JP2009295383A - Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has a high capacity, especially, has a high current density and superior charge and discharge characteristics. <P>SOLUTION: A positive electrode for the nonaqueous electrolyte secondary battery includes: a current collector and an active material layer; the active material layer has a first active material layer containing scale-like active material particles; the scale-like active material particles have the bottom part on the current collector side; the head part on the surface side of the first active material layer; and a flat part between the bottom part and the head part. The direction toward the head part from the bottom part is orthogonal to the thickness direction of the flat part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, and more particularly to a positive electrode for a non-aqueous electrolyte secondary battery that exhibits good charge / discharge characteristics at a high current density.

  In recent years, mobile devices such as personal computers and mobile phones are rapidly becoming mobile. As a power source for these electronic devices, a small, light and high capacity secondary battery is required. For these reasons, development of non-aqueous electrolyte secondary batteries capable of increasing energy density has been widely performed.

  In order to achieve higher energy density of nonaqueous electrolyte secondary batteries, development of high-capacity active materials has been underway. Various efforts have been made to improve the active material density (filling rate) of the electrodes. For example, in order to increase the active material density of an electrode, it has been proposed to form a dense active material layer by directly depositing an active material on the current collector surface without using a conductive agent or a resin binder. ing. Furthermore, in order to improve the charge / discharge characteristics at a high current density, research for controlling the structure of the active material has been conducted.

Patent Document 1 proposes that a positive electrode active material LiCoO ₂ is directly deposited on the surface of a current collector by an electron cyclotron resonance sputtering method in order to obtain an electrode having a high active material density. As an active material layer having a thickness of about 2.6 μm is disclosed. The film formation rate of the RF-sputtering method is 2.4 nm / min, whereas the film formation rate of the electron cyclotron resonance sputtering method is as high as about 16.6 nm / min. Moreover, the active material obtained by the electron cyclotron resonance sputtering method has a relatively higher crystallinity than that obtained by the RF-sputtering method, and the charge / discharge characteristics of the battery are improved.

  Patent Document 2 proposes to improve charge / discharge characteristics at a high current density by using active material particles having a large specific surface area. The active material particles are aggregates of primary particles having an average particle diameter of 0.1 to 1 μm, and are secondary particles including voids. These secondary particles are rod-shaped or plate-shaped with an average length in the longitudinal direction of 5 to 15 μm. Such active material particles have a large specific area, can sufficiently secure a lithium ion conduction path, and have good charge / discharge characteristics and cycle characteristics at a high current density. Furthermore, since the secondary particles are large, high filling is possible and high capacity is possible.

Patent Document 3 proposes a positive electrode with a high capacity and good cycle characteristics using a columnar structure film containing Fe formed by deposition on a current collector from a gas phase or a liquid phase as a positive electrode active material layer. . A high-capacity active material such as K _1.4 Fe ₁₁ O _{17 is formed} into a columnar structure by sputtering or the like, and the volume expansion and contraction of the positive electrode active material accompanying charge / discharge is easily changed in the film thickness direction. By doing in this way, even if it repeats a charging / discharging cycle, a film | membrane structure does not collapse easily and it becomes possible to reduce a capacity | capacitance fall.
JP 2007-5219 A JP 2004-265806 A JP 2002-29883 A

  Patent document 1 is related with the manufacturing method of the thin film electrode used for an all-solid-state battery etc. In general, the active material layer of the electrode for a nonaqueous electrolyte secondary battery has a thickness of 10 μm or more, for example, about 60 μm. Although the electron cyclotron resonance sputtering method proposed in Patent Document 1 has a higher film formation rate than the RF-sputtering method, the film formation rate is insufficient to form an active material layer having a general thickness. . Furthermore, since the active material layer obtained by the method of Patent Document 1 is a dense film, it is difficult to form an ion conductive path. Therefore, when the thickness of the active material layer is relatively large, the electrochemical reaction becomes difficult.

  When active material particles having a large specific surface area are used as in Patent Document 2, it is necessary to use a conductive agent and a binder in order to produce an electrode. When the binder is used, the active material density of the electrode becomes relatively small, so that the battery capacity is considered to decrease.

  Patent Document 3 relates to a positive electrode active material layer having a columnar structure. In the case of an active material layer having a general thickness, the specific surface area is reduced only by a simple columnar structure. Further, it is considered that the charge / discharge characteristics at a high current density are deteriorated because the liquid retention of the nonaqueous electrolyte is insufficient.

  Therefore, an object of the present invention is to provide a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have a high capacity and have particularly good charge / discharge characteristics at a high current density.

  The present invention includes a current collector and an active material layer, and the active material layer has a first active material layer including scaly active material particles, and the scaly active material particles include a bottom portion on the current collector side, Non-aqueous electrolyte secondary having a head portion on the surface side of the first active material layer and a flat portion between the bottom portion and the head portion, and a direction from the bottom portion to the head portion is orthogonal to a thickness direction of the flat portion A positive electrode for a battery is provided.

