116. 112 is held on the surface 115.

  In this way, the positive electrode active material film 112 held on the surface 115 of the positive electrode active material film 112 in a state where a part of the granular conductive material 114 is embedded in the pores 116 is formed on the positive electrode current collector 120. The formed positive electrode 110 is obtained. According to the above manufacturing method, since the nano-order pores 116 can be formed on the surface 115 of the positive electrode active material film 112, the amount of the particulate conductive material 114 embedded in the pores 116 can be controlled. This makes it easy to attach an appropriate amount of the granular conductive material 114 to the surface 115 of the positive electrode active material film 112. Therefore, the adhesion amount of the granular conductive material 114 can be adjusted so as to suppress an increase in reaction resistance, which is the contradiction, while improving the durability of the positive electrode active material due to the adhesion of the granular conductive material 114.

  The positive electrode for a lithium secondary battery provided by the present embodiment can firmly fix the conductive material to the positive electrode active material as described above, and is excellent in quality stability. It can be preferably used as a constituent element of a secondary battery or a constituent element (for example, positive electrode) of an electrode body incorporated in the lithium secondary battery. For example, any positive electrode disclosed herein, a negative electrode, an electrolyte disposed between the positive and negative electrodes, and a separator that typically separates the positive and negative electrodes (battery using a solid or gel electrolyte) Can be omitted) and can be preferably used as a component of a lithium secondary battery. Structure (for example, metal casing or laminate film structure) and size of an outer container constituting such a battery, or structure of an electrode body (for example, a wound structure or a laminated structure) having a positive / negative electrode current collector as a main component There is no particular restriction on the etc.

  Hereinafter, an embodiment of a lithium secondary battery constructed using the positive electrode (positive electrode sheet) 10 according to the first embodiment will be described with reference to a schematic diagram shown in FIG. The lithium secondary battery 100 includes a positive electrode current collector 20 as a positive electrode 10 and a positive electrode active material held on the surface of the positive electrode active material in a state where a part of the granular conductive material 14 is embedded in the pores 16. 12 is used.

  As shown in FIG. 7, the lithium ion battery 100 according to this embodiment includes a case 50 made of metal (a resin or a laminate film is also suitable). The case (outer container) 50 includes a flat rectangular parallelepiped case main body 52 whose upper end is opened, and a lid 54 that closes the opening. On the upper surface of the case 50 (that is, the lid 54), a positive electrode terminal 82 that is electrically connected to the positive electrode 10 of the wound electrode body 80 and a negative electrode terminal 84 that is electrically connected to the negative electrode 30 of the electrode body are provided. Yes. Further, the wound electrode body 80 is accommodated in the case 50 together with the electrolytic solution.

  The wound electrode body 80 according to the present embodiment is formed by laminating the positive electrode sheet 10 and the negative electrode sheet 30 together with a total of two separator sheets 40 in the same manner as the wound electrode body of a normal lithium ion battery. This is a flat wound electrode body 80 produced by winding the negative electrode sheet 30 with a slight shift, and then crushing the obtained wound body from the side surface direction and causing it to be ablated.

  As a result of the winding electrode body 80 being wound in the lateral direction with respect to the winding direction with a slight shift as described above, part of the ends of the positive electrode sheet 10 and the negative electrode sheet 30 are wound core portions (that is, the positive electrode). The portion of the sheet 10 where the positive electrode active material layer is formed, the portion of the negative electrode sheet 30 where the negative electrode active material layer is formed and the separator sheet 40 are closely wound) protrudes outward. A positive electrode lead terminal 86 and a negative electrode lead terminal 88 are respectively attached to the protruding portion 18 (that is, the non-forming portion of the positive electrode active material layer) 18 and the protruding portion 38 (that is, the non-forming portion of the negative electrode active material layer) 38. These are electrically connected to the positive terminal 82 and the negative terminal 84 described above.

