Secondary battery

Abstract

To reduce the number of steps in an electrode manufacturing process, to suppress destruction of the electrode, or to obtain a highly reliable lithium secondary battery by suppressing destruction of the electrode.SOLUTION: The present invention relates to the production of a negative electrode, which includes mixing graphene oxide, a plurality of particulate negative electrode active materials, and a polyimide precursor to form a slurry, applying the slurry to a negative electrode current collector, heating the slurry applied to the negative electrode current collector at a temperature of 200°C or more and 400°C or less to imidize the polyimide precursor, and reducing the graphene oxide by the heating for imidizing the polyimide precursor, and to the production of a lithium secondary battery having the negative electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the disclosed invention relates to a method for manufacturing a negative electrode and a method for manufacturing a lithium secondary battery. . [Background technology]

[0002] In recent years, mobile devices such as smartphones and portable game consoles have become widespread. With the growing interest in this issue, hybrid and electric cars are gaining attention, and lithium secondary batteries are becoming increasingly popular. Secondary batteries, including batteries, are becoming increasingly important.

[0003] The basic structure of a secondary battery is an electrolyte (liquid electrolyte or solid 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 material that absorbs and stores lithium. Materials capable of receiving and releasing charge are used as the active materials of the positive and negative electrodes.

[0004] In order to increase the contact area between the active material and the electrolyte, the active material may be made into a particulate active material. Therefore, a binder, a conductive additive, etc. are mixed with the particulate active material. The resulting active material layer may be provided on a current collector to form an electrode (positive electrode or negative electrode).

[0005] The negative electrode active material is, for example, a material containing ions (hereinafter referred to as "carriers") such as carbon or silicon. A material capable of absorbing and releasing carrier ions (referred to as carrier ions) is used. For example, silicon has the following properties: It can store approximately 10 times as many carrier ions as carbon, giving it a large theoretical capacity. This is advantageous in terms of increasing the capacity of lithium secondary batteries.

[0006] However, as the amount of carrier ions absorbed increases, the carrier ions increase during the charge-discharge cycle. The volume change due to the absorption and release of ions is large, and the adhesion between the current collector and silicon decreases, making it difficult to charge and discharge. Therefore, we have developed a method to apply silicon or other materials to the current collector. and providing a layer of graphite on the layer of silicon, This reduces the deterioration of battery characteristics due to the expansion and contraction of the silicon layer (see Patent Document 1). .

[0007] In addition, silicon has a lower electrical conductivity than carbon, so the surface of silicon particles is covered with graphite. The active material layer containing the silicon particles is formed on the current collector. We have created a negative electrode with increased electrical conductivity.

[0008] On the other hand, in recent years, graphene has been used as a conductive electronic material in semiconductor devices. Graphene is a sheet of carbon molecules with a single atomic layer that has π bonds. This is what is meant.

[0009] Graphene is chemically stable and has good electrical properties, making it suitable for use as a transistor channel. It is expected to be used in semiconductor devices, such as in panel regions, vias, and wiring. To increase the conductivity of the electrode material for the battery, graphite or graphene is added to the particulate active material. The coating is made of a thin film (see Non-Patent Document 1). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-283834 [Non-patent literature]

[0011] [Non-Patent Document 1] “In-Plane Vacancy-Enabled High-Power Si-Graphene Composite Electrode for Lithium-Ion Batteries”, Xin Zhao, Cary M. Hayner, Mayfair C. Kung, and Harold H. Kung, Adv. Energy Mater., 2011, 1, 1079-1084. Summary of the Invention [Problem to be solved by the invention]

[0012] In Non-Patent Document 1, graphene oxide is grown in an argon atmosphere. By heating in air or in an argon atmosphere containing 10% hydrogen at 700°C for 1 hour, It is being reduced.

[0013] Furthermore, by heating the silicon nanoparticles and the reduced graphene oxide described above, We are producing "Si-graphene paper."

[0014] As described above, in Non-Patent Document 1, two heating steps are performed to prepare an electrode (negative electrode). It is indispensable.

[0015] As described above, the particulate active material is mixed with a binder, a conductive additive, etc. to form an active material layer. However, in the electrode (negative electrode) manufacturing process, In the method, a slurry containing silicon, graphene oxide, and a binder as an active material is mixed with the above-mentioned If heated to a high temperature such as 700°C, the binder may decompose and the electrode (negative electrode) may be destroyed. occurs.

[0016] A lithium secondary battery in which the binder has decomposed and the electrode (negative electrode) has been destroyed is an unreliable power storage device. There is a risk that this will happen.

[0017] In view of the above, one embodiment of the disclosed invention is to reduce the number of manufacturing steps in an electrode manufacturing process. This is one of the challenges.

[0018] Another object of one embodiment of the disclosed invention is to suppress breakdown of electrodes.

[0019] Furthermore, one embodiment of the disclosed invention is to suppress breakdown of electrodes, thereby achieving highly reliable lithium ion batteries. One of the objectives is to obtain a lithium secondary battery. [Means for solving the problem]

[0020] In one embodiment of the disclosed invention, a silicon active material, graphene oxide, and a binder (binder) are used. The polyimide precursor is formed by baking a slurry containing the polyimide precursor. The precursor is imidized. In the heating step of imidizing the polyimide precursor, oxidation graphite is formed. That is, the slurry firing step and the graphene oxide reduction step are carried out simultaneously. This allows the number of steps in the electrode fabrication process to be reduced.

[0021] In one embodiment of the disclosed invention, the slurry baking step and the graphene oxide reduction step are carried out. The heat temperature must be such that the polyimide (or more precisely, the polyimide precursor) used as the binder is not decomposed. This prevents the binder from being decomposed. By heating at a temperature where decomposition does not occur, destruction of the electrodes can be suppressed. Therefore, it is possible to prevent the reliability of the lithium secondary battery from being reduced.

[0022] In addition, reduced graphene oxide has low dispersibility and is difficult to disperse as an active material (for example, in Non-Patent Document 1, silicon dioxide). When the reduced graphene oxide was mixed with the active carbon nanoparticles, The materials may not be mixed uniformly. Reduced graphene oxide and active material may not be mixed uniformly. If this is not done, there is a risk that the electrical characteristics of the manufactured lithium secondary battery will be poor.

[0023] Graphene oxide is formed by oxidizing graphite, but this oxidation The formed functional groups contribute to the dispersibility of graphene oxide, making it highly dispersible. In the process of reducing graphene oxide, the functional groups that contribute to the dispersibility are reduced. Therefore, the dispersibility of reduced graphene oxide is low.

[0024] After mixing graphene oxide with an active material, the mixture is heated to form an electrode (negative electrode). In the case of graphene oxide, the functional groups are dispersed before being reduced, and the functional groups are reduced. The graphene oxide particles are uniformly dispersed. Secondary batteries have the advantage of having high electrical properties.

[0025] One embodiment of the disclosed invention is a method for manufacturing a negative electrode active material having a graphene oxide, a plurality of particles, and a polyimide. The precursors of the cathode are mixed to form a slurry, and the slurry is applied onto a negative electrode current collector. The slurry applied to the negative electrode current collector is heated at a temperature of 200°C or higher and 400°C or lower, A method for imidizing a polyimide precursor and heating the polyimide precursor to imidize the polyimide precursor. The present invention relates to a method for manufacturing a negative electrode, which comprises reducing the graphene oxide.

[0026] One embodiment of the disclosed invention is a method for manufacturing a negative electrode active material having a graphene oxide, a plurality of particles, and a polyimide. The precursors of the cathode are mixed to form a slurry, and the slurry is applied onto a negative electrode current collector. The slurry applied to the negative electrode current collector is heated at a temperature between 200°C and 400°C. In order to imidize the precursor of the polyimide, The graphene oxide is reduced by heating to form a negative electrode, and a positive electrode is formed on the positive electrode current collector. An active material layer is formed to form a positive electrode, and an electrolyte is formed between the positive electrode and the negative electrode. The present invention relates to a method for producing a lithium secondary battery, characterized by the above.

[0027] In one embodiment of the disclosed invention, the particulate negative electrode active material is silicon particles. It is characterized by:

[0028] In one embodiment of the disclosed invention, the negative electrode current collector is made of titanium, aluminum, copper, or stainless steel. It is characterized by being a [Effects of the Invention]

[0029] According to one embodiment of the disclosed invention, the number of manufacturing steps in an electrode manufacturing process can be reduced. Cut.

