Coated carbon material, negative electrode, and secondary battery

Abstract

The present invention takes the relevant background of the invention into account and addresses the problem of providing a coated carbon material which makes it possible to obtain a secondary battery which has excellent initial efficiency while maintaining capacity in comparison to the prior art, and as a result thereof, also providing a high-performance secondary battery. A coated carbon material obtained by coating a carbon material with a coating film, wherein the coating film contains one or more crosslinked substances selected from the crosslinked substances of a compound represented by (X) and a compound group represented by (Y). (X): acetoacetyl group-containing resin (Y): polyvinyl alcohol resin and silicon atom-containing compound

Description

[Technical Field]

[0001] This invention relates to a coated carbon material, a negative electrode using the coated carbon material, a secondary battery equipped with the negative electrode, and a method for manufacturing the coated carbon material. [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 achieve a capacity close to the theoretical lithium storage capacity of graphite, which is 372 mAh / g, and it is also excellent in terms of cost and durability. On the other hand, when the density of the active material layer containing the negative electrode material is increased in order to increase capacity, problems such as an increase in the irreversible charge / discharge capacity during the initial cycle, a decrease in high-current charge / discharge characteristics, and a decrease in cycle characteristics occur due to material fracture and deformation.

[0004] Furthermore, when the above-mentioned carbon materials are used as active materials for the negative electrode of 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. However, although the spheroidized natural graphite disclosed in Patent Document 1 can be obtained with high capacity and good rapid charge-discharge characteristics, excessive decomposition of the electrolyte occurs, resulting in insufficient initial irreversible capacity and charge-discharge cycle characteristics, as well as a large amount of by-reaction product gases, and further improvements were needed.

[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] Patent No. 3534391 [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 Initiative] [Problems that the invention aims to solve]

[0010] However, according to our research, while the spheroidized natural graphite disclosed in Patent Document 1 can be obtained with high capacity and good rapid charge-discharge characteristics, excessive decomposition of the non-aqueous electrolyte occurs, resulting in insufficient initial charge-discharge efficiency and charge-discharge cycle characteristics, as well as a large amount of by-reaction product gases, requiring further improvement. Furthermore, when carbon materials are coated with ion-conducting polymers or water-soluble polymers disclosed in Patent Document 2, the adhesion to the carbon material is insufficient, and the polymers swell in the electrolyte. As a result, when such carbon materials are used as negative electrode active materials, the initial charge-discharge efficiency, charge-discharge cycle characteristics, and stability are still insufficient.

[0011] In the carbon material in which a polymer is attached to a carbon material as disclosed in Patent Document 3, although the initial charge-discharge efficiency and stability are improved by improving the adhesion between the polymer and the carbon material, it has become clear that the low-temperature input / output characteristics are insufficient because the Li ion insertion and deinsertion sites are excessively covered, and the ionic conductivity of the polymer used is also insufficient.

[0012] In the technology described in Patent Document 4, the coating boron elutes and the polyvinyl alcohol swells, leading to an increase in slurry viscosity and reduced coatability, resulting in insufficient improvement of initial efficiency.

[0013] 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 superior initial efficiency while maintaining capacity compared to the conventional technology, and as a result, to provide a high-performance secondary battery. [Means for solving the problem]

[0014] As a result of diligent research to solve the aforementioned problems, the inventors have found that a coated carbon material having a specific film formed on its surface, a negative electrode using the coated carbon material, and a secondary battery equipped with the negative electrode can solve the above problems, and have completed the present invention.

[0015] The inventors believe the reason why the coated carbon material according to the present invention exhibits the above-mentioned effects is as follows. In other words, the inventors believe it is important that the coating applied to the carbon material satisfies at least one of the following conditions (1) and (2). Condition (1): The coating contains an acetoacetyl group-containing resin. The resin, which has an acetoacetyl group as a self-crosslinking group, crosslinks on the surface of the coated carbon material, suppressing swelling and elution of the resin. This is thought to have resulted in significant improvements in slurry properties and increased initial efficiency due to the suppression of side reactions with the electrolyte by efficient coating. Condition (2): The coating contains a crosslinked product of a polyvinyl alcohol-based resin and a silicon-containing compound. The silicon-containing compound, acting as a crosslinking agent along with the polyvinyl alcohol-based resin, crosslinks on the surface of the coated carbon material, suppressing polymer swelling and elution. This is thought to have significantly improved slurry properties and increased initial efficiency due to the suppression of side reactions with the electrolyte through efficient coating. Furthermore, if the coating also contains a boron-containing compound (also simply called a boron compound), the crosslinked structure on the surface of the coated carbon material suppresses the elution of the boron compound, which is thought to have further significantly improved the effect.

[0016] In other words, the gist of this invention is as follows. [1] A coated carbon material in which a carbon material is coated with a film, A coated carbon material wherein the coating comprises at least one selected from the compounds (X) and crosslinked compounds of the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound [2] The coated carbon material according to [1], wherein the carbon material is graphite. [3] The coated carbon material according to [1] or [2], wherein the coating is applied to the basal surface of the carbon material. [4] The coated carbon material according to any one of [1] to [3], wherein the coating comprises the compound of (X) above. [5] The coated carbon material according to [4], wherein the acetoacetyl group-containing resin contains a hydroxyl group. [6] The coated carbon material according to [4] or [5], wherein the acetoacetyl group-containing resin is a polyvinyl alcohol-based resin containing an acetoacetyl group. [7] The coated carbon material according to any one of [1] to [3], wherein the coating comprises a crosslinked compound of the group of compounds (Y) described above. [8] The coated carbon material according to [7], wherein the polyvinyl alcohol-based resin comprises an acetoacetyl group. [9] The coated carbon material according to [7] or [8], wherein the coating further comprises a boron-containing compound.

[10] The coated carbon material according to [9], wherein the boron element-containing compound is at least one compound selected from boron oxide, metaboric acid, tetraboric acid, borate, and alkoxide having 1 to 3 carbon atoms bonded to boron.

[11] A method for manufacturing a coated carbon material in which a carbon material is coated with a film, A method for producing a coated carbon material, comprising the step of mixing a carbon material with the compound (X) and / or the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound

[12] comprising a current collector and an active material layer formed on the current collector, A negative electrode comprising the active material layer containing the coated carbon material described in any of [1] to

[10] .

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

[12] . [Effects of the Invention]

[0017] By using the coated carbon material of the present invention as a negative electrode active material for a secondary battery, it is possible to provide a secondary battery that maintains capacity while exhibiting excellent initial efficiency. [Modes for carrying out the invention]

[0018] 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.

[0019] <Coated carbon material> One embodiment of the present invention is a coated carbon material (which may also be called a negative electrode material) that is a coated carbon material capable of intercepting and releasing lithium ions, A coated carbon material in which a carbon material is coated with a film, The coating (also simply referred to as "film") is a coated carbon material that includes at least one selected from the compounds (X) and crosslinked compounds of the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound The above coating may be a coating comprising at least one film selected from a film containing the compound (X) and a film containing a crosslinked compound of the group of compounds (Y) (it may also be a coating made of such films). Furthermore, the above coating may or may not contain components other than the compound (X) and the crosslinked compound of the group of compounds (Y), may consist only of the compound (X), may consist only of a crosslinked compound of the group of compounds (Y), or may be a laminated film of a film containing the compound (X) and a film containing a crosslinked compound of the group of compounds (Y).

[0020] Examples of carbon materials include graphite, amorphous carbon, or 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.

[0021] 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. 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, or imide resin.

[0022] 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. 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.

[0023] For example, an apparatus can be used for the spheroidization process that repeatedly applies mechanical forces to the particles, such as compression, friction, or shear force, primarily through impact force, but also including the interaction of graphite carbonaceous particles. 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, or 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.

[0024] Preferred devices for applying mechanical action to carbon 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), or theta composers (manufactured by Tokuju Kogyo Co., Ltd.). Among these, the hybridization system manufactured by Nara Machine Works Co., Ltd. is preferred.

[0025] 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 carbon material simply by passing graphite through it, 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. Examples of amorphous carbon include particles obtained by calcining bulk mesophase, and particles obtained by infusibility treatment of carbon precursors followed by calcination.

[0026] Carbonaceous materials with a low degree of graphitization include organic materials that have been calcined at temperatures typically below 2500°C. Examples of organic materials include coal-based heavy oils such as coal tar pitch and carbonized liquefied oil; straight-run heavy oils such as atmospheric residue and vacuum residue; petroleum-based heavy oils such as crude oil and decomposition heavy oils such as ethylene tar produced as a by-product during the thermal decomposition of naphtha; aromatic hydrocarbons such as acenaphthylene, decacycline, and anthracene; nitrogen-containing cyclic compounds such as phenazine and acridine; sulfur-containing cyclic compounds such as thiophene; aliphatic cyclic compounds such as adamantane; polyphenylenes such as biphenyl and terphenyl; polyvinyl esters such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral; and thermoplastic polymers such as polyvinyl alcohol.

[0027] Depending on the degree of graphitization of the carbonaceous material, the firing temperature can be 600°C or higher, preferably 900°C or higher, more preferably 950°C or higher, and can also be less than 2500°C, preferably 2000°C or lower, more preferably 1400°C or lower. During firing, it is also possible to mix organic materials with acids such as phosphoric acid, boric acid, and hydrochloric acid, as well as alkalis such as sodium hydroxide.

[0028] As a carbon material, particles coated with amorphous carbon and / or graphitic material with a low degree of graphitization can also be used, which are natural graphite or artificial graphite as described above. The carbon materials that make up the carbon material can also be used in combination with one or more other carbon materials.

[0029] The carbon material may contain a Si-containing compound, and examples of Si-containing compounds include a negative electrode active material containing a composite oxide phase containing lithium silicate and silicon particles dispersed in the composite oxide phase.

[0030] <Physical properties of carbon materials> The following describes the desirable characteristics of the carbon material used as the raw material. Hereinafter, the carbon material of this embodiment may be referred to as "carbon material" or simply "carbon material" as appropriate.

[0031] • 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 and the loss of initial battery capacity of the secondary battery (especially a non-aqueous secondary battery) obtained using the carbon material, and to suppress the occurrence of process problems such as striking in slurry coating, a decrease in high current density charge / discharge characteristics, and a decrease in low temperature input / output characteristics.

[0032] 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.

[0033] • 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 secondary batteries (especially non-aqueous secondary batteries). 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) / (Actual perimeter of the particle projection)

[0034] As the circularity value, for example, using a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Co., Ltd.), about 0.2 g of a sample (carbon material) is dispersed in a 0.2 mass% aqueous solution (about 50 mL) of polyoxyethylene (20) sorbitan monolaurate which is a surfactant, and after irradiating the dispersion with ultrasonic waves of 28 kHz at an output of 60 W for 1 minute, the detection range is specified to 0.6 to 400 μm, and the value measured for particles in the range of particle diameters of 1.5 to 40 μm is used.

[0035] The method for improving the circularity is not particularly limited, but it is preferable to perform a spheroidization treatment to make it spherical because the shape of the inter-particle voids when used as the negative electrode becomes regular. Examples of the spheroidization treatment include a method of mechanically approaching a spherical shape by applying a shearing force and a compressive force, a mechanical and physical treatment method of granulating a plurality of carbon material fine particles by the adhesive force of a binder or the particles themselves, etc.

[0036] · Tap density The tap density of the carbon material of this 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, 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.

[0037] When the tap density is within the above range, the processability such as streak formation during the production of the electrode plate becomes good and the high-rate charge and discharge characteristics are excellent. Also, since it is difficult for the carbon density inside the particles to increase, the rolling property is good, and it tends to be easy to form a high-density negative electrode sheet. The tap density is measured using a powder density measuring instrument, with a diameter of 1.6 cm and a volume capacity of 20 cm 3The 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.

