Additive for positive electrode of electrochemical element, composition for positive electrode of electrochemical element containing the same, and electrochemical element

Abstract

The present invention relates to an additive for electrochemical element positive electrode, which comprises a specific surface area of 1300 to 2500 m 2 / g, pore volume of pores with a diameter of 2 nm or more is 0.35 cm 3 / g or less, and the pore volume of the pores with a diameter of less than 2nm is 0.5cm 3 / g or more and an ash content of 0.5 wt% or less.

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention based on Japanese Patent Application No. 2020-046095 (filing date: March 17, 2020) and Japanese Patent Application No. 2020-046096 (filing date: March 17, 2020), the entireties of which are hereby incorporated by reference into this specification.

[0002] The present invention relates to an electrochemical device positive electrode additive containing activated carbon, an electrochemical device positive electrode slurry stabilizer containing the same, and an electrochemical device positive electrode composition containing the electrochemical device positive electrode additive. Furthermore, the present invention relates to an electrochemical device having a positive electrode having a layer containing the electrochemical device positive electrode composition. Background Art

[0003] Demand for electrochemical devices such as lithium-ion secondary batteries, which are compact and lightweight, have high energy density, and can be repeatedly charged and discharged, is rapidly increasing due to their unique properties. Due to their high energy density, lithium-ion secondary batteries are used in fields such as mobile phones, notebook personal computers, and electric vehicles. As their applications expand and develop, these electrochemical devices are required to achieve further improvements, such as lower resistance, higher capacity, improved mechanical properties, and increased productivity.

[0004] Electrochemical elements such as lithium ion secondary batteries are developed for the purpose of high capacity, and in particular, positive electrode materials have a great influence on the capacity (miniaturization) of the battery, so high capacity and high performance are urgently needed. For example, in patent document 1, a positive electrode for lithium secondary batteries with excellent short-time output characteristics at low temperatures is studied. In addition, in patent document 2, a lithium secondary battery using a manganese-based positive electrode active material is studied, in which activated carbon is adsorbed to capture manganese ions.

[0005] Furthermore, Patent Documents 3 and 4 study lithium ion secondary batteries that can reduce a decrease in battery capacity by removing moisture within the battery using a moisture adsorbent.

[0006] Furthermore, Patent Document 5 studies a non-aqueous lithium-type storage element that exhibits excellent low-temperature properties while improving high-temperature durability. Furthermore, Patent Document 6 studies activated carbon having a particle size suitable for electric double-layer capacitors and further reduced surface functional groups.

[0007] Furthermore, the electrodes of electrochemical devices are generally obtained by laminating an active material layer formed by bonding an electrode active material and a conductive material used as needed with an adhesive on a current collector. For example, as positive electrode active materials for lithium-ion secondary batteries, LiCoO2, LiMn2O4, LiNi 1-x Co xOxides containing lithium and transition metals that have a structure capable of intercalating lithium, such as O2 (0<X<1). Furthermore, various carbon-based materials, including artificial and natural graphite and hard carbon, that can intercalate and deintercalate lithium, have been used as negative electrode active materials. However, in order to achieve higher battery capacity, research has recently been conducted on non-carbon-based negative electrode active materials, such as Si.

[0008] As mentioned above, LiCoO2 has a high capacity, but it is necessary to reduce the amount of Co used as a rare metal. As a result, LiNi has been developed as a positive electrode active material. (10-x-y) Co x Mn y O2 (0<x<10, 0<y<10), etc. However, when using such a positive electrode active material having a high nickel content, there is a problem that the slurry is easily gelled, especially when a fluorine-based binder is used.

[0009] To address this problem, a method has been investigated in which an acid component is copolymerized in a fluorine-based adhesive resin to acidify the adhesive component, thereby preventing fluorine removal by Ni and suppressing gelation (see Patent Document 7).

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-296431

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-059690

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2001-126766

[0015] Patent Document 4: Japanese Patent Application Laid-Open No. 2014-026819

[0016] Patent Document 5: Japanese Patent Application Publication No. 2020-013881

[0017] Patent Document 6: Japanese Patent No. 5027849

[0018] Patent document 7: Japanese Patent Application Publication No. 2019-200894. Summary of the Invention

[0019] Problems to be solved by the invention

[0020] The technology described in Patent Document 1 demonstrates that the carbonaceous material requires a pore volume of 20 Å or larger to be 0.418 cc / g or larger. However, the formation of excessively large mesopores has the problem of reducing the activated carbon yield, making it economically difficult. Furthermore, the strong adsorption of anions reduces ion diffusivity. Furthermore, the technology described in Patent Document 2 does not consider solutions for situations where the activated carbon contains other metals, such as alkaline earth metals such as calcium, which can cause gelation of fluorinated adhesives such as PVDF and significantly reduce coating properties.

[0021] Furthermore, in the technologies described in Patent Documents 3 and 4, the moisture adsorbent provided inside the lithium-ion secondary battery becomes an unnecessary component after absorbing moisture. Specifically, the moisture adsorbent itself does not contribute to improving battery performance after absorbing moisture, so the unnecessary component persists inside the battery, which is undesirable from the perspective of improving battery performance.

[0022] The activated carbon described in Patent Document 5 is used as a positive electrode active material in a storage element, at a content of 15% by mass or more in the positive electrode active material layer. Furthermore, the activated carbon described in Patent Document 6 is used in electric double-layer capacitors, in either the positive or negative electrode, as an active material, at a content of 80% by mass in the electric double-layer capacitor electrodes.

[0023] Furthermore, the technology described in Patent Document 7 presents problems with the modification of fluorine-based binder resins, including limited copolymerizable monomers, a limited copolymerization modification amount, and limited alkali resistance. Furthermore, alkali resistance is also affected by additives to the positive electrode material. Therefore, a more stable slurry stabilizer is required that can prevent slurry gelation and improve coating properties.

[0024] In view of the above problems, the object of the present invention is to provide an electrochemical element positive electrode additive that can improve the conductivity of the positive electrode, reduce the electrode resistance, and improve the lithium utilization efficiency; an electrochemical element positive electrode slurry stabilizer that can prevent the gelation of the slurry and improve the coating property and improve the battery characteristics; and an electrochemical element positive electrode composition containing the aforementioned electrochemical element positive electrode additive.

[0025] As yet another object of the present invention, an electrochemical device having excellent battery characteristics and comprising a positive electrode produced using the composition is provided.

[0026] Means for solving problems

[0027] As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by an additive for a positive electrode of an electrochemical device containing specific activated carbon, thereby completing the present invention.

[0028] That is, the present invention includes the following aspects.

[0029] [1] An additive for a positive electrode of an electrochemical device, comprising a material having a specific surface area of 1300 to 2500 m2 as determined by the BET method 2 / g, pore volume of pores with a diameter of 2 nm or more is 0.35 cm 3 / g or less, and the pore volume of the pores with a diameter of less than 2nm is 0.5cm 3 / g or more and an ash content of 0.5 wt% or less.

[0030] [2] The electrochemical device positive electrode additive according to [1], wherein the activated carbon has an oxygen content of 1.3 wt% to 3 wt% and a hydrogen content of 0.33 wt% to 0.55 wt%.

[0031] [3] The electrochemical device positive electrode additive according to [1] or [2], wherein the average particle size of the activated carbon is 2 μm to 20 μm.

[0032] [4] A slurry stabilizer for electrochemical device positive electrodes, comprising the additive for electrochemical device positive electrodes according to any one of [1] to [3].

[0033] [5] A composition for an electrochemical element positive electrode, comprising the electrochemical element positive electrode additive according to any one of [1] to [3] and a positive electrode active material, wherein the content of the electrochemical element positive electrode additive is 10% by weight or less relative to the total weight of the positive electrode active material.

[0034] [6] The electrochemical device positive electrode composition according to [5], further comprising 0.5 to 10% by weight of a binder relative to the total weight of the solid content of the electrochemical device positive electrode composition.

