Positive electrode for lithium secondary battery and lithium secondary battery

Abstract

Lithium-containing composite oxides with an olivine structure are capable of absorbing and releasing lithium ions. This tends to occur one-dimensionally along the b-axis of the crystal. The positive electrode is provided with the b-axis oriented perpendicular to the surface of the positive electrode current collector. The method comprises mixing graphene oxide with lithium-containing composite oxide particles and applying pressure. This makes it easier for rectangular or nearly rectangular particles to slide. By using rectangular or nearly rectangular particles that are shorter than the length in the c-axis direction, pressure can be applied in one direction. This allows the b axis to be oriented in the direction of pressure.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a method for producing the same. Regarding the next battery. [Background technology]

[0002] The recent spread of mobile devices such as smartphones and portable games, as well as interest in environmental issues With the increasing demand for lithium secondary batteries, the capacity and output of lithium secondary batteries that can be used for portable devices and automotive power sources are becoming increasingly There is a need to improve this.

[0003] The basic structure of secondary batteries, including lithium secondary batteries, is an electrolyte between the positive and negative electrodes. The positive and negative electrodes are respectively a current collector and a In the case of a lithium secondary battery, the active material is a lithium-ion battery. Materials capable of absorbing and releasing ions are used as the active materials of the positive and negative electrodes.

[0004] In order to improve the capacity and output characteristics of lithium secondary batteries, various approaches are being taken. One of these is the improvement of the capacity and output performance of the positive electrode active material.

[0005] The positive electrode active material is lithium iron phosphate (Li x FePO4(0 <x≦1))をは Lithium-containing composite oxides with an olivine structure, such as lithium iron phosphate, are attracting attention. The iron used in the ion exchange reaction is very cheap compared to cobalt (Co), and iron (Fe(II ) and Fe(III)) exhibits a high potential (approximately 3.5 V) as a material where oxidation-reduction occurs. The theoretical capacity is approximately 170 mAh / g, and the energy density is Conventional lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO 2) It has advantages such as being superior to materials such as fluorine and being highly safe.

[0006] Lithium iron phosphate, a lithium-containing composite oxide with an olivine structure, is a It is known that the pathway exists one-dimensionally in the b-axis direction of the crystal lattice (Non-Patent Document 1). . [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. WO2009 / 117871 Pamphlet [Non-patent literature]

[0008] [Non-Patent Document 1] S. Nishimura, G. Kobayashi, K. Ohoyama, R. Kanno, M. Yashima and A. Yamada, "Experimental visualization of lithium diffusion in LixFePO4," Nature Materials, 2008, Vol. 7, pp. 707-711. Summary of the Invention [Problem to be solved by the invention]

[0009] In other words, in the lithium-containing composite oxide with an olivine structure, lithium ions are transported in directions other than the b axis. Therefore, the lithium-containing composite oxide particles When the b axis of the positive electrode is not oriented perpendicular to the surface of the current collector, the absorption and desorption of lithium ions There were times when it was difficult to do so.

[0010] However, it is difficult to control the orientation of the crystal axes of the lithium-containing composite oxide having an olivine structure. For example, as shown in Figure 1 of Patent Document 1, a lithium-containing The composite oxide particles are usually approximately spherical. In Patent Document 1, the particles of the lithium-containing composite oxide are approximately spherical. The particles of the compound are mixed with acetylene black as a conductive agent and PVdF (polyfluoride) as a binder. A secondary battery made using polyvinylidene fluoride has been disclosed. A schematic diagram of this is shown in Figure 4. vinegar.

[0011] The positive electrode 200 in FIG. 4(B) has a positive electrode current collector 220 and a positive electrode active material layer 210. The material layer 210 is made of lithium-containing composite oxide particles 211 having an olivine structure and a conductive additive 21 2 and a binder (not shown).

[0012] The conductive additive 212 and the binder are mixed with the lithium-containing composite oxide particles 211 and the positive electrode current collector 2 In order to secure an electron path between the positive electrode active material layer 210 and the positive electrode current collector 220, However, materials such as acetylene black and PVdF are It is made up of fine particles of carbon or one-dimensional polymers, and has a high coefficient of friction. The lithium-containing composite oxide particles 211, the conductive additive 212, and the binder are supported by each other. The lithium-containing composite oxide particles 211 are substantially spherical and have an a-axis, a b-axis, or a c-axis. Therefore, as shown in Figure 4(A), the positive electrode current collection Even if pressure is applied to the positive electrode active material layer 210 perpendicularly or approximately perpendicularly to the body 220, the lithium-containing composite oxide The direction of the crystal axis of the solid particle 211 does not change.

[0013] Therefore, in the present invention, a positive electrode having a larger capacity is obtained by facilitating the absorption and desorption of lithium ions. To achieve this, the b-axis of the single crystal of the lithium-containing composite oxide is oriented perpendicular to the surface of the positive electrode current collector. We focused on this.

[0014] The present invention provides a method for manufacturing a lithium-containing composite oxide in which the b-axis of the single crystal of the lithium-containing composite oxide is oriented perpendicular to the surface of the positive electrode current collector. One object is to provide a positive electrode. [Means for solving the problem]

[0015] In order to achieve the above object, in one embodiment of the present invention, a lithium-containing composite oxide particle is Furthermore, we decided to mix graphene or multilayer graphene oxide with lithium-containing composite acid. The oxide particles are rectangular parallelepipeds or A single crystal having a substantially rectangular parallelepiped shape was used.