[0038] X-ray parameters The d-value (interlayer distance) of the lattice plane (002 plane) of the carbon material in 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. Here, the d-value is 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 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 are not excessively crystallin, and the reversible capacity is less likely to decrease when used in a secondary battery (especially a non-aqueous secondary battery). Note that the lower limit of Lc is the theoretical value for graphite.

[0039] ·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. When 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, especially in the case of secondary batteries (particularly non-aqueous secondary batteries). Furthermore, since the production of the carbon material does not require a great deal of time, energy, or equipment for preventing pollution, the increase in costs can also be kept down.

[0040] ·BET specific surface area (SA) The specific surface area (SA) of the carbon material of this embodiment, as measured by the BET method, is preferably 2 m². 2 / g or more, more preferably 2.4m 2 / g or more, more preferably 2.6m 2 / g or more, particularly preferably 2.8m 2 / g or more, most preferably 3.0m 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.

[0041] 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 characteristics and output performance. 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 secondary battery (especially a non-aqueous secondary battery).

[0042] The BET specific surface area is defined as the value measured using a surface area meter (e.g., Mountec Macsorb HM Model-1210), after pre-drying a carbon material sample under reduced pressure at 100°C for 30 minutes under a nitrogen flow, cooling to liquid nitrogen temperature, and then using nitrogen gas to measure the BET single-point nitrogen adsorption method.

[0043] • Pore volume in the range of 10 nm to 1000 nm In the carbon material of this embodiment, the pore volume in the range of 10 nm to 1000 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.

[0044] If the pore volume in the range of 10 nm to 1000 nm is within the above range, the amount of voids into which the electrolyte (especially 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 during rapid charging and discharging, resulting in the deposition of lithium metal and deterioration of cycle characteristics, can be better avoided. Furthermore, the binder is less likely to be absorbed into the voids during electrode fabrication, which can better avoid the tendency for electrode strength to decrease and initial efficiency to decrease.

[0045] 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 more easily obtained during electrode plate formation.

[0046] Furthermore, the average pore size 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 0.5 μm or more. The average pore size is preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 20 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.

[0047] 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).

[0048] 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%.

[0049] ·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. 3 The 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 in the case of a secondary battery (especially a non-aqueous secondary battery), the increase in its initial irreversible capacity tends to be suppressed.

[0050] Aspect ratio The aspect ratio of the carbon material in powder form in this embodiment is theoretically 1 or greater, preferably 1.1 or greater, and 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 formation, resulting in a uniform coating surface and a tendency to avoid a decrease in the high current density charge-discharge characteristics of secondary batteries (especially non-aqueous secondary batteries).

[0051] The aspect ratio is expressed as A / B, where A is the longest diameter of the carbon material particles (carbon material) 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.

[0052] ·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. 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.

[0053] • 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 aforementioned Raman R value 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.

[0054] When the Raman R value is within the above range, the crystallinity of the carbon material particle (carbon material) surface is less likely to increase, and when the density is increased, the crystals are less likely to orient in a direction 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 charge / discharge efficiency and an increase in gas generation in secondary batteries (especially non-aqueous secondary batteries). 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)

[0055] ·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.

[0056] 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. Furthermore, DBP oil absorption 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.

[0057] ·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, 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, even more preferably 10 μm or more, particularly preferably 11 μm or more, and most preferably 13 μm or more.

[0058] 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, and preventing a decrease in electrode strength and initial charge / discharge efficiency in secondary batteries (especially non-aqueous secondary batteries). 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%.

[0059] ·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 26 μm or more, even more preferably 30 μm or more, and particularly preferably 34 μm or more.

[0060] 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 (especially non-aqueous 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%.

[0061] <Resin> (X) Acetoacetyl group-containing resin When the coating according to this embodiment contains the acetoacetyl group-containing resin described in (X) above, the compound of this acetoacetyl group-containing resin may be a single compound or a mixture of two or more compounds. By using the acetoacetyl group-containing resin, it is possible to obtain a coated carbon material that can produce a secondary battery with maintained capacity compared to the conventional technology. Furthermore, a preferred structure for the acetoacetyl group-containing resin according to (X) of this embodiment is preferably one structure selected from the group consisting of a linear structure, a graft structure, a star structure, and a three-dimensional network structure. The acetoacetyl group-containing resin may have functional groups other than the acetoacetyl group, and it is preferable that it has hydroxyl groups (especially alcoholic hydroxyl groups) because they can form covalent bonds that have high reaction activity and excellent water resistance and solvent resistance. Note that since there may be overlaps between the crosslinked compounds of compound (X) and the compound group (Y), the compound (X) may be treated as excluding the crosslinked compounds of the compound group (Y). Examples of cases where such overlap occurs include when the polyvinyl alcohol-based resin of (Y) is an acetoacetyl group-containing resin.

[0062] In order to improve the resistance of the active material for the negative electrode of a secondary battery (especially the active material for the negative electrode of a non-aqueous secondary battery) to the electrolyte and to prevent the coating carbon material from dissolving into the electrolyte, it is preferable that the acetoacetyl group-containing resin is poorly soluble in the electrolyte (non-aqueous electrolyte). However, in this embodiment, even if the acetoacetyl group-containing resin is soluble in the electrolyte (especially the non-aqueous electrolyte), it can be made poorly soluble in the electrolyte by reaction curing with the crosslinking agent. Poor solubility in the electrolyte (non-aqueous electrolyte) means that when the acetoacetyl group-containing resin is immersed in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio of 3:7) at a mass ratio of 1:50 (acetoacetyl group-containing resin:solvent) at 60°C for 5 hours, the dry mass loss before and after immersion is 10% by mass or less.

[0063] The resin of the resin portion of the acetoacetyl group-containing resin according to (X) of this embodiment, excluding the acetoacetyl group, is not particularly limited. Specifically, polyol resins such as polyvinyl alcohol resins, acrylic polyol resins, polyester polyol resins, or polyether polyol resins, silicone resins, epoxy resins, acrylic resins having hydrolyzable silyl groups, or polyester resins are preferred, polyvinyl alcohol resins, acrylic polyol resins, polyester polyol resins, acrylic resins having hydrolyzable silyl groups, or polyester resins are more preferred, and polyvinyl alcohol resins, acrylic polyol resins, or polyester polyol resins are particularly preferred. Polyvinyl alcohol resins (for example, polyvinyl alcohol resins) are most preferred because they have excellent solvent resistance in cured products.

[0064] Polyvinyl alcohol-based resin in (Y) When the coating according to this embodiment includes a crosslinked product of the polyvinyl alcohol-based resin (Y) and a silicon-containing compound, the polyvinyl alcohol-based resin may be a single compound or a mixture of two or more compounds. Furthermore, a preferred structure for the polyvinyl alcohol-based resin according to (Y) in this embodiment is preferably one structure selected from the group consisting of a linear structure, a graft structure, a star structure, and a three-dimensional network structure. Polyvinyl alcohol-based resins may have substituents. These functional groups are preferably reactive substituents. While there are no particular limitations on the reactive substituents, alcoholic hydroxyl groups, carboxyl groups, carbonyl groups, (meth)acrylic groups, epoxy groups, vinyl groups, hydrolyzable silyl groups, silanol groups, hydrosilyl groups, or acetoacetyl 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. More preferably, alcoholic hydroxyl groups, carboxyl groups, carbonyl groups, hydrolyzable silyl groups, silanol groups, or acetoacetyl groups are preferred, even more preferably, alcoholic hydroxyl groups, acetoacetyl groups are particularly preferred, and acetoacetyl groups are most preferred. The substituted functional group may be one type or two or more types.

[0065] Polyvinyl alcohol-based resins are more preferably poorly soluble in electrolytes (especially non-aqueous electrolytes) because they improve the resistance of the active material for secondary battery negative electrodes (especially active material for non-aqueous secondary battery negative electrodes) to the electrolyte and make it less likely for the coating carbon material to dissolve into the electrolyte. However, in this embodiment, even if the polyvinyl alcohol-based resin is soluble in the electrolyte (non-aqueous electrolyte), it can be made poorly soluble in the electrolyte by reaction curing with a crosslinking agent. Poor solubility in electrolytes (especially non-aqueous electrolytes) means that when the polyvinyl alcohol-based resin, or the cured product obtained by the reaction of the resin and a silicon-containing compound as a crosslinking agent, is immersed in a mixed solvent of ethyl carbonate and ethyl methyl carbonate (volume ratio of 3:7) at 60°C for 5 hours, the dry mass loss rate before and after immersion is 10% by mass or less.

[0066] The film containing the crosslinked compound of (Y) in this embodiment may or may not have a structure derived from a resin other than polyvinyl alcohol-based resin (another resin). Specific examples of other resins are not particularly limited, but they are polyol-based resins such as acrylic polyol resin, polyester polyol resin, or polyether polyol resin, which have multiple hydroxyl groups in their molecule or groups that hydrolyze to form hydroxyl groups, and can react with the crosslinking agent to form a film that is poorly soluble in water or electrolyte. Therefore, acrylic polyol resin, polyester polyol resin, acrylic resin having hydrolyzable silyl groups, or polyester resin are preferred, acrylic polyol resin, polyester polyol resin, acrylic resin having hydrolyzable silyl groups, or polyester resin are more preferred, and acrylic polyol resin or polyester polyol resin is particularly preferred.

[0067] • Polyvinyl alcohol-based (PVOH-based) resins Polyvinyl alcohol-based resins (hereinafter sometimes referred to as PVOH-based resins) are not particularly limited in their specific structure as long as they have vinyl alcohol structural units. Typically, they are obtained by saponifying polycarboxylate vinyl esters, which are polymerized vinyl carboxylate monomers such as vinyl acetate, but are not limited to these.

[0068] 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.

[0069] 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, or α-octadecene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, or 5-hexen-1-ol, or derivatives such as their acylated products; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, or undecylenic acid, or their salts; monoesters or dialkyl esters; and diacetone. Examples include amides such as acrylamide, acrylamide, or methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, or methallyl sulfonic acid or their salts; substituted vinyl acetates such as isopropenyl acetate or 1-methoxyvinyl acetate; or allyl ethers having a poly(oxyalkylene) group, such as polyethylene glycol allyl ether, methoxypolyethylene glycol allyl ether, polypropylene glycol allyl ether, or polyethylene glycol-polypropylene glycol allyl ether; and so on.

[0070] 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, or glycerol monoallyl ether; or 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, or 1,3-dibutyronyloxy-2-methylenepropane.

[0071] Methods for post-modification of post-modified PVOH-based resins include esterification, acetalization, urethaneization, etherization, grafting, phosphate esterification, or oxyalkyleneization of unmodified PVOH or the above-mentioned modified PVOH-based resin.

[0072] 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 self-crosslinking in the case of (X) above, or sparingly soluble by a crosslinking agent in the case of (Y) above, and can be suitably used as a carbon material coating. As a result, in the case of unmodified PVOH, it becomes possible to use a partially saponified product that has good wettability to the hydrophobic surface of graphite and does not easily increase in viscosity of the aqueous solution even at low temperatures. Furthermore, in the case of modified PVOH, it becomes 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, or PVOH containing nonionic modified groups having hydroxyalkyl groups or oxyethylene groups, thereby reducing the resistance of the coating.

[0073] 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%.

[0074] 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.

[0075] 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 especially preferably 300 to 2600. In the case of PVOH-based resins having a modifying group, the average degree of polymerization is usually 100 or higher, preferably 200 or higher, and more preferably 250 or higher. Keeping it within this range makes it easier to prevent the solubility from becoming too high. Also, it is usually 4000 or lower, preferably 3500 or lower, and more preferably 2800 or lower. 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).

[0076] 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.

[0077] <Crosslinking agent> When the coating according to this embodiment has a film derived from a silicon-containing compound as a crosslinking agent as described in (Y) above, this silicon-containing compound is not particularly limited, but will be explained using a crosslinked product (coating) of an acetoacetyl group-containing PVOH resin and a crosslinking agent as an example. 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.