[0035] [7] The electrochemical device positive electrode composition according to [5] or [6], further comprising 1 to 10% by weight of a conductive material relative to the total weight of the solid content of the electrochemical device positive electrode composition.

[0036] [8] An electrochemical device comprising a positive electrode for an electrochemical device, wherein the positive electrode for an electrochemical device has a layer containing the composition for an electrochemical device positive electrode according to any one of [5] to [7].

[0037] [9] The electrochemical element according to [8] is characterized in that it operates at 2V~5V.

[0038]

[10] The electrochemical device according to [8] or [9], wherein the electrochemical device is a non-aqueous electrolyte secondary battery.

[0039] Effects of the Invention

[0040] According to the present invention, an electrochemical element positive electrode additive that can improve the conductivity of the positive electrode, reduce electrode resistance, and increase lithium utilization efficiency, an electrochemical element positive electrode slurry stabilizer that can prevent slurry gelation and improve coating properties, and an electrochemical element positive electrode composition containing the electrochemical element positive electrode additive can be provided. In addition, an electrochemical element having excellent battery characteristics having a positive electrode produced using the composition can be provided. DETAILED DESCRIPTION

[0041] Hereinafter, one embodiment of the present invention will be described in detail. However, this is presented as an example and does not limit the present invention. The present invention is defined by the claims.

[0042] [Additives for positive electrodes of electrochemical devices]

[0043] The electrochemical element positive electrode additive of the present invention comprises a specific surface area of 1300 to 2500 m 2 / g, pore volume of pores with a diameter of 2 nm or more is 0.35 cm 3 / g or less, and the pore volume of the pores with a diameter of less than 2nm is 0.5cm 3 / g or more, and an ash content of 0.5 wt % or less activated carbon. The electrochemical element positive electrode additive of the present invention is an activated carbon having such specific pores and low ash content, which adsorbs the metal dissolved from the positive electrode and precipitates on the negative electrode as the counter electrode, not only reducing the danger of short circuits, but also suppressing the alkalinization that is the cause of poor coating during electrode production, and can contribute to the manufacturing stability of the electrode. In addition, the battery characteristics of the electrochemical element produced using it (particularly the reduction in electrode resistance and the reduction in irreversible capacity) can be improved. Furthermore, the electrochemical element positive electrode slurry stabilizer containing such an electrochemical element positive electrode additive can prevent the gelation of the electrochemical element positive electrode slurry, and can also improve the battery characteristics of the electrochemical element produced using it.

[0044] (Activated carbon)

[0045] The specific surface area of the activated carbon used in the present invention is 1300 to 2500 m 2 / g. If the specific surface area is too small, the electrolyte in the electrolyte solution cannot be fully retained and cannot contribute to the reduction of resistance, so it is not preferred. If the specific surface area is too large, the mechanical strength is reduced, and the material is powdered in the battery or released from the electrode during charge and discharge, causing a short circuit and other reduction in battery performance, so it is not preferred. The specific surface area is preferably 1400m 2 / g or more, more preferably 1500m 2 / g or more. In addition, preferably 2400m 2 / g or less, more preferably 2300m2 / g or less, more preferably less than 2300m 2 / g, particularly preferably 2200m 2 / g or less. That is, the specific surface area is preferably 1400~2400m 2 / g, more preferably 1500~2300m 2 / g, more preferably 1500~2200m 2 The specific surface area can be adjusted to the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature and activation time in the activated carbon production method described below, and the like.

[0046] The activated carbon used in the present invention has a pore volume (mesopore volume) of pores with a diameter of 2 nm or more, as measured by pore distribution analysis based on the DFT method using a nitrogen adsorption method, of 0.35 cm 3 / g or less. When the pore volume with a pore diameter of 2nm or more is included in this range, the electrolyte retention capacity is excellent, and a sufficient electrolyte environment can be maintained around the positive electrode active material in the positive electrode, and a fast ion transfer environment can be provided. Thus, the efficiency characteristics can be improved. In addition, such electrolyte retention capacity does not deplete the electrolyte in the positive electrode during the charge and discharge cycle, and the ion transfer environment around the active material is maintained, thereby improving the cycle life. On the other hand, when the pore volume of 2nm or more is larger than the above range, the manufacturing yield of the activated carbon is significantly reduced, which is not only economically preferable, but also increases the bulk density of the activated carbon, resulting in a decrease in the volume capacity as a positive electrode, so it is not preferable. In addition, it is strongly adsorbed on the anions in the battery, and the ion diffusivity is strong, resulting in a decrease in the battery output, so it is not preferable. The pore volume of the pore diameter of 2nm or more is 0.35cm 3 / g or less, more preferably 0.33cm 3 / g or less, more preferably 0.30cm 3 / g or less, particularly preferably 0.25cm 3 / g or less. In addition, the lower limit is not particularly limited, but is preferably 0.02 cm 3 / g or more, more preferably 0.06cm 3 The pore volume of 2 nm or more can be adjusted to the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature and activation time in the activated carbon production method described below, and the like.

[0047] The activated carbon used in the present invention has a pore volume (micropore volume) of pores with a diameter of less than 2 nm as measured by a pore distribution analysis based on a DFT method using a nitrogen adsorption method, and is 0.5 cm 3 / g or more. By making the pore volume with a pore diameter of less than 2nm into the above range, Ni ions dissolved from the positive electrode active material can be adsorbed, which can reduce the risk of precipitation and short circuit on the negative electrode. In addition, it can adsorb Ni ions dissolved from the positive electrode active material and easily prevent the gelation of the slurry. Therefore, the pore volume with a pore diameter of less than 2nm is more preferably 0.53cm 3 / g or more, more preferably 0.55cm 3 On the other hand, if the pore volume of the pore diameter is less than 2nm, it will also adsorb Li ions, so the Li utilization efficiency may be reduced. Therefore, the pore volume of the pore diameter less than 2nm is preferably 1.5cm 3 / g or less, more preferably 1.0 cm 3 The pore volume of less than 2 nm can be adjusted to the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature and activation time in the activated carbon production method described below, and the like.

[0048] The ash content of the activated carbon used in the present invention is 0.5 wt % or less. It is more preferably 0.48 wt % or less, and further preferably 0.46 wt % or less. If the ash content is below the aforementioned upper limit, it is difficult to cause a short circuit, and in addition, it is not easy to react with lithium ions that may cause an increase in irreversible capacity. The heavy metal compounds contained in the ash are likely to diffuse in the positive electrode and precipitate during discharge, so the lower the content, the better. The lower limit of the ash content is not particularly limited and may be 0% or more. The ash content can be obtained by measuring the ignition residue, for example, by the method described in the examples below. Examples of ash that can be contained in activated carbon include nickel, iron, calcium, magnesium, aluminum, and the like. In particular, nickel is preferably 100 ppm or less, more preferably 80 ppm or less, and iron is preferably 100 ppm or less, more preferably 50 ppm or less. The above ash content can also be obtained by, for example, IPC emission spectrometry. The ash content can be adjusted to the above range by, for example, appropriately adjusting the type of activated carbon precursor, the type and concentration of the acid used in acid washing in the activated carbon production method described below, the acid washing time, and the like.

[0049] The oxygen content of the activated carbon used in the present invention is preferably not less than 1.3 wt % and not more than 3 wt %. The method for determining the oxygen content is described later in the examples. When the oxygen content is too low, the affinity for the electrolyte is low, which hinders the penetration of the electrolyte into the electrode, so there is a tendency that it is not preferred. When the oxygen content is too high, the electrochemical stability is sometimes reduced, so it is not only not preferred, but also the affinity with hydrophobic adhesives such as PVDF is reduced, and the electrode strength is sometimes reduced, so there is a tendency that it is not preferred. Therefore, as the oxygen content, it is preferably in the range of 1.3 to 2.9 wt %, more preferably in the range of 1.4 to 2.8 wt %. In addition, the metal dissolved from the positive electrode active material, such as nickel, grows on the negative electrode through charging and discharging when the battery is driven, and there is a possibility that the separator will rupture and cause a short circuit. By setting the oxygen content to the above range, the dissolved nickel can be captured and such a short circuit can be prevented. Furthermore, when the oxygen content is within the above range, the affinity with a hydrophobic adhesive such as PVDF will not be too high, so that gelation of the slurry due to hydrophobic interaction is unlikely to occur, and coating is facilitated.