[0030] Furthermore, according to one embodiment of the disclosed invention, damage to electrodes can be suppressed.

[0031] In addition, according to one embodiment of the disclosed invention, destruction of the electrodes can be suppressed, thereby achieving high reliability. A lithium secondary battery can be obtained.

[0032] According to one embodiment of the disclosed invention, a method for manufacturing a semiconductor device having uniformly dispersed reduced graphene oxide is provided. An electrode having the above structure can be obtained.

[0033] According to one embodiment of the disclosed invention, a method for manufacturing a semiconductor device having uniformly dispersed reduced graphene oxide is provided. By using such an electrode, a lithium secondary battery with excellent electrical properties can be obtained. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a flowchart showing a process for producing a negative electrode. [Figure 2] 3A and 3B are a cross-sectional view and a top view illustrating a negative electrode. [Figure 3] Cross-sectional SEM photograph of the negative electrode active material layer. [Figure 4] FIG. 1 is a diagram illustrating a coin-type lithium secondary battery. [Figure 5] 3A and 3B are a cross-sectional view and a top view illustrating a positive electrode. [Figure 6] FIG. 1 is a diagram illustrating a cylindrical lithium secondary battery. [Figure 7] FIG. 1 is a diagram illustrating an electrical device. [Figure 8] FIG. 1 is a diagram illustrating an electrical device. [Figure 9] FIG. 1 is a diagram illustrating an electrical device. [Figure 10] FIG. 2 is a graph showing charge / discharge characteristics of Example 1. [Figure 11] Cross-sectional SEM photograph of the negative electrode active material layer. [Figure 12] FIG. 10 is a graph showing charge / discharge characteristics of Example 2. [Figure 13] FIG. 10 is a diagram showing charge / discharge characteristics of a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, embodiments of the invention disclosed in this specification will be described with reference to the drawings. The invention disclosed herein can be embodied in many different forms, and Various changes in form and details may be made without departing from the spirit and scope of the invention disclosed herein. It will be readily understood by those skilled in the art that the present invention can be modified in various ways. In the drawings shown below, the same parts or similar functions are The same reference numerals are used to designate parts having the same functions, and the repeated explanations will be omitted. The same hatch pattern is used to refer to the following, and no specific symbol may be added.

[0036] The position, size, range, etc. of each component shown in the drawings may be changed to make the explanation easier to understand. Therefore, the actual location, size, range, etc. may not be shown. The invention is not necessarily limited to the position, size, range, etc. disclosed in the drawings, etc.

[0037] In this specification, ordinal numbers such as "first," "second," and "third" are used to avoid confusion of components. It should be noted that the numbers are added to avoid confusion and are not intended to limit the number.

[0038] [Embodiment 1] In this embodiment, first, a negative electrode of a lithium secondary battery and a method for manufacturing the same will be described with reference to FIG. This is explained below.

[0039] <Method for producing the negative electrode> First, a method for producing graphene oxide will be described. Graphite powder is subjected to oxidation reaction by adding a sulfuric acid solution of potassium permanganate and hydrogen peroxide. The graphite oxide dispersion can be prepared by reacting the graphite oxide with the silica gel to prepare a dispersion containing the graphite oxide. The graphite oxide is formed by oxidation of the carbon in the graphite, forming epoxy groups and carbonyl groups. It has functional groups such as carboxyl groups and hydroxyl groups.

[0040] In addition, since graphite oxide has the above-mentioned functional groups, the interlayers of multiple graphenes The distance is longer compared to graphite.

[0041] Next, ultrasonic vibrations were applied to the dispersion containing graphite oxide to form oxide particles with long interlayer distances. The graphite oxide is cleaved to separate the graphene oxide, and a dispersion containing the graphene oxide is obtained. Then, the solvent is removed from the dispersion containing graphene oxide. In this way, graphene oxide can be obtained (step S101).

[0042] In a polar solution, graphene oxide is negatively charged due to its functional groups. Therefore, in a polar liquid, Graphene oxide is easily dispersed uniformly.

[0043] The length of one side of the graphene oxide used (also called the flake size) is several μm to several tens of μm. It is preferable that m.

[0044] In this specification, graphene refers to a material having pores that allow ions such as lithium to pass through. A single flake consisting of one atomic layer of carbon molecules, or 2 to 100 of the single flake The laminated body can also be called reduced multilayer graphene. Cut.

[0045] Single-layer graphene (a thin sheet made up of the above single atomic layer of carbon molecules) has The six-membered rings are spread in the plane direction, and some of them are seven-membered rings, eight-membered rings, nine-membered rings, ten-membered rings, etc. Some carbon bonds in the six-membered ring are broken to form a multi-membered ring.

[0046] In this specification, graphene oxide refers to a compound having an oxide in a multi-membered ring such as a six-membered ring composed of carbon. Graphene is a compound in which elementary atoms are bonded together, specifically, a six-membered ring or multi-membered ring composed of carbon. Graphene having epoxy groups, carbonyl groups, carboxyl groups, or hydroxyl groups bonded to the ring Therefore, graphene oxide is made up of carbon, oxygen, and nitrogen atoms. The ratio of the atoms is more than 15 atomic %. Therefore, graphene oxide salt may be formed. The graphene oxide salt may be, for example, , epoxy groups, carbonyl groups, and carbonyl groups bonded to multi-membered rings such as six-membered rings composed of carbon. It is a salt in which an ammonium group, an amino group, an alkali metal, etc. is bonded to an xyl group or a hydroxyl group. Therefore, in this specification, "graphene oxide" includes "graphene oxide salt." The graphene oxide and the graphene oxide salt may be a single thin flake or a single sheet of the same. The laminate includes 2 to 100 thin flakes stacked together, and the laminate is made of multi-layer graphene oxide and It can also be called multilayer graphene oxide salt.

[0047] In this specification, reduced graphene oxide refers to a graphene in which the π bonds between carbon atoms are formed by reduction. (i.e., sp 2 It can be said that graphene oxide has The graphene oxide has C=C bonds, C-C bonds or C-H bonds, C-O bonds, It is preferable that the ratio of C=C bonds to the sum of =O bonds and O=CO bonds is 5% or more. stomach.

[0048] Reduced graphene oxide is a material that has been reduced to a lower oxygen content. The graphene oxide has a reduced amount of carbon atoms and oxygen atoms. The ratio of oxygen atoms to the sum of oxygen atoms and nitrogen atoms is 2 atomic % or more and 20 atomic % or less, preferably It is 3 atomic % or more and 15 atomic % or less.

[0049] In addition, the reduced graphene oxide is derived from the π bond formed between carbon atoms by reduction. It can also be said that the graphene oxide has improved electrical conductivity. is 10 -6 It is preferable that the value is S / m or more.

[0050] The graphene oxide was commercially available graphene oxide or a commercially available graphene oxide dispersion. It may be used.

[0051] Next, the particulate negative electrode active material, graphene oxide, and binder are mixed (step S10 2).

[0052] As described above, the negative electrode active material is a material that can absorb and release carrier ions, such as silicon. Silicon absorbs about 10 times more carrier ions than carbon. Since it is possible to store a large amount of electricity, the theoretical capacity is large, which is advantageous in terms of increasing the capacity of the storage device. Excellent.

[0053] In addition to silicon, other negative electrode active materials include, for example, lithium, aluminum, and carbon-based The material may be tin, tin oxide, silicon oxide, silicon carbide, a silicon alloy, or germanium. Alternatively, lithium, aluminum, carbonaceous materials, tin, tin oxide, etc. can be used. Choose from: silicon, silicon oxide, silicon carbide, silicon alloys, and germanium The compound may contain one or more of silicon, silicon alloy, germanium, lithium, etc. Lithium, aluminum, and tin are more capable of absorbing lithium ions than carbon-based materials. This is preferable because it has a large capacity.

[0054] In this embodiment, silicon particles are used as the particulate negative electrode active material.

[0055] The active material refers to a material involved in the insertion and desorption of ions, which act as carriers. When preparing a cathode or anode, conductive additives, binders, The active material layer is formed on the current collector by mixing the active material with other materials such as a solvent. Therefore, the positive electrode active material and the positive electrode active material layer, and the negative electrode active material and The negative electrode active material layer is distinguished.