  By including the scaly active material particles as described above, the specific surface area of the active material layer is increased. As a result, the area where the active material layer and the non-aqueous electrolyte are in contact with each other increases, so that the charge / discharge characteristics particularly at a high current density are improved.

The direction from the bottom to the head and the normal direction of the current collector preferably form an angle of 0 to 45 °.
The scaly active material particles preferably have a hexagonal layered crystal structure belonging to the space group R-3m.
The scale-like active material particles preferably have a peak intensity attributed to the (003) plane smaller than a peak intensity attributed to the (101) plane in X-ray diffraction.
The positive electrode for a nonaqueous electrolyte secondary battery may further include a second active material layer between the current collector and the first active material layer. The porosity of the second active material layer is preferably smaller than the porosity of the first active material layer.
The active material layer may further contain flower-shaped active material aggregates composed of petals and ovary.

  The present invention also provides a nonaqueous electrolyte having a positive electrode, a negative electrode, a nonaqueous electrolyte, and a porous insulating layer interposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode for a nonaqueous electrolyte secondary battery described above. A secondary battery is provided.

  By using the positive electrode of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that has a high capacity and has particularly good charge / discharge characteristics at a high current density.

The positive electrode for a non-aqueous electrolyte secondary battery of the present invention includes a current collector and an active material layer, and the active material layer includes a first active material layer including scaly active material particles. The scaly active material particles have a bottom on the current collector side, a head on the surface side of the first active material layer, and a flat part between the bottom and the head.
There may be a second active material layer between the first active material layer and the current collector. The second active material layer serves as a protective layer that protects the current collector.

  By including the scaly active material particles, the specific surface area of the active material layer is increased, so that a positive electrode for a non-aqueous electrolyte secondary battery having particularly good charge / discharge characteristics at a high current density can be obtained. In the scaly active material particles, the bottom is the current collector side of the first active material layer. The head is a surface side of the first active material layer and includes a surface facing the negative electrode or the porous insulating layer. The flat portion is a portion between the bottom portion and the head portion. It is preferable that the thickness direction of the flat part and the direction from the bottom part toward the head part are substantially perpendicular.

  The diffusion resistance of lithium ions is greater in the active material than in the nonaqueous electrolyte. Therefore, by shortening the diffusion distance of lithium ions in the active material, the discharge characteristics at a high current density are improved. Further, the active material does not include a resin binder that does not contribute to the charge / discharge capacity, and only the active material layer is exposed on the surface. Therefore, a positive electrode for a non-aqueous electrolyte secondary battery having a high capacity and good charge / discharge characteristics at a high current density can be obtained.

  The length (major axis) in the direction from the bottom to the head of the scaly active material particles is preferably 1 to 30 μm, and the length (minor axis) in the direction orthogonal to the major axis is 0.5 to It is preferably 20 μm. The thickness of the scaly active material particles is preferably 0.01 to 10 μm. In the present invention, for example, it is preferable to measure the length of the major axis, the length of the minor axis, and the thickness of 50 particles and determine the average value of each.

If the length of the major axis of the scaly active material particles is less than 1 μm, a sufficient specific surface area may not be obtained. On the other hand, if the length of the long axis exceeds 30 μm, the adhesion with the current collector may be insufficient.
If the length of the short axis is smaller than 0.5 μm, the adhesion with the current collector may be insufficient.
If the thickness of the scaly active material particles exceeds 10 μm, a sufficient specific surface area may not be obtained. On the other hand, if the thickness is less than 0.01 μm, the adhesion to the current collector may be insufficient.

  The porosity of the first active material layer is preferably 20 to 90%, and the porosity of the second active material layer is preferably 10 to 70%. Since the current collector can be well protected when the porosity of the second active material layer is in the above range when the first active material layer is formed, the deposition rate of the first active material layer Can be made faster.

  The thickness of the first active material layer is preferably 1 to 100 μm, and the thickness of the second active material layer is preferably 1/10 or less of the thickness of the first active material layer, for example, 0.01 to 10 μm is preferable.

  The second active material layer may include flaky active material particles smaller than the flaky active material particles contained in the first active material layer. Thereby, since the active material density is increased, the battery capacity is improved. In addition, since the current collector can be protected by forming the second active material layer, it is possible to obtain a positive electrode for a non-aqueous electrolyte secondary battery having good charge / discharge characteristics while maintaining high productivity. it can.

  From the viewpoint of sufficiently exerting the effect of protecting the current collector in order to increase the supply speed of the raw material and the effect of ensuring the liquid retaining property in the vicinity of the current collector, it is relatively small contained in the second active material layer. The long axis of the scaly active material particles is preferably 0.05 to 10 μm. The minor axis is preferably from 0.01 to 5 μm, and the thickness is preferably from 0.01 to 2.5 μm.

  The positive electrode for a non-aqueous electrolyte secondary battery including the scaly active material particles can be formed using, for example, a film forming apparatus using thermal plasma. Although the detailed mechanism by which the positive electrode is formed is unknown, it adheres to the current collector after a certain amount of particle growth occurs in the gas phase. It is thought to occur subsequently. Therefore, it is considered that the active material grows in the direction of thermal plasma, which is a heat source, to form a flat active material piece. By forming a film using thermal plasma, an active material layer containing no binder can be easily formed. Since the active material layer does not contain a binder, a battery having a higher capacity can be obtained.