  The positive electrode sheet 10 can be formed by applying a positive electrode active material on a long positive electrode current collector. For the positive electrode current collector, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. The positive electrode active material may be the same as that used for a typical lithium ion secondary battery. In this embodiment, lithium manganese phosphate is used as described above.

  The negative electrode sheet 30 may be formed by applying a negative electrode active material layer for a lithium ion battery on a long negative electrode current collector. For the negative electrode current collector, a copper foil (this embodiment) or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.

  Moreover, as a suitable separator sheet 40 used between the positive / negative electrode sheets 10 and 30, what was comprised with porous polyolefin resin is mentioned. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, there may be a case where a separator is unnecessary (that is, in this case, the electrolyte itself can function as a separator).

Then, the wound electrode body 80 is accommodated in the main body 52 from the upper end opening of the case main body 52 and an electrolytic solution containing an appropriate electrolyte is disposed (injected) in the case main body 52. The electrolyte is lithium salt such as LiPF _6, for example. For example, an appropriate amount (for example, concentration 1M) of a lithium salt such as LiPF ₆ is dissolved in a nonaqueous electrolytic solution such as a mixed solvent of diethyl carbonate and ethylene carbonate (for example, a mass ratio of 1: 1) and used as the electrolytic solution. be able to.

  Thereafter, the opening is sealed by welding with the lid 54 or the like, and the assembly of the lithium secondary battery 100 according to the present embodiment is completed. The sealing process of the case 52 and the arrangement (injection) process of the electrolyte may be the same as the method used in the manufacture of the conventional lithium secondary battery, and do not characterize this embodiment. In this way, the construction of the lithium secondary battery 100 according to this embodiment is completed. Since the lithium secondary battery 100 constructed in this way is constructed using the positive electrode for a lithium secondary battery, the lithium secondary battery 100 is excellent in quality stability and exhibits better battery performance (for example, charge / discharge cycle characteristics). The battery has a low internal resistance and a high battery durability).

  In order to confirm that a lithium secondary battery excellent in quality stability (charge / discharge cycle characteristics) can be constructed by constructing a lithium secondary battery using the positive electrode 10 according to the first embodiment, Examples 1 to The following experiment was conducted as 5. Hereinafter, the present invention will be specifically described by Examples 1 to 5.

Example 1
Lithium phosphate, manganese acetate, and phosphoric acid are weighed so that a molar ratio of Li: Mn: P = 1: 1: 1 is obtained, and an appropriate amount of citric acid added thereto is dissolved in water, and then a raw material mixed solution Was prepared. Next, the raw material mixture was dried at 60 ° C. for 24 hours to obtain a gel composition. Thereafter, in the air the gel composition and baked at 700 ° C., to obtain a LiMnPO ₄ particles formed into particles of a porous structure.

The surface of LiMnPO ₄ particles having the above porous structure is sputtered using indium tin oxide (granular conductive material) as a target using a general sputtering apparatus, so that indium tin oxide is attached to the surface of LiMnPO ₄ particles. In addition, a part of the indium tin oxide was embedded in the pores of the LiMnPO ₄ particles. The amount of indium tin oxide deposited was controlled by changing the sputtering time. In Example 1, the sputtering time was 1 hour. The sputtering conditions at this time were an atmospheric pressure of 0.5 Pa and a sputtering output of 100 W (RF). In the sputtering apparatus, a mixed gas in which Ar gas and O ₂ gas were mixed at a molar ratio Ar: O ₂ = 99: 1 was used. Introduced. As the indium tin oxide, Sn having an atomic composition percentage of Sn / (In + Sn) = 3 at% was used. As a result of observation by an electron microscope, it was observed that a part of indium tin oxide was retained on the surface of the LiMnPO ₄ particles in a state of being embedded in the pores. In this way, LiMnPO ₄ particles of Example 1 were obtained.