[0056] Silicon has lower conductivity than carbon, and the amorphous state caused by charging and discharging further increases the electrical conductivity. However, the electrical conductivity of the negative electrode using silicon as the active material is reduced. Since graphene has high conductivity, the carrier Graphene, where ions pass through, can speed up the movement of electrons. In other words, graphene also functions as a conductive additive. Because of this, by covering multiple silicon particles with graphene, the silicon contained in the active material layer can be In other words, graphene also functions as a binder. By covering multiple silicon particles with graphene, the amount of silicon contained in the active material layer can be increased. It is possible to increase the number of carriers, and the movement of carrier ions is easier than with graphite. As a result, the conductivity of the carrier ions can be increased, and the silicon, which is the active material, It is possible to increase the reactivity of ions and carrier ions, and the carrier ions are attached to silicon. Therefore, in a non-aqueous secondary battery using the negative electrode, rapid charge and discharge This becomes possible.

[0057] In this embodiment, a binder having high heat resistance, such as polyimide, is used as the binder. However, the material mixed in the mixing step (step S102) is polyimide. In the subsequent heating step, the precursor is imidized to form polyimide.

[0058] The method for mixing the particulate negative electrode active material, graphene oxide, and binder includes, for example, A specific method is, for example, a ball mill treatment. A solvent is added to the graphene oxide and the binder (step S103), and a metal or ceramic The material is placed in a container along with the balls made of PET bottles and the container is rotated. This allows the particulate negative electrode active material, graphene oxide, and binder to be mixed and simultaneously microparticulated. This allows the electrode material to be finely divided after fabrication. By performing the treatment, raw materials of particulate negative electrode active material, graphene oxide, and binder are It is possible to mix the raw materials uniformly. In addition, the raw materials do not dissolve in the solvent, but are dispersed in the solvent. In this embodiment, the negative electrode active material is a polymer having an average particle size of 60 nm. Silicon particles are used, and graphene oxide is used as a conductive additive and binder, and polyimide is used as a binder. The weight ratio of the two materials was 40:40:20. The masses of the silicon particles and graphene oxide, which are the electrode active materials, are the same. In this state, N-methylpyrrolidone (N-methylpyrrolidone) is used as the solvent. (NMP) is used.

[0059] Through the above steps, the particulate negative electrode active material, graphene oxide, binder, and solvent were mixed. A slurry is formed (step S104).

[0060] Next, the slurry is applied onto the negative electrode current collector (step S105). A drying step is performed to remove the solvent by drying the substrate (step S106). For example, it can be carried out in a dry atmosphere at room temperature. If it is removable, the drying step is not necessarily required.

[0061] The negative electrode current collector is made of a conductive material such as titanium, aluminum, copper, or stainless steel in the form of a foil, plate, or mesh. In this embodiment, the negative electrode current collector is made of titanium. Use foil.

[0062] Next, the negative electrode current collector coated with the slurry is heated. The temperature is 200°C or higher and 400°C or lower, preferably 300°C, and the heating time is 1 hour or higher and 2 hours or lower. The heating step is carried out for a period of time not longer than 1 hour, preferably 1 hour. The slurry is baked by the heating step, and the poly The imide precursor is imidized to form polyimide. At the same time, the heating step The graphene oxide can be reduced to form graphene (step S107). In this manner, the negative electrode active material layer is formed.

[0063] According to this embodiment, the heating step for firing the slurry is replaced with the heating step for reducing graphene oxide. Therefore, it is not necessary to perform the heating process twice. It is possible to reduce it.

[0064] In this embodiment, the heating steps for firing the slurry and reducing the graphene oxide are performed by A temperature at which the adhesive does not decompose, for example, a temperature of 200°C or higher and 400°C or lower, preferably 300°C or lower This prevents the binder from being decomposed. By heating at a temperature that does not cause damage to the negative electrode, damage to the negative electrode can be prevented. This makes it possible to prevent the reliability of the lithium secondary battery from being reduced.

[0065] In addition, as mentioned above, the reduced graphene oxide has low dispersibility, and the active material and the reduced graphene oxide When graphene is mixed, there is a risk that the reduced graphene oxide and the active material will not be mixed uniformly. If the reduced graphene oxide and the active material are not mixed uniformly, the lithium There is a risk that the electrical characteristics of the secondary battery will be poor.

[0066] Graphene oxide is formed by oxidizing graphite, but this oxidation The formed functional groups contribute to the dispersibility of graphene oxide, making it highly dispersible. In the process of reducing graphene oxide, the functional groups that contribute to the dispersibility are reduced. Therefore, the dispersibility of reduced graphene oxide is low.

[0067] After mixing graphene oxide with an active material, the mixture is heated to form an electrode (negative electrode). In the case of graphene oxide, the functional groups are dispersed before being reduced, and the functional groups are reduced. The graphene oxide is uniformly dispersed. Secondary batteries have the advantage of having high electrical properties.

[0068] By the above-described manufacturing process, a negative electrode having a negative electrode active material layer formed on a negative electrode current collector is formed. (Step S108).

[0069] <Negative electrode structure> The negative electrode fabricated by the above-described fabrication process is shown in FIG. 2. FIG. 2(A) is a cross-sectional view of the negative electrode 101. The negative electrode 101 has a negative electrode active material layer 109 formed on a negative electrode current collector 107. The body 107 may be a negative electrode current collector made of the above-mentioned material and having the above-mentioned shape.

[0070] FIG. 2B shows a negative electrode active material layer 109 made of particles capable of absorbing and releasing carrier ions. a negative electrode active material 121 in a shape of a powder; and a negative electrode active material 121 in a shape of a powder while covering the negative electrode active material 121. Graphene 123 (the reduced graphene oxide) with 1 packed inside, and a binder 1 is a top view of a negative electrode active material layer 109 configured by a plurality of negative electrode active materials 121 having different surfaces. The negative electrode active material 121 is covered with graphene 123. good.

[0071] Furthermore, sufficient characteristics can be obtained even if the surface of the negative electrode active material 121 is not covered with the graphene 123. However, when the graphene 123 sufficiently covers the negative electrode active material 121, the carrier This is more preferable because the on-state hops between the negative electrode active materials 121, making it easier for current to flow.

[0072] FIG. 2(C) is a cross-sectional view of a part of the negative electrode active material layer 109 in FIG. 2(B). The negative electrode active material 121 is covered with a graphene 123. The graphene is observed as a line in the cross-sectional view. That is, the negative electrode active material 121 is formed by the same graphene or by a plurality of graphene particles. A plurality of particles of the negative electrode active material 121 are present between the graphenes. In some cases, a plurality of negative electrode active materials 121 are contained therein. There are cases where the negative electrode active material 121 is not covered by the gate 123 and is partly exposed.

[0073] In addition, the negative electrode active material 121 expands in volume due to the absorption of carrier ions, and The negative electrode active material layer 109 may become brittle, causing a portion of the negative electrode active material layer 109 to collapse. If a part of the negative electrode active material layer 109 collapses, the reliability of the power storage device will decrease. Even if the negative electrode active material 121 expands in volume due to charge and discharge, the graphene 123 surrounds the negative electrode active material 121. Therefore, the graphene 123 prevents the dispersion of the negative electrode active material 121 and the collapse of the negative electrode active material layer 109. That is, the graphene 123 can prevent the negative electrode active material 12 from being broken down during charging and discharging. Even if the volume of the negative electrode active material 121 increases or decreases, the negative electrode active material 121 has a function of maintaining the bond between itself.

[0074] The graphene 123 is in contact with the plurality of negative electrode active material particles 121 and serves as a conductive additive. In addition, the negative electrode active material 121 has a function of holding the negative electrode active material 121, which can store and release carrier ions. Therefore, by increasing the proportion of the negative electrode active material in the negative electrode active material layer 109, This makes it possible to increase the discharge capacity of the lithium secondary battery.

[0075] 3 is a cross-sectional SEM photograph of the negative electrode active material layer 109 of this embodiment. The photo shows multiple silicon particles sandwiched between multiple layers of graphene. In other words, the silicon particles are held together by the graphene layers. This allows the silicon to be covered with highly conductive graphene, which allows electrons to pass through. It can also absorb about 10 times more carrier ions than carbon. Silicon absorbs carrier ions, but the expansion rate of the volume increases due to the absorption of carrier ions. However, as described above, the plurality of silicon particles are covered with graphene. Therefore, the silicon particles are dispersed, and the dispersed silicon particles form the negative electrode active material layer 1. It is possible to prevent 09 from collapsing.

[0076] As described above, according to this embodiment, the number of manufacturing steps in the electrode manufacturing process can be reduced.

[0077] Furthermore, according to this embodiment, destruction of the electrodes can be suppressed.

