Lithium ion secondary battery

Abstract

To increase the conductivity and the electric capacitance of an electrode formed of an active material particle used for a battery, for example.SOLUTION: Instead of conventionally used conductive auxiliary agent or binder, a graphene net formed of 1 to 100 graphenes is used. The graphene net with the two-dimensional spread and the three-dimensional structure improves the possibility of contact with active material particles or another conductive auxiliary agent, so that the conductivity is enhanced and the binding power between the active material particles is increased. The graphene net can be obtained by mixing graphene oxide and the active material particles and then heating the mixture in vacuum or reductive atmosphere.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to various electrical devices using particulate materials, particularly to power storage devices such as batteries, and This relates to various electrical devices having [Background technology]

[0002] Manganese batteries, alkaline batteries, nickel-metal hydride batteries, lithium batteries, lithium-ion secondary batteries In ponds, etc., particulate materials are used as active materials to store electricity, and they are bonded A binder is required to make the material adhere to the substrate. A typical binder is a polymeric organic compound. Therefore, acetylene black, graphite particles, carbon fiber Conductivity has been increased by mixing a conductive additive such as fiber (see Patent Document 1).

[0003] Specifically, the active material particles, the conductive additive, and the binder are mixed and applied to a current collector. After molding, the dried material is used as an electrode such as a positive or negative electrode. Similar measures are taken for electrical equipment that uses particulate matter.

[0004] Incidentally, when the conductivity of the active material particles themselves is low, the amount of the conductive additive added can be increased. It is necessary to form a conductive film (carbon coating) on ​​the surface of the active material particles. In addition, in a power storage device that uses ionic conduction (for example, a lithium ion secondary battery), When the ionic conductivity of the active material particles is low, it is necessary to use active material particles with small particle diameters. be.

[0005] For example, lithium cobalt oxide is used as the positive electrode active material for lithium ion secondary batteries. Lithium cobalt oxide has relatively high electrical and ionic conductivity, so it is suitable for lithium-ion batteries. However, the raw material, carbon, is a preferred positive electrode active material for carbon secondary batteries. Baltic reserves are small and are only produced in limited areas, so it is a low-cost alternative. There are also problems in terms of stable supply of food.

[0006] In contrast, lithium iron phosphate, which uses iron as a raw material and is inexpensive and widely produced, is a lithium-ion battery. Non-Patent Document 1 has revealed that it works as a positive electrode material for secondary batteries. However, the lithium ion conductivity and electrical conductivity of lithium iron phosphate are higher than those of lithium cobalt oxide. Therefore, carbon coating is required and the average particle size is 150 nm or less, preferably 20 nm or less. It is necessary to use fine particles with a particle size of up to 100 nm. Note that the particle size refers to primary particles.

[0007] However, such fine particles tend to aggregate, and the lithium iron phosphate particles and the conductive additive It is difficult to mix the particles evenly. To prevent particle aggregation, the ratio of the conductive additive should be increased. However, this makes it difficult to maintain the shape of the electrode, so the binder The ratio of must also be increased, resulting in a decrease in storage capacity.

[0008] Furthermore, when graphite particles are used as a conductive additive, natural graphite is often used due to cost considerations. In this case, graphite particles are usually used as impurities. Iron, lead, copper, etc. react with the active material and current collector, causing a decrease in the battery's potential and capacity. There is a problem.

[0009] In addition, acetylene black has fewer impurities than graphite particles and has a chain structure. The developed electrolyte has a large capacity to retain the electrolyte, which improves the utilization rate of the active material. Cetylene black is a fine particle with a diameter of about 10 nm, so the current flows through the lithium iron phosphate Conduction occurs from the particles by hopping between individual acetylene black particles or particle clusters. do.

[0010] That is, the resistance increases with each hopping, and the discharge voltage decreases when the storage device discharges. This problem can be solved by using graphite particles. The same is true for the electrode using acetylene black as a conductive additive. As shown in A).

[0011] As mentioned above, when the active material particles are made into fine particles, they tend to aggregate, and the binder and acetylene bromide It is difficult to mix it evenly with the rack (or to disperse it evenly in the binder). As a result, there are dense areas of active material particles (areas where the active material particles are aggregated) and sparse areas. The ratio of active material in the electrode decreases. Also, in the dense part of the active material particles, acetylene bromide There are areas where there are no racks, etc., and the conductivity in those areas is poor, so active materials cannot contribute to the capacity. Quality arises.

[0012] Figure 2(B) shows an SEM photograph of the positive electrode of a conventional lithium-ion secondary battery. Conventional electrodes contain more than 15% of materials other than the active material. To achieve this, it is necessary to reduce the weight and volume of materials other than the active material. The material (especially the binder) may swell, causing deformation or destruction of the electrode, and measures to prevent this are also required. can be. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 6-60870 [Patent Document 2] US Patent Application Publication No. 2009 / 0110627 [Patent Document 3] US Patent Application Publication No. 2007 / 0131915 [Non-patent literature]

[0014] [Non-Patent Document 1] Padhi et al., ``Phospho-olivines as positive-electrode materials for rechargeable lithium batteries'', J. Electrochem. Soc. 144, 1188-1194 (1997). Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made in view of the above, and one aspect of the present invention is to provide a capacitor having a larger electric capacity. Battery or electrical equipment with excellent electrical properties, or equipment that is reliable or can withstand long-term use The present invention aims to provide an electrical device that can prevent a voltage drop. An object of the present invention is to provide a power storage device. [Means for solving the problem]

[0016] A mesh-like graphene (graphene net) consisting of 1 to 100 graphene stacks By mixing with active material particles, either or both of the conductivity and the bonding between the active material particles can be improved. The mesh shape here refers to both two-dimensional and three-dimensional shapes. The average particle size of the active material particles is 150 nm or less, preferably 20 nm to 100 nm. In addition, the graphene net has gaps that allow ions to pass through.