[0078] There are no particular limitations on the type of silicon-containing compound used as a crosslinking agent in the crosslinking agent treatment. For example, from the viewpoint of forming a coating with excellent water resistance and solvent resistance, components having a three-dimensional siloxane crosslink structure derived from alkoxysilanes and / or hydrolyzed polycondensates of their low-level condensates are recommended. In addition to the silicon-containing compounds mentioned above, other crosslinking agents (other crosslinking agents) may or may not be used as crosslinking agents. Specific examples of other crosslinking agents include those known as crosslinking agents for PVOH-based resins having carboxyl groups, acetoacetyl groups, etc. For example, monoaldehyde compounds such as formaldehyde or acetaldehyde; aldehyde compounds such as polyhydric aldehyde compounds such as glyoxal, glutaraldehyde, or dialdehyde starch; metaxylenediamine, norbornanediamine, 1,3-bisaminomethylcyclohexane, bisaminopropylpiperazine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane Minodiphenylmethane, 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-phenyl Amine compounds such as diamine, 4-methyl-1,2-phenylenediamine, 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, or 2-chloro-1,4-phenylenediamine; methylol compounds such as methylolated urea or methylolated melamine; reaction products of ammonia and formaldehyde such as hexamethylenetetramine; boron compounds such as boric acid or borax; zirconium compounds such as basic zirconyl chloride, zirconyl nitrate, or zirconium ammonium acetate; titanium orthoesters such as tetramethyl titanate; titanium chelates such as titanium ethyl acetoacetonate; titanium compounds such as titanium acylates such as polyhydroxytitanium stearate;Examples include aluminum compounds such as aluminum organic acid chelates like aluminum acetylacetonate; 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, or trimethylolpropane triglycidyl ether; or various isocyanate compounds, or polyamide polyamine-epihalohydrin resins such as polyamide polyamine-epichlorohydrin resins.

[0079] The content of such crosslinking agent (especially silicon-containing compounds) is preferably 0.05 to 50 parts by mass, more preferably 0.5 to 35 parts by mass, and particularly preferably 1 to 25 parts by mass, as solid content per 100 parts by mass of PVOH-based 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.

[0080] 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.

[0081] PVOH-based resins may be obtained using commercially available materials or by synthesis. If synthesized, they can be produced using known methods.

[0082] <Components with a three-dimensional cross-linked structure> When the coating according to this embodiment has a film derived from a silicon-containing compound as a crosslinking agent as described in (Y) above, it is preferable that the coating on the surface and / or inside the coated carbon material contains a component having a three-dimensional crosslink structure, and it is more preferable that it contains a component having a three-dimensional siloxane crosslink structure derived from an alkoxysilane and / or a hydrolyzed polycondensate of its low-level condensate. 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 be suppressed.

[0083] 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.

[0084] The three-dimensional siloxane crosslinked structure is derived from hydrolyzed polycondensates of alkoxysilanes and / or their low-level condensates, and has T units and / or Q units as constituent units. A T unit represents a unit in which three oxygen atoms are bonded to a Si atom, and a Q unit represents a unit in which four oxygen atoms are bonded to a Si atom. Alkoxysilanes may also contain units other than T and Q units, such as M units in which one oxygen atom is bonded to a Si atom, and D units in which two oxygen atoms are bonded to a Si atom.

[0085] In alkoxysilanes and / or their low condensates, the T unit is usually 0 mol% or more, and usually 20 mol% or less, preferably 10 mol% or less, and particularly preferably 5 mol% or less. In addition, in alkoxysilanes and / or their low condensates, the Q unit is usually 80 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more, and usually 100 mol% or less. Furthermore, in alkoxysilanes and / or their low condensates, the total amount of T units and Q units is usually 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and usually 100 mol% or less.

[0086] Alkoxysilanes are not particularly limited as long as they are silanes having an alkoxy group. Examples of alkoxy groups include aliphatic alkoxy groups having 1 to 10 carbon atoms, such as methoxy, ethoxy, propoxy, and butoxy groups, and aromatic alkoxy groups having 6 to 15 carbon atoms, such as phenoxy and aryloxy groups. Aliphatic alkoxy groups having 1 to 4 carbon atoms are preferred because they allow for easier control of the hydrolysis reaction.

[0087] Examples of alkoxysilanes include monoalkoxysilanes, dialkoxysilanes, trialkoxysilanes, or tetraalkoxysilanes. More specifically, examples include monoalkoxysilanes such as vinyldimethylethoxysilane; dialkyldialkoxysilanes such as dimethyldimethoxysilane; diaryldialkoxysilanes; amino group-containing dialkoxysilanes such as 3-aminopropylmethyldimethoxysilane or 3-[N-(2-aminoethyl)amino]propylmethyldimethoxysilane; mercapto group-containing dialkoxysilanes such as 3-mercaptopropylmethyldimethoxysilane; (meth)acryloyl group-containing dialkoxysilanes such as 3-(meth)acryloxypropylmethyldimethoxysilane; alkenyl group-containing dialkoxysilanes such as vinyldimethoxymethylsilane or vinylmethyldiethoxysilane; or epoxy group-containing dialkoxysilanes such as 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, or 3-glycidyloxypropylethyldiethoxysilane.

[0088] Furthermore, trialkoxysilanes having a hydrosilyl group such as trimethoxysilane; alkyltrialkoxysilanes such as methyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, or ethyltriethoxysilane; aryltrialkoxysilanes such as phenyltrimethoxysilane or phenyltriethoxysilane; trialkoxysilanes containing a mercapto group such as 3-mercaptopropyltrimethoxysilane; trialkoxysilanes containing an alkenyl group such as vinyltrimethoxysilane; 2-(meth)acryloxyethyltrimethoxysilane, or 2-(meth)acryloxyethyltriethoxysilane Examples of trialkoxysilanes include (meth)acryloyl group-containing trialkoxysilanes such as lan; (glycidyloxyalkyl)trialkoxysilanes (for example, epoxy group-containing trialkoxysilanes such as 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane; or trialkoxysilanes having an isocyanate group such as γ-isocyanopropyltrimethoxysilane or γ-isocyanopropyltriethoxysilane).

[0089] Furthermore, examples include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, or tetrabutoxysilane.

[0090] Among these, when used as a composite coating with a PVOH-based resin, the three-dimensional siloxane crosslinking structure becomes highly crosslinked, resulting in a greater effect in suppressing swelling and dissolution of the coating. Therefore, tetraalkoxysilane or trialkoxysilane is preferred, with tetraalkoxysilane being more preferred. Furthermore, if flexibility is desired in the resulting composite coating, the proportion of trialkoxysilane may be increased. These alkoxysilanes may be used individually or in combination of two or more.

[0091] From the perspective that the objective of this embodiment is to introduce a three-dimensional crosslinked structure, and more specifically, to suppress the solubility and swelling of PVOH-based resin coatings by introducing a three-dimensional siloxane crosslinked structure, it is preferable that the low crosslinking component, monoalkoxysilane or dialkoxysilane, is used as an additive to impart functionality such as flexibility and lithium-ion conductivity, and is used in the minimum amount necessary so as not to promote the dissolution or swelling of the PVOH-based resin component in the composite particles.

[0092] Alkoxysilanes and / or their low-level condensates undergo hydrolysis in a solvent to form a three-dimensional siloxane crosslinked structure as hydrolyzed polycondensates. Here, "low-level condensates" refers to oligomers of approximately 2 to 10 alpha-mers of alkoxysilane, which may be oligomers of approximately 2 to 8 alpha-mers, or oligomers of approximately 2 to 5 alpha-mers. Typically, lower alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, or propanol, or mixtures thereof with water, are used as solvents.

[0093] The component having a three-dimensional crosslinked structure contained in the coated carbon material of this embodiment, more specifically, the component having a three-dimensional siloxane crosslinked structure, has a Si content of 0.01% by mass or more, preferably 0.05% by mass or more, and preferably 50% by mass or less, and preferably 20% by mass or less, in terms of SiO2 equivalent, relative to the total mass of the coated carbon material. The Si content relative to the total mass of the coated carbon material will be explained in the section describing the coating amount of the coated carbon material, which will be described later. By including components having a three-dimensional crosslinked structure within the above range, more specifically, components having a three-dimensional siloxane crosslinked structure, in the coated carbon material particles, the dissolution of PVOH-based resins contained in the coating of the coated carbon material into water is restricted, preventing thickening of the water slurry during electrode coating and clogging during the slurry filtration process. Furthermore, when boric acid is used in combination to reduce coating resistance, the elution of boric acid from the coating is suppressed, allowing low resistance to be maintained over a long period of time.

[0094] The presence or absence of components having a three-dimensional crosslinked structure in the coated carbon material, for example, components having a three-dimensional siloxane crosslinked structure, is determined by, for example, the solid. 29This can be confirmed by Si-NMR (nuclear magnetic resonance spectroscopy). If a component having a three-dimensional siloxane crosslinking structure is present, then solid 29 In the measurement of Si-NMR spectra, the carbon atoms of the organic group R are directly bonded to trifunctional silicon units (T units: RSiO 1.5 A broad group of peaks is observed, originating from bridged structures of tetrafunctional silicon units (Q units: SiO2) that are not bonded to the carbon atoms of the organic group.

[0095] The above solid 29 For measuring Si-NMR, the coated carbon material itself containing a component with a three-dimensional siloxane crosslinking structure can be used as a sample. Alternatively, the coated carbon material particles can be crushed to remove the coating, and the coating powder, dispersed in water, can be recovered by filtration or centrifugation, dried, and used as a sample. Furthermore, if the coated carbon material has a structure coated with a hybrid film of a PVOH-based resin and the SiO2 layer, the hybrid film can be peeled off and recovered as a sample. Alternatively, the shell-like or gel-like silica residue remaining after dissolving all the PVOH-based resin in the coated carbon material in water can be recovered by filtration or centrifugation, dried, and used as a sample.

[0096] <Boron-containing compounds> If the coating according to this embodiment has a film derived from a boron-containing compound as a crosslinking agent (Y) above, from the viewpoint of reducing resistance, it is preferable that this film (Y) further contains boron derived from the boron-containing compound. The content of boron-containing compounds (including parts corresponding to structures derived from boron-containing compounds) in the film of (Y) is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, and also preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the total mass of the coated carbon material. The type of boron-containing compound is not particularly limited. Examples include boron oxide, metaboric acid, tetraboric acid, borate, alkoxides with 1 to 3 carbon atoms bonded to boron, lithium borate, etc. It is preferable that at least one compound is selected from boron oxide, metaboric acid, tetraboric acid, borate, and alkoxides with 1 to 3 carbon atoms bonded to boron, as coating is easy. These boron-containing compounds may be used individually or in combination of two or more.

[0097] In this embodiment, the coating of the carbon material can be coated with any additives that improve battery performance, as long as they do not affect the curability, water resistance, solvent resistance, or long-term characteristics 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.

[0098] <Physical properties of coated carbon materials> • Content of crosslinks in compound (X) and compound group (Y) When the coating contains the compound (X) described above, the content of the compound (X) relative to the total mass of the coated carbon material is not particularly limited, but from the viewpoint of improving charge-discharge efficiency and reducing specific surface area, it is usually 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.04% by mass or more, particularly preferably 0.05% by mass or more, and also preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 0.9% by mass or less. When the coating contains a crosslinked compound of the compound group (Y) described above, there are no particular restrictions on the content of the crosslinked compound of the compound group (Y) relative to the total mass of the coated carbon material. However, from the viewpoint of ensuring sufficient crosslinking, it is usually 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.04% by mass or more, particularly preferably 0.05% by mass or more, and also preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 0.9% by mass or less.

