Electrodes and lithium-ion batteries

Abstract

The present invention provides electrodes and lithium-ion batteries suitable for constructing lithium-ion batteries with excellent low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics at high output. [Solution] The electrode comprises a current collector and an electrode composite film formed on the current collector. The electrode composite film contains an active material, a binder, and a conductive additive containing a carbon material. The total pore volume (V) of the carbon material is 1.00 cc / g or more, and the spatial index (I) is the ratio (V / S) of the total pore volume (V) of the carbon material to the specific surface area (S). V ) is 0.0015 cc / m³ 2 The above is the result of Raman spectroscopy measurements of carbon materials, specifically the intensity of the G band (I G ) 2D band intensity (I 2D Intensity ratio (I G / I 2D ) is 5.00 or less.

Description

[Technical Field]

[0001] This invention relates to electrodes and lithium-ion batteries. [Background technology]

[0002] Since its inception, lithium-ion batteries have seen a wide range of applications in everyday life, including smartphones and electric vehicles (EVs). As a result, lithium-ion battery manufacturing faces ongoing competition in terms of cost, as well as continuous demands for higher performance in the market. For EVs, which emit less carbon dioxide (CO2), to replace gasoline-powered vehicles in order to protect the global environment, the lithium-ion batteries they use need to have high performance characteristics such as rapid discharge, long lifespan, high capacity, and charge / discharge characteristics.

[0003] In lithium-ion batteries, where such high performance is required, carbon materials are widely used. For example, Patent Document 1 discloses that in a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, flake graphite and carbon black are used as conductive additives, and high-rate discharge characteristics can be improved. However, even with the use of such carbon materials, there are problems such as insufficient low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics at high output. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-22177 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide an electrode and a lithium-ion battery suitable for constructing a lithium-ion battery with excellent low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics at high output. [Means for solving the problem]

[0006] To achieve the above object, the gist configuration of the present invention is as follows. [1] An electrode comprising a current collector and an electrode composite material film formed on the current collector, The electrode composite material film contains an active material, a binder, and a conductive auxiliary agent containing a carbon material, The total pore volume (V) of the carbon material is 1.00 cc / g or more, The space index (I 90 , , 2D , , 2D , , 2 , 90 , , , 50 , 50 , , G , , G , V , , , , ) which is the ratio (V / S) of the total pore volume (V) of the carbon material to the specific surface area (S) is 0.0015 cc / m 2 or more, <00002​​​​​​​​​​​​​​​​​​​​​​​​​​​​[6] The electrode composite film is defined as having a ratio of the conductive additive calculated from Raman spectra measured at the surface, at a depth corresponding to 50% of the thickness of the electrode composite film from the surface, and at a depth corresponding to 90% of the thickness of the electrode composite film from the surface, respectively, R0 and R 50 , and R 90 In that case, The ratio of the aforementioned conductive additives is R0, R 50 , and R 90 One of the electrodes described in [1] to [5] has a higher value than the other two. [7] The ratio of the conductive additive is such that R0 is R 50 and R 90 The electrode described in [6] is 1.1 times higher than the one described above. [8] The ratio of the conductive additive is R 50 However, R0 and R 90 The electrode described in [6] is 1.1 times higher than the one described above. [9] The ratio of the conductive additive is R 90 However, R0 and R 50 The electrode described in [6] is 1.1 times higher than the one described above.

[10] The positive electrode, as described in any one of [1] to [9].

[11] A lithium-ion battery having one of the electrodes described in [1] to

[10] . [Effects of the Invention]

[0007] According to the present invention, it is possible to provide electrodes and lithium-ion batteries that are suitable for constructing lithium-ion batteries with excellent low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics at high output. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing an example of a lithium-ion battery according to an embodiment. [Figure 2] Figure 2 shows the results of the Raman spectrum measured for the upper electrode sample of Example 1. [Figure 3]Figure 3 is a schematic diagram illustrating the ultra-high-sensitivity vacuum desorption mass spectrometer used for temperature-controlled desorption mass spectrometry. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and various modifications are possible without altering the essence of the invention.

[0010] <<Electrode>> The electrode of this embodiment comprises a current collector and an electrode composite film formed on the current collector, wherein the electrode composite film contains an active material, a binder, and a conductive additive containing a carbon material, the total pore volume (V) of the carbon material is 1.00 cc / g or more, and the spatial index (I) is the ratio (V / S) of the total pore volume (V) of the carbon material to the specific surface area (S). V ) is 0.0015 cc / m³ 2 The above is the result of Raman spectroscopy measurements of carbon materials, specifically the intensity of the G band (I G ) 2D band intensity (I 2D Intensity ratio (I G / I 2D The ratio is 5.00 or less. By using a carbon material having a predetermined total pore volume, spatial index, and intensity ratio in the Raman spectrum as a conductive additive for use in electrodes, a lithium-ion battery with excellent initial capacity characteristics, low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics at high output can be provided. For the convenience of explanation, in this specification, the carbon material having a predetermined total pore volume, spatial index, and intensity ratio in the Raman spectrum is simply referred to as "carbon material," and other carbon materials are referred to as "other carbon materials."

[0011] <Current collector> Examples of current collectors include those used in the positive electrode and negative electrode of lithium-ion batteries.

[0012] The current collector for the positive electrode is not particularly limited as long as it is a commonly used material, but aluminum foil, nickel foil, titanium foil, and stainless steel foil are preferred, and rolled aluminum foil is more preferred.

[0013] The current collector for the negative electrode is not particularly limited, but for example, a material that does not exhibit electrochemical reactivity to the potential generated by the negative electrode is used. Suitable materials for the negative electrode current collector include copper foil, nickel foil, titanium foil, and stainless steel foil, with electrolytic copper foil and rolled copper foil being more preferred.

[0014] <Electrode composite film> The electrode composite film contains an active material, a binder, and a conductive additive containing a carbon material.

[0015] [Active material] Examples of active materials include positive electrode active materials used in the positive electrode of lithium-ion batteries and negative electrode active materials used in the negative electrode.

[0016] The positive electrode active material is not particularly limited, and the optimal composition can be appropriately selected from viewpoints such as material manufacturability, electrode manufacturability, charge / discharge capacity, cycle characteristics, storage characteristics, and safety.

[0017] Examples of positive electrode active materials include transition metal compounds containing lithium. Preferably, the material is highly improved so that the deintercalation and deintercalation reactions of lithium ions in the compound crystal structure during charge-discharge cycles are less prone to crystal structure destruction or defects in deintercalation and deintercalation.

[0018] The positive electrode active material is an ABO2 type lithium transition metal compound, where A is Li x (x=0.96~1.05), and B is Ni(Ni α In this case, compounds containing α (0.8~1.05) are preferred. B is Mn(Mn β In this case, β = 0.3 or less) and / or Co(Co γ In this case, it may further contain elements (γ = 0.2 or less), and may also contain elements other than Ni, Mn, and Co.

[0019] Examples of other elements that the above transition metal compound may contain include Mg, Ti, V, Nb, Ta, Cr, Fe, Cu, Zn, Al, Ga, Ge, Sn, Si, S, P, F, B, Na, etc. These elements preferably exist in the form of a single-phase solid solution incorporated into the crystal structure or in the form of a compound such as an oxide. These preferably function as skeleton reinforcing elements that stabilize the whole or a part of the crystal structure in the positive electrode active material.

[0020] By causing the above skeleton reinforcing element to exist on the crystal surface, it is also possible to confine the catalytic activity of the transition metal oxide, prevent contact with an electrolytic solution, etc., and suppress oxidative degradation.

[0021] In addition, examples of the positive electrode active material include lithium-manganese-based oxides (preferably LiMnO2, LiMn2O4), lithium-cobalt-based oxides (preferably LiCoO2), lithium-nickel-based oxides (preferably LiNiO2), lithium-nickel-manganese-based oxides (preferably LiNi 1-a Mn a O2 (0 < a < 1), LiMn 2-b Ni b O4 (0 < b < 2)), lithium-nickel-cobalt-based oxides (preferably LiNi 1-c Co c O2 (0 < c < 1)), lithium-manganese-cobalt-based oxides (preferably LiCo 1-d Mn d O2 (0 < d < 1), LiMn 2-e Co e O4 (0 < e < 2)), lithium-nickel-manganese-cobalt-based oxides (preferably Li(Ni f Mn g Co h )O2 (0 < f < 1, 0 < g < 1, 0 < h < 1, f + g + h = 1), Li(Ni j Mn k Co m )O4 (0 < j < 2, 0 < k < 2, 0 < m < 2, j + k + m = 2)), lithium-nickel-cobalt-transition metal (M) oxides (preferably Li(Ni p Co qMn r M S )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p, q, r, and s are atomic fractions of independent elements, where 0 < p < 1, 0 < q < 1, 0 < r < 1, 0 < s < 1, and p + q + r + s = 1) is preferred, and one or more of these compounds may be included.)

[0022] Among these, from the perspective of enhancing the capacity characteristics and stability of the battery, LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt-based oxides (preferably Li(Ni 0.6 Mn 0.2 Co 0.2 [[ID=1,4]])O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2)), lithium-nickel-cobalt-aluminum-based oxides (preferably LiNi 0.8 Co 0.15 Al 0.05 O2), Li 0.975 Ni 1.025 O2 are preferred.)

[0023] Also, as the positive electrode active material, the following compounds are also preferred.) Li y Ni d M2 e O 2-f (In the formula, M2 is at least one element selected from the group consisting of cobalt, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium, tungsten, zirconium, and silicon, and y, d, e, and f are respectively 0.8 ≤ y ≤ 1.2, 0.3 ≤ d ≤ 0.98, 0.02 ≤ e ≤ 0.7, and -0.1 ≤ f ≤ 0.2.))

[0024] Furthermore, as a positive electrode active material, a lithium atom-containing oxide (preferably an olivine-type lithium-containing phosphate compound) that is represented by the following formula (4) and has an olivine-type crystal structure is preferred as a highly stable material.

[0025] Li 1-x M x (AO4) Equation (4)

[0026] In formula (4) above, M is at least one metallic element selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, and Sn, A is at least one element selected from the group consisting of Si, S, P, and V, and x is greater than 0 and less than 1. Note that the value of x in formula (4) is selected according to the valencies of M and A such that the overall valency of formula (4) becomes 0.

[0027] Examples of olivine-type lithium-containing phosphate compounds include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4 is preferred, and LiFePO4 is more preferred because the iron compounds used as raw materials are readily available and inexpensive.

[0028] Furthermore, suitable positive electrode active materials include organic compounds such as polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, and N-fluoropyridinium salts.

[0029] The physical properties of the positive electrode active material are determined by requirements in the battery design and manufacturing process, which are constrained by the usage patterns of lithium-ion batteries. In the manufacturing of the positive electrode active material, process design and other measures are taken to achieve these desired physical properties. Examples of physical properties include powder particle size and distribution, specific surface area, and density.

[0030] As an example, the powder particle size is appropriately selected in consideration of other components of the lithium ion battery. From the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the average value is preferably 1 μm or more and 30 μm or less, and more preferably 1 μm or more and 10 μm or less.

[0031] These cathode active materials can be used alone or in combination of two or more.

[0032] As the anode active material, those that can bind and stabilize Li ions and electrons flowing from the external circuit, and have a large number of stabilization sites inside are preferred. Those originating from organic substances, whether highly crystalline or lowly crystalline, can all be used, and graphite, coke, amorphous carbon, hard carbon, and polymer carbon are preferred. In this case, in principle, Li ions are sandwiched between graphene layers and the like and combined with electrons to be stabilized. In addition, as another stabilization mechanism, a method of electrochemically forming an intermetallic compound can also be used, and silicon, tin, zinc, bismuth, antimony, cadmium, lead, germanium are preferably used. In addition, other materials showing a low electrochemical reaction potential that control the anode side of the lithium ion battery can also be used. Preferably, compounds of metals and oxygen, sulfur, halogen, nitrogen, phosphorus, etc. are included.

[0033] Specific examples of the anode active material include compounds capable of reversible intercalation and deintercalation of lithium, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiOx (0 < x = 2), SnO2, vanadium oxides, and lithium vanadium oxides; composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, are preferred.

[0034] Furthermore, a thin film of metallic lithium is preferred as the negative electrode active material. The carbonaceous material may be either low-crystalline carbon or high-crystalline carbon. Suitable low-crystalline carbon includes softened carbon and hardened carbon, while suitable high-crystalline carbon includes amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, quiche graphite, pyrolysis carbon, mesophase pitch carbon fibers, mesocarbon microspheres, mesophase pitch, and high-temperature calcined carbon such as petroleum and coal-based coke.

[0035] The physical properties of the negative electrode active material are determined by requirements in the device design and manufacturing process (e.g., rechargeable battery) due to constraints such as the intended use of lithium-ion batteries. In the manufacturing of the negative electrode active material, process design is carried out to achieve these physical properties. Examples of physical properties include powder particle size and distribution, specific surface area, and density.

[0036] As an example, the powder particle size is appropriately selected in consideration of other constituent requirements of the lithium-ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, an average value of 1 μm to 70 μm is preferred, and 3 μm to 30 μm is more preferred.

[0037] These negative electrode active materials can be used individually or in combination of two or more.

[0038] The carbon materials described later may be used as negative electrode active materials and are suitable for use as conductive additives for the negative electrode. For example, although the above negative electrode active materials generally have high electronic conductivity, some materials have a smooth surface and insufficient contact between particles. In such cases, the carbon materials described later can be used as conductive additives to enhance electronic conductivity. Furthermore, while flake-shaped graphite and artificial graphite used as negative electrode active materials have high electronic conductivity, they have poor ion storage capacity and inferior ionic conductivity. By combining materials with such properties with the carbon materials described later, it is possible to construct a good battery reaction support system that adds ionic conductivity to electronic conductivity. In addition, even when the three-dimensional structure of the negative electrode active material is compressed and flattened like flake-shaped graphite, the carbon materials described later can be applied to add ionic conductivity while maintaining electronic conductivity.

[0039] The proportion of active material in 100% by weight of the electrode composite film is not particularly limited, but is preferably 90.0% by weight or more and 99.5% by weight or less, more preferably 95.0% by weight or more and 99.0% by weight or less, and even more preferably 96.0% by weight or more and 99.0% by weight or less. When the proportion of active material is within the above range, battery capacity, conductivity, and adhesion are highly balanced.

[0040] The proportion of positive electrode active material in 100% by weight of the positive electrode electrode composite film is not particularly limited, but is preferably 90.0% by weight or more and 99.5% by weight or less, more preferably 95.0% by weight or more and 99.0% by weight or less, and even more preferably 96.0% by weight or more and 99.0% by weight or less. When the proportion of positive electrode active material is within the above range, battery capacity, conductivity, and adhesion are highly balanced.

[0041] The proportion of the negative electrode active material in 100% by weight of the negative electrode electrode composite film is not particularly limited, but is preferably 95.5% by weight or more and 99.0% by weight or less, more preferably 96.0% by weight or more and 98.7% by weight or less, and even more preferably 97.0% by weight or more and 98.0% by weight or less. When the proportion of the negative electrode active material is within the above range, the battery capacity, conductivity, and adhesion are highly balanced.

[0042] [binder] Examples of binders include binders used in the positive electrode and binders used in the negative electrode of lithium-ion batteries.

[0043] The binder for the positive electrode is a component that helps bond the positive electrode active material, conductive additive, and current collector, and is usually an organic polymer. Suitable binders for the positive electrode include fluororesins such as polyvinyl fluoride, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; and acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl polyacrylate, polyethyl polyacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide. Furthermore, the binder for the positive electrode may be a modified or derivative of the above-mentioned organic polymer.