(Examples 2 to 4)
Further, as Examples 2-4, it was prepared LiMnPO ₄ particles used in which changing the deposition amount of indium tin oxide. The adhesion amount of indium tin oxide was controlled by changing the sputtering time. Specifically, the sputtering time was increased to 3 hours, 5 hours, and 10 hours in the order of Examples 2, 3, and ₄ to increase the adhesion amount of indium tin oxide held on the surface of the LiMnPO ₄ particles. Things were made. It produced on the conditions similar to Example 1 except having changed the adhesion amount of indium tin oxide.

(Example 5)
Further, as Example 5, LiMnPO ₄ particles were produced using a granular conductive material changed to ZrO ₂ . ZrO ₂ was formed by sputtering using a general sputtering apparatus with ZrO ₂ as a target. The amount of ZrO ₂ deposited was controlled by changing the sputtering time. In Example 5, the sputtering time was 5 hours. The sputtering conditions at this time were an atmospheric pressure of 0.5 Pa and a sputtering output of 100 W (RF). In the sputtering apparatus, a mixed gas in which Ar gas and O ₂ gas were mixed at a molar ratio Ar: O ₂ = 90: 10 was used. Introduced. Other than changing the granular conductive material ZrO ₂ was prepared under the same conditions as in Example 1.

(Comparative Example 1)
As Comparative Example 1, LiMnPO ₄ particles in which no particulate conductive material was retained on the surface of LiMnPO ₄ particles were produced. Specifically, to prepare the LiMnPO ₄ particles by omitting the step of depositing indium tin oxide on the surface of LiMnPO ₄ particles. It was produced under the same conditions as in Example 1 except that the step of attaching indium tin oxide to the surface of LiMnPO ₄ particles was omitted.

(Comparative Example 2)
Further, as Comparative Example 2, LiMnPO ₄ particles were prepared by attaching ZrO ₂ as a granular conductive material to the surface of LiMnPO ₄ particles having no porous structure. Specifically, lithium acetate, manganese acetate, and ammonium hydrogen phosphate are weighed so that the molar ratio is Li: Mn: P = 1: 1: 1, and an appropriate amount of zirconia salt solution (zirconium butoxide) is added thereto. The added material was dissolved in water to prepare a raw material mixture. Next, the raw material mixture was dried at 60 ° C. for 24 hours to obtain a gel composition. Thereafter, the gel-like composition was baked at 700 ° C. in the air to prepare LiMnPO ₄ particles in which ZrO ₂ as a granular conductive material was adhered to the surface of LiMnPO ₄ particles having no porous structure. .

(Production of lithium secondary battery)
An appropriate solvent together with 75 parts by mass of LiMnPO ₄ particles obtained in Examples and Comparative Examples together with 20 parts by mass of carbon black (CB) as a conductive additive and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder A paste-like composition is prepared by dispersing and kneading in (N-methylpyrrolidone), this paste-like composition is applied to a positive electrode current collector (aluminum foil having a thickness of 15 μm), and the solvent is volatilized. A positive electrode having a positive electrode active material layered on one side of the body was produced. The produced positive electrode was formed into a pellet (φ16 mm).

The above-described positive electrode and a negative electrode (φ19 mm) made of metallic lithium are arranged opposite to each other with a polypropylene porous separator interposed therebetween, and this is accommodated in a coin-type case (CR 2032 type cell) together with an electrolytic solution. A battery was produced. As an electrolytic solution, about 1 mol / L LiPF ₆ was dissolved as a supporting salt in a 3: 3: 4 (mass ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Used.

The test lithium secondary batteries produced by using the LiMnPO ₄ particles obtained in Examples 1 to 5 and Comparative Examples 1 and 2 as the positive electrode active material by the above-described method are the batteries according to Examples 1 to 5 and Comparative Examples, respectively. The batteries according to 1 and 2 are used.

(Charge / discharge cycle test)
Charging / discharging was repeated 1000 cycles for the batteries according to Examples 1 to 5 and the batteries according to Comparative Examples 1 and 2, and their charge / discharge cycle characteristics were evaluated. The charge / discharge cycle test was performed as follows. The charging condition was a constant current-constant voltage method with a current of 1/20 C and an upper limit voltage of 4.8 V, and the discharging condition was a constant current method with a current of 1/20 C and a lower limit voltage of 2.0 V. Table 1 shows the initial capacity (mAh / g) and the percentage of the discharge capacity at the 1000th cycle with respect to the initial capacity as the cycle maintenance ratio (%).