[0099] • 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 suppress the increase in irreversible capacity and the loss of initial battery capacity of secondary batteries (especially non-aqueous secondary batteries) obtained using the coated carbon material, and it is also possible to suppress the occurrence of process problems such as striating during slurry coating, a decrease in high current density charge / discharge characteristics, and a decrease in low-temperature input / output characteristics.

[0100] 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.

[0101] • 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 secondary batteries (especially non-aqueous secondary batteries). 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) / (Actual perimeter of the particle projection)

[0102] 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 (20) 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.

[0103] 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.

[0104] • 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 3The following, and more preferably 1.1 g / cm³ 3 The following applies:

[0105] When the tap density is within the above range, processability such as scribing during electrode plate fabrication is improved, resulting in excellent high-speed charge-discharge characteristics. Furthermore, because the carbon density within the particles 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. 3 The 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.

[0106] 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 (especially a non-aqueous secondary battery). Note that the lower limit of Lc is the theoretical value for graphite.

[0107] ·ash The ash content in the coated carbon material of this embodiment is preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% 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. When 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, especially in the case of secondary batteries (particularly non-aqueous secondary batteries). 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 down.

[0108] ·BET specific surface area (SA) The specific surface area (SA) of the coated carbon material of this embodiment, as measured by the BET method, is preferably 1 m². 2 / g or more, more preferably 2m 2 / g or more, more preferably 2.5m 2 / g or more, particularly preferably 2.8m 2 / g or more, most preferably 3m 2 It is 11m or more. 2 / g or less, more preferably 9m 2 / g or less, more preferably 8m 2 / g or less, particularly preferably 7m 2 / g or less, most preferably 6m 2 It is less than / g.

[0109] 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 characteristics and output performance. 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 coated 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 secondary battery (especially a non-aqueous secondary battery).

[0110] BET specific surface area is defined as the value measured using a surface area meter (for example, the Gemini 2360 specific surface area measuring device manufactured by Shimadzu Corporation) after pre-drying a coated carbon material sample under reduced pressure at 100°C for 3 hours under nitrogen flow, cooling to liquid nitrogen temperature, and then measuring it by the nitrogen adsorption BET single-point method.

[0111] • Pore volume in the range of 10 nm to 1000 nm In the coated carbon material of this embodiment, the pore volume in the range of 10 nm to 1000 nm is a value measured using the mercury intrusion method (mercury porosimetry), and is preferably 0.01 mL / g or more, more preferably 0.03 mL / g or more, even more preferably 0.05 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.

[0112] If the pore volume in the range of 10 nm to 1000 nm is within the above range, the amount of voids into which the electrolyte (especially 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 during rapid charging and discharging, resulting in the deposition of lithium metal 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 leads to a decrease in electrode strength and a decrease in initial efficiency, can be better avoided.

[0113] 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 more easily obtained during electrode plate formation.

[0114] Furthermore, the average pore size of the coated 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 0.5 μm or more. The average pore size is preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 20 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.

[0115] 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).

[0116] 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%.

[0117] ·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 the initial irreversible capacity when used in a secondary battery (especially a non-aqueous secondary battery) can be suppressed.

[0118] 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 secondary batteries (especially non-aqueous secondary batteries).

[0119] 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.

[0120] ·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.

[0121] • 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 aforementioned Raman R value 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 AIt 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.

[0122] 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 become disordered, which suppresses an increase in reactivity with the electrolyte of the negative electrode, and tends to avoid a decrease in charge / discharge efficiency and an increase in gas generation in secondary batteries (especially non-aqueous secondary batteries).

[0123] 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)

[0124] ·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.

[0125] 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. Furthermore, DBP oil absorption is defined in accordance with ISO 4546, as the measured value obtained 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.

[0126] ·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 3 μm or more, even more preferably 5 μm or more, particularly preferably 8 μm or more, and most preferably 10 μm or more.

[0127] 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, and preventing a decrease in electrode strength and initial charge / discharge efficiency in secondary batteries (especially non-aqueous secondary batteries). 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%.

[0128] ·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 by volume, 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 26 μm or more, even more preferably 30 μm or more, and particularly preferably 34 μm or more.

[0129] 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 (especially non-aqueous 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%.

[0130] • Resin elution The elution properties of the acetoacetyl group-containing resin (X) or the polyvinyl alcohol-based resin (Y) in the coated carbon material of this embodiment (hereinafter, these resins are collectively referred to simply as "resin") can be evaluated by measuring the amount of resin eluted into the solution when the coated carbon material is immersed in a salt-free non-aqueous solvent at 25°C for 5 hours. The amount of elution is preferably 20% by mass or less of the total amount of resin contained in the coating carbon material, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0131] Within the above range, the resin becomes less likely to peel off during high-temperature storage or charge-discharge cycles, effectively suppressing the deterioration of storage characteristics and charge-discharge cycle characteristics. The solvent used in the evaluation of the elution properties described above shall be a mixed solvent of ethylene carbonate and ethyl methyl carbonate without salt (volume ratio = 3:7).

[0132] One method for quantifying the amount of resin eluted is to immerse the active material for the negative electrode of a secondary battery in a solvent component, collect the supernatant, dry it to remove the solvent, and calculate the amount of eluted component as a ratio of the peak intensity of the eluted component to the peak intensity of 100% elution in GPC.

[0133] • Evaluation of coatings on the basal surface of carbon materials In the coated carbon material of this embodiment, from the viewpoint of suppressing an increase in resistance, it is preferable that the coating is applied to the basal surface of the carbon material. Furthermore, although the coverage rate of the basal surface of the carbon material is not particularly limited, from the viewpoint of efficiently improving the initial efficiency, it is usually 30% or more, preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, and usually 100% or less, preferably 98% or less, more preferably 96% or less, and even more preferably 95% or less. Whether or not a coating is present on the basal surface of a carbon material can be evaluated by simultaneously measuring the adsorption isotherm and heat of adsorption using toluene gas. Specifically, the basal surface is defined as the carbon material surface with high affinity for toluene, where the heat of adsorption is 67 kJ / mol or higher. By comparing the amount of toluene adsorbed in this region with the carbon material before coating, it can be confirmed that the basal surface is coated with an organic compound. The coverage rate of the basal surface of a carbon material 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. 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

[0134] <Method for manufacturing coated carbon material> The coated carbon material (also referred to as a secondary battery negative electrode active material, or simply a coated carbon material) according to the above embodiment is, for example, a method for producing a coated carbon material that includes the step of mixing a carbon material with at least one compound or group of compounds selected from the compound (X) and the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound Specifically, it can be manufactured by the following method. For convenience, the following explanation will refer to the materials as follows: carbon material (A), coating material (B), active material for secondary battery negative electrode (C), and solution (D).

[0135] Compound (X) When the coating according to this embodiment contains the compound (X) above, the acetoacetyl group-containing resin (B1) can be obtained by 1) adding an organic solvent, water, or a mixture thereof to a mixing step, mixing the solution (D) with the carbon material (A), and then 2) drying it by heating and / or reduced pressure in a drying step, thereby obtaining an active material for a secondary battery negative electrode in which the carbon material (A) contains the coating material (B).

[0136] The solvent used is not particularly limited as long as it dissolves or disperses the acetoacetyl group-containing resin (B1), but water, ethyl methyl ketone, toluene, acetone, methyl isobutyl ketone, ethanol, or methanol are preferred. Among these, water, ethyl methyl ketone, acetone, methyl isobutyl ketone, ethanol, or methanol are more preferred due to cost and ease of drying.

[0137] Crosslinked compounds of the group of compounds (Y) When the coating according to this embodiment contains a crosslinked product of the compound group (Y) above, the polyvinyl alcohol-based resin (B1), the silicon element-containing compound (B2) as a crosslinking agent, and optionally the boron compound (B3) are added to an organic solvent, water, or a mixture thereof in a mixing step (1) and the solution (D) is mixed with the carbon material (A), and then dried by heating and / or reduced pressure in a drying step (2) to obtain an active material for a secondary battery negative electrode in which the carbon material (A) contains the coating material (B).

[0138] For example, the polyvinyl alcohol resin (B1) solution, the silicon-containing compound (B2) solution as a crosslinking agent, and the boron compound (B3) solution may be prepared separately, or the polyvinyl alcohol resin (B1) solution, the silicon-containing compound (B2) solution, and the boron compound (B3) solution may be prepared by adding them to the same solvent. From the viewpoint of the initial charge and discharge efficiency of the lithium-ion secondary battery, it is preferable to prepare the polyvinyl alcohol resin (B1) solution, the silicon-containing compound (B2) solution, and the boron compound (B3) solution separately.

[0139] The solvent used is not particularly limited as long as it dissolves or disperses the polyvinyl alcohol-based resin (B1), silicon-containing compound (B2), and boron compound (B3), but water, ethyl methyl ketone, toluene, acetone, methyl isobutyl ketone, ethanol, or methanol are preferred. Among these, water, ethyl methyl ketone, acetone, methyl isobutyl ketone, ethanol, or methanol are more preferred due to cost and ease of drying.

[0140] Process (1): Mixing process Compound (X) When the coating according to this embodiment contains the compound (X) described above, there are no particular restrictions on the method of mixing the carbon material (A) and the coating material (B). However, from the viewpoint of suppressing the initial gas amount and the amount of stored gas, it is desirable to be able to uniformly coat the surface of the carbon material (A) with the organic compound (B). 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 container in this case may be an inverted cone, a vertically oriented cylindrical shape, a horizontally oriented cylindrical shape, or a U-shaped trough, but a horizontally oriented cylindrical shape is preferred from the viewpoint of preventing adhesion inside the machine and ensuring uniform mixing.

[0141] The shape 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 blades of the horizontal axis system are 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.

[0142] 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 min or more, more preferably 1 min or more, even more preferably 5 min or more, preferably 5 hr or less, more preferably 1 hr or less, and even more preferably 20 min or less. When the processing time is within the above range, more uniform mixing can be achieved while maintaining processing capacity.

[0143] 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 viscosity increase of the coating material (B) can be suppressed, and more uniform mixing can be achieved. Furthermore, the cost of temperature control can be reduced.

[0144] To improve uniform mixing, if the solution of the acetoacetyl group-containing resin (B1) is in a highly viscous state or is solid or gel-like, it is preferable to pre-dilute the coating material (B) with a solvent when mixing with the carbon material (A), from the viewpoint of uniform mixing.

[0145] The ratio of the diluted solution of the coating material (B) to the carbon material (A) is preferably 1% by mass or more, more preferably 5% by mass or more, preferably 200% by mass or less, and more preferably 150% by mass or less. By keeping the ratio within the above range, the ratio can be mixed uniformly, and the drying time in the subsequent process can be shortened. Furthermore, when preparing the slurry in which the carbon material (A) is dispersed, a solution of acetoacetyl group-containing resin (B1) may be added. This is because, after coating the negative electrode plate with the active material for secondary battery negative electrodes, drying the solvent of the polymer (B1) having a crosslinkable substituent can also improve initial charge-discharge efficiency and suppress gas generation, and simplify the manufacturing process.

[0146] The slurry in which the carbon material (A) is dispersed is one embodiment used in the process of applying the secondary battery negative electrode active material according to this embodiment to the electrode surface for the negative electrode in order to manufacture a negative electrode for a secondary battery.

[0147] When mixing with the carbon material (A), the concentration of the acetoacetyl group-containing resin (B1) in the solvent is preferably 0.01% by mass or more and 20% by mass or less. Within this range, it can be expected that the acetoacetyl group-containing resin (B1) will be uniformly present on the surface of the carbon material (A) in the active material for the negative electrode of the secondary battery, and the effect can be obtained efficiently. The concentration of the acetoacetyl group-containing resin (B1) in the solution is preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and preferably 15% by mass or less, and more preferably 10% by mass or less.