[0050] The hydrogen content of the activated carbon used in the present invention is preferably not less than 0.33 wt % and not more than 0.55 wt %. The method for determining the hydrogen content will be described later in the examples. When the hydrogen content is too low, the affinity for the electrolyte is low, which sometimes hinders the penetration of the electrolyte into the electrode, so there is a tendency that it is not preferred. When the hydrogen content is too high, the electrochemical stability is sometimes reduced, so it is not only not preferred, but also the affinity with hydrophobic adhesives such as PVDF is reduced, and the electrode strength is reduced, so there is a tendency that it is not preferred. Therefore, as the oxygen content, it is in the range of 0.33~0.53 wt %, more preferably 0.34~0.52 wt %. The oxygen and hydrogen contents can be adjusted to the above ranges by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature, activation time, activation atmosphere, etc. in the activated carbon manufacturing method described later.

[0051] The particle size of the activated carbon used in the present invention is preferably an average particle size of 2 μm to 20 μm as determined by laser scattering. Excessively large particles may hinder conductivity within the positive electrode, which is not preferred. Excessively small particle sizes are not only economically unfavorable, but also contain fine particles, which cannot be completely contained by a binder, making them easily released from the electrode and potentially causing a short circuit or other deterioration in battery performance, which is not preferred.

[0052] (Method for producing activated carbon)

[0053] In the present invention, as the raw material of activated carbon, i.e. carbon precursor, there is no particular restriction, can illustrate for example coconut shell, coffee bean, tealeaves, sugar cane, fruit (such as orange, banana), rice straw, rice husk, broad-leaved tree, conifer, bamboo and other plant materials, lignin, lignocellulose and other plant material processed products, phenolic resin, furan resin, melamine resin and other thermosetting resins, coal, coal tar, petroleum asphalt and other fossil fuels.These raw materials can be used alone, and two or more can be used in combination.Among these plant raw materials, from the viewpoint of obtaining easy and being able to manufacture the activated carbon with various characteristics, preferably plant-derived raw material, preferably coconut shell.

[0054] Coconut shells are not particularly limited, and examples thereof include shells of palm (oil coconut), coconut trees, snake apples, and sea coconuts. These coconut shells may be used alone or in combination of two or more. Coconut shells from coconut trees and palm trees, which are biomass waste generated in large quantities when coconuts are used as food, detergent raw materials, biodiesel raw materials, etc., are particularly preferred from the perspective of easy availability.

[0055] The activated carbon used in the present invention is preferably produced by carbonizing a plant-derived carbon precursor, performing a primary activation, washing, and further performing a higher activation.

[0056] The carbonization and activation method is not particularly limited, and the carbonization and activation can be carried out by known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a multi-stage bed method, and a rotary kiln.

[0057] In the method for producing activated carbon used in the present invention, a plant-derived carbon precursor is first carbonized. The carbonization method is not particularly limited, and examples thereof include methods of carbonizing at a temperature of approximately 400 to 800°C in an atmosphere of an inert gas such as nitrogen, carbon dioxide, helium, argon, carbon monoxide, or fuel exhaust gas, a mixture of these inert gases, or a mixture of these inert gases as a main component with other gases.

[0058] After carbonizing the carbon precursor, a primary activation is performed. There are two activation methods: gas activation and chemical activation. In the present invention, gas activation is preferred due to the low residual impurities. The gas activation method can be performed by reacting the carbonized carbon precursor with an activation gas (e.g., water vapor, carbon dioxide gas, etc.).

[0059] In the primary activation, from the perspective of efficient activation, a mixture of the same inert gas and water vapor as used during carbonization is preferably used, and the partial pressure of water vapor in this case is preferably in the range of 10 to 60%. If the water vapor partial pressure is 10% or more, sufficient activation is easily achieved, while if it is 60% or less, a rapid activation reaction is suppressed, making the reaction easier to control.

[0060] The total amount of the activating gas supplied in one activation is preferably 50 to 10,000 parts by weight, more preferably 100 to 5,000 parts by weight, and even more preferably 200 to 3,000 parts by weight, relative to 100 parts by weight of the carbon precursor. When the total amount of the activating gas supplied is within this range, the activation reaction can proceed more efficiently.

[0061] The activation temperature in the primary activation is generally 700-1100°C, preferably 800-1000°C. The activation time and temperature rise rate are not particularly limited and will undoubtedly vary depending on the type, shape, size, and desired pore diameter distribution of the selected plant-derived carbon precursor. It should be noted that increasing the activation temperature or extending the activation time in the primary activation process tends to increase the BET specific surface area of the resulting activated carbon. Therefore, in order to obtain activated carbon with a BET specific surface area within the desired range, it is necessary to adjust the activation temperature and activation time.

[0062] The activation time for the primary activation is not particularly limited, but is usually in the range of 0.5 to 24 hours, preferably in the range of 1 to 20 hours, and more preferably in the range of 1.5 to 18 hours.

[0063] Next, it is preferred to wash the activated carbon obtained after the primary activation to reduce the ash content. Washing can be performed by immersing the activated carbon obtained after the primary activation in a washing liquid containing an acid. Examples of washing liquids include inorganic acids or organic acids. Examples of inorganic acids include hydrochloric acid and sulfuric acid. Examples of organic acids include saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, and citric acid, and aromatic carboxylic acids such as benzoic acid and terephthalic acid. From the perspective of washing properties, the acid used in the washing liquid is preferably an inorganic acid, more preferably hydrochloric acid. It should be noted that after washing with an acid, it is preferred to further wash with water or the like to remove the remaining acid, and this operation can reduce the load on the activation equipment after the secondary activation.

[0064] The washing liquid can be prepared by mixing an acid and an aqueous solution. Examples of the aqueous solution include water, a mixture of water and a water-soluble organic solvent, and alcohols such as methanol, ethanol, propylene glycol, and ethylene glycol.

[0065] The concentration of the acid in the washing liquid is not particularly limited and can be appropriately adjusted depending on the type of acid used. The acid concentration of the washing liquid is preferably 0.01 to 3.5% by weight, more preferably 0.02 to 2.2% by weight, and even more preferably 0.03 to 1.6% by weight, based on the total amount of the washing liquid. Acid concentrations within the above range are preferred because they allow efficient removal of impurities contained in the activated carbon.

[0066] The temperature of the washing liquid during immersion of the activated carbon is not particularly limited, but is preferably 0 to 98° C., more preferably 10 to 95° C., and even more preferably 15 to 90° C. When the temperature of the washing liquid during immersion of the activated carbon is within this range, washing can be performed in a practical time while minimizing the load on the apparatus, which is desirable.

[0067] The method for washing activated carbon is not particularly limited, as long as the activated carbon can be immersed in the washing liquid. It can be a method in which the washing liquid is continuously added, held for a predetermined period, and then removed while being immersed. Alternatively, the activated carbon is immersed in the washing liquid for a predetermined period, dehydrated, and then re-added, repeating the immersion and dehydration cycles. Furthermore, the entire washing liquid can be refreshed, or a portion of the washing liquid can be refreshed. The time the activated carbon is immersed in the washing liquid can be appropriately adjusted depending on the acid used, the acid concentration, the treatment temperature, and other factors.

[0068] The washing time is not particularly limited, but is preferably 0.05 to 4 hours, more preferably 0.1 to 3 hours, from the viewpoint of economic efficiency of the reaction equipment and structural retention of the activated carbon.

[0069] When the activated carbon is immersed in a washing liquid, the weight ratio of the washing liquid to the activated carbon can be appropriately adjusted depending on the type, concentration, and temperature of the washing liquid used. The weight of the activated carbon immersed relative to the weight of the washing liquid is generally 0.1 to 50% by weight, preferably 1 to 20% by weight, and more preferably 1.5 to 10% by weight. Within this range, impurities dissolved in the washing liquid are less likely to precipitate from the washing liquid, which makes it easier to suppress re-adhesion to the activated carbon. Furthermore, the volumetric efficiency is optimal, which is desirable from an economical perspective.