[0044] In particular, a fluororesin is preferred for the positive electrode binder, and polyvinylidene fluoride (PVDF) is especially preferred. The weight-average molecular weight of the positive electrode binder can be appropriately selected according to the intended use of the electrode, and is preferably 10,000 to 8,000,000, with the following order of preference: 10,000 to 5,000,000, 50,000 to 5,000,000, 80,000 to 3,000,000, and 100,000 to 1,000,000. When the weight-average molecular weight of the positive electrode binder is 10,000 or more, the strength of the coating film is improved, and when the weight-average molecular weight of the positive electrode binder is 8,000,000 or less, the viscosity is reduced, making electrode formation easier.

[0045] The positive electrode binder can be used individually or in combination of two or more types.

[0046] The binder for the negative electrode is a component that helps bond the negative electrode active material, conductive additive, and current collector, and is usually an organic polymer. Suitable binders for the negative electrode include fluororesins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl polyacrylate, polyethyl polyacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; carboxymethylcellulose; and styrene-butadiene rubber. Furthermore, the binder for the negative electrode may be a modified or derivative of the above-mentioned organic polymer.

[0047] In particular, carboxymethylcellulose and styrene-butadiene rubber are preferred as binders for the negative electrode. The weight-average molecular weight of the negative electrode binder can be appropriately selected according to the intended use of the electrode, and is preferably 10,000 to 8,000,000, with the following order of preference: 10,000 to 5,000,000, 50,000 to 4,000,000, 80,000 to 3,000,000, and 100,000 to 1,000,000. When the weight-average molecular weight of the negative electrode binder is 10,000 or more, the strength of the coating film is improved, and when the weight-average molecular weight of the negative electrode binder is 8,000,000 or less, the viscosity is reduced, making electrode formation easier.

[0048] The negative electrode binder can be used individually or in combination of two or more types.

[0049] The binder content is preferably 0.7% to 5.0% by weight, more preferably 1.0% to 2.5% by weight, and even more preferably 1.0% to 2.2% by weight, relative to 100% by weight of the electrode composite film. When the binder content is within the above range, the adhesive strength between the active materials and between the active materials and the conductive additive can be improved, and consequently, the bonding strength between these materials and the current collector can be improved.

[0050] The proportion of the binder in the positive electrode is preferably 0.7% to 4.0% by weight, more preferably 1.0% to 2.5% by weight, and even more preferably 1.0% to 2.2% by weight, relative to 100% by weight of the electrode composite film of the positive electrode. When the binder content of the positive electrode is within the above range, the adhesive strength between the positive electrode active materials and between the positive electrode active materials and the conductive additive can be improved, and consequently, the bonding strength between these materials and the current collector can be improved.

[0051] The proportion of the binder in the negative electrode is preferably 0.8% to 3.0% by weight, more preferably 1.0% to 2.5% by weight, and even more preferably 1.0% to 2.2% by weight, relative to 100% by weight of the electrode composite film of the negative electrode. When the binder content of the negative electrode is within the above range, the adhesive strength between the negative electrode active materials and between the negative electrode active materials and the conductive additive can be improved, and consequently, the bonding strength between these materials and the current collector can be improved.

[0052] [Conductive additive] The conductive additive contains carbon material.

[0053] [Carbon materials] The total pore volume (V) of the carbon material is 1.00 cc / g or more, and the spatial index (I) is the ratio (V / S) of the total pore volume (V) of the carbon material to its specific surface area (S). V ) is 0.0015 cc / m³ 2The intensity ratio (I G ) of the G band to the intensity of the 2D band (I 2D ) in the Raman spectrum of the carbon material obtained by Raman spectroscopy is 5.00 or less.

[0054] The total pore volume (V) of the carbon material is a value measured by nitrogen adsorption - desorption measurement, and is 1.00 cc / g or more, preferably 1.50 cc / g or more, 2.00 cc / g or more, 2.20 cc / g or more, 2.95 cc / g or more in this order. Also, the upper limit value of the total pore volume (V) of the carbon material is preferably 20.00 cc / g or less, preferably 15.00 cc / g or less, 10.00 cc / g or less, 8.00 cc / g or less, 7.00 cc / g or less, 6.10 cc / g or less, 5.70 cc / g or less in this order.

[0055] When the total pore volume of the carbon material is 20.00 cc / g or less, the strength of the carbon material is improved and the shape of the carbon material tends to be well maintained. When the total pore volume of the carbon material is 1.00 cc / g or more, the amount of electrolyte retained in the carbon material increases. Thus, when the total pore volume of the carbon material is within the above range, the carbon material has good strength, contributes to the stability of the carbon material, and the shape of the carbon material is well maintained. Therefore, the carbon material can keep a good balance between electronic conductivity and the supply of ions retained in the pores.

[0056] The space index (I V ) is 0.0015 cc / m 2 or more, preferably 0.0020 cc / m 2 or more, more preferably 0.0026 cc / m 2 or more, still more preferably 0.0030 cc / m 2 or more, particularly preferably 0.0032 cc / m 2 or more. Also, the space index (I V ) is preferably 0.0060 cc / m 2 or less, more preferably 0.0050 cc / m 2 or less, still more preferably 0.0040 cc / m 2 ​​​​It is as follows.

[0057] When the space index is 0.0015 cc / m 2 or more, there are few boundary walls that divide the space in the carbon material, and ions can move smoothly in the electrolyte held in the space. When the space index of the carbon material is 0.0060 cc / m 2 or less, the strength for maintaining the shape of the space is sufficient, the structure is not easily destroyed by pressing during electrode fabrication, and the substantial electrolyte retention amount is not easily reduced.

[0058] The state of the fine crystal structure of the carbon material can be analyzed by Raman spectroscopy. In the Raman spectrum obtained by Raman spectroscopic measurement of the carbon material, the peak existing around the wave number 1593 cm -1 is called the G band and indicates the sp2 bond (aromatic ring C=C stretching motion) of the carbon material. Also, in the above Raman spectrum, the peak existing around the wave number 1356 cm -1 is called the D band and indicates the sp3 bond (C-H stretching motion) of the carbon material. When the sp2 bond is broken and the sp3 bond is formed, the D band increases. Also, in the above Raman spectrum, the peak existing around the wave number 2680 cm -1 is called the 2D band and indicates second-order phonon scattering (C-H stretching motion). Also, the 2D band indicates the number of stacked graphene layers.

[0059] The intensity ratio (I G ) of the intensity of the G band to the intensity of the 2D band (I 2D ) (I G / I 2D ) is said to be an index indicating the stacked state of the graphene layers (D. Graf, et al., NANO LETTERS, 7, 238 - 242; (2007)). In this paper, it is described that when the intensity ratio (I G / I 2D ) is 0.2, the graphene layer is one layer.

[0060] In the Raman spectrum of the carbon material obtained by Raman spectroscopic measurement, the intensity of the G band (I G ) and the intensity of the 2D band (I2D Intensity ratio (I G / I 2D The strength ratio (I) is preferably 0.40 or higher, more preferably 1.00 or higher, even more preferably 1.10 or higher, particularly preferably 1.20 or higher, and most preferably 1.43 or higher. G / I 2D The value is 5.00 or less, and is preferably in the order of 4.50 or less, 4.00 or less, 3.57 or less, 3.00 or less, 2.50 or less, and 2.08 or less.

[0061] The above strength ratio of carbon materials (I G / I 2D When the above strength ratio (I) is within the above range, the strength properties and elastic deformability that maintain the hollow structure of the carbon material are highly balanced. Furthermore, when the carbon material is used as a conductive additive in lithium-ion batteries, the battery characteristics such as rapid discharge performance, capacity characteristics, and durability of the lithium-ion battery can be improved. G / I 2D If the intensity ratio (I) of the carbon material is less than 0.40, the formation of the graphene crystal structure tends to be insufficient. As a result, a decrease in electronic conductivity occurs, and the discharge capacity tends to decrease. G / I 2D If the value exceeds 5.00, the number of graphene layers increases excessively, reducing the flexibility of the carbon material. As a result, the electrode density decreases, and the battery charging capacity decreases.

[0062] The carbon material preferably comprises a connected structure having an extended shape. The connected structure having an extended shape consists of multiple hollow particulate parts connected in a bead-like manner. The hollow particulate parts have surrounding walls, and the interior of the hollow particulate parts is hollow. The surrounding walls partition the internal space of the hollow particulate parts in the connected structure. Furthermore, the surrounding walls have multiple pores and possess a graphene crystalline structure.

[0063] The carbon material is preferably hollow. At least the internal spaces of the connecting structures are in communication with each other, including the internal space of the hollow particulate portion. Such a carbon material is porous, having micropores, mesopores, and macropores.

[0064] The surrounding wall of the carbon material is preferably composed of graphene or multilayer graphene, and graphene and multilayer graphene may be mixed. The surrounding wall of the carbon material is preferably composed mainly of thin-layer graphene. In this specification, the structure of multilayer graphene is a structure in which single layers of graphene are stacked, but with fewer layers than graphite. Among these, the structure of thin-layer graphene has a relatively small number of layers, and therefore provides good elastic deformability. When the surrounding wall of the carbon material is mainly composed of thin-layer graphene, it may be partially composed of graphene, or partially composed of multilayer graphene with a relatively large number of layers. The fact that the surrounding wall of the carbon material is mainly composed of thin-layer graphene is due to the above strength ratio (I G / I 2D This can also be confirmed from the fact that the ratio is between 0.40 and 5.00. Graphene is a sheet-like material of SP2-bonded carbon, and the six-membered carbon ring structure is linked together to form a honeycomb-like hexagonal lattice structure. Thus, the surrounding wall has a six-membered carbon ring structure. The connecting structure is preferably graphene mesosponge (GMS).

[0065] Carbon materials consist of structures that are elastically deformable and structures that are plastically deformable. Plastically deformable structures deform and develop strain when subjected to an external force below a predetermined value, but when subjected to an external force exceeding the elastic limit, they do not return to their original shape even after the force is removed, resulting in permanent strain. The degree of elastic and plastic deformation of carbon materials can be measured by a micro-load unloading test.

[0066] Carbon materials possess the property of returning to their original shape without plastic deformation under weak external forces, such as in micro-load unloading tests, meaning they have a large elastic deformation work rate. In carbon materials, the graphene portion, which makes up the majority, mainly exhibits elastic deformability, while non-graphene structural parts, such as defects in the graphene structure and amorphous carbon portions, mainly exhibit plastic deformability. Therefore, carbon materials are considered to have good properties against deformation by external forces. In other words, thin-layer graphene is a structure that provides this good elastic deformability. Furthermore, if the number of graphene layers is excessively large, elastic deformability is maintained under external forces below a certain value, but under external forces exceeding the elastic limit, plastic deformation occurs rapidly, and hollow particulate portions tend to break.

[0067] Furthermore, the carbon material preferably has branched sections in the connecting structure, and more preferably has multiple branched sections. Also, the carbon material preferably has ring-shaped sections in the connecting structure, and more preferably has multiple ring-shaped sections. The connecting structure having an extended shape may have only branched sections, only ring-shaped sections, or both branched sections and ring-shaped sections. For example, one end of the connecting structure may be connected to form a ring-shaped section. Alternatively, the tips of multiple branched and extending sections may be connected to form a ring-shaped section. Furthermore, ring-shaped sections may be formed in parts of the connecting structure other than the ends.

[0068] The size of the multiple pores provided in the connecting structure is preferably 0.1 nm to 100.0 nm, more preferably 1.0 nm to 80.0 nm, and even more preferably 5.0 nm to 50.0 nm. The length of the connecting structure is preferably 0.01 μm to 100.00 μm, more preferably 0.05 μm to 80.00 μm, and even more preferably 0.10 μm to 50.00 μm. The average particle size (average outer diameter) of the hollow particulate portion in the connecting structure is preferably 0.05 μm to 50.00 μm, more preferably 0.05 μm to 6.00 μm, even more preferably 0.10 μm to 10.00 μm, particularly preferably 0.10 μm to 5.00 μm, and most preferably 0.50 μm to 5.00 μm.

[0069] A constricted portion may be provided at the connecting (joining) parts of the interconnected hollow particulate matter. For example, when two hollow particulate matter are connected, they may take on a peanut shell-like or dumbbell-like shape. Multiple such hollow particulate matter are connected to form a connected structure. The connected structure is a complex structure that does not have a fixed shape.

[0070] As described above, the carbon material is preferably a linked structure in which multiple hollow particulate parts are connected in a bead-like manner. The term "structure" is used to describe the complex structure of carbon black, and refers to an aggregate structure in which multiple primary particles in carbon black are linked together while having multiple branching points. In other words, a linked structure carbon material can be likened to a structure in which the inside of the highly conductive primary particles of carbon black is hollow, the outer shell (the surrounding wall that constitutes the hollow particulate part in the carbon material) is made up of multiple carbon atoms having a graphene crystal structure, and the internal spaces of the carbon black aggregates are interconnected. Therefore, a linked structure carbon material has high conductivity and can also stably secure an electrolyte. Carbon materials can significantly improve battery characteristics such as rapid discharge performance, battery capacity characteristics, and charge / discharge characteristics of lithium secondary batteries.

[0071] When many hollow particulate parts are connected, and the surface area of ​​the connected structure increases, the electronic conductivity of the carbon material increases. Furthermore, as the overall complexity of the connected structure increases, voids are formed not only within the internal space of the connected structure but also surrounded by the outer surface of the surrounding walls of the connected structure. When a carbon material with such a connected structure is included in the electrodes of a battery, the electrolyte enters these spaces and voids. In other words, the larger the volume of the internal space of the connected structure and the volume of the voids surrounded by the surrounding walls, the greater the amount of electrolyte that the carbon material can hold. The volume of the internal space of the connected structure and the volume of the voids surrounded by the surrounding walls in the carbon material can be compared with the volume of conventionally used conductive additives, using the oil absorption amount described later as an indicator.

[0072] The positive electrode material of lithium-ion batteries uses a lithium-containing transition metal oxide powder with a particle size distribution and low electronic conductivity. In conventional technology, an electron conduction path is established by pressing and fixing a mixture of a conductive additive made of carbon material, which aids in electron conduction, and a binder resin onto a current collector for the battery reaction. The materials other than the binder resin are powder particles, and the electrolyte exists in the spaces between the particles. For this reason, it has been difficult to actively place the electrolyte, or in other words lithium ions, near the positive electrode material using conventional technology.

[0073] Furthermore, conventionally, complexly shaped carbon black has been widely used as a conductive additive. In contrast, by using a carbon material that is a linked structure instead of the conventionally used conductive additive, the hollow particulate portion of the linked structure has space inside, allowing the electrolyte to be held within that space. The carbon material that is a linked structure has a larger internal space compared to carbon black, which has been conventionally used as a conductive additive. Therefore, the carbon material that is a linked structure simultaneously assists in the supply of electrons and ions necessary for the battery reaction, making it a material that can realize a rapid battery reaction.

[0074] The oil absorption of carbon materials, as measured in accordance with JIS K5101-13-1:2004 (Pigment Test Methods - Part 13: Oil Absorption - Section 1: Refined Linseed Oil Method), is preferably 500 mL / 100g or more, more preferably 600 mL / 100g or more, even more preferably 800 mL / 100g or more, particularly preferably 1000 mL / 100g or more, and most preferably 1400 mL / 100g or more. When the oil absorption of carbon materials is within the above range, battery characteristics such as the 2C maintenance rate can be improved. Furthermore, there is no particular upper limit to the oil absorption of carbon materials, but for example, it is preferable in the following order: 5000 mL / 100g or less, 4000 mL / 100g or less, 3500 mL / 100g or less, 3000 mL / 100g or less, and 2500 mL / 100g or less.

[0075] Carbon materials, which are interconnected structures, can hold a large amount of electrolyte because they can retain electrolyte in the internal spaces of the interconnected structures and in the voids surrounded by the outer walls of the interconnected structures. Therefore, the oil absorption capacity of carbon materials is significantly higher than that of carbon black, which is commonly used as a conductive additive in lithium-ion batteries, making it possible to stably supply lithium ions and contributing to improvements in battery characteristics such as rapid charging, charge / discharge characteristics, and battery capacity of lithium-ion batteries. On the other hand, if the oil absorption capacity of the carbon material is less than 500 mL / 100 g, the amount of electrolyte that can be retained is small, which tends to cause a delay in ion supply during rapid reactions and a decrease in discharge capacity. Furthermore, if the oil absorption capacity of the carbon material is excessively high, it may be difficult to maintain the structure of the carbon material and control the amount of electrolyte that can be retained.