[0148] Crosslinked compounds of the group of compounds (Y) When the coating according to this embodiment includes a crosslinked compound of the above-mentioned (Y) group, there are no particular restrictions on the method of mixing the carbon material (A) and the coating material (B). However, from the viewpoint of suppressing the initial gas amount and the amount of stored gas, it is desirable to be able to uniformly coat the surface of the carbon material (A) with the coating material (B). 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 container in this case may be an inverted cone, a vertically oriented cylindrical shape, a horizontally oriented cylindrical shape, or a U-shaped trough, but a horizontally oriented cylindrical shape is preferred from the viewpoint of preventing adhesion inside the machine and ensuring uniform mixing.

[0149] The shape 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 blades of the horizontal axis system are 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.

[0150] 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 min or more, more preferably 1 min or more, even more preferably 5 min or more, preferably 5 hr or less, more preferably 1 hr or less, and even more preferably 20 min or less. When the processing time is within the above range, more uniform mixing can be achieved while maintaining processing capacity.

[0151] 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 viscosity increase of the coating material (B) can be suppressed, and more uniform mixing can be achieved. Furthermore, the cost of temperature control can be reduced. When a solution of polyvinyl alcohol-based resin (B1) and solutions of silicon-containing compound (B2) and boron compound (B3) as crosslinking agents are prepared separately, these solutions may be mixed with the carbon material (A) simultaneously, or the carbon material (A) may be mixed after these solutions are mixed, or two of the solutions of polyvinyl alcohol-based resin (B1), silicon-containing compound (B2), and boron compound (B3) may be mixed with the carbon material (A) and then the third solution may be added, or each solution may be mixed with the carbon material A in sequence. The mixing order does not matter, starting with the polyvinyl alcohol-based resin (B1) solution, then the silicon-containing compound (B2), and then the boron compound (B3). If mixing sequentially, a drying step may be included in between. The boron compound (B3) may or may not be included.

[0152] To improve uniform mixing, if the mixture of the polyvinyl alcohol resin (B1) solution and any two or all of the silicon element-containing compound (B2) and boron compound (B3) solutions is in a highly viscous state, solid, or gel-like state, it is preferable to pre-dilute the coating material (B) with a solvent when mixing the carbon material (A), from the viewpoint of uniform mixing. More preferably, the polyvinyl alcohol resin (B1) is diluted with a solvent, then mixed with the silicon element-containing compound (B2) and boron compound (B3), and then mixed with the carbon material (A). The time from mixing the polyvinyl alcohol resin (B1) solution with the silicon element-containing compound (B2) and boron compound (B3) solutions and then mixing with the carbon material (A) is preferably within 1 hour, but preferably within 20 minutes from the viewpoint of cycle time.

[0153] The ratio of the diluted solution of the coating material (B) to the carbon material (A) is preferably 1% by mass or more, more preferably 5% by mass or more, preferably 200% by mass or less, and more preferably 150% by mass or less. By keeping the ratio within the above range, the ratio can be mixed uniformly, and the drying time in the subsequent process can be shortened. Furthermore, when preparing the slurry in which the carbon material (A) is dispersed, a solution of polyvinyl alcohol-based resin (B1) and solutions of silicon-containing compound (B2) and boron compound (B3) may be added. This is because, after coating the negative electrode plate with the active material for secondary battery negative electrodes, drying the solvents of the polyvinyl alcohol-based resin (B1) and silicon-containing (B2) and boron compound (B3) can also improve initial charge-discharge efficiency, suppress gas generation, and simplify the manufacturing process.

[0154] The slurry in which the carbon material (A) is dispersed is one embodiment used in the process of applying the secondary battery negative electrode active material according to this embodiment to the electrode surface for the negative electrode in order to manufacture a negative electrode for a secondary battery.

[0155] In particular, from the viewpoint of initial charge and discharge efficiency, it is preferable to separately prepare a solution of polyvinyl alcohol resin (B1), a solution of silicon element-containing compound (B2), and a solution of boron compound (B3), and then simultaneously mix these solutions with the carbon material (A) to produce a slurry in which the active material (A) is dispersed. Furthermore, from the viewpoint of uniformly coating the surface of the carbon material (A), it is even more preferable to simultaneously mix the boron compound (B3) solution and the carbon material (A), then filter or dry the mixture, and then mix in the polyvinyl alcohol resin (B1) solution and the silicon element-containing (B2) solution.

[0156] When mixing with the carbon material (A), the concentrations of the polyvinyl alcohol-based resin (B1), silicon-containing compound (B2), or boron compound (B3) in the solvent are preferably 0.01% by mass or more and 20% by mass or less, respectively. Within this range, the polyvinyl alcohol-based resin (B1), silicon-containing compound (B2), and boron compound (B3) can be expected to be uniformly present on the surface of the carbon material (A) in the active material for the negative electrode of the secondary battery, and the effect can be obtained efficiently. The concentrations of the polyvinyl alcohol-based resin (B1) or the silicon element-containing compound (B2) and boron compound (B3) in the solution are preferably 0.03% by mass or more, more preferably 0.05% by mass or more, preferably 15% by mass or less, and more preferably 10% by mass or less.

[0157] However, the above solution concentrations refer to the concentrations of the solutions when they are in contact with the carbon material (A). When the polyvinyl alcohol resin (B1) solution, the silicon element-containing compound (B2) solution, and the boron compound (B3) solution are mixed simultaneously with the carbon material (A), or when these solutions are mixed before mixing with the carbon material (A), the concentration refers to the total concentration of the coating material (B), which is the sum of the polyvinyl alcohol resin (B1), the silicon element-containing compound (B2), and the boron compound (B3). Furthermore, when the carbon material (A) is mixed with either the polyvinyl alcohol resin (B1) solution or the silicon element-containing compound (B2) or the boron compound (B3) solution, and then other solutions are added, the concentrations refer to the individual concentrations of the polyvinyl alcohol resin (B1) solution, the silicon element-containing compound (B2) solution, and the boron compound (B3) solution. Furthermore, the amounts of polyvinyl alcohol-based resin (B1) and silicon-containing compound (B2) can be adjusted as appropriate, and it is preferable to adjust the blending amounts so that they result in the preferred content in the secondary battery negative electrode active material of this embodiment as described above.

[0158] Process (2): Drying process When the coating according to this embodiment contains the crosslinked material (X) above, when drying the solution of the acetoacetyl group-containing resin (B1) by heating, it is preferable that the temperature be below the decomposition temperature of the acetoacetyl group-containing resin (B1), and more preferably above the boiling point of the solvent. Preferably, the temperature is 50°C or higher and 300°C or lower. Within this range, the drying efficiency is sufficient, a decrease in battery performance due to residual solvent is avoided, and it is easy to prevent the decomposition of the acetoacetyl group-containing resin (B1) and the reduction in effect due to a weakening of the interaction between the carbon material (A) and the acetoacetyl group-containing resin (B1). Furthermore, when the coating according to this embodiment includes a crosslinked product of the compound group (Y) above, when drying the solution of the polyvinyl alcohol resin (B1) and / or the silicon element-containing compound (B2) and boron compound (B3) as crosslinking agents by heating, it is preferable that the temperature be below the decomposition temperature of the polyvinyl alcohol resin (B1) and the silicon element-containing compound (B2) and boron compound (B3), and more preferably above the boiling point of the solvent. Preferably, the temperature is 50°C or higher and 300°C or lower. Within this range, the drying efficiency is sufficient, a decrease in battery performance due to residual solvent is avoided, and it is easy to prevent the decomposition of the polyvinyl alcohol resin (B1) and the silicon element-containing compound (B2) and boron compound (B3), as well as prevent a reduction in effectiveness due to weakened interaction between the carbon material (A) and the polymer (B1) having reactive substituents and the silicon element-containing compound (B2) and boron compound (B3).

[0159] The temperature is preferably 250°C or lower, and also preferably 100°C or higher. When the coating according to this embodiment contains the compound (X) above, and the solution of the acetoacetyl group-containing resin (B1) is dried under reduced pressure, or when the coating according to this embodiment contains a crosslinked product of the compound group (Y) above, and the solution of the polyvinyl alcohol-based resin (B1) and / or silicon element-containing compound (B2) and boron compound (B3) is dried under reduced pressure, the pressure is usually 0 MPa or less and -0.2 MPa or more in gauge pressure notation (difference from atmospheric pressure). Within this range, drying can be performed relatively efficiently. The pressure is preferably -0.03 MPa or less, and also preferably -0.15 MPa or more.

[0160] In the drying process, there are no particular restrictions on the method of drying the mixture of carbon material (A) and coating material (B), but it is desirable to be able to coat it uniformly from the viewpoint of suppressing the amount of initial gas and the amount of stored gas. By making it uniform, the coating material (B) can be efficiently adsorbed onto specific mesopore surfaces, and the effect of suppressing gas generation is easily obtained. 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.

[0161] 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.

[0162] 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.

[0163] The stirring tank in this case can be an inverted cone, a vertical cylindrical type, a horizontal cylindrical type, or a U-shaped trough, but a horizontal cylindrical type is preferred from the viewpoint of yield, workability, and installation space. The shape of the stirring blade can be ribbon-shaped, screw-shaped, single-axis paddle-shaped, double-axis paddle-shaped, anchor-shaped, plow-shaped, or hollow wedge-shaped if it is a horizontal-axis system, and ribbon-shaped, screw-shaped, conical screw-shaped, or lower high-speed rotating blade if it is a vertical-axis system, but a single-axis paddle-shaped or plow-shaped blade for the horizontal-axis system is preferred.

[0164] 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 to be 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.

[0165] 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 (Okawara Manufacturing Co., Ltd.); or 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 in a vertical cylindrical agitator.

[0166] If the coating according to this embodiment contains the compound (X) above, the process may include filtering the solution containing the carbon material (A) and the acetoacetyl group-containing resin (B1) prior to drying, and washing the resulting residue with water. This is preferable because it removes excess acetoacetyl group-containing resin (B1) 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. If the coating according to this embodiment includes a crosslinked compound of the compound group (Y) above, the process may include filtering a solution containing the carbon material (A), polyvinyl alcohol-based resin (B1), and silicon-containing compound (B2) and boron compound (B3) as crosslinking agents, and washing the resulting residue with water prior to drying. This is preferable because it removes excess polyvinyl alcohol-based resin (B1) and silicon-containing compound (B2) and boron compound (B3) that are 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.

[0167] Furthermore, if the coating according to this embodiment contains a crosslinked compound of the compound group (Y) above, when other components are to be included in the active material for the negative electrode of the secondary battery according to this embodiment, similar to the acetoacetyl group-containing resin (B1), an organic solvent, water, or a mixture thereof is added to form a solution, and after mixing the solution with the carbon material (A), it is dried by heating and / or reduced pressure. When adding other components, a separate solution of the other components may be prepared in addition to the solution of the acetoacetyl group-containing resin (B1), or the solution may be prepared by adding the other components to the same solvent as the solution of the acetoacetyl group-containing resin (B1). Furthermore, if the coating according to this embodiment includes a crosslinked compound of the compound group (Y) above, when other components are to be included in the active material for the negative electrode of the secondary battery according to this embodiment, they are added to an organic solvent, water, or a mixture thereof to form a solution, similar to the polyvinyl alcohol resin (B1), silicon element-containing compound (B2), and boron compound (B3), and after mixing the solution with the carbon material (A), it is dried by heating and / or reduced pressure. When adding other components such as organic compounds (B3), a separate solution for the other components may be prepared in addition to the solutions for the polyvinyl alcohol-based resin (B1) and silicon-containing compound (B2), or the solution may be prepared by adding the other components to the same solvent as the solutions for the polyvinyl alcohol-based resin (B1) and silicon-containing compound (B2).

[0168] <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 above-described coating carbon material, and is preferably a negative electrode for a non-aqueous secondary battery. More preferably contains a binder. As the 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. By using such a binder having olefinic unsaturated bonds, the swelling of the active material layer in the electrolyte can be reduced. Among these, styrene-butadiene rubber is preferred due to its availability.