[0017] In this specification, graphene refers to sp 2 A sheet of one-atom-thick carbon molecules with bonds Graphite is made up of multiple graphenes that are held together by van der Waals forces. In addition, among the elements that make up the graphene net, only hydrogen and carbon are bonded together. If the ratio of elements is 15 atomic % or less, or the ratio of elements other than carbon is 30 atomic % or less, good.

[0018] A schematic cross-sectional view of an electrode using such a graphene net is shown in Figure 1(A ) is shown. Here, multiple graphene nets and multiple active material particles are shown. Although the mechanism is unclear, it is thought that single-layer or multi-layer graphene can be bonded in multiple parts to form complex structures. The graphene net structure increases the conductivity and the active material particles By being entangled in the particles, the active material particles can be bonded together.

[0019] The graphene net has a two-dimensional extension and a three-dimensional structure with concave and convex portions. Therefore, the same graphene net or multiple graphene nets can form an active material Particles are contained within the same graphene net or between multiple graphene nets. A plurality of active material particles are present inside.

[0020] The graphene net is bag-shaped and contains a plurality of active material particles. In addition, the graphene net has some open areas, and in the open areas, The active material particles may be exposed. The graphene net prevents the active material particles from dispersing or collapsing. It is possible to do this.

[0021] As a result, the graphene net remains the same even if the volume of the active material particles increases or decreases with charging and discharging. The graphene net has the function of maintaining the bond between active material particles. Since the electrodes are in contact with each other, the conductivity of the electrodes can be increased.

[0022] In addition, the active material particles can be packed into the bag-like part of the graphene net. In addition, since the graphene net is made up of a limited number of graphene layers as described above, Therefore, it is extremely thin and therefore has a linear cross section.

[0023] In addition, SEM images of electrodes in which such graphene nets are mixed with active material particles are shown. The method for fabricating this electrode will be described in detail later. The surface of the active material particles is covered with a film-like graphene net, making it difficult to distinguish individual particles. It's nice.

[0024] In addition, the particles are seen to be bonded together by a graphene network. The active material particles and other active material particles are covered by a graphene net. The graphene functions as a binder that connects the particles. Because of the increased bonding, the graphene net can also be responsible for electrical conduction between particles.

[0025] Of course, the graphene net also comes into contact with the current collector, resulting in a strong bond between the current collector and the active material particles. In this case, the graphene net also plays a role in electrical conduction between the current collector and the active material particles. It is possible to do so.

[0026] Thus, graphene nets with two-dimensional expansion and negligible thickness can be used as conductive additives. As a result, the graphene net content is at least , sufficient conductivity can be ensured. In addition, by shortening the distance between different graphene nets, It is possible to reduce the resistance between graphene nets, thereby reducing the voltage drop. can be done.

[0027] As a result, the content of conductive additives such as acetylene black and binders, which were previously required, has been reduced. In some cases, it is possible to reduce the amount of conductive additives and barriers that were previously required. Therefore, the active material accounts for a small proportion of the electrode volume and weight. The ratio of substances can be improved.

[0028] In particular, the graphene net is a stack of 1 to 100 graphene layers, and the doping treatment The conductivity of the treated material is 1×10 5 This means that the conductivity of the conductive additive is Doping can be performed by adding an alkali metal such as potassium. .

[0029] In addition, graphene nets are characterized by their high flexibility and mechanical strength. As shown in Figure 1(B), the graphene net encases the active material particles, allowing for rapid charging. Even if the volume of the active material particles increases or decreases with charging or discharging, the bonds between the active material particles can be maintained.

[0030] In addition, graphene nets have higher heat resistance than organic materials typically used as binders. Therefore, when graphene nets are used as electrode materials, they are heated to 300°C or higher. The water in the electrode can be evaporated and its concentration can be reduced sufficiently. Therefore, the graphene net swells in the electrolyte, causing the electrode to deform. , and can prevent destruction.

[0031] In addition to the graphene net, an adhesive having a volume between 0.1 and 10 times that of the graphene net is also used. Cetylene black particles and carbon particles with one-dimensional expansion (carbon nanofibers) etc.), and may have a known binder.

[0032] Another aspect of the present invention is a porous carbon nanotube having a plurality of graphene nets encapsulating a plurality of active material particles. and a plurality of graphene nets having a plurality of active material particles therebetween are arranged at short distances. The electricity storage device is characterized by the above.

