Carbon material, and positive electrode, negative electrode, and power storage device for power storage devices using same

Abstract

The purpose of the present invention is to provide: a carbon material which is capable of achieving flexibility against compression and which is capable of achieving high conductivity and durability; and a power storage device in which the carbon material is housed inside an electrode. The present invention provides: a carbon material having a volume elastic modulus K of 2 GPa or less and an average graphene mesh size L of 50 nm or more; a positive electrode (212) for a power storage device and a negative electrode (214) for a power storage device, each of which uses a carbon material as a conductive auxiliary agent; and a power storage device (200) provided with a positive electrode and / or a negative electrode containing a carbon material as a conductive auxiliary agent.

Description

Technical Field

[0001] The present invention relates to a carbon material and a conductive additive using the carbon material. Background Art

[0002] In recent years, measures to achieve a sustainable society have attracted much attention. In particular, research and development aimed at achieving carbon balance with zero greenhouse gas emissions is being actively carried out, and research on new carbon materials for improving the performance of power storage devices such as secondary batteries and electric double-layer capacitors (EDLCs) is being promoted around the world.

[0003] Carbon materials including graphene have excellent thermal conductivity, electrical conductivity, and mechanical (ductility) strength, and people are studying their applications in various fields such as electronics and energy materials. Among them, from the perspective of catalysts as reaction fields and electrical conductivity, due to the size of the specific surface area, porous carbon materials are being actively studied as electrodes and peripheral materials for energy devices such as batteries and capacitors. Summary of the invention Technical problem to be solved by the invention

[0004] As an example of expected application of porous and soft carbon materials with conductivity, for example, lithium-ion batteries using silicon in the negative electrode can be cited. In the charge and discharge cycle characteristics of lithium-ion batteries, it is pointed out that the silicon particles of the active material of the negative electrode expand relative to the repetition of charge and discharge, resulting in a phenomenon of life degradation. If the expansion of the tiny silicon particles can be absorbed by the compression of soft particles, it is expected to be solved, but the understanding of softness relative to compression is still insufficient, and there is a problem that the parameters related to softness and the design guidelines have not yet been obtained.

[0005] In addition, the positive electrode, which is another protagonist of lithium-ion batteries, does not undergo volume changes during charge and discharge like the negative electrode, but the size of the crystal lattice will undoubtedly change microscopically as lithium ions are extracted and inserted. Obviously, the micro-vibration caused by the size change of the hard crystal particles in the positive electrode will eventually increase the resistance of the electrode and affect the charge and discharge life.

[0006] Furthermore, the application range of lithium-ion batteries has expanded from power sources for portable devices to power sources for electric vehicles (EVs). Under such circumstances, countermeasures against the effects of mechanical stress, which is an external factor of the battery, on the increase in electrode resistance, including the adverse effects of body vibration during EV driving on battery life, are still insufficient, which is also a major issue.

[0007] The present invention has been completed in view of the above situation, and its purpose is to provide a carbon material and a storage device in which the carbon material is housed inside an electrode, wherein the carbon material can obtain flexibility in response to compression caused by stress generated by macroscopic and / or microscopic mechanical vibrations generated from inside and outside the battery, and can obtain higher conductivity and durability. Solutions for solving technical problems

[0008] The inventors of the present invention have repeatedly conducted in-depth research and discovered an indicator related to flexibility, such as the bulk elastic modulus K. They found that by setting the bulk elastic modulus K to below 2 GPa and the average graphene mesh size L to above 50 nm, a carbon material with excellent flexibility to compression, conductivity and durability can be achieved.

[0009] The present invention provides the following structure in order to solve the above-mentioned problems. (1) A carbon material having a bulk elastic modulus K of 2 GPa or less and an average graphene network size L of 50 nm or more.

[0010] (2) The carbon material according to (1), wherein the average stacking number n is 1 or more and 6 or less.

[0011] (3) The carbon material according to (1) or (2), wherein the pore diameter d is 5 nm or more and 65 nm or less.

[0012] (4) The carbon material according to any one of (1) to (3), wherein the nitrogen content N in the graphene network plane is 0 wt % or more and 10 wt % or less.

[0013] (5) The carbon material according to any one of (1) to (4), wherein the BET specific surface area S is 400 m 2 / g and above 2600m 2 / g or less.

[0014] (6) The carbon material according to any one of (1) to (5), wherein the edge site quantity N edge It is less than 500 μmol / g.

[0015] (7) The carbon material according to any one of (1) to (6), wherein the edge site specific surface area S edge 30m 2 / g or less.

[0016] (8) The carbon material according to any one of (1) to (7), wherein the pore volume V total 1.9cm 3 / g or more and 5cm 3 / g or less.

[0017] (9) A negative electrode for an electrical storage device, comprising the carbon material according to any one of (1) to (8) as a conductive additive.

[0018] (10) A positive electrode for an electrical storage device, wherein the carbon material according to any one of (1) to (8) is used as a conductive additive.

[0019] (11) An electric storage device comprising a positive electrode and / or a negative electrode using the carbon material according to any one of (1) to (8) as a conductive additive. Effects of the Invention

[0020] According to the present invention, there can be provided a carbon material that can obtain flexibility against compression and can obtain conductivity and durability, and a long-life power storage device using the carbon material at least as a conductive additive in a positive electrode and / or a negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a perspective view showing an example of the structure of a carbon material according to one embodiment of the present invention. Figure 2 This is a flowchart showing an example of a method for producing a carbon material according to one embodiment of the present invention. Figure 3 It is a diagram for explaining a method for producing a carbon material according to an embodiment of the present invention, and is a diagram showing a coating step. Figure 4 It is a diagram for explaining a method for producing a carbon material according to an embodiment of the present invention, and is a diagram showing a state of a separation step. Figure 5A This is a graph showing the results of mercury intrusion measurement in Example 1. Figure 5B This is a graph showing the results of mercury intrusion measurement in Example 2. Figure 5C This is a graph showing the results of mercury intrusion measurement in Example 3. Figure 5D This is a graph showing the results of mercury intrusion measurement in Example 4. Figure 5E This is a graph showing the results of mercury intrusion measurement in Example 5. Fig. 6A This is a graph showing the results of mercury intrusion measurement in Comparative Example 1. Figure 6B This is a graph showing the results of mercury intrusion measurement in Comparative Example 2. Figure 6C This is a graph showing the results of mercury intrusion measurement in Comparative Example 3. Fig. 7A This is a graph showing the results of mercury intrusion measurement in Comparative Example 4. Figure 7B This is a graph showing the results of mercury intrusion measurement in Comparative Example 5. Figure 7C This is a graph showing the results of mercury intrusion measurement in Comparative Example 6. Fig.7D This is a graph showing the results of mercury intrusion measurement in Comparative Example 7. Fig. 7E This is a graph showing the results of mercury intrusion measurement in Comparative Example 8. Fig. 8A This is a graph showing the results of mercury intrusion measurement in Comparative Example 9. Figure 8B This is a graph showing the results of mercury intrusion measurement in Comparative Example 10. Figure 8C This is a graph showing the results of mercury intrusion measurement in Comparative Example 11. Fig. 9 This is a diagram for explaining an ultra-high sensitivity vacuum TPD device 60 used in temperature rise desorption analysis. Fig. 10A This is the gas discharge pattern when the temperature rise desorption analysis of Example 1 is performed. Fig. 10B This is the gas discharge pattern when the temperature rise desorption analysis of Example 2 is performed. Fig. 10C This is the gas discharge pattern when the temperature rise desorption analysis of Example 3 is performed. Fig. 10D This is the gas discharge pattern when the temperature rise desorption analysis of Example 4 is performed. Fig.10E This is the gas discharge pattern when the temperature rise desorption analysis of Example 5 is performed. Fig.11A This is the gas exhaust mode of Comparative Example 1. Fig. 11B This is the gas exhaust mode of Comparative Example 2. Fig. 11C This is the gas exhaust mode of Comparative Example 3. Fig. 12A This is the gas discharge pattern of Comparative Example 4. Fig. 12B This is the gas exhaust mode of Comparative Example 5. Fig. 12C This is the gas discharge pattern of Comparative Example 6. Fig.12D This is the gas discharge pattern of Comparative Example 7. Fig.12E This is the gas discharge pattern of Comparative Example 8. Fig.13A This is the gas discharge pattern of Comparative Example 9. Fig. 13B This is the gas discharge pattern of Comparative Example 10. Fig. 13C This is the gas discharge pattern of Comparative Example 11. Fig.14A These are the nitrogen adsorption-desorption isotherms of Examples 1 to 5. Fig. 14B These are the nitrogen adsorption-desorption isotherms of Comparative Examples 1 to 3. Fig. 14C These are the nitrogen adsorption-desorption isotherms of Comparative Examples 4 to 8. Fig.14D This is the nitrogen adsorption-desorption isotherm of Comparative Example 9. Fig.14E : These are the nitrogen adsorption-desorption isotherms of Comparative Examples 10 and 11. Fig.15A is a schematic diagram of type I adsorption isotherm; Fig. 15B is a schematic diagram of the type IV adsorption isotherm. Fig.16A This is the pore size distribution of Examples 1 to 5. Fig. 16B These are the pore size distributions of Comparative Examples 1 to 3. Fig. 16C These are the pore size distributions of Comparative Examples 4 to 8. Fig.16D This is the pore size distribution of Comparative Example 9. Fig.16E The pore size distributions of Comparative Examples 10 and 11 are shown. Fig.17 This is a graph showing the relationship between the bulk modulus K and the structural characteristics of Examples 1 to 5 and Comparative Examples 1 to 11. Fig.18A This is a SEM image of Example 1. Fig.18B This is a SEM image of Comparative Example 2. Fig.18C This is a SEM image of Comparative Example 3. Fig.18D This is a SEM image of Comparative Example 4. Fig.19 These are the Raman spectra of Examples 1 to 5. Fig. 20 It is a diagram showing an example of a cross-sectional structure of an electric storage device according to an embodiment of the present invention. Fig.21This is a graph comparing the relationship between the amount of conductive additive added (wt %) in the positive electrode and the charge / discharge capacity (mAh) in Examples and Comparative Examples. Fig. 22 This is a graph comparing the relationship between the amount of conductive additive added (wt %) in the negative electrode and the charge and discharge capacity (mAh) in Examples and Comparative Examples. Fig.23 This is a graph comparing the relationship between the amount of the conductive additive added in the positive electrode and the initial efficiency, and the relationship between the amount of the conductive additive added and the 10-cycle retention rate in Examples and Comparative Examples. Fig.24 This is a graph comparing the relationship between the amount of the conductive aid added in the negative electrode and the initial efficiency, and the relationship between the amount of the conductive aid added and the 10-cycle retention rate in Examples and Comparative Examples. DETAILED DESCRIPTION

[0022] Hereinafter, an example of an embodiment of the present invention will be described. The present invention is not limited to the following examples. The accompanying drawings used in the following description are schematic diagrams that are sometimes enlarged representations of the features in order to facilitate understanding of the features of the present invention. Therefore, the number of components, dimensional ratios, etc. are sometimes different from the actual ones. The materials, dimensions, quantities, etc. illustrated in the following description are examples, and the present invention is not limited to these data, and can be implemented by appropriate changes within the scope of not changing its purpose.

[0023] [Carbon material] Figure 1 It is a perspective view showing an example of the structure of a carbon material according to one embodiment of the present invention. Figure 1 The bulk elastic modulus K of the carbon material 100 shown is less than 2 GPa, and the average graphene mesh size L is greater than 50 nm. The carbon material 100 has, for example, a three-dimensional porous structure. The carbon material 100 has, for example, a graphene skeleton 10. The graphene skeleton 10 is, for example, composed of a plurality of graphene sheets 1. The carbon material 100 is confirmed to have a graphene skeleton by Raman spectroscopy. The carbon material 100 has, for example, a pore structure corresponding to the shape of the molded nanoparticles described later.