[0169] 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.

[0170] 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 More than 10 moles, 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, but 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.

[0171] 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, a binder 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.

[0172] 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.

[0173] When the coated carbon material of this embodiment is used in combination with the binder having the olefinic unsaturated bonds 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 not having 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 binder ratio 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.

[0174] The coated carbon material of this embodiment is formed by dispersing the coated carbon material of this embodiment and a binder in a dispersion medium to form a slurry, and then applying this slurry to a current collector. An organic solvent such as alcohol or water can be used as the dispersion medium. A conductive agent may be added to this slurry as desired. Examples of conductive agents include carbon black such as acetylene black, Ketjen black, or furnace black, artificial graphite powder, and fine powders consisting of Cu, Ni, or alloys thereof with an average particle size of 1 μm or less. The amount of conductive agent added is preferably about 10% by mass or less relative to the coated carbon material of this embodiment.

[0175] As the current collector for applying the slurry, those conventionally known can be used. Specifically, examples include metal thin films such as rolled copper foil, electrolytic copper foil, or stainless steel foil. The thickness of the current collector is preferably 4 μm or more, more preferably 6 μm or more, preferably 30 μm or less, and more preferably 20 μm or less. This slurry was applied to a 20-μm-thick copper foil serving as a current collector to a width of 5 cm using a doctor blade so that 10.0 ± 0.3 mg / cm 2 of the coated carbon material adhered thereto. After drying at 110°C for 30 minutes, roll pressing was performed using a 20-cm-diameter roller to adjust the density of the active material layer to 1.60 ± 0.03 g / cm 3 to obtain an electrode sheet.

[0176] After applying the slurry onto the current collector, it is preferably dried in dry air or an inert atmosphere at a temperature of 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, it is excellent in practicality as a negative electrode in view of the balance with the particle size of the coated carbon material, and a sufficient function of lithium storage and release for a high-density current value can be obtained.

[0177] The density of the coated carbon material in the active material layer varies depending on the application. In applications where capacity is emphasized, it is preferably 1.55 g / cm 3 or more, more preferably 1.6 g / cm 3 or more, still more preferably 1.65 g / cm 3 or more, particularly preferably 1.7 g / cm 3 or more. Also, it is preferably 1.9 g / cm 3 or less. When the density is within the above range, the capacity of the battery per unit volume can be sufficiently ensured, and the rate characteristics are also less likely to deteriorate.

[0178] When manufacturing a negative electrode for a secondary battery using the coated carbon material of the present embodiment described above, there are no particular restrictions on the method or the selection of other materials. Also, when manufacturing a lithium-ion secondary battery using this negative electrode, there are no particular restrictions on the selection of members necessary for the battery configuration, such as the positive electrode and electrolyte solution that constitute the lithium-ion secondary battery. Hereinafter, the details of the negative electrode for a lithium-ion secondary battery and the lithium-ion secondary battery using the coated carbon material of the present embodiment will be illustrated, but the materials that can be used, the manufacturing method, etc. are not limited to the following specific examples.

[0179] <Secondary battery> The basic configuration of the secondary battery, particularly the lithium-ion secondary battery, according to another embodiment of the present embodiment is the same as that of a conventionally known lithium-ion secondary battery, and usually includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, and an electrolyte. This secondary battery is preferably a non-aqueous secondary battery in particular. As the negative electrode, the coated carbon material described above is used. The positive electrode is formed by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.

[0180] Examples of the positive electrode active material include metal chalcogen compounds that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Examples of the metal chalcogen compound include transition metal oxides such as vanadium oxides, molybdenum oxides, manganese oxides, chromium oxides, titanium oxides, tungsten oxides, transition metal sulfides such as vanadium sulfides, molybdenum sulfides, titanium sulfides, CuS, or transition metal phosphorus-sulfur compounds such as NiPS3, FePS3, transition metal selenium compounds such as VSe2, or NbSe3, Fe 0.25 V 0.75 S2, or Na 0.1 [[ID=​​​​, VO2, Cr2O5, MnO2, TiO2, MoV2O8, LiCoO2, LiNiO2, LiMn2O4, TiS2, V2S5, Cr 0.25 V 0.75 S2, or Cr 0.5 V 0.5 S2 is preferred, and particularly preferred are LiCoO2, LiNiO2, or LiMn2O4, or lithium transition metal composite oxides in which some of these transition metals are substituted with other metals. These positive electrode active materials may be used individually or in combination.

[0182] Any known binder can be arbitrarily selected and used to bind the positive electrode active material. Examples include inorganic compounds such as silicates and water glass, and resins that do not have unsaturated bonds, such as Teflon® or polyvinylidene fluoride. Among these, resins that do not have unsaturated bonds are preferred. If a resin with unsaturated bonds is used as the resin to bind the positive electrode active material, there is a risk of decomposition during the oxidation reaction. The weight-average molecular weight of these resins is usually in the range of 10,000 or more, preferably 100,000 or more, and usually 3 million or less, preferably 1 million or less.

[0183] The positive electrode active material layer may contain a conductive material to improve the conductivity of the electrode. There are no particular restrictions on the conductive material as long as it can impart conductivity when mixed in an appropriate amount with the active material, but common examples include acetylene black, carbon black, or carbon powder such as graphite, or fibers, powders, or foils of various metals. The positive electrode plate is formed by slurring the positive electrode active material and binder with a solvent, applying it to a current collector, and drying it, using the same method as for manufacturing the negative electrode described above. The current collector for the positive electrode can be made of aluminum, nickel, or stainless steel (SUS), but is not limited to these materials. As electrolytes, electrolytes (especially non-aqueous electrolytes) obtained by dissolving lithium salts in a solvent (especially non-aqueous solvents), or these electrolytes made into gel-like, rubber-like, or solid sheet-like forms using organic polymer compounds, etc., are used.

[0184] The solvent used in the electrolyte is not particularly limited, and it can be appropriately selected and used from known solvents that have been conventionally proposed as solvents for electrolytes. For example, chain carbonates such as diethyl carbonate, dimethyl carbonate, or ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, or butylene carbonate; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane; chain esters such as methyl formate, methyl acetate, or methyl propionate; or cyclic esters such as γ-butyrolactone or γ-valerolactone, etc. can be mentioned.

[0185] Any one of these solvents may be used alone, or two or more of them may be used in combination. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferred. When the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate, it is particularly preferred in that high ionic conductivity can be exhibited even at low temperatures and the low-temperature charging inapplicable characteristic is improved. Among them, the range of 2% by mass or more and 80% by mass or less of propylene carbonate with respect to the whole solvent is preferred, the range of 5% by mass or more and 70% by mass or less is more preferred, and the range of 10% by mass or more and 60% by mass or less is even more preferred. If the proportion of propylene carbonate is lower than the above, the ionic conductivity at low temperatures decreases. If the proportion of propylene carbonate is higher than the above, when a graphite-based electrode is used, propylene carbonate solvated with lithium ions co-intercalates into the graphite phase, resulting in interlayer peeling deterioration of the graphite-based negative electrode active material and a problem that sufficient capacity cannot be obtained.

[0186] The lithium salt used in the electrolyte is not particularly limited, and it can be appropriately selected from known lithium salts known to be usable for this application. For example, inorganic lithium salts such as halides such as LiCl or LiBr, perhalogenates such as LiClO4, LiBrO4, or LiClO4, inorganic fluoride salts such as LiPF6, LiBF4, or LiAsF6, perfluoroalkanesulfonates such as LiCF3SO3 or LiC4F9SO3, or fluorine-containing organic lithium salts such as perfluoroalkanesulfonimide salts such as Li trifluoromethanesulfonimide ((CF3SO2)2NLi), etc. Among these, LiClO4, LiPF6, or LiBF4 is preferable.

[0187] The lithium salt may be used alone or in combination of two or more. The concentration of the lithium salt in the electrolyte is usually in the range of 0.5 mol / L or more and 2.0 mol / L or less. In addition, when an organic polymer compound is included in the above-mentioned electrolyte and used in a gel-like, rubber-like, or solid sheet form, specific examples of the organic polymer compound include polyether-based polymer compounds such as polyethylene oxide or polypropylene oxide; cross-linked polymer of polyether-based polymer compounds; vinyl alcohol-based polymer compounds such as polyvinyl alcohol or polyvinyl butyral; insoluble products of vinyl alcohol-based polymer compounds; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl-based polymer compounds such as polyvinyl pyrrolidone, polyvinylidene carbonate, or polyacrylonitrile; or polymer copolymers such as poly(ω-methoxyoligooxyethylene methacrylate), poly(ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), or poly(hexafluoropropylene-vinylidene fluoride), etc.

[0188] The 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, or methylphenyl carbonate; alkene sulfides such as ethylene sulfide or propylene sulfide; sultone compounds such as 1,3-propanesultone or 1,4-butanesultone; or acid anhydrides such as maleic anhydride or succinic anhydride. Furthermore, an overcharge prevention agent such as diphenyl ether or cyclohexylbenzene may be added.

[0189] When using the above-mentioned additives, their 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 additives 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.

[0190] A porous separator, such as a porous membrane or nonwoven fabric, is typically interposed between the positive and negative electrodes to prevent short circuits. In this case, the electrolyte is impregnated into the porous separator. Polyethylene, polypropylene, or other polyolefins, or polyethersulfone are used as the separator material, with polyolefins being preferred.

[0191] 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.

[0192] 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 a gasket or sealing plate. [Examples]

[0193] 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(B1-1): Polyvinyl alcohol containing acetoacetyl groups (average degree of polymerization 1500) • PVOH(B1-2): Polyvinyl alcohol containing acetoacetyl groups (average degree of polymerization 500) • PVOH(B1-3): Acetoacetyl group-free polyvinyl alcohol (average degree of polymerization 500) • Labellin: Sodium naphthalene sulfonate formalin condensate

[0194] <Experiment 1: Compound (X)> <Fabrication of electrode sheets> Using the coated carbon material of the example or comparative example from Experiment 1, the active material layer density was 1.60 ± 0.03 g / cm³. 3An electrode plate having an active material layer was prepared. Specifically, 20.00±0.02 g of coated carbon material was mixed with 20.00±0.02 g (0.200 g in terms of solid content) of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt, and 0.42±0.02 g (0.2 g in terms of solid content) of styrene-butadiene rubber aqueous dispersion. This mixture was stirred for 5 minutes using a THINKY foam remover, and then degassed for 30 seconds to obtain a slurry.

[0195] This slurry is then applied to a 10 μm thick copper foil, which serves as the current collector, with a coating carbon material concentration of 10.10 ± 0.3 mg / cm³. 2 To ensure adhesion, the material was applied in a 10cm wide strip using a die coating machine, 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.

[0196] <Manufacturing of a rechargeable 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 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3:7) to a concentration of 1 mol / L, with 2% by mass of vinylene carbonate added, was placed to fabricate 2032 coin-type batteries.

[0197] <Method for measuring discharge capacity and initial efficiency> Using the secondary battery (2032 coin-type battery) prepared by the method described above, the capacity during battery charging and discharging was measured using the following measurement method. The electrolyte secondary battery was allowed to stand at 25°C for 24 hours, charged to 5 mV with respect to the lithium counter electrode at a constant current corresponding to 0.04 C at 25°C, then charged at a constant voltage of 5 mV until it reached 0.004 C, and discharged at a constant current of 0.08 C until 1.5 V. This was repeated three times to complete the coin cell evaluation. The initial efficiency (%) was determined from (discharge capacity of the first cycle) ÷ (charge capacity of the first cycle) × 100. The capacity (mAh / g) was determined from the discharge capacity of the third cycle. The initial efficiency shown in Table 2 is the initial efficiency of each example and comparative example when the initial efficiency of Comparative Example 1-1 is set to 100.0, and the initial efficiency shown in Table 3 is the initial efficiency of each example and comparative example when the initial efficiency of Comparative Example 1-2 is set to 100.0.