[0016] Graphene oxide or multi-layer graphene oxide is in sheet form, and especially when multi-layered, it has low friction Therefore, graphene oxide or multi-layer graphene oxide is When mixed with titanium-containing composite oxide particles, graphene oxide or multi-layer graphene oxide particles When this mixture is pressed, the lithium ion battery is formed into a rectangular or nearly rectangular parallelepiped. The contained composite oxide particles can easily slide on the graphene oxide or multilayer graphene oxide. Furthermore, reduced graphene oxide or multilayer graphene oxide exhibits high electrical conductivity, It functions as a conductive additive. The graphene oxide is in the form of a sheet and covers the lithium-containing composite oxide particles, so it does not act as a binder. Therefore, reduced graphene oxide or reduced multilayer oxide When graphene is used, conductive additives and binders are unnecessary, or the proportion of these additives can be reduced. This allows the proportion of the lithium-containing composite oxide to be increased.

[0017] In addition, the length of the lithium-containing composite oxide particles along the b axis is greater than the lengths along the a axis and the c axis. Since a rectangular or nearly rectangular single crystal is used, the b axis can be oriented by applying pressure. For example, by applying pressure perpendicular or nearly perpendicular to the surface of the positive electrode current collector, the b axis can be aligned in a positive direction. It can be oriented perpendicular to the surface of the electrode current collector.

[0018] One aspect of the present invention is to provide a lithium-containing composite oxide having an olivine structure, the lithium-containing composite oxide having a rectangular parallelepiped or approximately rectangular parallelepiped particle shape. A mixture of the polymer and graphene oxide or 2 to 100 multilayer graphene oxide is used as a positive electrode collector. and forming a positive electrode active material layer by applying pressure perpendicular or substantially perpendicular to the surface of the electrode. This is a method for producing a positive electrode for a lithium secondary battery.

[0019] Another embodiment of the present invention is a positive electrode active material layer including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The active material layer is a lithium-containing composite with an olivine structure, in which the b-axis is oriented perpendicular to the surface of the positive electrode current collector. A rectangular or nearly rectangular parallelepiped single crystal of a composite oxide and reduced graphene oxide or 2 to 10 0 reduced multilayer graphene oxide and a mixture of .

[0020] The lithium-containing composite oxide having an olivine structure may be lithium iron phosphate.

[0021] In addition, the positive electrode active material layer is a lithium-containing composite with an olivine structure in the X-ray diffraction spectrum. The diffraction peak intensity ratio between the (020) and (101) planes of the oxide (I (020) / I(101) ) may be 4.5 or more and 5.5 or less. [Effects of the Invention]

[0022] According to one embodiment of the present invention, the b-axis of the single crystal of the lithium-containing composite oxide is perpendicular to the surface of the positive electrode current collector. A vertically oriented positive electrode can be provided. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view illustrating a positive electrode of one embodiment of the present invention. [Figure 2] 1A and 1B are a plan view and a cross-sectional view illustrating a lithium secondary battery of one embodiment of the present invention. [Figure 3] 1A and 1B are diagrams for explaining application forms of lithium secondary batteries. [Figure 4] FIG. 1 is a cross-sectional view illustrating a conventional example of a positive electrode. [Figure 5] 1 is a scanning electron microscope photograph of lithium iron phosphate particles used in a positive electrode according to one embodiment of the present invention. [Figure 6] 1 shows XRD measurement results of a positive electrode according to one embodiment of the present invention. [Figure 7] XRD measurement results for the reference example. [Figure 8] Charging and discharging characteristics of a lithium secondary battery using a positive electrode of one embodiment of the present invention. [Figure 9] Charge and discharge characteristics of a lithium secondary battery using a conventional positive electrode. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, the embodiments will be described in detail with reference to the drawings. and deviates from the spirit of the invention disclosed in this specification and the like. It will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the present invention. The configurations according to the embodiments can be implemented in appropriate combinations. In the configuration of the invention described above, the same parts or parts having similar functions are denoted by the same reference numerals. is used, and a repeated explanation thereof will be omitted.

[0025] In addition, the position, size, range, etc. of each component shown in the drawings etc. are not necessarily shown in order to facilitate understanding. The actual position, size, range, etc. may not be shown. The position, size, range, etc. are not necessarily limited to those disclosed in the drawings, etc.

[0026] In addition, in this specification, the term "oriented" means that the directions of the crystal axes of a plurality of single crystal grains are the same. When we say "the crystal axes of multiple single crystal particles are aligned," It is not necessary for all the crystal axes of multiple particles to be aligned. It is enough if the number of single crystal grains is greater than the number of single crystal grains aligned in other directions. The particles do not need to be single crystals. Orientation can be determined by XRD (X-ray diffraction, The degree of orientation can be analyzed by X-ray diffraction, etc. Also, the peak intensity ratio of XRD, etc. It is possible.

[0027] (Embodiment 1) In this embodiment, an example of a positive electrode 100 according to one embodiment of the present invention and a manufacturing method thereof will be described with reference to FIGS. 1 will be used to explain.

[0028] In the positive electrode 100 of one embodiment of the present invention, graphite oxide is added to the positive electrode active material layer 110 in the manufacturing process. FIG. 1B shows a positive electrode 100 according to one embodiment of the present invention. The positive electrode 100 includes a positive electrode current collector 120 and a positive electrode active material layer 110. The layer 110 is made of olivine-type lithium-containing composite oxide particles 111 and graphene oxide or poly The lithium-containing composite oxide particle 111 has a layer of graphene oxide 112. 113 indicates the b-axis direction of the crystal.