[0076] Furthermore, the intensity of the D band (I) in the Raman spectrum obtained by Raman spectroscopy of carbon materials. D ) G-band intensity (I G Intensity ratio (I D / I G The strength ratio (I) of the carbon material is preferably 0.1 to 10.0, more preferably 0.5 to 5.0, even more preferably 1.0 to 3.0, particularly preferably 1.2 to 2.5, and most preferably 1.4 to 2.0. D / I G When the above range is maintained, the sp2 and sp3 orbitals in the carbon material are in an even better state, and the electron conduction paths and ion conduction paths are highly balanced. Furthermore, the rapid discharge performance, capacity characteristics, and charge / discharge characteristics of the lithium-ion battery are further improved.

[0077] Furthermore, the interplanar spacing d002 of the (002) plane, as measured by X-ray diffraction (XRD) of the carbon material, is preferably 0.30 nm or more and 0.50 nm or less, more preferably 0.33 nm or more and 0.45 nm or less, even more preferably 0.30 nm or more and 0.50 nm or less, particularly preferably 0.33 nm or more and 0.39 nm or less, and most preferably 0.33 nm or more and 0.38 nm or less.

[0078] Furthermore, the size of the crystallites in the c-axis direction, Lc(002), measured by X-ray diffraction of the carbon material, is preferably 0.10 nm or more, with 0.30 nm or more, 0.50 nm or more, 1.00 nm or more, and 1.10 nm or more being preferred in that order. Also, the upper limit of the size of the crystallites in the c-axis direction, Lc(002), is preferably 20.00 nm or less, with 5.00 nm or less, 3.00 nm or less, 2.50 nm or less, 2.00 nm or less, 1.90 nm or less, 1.50 nm or less, 1.25 nm or less, and 1.21 nm or less being preferred in that order. When the above Lc(002), which indicates the degree of crystallinity of the carbon material, is within the above range, the carbon material tends to have mesopores and macropores.

[0079] Furthermore, the lower limit of the crystallite size La(10) in the a-axis direction of the (10) plane, as measured by X-ray diffraction of the carbon material, is preferably 0.1 nm or more, and is preferred in the order of 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, and 1.8 nm or more. The upper limit of the above La(10) is preferably 10.0 nm or less, and is preferred in the order of 5.0 nm or less, 4.5 nm or less, 4.0 nm or less, and 3.8 nm or less.

[0080] Furthermore, the BET specific surface area (S) of the carbon material is the specific surface area calculated from nitrogen adsorption as specified in JIS Z8830, preferably 100 m². 2 / g or more 2700m 2 It is less than / g and 300m 2 / g or more 2500m 2 / g or less, 500m 2 / g2000m 2 / g or less, 600m 2 / g or more 1800m 2 / g or less, 800m 2 / g or more 1200m 2 The order of preference is from less than / g. When the BET specific surface area of ​​the carbon material is within the above range, the conductivity and oil absorption of the carbon material are further improved.

[0081] Furthermore, the micropore volume of the carbon material is a pore volume with a pore diameter of less than 2 nm, preferably 5.00 cc / g or less, and preferably 2.00 cc / g or less, 1.00 cc / g or less, 0.50 cc / g or less, and 0.40 cc / g or less, in that order. Also, the lower limit of the micropore volume of the carbon material is preferably 0.01 cc / g or more, and preferably 0.05 cc / g or more, 0.10 cc / g or more, 0.20 cc / g or more, and 0.30 cc / g or more, in that order. When the micropore volume of the carbon material is 5.00 cc / g or less, the ionic conductivity is further improved, and when the micropore volume of the carbon material is 0.01 cc / g or more, the strength properties of the carbon material are further improved.

[0082] Furthermore, the ratio of micropore volume to total pore volume in the carbon material is preferably 20% or less, and is preferably 15% or less, 12% or less, 10% or less, and 9% or less, in that order. The lower limit of the above ratio of micropore volume in the carbon material is preferably 5% or more. When the above ratio of micropore volume is 20% or less, the ionic conductivity is further improved, and when the above ratio of micropore volume is 5% or more, the strength properties of the carbon material are further improved.

[0083] Furthermore, the mesopore volume of the carbon material is a pore volume with a pore diameter of 2 nm to 50 nm, preferably 0.1 cc / g or more, and preferably in the order of 0.5 cc / g or more, 1.0 cc / g or more, 1.5 cc / g or more, and 2.0 cc / g or more. The upper limit of the mesopore volume of the carbon material is preferably 15.0 cc / g or less, and preferably in the order of 10.0 cc / g or less, 5.0 cc / g or less, 4.0 cc / g or less, and 3.5 cc / g or less. When the mesopore volume of the carbon material is within the above range, the ionic conductivity and strength characteristics of the carbon material are further balanced.

[0084] Furthermore, the ratio of mesopore volume to total pore volume in the carbon material is preferably 10% or more, and is preferably 20% or more, 30% or more, 40% or more, and 50% or more, in that order. The upper limit of the above ratio of mesopore volume in the carbon material is preferably 90% or less, and is preferably 85% or less, 80% or less, 75% or less, and 70% or less, in that order. When the above mesopore volume of the carbon material is within the above range, the carbon material has good strength, contributes to the stability of the carbon material, and maintains the shape of the carbon material well. Therefore, the carbon material can maintain a good balance between electronic conductivity and the supply of ions held in the pores.

[0085] Furthermore, the pore volume of the carbon material with a pore diameter of 2 nm or more and less than 10 nm is preferably 0.05 cc / g or more, and is preferred in the order of 0.01 cc / g or more, 0.05 cc / g or more, 0.10 cc / g or more, and 0.50 cc / g or more. Also, the upper limit of the pore volume of the carbon material is preferably 10.00 cc / g or less, and is preferred in the order of 5.00 cc / g or less, 2.00 cc / g or less, 1.50 cc / g or less, and 1.00 cc / g or less. When the pore volume of the carbon material with a pore diameter of 2 nm or more and less than 10 nm is within the above range, the ionic conductivity and strength characteristics of the carbon material are highly balanced.

[0086] Furthermore, in carbon materials, the ratio of pore volume with a diameter of 2 nm or more and less than 10 nm to the total pore volume is preferably 0.1% or more, and is preferred in the order of 1.0% or more, 3.0% or more, 5.0% or more, and 10.0% or more. Also, the upper limit of the above ratio of pore volume in carbon materials is preferably 50.0% or less, and is preferred in the order of 40.0% or less, 30.0% or less, 26.0% or less, and 20.0% or less. When the ratio of pore volume with a diameter of 2 nm or more and less than 10 nm to the total pore volume in carbon materials is within the above range, the ionic conductivity and strength characteristics of the carbon material are highly balanced.

[0087] Furthermore, the pore volume of the carbon material with a pore diameter of 10 nm to 50 nm is preferably 0.05 cc / g or more, and is preferred in the order of 0.10 cc / g or more, 0.50 cc / g or more, 1.00 cc / g or more, 1.35 cc / g or more, 1.50 cc / g or more, and 2.00 cc / g or more. Also, the upper limit of the pore volume of the carbon material is preferably 15.00 cc / g or less, and is preferred in the order of 10.00 cc / g or less, 5.00 cc / g or less, 4.00 cc / g or less, and 3.00 cc / g or less. When the pore volume of the carbon material with a pore diameter of 10 nm to 50 nm is within the above range, the carbon material has good strength, contributes to the stability of the carbon material, and maintains the shape of the carbon material well. Therefore, the carbon material can maintain a good balance between electronic conductivity and the supply of ions held in the pores.

[0088] Furthermore, in carbon materials, the ratio of pore volume with a pore diameter of 10 nm to 50 nm to the total pore volume is preferably 10% or more, and is preferably 15% or more, 20% or more, 25% or more, and 30% or more in that order. Also, the upper limit of the above ratio of pore volume in carbon materials is preferably 80% or less, and is preferably 70% or less, 60% or less, 55% or less, and 50% or less in that order. When the ratio of pore volume with a pore diameter of 10 nm to 50 nm to the total pore volume in carbon materials is within the above range, the ionic conductivity and strength characteristics of the carbon material are highly balanced.

[0089] Furthermore, the macropore volume of the carbon material is the pore volume of pores with a diameter of more than 50 nm, preferably 0.01 cc / g or more, and preferably in the order of 0.05 cc / g or more, 0.10 cc / g or more, 0.48 cc / g or more, and 1.00 cc / g or more. The upper limit of the macropore volume of the carbon material is preferably 15.00 cc / g or less, and preferably in the order of 10.00 cc / g or less, 5.00 cc / g or less, 3.00 cc / g or less, and 2.57 cc / g or less. When the macropore volume of the carbon material is within the above range, the carbon material has good strength, contributes to the stability of the carbon material, and maintains the shape of the carbon material well. Therefore, the carbon material can maintain a good balance between electronic conductivity and the supply of ions held in the pores.

[0090] Furthermore, the ratio of macropore volume to total pore volume in the carbon material is preferably 5% or more, with 10% or more, 15% or more, 20% or more, and 25% or more being preferred in that order. Also, the upper limit of the above-mentioned ratio of macropore volume in the carbon material is preferably 80% or less, with 70% or less, 60% or less, 50% or less, and 45% or less being preferred in that order. When the above-mentioned ratio of macropore volume in the carbon material is 5% or more, the ionic conductivity of the carbon material is further improved, and when the above-mentioned ratio of macropore volume in the carbon material is 80% or less, the strength properties of the carbon material are further improved.

[0091] Furthermore, in carbon materials, the proportion of pore volume with a diameter of 10 nm or more to the total pore volume is preferably 50% or more, with 55% or more, 60% or more, 65% or more, and 70% or more being preferred in that order. Also, the upper limit of the above proportion of pore volume in carbon materials is preferably 95% or less, with 92% or less, 90% or less, 88% or less, and 85% or less being preferred in that order. When the proportion of pore volume with a diameter of 10 nm or more to the total pore volume in carbon materials is 50% or more, the ionic conductivity of the carbon material is further improved, and when the above proportion is 95% or less, the strength properties of the carbon material are further improved.

[0092] Furthermore, the mode pore diameter (M) in the pore distribution of the carbon material is the value of the peak top in the pore distribution curve, preferably between 1 nm and 500 nm, and preferably in the order of 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 40 nm, and 15 nm to 30 nm. When the mode pore diameter of the carbon material is within the above range, the oil absorption capacity is further improved, and high levels of ionic and electronic conductivity can be achieved.

[0093] Furthermore, the average pore size of the carbon material is preferably 1 nm to 500 nm, with the order of preference being 5 nm to 100 nm, 10 nm to 75 nm, 15 nm to 50 nm, and 20 nm to 40 nm. When the average pore size of the carbon material is within the above range, the oil absorption capacity is further improved, and high levels of ionic and electronic conductivity can be achieved.

[0094] Furthermore, the volume-based particle size distribution curve of carbon material, measured using laser diffraction scattering, can be obtained by immersing the unground carbon material in a solvent for 9 minutes before measurement, revealing differences in the cohesive force of the carbon material.

[0095] D50, obtained from the volume-based particle size distribution curve measured by laser diffraction scattering, is the particle size at which 50% of particles have a particle size of D50 or less, preferably between 1 μm and 100 μm, and in order of preference between 5 μm and 90 μm, 10 μm and 80 μm, 15 μm and 60 μm, 20 μm and 50 μm, 25 μm and 45 μm, and 30 μm and 40 μm. When the D50 of the carbon material is within the above range, the electronic conductivity and ionic conductivity of the carbon material are further improved.

[0096] Furthermore, D10 obtained from the above particle size distribution curve is a particle size where the proportion of particles with a particle size of D10 or less is 10%, preferably 0.1 μm to 100.0 μm, and preferably in the order of 0.5 μm to 50.0 μm, 1.0 μm to 50.0 μm, 5.0 μm to 30.0 μm, and 10.0 μm to 15.0 μm.

[0097] Furthermore, D90 obtained from the above particle size distribution curve is a particle size in which the proportion of particles with a particle size of D90 or less is 90%, preferably 5 μm to 250 μm, and preferably in the order of 10 μm to 150 μm, 20 μm to 100 μm, 30 μm to 70 μm, 40 μm to 60 μm, 45 μm to 65 μm, and 45 μm to 55 μm. When the D90 of the carbon material is within the above range, the conductivity of the carbon material is further improved.

[0098] Furthermore, the ratio of D90 to D10 of the carbon material obtained from the above particle size distribution curve (D90 / D10) is preferably 100 or less, and is preferred in the order of 50 or less, 10 or less, and 5 or less. When the above ratio of carbon material (D90 / D10) is 100 or less, the dispersibility of the carbon material is further improved, and the conductivity of the lithium-ion battery is further improved.

[0099] Furthermore, the ratio of D90 of the carbon material obtained from the above particle size distribution curve to the mode pore size M (D90 / M) divided by 1000 (D90 / M × 1000) is preferably 50 or less, and is preferred in the order of 20 or less, 10 or less, 6 or less, and 4 or less. When (D90 / M × 1000) is 50 or less, the dispersibility of the carbon material is further improved, and the conductivity of the lithium-ion battery is further improved.

[0100] Furthermore, it is preferable that the carbon material contained in the electrodes of lithium-ion batteries has high conductivity. Since electron transfer in carbon occurs through the movement of π electrons, in order to form ideal conductive paths within the electrode using a carbon material, it is necessary to arrange single-layer graphene, in which carbon atoms are bonded in the planar direction, in a mesh-like structure. Also, when a conductive material such as carbon material is filled into a non-conductive material such as a positive electrode material, if the filling rate of the conductive material is low, conductivity will not be exhibited. When the filling rate of the conductive material reaches a certain level, paths of the conductive material are formed within the compound, and the electronic conductivity increases rapidly, after which the electronic conductivity becomes constant. The lower the threshold for the filling rate at which such a rapid increase in electronic conductivity occurs, the more suitable the carbon material is as a conductive material. Therefore, when multiple hollow particulate parts having surrounding walls of graphene structures that extend in the planar direction are connected, it is thought that the carbon material exhibits higher conductivity because the in-plane conductivity and path-forming conductivity are more highly balanced.

[0101] Furthermore, the electrical conductivity of carbon materials can be measured by the following method of measuring the electrical conductivity of powder using uniaxial compression with lateral constraint. Dry carbon material is filled into a cylindrical container consisting of an insulating cylinder and a negative electrode. A positive electrode is inserted into the insulating cylindrical container filled with carbon material, and the carbon material is sandwiched between the negative and positive electrodes and placed on a force gauge stand. A spring-type force gauge installed on the force gauge stand is lowered to apply force to the carbon material inside the cylindrical container and compress it. While measuring the compressive force and the height of the carbon material with a length measuring instrument, the resistance value of the carbon material is measured with a digital multimeter connected to the positive and negative electrodes. The electrical conductivity of the carbon material powder during compression is calculated from the obtained resistance value, the filled cross-sectional area of ​​the carbon material, and the filled height.

[0102] The electrical conductivity of carbon materials, when pressurized at 10 MPa, is preferably 1 S / cm to 100 S / cm, with a preference for 5 S / cm to 70 S / cm, 10 S / cm to 50 S / cm, and 20 S / cm to 30 S / cm, in that order. The electrical conductivity of carbon materials can be determined by the reciprocal of their electrical resistivity. The electrical resistivity of carbon materials can be measured according to JIS K1469.

[0103] Furthermore, one indicator of the structural complexity of carbon materials is the shape index and aggregate shape classification, which are measured by the image analysis method described later.