According to the results shown in Table 1, the batteries according to Examples 1 to 5 in which a part of the granular conductive material is held on the surface of the LiMnPO ₄ particles in a state of being embedded in the pores are the Comparative Example 1 Compared with the battery according to No. 2, the initial capacity was high, and the cycle maintenance rate after 1000 cycles of charge and discharge was also relatively high. In particular, the batteries according to Examples 1 to 4 in which indium tin oxide is used as the granular conductive material have a very high initial capacity, and the cycle maintenance rate after 1000 cycles of charge / discharge is also dramatically increased. Improved. Therefore, by using granular conductive material, in particular LiMnPO ₄ particles held on the surface of LiMnPO ₄ particles with a portion of the indium tin oxide is embedded in the pores as a positive electrode active material, charge and discharge It was confirmed that a lithium secondary battery excellent in cycle characteristics can be provided.

  Furthermore, in order to confirm that a lithium secondary battery excellent in quality stability (charge / discharge cycle characteristics) can be constructed by constructing a lithium secondary battery using the positive electrode according to the second embodiment, Example 6 The following experiment was conducted as .about.9.

(Example 6)
A LiMnPO ₄ film (film thickness: about 1 μm) is formed on one surface of an aluminum foil by sputtering on one surface of a 15 μm-thick aluminum foil as a positive electrode current collector using LiMnPO ₄ as a target using a general sputtering apparatus. Formed. The sputtering conditions at this time were an atmospheric pressure of 0.5 Pa and a sputtering power of 100 W (RT). In the sputtering apparatus, Ar gas and O ₂ gas were mixed at a molar ratio of Ar: O ₂ = 1: 1. Gas was introduced. Then, by performing Ar etching process on the surface of the LiMnPO ₄ film by applying a bias (voltage) to the substrate side, to form pores on the surface of the LiMnPO ₄ film. When the average pore diameter of the pores was determined by analysis by the BET method, it was about 10 nm.

Sputtering is performed on the surface of the LiMnPO ₄ film having pores by using indium tin oxide (granular conductive material) as a target using a general sputtering apparatus, thereby attaching indium tin oxide to the surface of the LiMnPO ₄ particles. At the same time, a part of the indium tin oxide was embedded in the pores of the LiMnPO ₄ film. The amount of indium tin oxide deposited was controlled by changing the sputtering time. In Example 6, the sputtering time was 1 hour. The sputtering conditions at this time were an atmospheric pressure of 0.5 Pa and a sputtering output of 100 W (RF). In the sputtering apparatus, a mixed gas in which Ar gas and O ₂ gas were mixed at a molar ratio Ar: O ₂ = 99: 1 was used. Introduced. As the indium tin oxide, Sn having an atomic composition percentage of Sn / (In + Sn) = 3 at% was used. As a result of observation by an electron microscope, it was observed that a part of indium tin oxide was held on the surface of the LiMnPO ₄ film in a state of being embedded in the pores. In this way, a positive electrode provided with the LiMnPO ₄ film of Example 1 was obtained. This positive electrode was formed into a pellet (φ16 mm).

(Examples 7 to 9)
As Examples 7 to 9, positive electrodes were produced using different amounts of indium tin oxide retained on the surface of the LiMnPO ₄ film. The adhesion amount of indium tin oxide was controlled by changing the sputtering time. Specifically, the sputter time is increased to 1.5 hours, 2 hours, and 5 hours in the order of Examples 7, 8, and 9 to increase the adhesion amount of indium tin oxide held on the surface of the LiMnPO ₄ film. A positive electrode was produced. It produced on the conditions similar to Example 6 except having changed the adhesion amount of indium tin oxide.