[0024] The smaller the bulk modulus K of the carbon material 100, the higher the mechanical flexibility is, preferably 1.5 GPa or less, more preferably 1.0 GPa or less, and further preferably 0.7 GPa or less. Here, in the present embodiment, the bulk modulus K is calculated by mercury penetration measurement. In the present embodiment, mechanical flexibility is an index related to the difficulty of destruction when mechanical stress is applied to the carbon material.

[0025] The average graphene mesh size L of the carbon material 100 is preferably greater than 70 nm, more preferably greater than 100 nm, and further preferably greater than 150 nm. The larger the average graphene mesh size L of the carbon material 100, the smaller the amount of edge sites, which can improve the durability of the structure and improve the energy density when applied to power storage devices. The average graphene mesh size L of the carbon material 100 is the average value of the size of the graphene in the extension direction of the multiple graphene sheets 1 included in the graphene skeleton 10 constituting the carbon material 100. The average graphene mesh size L of the carbon material 100 is based on the edge site amount N of the carbon material 100 measured by the temperature rise desorption method. edge (μmol / g) and substrate site N basal (μmol / g). Since the graphene mesh size L is relatively large, when the carbon material 100 is applied to an electrode of an electric double layer capacitor (EDLC), the electrolyte is difficult to decompose even if a higher voltage is applied. Since a higher voltage can be applied, the energy density can be further increased, and the reliability can also be improved.

[0026] The edge site quantity N of the carbon material 100 edge For example, it is 600 μmol / g or less, preferably 500 μmol / g or less, more preferably 300 μmol / g or less, and may be 250 μmol / g or less, or 150 μmol / g or less. In the carbon material 100 having a large graphene mesh size L, if the edge site quantity N edge The smaller the value, the easier it is to obtain the effect when applied to an electrode of an EDLC as described in the previous paragraph.

[0027] The edge site specific surface area S of the carbon material 100 edge For example, 100m 2 / g or less, preferably 30m 2 / g or less, more preferably 20m 2 / g or less, more preferably 15nm or less, and may be 10bn or less.

[0028] The carbon material 100 is composed of, for example, a porous carbon material. In the carbon material 100, the graphene sheets 1 constituting the graphene skeleton 10 each contain a structure other than a 6-membered ring. Specifically, the graphene sheets 1 each contain, for example, at least one selected from the group consisting of a 5-membered ring, a 7-membered ring, and an 8-membered ring. Since the graphene sheet 1 contains a structure other than a 6-membered ring, the planar network of the graphene skeleton is strained, forming a structure such as Figure 1 The three-dimensional porous structure of the carbon material 100 is shown.

[0029] The nitrogen content N in the graphene web of the carbon material 100 is, for example, 0 wt% or more and 20 wt% or less, preferably 0 wt% or more and 10 wt% or less, and more preferably 0 wt% or more and 5 wt% or less. The nitrogen content N in the graphene web of the carbon material 100 may also be 0 wt%. From the viewpoint of flexibility, the nitrogen content N in the graphene web of the carbon material 100 is preferably within the above range. The nitrogen content N in the graphene web of the carbon material 100 is measured by methods such as organic element analysis, X-ray photoelectron spectroscopy, and TPD measurement.

[0030] The BET specific surface area S of the carbon material 100 is, for example, 400 m 2 / g and above 2600m 2 / g or less, preferably 1000m 2 / g or more, 1500m 2 / g and above 2600m 2 / g or less, more preferably 1800m 2 / g and above 2600m 2 / g or less.

[0031] The average stacking number n of the carbon material 100 is, for example, 1 to 6, preferably 1 to 3, and more preferably 1 to 2. The average stacking number n of the carbon material 100 is expressed as the following formula (1), and the theoretical specific surface area S of graphene is obtained by graphene (2627m 2 / g) relative to the substrate specific surface area S basal The average number of carbon layers n is calculated by the ratio of the base surface area S. basal is the specific surface area S as With S edge The difference between the specific surface area S as is the specific surface area of ​​the carbon material 100, and is calculated from the nitrogen adsorption isotherm.

[0032] [Number 1]

[0033] The pore diameter d of the carbon material 100 is, for example, greater than 1 nm and less than 100 nm, preferably greater than 5 nm and less than 65 nm, and may also be less than 20 nm, less than 15 nm, or less than 12 nm. The pore diameter d of the carbon material 100 is calculated by the BJH method according to JIS Z8831-2: 2010, or the DFT method according to JIS Z8831-3: 2010. The BJH method is particularly capable of accurately measuring pore diameters of 2 nm to 50 nm in size, so the calculation of the pore diameter in this range is performed by the BJH method, and the pore diameter outside this range is calculated by the DFT method. That is, when the pore diameter is less than 2 nm or greater than 50 nm calculated by the BJH method, the pore diameter is calculated by the DFT method. The pore diameter d can be adjusted by, for example, the particle diameter of the nanoparticles constituting the mold.

[0034] The pore volume V of the carbon material 100 total For example, 1.3 cm 3 / g or more and 5cm 3 / g or less, preferably 1.9cm 3 / g or more and 5cm 3 / g or less, more preferably 2.5cm 3 / g or more and 5cm 3 The pore volume of the carbon material 100 is calculated by nitrogen adsorption-desorption measurement.

[0035] The carbon material involved in one embodiment of the present invention is, for example, a porous carbon material having pores corresponding to the shape of the nanoparticles constituting the casting mold, with a bulk elastic modulus K of less than 2 GPa and an average graphene mesh size L of more than 50 nm, thereby being able to obtain higher mechanical softness as well as higher conductivity and durability.

[0036] [Method for producing carbon material] Figure 2 1 is a flowchart showing an example of a method for producing a carbon material according to the present embodiment. The method for producing a carbon material according to the present embodiment further comprises, for example, a covering step of covering a mold with a carbon layer to obtain a molded product, a separation step of dissolving the mold with an acid to separate the molded product from the mold, and a stabilization step of heat-treating the molded product separated from the mold by the separation step after the separation step.

[0037] <Covering process> First, a mold is covered with a carbon layer to obtain a molded product. Figure 3 1 is a diagram for explaining a method for producing a carbon material according to an embodiment of the present invention, and is a diagram showing a coating process. Specifically, Figure 3The figure is a partial cross-sectional stereoscopic view of a molded product formed by covering a carbon layer on a mold nanoparticle and an enlarged cross-sectional view of the vicinity of a mold nanoparticle. Figure 3 In the molded product 30 shown, the mold T is covered with a carbon layer 11 (black thick line). Figure 3 The particle size d of the nanoparticles in the mold T is shown in 0 .

[0038] As the casting mold T, for example, a casting mold composed of metal nanoparticles that can be dissolved by acid in the separation process is used. When hydrofluoric acid is used in the separation process, a casting mold T composed of nanoparticles of aluminum oxide, zeolite, etc. can be used. In the separation process, from the viewpoint of avoiding the use of hydrofluoric acid, it is preferred to use a casting mold T composed of metal nanoparticles composed of an oxide of an alkaline earth metal, specifically, a casting mold T composed of nanoparticles of magnesium oxide, calcium carbonate, and calcium oxide can be used.

[0039] The carbon layer 11 covering the mold T may be performed by any of a wet method such as an immersion method, a dry method such as a chemical vapor deposition (CVD) method, or a combination of a wet method and a dry method, where the dry method is performed after the wet method. From the viewpoint of controlling the number of stacked layers of the formed carbon layer 11 to be 1 layer or more, the covering of the carbon layer 11 in the covering step is preferably performed by a chemical vapor deposition (CVD) method which is a dry method.

[0040] Hereinafter, this embodiment will be described by taking as an example a method of obtaining a molded product 30 by coating a mold T with a carbon layer 11 by a CVD method. The coating with the carbon layer 11 by the CVD method may be performed in a plurality of steps.

[0041] In the covering step, as the raw material gas of the CVD method, acetylene, methylacetylene, ethylene, propylene, isoprene, cyclopropane, methane, ethane, propane, benzene, toluene, vinyl compounds, ethylene oxide, methanol, ethanol, acetonitrile, acrylonitrile and the like are used. From the viewpoint of making it easy for the gas to enter the gap G of the mold T, acetylene, ethylene, propylene, methane and ethane are preferably used as the raw material gas.

[0042] When the coating process is performed by CVD, heating is performed at a temperature of, for example, 400° C. to 1500° C., and a pressure of, for example, 1 kPa to 200 kPa. The heating rate in the coating process is, for example, 1° C. / min to 50° C. / min.

[0043] In the covering process, in addition to the above-mentioned raw material gas, for example, an inert gas may be used as a carrier gas. In addition, as a carrier gas, in addition to the inert gas, a gas containing oxygen, hydrogen, etc. may be used. In the covering process, from the viewpoint of covering one to two carbon layers 11, it is preferred to control the flow rate of the carrier gas to 0.05 m / min to 1.00 m / min, and control the amount of the raw material gas to 1 volume % to 60 volume % relative to the total amount of the raw material gas and the carrier gas.

[0044] In the coating step, when a wet method is performed, for example, an organic compound may be impregnated and carbonized.

[0045] In addition, the covering process can also be carried out using a nitrogen-containing solvent to dope the formed carbon layer with nitrogen. For example, an inert gas can also be circulated in the nitrogen-containing solvent to perform chemical vapor deposition on the mold nanoparticles T. As the nitrogen-containing solvent, acetonitrile, acrylonitrile, ethylenediamine, pyridine, etc. can be used.

[0046] <Separation process> Next, the mold T is dissolved by acid or the like, and the molded object 30 and the mold T are separated. Figure 4 It is a diagram for explaining a method for producing a carbon material according to an embodiment of the present invention, and is a diagram showing a state of a separation step. Figure 4 The molded article 50 shown is a precursor of a carbon material 100 composed of a carbon layer 12 . Figure 4 The molded article 50 shown is referred to as a carbon mesoporous sponge (CMS). Figure 4 . ...

[0047] In the separation process, for example, use inorganic acids such as hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, organic acids or their mixtures having carboxyl, hydroxyl, thiol group, enol structure etc. in the molecule. When the casting mold consisting of alkaline earth metal is used as casting mold T, dissolve the porous casting mold with the acid that does not contain hydrofluoric acid. Consider safety aspect, environmental load, cost aspect, expect not to use hydrofluoric acid. If use the casting mold consisting of alkaline earth metal that can be dissolved by acid other than hydrofluoric acid such as hydrofluoric acid, sulfuric acid, then can avoid using hydrofluoric acid.

[0048] In addition, fluorine-containing acids such as hydrofluoric acid usually form insoluble compounds with the alkaline earth metal contained in alkaline earth metal oxides, so in the dissolution process of alkaline earth metal oxides, insoluble compounds are formed in aqueous media. In contrast, by using fluorine-free acids, insoluble salts can be formed, and compounds that are easily dissolved in aqueous media can be formed. That is, according to the present embodiment, by using acids that do not contain hydrofluoric acid, in the case of using alkaline earth metal oxides, particularly magnesium oxide or calcium oxide constituting mold T as molds, porous molds can be easily dissolved. Here, dissolving refers to when molds are contacted with the acid of aqueous media, and finally insoluble compounds are not left in aqueous media and transparent and uniform liquids without turbidity are formed.

[0049] In the separation step, the amount of the acid used to separate the molded product 30 from the mold T is, for example, 1 time or more, preferably 1.2 times or more, relative to the mold T in terms of a stoichiometric ratio. In the separation step, the temperature at which the mold T is dissolved by the acid is, for example, in the range of 5° C. to 100° C. In the separation step, for example, stirring or vibrating operation may be performed on the acid mixed with the porous mold.