[0104] The circularity calculated by the image analysis method for carbon materials may be 0.1 or higher, 0.2 or higher, 0.25 or higher, or 0.8 or lower, 0.6 or lower, 0.5 or lower, or 0.4 or lower. The circularity in the image analysis method is an indicator of the complexity of the aggregate structure, and if it is within the above range, the oil absorption capacity of the carbon material will further improve.

[0105] Furthermore, the shape factor (ML2 / A), which indicates the sphericity calculated by the image analysis method of carbon materials, may be 1.00 or higher, 2.00 or higher, 2.25 or higher, 2.40 or higher, or 4.00 or lower, 3.50 or lower, or 3.10 or lower.

[0106] Furthermore, the shape factor (PM2 / A), which indicates the degree of surface roughness calculated by the image analysis method for carbon materials, may be 2.0 or higher, 3.0 or higher, 3.5 or higher, or 8.0 or lower, 7.0 or lower, 6.0 or lower, or 5.5 or lower.

[0107] Furthermore, the (PM2 / A)-(ML2 / A) value calculated by the image analysis method of the carbon material is preferably 0 or greater, and is preferably 0.4 or greater, followed by 1.0 or greater. When the above value ((PM2 / A)-(ML2 / A)) is within the above range, the oil absorption capacity of the carbon material is further improved.

[0108] Furthermore, the area circle equivalent diameter calculated by the image analysis method for carbon materials may be 100 nm or more, 200 nm or more, 250 nm or more, or 1000 nm or less, 800 nm or less, 600 nm or less, or 400 nm or less.

[0109] Furthermore, the proportion of "spheroidal" shapes in the shape classification calculated by the image analysis method for carbon materials is preferably 50% or less, and is preferably in the order of 30% or less, 20% or less, 10% or less, 5% or less, and 2% or less. When the proportion of spherical shapes in the image analysis method for carbon materials is within the above range, the oil absorption capacity of the carbon material is further improved.

[0110] Furthermore, the proportion of "ellipsoidal" shapes in the shape classification calculated by the image analysis method for carbon materials is preferably 5% to 80%, with the following preference being 10% to 70%, 15% to 60%, 20% to 50%, and 25% to 45%. When the proportion of ellipsoidal shapes in the image analysis method for carbon materials is within the above range, the oil absorption capacity of the carbon material is further improved.

[0111] Furthermore, the proportion of "branched" shapes in the shape classification calculated by the image analysis method for carbon materials is preferably 5% to 80%, with the following preference ranges being: 10% to 70%, 20% to 50%, 20% to 45%, 25% to 45%, and 25% to 36%. When the proportion of branched shapes in the image analysis method for carbon materials is within the above range, the oil absorption capacity of the carbon material is further improved.

[0112] Furthermore, the apparent density of the carbon material is preferably 2.00 g / cc or less, and is preferably 1.50 g / cc or less, 1.00 g / cc or less, 0.50 g / cc or less, and 0.30 g / cc or less, in that order. Also, the lower limit of the apparent density of the carbon material is preferably 0.05 g / cc or more, 0.10 g / cc or more, and 0.15 g / cc or more, in that order. When the apparent density of the carbon material is within the above range, the hollow structure in the carbon material is maintained, and the carbon material is suitably used as a material constituting a battery.

[0113] The apparent density of carbon materials can be calculated using the total pore volume and true density from the following formula (1). The total pore volume (cc / g) is calculated using P / P0 = 0.99, and the true density is the value for graphite, 2.2 g / cc.

[0114] Apparent density (g / cc) = 1 / (total pore volume + (1 / true density)) Equation (1)

[0115] Furthermore, the bulk density of the carbon material is preferably 0.01 g / L or more and 1000.00 g / L or less, with the following ranges being preferable: 0.10 g / L or more and 100.00 g / L or less, 0.50 g / L or more and 50.00 g / L or less, and 1.00 g / L or more and 25.00 g / L or less. When the bulk density of the carbon material is within the above range, the conductivity of the carbon material is further increased, and the electrolyte penetrates the carbon material more easily. Bulk density is the mass per unit volume of carbon material when it is filled into a container of a certain volume under certain conditions. Bulk density can be measured according to JIS K6219-2.

[0116] Furthermore, the number density of the carbon material is a value calculated by the method described later, preferably 5 × 10⁻¹⁶. 14 pcs / g or more 1×10 20 It is less than or equal to 1 × 10⁻¹⁰ pieces / g. 16 pcs / g or more 1×10 19 pcs / g or less, 5×10 16 pcs / g or more 5×10 18 pcs / g or less, 1×10 17 pcs / g or more 1×10 18 pcs / g or less, 3×10 17 pcs / g or more 7×10 17 The order of preference is from less than or equal to the number density of carbon particles per gram. When the number density of the carbon material is within the above range, the amount of oil absorbed by the carbon material is further improved.

[0117] The number density P (particles / g) of a carbon material is equal to the volume V (m³) of a single primary particle. 3 ) and carbon density ρ(g / m³) 3 From this, it can be calculated from the following formula (2). Here, the carbon density ρ is the true density of graphite, which is 2.2 g / cc. Volume V (m³ 3) can be calculated from the following formula (3).

[0118] Number density P = 1 / (V × ρ) Equation (2)

[0119] Volume V = π × (D1 - D0) 3 / 6 formula (3)

[0120] Here, D0 is the inner diameter of the primary particle, and D1 is the outer diameter of the primary particle. D0 can be obtained using the mode pore diameter described above. D1 can be obtained by adding twice the value obtained by multiplying D0 by the average number of layers n and the interplanar spacing d002 of the (002) plane to the mode pore diameter. Alternatively, D1 may be obtained by TEM image analysis or the like. Although it is not the carbon material of the embodiment, for example, the known DENKA BLACK Li-100 can be calculated with an average particle size of 35 nm and D0=0 as the particle outer diameter (D1).

[0121] To improve the performance and lifespan of lithium-ion batteries, a highly efficient battery reaction is required that does not result in efficiency reduction due to side reactions. Therefore, the carbon material in the electrodes needs electrochemical stability, i.e., oxidation resistance and corrosion resistance. Electrochemical side reactions such as oxidation are said to originate from oxygen-containing functional groups and edge surfaces of the carbon material. To improve the oxidation resistance of carbon materials, it is necessary to reduce the oxygen-containing functional groups and the edge surfaces with low oxidation resistance. This is effective.

[0122] The ultra-high-sensitivity vacuum desorption mass spectrometer 300 (developed at Tohoku University, see T. Ishii et al. CARBON 80, 2014, 135-145) shown in Figure 3 allows for accurate qualitative and quantitative analysis of oxygen-containing functional groups and hydrogen-terminated edge sites using TPD-MS. More specifically, 1 to 3 mg of each carbon material is placed on a graphite sample stage, vacuum-heated to 1800°C at a heating rate of 10°C / min, and the gas released during heating is analyzed by the mass spectrometer 300 to accurately qualitatively and quantitatively analyze oxygen-containing functional groups and hydrogen-terminated edge sites. The TPD-MS 300 includes a radioactive thermometer 311, a sample holder 312, a quartz reactor 310 equipped with a high-frequency induction coil 313, and a detection unit 320 connected to the quartz reactor 310. The detection unit 320 includes, for example, a gas storage unit 327, a turbomolecular pump 324, a rotary pump 325, a cold cathode Pirani gauge 321, and a capacitance gauge 322.

[0123] The oxygen content of the carbon material is a value calculated from the amount of H2O, CO, and CO2 released by temperature-controlled desorption mass spectrometry, and is preferably 5.0% by mass or less, with 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, and 0.6% by mass or less being preferred in that order. When the oxygen content of the carbon material is within the above range, the stability of the lithium-ion battery is further improved, and this can further contribute to the high performance of the lithium-ion battery.

[0124] The temperature-controlled desorption mass spectrometer 300, which measures the desorbed gases from carbon materials during heating, measures the amount of H2, H2O, CO, and CO2 released from the carbon material. These released gases originate from oxygen-containing functional groups such as hydroxyl groups (including phenolic groups), carbonyl groups (including quinones), ethers, acid anhydrides, carboxyl groups, and lactones at the edge ends of the carbon material. Therefore, a high amount of oxygen-containing functional groups in the carbon material means a high amount of oxygen-containing functional groups and edge elements in the structure of the carbon material. The amount of oxygen-containing functional groups and edge elements in the carbon material can be adjusted by the CVD conditions and heat treatment temperature described later.

[0125] Furthermore, the amount of gas measured by the thermal desorption mass spectrometer 300 for carbon materials is preferably 5000 μmol / g or less, and is preferably in the order of 3000 μmol / g or less, 1000 μmol / g or less, 750 μmol / g or less, and 500 μmol / g or less. When the above amount of gas in the carbon material is within the above range, it can further contribute to extending the lifespan and improving the performance of lithium-ion batteries.

[0126] Furthermore, the edge amount of the carbon material is a value calculated from the amount of gas measured by the temperature-controlled desorption mass spectrometer 300, and is preferably 500 m. 2 It is less than / g and 300m 2 / g or less, 100m 2 / g or less, 50m 2 / g or less, 30m 2 The order of preference is from 750 μmol / g or less to 500 μmol / g or less. Furthermore, the edge content of the carbon material is preferably 750 μmol / g or less, followed by 500 μmol / g or less. When the edge content of the carbon material is within the above range, durability is further improved, which can further contribute to the stability and high performance of lithium-ion batteries.

[0127] Furthermore, the ash content of the carbon material is preferably 10,000 ppm or less, and is preferably 5,000 ppm or less, 4,000 ppm or less, 3,500 ppm or less, and 3,000 ppm or less, in that order. When the ash content of the carbon material is within the above range, the stability of the electrolyte is further improved, and the durability and performance of the lithium-ion battery can be further enhanced.

[0128] Furthermore, the carbon content of the carbon material is preferably 95.0% by mass or more, and is preferably 97.0% by mass or more, 98.0% by mass or more, 99.0% by mass or more, and 99.3% by mass or more, in that order. The carbon content is calculated using the following formula. The amount of generated gas is the total amount of gas (H2, H2O, CO, and CO2) measured by the temperature-controlled desorption mass spectrometer 300. Carbon content (mass%) of carbon material = 100 - (Ash content (mass%) + Amount of generated gas (mass%))

[0129] Furthermore, the ratio of oxygen content to carbon content (O / C) of the carbon material is preferably 1.00 or less, and is preferably 0.50 or less, 0.10 or less, 0.05 or less, and 0.01 or less, in that order. When the above ratio (O / C) of the carbon material is within the above range, it can further contribute to extending the lifespan and improving the performance of lithium-ion batteries.

[0130] Furthermore, the pH of the carbon material is preferably between 5.0 and 10.0, with the following ranges being preferable: 5.5 to 9.5, 6.0 to 9, 6 or less, 5.0 to 8.5, and 7.0 to 8.0. When the pH of the carbon material is within the above range, its stability is further improved.

[0131] Furthermore, the combustion temperature of the carbon material is preferably 300°C or higher, and is preferably 400°C or higher, 450°C or higher, 500°C or higher, and 550°C or higher, in that order. The combustion temperature test of the carbon material is performed as a simple test of corrosion resistance, and when the combustion temperature of the carbon material is 300°C or higher, the electrochemical stability within the electrode is good.

[0132] Furthermore, carbon materials, when containing graphene, exhibit excellent electron transport properties. Therefore, such carbon materials, when incorporated into the electrodes of lithium-ion batteries, can assist in the battery reaction. Additionally, carbon materials possess a linked structure in which multiple hollow particulate portions, each having a surrounding wall with multiple pores, are connected in a bead-like fashion. If this linked structure has internal spaces within the hollow particulate portions, it can permeate and retain the electrolyte containing dissolved lithium ions, thus providing excellent ion supply during the reaction. For this reason, such carbon materials are suitable for secondary battery reactions and are therefore ideal materials for secondary batteries.

[0133] The carbon material content in 100% by weight of the conductive additive is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may also be 100% by weight.

[0134] The proportion of carbon material is preferably 0.01% to 20% by weight, more preferably 0.1% to 10% by weight, and even more preferably 0.2% to 5% by weight, relative to 100% by weight of the electrode composite film. The desired effect is more likely to be obtained within the above numerical range.

[0135] (Method of manufacturing carbon materials) A method for producing carbon material includes a removal step to obtain carbon material by removing the template material, which is an aggregate in which multiple primary particles are aggregated and linked together in a bead-like manner, and which has a carbonaceous layer covering its surface.

[0136] In the removal process, the template material in the carbon material precursor, which has a carbonaceous layer covering its surface, is removed. In this way, the carbon material can be obtained.

[0137] The carbonaceous layer covers the entire surface of the mold material. The mold material removed in the removal process is an aggregate in which multiple primary particles are clustered together in a bead-like manner. Preferably, the primary particles constituting the aggregate are nano-primary particles with a size on the order of nanometers. The aggregate has an extended shape.

[0138] Furthermore, it is preferable that the mold material has branched sections where the aggregate is divided. If the mold material has branched sections, the resulting carbon material will have branched sections. It is also preferable that the mold material has one or more ring-shaped sections where the aggregate is divided. If the mold material has ring-shaped sections, the resulting carbon material will have ring-shaped sections. For example, one end of the aggregate may be connected to the other to form a ring-shaped section, or the tips of branches extending from the branched section may be connected to form a ring-shaped section, or a link-shaped section may be formed in a part of the aggregate other than the end.

[0139] The particle size of the primary particles constituting the mold material is preferably 1 nm to 150 nm, more preferably 5 nm to 100 nm, even more preferably 10 nm to 60 nm, particularly preferably 15 nm to 50 nm, and most preferably 20 nm to 40 nm. When the particle size of the primary particles is within the above range, the oil absorption capacity and mesopore volume of the resulting carbon material can be further increased. Furthermore, the mold material is easy to handle. In addition, the permeability of the raw material gas that serves as the carbon source for the carbonaceous layer formed on the surface of the mold material is improved, making it easier to uniformly coat the surface of the mold material with the carbonaceous layer.

[0140] Furthermore, the BET specific surface area of ​​the mold material is preferably 1 m². 2 / g or more 1000m 2 / g or less, more comfortably 10m 2 / g or more 500m 2 / g or less, more preferably 20m 2 / g or more 200m 2 / g or less, particularly preferably 40m 2 / g or more 160m 2 / g or less, most preferably 50m 2 / g or more 120m 2 It is less than / g. If the BET specific surface area of ​​the mold material is within the above range, the oil absorption amount and mesopore volume of the resulting carbon material can be further increased.

[0141] The specific surface area of ​​the resulting carbon material depends on the specific surface area of ​​the template material. The ratio of particle volume to surface area increases as the particle size decreases; therefore, the smaller the particle size, the larger the surface area per unit volume, i.e., the surface area per unit mass. Consequently, a carbon material with a high specific surface area can be obtained by using aggregates of nanoparticles with small primary particle sizes.

[0142] The average particle size of the primary particles constituting the mold material is preferably 1 nm to 100 nm, followed by 2 nm to 50 nm, 4 nm to 50 nm, and 3 nm to 30 nm in that order. The length of the aggregate is preferably 0.01 μm to 100.00 μm, more preferably 0.05 μm to 10.00 μm, and even more preferably 0.10 μm to 5.00 μm. The average particle size of the aggregate is preferably 0.05 μm to 10.00 μm, and more preferably 0.10 μm to 5.00 μm.

[0143] Furthermore, the bulk density of the mold material is preferably 0.1 g / L to 500.0 g / L, more preferably 0.5 g / L to 250.0 g / L, even more preferably 1.0 g / L to 200.0 g / L, particularly preferably 10.0 g / L to 100.0 g / L, and most preferably 30.0 g / L to 70.0 g / L. When the bulk density of the mold material is within the above range, the conductivity of the resulting carbon material can be further increased, and the oil absorption and mesopore volume can be further increased.