(Comparative Example 3)
As Comparative Example 3, a positive electrode was produced using a LiMnPO ₄ film on which no granular conductive material was retained. Specifically, the step of attaching indium tin oxide to the surface of the LiMnPO ₄ film was omitted to produce a positive electrode. It was produced under the same conditions as in Example 6 except that the step of attaching indium tin oxide to the surface of the LiMnPO ₄ film was omitted.

(Comparative Example 4)
As Comparative Example 4, a positive electrode was produced using a LiMnPO ₄ film having no porous structure (pores) with ZrO ₂ as a granular conductive material adhered to the surface thereof. Specifically, the step of forming pores on the surface of the LiMnPO ₄ film was omitted, and a positive electrode was produced using a granular conductive material changed to ZrO ₂ . ZrO ₂ was formed by sputtering using a general sputtering apparatus with ZrO ₂ as a target. In Example 5, the sputtering time was 5 hours. The sputtering conditions at this time were an atmospheric pressure of 0.5 Pa and a sputtering output of 100 W (RF). In the sputtering apparatus, a mixed gas in which Ar gas and O ₂ gas were mixed at a molar ratio Ar: O ₂ = 90: 10 was used. Introduced. It was produced under the same conditions as in Example 6 except that the step of forming pores on the surface of the LiMnPO ₄ film was omitted and that the granular conductive material was changed to ZrO ₂ .

(Production of lithium secondary battery)
The positive electrode obtained in the example and the comparative example and the negative electrode (φ19 mm) made of metallic lithium are arranged opposite to each other with a polypropylene porous separator interposed therebetween, and this is accommodated in a coin-type case (CR 2032 type cell) together with the electrolyte. Thus, a test lithium secondary battery was produced. As an electrolytic solution, about 1 mol / L LiPF ₆ was dissolved as a supporting salt in a 3: 3: 4 (mass ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Used.

  Test lithium secondary batteries produced using the positive electrodes obtained in Examples 6 to 9 and Comparative Examples 3 and 4 by the above method were used as the batteries according to Examples 6 to 9 and the batteries according to Comparative Examples 3 and 4, respectively. And

(Charge / discharge cycle test)
Charging / discharging was repeated 1000 cycles for the batteries according to Examples 6 to 9 and the batteries according to Comparative Examples 3 and 4, and their charge / discharge cycle characteristics were evaluated. The charge / discharge cycle test was performed as follows. The charging condition was a constant current-constant voltage method with a current of 1/20 C and an upper limit voltage of 4.8 V, and the discharging condition was a constant current method with a current of 1/20 C and a lower limit voltage of 2.0 V. Table 2 shows the initial capacity (mAh / g) and the percentage of the discharge capacity at the 1000th cycle with respect to the initial capacity as the cycle maintenance ratio (%).

According to the results shown in Table 2, the batteries according to Examples 6 to 9 in which a part of the granular conductive material is held on the surface of the LiMnPO ₄ film in a state where a part of the granular conductive material is embedded in the pores are Comparative Example 3 Compared with the battery according to No. 4, the initial capacity was high, and the cycle maintenance rate after 1000 cycles of charge and discharge was also relatively high. Therefore, by using the LiMnPO ₄ film which is held on the surface of the LiMnPO ₄ film with a portion of the granular conductive material is embedded in the pores as part of the positive electrode, it is excellent in charge-discharge cycle characteristics It was confirmed that a lithium secondary battery can be provided.

  Since the lithium secondary battery (for example, lithium ion secondary battery) according to the present invention is excellent in quality stability and exhibits better battery performance as described above, it is particularly a motor (electric motor) mounted on a vehicle such as an automobile. It can be suitably used as a power source. Accordingly, as schematically shown in FIG. 9, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile) provided with such a lithium secondary battery (typically, a battery pack formed by connecting a plurality of series batteries) 100 as a power source. , An automobile equipped with an electric motor such as an electric vehicle and a fuel cell vehicle.

  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.

