Coated carbon material, negative electrode, and secondary battery

Abstract

Provided is a coated carbon material from which it is possible to obtain a secondary battery exhibiting an excellent initial efficiency and high peel strength. As a result, the present invention addresses the problem of providing a high-performance secondary battery, and the problem is solved by a coated carbon material that is for secondary batteries, that is capable of occluding / discharging lithium ions, and that has, on a carbon material, a specific coating formed from an organic compound.

Description

[Technical Field]

[0001] This invention relates to a coated carbon material, a secondary battery negative electrode using the coated carbon material, and a secondary battery equipped with the negative electrode. [Background technology]

[0002] In recent years, with the miniaturization of electronic devices, the demand for high-capacity rechargeable batteries has been increasing. In particular, lithium-ion rechargeable batteries, which have a higher energy density and superior high-current charge / discharge characteristics compared to nickel-cadmium batteries and nickel-metal hydride batteries, have been attracting attention. While increasing the capacity of lithium-ion rechargeable batteries has been widely studied, in recent years there has been a growing demand for even higher performance lithium-ion rechargeable batteries, requiring the achievement of even higher capacity, higher input / output capabilities, and longer lifespan.

[0003] For lithium-ion secondary batteries, it is known that carbon materials such as graphite are used as the negative electrode active material. Among these, graphite with a high degree of graphitization is known to be preferable as a negative electrode active material for lithium-ion secondary batteries because, when used as a negative electrode active material, it can obtain a capacity close to the theoretical lithium storage capacity of graphite, which is 372 mAh / g, and furthermore, it is excellent in terms of cost and durability.

[0004] When such carbon materials are used as the negative electrode active material in lithium-ion secondary batteries, a protective film called SEI (Solid Electrolyte Interface) is usually formed on the surface of the carbon material through a reaction with polymer compounds used as binders and non-aqueous electrolytes. It is known that the SEI prevents contact between the carbon material and the electrolyte, suppresses the decomposition of the electrolyte by the active carbon material, and maintains the chemical stability of the negative electrode surface.

[0005] However, lithium-ion secondary batteries using carbon materials as the negative electrode active material faced challenges such as increased irreversible charge / discharge capacity during the initial cycle due to SEI film formation and gas generation as a by-reaction product, resulting in a failure to achieve high capacity. Furthermore, the formation of a stable SEI film increased the interfacial resistance at the negative electrode, leading to a decrease in the battery's input / output characteristics.

[0006] To solve the above problems, for example, Patent Document 1 describes a technology developed to produce spheroidized natural graphite by subjecting natural graphite to a spheroidization treatment (mechanical energy treatment), and further to use the spheroidized natural graphite as a core graphite and coat its surface with amorphous carbon.

[0007] On the other hand, a known technique for suppressing excessive decomposition of the electrolyte involves coating the carbon material, which is the active material for the negative electrode, with polymers or the like. For example, Patent Document 2 discloses a method for providing a coating layer on the surface of a carbon material, consisting of an ion-conducting polymer such as polyethylene oxide or a water-soluble polymer such as polyvinyl alcohol, with the aim of suppressing the decomposition of the non-aqueous electrolyte and the deposition of its decomposition products on the negative electrode surface, thereby improving the initial charge-discharge efficiency and charge-discharge cycle characteristics.

[0008] Furthermore, with the aim of suppressing the decomposition of the non-aqueous electrolyte and improving the initial charge-discharge efficiency, Patent Document 3 discloses a method for impregnating spheroidal natural graphite, which has surface oxygen functional groups to improve adhesion with water-soluble polymers, with a water-soluble polymer. Patent Document 4 discloses a method for impregnating the surface of a carbon material with a coating comprising boron atoms and a COC bonding portion, and a crosslinking portion interposed between the boron atoms and the negative electrode active material, with the aim of suppressing the increase in internal resistance after the charge-discharge cycle and improving the cycle characteristics. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2000-340232 [Patent Document 2] Japanese Patent Application Publication No. 11-120992 [Patent Document 3] Japanese Patent Publication No. 2011-198710 [Patent Document 4] Japanese Patent Publication No. 2019-87443 [Overview of the project] [Problems that the invention aims to solve]

[0010] All of the prior art described in the above patent documents aims to improve initial charge-discharge efficiency and cycle characteristics by forming a coating on the surface of a carbon material to suppress the decomposition of the electrolyte. However, as clearly shown in Figure 1 of Patent Document 4, these prior art methods are characterized by coating the outer surface of particles made of carbon material. However, according to the inventors' research, when using carbon material particles such as granulated spheroidal graphite consisting of multiple fine graphite particles, or porous artificial graphite obtained by graphitizing coke using Si as a graphitization catalyst, simply coating the outer surface of the carbon material particles with conventional surface coating methods resulted in insufficient initial efficiency and peel strength, requiring further improvement.

[0011] This invention has been made in view of the above background art, and aims to provide a coated carbon material that can produce a secondary battery with excellent initial efficiency and high peel strength, and as a result, to provide a high-performance secondary battery. [Means for solving the problem]

[0012] The inventors of the present invention conducted diligent studies to solve the aforementioned problems and found that a coated carbon material having a specific film formed on it, a secondary battery anode using the coated carbon material, and a secondary battery can solve the above problems, thus completing the present invention.

[0013] The reason why the coated carbon material according to the present invention exhibits the above-mentioned effects is as follows. In other words, although it has not been given much attention in the past, in coated carbon material particles with many intraparticle pores, it is important to suppress the decomposition of the electrolyte occurring on the inner walls of the intraparticle pores. By forming a specific coating made of organic compounds on the inner walls of the intraparticle pores, it is possible to significantly achieve both improved initial efficiency due to the suppression of side reactions with the electrolyte and high peel strength.

[0014] In other words, the gist of this invention is as follows. [1] A coated carbon material in which an organic compound is coated on a carbon material, wherein the ratio of the BET specific surface area Tol-SA due to toluene adsorption to the BET specific surface area N2-SA due to nitrogen adsorption, Tol-SA / N2-SA, is 0.70 to 0.95. [2] A coated carbon material in which an organic compound is coated on a carbon material, wherein the coating rate of the basal surface of the carbon material is 30% to 90%. [3] A coated carbon material in which an organic compound is coated on a carbon material, wherein the specific basal surface area due to toluene adsorption and the specific BET surface area due to toluene adsorption Tol-SA are 0.15 to 0.65. [4] A coated carbon material in which an organic compound is coated on a carbon material, wherein the mass loss rate from 200°C to 700°C, as measured by TG-DTA, is 0.10 mass% to 0.42 mass%. [5] The coated carbon material according to any one of [1] to [4], wherein the carbon material is graphite. [6] The coated carbon material according to any one of [1] to [5], wherein the carbon material has pores. [7] The coated carbon material according to any one of [1] to [6], wherein the organic compound comprises a compound derived from polyvinyl alcohol resin. [8] The coated carbon material according to [7], wherein the compound derived from the polyvinyl alcohol resin comprises a reactive substituent. [9] The coated carbon material according to [8], wherein the reactive substituent comprises at least one substituent selected from a hydroxyl group, a carboxyl group, a carbonyl group, an acetyl group, a (meth)acrylic group, an epoxy group, a vinyl group, a hydrolyzable silyl group, a silanol group, and a hydrosilyl group.

[10] A negative electrode comprising a current collector and an active material layer formed on the current collector, wherein the active material layer comprises a coated carbon material according to any one of [1] to [9].

[11] A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in

[10] . [Effects of the Invention]

[0015] By using the coated carbon material of the present invention as a negative electrode active material for secondary batteries, it is possible to provide a secondary battery with excellent initial efficiency and high peel strength. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram representing the coated carbon material disclosed in Patent Document 4, in which the outer surface of particles made of carbon material is coated. [Figure 2] This is a schematic diagram showing the coating configuration of the coated carbon material. [Figure 3] This is a cross-sectional SEM image of the graphite used in the example (photograph used as a substitute for drawing). [Modes for carrying out the invention]

[0017] The present invention will now be described in detail. The following description of the constituent elements of the invention is merely an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these forms unless it exceeds the essence of the invention. In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, and "A~B" means that it is greater than or equal to A and less than or equal to B.

[0018] One embodiment of the coated carbon material of the present invention is a coated carbon material in which an organic compound is coated onto a carbon material, and the ratio of the BET specific surface area Tol-SA due to toluene adsorption to the BET specific surface area N2-SA due to nitrogen adsorption, Tol-SA / N2-SA (hereinafter also referred to as the BET specific surface area ratio), is 0.70 to 0.95. Because the BET specific surface area ratio is within the above range, a secondary battery using the coated carbon material of this embodiment becomes a secondary battery with excellent initial efficiency.

[0019] The BET specific surface area ratio is preferably 0.70 or higher, more preferably 0.95 or lower, and more preferably 0.85 or lower. Adjusting the BET specific surface area ratio within the above range can be achieved, for example, by appropriately adjusting the ratio of the amount of covering organic matter to N2-SA in the carbon material.

[0020] The BET specific surface area is determined using a differential adsorption thermal analyzer (e.g., Tokyo Riko Co., Ltd., thermal surface analysis instrument CSA-25G and multi-microcalorimeter MMC-5111). After pre-drying the coated carbon material sample under reduced pressure at 100°C for 30 minutes under nitrogen flow, the value obtained by linear regression in the range of P / P0 = 0.05 to 0.18 using the toluene adsorption BET method with toluene gas at 25°C is defined as Tol-SA. In addition, the value obtained by the nitrogen adsorption BET single-point method using nitrogen gas with nitrogen gas at liquid nitrogen temperature using a fully automatic specific surface area analyzer (e.g., Mountec, Macsorb HM Model-1210) is defined as N2-SA.

[0021] Another embodiment of the coated carbon material is a coated carbon material in which an organic compound is coated onto the carbon material, and the coating rate of the basal surface of the carbon material is 30% to 90%. Because the coating rate of the basal surface of the carbon material is within the above range, the secondary battery using the coated carbon material of this embodiment becomes a secondary battery with excellent initial efficiency. The basal surface refers to the benzene condensation plane of the carbon material, and as will be described later, it is a carbon material surface with high affinity for toluene, where the heat of adsorption of toluene gas is 67 kJ / mol or more.

[0022] The coverage rate of the basal surface is preferably 30% or more, more preferably 50% or more, and even more preferably 60% or more. If the basal surface coverage rate is above the lower limit, when used as a negative electrode material for a non-aqueous secondary battery, side reactions of the electrolyte on the basal surface are suppressed, and the initial efficiency is significantly improved. It is also preferably 90% or less, and more preferably 80% or less. If the basal surface coverage rate is below the upper limit, sufficient adhesion to the binder resin such as CMC or SBR that forms the negative electrode plate is ensured, so peeling of the negative electrode plate can be suppressed. In addition, the electronic conductivity of the negative electrode plate is ensured. Adjusting the basal surface coverage rate within the above range can be achieved, for example, by appropriately adjusting the ratio of the amount of covering organic material to N2-SA of the carbon material.

[0023] The coverage of the basal surface can be measured using a differential adsorption heat analyzer by following the procedure below. First, the adsorption isotherm and heat of adsorption of the carbon material before coating with the organic compound are simultaneously measured using toluene gas. The carbon material surface with high affinity for toluene, where the heat of adsorption is 67 kJ / mol or higher, is defined as the basal surface, and the molecular cross-sectional area of ​​toluene = 5.5 × 10⁻⁶ -19 m 2 The specific surface area of ​​the basal surface of the carbon material is determined from the amount of toluene adsorbed onto the basal surface.

[0024] Next, the adsorption isotherm and heat of adsorption were simultaneously measured using toluene gas for coated carbon materials coated with organic compounds, and the specific surface area of ​​the basal surface was determined from the amount of toluene adsorbed on the basal surface with a heat of adsorption of 67 kJ / mol or more. At this time, when a part of the basal surface of the raw carbon material is coated with an organic compound, the affinity with toluene decreases and the heat of adsorption decreases, so the specific surface area of ​​the basal surface of the coated carbon material coated with an organic compound is lower than that of the raw carbon material. The basal surface coverage rate is calculated using the following formula (A). Formula (A) Basal surface coverage rate (%) = [1 - (Specific surface area of ​​the basal surface of the coated carbon material) / (Specific surface area of ​​the basal surface of the raw carbon material)] × 100

[0025] Another embodiment of the coated carbon material is a coated carbon material in which an organic compound is coated onto the carbon material, and the ratio of the basal surface specific surface area due to toluene adsorption to the BET specific surface area due to toluene adsorption (Tol-SA) (hereinafter also referred to as the basal surface specific surface area ratio) is 0.15 to 0.65. Because the basal surface specific surface area ratio is within the above range, the secondary battery using the coated carbon material of this embodiment becomes a secondary battery with excellent initial efficiency.