  In order to improve the film formation speed, it is necessary to increase the supply speed of the raw material of the active material, but the amount of energy required increases accordingly. However, if the amount of energy is too large, the active material and the current collector may be altered and the battery capacity may be reduced. Therefore, it is preferable to form a first active material layer containing scaly active material particles and a second active material layer containing relatively small active material particles.

  First, the second active material layer is formed with relatively small energy. Since the second active material layer has a role of protecting the current collector, the feed rate of the raw material can be increased while suppressing the deterioration of the current collector. Thereby, the first active material layer can be formed at a high deposition rate.

An example of a film forming apparatus using thermal plasma will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an outline of a film forming apparatus. The film forming apparatus includes a chamber 1 that provides a space for film formation and a thermal plasma generation source. The thermal plasma generation source includes a torch 10 that provides a space for generating thermal plasma, and an induction coil 2 that surrounds the torch 10. A power source 9 is connected to the induction coil 2.

  The chamber 1 may or may not include the exhaust pump 5 as necessary. By removing the air remaining in the chamber 1 with the exhaust pump 5 and then generating thermal plasma, contamination of the active material can be suppressed. By using the exhaust pump 5, the shape of the plasma gas flow can be easily controlled. Furthermore, it becomes easy to control the film forming conditions such as the pressure in the chamber 1. The chamber 1 may include a filter (not shown) for collecting dust.

  A stage 3 is installed vertically below the torch 10. Although the material of the stage 3 is not specifically limited, It is preferable that it is excellent in heat resistance, for example, stainless steel etc. are mentioned. A current collector 4 is disposed on the stage 3. The stage 3 may have a cooling unit (not shown) that cools the current collector as necessary.

  One end of the torch 10 is released to the chamber 1 side. When a high frequency voltage is used, the torch 10 is preferably made of a material having excellent heat resistance and insulation, and is preferably made of ceramics (quartz or silicon nitride), for example. The inner diameter of the torch 10 is not particularly limited. By increasing the inner diameter of the torch, the reaction field can be made wider. Therefore, an active material layer can be formed efficiently.

  A gas supply port 11 and a raw material supply port 12 are arranged at the other end of the torch 10. The gas supply port 11 is connected to gas supply sources 6a and 6b through valves 7a and 7b, respectively. The raw material supply port 12 is connected to the raw material supply source 8. By supplying gas from the gas supply port 11 to the torch 10, thermal plasma can be generated efficiently.

  From the viewpoint of stabilizing the thermal plasma and controlling the gas flow in the thermal plasma, a plurality of gas supply ports 11 may be provided. When a plurality of gas supply ports 11 are provided, the direction in which the gas is introduced is not particularly limited, and may be the axial direction of the torch 10, a direction perpendicular to the axial direction of the torch 10, or the like. The ratio between the gas introduction amount from the axial direction of the torch 10 and the gas introduction amount from the direction perpendicular to the axial direction of the torch 10 is preferably 100: 0 to 10:90. As the amount of gas introduced from the axial direction of the torch 10 increases, the gas flow in the thermal plasma becomes thinner and the central portion of the gas flow becomes higher temperature, so that the raw material is easily vaporized and decomposed. From the viewpoint of stabilizing the thermal plasma, it is preferable to control the gas introduction amount using a mass flow controller (not shown) or the like.

  When a voltage is applied from the power source 9 to the induction coil 2, thermal plasma is generated in the torch 10. The voltage to be applied may be a high frequency voltage or a DC voltage. Alternatively, a high frequency voltage and a DC voltage may be used in combination. When a high frequency voltage is used, the frequency is preferably 1000 Hz or more. The material of the induction coil 2 is not particularly limited, but a metal having low resistance such as copper may be used.

  When the thermal plasma is generated, the induction coil 2 and the torch 10 become high temperature. Therefore, it is preferable to provide a cooling unit (not shown) around the induction coil 2 and the torch 10. For example, a water-cooled cooling device or the like may be used as the cooling unit.

  FIG. 2 is an electron micrograph showing a cross section of an example of the positive electrode for a nonaqueous electrolyte secondary battery of the present invention. However, the surface of the active material layer is coated with a thermosetting resin. The positive electrode includes a current collector 20 and an active material layer 21. The active material layer includes scaly active material particles. Each particle has a thin plate shape having a flat portion and grows from the current collector side toward the surface side of the active material layer.

In the present invention, the direction from the bottom to the head of the scaly active material particles and the normal direction of the current collector preferably form an angle of 0 to 45 °.
In the positive electrode for a nonaqueous electrolyte secondary battery, it is preferable that the plurality of scaly active material particles are upright. The state in which the plurality of scaly active material particles are upright means that the direction from the bottom to the head of 20% or more scaly active material particles per 20 μm square of the active material layer, and the normal direction of the current collector Is a state that forms an angle of 0 to 45 °. Especially, it is preferable that 40% or more of scaly active material particles per unit area satisfy the above.