[0033] Another aspect of the present invention is a method for producing a graphene net using a method comprising the steps of: mixing a precursor of the graphene net with active material particles; and heating the mixture in a vacuum or in a reducing atmosphere. In another aspect of the present invention, a graphene net precursor is mixed with active material particles. and reducing the mixture with a reducing material. .

[0034] As a precursor of graphene net, graphene oxide with a single layer or multiple layer structure is used. In this case, the precursor must have a particularly large extension or It is not required to be a polymer compound, but the precursors bond together during the heating process. , polymerize or polymerize to form a larger three-dimensional network.

[0035] It should be noted that what is referred to as a graphene net in this specification does not necessarily have to be a purely two-dimensional structure. For example, a graphene layer may be placed in a certain place and another graphene layer may be placed in a certain place. A structure in which phenes are bonded together is also called a graphene net. [Effects of the Invention]

[0036] The graphene net structure between the active material particles improves electrical conductivity and bonding between the active material particles. In addition, at least one of the dispersibility of the particles can be improved. As a result, it is possible to manufacture electrical equipment with a small voltage drop and a large storage capacity.

[0037] By having the above-mentioned structure, the density of the active material or the electrode can be increased. This reduces the resistance between the electrode and the current collector, thereby suppressing voltage drop. In secondary batteries, it is advantageous to have low electrode resistance (internal resistance), because The above configuration is suitable for applications where force is required.

[0038] For example, the power source of an electric vehicle consumes relatively little power when traveling on flat ground. However, when accelerating suddenly or going up a slope, a lot of power is consumed. The power source needs to pass a large amount of current, but if the internal resistance is large, the voltage drop will be significant and In addition, losses due to internal resistance also occur. In this case, the greater the weight of the battery, the greater the losses. It becomes.

[0039] As a result, in such a situation, a certain percentage of the power that could be used is lost. For example, if a secondary battery is used as the power source, the stored power will be approximately 10 times as much as when traveling on flat ground. Although 0% of the internal resistance can be used, some of it is lost when climbing or accelerating. By reducing the weight of the battery (or increasing the battery capacity), such losses can be reduced. It can be suppressed.

[0040] Although sufficient characteristics can be obtained even if active material particles whose surfaces are not coated with carbon are used, The active material particles coated with carbon or the active material particles with high conductivity are graphene It is more preferable to use it together with a . [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a cross-sectional schematic diagram and an SEM photograph of a graphene net and active material particles. [Figure 2] 1 is a cross-sectional schematic diagram and an SEM photograph of a conventional conductive additive (acetylene black particles) and active material particles. [Figure 3] FIG. 1 is a graph showing the weight change, differential heat, and amount of carbon dioxide released of graphene oxide upon heating. [Figure 4] FIG. 1 shows changes in the infrared spectrum of graphene oxide caused by heating. [Figure 5] FIG. 1 is a diagram illustrating an example of a secondary battery. [Figure 6] 1 is a cross-sectional SEM photograph of an electrode produced in an example. [Figure 7] FIG. 1 is a diagram showing a cross-sectional SEM photograph of an electrode fabricated in an example and graphene. [Figure 8] FIG. 1 is a graph showing the characteristics of lithium secondary batteries prepared in Examples. [Figure 9] FIG. 1 is a graph showing the characteristics of lithium secondary batteries prepared in Examples. [Figure 10] 1A and 1B are diagrams illustrating examples of usage of a power storage device. DETAILED DESCRIPTION OF THE INVENTION

[0042] Hereinafter, embodiments will be described with reference to the drawings. The present invention can be implemented in various forms and in various ways without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the design and details of the present invention. The present invention should not be construed as being limited to the following description of the embodiments.

[0043] (Embodiment 1) In this embodiment, a method for manufacturing a lithium-ion secondary battery according to one embodiment of the present invention will be described. The electrode of the lithium ion secondary battery is made of a graphene net precursor and active material particles. and a process of applying the mixture to a current collector and then heating it in a vacuum or a reducing atmosphere. The precursor of the graphene net is graphene oxide (or Multilayer graphene oxide) can be used.

[0044] The precursor of the graphene network is particularly large in size or is a polymer compound. It is not required that the precursors are bonded together during the heating process, and polymerization or It polymerizes to form a larger, three-dimensional network, becoming a graphene net.

[0045] The details are explained below. In this embodiment, an oxidation method called the Hummers method is used. First, graphite such as flake graphite is oxidized to obtain graphite oxide. Oxidized graphite is graphite that has been oxidized in places, resulting in carbonyl groups, carboxyl groups, etc. It is a compound in which functional groups such as silyl groups and hydroxyl groups are bonded, and the crystallinity of graphite is not impaired. The distance between the graphenes is also large. The layers separate.

[0046] As a result, graphite oxide, which is composed of 1 to 100 stacked carbon sheets (equivalent to graphene), was produced. In addition, since graphene oxide is terminated with functional groups, it is difficult to absorb water and C12H2O3, N,N-dimethylformamide (DMF), and N-methyl It can be suspended in polar solvents such as 1-pyrrolidone (NMP) using ultrasonic waves. The graphene oxide solution obtained after the treatment is dried to obtain powdered graphene oxide. .