[0026] The basal surface specific surface area ratio is preferably 0.15 or higher, more preferably 0.20, and also preferably 0.65 or lower, and more preferably 0.60 or lower. Adjusting the basal surface specific surface area ratio within the above range can be achieved by adjusting the basal surface so that it is partially covered, for example by appropriately adjusting the ratio of the amount of covering organic material to the carbon material.

[0027] The basal surface specific surface area and Tol-SA can be measured by the method described above.

[0028] Another embodiment of the coated carbon material is a coated carbon material in which an organic compound is coated onto the carbon material, and the mass loss rate from 200°C to 700°C, as measured by TG-DTA, is 0.10 mass% to 0.42 mass%. Because the mass loss rate is within the above range, the secondary battery using the coated carbon material of this embodiment becomes a secondary battery with excellent initial efficiency.

[0029] The mass loss rate is preferably 0.10% by mass or more, more preferably 0.20% by mass or more. It is also preferably 0.42% by mass or less, and more preferably 0.35% by mass or less. Adjusting the mass loss rate within the above range can be achieved, for example, by appropriately adjusting the ratio of the amount of covering organic material to the N2-SA of the carbon material. The mass loss rate can be measured using a differential thermogravimetric analyzer STA300 manufactured by Hitachi High-Tech Science Corporation by following the procedure below. Specifically, approximately 50 mg of coating carbon material is accurately weighed, placed in an alumina sample container, and heated in a nitrogen atmosphere at a heating rate of 10°C / min from 25°C to 700°C. The resulting mass loss between 200°C and 700°C is defined as the amount of coating carbon material applied. The mass reduction rate is calculated using the following formula (B). Formula (B) Mass reduction rate (%) = [Mass reduction of coated carbon material / Mass of coated carbon material before heating] × 100

[0030] Examples of carbon materials include graphite, amorphous carbon, and carbonaceous materials with a low degree of graphitization. Among these, graphite is preferred because it is readily available commercially, theoretically has a high charge / discharge capacity of 372 mAh / g, and furthermore, it has a greater effect in improving charge / discharge characteristics at high current densities compared to when other negative electrode active materials are used. Graphite with few impurities is preferred, and can be used after undergoing various known refining treatments as needed. Examples of graphite types include natural graphite and artificial graphite, with natural graphite being more preferred.

[0031] Alternatively, these materials may be coated with carbonaceous materials, such as amorphous carbon or graphite. In this embodiment, these materials can be used individually or in combination of two or more.

[0032] Examples of artificial graphite include those obtained by calcining and graphitizing organic materials such as coal tar pitch, coal-based heavy oil, atmospheric pressure residue, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin. The firing temperature can be in the range of 2500°C or higher and 3200°C or lower, and silicon-containing compounds or boron-containing compounds can be used as graphitization catalysts during firing.

[0033] Examples of natural graphite include highly purified flake graphite and graphite that has undergone spheroidization treatment. Among these, natural graphite that has undergone spheroidization treatment is even more preferable from the viewpoint of particle packing properties and charge / discharge load characteristics. For example, an apparatus can be used that repeatedly applies mechanical forces to the particles, primarily impact forces, but also including the interaction of graphite carbonaceous particles, such as compression, friction, and shear forces.

[0034] Specifically, a device is preferred that has a rotor with numerous blades installed inside a casing, and that the rotor rotates at high speed to apply mechanical forces such as impact compression, friction, and shear force to the carbon material introduced inside, thereby performing surface treatment. Furthermore, it is preferable that the device has a mechanism to repeatedly apply mechanical forces by circulating graphite.

[0035] Preferred devices for applying mechanical action to graphite materials include, for example, hybridization systems (manufactured by Nara Machine Works Co., Ltd.), cryptrons (manufactured by Earth Technica Co., Ltd.), CF mills (manufactured by Ube Industries, Ltd.), mechanofusion systems (manufactured by Hosokawa Micron Corporation), and theta composers (manufactured by Tokuju Kogyo Co., Ltd.). Among these, the hybridization system manufactured by Nara Machine Works Co., Ltd. is preferred.

[0036] When processing using the above-mentioned apparatus, for example, the peripheral speed of the rotating rotor is preferably 30 to 100 m / s, more preferably 40 to 100 m / s, and particularly preferably 50 to 100 m / s. Furthermore, while it is possible to apply a mechanical action to the graphite material simply by passing the graphite through, it is preferable to circulate or retain the graphite in the apparatus for 30 seconds or more, and more preferably circulate or retain it in the apparatus for 1 minute or more.

[0037] Furthermore, natural graphite that has undergone spheroidization treatment can also be used as a carbon material after being subjected to isotropic pressure treatment. By applying isotropic pressure to the raw carbon material, the internal voids are compressed, resulting in an increase in the density of the carbon material after pressure treatment and subsequent crushing, thereby improving the fast charging characteristics. Furthermore, the organic compounds of the coating material are not excessively absorbed into the internal pores of the raw carbon material, allowing for efficient coating of the carbon material. In addition, isotropic pressure makes it less likely for particles to flatten, allowing them to maintain their spherical shape and preventing a decrease in fluidity when the material is formed into a slurry.

[0038] The pressurizing means can include a roll compactor, roll press, pricketing machine, cold isostatic pressurizing device (CIP), uniaxial molding machine, tablet machine, etc. Among these pressurizing means, a cold isostatic pressurizing device is preferred because it can reduce internal pores while maintaining the particle shape.

[0039] <Physical properties of carbon materials> The following describes the preferred characteristics of the raw material carbon material when the coated carbon material has a coating made of an organic compound on the carbon material. Hereinafter, it may be referred to as the carbon material of this embodiment, but this will not limit the scope of the present invention.

[0040] • Volume-based average particle size (average particle size d50) The volume-based average particle size (also referred to as "average particle size d50") of the carbon material in this embodiment is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, particularly preferably 15 μm or more, and most preferably 16.5 μm or more. Furthermore, the average particle size d50 is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 35 μm or less, particularly preferably 30 μm or less, and most preferably 25 μm or less. If the average particle size d50 is within the above range, it is possible to suppress the increase in irreversible capacity of the secondary battery obtained using the carbon material, the loss of initial battery capacity, the occurrence of process problems such as striking in slurry coating, the decrease in high current density charge / discharge characteristics, and the decrease in low temperature input / output characteristics.

[0041] Furthermore, in this specification, the average particle size d50 is defined as the size obtained by suspending 0.01 g of carbon material in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Zween 20®), introducing this as a measurement sample into a commercially available laser diffraction / scattering particle size distribution analyzer (e.g., HORIBA LA-920), irradiating the measurement sample with 28 kHz ultrasound at an output of 60 W for 1 minute, and then measuring it as the volume-based median diameter in the said analyzer.

[0042] • Circularity The circularity of the carbon material in this embodiment is 0.88 or higher, preferably 0.90 or higher, and more preferably 0.91 or higher. Furthermore, the circularity is preferably 1 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower. When the circularity is within the above range, it tends to suppress the decrease in the high current density charge-discharge characteristics of the secondary battery. The circularity is defined by the following formula, and a circularity of 1 results in a theoretically perfect sphere. Circularity = (Perimeter of an equivalent circle with the same area as the particle projection shape) / (Actual perimeter of the particle projection shape)

[0043] For the circularity value, for example, a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Corporation) is used. Approximately 0.2 g of the sample (carbon material) is dispersed in a 0.2 mass% aqueous solution (approximately 50 mL) of polyoxyethylene sorbitan monolaurate, a surfactant. The dispersion is then irradiated with 28 kHz ultrasound at an output of 60 W for 1 minute. The detection range is set to 0.6 to 400 μm, and the values ​​measured for particles with a particle size in the range of 1.5 to 40 μm are used.

[0044] While there are no particular limitations on the method for improving circularity, it is preferable to use particles that have been spheroidized to form a spherical shape, as this results in a more uniform shape of interparticle voids when used as the negative electrode. Examples of spheroidization methods include mechanically shaping particles by applying shear or compressive forces, and mechanical / physical processing methods that granulate multiple carbon material fine particles using the adhesive force of a binder or the particles themselves.

[0045] • Tap density The tap density of the carbon material of the present embodiment is preferably 0.7 g / cm 3 or more, more preferably 0.8 g / cm 3 or more, still more preferably 0.85 g / cm 3 or more, particularly preferably 0.9 g / cm 3 or more, most preferably 0.95 g / cm 3 or more, and preferably 1.3 g / cm 3 or less, more preferably 1.2 g / cm 3 or less, still more preferably 1.1 g / cm 3 or less.

[0046] When the tap density falls within the above range, processability such as streak formation during electrode plate production is improved, and high-rate charge-discharge characteristics are excellent. In addition, since the carbon density in the negative electrode coating film hardly increases, rollability is also good, and it tends to be easy to form a high-density negative electrode sheet. The tap density is measured using a powder density meter, with a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm 3 into which the carbon material of the present embodiment is dropped through a sieve with an opening of 300 μm, after the cell is filled to full capacity, tapping with a stroke length of 10 mm is performed 1000 times, and is defined as the bulk density obtained from the volume at that time and the mass of the sample.

[0047] • X-ray parameters For the carbon material of the present embodiment, the d-value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction according to the Gakushin method is preferably 0.335 nm or more and less than 0.340 nm. Here, the d-value is more preferably 0.339 nm or less, still more preferably 0.337 nm or less. When the d002 value falls within the above range, the crystallinity of graphite is high, which tends to suppress an increase in initial irreversible capacity. Here, 0.335 nm is the theoretical value for graphite. Further, the crystallite size (Lc) of the carbon material determined by X-ray diffraction according to the Gakushin method is preferably 1.5 nm or more, more preferably 3.0 nm or more. When the value falls within the above range, the particles do not have excessively low crystallinity, and the reversible capacity hardly decreases when used in a secondary battery. Note that the lower limit of Lc is the theoretical value for graphite.

[0048] ·ash The ash content in the carbon material of this embodiment is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, relative to the total mass of the carbon material. Furthermore, the lower limit of the ash content is preferably 1 ppm or more. If the ash content is within the above range, the degradation of battery performance due to the reaction between the carbon material and the electrolyte during charging and discharging can be kept to a negligible level when used in a secondary battery. Furthermore, since the production of the carbon material does not require a great deal of time, energy, or equipment for preventing contamination, the increase in costs can also be kept down.

[0049] BET specific surface area (N2-SA) due to nitrogen adsorption The specific surface area (N2-SA) of the carbon material in this embodiment, as measured by the BET method using nitrogen gas, is preferably 3 m². 2 / g or more, more preferably 4m 2 / g or more, more preferably 4.5m 2 / g or more, particularly preferably 5.0m 2 / g or more, most preferably 6.0m 2 It is 13m or more. 2 / g or less, more preferably 12m 2 / g or less, more preferably 11m 2 / g or less, particularly preferably 10m 2 / g or less, most preferably 9m 2 It is less than / g.

[0050] When the specific surface area is within the above range, sufficient space can be secured for Li to enter and exit, resulting in excellent high-speed charge / discharge output characteristics. Furthermore, the activity of the active material in the electrolyte can be appropriately suppressed, which tends to prevent the initial irreversible capacity from becoming large, allowing for the manufacture of high-capacity batteries. Furthermore, when a carbon material is used to form the negative electrode, the increase in reactivity with the electrolyte can be suppressed, and gas generation can be reduced, thus providing a desirable non-aqueous secondary battery.

[0051] The specific surface area of ​​the BET due to nitrogen adsorption is defined as the value measured by a single-point nitrogen adsorption BET method using nitrogen gas after pre-drying the carbon material sample under reduced pressure at 100°C for 30 minutes under nitrogen flow using a surface area meter (e.g., Mountec, Macsorb HM Model-1210), followed by cooling to liquid nitrogen temperature.

[0052] • Pore volume in the range of 10 nm to 1500 nm The carbon material in this embodiment preferably has pores. In the carbon material of this embodiment, the pore volume in the range of 10 nm to 1500 nm is a value measured using the mercury intrusion method (mercury porosimetry), and is preferably 0.05 mL / g or more, more preferably 0.07 mL / g or more, even more preferably 0.1 mL / g or more, and also preferably 0.3 mL / g or less, more preferably 0.28 mL / g or less, and even more preferably 0.25 mL / g or less.

[0053] If the pore volume in the range of 10 nm to 1500 nm is within the above range, the amount of void space into which the electrolyte can penetrate is less likely to decrease, and the tendency for lithium ions to not be able to insert and deinsert quickly enough during rapid charging and discharging, leading to lithium metal deposition and deterioration of cycle characteristics, can be better avoided. Furthermore, the binder is less likely to be absorbed into the voids during electrode fabrication, and the tendency for a decrease in electrode strength and initial efficiency to be reduced can be better avoided.