[0070] The atmosphere for washing is not particularly limited and can be appropriately selected according to the method used for washing. In the present invention, washing is usually performed in an air atmosphere.

[0071] In the present invention, it is preferred to perform a secondary activation of the activated carbon obtained after washing. This secondary activation can be performed under the same conditions as the primary activation described above. It should be noted that, similarly to the secondary activation, increasing the activation temperature or extending the activation time tends to increase the BET specific surface area of the resulting activated carbon. Therefore, to obtain activated carbon with a BET specific surface area within the desired range, the activation temperature and activation time can be adjusted.

[0072] After the secondary activation, a tertiary activation or a higher activation can be performed. Furthermore, washing can be performed between activations after the secondary activation. From an economical perspective, it is preferred to perform the secondary or tertiary activation. In the present invention, the tertiary activation and higher activation can be performed under the same conditions as the primary activation.

[0073] The activated carbon obtained after secondary activation or further high-order activation can also be further washed to remove ash and metal impurities contained in the activated carbon. In addition, the activated carbon obtained after secondary activation or further high-order activation can be heat-treated in an inert gas atmosphere or a vacuum atmosphere at a temperature of 500°C to 1500°C, preferably below 800°C, to remove the residual residue after washing and remove unnecessary surface functional groups, thereby further improving the crystallization of the carbon and increasing the conductivity. The heat treatment time is not particularly limited and is generally in the range of 10 minutes to 3 hours.

[0074] The activated carbon obtained in this manner is preferably then pulverized. The pulverization method is not particularly limited, and a known pulverization method such as a ball mill, a roller mill, or a jet mill, or a combination thereof can be used.

[0075] In the present invention, the activated carbon obtained by crushing can be classified and used. For example, activated carbon particles with a narrow particle size distribution width can be obtained by removing particles with a particle size of 1 μm or less. By removing such fine particles, the amount of binder during electrode formation can be reduced. There are no particular restrictions on the classification method, and examples include classification using a sieve, wet classification, and dry classification. As wet classifiers, there can be mentioned classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, centrifugal classification, etc. As dry classifiers, there can be mentioned classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. From the viewpoint of economy, it is preferred to use a dry classification device.

[0076] The resulting activated carbon can be dried. Drying is an operation used to remove moisture adsorbed on the activated carbon. For example, heating the activated carbon can remove moisture adsorbed on the activated carbon. In addition to or in lieu of heating, drying can be performed by methods such as reduced pressure, reduced pressure heating, and freezing to remove moisture adsorbed on the activated carbon.

[0077] The drying temperature is preferably 100 to 330°C, more preferably 110 to 300°C, and even more preferably 120 to 250°C from the viewpoint of removing moisture adsorbed on the activated carbon.

[0078] The drying time varies depending on the drying temperature used, but from the perspective of removing moisture adsorbed on the activated carbon, it is preferably 0.1 hours or longer, more preferably 0.5 hours or longer, and even more preferably 1 hour or longer. Furthermore, from the perspective of economic efficiency, it is preferably 24 hours or shorter, more preferably 12 hours or shorter, and even more preferably 6 hours or shorter.

[0079] Drying can be performed under normal pressure or reduced pressure. When drying under normal pressure, it is preferably performed under an inert gas atmosphere such as nitrogen or argon, or under air atmosphere with a dew point of -20°C or lower.

[0080] The activated carbon obtained in the above manner can be preferably used as the electrochemical device positive electrode additive of the present invention. In addition, the electrochemical device positive electrode additive of the present invention can also be preferably used as an electrochemical device positive electrode slurry stabilizer. Therefore, the present invention also includes an electrochemical device positive electrode slurry stabilizer containing the electrochemical device positive electrode additive.

[0081] [Composition for positive electrode of electrochemical device]

[0082] The electrochemical device positive electrode composition of the present invention comprises the above-mentioned electrochemical device positive electrode additive and a positive electrode active material. Furthermore, the electrochemical device positive electrode composition of the present invention may optionally comprise other components in addition to the above-mentioned components.

[0083] The content of the electrochemical element positive electrode additive is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 6% by weight or less, relative to the total weight of the positive electrode active material. In addition, the lower limit of the content of the electrochemical element positive electrode additive is not particularly limited, but is preferably 0.5% by weight or more, and more preferably 1% by weight or more.

[0084] The mixing ratio of the electrochemical device positive electrode additive to the positive electrode active material described below can be 1:99 to 10:90 by weight. When the mixing ratio of the electrochemical device positive electrode additive to the positive electrode active material falls within this range, the output characteristics and capacity characteristics tend to be improved.

[0085] [Slurry for positive electrode of electrochemical device]

[0086] The electrochemical device positive electrode slurry comprises the electrochemical device positive electrode slurry stabilizer of the present invention, a positive electrode active material, and a solvent. The electrochemical device positive electrode slurry is stable and resists gelation, resulting in excellent coating properties, allowing the electrochemical device positive electrode to be easily formed on the current collector. Furthermore, the electrochemical device positive electrode slurry may optionally contain other components in addition to those listed above.

[0087] In the electrochemical element positive electrode slurry, the content of the electrochemical element positive electrode slurry stabilizer is preferably 10% by weight or less, more preferably 8% by weight or less, and further preferably 6% by weight or less relative to the total weight of the positive electrode active material. If the content of the electrochemical element positive electrode slurry stabilizer is within the above range, the amount of solvent during slurry adjustment can be reduced, that is, the solid content concentration in the slurry is increased, and together with the coating stability, the time for removing the solvent can be shortened, making the equipment miniaturized. In addition, the lower limit of the content of the electrochemical element positive electrode slurry stabilizer is not particularly limited, but is preferably 0.5% by weight or more, and more preferably 1% by weight or more.

[0088] The mixing ratio of the electrochemical device positive electrode slurry stabilizer to the positive electrode active material described below can be 1:99 to 10:90 by weight. When the mixing ratio of the electrochemical device positive electrode slurry stabilizer to the positive electrode active material is within this range, the output characteristics and capacity characteristics are likely to be improved.

[0089] (Positive electrode active material)

[0090] There are no particular limitations on the positive electrode active material used in the electrochemical element positive electrode composition or the electrochemical element positive electrode slurry, and known positive electrode active materials can be used. For example, lithium-containing cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium-containing nickel oxide (LiNiO2), Co-Ni-Mn lithium-containing composite oxides, Ni-Mn-Al lithium-containing composite oxides, Ni-Co-Al lithium-containing composite oxides, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li 1+x Mn 2-x O4 (0 < X < 2) represented by the lithium-excess spinel compound, Li [Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O2、LiNi 0.5 Mn 1.5 Organic radicals such as metal oxides such as O4, sulfur, compounds having nitroxyl radicals, polymers, compounds having oxygen radicals, polymers, compounds having nitrogen radicals, polymers, compounds having a fulvalene skeleton, and polymers.

[0091] They can be used alone or in combination of two or more. Among the above, from the viewpoint of improving the battery capacity of the secondary battery, lithium-containing cobalt oxide (LiCoO2); lithium-containing nickel oxide (LiNiO2); lithium-containing composite oxides of Co-Ni-Mn, such as LiNi 1 / 3 Co 1 / 3 Mn1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.; Ni-Co-Al lithium-containing composite oxides, such as LiNi 0.8 Co 0.1 Al 0.1 O2、LiNi 0.8 Co 0.15 Al 0.05 O2, etc.

[0092] The particle size of the positive electrode active material is not particularly limited and can be the same as that of conventionally used positive electrode active materials, but is generally in the range of 0.1 μm to 40 μm, more preferably 0.5 μm to 20 μm.

[0093] In the electrochemical device positive electrode composition of the present invention, the content of the positive electrode active material may be 40 to 90% by weight relative to the total weight of the solid components of the composition.