  The scaly active material particles preferably have a peak intensity I (003) attributed to the (003) plane smaller than a peak intensity I (101) attributed to the (101) plane, and I (101) / I (003). )> 0.91 is more preferable. At this time, it is considered that the scaly active material particles have more crystallographic edge surfaces exposed at the head than at the surface of the flat part. At the crystallographic edge surface, lithium ions are easily occluded and released. Therefore, many crystallographic edge surfaces are exposed at the head portion facing the negative electrode, so that the charge / discharge characteristics at a particularly high current density are improved.

Here, the edge surface refers to a surface from which the a and b axes which are crystal lattices protrude. On the other hand, a plane perpendicular to the c-axis is called a basal plane. For example, a layered rock salt structure compound (such as LiCoO ₂ ) having a hexagonal crystal structure and belonging to the space group R-3m has many (003) planes that are basal planes. The basal surface is preferably exposed more on the surface of the flat part than the head.

For example, in the case of LiCoO ₂ , the surface (104), (101), (110), which is the edge surface, rather than the (003) surface, which is the basal surface, is the surface of the active material layer facing the negative electrode (that is, scale It is preferable that a large amount of the active material particles are exposed on the head). Thereby, since insertion and extraction of lithium ions are likely to occur, the charge / discharge characteristics particularly at a high current density are improved.

  The positive electrode for a non-aqueous electrolyte secondary battery of the present invention preferably further has a second active material layer between the current collector and the first active material layer. FIG. 3 is an electron micrograph showing a cross section of another example of the positive electrode for a non-aqueous electrolyte secondary battery of the present invention. The positive electrode in FIG. 3 includes a current collector 20, a first active material layer 22, and a second active material layer 23. The porosity of the second active material layer is preferably smaller than the porosity of the first active material layer.

  The active material layer may further include flower-shaped active material aggregates composed of petals and ovaries. Among the flower-shaped active material aggregates, the ovary portion is considered to contribute to the improvement of the battery capacity. The diameter of the ovary is preferably 0.5 to 10 μm from the viewpoint of securing the battery capacity. When the diameter of the ovary exceeds 10 μm, the adhesion is insufficient, and the active material aggregate may peel off from the current collector.

  Among the flower-shaped active material aggregates, the petal portion has a relatively large specific surface area, which is considered to contribute to the improvement of charge / discharge characteristics at a high current density. The shape of the petals is not particularly limited, and for example, the scaly active material particles may be petals. The active material aggregate preferably includes a plurality of petals. This further improves the charge / discharge characteristics of the battery at a high current density.

  The petal preferably has a major axis of 1 to 30 μm and a minor axis of 0.5 to 20 μm. The petal thickness is preferably 0.01 to 10 μm. When the petal major axis is less than 1 μm, the minor axis exceeds 20 μm, or the petal thickness exceeds 10 μm, a sufficient specific surface area may not be obtained. On the other hand, when the petal major axis exceeds 30 μm, when the petal minor axis is smaller than 0.5 μm, or when the petal thickness is thinner than 0.01 μm, the adhesion between the petal and the ovary becomes insufficient. Sometimes.

The positive electrode active material includes a lithium-containing composite oxide. The lithium-containing composite oxide preferably has a hexagonal layered crystal structure belonging to the space group R-3m. The lithium-containing composite oxide preferably contains a transition metal such as Co, Ni, Mn, and Fe. Specifically, LiCoO ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _1/2 Co _1/2 O ₂ , LiNiO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _{1 / 2} Fe _1/2 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li _4/3 Ti _5/3 O _{4 and the} like. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.

The positive electrode current collector is not particularly limited, and for example, a conductive material generally used in an electrochemical element can be used. Specifically, it is desirable to use Al, Ti, stainless steel (SUS), Au, Pt, or the like. These current collectors are preferable in that the elution of metal from the current collector is relatively small even when the Li desorption reaction is performed to about 3.5 to 4.5 V (vs. Li / Li ⁺ ).

The nonaqueous electrolyte secondary battery of the present invention will be described.
The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a nonaqueous electrolyte, and a porous insulating layer interposed between the positive electrode and the negative electrode. The non-aqueous electrolyte secondary battery of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery described above, and other configurations are not particularly limited.

An example of the nonaqueous electrolyte secondary battery will be described with reference to the drawings.
FIG. 4 is a longitudinal sectional view schematically showing a coin-type nonaqueous electrolyte secondary battery. The coin-type non-aqueous electrolyte secondary battery includes a positive electrode active material layer 33, a negative electrode 36, a porous insulating layer 35 interposed therebetween, and a non-aqueous electrolyte (not shown). The positive electrode includes a positive electrode current collector 34 and a positive electrode active material layer 33 formed on the positive electrode current collector. A disc spring 37 is connected to the positive electrode current collector 34. The disc spring 37 compresses the positive electrode, the negative electrode, and the porous insulating layer. The porous insulating layer 35 is impregnated with a nonaqueous electrolyte. The case 31 that also serves as the positive terminal and the sealing plate 38 that also serves as the negative terminal are insulated from each other by the gasket 32.