[0054] Furthermore, the total pore volume of the carbon material in this embodiment is preferably 0.1 mL / g or more, more preferably 0.2 mL / g or more, even more preferably 0.25 mL / g or more, and particularly preferably 0.5 mL / g or more. Also, the total pore volume is preferably 10 mL / g or less, more preferably 5 mL / g or less, even more preferably 2 mL / g or less, and particularly preferably 1 mL / g or less. If the total pore volume is within the above range, there is no need to use an excessive amount of binder when forming the electrode plate, and the dispersion effect of the thickener and binder is also more easily obtained during electrode plate formation.

[0055] Furthermore, the average pore diameter of the carbon material in this embodiment is preferably 0.03 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, and particularly preferably 0.3 μm or more. The average pore diameter is preferably 20.0 μm or less, more preferably 10.0 μm or less, and even more preferably 5.0 μm or less. When the average pore size is within the above range, there is no need to use an excessive amount of binder when forming the electrode plates, and this tends to avoid a decrease in the high-current-density charge-discharge characteristics of the battery.

[0056] For the mercury porosimetry described above, a mercury porosimemeter (Autopore 9520: manufactured by Micromeritex) can be used. The sample (carbon material) is weighed to approximately 0.2 g, sealed in a powder cell, and pre-treated by degassing at 25°C under vacuum (50 μmHg or less) for 10 minutes. Next, the pressure is reduced to 4 psia (approximately 28 kPa) and mercury is introduced into the cell. The pressure is then increased in steps from 4 psia (approximately 28 kPa) to 40,000 psia (approximately 280 MPa), and then reduced to 25 psia (approximately 170 kPa).

[0057] The number of steps during the pressurization process will be set to 80 or more points. After a 10-second equilibrium period at each step, the amount of mercury injected will be measured. From the resulting mercury injection curve, the pore distribution will be calculated using Washburn's equation. The surface tension (γ) of mercury is assumed to be 485 dyne / cm, and the contact angle (ψ) is assumed to be 140°. The average pore diameter is defined as the pore diameter when the cumulative pore volume reaches 50%. The average pore diameter of the carbon material includes the pores inside the carbon material and the gaps between carbon materials.

[0058] ·True density The true density of the carbon material in this embodiment is preferably 1.9 g / cm³. 3 More preferably 2 g / cm³ 3 More preferably 2.1 g / cm³ 3 In particular, 2.2 g / cm³ is preferred. 3 The above is true, and the upper limit is 2.26 g / cm³. 3The upper limit is the theoretical value for graphite. When the true density is within the above range, the crystallinity of carbon is not too low, and there is a tendency to suppress the increase in the initial irreversible capacity when used as a secondary battery.

[0059] Aspect ratio The aspect ratio of the carbon material in powder form in this embodiment is theoretically 1 or greater, but since it is costly to make it as close to a perfect sphere as necessary, it is preferably 1.1 or greater, more preferably 1.2 or greater. Furthermore, the aspect ratio is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. When the aspect ratio is within the above range, streaking of the slurry containing carbon material (negative electrode forming material) is less likely to occur during electrode plate formation, resulting in a uniform coating surface and a tendency to avoid a decrease in the high current density charge-discharge characteristics of the secondary battery.

[0060] The aspect ratio is expressed as A / B, where A is the longest diameter of the carbon material particle when observed in three dimensions, and B is the shortest diameter perpendicular to it. The carbon material particles are observed using a scanning electron microscope capable of magnification. Fifty arbitrary carbon material particles are selected and fixed to the end face of a metal with a thickness of 50 microns or less. For each particle, the stage on which the sample is fixed is rotated and tilted, A and B are measured, and the average value of A / B is calculated.

[0061] ·Maximum particle size dmax The maximum particle size dmax of the carbon material in this embodiment is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 120 μm or less, particularly preferably 100 μm or less, and most preferably 80 μm or less. When dmax is within the above range, it tends to suppress the occurrence of process problems such as slicing. The maximum particle size is defined as the largest particle size measured in the particle size distribution obtained when measuring the average particle size d50.

[0062] • Raman R value The Raman R value of the carbon material in this embodiment is preferably 0.1 or higher, more preferably 0.15 or higher, and even more preferably 0.2 or higher. Furthermore, the Raman R value is preferably 0.6 or lower, more preferably 0.5 or lower, and even more preferably 0.4 or lower. The Raman R value mentioned above is the 1580 cm⁻¹ value in the Raman spectrum obtained by Raman spectroscopy. -1 Nearby Peak P A Intensity I A And, 1360cm -1 Nearby Peak P B Intensity I B Measure and the intensity ratio (I B / I A It is defined as calculated as ). In this specification, "1580cm" is used. -1 "Nearby" means 1580-1620cm -1 The range is "1360cm -1 "Nearby" means 1350-1370 cm -1 It refers to the range.

[0063] When the Raman R value is within the above range, the crystallinity of the carbon material particle surface is less likely to increase, and when the density is increased, the crystals are less likely to orient parallel to the negative electrode plate, thus tending to avoid a decrease in load characteristics. Furthermore, the crystals on the particle surface are less likely to become disordered, which suppresses an increase in reactivity with the electrolyte of the negative electrode, and tends to avoid a decrease in the charge / discharge efficiency of the secondary battery and an increase in gas generation. The aforementioned Raman spectrum can be measured using a Raman spectrometer. Specifically, the sample is filled by allowing the target particles to fall naturally into the measurement cell, and the measurement is performed while irradiating the measurement cell with argon ion laser light and rotating the measurement cell in a plane perpendicular to the laser light. The measurement conditions are as follows. Wavelength of argon ion laser light: 514.5 nm Laser power on the sample: 25mW Resolution: 4cm -1 Measurement range: 1100cm -1 ~1730cm -1Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)

[0064] ·DBP oil absorption The amount of DBP (dibutyl phthalate) absorbed by the carbon material in this embodiment is preferably 65 ml / 100g or less, more preferably 62 ml / 100g or less, even more preferably 60 ml / 100g or less, and particularly preferably 57 ml / 100g or less. Furthermore, the amount of DBP absorbed is preferably 30 ml / 100g or more, more preferably 40 ml / 100g or more.

[0065] When the DBP oil absorption amount is within the above range, it means that the spheroidization of the carbon material is sufficiently advanced, and when the slurry containing the carbon material is applied, it tends not to cause streaking, and because a pore structure exists within the particles, it tends to avoid a decrease in the reaction surface. The DBP oil absorption amount is defined in accordance with ISO 4546, as the measured value when 40g of the measurement material (carbon material) is added, the dropping rate is 4ml / min, the rotation speed is 125rpm, and the set torque is 500N·m. For measurement, for example, a Brabender Type E absorbometer can be used.

[0066] ·Average particle size d10 In this embodiment, the particle size (d10) corresponding to the cumulative 10% from the smallest particle side, measured on a volume basis for the carbon material, is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 17 μm or less, preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0067] When d10 is within the above range, the tendency for particle aggregation does not become too strong, thus avoiding process problems such as increased slurry viscosity, a decrease in electrode strength in secondary batteries, and a decrease in initial charge-discharge efficiency. It also tends to avoid a decrease in high-current-density charge-discharge characteristics and a decrease in low-temperature input / output characteristics. d10 is defined as the value obtained when the particle size distribution, when the average particle size d50 is measured, where the cumulative percentage of particle frequency from the smallest particle size reaches 10%.

[0068] ·Average particle size d90 In this embodiment, the particle size (d90) corresponding to 90% of the cumulative particle size from the smallest particle side, measured on a volume basis, is preferably 100 μm or less, more preferably 70 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, particularly preferably 45 μm or less, most preferably 42 μm or less, preferably 20 μm or more, more preferably 23 μm or more, and even more preferably 25 μm or more.

[0069] When d90 is within the above range, it is possible to avoid a decrease in electrode strength and initial charge / discharge efficiency in secondary batteries, and it is also possible to avoid process problems such as streaking during slurry application, a decrease in high current density charge / discharge characteristics, and a decrease in low-temperature input / output characteristics. d90 is defined as the value obtained when the particle size distribution, when the average particle size d50 is measured, where the cumulative percentage of particle frequency from the smallest particle size reaches 90%.

[0070] <Organic compounds> The organic compound used to coat the carbon material may be a single compound or a mixture of two or more compounds. The organic compound is not particularly limited, but it is preferably a polymer having reactive substituents.

[0071] A preferred structure for a polymer having reactive substituents is one selected from the group consisting of a linear structure, a graft structure, a star structure, and a three-dimensional network structure. While there are no particular limitations on the reactive substituents, hydroxyl groups, carboxyl groups, carbonyl groups, (meth)acrylic groups, epoxy groups, vinyl groups, hydrolyzable silyl groups, silanol groups, hydrosilyl groups, and acetyl groups are preferred because they have high reactive activity and can form covalent bonds with crosslinking agents that are excellent in water resistance and solvent resistance. Hydroxyl groups, carboxyl groups, carbonyl groups, hydrolyzable silyl groups, silanol groups, and acetyl groups are more preferred, alcoholic hydroxyl groups, carbonyl groups, silanol groups, and acetyl groups are particularly preferred, and alcoholic hydroxyl groups and acetyl groups are most preferred.

[0072] From the standpoint of improving the resistance of the negative electrode active material to the electrolyte and preventing the negative electrode material coating from dissolving into the electrolyte, polymers having reactive substituents that are poorly soluble in non-aqueous electrolytes are more preferable. However, in the present invention, even if a polymer having reactive substituents is soluble in a non-aqueous electrolyte, it can be made poorly soluble in the electrolyte by reaction curing with a crosslinking agent. Poor solubility in a non-aqueous electrolyte means that when a polymer having reactive substituents is immersed in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 at 60°C for 5 hours, the dry mass loss before and after immersion is 10% by mass or less.

[0073] Specific examples of polymers having reactive substituents are not particularly limited, but they have multiple hydroxyl groups in the molecule or groups that hydrolyze to form hydroxyl groups, and can react with crosslinking agents to form films that are poorly soluble in water and electrolytes. Therefore, polyol resins such as polyvinyl alcohol resins, acrylic polyol resins, polyester polyol resins, and polyether polyol resins, silicone resins having silanol or hydrolyzable silyl groups, epoxy resins, and acrylic or polyester resins having hydrolyzable silyl groups are preferred, polyvinyl alcohol resins, acrylic polyol resins, polyester polyol resins, and acrylic or polyester resins having hydrolyzable silyl groups are more preferred, and polyvinyl alcohol resins, acrylic polyol resins, and polyester polyol resins are particularly preferred, with polyvinyl alcohol resins being the most preferred due to their excellent solvent resistance of the cured product.

[0074] • Compounds derived from polyvinyl alcohol resin (PVOH-based resins) Compounds derived from polyvinyl alcohol resins (hereinafter sometimes referred to as PVOH-based resins) are not particularly limited in their specific structure as long as they are derived from resins having vinyl alcohol structural units. Typically, they are obtained by saponifying polycarboxylate vinyl esters obtained by polymerizing vinyl carboxylate monomers such as vinyl acetate, but are not limited to this.

[0075] Examples of the PVOH-based resins include unmodified PVOH and modified PVOH-based resins. The modified PVOH resin may be a copolymerized modified PVOH resin synthesized by copolymerizing monomers other than vinyl ester monomers that donate PVOH structural units, or it may be a modified PVOH resin after synthesizing unmodified PVOH and then modifying the main chain or side chains with an appropriate compound.

[0076] Copolymer monomers (unsaturated monomers) that can be used in copolymer-modified PVOH resins include, for example, olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, and their derivatives such as acylated products; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid, or their salts; monoesters or dialkyl esters; di Examples include amides such as acetone acrylamide, acrylamide, and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or their salts; substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate; and allyl ethers having a poly(oxyalkylene) group, such as polyethylene glycol allyl ether, methoxypolyethylene glycol allyl ether, polypropylene glycol allyl ether, and polyethylene glycol-polypropylene glycol allyl ether.

[0077] Furthermore, copolymer-modified PVOH resins include PVOH resins having primary hydroxyl groups in their side chains. Examples of such PVOH resins include PVOH resins with 1,2-diol side chains obtained by copolymerizing 3,4-diacetoxy-1-butene, vinylethylene carbonate, glycerol monoallyl ether, etc.; PVOH resins having hydroxymethyl groups in their side chains obtained by copolymerizing and saponifying hydroxymethyl vinylidene diacetates such as 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane.

[0078] Methods for post-modification of post-modified PVOH-based resins include esterification, acetalization, urethaneization, etherization, grafting, phosphate esterification, and oxyalkyleneization of unmodified PVOH or the above-mentioned modified PVOH-based resin.

[0079] In this embodiment, both unmodified and modified PVOH can be used. A feature of this embodiment is that even PVOH that is easily soluble in cold water and therefore could not be used as a coating on its own in conventional methods, can be made sparingly soluble by the crosslinking agent and used suitably as a coating carbon material film. This allows the use of partially saponified PVOH, which has good wettability to the hydrophobic surface of graphite and does not easily increase the viscosity of the aqueous solution even at low temperatures, in the case of unmodified PVOH. Furthermore, in the case of modified PVOH, it is possible to use PVOH containing anionic modified groups having functional groups with excellent lithium conductivity in the side chain, such as carboxylic acid groups or sulfonic acid groups, and PVOH containing nonionic modified groups having hydroxyalkyl groups or oxyethylene groups, thereby reducing the resistance of the coating.