[0094] (Solvent)

[0095] The electrochemical device positive electrode composition of the present invention may contain a solvent. As the solvent used in the electrochemical device positive electrode composition or the electrochemical device positive electrode slurry, for example, an organic solvent can be used, and among them, a polar organic solvent capable of dissolving the binder described below is preferred.

[0096] Specifically, as the organic solvent, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, etc. can be used. Among these, N-methylpyrrolidone (NMP) is most preferred from the viewpoints of ease of handling, safety, ease of synthesis, etc.

[0097] In addition, these organic solvents may be used alone or in combination of two or more.

[0098] The amount of the solvent used is such that the solid content concentration in the electrochemical device positive electrode composition or the electrochemical device positive electrode slurry reaches a range of preferably 1 to 80% by weight, more preferably 5 to 70% by weight, and even more preferably 10 to 60% by weight. By setting the solid content concentration in the above range, the positive electrode active material, electrochemical device positive electrode additive, or electrochemical device positive electrode slurry stabilizer and other contained components can be uniformly dispersed, which is suitable.

[0099] (Adhesive)

[0100] The electrochemical element positive electrode composition or the electrochemical element positive electrode slurry preferably contains a binder for making the positive electrode active material particles adhere well to each other, and further for making the positive electrode active material adhere well to the current collector. As examples of binders, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited thereto. It can be used alone or in combination.

[0101] In the electrochemical device positive electrode composition or the electrochemical device positive electrode slurry, the content of the binder may be 0.5 to 10 wt %, or 1 to 7 wt %, relative to the total weight of the solid components in the composition or slurry.

[0102] (Conductive materials)

[0103] The electrochemical element positive electrode composition or electrochemical element positive electrode slurry may further contain a conductive material in order to further improve the conductivity of the positive electrode formed on the current collector. As the conductive material, any material can be used as long as it is an electronic conductive material that does not cause chemical changes in the electrochemical element. As a specific example of the conductive material, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powders such as copper, nickel, aluminum, silver, metal fibers, etc. can be used. In addition, one or a mixture of two or more conductive materials such as polyphenylene derivatives can be used.

[0104] In the electrochemical device positive electrode composition or the electrochemical device positive electrode slurry, the content of the conductive material may be 1 to 10 wt %, or 1 to 7 wt %, relative to the total weight of the solid components in the composition.

[0105] (Method for producing a positive electrode composition for an electrochemical device)

[0106] The method for producing a positive electrode composition for an electrochemical element can be produced by mixing the above-mentioned electrochemical element positive electrode additive, the positive electrode active material, and a solvent and other components as needed. The mixing method is not particularly limited, and general mixing devices such as a disperser, a mill, and a kneader can be used. For example, stirring is preferably performed for more than 20 minutes and less than 120 minutes.

[0107] The mixing temperature is not particularly limited and is, for example, in the range of 0° C. to 160° C., more preferably in the range of 20° C. to 80° C. Excessively low temperatures are not preferred because the viscosity becomes high and coating becomes impossible. Excessively high temperatures are not preferred from the viewpoints of safety and machine operability due to volatilization of the organic solvent and the accompanying viscosity change.

[0108] (Method for producing slurry for positive electrode of electrochemical device)

[0109] As a method for manufacturing a slurry for an electrochemical element positive electrode, similar to the above-mentioned electrochemical element positive electrode composition, it can be manufactured by mixing a slurry stabilizer for an electrochemical element positive electrode, a positive electrode active material, and other components as needed in a solvent. The mixing method is not particularly limited, and general mixing devices such as a disperser, a mill, and a kneader can be used. For example, stirring is preferably performed for more than 20 minutes and less than 120 minutes.

[0110] The mixing temperature is not particularly limited and is, for example, in the range of 0° C. to 160° C., more preferably in the range of 20° C. to 80° C. Excessively low temperatures are not preferred because the viscosity becomes high and coating becomes impossible. Excessively high temperatures are not preferred from the viewpoints of safety and machine operability due to volatilization of the organic solvent and the accompanying viscosity change.

[0111] [Electrochemical Components]

[0112] Such an electrochemical element positive electrode composition or electrochemical element positive electrode slurry of one embodiment of the present invention can be usefully used in an electrochemical element. The present invention also includes an electrochemical element having a positive electrode made using the above-mentioned electrochemical element positive electrode composition or electrochemical element positive electrode slurry. The electrochemical element of the present invention can improve the conductivity of the positive electrode and reduce the electrode resistance by containing the above-mentioned electrochemical element positive electrode additive. In addition, it is possible to improve the lithium utilization efficiency and reduce the irreversible capacity. The electrochemical element of the present invention preferably operates at 2V~5V, and as an example, a lithium ion secondary battery or a capacitor can be cited.

[0113] For example, when the electrochemical device of the present invention is a lithium ion secondary battery, the lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte.

[0114] (positive electrode)

[0115] The positive electrode is produced using the electrochemical device positive electrode composition or electrochemical device positive electrode slurry of the present invention, and comprises a current collector and a positive electrode active material layer. The positive electrode active material layer is formed by coating the electrochemical device positive electrode composition or electrochemical device positive electrode slurry of the present invention onto the current collector.

[0116] As a method for coating the above-mentioned electrochemical element positive electrode composition or electrochemical element positive electrode slurry on the current collector, there is no particular limitation, and known methods can be used. Specifically, as a coating method, a doctor blade coating method, an immersion method, a reverse roller method, a direct roller method, a gravure method, an extrusion method, a brush coating method, etc. can be used. At this time, the electrochemical element positive electrode composition or the electrochemical element positive electrode slurry can be coated on only one side of the current collector, or on both sides. The thickness of the composition film on the current collector before drying after coating can be appropriately set according to the thickness of the positive electrode active material layer obtained by drying. The positive electrode active material layer is not a composition or slurry containing a solvent, but only a solid component of the electrochemical element positive electrode composition forms a layer on the current collector. There is no particular limitation on the molding method. Dry mixing can be performed while applying mechanical crushing energy using a ball mill, a bead mill, a jet mill, or the like. The powder can be directly formed into a film on the current collector by air deposition or cold spraying to form an electrode. The powder can also be mixed with a polymer adhesive and pressurized and stretched to form a film to form an electrode on the current collector.

[0117] As the current collector for coating the electrochemical device positive electrode composition or electrochemical device positive electrode slurry, a material having electrical conductivity and electrochemical durability is used. Specifically, a current collector comprising aluminum or an aluminum alloy can be used. In this case, aluminum and aluminum alloys can be used in combination, or different types of aluminum alloys can be used in combination. Aluminum and aluminum alloys are excellent current collector materials due to their heat resistance and electrochemical stability.

[0118] The method for drying the electrochemical device positive electrode composition or electrochemical device positive electrode slurry on the current collector is not particularly limited, and known methods can be used, such as drying using warm air, hot air, or low-humidity air, vacuum drying, or drying using irradiation with infrared rays, electron beams, etc. By drying the electrochemical device positive electrode composition or electrochemical device positive electrode slurry on the current collector in this manner, a positive electrode active material layer is formed on the current collector, thereby obtaining a positive electrode having a current collector and a positive electrode active material layer.

[0119] In particular, in order to maintain the metal-capturing capacity of the added activated carbon, it is preferable to fully perform the drying step during positive electrode manufacturing. Preferably, the drying step is performed within a range where the current collector (e.g., aluminum foil) is not affected and the water adsorbed on the surface of the positive electrode active material and the activated carbon can be volatilized. The drying temperature is preferably 100°C to 160°C, at atmospheric pressure or under reduced pressure, for a period of 1 to 12 hours.

[0120] After the drying step, the positive electrode active material layer may be subjected to a press treatment using a press machine, a roll press, etc. The press treatment can improve the adhesion between the positive electrode active material layer and the current collector.

[0121] (negative electrode)

[0122] The negative electrode comprises a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material. The steps of manufacturing the negative electrode are widely known in the art.