[0047] The graphene oxide thus obtained has an average particle size of 150 nm or less, preferably 20 nm to Mix with 100 nm active material particles. When mixing, the ratio of active material particles is 90% of the mixture. Before mixing, the graphene oxide alone should be mixed with the water to obtain a concentration of 95% or more. It is advisable to suspend the active material particles in water or a solution such as NMP. A slurry is obtained. Other conductive additives such as acetylene black and binders are mixed in as needed. That's fine.

[0048] In addition, carbohydrates such as glucose are mixed in to the active material particles, and carbon is then added to the particles during the subsequent firing process. Of course, it is also possible to use active material particles that have been previously coated with carbon. It may be used.

[0049] Various materials can be used as the active material. For example, the positive electrode active material lithium cobalt oxide, lithium ferrate, lithium nickel oxide, lithium manganese oxide, etc. Lithium compounds, lithium iron phosphate, lithium manganese phosphate, lithium manganese silicate, Lithium-containing composite oxides such as lithium iron silicate can be used, but are not limited to this.

[0050] Lithium iron phosphate is an oxide containing lithium, phosphorus, and iron. When used as an active material, it is preferable that the The concentration of lithium varies widely. The ratio of phosphorus to iron is important, and ideally, the ratio (number of phosphorus atoms) / (number of iron atoms) The ratio (number of phosphorus atoms) / (number of iron atoms) is 1. However, the ratio (number of phosphorus atoms) / (number of iron atoms) is greater than 0.7 and less than 1. It may be 5 or less. The same applies to other lithium-containing composite oxides.

[0051] In addition, the carrier ion in a lithium ion secondary battery is a lithium ion. The battery is made of alkali metal ions, alkaline earth metal ions, or magnesium ions other than lithium ions. In the case of metal ion secondary batteries such as neodymium ion batteries, the above lithium is used as the positive electrode active material. In the compounds and lithium-containing composite oxides, an alkali metal (e.g., sodium and potassium), alkaline earth metals (e.g., calcium, strontium, Alternatively, magnesium may be used.

[0052] The lithium-containing composite oxide having an olivine structure is represented by the general formula LiMPO4 (where M is F one or more of Mn(II), Mn(II), Co(II), Ni(II), or general formula L i (2-j) MSiO4 (M is Fe(II), Mn(II), Co(II), Ni(I) I) and 0≦j≦2).

[0053] The obtained slurry is applied onto the current collector. The thickness can be set arbitrarily, but it is generally in the range of 1 μm to 1 μm. After that, the slurry is dried. After drying, it can be pressed if necessary. stomach.

[0054] Then, to reduce the graphene oxide, the mixture was placed in a vacuum or a reducing atmosphere such as nitrogen or argon. Heating is carried out in an atmosphere at 150 to 900°C. Depending on the temperature, heating may be carried out in air. The temperature is determined taking into consideration the heat resistance of the current collector and active material, the conductivity required for graphene oxide, etc. As a result of the experiment conducted by the inventor, when graphene oxide is heated, it is possible to obtain a temperature of 170 to 200°C. It was found that the reduction proceeded rapidly.

[0055] Figure 3(A) shows the graphene oxide prepared by the above method in a helium atmosphere from room temperature to 1 The weight change (solid line) and differential heat (dotted line) when heated to 000°C at a heating rate of +2°C / min. An exothermic peak accompanied by a large weight loss was observed around 200°C, indicating some kind of chemical change. It was shown that this was occurring.

[0056] The molecules released during the above measurements were analyzed by mass spectrometry. Figure 3(B) shows the results. The figure shows the amount of released molecules with a mass number of 44 (presumably carbon dioxide). A molecule with mass number 44 was observed to be suddenly released at around 0°C.

[0057] Although not shown in the figure, a molecule with a mass number of 12 (carbon atom, but carbon atom) (presumably produced by the decomposition of a molecule containing ), a molecule with a mass number of 16 (presumably an oxygen atom) A molecule with mass number 18 (presumably water) was also observed in large numbers around 200°C. At this temperature, oxygen and hydrogen are released from graphene oxide along with carbon. This suggests that a reduction reaction occurs.

[0058] In the Hummers method, graphite is treated with sulfuric acid, so multilayer graphene oxide is produced. The sulfonic acid group is also bonded to the polymer, but this decomposition (elimination) occurs at around 200 to 300°C. Therefore, the reduction of graphene oxide is preferably carried out at temperatures above 200°C. It is preferable to carry out the treatment at 300°C or higher.

[0059] The higher the temperature, the more the reduction progresses and the higher the carbon ratio of the resulting graphene net. The repair of defects also progresses, improving conductivity. At a heating temperature of 200°C, the resistivity of the graphene net is about 240 MΩcm. At 300°C, it is about 2.8Ωcm (both are van der Pa (Measurement by the UW method).

[0060] In addition, during this reduction process, graphene oxide molecules are separated from adjacent graphene oxide molecules. The molecules bond with each other, growing into larger graphene molecules and forming a three-dimensional network like a mesh. At this time, the active material particles are incorporated into the molecules, resulting in the formation of an active material The bonding strength between the particles is increased.