[0080] The solubility of PVOH-based resins varies depending on the degree of saponification and polymerization. While the degree of saponification of PVOH-based resins is not particularly limited, in this embodiment, a wide range of saponification degrees can be selected because the resin can be made less soluble by using a crosslinking agent. In the case of unmodified PVOH, the degree of saponification is usually 70 mol% or higher, preferably 78-100 mol%, and particularly preferably 85-99.8 mol%. Generally, PVOH-based resins tend to have the highest elution rate in water around a degree of saponification of 88 mol%, although there are some differences depending on the degree of polymerization, type of modification, etc. Therefore, in order to improve the water resistance of the cured product reacted with the crosslinking agent, it is preferable to set the degree of saponification higher or lower than around 88%.

[0081] In the case of PVOH-based resins containing a modifying group, crystallization is difficult even at high saponification levels, and they have high solubility in water. Therefore, the saponification level is usually 85 mol% or higher, preferably 90 mol% or higher, and more preferably 98 mol% or higher. The upper limit is usually 100 mol% or less, preferably 99.8 mol% or less. The saponification level is measured in accordance with ISO 15023-2. When coating with a solvent system, low-saponification PVOH with a saponification degree of 38-55 mol% can be used in combination with a crosslinking agent.

[0082] The average degree of polymerization of PVOH-based resins is not particularly limited, but in the case of unmodified PVOH, it is usually 200 to 3000, preferably 250 to 2800, and particularly preferably 300 to 2600. In the case of PVOH-based resins with a modifying group, the average degree of polymerization is usually 100 or more, preferably 200 or more, and more preferably 250 or more. Keeping it within this range makes it easier to prevent the solubility from becoming too high. Also, it is usually 4000 or less, preferably 3500 or less, and more preferably 2800 or less. Keeping it within this range makes it easier to prevent the solubility from becoming too low. The average degree of polymerization is the value measured by the aqueous solution viscosity measurement method (ISO 15023-2).

[0083] PVOH-based resins may be used as a single resin or as a blend of two or more resins. In this case, the structural units may differ, the degrees of saponification may differ, and the average degrees of polymerization may differ. When used as a blend, the average values ​​of the degrees of saponification, average degrees of polymerization, etc., of all PVOH-based resins should be within the above range. Furthermore, the PVOH-based resin may be partially modified. If it is modified, the modification rate of the PVOH-based resin is preferably in the range where 90% by mass or more dissolves within 60 minutes after dispersing 10 g of the resin particles in 100 g of water at 20°C under stirring, and then raising the temperature to 90°C at a rate of 1°C / min under stirring.

[0084] In this embodiment, a crosslinking agent can be used to improve the solvent resistance of the coating made of an organic compound. Methods for forming the aforementioned crosslinked material (crosslinking method) include, for example, heat treatment, crosslinking agent treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, etc. Among these, a thermally crosslinked material formed by heat treatment is preferred.

[0085] The crosslinking agent used in the crosslinking agent treatment is not particularly limited, but organic and / or inorganic crosslinking agents having two or more crosslinkable reactive groups are preferred, and more specifically, known crosslinking agents for PVOH resins having carboxyl groups, acetoacetyl groups, etc., can be used. For example, monoaldehyde compounds such as formaldehyde and acetaldehyde; aldehyde compounds such as polyhydric aldehyde compounds such as glyoxal, glutaraldehyde, and dialdehyde starch; metaxylenediamine, norbornanediamine, 1,3-bisaminomethylcyclohexane, bisaminopropylpiperazine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodiphenylmethane, 3,3 ',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diamino-5,5'-diethyldiphenylmethane, 4,4'-diaminodiphenyl ether, diaminodiphenylsulfone, 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 3-methyl-1,2-phenylenediamine, 4-methyl-1,2-phenyl Amine compounds such as didiamine, 2-methyl-1,3-phenylenediamine, 4-methyl-1,3-phenylenediamine, 2-methyl-4,6-diethyl-1,3-phenylenediamine, 2,4-diethyl-6-methyl-1,3-phenylenediamine, 2,4,6-trimethyl-1,3-phenylenediamine, and 2-chloro-1,4-phenylenediamine; methylol compounds such as methylolated urea and methylolated melamine; reaction products of ammonia and formaldehyde such as hexamethylenetetramine; boron compounds such as boric acid and borax; zirconium compounds such as basic zirconyl chloride, zirconyl nitrate, and zirconium ammonium acetate; titanium orthoesters such as tetramethyl titanate; titanium chelates such as titanium ethylacetoacetonate; titanium compounds such as titanium acylates such as polyhydroxytitanium stearate; and aluminum compounds such as aluminum organic acid chelates such as aluminum acetylacetonate.Examples include organoalkoxysilane compounds having organic reactive groups such as silane coupling agents; polyvalent epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, hexanediol diglycidyl ether, and trimethylolpropane triglycidyl ether; various isocyanate compounds; polyamide polyamine-epihalohydrin resins such as polyamide polyamine-epichlorohydrin resins; and components having a three-dimensional siloxane crosslinking structure derived from hydrolyzed polycondensates of alkoxysilanes and / or their low-level condensates. In particular, components having a three-dimensional siloxane crosslinking structure derived from hydrolyzed polycondensates of alkoxysilanes and / or their low-level condensates are preferred because they can form a coating with excellent water resistance and solvent resistance.

[0086] The content of the crosslinking agent is preferably 0.05 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and particularly preferably 1 to 10 parts by mass, as solid content per 100 parts by mass of PVOH resin. If the crosslinking agent content is too low, the effect of the crosslinking agent tends to be poor, and if it exceeds the upper limit, unreacted crosslinking agent is likely to dissolve or precipitate.

[0087] Methods for mixing PVOH-based resins and crosslinking agents include, for example, (i) mixing an aqueous solution of the PVOH-based resin with an aqueous solution of the crosslinking agent, (ii) spraying an aqueous solution of the crosslinking agent onto a solid PVOH-based resin, and (iii) spraying an aqueous solution of the PVOH-based resin onto a solid crosslinking agent.

[0088] PVOH-based resins may be obtained using commercially available materials or by synthesis. If synthesized, they can be produced using known methods.

[0089] <Components with a three-dimensional cross-linked structure> The coated carbon material of this embodiment may contain a component having a three-dimensional crosslink structure in the coating formed on the inner wall of the pores within its particles, and may also contain a component having a three-dimensional siloxane crosslink structure derived from alkoxysilane and / or hydrolyzed polycondensates of its low-level condensates. By containing a component having a three-dimensional siloxane crosslink structure in the coating, the elution of the PVOH-based resin contained in the coating into the aqueous slurry or electrolyte can be suppressed, and swelling of the coating can also be suppressed.

[0090] In this specification, a three-dimensional crosslinked structure is, for example, a structure formed by crosslinking organic and / or inorganic crosslinking agents having two or more crosslinkable reactive groups, and a three-dimensional siloxane crosslinked structure means a stereochemical network structure mainly composed of siloxane units formed by the hydrolysis and polycondensation of trialkoxysilane having three alkoxy groups per molecule and / or tetraalkoxysilane having four alkoxy groups per molecule as the alkoxysilane.

[0091] In this embodiment, any additives that improve battery performance can be used in combination with the coating carbon material, as long as they do not affect the curability, water resistance, or solvent resistance of the coating. For example, known surfactants and silane coupling agents that contribute to wettability and adhesion with the negative electrode active material and binder resin, conductive polymers such as inorganic oxide particles, lithium compound particles, and polyaniline sulfonic acid that are effective in reducing the resistance of the coating, and organic compounds that form complex ions with lithium ions, such as polyethylene oxide and complex hydrides, are preferred examples.

[0092] <Physical properties of coated carbon materials> • Volume-based average particle size (average particle size d50) The volume-based average particle size (also referred to as "average particle size d50") of the coated carbon material in this embodiment is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, particularly preferably 15 μm or more, and most preferably 16.5 μm or more. Furthermore, the average particle size d50 is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 35 μm or less, particularly preferably 30 μm or less, and most preferably 25 μm or less. When the average particle size d50 is within the above range, there is a tendency to increase the irreversible capacity of the secondary battery obtained using the coated carbon material, suppress the loss of initial battery capacity, and also suppress the occurrence of process problems such as striking during slurry coating, a decrease in high current density charge / discharge characteristics, and a decrease in low temperature input / output characteristics.

[0093] Furthermore, in this specification, the average particle size d50 is defined as the size obtained by suspending 0.01 g of coated carbon material in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Zeen 20®), introducing this as a measurement sample into a commercially available laser diffraction / scattering particle size distribution analyzer (e.g., HORIBA LA-920), irradiating the measurement sample with 28 kHz ultrasound at an output of 60 W for 1 minute, and then measuring it as the volume-based median diameter in the said analyzer.

[0094] • Circularity The circularity of the coated carbon material in this embodiment is 0.88 or higher, preferably 0.90 or higher, and more preferably 0.91 or higher. Furthermore, the circularity is preferably 1 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower. When the circularity is within the above range, it tends to suppress the decrease in the high current density charge-discharge characteristics of the secondary battery. Note that circularity is defined by the following formula, and a circularity of 1 results in a theoretically perfect sphere. Circularity = (Perimeter of an equivalent circle with the same area as the particle projection shape) / (Actual perimeter of the particle projection shape)

[0095] For the circularity value, for example, a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Corporation) is used. Approximately 0.2 g of the sample (coated carbon material) is dispersed in a 0.2 mass% aqueous solution (approximately 50 mL) of polyoxyethylene sorbitan monolaurate, a surfactant. The dispersion is then irradiated with 28 kHz ultrasound at an output of 60 W for 1 minute. The detection range is set to 0.6 to 400 μm, and the values ​​measured for particles with a particle size in the range of 1.5 to 40 μm are used.

[0096] While there are no particular limitations on the method for improving circularity, it is preferable to use particles that have been spheroidized to form a spherical shape, as this results in a more uniform shape of interparticle voids when used as the negative electrode. Examples of spheroidization methods include mechanically shaping particles by applying shear or compressive forces, and mechanical / physical processing methods that granulate multiple coated carbon material fine particles using the adhesive force of a binder or the particles themselves.

[0097] • Tap density The tap density of the coated carbon material in this embodiment is preferably 0.7 g / cm³. 3 More preferably 0.8 g / cm³ 3 More preferably 0.85 g / cm³ 3 In particular, 0.9 g / cm³ is preferred. 3 In summary, the most preferred value is 0.95 g / cm³. 3 Preferably 1.3 g / cm³ 3 The following, and more preferably 1.2 g / cm³ 3 The following, and more preferably 1.1 g / cm³ 3 The following applies:

[0098] When the tap density is within the above range, processability such as scribing during electrode plate manufacturing is improved, resulting in excellent high-speed charge-discharge characteristics. In addition, since the carbon density within the negative electrode coating does not increase easily, the rolling properties are also good, and it tends to be easier to form high-density negative electrode sheets. The aforementioned tap density was determined using a powder density meter with a diameter of 1.6 cm and a volume of 20 cm³. 3The coated carbon material of this embodiment is dropped into a cylindrical tap cell through a sieve with a mesh size of 300 μm until the cell is completely filled. Then, tapping is performed 1000 times with a stroke length of 10 mm, and the density is defined as the volume and mass of the sample obtained at that time.

[0099] X-ray parameters The d-value (interlayer distance) of the lattice plane (002 plane) of the coated carbon material of this embodiment, as determined by X-ray diffraction using the JSPS method, is preferably 0.335 nm or more and less than 0.340 nm, more preferably 0.339 nm or less, and even more preferably 0.337 nm or less. When the d002 value is within the above range, the crystallinity of the graphite is high, which tends to suppress the increase in initial irreversible capacity. Here, 0.335 nm is the theoretical value for graphite. Furthermore, the crystallite size (Lc) of the coated carbon material, as determined by X-ray diffraction using the JSPS method, is preferably in the range of 1.5 nm or more, and more preferably 3.0 nm or more. Within this range, the particles have sufficient crystallinity, which helps to suppress the reduction in reversible capacity when used in a secondary battery. Note that the lower limit of Lc is the theoretical value for graphite.

[0100] ·ash The ash content in the coated carbon material of this embodiment is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, relative to the total mass of the coated carbon material. Furthermore, the lower limit of the ash content is preferably 1 ppm or more. If the ash content is within the above range, the degradation of battery performance due to the reaction between the coating carbon material and the electrolyte during charging and discharging can be kept to a negligible level when used as a secondary battery. Furthermore, since the manufacturing of the coating carbon material does not require a great deal of time, energy, or equipment for preventing contamination, the increase in costs can also be kept to a minimum.