As the negative electrode active material, a carbon material, a metal, an alloy, a metal oxide, a metal nitride, or the like is used. As the carbon material, natural graphite, artificial graphite and the like are preferable. As the metal or alloy, lithium alone, lithium alloy, silicon alone, silicon alloy, tin alone, tin alloy and the like are preferable. The metal oxide is preferably SiO _x (0 <x <2, preferably 0.1 ≦ x ≦ 1.2).

  As the negative electrode current collector, it is desirable to use Cu, Ni, stainless steel (SUS) or the like. These current collectors are preferable in that the metal elution from the current collector is relatively small even when Li insertion reaction is performed up to about 0 to 3.5 V (vs. Li / Li +).

  For the porous insulating layer, for example, a nonwoven fabric or a microporous film made of polyethylene, polypropylene, aramid resin, amideimide, polyphenylene sulfide, polyimide, or the like can be used. The nonwoven fabric or microporous film may be a single layer or a multilayer structure. The inside or the surface of the porous insulating layer may contain a heat resistant filler such as alumina, magnesia, silica, titania.

The non-aqueous electrolyte includes a non-aqueous solvent and a solute dissolved in the non-aqueous solvent. The solute is not particularly limited, and may be appropriately selected in consideration of the redox potential of the active material. Preferred solutes include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiOCOCF ₃ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiF, LiCl , LiBr, LiI, chloroborane lithium, bis (1,2-benzenediolate (2-)-O, O ') lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O' ) Lithium borate, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) borates of lithium _{borate, LiN (CF 3 SO 2)} 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiN (C 2 F 5 SO 2) 2, Te Lithium Rafeniruhou acid and the like.

  The non-aqueous solvent is not particularly limited. For example, ethylene carbonate (EC), propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate (EMC), dipropyl carbonate, methyl formate, methyl acetate, methyl propionate, ethyl propionate , Tetrahydrofuran derivatives such as dimethoxymethane, γ-butyrolactone, γ-valerolactone, 1,2-diethoxyethane, 1,2-dimethoxyethane, ethoxymethoxyethane, trimethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, dioxolane derivatives such as 4-methyl-1,3-dioxolane, formamide, acetamide, dimethylformamide, a Cetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, acetic acid ester, propionic acid ester, sulfolane, 3-methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, A propylene carbonate derivative, ethyl ether, diethyl ether, 1,3-propane sultone, anisole, fluorobenzene, or the like may be used. These may be used alone or in combination of two or more.

  The non-aqueous electrolyte may contain an additive. The additive is not particularly limited. For example, vinylene carbonate, cyclohexyl benzene, biphenyl, diphenyl ether, vinyl ethylene carbonate, divinyl ethylene carbonate, phenyl ethylene carbonate, diallyl carbonate, fluoroethylene carbonate, catechol carbonate, vinyl acetate, ethylene sulfite, propane Examples include sultone, trifluoropropylene carbonate, dibenzofuran, 2,4-difluoroanisole, o-terphenyl, and m-terphenyl.

The nonaqueous electrolyte may be a solid electrolyte containing a polymer material, or may be a gel electrolyte containing a nonaqueous solvent. Examples of the polymer material include polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene.
Further, lithium nitride, lithium halide, lithium oxyacid _{salt, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, Li 3 PO 4 -Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li An inorganic material such as ₂ S—SiS ₂ or a phosphorus sulfide compound may be used as the solid electrolyte.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. These examples and comparative examples do not limit the present invention.
Example 1
(1) Production of positive electrode As a film forming apparatus, a high frequency induction thermal plasma generator (TP-12010) manufactured by JEOL Ltd. having a chamber with an internal volume of 6250 m ³ and a thermal plasma generation source was used. As the thermal plasma generation source, a torch made of a silicon nitride tube having a diameter of 42 mm and a copper induction coil surrounding the torch were used.

  A stage was placed at a position of 345 mm from the lower end of the torch in the chamber. A current collector (thickness: 0.1 mm) made of a SUS plate was placed on the stage. Thereafter, the air in the chamber was replaced with argon gas.

  Argon gas was introduced into the chamber at a flow rate of 50 L / min, and oxygen gas was introduced at a flow rate of 30 L / min. The pressure in the chamber was 18 kPa. A high frequency voltage of 42 kW and a frequency of 3.5 MHz was applied to the induction coil to generate thermal plasma.

As a raw material, a mixture of Li ₂ O and Co ₃ O ₄ was used. Li ₂ O was classified to 30 μm or less. The average particle diameter D50 (based on volume) of Co ₃ O ₄ was 5 μm. Li ₂ O and Co ₃ O ₄ were mixed so that the stoichiometric ratio was Li: Co = 1.5: 1. Argon gas was introduced into one flow path at 50 L / min and oxygen gas at 30 L / min, and these mixed gases were introduced into the chamber from two directions. Here, the ratio of the gas introduction amount from the axial direction of the torch and the gas introduction amount from the direction substantially perpendicular to the axial direction of the torch (hereinafter referred to as D _x : D _y ) was set to 35:45. The supply rate of the raw material into the thermal plasma was set to 0.11 g / min (Condition A).