[0050] In the separation process, the porous carbon material separated from the mold T can be recovered by filtering, for example, and then dried by vacuum heating and drying. The recovery of the molded object 50 can also be performed, for example, by suction filtration. The vacuum drying and heating for obtaining the porous carbon material can be performed, for example, at a temperature of 100°C to 200°C and for 1 hour to 10 hours. From the viewpoint of avoiding the capillary shrinkage of the molded object 50 caused by vacuum drying and heating, it can also be replaced with a solvent with a small surface tension such as acetone or alcohol after suction filtration. The molded object 50 obtained by this process is CMS, which will be described later in detail. The degree of capillary shrinkage depends on the shape and size of the molded object 50, and sometimes shrinks to about half.

[0051] The shape of the carbon layer 12 of the molded product 50 after the separation step is changed from the shape of the carbon layer 11 before the separation step due to the capillary contraction described above, and becomes a locally strained structure. The pore diameter d of the carbon layer 12 is larger than the particle diameter d of the molded nanoparticles T. 0 That is, the pore diameter d of the carbon layer 12 is smaller than the particle diameter d of the mold nanoparticles T. 0 The ratio d / d 0 Use a value less than 1.

[0052] <Stabilization process> Next, after the separation step, the molded product separated from the casting mold T obtained in the separation step is heat treated. In the stabilization step, the heat treatment of the molded product can be performed at 900° C. to 2000° C. for 0.1 hour to 5 hours, for example. The heat treatment of the molded product in the stabilization step is preferably performed at 1600° C. to 1800° C. for 0.5 hour to 2 hours.

[0053] Through the stabilization process, the graphene mesh size L of the carbon layer 12 of the molded product 50 is expanded to form a carbon layer (graphene sheet) 1, and the obtained Figure 1 The carbon material 100 is shown.

[0054] In addition, the manufacturing method of the carbon material involved in the present embodiment may also include manufacturing processes not described in the above-mentioned manufacturing method. For example, a heat treatment process may be provided before the covering process. In addition, between the separation process and the stabilization process, a hot pressing process for high-temperature compression of the molded product may be provided. In addition, an adjustment process for adjusting the structure of the molded carbon material may be provided. The adjustment process may be performed, for example, before the covering process, between the covering process and the separation process, or between the separation process and the stabilization process.

[0055] <Heat treatment process> The method for manufacturing the carbon material involved in the above-mentioned embodiment may also have a heat treatment step of heat-treating the mold T before the covering step. The heat treatment of the mold T is performed, for example, in an inert gas atmosphere, an air atmosphere, or a vacuum. The heat treatment of the mold T is, for example, heated at 400°C to 1100°C, preferably heated at 500°C to 1000°C, and more preferably heated at 600°C to 950°C. The heat treatment of the mold T is performed, for example, for 0.1 hour to 3 hours, preferably for 0.2 hour to 1 hour. By heat-treating the mold T under the above-mentioned conditions before the covering step, when impurities are mixed in the mold T, the impurities can be decomposed. As a specific example, when a mold T composed of magnesium oxide is used, magnesium hydroxide and magnesium carbonate mixed in the mold T are decomposed and separated from the mold T by heat treatment. Through the above-mentioned heat treatment step, the specific surface area S of the mold T can be increased, and the pore diameter d can be increased.

[0056] <Hot Pressing Process> In the hot pressing process, for example, pressure is applied to the molded object 50 and the molded object 50 is heated. Specifically, the molded object 50 is placed in a mold, pressure is applied, and it is heated to a high temperature. By performing the hot pressing process between the separation process and the stabilization process, a carbon material with a small pore volume can be obtained.

[0057] <Adjustment process> In the adjustment process, the structure of the carbon material is adjusted based on the following formula (2). Specifically, the manufacturing conditions are adjusted so that the graphene mesh size L of the carbon material, the average number of layers n of the carbon material, the nitrogen content N in the graphene mesh of the carbon material, the pore diameter d of the porous carbon material, and the surface distortion t are the desired values, so that the bulk modulus K is the desired value. The following formula (2) is a formula discovered by the inventors, etc., which represents the correlation between the bulk modulus of the carbon material and the five variables.

[0058] [Number 2] (where L: graphene mesh size of carbon material [nm], n: average number of carbon layers stacked in carbon material, N: nitrogen content in graphene mesh of carbon material [wt%], d: pore size of carbon material [nm], t: surface distortion)

[0059] In the adjustment step, in formula (2), the graphene mesh size L (nm) of the carbon material is adjusted to satisfy 70≤L≤1000, preferably adjusted to satisfy 100≤L≤1000, the average stacking number n of the carbon layers of the carbon material is adjusted to satisfy 1≤n≤6, preferably adjusted to satisfy 1≤n≤3, the nitrogen content N (wt%) in the graphene mesh of the carbon material is adjusted to satisfy 0≤N≤20, preferably adjusted to satisfy 0≤N≤10, the pore diameter d (nm) is adjusted to satisfy 1≤d≤100, preferably adjusted to satisfy 5≤d≤70, and the surface distortion t is adjusted to satisfy 1.1≤t≤20, preferably adjusted to satisfy 1.3≤t≤10. Here, in the case where a method including a stabilization step is adopted as the manufacturing method of the above-mentioned carbon material, d in the above-mentioned formula (2) represents the pore diameter of the carbon material after the stabilization step.

[0060] The graphene mesh size L is adjusted, for example, by adjusting the conditions of the covering step and the stabilization step in the above-mentioned manufacturing method. The graphene mesh size L is increased by increasing the carbon covering amount in the covering step, increasing the heating temperature in the stabilization step, or extending the reaction time. The average number of carbon layers stacked n of the carbon material is adjusted by adjusting the conditions of the coating step and the stabilization step in the above-mentioned production method, for example. The average number of carbon layers stacked n is increased by increasing the heating temperature in the coating step and increasing the reaction time. The nitrogen content N within the graphene network of the carbon material is adjusted by, for example, adjusting the conditions during the covering step in the above-mentioned production method. The pore diameter d of the porous carbon material is adjusted by at least one of adjusting the casting mold used and adjusting the conditions of the separation process. The pore diameter d is increased by at least one of using a casting mold with a larger particle size and adjusting the drying conditions in the separation process. The surface distortion t is a variable related to the shrinkage generated when the mold is removed and dried in the separation process. The surface distortion t is defined by the following formula (3). That is, the surface distortion t is obtained by the ratio of the surface area of ​​the mold particle to the surface area of ​​a sphere assumed by the pore diameter of the mold graphene. The surface distortion t is adjusted by adjusting at least one of the mold, the pore diameter d, and the average number of stacking n.

[0061] [Number 3]

[0062] By adjusting the process, a carbon material having a graphene mesh surface size L and a bulk elastic modulus K of desired sizes can be produced.

[0063] [Design method of carbon materials] Taking the above-described method for producing a carbon material into consideration, the carbon material can be applied to a method for designing flexibility. For example, the following design method can be implemented.

[0064] First, as a process for setting the softness parameters of the carbon material, five parameters constituting the bulk elastic modulus K of the carbon material, the graphene mesh size L of the carbon material, the average stacking number n of the carbon material, the nitrogen content N in the graphene mesh of the carbon material, the pore diameter d of the porous carbon material, and the surface distortion t are set as the softness parameters of the carbon material.

[0065] Next, as a step of setting the flexibility of the product, the range of the bulk modulus K of the carbon material constituting the product is set.

[0066] Next, as a parameter identification step, parameters specified in product design and parameters that can be freely designed are identified.

[0067] Then, for the freely designed parameters, the above-mentioned formula (2) is used to set parameters that realize the set range of the bulk modulus K. Thus, the flexibility parameter of the carbon material constituting the product is set.

[0068] The specific flexibility parameter is set by an adjustment step in the method for producing the carbon material, etc.

[0069] Next, a lithium ion secondary battery as the power storage device of the present invention will be described.

[0070] Fig. 20An example of a cross-sectional structure of a coin-type power storage device (lithium battery) 200 according to an embodiment of the present invention is shown. The power storage device 200 is formed by stacking a disk-shaped positive electrode 212 housed in a metal outer casing 211 and a disk-shaped negative electrode 214 housed in a metal outer casing 113 via a separator 215. In addition, a metal spring 218 and a spacer 219 are arranged between the outer casing 213 and the negative electrode 214. The interior of the outer casing 211 and the outer casing 213 is filled with a liquid electrolyte, and the peripheral portions of the outer casing 211 and the outer casing 213 are sealed by riveting via a sealing gasket 217.

[0071] The positive electrode will be described. The positive electrode 212 is obtained, for example, by applying a slurry mixed with a metal oxide material, a conductive auxiliary material that assists electronic conductivity, a binder, and a solvent onto a metal foil for current collection such as a rolled aluminum foil to form a coating, and after heating and drying to remove the solvent, forming a specified size and density.

[0072] The metal compound material that can be used as the positive electrode active material refers to a material that can release Li ions to the electrolyte while releasing electrons toward the external circuit of the battery. The amount of Li ions contained varies depending on its chemical composition, crystal structure, etc., and it is preferred that the material can reversibly take in and release a large amount of Li ions.

[0073] As the material, transition metal oxides, composite oxides of lithium and transition metals, transition metal sulfides, etc. are mentioned. As transition metals, Fe, Co, Ni, Mn, etc. are used. As specific examples, MnO, V 2 O 5 、V 6 O 13 、TiO 2 Transition metal oxides, LiNiO 2 、LiCoO 2 、LiMn 2 O 4 TiS 2 , FeS, MoS 2 Inorganic compounds such as quartz and tantalum may also be used in which a specific element is partially replaced with a certain element in order to improve their properties.

[0074] In addition to the above-mentioned inorganic compounds, there are also positive electrode materials composed of organic compounds. For example, polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts, etc. can be cited. The positive electrode material can also be a mixture of the above-mentioned inorganic compounds and organic compounds.

[0075] The physical properties of the positive electrode material are determined by the requirements of the battery design and manufacturing process due to the constraints such as the use of the storage device. In the manufacture of the positive electrode material, the process design is performed in a manner that can achieve its physical properties. Examples of physical property values ​​include powder particle size and distribution, specific surface area, density, etc.

[0076] For example, the powder particle size is appropriately selected in consideration of other constituent elements of the power storage device, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the average value is usually preferably 1 μm to 30 μm, more preferably 1 μm to 10 μm.

[0077] Since the positive electrode materials generally have low electron conductivity, it is preferred that a conductive aid to assist electron conductivity coexists in the positive electrode. The conductive aid may be made of carbon-based materials, metal-based materials, or other materials with high electron conductivity, but carbon-based materials are preferred.

[0078] The amount of the conductive auxiliary agent to be present is limited to the necessary minimum, and the content of the positive electrode material that specifies the capacity of the electrical storage device should be maximized.

[0079] Examples of conventional carbon-based materials include soot, acetylene black, Ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0080] Compared with these, the conductive aid of the present embodiment has a greater feature not found in existing materials as described above. That is, the conductive aid of the present embodiment is characterized in that it has a fine structure like nanocarbon and has elasticity against stress, and also has a high specific surface area and less oxygen-containing functional groups. Due to this feature, the conductive additive can maintain the electronic conductivity of the electrode even in an electrochemical oxidation environment or stress environment to which the battery is exposed, thereby suppressing degradation of the characteristics.

[0081] The preferred ratio of the conductive aid composed of the carbon material of this embodiment contained in the positive electrode varies depending on the type of positive electrode material, the type and amount of binder, battery capacity design, etc., and is preferably 0.03 wt % or more in the positive electrode mixture.

[0082] The positive electrode material and the conductive aid are mostly powdered, and in order to fix them to each other and to the current collecting metal foil, a small amount of binding material is preferably mixed and used. The binding material is required to be chemically and electrochemically inactive and have certain flexibility and affinity, and preferably a plastic resin material is used.