[0101] • BET specific surface area due to nitrogen adsorption (N2-SA) The BET specific surface area (N2-SA) of the coated carbon material due to nitrogen adsorption in this embodiment is preferably 1.5 m². 2 / g or more, more preferably 2.5m 2 It is 11m or more, and usually 11m 2It is less than or equal to / g, preferably 8.0m 2 It is less than or equal to / g, and more preferably 6.0m 2 It is less than / g. When the BET specific surface area (N2-SA) is above the lower limit, sufficient space can be secured for Li to enter and exit, resulting in excellent high-speed charge / discharge characteristics and output characteristics. Furthermore, when the specific surface area is below the upper limit, the activity of the active material in the electrolyte can be moderately suppressed, which tends to suppress the increase in initial irreversible capacity and allows for the manufacture of high-capacity batteries.

[0102] • BET specific surface area (Tol-SA) due to toluene adsorption The BET specific surface area (Tol-SA) of the coated carbon material due to toluene adsorption in this embodiment is preferably 1.1 m². 2 / g or more, more preferably 1.8m 2 It is 1 / g or more, and preferably 7.6m 2 It is less than or equal to / g, and more preferably 5.7m 2 The value is less than / g. Because the BET specific surface area (Tol-SA) is within the above range, sufficient space for Li to enter and exit can be secured, resulting in excellent high-speed charge / discharge characteristics and output characteristics. Furthermore, the activity of the active material in relation to the electrolyte can be appropriately suppressed, thus preventing an increase in initial irreversible capacity and enabling the manufacture of high-capacity batteries. Additionally, gas generation due to side reactions with the electrolyte can be suppressed, providing a desirable non-aqueous secondary battery.

[0103] • Basal surface area due to toluene adsorption The basal surface area of ​​the coated carbon material due to toluene adsorption in this embodiment is preferably 0.5 m². 2 / g or more, more preferably 0.7m 2 It is 1 / g or more, and preferably 4.0m 2 It is less than or equal to / g, and more preferably 3.0m 2 The basal surface specific surface area is within the above range, which moderately suppresses the activity of the active material with respect to the electrolyte. This suppresses the increase in initial irreversible capacity and tends to enable the manufacture of high-capacity batteries. Furthermore, it suppresses gas generation due to side reactions with the electrolyte, thus providing a desirable non-aqueous secondary battery.

[0104] • Pore volume in the range of 10 nm to 1500 nm In the coated carbon material of this embodiment, the pore volume in the range of 10 nm to 1500 nm is a value measured using the mercury intrusion method (mercury porosimetry), and is preferably 0.03 mL / g or more, more preferably 0.05 mL / g or more, even more preferably 0.08 mL / g or more, and also preferably 0.3 mL / g or less, more preferably 0.25 mL / g or less, and even more preferably 0.2 mL / g or less.

[0105] If the pore volume in the range of 10 nm to 1500 nm is within the above range, the amount of voids into which non-aqueous electrolytes can penetrate is less likely to decrease, and the tendency for lithium ions to not be able to insert and deinsert quickly enough during rapid charging and discharging, leading to lithium metal deposition and deterioration of cycle characteristics, can be better avoided. Furthermore, the tendency for the binder to be easily absorbed into the voids during electrode fabrication, which in turn leads to a decrease in electrode strength and a decrease in initial efficiency, can be better avoided.

[0106] Furthermore, the total pore volume of the coated carbon material in this embodiment is preferably 0.1 mL / g or more, more preferably 0.2 mL / g or more, even more preferably 0.25 mL / g or more, and particularly preferably 0.5 mL / g or more. Also, the total pore volume is preferably 10 mL / g or less, more preferably 5 mL / g or less, even more preferably 2 mL / g or less, and particularly preferably 1 mL / g or less. If the total pore volume is within the above range, there is no need to use an excessive amount of binder when forming the electrode plate, and the dispersion effect of the thickener and binder is also more easily obtained during electrode plate formation.

[0107] Furthermore, the coated carbon material of this embodiment has pores with a diameter of 10 nm to 500 nm inside. That is, it is characterized by having a peak in the distribution of pore diameters between 10 nm and 500 nm.

[0108] For the mercury porosimetry described above, a mercury porosimemeter (Autopore 9520: manufactured by Micromeritex) can be used. The sample (coated carbon material) is weighed to approximately 0.2 g, sealed in a powder cell, and pre-treated by degassing at 25°C under vacuum (50 μmHg or less) for 10 minutes. Next, the pressure is reduced to 4 psia (approximately 28 kPa) and mercury is introduced into the cell. The pressure is then increased in steps from 4 psia (approximately 28 kPa) to 40,000 psia (approximately 280 MPa), and then reduced to 25 psia (approximately 170 kPa).

[0109] The number of steps during the pressurization process will be set to 80 or more points. After a 10-second equilibrium period at each step, the amount of mercury injected will be measured. From the resulting mercury injection curve, the pore distribution will be calculated using Washburn's equation. The surface tension (γ) of mercury is assumed to be 485 dyne / cm, and the contact angle (ψ) is assumed to be 140° for the calculation.

[0110] ·True density The true density of the coated carbon material in this embodiment is preferably 1.9 g / cm³. 3 More preferably 2 g / cm³ 3 More preferably 2.1 g / cm³ 3 In particular, 2.2 g / cm³ is preferred. 3 The above is true, and the upper limit is 2.26 g / cm³. 3 The upper limit is the theoretical value for graphite. Within this range, the crystallinity of carbon is not too low, and the increase in its initial irreversible capacity when used as a secondary battery can be suppressed.

[0111] Aspect ratio The aspect ratio of the coated carbon material in powder form in this embodiment is theoretically 1 or more, preferably 1.1 or more, and more preferably 1.2 or more. Furthermore, the aspect ratio is preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, and particularly preferably 3 or less. When the aspect ratio is within the above range, streaking of the slurry (negative electrode forming material) containing the coating carbon material is less likely to occur during electrode formation, resulting in a uniform coating surface and a tendency to avoid a decrease in the high current density charge-discharge characteristics of the secondary battery.

[0112] The aspect ratio is expressed as A / B, where A is the longest diameter of the coated carbon material particle when observed in three dimensions, and B is the shortest diameter perpendicular to it. The coated carbon material particles are observed using a scanning electron microscope capable of magnification. Fifty arbitrary coated carbon material particles are selected and fixed to the end face of a metal with a thickness of 50 microns or less. For each particle, the stage on which the sample is fixed is rotated and tilted, A and B are measured, and the average value of A / B is calculated.

[0113] ·Maximum particle size dmax The maximum particle size dmax of the coated carbon material in this embodiment is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 120 μm or less, particularly preferably 100 μm or less, and most preferably 80 μm or less. When dmax is within the above range, it tends to suppress the occurrence of process problems such as slicing. Furthermore, the maximum particle size is defined as the largest particle size value measured in the particle size distribution obtained when measuring the average particle size d50.

[0114] • Raman R value The Raman R value of the coated carbon material in this embodiment is preferably 0.1 or higher, more preferably 0.15 or higher, and even more preferably 0.2 or higher. Furthermore, the Raman R value is preferably 0.6 or lower, more preferably 0.5 or lower, and even more preferably 0.4 or lower. The Raman R value mentioned above is the 1580 cm⁻¹ value in the Raman spectrum obtained by Raman spectroscopy. -1 Nearby Peak P A Intensity I A And, 1360cm -1 Nearby Peak P B Intensity I B Measure and the intensity ratio (I B / I A It is defined as being calculated as follows: In this specification, "1580cm" -1 "Nearby" means 1580-1620cm -1 The range is "1360cm -1 "Nearby" means 1350-1370 cm -1 It refers to the range.

[0115] When the Raman R value is within the above range, the crystallinity of the coated carbon material particle surface is less likely to increase, and when the density is increased, the crystals are less likely to orient parallel to the negative electrode plate, thus tending to avoid a decrease in load characteristics. Furthermore, the crystals on the particle surface are less likely to be disordered, which suppresses an increase in reactivity with the electrolyte of the negative electrode, and tends to avoid a decrease in the charge / discharge efficiency of the secondary battery and an increase in gas generation.

[0116] The aforementioned Raman spectrum can be measured using a Raman spectrometer. Specifically, the sample is filled by allowing the target particles to fall naturally into the measurement cell, and the measurement is performed while irradiating the measurement cell with argon ion laser light and rotating the measurement cell in a plane perpendicular to the laser light. The measurement conditions are as follows. Wavelength of argon ion laser light: 514.5 nm Laser power on the sample: 25mW Resolution: 4cm -1 Measurement range: 1100cm -1 ~1730cm -1 Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)

[0117] ·DBP oil absorption The amount of DBP (dibutyl phthalate) absorbed by the coated carbon material in this embodiment is preferably 65 ml / 100g or less, more preferably 62 ml / 100g or less, even more preferably 60 ml / 100g or less, and particularly preferably 57 ml / 100g or less. Furthermore, the amount of DBP absorbed is preferably 30 ml / 100g or more, more preferably 40 ml / 100g or more.

[0118] When the DBP oil absorption amount is within the above range, it means that the spheroidization of the coated carbon material is sufficiently advanced, which tends to make it less likely to cause streaking when applying the slurry containing the coated carbon material, and because a pore structure exists within the particles, it tends to avoid a decrease in the reaction surface. The DBP oil absorption amount is defined in accordance with ISO 4546, as the measured value when 40g of the measurement material (coated carbon material) is added, the dropping rate is 4ml / min, the rotation speed is 125rpm, and the set torque is 500N·m. For measurement, for example, a Brabender Type E absorbometer can be used.

[0119] ·Average particle size d10 In this embodiment, the particle size (d10) corresponding to the cumulative 10% from the smallest particle side of the volume-based particle size of the coated carbon material is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 17 μm or less, preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0120] When d10 is within the above range, the tendency for particle aggregation does not become too strong, thus avoiding process problems such as increased slurry viscosity, a decrease in electrode strength in secondary batteries, and a decrease in initial charge-discharge efficiency. It also tends to avoid a decrease in high-current-density charge-discharge characteristics and a decrease in low-temperature input / output characteristics. d10 is defined as the value obtained when the particle size distribution, when the average particle size d50 is measured, where the cumulative percentage of particle frequency from the smallest particle size reaches 10%.

[0121] ·Average particle size d90 In this embodiment, the particle size (d90) corresponding to 90% of the cumulative particle size from the smallest particle side, measured on a volume basis, is preferably 100 μm or less, more preferably 70 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, particularly preferably 45 μm or less, most preferably 42 μm or less, preferably 20 μm or more, more preferably 23 μm or more, and even more preferably 25 μm or more.

[0122] When d90 is within the above range, it is possible to avoid a decrease in electrode strength and initial charge / discharge efficiency in secondary batteries, and it is also possible to avoid process problems such as streaking during slurry application, a decrease in high current density charge / discharge characteristics, and a decrease in low-temperature input / output characteristics. d90 is defined as the value obtained when the particle size distribution, when the average particle size d50 is measured, where the cumulative percentage of particle frequency from the smallest particle size reaches 90%.

[0123] The amount of organic compound coating on the coated carbon material is not particularly limited, but is 0.05% by mass or more, preferably 0.1% by mass or more, and 3% by mass or less, preferably 1% by mass or less. The amount of organic compound coating on the coated carbon material can be measured from the amount of mass loss due to heating the coated carbon material.

[0124] <Method for manufacturing coated carbon material> The carbon coating material for secondary batteries (also known as the active material for the negative electrode of secondary batteries) according to this embodiment can be manufactured, for example, by the following method. For convenience, the following explanation will refer to the materials as follows: carbon material (A), organic compound (B), active material for secondary battery negative electrode (C), and solution (D). 1) Mixing process 2) Internal immersion process 3)Drying process

[0125] The organic compound (B) is added to an organic solvent, water, or a mixture thereof in step 1) mixing, and the solution (D) is mixed with the carbon material (A), 2) In the internal immersion process, the carbon material (A) is immersed in the solution (D) as described in 2-1) or 2-2) below. 2-1) The carbon material (A) is subjected to isotropic pressure treatment in solution (D). 2-2) Boil the carbon material (A) in the solution (D), then lower the temperature and mix. Subsequently, after filtering or washing away the solution (D), the carbon material (A) is dried by heating and / or reduced pressure in the 3) drying step to obtain an active material for a secondary battery negative electrode in which the carbon material (A) is coated with an organic compound (B).

[0126] In this embodiment, the inner walls of the pores of the coated carbon material particles are partially coated with an organic compound. Partially coated does not mean that the inner walls of the pores are not coated, as in patterns A and B in Figure 2. In such cases, the electrolyte that penetrates into the pores undergoes a decomposition reaction on the inner walls of the pores, reducing the initial efficiency. Furthermore, this does not mean that the inner walls of the pores are completely covered, as shown in pattern E in Figure 2. In such cases, the interfacial resistance at the negative electrode increases, leading to a problem where the input / output characteristics of the battery deteriorate. In this embodiment, partial covering refers to covering as shown in patterns C and D in Figure 2, preferably covering 30% to 90% of the area of ​​the inner wall of the pore, and more preferably covering 50% to 85%. The coverage rate can be controlled, for example, by appropriately adjusting the concentration of solution (D), resulting in patterns C, D, and E.