[0144] Furthermore, the mold material is preferably basic or acidic. Suitable basic mold materials include magnesium oxide and calcium carbonate. Suitable acidic mold materials include aluminum oxide and silica compounds containing silanol. The acidic pH is 7.0 or less in 4% moisture, preferably 6.5 or less, more preferably 6.0 or less, even more preferably 5.5 or less, and particularly preferably 5.0 or less. The above acidic pH is preferably 1.0 or higher, more preferably 2.0 or higher, even more preferably 3.0 or higher, particularly preferably 3.5 or higher, and most preferably 4.0 or higher.

[0145] Furthermore, the carbon content of the mold material is preferably 0.0001% by weight or more, more preferably 0.0100% by weight or more, even more preferably 0.0500% by weight or more, particularly preferably 0.100% by weight or more, and most preferably 0.500% by weight or more. The upper limit of the carbon content of the mold material is preferably 5.0000% by weight or less, more preferably 4.0000% by weight or less, even more preferably 3.0000% by weight or less, particularly preferably 2.5000% by weight or less, and most preferably 2.0000% by weight or less. When the carbon content of the mold material is within the above range, the formation of a carbonaceous layer on the mold surface becomes easier.

[0146] Furthermore, the mold material is preferably a compound that has catalytic activity in the carbon deposition reaction. Such compounds are preferably nonmetallic compounds, metalloid (semimetallic) compounds, and metallic compounds, and more preferably metalloid compounds and metallic compounds.

[0147] As nonmetallic compounds, ceramic compounds (nonmetallic inorganic solid materials) are preferred. As ceramics, glass, cement, and fine ceramics are preferred.

[0148] Preferably, the metalloid compound is a boron compound, a silicon compound, a germanium compound, or an antimony compound, and more preferably a silicon compound. Preferably, the silicon compound is silicon monoxide, silicon dioxide, silicon nitride, silicon carbide, or silicone, and more preferably silicon dioxide.

[0149] Preferably, the metal compound is a monovalent metal compound or a polyvalent metal compound, and more preferably a polyvalent metal compound. Suitable monovalent metal compounds include chlorides, sulfates, nitrates, phosphates, and carbonates of alkali metals such as sodium and potassium. Preferably, the polyvalent metal compound is an alkaline earth metal compound such as calcium and magnesium, or a trivalent metal compound such as aluminum, and more preferably a calcium compound, a magnesium compound, or an aluminum compound. Preferably, the calcium compound is a chloride, sulfate, nitrate, phosphate, carbonate, or oxide, more preferably a carbonate, an oxide, and even more preferably an oxide. Preferably, the magnesium compound is a chloride, sulfate, nitrate, phosphate, carbonate, or oxide, more preferably a carbonate, an oxide, and even more preferably an oxide. Preferably, the aluminum compound is a chloride, sulfate, nitrate, phosphate, carbonate, or oxide, more preferably a carbonate, an oxide, and even more preferably an oxide.

[0150] Furthermore, since atomized compounds form aggregates in which multiple nanoprimary particles are linked together in a bead-like manner with multiple branching structures, they can be suitably used as template materials. As atomized compounds, compounds obtained by flame hydrolysis, which is one of the dry manufacturing methods for inorganic materials, are preferred.

[0151] As the atomized compound, atomized silicon dioxide is preferred. Atomized silicon dioxide produced by flame hydrolysis does not go through a liquid phase process during its production, resulting in slow aggregation. Therefore, atomized silicon dioxide has excellent dispersibility in the liquid phase and in the compound (solid phase). Atomized silicon dioxide is produced by high-temperature gas-phase hydrolysis of silicon tetrachloride in an oxyhydrogen flame, accompanied by hydrochloric acid as a byproduct. By changing the production conditions such as the flame temperature, the supply ratio of oxygen and hydrogen, the amount of raw materials supplied, and the residence time, an average particle size of 7 nm to 40 nm and a specific surface area of ​​50 m² can be obtained. 2 / g or more 380m 2 Particles of silicon dioxide less than / g can be obtained.

[0152] Besides fumid silicon dioxide, suitable atomized compounds produced by flame hydrolysis include fumidized alumina, fumidized titania, and fumidized wet zirconia. Suitable other atomized metal compounds include chlorides of Na, Ba, or Sr; sulfates of K, Na, Sr, or Mg; nitrates of Na or K; phosphates of Na or K; carbonates of Na, K, Ca, or Mg; and metal oxides of Na, K, Ca, or Ba. The shape of the mold material is preferably in a fumid form.

[0153] Furthermore, precipitated silica can also be used as a mold material. Precipitated silica is obtained by reacting a sodium silicate solution with an acid in the liquid phase, followed by precipitation, filtration, washing, drying, and grinding. By adjusting the reaction conditions, an average particle size of approximately 7 nm to 140 nm and a specific surface area of ​​approximately 20 nm can be obtained. 2 / g or more 400m 2 Particles of silicon dioxide less than / g can be obtained.

[0154] The moisture content of the mold material is preferably 5.0% or less, more preferably 3.0% or less, even more preferably 1.5% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less.

[0155] When using the CVD method to form a carbonaceous layer on the surface of a mold material, the amount of carbon deposited on the mold material surface is influenced by CVD reaction conditions such as the type of raw material gas, raw material gas concentration, flow rate, reaction temperature, and reaction time, as well as the surface of the mold material, with the surface having the greatest influence. Suitable mold materials for carbon deposition by the CVD method are compounds containing oxygen atoms (oxygen-containing compounds), where the carbon in the raw material gas is replaced by the oxygen atoms of the oxygen-containing compound, and this becomes the starting point for the precipitation of carbonaceous material. Preferably, the oxygen-containing compound is a metal oxide or metal carbonate, and more preferably an acidic or basic compound. Suitable basic oxygen-containing compounds include magnesium oxide and calcium carbonate.

[0156] Furthermore, for a mold material surface suitable for carbonaceous layer formation in the CVD method, it is preferable that the surface contains hydrocarbons that serve as a carbon source. Hydrocarbons are compounds that act as raw material gases, and are preferably compounds containing methyl groups or carbon-carbon unsaturated bonds. Suitable mold materials are inorganic compounds that have hydrocarbons on their surface.

[0157] Furthermore, the inorganic compound having hydrocarbons on its surface is preferably an inorganic material surface-treated with a silane coupling agent, and more preferably a silica compound surface-treated with a silane coupling agent. As the silane coupling agent, those commonly used as surface pretreatment agents can be used without limitation, with methoxy-type silane coupling agents, ethoxy-type silane coupling agents, vinyl-type silane coupling agents, dialkoxy-type silane coupling agents, and trialkoxy-type silane coupling agents being preferred, trialkoxy-type silane coupling agents with a high number of methyl groups per molecule being more preferred, and trimethoxysilane compounds being even more preferred.

[0158] The amount of silane coupling agent is appropriately selected depending on the intended use, but is expressed as the amount of hydrocarbons in the inorganic material, preferably 0.01% to 10.00% by weight, more preferably 0.02% to 8.00% by weight, even more preferably 0.05% to 5.00% by weight, particularly preferably 0.10% to 3.00% by weight, and most preferably 0.50% to 1.50% by weight. When the amount of silane coupling agent (amount of hydrocarbons) in the inorganic material is within the above range, the amount of carbonaceous layer formed on the surface of the mold material can be easily adjusted.

[0159] The mold material can be used individually or in combination of two or more types.

[0160] In the removal process, any method for removing the mold material that removes the mold material while leaving a carbonaceous layer is acceptable, preferably a dissolution method using an acid or alkali, and more preferably an acid dissolution method.

[0161] The acid used to dissolve and remove the mold material is appropriately selected depending on the type of mold material, but is preferably hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, or hydrofluoric acid, and more preferably hydrochloric acid or hydrofluoric acid. The concentration of the acid used to dissolve and remove the mold material is appropriately adjusted within a range that allows for the dissolution and removal of the mold material. The amount of acid used is not particularly limited as long as it is within a range that allows for the dissolution and removal of the mold material, but for example, it is 30 times or more the stoichiometric ratio or 50 times or more the stoichiometric ratio relative to the mold material.

[0162] The temperature for dissolving and removing the mold material is preferably 5°C to 100°C, more preferably 10°C to 50°C, and even more preferably 20°C to 30°C. The removal process may be carried out with stirring, vibration, and other operations. The time required for the removal process is appropriately selected within a range that allows for the removal of the mold material.

[0163] The carbonaceous layer, after the mold material has been removed, can be recovered, for example, by filtration, and then washed with pure water. Washing conditions can be selected as appropriate, and the process is completed after confirming that the pH of the washing solution used on the carbonaceous layer is neutral.

[0164] The carbonaceous layer after washing can be dried by vacuum heating and drying. The conditions for vacuum heating and drying are not particularly limited, but it is preferable to set the vacuum heating and drying temperature to 100°C or higher and 200°C or lower, and the vacuum heating and drying time to 1 hour or higher and 10 hours or lower.

[0165] Furthermore, it is preferable that the method for producing the carbon material further includes a heating step in which the carbon material is heated to a temperature of 1000°C or higher and 3000°C or lower after the removal step.

[0166] In the heating step performed after the removal step, the carbon material obtained in the removal step is heated. The heating temperature is 1000°C to 3000°C, preferably 1300°C to 2500°C, more preferably 1500°C to 2000°C, even more preferably 1600°C to 1900°C, and particularly preferably 1750°C to 1850°C.

[0167] Furthermore, the heating time in the heating process (holding time at a predetermined heating temperature) is preferably 0.1 hours or more and 10.0 hours or less, more preferably 0.2 hours or more and 5.0 hours or less, and even more preferably 0.5 hours or more and 5.0 hours or less. In addition, the atmospheric pressure in the heating process is preferably atmospheric pressure or reduced pressure.

[0168] Furthermore, by performing the heating process, functional groups (mainly oxygen-containing functional groups) that bond to the carbon atoms constituting the carbon material, as well as carbon chains that do not form six-membered rings, detach from the carbon material at temperatures above 1000°C, forming unbonded bonds. When these unbonded bonds bond to other nearby carbon atoms, the surface of the carbon material becomes less receptive to the bonding of functional groups. By heat-treating the carbon material preferably at 1500°C or higher, and more preferably at 1600°C or higher, the carbon material can acquire functions such as further improved electronic conductivity and maintenance of internal space.

[0169] Furthermore, the heating process allows for the adjustment of structural defects in the graphene and non-graphene components that constitute the surrounding wall of the carbon material. These structural defects include spaces created within the interconnected structure of the carbon material due to the dissolution of the template material, and intrusion holes created in the surrounding wall of the carbon material. By adjusting the heating process conditions, such as heating temperature and heating time, the degree of these structural defects can be controlled; that is, the size of the spaces within the carbon material and the size of the intrusion holes that allow the electrolyte to penetrate into the carbon material can be adjusted.

[0170] (Carbon material precursor) The carbon material precursor comprises a template material composed of aggregates in which multiple primary particles are aggregated and linked together in a bead-like manner, and a carbonaceous layer covering the surface of the template material and having multiple pores.

[0171] The template material for the carbon material precursor is an aggregate in which multiple primary particles are aggregated and linked together in a bead-like manner, and preferably has the same configuration as the template material that constitutes the carbon material precursor used in the carbon material manufacturing method of the above embodiment.

[0172] The carbonaceous layer formed on the surface of the mold material has multiple pores. Preferably, the carbonaceous layer covers the entire surface of the mold material. Furthermore, it is preferable that the carbonaceous layer has a graphene crystalline structure.

[0173] (Method for producing carbon material precursors) A method for producing a carbon material precursor includes a coating step in which a carbonaceous layer is applied to the surface of a template material, which is an aggregate in which multiple primary particles are aggregated and linked together in a bead-like manner, in order to obtain a carbon material precursor.

[0174] In the coating process, the surface of the template material is coated with a carbonaceous layer to obtain a carbon material precursor. The template material is an aggregate in which multiple primary particles are aggregated and linked together in a bead-like manner, and preferably has the same configuration as the template material that constitutes the carbon material precursor in the above embodiment.

[0175] A carbonaceous layer can be formed on the surface of the mold material by bringing an organic substance that serves as a carbon source into contact with the mold material and performing a carbonization heat treatment. Contact with the carbon source and the carbonization heat treatment can be performed simultaneously or separately. The contact between the mold material and the carbon source is preferably carried out at room temperature (25°C) or higher and 1000°C or lower.

[0176] The number of carbonaceous layers is appropriately selected according to the intended use, preferably 1.0 layers or more, more preferably 1.2 layers or more, even more preferably 1.5 layers or more, particularly preferably 2.0 layers or more, and most preferably 2.2 layers or more. The upper limit of the number of carbonaceous layers is preferably 15.0 layers or less, more preferably 10.0 layers or less, even more preferably 8.0 layers or less, particularly preferably 6.0 layers or less, and most preferably 5.0 layers or less. When the number of carbonaceous layers is within the above range, the strength properties and elastic deformation of the carbon material obtained by heating the carbonaceous layers are excellent, and the hollow structure of the hollow particulate portion in the carbon material can be well maintained, thereby greatly improving the characteristics of lithium-ion batteries. The number of carbonaceous layers is calculated by forming a carbonaceous layer on the surface of the mold material, then calculating the weight of the carbonaceous layer using thermogravimetric analysis (TG), and calculating the weight of the carbonaceous layer per unit area of ​​the mold material from the weight of the carbonaceous layer and the surface area of ​​the mold material, and this value is used as the weight per unit area of ​​single-layer graphene (7.61 × 10⁻¹⁰).-4 g / m 2 This value is calculated by dividing by ).

[0177] Methods for bringing a carbon source into contact with a mold material can be broadly classified into liquid-phase contact methods and gas-phase contact methods, with gas-phase contact methods being preferred. Liquid-phase contact methods involve, for example, immersing the mold material in a liquid of organic matter. Gas-phase contact methods involve, for example, introducing an organic gas at high temperatures and bringing it into contact with the mold material; this is the so-called CVD method.

[0178] In the liquid-phase contact method, organic compounds having functional groups that react with functional groups present on the surface of the mold material, specifically hydroxyl groups, are preferably used, and benzene-based hydrocarbon compounds having functional groups that react with hydroxyl groups are particularly preferred. Among these, benzene-based aromatic hydrocarbon compounds having at least one of a hydroxyl group and a carboxyl group are preferred, with phenol, hydronaphthalene, and dihydronaphthalene being more preferred. When an organic compound having a functional group that reacts with functional groups present on the surface of the mold material is used, strong bonds such as ester bonds are formed between the mold material and the organic compound, and the organic compound tends to carbonize in situ during the carbonization heat treatment without volatilizing.

[0179] In the liquid-phase contact method, an organic compound acting as a carbon source is dissolved in a solvent, and the template material is impregnated into the solution at room temperature, thereby bringing the template material into contact with the organic carbon source. To strongly bond the template material and the organic material, the mixture is then maintained at a temperature range of 250°C to 600°C for a certain period of time. In this way, the hydroxyl groups on the surface of the template material and the organic material undergo dehydration condensation reactions such as esterification, fixing them through bonds such as ester bonds, making it easier to obtain a carbonaceous layer with a graphene structure. After that, the temperature is lowered, and any excess organic material that did not react with the template material is washed and removed with a solvent.

[0180] Subsequently, heat treatment is performed to carbonize the organic compound acting as a carbon source in contact with the mold material. This heat treatment causes dehydrogenation reactions in organic substances such as hydrocarbons, further promoting graphene structuring in the carbonaceous layer. The heat treatment temperature is preferably 600°C to 1500°C, more preferably 750°C to 1500°C, and even more preferably 800°C to 1000°C. However, the heat treatment may be performed at 1500°C or higher, as long as the mold material does not collapse or melt.

[0181] In the vapor-phase contact method, an organic compound as a carbon source is brought into contact with the template material. To strongly bond the carbon source and the template material, the CVD (Chemical Vapor Deposition) method is preferably carried out in a temperature range in which the dehydrogenation reaction can proceed, specifically between 400°C and 1000°C.