[0029] Graphene oxide or multi-layer graphene oxide is a material that can be used in a wide range of applications, including materials such as acetylene black and PVdF. Therefore, as shown in FIG. 1(A), the surface of the positive electrode current collector 120 is When the positive electrode active material layer 110 is pressed directly or substantially vertically, graphene oxide or multilayer graphene oxide is formed. The lithium-containing composite oxide particles 111 in contact with the fen 112 are slippery.

[0030] Furthermore, in one embodiment of the present invention, the lithium-containing composite oxide particles 111 have a length in the b-axis direction. A rectangular or nearly rectangular single crystal whose length is shorter than the length in the a-axis and c-axis directions is used. These particles were mixed with graphene oxide or multilayer graphene oxide and pressed. By this, the b-axis is perpendicular to the surface of the positive electrode current collector 120, which is the thickness direction of the positive electrode active material layer 110. When the b axis is oriented perpendicular to the surface of the positive electrode current collector 120, the lithium ions are easily oriented. This facilitates the absorption and release of ions.

[0031] Note that in FIG. 1, graphene oxide or multilayer graphene oxide is used to illustrate a method for manufacturing the positive electrode 100. Graphene 112 is shown, but it will be grown in a later process as graphene oxide or multi-layer graphene oxide. Therefore, the reduced graphene oxide or the reduced multilayer graphene oxide can be obtained. The positive electrode 100 may have an electron beam.

[0032] The positive electrode active material layer 110 in FIG. 1 is made of olivine-type lithium-containing composite oxide particles 111 and an oxide. In addition to graphene oxide or multi-layer graphene oxide 112, a conductive additive, a binder, etc. are also included. It's okay to be.

[0033] <Production of Lithium-Containing Composite Oxide Particles> Hereinafter, the method for producing the positive electrode 100, which is one aspect of the present invention, will be described in detail with reference to FIG. 1. Also first, produce single crystal lithium-containing composite oxide particles 111 in the shape of a rectangular parallelepiped or a substantially rectangular parallelepiped, whose length in the b-axis direction is shorter than the lengths in the a-axis and c-axis directions.

[0034] In this specification, the rectangular parallelepiped and the substantially rectangular parallelepiped do not necessarily have to be a rectangular parallelepiped in the strict sense, as long as the length in the b-axis direction is shorter than the lengths in the a-axis and c-axis directions. Therefore, for example, a shape with rounded corners from a rectangular parallelepiped or a shape with irregularities on the surface may be acceptable. Also it may be a flat polygonal columnar shape, a plate shape, etc.

[0035] As the lithium-containing composite oxide particles 111, materials represented by Li x MPO4 (0 < x ≦ 1) (M = Fe , Mn, Co, Ni) can be used. Particularly, lithium iron phosphate (L i x FePO4 (0 < x ≦ 1)) is preferable because it uses inexpensive and abundant iron resources. In this embodiment, lithium iron phosphate will be used. [[ID=3�]]

[0036] As a method for producing the rectangular parallelepiped or substantially rectangular parallelepiped single crystal grains of the lithium-containing composite oxide particles 111 as described above, a sol-gel method, a hydrothermal method, etc. can be used. Particularly, the hydrothermal method is preferable because it is possible to control the shape and particle size of the generated particles by adjusting the pH during synthesis, the concentration of raw materials, the reaction time, the reaction temperature, additives, etc.

[0037] By the hydrothermal method, a rectangular parallelepiped or substantially rectangular parallelepiped ​​​​​To synthesize lithium iron phosphate single crystals, for example, the raw material for lithium iron phosphate is dissolved in water. Suspend at 0.3 mol / L and autoclave at 150°C for 15 hours under 0.4 MPa. That's fine.

[0038] <Preparation of graphene oxide or multi-layer graphene oxide> The method for producing the graphene oxide or multilayer graphene oxide 112 is not particularly limited. For example, For example, graphite is oxidized to form graphite oxide, which is then thinned by ultrasonic waves in a solution. It can be produced by converting

[0039] In this specification, graphene is a 2 Sheet of a single carbon molecule with a bond Graphene stacked with 2 to 100 layers is called multi-layer graphene. The multilayer graphene may contain 30 atomic % or less of elements other than carbon. It may contain elements other than carbon and hydrogen at atomic percent or less. Graphene oxide or multi-layer graphene is also called graphene oxide. It can also be said that part of the end of the phenylene is terminated with a carboxyl group (-COOH) or the like. .

[0040] Graphene or multi-layer graphene may also be referred to as a graphene net. While one layer of graphene is a series of six-membered carbon rings, The carbon atoms are not limited to six-membered rings. For example, eight-membered rings, nine-membered rings, etc. can be found in one layer of the graphene net. Carbocyclic rings of one or more ring members may be present.

[0041] <Preparation of positive electrode> Next, the lithium-containing composite oxide particles 111 and the graphene oxide or multilayer graphene oxide The mixture is mixed with the solvent 112 to prepare a slurry.

[0042] The slurry is applied to the positive electrode current collector 120 and dried, forming a positive electrode active material layer on the positive electrode current collector 120. In FIG. 1, the positive electrode active material layer 110 is formed on one surface of the positive electrode current collector 120. However, it may be formed on both sides.

[0043] Furthermore, the positive electrode active material layer 110 is pressed perpendicularly or approximately perpendicularly to the surface of the positive electrode current collector 120 ( 1(A)), any method of applying pressure can be used as long as it can apply pressure to the positive electrode active material layer 110 in approximately one direction. For example, this can be done using a roll press.