[0127] Furthermore, the outer periphery of the secondary battery negative electrode active material (C) can be removed by washing the coated carbon material particles with an organic solvent or water after the above coating treatment. By eliminating the coating on the outer periphery of the secondary battery negative electrode active material (C), conductivity between the particles of the secondary battery negative electrode active material (C) is improved when forming the negative electrode plate, and the bond between the secondary battery negative electrode active material (C) and the binder resin and current collector copper foil becomes stronger, thus preventing the negative electrode layer from peeling off from the current collector copper foil.

[0128] The solvent used is not particularly limited as long as it dissolves or disperses the organic compound, but preferred solvents include water, ethyl methyl ketone, toluene, acetone, methyl isobutyl ketone, ethanol, and methanol. Among these, water, ethyl methyl ketone, acetone, methyl isobutyl ketone, ethanol, and methanol are more preferred due to cost and ease of drying.

[0129] Process (1): Mixing process There are no particular restrictions on the method of mixing the carbon material (A) and the organic compound (B), but it is desirable that the carbon material (A) and the organic compound (B) be mixed uniformly. Mixing methods include stirring with an agitator in a fixed container, mixing by rotating the container itself to tumble the powder, and mixing by fluidizing with airflow. Of these, stirring with an agitator in a fixed container is preferred from the viewpoint of mixing uniformity. The fixed containers used in this case can be inverted cone-shaped, vertically oriented cylindrical, horizontally oriented cylindrical, or U-shaped trough, but from the viewpoint of preventing adhesion inside the machine and ensuring uniform mixing, the horizontally oriented cylindrical type is preferred.

[0130] The shapes of the stirring blades can be ribbon-shaped, screw-shaped, single-axis paddle-shaped, double-axis paddle-shaped, anchor-shaped, or plow-shaped if using a horizontal axis system, and ribbon-shaped, screw-shaped, planetary-shaped, conical screw-shaped, or lower high-speed rotating blades if using a vertical axis system. However, from the viewpoint of uniform mixing, the plow-shaped blade of the horizontal axis system is preferred. Furthermore, it is preferable to use a mixer with a horizontally oriented cylindrical container and a plow-shaped stirring blade with a horizontal axis.

[0131] The peripheral speed of the stirring blade is preferably 0.1 m / s or more, but more preferably 1 m / s or more, even more preferably 2 m / s or more, particularly preferably 3 m / s or more, preferably 100 m / s or less, more preferably 80 m / s or less, and even more preferably 50 m / s or less. The processing time is preferably 0.5 minutes or more, more preferably 1 minute or more, even more preferably 5 minutes or more, preferably 5 hours or less, more preferably 1 hour or less, and even more preferably 20 minutes or less. When the processing time is within the above range, more uniform mixing can be achieved while maintaining processing capacity.

[0132] The mixing temperature is preferably 1°C or higher, more preferably 10°C or higher, more preferably 100°C or lower, and more preferably 80°C or lower. When the mixing temperature is within the above range, the increase in viscosity of solution (D) can be suppressed, and more uniform mixing can be achieved. Furthermore, the cost of temperature control can be reduced.

[0133] In a solution obtained by diluting the organic compound (B) with the carbon material (A), the ratio of the organic compound to the carbon material is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, preferably 10% by mass or less, and more preferably 3% by mass or less. By keeping the ratio within the above range, the ratio can be mixed uniformly, and a uniform coating can be formed.

[0134] Process (2): Internal immersion process The method for immersing the carbon material (A) in the solution (D) is not particularly limited, but for example, the organic compound can be immersed inside the carbon material (A) by the following methods 2-1) or 2-2). 2-1) The carbon material (A) is subjected to isotropic pressure treatment in solution (D). 2-2) Boil the carbon material (A) in the solution (D), then lower the temperature and mix.

[0135] 2-1) The process of isotropically pressurizing the carbon material (A) in solution (D) will be described in detail. The conditions for isotropic pressurization are not particularly limited, but by pressurizing at 0.1 MPa to 100 MPa, the solution (D) can be forced into the pores within the particles of the carbon material (A). The pressurization conditions need to be appropriately selected depending on the amount and shape of the pores within the particles, but in order to sufficiently wet the inner walls of the pores with the solution (D), the conditions are preferably 0.1 MPa or higher, more preferably 1 MPa or higher, even more preferably 5 MPa or higher, and preferably 100 MPa or lower, more preferably 50 MPa or lower, and even more preferably 10 MPa or lower. Furthermore, by pressurizing for a period of 1 minute or more and 30 minutes or less, the solution (D) can be forced into pores with small inlet diameters that are difficult for the solution (D) to penetrate. The pressurizing time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more, in order to sufficiently wet the inner walls of the pores with small diameters with the solution (D), and preferably 30 minutes or less, more preferably 20 minutes or less, in order to reduce the load on the pressurizing device. After pressurization, the solution (D) that did not enter the pores of the carbon material (A) may be removed from the mixture of carbon material (A) and solution (D) by filtration. Alternatively, the filtered carbon material (A) may be washed with a solvent to remove excess organic compounds (B).

[0136] Furthermore, 2-2) the process of boiling the carbon material (A) in solution (D) will be described in detail. The conditions for boiling are not particularly limited, but the mixture of carbon material (A) and solution (D) should be heated while being mixed and stirred. The boiling temperature should be above the boiling point of the solvent used to prepare the solution, and below the boiling point + 40°C, which will cause the solution (D) to boil. Furthermore, the boiling treatment can be performed for 5 minutes to 1 hour to expel the air trapped in the pores of the carbon material (A) particles and replace it with the solution (D). The boiling treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 20 minutes or more, in order to sufficiently wet the inner walls of the pores with small opening diameters with the solution (D). However, extending the treatment time unnecessarily will saturate the treatment effect, so it is preferably 1 hour or less, and more preferably 30 minutes or less. After boiling, the temperature of the mixture of carbon material (A) and solution (D) is lowered, and mixing and stirring are continued to further fill the pores of the carbon material (A) with solution (D). Subsequently, the solution (D) that did not enter the pores of the carbon material (A) may be removed by filtration. Alternatively, the filtered carbon material (A) may be washed with a solvent to remove excess organic compounds (B).

[0137] In addition to the methods described in 2-1) or 2-2) above, organic compounds (B) can be immersed in the internal pores of the carbon material (A) by methods such as mixing the carbon material (A) and the solution (D) under reduced pressure, or by pre-treating the carbon material (A) with ozone to improve its wettability to the solution (D).

[0138] Process (3): Drying process When drying a mixture of carbon material (A) and solution (D) by heating, the temperature is preferably below the decomposition temperature of the organic compound (B), and more preferably above the boiling point of the solvent. Preferably, the temperature is between 50°C and 300°C. Within this range, the drying efficiency is sufficient, and a decrease in battery performance due to residual solvent is avoided.

[0139] The temperature is preferably 250°C or lower, and preferably 100°C or higher. When drying solution (D) by reduced pressure, the pressure is usually 0 MPa or lower and -0.2 MPa or higher in gauge pressure (difference from atmospheric pressure). Within this range, drying can be performed relatively efficiently. The pressure is preferably -0.03 MPa or lower, and preferably -0.15 MPa or higher.

[0140] In the drying process, there are no particular restrictions on the method of drying the mixture of carbon material (A) and organic compound (B), but it is desirable to avoid segregation of the organic compound (B) during the drying process and to ensure a uniform coating. Heat transfer methods include convection heat transfer, which dries by directly applying hot air, and conduction heat transfer, which transfers heat from a heat transfer medium through a conductive heating plate. However, conduction heat transfer is preferred from the viewpoint of yield.

[0141] The materials to be dried can be transported in three ways: static drying, where the materials are left to dry; hot air transport drying, where the materials are dispersed in hot air or sprayed with hot air; and agitated drying, where the materials are dried while being agitated. Of these, agitated drying is preferable from the viewpoint of uniformly drying the particles. Furthermore, the drying process can be carried out using the same equipment as the mixing process, or using separate equipment, as long as the uniformity of the mixing and drying capacity are maintained.

[0142] Methods of stirring and drying include drying the mixture while stirring with a stirring blade in a fixed container, drying the powder while the container itself rotates and rolls it around, and drying the mixture while stirring by fluidizing it by blowing hot air from below. From the viewpoint of uniformity and yield, it is preferable to use the method of drying the mixture while stirring with a stirring blade in a fixed container.

[0143] The stirring tanks used in this process can be inverted cone-shaped, vertically mounted cylindrical, horizontally mounted cylindrical, or U-shaped trough, but a horizontally mounted cylindrical type is preferred from the viewpoint of yield, workability, and installation space. For horizontal-axis systems, the shapes of the stirring blades include ribbon type, screw type, single-axis paddle type, double-axis paddle type, anchor type, plow type, and hollow wedge type. For vertical-axis systems, examples include ribbon type, screw type, conical screw type, and lower high-speed rotating blades, but the single-axis paddle type and plow type for horizontal-axis systems are preferred.

[0144] The peripheral speed of the stirring blade varies depending on the stirring and drying method, but from the viewpoint of uniformity, it is preferably 0.01 m / s or more, more preferably 0.2 m / s or more, even more preferably 1 m / s or more, particularly preferably 2 m / s or more, preferably 40 m / s or less, more preferably 20 m / s or less, and even more preferably 10 m / s or less. In the conductive heat transfer method, the types of heat transfer fluids include heat transfer oil, steam, and electric heaters, but steam is preferred from a cost perspective. Furthermore, the heat transfer fluid is flowed through the stirring tank jacket, stirring blades, or stirring shaft to transfer heat to the material being dried via the heat transfer surface, but from the viewpoint of heat transfer efficiency, it is preferable to flow the heat transfer fluid through the stirring tank jacket, stirring blades, and stirring shaft.

[0145] For example, there is a horizontal cylindrical agitator that can be heated by flowing a heat transfer medium through the agitator jacket and has a horizontal-axis plow-type agitator blade; a CD dryer (Kurimoto Iron Works) that can be heated by flowing a heat transfer medium through both the rotating shaft with two interlocking horizontal-axis hollow wedge-type agitator blades and the horizontal jacketed casing; a horizontal cylindrical agitator that can be heated by flowing a heat transfer medium through the agitator jacket and agitator blades and has a horizontal-axis single-axis paddle-type agitator blade; a reverse cone-shaped agitator that can be heated by flowing a heat transfer medium through the agitator jacket and has a vertical-axis ribbon-type agitator blade; and an Amixon (Toyo High-Tech) that can be heated by flowing a heat transfer medium through the agitator jacket and has a vertical-axis ribbon-type agitator blade.

[0146] Prior to drying, the process may include a step of filtering the solution containing the carbon material (A) and the organic compound (B), and a step of washing the resulting residue with water. This is preferable because it removes excess organic compound (B) that is not directly attached to the carbon material (A), thereby improving low-temperature input / output characteristics without reducing effects such as improved initial efficiency and suppression of gas generation.

[0147] <Negative electrode for secondary batteries> The negative electrode for a secondary battery of this embodiment (hereinafter also referred to as "electrode sheet" as appropriate) comprises a current collector and a negative electrode active material layer formed on the current collector, wherein the active material layer contains at least the coating carbon material of this embodiment. More preferably, it contains a binder. As a binder, one having olefinic unsaturated bonds in its molecule is used. The type is not particularly limited, but specific examples include styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Using such a binder with olefinic unsaturated bonds can reduce the swelling of the active material layer in the electrolyte. Among these, styrene-butadiene rubber is preferred due to its availability.

[0148] By using a binder having such olefinic unsaturated bonds in combination with the aforementioned coated carbon material, the strength of the negative electrode plate can be increased. Higher negative electrode strength suppresses deterioration of the negative electrode due to charging and discharging, thereby extending the cycle life. Furthermore, in the negative electrode according to this embodiment, since the adhesive strength between the active material layer and the current collector is high, it is presumed that even if the binder content in the active material layer is reduced, the problem of the active material layer peeling off from the current collector when the negative electrode is wound to manufacture the battery will not occur.

[0149] For binders having olefinic unsaturated bonds within the molecule, it is desirable that they have a large molecular weight or a large proportion of unsaturated bonds. Specifically, in the case of binders with a large molecular weight, it is desirable that their weight-average molecular weight is preferably in the range of 10,000 or more, more preferably 50,000 or more, and preferably 1,000,000 or less, and more preferably 300,000 or less. In the case of binders with a large proportion of unsaturated bonds, the number of moles of olefinic unsaturated bonds per gram of the total binder is preferably 2.5 × 10⁻⁶. -7 Moles or more, more preferably 8 × 10 -7 More than 1 mole, preferably 1 × 10⁻⁶. -6 Less than a mole, more preferably 5 × 10 -6 It is desirable that the molecular weight is within the range of less than or equal to the mole. As a binder, it is sufficient to satisfy at least one of the following requirements: the molecular weight requirement and the ratio of unsaturated bonds. However, it is more preferable that it satisfies both requirements simultaneously. When the molecular weight of a binder having olefinic unsaturated bonds is within the above range, it exhibits excellent mechanical strength and flexibility.