[0182] As organic compounds used as carbon sources in the gas-phase contact method, they can be appropriately selected according to the intended use, and hydrocarbons such as saturated hydrocarbons, unsaturated hydrocarbons having at least one of a double bond and a triple bond, alicyclic hydrocarbons, and aromatic hydrocarbons are preferably used. As saturated hydrocarbons, they can be either straight-chain or branched-chain, and methane, ethane, and propane are preferred. As unsaturated hydrocarbons, they can be either straight-chain or branched-chain, and ethylene, propylene, isoprene, and acetylene are preferred. As alicyclic hydrocarbons, cyclopropane and cyclohexane are preferred. As aromatic hydrocarbons, benzene and toluene are preferred. Among these hydrocarbons, methane, ethane, acetylene, ethylene, propylene, and benzene are preferred, and from the viewpoint of precipitating highly crystalline carbon, methane, propylene, and benzene are preferred. In particular, methane is preferred from the viewpoint of obtaining highly crystalline carbon at a high thermal decomposition temperature.

[0183] In addition to the substances mentioned above, suitable organic compounds used in the gas-phase contact method include alcohols such as methanol, ethanol, propanol, and butanol, as well as nitrogen-containing compounds such as acetonitrile and acrylonitrile.

[0184] Furthermore, the reaction temperature in the CVD reaction is appropriately selected depending on the type of template material and the decomposition temperature of the organic compound used as a carbon source, but is preferably 400°C to 1000°C, more preferably 600°C to 950°C, and even more preferably 800°C to 900°C.

[0185] Furthermore, the reaction time in the CVD reaction (CVD treatment time at a predetermined heating temperature) is appropriately selected depending on the type of template material and organic compound used as a carbon source, and the number of carbonaceous layers deposited, but is preferably 0.1 hours or more and 10.0 hours or less, more preferably 0.5 hours or more and 5.0 hours or less, and even more preferably 1.0 hour or more and 3.0 hours or less. In addition, the product can be analyzed by applying the analytical methods disclosed herein, and the time required for sufficient carbon deposition can be appropriately set based on the results.

[0186] Furthermore, the CVD reaction may be carried out under an inert gas atmosphere if necessary. Preferably, the inert gas is nitrogen, helium, neon, or argon, and more preferably argon. In the CVD method, carbon can be easily adsorbed or deposited on the mold material in the gas phase by heating while passing a gaseous organic compound in contact with the mold material together with a carrier gas. The type of carrier gas, flow rate, flow rate, and heating temperature can be appropriately adjusted depending on the type of organic compound used. The carrier gas may be, for example, one of the inert gases mentioned above, but may also be a mixture with oxygen gas or hydrogen gas. Preferably, the carrier gas is argon.

[0187] Furthermore, the number of carbonaceous layers formed on the mold material can be appropriately selected by the CVD reaction time. To form a small number of carbonaceous layers, the carrier gas flow rate is preferably 0.05 m / min or more and 5.00 m / min or less, more preferably 0.10 m / min or more and 1.00 m / min or less, even more preferably 0.20 m / min or more and 0.80 m / min or less, and particularly preferably 0.32 m / min or more and 0.64 m / min or less. In addition, the amount of organic compound introduced is preferably 1 volume% or more and 70 volume% or less, more preferably 5 volume% or more and 50 volume% or less, even more preferably 10 volume% or more and 40 volume% or less, and particularly preferably 15 volume% or more and 35 volume% or less, relative to the total amount of carrier gas and organic compound.

[0188] Since carbonization of the carbonaceous layer can also proceed by CVD reactions, other special carbonization treatments are not necessary, but they may be performed.

[0189] [Other conductive additives] Conductive additives can be a combination of carbon materials and other conductive substances. Suitable other conductive substances include other carbon materials such as graphite, carbon black, carbon nanotubes, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; conductive fibers such as metal fibers; metal powders such as aluminum powder and nickel powder; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0190] Other conductive materials can be used individually or in combination of two or more. The amount of other conductive materials used is appropriately selected according to the intended use of the electrode and is selected within the same range as the carbon material. The ratio of carbon material to other conductive materials is appropriately selected according to the intended use of the electrode and is preferably 10:90 to 90:10 by weight ratio of [carbon material] to [other conductive materials], more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, and particularly preferably 40:60 to 60:40.

[0191] Furthermore, carbon materials can be made even more effective by combining them with conventionally used conductive additives. For example, carbon blacks such as acetylene black are composed of linked particles with a diameter of several tens of nanometers, but the crystallinity of carbon is not very high, the structural length is short, and it is easily broken down, making it poor at long-distance electron transport. By combining carbon blacks with carbon materials, it is possible to realize a system that maintains electron conductivity and ion supply capabilities, whether the three-dimensional structure is maintained or the three-dimensional structure is compressed and flattened like flaky graphite.

[0192] [Percentage of conductive additives] The electrode composite film is analyzed by determining the ratio of conductive additives from Raman spectra measured at the surface, a depth equivalent to 50% of the electrode composite film thickness from the surface, and a depth equivalent to 90% of the electrode composite film thickness from the surface, respectively, using R0 and R 50 , and R 90 In this case, the ratio of conductive additives is R0, R 50 , and R 90 Preferably, at least one of these values ​​is 0.08 or higher. This makes it easier to particularly improve any of the low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics during high-power discharge, and facilitates performance design according to the application.

[0193] The Raman spectra measured at each location show 2D peaks of 2500-3000 cm², which are attributed to conductive additives (especially carbon materials). -1 Nearby peaks and 200-800 cm due to active material -1 Nearby peaks appear. In this specification, the heights of these peaks are referred to as H x and H z Toshi, H x / H zThis is defined as the "proportion of conductive additives." A high proportion of conductive additives means a high concentration of conductive additives (especially carbon materials). Compared to wet chemical analysis methods that measure the content of conductive additives by extracting them using a solvent that dissolves other compounding agents, the method using Raman spectroscopy, which can be performed entirely dry, saves time, and the proportion can be easily determined if the Raman signal positions of the compounding agents used in the electrode composite film are measured in advance.

[0194] When R0 is 0.08 or higher, low-temperature cycle characteristics tend to improve. The reason for this is presumed to be as follows: At low temperatures, the rising overpotential causes Li to precipitate unevenly on the negative electrode, and the resulting irregularities compress the separator, pushing out the electrolyte. This reduces reactivity and accelerates cycle degradation. When a large amount of carbon material is present near the surface (upper part) of the electrode composite film, the carbon material, which has a large total pore volume, is flexible, mitigating the effects of the above compression and improving low-temperature cycle characteristics.

[0195] R0 is more preferably 0.1 or higher, even more preferably 0.2 or higher, and particularly preferably 0.3 or higher. There is no particular upper limit, but from the viewpoint of battery capacity, it may be, for example, 1 or less, 0.9 or less, 0.7 or less, or 0.6 or less.

[0196] R 50 However, a value of 0.08 or higher makes it easier to improve high-rate characteristics. The reason for this is presumed to be as follows: For example, in lithium-ion batteries designed for high capacity, such as those used in EVs, the electrode composite film is made thicker to allow for a larger amount of active material to be packed in. When the electrode composite film is thick, it becomes more difficult for electrons from the current collector side and ions from the separator side to reach the central part of the electrode composite film. When a large amount of conductive additives such as carbon material are present in the central part of the electrode composite film, even at a 3C rate used in EV rapid charging, the battery reaction occurs uniformly, resulting in high performance.

[0197] R 50The value is more preferably 0.1 or higher, even more preferably 0.2 or higher, and particularly preferably 0.3 or higher. The upper limit is not particularly limited, but from the viewpoint of battery capacity, it may be, for example, 1 or less, 0.9 or less, 0.7 or less, or 0.6 or less.

[0198] R 90 However, a value of 0.08 or higher makes it easier to improve the voltage characteristics during high-power discharge. The reason for this is presumed to be as follows: In lithium-ion batteries for EV applications, especially in extremely cold conditions or during initial operation, when a rapid current flows, and the battery capacity is particularly low, overvoltage can occur due to the internal resistance of the battery. This can cause the voltage drop to fall below the set discharge termination voltage (cutoff voltage), resulting in problems where EVs and other vehicles cannot start operating. One cause of this phenomenon is high internal resistance of the battery, and it is known that the above problem becomes apparent when the contact resistance at the junction between the current collector and the electrode composite film is high. Therefore, by including a large amount of the above carbon material, which has high electronic conductivity and ionic conductivity, near the current collector (lower part) of the electrode composite film, the voltage fluctuation range during high output is reduced, and the above problem can be solved.

[0199] R 90 The value is more preferably 0.1 or higher, even more preferably 0.2 or higher, and particularly preferably 0.3 or higher. The upper limit is not particularly limited, but from the viewpoint of battery capacity, it may be, for example, 1 or less, 0.9 or less, 0.7 or less, or 0.6 or less.

[0200] Furthermore, the electrode composite film preferably includes a high-concentration layer in which the proportion of conductive additive is partially high, and more preferably the proportion of conductive additive in the high-concentration layer is 1.1 times or more higher than in other parts of the electrode composite film, with the preferred ratios being 1.3 times or more, 1.5 times or more, 2 times or more, 2.5 times or more, and 3 times or more, in that order. The upper limit of the ratio is not particularly limited, but may be, for example, 10 times or less, 8 times or less, 6 times or less, or 5 times or less. This makes it easier to particularly improve at least one of the low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics during high-power discharge while maintaining battery capacity, and makes it easier to design performance according to the application. The preferred range for the proportion of conductive additive in the high-concentration layer is the above-mentioned R0, R50 , and R 90 It is similar to that.

[0201] The thickness of the high-concentration layer is not particularly limited, but may be, for example, 1-80%, 3-60%, or 5-50% of the thickness of the electrode composite film.

[0202] Preferably, the high-concentration layer is positioned at least one of the following locations: on the surface of the electrode composite film, at a depth corresponding to 50% of the thickness of the electrode composite film from the surface, and at a depth corresponding to 90% of the thickness of the electrode composite film from the surface. This makes it easier to improve at least one of the low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics during high-power discharge while maintaining battery capacity, and facilitates performance design according to the application.

[0203] When the high-concentration layer is positioned to include the surface of the electrode composite film, it is particularly easy to improve low-temperature cycle characteristics while maintaining battery capacity. This is because the carbon material is relatively concentrated near the surface (upper part) of the electrode composite film, ensuring sufficient active material content and improving low-temperature cycle characteristics without reducing battery capacity.

[0204] When the high-concentration layer is positioned to include a depth equivalent to 50% of the electrode composite film thickness from the surface, it is particularly easy to improve high-rate characteristics while maintaining battery capacity. This is because the carbon material is relatively concentrated in the middle of the electrode composite film, ensuring sufficient active material content and improving high-rate characteristics without reducing battery capacity.

[0205] When the electrode composite film is positioned to include a depth equivalent to 90% of its thickness from the surface, it is easier to improve the voltage characteristics during high-power discharge while maintaining battery capacity. Because the carbon material is relatively concentrated at the bottom of the electrode composite film, the amount of active material is ensured, and it is thought that the voltage characteristics during high-power discharge are improved without reducing battery capacity.

[0206] The electrode composite material film may contain one high-concentration layer or two or more high-concentration layers. For example, the high-concentration layer may be divided into two layers, with one high-concentration layer arranged to include the surface position of the electrode composite material film, and the other high-concentration layer arranged to include the depth position corresponding to 90% of the thickness of the electrode composite material film from the surface.

[0207] Furthermore, the abundance ratio of the conductive assistant is such that any one of R0, R 50 , and R 90 is preferably higher than the other two. Thereby, while maintaining the battery capacity, it is particularly easy to improve at least one of the low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics during high-power discharge, and it is easy to perform performance design according to the application.

[0208] When R0 is higher than R 50 and R 90 , it is easy to improve the low-temperature cycle characteristics while maintaining the battery capacity. Since the carbon material is relatively biased near the surface (upper part) of the electrode composite material film, the content of the active material is ensured, and it is considered that the low-temperature cycle characteristics are improved without reducing the battery capacity.

[0209] From the point of view of being easy to improve the low-temperature cycle characteristics while maintaining the battery capacity, R0 is preferably 1.1 times or more higher than R 50 and R 90 , and the magnification is preferably 1.3 times or more, 1.5 times or more, 2 times or more, 2.5 times or more, 3 times or more in this order. The upper limit of the magnification is not particularly limited, but it may be, for example, 10 times or less, 8 times or less, 6 times or less, or 5 times or less.

[0210] When R 50 is higher than R0 and R 90 , it is easy to improve the high-rate characteristics while maintaining the battery capacity. Since the carbon material is relatively biased in the middle of the electrode composite material film, the content of the active material is ensured, and it is considered that the high-rate characteristics are improved without reducing the battery capacity.

[0211] From the point of view of being easy to improve the high-rate characteristics while maintaining the battery capacity, R50 R0 and R 90 It is preferable that the ratio is 1.1 times or higher than the given ratio, and the preferred ratios are in the order of 1.3 times or higher, 1.5 times or higher, 2 times or higher, 2.5 times or higher, and 3 times or higher. The upper limit of the ratio is not particularly limited, but for example it may be 10 times or less, 8 times or less, 6 times or less, or 5 times or less.

[0212] R 90 However, R0 and R 50 A higher value compared to the above makes it easier to improve voltage characteristics during high-power discharge while maintaining battery capacity. Because the carbon material is relatively concentrated at the bottom of the electrode composite film, the amount of active material is ensured, and it is thought that the voltage characteristics during high-power discharge are improved without reducing battery capacity.

[0213] Because it is easy to improve the voltage characteristics during high-power discharge while maintaining battery capacity, R 90 R0 and R 50 It is preferable that the ratio is 1.1 times or higher than the given ratio, and the preferred ratios are in the order of 1.3 times or higher, 1.5 times or higher, 2 times or higher, 2.5 times or higher, and 3 times or higher. The upper limit of the ratio is not particularly limited, but for example it may be 10 times or less, 8 times or less, 6 times or less, or 5 times or less.

[0214] Methods for adjusting the distribution of the proportion of conductive additives include, for example, applying electrode slurries containing carbon materials as conductive additives at different concentrations multiple times to form an electrode composite film, and utilizing migration due to temperature gradients during coating and drying.

[0215] <Method of manufacturing electrodes> Electrodes can be obtained, for example, by applying an electrode slurry onto a current collector to form a coating film, and then drying the coating film. Examples of electrode slurries include a positive electrode forming slurry used for forming a positive electrode, and a negative electrode forming slurry used for forming a negative electrode.

[0216] The slurry for forming the positive electrode is a mixture of the above-mentioned positive electrode active material, conductive additive, and binder in a dispersion medium. The slurry for forming the positive electrode may also contain an electrolyte. When the slurry for forming the positive electrode contains an electrolyte, the slurry is preferably in the form of a clay-like substance in which the above-mentioned positive electrode active material, conductive additive, and electrolyte are kneaded together. In this case, the slurry for forming the positive electrode does not need to contain a binder.

[0217] Furthermore, the cathode forming slurry may contain other compounding agents as needed. These other compounding agents can be appropriately selected according to the intended use of the electrode, and those used in lithium-ion batteries can be used in their normal usage range.

[0218] While there are no particular limitations on the dispersion medium for the slurry, it is preferable to use a medium that dissolves only the binder and not the other constituent materials in order to sufficiently distribute the binder uniformly and to form a coating film of the slurry to a predetermined size. Among these, organic solvents such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, and acetone, as well as water, are preferred, and one of these can be used alone or in combination of two or more.

[0219] When polyvinylidene fluoride is used as a binder, dimethylformamide and N-methyl-2-pyrrolidone (NMP) are preferred as dispersion media, with NMP being more preferred.