[0123] The negative electrode active material includes a substance capable of reversibly intercalating and deintercalating lithium ions, lithium metal, a lithium metal alloy, a substance capable of doping and dedoping lithium, or a transition metal oxide.

[0124] As the material capable of reversibly intercalating and deintercalating lithium ions, crystalline carbon, amorphous carbon, or a combination thereof can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, scaly, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbonization, and calcined coke.

[0125] As the alloy of the above-mentioned lithium metal, an alloy of lithium and a metal selected from Na, K, Mg, Ca, Sr, Si, Sb, In, Zn, Ge, Al and Sn can be used.

[0126] Examples of the substances that can be doped and dedoped in lithium include Si, SiMg alloys, SiO x (0<x<2), Sn, SnO2, etc.

[0127] The content of the negative electrode active material in the negative electrode active material layer may be 70 wt % to 100 wt % relative to the total weight of the negative electrode active material layer. The negative electrode active material layer may consist solely of the negative electrode active material.

[0128] The negative electrode active material layer may also contain a binder and may optionally further contain a conductive material. The binder content in the negative electrode active material layer may be 1% to 5% by weight relative to the total weight of the negative electrode active material layer. Furthermore, when a conductive material is further included, the negative electrode active material may be 80% to 98% by weight, the binder may be 1% to 10% by weight, and the conductive material may be 1% to 10% by weight.

[0129] The binder plays a role in making the negative electrode active material particles adhere well to each other and to the current collector. As the binder, a non-water-soluble binder, a water-soluble binder, or a combination thereof can be used.

[0130] Examples of the water-insoluble adhesive include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, and combinations thereof.

[0131] Examples of the water-soluble adhesive include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, copolymers of propylene and an olefin having 2 to 8 carbon atoms, copolymers of (meth)acrylic acid and an alkyl (meth)acrylate, and combinations thereof.

[0132] When a water-soluble binder is used as the negative electrode binder, a cellulose compound that imparts viscosity may be further used as a thickener. Examples of such cellulose compounds include carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and alkali metal salts thereof. The amount of such a thickener used may be 0.1 to 100 parts by weight relative to 100 parts by weight of the binder.

[0133] The above-mentioned conductive material can be used to impart conductivity to the electrode. In the battery constructed, any material can be used as long as it is an electronic conductive material that does not cause chemical changes. As an example, a conductive material containing carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber; metal-based substances such as metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof can be used.

[0134] As the current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof can be used.

[0135] (Electrolyte)

[0136] The electrolyte preferably contains at least a non-aqueous organic solvent and a lithium salt.

[0137] The non-aqueous organic solvent functions as a medium through which ions participating in the electrochemical reaction of the battery can move.

[0138] As non-aqueous organic solvent, carbonate system, ester system, ether system, ketone system, alcohol system or non-cationic solvent can be used.As above-mentioned carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) etc. can be used, as above-mentioned ester solvent, n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, decanolactone, valerolactone, mevalonolactone, caprolactone etc. can be used.As above-mentioned ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran etc. can be used, as above-mentioned ketone solvent, cyclohexanone etc. can be used. In addition, as the above-mentioned alcohol solvent, ethanol, isopropanol, etc. can be used, and as the above-mentioned non-cationic solvent, nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. can be used.

[0139] The above-mentioned non-aqueous organic solvents may be used alone or in combination of two or more. When two or more kinds are used in combination, the mixing ratio may be appropriately adjusted according to the target battery performance.

[0140] In addition, in the case of the carbonate solvent, a cyclic carbonate and a chain carbonate may be mixed and used. In this case, if the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte solution can be better exhibited.

[0141] The above-mentioned lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery. It can perform basic lithium ion secondary battery operations and promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiClO4, LiAlO4, LiAlCl4, LiN(C x F 2x+1 SO2)(CyF 2y+1SO2) (here, x and y are natural numbers), LiCl, LiI and LiB(C2O4)2 (lithium bis(oxalatoborate) (LiBOB)). They can be used alone or in combination of two or more. The concentration of the lithium salt can be used in the range of 0.1 to 2.0 M. If the concentration of the lithium salt is lower than 0.1 M, the conductivity of the electrolyte becomes lower and there is a tendency for the electrolyte performance to decrease. In the case of more than 2.0 M, there is a tendency for the viscosity of the electrolyte to increase and the mobility of lithium ions to decrease.

[0142] The electrolyte may further contain vinylene carbonate or an ethylene carbonate-based compound as a life enhancer in order to increase battery life.

[0143] Representative examples of the above-mentioned ethylene carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, and fluoroethylene carbonate. When further using such a life-extending agent, its usage amount can be appropriately adjusted.

[0144] In the lithium-ion secondary battery of the present invention, a separator may be present between the positive electrode and the negative electrode. Such a separator may be polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Alternatively, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0145] Lithium-ion secondary batteries are generally formed by placing the aforementioned positive electrode and negative electrode (via a separator as needed) facing each other and immersing them in an electrolyte solution. Example

[0146] Hereinafter, examples and comparative examples will be described. However, the following example is merely one example, and the concept of the present invention is not limited to the following example.

[0147] (Specific surface area by nitrogen adsorption BET method)

[0148] The approximate formula derived from the BET formula is described below.

[0149] [Number 1]

[0150]

[0151] Using the above approximate formula, the adsorption amount (v) measured by the multi-point method using nitrogen adsorption at liquid nitrogen temperature at a predetermined relative pressure (p / p0) is substituted to obtain v m The specific surface area (SSA: unit is m 2 / g).

[0152] [Number 2]

[0153]

[0154] In the above formula, v m is the amount of adsorption required to form a monolayer on the sample surface (cm 3 / g), v is the measured adsorption capacity (cm 3 / g), p0 is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the adsorption heat), and N is the Avogadro constant of 6.022×10 23 , a(nm 2 ) is the area occupied by the adsorbed molecules on the sample surface (cross-sectional area occupied by molecules).

[0155] Specifically, the amount of nitrogen adsorbed on activated carbon at liquid nitrogen temperature was measured using the "Autosorb-iQ-MP" manufactured by Quantachrome as follows. The activated carbon sample was filled into a sample tube. The tube was cooled to -196°C and temporarily depressurized. Nitrogen (99.999% purity) was then allowed to adsorb at the desired relative pressure. The amount of nitrogen adsorbed on the sample at equilibrium pressure at each desired relative pressure was recorded as the adsorbed gas volume v.

[0156] (pore volume)

[0157] The adsorption isotherm obtained from the above-mentioned nitrogen adsorption amount measurement was analyzed by the NL-DFT method, and the volume of pores with a pore diameter (pore diameter) less than 2 nm was calculated as the micropore volume, and the volume of pores with a pore diameter (pore diameter) greater than 2 nm and less than 50 nm was calculated as the mesopore volume.

[0158] (Elemental Analysis)

[0159] Elemental analysis was performed using an oxygen, nitrogen, and hydrogen analyzer EMGA-930 manufactured by Horiba, Ltd., using the inert gas dissolution method.

[0160] The device uses oxygen: inert gas fusion-nondispersive infrared absorption (NDIR), nitrogen: inert gas fusion-thermal conductivity (TCD), and hydrogen: inert gas fusion-nondispersive infrared absorption (NDIR). Calibration is performed using a Ni capsule (oxygen and nitrogen), TiH2 (H standard sample), and SS-3 (N and O standard sample). A 20mg sample, pre-treated for water content measurement at 250°C for approximately 10 minutes, is placed in the Ni capsule and degassed for 30 seconds in the elemental analyzer before measurement. Three samples are analyzed, and the average value is used as the analysis value.

[0161] (Average particle size by laser scattering method)

[0162] The average particle size (particle size distribution) of plant-derived coke (char) and activated carbon was measured using the following method. The sample was placed in an aqueous solution containing 5% by weight of a surfactant (Toriton X100, manufactured by Wako Pure Chemical Industries, Ltd.) and treated with an ultrasonic scrubber for at least 10 minutes to disperse the sample in the aqueous solution.