[0198] <Swelling and Solubility Evaluation in Water> The polyvinyl alcohol film described in the example or comparative example was immersed in pure water having a mass 50 times the mass of the film mass (W1) at 25°C for 1 day, the composite film was taken out, the pure water adhering to the surface was removed, the mass (W2) was measured, and then it was dried under reduced pressure at 110°C for 5 hours to measure the mass (W3). The swelling rate and dissolution rate were calculated using the following formula. Swelling rate = (W2 - W3) / W3 × 100 Dissolution rate = (W1 - W3) / W1 × 100

[0199] <BET Specific Surface Area (SA)> Using a fully automatic specific surface area measuring device (manufactured by Mountech, Macsorb HM Model - 1210), after pre - drying the coated carbon material sample under nitrogen flow at 100°C for 30 minutes, it was cooled to liquid nitrogen temperature, and measured by the BET one - point method using nitrogen gas.

[0200] <Evaluation of Coating on the Basal Plane> By simultaneously measuring the adsorption isotherm and the heat of adsorption using toluene gas, it was evaluated whether the film was coated on the basal plane of the carbon material.

[0201] [Reference Example 1 - 1] An aqueous solution of PVOH (B1-1) with a solid content of 10% by mass was dried to obtain a film. The swelling and dissolution rates in water were measured by the above measurement method. The results are shown in Table 1.

Table 1

[0202] [Example 1-1] 100 g of spheroidized natural graphite (carbon material (A)) with SA of 6.4 m 2 / g and d50 of 17.3 μm and 100 g of an aqueous PVOH (B1-1) solution (PVOH (B1-1) solid content concentration: 0.5% by mass) were mixed in a glass container using a three-one motor. The obtained sample was dried and subjected to sieving treatment to obtain a powdery coated carbon material (C). For the obtained coated carbon material (C), SA and the initial efficiency were measured by the above measurement method. The results are shown in Table 2. Further, as a result of evaluating whether or not the film was coated on the basal plane of the carbon material by the above evaluation method, it was found that it was coated.

[0203] [Example 1-2] 100 g of spheroidized natural graphite (carbon material (A)) with SA of 6.4 m 2 / g and d50 of 17.3 μm and 100 g of an aqueous PVOH (B1-1) solution (PVOH (B1-1) solid content concentration: 1.0% by mass) were mixed in a glass container using a three-one motor. The obtained sample was dried and subjected to sieving treatment to obtain a powdery coated carbon material (C). The characteristics of the obtained coated carbon material (C) were evaluated in the same manner as in Example 1-1. The results are shown in Table 2. Further, as a result of evaluating whether or not the film was coated on the basal plane of the carbon material by the above evaluation method, it was found that it was coated.

[0204] [Comparative Example 1-1] Using spheroidized natural graphite with SA of 6.4 m 2 / g and d50 of 17.3 μm, an electrode sheet was produced by the above method and the initial efficiency was measured. The results are shown in Table 2.

[0205]

Table 2

[0206] Reference Example 1-1 shows that by heat-treating a resin (B1) having hydroxyl and acetoacetyl groups as self-crosslinking groups, a resin film with moderate elasticity and suppressed swelling and dissolution in water was formed. In Examples 1-1 to 1-2, coating with a resin containing self-crosslinking groups reduced the SA of graphite, effectively suppressing side reactions with the electrolyte and demonstrating good initial efficiency.

[0207] [Examples 1-3] SA is 6.3m 2 100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 16.3 μm and 100 g of PVOH(B1-2) aqueous solution (PVOH(B1-2) solid content concentration 0.5 mass%) were mixed in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA, volume, and initial efficiency of the obtained coated carbon material (C) were measured using the measurement method described above. The results are shown in Table 3. Furthermore, evaluation using the evaluation method described above revealed that the coating was present on the basal surface of the carbon material.

[0208] [Comparative Example 1-2] SA is 6.3m 2 Using spheroidized natural graphite with a density of 16.3 μm / g and a d50 of 16.3 μm, electrode sheets were prepared using the method described above, and the initial efficiency was measured. The results are shown in Table 3.

[0209] [Comparative Examples 1-3] SA is 6.3m 2100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 16.3 μm and 100 g of PVOH(B1-3) aqueous solution (PVOH(B1-3) solid content concentration 0.5 mass%) were mixed in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA, volume, and initial efficiency of the obtained coated carbon material (C) were measured using the measurement method described above. The results are shown in Table 3. Furthermore, evaluation using the evaluation method described above revealed that the coating was present on the basal surface of the carbon material.

[0210] [Table 3]

[0211] In Examples 1-3, coating with an acetoacetyl group-containing resin having a self-crosslinking group reduced the SA of graphite, effectively suppressing side reactions with the electrolyte and achieving good initial efficiency while maintaining capacity compared to the conventional technology. In particular, a comparison between Examples 1-3 and Comparative Examples 1-3 showed that using an acetoacetyl group-containing resin made it possible to maintain capacity compared to the conventional technology. This is thought to be because the selective coating of the acetoacetyl group-containing resin on the basal surface does not inhibit the desorption and insertion of Li ions at the edges. Furthermore, it is thought that the presence of acetoacetyl groups improves solvent resistance through a crosslinked structure, suppressing path interruptions within the battery that lead to capacity reduction. The inventors speculate that this trend will be similarly observed in other examples and comparative examples.

[0212] <Experiment 2: Crosslinked compounds of compound group (Y)> <Fabrication of electrode sheets> Using the coated carbon materials of Examples 2-1 to 2-5 or Comparative Examples 2-1 and 2-2 described later, with an active material layer density of 1.60 ± 0.03 g / cm³ 3An electrode plate having an active material layer was prepared. Specifically, 20.00±0.02 g of coated carbon material was mixed with 20.00±0.02 g (0.200 g in terms of solid content) of 1% by mass carboxymethylcellulose sodium salt aqueous solution and 0.42±0.02 g (0.2 g in terms of solid content) of styrene-butadiene rubber aqueous dispersion. This mixture was stirred for 5 minutes using a THINKY foam remover, and degassed for 30 seconds to obtain a slurry. Furthermore, using the coated carbon material of Example 2-6 or Comparative Examples 2-3 to 2-5 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 (0.14g in solid content) of 0.7% by mass of carboxymethylcellulose sodium salt aqueous solution, and 0.42±0.02g (0.2g in solid content) of styrene-butadiene rubber aqueous dispersion. This mixture was stirred for 5 minutes using a THINKY foam remover, and degassed for 30 seconds to obtain a slurry.

[0213] 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. 2 To ensure adhesion, the material was applied in a 5cm width using a Tester Industries automatic coating machine and 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.

[0214] <Manufacturing of secondary batteries (2032 coin-type and 2016 coin-type batteries)> For Examples 2-1 to 2-5 or Comparative Examples 2-1 and 2-2 described below, electrode sheets prepared by the above method were punched out into a 12.5 mm diameter disc shape, and 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 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3:7) to a concentration of 1 mol / L, and adding 2% by mass of vinylene carbonate was placed to fabricate a 2032 coin-type battery. Furthermore, in Example 2-6 or Comparative Examples 2-3 to 2-5 described later, the electrode sheets prepared by the above method were punched out into a 12.5 mm diameter disc shape, and 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 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3:7) to a concentration of 1 mol / L, and adding 2% by mass of vinylene carbonate was placed to fabricate 2016 coin-type batteries.

[0215] <Method for measuring discharge capacity and initial efficiency> The capacity of the rechargeable batteries (2032 coin-type batteries and 2016 coin-type batteries) prepared using the method described above was measured during charging and discharging using the following measurement method. The electrolyte secondary battery was left standing at 25°C for 24 hours, then charged to 5mV relative to the lithium counter electrode with a constant current equivalent to 0.04C at 25°C, then charged again with a constant voltage of 5mV until it reached 0.004C, and finally 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. The initial efficiencies shown in Table 6 are the initial efficiencies of each example and comparative example, with the initial efficiency of Comparative Example 2-1 set to 100.0, and the initial efficiencies shown in Table 7 are the initial efficiencies of each example and comparative example, with the initial efficiency of Comparative Example 2-5 set to 100.0.

[0216] <Evaluation of swelling and solubility in water> The polyvinyl alcohol and silica composite film described in the Examples or Comparative Examples was immersed in 50 times the mass of the film (W1) of pure water at 25°C for 1 day. The composite film was then removed, the pure water adhering to the surface was removed, and the mass (W2) was measured. Subsequently, it was dried under reduced pressure at 110°C for 5 hours and the mass (W3) was measured. The swelling rate and dissolution rate were then calculated using the following formula. Swelling rate = (W2 - W3) / W3 × 100 Dissolution rate=(W1-W3) / W1×100

[0217] <Evaluation of boron leaching into water> The composite film of polyvinyl alcohol, silica, and boron oxide described in the examples or comparative examples was stirred in pure water at 25°C for 1 hour with a mass 100 times that of the film mass (W1), and the supernatant was filtered off, and the elution amount of boron was quantified by ICP.

[0218] <BET specific surface area (SA)> Using a fully automatic specific surface area measuring device (manufactured by Mountech, Macsorb HM Model-1210), after pre-drying the coated carbon material sample at 100°C for 30 minutes under a nitrogen flow, it was cooled to the liquid nitrogen temperature, and measured by the BET one-point method using nitrogen gas.

[0219] <Peel strength> The peel strength was measured by the following procedure using a light load type adhesion / film peeling analysis device (VPA-3S manufactured by Kyowa Interface Science Co., Ltd.). That is, after drying the electrode sheet prepared by the above method at 110°C for 24 hours, it was cut into 2.5 cm × 7 cm, the negative electrode surface was faced towards the test plate and pasted with double-sided tape with a width of 2 cm, the test plate was set in the measuring device, and the end of the electrode plate sheet was pasted on 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.

[0220] <Evaluation of the coating on the basal plane> By simultaneously measuring the adsorption isotherm and the heat of adsorption using toluene gas, it was evaluated whether or not the film was coated on the basal plane of the carbon material.

[0221] [Reference Example 2-1] Polytetramethoxysilane (Si content in terms of SiO2: 52% by mass) was hydrolyzed in a methanol solvent using aluminum acetylacetone as a catalyst, and the hydrolysis solution was adjusted so that the solid content was 16% by mass in terms of SiO2. A composite film was obtained by mixing an aqueous solution of PVOH(B1-1) (solid content concentration 10% by mass) with a hydrolysis solution of polytetramethoxysilane having a solid content of 16% by mass (based on SiO2) and mixing and drying the mixture so that the PVOH(B1-1) and SiO2 content in the film were 80% by mass and 20% by mass, respectively. The swelling and solubility in water were measured using the aforementioned measurement method. The results are shown in Table 4.

[0222] [Reference Comparison Example 2-1] A film was obtained by drying an aqueous solution of PVOH(B1-1) (solid content concentration 10% by mass). The swelling and solubility in water were measured using the method described above. The results are shown in Table 4. [Table 4]

[0223] [Reference example 2-2] A composite film was obtained by mixing PVOH(B1-1) with a solid content of 5% by mass, a hydrolysis solution of polytetramethoxysilane with a solid content of 16% by mass (based on SiO2), and an aqueous solution of boron oxide with a solid content of 2% by mass (based on boron oxide), so that the content of PVOH(B1-1), SiO2, and boron oxide in the film was 47.5% by mass, 47.5% by mass, and 5% by mass, respectively, and then drying the mixture. The elution rate of boron into water was measured using the above measurement method. The results are shown in Table 5.

[0224] [Reference Comparison Example 2-2] A composite film was obtained by mixing PVOH(B1-1) with a solid content of 5% by mass and an aqueous boron oxide solution with a solid content of 2% by mass (in terms of boron oxide equivalent) such that the PVOH(B1-1) and boron oxide content in the film were 95% by mass and 5% by mass, respectively, and then drying the mixture. The elution rate of boron into water was measured using the aforementioned measurement method. The results are shown in Table 5.