[0078] Furthermore, according to this embodiment, destruction of the electrodes is suppressed, thereby providing a highly reliable power storage device. can be obtained.

[0079] Furthermore, according to this embodiment, an electrode having uniformly dispersed reduced graphene oxide can be obtained. can be obtained.

[0080] Furthermore, according to this embodiment, an electrode having uniformly dispersed reduced graphene oxide can be obtained. By using this, a lithium secondary battery with excellent electrical characteristics can be obtained.

[0081] [Embodiment 2] In this embodiment, a structure of a lithium secondary battery and a manufacturing method thereof will be described below. do.

[0082] FIG. 4(A) is an external view of a coin-type (single-layer flat type) lithium secondary battery, and FIG. 4(B) ) is a cross-sectional view thereof.

[0083] The coin-type lithium secondary battery 600 has a positive electrode can 603 that also serves as a positive electrode terminal and a negative electrode can 604 that also serves as a negative electrode terminal. The negative electrode can 601 is insulated and sealed with a gasket 602 made of polypropylene or the like. The positive electrode 610 is composed of a positive electrode current collector 608 and a positive electrode active material layer provided in contact with the positive electrode current collector. On the other hand, the negative electrode 609 is formed by a negative electrode current collector 604 and a The cathode active material layer 607 and the anode active material layer 605 are formed. Between the separator 606 and the electrode 605 is a non-aqueous electrolyte (not shown). do.

[0084] The negative electrode may be formed using the negative electrode 101 described in Embodiment 1 as appropriate.

[0085] The positive electrode current collector 608 and the positive electrode active material layer 607 are respectively the positive electrode current collector and the positive electrode active material shown below. A porous layer can be used as appropriate.

[0086] The positive electrode current collector 608 may be made of stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, etc. Highly conductive materials such as metals and alloys thereof can be used. Elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, are added. Aluminum alloys that react with silicon to form silicide can also be used. The metal element may be a metal element that reacts with silicon to form silicide. These include zirconium, titanium, hafnium, vanadium, niobium, tantalum, and chromium. , molybdenum, tungsten, cobalt, nickel, etc. The positive electrode current collector 608 is a foil , plate (sheet), mesh, punched metal, expanded metal, etc. It can be used.

[0087] The positive electrode active material layer 607 is made of LiFeO2, LiCoO2, LiNiO2, LiMn2O4, Compounds such as V2O5, Cr2O5, and MnO2 can be used as materials.

[0088] Alternatively, a lithium-containing composite oxide having an olivine-type structure (general formula LiMPO4 (M is one or more of Fe( II), Mn(II), Co(II), Ni(II))) can be used. . Representative examples of the general formula LiMPO4 include LiFePO4, LiNiPO4, LiCoP O4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO 4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 [[ID=5�]]< e < 1), LiFe f Ni g Co h Mn i [[ID=dž4]]PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc., can be used as materials.

[0089] Alternatively, a composite oxide such as the general formula Li (2-j) MSiO4 (M is one or more of Fe(II), Mn(II), Co( II), Ni(II), 0 ≦ j ≦ 2) can be used. One general formula Li​(2-j) As representative examples of MSiO4, Li (2-j) FeSiO4, Li ( 2-j) NiSiO4, Li (2-j) CoSiO4, Li (2-j) MnSiO4, L i (2-j) Fe k Ni l SiO4, Li (2-j) Fe k Co l SiO4, Li (2- j) Fe k Mn l SiO4, Li (2-j) Ni[[ID=?]] k [[ID=?]]Co[[ID=?]] l [[ID=?]]SiO4, Li[[ID=?]] (2-j) [[ID=?]]Ni[[ID=?]] [[ID=?]] k [[ID=?]]Mn[[ID=?]] l [[ID=?]]SiO4 (k + l is 1 or less, 0 < k < 1, 0 < l < 1), Li[[ID=?]] (2-j) [[ID=?]]Fe[[ID=?]] m [[ID=?]] [[ID=?]]Ni[[ID=?]] n [[ID=?]]Co[[ID=?]]<000005?]] q [[ID=?]]SiO4, Li[[ID=?]] (2-j) [[ID=?]]Fe[[ID=?]] m [[ID=?]]Ni[[ID=?]] n [[ID=?]]Mn[[ID=?]] q [[ID=?]]SiO4, Li[[ID=?]] (2-j) [[ID=?]]N[[ID=?]] [[ID=?]]i[[ID=?]] m [[ID=?]]Co[[ID=?]] n [[ID=?]]Mn[[ID=?]] q [[ID=?]]SiO4 (m + n + q is 1 or less, 0 < m < 1, 0 < n < 1, 0 < q < 1[[ID=?]] [[ID=?]]), Li[[ID=?]] (2-j) [[ID=?]]Fe[[ID=?]] r [[ID=?]]Ni[[ID=?]] s [[ID=?]]Co[[ID=?]] t [[ID=?]]Mn[[ID=?]] u [[ID=?]]SiO4 (r + s + t + u is 1 or less, 0 <[[ID=?]] [[ID=?]]r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1) etc. can be used as materials. [[ID=?]] [[ID=?]] [[ID=?]]

[0090] [[ID=?]] [[ID=?]]Note that the carrier ion is an alkali metal ion other than lithium ion, an alkaline earth metal[[ID=?]] Some of the "?" marked lines seem to have incorrect or incomplete tags in the original. Please check and correct if possible for a more accurate translation.In the case of ions, beryllium ions, or magnesium ions, the positive electrode active material layer 607 In the above lithium compounds and composite oxides, an alkali metal ( sodium and potassium), alkaline earth metals (e.g., calcium, strontium, etc.), Alternatively, titanium, barium, beryllium, or magnesium may be used.

[0091] The positive electrode active material layer 607 is not limited to being formed directly on the positive electrode current collector 608. Between the positive electrode current collector 608 and the positive electrode active material layer 607, The adhesive layer is designed to improve adhesion with 07, and the surface irregularities of the positive electrode current collector 608 are reduced. a planarizing layer for dissipating heat, a heat dissipation layer for dissipating heat, a positive electrode current collector 608 or a positive electrode active material layer 607 A functional layer such as a stress relief layer for relieving stress may be formed using a conductive material such as metal. good.

[0092] The positive electrode active material layer 607 is formed of graphene, similarly to the negative electrode active material layer 109 in Embodiment 1. The case where the positive electrode active material layer 607 contains graphene will be described below. will be explained.

[0093] FIG. 5(A) shows a positive electrode current collector 608 and a positive electrode active material layer 607 provided in contact with the positive electrode current collector. 5B is a cross-sectional view of a positive electrode 610 having a carrier A particulate positive electrode active material 303 capable of absorbing and releasing ions and a plurality of the positive electrode active materials 303 The positive electrode active material 303 is packed in the graphene 304. 6 is a top view of an active material layer 607. The surfaces of the plurality of positive electrode active materials 303 are covered with different graphenes 30 In addition, the positive electrode active material 303 may be partially exposed.

[0094] Furthermore, sufficient characteristics can be obtained even if the surface of the positive electrode active material 303 is not covered with the graphene 304. However, when the positive electrode active material 303 covered with graphene 304 is used, the carrier This is more preferable because ions hop between the positive electrode active materials 303, facilitating the flow of current.

[0095] FIG. 5C is a cross-sectional view of a part of the positive electrode active material layer 607 in FIG. 5B. The positive electrode active material 303 is covered with graphene 304. The graphene is observed as a line in the cross-sectional view. In other words, the positive electrode active material is contained in the same graphene or between multiple graphenes. The graphene has a bag-like shape, and a plurality of positive electrode active materials are present inside the bag-like shape. In some cases, a plurality of positive electrode active materials are enclosed within the graphene. Material may be exposed.

[0096] The positive electrode active material layer 607 is formed of acetylene having a volume that is 0.1 to 10 times the volume of graphene. Carbon particles such as black particles and carbon nanofibers with one-dimensional expansion are The conductive material may contain a conductive additive.

[0097] The separator 606 may be made of cellulose (paper), or porous polypropylene, An insulator such as polyethylene can be used.

[0098] The solute of the non-aqueous electrolyte is a material having carrier ions. Typical examples of solutes of non-aqueous electrolytes Examples include LiClO4, LiAsF6, LiBF4, LiPF6, and Li(C2F5SO 2) There are lithium salts such as 2N.