[0163] The particle size distribution was measured using this dispersion. Particle size distribution was measured using a particle size analyzer (Microtrac MT3300EXII, manufactured by Microtrac BEL Co., Ltd.). D50 represents the particle size at which the cumulative volume reaches 50%, and this value was used as the average particle size.

[0164] (Ash content determination method)

[0165] Measure the weight of an alumina crucible that has been calcined at 900°C and cooled in a desiccant containing silica gel. After vacuum drying in a constant-temperature desiccator set at 120°C for 8-10 hours, add 20g of activated carbon, which has been cooled in a desiccant containing silica gel as a desiccant, to a 50ml alumina crucible. The crucible and activated carbon are weighed to the nearest 0.1mg. The alumina crucible containing the sample is placed in an electric furnace. While dry air is introduced at 20L / min, the temperature is raised to 200°C over 1 hour, then to 700°C over 2 hours, and then maintained at 700°C for 14 hours for ashing. After ashing, cool in a desiccant containing silica gel. The crucible and ash are weighed to the nearest 0.1mg, and the ash content is calculated using the following formula.

[0166] [Number 3]

[0167] .

[0168] (Lithium-ion secondary battery positive electrode composition or lithium-ion secondary battery positive electrode slurry)

[0169] 30 parts by weight of N-methylpyrrolidone solution in which 3 parts by weight of polyvinylidene fluoride (KF polymer 7200 manufactured by Kureha Corporation) was dissolved, and LiNi as a positive electrode active material were added. 1 / 3 Co 1 / 3 Mn 1 / 393 parts by weight of O2 (manufactured by Nippon Chemical Industry Co., Ltd., "cellSeed C-5H"), 2 parts by weight of acetylene black (manufactured by Electrochemical Industry Co., Ltd., "Denka Black") as a conductive material, and 2 parts by weight of activated carbon prepared in the examples and comparative examples described later are mixed, and N-methylpyrrolidone is appropriately added so that the solid content concentration of the composition reaches 50% by weight. At the same time, the mixture is stirred and dispersed using a homogenizer manufactured by Primix (4500 rpm) to obtain a composition for a positive electrode of a lithium ion secondary battery or a slurry for a positive electrode of a lithium ion secondary battery.

[0170] (Positive electrode for lithium-ion secondary batteries)

[0171] The above-mentioned lithium-ion secondary battery positive electrode composition or lithium-ion secondary battery positive electrode slurry was applied to the current collector aluminum foil ("1N30-H", Fuji Kaji Paper) using a bar coater ("T101", manufactured by Matsuo Sangyo). After primary drying at 80°C for 30 minutes using a hot air dryer (manufactured by Yamato Scientific), it was rolled using a roller press (manufactured by Hohsen). After punching out into lithium-ion secondary battery positive electrodes (φ14 mm), it was secondary dried at 120°C under reduced pressure for 3 hours to produce lithium-ion secondary battery positive electrodes. The moisture content at this time was measured by heating the prepared and dried electrodes (φ14 mm) to 250°C using a Karl Fischer (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under a nitrogen flow. The moisture content was controlled to below 20 ppm to allow the added activated carbon to perform its functions other than water absorption.

[0172] (Manufacturing of lithium-ion secondary batteries)

[0173] The positive electrode of the lithium ion secondary battery was transferred to a glove box (manufactured by Miwa Manufacturing Co., Ltd.) under an argon gas atmosphere. The negative electrode used a laminate consisting of a metal lithium foil (thickness 0.2 mm, φ16 mm) as the negative electrode active material layer and a stainless steel foil (thickness 0.2 mm, φ17 mm) as the current collector. In addition, a polypropylene system (cell Guard #2400, manufactured by Polypore) was used as a separator, and a mixed solvent system (1M-LiPF6, EC / EMC=3 / 7 volume%, VC2 weight%) of vinylene carbonate (VC) added to ethylene carbonate (EC) and ethyl methyl carbonate (EMC) of lithium hexafluorophosphate (LiPF6) was used as the electrolyte and injected to produce a coin-shaped lithium ion secondary battery (2032 type).

[0174] 1. Additives for positive electrodes of lithium-ion secondary batteries

[0175] [Example 1]

[0176] The coke (specific surface area: 370m 2 / g), using propane combustion gas + water vapor (water vapor partial pressure: 25%), it was activated once at 850°C for 2 hours. Thereafter, it was acid-washed with hydrochloric acid (concentration: 0.5N, diluent: ion-exchanged water) at a temperature of 85°C for 30 minutes. In order to remove the residual acid, it was thoroughly washed with ion-exchanged water and dried to obtain a once-activated granular activated carbon. Furthermore, a heat treatment at 700°C for 1 hour was implemented under a nitrogen atmosphere. The granular activated carbon was finely pulverized to an average particle size of 6μm to obtain activated carbon.

[0177] [Example 2]

[0178] Following the same procedure as in Example 1, acid-water washing and drying were performed to obtain primary activated granular activated carbon. This granular activated carbon was further secondary activated using propane combustion gas (water vapor partial pressure 15%) at 970°C for 2 hours to obtain granular activated carbon. The secondary activated granular activated carbon was further acid-water washed and dried, then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. This granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0179] [Example 3]

[0180] The activation time of Example 1 was extended to 3 hours, and the specific surface area was 1810 m 2 / g of primary activated granular activated carbon. This granular activated carbon was further secondary activated at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The secondary activated granular activated carbon was further acid-washed and dried, and then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. Activated carbon was obtained in the same manner as in Example 1, except that the acid-washed granular activated carbon was then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon.

[0181] [Example 4]

[0182] The same preparation as in Example 1 was carried out except that the heat treatment was carried out by discharging the mixture into a nitrogen gas flow container having a purity of 99.99% and cooling the mixture to below 200° C. in a nitrogen gas atmosphere.

[0183] The granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0184] [Example 5]

[0185] The same method as in Example 1 was used to obtain a primary activated granular activated carbon. The granular activated carbon was further secondary activated at 970°C using propane combustion gas + steam (steam partial pressure 15%) until the specific surface area reached the following value: a specific surface area of 2252 m 2 / g of secondary activated granular activated carbon. The resulting secondary activated granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. The granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0186] [Example 6]

[0187] Activated carbon was obtained in the same manner as in Example 1 except that the granular activated carbon was finely pulverized to an average particle size of 2.4 μm.

[0188] [Comparative Example 1]

[0189] Activated carbon was obtained in the same manner as in Example 1 except that acid washing was not performed.

[0190] [Comparative Example 2]

[0191] Activated carbon was obtained in the same manner as in Example 1 except that the primary activation temperature was set to 920°C.

[0192] Table 1 shows the physical properties of the activated carbons obtained in Examples and Comparative Examples.

[0193] [Table 1]

[0194] .

[0195] [Examples 7 to 12 and Comparative Examples 3 to 4]

[0196] Using the activated carbon obtained in Examples 1 to 6 and Comparative Examples 1 to 2, a lithium ion secondary battery was prepared according to the above description. For the obtained lithium ion secondary battery, a charge and discharge test device (manufactured by Toyo System Co., Ltd., "TOSCAT") was used to measure the DC resistance value before initial charging, and then a charge and discharge test was performed. For the DC resistance, the resistance value when 0.5 mA was circulated for 3 seconds was measured. Lithium doping was carried out at a rate of 70 mA / g for the weight of the active material until the potential reached 1 mV relative to the lithium. Further, a constant voltage of 1 mV relative to the lithium potential was applied for 8 hours to terminate the doping. The capacity (mAh / g) at this time was recorded as the charge capacity. Then, dedoping was carried out at a rate of 70 mA / g for the weight of the active material until the potential reached 2.5 V relative to the lithium, and the capacity discharged at this time was recorded as the discharge capacity. The percentage of discharge capacity / charge capacity was recorded as the charge and discharge efficiency (initial charge and discharge efficiency), which was used as an indicator of the utilization efficiency of lithium ions in the battery. In addition, the discharge capacity was subtracted from the charge capacity to calculate the irreversible capacity. The results are shown in Table 2.