[0220] Furthermore, the solid content concentration of the cathode forming slurry, excluding the dispersion medium, can be appropriately selected depending on the method of applying the slurry to the current collector, preferably 10% by weight or more and 90% by weight or less, more preferably 20% by weight or more and 80% by weight or less, even more preferably 40% by weight or more and 80% by weight or less, particularly preferably 40% by weight or more and 70% by weight or less, and most preferably 50% by weight or more and 65% by weight or less.

[0221] The viscosity of the cathode forming slurry is preferably 1000 cP to 50000 cP, more preferably 2000 cP to 40000 cP, even more preferably 5000 cP to 35000 cP, particularly preferably 10000 cP to 35000 cP, and most preferably 10000 cP to 30000 cP at a temperature of 24°C to 26°C. When the viscosity of the cathode forming slurry is within the above range, the slurry can be applied with a uniform thickness while maintaining a constant dispersion of the solid content excluding the dispersion medium.

[0222] The positive electrode can be manufactured by applying the above-mentioned slurry for forming the positive electrode onto a current collector and drying it as necessary.

[0223] For applying the slurry for forming the positive electrode to the current collector, commonly used printing techniques can be employed. When the thickness of the coating is small, gravure printing is suitable, while when the thickness of the coating is large, printing methods such as doctor blade printing and die printing are suitable.

[0224] Subsequently, the coating film is heat-dried as needed. Any drying method is available, but the method that achieves the desired bonding strength with the binder is preferred.

[0225] When forming the positive electrode to the predetermined dimensions after drying, it is preferable to use a method employing industrially available cutting blades. Furthermore, to achieve the predetermined density, it is preferable to use a method employing industrially available pressurizing equipment as needed.

[0226] The slurry for forming the negative electrode is a mixture of the above-mentioned negative electrode active material, conductive additive, and binder in a dispersion medium. The slurry for forming the negative electrode may also contain an electrolyte. When the slurry for forming the negative electrode contains an electrolyte, the slurry is preferably in the form of a clay-like substance in which the above-mentioned negative electrode active material, conductive additive, and electrolyte are kneaded together. In this case, the slurry for forming the negative electrode does not need to contain a binder.

[0227] The dispersion medium of the slurry is not particularly limited as long as it is a solvent generally used in the technical field. Organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, and acetone, and water are preferred, and one of these can be used alone or in combination of two or more. The dispersion medium is used to dissolve or disperse the negative electrode active material, conductive assistant, and binder in consideration of the coating thickness of the slurry for forming the negative electrode and the production yield.

[0228] The amount of the dispersion medium used is not particularly limited, but the concentration of the solid content including the negative electrode active material, conductive assistant, and binder in the slurry for forming the negative electrode is preferably 10% by weight or more and 90% by weight or less, more preferably 20% by weight or more and 80% by weight or less, still more preferably 30% by weight or more and 75% by weight or less, particularly preferably 40% by weight or more and 70% by weight or less, and most preferably 50% by weight or more and 65% by weight or less.

[0229] Coating of the slurry for forming the negative electrode onto the current collector can utilize generally used printing techniques. When the thickness dimension of the coating film is small, gravure printing is preferred, and when the thickness dimension of the coating film is large, printing methods such as doctor blade printing and die printing are preferred.

[0230] Thereafter, if necessary, the coating film is dried by heating, and any drying method can be used, and a method that can achieve the desired binding strength by the binder is preferred.

[0231] After drying, when forming the negative electrode into a predetermined dimension, it is preferable to perform a method using an industrially available cutting blade. Also, in order to achieve a predetermined density, if necessary, it is preferable to perform a method using an industrially available pressurizing device.

[0232] <<Lithium Ion Battery>> A lithium-ion battery comprises the electrodes described above. Specifically, a lithium-ion battery has a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, and at least one of the positive electrode and the negative electrode, preferably both the positive and negative electrodes, is the electrode (positive electrode, negative electrode) of the above embodiment. The lithium-ion battery may further include a battery container that houses the electrode assembly consisting of the positive electrode, negative electrode and separator, and a sealing member that seals the battery container. Note that the positive electrode and negative electrode of a lithium-ion battery are substantially the same as the positive electrode and negative electrode described above, so a detailed explanation is omitted.

[0233] The separator in a lithium-ion battery separates the negative electrode and the positive electrode and provides a pathway for lithium ions to move. It is not particularly limited as long as it is a material that is normally used as a separation membrane in a lithium-ion battery, but it is preferable that it has low resistance to ion movement of the electrolyte while having excellent electrolyte impregnation ability.

[0234] Specifically, examples of separators include porous polymer films, and porous polymer films made from polyolefins such as polyethylene, polypropylene, polybutene, polyvinyl chloride, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers of these films are preferred. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, are also preferred as separators. Furthermore, coated separation membranes containing ceramic components or polymeric substances are preferred to ensure heat resistance or mechanical strength. Separators may be used selectively in single-layer or multi-layer structures.

[0235] Polyethylene and polypropylene are suitable materials for porous polymer films. Polyethylene has a relatively low melting point, and when the battery temperature rises for any reason (for example, an unsafe condition such as a short circuit), the pores in the film become blocked by thermal melting, inhibiting the movement of driving ions, thereby stopping the reaction and ensuring safety. Polypropylene is also suitable because it can be made porous by stretching without the use of plasticizers.

[0236] Furthermore, polymer compounds can be applied to both sides of the separator for use. The polymer compound provided on the surface of the separator may be gelled with an electrolyte. Suitable polymer compounds include ether-based polymer compounds such as polyvinyl formal, polyethylene oxide, and crosslinked polyethylene oxide; ester-based polymer compounds such as polymethacrylate; acrylate-based polymer compounds; polyvinylidene fluoride; and fluorine-based polymer compounds such as polyvinylidene fluoride-hexafluoropropylene copolymer. Among these, fluorine-based polymer compounds are preferred from the viewpoint of preventing swelling during high-temperature storage and gelation, and polyvinylidene fluoride is more preferred.

[0237] Lithium-ion batteries typically use a non-aqueous electrolyte solution, which is an electrolyte dissolved in an organic solvent.

[0238] Lithium salts are preferred as electrolytes for lithium-ion batteries. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2)(C4F9SO2), and LiC(CF3SO2) LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, Li-cyclic 1,2-perfluoroethanedisulfonylimide, and Li-cyclic 1,3-perfluoropropanedisulfonylimide are preferred. Among these, LiPF6, LiBF4, LiClO4, CF3SO3Li, LiN(CF3SO2)2, and LiN(C2F5SO2)2 are preferred because they are easily soluble in the solvent and exhibit a high degree of dissociation, with LiPF6 and LiBF4 being more preferred.

[0239] Furthermore, as the electrolyte, a gel-like electrolyte is preferred, which contains a polymer compound that swells in an organic solvent to form a retainer that holds the non-aqueous electrolyte. By including a polymer compound that swells in an organic solvent, high ionic conductivity can be obtained, excellent charge and discharge efficiency can be achieved, and leakage of the battery can be prevented. The content of this polymer compound is preferably 0.1% by weight or more and 10.0% by weight or less of the electrolyte. The polymer compound is preferably polyvinylidene fluoride.

[0240] The above electrolytes can be used individually or in combination of two or more. The concentration of the electrolyte in the electrolyte solution is preferably 5% by weight or more and 15% by weight or less, more preferably 5% by weight or more and 13% by weight or less, and even more preferably 5% by weight or more and 10% by weight or less.

[0241] The organic solvent for the electrolyte is not particularly limited as long as it can dissolve the above electrolyte, but cyclic carbonates; linear carbonates; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolanes and dimethyl sulfoxide are preferred. These organic solvents can be used individually or in combination of two or more.

[0242] Among these, cyclic carbonates and linear carbonates are preferred because they have high dielectric constants and suitable viscosity and solvation capacity that affect the movement of Li ions. Solvation capacity is the force that dissociates dissolved ions; if it is too strong, it inhibits ion movement, so there is an optimal value.

[0243] As cyclic carbonates, alkylene carbonates having alkylene groups with 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, and butylene carbonate, are preferred. Among these, ethylene carbonate and propylene carbonate are preferred from the viewpoint of improving battery characteristics, and ethylene carbonate is more preferred.

[0244] Dialkyl carbonates are preferred as chain-like carbonates. The number of carbon atoms in the constituent alkyl group is preferably 1 to 5, and more preferably 1 to 4. Specifically, symmetric chain-like alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; and dialkyl carbonates such as asymmetric chain-like alkyl carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate are preferred. Among these, dimethyl carbonate and diethyl carbonate are preferred from the viewpoint of viscosity and boiling point, and diethyl carbonate is more preferred.

[0245] Furthermore, practical lithium-ion batteries operate under a wide range of environmental conditions, and in particular, the physical properties of non-aqueous solvents, such as their melting and boiling points, must be kept within a certain range. Therefore, it is preferable to use a mixture of cyclic carbonates and linear carbonates.

[0246] As a combination of cyclic carbonates and linear carbonates, a combination of ethylene carbonate and linear carbonate is preferred. Specifically, because it offers a good balance between cycle characteristics and high-power discharge characteristics, the following combinations are preferred: ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0247] The mixing ratio of cyclic carbonates and linear carbonates is appropriately selected according to the desired practical properties, and the weight ratio of [cyclic carbonates]:[linear carbonates] is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, and particularly preferably 40:60 to 60:40.

[0248] The content of cyclic carbonates in the electrolyte is preferably 1% to 70% by weight, with the following order of preference: 1% to 35% by weight, 3% to 30% by weight, and 4% to 50% by weight. Multiple cyclic carbonates can be used in mixture form. The content of linear carbonates in the electrolyte is preferably 40% to 70% by weight, with the following order of preference: 43% to 68% by weight. Multiple linear carbonates can be used in mixture form.

[0249] Furthermore, fluorine-containing carbonates are preferred as organic solvents. Specifically, cyclic carbonates having one fluorine atom, chain carbonates having one fluorine atom, cyclic carbonates having two or more fluorine atoms, and chain carbonates having two or more fluorine atoms are preferred, and fluorine-containing cyclic carbonates having two or more fluorine atoms are more preferred from the viewpoint of improving battery characteristics.

[0250] Preferred fluorine-containing cyclic carbonates having two or more fluorine atoms include cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one.

[0251] The above-mentioned fluorine-containing carbonates can be used individually or in combination of two or more types. The proportion of fluorine-containing carbonate in the electrolyte is preferably 0.001% by weight or more and 10.000% by weight or less, more preferably 0.010% by weight or more and 5.000% by weight or less, even more preferably 0.100% by weight or more and 2.000% by weight or less, particularly preferably 0.200% by weight or more and 1.000% by weight or more, and most preferably 0.250% by weight or more and 0.500% by weight or less. When the content of fluorine-containing carbonate is 0.001% by weight or more, the effect of the fluorine-containing carbonate is well expressed, and when the content of fluorine-containing carbonate is 10.000% by weight or less, the increase in internal pressure of the battery during high-temperature storage can be suppressed.

[0252] Furthermore, cyclic carbonates having unsaturated bonds or aromatic compounds with 7 to 18 carbon atoms may be mixed into the electrolyte as organic solvents.

[0253] As cyclic carbonates having unsaturated bonds, vinylene carbonate, vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, and 4,5-divinylethylene carbonate are preferred from the viewpoint of improving cycle properties, and vinylene carbonate and vinylethylene carbonate are more preferred.

[0254] As aromatic compounds having 7 to 18 carbon atoms, from the viewpoint of suppressing a significant decrease in discharge characteristics after high-temperature storage by suppressing side reactions with the negative and positive electrodes, partially hydrogenated forms of biphenyl, alkylbiphenyl, terphenyl, terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferred.

[0255] These cyclic carbonates having unsaturated bonds and aromatic compounds with 7 to 18 carbon atoms can be used individually or in combination of two or more. The proportion of each in the electrolyte is preferably 0.001% to 5.000% by weight, more preferably 0.100% to 4.000% by weight, even more preferably 0.300% to 3.000% by weight, particularly preferably 0.400% to 2.500% by weight, and most preferably 0.500% to 2.000% by weight. A proportion of 0.001% by weight or more further improves safety during overcharging. A proportion of 5.000% by weight or less further improves battery characteristics such as high-temperature storage characteristics.

[0256] Figure 1 is a cross-sectional view showing an example of a lithium-ion battery according to an embodiment, and more specifically, a cross-sectional view showing an example of the cross-sectional structure of a coin-type lithium-ion battery. As shown in Figure 1, the lithium-ion battery 200 has a disc-shaped positive electrode 212 housed in a metal casing 211 and a disc-shaped negative electrode 214 housed in a metal casing 213, with the positive electrode 212 and the negative electrode 214 stacked via a separator 215. A metal spring 218 and a spacer 219 are placed between the casing 213 and the negative electrode 214. The interiors of the casing 211 and casing 213 are filled with a liquid electrolyte. The peripheral edges of the casing 211 and casing 213 are sealed by crimping via a seal gasket 217.

[0257] For example, a lithium-ion battery can be manufactured by stacking a positive electrode and a negative electrode with a separator in between, winding or folding them as needed according to the battery shape, placing them in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent pressure buildup inside the lithium-ion battery and overcharging / discharging, fuses, overcurrent protection elements such as PTC elements, expanded metal, lead plates, etc., may be provided as needed. The shape of the lithium-ion battery can be any of the following: coin-shaped, button-shaped, sheet-shaped, cylindrical, prismatic, flat, etc. [Examples]

[0258] Next, examples and comparative examples will be described, but the present invention is not limited to these examples. In the following, "%", "ppm", and "parts" used to express quantities refer to weight unless otherwise specified.

[0259] [Experiment 1] (Production of carbon material A) -CVD reaction: Formation of a carbonaceous layer on the template material- As a raw material for the mold material, fumed silica (SiO2 / AEROSIL(registered trademark)NX90G; particle size 38nm, BET specific surface area 71m²) is used. 2 Approximately 1 g of (carbon content 0.5-1.5%, manufactured by Nippon Aerosil Co., Ltd.) was spread on a quartz boat and placed in the center of a quartz reaction tube in a horizontal CVD apparatus (transparent electric furnace manufactured by Ishikawa Sangyo Co., Ltd.). Argon gas was flowed into the reaction tube at a flow rate of 400 mL / min while the temperature was raised to 900°C at a heating rate of 10°C / min and held for 30 minutes. While maintaining 900°C, argon gas was flowed at a flow rate of 320 mL / min while methane gas was flowed at a flow rate of 80 mL / min (raw material gas concentration 20%) and held for 90 minutes. After that, the material was cooled to room temperature while argon gas was flowed at a flow rate of 400 mL / min, the quartz boat was removed, and a carbon material precursor was obtained by coating the surface of the template material with a carbonaceous layer. At this time, it was confirmed by electron microscopy that the template material was an aggregate in which multiple nanoprimary particles were linked together in a bead-like manner with multiple branching structures.

[0260] -Removal of mold material- Next, the template material was removed from the obtained carbon material precursor by the following procedure to obtain the carbon material.

[0261] (1) A carbon material precursor was placed in a 100 ml PFA beaker, and ultrapure water was added until the entire carbon material precursor was wet. (2) After adding 46% hydrofluoric acid, the mixture was stirred with a stirrer for 2 hours. (3) After stirring was stopped, the sample was left to stand until it settled. (4) Using a PTFE membrane filter (47 mmφ, pore size 0.1 μm), the supernatant was filtered by suction. (5) The sample on the filter paper was washed with approximately 39 mL of ultrapure water and filtered by suction. This procedure was repeated three times. (6) The sample on the filter paper was collected and returned to the original PFA beaker. (7) Repeat the operations in (2) to (6) above. (8) Add approximately 40 mL of ultrapure water and stir with a stirrer for 1 hour. (9) After stirring was stopped, the sample was allowed to stand until it settled. (10) Discard the supernatant, add 5% caustic soda, and stir for 12 hours while heating to 80°C. (11) After stirring was stopped, the sample was allowed to stand until it settled. (12) Using a PTFE membrane filter (47 mmφ, pore size 0.1 μm), the supernatant was filtered by suction. (13) The sample on the filter paper was washed with ultrapure water and filtered by suction. This procedure was repeated until the filtrate was neutral. (14) The sample on the filter paper was collected in a petri dish and dried in a 110°C oven for 8 hours.