[0099] In addition, the carrier ions are alkali metal ions other than lithium ions, alkaline earth metal ions, etc. ions, beryllium ions, or magnesium ions as solutes in non-aqueous electrolytes In the lithium salt, an alkali metal (e.g., sodium or potassium, etc.), alkaline earth metals (e.g., calcium, strontium, barium, etc.) , beryllium, or magnesium may also be used.

[0100] In addition, a material capable of transporting carrier ions is used as the solvent for the non-aqueous electrolyte. The solvent for the solution is preferably an aprotic organic solvent. Representative examples of aprotic organic solvents are: Examples include ethylene carbonate (EC), propylene carbonate, and dimethyl carbonate. diethyl carbonate (DEC), γ-butyrolactone, acetonitrile, dimethicone Examples of the methyl ether include methyl ethane and tetrahydrofuran, and one or more of these can be used. In addition, by using a polymer material that gels as a solvent for the non-aqueous electrolyte, it is possible to reduce leakage and other issues. This improves safety against electrolytic degradation. It also makes it possible to make non-aqueous secondary batteries thinner and lighter. Typical examples of polymeric materials are silicone gel, acrylic gel, and acrylonitrile. Gel, polyethylene oxide, polypropylene oxide, fluorine-based polymer, etc. In addition, ionic liquids (room-temperature molten salts), which are flame-retardant and non-volatile, are used as solvents for non-aqueous electrolytes. By using one or more of these, the internal temperature of the secondary battery can be prevented from rising due to an internal short circuit or overcharging. Even if the temperature rises, the secondary battery can be prevented from exploding or catching fire.

[0101] In addition, instead of non-aqueous electrolytes, solid electrolytes containing inorganic materials such as sulfides or oxides are used. It is possible to use a solid electrolyte containing a polymer material such as PEO (polyethylene oxide). When a solid electrolyte is used, there is no need to install a separator or spacer. Since the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.

[0102] The positive electrode can 603 and the negative electrode can 601 are made of corrosion-resistant materials such as iron, nickel, aluminum, and titanium. These metals, or their alloys or alloys of these with other metals (stainless steel, etc.) are used. In particular, in order to prevent corrosion caused by the non-aqueous electrolyte solution that occurs during charging and discharging of the secondary battery, It is preferable to plate the corrosive metal such as nickel on the cathode can 603. The negative electrode cans 601 are electrically connected to the negative electrodes 609, respectively.

[0103] The negative electrode 609, the positive electrode 610, and the separator 606 are impregnated with a non-aqueous electrolyte solution, and the negative electrode 609, the positive electrode 610, and the separator 606 are then immersed in a non-aqueous electrolyte solution. ) the positive electrode can 603 is placed downwards, and the positive electrode 610, separator 606, negative electrode 609, The positive electrode can 603 and the negative electrode can 601 are stacked in this order, and the positive electrode can 603 and the negative electrode can 601 are secured together with a gasket 602 interposed therebetween. Then, the laminate is pressed to manufacture a coin-type lithium secondary battery 600.

[0104] In addition, a lithium secondary battery having a structure different from that shown in FIG. 4 will be described below.

[0105] The structure of a cylindrical non-aqueous secondary battery will be described with reference to Figs. 6(A) and 6(B). As shown in FIG. 6(A), the lithium secondary battery 700 has a positive electrode cap (battery lid) 70 on the top surface. 1, and a battery can (external can) 702 on the side and bottom. The battery case (external case) 702 is insulated by a gasket (insulating packing) 710. do.

[0106] FIG. 6(B) is a schematic diagram showing the cross section of a cylindrical lithium secondary battery. Inside the battery can 702, a strip-shaped positive electrode 704 and a negative electrode 706 are placed with a separator 705 in between. The battery element is wound around the center pin (not shown). The battery can 702 is closed at one end and open at the other. 02 is made of corrosion-resistant metals such as iron, nickel, aluminum, titanium, or Alloys and alloys of these with other metals (such as stainless steel) can be used. To prevent corrosion caused by non-aqueous electrolytes during charging and discharging of the battery, nickel and other corrosive metals are used. It is preferable to plate the positive electrode, the negative electrode and the separator on the inside of the battery can 702. The battery element with the coil wound around it is sandwiched between a pair of opposing insulating plates 708 and 709. The inside of the battery can 702 in which the battery element is provided is filled with a non-aqueous electrolyte (not shown). The non-aqueous electrolyte used is the same as that used in the coin-type lithium secondary battery described above. It is possible.

[0107] The positive electrode 704 and the negative electrode 706 are the same as the positive electrode and the negative electrode of the coin-type lithium secondary battery described above. However, the positive and negative electrodes used in cylindrical lithium secondary batteries are wound up, The negative electrode 706 differs from the negative electrode 702 in that an active material is formed on both surfaces of a current collector. By using the negative electrode, a high capacity secondary battery can be manufactured. A positive electrode terminal (positive electrode current collecting lead) 703 is connected to the negative electrode 706. The positive terminal 703 and the negative terminal 707 are both made of aluminum or the like. The positive terminal 703 is connected to the safety valve mechanism 712, and the negative terminal 70 7 are resistance welded to the bottom of the battery can 702. The safety valve mechanism 712 is Positive via 1 (Positive Temperature Coefficient) The safety valve mechanism 712 is electrically connected to the electrode cap 701. When a certain threshold is exceeded, the electrical connection between the positive electrode cap 701 and the positive electrode 704 is cut off. The PTC element 711 is a thermally sensitive resistor whose resistance increases when the temperature rises. It is a PTC element that limits the amount of current by increasing the resistance, preventing abnormal heat generation. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the element. do.

[0108] In this embodiment, the lithium secondary battery is a coin-type or cylindrical non-aqueous secondary battery. Although the battery shown here is a sealed non-aqueous secondary battery, there are various types of non-aqueous secondary batteries, such as a prismatic non-aqueous secondary battery. In addition, a structure in which a positive electrode, a negative electrode, and a separator are stacked in multiple layers, The electrode, the negative electrode, and the separator may be wound together.

[0109] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0110] [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.

[0111] Specific examples of electrical appliances using a lithium secondary battery according to one embodiment of the present invention include televisions, monitors, and the like. display devices such as LCDs, lighting devices, desktop or notebook personal computers, Word processors, DVD (Digital Versatile Disc) and other recording media Image playback devices that play back still images or videos stored on recording media, portable CD players, Radios, tape recorders, headphone stereos, stereos, table clocks, wall clocks, Dress telephone handsets, transceivers, portable radios, mobile phones, car phones, portable game consoles, Calculators, mobile information terminals, electronic organizers, e-books, electronic translators, voice input devices, video cameras, Digital still cameras, electric shavers, microwave ovens and other high-frequency heating devices, electric rice cookers, Washing machines, vacuum cleaners, water heaters, electric fans, hair dryers, air conditioners, humidifiers, Air conditioning equipment such as dehumidifiers, dishwashers, dish dryers, clothes dryers, futon dryers, electric refrigerators , electric freezers, electric refrigerator-freezers, freezers for storing nucleic acids, flashlights, tools such as chainsaws, Examples include medical equipment such as smoke detectors and dialysis machines. conveyors, elevators, escalators, industrial robots, power storage systems, power leveling and industrial equipment such as power storage devices for smart grids. Vehicles propelled by electric motors using electricity from a pond are also included in the category of electrical equipment. The above-mentioned moving body may be, for example, an electric vehicle (EV), a vehicle that has both an internal combustion engine and an electric motor. Hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and Tracked vehicles with wheels replaced with tracks, motorized bicycles including electrically assisted bicycles, and motorcycles. Wheeled vehicles, electric wheelchairs, golf carts, small or large boats, submarines, helicopters, and aircraft Examples include rockets, satellites, space probes, planetary probes, and spacecraft.

[0112] The electrical equipment is powered by a power supply according to one embodiment of the present invention. Alternatively, the electric device may be provided with a lithium secondary battery according to the present invention. When the power supply from the commercial power source is stopped, it is possible to supply power to electrical equipment. The lithium secondary battery according to one embodiment of the present invention can be used as the uninterruptible power supply. Alternatively, the electrical equipment may be supplied with power from the main power source or commercial power source in parallel with the supply of power to the electrical equipment. The lithium battery according to one embodiment of the present invention is used as an auxiliary power source for supplying power to an electrical device. A secondary battery can be used.