[0083] Examples of the plastic resin material include fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, CN-containing polymers such as polyacrylonitrile and polyvinylidene fluoride, polyvinyl acetate and polyvinyl alcohol and other polyvinyl alcohol polymers, halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride, conductive polymers such as polyaniline, alkane polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, polymers having rings such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone, acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, etc. In addition, the above resin materials may be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, preferably 100,000 to 1,000,000. If the molecular weight is too small, the strength of the coating film decreases, while if it is too large, the viscosity increases, making it difficult to form an electrode.

[0084] In order to make the binding material fully evenly distributed and to form the slurry coating into a specified size, it is possible to use an appropriate slurry solvent that only dissolves the binding material resin but does not dissolve other materials. For example, when polyvinylidene fluoride is used, dimethylformamide is preferably used as a solvent. Alternatively, the solvent can use N-methylpyrrolidone or can be appropriately selected and used according to the conditions of the manufacturing process.

[0085] The metal foil for current collection is preferably a material that can be obtained cheaply and can withstand industrial use, and preferably a material that has electrochemical resistance to the potential displayed by the positive electrode. As examples of metal foil for current collection, aluminum foil, nickel foil, titanium foil, stainless steel foil are preferred, and rolled aluminum foil that is usually easily available is more preferred.

[0086] As a method for forming the coating film of the slurry, a commonly used printing technique can be used. When the thickness of the coating film is small, gravure printing is preferably used, and when the thickness of the coating film is large, a printing method such as doctor blade printing or die printing is preferably used.

[0087] Thereafter, the coating film is dried by heating. Any drying method may be used, but it is preferable to use a method that can achieve a desired adhesive strength with the adhesive material.

[0088] Then, when the positive electrode is formed into a predetermined size, it is preferable to use an industrially available cutting blade and its method. In addition, in order to achieve a predetermined density, it is preferable to use an industrially available pressurizing device and its method as needed.

[0089] Next, the negative electrode will be described. The negative electrode 214 is obtained, for example, by applying a slurry obtained by mixing a carbon-based material, a binder, and a solvent onto a current collecting metal foil such as a rolled copper foil, and heating and drying to remove the solvent to obtain a predetermined size and density.

[0090] As the carbon-based material that can be used for the negative electrode, a carbon-based material that can stabilize the bonding between Li ions and electrons flowing from an external circuit and has a plurality of stabilizing sites inside the carbon-based material is preferred.

[0091] As an example, any organic material can be used regardless of whether it has high or low crystallinity, and preferably graphite, coke, amorphous carbon, hard carbon, polymer carbon, etc. In this case, the principle is that Li ions are combined with electrons in the state of being sandwiched between graphene layers, etc., and stabilized.

[0092] In addition, as another stabilizing mechanism, a method of electrochemically forming an intermetallic compound may be used, and silicon, tin, zinc, bismuth, antimony, cadmium, lead, germanium, etc. can be preferably used.

[0093] In addition, other materials that manage the negative electrode side of the power storage device and exhibit a relatively low electrochemical reaction potential may also be used, preferably compounds of metals and oxygen, sulfur, halogens, nitrogen, phosphorus, and the like.

[0094] Furthermore, in order to obtain an arbitrary discharge curve according to the application of the electric storage device, the above-mentioned negative electrode materials can be mixed and used at a plurality of predetermined ratios.

[0095] The physical properties of the negative electrode material are determined by the design of the device (e.g., battery) and the requirements in the manufacturing process due to the constraints such as the utilization form of the storage device. In the manufacture of the material, the process design is performed in a manner that can achieve its physical properties. Examples of physical property values ​​include powder particle size and distribution, specific surface area, density, etc.

[0096] For example, the powder particle size is appropriately selected in consideration of other constituent elements of the power storage device, but is generally preferably 1 μm to 70 μm, more preferably 3 μm to 30 μm, as an average value from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics.

[0097] The above-mentioned negative electrode material generally has high electron conductivity, but has a smooth surface depending on the material. In the case where the contact between the particles is insufficient, it is also preferred to coexist with a conductive auxiliary agent that assists electron conductivity. As a material, carbon-based materials, metal-based materials, and other materials with high electron conductivity can also be used, among which carbon-based materials are preferred.

[0098] The amount of the conductive auxiliary agent to be present is limited to the necessary minimum, and the content of the negative electrode material that specifies the capacity of the electrical storage device should be maximized.

[0099] Examples of conventional carbon-based materials include carbon black, acetylene black, Ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0100] Compared with these, the conductive aid of the present embodiment has a greater feature not found in existing materials as described above. That is, the conductive aid of the present embodiment is characterized in that it has a fine structure like nanocarbon and has elasticity against stress, and also has a high specific surface area and less oxygen-containing functional groups.

[0101] Due to this feature, the conductive agent can maintain the electronic conductivity of the electrode even in an electrochemical reduction environment or stress environment to which the battery is exposed, thereby suppressing degradation of the characteristics.

[0102] The preferred ratio of the conductive aid composed of the carbon material of this embodiment contained in the negative electrode varies depending on the type of negative electrode material, the type and amount of binder, battery capacity design, etc., but is preferably 0.03 wt % or more per unit of negative electrode mixture.

[0103] The metal foil for current collection is preferably a material that can be obtained cheaply and can withstand industrial use, and preferably a material that does not have electrochemical reactivity to the potential displayed by the negative electrode. For example, as the metal foil for current collection, copper foil, nickel foil, titanium foil, stainless steel foil are preferred, and electrolytic copper foil and rolled copper foil that are usually easily available are more preferred.

[0104] As a method for forming a coating film of the slurry, a commonly used printing technique can be used. When the thickness dimension is small, gravure printing or the like is preferably used, and when the thickness dimension is large, a printing method such as doctor blade printing or die printing is preferably used.

[0105] Thereafter, the coating film is dried by heating. Any drying method may be used, but it is preferable to use a method that can achieve a desired adhesive strength with the adhesive material.

[0106] Then, when the negative electrode is formed into a predetermined size, it is preferable to use an industrially available cutting blade and its method. In addition, in order to achieve a predetermined density, it is preferable to use an industrially available pressurizing device and its method as needed.

[0107] The above-mentioned negative electrode material and conductive aid are mostly powdered, and in order to fix them to each other and to the current collecting metal foil, it is preferred to mix and use a small amount of binding material. The binding material is required to be chemically and electrochemically inactive and have certain flexibility and affinity, and preferably a plastic resin material is used.

[0108] Examples of the plastic resin material include fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, CN-containing polymers such as polyacrylonitrile and polyvinylidene fluoride, polyvinyl acetate and polyvinyl alcohol and other polyvinyl alcohol polymers, halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride, conductive polymers such as polyaniline, alkane polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, polymers having rings such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone, acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, carboxymethyl cellulose, styrene-butadiene rubber, etc. In addition, the above resin materials may be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, preferably 100,000 to 1,000,000. When the molecular weight is too small, the strength of the coating film decreases, and when it is too large, the viscosity increases, making it difficult to form an electrode.

[0109] In order to make the binding material fully and evenly distributed and to form the slurry coating into a specified size, an appropriate slurry solvent that only dissolves the binding material resin but does not dissolve other materials can be used. For example, in the case of using polyvinylidene fluoride, dimethylformamide is preferably used as a solvent. Alternatively, the solvent can use N-methylpyrrolidone or can be appropriately selected and used according to the conditions of the manufacturing process.

[0110] The battery electrolyte of the present invention will be described.

[0111] Electrolytes are made by dissolving solutes in organic solvents, which are usually the main components.

[0112] One of the compositions of the electrolyte first has a solute that serves as a source of ions, that is, a Li salt.

[0113] The type of solute is not particularly limited, and any solute may be used as long as it is a solute known to be used for the purpose of the electrical storage device. Specific examples include the following.

[0114] As an example of solute, LiPF 6, LiBF 4 Inorganic salts, LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2 , cyclic 1,2-perfluoroethane bissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )、LiC(CF 3 SO 2 ) 3 、LiPF 4 (CF 3 ) 2 、LiPF 4 (C2F 5 ) 2 、LiPF 4 (CF 3 SO 2 ) 2 、LiPF 4 (C 2 F 5 SO 2 ) 2 , LiBF 2 (CF 3 ) 2 , LiBF 2 (C 2 F 5 ) 2 , LiBF 2 (CF 3 SO 2 ) 2 , LiBF 2 (C 2 F 5 SO 2 ) 2 Fluorine-containing organic Li salts and Li bis(oxalate)borate, etc.

[0115] Among them, LiPF is preferred from the perspective of battery performance. 6 , LiBF 4 、LiN(CF 3 SO 2 ) 2 and LiN(C 2 F 5 SO2 ) 2 , LiPF is particularly preferred 6 and LiBF 4 .

[0116] In addition, these Li salts may be used alone or in combination of two or more.

[0117] Regarding the content ratio of the Li salt in the electrolyte, the ratio varies depending on the type of solvent that dissolves the Li salt and the mixed composition. The content ratio of the Li salt in the electrolyte is preferably 7 wt % to 190 wt %, more preferably 10 wt % to 180 wt %, and further preferably 13 wt % to 150 wt %.

[0118] Next, the organic solvent used in the electrolyte is described.

[0119] Its kind is not particularly limited, can be appropriately selected from existing solvents known as solvents for use. For example, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylates, chain carboxylates, phosphorus-containing organic solvents etc. that do not have unsaturated bonds can be enumerated.

[0120] Factors that affect the movement of Li ions include the viscosity and solvation power of the organic solvent in addition to viscosity. The solvation power is the force that dissociates dissolved ions. If it is too strong, the movement of ions is hindered, so there is an optimal value.

[0121] In addition, practical power storage devices are used in a wide range of environmental conditions, and in particular, the physical properties of organic solvents, such as melting point and boiling point, also need to be within a certain range.

[0122] A practical solution to the above requirements is to use a mixture of multiple organic solvents. The composition of the mixture is determined based on the combination of various physical properties, such as organic solvents with higher melting points and organic solvents with lower melting points, organic solvents with higher solvating power and organic solvents with lower solvating power, etc., taking practical characteristics into consideration.

[0123] In the electrolyte of the present embodiment, it is preferred to use a mixture of a cyclic carbonate and a chain carbonate, both of which have no carbon-carbon unsaturated bond.

[0124] Examples of the cyclic carbonate include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, and butylene carbonate. Among them, ethylene carbonate and propylene carbonate are preferred, and ethylene carbonate is particularly preferred from the viewpoint of improving battery characteristics.

[0125] As the chain carbonates, dialkyl carbonates are preferred, and the carbon number of the constituting alkyl group is preferably 1 to 5, particularly preferably 1 to 4. Specifically, examples thereof include symmetrical chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; and asymmetrical chain alkyl carbonates such as ethyl methyl carbonate, methyl n-propyl carbonate, and ethyl n-propyl carbonate. Among them, dimethyl carbonate has the lowest viscosity and is preferred.

[0126] However, since the boiling point of dimethyl carbonate is slightly low, better properties can be obtained by further mixing and using the chain carbonates showing a higher boiling point. As the mixed chain carbonate, diethyl carbonate is preferred, but there is no problem even if other chain carbonates are used.

[0127] The mixing ratio varies depending on the desired practical properties. The ratio of the chain carbonate to the cyclic carbonate has an optimal composition when the ratio of the Li salt is also included.

[0128] The content of the cyclic carbonate in the electrolyte is preferably 1% to 35% by weight, more preferably 3% to 30% by weight, and further preferably 4% to 25% by weight. A plurality of cyclic carbonates may be used in combination.

[0129] On the other hand, the content of the chain carbonate in the electrolyte is preferably 40% to 70% by weight, and more preferably 43% to 68% by weight. A plurality of chain carbonates may be used in combination.