[0061] As mentioned above, the conductivity of the graphene net changes depending on the reduction temperature. In addition, flexibility and strength also change. Considering the required conductivity, flexibility, strength, etc., The temperature should be determined. In addition, graphene nets, which do not have sufficient conductivity, can be used instead of binders. If the conductive material is to be used in a conductive manner, it is preferable to add a necessary amount of a known conductive additive to supplement the conductivity. I wish.

[0062] As a result of the inventor's investigation, it was found that reduction proceeds even at 150°C by prolonged heating. Figure 4 shows the results when graphene oxide is heated at 150°C for 1 hour and when it is heated at 10°C for 1 hour. The results of infrared spectroscopy (transmittance) are shown below. If this is the case, many absorptions associated with C=O bonds, C=C bonds, CO bonds, etc. will be observed. When heated for 10 hours, the absorption due to the carbon-oxygen bond decreases.

[0063] 5 is a schematic diagram showing the structure of a coin-type secondary battery. The positive electrode active material layer 130 is formed by applying the positive electrode active material to the positive electrode current collector 130 and molding the positive electrode active material layer 130, followed by drying and reducing the positive electrode active material layer 130. The material of the body 128 is preferably aluminum. In this case, the reduction temperature is set to 20 The temperature may be 0°C to 600°C, for example, 300°C.

[0064] As shown in FIG. 5, the coin-type secondary battery includes a negative electrode 104, a positive electrode 132, a separator, 110, an electrolyte (not shown), a housing 106 and a housing 144. The positive electrode 132 has a cylindrical insulator 120, a spacer 140, and a washer 142. The positive electrode current collector 128 obtained by the process and provided with the positive electrode active material layer 130 is used.

[0065] The electrolyte is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). It is preferable to use a solvent in which LiPF6 is dissolved, but the present invention is not limited to this.

[0066] The negative electrode 104 has a negative electrode active material layer 102 on a negative electrode current collector 100. For example, copper is preferably used as the negative electrode active material. Polyacene, silicon, etc. are used alone or mixed with a binder to form the negative electrode. It is preferable to use it as the active material layer 102 .

[0067] The separator 110 may be made of an insulating material with holes (for example, polypropylene). However, a solid electrolyte that is permeable to lithium ions may also be used.

[0068] The housing 106, the housing 144, the spacer 140 and the washer 142 are made of metal (e.g., stainless steel). The housing 106 and the housing 144 are made of anode 104 and cathode 106, respectively. 132 to the outside.

[0069] The negative electrode 104, the positive electrode 132, and the separator 110 are impregnated with an electrolyte, and as shown in FIG. As shown, the negative electrode 104, separator 110, ring-shaped insulator 120, and positive electrode 104 are placed with the housing 106 facing downwards. The pole 132, the spacer 140, the washer 142, and the housing 144 are stacked in this order. The battery 6 and the housing 144 are pressed together to form a coin-type secondary battery.

[0070] (Embodiment 2) Examples of the electrical device of the present invention include various dry batteries, rechargeable batteries, etc. Alternatively, the graphene net shown in the first embodiment may be used as an additive for the negative electrode. stomach.

[0071] Examples of the electrical appliances of the present invention include power tools, personal computers, mobile phones, etc. Mobile phones, portable game consoles, personal digital assistants, e-books, video cameras, digital still cameras These electrical devices are not necessarily powered by wires, so The rechargeable battery is provided in the positive or negative electrode of the rechargeable battery. The graphene net shown in Example 1 may be used.

[0072] In particular, applications that require a large current to flow instantaneously, or In applications where values ​​fluctuate greatly, a rechargeable battery with low internal resistance is required, so this invention is applied. In addition, for portable or mobile devices, the use of high-capacity There is a demand for rechargeable batteries, and by applying the present invention, sufficient effects can be obtained.

[0073] Other examples of electronic devices and electric devices using a power storage device according to one embodiment of the present invention include: , display devices, lighting devices, DVDs (Digital Versatile Discs), etc. image playback devices that play back still or moving images stored on recording media, high frequency devices such as microwave ovens, Wave heating devices, electric rice cookers, electric washing machines, air conditioning equipment such as air conditioners, electric refrigeration Examples include refrigerators, electric freezers, electric refrigerator-freezers, freezers for DNA storage, and dialysis machines.

[0074] In addition, vehicles propelled by electric motors using power from storage devices are also subject to the electronic equipment and electrical The above-mentioned mobile objects include, for example, electric vehicles, internal combustion engines, and Hybrid cars with electric motors (hybrid cars), and motor-assisted bicycles Examples include motorized bicycles.

[0075] The above electronic and electrical devices require a power storage device (main power source) to cover almost all of the power consumption. The power storage device according to one embodiment of the present invention can be used as the above-described power storage device. If the supply of power from the commercial power source is interrupted, the equipment and electrical equipment As a power storage device (called an uninterruptible power supply) capable of supplying the above electric power, one of the present invention is The power storage device according to the embodiment can be used.

[0076] Or, the above electronic and electrical equipment may be connected to the main power source or commercial power source. A power storage device that supplies power to electronic and electrical equipment in parallel with the supply of power to the The power storage device of one embodiment of the present invention can be used as an auxiliary power supply.