[0113] 7 shows a specific configuration of the above-mentioned electric device. In FIG. 7, a display device 8000 is 8 is an example of an electrical device using a lithium secondary battery 8004 according to one embodiment of the present invention. The display device 8000 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 800 2, a speaker unit 8003, a lithium secondary battery 8004, etc. The lithium secondary battery 8004 is provided inside the housing 8001. The power supply can be supplied from a commercial power source or stored in a lithium secondary battery 8004. Therefore, if power is not supplied from the commercial power source due to a power outage or other reason, Even when the power is not available, the lithium secondary battery 8004 according to one embodiment of the present invention can be used as an uninterruptible power supply. By using this, the display device 8000 can be used.

[0114] The display unit 8002 includes a liquid crystal display device, an emitting device having a light emitting element such as an organic EL element in each pixel, and 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.

[0115] In addition to TV broadcast reception, display devices are also used for personal computers and advertising displays. , including all display devices for displaying information.

[0116] In FIG. 7, a stationary lighting device 8100 includes a lithium secondary battery according to one embodiment of the present invention. 8103. Specifically, the lighting device 8100 is an example of an electric device using a battery 8103. 1, a light source 8102, a lithium secondary battery 8103, etc. In FIG. 8103 is provided inside the ceiling 8104 on which the housing 8101 and the light source 8102 are installed. The lithium secondary battery 8103 is installed inside the housing 8101. The lighting device 8100 may be supplied with power from a commercial power source. It is also possible to use the power stored in the lithium secondary battery 8103. 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 8100 can be used by using the lithium secondary battery 8103 as an uninterruptible power supply. This becomes:

[0117] 7 illustrates a lighting device 8100 that is a fixed type provided on a ceiling 8104. However, in the lithium secondary battery according to one embodiment of the present invention, the side wall 8105, for example, is not included in the ceiling 8104. It can also be used in a fixed lighting device provided on a floor 8106, a window 8107, etc. It can also be used as a tabletop lighting device.

[0118] The light source 8102 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.

[0119] In FIG. 7, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is 8 is an example of an electrical device using a lithium secondary battery 8203 according to one embodiment of the present invention. The indoor unit 8200 includes a housing 8201, an air outlet 8202, a lithium secondary battery 8203, etc. In FIG. 7, the lithium secondary battery 8203 is installed in the indoor unit 8200. Although shown as an example, the lithium secondary battery 8203 may be provided in the outdoor unit 8204 . Alternatively, both the indoor unit 8200 and the outdoor unit 8204 are provided with a lithium secondary battery 8203. The air conditioner may be powered by a commercial power source. In addition, the power stored in the lithium secondary battery 8203 can also be used. If both the 8200 and the outdoor unit 8204 are equipped with a lithium secondary battery 8203, 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 Um secondary battery 8203 as an uninterruptible power supply, the use of air conditioners It becomes possible.

[0120] In Figure 7, 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.

[0121] In FIG. 7, an electric refrigerator-freezer 8300 includes a lithium secondary battery 83 according to one embodiment of the present invention. 8300 is an example of an electric appliance using the housing 830 1, a refrigerator door 8302, a freezer door 8303, a lithium secondary battery 8304, etc. In FIG. 7, a lithium secondary battery 8304 is provided inside a housing 8301. The Refrigerator 8300 can be powered by commercial power or by lithium secondary batteries. It is also possible to use the power stored in the battery 8304. Even when power cannot be supplied from the By using it as an uninterruptible power supply, it becomes possible to use the electric refrigerator-freezer 8300.

[0122] 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.

[0123] 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 8300, the temperature is low and the refrigerator compartment During the night when the door 8302 and the freezer door 8303 are not opened or closed, the lithium secondary battery 8 As the temperature rises, the refrigerator door 8302 and the freezer door 83 During the daytime when the 03 is opened and closed, a lithium secondary battery 8304 is used as an auxiliary power source. This allows for lower electricity usage during the day.

[0124] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0125] [Embodiment 4] Next, a portable information terminal, which is an example of an electrical device, will be described with reference to FIG.

[0126] Figures 8(A) and 8(B) show tablet terminals that can be folded in half. The tablet terminal is in a state where the display unit 9631a is in a housing 9630. 1b, display mode switch 9034, power switch 9035, power saving mode switch It has a replacement switch 9036, a fastener 9033, and an operating switch 9038.

[0127] A part of the display unit 9631a can be used as a touch panel area 9632a. By touching the operation keys 9638, data can be input. In 1a, for example, half of the area has a display function only, and the other half The display unit 963 has a touch panel function, but is not limited to this. The entire area of ​​the display unit 96 may have a touch panel function. The entire surface of 31a is displayed as a keyboard button to serve as a touch panel, and the display part 9631b is displayed. It can be used as a screen.

[0128] In addition, in the display unit 9631b, as in the display unit 9631a, a part of the display unit 9631b The area 9632b of the touch panel can be used as the keyboard of the touch panel. By touching the area where the display switch button 9639 is displayed with your finger or a stylus, A keyboard can be displayed on the display portion 9631b.

[0129] In addition, touch panel area 9632a and touch panel area 9632b can be touched simultaneously. You can also input characters using the touchpad.

[0130] The display mode switch 9034 is used to change the display orientation, such as portrait or landscape. You can switch between black and white and color display. The Switch 9036 detects external light during use using a light sensor built into the tablet device. The tablet device has a light sensor, which can adjust the display brightness to suit the amount of light. In addition to sensors, other detection devices such as gyros and acceleration sensors that detect tilt are also included. It may be built-in.

[0131] FIG. 8A shows an example in which the display area of ​​the display portion 9631b is the same as that of the display portion 9631a. However, there is no particular limitation, and one size may be different from the other size. The quality may also be different. For example, one display panel may be capable of displaying images with higher resolution than the other. You may do so.

[0132] FIG. 8B shows the tablet terminal in a closed state. The tablet terminal includes a housing 9630 and a solar cell 963 3. Includes a charge / discharge control circuit 9634, a battery 9635, and a DC / DC converter 9636 8B, a battery 9635, a DCD The battery 9635 is a The lithium secondary battery has the configuration described above.

[0133] In addition, since the tablet device can be folded in half, the housing 9630 can be folded when not in use. Therefore, the display portions 9631a and 9631b can be protected, and thus the display portions 9631a and 9631b can be withstood. This makes it possible to provide a tablet terminal that is highly durable and reliable even from the perspective of long-term use.

[0134] In addition, the tablet terminals shown in Fig. 8(A) and Fig. 8(B) can store various information ( Functions that display still images, videos, text images, etc., calendars, dates, or times, etc. A function to display information on the display unit, and a touch input device to operate or edit the information displayed on the display unit by touch input. It can have functions such as the ability to control processing by various software (programs), etc. can.

[0135] The solar cell 9633 attached to the surface of the tablet terminal supplies power to the touch panel, The solar cell 9633 can be supplied to a display unit, a video signal processor, or the like. The housing 9630 is configured to efficiently charge the battery 9635 on one or both sides. The battery 9635 is preferably a lithium battery according to one embodiment of the present invention. The use of a secondary battery has the advantage of enabling miniaturization.

[0136] The configuration and operation of the charge / discharge control circuit 9634 shown in FIG. 8B will be described with reference to FIG. 8C. A block diagram is shown and explained. In FIG. 8(C), a solar cell 9633, a battery 9635, and a D CDC converter 9636, converter 9637, switches SW1 to SW3, display unit 9 631, battery 9635, DC / DC converter 9636, converter The capacitor 9637 and the switches SW1 to SW3 are connected to the charge / discharge control circuit 9634 shown in FIG. This is the corresponding location.

[0137] First, an example of operation when power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is converted to a DC power supply to charge the battery 9635. The voltage is increased or decreased by the C converter 9636. When power is being used from the solar cell 9633, switch SW1 is turned on and the converter 9 637 increases or decreases the voltage to the voltage required for the display unit 9631. When not displaying on the 9631, turn SW1 off and SW2 on to charge the battery. 635 may be configured to charge.

[0138] The solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto. Other power generation methods such as piezoelectric elements and thermoelectric conversion elements (Peltier elements) For example, the battery 9635 may be configured to be charged wirelessly (contactlessly). A wireless power transmission module that charges by transmitting power, or a structure that combines other charging methods It may also be composed.

[0139] Furthermore, if the lithium secondary battery described in the above embodiment is provided, the electric It goes without saying that there is no particular limitation on the device.

[0140] [Embodiment 5] Furthermore, an example of a moving object, which is an example of an electrical device, will be described with reference to FIG.

[0141] The lithium secondary battery described in the first and second embodiments is used as a control battery. The control battery can be powered externally using plug-in technology or wireless power supply. If the moving object is an electric rail vehicle, it can be charged by the power supply from the overhead line. It can be charged by power supply from a conductive rail.