[0130] As a comprehensive composition, the following combination is preferred. In the combination of ethylene carbonate and dialkyl carbonate, ethylene carbonate and dimethyl carbonate are preferred, and symmetrical chain dialkyl carbonate and / or asymmetrical chain dialkyl carbonate may also be contained. For example, when containing ethylene carbonate such as ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, symmetrical chain dialkyl carbonate and asymmetrical chain dialkyl carbonate, the balance between the cycle characteristics and the high output discharge characteristics is good, so it is preferred. Among them, the asymmetrical chain dialkyl carbonate is preferably ethyl methyl carbonate, and the alkyl group of the alkyl carbonate preferably has 1 to 2 carbon atoms.

[0131] Furthermore, as a solvent that assists the dissociation and migration of ions, cyclic ethers, chain ethers, cyclic carboxylates, chain carboxylates, etc. may be added to the above-mentioned main organic solvents.

[0132] Examples of the cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran, and examples of the chain ethers include dimethoxyethane and dimethoxymethane.

[0133] Examples of the cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone, and examples of the chain carboxylic acid esters include methyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.

[0134] Among them, chain carboxylic acid esters are particularly preferred.

[0135] Furthermore, it is also preferable that the electrolyte of the present embodiment contains a fluorine-containing cyclic carbonate having two or more fluorine atoms.

[0136] The number of fluorine atoms in the fluorinated cyclic carbonate having two or more fluorine atoms is not particularly limited. In the case of fluorinated ethylene carbonate, the lower limit is usually two or more, and the upper limit is usually 4 or less, preferably 3 or less.

[0137] In the case of fluorinated propylene carbonate, the lower limit is usually two or more, and the upper limit is usually 6 or less, preferably 5 or less. In particular, from the viewpoint of improving cycle characteristics and storage characteristics, it is preferred that two or more fluorine atoms are bonded to the carbon forming the ring structure.

[0138] Among them, from the viewpoint of improving battery characteristics, fluorinated ethylene carbonate having two or more fluorine atoms is preferred, among which cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one and 4,4-difluoro-1,3-dioxolane-2-one are particularly preferred.

[0139] The fluorinated cyclic carbonate with more than two fluorine atoms can be used alone, or two or more can be used in combination. In order to show the effect of the present embodiment, the ratio of the fluorinated cyclic carbonate compound with more than two fluorine atoms in the non-aqueous electrolyte is not particularly limited, usually more than 0.001 weight %, preferably more than 0.01 weight %, more preferably more than 0.1 weight %, particularly preferably more than 0.2 weight %, most preferably more than 0.25 weight %. At a concentration lower than it, it is sometimes difficult to show the effect of the present embodiment. On the contrary, if the concentration is too high, then the internal pressure of the battery increases when the high temperature is preserved sometimes, so the upper limit is usually less than 10 weight %, preferably less than 4 weight %, more preferably less than 2 weight %, particularly preferably less than 1 weight %, most preferably less than 0.5 weight %.

[0140] In addition, cyclic carbonates having an unsaturated bond and aromatic compounds having a total carbon number of 7 to 18 may be mixed in the electrolyte for use.

[0141] In the cyclic carbonates with unsaturated bond, from the viewpoint of improving cycle characteristics, preferred vinylene carbonate, vinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate or 4,5-divinyl ethylene carbonate, wherein, more preferably vinylene carbonate or vinyl ethylene carbonate.They can be used alone, and also can use two or more.

[0142] Preferred aromatic compounds having a total carbon number of 7 to 18 include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and dibenzofuran.

[0143] It is considered that by suppressing the side reaction of the aromatic compound having a total carbon number of 7 or more and 18 or less with the negative electrode and the positive electrode, a significant decrease in discharge characteristics after high-temperature storage can be suppressed.

[0144] In order to show the effect of the present embodiment, the total carbon atoms in the electrolyte are more than 7 and the ratio of the aromatic compounds below 18 is usually more than 0.001 weight %, preferably more than 0.1 weight %, particularly preferably more than 0.3 weight %, most preferably more than 0.5 weight %, and the upper limit is usually less than 5 weight %, preferably less than 3 weight %, particularly preferably less than 2 weight %. When concentration is lower than this lower limit, it is sometimes difficult to show the effect of safety when improving overcharge. On the contrary, when concentration is too high, the characteristics of batteries such as high temperature storage characteristics are reduced sometimes.

[0145] The separator 215 separates the positive electrode 212 from the negative electrode 214 and allows lithium ions to pass therethrough while preventing short circuit of current due to contact between the two electrodes. A porous film made of resin is preferably used.

[0146] As the form of the film, it is preferable to use a stretched film in which pores are formed by stretching a bulk resin, a nonwoven fabric having a pore structure such that a porous film can be produced by laminating a plurality of fibrous resin fibers, or the like.

[0147] As the material of the resin, polyolefins can be cited, and polyethylene is particularly preferred. Polyethylene has a relatively low melting point. When the temperature of the battery rises due to some reasons (such as unsafe conditions such as short circuits, etc.), the pores in the membrane are blocked due to thermal melting, hindering the movement of driving ions, thereby stopping the reaction and ensuring safety.

[0148] A porous film formed by stretching is usually formed by adding a plasticizer to polyolefin, removing the plasticizer before or after stretching, and the portion where the plasticizer exists becomes a base point, thus having a relatively uniform microporous structure.

[0149] When producing a stretched film, stretching is usually performed in both the longitudinal direction and the width direction. A preferred stretched film can be obtained by removing the above-mentioned plasticizer and the like while appropriately combining any atmosphere medium, temperature, speed, stress, number of process repetitions, and the like.

[0150] The above-mentioned manufacturing process can obtain a high-quality stretched film, but it is a multi-step process, so it is difficult to reduce the manufacturing cost such as process cost, which may become a negative factor in the popularization of power storage devices.

[0151] On the other hand, by simplifying the process by only extending in the longitudinal direction without using a plasticizer, a porous membrane that can be manufactured at an industrial level and can reduce the manufacturing cost can be obtained. In this case, the applicable resin is polyolefin, preferably polypropylene.

[0152] The separator between the positive electrode and the negative electrode can be formed by an electrically insulating porous body. As the separator, for example, a film or fiber nonwoven fabric made of a polymer such as polyethylene, polypropylene, polyester, polyethylene terephthalate, polyimide, etc. can be applied. The material of the separator can be used alone or in multiple forms. In addition, the separator can be a single layer or a multilayer (composite film). In addition, the separator can also contain inorganic material nanoparticles such as ceramics. In addition, a polymer compound such as polyvinylidene fluoride can also be applied to both sides of the separator.

[0153] In the non-aqueous electrolyte battery involved in the present embodiment, it is also possible to use an electrolyte that becomes gel-like by including a polymer compound, which is swollen by an organic solvent to become a retainer for maintaining a non-aqueous electrolyte. The reason is that by including a polymer compound swollen by an organic solvent, a higher ion conductivity can be obtained, an excellent charge and discharge efficiency can be obtained, and leakage of the battery can be prevented. In the case of containing a polymer compound in a non-aqueous electrolyte, the content of the polymer compound is preferably set to a range of more than 0.1 mass % and less than 10 mass % of the non-aqueous electrolyte.

[0154] When a polymer compound such as polyvinylidene fluoride is applied to both surfaces of the separator, the mass ratio of the nonaqueous electrolyte to the polymer compound is preferably within a range of 50:1 to 10:1. Within this range, higher charge and discharge efficiency can be obtained.

[0155] As the above-mentioned macromolecular compound, for example, ether macromolecular compounds such as polyvinyl formal, polyethylene oxide and crosslinked bodies containing polyethylene oxide, ester macromolecular compounds such as polymethacrylate, acrylate macromolecular compounds, polyvinylidene fluoride, and polymers of vinylidene fluoride such as copolymers of vinylidene fluoride and hexafluoropropylene can be cited. The macromolecular compound can be used alone or in combination. In particular, from the viewpoint of preventing the swelling effect during high temperature storage, fluorine-based macromolecular compounds such as polyvinylidene fluoride are preferably used.

[0156] The electric storage device having the above-described structure functions as follows. When the power storage device is charged, Li ions contained in the positive electrode 212 are inserted into the interlayers of the layered structure of graphite contained in the negative electrode 214 through the separator 215. Then, when the power storage device is discharged, the Li ions are separated from the interlayers of the layered structure contained in the negative electrode 214, and return to the positive electrode 212 through the separator 215.

[0157] As mentioned above, although one embodiment of the present invention has been described in detail, the present invention is not limited to the above embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0158] In the above embodiment, a coin-shaped lithium-ion battery is used as an example of an electric storage device, but the electric storage device of this embodiment is also applicable to electric storage devices having other shapes such as button-shaped, paper-shaped, square-shaped, or cylindrical-shaped with a spiral structure. In addition, the electric storage device of this embodiment can be made into various sizes such as thin and large.

[0159] Furthermore, in the above description, an embodiment is described assuming a case where the power storage device has a liquid electrolyte as the electrolyte involved in this embodiment, but any other electrolytes can be applied, and as an example, a gel electrolyte or a solid electrolyte can also be preferably used. [Example]

[0160] Hereinafter, examples of the present embodiment will be described. The present invention is not limited to the following examples. First, examples of the carbon material according to the present embodiment will be described.

[0161] [Example 1] (Mold) First, as nanoparticles for the mold, aluminum oxide nanoparticles (TM-100 manufactured by Daimei Chemical Industry Co., Ltd.) were prepared. The BET specific surface area of ​​the aluminum oxide nanoparticles was denoted as S [m 2 / g], and the density of alumina is set to ρ[g / m 3 ], through the formula d 0[nm] = 6 / (S BET ×ρ)×10 9 Calculate the average particle size d 0 The result is the average particle size d of aluminum oxide nanoparticles. 0 =14nm.

[0162] (Covering process) In the covering process, chemical vapor deposition was performed at 900° C. for 2 hours using methane as the raw material gas and argon as the process gas. Then, the flow rate of the methane gas was set to 0 ml / min and maintained for 30 minutes, followed by natural cooling to room temperature.

[0163] (Separation process) Next, the molded product obtained by the covering process and hydrofluoric acid were placed in a beaker for mixing and stirred at room temperature for 2 hours. Then, the separated molded product was taken out from the mold, and the sample was filtered using a membrane filter (0.1 μm) while being washed 5 times with pure water and filtered. Then, the molded product and hydrofluoric acid were mixed and stirred again by the same method as before, and the molded product was filtered using pure water.

[0164] Next, the molded product is placed in a spiral tube bottle filled with acetone, covered with a lid, and shaken thoroughly. Then, it is allowed to stand overnight at 60°C in a constant temperature dryer. The next day, the supernatant is discarded, acetone is added again, and it is allowed to stand at 60°C in a constant temperature dryer for 3 hours. Next, the supernatant is discarded, acetone is added again, and it is allowed to stand at 60°C in a constant temperature dryer again for 3 hours. Then, the acetone is removed by suction filtration, and a constant temperature dryer is used to perform reduced pressure drying at 150°C, 10 hours, and below 1000Pa twice to produce CMS (carbon mesoporous sponge) as a molded product.

[0165] (Stabilization process) Next, the CMS was placed in a sample chamber of a high-temperature heating furnace (IZU-SMS005, manufactured by Izumi-Tech Co., Ltd.). After the sample chamber was evacuated, the temperature was raised to 1800°C at a rate of 15°C / min while argon gas was flowing at 10 ml / min. The CMS was heat treated at 1800°C for 1 hour to sinter the CMS to produce GMS (graphene mesoporous sponge) as a carbon material.

[0166] [Example 2] A carbon material was prepared in the same manner as in Example 1 except that alumina nanoparticles (TM-300 manufactured by Daimei Chemical Industry Co., Ltd.) were used as nanoparticles for the mold and the heat treatment temperature in the stabilization step was changed to 1600° C. The average particle size of the alumina nanoparticles was measured in the same manner as in Example 1 and was 7 nm.