[0150] Furthermore, the binder having olefinic unsaturated bonds preferably has a degree of unsaturation of 15% or more, more preferably 20% or more, even more preferably 40% or more, and preferably 90% or less, and more preferably 80% or less. The degree of unsaturation represents the ratio (%) of double bonds to repeating units of the polymer. In this embodiment, binders without olefinic unsaturated bonds can also be used in combination with the binder having olefinic unsaturated bonds as described above, as long as the effects of the present invention are not lost. The mixing ratio of the binder without olefinic unsaturated bonds to the binder having olefinic unsaturated bonds is preferably in the range of 150% by mass or less, more preferably 120% by mass or less.

[0151] By using a binder that does not contain olefinic unsaturated bonds in combination, the coating properties can be improved, but if too much is used, the strength of the active material layer will decrease. Examples of binders that do not have olefinic unsaturated bonds include thickening polysaccharides such as methylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, and xanthan gum; polyethers such as polyethylene oxide and polypropylene oxide; vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral; polyacids such as polyacrylic acid and polymethacrylic acid; metal salts of these polymers; fluorine-containing polymers such as polyvinylidene fluoride; alkane polymers such as polyethylene and polypropylene; and copolymers thereof.

[0152] When the coated carbon material of this embodiment is used in combination with the binder having olefinic unsaturated bonds as described above, the ratio of binder used in the active material layer can be reduced compared to conventional methods. Specifically, the mass ratio of the coated carbon material of this embodiment to the binder (which may, in some cases, be a mixture of a binder having unsaturated bonds and a binder without unsaturated bonds as described above) is preferably 90 / 10 or more, more preferably 95 / 5 or more, preferably 99.9 / 0.1 or less, and more preferably 99.5 / 0.5 or less, based on their respective dry mass ratios. When the proportion of binder is within the above range, a decrease in capacity and an increase in resistance can be suppressed, and the electrode plate strength is also excellent.

[0153] The negative electrode of the present embodiment is formed by dispersing the coated carbon material of the above-described present embodiment and a binder in a dispersion medium to form a slurry, and applying this slurry to a current collector. As the dispersion medium, organic solvents such as alcohol, and water can be used. A conductive agent may be further added to this slurry as desired. Examples of the conductive agent include carbon blacks such as acetylene black, Ketjen black, and furnace black, and fine powder made of Cu, Ni or alloys thereof having an average particle diameter of 1 µm or less. The addition amount of the conductive agent is preferably about 10 mass% or less with respect to the coated carbon material of the present embodiment.

[0154] As the current collector to which the slurry is applied, conventionally known ones can be used. Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil. The thickness of the current collector is preferably 4 µm or more, more preferably 6 µm or more, and preferably 30 µm or less, more preferably 20 µm or less.

[0155] After applying the slurry onto the current collector, drying is performed in dry air or an inert atmosphere at a temperature of preferably 60°C or higher, more preferably 80°C or higher, and preferably 200°C or lower, more preferably 195°C or lower, to form an active material layer. The thickness of the active material layer obtained by applying and drying the slurry is preferably 5 µm or more, more preferably 20 µm or more, still more preferably 30 µm or more, and preferably 200 µm or less, more preferably 100 µm or less, still more preferably 75 µm or less. When the thickness of the active material layer is within the above range, the negative electrode has excellent practical utility in terms of balance with the particle diameter of the coated carbon material, and sufficient Li insertion and extraction functions for high-density current values can be obtained.

[0156] The density of the coated carbon material in the active material layer varies depending on the application, but for applications that emphasize capacity, it is preferably 1.55g / cm 3 or more, more preferably 1.6g / cm 3 or more, still more preferably 1.65g / cm 3 or more, particularly preferably 1.7g / cm 3 or more. Also, it is preferably 1.9g / cm3 The following applies: When the density is within the above range, sufficient battery capacity per unit volume can be ensured, and the rate characteristics are less likely to deteriorate.

[0157] When manufacturing a negative electrode for a secondary battery using the coated carbon material of this embodiment described above, there are no particular restrictions on the method or the selection of other materials. Similarly, when manufacturing a lithium-ion secondary battery using this negative electrode, there are no particular restrictions on the selection of necessary components for the battery structure, such as the positive electrode and electrolyte. The following examples illustrate the details of the negative electrode for a lithium-ion secondary battery and the lithium-ion secondary battery using the coated carbon material of this embodiment, but the materials and manufacturing methods that can be used are not limited to the following specific examples.

[0158] <Secondary battery> The basic configuration of the secondary battery of this embodiment, particularly the lithium-ion secondary battery, is the same as that of conventionally known lithium-ion secondary batteries, and typically comprises a positive electrode and a negative electrode capable of intercalating and releasing lithium ions, as well as an electrolyte. The coated carbon material of this embodiment described above is used as the negative electrode. The positive electrode is formed by creating a positive electrode active material layer containing positive electrode active material and a binder on a current collector.

[0159] Examples of positive electrode active materials include metal chalcogen compounds that can intercept and release alkali metal cations such as lithium ions during charging and discharging. Examples of metal chalcogen compounds include transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, and tungsten oxide; vanadium sulfide, molybdenum sulfide, titanium sulfide, transition metal sulfide such as CuS; transition metal phosphorus-sulfur compounds such as NiPS3 and FePS3; transition metal selenium compounds such as VSe2 and NbSe3; and Fe 0.25 V 0.75 S2, Na 0.1 Examples include complex oxides of transition metals such as CrS2, and complex sulfides of transition metals such as LiCoS2 and LiNiS2.

[0160] Among these, V2O5 and V5O13 , VO₂, Cr₂O₅, MnO₂, TiO₂, MoV₂O₈, LiCoO₂, LiNiO₂, LiMn₂O₄, TiS₂, V₂S₅, Cr 0.25 V 0.75 S₂, Cr 0.5 V 0.5 S₂ are preferable, and particularly preferable are LiCoO₂, LiNiO₂, LiMn₂O₄, and lithium transition metal composite oxides obtained by substituting a part of the transition metals in these compounds with other metals. These positive electrode active materials may be used alone or in a mixture of two or more.

[0161] As the binder for binding the positive electrode active material, any known binder can be arbitrarily selected and used. Examples thereof include inorganic compounds such as silicate and water glass, and resins having no unsaturated bonds such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, resins having no unsaturated bonds are preferable. If a resin having an unsaturated bond is used as the resin for binding the positive electrode active material, it may be decomposed during the oxidation reaction. The weight average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more, and usually 3,000,000 or less, preferably 1,000,000 or less.

[0162] A conductive material may be contained in the positive electrode active material layer to improve the conductivity of the electrode. The conductive material is not particularly limited as long as it can impart conductivity to the active material by mixing an appropriate amount thereof, and usually includes carbon powder such as acetylene black, carbon black and graphite, fibers and powders of various metals, and metal foil. The positive electrode plate is formed by slurrying a positive electrode active material and a binder with a solvent, coating the slurry on a current collector, and drying the same in the same manner as the method for producing the negative electrode described above. As the current collector of the positive electrode, aluminum, nickel, stainless steel (SUS) or the like is used, but the current collector is not limited at all. As the electrolyte, a non-aqueous electrolyte solution obtained by dissolving a lithium salt in a non-aqueous solvent, or a product obtained by processing the non-aqueous electrolyte solution into a gel, rubber or solid sheet form with an organic polymer compound or the like is used.

[0163] The non-aqueous solvent used in the non-aqueous electrolyte is not particularly limited, and can be appropriately selected from known non-aqueous solvents that have been conventionally proposed as solvents for non-aqueous electrolytes. Examples include: linear carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; linear ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane; linear esters such as methyl formate, methyl acetate, and methyl propionate; and cyclic esters such as γ-butyrolactone and γ-valerolactone.

[0164] These non-aqueous solvents may be used individually or in mixtures of two or more. In the case of a mixed solvent, a combination of a cyclic carbonate and a linear carbonate is preferred, and it is particularly preferable that the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate, as this allows for high ionic conductivity even at low temperatures and improves low-temperature chargeability. In particular, the amount of propylene carbonate relative to the total non-aqueous solvent is preferably in the range of 2% to 80% by mass, more preferably in the range of 5% to 70% by mass, and even more preferably in the range of 10% to 60% by mass. If the proportion of propylene carbonate is lower than the above, the ionic conductivity at low temperatures decreases, and if the proportion of propylene carbonate is higher than the above, when a graphite-based electrode is used, the propylene carbonate solvated with lithium ions co-inserts between the graphite phases, causing delamination and degradation of the graphite-based negative electrode active material, resulting in a problem where sufficient capacity cannot be obtained.

[0165] The lithium salt used in the non-aqueous electrolyte is not particularly limited, and can be appropriately selected from known lithium salts that are known to be usable for this purpose. Examples include halides such as LiCl and LiBr, perhalates such as LiClO4, LiBrO4, and LiClO4, inorganic lithium salts such as inorganic fluoride salts such as LiPF6, LiBF4, and LiAsF6, perfluoroalkanesulfonates such as LiCF3SO3 and LiC4F9SO3, and fluorine-containing organic lithium salts such as perfluoroalkanesulfonate imide salts such as Li-trifluorosulfonimide ((CF3SO2)2NLi). Among these, LiClO4, LiPF6, and LiBF4 are preferred.

[0166] Lithium salts may be used alone or in mixtures of two or more types. The concentration of lithium salt in a non-aqueous electrolyte is usually in the range of 0.5 mol / L or more and 2.0 mol / L or less. Furthermore, when an organic polymer compound is added to the above-mentioned non-aqueous electrolyte and used in the form of a gel, rubber, or solid sheet, specific examples of organic polymer compounds include: polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; insoluble products of vinyl alcohol polymer compounds; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile; and polymer copolymers such as poly(ω-methoxyoligooxyethylene methacrylate), poly(ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), and poly(hexafluoropropylene-vinylidene fluoride).

[0167] The non-aqueous electrolyte described above may further contain a film-forming agent. Specific examples of film-forming agents include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methylphenyl carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propanesultone and 1,4-butanesultone; and acid anhydrides such as maleic anhydride and succinic anhydride. Furthermore, overcharge inhibitors such as diphenyl ether and cyclohexylbenzene may be added.

[0168] When using the above-mentioned additive, its content is usually 10% by mass or less, preferably 8% by mass or less, even more preferably 5% by mass or less, and especially preferably 2% by mass or less. If the content of the above-mentioned additive is too high, it may adversely affect other battery characteristics such as an increase in initial irreversible capacity and a decrease in low-temperature characteristics and rate characteristics. Furthermore, polymer solid electrolytes, which are conductors of alkali metal cations such as lithium ions, can also be used as electrolytes. Examples of polymer solid electrolytes include those obtained by dissolving lithium salts in the aforementioned polyether polymer compounds, and polymers in which the terminal hydroxyl groups of polyethers are replaced with alkoxides.

[0169] Typically, a porous separator, such as a porous membrane or nonwoven fabric, is interposed between the positive and negative electrodes to prevent short circuits. In this case, the non-aqueous electrolyte is impregnated into the porous separator. Suitable materials for the separator include polyethylene, polyolefins such as polypropylene, and polyethersulfone, with polyolefin being preferred.

[0170] The form of the secondary battery in this embodiment is not particularly limited. Examples include a cylinder type with a spiral-shaped sheet electrode and separator, an inside-out cylinder type combining a pellet electrode and separator, and a coin type with stacked pellet electrodes and separators. Furthermore, by housing these types of batteries in any outer case, they can be used in any shape such as coin-shaped, cylindrical, or rectangular.

[0171] The procedure for assembling the secondary battery of this embodiment is not particularly limited, and it can be assembled in an appropriate procedure depending on the structure of the battery. For example, the negative electrode can be placed on the outer casing, the electrolyte and separator can be placed on top of it, and then the positive electrode can be placed opposite the negative electrode, and the battery can be assembled by crimping it together with the gasket and sealing plate. [Examples]

[0172] The specific embodiments of the present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. The abbreviations used in the examples are as follows: PVOH(A): Polyvinyl alcohol with reactive substituents (saponification: 98.0-99.0 mol%, viscosity: 24.0-30.0 mPa·s (4% aqueous solution, 20℃)) PVOH(B): Polyvinyl alcohol with reactive substituents (saponification: >98.5 mol%, viscosity: 4.5~6.0 mPa·s (4% aqueous solution, 20℃))

[0173] <Fabrication of electrode sheets> Using the coated carbon material of the example or comparative example described later, the active material layer density was 1.60 ± 0.03 g / cm³. 3 An electrode plate having an active material layer was prepared. Specifically, 20.00±0.02g of coated carbon material was mixed with 20.00±0.02g (0.200g in solid content) of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt (manufactured by Nippon Paper Industries, MAC500LC) and 0.42±0.02g (0.2g in solid content) of styrene-butadiene rubber aqueous dispersion (manufactured by JSR, TRD102A), and stirred for 5 minutes in a THINKY Awatori Rentaro ARE-310, and degassed for 30 seconds to obtain a slurry.