[0077] FIG. 10 shows a specific configuration of the electronic device or electric device. 01 is an example of an electronic device or an electric device using a power storage device 205 of one embodiment of the present invention. Specifically, the display device 201 corresponds to a display device for receiving TV broadcasts, and includes a housing 202, a display The power storage device 205 includes a power storage unit 203, a speaker unit 204, a power storage device 205, and the like. The device 205 is provided inside the housing 202 .

[0078] The display device 201 can receive power from a commercial power source or can store power in a power storage device 205. The stored power can also be used. Therefore, in the event of a power outage, the power supply from the commercial power source can be reduced. The power storage device 205 according to one embodiment of the present invention can be used as an uninterruptible power supply even when power is not available. This allows the display device 201 to be used.

[0079] The display unit 203 may be a liquid crystal display device, a light emitting device having a light emitting element such as an organic EL element in each pixel, or the like. Device, electrophoretic display, DMD (Digital Micromirror Device) e), PDP (Plasma Display Panel), FED (Field E A semiconductor display device such as a mission display can be used.

[0080] In addition to TV broadcast reception, display devices are also used for personal computers and advertising displays. , including all display devices for displaying information.

[0081] In FIG. 10, a stationary lighting device 211 includes a power storage device 214 according to one embodiment of the present invention. Specifically, the lighting device 211 includes a housing 212, a light source 213, and a 10, the power storage device 214 is connected to the housing 212 and the light source 21. 3 is installed inside the ceiling 215, 214 may be provided inside the housing 212.

[0082] The lighting device 211 can receive power from a commercial power source or can store power in the power storage device 214. The stored power can also be used. Therefore, in the event of a power outage, the power supply from the commercial power source can be reduced. The power storage device 214 of one embodiment of the present invention can be used as an uninterruptible power supply even when power is not available. This allows the lighting device 211 to be used.

[0083] Although FIG. 10 illustrates a fixed lighting device 211 provided on the ceiling 215, The power storage device of one embodiment of the present invention may be configured to cover any part of the ceiling 215, such as the sidewall 216, the floor 217, the window It can be used for a fixed lighting device installed in a room such as 218, or for a tabletop lighting device. It can also be used for the following purposes.

[0084] Furthermore, the light source 213 can be an artificial light source that artificially obtains light using electricity. Specifically, incandescent lamps, fluorescent lamps and other discharge lamps, and light-emitting elements such as LEDs and organic EL elements An example of the artificial light source is a lamp.

[0085] In FIG. 10, an air conditioner having an indoor unit 221 and an outdoor unit 225 is 1 is an example of an electrical device using a power storage device 224 according to one embodiment of the present invention. 1 includes a housing 222, an air outlet 223, a power storage device 224, etc. In FIG. 24 is provided in the indoor unit 221, but the power storage device 224 is provided in the outdoor unit Alternatively, both the indoor unit 221 and the outdoor unit 225 may be provided with a power storage device. A position 224 may be provided.

[0086] The air conditioner can be supplied with power from a commercial power source, or it can be powered by the power storage device 2. In particular, the electric power stored in both the indoor unit 221 and the outdoor unit 225 can be used. When the power storage device 224 is provided, if the power supply from the commercial power source is interrupted due to a power outage or the like, Even when power is not available, the power storage device 224 of one embodiment of the present invention can be used as an uninterruptible power supply. , air conditioning will be available.

[0087] In Figure 10, a separate type air conditioner consisting of an indoor unit and an outdoor unit is shown. As an example, it is an all-in-one air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing. The power storage device according to one embodiment of the present invention can also be used in the conditioner.

[0088] In FIG. 10, an electric refrigerator-freezer 231 uses a power storage device 235 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 231 includes a housing 232, a refrigerator compartment door, 233, a freezer door 234, and a power storage device 235. In FIG. The electric refrigerator-freezer 231 is provided inside a housing 232. The electric refrigerator-freezer 231 is supplied with power from a commercial power source. It is also possible to use electricity stored in the power storage device 235. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, one aspect of the present invention By using the power storage device 235 as an uninterruptible power supply, the electric refrigerator-freezer 231 can be used. It becomes Noh.

[0089] Among the above-mentioned electronic and electrical appliances, high-frequency heating devices such as microwave ovens, electric rice cookers, etc. Electrical devices such as these require high power for a short period of time, and therefore cannot be supplied by commercial power. When the power storage device of one embodiment of the present invention is used as an auxiliary power source for supplementing electric power, This prevents the commercial power breaker from tripping when electrical equipment is in use.

[0090] In addition, during times when electronic and electrical equipment are not in use, especially when commercial power sources are available, During times when the ratio of the amount of electricity actually used to the total amount of electricity (called the power usage rate) is low, By storing electricity in a power storage device, the electricity usage rate increases outside of the above time periods. For example, in the case of an electric refrigerator-freezer 231, when the temperature is low and the refrigerator compartment During the night when the door 233 and the freezer door 234 are not opened or closed, the power storage device 235 is powered. Then, as the temperature rises, the refrigerator door 233 and the freezer door 234 open and close. During the daytime, when the electricity is consumed, the power storage device 235 is used as an auxiliary power source, thereby reducing the power consumption during the daytime. The usage rate can be kept low. [Example]

[0091] To verify the effectiveness of the graphene net obtained by reducing graphene oxide, the following two Sample A was made of active material (lithium iron phosphate) particles and acid The mixture was coated on a current collector (aluminum) and heated in a vacuum. It is something.