At this time, the temperature of the thermal plasma in the vicinity of the current collector is considered to be 600 to 700 ° C. The particles generated in the thermal plasma were supplied from a substantially normal direction of the surface of the current collector and deposited on the current collector. An active material was deposited under condition A for 8 minutes to form a 3 μm thick active material layer. This formed the active material layer containing scaly active material particles.
When ICP analysis of the active material layer was performed, it was confirmed that the element ratio in the active material layer was Li: Co = 1.2: 1 (molar ratio).

In the ICP analysis, the electrode plate was completely dissolved to determine the absolute amounts of Li and Co, and then the amount of Co was calculated. Assuming that all Co is LiCoO ₂ , the weight of the LiCoO ₂ active material in the electrode plate was calculated from the amount of Co.

(2) Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.25 mol / L in a non-aqueous solvent. As the non-aqueous solvent, a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 3 was used.

(3) Production of Battery A coin type battery as shown in FIG. 4 was produced.
A lithium foil having a thickness of 0.3 mm was attached as the negative electrode 36 inside the sealing plate 38. A porous insulating layer 35 was disposed thereon. A positive electrode was disposed on the porous insulating layer 35 such that the positive electrode active material layer 33 faced the porous insulating layer. A disc spring 37 is disposed on the positive electrode current collector 34. After injecting the nonaqueous electrolyte until the sealing plate was filled, the case 31 was fitted into the sealing plate via the gasket 32 to complete the coin-type battery.

Example 2
The same high frequency induction thermal plasma apparatus as in Example 1 was used as the film forming apparatus. Thermal plasma was generated in the same manner as in Example 1.

As a raw material, the same mixture of Li ₂ O and Co ₃ O ₄ as in Example 1 was used.
D _x: the gas flow ratio of D _y, 30: as 50, was introduced the gases as in Example 1 to the chamber. Film formation was performed for 5 minutes at a feed rate of the raw material into the thermal plasma of 0.035 g / min. Other than that, the second active material layer was formed under the same conditions as in Example 1 (Condition B).

Next, gas was introduced into the chamber at a gas flow ratio of D _x : D _y of 35:45. Film formation was performed for 5 minutes at a supply rate of the raw material into the thermal plasma of 0.11 g / min (condition A of Example 1). Other than that, the first active material layer was formed under the same conditions as in Example 1. The total thickness of the obtained active material layers was 3.5 μm.
When ICP analysis of the active material layer was performed, it was confirmed that the element ratio in the active material layer was Li: Co = 1.2: 1.
A coin-type battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

Example 3
The same high frequency induction thermal plasma apparatus as in Example 1 was used as the film forming apparatus. Thermal plasma was generated in the same manner as in Example 1.

As a raw material, the same mixture of Li ₂ O and Co ₃ O ₄ as in Example 1 was used. The second active material layer was formed under the same conditions as in Condition B of Example 2.

Next, gas was introduced into the chamber at a gas flow ratio of D _x : D _y of 35:45. Film formation was performed for 5 minutes at a supply rate of the raw material into the thermal plasma of 0.11 g / min (condition A of Example 1). At this time, LiCoO ₂ was supplied at 0.05 g / min from the vicinity of the flame of the thermal plasma at the top of the chamber. The D50 of LiCoO ₂ was 10 μm. Thereby, the first active material layer was formed. The total thickness of the obtained active material layers was 3.5 μm. In the active material layer, flower-shaped active material aggregates composed of petals and ovaries were formed.
When ICP analysis of the active material layer was performed, it was confirmed that the element ratio in the active material layer was Li: Co = 1.2: 1.
A coin-type battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

<< Comparative Example 1 >>
A current collector (thickness 1 mm) made of an Au plate was placed on the stage, and an active material layer was formed on the current collector using a magnetron sputtering apparatus. LiCoO ₂ was used as a target. The target diameter was 3 inches. The distance between the current collector on the stage and the target was 3.5 cm.

The degree of vacuum in the chamber was set to 5 × 10 ⁻² Pa using a rotary pump and a diffusion pump. Thereafter, argon gas was introduced into the chamber at a flow rate of 8 × 10 ⁻² L / min and oxygen gas was introduced at a flow rate of 2 × 10 ⁻² L / min so that the degree of vacuum in the chamber was 1 Pa. A high frequency voltage of 80 W and a frequency of 13.56 MHz was applied to the target to generate plasma. The temperature in the vicinity of the current collector was 25 ° C., the film formation time was 8 hours, and the active material layer was formed. Thereafter, the current collector on which the active material layer was formed was fired at 800 ° C. for 1 hour using a muffle furnace. The thickness of the obtained active material layer was 3.5 μm.