[0225] [Reference Comparison Example 2-3] A hydrolysis solution of polytetramethoxysilane with a solid content of 16% by mass (based on SiO2) and an aqueous solution of boron oxide with a solid content of 2% by mass (based on boron oxide) were mixed and dried to obtain an SiO2 / boron oxide composite film. The SiO2 and boron oxide content were 95% by mass and 5% by mass, respectively. The elution rate of boron into water was measured using the aforementioned measurement method. The results are shown in Table 5. [Table 5]

[0226] [Example 2-1] SA is 6.4m 2 100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 17.3 μm and a PVOH(B1-1) aqueous solution and 100 g of a solution prepared by mixing a PVOH(B1-1) aqueous solution with a hydrolyzed polytetramethoxysilane crosslinking agent (B2) (PVOH(B1-1) solid content concentration 0.5% by mass, polytetramethoxysilane hydrolyzate solid content concentration 0.5% by mass) were mixed in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA and initial efficiency were measured for the obtained coated carbon material (C) using the measurement method described above. The results are shown in Table 6. Furthermore, evaluation using the evaluation method described above revealed that the coating was present on the basal surface of the carbon material.

[0227] [Example 2-2] As carbon material (A), SA is 6.4m 2100 g of spheroidized natural graphite with a d50 of 17.3 μm and an aqueous solution of boron oxide (B3) adjusted to a concentration of 0.5% by mass were mixed in a glass container using a three-one motor. After drying, the resulting powder was mixed with 100 g of a solution (PVOH(B1-1) solid content concentration 0.25% by mass, polytetramethoxysilane hydrolysate solid content concentration 0.25% by mass) of aqueous PVOH(B1-1) and hydrolysis solution of polytetramethoxysilane as a crosslinking agent (B2), in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). The obtained coated carbon material (C) was evaluated in the same manner as in Example 2-1. The results are shown in Table 6. Furthermore, evaluation using the above evaluation method revealed that the coating was present on the basal surface of the carbon material.

[0228] [Examples 2-3] As carbon material (A), SA is 6.4m 2 100 g of spheroidized natural graphite with a d50 of 17.3 μm / g and an aqueous solution of boron oxide (B3) adjusted to a concentration of 0.5% by mass as a boron compound (B3) was mixed in a glass container using a three-one motor, filtered, and dried to obtain a powder. This powder was then mixed in a glass container using a three-one motor with 100 g of a solution of aqueous PVOH (B1-1) and hydrolyzed polytetramethoxysilane (B2) as a crosslinking agent (PVOH (B1-1) solid content concentration 0.8% by mass, polytetramethoxysilane hydrolyzate solid content concentration 0.2% by mass), filtered, dried, and sieved to obtain a powdered coated carbon material (C). The obtained coated carbon material (C) was evaluated in the same manner as in Example 2-1. The results are shown in Table 6. Furthermore, evaluation using the above evaluation method revealed that the coating was present on the basal surface of the carbon material.

[0229] [Examples 2-4] The procedure was carried out in the same manner as in Example 2-1, except that 100 g of a solution was used, which was a mixture of an aqueous solution of PVOH(B1-1), a hydrolyzed solution of polytetramethoxysilane as a crosslinking agent (B2), and boron oxide as a boron compound (B3) (PVOH(B1-1) solid content concentration 0.5% by mass, polytetramethoxysilane hydrolyzate solid content concentration 0.5% by mass, boron oxide solid content concentration 0.5% by mass). The obtained coated carbon material (C) was evaluated in the same manner as in Example 2-1. Furthermore, the evaluation method described above was used to determine whether or not the coating was present on the basal surface of the carbon material, and it was found that it was indeed coated.

[0230] [Comparative Example 2-1] SA is 6.4m 2 Using spheroidized natural graphite with a density of 17.3 μm / g and a d50 of 17.3 μm, electrode sheets were prepared using the method described above, and the initial efficiency was measured. The results are shown in Table 6.

[0231] [Examples 2-5] As carbon material (A), SA is 11.9m 2 Granulated spheroidal natural graphite with a density of 1 / g and a d50 of 15.7 μm was used, and the procedure was carried out in the same manner as in Example 2-1, except that 100 g of a solution was prepared by mixing an aqueous solution of PVOH(B1-1) with a hydrolyzed solution of polytetramethoxysilane as a crosslinking agent (B2), and 100 g of a solution prepared by mixing an aqueous solution of PVOH(B1-1) with a hydrolyzed solution of polytetramethoxysilane (PVOH(B1-1) solid content concentration 1.0% by mass, polytetramethoxysilane hydrolyzate solid content concentration 1.0% by mass) was used. The obtained coated carbon material (C) was evaluated in the same manner as in Example 2-1. The results are shown in Table 7. Furthermore, evaluation using the above evaluation method revealed that the coating was present on the basal surface of the carbon material.

[0232] [Comparative Example 2-2] SA is 11.9m 2 Using granulated spheroidized natural graphite with a density of 15.7 μm / g and a d50 of 15.7 μm, electrode sheets were prepared using the method described above, and the initial efficiency was measured. The results are shown in Table 7.

[0233] [Table 6]

[0234] [Table 7]

[0235] Reference Examples 2-1 and 2-2 demonstrate that by combining a polyvinyl alcohol-based resin (B1) having hydroxyl and acetoacetyl groups with a silicon-containing compound (B2) as a crosslinking agent, a resin film with moderate elasticity that exhibits almost no swelling or dissolution in water can be formed, and the elution of boron into water can also be suppressed. In Examples 2-1 to 2-5, coating with a polyvinyl alcohol-based resin containing a crosslinking agent reduced the SA of graphite, effectively suppressing side reactions with the electrolyte and demonstrating good initial efficiency.

[0236] On the other hand, in comparative examples 2-1 and 2-2, which did not contain a crosslinking agent, the swelling of the polyvinyl alcohol-based resin was very large, and the elution of boron was hardly suppressed. In comparative example 2-3, which contained a crosslinking agent but did not contain a polyvinyl alcohol-based resin, although the elution of boron was suppressed, the film lacked flexibility and was prone to cracking, resulting in more than half of the boron being eluted. Comparative examples 2-1 and 2-2, which did not have a coating, showed a decrease in initial efficiency due to excessive side reactions with the electrolyte.

[0237] [Examples 2-6] SA is 6.3m 2100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 16.3 μm and a PVOH(B1-3) aqueous solution and a hydrolyzed solution of polytetramethoxysilane (crosslinking agent (B2)) were mixed in a glass container using a three-one motor. The mixture consisted of 100 g of a solution (PVOH(B1-3) solid content concentration 0.5 mass%, polytetramethoxysilane hydrolyzate solid content concentration 0.125 mass%). The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA, initial efficiency, and peel strength were measured for the obtained coated carbon material (C) using the measurement method described above. The results are shown in Table 8. Furthermore, the evaluation method described above was used to determine whether the coating was present on the basal surface of the carbon material, and it was found that it was present. Volume retention was also confirmed.

[0238] [Comparative Example 2-3] SA is 6.3m 2 100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 16.3 μm and 100 g of a solution of PVOH(B1-3) aqueous solution (PVOH(B1-3) solid content concentration 0.5 mass%) was mixed in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA, initial efficiency, and peel strength were measured for the obtained coated carbon material (C) using the measurement method described above. The results are shown in Table 8. Furthermore, evaluation using the evaluation method described above revealed that the coating was present on the basal surface of the carbon material.

[0239] [Comparative Example 2-4] SA is 6.3m 2100 g of spheroidized natural graphite (carbon material (A)) with a d50 of 16.3 μm and a spheroidal density of 16.3 μm was mixed with 100 g of a solution (labelin solid content 0.5% by mass, polytetramethoxysilane hydrolysate solid content 0.125% by mass) prepared by mixing it with an aqueous solution of lavelin (sodium naphthalene sulfonate formalin condensate) and a crosslinking agent (B2) of polytetramethoxysilane hydrolysate. This solution was mixed in a glass container using a three-one motor. The resulting sample was dried and sieved to obtain powdered coated carbon material (C). SA, initial efficiency, and peel strength were measured for the obtained coated carbon material (C) using the measurement method described above. The results are shown in Table 8.

[0240] [Comparative Example 2-5] SA is 6.3m 2 Using spheroidized natural graphite with a density of 16.3 μm / g and a d50 of 16.3 μm, electrode sheets were prepared using the method described above, and the initial efficiency and peel strength were measured. The results are shown in Table 8.

[0241] [Table 8]

[0242] In Examples 2-6, coating with a polyvinyl alcohol-based resin containing a crosslinking agent effectively suppressed side reactions with the electrolyte, resulting in good initial efficiency and peel strength. [Industrial applicability]

[0243] The coated carbon material of the present invention, when used as an active material for the negative electrode of a secondary battery, can provide a lithium-ion secondary battery that maintains capacity while exhibiting superior high-temperature storage characteristics, input / output characteristics, and low gas generation compared to conventional technologies. Furthermore, the manufacturing method of this material involves fewer steps, allowing for stable, efficient, and inexpensive production.

Claims

1. A coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The true density of the carbon material is 2.2 g / cm³ or more and 2.26 g / cm³ or less. A coated carbon material wherein the coating comprises at least one selected from the compounds (X) and crosslinked compounds of the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds

2. A coated carbon material having a coating applied to a carbon material, The carbon material is graphite, The coating comprises at least one selected from the following compounds (X) and crosslinked compounds of the group of compounds (Y), A coated carbon material having a true density of 2.2 g / cm³ or more and 2.26 g / cm³ or less. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds

3. The coated carbon material according to claim 1 or 2, wherein the pore volume in the range of 10 nm to 1000 nm of the carbon material is 0.05 mL / g or more and 0.3 mL / g or less.

4. The coated carbon material according to claim 1 or 2, wherein the pore volume in the range of 10 nm to 1000 nm of the coated carbon material is 0.01 mL / g or more and 0.3 mL / g or less.

5. The coated carbon material according to any one of claims 1 to 4, wherein the coating is applied to the basal surface of the carbon material.

6. The coated carbon material according to any one of claims 1 to 5, wherein the coating comprises the compound (X) described above.

7. The coated carbon material according to claim 6, wherein the acetoacetyl group-containing resin contains a hydroxyl group.

8. The coated carbon material according to claim 6 or 7, wherein the acetoacetyl group-containing resin is a polyvinyl alcohol-based resin containing acetoacetyl groups.

9. The coated carbon material according to any one of claims 1 to 5, wherein the coating comprises a crosslinked compound of the group of compounds (Y) mentioned above.

10. The coated carbon material according to claim 9, wherein the polyvinyl alcohol-based resin contains an acetoacetyl group.

11. The coated carbon material according to claim 9 or 10, wherein the coating further comprises a boron-containing compound.

12. The coated carbon material according to claim 11, wherein the boron element-containing compound is at least one compound selected from boron oxide, metaboric acid, tetraboric acid, borate, and alkoxide having 1 to 3 carbon atoms bonded to boron.

13. A method for manufacturing a coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The true density of the carbon material is 2.2 g / cm³ or more and 2.26 g / cm³ or less. A method for producing a coated carbon material, comprising the step of mixing a carbon material with the compound (X) and / or the group of compounds (Y) described below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds

14. A method for manufacturing a coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The process includes a step of mixing a carbon material with the compound (X) and / or the group of compounds (Y) below, A method for manufacturing a coated carbon material, wherein the true density of the coated carbon material is 2.2 g / cm³ or more and 2.26 g / cm³ or less. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds

15. The device comprises a current collector and an active material layer formed on the current collector, A negative electrode wherein the active material layer includes the coated carbon material described in any one of claims 1 to 12.

16. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery wherein the negative electrode is the negative electrode described in claim 15.

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