[0044] By applying pressure, the lithium-containing composite oxide particles of the positive electrode active material layer 110 are converted into graphene oxide or The lithium-containing composite oxide particles slide on the multilayer graphene oxide, and the b-axis of the particles is aligned with the positive electrode current collector. The surface of the nanotube can be oriented perpendicular to the nanotube surface (Fig. 1(B)).

[0045] Then, the graphene oxide or multilayer graphene oxide in the positive electrode active material layer 110 is reduced. The reduction can be carried out by, for example, calcination.

[0046] By the above reduction, the lithium-containing composite oxide particles 111 are converted into reduced graphene oxide or The structure is covered with reduced multilayer graphene oxide.

[0047] Thereafter, the positive electrode current collector 120 and the positive electrode active material layer 110 are processed into a desired shape to form the positive electrode 100. In this manner, the positive electrode 100 of one embodiment of the present invention can be manufactured.

[0048] (Embodiment 2) In this embodiment, a lithium secondary battery 151 according to one embodiment of the present invention and an example of a manufacturing method thereof will be described. This will be explained using FIG. 2.

[0049] The lithium secondary battery 151 according to one embodiment of the present invention includes at least a positive electrode, a negative electrode, and an electrolyte. The positive electrode is the positive electrode 100 described in the first embodiment.

[0050] The electrolyte is a non-aqueous solution containing a salt or an aqueous solution containing a salt. The salt is a carrier ion. Any salt containing lithium ions may be used.

[0051] The lithium secondary battery 151 shown in FIG. 2(A) has a storage cell 155 inside an exterior member 153. The exterior member 15 also has terminals 157 and 159 that are connected to the storage cell 155. 3. Laminated film, polymer film, metal film, metal case, plastic A case or the like can be used.

[0052] FIG. 2B shows a cross section of the lithium secondary battery 151 shown in FIG. 2A taken along line XY. As shown in FIG. 2(B), the storage cell 155 includes a negative electrode 163, a positive electrode 165, and A separator 167 is provided between the negative electrode 163 and the positive electrode 165, and the exterior member 153 is filled with the separator 167. and an electrolyte 169.

[0053] The positive electrode 165 is the positive electrode 100 described in the first embodiment. The negative electrode current collector 171 is connected to the terminal portion 159. The terminal portion 1 57 and terminal portion 159 are each partially led out to the outside of exterior member 153.

[0054] The negative electrode 163 includes a negative electrode current collector 171 and a negative electrode active material layer 173. is formed on one or both surfaces of the negative electrode current collector 171. In addition, the negative electrode active material layer 173 A binder and a conductive additive may also be included.

[0055] In this embodiment, the external form of the lithium secondary battery 151 is a sealed thin lithium secondary battery. The external shape of the lithium secondary battery 151 is shown, but is not limited to this. The types of batteries are button-type lithium secondary batteries, cylindrical lithium secondary batteries, and square lithium secondary batteries. In this embodiment, the positive electrode, the negative electrode, and the separator may be formed in various shapes. The structure shown is a stacked structure of positive electrodes, negative electrodes, and separators, but the structure is a wound structure of positive electrodes, negative electrodes, and separators. It is also possible.

[0056] The negative electrode current collector 171 is made of a conductive material such as titanium, aluminum, or stainless steel in the form of a foil, plate, or A conductive layer formed by depositing a film on a substrate is also used. It can also be peeled off and used as the negative electrode current collector 171.

[0057] The negative electrode active material layer 173 is made of a material capable of electrochemically absorbing and releasing lithium ions. Use materials that can be used, such as lithium, aluminum, carbon-based materials, tin, and tin oxide. , silicon, silicon oxide, silicon carbide, silicon alloy, or germanium, etc. Alternatively, lithium, aluminum, carbon-based materials, tin, tin oxide, silicon silicon dioxide, silicon carbide, silicon alloy, and germanium The carbonaceous material capable of absorbing and releasing lithium ions may also be a compound containing the above. As the material, powdered or fibrous graphite or the like can be used. Copper alloys, germanium, lithium, aluminum, and tin are more favorable than carbon-based materials. Therefore, the material used for the negative electrode active material layer 173 has a large capacity for absorbing lithium ions. The amount of material can be reduced, which reduces costs and allows the lithium secondary battery 151 to be made smaller. It becomes Noh.

[0058] The negative electrode active material layer 173 can be formed by depositing the above-listed materials using a printing method, an inkjet method, a CVD method, or the like. Alternatively, the above-listed materials may be applied by coating or sputtering. After forming a film by a method such as a ring method or vacuum deposition, the film material is partially removed to form a surface It may be formed in an uneven shape.

[0059] It should be noted that the negative electrode current collector 171 is not used, and the negative electrode active material layer 173 can be formed by simply using the materials listed above. The body may be used as the negative electrode.

[0060] In addition, the negative electrode active material layer 173 may be formed of graphene, multilayer graphene, reduced graphene oxide, or the like. For example, the negative electrode active material may be wrapped in a multilayer graphene oxide. Graphene, multilayer graphene, reduced graphene oxide or reduced multilayer graphene Graphene may be provided. By doing so, it is possible to absorb and store lithium ions. The negative electrode active material layer 173 can be prevented from being affected by the release of the negative electrode active material. The expansion or contraction of the active material layer 173 may result in the negative electrode active material layer 173 being pulverized or peeled off. In addition, multi-layer graphene can absorb and release lithium ions, Therefore, the capacity of the negative electrode to absorb lithium ions can be increased.