[0197] [Comparative Example 5]

[0198] A lithium ion secondary battery was produced in the same manner as in Example 7 except that no activated carbon was added, and its characteristics were measured. The obtained results are shown in Table 2.

[0199] [Table 2]

[0200] .

[0201] As shown in the results of Table 2, when using the electrochemical element positive electrode additive of the present invention, the DC resistance is low and the conductivity of the positive electrode is improved. In addition, it is known that the initial charge and discharge efficiency is high and the irreversible capacity is low, so the utilization efficiency of the lithium ions in the battery is improved. On the other hand, when using the activated carbon of Comparative Example 1 whose ash content does not meet the scope of the present invention, the lithium ion secondary battery is short-circuited and the battery characteristics cannot be measured. In addition, when using the activated carbon of Comparative Example 2 whose specific surface area and pore volume do not meet the scope of the present invention, compared with Comparative Example 3 without activated carbon, the DC resistance is improved, and in addition, for the initial charge and discharge efficiency and other battery characteristics, poor results are also obtained.

[0202] 2. Lithium ion secondary battery positive electrode slurry stabilizer

[0203] [Example 13]

[0204] The coke (specific surface area: 370m 2 / g) and activated once at 850°C for 2 hours using propane combustion gas + water vapor (water vapor partial pressure: 25%). Subsequently, the activated carbon was acid-washed with hydrochloric acid (concentration: 0.5N, diluent: ion-exchanged water) at 85°C for 30 minutes. To remove residual acid, the activated carbon was thoroughly washed with ion-exchanged water, dried, and then heat-treated at 700°C for 1 hour under a nitrogen atmosphere. The granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0205] [Example 14]

[0206] Following the same procedures as in Example 13, acid-water washing and drying were performed to obtain primary activated granular activated carbon. This granular activated carbon was further activated secondary at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The secondary activated granular activated carbon was further acid-water washed and dried, then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. This granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0207] [Example 15]

[0208] The activation time of Example 13 was extended by 3 hours to obtain a specific surface area of 1810 m 2 / g of primary activated granular activated carbon. This granular activated carbon was further secondary activated at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The secondary activated granular activated carbon was further acid-washed and dried, and then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. Activated carbon was obtained in the same manner as in Example 13 except that the acid-washed granular activated carbon was not further activated.

[0209] [Example 16]

[0210] The same method as in Example 13 was used for preparation, except that the heat treatment was discharged into a nitrogen gas flow container with a purity of 99.99% and cooled to below 200°C under a nitrogen gas atmosphere. The granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0211] [Example 17]

[0212] The same method as in Example 13 was used to obtain a primary activated granular activated carbon. The granular activated carbon was further secondary activated at 970°C using propane combustion gas + steam (steam partial pressure 15%) until the specific surface area reached the following value: a specific surface area of 2252 m 2 / g of secondary activated granular activated carbon. The resulting secondary activated granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C under a nitrogen atmosphere for 1 hour to obtain secondary washed granular activated carbon. The granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0213] [Example 18]

[0214] Activated carbon was obtained in the same manner as in Example 13 except that the granular activated carbon was finely pulverized to an average particle size of 2.4 μm.

[0215] [Comparative Example 6]

[0216] Activated carbon was obtained in the same manner as in Example 13 except that the heat treatment temperature was set to 830°C.

[0217] [Comparative Example 7]

[0218] Activated carbon was obtained in the same manner as in Example 13 except that the primary activation temperature was set to 920°C.

[0219] [Comparative Example 8]

[0220] Activated carbon was obtained in the same manner as in Example 14 except that the secondary activation temperature was set to 870°C.

[0221] Table 3 shows the physical properties of the activated carbons obtained in Examples and Comparative Examples.

[0222] [Table 3]

[0223] .

[0224] [Examples 19 to 24 and Comparative Examples 9 to 12]

[0225] Using the activated carbon obtained in Examples 13 to 18 and Comparative Examples 6 to 8, according to the above description, a slurry for a positive electrode of a lithium ion secondary battery and a lithium ion secondary battery were prepared. A charge and discharge test device (manufactured by Toyo System Co., Ltd., "TOSCAT") was used to perform a charge and discharge test on the obtained lithium ion secondary battery. Lithium doping was performed at a rate of 70 mA / g for the mass of the active material until the potential reached 1 mV relative to the lithium. Further, a constant voltage of 1 mV relative to the lithium potential was applied for 8 hours to terminate the doping. The capacity (mAh / g) at this time was recorded as the charge capacity. Next, dedoping was performed at a rate of 70 mA / g for the mass of the active material until the potential reached 2.5 V relative to the lithium, and the capacity discharged at this time was recorded as the discharge capacity. The percentage of discharge capacity / charge capacity was recorded as the charge and discharge efficiency (initial charge and discharge efficiency), which was used as an indicator of the utilization efficiency of lithium ions in the battery. In addition, the charge and discharge efficiency was calculated by subtracting the discharge capacity from the charge capacity to obtain the irreversible capacity. The results are shown in Table 4.

[0226] (Applicability Evaluation)

[0227] The coating properties of the lithium-ion secondary battery positive electrode composition obtained above were evaluated as follows. After hot air drying the coated electrode at 80°C for 30 minutes as described above, a rating of ◎ was given if there were no bubbles or aggregates on the coated surface; a rating of 0 was given if there were no bubbles but some aggregates; a rating of △ was given if only slight aggregates were observed; and a rating of × was given if aggregates were present throughout. The results are shown in Table 4.

[0228] [Comparative Example 12]

[0229] A lithium ion secondary battery was produced in the same manner as in Example 19 except that no activated carbon was added, and its characteristics were measured. The obtained results are shown in Table 4.

[0230] [Table 4]

[0231] .

[0232] As shown in Table 4, when the electrochemical element positive electrode slurry stabilizer of the present invention is used, the slurry coating properties are excellent, and the lithium ion secondary battery produced using the slurry has excellent battery characteristics. On the other hand, when activated carbon that does not meet the scope of the present invention is used or when no activated carbon is used as a slurry stabilizer, the slurry coating properties are poor, and the battery characteristics of the resulting lithium ion secondary battery are also poor.

Claims

1. An additive for an electrochemical device positive electrode, comprising activated carbon, wherein the activated carbon has a specific surface area of 1300 to 2500 m2 as measured by the BET method. 2 / g; the pore volume of pores with a diameter of 2nm or more is 0.35cm 3 / g or less; pore diameter less than 2nm and pore volume of 0.5cm 3 / g or more; ash content is 0.5 wt% or less; oxygen content is 1.3 wt% or more and 3 wt% or less; and the average particle size is 2 μm to 20 μm.

2. The electrochemical device positive electrode additive according to claim 1, wherein The activated carbon has a hydrogen content of 0.33% by weight or more and 0.55% by weight or less. 3 . A slurry stabilizer for electrochemical device positive electrodes, comprising the additive for electrochemical device positive electrodes according to claim 1 .

4. A composition for an electrochemical element positive electrode, comprising the electrochemical element positive electrode additive according to claim 1 or 2 and a positive electrode active material, wherein the content of the electrochemical element positive electrode additive is 10% by weight or less relative to the total weight of the positive electrode active material. 5 . The electrochemical device positive electrode composition according to claim 4 , further comprising 0.5 to 10 wt % of a binder based on the total weight of the solid content of the electrochemical device positive electrode composition. 6 . The electrochemical device positive electrode composition according to claim 4 , further comprising 1 to 10% by weight of a conductive material based on the total weight of the solid content of the electrochemical device positive electrode composition. 7 . An electrochemical device comprising a positive electrode for an electrochemical device, the positive electrode for an electrochemical device comprising a layer containing the composition for an electrochemical device positive electrode according to claim 4 .

8. The electrochemical element according to claim 7, characterized in that Works at 2V~5V.

9. The electrochemical element according to claim 7 or 8, wherein The electrochemical element is a non-aqueous electrolyte secondary battery.