[0174] This slurry is then applied to a 20 μm thick copper foil, which serves as the current collector, with a coating carbon material concentration of 10.00 ± 0.3 mg / cm³. 2To ensure adhesion, the material was applied in a 5cm width using an automatic coating machine (Tester Industries PI-1210) and a doctor blade, and then roll-pressed using a 20cm diameter roller to obtain an active material layer with a density of 1.60±0.03g / cm³. 3 The electrode sheet was obtained by adjusting it to achieve the desired result.

[0175] <Fabrication of a non-aqueous secondary battery (2032 coin-type battery)> The electrode sheet prepared using the above method was punched out into a 12.5 mm diameter disc shape, and a lithium metal foil was punched out into a 14 mm diameter disc shape to serve as the counter electrode. Between the two electrodes, a separator (made of porous polyethylene film) impregnated with an electrolyte solution prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3:7) was placed to fabricate 2032 coin-type batteries.

[0176] <Method for measuring initial efficiency> Using a non-aqueous secondary battery (2032 coin-type battery) prepared by the method described above, the initial efficiency during battery charging and discharging was measured using the following measurement method. A non-aqueous electrolyte secondary battery was left standing at 25°C for 24 hours. Then, it was charged to 5mV relative to the lithium counter electrode with a constant current equivalent to 0.04C at 25°C. After that, it was charged again with a constant voltage of 5mV until it reached 0.004C, and then discharged to 1.5V with a constant current of 0.08C. This was repeated three times to complete the coin cell evaluation. The initial efficiency (%) was calculated from (discharge capacity in the first cycle) ÷ (charge capacity in the first cycle) × 100.

[0177] <Specific surface area of ​​BET due to nitrogen adsorption (N2-SA)> Using a fully automated specific surface area analyzer (Mountec, MacSorb HM Model-1210), the coated carbon material sample was pre-dried at 100°C for 30 minutes under nitrogen flow, then cooled to liquid nitrogen temperature, and measured using the BET single-point method with nitrogen gas.

[0178] <BET specific surface area (Tol-SA) due to toluene adsorption> Using a differential heat of adsorption measuring apparatus (manufactured by Tokyo Rikou Co., Ltd., thermal measurement method surface analyzer CSA-25G and multi-microcalorimeter MMC-5111), a coated carbon material sample was pre-dried at 100°C for 30 minutes under nitrogen flow, and then determined at 25°C by linear regression in the range of P / P0=0.05 to 0.18 according to the BET method using toluene gas.

[0179] <BET specific surface area ratio> The ratio of BET specific surface area Tol-SA determined by toluene adsorption to BET specific surface area N2-SA determined by nitrogen adsorption (Tol-SA / N2-SA) is defined as the BET specific surface area ratio.

[0180] <Basal plane coverage> The basal plane coverage was measured by the following procedure using a differential heat of adsorption measuring apparatus (manufactured by Tokyo Rikou Co., Ltd., thermal measurement method surface analyzer CSA-25G and multi-microcalorimeter MMC-5111). First, for the carbon material before being coated with an organic compound, the adsorption isotherm and heat of adsorption were simultaneously measured using toluene gas. A carbon material surface with high affinity for toluene that exhibits a heat of adsorption of 67 kJ / mol or more is defined as the basal plane, and the specific surface area of the basal plane of the carbon material was determined from the molecular cross-sectional area of toluene and the adsorption amount of toluene on the basal plane. Next, for the coated carbon material coated with an organic compound, the adsorption isotherm and heat of adsorption were also simultaneously measured using toluene gas in the same manner, and the specific surface area of the basal plane was determined from the adsorption amount of toluene on the basal plane that exhibits a heat of adsorption of 67 kJ / mol or more. At this time, when a part of the basal plane of the raw material carbon material is coated with an organic compound, the affinity with toluene decreases and the heat of adsorption becomes smaller, so that the coated carbon material coated with the organic compound has a lower specific surface area of the basal plane compared to the raw material carbon material. The basal plane coverage was calculated by the following formula (A). Formula (A) Basal plane coverage (%) = [1 - (specific surface area of basal plane of coated carbon material) / (specific surface area of basal plane of raw material carbon material)] × 100

[0181] <Basal plane specific surface area ratio> The ratio of the basal surface specific surface area due to toluene adsorption to the BET specific surface area (Tol-SA) due to toluene adsorption (basal surface specific surface area / Tol-SA) was defined as the basal surface specific surface area ratio.

[0182] <Mass reduction rate> The mass loss rate was measured using a TG-DTA measuring device (Differential Thermogravimetric Analyzer STA300, manufactured by Hitachi High-Tech Science Corporation) according to the following procedure. Approximately 50 mg of coating carbon material was accurately weighed, placed in an alumina sample container, and heated in a nitrogen atmosphere at a heating rate of 10°C / min from 25°C to 700°C. The amount of mass loss between 200°C and 700°C was defined as the amount of coating carbon material applied. The mass reduction rate was calculated using the following formula (B). Formula (B) Mass reduction rate (%) = [Mass reduction of coated carbon material / Mass of coated carbon material before heating] × 100

[0183] <Peel strength> The peel strength was measured using a light-load type adhesive / film peel analysis device (VPA-3S, manufactured by Kyowa Interface Science Co., Ltd.) according to the following procedure. Specifically, the electrode sheet prepared by the method described above was dried at 110°C for 24 hours, then cut to 2.5 cm x 7 cm. The negative electrode side was placed facing the test plate and attached with 2 cm wide double-sided tape. The test plate was then set in the measuring device, and the edge of the electrode sheet was attached to the load cell. Peeling was performed at a peeling angle of 90° and a peeling speed of 50 mm / min, and the force required for peeling was measured.

[0184] [Example 1] As a carbon material, N2-SA is 6.3m 2Granulated spheroidal natural graphite with a particle size of 15.9 μm and a d50 of 15.9 μm was used. This graphite powder had pores inside the particles, and mercury porosimetry results showed that the pore volume in the range of 10 nm to 1500 nm was 0.14 mL / g, the total pore volume was 0.56 mL / g, and the peak of the pore size distribution was 360 nm. A mixture of 100 g of this granulated spheroidal natural graphite and 200 g of a 0.15% aqueous solution of PVOH(A) as an organic compound was heated to 125°C in a glass container while stirring with a three-one motor. After boiling the mixture for 5 minutes, it was cooled and stirred at 50°C for 1 hour, and the graphite powder was filtered off by suction filtration. After drying, it was sieved to obtain a powdered carbon coating material for the negative electrode of a non-aqueous secondary battery. For the obtained carbon coating material for the anode of a non-aqueous secondary battery, the basal surface specific surface area, Tol-SA, N2-SA, BET specific surface area ratio, basal surface coverage rate, basal surface specific surface area ratio, mass loss rate, initial efficiency, and peel strength were measured using the aforementioned measurement method. The results are shown in Table 1.

[0185] [Example 2] A carbon coating material for a negative electrode of a non-aqueous secondary battery was obtained in the same manner as in Example 1, except that a 0.2% aqueous solution of PVOH(B) was used instead of the 0.15% aqueous solution of PVOH(A) used in Example 1 described above. The basal surface specific surface area, Tol-SA, N2-SA, BET specific surface area ratio, basal surface coverage rate, basal surface specific surface area ratio, mass loss rate, initial efficiency, and peel strength of the obtained carbon coating material for a negative electrode of a non-aqueous secondary battery were measured using the measurement method described above. The results are shown in Table 1.

[0186] [Example 3] A coating carbon material for a negative electrode of a non-aqueous secondary battery was obtained in the same manner as in Example 1, except that a 0.25% aqueous solution of PVOH(B) was used instead of the 0.15% aqueous solution of PVOH(A) used in Example 1 described above. The basal surface specific surface area, Tol-SA, N2-SA, BET specific surface area ratio, basal surface coverage rate, basal surface specific surface area ratio, mass loss rate, initial efficiency, and peel strength of the obtained coating carbon material for a negative electrode of a non-aqueous secondary battery were measured using the measurement method described above. The results are shown in Table 1.

[0187] [Comparative Example 1] The N2-SA used in Example 1 was 6.3 m2 Granulated spheroidized natural graphite having a d50 of 15.9 µm was used as a carbon material for a non-aqueous secondary battery negative electrode. The basal plane specific surface area, Tol-SA, N2-SA, BET specific surface area ratio, basal plane coverage, basal plane specific surface area ratio, mass reduction rate, initial efficiency, and peel strength were measured by the aforementioned measurement method. The results are shown in Table 1.

[0188] Comparative Example 2 A coated carbon material for a non-aqueous secondary battery negative electrode was obtained in the same manner as in Example 1, except that a 0.5% aqueous solution of PVOH(B) was used instead of the 0.15% aqueous solution of PVOH(A) used in Example 1 above. For the obtained coated carbon material for a non-aqueous secondary battery negative electrode, the basal plane specific surface area, Tol-SA, N2-SA, BET specific surface area ratio, basal plane coverage, basal plane specific surface area ratio, mass reduction rate, initial efficiency, and peel strength were measured by the aforementioned measurement method. The results are shown in Table 1.

[0189] Table 1

[0190] Compared to Comparative Example 1 in which no organic compound coating was performed, the coated carbon materials of Examples 1, 2 and 3 were able to reduce the specific surface area with a smaller coating amount, and exhibited high initial efficiency by effectively suppressing side reactions with the electrolyte solution.

[0191] On the other hand, the coated carbon material of Comparative Example 2, in which graphite particles were coated with an excessive amount of organic compound, had poor peel strength of the negative electrode plate. Industrial Applicability

[0192] By using the coated carbon material of the present invention as an active material for a negative electrode of a secondary battery, a lithium ion secondary battery having excellent initial efficiency and high peel strength can be provided. Description of Reference Numerals

[0193] 1 Carbon material 2 Coating material

Claims

1. A coated carbon material in which an organic compound is coated onto a carbon material, wherein the BET specific surface area Tol-SA is obtained by toluene adsorption and the BET specific surface area N is obtained by nitrogen adsorption. ２ -SA ratio Tol-SA / N ２ -SA is between 0.70 and 0.

95. The pore volume of the carbon material in the range of 10 nm to 1500 nm is 0.05 mL / g or more. A carbon coating material for secondary batteries with a concentration of 3 mL / g.

2. A coated carbon material in which an organic compound is coated onto a carbon material, wherein the BET specific surface area Tol-SA is obtained by toluene adsorption and the BET specific surface area N is obtained by nitrogen adsorption. ２ -SA ratio Tol-SA / N ２ -SA is between 0.70 and 0.

95. The pore volume of the coated carbon material in the range of 10 nm to 1500 nm is 0.03 mL / g or less. The carbon coating material for secondary batteries has a concentration of 0.3 mL / g.

3. A coated carbon material for a secondary battery according to claim 1 or 2, wherein a carbon material is coated with an organic compound, and the coating rate of the basal surface of the carbon material is 30% to 90%.

4. A coated carbon material for secondary batteries according to any one of claims 1 to 3, wherein the specific basal surface area / Tol-SA ratio of the basal surface specific surface area due to toluene adsorption to the BET specific surface area due to toluene adsorption is 0.15 to 0.

65.

5. A coated carbon material for secondary batteries according to any one of claims 1 to 4, wherein the carbon material is coated with an organic compound, and the mass loss rate from 200°C to 700°C, as measured by TG-DTA, is 0.10% by mass to 0.42% by mass.

6. The carbon coating material for a secondary battery according to any one of claims 1 to 5, wherein the carbon material is graphite.

7. The carbon coating material for secondary batteries according to any one of claims 1 to 6, wherein the organic compound includes a compound derived from polyvinyl alcohol resin.

8. The carbon coating material for secondary batteries according to claim 7, wherein the compound derived from the polyvinyl alcohol resin contains a reactive substituent.

9. The carbon coating material for secondary batteries according to claim 8, wherein the reactive substituent comprises at least one substituent selected from a hydroxyl group, a carboxyl group, a carbonyl group, an acetyl group, a (meth)acrylic group, an epoxy group, a vinyl group, a hydrolyzable silyl group, a silanol group, and a hydrosilyl group.

10. A negative electrode comprising a current collector and an active material layer formed on the current collector, wherein the active material layer comprises a coating carbon material for a secondary battery as described in any one of claims 1 to 9.

11. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode described in claim 10.

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