When ICP analysis of the active material layer was performed, it was confirmed that the element ratio in the active material layer was Li: Co = 0.98: 1.
A coin-type battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

The batteries of Examples 1 to 3 and Comparative Example 1 were charged and discharged. Charging / discharging was performed in the range of 3.05 to 4.25 V with respect to Li / Li ^+, and the discharge capacities of 0.2C and 2C were measured. The temperature condition was 20 ° C. The results are shown in Table 1. In Example 3 only, the discharge capacities of 0.2C, 0.5C, 1C, and 2C were measured. The charge / discharge characteristics of the nonaqueous electrolyte secondary battery produced in Example 3 are shown in FIG.

  It turned out that the discharge capacity of the battery of Examples 1 to 3 is larger than the discharge capacity of the battery of Comparative Example 1. In particular, all of Examples 1 to 3 had a large discharge capacity at 2C, which is a high current density.

2 is an electron micrograph showing a cross section of the positive electrode active material layer of Example 1. FIG.
In Example 1, a plurality of scaly active material particles were formed. In Example 1, the average value of the major axis length of the flat portion of the 16 scaly active material particles was 2.8 μm, and the average value of the minor axis length was 2.6 μm. The average thickness of the scaly active material particles was 0.3 μm. In Example 1, the direction from the bottom of the scaly active material particles of 57% per unit area toward the head and the normal direction of the current collector formed an angle of 0 to 15 °. The ratio I (101) / I (003) between the peak intensity I (003) attributed to the (003) plane and the peak intensity I (101) attributed to the (101) plane was 1.4.

FIG. 3 is an electron micrograph showing a cross section of the active material layer of the positive electrode of Example 2.
Also in the positive electrode of Example 2, a plurality of scaly active material particles were formed as in Example 1. In Example 2, an active material layer including a second active material layer having a thickness of about 0.5 μm and a first active material layer having a thickness of about 3 μm formed on the second active material layer is formed. It was. The first active material layer contained scaly active material particles. In the first active material layer, the average value of the major axis length of the flat portions of the 10 scale-like active material particles was 2.8 μm, and the average value of the minor axis length was 2.6 μm. It was. Further, the average thickness of the scaly active material particles was 0.2 μm. The second active material layer contained relatively small active material particles. In Example 2, the direction from the bottom of the scaly active material particles of 40% per unit area to the head and the normal direction of the current collector formed an angle of 0 to 15 °. The ratio I (101) / I (003) between the peak intensity I (003) attributed to the (003) plane and the peak intensity I (101) attributed to the (101) plane was 1.5.

  6 is an electron micrograph showing the surface of the active material layer of the positive electrode of Example 3. FIG. From FIG. 6, the active material layer of the positive electrode of Example 3 contained a plurality of scaly active material particles, and further, flower-shaped active material aggregates were formed. In Example 3, the average value of the major axis length of the flat portion of the 16 scale-like active material particles was 4 μm, and the average value of the minor axis length was 2.8 μm. Further, the average thickness of the scaly active material particles was 0.2 μm. In Example 3, the direction from the bottom of the scaly active material particles of 40% per unit area to the head and the normal direction of the current collector formed an angle of 0 to 15 °.

  7 is an electron micrograph showing the surface of the active material layer of the positive electrode of Comparative Example 1. FIG. As shown in FIG. 7, the positive electrode active material layer of Comparative Example 1 had a dense structure with no scaly active material particles formed.

  8 is an electron micrograph showing a cross section of the positive electrode active material layer of Example 3. FIG. In Example 3, an active material layer including a second active material layer having a thickness of about 0.5 μm and a second active material layer having a thickness of about 3 μm formed on the second active material layer is formed. It was. The first active material layer contained relatively large scaly active material particles and flower-shaped active material aggregates. The second active material layer contained relatively small active material particles. The flower-shaped active material aggregate had a structure in which a plurality of petals (scale-like active material particles) having a major axis of about 4 μm adhered to the ovary portion having a diameter of about 2 μm.

  When comparing FIGS. 6 and 8 (Example 3) and FIG. 7 (Comparative Example 1), Example 3 has a larger specific surface area of the active material than Comparative Example 1, and the non-aqueous electrolyte reaches the vicinity of the current collector. Was found to have penetrated sufficiently. Therefore, it is considered that the active material layer of Example 3 secured a good lithium ion conductive path and improved charge / discharge characteristics at a high current density.

  From the above, it was found that the active material layers of Examples 1 to 3 show a good charge / discharge characteristic at a high current density because they contain a plurality of scaly active material particles.

  Although the details of the reason why the discharge capacity of Example 1 is low compared to Examples 2 and 3 are unclear, in Example 1, the second active material layer (protective layer) is not provided in advance at the time of film formation. Therefore, it is considered that some deteriorated layer is formed between the current collector and the active material layer, and the discharge capacity is slightly reduced. In addition, it is considered that Example 1 did not have sufficient retention of the nonaqueous electrolyte as compared with Examples 2 and 3.