[0061] The electrolyte 169 uses a salt containing lithium ions. For example, LiClO4, LiA Using lithium salts such as sF6, LiBF4, LiPF6, and Li(C2F5SO2)2N It is possible.

[0062] The electrolyte 169 is preferably a non-aqueous solution containing salt. The solvent is preferably an aprotic organic solvent. Examples of the aprotic organic solvent include: Ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane and tetrahydrofuran One or more of these can be used. As the organic solvent, one ionic liquid or a plurality of ionic liquids may be used. Since it is flame-retardant and non-volatile, when the internal temperature of the lithium secondary battery 151 rises, This can prevent the lithium secondary battery 151 from exploding or catching fire, thereby improving safety. do.

[0063] Furthermore, by using a polymer material that contains salt and is gelled as the electrolyte 169, leakage can be prevented. Safety, including the liquidity, is improved, and the lithium secondary battery 151 can be made thinner and lighter. Typical examples of gelatinized polymer materials include silicone gel, acrylic gel, and acrylonitrile Trilgel, polyethylene oxide, polypropylene oxide or fluorine-based polymer etc.

[0064] Furthermore, the electrolyte 169 may be a solid electrolyte such as Li3PO4.

[0065] The lithium secondary battery 151 preferably has a separator. For example, an insulating porous material such as paper, glass fiber, or ceramics can be used. , or nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester Made of synthetic fibers such as terephthalate, acrylic, polyolefin, and polyurethane. However, it is necessary to select a material that does not dissolve in the electrolyte 169.

[0066] Lithium secondary batteries have a small memory effect, high energy density, and large charge / discharge capacity. In addition, the output voltage is high. Therefore, compared to conventional secondary batteries, it can be made smaller with the same capacity. It is also possible to reduce the weight. It is also less likely to deteriorate with repeated charging and discharging, making it suitable for long-term use. By using a positive electrode according to one embodiment of the present invention, a lithium secondary battery with a larger capacity can be obtained. It can be a pond.

[0067] This embodiment mode may be implemented by appropriately combining it with the configurations described in other embodiment modes or examples. It is possible to implement this.

[0068] (Embodiment 3) The lithium secondary battery according to one embodiment of the present invention can be used as a power source for various electrical devices driven by electricity. It can be used as follows.

[0069] Specific examples of electrical devices using the lithium secondary battery according to one embodiment of the present invention include display devices, lighting devices, and the like. Lighting equipment, desktop or notebook personal computers, DVD (Digit Playback of still images or videos stored on recording media such as a Versatile Disc image playback devices, mobile phones, portable game consoles, personal digital assistants, tablet terminals, Children's books, video cameras, digital still cameras, microwave ovens and other high-frequency heating devices, electric cookers Rice cookers, electric washing machines, air conditioning equipment such as air conditioners, electric refrigerators, electric freezers, Examples include medical electrical equipment such as refrigerator-freezers, freezers for storing DNA, and dialysis machines. In addition, vehicles propelled by electric motors using power from lithium secondary batteries are also considered electrical equipment. The above-mentioned moving body includes, for example, an electric vehicle, an internal combustion engine and an electric vehicle. Hybrid cars that combine a motor with other vehicles (hybrid cars), and motorized vehicles including electrically assisted bicycles Bicycles, for example.

[0070] The above electrical equipment uses a lithium secondary battery (called the main power source) to cover almost all of the power consumption. The lithium secondary battery according to one embodiment of the present invention can be used as the above-mentioned battery. The electrical equipment is designed to withstand the power supply interruption from the main power source or commercial power source. As a lithium secondary battery (called an uninterruptible power supply) capable of supplying power, The lithium secondary battery according to one embodiment can be used. Alternatively, the electrical device can be Supplying power to electrical equipment in parallel with the supply of power from the power supply or commercial power source to electrical equipment. As a lithium secondary battery (called an auxiliary power source) for use in A secondary battery can be used.

[0071] 3 shows a specific configuration of the above-mentioned electric device. In FIG. 3, a display device 1000 is 1 is an example of an electrical device using a lithium secondary battery 1004 according to one embodiment of the present invention. The display device 1000 corresponds to a display device for receiving TV broadcasts, and includes a housing 1001, a display unit 100 2, a speaker unit 1003, a lithium secondary battery 1004, etc. The lithium secondary battery 1004 is provided inside the housing 1001. The power supply can be supplied from a commercial power source or stored in a lithium secondary battery 1004. Therefore, if the power supply from the commercial power source is interrupted due to a power outage, etc., Even when the power is not available, the lithium secondary battery 1004 according to one embodiment of the present invention can be used as an uninterruptible power source. By using the display device 1000 in this way, the display device 1000 can be used.

[0072] The display unit 1002 may be a liquid crystal display device, an illuminating device having light emitting elements such as organic EL elements in each pixel, or the like. Device, electrophoretic display device, DMD (Digital Micromirror Device) ce), PDP (Plasma Display Panel), FED (Field A semiconductor display device such as a reflective LED (emission display) can be used.

[0073] In addition to TV broadcast reception, display devices are also used for personal computers and advertising displays. , including all display devices for displaying information.