[0092] Sample B is composed of active material (lithium iron phosphate) particles and binder (polyvinylidene fluoride (PV DF, manufactured by Kureha Chemical Co., Ltd.) and a conductive additive (acetylene black, manufactured by Denki Kagaku Kogyo Co., Ltd.) were mixed. The active material particles and the current collector were used as samples. The same material as in A was used.

[0093] Lithium iron phosphate particles and graphene oxide were obtained by the following method. Lithium oxalate (Li2CO3), iron oxalate (Fe(C2O4)·2H2O), and dihydrogen phosphate Weigh out ammonium (NH4H2PO4) in a molar ratio of 1:2:2 and mix it in a wet ball mill. The mixture was milled and mixed in a 3 mm ball mill at 400 rpm for 2 hours. was carried out.

[0094] After drying, the mixture was pre-baked at 350°C for 10 hours in a nitrogen atmosphere, and then again in a wet ball. The mixture was milled and mixed in a mill (ball diameter 3 mm) at 400 rpm for 2 hours. The resulting lithium iron phosphate was baked at 00°C for 10 hours in a nitrogen atmosphere. The particles are not carbon coated.

[0095] Graphene oxide was produced as follows: Graphite (flake carbon) was mixed with concentrated sulfuric acid. After adding potassium permanganate to the mixture, the mixture was stirred for 2 hours. The mixture was heated and stirred for 15 minutes, and then hydrogen peroxide was added to form a graphite oxide-containing mixture. A yellowish-brown solution containing ammonium hydroxide was obtained. This was then filtered, hydrochloric acid was added, and the solution was washed with pure water. The graphite oxide was then converted to graphene oxide by ultrasonic treatment for 2 hours.

[0096] The detailed preparation conditions for the samples are as follows: Sample A consisted of 3 wt% graphene oxide and 97% active material particles. The aluminum was collected by mixing the aluminum particles with NMP in an amount of about twice the total weight of the aluminum particles. Apply to a dielectric (20 μm), dry at 120°C for 15 minutes, then ventilate and dry at 300°C for 8 hours in a vacuum. Heating was carried out for 10 hours.

[0097] Sample B is a mixture of 85 wt% active material particles, 7 wt% binder, and 8 wt% conductive additive. Mix with approximately twice the weight of NMP and apply to an aluminum current collector (20 μm). The coating was then dried under air at 120°C for 15 minutes, and then heated in a vacuum at 180°C for 10 hours.

[0098] The cross-sectional SEM images (backscattered electron images) of Sample A and Sample B obtained in this manner are shown in Figure 6. Figure 6(A) is an SEM image of sample A, and Figure 6(B) is an SEM image of sample B. Both have low contrast. The white parts are the active material particles. As can be seen, the active material particles occupy a large portion of the sample A, while the active material particles occupy a small portion of the sample B. It can be seen that sample B has a higher density of the active material than sample B.

[0099] FIG. 7(A) shows a secondary electron image of another cross-sectional SEM image of sample A. The graphene net structure can be seen, and the active material particles are embedded in the graphene net. The graphene net portion of Figure 7(A) is shown in Figure 7(B). Shown below.

[0100] The obtained samples A and B were punched into a circle together with the current collector. The negative electrode is made of metal lithium, and the positive electrode is made of ethylene carbonate (EC) and diethyl carbonate (DEC). A mixture (volume ratio 1:1) in which lithium hexafluorophosphate (LiPF6) is dissolved (concentrated The electrolyte was 1 mol / L, and a polypropylene separator was used as the separator. Each battery was fabricated.

[0101] The discharge characteristics of these batteries were then measured, and then the charge characteristics were measured. The charging time was 0.2C and the charging rate was 1C. The charging termination conditions were a constant voltage of 4.3V and a current of 0.01 Until it dropped to 6C.

[0102] Figure 8 shows the discharge and charge characteristics of a battery using sample A and a battery using sample B. It was clear that sample A was superior to sample B in both discharge and charge. The values ​​are per weight of the active material. As mentioned above, even though the electrodes were of the same weight, sample A had a higher Since the amount of active material is larger than that of sample B, the capacity per weight of the electrode is even higher in sample A. surpasses B. [Example]

[0103] To verify the effectiveness of the graphene net obtained by reducing graphene oxide, the following two Sample C was prepared using the same active material (phosphate) as in Example 1, and the properties were compared. Current collection by mixing only lithium iron particles (not carbon coated) and graphene oxide The coating was applied to a body (aluminum) and heated in a vacuum at 300°C for 10 hours. The ratio of graphene oxide to lithium iron phosphate used was 5:95. It is estimated that the graphene oxide has been reduced and its weight has been reduced by half.

[0104] Sample D is made of active material (lithium iron phosphate) particles with a carbon coating on the surface and a binder (poly Polyvinylidene fluoride (PVDF, manufactured by Kureha Chemical Co., Ltd.) and conductive additive (acetylene black, The mixture was mixed with a cellulose acetate solution (manufactured by KIKAGAKU KOGYO CO., LTD.) and applied to a current collector (aluminum), which was then dried. The current collector used was the same as that used in sample C. Generally, lithium iron phosphate particles are coated with carbon. By doing so, electricity can be stored at a theoretical capacity.