1 Vehicle 10, 110 Cathode 12 Cathode Active Material Particles 14, 114 Granular Conductive Material 15 Surface 16, 116 Pore 20, 120 Cathode Current Collector 22 Cathode Active Material Layer 30 Anode 40 Separator 50 Battery Case 52 Battery Case Body 54 Battery Lid 80 Winding electrode 82 Positive electrode terminal 84 Negative electrode terminal 86 Positive electrode lead terminal 88 Negative electrode lead terminal 100 Lithium secondary battery 112 Positive electrode active material film

Claims (18)

A positive electrode for a battery comprising a positive electrode current collector and a positive electrode active material,
The positive electrode active material has a granular conductive material on its surface,
At least the surface portion of the positive electrode active material has a porous structure in which pores are formed,
The positive electrode for a battery, wherein the granular conductive material is held on the surface of the positive electrode active material in a state where a part thereof is embedded in the pores.   Of the whole of the granular conductive material held on the surface of the positive electrode active material, the volume of the portion exposed to the outside of the pore is larger than the volume of the portion embedded in the pore. The positive electrode for a battery according to claim 1.   The positive electrode for a battery according to claim 1 or 2, wherein an average pore diameter of the pores opened on the surface of the positive electrode active material is in a range of 5 nm to 500 nm.   4. The positive electrode for a battery according to claim 1, wherein the positive electrode active material is formed in a particle shape having a porous structure. 5. The positive electrode active material is disposed in a thin film on a positive electrode current collector,
The granular conductive material is held on the surface of the thin film made of the positive electrode active material in a state where a part thereof is embedded in the pores of the surface of the thin film made of the positive electrode active material. The positive electrode for a battery according to any one of the above.   The battery positive electrode according to claim 1, wherein indium tin oxide is used as the granular conductive material.   The battery positive electrode according to any one of claims 1 to 6, wherein lithium manganese phosphate is used as the positive electrode active material. A method for producing a positive electrode for a battery comprising a positive electrode current collector and a positive electrode active material,
A step of preparing a positive electrode active material having a porous structure in which at least a surface portion is formed with pores;
Providing a granular conductive material on the surface of the positive electrode active material,
Here, in the step of applying the granular conductive material, a positive electrode for a battery in which the granular conductive material is held on the surface of the positive electrode active material so that a part of the granular conductive material is embedded in the pores. Manufacturing method.   The manufacturing method according to claim 8, wherein a positive electrode active material prepared in a particulate form having a porous structure by a sol-gel method is used as the positive electrode active material. Forming a thin film made of the positive electrode active material on the positive electrode current collector;
The manufacturing method of Claim 8 which provides the said granular conductive material with respect to the surface of this thin film.   The manufacturing method according to claim 10, wherein the pores on the surface of the thin film made of the positive electrode active material are formed by performing a dry etching process on the surface of the thin film.   The production method according to any one of claims 8 to 11, wherein a positive electrode active material having an average pore diameter of 5 nm to 500 nm in the pores opened on the surface is used as the positive electrode active material.   In the step of applying the granular conductive material, the granular conductive material is made to be embedded in the pores by sputtering using the granular conductive material as a target. The manufacturing method as described in any one of Claims 8-12 made to hold | maintain on the surface of a positive electrode active material.   In the granular conductive material application step, the volume of the portion of the whole of the granular conductive material held on the surface of the positive electrode active material that is exposed to the outside of the pores is embedded in the pores. The manufacturing method according to any one of claims 8 to 13, wherein the granular conductive material is held on the surface of the positive electrode active material so as to be larger than the volume of the portion.   The manufacturing method according to claim 8, wherein indium tin oxide is used as the granular conductive material.   The manufacturing method according to claim 8, wherein lithium manganese phosphate is used as the positive electrode active material.   A lithium secondary battery comprising the battery positive electrode according to claim 7 or the battery positive electrode obtained by the production method according to claim 16.   A vehicle comprising the lithium secondary battery according to claim 17.

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