[0074] In FIG. 3, a stationary lighting device 1100 is a lithium secondary battery according to one embodiment of the present invention. The lighting device 1100 is an example of an electrical device using a battery 1103. Specifically, the lighting device 1100 is 1, a light source 1102, a lithium secondary battery 1103, etc. In FIG. 1103 is provided inside the ceiling 1104 on which the housing 1101 and the light source 1102 are installed. However, the lithium secondary battery 1103 is not necessarily installed inside the housing 1101. The lighting device 1100 may be supplied with power from a commercial power source. In addition, the power stored in the lithium secondary battery 1103 can be used. Even when power cannot be supplied from a commercial power source due to a power outage or other reasons, the lithium battery according to one aspect of the present invention can be used. The lighting device 1100 can be used by using the lithium secondary battery 1103 as an uninterruptible power supply. This becomes:

[0075] 3 illustrates a lighting device 1100 that is a fixed type provided on a ceiling 1104. However, in the lithium secondary battery according to one embodiment of the present invention, the side wall 1105, for example, is not included in the ceiling 1104. It can also be used in a fixed lighting device provided on a floor 1106, a window 1107, etc. It can also be used as a tabletop lighting device.

[0076] The light source 1102 may be an artificial light source that artificially obtains light using electricity. Specifically, incandescent lamps, fluorescent lamps and other discharge lamps, and light-emitting devices such as LEDs and organic EL elements The element is an example of the artificial light source.

[0077] In FIG. 3, an air conditioner having an indoor unit 1200 and an outdoor unit 1204 is 1 is an example of an electrical device using a lithium secondary battery 1203 according to one embodiment of the present invention. The indoor unit 1200 includes a housing 1201, an air outlet 1202, a lithium secondary battery 1203, etc. In FIG. 3, the lithium secondary battery 1203 is installed in the indoor unit 1200. Although shown as an example, the lithium secondary battery 1203 may be provided in the outdoor unit 1204 . Alternatively, both the indoor unit 1200 and the outdoor unit 1204 are provided with a lithium secondary battery 1203. The air conditioner may be powered by a commercial power source. In addition, the power stored in the lithium secondary battery 1203 can also be used. When the lithium secondary battery 1203 is installed in both the outdoor unit 1200 and the outdoor unit 1204, Even when power cannot be supplied from a commercial power source due to a power outage or other reasons, the lithium battery according to one aspect of the present invention can be used. By using the Umium secondary battery 1203 as an uninterruptible power supply, the use of air conditioners It becomes possible.

[0078] In Figure 3, we use a separate air conditioner consisting of an indoor unit and an outdoor unit as an example. Although the figure shows an integrated air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing, The lithium secondary battery according to one embodiment of the present invention can also be used in the partitioner.

[0079] In FIG. 3, an electric refrigerator-freezer 1300 includes a lithium secondary battery 13 according to one embodiment of the present invention. 13. Specifically, the electric refrigerator-freezer 1300 is an example of an electric device using the housing 130 1, a refrigerator door 1302, a freezer door 1303, a lithium secondary battery 1304, etc. In FIG. 3, a lithium secondary battery 1304 is provided inside a housing 1301. The refrigerator / freezer 1300 can be supplied with power from a commercial power source or can be powered by a lithium secondary battery. It is also possible to use the power stored in the battery 1304. Even when power cannot be supplied from the lithium secondary battery 1304 according to one embodiment of the present invention, By using it as an uninterruptible power supply, it becomes possible to use an electric refrigerator-freezer 1300.

[0080] Among the above-mentioned electrical appliances, high-frequency heating devices such as microwave ovens and electric rice cookers Equipment requires high power for a short period of time, so it supplements the power that cannot be supplied by commercial power. By using a lithium secondary battery according to one embodiment of the present invention as an auxiliary power source for This can prevent the commercial power breaker from tripping when using electrical equipment.

[0081] In addition, during periods when electrical equipment is not in use, especially when the total amount of power that can be supplied by the commercial power supplier is low, During the time period when the ratio of the amount of electricity actually used (called the power usage rate) is low, By storing power in a lithium secondary battery, the power usage rate increases outside of the above time periods. For example, in the case of an electric refrigerator / freezer 1300, when the temperature is low and the refrigerator compartment During the night when the door 1302 and the freezer door 1303 are not opened or closed, the lithium secondary battery 1 As the temperature rises, the refrigerator door 1302 and the freezer door 13 During the daytime when the door 03 is opened and closed, a lithium secondary battery 1304 is used as an auxiliary power source. This allows for lower electricity usage during the day.

[0082] In FIG. 3, a tablet terminal 1400 includes a lithium secondary battery 1 according to one embodiment of the present invention. 1403. Specifically, the tablet terminal 1400 has a housing 1 The housing 1401 and the housing 1402 include a lithium secondary battery 1403. Each of the 1402 has a display unit with a touch panel function, and the display unit can be changed by touching it with a finger or the like. The tablet terminal 1400 has a housing 1401 and a The display unit of the housing 1402 can be folded inward, making it compact and reducing the size of the display. The lithium secondary battery 1403 according to one embodiment of the present invention can be used to protect the battery. This allows the tablet terminal 1400 to be made smaller and to be used mobile for a long period of time. .

[0083] This embodiment mode may be implemented by appropriately combining it with the configurations described in other embodiment modes or examples. It is possible to implement this. [Example]

[0084] In this example, a positive electrode for a lithium secondary battery according to one embodiment of the present invention was actually produced, and a positive electrode active material The results of evaluation of the orientation of the polymer layer and the battery characteristics will be explained with reference to FIGS.

[0085] <Preparation of lithium-containing composite oxide> In this example, a phosphoric acid compound synthesized by a hydrothermal method was used as the lithium-containing composite oxide with an olivine structure. Lithium iron was used.

[0086] The raw materials for lithium iron phosphate are lithium hydroxide monohydrate (LiOH·H2O) and iron chloride. (II) tetrahydrate (FeCl2·4H2O) and ammonium dihydrogen phosphate (NH4H 2PO4) was used.