[0167] [Example 3] A carbon material was prepared in the same manner as in Example 1 except that alumina nanoparticles (TM-300, manufactured by Daimei Chemical Industry Co., Ltd.) were used as nanoparticles for the mold.

[0168] [Example 4] A carbon material was prepared in the same manner as in Example 1 except that alumina nanoparticles (product name: SBa-200, manufactured by Sasol Chemical) were used as nanoparticles for the mold. The average particle size of the alumina nanoparticles was measured in the same manner as in Example 1 and was 8 nm.

[0169] [Example 5] The carbon material was prepared in the same manner as in Example 1 except that magnesium oxide nanoparticles (manufactured by US Research Nanomaterials, model: Magnesium Oxide MgO Nanopowder / Nanoparticles (MgO, 99+%, 20 nm)) were used as nanoparticles for the mold, the conditions of the coating process were changed, and hydrochloric acid was used instead of hydrofluoric acid in the separation process. The average particle size of the magnesium oxide nanoparticles was measured in the same manner as in Example 1, and the result was 30 nm.

[0170] In Example 5, the flow rates of methane gas and argon gas were changed in the covering process to adjust the covering amount. In addition, the treatment time under the condition of 900° C. was changed to 50 minutes. The other conditions in the covering process were the same as those in Example 1.

[0171] [Comparative Example 1] In Comparative Example 1, zeolite mold carbon (ZTC) was prepared as a carbon material by the following method. First, 15 g of Y-type zeolite (HZS-320NAA manufactured by Tosoh Corporation) dried overnight at 150°C in a heated environment was impregnated with furfuryl alcohol (FA) in a round-bottom flask under reduced pressure using a vacuum pump to obtain a FA / zeolite composite. Next, the FA / zeolite composite was placed in a quartz reaction tube and heated under N 2 After heat treatment was performed at 80° C. for 24 hours under circulation, the mixture was kept at 150° C. for 8 hours to obtain a polyfurfuryl alcohol (PFA) / zeolite composite.

[0172] Next, the PFA / zeolite composite was used as a mold to cover the carbon layer. Specifically, 15 g of the PFA / zeolite composite was placed in a horizontal CVD apparatus and heated in N2O3 containing 4 vol% propane. 2The carbon layer was coated on the PFA / zeolite composite by chemical vapor deposition at a maximum temperature of 700°C for 2 hours under N2 gas flow. 2 The mixture was heat treated at 900°C for 3 hours under a flow condition to obtain a zeolite / carbon composite. Next, the zeolite / carbon composite is treated with hydrofluoric acid (HF) to remove the zeolite serving as a casting mold, thereby obtaining ZTC.

[0173] [Comparative Example 2] ZTC was prepared as a carbon material in the same manner as in Comparative Example 1 except that the conditions for preparing the zeolite / carbon composite were changed.

[0174] In Comparative Example 2, first, 15 g of the same Y-type zeolite as used in Comparative Example 1 was dried overnight at 150°C under vacuum. Then, the Y-type zeolite was used as a mold and placed in a rotary kiln type CVD apparatus. A chemical vapor deposition method was performed at a maximum temperature of 600°C for 4 hours under the flow of argon gas containing 15 vol% acetylene, thereby covering the mold with a carbon layer. Then, the introduction of acetylene gas was stopped, and the mold was heated under N2 in the same manner as in Comparative Example 1. 2 Heat treatment was performed at 900°C for 3 hours under a flow condition to obtain a zeolite / carbon composite having a stable carbon skeleton structure. Next, the mold was removed in the same manner as in Comparative Example 1 to obtain ZTC.

[0175] [Comparative Example 3] ZTC was prepared as a carbon material in the same manner as in Comparative Example 1 except that the conditions for preparing the zeolite / carbon composite were changed.

[0176] In Comparative Example 3, first, 0.5 g of X-type zeolite (Molecular sieve 13X powder manufactured by UNION Showa Co., Ltd.) was vacuum dried at 150° C. for 6 hours. Next, 0.5 g of the X-type zeolite was used as a mold and placed in a quartz reaction tube. 2 Chemical vapor deposition was carried out at 600°C for 4 hours under the circulation to cover the mold with a carbon layer. Then, the introduction of acetylene gas was stopped and heat treatment was carried out at 850°C for 3 hours to obtain a zeolite / carbon complex with a stable carbon skeleton structure. Then, the mold was removed in the same manner as in Comparative Example 1 to obtain ZTC.

[0177] [Comparative Example 4] A molded product of CMS, which is a precursor of GMS, was obtained by the same method as in Example 1 except that the stabilization step was not performed.

[0178] [Comparative Example 5] A molded product of CMS, which is a precursor of GMS, was obtained by the same method as in Examples 2 and 3 except that the stabilization step was not performed.

[0179] [Comparative Example 6] A molded product of CMS, which is a precursor of GMS, was obtained by the same method as in Example 4 except that the stabilization step was not performed.

[0180] [Comparative Example 7] A molded product of CMS, which is a precursor of GMS, was obtained by the same method as in Comparative Example 6 except that the following hot pressing step was performed. First, a molded product covered with a carbon layer on a casting mold is prepared by the same method as in Comparative Example 6. Next, the molded product is placed in a mold and placed in a hot pressing device (AG-50kNXDp, manufactured by Shimadzu Corporation). Next, pressure is applied at a sliding speed of 0.01 mm / sec under vacuum at room temperature, and the temperature is raised when it reaches 30 MPa. When it reaches 600°C, the pressure and temperature are maintained for 3 hours, and the molded product is taken out after sufficient cooling. Next, the casting mold is removed by the same method as in Comparative Example 6 to obtain a molded product of CMS, which is a precursor of GMS.

[0181] [Comparative Example 8] A molded product of CMS, which is a precursor of GMS, was obtained by the same method as in Comparative Example 6 except that the conditions of the covering step were changed. In the covering step of Comparative Example 8, first, argon was circulated at a flow rate of 225 ml / min in an acetonitrile solvent, and aluminum oxide nanoparticles were chemically vapor deposited at 650° C. for 200 minutes to cover the mold with a carbon layer of a graphene skeleton doped with nitrogen to obtain a molded product. Next, the molded product was heat treated at 1800° C. for 1 hour and then naturally cooled to room temperature. CMS, a precursor of GMS, was produced.

[0182] [Comparative Example 9] As Comparative Example 9, single-walled carbon nanotubes (SWCNT) (manufactured by Zeon Corporation, model number: SG101) were prepared.

[0183] [Comparative Example 10] As Comparative Example 10, activated carbon (MSC-30 manufactured by Kansai Thermochemical Co., Ltd.) was prepared. MSC-30 is synthesized by activating petroleum coke with an alkali.

[0184] [Comparative Example 11] As Comparative Example 11, activated carbon (Shirasagi-P, manufactured by Osaka Gas Chemical Co., Ltd.) was prepared. Shirasagi-P is synthesized by activating a wood-based carbon with steam.

[0185] [Characteristics evaluation] The carbon materials of Examples 1 to 5 and Comparative Examples 1 to 11 were evaluated for their properties by the following methods.

[0186] (Measurement of bulk elastic modulus K by mercury penetration method) First, the sample is placed in a vacuum container, mercury is introduced, and isostatic pressure is applied to the sample in the range of 3KPa to 400MPa to obtain a correlation curve between the volume change ΔV of the mercury contained in the vacuum container and the pressure P. Under low pressure conditions, the volume of mercury decreases rapidly due to the impregnation of the interparticle space, and ΔV decreases rapidly. Based on this result and the initial volume V of the sample 0 Plotting the volume change rate ΔV / V 0 Correlation curve with pressure P. Figure 5A to Figure 5E : is a graph showing the results of mercury intrusion measurement of Examples 1 to 5, Figure 6A to Figure 6C : is a graph showing the results of mercury intrusion measurement of Comparative Examples 1 to 3. Figure 7A to Figure 7E is a graph showing the results of mercury intrusion measurement in Comparative Examples 4 to 8. Figure 8A to Figure 8C This is a graph showing the results of mercury intrusion measurement in Comparative Examples 9 to 11. The bulk modulus K is defined by using a range in which aggregation of primary particles does not occur and the linearity of mercury intrusion into pores is considered to be good in the measured graph.

[0187] In mercury intrusion measurement, considering that the range causing a sharp volume change will cause the aggregation of primary particles and the intrusion of mercury into pores, it is considered preferable to use a smaller linear range that does not cause a sharp volume change for calculation. Therefore, when calculating the bulk modulus based on the results of mercury intrusion measurement, in addition to the range of mercury intrusion between particles and into pores of the sample, the range where only compression of the sample occurs is used as the stress-strain curve (in the figure, the thick line portion). The bulk modulus K is calculated based on the stress-strain curve by the following formula (4). In the formula, V 0 is the volume of mercury under a certain mercury pressure P, and ΔV is the change in volume when the mercury pressure increases by ΔP, which is a negative value. K=-V 0 (ΔP / ΔV) ··· (4)

[0188] exist Figure 5A to Figure 5E Examples 1 to 5 showing the measurement results are all examples in which GMS was prepared and measured. Since it is a mesoporous body, the pressure range in which mercury invades the pores is small. 7A to 7E The same is true for the CMS shown. On the other hand, due to Figure 6A to Figure 6C The ZTC shown is a micro-polyparticle, so the pressure range for mercury to penetrate into the pores is relatively large. Figure 5A The results of Example 1 are shown in Fig. 7A In Comparative Example 4, the results of which are shown in Figure 2, no mercury intrusion between particles was observed, and the volume change rate with respect to the pressure change was gentle at 5.0×10 -5 GPa~5.0×10 -3 The region around GPa is used for bulk modulus calculation. Fig. 8A In Comparative Example 9, in which the measurement results are shown, no mercury intrusion into the tube was confirmed, so the region used as the pressure-strain curve was determined based on the inner diameter of the SWCNT observed by TEM. Figure 8B Comparative Example 10, in which the measurement results are shown in FIG. , undergoes a sharp volume change in the region of 0.0001 GPa to 0.01 GPa and above 0.1 GPa. Figure 8C The comparative example 11 in which the measurement results are shown in the figure has a small pore diameter, so mercury does not penetrate into the pores. According to the pore diameter distribution, 2.4×10 -2 GPa~1.3×10 -1 GPa is used in calculations.

[0189] (Evaluation of average graphene mesh size L_Determination of edge site quantity) Next, for Examples 1 to 6 and Comparative Examples 4 to 8, the average graphene mesh size L was calculated using the coronene model. The average graphene mesh size L is the size of a graphene sheet constituting the carbon material and is calculated using the following formula (5). edge is the average edge site amount in the carbon material, a 0 is the lattice constant of the carbon material in the a-axis direction (0.2461 nm). L=(a 0 / N edge ) ··· (5)

[0190] The average edge site number N in carbon materials edge It was measured by a temperature-dependent desorption method (TPD method) using an ultra-high-sensitivity vacuum TPD device (developed at Tohoku University, see T. Ishii et al., CARBON, 80, 2014, 135). Fig. 9 : is a diagram for explaining an ultra-high sensitivity vacuum TPD device 60 used in temperature rise desorption analysis. The ultra-high sensitivity vacuum TPD device 60 comprises: a quartz reactor having a radioactive thermometer 41, a sample holder 42 and a high-frequency induction coil 43; and a detection unit connected to the quartz reactor. The detection unit comprises, for example, a gas reservoir, a turbomolecular pump TMP, a rotary pump RP, a cold cathode Pirani pressure gauge P1, and an electrostatic capacitance gauge P2. Specifically, according to the method described in the above document, first, a sample of approximately 1 mg is placed on the sample holder, and a sample of approximately 1.0×10 -5The sample was heated to 1800°C at a rate of 10°C / min under a high vacuum of 1.37 Pa, and the gas released from the sample was quantified using a mass analyzer. 2 , H 2 O, CO, and CO 2 The gas after desorption was quantitatively determined. Here, the measurement data was corrected by measuring blank data obtained by measuring only the sample stage.