[0142] 9(A) and 9(B) show an example of an electric vehicle. The electric vehicle 9700 includes: The lithium secondary battery 9701 is mounted on the The output is adjusted by the control circuit 9702 and supplied to the driver 9703. 02 is controlled by a processing unit 9704 having a ROM, RAM, CPU, etc. (not shown). can be.

[0143] The driving device 9703 is a DC motor or an AC motor alone, or a combination of a motor and an internal combustion engine. The processing device 9704 is configured in combination with the electric vehicle 9700. (acceleration, deceleration, stopping, etc.) and driving information (uphill and downhill slopes, etc., load on the drive wheels) Based on input information (such as cargo information), the control circuit 9702 outputs a control signal. 702 is supplied with power from a lithium secondary battery 9701 in response to a control signal from a processing unit 9704. The electric energy is adjusted to control the output of the drive unit 9703. If a power supply is used, an inverter (not shown) for converting direct current to alternating current is also built in.

[0144] The lithium secondary battery 9701 is charged by an external power supply using plug-in technology. For example, the lithium secondary battery 9701 can be charged from a commercial power source through a power plug. Charging is performed by converting a constant voltage to a direct current via a conversion device such as an AC / DC converter. The lithium secondary battery 9701 can be used as an embodiment of the present invention. By installing the lithium secondary battery, it will be possible to contribute to shortening the charging time. This will improve convenience. In addition, the improved charging and discharging speed will make it possible to It can contribute to improving the acceleration of the 9700 and contribute to improving the performance of the electric vehicle 9700. In addition, the improved characteristics of the lithium secondary battery 9701 make it possible to If the 9701 itself could be made smaller and lighter, it could contribute to reducing the weight of the vehicle.

[0145] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0146] Example 1 In this example, the electrical characteristics of a lithium secondary battery using the negative electrode described in Embodiment 1 were evaluated. explain.

[0147] The negative electrode of this example uses a titanium foil having a thickness of 15 μm as a negative electrode current collector and a negative electrode active material layer. The negative electrode active material is silicon particles (average particle size 60 nm), graphene oxide, and The mixing ratio of the binder polyimide (more precisely, the precursor of polyimide) was 40: 40:20 (wt%), more specifically, 0.08 g of silicon particles and 0.08 g of graphene oxide 0.08g of the polyimide precursor and 0.292g of the polyimide precursor were mixed. After the heating process, 13.7% of the precursor of the imide is imidized to become polyimide. The weight of the imidized polyimide is 0.04g (0.292g x 0.137). According to the manufacturing process shown in FIG. 1, a negative electrode was manufactured in which a negative electrode active material layer was formed on a negative electrode current collector. did.

[0148] The heating step (step S10 in FIG. 1) serves both to bake the slurry and reduce the graphene oxide. 7) Heat at 120°C for 0.5 hours, then increase the temperature to 250°C and keep at 250°C for 0. The pretreatment was carried out by heating for 5 hours, and then the temperature was raised to 300°C and heated at 300°C for 1 hour. A thermal process was carried out.

[0149] FIG. 10 shows the charge-discharge characteristics of a lithium secondary battery using the negative electrode prepared as described above. The results are shown for a half-cell. In the measurements, metallic lithium was used for the positive electrode. A basic cell manufactured by Japan Tomcell Co., Ltd. was used.

[0150] The electrolyte is lithium hexafluorophosphate (LiPF6) and ethylene carbonate (E The separator was dissolved in a mixed solution of PEG (PEG-100) and diethyl carbonate (DEC). Polypropylene was used for the data.

[0151] The charge-discharge characteristics shown in FIG. 10 were measured as follows. The charge and discharge of the secondary battery was carried out at 0.05C (current density 0.1A / g). This is to store as much charge as possible in the battery. After the second charge and discharge, the current is 1C ( The measurement was carried out at a density of 2 A / g. In addition, charging and discharging were carried out at a constant current. The charge / discharge voltage range was 0.03 V or more and 1 V or less. One discharge is considered as one cycle. In other words, in this example, the first cycle is performed at 0.05C. The second to tenth cycles were carried out at 1C.

[0152] Figure 10 shows the charge / discharge curves obtained from the measurements. In Figure 10, the vertical axis shows voltage and the horizontal axis shows The solid line in the figure indicates charging, and the dotted line indicates discharging. It was done 10 times.

[0153] In Figure 10, "charge" indicates charging, "discharge" indicates discharging, and the numbers indicate the number of times. For example, "Charge 5" indicates the fifth charge.

[0154] As shown in FIG. 10, the lithium secondary battery of this example was charged and discharged for the first time, and then discharged for the second time. The capacity decreases rapidly during charging and discharging. This is because the first charging and discharging is at 0.05C. In contrast, the second charge / discharge is at 1C, so this is due to the difference in rate. (For example, 0.05C) allows sufficient time for carrier ions to travel, so a large capacity is required. On the other hand, a high rate (e.g., 1 C) can be obtained compared to a high rate (e.g., 0.05 C). ) the capacity is small because the carrier ions do not have enough time to travel.

[0155] However, from the third charge / discharge onwards, the number of charge / discharge cycles increases with each charge / discharge (as the number of cycles increases). The reason for the increase in charge capacity and discharge capacity is as follows: The graphene oxide is reduced by the heat treatment described above, but the In Figure 10, there is unreduced graphene oxide remaining after the heat treatment. When the battery is first charged, the reduction of graphene oxide is insufficient. However, with each charge and discharge, With increasing cycle number, the under-reduced graphene oxide is electrically reduced. As a result, both the charge capacity and the discharge capacity increase with each charge / discharge cycle. [Example]

[0156] In this example, silicon particles having a different shape from those in Example 1 were used as the negative electrode active material. The negative electrode and the lithium secondary battery fabricated using the negative electrode are described below.

[0157] The negative electrode of this example uses a titanium foil having a thickness of 15 μm as a negative electrode current collector and a negative electrode active material layer. The negative electrode active material is silicon particles (average particle size 3 μm), graphene oxide, and The mixing ratio of the binder polyimide (more precisely, the polyimide precursor) was 40:4. 0:20 (wt%), more specifically, 0.08 g of silicon particles and 0 g of graphene oxide 0.08g, and the polyimide precursor was 0.292g (0.04g as polyimide). The materials were mixed, and a negative electrode active material layer was formed on the negative electrode current collector according to the manufacturing process shown in FIG. poles were made.

[0158] The heating step (step S10 in FIG. 1) serves both to bake the slurry and reduce the graphene oxide. 7) Heat at 120°C for 0.5 hours, then increase the temperature to 250°C and keep at 250°C for 0. The pretreatment was carried out by heating for 5 hours, and then the temperature was raised to 300°C and heated at 300°C for 1 hour. A thermal process was carried out.

[0159] The difference between this example and Example 1 is that the silicon particles, which are particulate negative electrode active materials, are Silicon particles with a particle size of 5 μm are crushed in a micronizer to produce silicon with an average particle size of 3 μm. More specifically, silicon particles with an average particle size of 5 μm (powdered silicon) are used. The silicon particles dispersed in the pure water were then heated at a pressure of 200 MPa. The particles are then subjected to 10 collisions in the device. As a result, silicon particles with an average particle size of 5 μm are crushed. As a result, silicon particles with an average particle size of 3 μm were obtained.

[0160] 11A and 11B are cross-sectional SEM photographs of the negative electrode active material layer of this example. The photo shows graphene attached to the surface of silicon particles. In Figure 11(B), a silicon particle is shown sandwiched between multiple graphene layers. It is being done.

[0161] FIG. 12 shows the charge-discharge characteristics of a lithium secondary battery using the negative electrode prepared as described above. The results are shown for a half-cell. In the measurements, metallic lithium was used for the positive electrode. A basic cell manufactured by Japan Tomcell Co., Ltd. was used.

[0162] The electrolyte is lithium hexafluorophosphate (LiPF6) and ethylene carbonate (E The separator was dissolved in a mixed solution of PEG (PEG-100) and diethyl carbonate (DEC). Polypropylene was used for the data.

[0163] The charge-discharge characteristics shown in Figure 12 were measured as follows. First, the first charge-discharge This was carried out at 0.05C (current density 0.1 A / g). The second and subsequent charge / discharge cycles are performed at 1C (current density 2A / In this measurement, charging and discharging were performed at a constant current, and the charging and discharging voltage The range was from 0.03V to 1V.