[0087] LiOH·H2O:FeCl2·4H2O:NH4H2PO4=2:1:1[mol ratio In this example, 0.06 mol of LiOH·H2O and 0.06 mol of FeCl2 0.03 mol of 4H2O and 0.03 mol of NH4H2PO4 were weighed out.

[0088] The subsequent experiments were carried out under a nitrogen atmosphere. First, each of the above raw materials was dissolved in 30 ml of deoxygenated water. The water was deoxygenated by bubbling nitrogen through it beforehand.

[0089] Next, while stirring the ammonium dihydrogen phosphate solution with a stirrer, add the lithium hydroxide solution was slowly added to prepare a solution in which lithium phosphate (Li3PO4) precipitated.

[0090] Next, the lithium phosphate was suspended in the iron(II) chloride solution while stirring it with a stirrer. The solution was gradually added to prepare a suspension containing the precursor of lithium iron phosphate. Water was added to bring the total volume to 100 ml.

[0091] Next, the suspension containing the precursors was placed in a hydrothermal synthesis reaction vessel (mini) having a fluororesin inner cylinder. Place in a reactor MS type MS200-C (manufactured by OM Labotech Co., Ltd.) and stir. The mixture was subjected to a hydrothermal reaction at about 150°C and about 0.4 MPa for 15 hours.

[0092] After the reaction, the resulting lithium iron phosphate was collected by filtration and washed 10 times with pure water. The mixture was dried under pressure at 50°C for at least 12 hours.

[0093] Figure 5 shows a scanning electron microscope photograph of the obtained lithium iron phosphate. As shown in Figure 5, the specimen was placed in a flat rectangular parallelepiped or flat A large number of polygonal columnar particles were observed. This lithium iron phosphate was used as the positive electrode.

[0094] <Preparation of graphene oxide or multi-layer graphene oxide> First, graphite was oxidized to form graphite oxide. The graphene oxide or multi-layer graphene oxide was then thinned by ultrasonic waves. , graphene oxide or multilayer graphene oxide powder.

[0095] <Preparation of positive electrode> Lithium iron phosphate and graphene oxide or multilayer graphene oxide were mixed in a ratio of 97.5:2.5 [weight ratio]. In this example, 0.1380 g of lithium iron phosphate, 0.1380 g of glycerol oxide, and 0.1380 g of glycerol were mixed and crushed. 0.0072 g of laphene was used. Ethanol was used as the solvent for grinding, and a ball mill was used. The mixture was then dried by evaporating the ethanol. made him do so.

[0096] A mixture of dried lithium iron phosphate and graphene oxide or multi-layer graphene oxide was N-methyl-2-pyrrolidone (NMP) was mixed to form a slurry. 0.478g of P was mixed.

[0097] Aluminum foil was used as the positive electrode current collector. The slurry was applied to the aluminum positive electrode current collector to form a film of about 100 μm. The coating was thick and dried at 120°C using a vacuum dryer to form a positive electrode active material layer. The lumi-positive electrode current collector and the positive electrode active material layer were pressed together using a roll press.

[0098] Then, baking is performed to reduce the graphene oxide or multilayer graphene oxide in the positive electrode active material layer. The graphene oxide was then baked to obtain reduced graphene oxide or reduced multilayer graphene oxide. The test was carried out in a tube oven at 200°C for 1 hour under reduced pressure using a diaphragm pump. Then, the temperature was raised to 300°C and the reaction was continued for 10 hours.

[0099] Then, the aluminum positive electrode current collector and the positive electrode active material layer were punched into a circle with a diameter of 12 mm to form a positive electrode. .

[0100] <XRD analysis of positive electrode> The XRD measurement results of the positive electrode prepared as described above are shown in Figure 6. Also, as a reference example, Figure 7 shows The XRD measurement results of lithium iron phosphate particles synthesized by the solid phase method are shown. The horizontal axis is the diffraction angle (2 θ), and the vertical axis is the diffraction intensity.

[0101] In the XRD spectrum of lithium iron phosphate, the peak of the (020) plane perpendicular to the b axis is a diffraction peak. The peak of the (101) plane, which is not perpendicular to the b axis, is at a diffraction angle of around 20.8°. It is known that the peak of the (301) plane, which is not perpendicular to the axis, appears at a diffraction angle of around 32.2°. Ru. (Anna S Andersson et al.,Lithium extra ction / insertion in LiFePO4: an X-ray dif fraction and Mossbauer spectroscopy stud y, Solid State Ionics, volume 130, pp.4 1-52 (2000))

[0102] The positive electrode in Figure 6 shows diffraction peaks for the (020) plane perpendicular to the b axis and the (101) plane not perpendicular to the b axis. Intensity ratio (I (020) / I (101) ) was 4.60. Also, the (02 The diffraction peak intensity ratio (I (020) / I (301 ) ) was 4.01.

[0103] The lithium iron phosphate particle in Fig. 7 has a (020) plane perpendicular to the b axis and a (101 ) diffraction peak intensity ratio (I (020) / I (101) ) was 0.93. The diffraction peak intensity ratio (I (02 0) / I (301) ) was 2.25.

[0104] 6 and 7, the positive electrode of one embodiment of the present invention exhibits a higher ionic strength than the reference lithium iron phosphate particles. The peak of the (020) plane perpendicular to the b axis is relatively high, and the peaks of the (101) and (301) planes are It is clear that the peaks of the planes not perpendicular to the b axis, such as That is, in the positive electrode of one embodiment of the present invention, the lithium iron phosphate single crystal in the positive electrode active material layer It was revealed that the b-axes of the particles were oriented perpendicular to the surface of the positive electrode current collector.