[0191] Figures 10A to 10E This is the gas discharge mode when performing the temperature rise desorption analysis of Examples 1 to 5. Figures 11A to 11C The gas discharge patterns of Comparative Examples 1 to 3 are shown in FIG. Figures 12A to 12E The gas discharge patterns of Comparative Examples 4 to 8 are shown in FIG. Figures 13A to 13C These are the gas discharge patterns of Comparative Examples 9 to 11.

[0192] The edge point quantity N is calculated using the following formula (6): edge [μmol / g] was quantified. H2 、N CO 、N CO2 These are the desorbed amounts of hydrogen, water, carbon monoxide, and carbon dioxide measured by the TPD method. N edge =2·N H2 +2·N H2O +N CO ++N CO2 ··· (6)

[0193] [Edge site specific surface area S edge Determination of Furthermore, using the above edge point quantity N edge The edge site specific surface area S of Examples 1 to 5 and Comparative Examples 1 to 11 was calculated using the following formula (7): edge Where N edge is the edge site amount of carbon material, A edge is the specific surface area per edge site, N A is Avogadro's constant. edge The average area occupied by the graphite is calculated geometrically based on the crystal structure of graphite, using the 0.083nm 2 . S edge =N edge ×A edge ×N A ··· (7)

[0194] In addition, the doped nitrogen is divided into pyrrolic type, pyridinic type, and quaternary nitrogen. 2, HCN and NH 3 The quaternary nitrogen in the graphene network is separated from the above classification as N 2 Therefore, the nitrogen content N in the graphene network is calculated by the following formula (8) for N above 900°C: 2 Calculated by quantitative analysis. In the formula, N N2 (>900℃) refers to N released at above 900℃ 2 The amount. N=N N2 (>900℃)×10 -6 ×28.0×100··· (8)

[0195] [Average stacking number n_Nitrogen adsorption and desorption measurement] The carbon materials of Examples 1 to 5 and Comparative Examples 1 to 11 were subjected to nitrogen adsorption and desorption measurements to determine the BET specific surface area S of the carbon materials. Next, the graphene theoretical specific surface area S was calculated according to the above formula (1): graphene Relative to the BET specific surface area S and edge site specific surface area S of carbon materials edge The average stacking number n of the carbon material is calculated by the ratio of the difference between the theoretical specific surface area S and the theoretical specific surface area S. graphene Set to 2627m 2 The BET specific surface area S of the carbon material was calculated by the following nitrogen adsorption and desorption measurement: as Here, the BET specific surface area S of the carbon material is obtained by the BET method.

[0196] Nitrogen adsorption and desorption measurements were performed at -196°C using a specific surface area and pore distribution measuring apparatus (BELSORP max, manufactured by BEL Japan). Degassing treatment was performed by vacuum drying at 150°C for 6 hours before the measurement. The equilibrium judgment condition for measuring the pressure in the sample tube was set to 300 seconds. Fig.14A is the nitrogen adsorption-desorption isotherm of Examples 1 to 5, Fig. 14B is the nitrogen adsorption-desorption isotherm of Comparative Examples 1 to 3, Fig. 14C are the nitrogen adsorption-desorption isotherms of Comparative Examples 4 to 8, Fig.14D is the nitrogen adsorption-desorption isotherm of Comparative Example 9, Fig.14E is the nitrogen adsorption-desorption isotherm of Comparative Example 10 and Comparative Example 11. Figures 14A to 14E In the figure, the graph with filled circles represents the nitrogen adsorption isotherm, and the graph with unfilled circles represents the nitrogen desorption isotherm.

[0197] [Pore volume V total ] Based on the nitrogen adsorption-desorption isotherm, the relative pressure P / P at -196 °C 0= 0.96 was converted into a volume of liquid nitrogen density, and the pore volume V was determined from this total .

[0198] [Pore size distribution] Adsorption isotherms can be roughly divided into two types: Type I and Type IV. Fig.15A , Fig. 15B is a schematic diagram for explaining the general shape of the adsorption isotherm. Fig.15A A schematic diagram of the adsorption isotherm of type I is shown in Fig. 15B Schematic diagram of the adsorption isotherm of type IV is shown in . Next, for the sample showing the adsorption isotherm of type I, the pore size distribution was analyzed using the software Autosorb1 with reference to the core calculated by density functional theory (DFT method) assuming slit-type pores. Next, for the sample showing the adsorption isotherm of type IV, the pore size distribution was analyzed by applying the Barrett-Joyner-Halenda method (BJH method) to each adsorption isotherm. Fig.16A is the pore size distribution of Examples 1 to 5, Fig. 16B is the pore size distribution of Comparative Examples 1 to 3, Fig. 16C is the pore size distribution of Comparative Examples 4 to 8, Fig.16D is the pore size distribution of Comparative Example 10, Fig.16E These are the pore diameter distributions of Comparative Examples 10 and 11. In addition, the pore diameter d of the carbon material was calculated by fitting the pore diameter distribution with a Gaussian function.

[0199] [Surface distortion t] For the samples of Examples 1 to 5 and Comparative Examples 4 to 8, the above-mentioned pore diameter d and the average particle diameter d of the mold nanoparticles were used. 0 , the surface distortion t was calculated by the following formula (3). In addition, for Comparative Example 7, the surface distortion t before the hot pressing step was calculated.

[0200] t=4πr 0 2 / 4πr 2 =d 0 2 / d 2 ··· (3)

[0201] Table 1 summarizes the properties of the carbon materials of Examples 1 to 5 and Comparative Examples 1 to 11.

[0202] [Table 1]

[0203] It was confirmed that the surface distortion t of Examples 1 to 5 and Comparative Examples 4 to 8 was affected by the average particle size d of the molded nanoparticles. 0 And the average stacking number n affects the average particle size d 0 The larger the value and the smaller the average stacking number n, the larger the surface distortion t. The reason is considered to be that in the separation process, when the mold is removed, the material having the structural characteristics as described above is easily affected by capillary contraction. In Example 1 and Comparative Example 4, Example 2, Example 3 and Comparative Example 5, Example 4 and Comparative Examples 6 to 8, the same mold was used. If the example (GMS) and the comparative example (CMS) wp using the same mold are compared, the example with a larger graphene mesh size L shows a larger bulk elastic modulus K. In addition, the larger the graphene mesh size L, the larger the edge site quantity N. edge The fewer continuous structures there are, the more durable the structure characteristics are.

[0204] In carbon materials, the larger the pore diameter d, the smaller the curvature of the graphene sheet. In addition, the larger the surface distortion t, the more the carbon material shows a strained structure, which makes it difficult to apply force evenly and easy to deform. Therefore, it is considered that the larger the pore diameter d and the larger the surface distortion t, the higher the mechanical flexibility, and the smaller the value of the bulk elastic modulus K.

[0205] When comparing Comparative Example 6 with Comparative Example 8, it was confirmed that in Comparative Example 8 with a higher nitrogen doping concentration, the bulk modulus K was larger, and the carbon material with a higher nitrogen doping concentration in the graphene network became harder. The reason for this is believed to be that since the double bond energy between carbon and nitrogen is higher than the double bond energy between carbon and carbon, it is easy to maintain a planar network of 6-membered rings that ensures planarity.

[0206] Fig.17 This is a graph showing the relationship between the bulk modulus K and the structural characteristics of Examples 1 to 5 and Comparative Examples 1 to 11. Fig.17 In the figure, the vertical axis represents the bulk modulus K measured by mercury intrusion porosimetry, and the horizontal axis represents the structural properties of the carbon material represented by the following formula (9). Fig.17 This is a graph in which the index is optimized by the least square method to obtain the relationship between the bulk modulus and the wire diameter of the following equation (9). (L 0.8 ·n 0.8 ·N 0.8 ) / (d 0.5 ·t 5.9 )···(9) like Fig.17 As shown in FIG. 1 , the bulk elastic modulus K of the carbon material is proportional to the structural characteristics of the carbon material as shown in the above formula (9). That is, the bulk elastic modulus K is approximated by the following formula (10). In the formula, α is a proportional constant. Fig.17 In the graph shown, α=0.16.

[0207] K = α × (L 0.8 ·n 0.8 ·N 0.8 ) / (d 0.5 ·t 5.9 ) ··· (10)

[0208] Therefore, based on this proportional relationship, it is effective to adjust the manufacturing conditions in advance or during the production of the carbon material as an adjustment process so that the carbon material has the desired structural characteristics. In addition, the above proportional relationship is not limited to the carbon material of the embodiment, but also holds true for the carbon material of the comparative example. For example, it is effective to adjust the manufacturing conditions based on the above formula (10) so that the activated carbon, SWCNT, ZTC, and CMS have the desired structural characteristics.

[0209] [SEM observation] Fig.18A , Fig.18B , Fig.18C , Fig.18D These are SEM images of Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. In Example 1 and Comparative Example 4 where the surface distortion t is small, the surface distortion t is not large, and wrinkles accompanying shape strain are not confirmed, but in the experimental data (not shown) where the surface distortion t is large, wrinkles accompanying shape strain may be confirmed.

[0210] [Raman spectroscopy] The Raman spectra of the carbon materials of Examples 1 to 5 were measured using a Raman microscope (LabRAM HR-800, manufactured by Horiba, Ltd.). A 532 nm laser was used for the measurement, and the filter was set to D1 and the aperture was set to 100 μm. The measurement range was 300 cm -1 ~3500cm -1 . Fig.19 These are the Raman spectra of Examples 1 to 5. Fig.17 The horizontal axis represents the Raman shift (cm -1 ), the vertical axis represents intensity (au). Fig.19 In the figure, the graphs of Example 1, Example 2, Example 3, Example 5, and Example 4 are listed in order from the graph with the lowest intensity.

[0211] In Examples 1 to 5, the presence of D bands and D' bands from defects such as non-hexagonal sites including edge sites, G bands from skeleton vibrations of graphene sheets, and 2D bands based on secondary phonon scattering were confirmed. The D band appears as a hexagonal leakage mode at sites where the hexagonal symmetry of the graphene mesh is broken. The peaks of the Raman spectra of Examples 1 to 5 are shifted from Raman shift (cm -1 ) Smaller peaks are the D band, G band, D' band, and 2D band peaks in sequence. The D' band is a hexagonal variable angle mode, which is prohibited in an infinitely wide hexagonal mesh. Therefore, according to the Raman spectrum, it is also confirmed that the carbon materials of Examples 1 to 5 also have a graphene skeleton. In addition, in any one of Examples 1 to 5, the 2D peak exists on the low-lying layer side compared to the 2D peak of HOPG, and can be fitted with a single Lorentzian function. In Examples 1 to 5, a single layer of graphene grows.

[0212] Next, an example of the power storage device according to the present embodiment, specifically, an example of a coin-type lithium battery as an example of the power storage device will be described.

[0213] [Example 6] <Production of positive electrode> LiCoO with an average particle size of 3 μm 2 ) powder 93 wt%, acetylene black as a conductive aid 2 wt%, PVdF 5 wt% were uniformly stirred and mixed with N-methyl-pyrrolidone (NMP) as a solvent to prepare a paste of positive electrode material. The obtained paste was coated on an aluminum foil with a thickness of 20 μm and dried. After punching it into a diameter of 14 mm, it was pressed to obtain a positive electrode.

[0214] <Production of negative electrode> 97 wt% of artificial graphite, 1 wt% of the carbon material of Example 1 as a conductive aid, 1 wt% of carboxymethyl cellulose, and 1 wt% of styrene-butadiene rubber (SBR) were uniformly stirred and mixed with distilled water as a solvent to prepare a paste of negative electrode material. The obtained paste was applied on a copper foil with a thickness of 20 μm and dried. After punching it into a diameter of 15 mm, it was pressed to obtain a negative electrode.