[0262] -Heat treatment- The carbonaceous layer obtained above was placed in a rectangular high-temperature heating furnace (manufactured by Izumi Tech Co., Ltd.) under reduced pressure (10 -1 After heating to the Pa order, the material was heated to 1600°C under argon gas flow (10 mL / min) at a heating rate of 15°C / min and held at that temperature for 1 hour to calcinate. It was then cooled to room temperature to obtain carbon material A.

[0263] (Specific surface area, total pore volume, and spatial index) Nitrogen adsorption and desorption measurements were performed on the obtained carbon material A and carbon material B (manufactured by Lion Specialty Chemicals, trade name: Ketjenbrack EC300J) using a specific surface area and pore distribution analyzer (BELSORP MAX, manufactured by Microtrac-Bel Corporation) at -196°C under relative pressure P / P0 = 0.96. Before measurement, the samples were degassed by vacuum drying at 150°C for 6 hours. The equilibrium judgment condition when measuring the pressure in the sample tube was set to 300 seconds. From the obtained nitrogen adsorption and desorption isotherms, the BET specific surface area S(m²) was calculated using the BET method. 2 We calculated / g). Based on the obtained adsorption / desorption isotherms, analysis was performed using the software Autosorb 1 (Anton Paar Japan). For type I adsorption / desorption isotherms, the pore size distribution was analyzed by referring to a kernel calculated using density functional theory (DFT) assuming slit-type pores, and the total pore volume was determined. For type IV adsorption / desorption isotherms, the pore size distribution was analyzed by applying the Barrett-Joyner-Halenda method (BJH method) to each adsorption / desorption isotherm, and the total pore volume V (cc / g) was determined. The spatial index I is the value obtained by dividing the total pore volume by the specific surface area. V (cc / m 2 ) was defined as Spatial Index I V This represents the contribution rate of the carbonaceous layer surface to the obtained total pore volume V. These results are shown in Table 1.

[0264] (Raman spectroscopy measurement) Raman spectra were measured for the obtained carbon materials A and B using a micro-Raman spectrometer (Thermo Fisher Scientific K.K., DXR3 micro-laser Raman). A 532 nm (2 mW) laser was used for the measurement, with the following settings: grating: 900 lines / mm, spectrometer aperture: 50 μmφ, exposure time: 0.500 sec (2 Hz), and integration count: 10 (5 min). The measurement range was 300-3500 cm².-1 This was determined from the measured Raman spectrum (I G / I 2D The intensity ratio of ) was calculated. The results are shown in Table 1.

[0265] [Table 1]

[0266] [Experiment 2] (Manufacturing of slurry for cathode formation) The active material is a ternary cathode material NCM (LiNi) with an average particle size of 8 μm. 0.333 Co 0.334 Mn 0.333 O2 (manufactured by Kelong) powder, carbon material A or carbon material B obtained above as a conductive additive, and PVDF (manufactured by Kureha Corporation) as a binder were weighed in the weight ratios shown in Tables 2 and 3, respectively, and mixed with N-methylpyrrolidone (NMP) as a solvent. Note that the conductive additive used was a dispersion of carbon material A or carbon material B dispersed in NMP solvent. The mixture of active material, conductive additive, and binder was placed in a planetary mixer and mixed at a rotation speed of 2000 rpm while adding NMP in several batches until a uniform and appropriate viscosity was achieved, thereby preparing slurries 1 to 7 for cathode formation.

[0267] [Table 2]

[0268] [Table 3]

[0269] [Experiment 3] (Manufacturing of electrodes and batteries) <Example 1> (Fabrication of positive electrode) Slurry 3 was applied to 15 μm thick aluminum foil at a constant speed using a doctor blade type coating device with a micrometer. Subsequently, the material was placed in a vacuum dryer set to 150°C for 5 minutes to dry, and then placed in a vacuum dryer set to 110°C for 1 hour to dry, thereby obtaining a positive electrode base. The thickness after drying was 120 μm. The positive electrode base was then punched out using a φ15 mm punch-type die-cutting machine, pressurized with 45 kN using a cylinder-type jig, and then vacuum-dried at 120°C to obtain a positive electrode for battery integration.

[0270] (Manufacturing of lithium-ion secondary batteries) Using the positive electrode prepared as described above and a φ16mm die-cut piece of metallic Li punched out in a glove box under an argon gas atmosphere, a 25μm thick separator (microporous film made of polypropylene) was placed between the positive electrode composite layer and the negative electrode's metallic Li. A 1M LiPF6 solution (a 1:1 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC)) was added as the electrolyte, and the device was crimped and sealed to produce a 2032 size coin-type test battery. Afterwards, it was washed with ethanol and subjected to the battery evaluation described below.

[0271] <Example 2> A test battery was prepared in the same manner as in Example 1, except that slurry 1 was used instead of slurry 3, and was subjected to the battery evaluation described below.

[0272] <Example 3> Slurry 2 was applied to a 15 μm thick aluminum foil at a constant speed using a doctor blade coating device with a micrometer, so that the thickness after drying was 80 μm, and dried in the same manner as in Example 1. Similarly, slurry 4 was applied to the dried film of slurry 2 so that the thickness after drying was 40 μm, and dried to obtain a positive electrode base. Thereafter, a test battery was prepared in the same manner as in Example 1 and subjected to the battery evaluation described below.

[0273] <Example 4> Slurry 2 was applied to a 15 μm thick aluminum foil at a constant speed using a doctor blade coating device with a micrometer, so that the thickness after drying was 40 μm, and dried in the same manner as in Example 1. Similarly, slurry 4 was applied to the dried film of slurry 2 so that the thickness after drying was 40 μm, and dried. Furthermore, slurry 2 was applied to the dried film of slurry 4 so that the thickness after drying was 40 μm, and dried to obtain a positive electrode base. Thereafter, a test battery was prepared in the same manner as in Example 1 and subjected to the battery evaluation described below.

[0274] <Example 5> Slurry 4 was applied to a 15 μm thick aluminum foil at a constant speed using a doctor blade coating device with a micrometer, so that the thickness after drying was 40 μm, and dried in the same manner as in Example 1. Similarly, slurry 2 was applied to the dried film of slurry 4 so that the thickness after drying was 80 μm, and dried to obtain a positive electrode base. Thereafter, a test battery was prepared in the same manner as in Example 1 and subjected to the battery evaluation described below.

[0275] <Example 6> A test battery was prepared in the same manner as in Example 1, except that slurry 4 was used instead of slurry 3, and was subjected to the battery evaluation described below.

[0276] <Example 7> A test battery was prepared in the same manner as in Example 1, except that slurry 5 was used instead of slurry 3, and was subjected to the battery evaluation described below.

[0277] <Comparative Example 1> A test battery was prepared in the same manner as in Example 1, except that slurry 6 was used instead of slurry 3, and was subjected to the battery evaluation described below.

[0278] <Comparative Example 2> A test battery was prepared in the same manner as in Example 1, except that slurry 7 was used instead of slurry 3, and was subjected to the battery evaluation described below.

[0279] [Experiment 4] (Measurement of the proportion of conductive additive and battery evaluation test) The proportion of conductive additive was measured using the fabricated test batteries according to the following procedure. Evaluation tests 1-4 were also conducted. The results, along with the type of carbon material and the concentration of carbon material in the slurry used, are shown in Table 4.

[0280] <Measurement of the proportion of conductive additives> (Sample preparation) Using a cross-section polisher (manufactured by JEOL Ltd., product number IB-09020CP), the fabricated positive electrode was ground from the side of the positive electrode composite layer opposite to the aluminum foil, forming a ground cross section 50% deep in the thickness direction of the positive electrode composite layer, and a sample of the middle part of the electrode was prepared. A sample of the lower part of the electrode was also prepared by forming a ground cross section 90% deep in the thickness direction of the positive electrode composite layer. Furthermore, an upper part of the electrode was prepared from the fabricated positive electrode without grinding, retaining the surface of the positive electrode composite layer opposite to the aluminum foil.

[0281] (Raman spectroscopy measurement) Raman spectra were measured for each sample using a micro-Raman spectrometer (Thermo Fisher Scientific K.K., DXR3 micro-laser Raman). A 532 nm (2 mW) laser was used for the measurements, with the following settings: grating: 900 lines / mm, spectrometer aperture: 50 μmφ, exposure time: 0.500 sec (2 Hz), and integration count: 10 (5 min). The measurement range was 300–3500 cm². -1 The Raman spectra measured for the upper electrode sample of Example 1 are shown in Figure 2.

[0282] In the obtained spectrum, the 2D peaks of the conductive additive are at 2500-3000 cm⁻¹. -1 The height of the nearby peak is H x , 1500-1700cm caused by the G band -1 The height of the nearby peak is H y , 200-800 cm² due to positive electrode active material (CA) -1 The height of the nearby peak is H zThe ratio was calculated as follows, and Hx / Hz was calculated as the proportion of the conductive additive. The proportion of the conductive additive in the upper electrode sample was R0, and the proportion of the conductive additive in the middle electrode sample was R 50 The ratio of the conductive additive in the sample below the electrode is R 90 That's what I decided.

[0283] <Test 1> (Initial Capacity Characteristics) At room temperature (25°C), the test batteries were charged from the open-circuit voltage to 4.2V with a constant current of 1.25mA (equivalent to 0.2C) (constant current charging). After reaching 4.2V, constant voltage charging was performed and continued until the current reached 0.31mA (0.05C). Subsequently, the batteries were discharged to 3V with a constant current of 1.25mA. The capacity ratio of each example and comparative example was calculated, with the capacity of Example 1 set to 100. A higher value indicates superior capacity.

[0284] <Test 2> (Low-temperature cycle characteristics) At room temperature (25°C), a constant current of 1.25mA (equivalent to 0.2C) was applied to each test battery from the open-circuit voltage up to 4.2V (constant current charging). After reaching 4.2V, constant voltage charging was applied and continued until the current reached 0.31mA (0.05C). Subsequently, the battery was discharged to 3V with a constant current of 1.25mA. Next, using the same test battery, at a low temperature (0°C), a constant current of 3.13mA (equivalent to 0.5C) was applied from the open-circuit voltage up to 4.2V. After reaching 4.2V, constant voltage charging was applied and continued until the current reached 0.31mA (0.05C). Subsequently, the battery was discharged to 3V with a constant current of 3.13mA (equivalent to 0.5C). The low-temperature charge-discharge cycle was repeated 50 times, and the retention rate (%) of the discharge capacity after 50 cycles relative to the initial discharge capacity was calculated (discharge capacity after 50 cycles / initial discharge capacity). A higher value indicates superior low-temperature cycle characteristics.

[0285] <Test 3> (High-rate characteristics) At room temperature (25°C), each test battery was charged from the open-circuit voltage to 4.2V with a constant current of 1.25mA (equivalent to 0.2C) (constant current charging). After reaching 4.2V, constant voltage charging was performed and continued until the current reached 0.31mA (0.05C). Subsequently, the battery was discharged to 3V with a high-rate constant current of 18.8mA (equivalent to 3C). From the discharge capacity of the obtained test batteries, the 3C maintenance rate (3C capacity / 0.2C capacity) (%) for each test battery was calculated. A higher value indicates superior high-rate characteristics.

[0286] <Test 4> (Voltage characteristics during high-power discharge) At room temperature (25°C), the test batteries were charged from the open-circuit voltage to 4.2V with a constant current of 1.25mA (equivalent to 0.2C) (constant current charging). After reaching 4.2V, constant voltage charging was performed and continued until the current reached 0.31mA (0.05C). Subsequently, the batteries were discharged to 3V with a high-rate constant current of 31.3mA (equivalent to 5C). The voltage was measured 1 second after the start of discharge, and the difference between this voltage and the voltage at the end of charging was calculated. A lower value indicates superior voltage characteristics during high-power discharge.

[0287] [Table 4]

[0288] As is clear from Table 4, the example using carbon material A having the predetermined properties showed higher performance in all aspects, including normal rate characteristics, low-temperature cycle characteristics, high-rate characteristics, and voltage characteristics during high-power discharge, compared to the comparative example using carbon material B which does not have the predetermined properties.

[0289] Furthermore, as is clear from the comparison between Example 1 and Examples 3-5, R0, R 50 and R 90 When any one of these parameters was higher than the other two, even higher performance was achieved in one of the following areas: low-temperature cycle characteristics, high-rate characteristics, or voltage characteristics during high-power discharge. [Explanation of Symbols]

[0290] 200 Lithium-ion batteries 211 Exterior parts 212 Positive electrode 213 Exterior parts 214 Negative electrode 215 Separator 217 Seal gasket 218 Spring 219 Spacer 300 Ultra-high sensitivity vacuum temperature-controlled desorption mass spectrometer 310 Quartz Reactor 311 Radioactive Thermometer 312 Sample holder 313 High-frequency induction coil 320 detection units 321 Cold Cathode Pirani Gauge 322 Capacitance Gauge 323 Quadrupole mass spectrometer 324 Turbomolecular pump 325 Rotary Pump 326 Valves 327 Gas storage 328 resistors g Calibration gas w Cooling water

Claims

1. An electrode comprising a current collector and an electrode composite film formed on the current collector, The electrode composite film contains an active material, a binder, and a conductive additive containing a carbon material. The total pore volume (V) of the carbon material is 1.00 cc / g or more. The spatial index (I) is the ratio (V / S) of the total pore volume (V) of the carbon material to its specific surface area (S). Ｖ ) is 0.0015 cc / m³ ２ That's all. The intensity of the G band (I) in the Raman spectrum of the carbon material obtained by Raman spectroscopy. Ｇ ) intensity of the 2D band (I ２Ｄ ) intensity ratio (I Ｇ / I ２Ｄ The electrode is 5.00 or less.

2. The electrode according to claim 1, wherein the carbon material is mainly composed of thin-layer graphene.

3. When the presence ratios of the conductive auxiliary agent calculated from the Raman spectra measured at the surface position, the depth position corresponding to 50% of the thickness of the electrode composite film from the surface, and the depth position corresponding to 90% of the thickness of the electrode composite film from the surface are respectively R ０ , R ５０ , and R ９０ , then The ratio of the aforementioned conductive additive is R ０ , R ５０ , and R ９０ The electrode according to claim 1, wherein at least one of the values ​​is 0.08 or greater.

4. The electrode according to claim 1, wherein the electrode composite film includes a high-concentration layer in which the proportion of the conductive additive is partially high.

5. The electrode according to claim 4, wherein the high-concentration layer has a present ratio of the conductive additive that is 1.1 times or higher than that of other parts of the electrode composite film.

6. The electrode composite film is defined as having a ratio of the conductive additive calculated from Raman spectra measured at the surface, at a depth corresponding to 50% of the thickness of the electrode composite film from the surface, and at a depth corresponding to 90% of the thickness of the electrode composite film from the surface, respectively, R ０ , R ５０ , and R ９０ In that case, The ratio of the aforementioned conductive additive is R ０ , R ５０ , and R ９０ The electrode according to claim 1, wherein one of the values ​​is higher than the other two.

7. The ratio of the aforementioned conductive additive is R ０ However, R ５０ and R ９０ The electrode according to claim 6, which is 1.1 times or more higher than the one described above.

8. The ratio of the aforementioned conductive additive is R ５０ However, R ０ and R ９０ The electrode according to claim 6, which is 1.1 times or more higher than the one described above.

9. The ratio of the aforementioned conductive additive is R ９０ However, R ０ and R ５０ The electrode according to claim 6, which is 1.1 times or more higher than the one described above.

10. The electrode according to claim 1, which is the positive electrode.

11. A lithium-ion battery comprising the electrode described in any one of claims 1 to 10.

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