[0105] <Preparation of Positive Electrode of Comparative Example> In the conventional positive electrode, acetylene bromide was used as a conductive additive instead of reduced graphene oxide. The positive electrode was fabricated using PVdF as a binder and iron phosphate as the binder. The ratio of PVdF to acetylene black was 85:8:7. The cathode was fabricated in the same manner as the cathode.

[0106] <Battery characteristics> The battery characteristics were evaluated for the positive electrode in which the b axis was oriented perpendicular to the surface of the positive electrode current collector.

[0107] To evaluate the battery characteristics, the positive electrode prepared as described above was used as the working electrode, and the L The cell was fabricated using i metal. The separator was polypropylene (PP) and the electrolyte was 1 mol / L of lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC) The solution was dissolved in a mixture of ethanol and diethyl carbonate (DEC) (volume ratio 1:1). .

[0108] FIG. 8 shows the charge-discharge characteristics of a positive electrode according to one embodiment of the present invention, and FIG. 9 shows the charge-discharge characteristics of a conventional positive electrode. The vertical axis represents voltage, The horizontal axis shows the capacity.

[0109] 8 and 9, the positive electrode of one embodiment of the present invention has a higher charge capacity and discharge capacity than the conventional example. It was found that the capacity was improved. [Explanation of symbols]

[0110] 100 positive electrode 110 Cathode active material layer 111 Lithium-containing composite oxide particles 112 Graphene oxide or multilayer graphene oxide 113 Arrow 120 Positive electrode current collector 151 Lithium secondary battery 153 Exterior materials 155 Energy Storage Cells 157 Terminal section 159 Terminal section 163 Negative electrode 165 Positive electrode 167 Separator 169 Electrolyte 171 Negative electrode current collector 173 Negative electrode active material layer 175 Positive electrode current collector 200 positive electrode 210 Cathode active material layer 211 Lithium-containing composite oxide particles 212 Conductive additives 220 Positive electrode current collector 1000 display devices 1001 Case 1002 Display section 1003 Speaker section 1004 Lithium secondary battery 1100 Lighting equipment 1101 Case 1102 Light source 1103 Lithium secondary battery 1104 Ceiling 1105 Side wall 1106 beds 1107 Window 1200 indoor unit 1201 Case 1202 Ventilation vent 1203 Lithium secondary battery 1204 Outdoor unit 1300 Electric refrigerator-freezer 1301 Case 1302 Refrigerator door 1303 Freezer door 1304 Lithium secondary battery 1400 tablet devices 1401 Case 1402 Case 1403 Lithium secondary battery

Claims

1. a positive electrode current collector; and a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer is First lithium-containing composite oxide particles and second lithium-containing composite oxide particles; graphene covering the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles; the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have an olivine structure, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have a rectangular parallelepiped or approximately rectangular parallelepiped shape, the length in the b-axis direction being shorter than the length in the a-axis direction and the length in the c-axis direction, The positive electrode for a lithium secondary battery, wherein the b-axis is oriented perpendicular or approximately perpendicular to the surface of the positive electrode current collector.

2. a positive electrode current collector; and a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer is First lithium-containing composite oxide particles and second lithium-containing composite oxide particles; multilayer graphene covering the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have an olivine structure, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have a rectangular parallelepiped or approximately rectangular parallelepiped shape, the length in the b-axis direction being shorter than the length in the a-axis direction and the length in the c-axis direction, The positive electrode for a lithium secondary battery, wherein the b-axis is oriented perpendicular or approximately perpendicular to the surface of the positive electrode current collector.

3. In claim 1, The graphene has a region in contact with the positive electrode current collector.

4. In claim 2, The multilayer graphene has a region in contact with the positive electrode current collector.

5. In any one of claims 1 to 4, The positive electrode active material layer has a diffraction peak intensity ratio (I （０２０） / I （１０１） ) is 4.5 or more and 5.5 or less.

6. In any one of claims 1 to 5, The positive electrode for a lithium secondary battery, wherein the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles are each lithium iron phosphate.

7. having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer is First lithium-containing composite oxide particles and second lithium-containing composite oxide particles; graphene covering the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles; the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have an olivine structure, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have a rectangular parallelepiped or approximately rectangular parallelepiped shape, the length in the b-axis direction being shorter than the length in the a-axis direction and the length in the c-axis direction, the b-axis is oriented perpendicular or approximately perpendicular to the surface of the positive electrode current collector.

8. having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer is First lithium-containing composite oxide particles and second lithium-containing composite oxide particles; multilayer graphene covering the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have an olivine structure, the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles each have a rectangular parallelepiped or approximately rectangular parallelepiped shape, the length in the b-axis direction being shorter than the length in the a-axis direction and the length in the c-axis direction, the b-axis is oriented perpendicular or approximately perpendicular to the surface of the positive electrode current collector.

9. In claim 7, The graphene has a region in contact with the positive electrode current collector.

10. In claim 8, The multilayer graphene has a region in contact with the positive electrode current collector.

11. In any one of claims 7 to 10, The positive electrode active material layer has a diffraction peak intensity ratio (I （０２０） / I （１０１） ) is 4.5 or more and 5.5 or less.

12. In any one of claims 7 to 11, The lithium secondary battery, wherein the first lithium-containing composite oxide particles and the second lithium-containing composite oxide particles are each lithium iron phosphate.

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