[0105] The lithium iron phosphate particles of Sample C were the same as those used in Example 1. The graphene used was the same as that used in Example 1. Sample C was prepared in the same manner as Sample A. It was carried out.

[0106] The lithium iron phosphate particles of sample D were prepared as follows. 2CO3), iron oxalate (Fe(C2O4)·2H2O), ammonium dihydrogen phosphate (NH 4H2PO4) were weighed in a molar ratio of 1:2:2 and mixed in a wet ball mill (ball diameter 3 mm) The mixture was ground and mixed in a 2000 rpm oven (using acetone as the solvent) for 2 hours.

[0107] After drying, the mixture was pre-baked at 350°C for 10 hours in a nitrogen atmosphere, and then again in a wet ball. The mixture was milled and mixed at 400 rpm for 2 hours using a mill (ball diameter 3 mm). Glucose was added at a volume ratio of 10%, and the mixture was fired at 600°C for 10 hours in a nitrogen atmosphere.

[0108] Sample D is composed of 80 wt% active material particles (including the weight of the carbon coat) and 5 wt% binder. 15 wt% of the conductive additive was mixed with NMP in an amount of about twice the total weight of the conductive additive and the NMP. It was applied to an aluminum current collector (20 μm), dried at 120°C for 15 minutes under forced air, and then Heated in air at 180°C for 10 hours.

[0109] The obtained samples C and D were punched into a circle together with the current collector. The negative electrode is made of metal lithium, and the positive electrode is made of ethylene carbonate (EC) and diethyl carbonate (DEC). A mixture (volume ratio 1:1) in which lithium hexafluorophosphate (LiPF6) is dissolved (concentrated The electrolyte was 1 mol / L, and a polypropylene separator was used as the separator. Each battery was fabricated.

[0110] The discharge characteristics of these batteries were then measured, and then the charge characteristics were measured. The current was set to 0.2C and the charging rate was set to 0.2C.

[0111] In this example, the charge capacity and discharge capacity per weight of the active material layer actually used are compared. As described above, the active material layer formed on the current collector contains only the active material (or active material particles). It contains binders, conductive additives, graphene nets, etc., and without these, charging and discharging would be impossible. Therefore, to properly compare battery performance, the capacity per weight of the active material layer must be calculated. It is required to compare the following.

[0112] FIG. 9 shows the discharge and charge characteristics of Samples C and D. The capacity here is the weight of the positive electrode active material layer. Sample D contains 20 wt% of binder and conductive additive in addition to the active material. In contrast, sample C only contains about 2.5 wt% graphene nets in addition to the active material. Therefore, when comparing the positive electrode active material layers with the same weight, sample C has a larger electric charge. can be accumulated. [Explanation of symbols]

[0113] 100 Negative electrode current collector 102 Negative electrode active material layer 104 Negative electrode 106 Case 110 Separator 120 Ring-shaped insulator 128 Positive electrode current collector 130 Cathode active material layer 132 Positive electrode 140 spacer 142 Washer 144 Case 201 Display device 202 Case 203 Display section 204 Speaker section 205 Electricity storage device 211 Lighting equipment 212 Case 213 Light source 214 Electricity storage device 215 Ceiling 216 Side wall 217 beds 218 Window 221 Indoor unit 222 Case 223 Ventilation vent 224 Energy storage device 225 Outdoor unit 231 Electric refrigerator-freezer 232 Case 233 Refrigerator door 234 Freezer door 235 Electricity storage device

Claims

1. A lithium ion secondary battery having a positive electrode, the positive electrode has a current collector and a positive electrode active material layer, the positive electrode active material layer includes a mixture of a plurality of active material particles and a conductive additive, and does not include a binder; the plurality of active material particles are contained in the mixture at a ratio of 95 wt % or more, At least one of the plurality of active material particles is in contact with the current collector, the conductive additive is in contact with at least two of the plurality of active material particles, The lithium ion secondary battery, wherein the conductive additive contains a graphene net.

2. A lithium ion secondary battery having a positive electrode, the positive electrode has a current collector and a positive electrode active material layer, the positive electrode active material layer includes a mixture of a plurality of active material particles and a conductive additive, and does not include a binder; the plurality of active material particles are contained in the mixture at a ratio of 95 wt % or more, At least one of the plurality of active material particles is in contact with the current collector, the conductive additive is in contact with at least two of the plurality of active material particles, The lithium ion secondary battery, wherein the conductive additive contains mesh-like graphene.

3. A lithium ion secondary battery having a positive electrode, the positive electrode has a current collector and a positive electrode active material layer, the positive electrode active material layer includes a mixture of a plurality of active material particles and a conductive additive, and does not include a binder; the plurality of active material particles are contained in the mixture at a ratio of 95 wt % or more, At least one of the plurality of active material particles is in contact with the current collector, the conductive additive is in contact with at least two of the plurality of active material particles, The conductive additive comprises 1 to 100 graphene stacks.

4. In any one of claims 1 to 3, The conductive additive is in contact with the current collector.

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