FIG. 9 shows the LiCoO ₂ / SUS positive electrode produced in Example 3 and the X-ray diffraction pattern of LiCoO ₂ powder produced by the following method. LiCoO ₂ powder was first pulverized after mixing Li ₂ CO ₃ and Co ₃ O ₄ , calcining at 600 ° C. for 5 hours. Then calcined 5 hours at 1000 ° C., was further pulverized to prepare a LiCoO ₂ powder. In the positive electrode produced in Example 3, LiCoO ₂ having a crystal structure of R-3m was confirmed as a main peak, but the intensity ratio of LiCoO ₂ powder and the peak was different. In FIG. 9, the peak at 19 ° is diffraction from the (003) plane, and the peak at 37.5 ° is diffraction from the (101) plane. In the positive electrode of Example 3, diffraction from the (101) plane was larger than that of the LiCoO ₂ powder.

On the other hand, in the XRD pattern (not shown) of the positive electrode of Comparative Example 1, LiCoO ₂ was confirmed as the main peak, and the intensity ratio between the LiCoO ₂ powder and the peak was comparable. From the above, it is considered that the positive electrode of the present invention has many crystal planes (crystallographic edge surfaces) that are liable to occlude and release lithium ions exposed at the heads of the scaly active material particles. This is considered to be one of the reasons why the positive electrode of the present invention exhibits good charge / discharge characteristics particularly at a high current density.

The AC impedance of the coin batteries of Example 3 and Comparative Example 1 was measured at a measurement temperature of 20 ° C. A complex impedance plot is shown in FIG.
In Example 3, the arc indicating the AC impedance was small. Since the active material layer of Example 3 has a larger specific surface area than the active material layer of Comparative Example 1, it is considered that the AC impedance is reduced. This is considered to be one of the reasons why the positive electrode of the present invention has a high capacity.

  From the above, it was found that by using the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, a non-aqueous electrolyte secondary battery having a high capacity and particularly good charge / discharge characteristics at a high current density can be obtained. .

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary batteries which are high capacity | capacitance and have favorable charging / discharging characteristics by especially a high current density can be provided. The nonaqueous electrolyte secondary battery of the present invention is useful as a power source for small electronic devices such as mobile phones and large electronic devices.

It is a longitudinal cross-sectional view which shows an example of the film-forming apparatus roughly. It is an electron micrograph which shows the cross section of the positive electrode for nonaqueous electrolyte secondary batteries which concerns on one Embodiment of this invention. It is an electron micrograph which shows the cross section of the positive electrode for nonaqueous electrolyte secondary batteries which concerns on other embodiment of this invention. 1 is a longitudinal sectional view schematically showing a coin-type non-aqueous electrolyte secondary battery. It is a figure which shows the charging / discharging characteristic of the nonaqueous electrolyte secondary battery of this invention. It is an electron micrograph which shows the surface of the active material layer of the positive electrode which concerns on the Example of this invention. It is an electron micrograph which shows the surface of the active material layer of the positive electrode which concerns on a comparative example. It is an electron micrograph which shows the cross section of the active material layer of the positive electrode which concerns on the Example of this invention. And X-ray diffraction pattern of the positive electrode of the present invention, showing an X-ray diffraction pattern of LiCoO ₂ powder. 6 is a complex impedance plot diagram showing AC impedance characteristics of the nonaqueous electrolyte secondary batteries of Example 3 and Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Induction coil 3 Stage 4 Current collector 5 Exhaust pump 6a, 6b Gas supply source 7a, 7b Valve 8 Raw material supply source 9 Power supply 10 Torch 11 Gas supply port 12 Raw material supply port 20 Current collector 21, 22 Material layer 23 Second active material layer 31 Exterior case 32 Gasket 33 Positive electrode active material layer 34 Positive electrode current collector 35 Porous insulating layer 36 Negative electrode 37 Disc spring 38 Sealing plate

Claims (7)

Including a current collector and an active material layer;
The active material layer has a first active material layer containing scaly active material particles,
The scaly active material particles have a bottom part on the current collector side, a head part on the surface side of the first active material layer, and a flat part between the bottom part and the head part,
A positive electrode for a non-aqueous electrolyte secondary battery, wherein a direction from the bottom to the head is orthogonal to a thickness direction of the flat portion.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein a direction from the bottom to the head and a normal direction of the current collector form an angle of 0 to 45 °.   The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the scaly active material particles have a hexagonal layered crystal structure belonging to the space group R-3m.   The positive electrode for a nonaqueous electrolyte secondary battery according to claim 3, wherein in X-ray diffraction, the peak intensity attributed to the (003) plane is smaller than the peak intensity attributed to the (101) plane. A second active material layer is further provided between the current collector and the first active material layer,
The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the porosity of the second active material layer is smaller than the porosity of the first active material layer.   The positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the active material layer further includes a flower-shaped active material aggregate composed of petals and ovaries. A positive electrode, a negative electrode, a non-aqueous electrolyte, and a porous insulating layer interposed between the positive electrode and the negative electrode;
The nonaqueous electrolyte secondary battery whose said positive electrode is a positive electrode for nonaqueous electrolyte secondary batteries in any one of Claims 1-6.