[0215] <Preparation of non-aqueous electrolyte> LiPF 6 ) was added to a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) adjusted in a volume ratio of 3:7 in such a way that the electrolyte concentration became 13 wt %, and dissolved to obtain an electrolyte solution.

[0216] <Coin-type battery assembly> The above-mentioned positive electrode and negative electrode are sandwiched with a microporous membrane made of polypropylene stretched uniaxially, a specified amount of the above-mentioned electrolyte is added, and it is housed together with a metal spring and a spacer in an outer component of a 2032-type coin battery (height 3.2mm, diameter 20mm), and sealed by riveting a sealing gasket to produce a coin-type battery.

[0217] [Example 7] A coin battery was prepared in the same manner as in Example 6 except that the carbon material of Example 3 was used as the conductive additive of the negative electrode.

[0218] [Example 8] The positive electrode uses lithium cobalt oxide (LiCoO) with an average particle size of 3 μm. 2 ) powder 94 wt%, the carbon material of the above-mentioned Example 1 as a conductive aid 1 wt%, PVdF 5 wt%, and acetylene black as a conductive aid for the negative electrode 1 wt%, except that a coin-type battery is made in the same manner as in Example 6.

[0219] [Example 9] A coin-type battery was prepared in the same manner as in Example 8 except that the carbon material of Example 1 was used as the positive electrode conductive aid and the negative electrode conductive aid.

[0220] [Example 10] For the positive electrode, lithium cobalt oxide (LiCoO 2 ) powder in an amount of 94.5 wt % and the carbon material of Example 1 was used as a positive electrode conductive aid at a weight of 0.5 wt %. A coin-type battery was prepared in the same manner as in Example 9.

[0221] [Example 11] A coin-type battery was produced in the same manner as in Example 9, except that 94.8 wt % of lithium cobalt oxide (LiCoO 2 ) powder was used as the positive electrode and 0.2 wt % of the carbon material of Example 1 was used as the positive electrode conductive aid.

[0222] [Example 12] A coin-type battery was produced in the same manner as in Example 9, except that 97.4 wt % of artificial graphite was used for the negative electrode and 0.6 wt % of the carbon material of Example 1 was used as the negative electrode conductive aid.

[0223] [Example 13] A coin-type battery was produced in the same manner as in Example 9 except that 97.9 wt % of artificial graphite was used for the negative electrode and 0.1 wt % of the carbon material of Example 1 was used as the negative electrode conductive aid.

[0224] [Example 14] A coin-type battery was produced in the same manner as in Example 9 except that 97.97 wt % of artificial graphite was used for the negative electrode and 0.03 wt % of the carbon material of Example 1 was used as the negative electrode conductive aid.

[0225] [Comparative Example 12] A coin-type battery was prepared in the same manner as in Example 6 except that acetylene black was used as the conductive auxiliary agent of the negative electrode.

[0226] [Comparative Example 13] A coin-type battery was prepared in the same manner as in Example 6 except that the carbon material of Comparative Example 1 was used as the conductive auxiliary agent of the negative electrode.

[0227] [Comparative Example 14] A coin-type battery was prepared in the same manner as in Example 6 except that the carbon material of Comparative Example 9 was used as the conductive auxiliary agent of the negative electrode.

[0228] [Comparative Example 15] A coin-type battery was prepared in the same manner as in Example 9 except that the carbon material of Comparative Example 1 was used as the conductive additive for the positive electrode and the negative electrode.

[0229] [Comparative Example 16] For the positive electrode, lithium cobalt oxide (LiCoO 2 A coin-type battery was prepared in the same manner as in Comparative Example 12, except that 93.5 wt % of ) powder was added and 1.5 wt % of acetylene black was used as a positive electrode conductive additive.

[0230] [Comparative Example 17] For the positive electrode, lithium cobalt oxide (LiCoO 2 A coin-type battery was prepared in the same manner as in Comparative Example 12, except that 94.5 wt % of ) powder was added and 0.5 wt % of acetylene black was used as a positive electrode conductive additive.

[0231] [Comparative Example 18] For the positive electrode, lithium cobalt oxide (LiCoO 2 A coin-type battery was prepared in the same manner as in Comparative Example 12, except that 94.8 wt % of ) powder was added and 0.2 wt % of acetylene black was used as a positive electrode conductive additive.

[0232] [Comparative Example 19] A coin-type battery was prepared in the same manner as in Example 12 except that 0.6% by weight of acetylene black was used as a negative electrode conductive aid for the negative electrode.

[0233] [Comparative Example 20] A coin-type battery was prepared in the same manner as in Example 12, except that 97.9 wt % of artificial graphite was used in the negative electrode and 0.1 wt % of acetylene black was used as the negative electrode conductive additive.

[0234] [Comparative Example 21] A coin-type battery was prepared in the same manner as in Example 12 except that 97.97 wt % of artificial graphite was used in the negative electrode and 0.03 wt % of acetylene black was used as the negative electrode conductive aid.

[0235] The coin-type batteries prepared in Examples 6 to 14 and Comparative Examples 12 to 21 were charged to 4.35 V at a constant current of 2.0 mA at 0° C., and then discharged to 3.0 V at a constant current of 2.0 mA at 0° C. Thereafter, the charge and discharge were repeated 10 times in the same manner, and the retention rate of the discharge capacity was measured. The results are shown in Table 2.

[0236] [Table 2]

[0237] When the carbon material of this embodiment is used as a conductive auxiliary agent for the positive electrode, the cycle characteristics of the battery are improved although the test is conducted at low temperature. The reason is presumably that the overvoltage during charging is low, lithium does not escape more than the design reference, and the burden on the negative electrode is small.

[0238] In addition, when the carbon material of the present embodiment is used as a conductive auxiliary agent for the negative electrode, the initial loss capacitance of the negative electrode is smaller, the initial efficiency is improved, and the initial discharge capacitance is higher than that of the comparative example. Although the test is conducted at low temperature, the cycle characteristics of the battery are improved. The reason is presumably that the overvoltage during charging is lower, lithium will not be more detached than the design benchmark, and the burden on the negative electrode is smaller.

[0239] Fig.21 This is a graph comparing the relationship between the amount of conductive additive added (wt%) in the positive electrode and the charge and discharge capacity (mAh) in the examples and comparative examples for the coin-type batteries prepared in Examples 6 to 14 and Comparative Examples 12 to 21. The horizontal axis represents the amount of conductive additive added, the vertical axis represents the capacitance, ▲ represents the charge capacitance in the examples, × represents the discharge capacitance in the examples, 0 represents the charge capacitance in the comparative examples, and ● represents the discharge capacitance in the comparative examples.

[0240] Fig. 22This is a graph comparing the relationship between the amount of conductive additive added (wt%) in the negative electrode and the charge and discharge capacity (mAh) in the examples and comparative examples for the coin-type batteries prepared in Examples 6 to 14 and Comparative Examples 12 to 21. The horizontal axis represents the amount of conductive additive added, the vertical axis represents the capacitance, ▲ represents the charge capacitance in the examples, × represents the discharge capacitance in the examples, 0 represents the charge capacitance in the comparative examples, and ● represents the discharge capacitance in the comparative examples.

[0241] The higher the positive electrode potential, the higher the capacitance. Therefore, charging is usually performed at a constant voltage in order to limit the capacitance to the design value. Here, (1) when the positive electrode has a high resistance, the positive electrode itself has a high potential and becomes a high-charge capacitor, (3) when the negative electrode has a high resistance, (battery voltage) = (positive electrode potential) - (negative electrode potential), so the negative electrode high resistance = negative overvoltage, the positive electrode potential becomes high and becomes a high-charge capacitor.

[0242] Discharge is continued until a certain end voltage is reached. However, in the case of high electrode resistance, the end voltage is quickly cut off due to the voltage drop caused by overvoltage, resulting in low capacitance. As a result, the state of charge and discharge capacitance is reflected in the charge and discharge efficiency. Of course, when the efficiency is high, the loss of battery capacitance is small, which is preferred. Fig.21 as well as Fig. 22 It is understood that the Examples exhibit high discharge capacity due to the addition of a smaller amount of the conductive auxiliary agent than the Comparative Examples, and the positive electrode material content per unit electrode is higher, resulting in a higher capacity per unit electrode.

[0243] Fig.23 This is a graph comparing the relationship between the amount of conductive additive added in the positive electrode and the initial efficiency & 10 cycle maintenance rate in the examples and comparative examples for the coin-type batteries produced in Examples 6 to 14 and Comparative Examples 12 to 21. ▲ represents the initial efficiency in the examples, × represents the 10 cycle maintenance rate in the examples, 0 represents the initial efficiency in the comparative examples, and ● represents the 10 cycle maintenance rate in the comparative examples.

[0244] Fig.24 This is a graph comparing the relationship between the amount of conductive additive added in the negative electrode and the initial efficiency & 10 cycle maintenance rate in the examples and comparative examples for the coin-type batteries prepared in Examples 6 to 14 and Comparative Examples 12 to 21. ▲ represents the initial efficiency in the examples, × represents the 10 cycle maintenance rate in the examples, 0 represents the initial efficiency in the comparative examples, and ● represents the 10 cycle maintenance rate in the comparative examples.

[0245] The charge and discharge efficiency reflects the condition of the charge and discharge capacitance. Of course, when the efficiency is high, the loss of the battery capacitance is less, which is preferred. Furthermore, the amount of electricity lost in the battery capacitance is consumed by side reactions, and the film generated in the side reactions becomes the main reason for the increase in resistance. When the cycle is repeated, the initial loss of the battery capacitance does not occur, but when the reaction potential rises compared to the usual reaction potential due to the overvoltage of the electrode, other side reactions occur. In this side reaction, the film is repeatedly generated, the resistance is further increased, the degradation is continuously promoted, and the cycle maintenance rate continues to decrease.

[0246] Depend on Fig.23 as well as Fig.24 It can be seen that in the examples, compared with the comparative examples, it can be understood that the conductive aid with a small amount of addition exhibits high efficiency and high maintenance rate. Therefore, it is estimated that the conductive aid of the present embodiment reduces the electrode resistance, suppresses the accumulation of side reactions caused by repeated cycles, and can maintain high capacitance even after repeated cycles. [Explanation of Reference Numerals]

[0247] 1. Graphene sheet; 10. Graphene skeleton; 11. Carbon layer; 12. Carbon layer; 30. Molded object; 50. Molded object; 100. Carbon material; 200. Power storage device (lithium-ion battery); 211. External component; 212. Positive electrode; 213. External component; 214. Negative electrode; 215. Diaphragm; 217. Sealing gasket; 218. Spring; 219. Spacer.

Claims

1. A carbon material, in, The bulk elastic modulus K is less than 2 GPa, and the average graphene network size L is greater than 50 nm.

2. The carbon material according to claim 1, in, The average stacking number n is 1 or more and 6 or less.

3. The carbon material according to claim 1 or 2, in, The pore diameter d is 5 nm or more and 65 nm or less.

4. The carbon material according to claim 1 or 2, in, The nitrogen content N in the graphene network plane is greater than or equal to 0 wt % and less than or equal to 10 wt %.

5. The carbon material according to claim 1, in, BET specific surface area S is 400m 2 / g and above 2600m 2 / g or less.

6. The carbon material according to claim 1, in, Edge site quantity N edge It is less than 500 μmol / g.

7. The carbon material according to claim 1, in, Edge site specific surface area S edge 30m 2 / g or less.

8. The carbon material according to claim 1, in, Pore ​​volume V total 1.9cm 3 / g or more and 5cm 3 / g or less.

9. A negative electrode for an electric storage device, in, The carbon material according to claim 1 is contained as a conductive aid.

10. A positive electrode for an electric storage device, in, The carbon material according to claim 1 is contained as a conductive aid.

11. An electric storage device, in, The electrical storage device comprises a positive electrode and / or a negative electrode containing the carbon material according to claim 1 as a conductive auxiliary agent.

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