[0164] Figure 12 shows the charge / discharge curves obtained from the measurements. In Figure 12, the vertical axis shows voltage and the horizontal axis shows The solid line in the figure indicates charging, and the dotted line indicates discharging. It was done 10 times.

[0165] In addition, in FIG. 12, "charge" indicates charging, "discharge" indicates discharging, and the numbers indicate the number of times. For example, "Charge 5" indicates the fifth charge.

[0166] As shown in Figure 12, after the first charge / discharge, the capacity decreased rapidly during the second charge / discharge. This is because the first charge / discharge is 0.05C, while the second charge / discharge is 1C. This is due to the difference in the rate. At low rates (e.g., 0.05C), Since the transit time of rear ions is sufficient, a large capacity can be obtained. At a high rate (e.g., 1 C compared to 0.05 C), the carrier ions move faster. There is not enough space, so the capacity is small.

[0167] However, from the third charge / discharge onwards, the number of charge / discharge cycles increases with each charge / discharge (as the number of cycles increases). The charge capacity increases with the number of cycles. Although the capacity also tends to increase, the discharge capacity does not increase monotonically even with the number of cycles. Figure 12 shows that the discharge capacity repeatedly increases and decreases with increasing cycle number. It is being done.

[0168] The reason why the charge capacity and discharge capacity increase is as follows: However, unreduced graphene oxide remains in the negative electrode active material layer after the heat treatment. In Figure 12, when charging and discharging are just started, the reduction of graphene oxide is insufficient. However, as the number of charge / discharge cycles increases, the reduction becomes insufficient. Graphene is electrically reduced, which increases the charge capacity and discharge capacity with each charge / discharge. The capacity increases together.

[0169] On the other hand, the reason why the discharge capacity decreases even with an increase in the number of cycles is due to the deterioration of the electrodes and / or electrolyte. Therefore, the silicon dioxide particles, which are particulate negative electrode active materials used in one embodiment of the present invention, It can be said that the silicon particles are preferably in the form of fine powder as used in Example 1.

[0170] <Reference example> In this reference example, a lithium secondary battery that does not use graphene as a material for the negative electrode active material layer is described. Reveal.

[0171] The negative electrode of this reference example uses a titanium foil having a thickness of 15 μm as a negative electrode current collector and a negative electrode active material layer. Silicon particles (average particle size 5 μm), which are particulate negative electrode active material, are added to the cathode as a conductive additive. Chain black and the binder polyimide (more precisely, the precursor of polyimide) The mixture ratio was 80:5:10 (wt%). 0.4g of bon-coated silicon particles, 0.025g of Ketjen black, and polyisocyanate 0.75 g of the precursor of the mide was mixed.

[0172] After mixing the above materials, a solvent is added to the mixed materials to form a slurry, which is then used to form a negative electrode current collector. The slurry was then applied to the negative electrode current collector by heating. The resultant was fired to prepare a negative electrode in which a negative electrode active material layer was formed on the negative electrode current collector.

[0173] In the heating step, the polyimide precursor is imidized to form polyimide.

[0174] In this example, silicon particles, which are particulate negative electrode active materials, were mixed in a molten state. In this specification, the term "carbon coating" refers to the surface of an active material. The carbon-coated silicon particles are The carbon particles are added with a substance that can generate conductive carbon by thermal decomposition (hereinafter referred to as "conductive carbon precursor"). ) and then heated. For example, sugars, specifically glucose, may be used.

[0175] More specifically, 4 g of silicon particles (average particle size 5 μm) and 0.4 g of glucose were mixed. Acetone is then added as a solvent. , mixed in a ball mill, and then heated at 600°C for 10 hours in a nitrogen atmosphere. In this way, carbon-coated silicon particles (with carbon material on the surface) were prepared. Supported silicon particles were prepared.

[0176] FIG. 13 shows the charge-discharge characteristics of a lithium secondary battery using the negative electrode prepared as described above. The results are shown for a half-cell. In the measurements, metallic lithium was used for the positive electrode. A basic cell manufactured by Japan Tomcell Co., Ltd. was used.

[0177] The electrolyte is lithium hexafluorophosphate (LiPF6) and ethylene carbonate (E The separator was dissolved in a mixed solution of PEG (PEG-100) and diethyl carbonate (DEC). Polypropylene was used for the data.

[0178] The charge-discharge characteristics shown in Figure 13 were measured as follows. First, the first charge-discharge This was carried out at 0.05C (current density 0.1 A / g). The second and subsequent charge / discharge cycles are performed at 1C (current density 2A / In this measurement, charging and discharging were performed at a constant current, and the charging and discharging voltage The range was from 0.03V to 1V.

[0179] Figure 13 shows the charge / discharge curves obtained from the measurements. In Figure 13, the vertical axis shows voltage and the horizontal axis shows The solid line in the figure indicates charging, and the dotted line indicates discharging. It was done 10 times.

[0180] In addition, in FIG. 13, "charge" indicates charging, "discharge" indicates discharging, and the numbers indicate the number of times. For example, "Charge 5" indicates the fifth charge.

[0181] As shown in FIG. 13, in the lithium secondary battery of this reference example, after the first charge and discharge, The capacity decreases rapidly after the first charge and discharge. The charge capacity decreases with each charge / discharge. is decreasing.

[0182] In this reference example, graphene (reduced graphene oxide) was used as the material for the negative electrode active material layer. It has been revealed that the capacity of lithium secondary batteries that do not use lithium ions decreases with repeated charging and discharging. .

[0183] On the other hand, when graphene is used as the material for the negative electrode active material layer, the capacity increases with repeated charge and discharge. However, when graphene is used as the material for the negative electrode active material layer, However, the catalyst for reducing graphene oxide is not available. The heating step and the heating step for baking the slurry (imidization of the polyimide precursor) are carried out separately. However, in one embodiment of the disclosed invention, the oxidation graph The reduction of the phenanthroline and the baking of the slurry (imidization of the polyimide precursor) are carried out in the same heating step. This makes it possible to reduce the number of steps in the process of producing the negative electrode. [Explanation of symbols]

[0184] 101 Negative electrode 107 Negative electrode current collector 109 Negative electrode active material layer 121 Negative electrode active material 123 Graphene 303 Cathode active material 304 Graphene 600 Lithium secondary battery 601 Anode can 602 Gasket 603 Positive electrode can 604 Negative electrode current collector 605 Negative electrode active material layer 606 Separator 607 Positive electrode active material layer 608 Positive electrode current collector 609 Negative electrode 610 Positive electrode 700 Lithium secondary battery 701 Positive electrode cap 702 Battery can 703 Positive terminal 704 Positive electrode 705 Separator 706 negative electrode 707 Negative terminal 708 Insulating board 709 Insulating board 711 PTC element 712 Safety valve mechanism 8000 display device 8001 Case 8002 Display section 8003 Speaker section 8004 Lithium secondary battery 8100 Lighting equipment 8101 Housing 8102 Light source 8103 Lithium secondary battery 8104 Ceiling 8105 Side wall 8106 floors 8107 Window 8200 indoor unit 8201 Case 8202 Ventilation outlet 8203 Lithium secondary battery 8204 Outdoor unit 8300 Electric refrigerator-freezer 8301 Housing 8302 Refrigerator door 8303 Freezer door 8304 Lithium secondary battery 9033 Fasteners 9034 Switch 9035 Power Switch 9036 Switch 9038 Operation switch 9630 chassis 9631 Display section 9631a Display section 9631b Display section 9632a area 9632b area 9633 Solar Cells 9634 Charge / Discharge Control Circuit 9635 Battery 9636 DC / DC Converter 9637 Converter 9638 Operation Key 9639 Button 9700 Electric Vehicle 9701 Lithium secondary battery 9702 Control circuit 9703 Drive unit 9704 Processing equipment

Claims

1. a negative electrode active material layer including a plurality of graphenes and a plurality of silicon particles; a secondary battery, wherein in a cross-sectional SEM image of the negative electrode active material layer, the negative electrode active material layer has a region in which the plurality of silicon particles are sandwiched between the plurality of graphene layers.

2. The secondary battery according to claim 1 , wherein the graphene has voids that allow lithium ions to pass through.

3. a negative electrode active material layer including multilayer graphene and a plurality of silicon particles; a cross-sectional SEM image of the negative electrode active material layer, the negative electrode active material layer having a region in which the plurality of silicon particles are sandwiched between the multilayer graphene layers.

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