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

Abstract

The present invention pertains to an additive for a electrochemical element positive electrode, the additive having a specific surface area, determined by the BET method, of 1300-2500 m2 / g, a pore volume of pores having a diameter of 2 nm or more of 0.35 cm3 / g or less, a pore volume of pores having a pore diameter less than 2 nm of 0.5 cm3 / g or more, and an ash content of 0.5 wt% or less, and the additive comprising activated carbon.

Description

[Technical field]

[0001] This patent application claims priority under the Paris Convention to Japanese Patent Application No. 2020-046095 (filed March 17, 2020) and Japanese Patent Application No. 2020-046096 (filed March 17, 2020), the entireties of which are incorporated herein by reference. The present invention relates to an additive for electrochemical element positive electrodes comprising activated carbon, a slurry stabilizer for electrochemical element positive electrodes comprising the same, and a composition for electrochemical element positive electrodes comprising the additive for electrochemical element positive electrodes. The present invention also relates to an electrochemical element comprising a positive electrode having a layer made of the composition for electrochemical element positive electrodes. [Background technology]

[0002] Demand for electrochemical elements such as lithium-ion secondary batteries is rapidly expanding due to their characteristics: they are small, lightweight, have a high energy density, and can be repeatedly charged and discharged. Lithium-ion secondary batteries are used in fields such as mobile phones, notebook personal computers, and electric vehicles because of their relatively high energy density. As the applications of these electrochemical elements expand and develop, further improvements are required, such as lower resistance, higher capacity, improved mechanical properties, and improved productivity.

[0003] Electrochemical elements such as lithium ion secondary batteries are being developed with the aim of increasing capacity, and since the positive electrode material in particular has a large effect on the capacity (miniaturization) of the battery, there is an urgent need to increase the capacity and performance of the positive electrode material. For example, Patent Document 1 studies a positive electrode for lithium secondary batteries that has excellent short-time output characteristics at low temperatures. In addition, Patent Document 2 studies a lithium secondary battery using a manganese-based positive electrode active material in which manganese ions are adsorbed and trapped by activated carbon.

[0004] In addition, Patent Documents 3 and 4 have studied a lithium-ion secondary battery capable of reducing a decrease in battery capacity by removing moisture in the battery using a moisture adsorbent.

[0005] Furthermore, Patent Document 5 has studied a non-aqueous lithium-based energy storage element that exhibits excellent low-temperature characteristics while adding high-temperature durability. In addition, Patent Document 6 has studied activated carbon having a particle size suitable for an electric double layer capacitor and a reduced amount of surface functional groups.

[0006] In addition, an electrochemical element electrode is usually formed by laminating an active material layer formed by binding an electrode active material and a conductive material used as needed with a binder on a current collector. For example, as the positive electrode active material of a lithium-ion secondary battery, oxides composed of lithium and transition metals having a structure capable of lithium intercalation such as LiCoO2, LiMn2O4, LiNi 1-x Co x O2 (0 < X < 1) are mainly known. As the negative electrode active material, various forms of carbon-based materials including artificial and natural graphite and hard carbon capable of lithium intercalation / deintercalation have been applied. However, in order to exhibit a higher battery capacity, recently, research on non-carbon-based negative electrode active materials such as Si has been conducted.

[0007] As described above, although LiCoO2 has a high capacity, it is necessary to reduce the amount of Co, which is a rare metal, used. As a result, LiNi (10-x-y) Co x Mn y O2 (0 < x < 10, 0 < y < 10) and the like have been developed. However, when using such a positive electrode active material with a high nickel content, there is a problem that the slurry easily gels, especially when using a fluorine-based binder.

[0008] To address this problem, methods have been investigated in which an acid component is copolymerized with a fluorine-based binder resin to acidify the binder component, thereby preventing fluorine abstraction by Ni and suppressing gelation (see Patent Document 7). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2004-296431 A [Patent Document 2] JP 2012-059690 A [Patent Document 3] JP 2001-126766 A [Patent Document 4] JP 2014-026819 A [Patent Document 5] JP 2020-013881 A [Patent Document 6] Patent No. 5027849 [Patent Document 7] JP 2019-200894 A Summary of the Invention [Problem to be solved by the invention]

[0010] The technology described in Patent Document 1 indicates that the carbonaceous material must have a pore volume of 0.418 cc / g or more with a pore size of 20 Å or more, but the formation of excessively large mesopores reduces the activated carbon yield, making it economically difficult, and furthermore, has the problem of strong adsorption to anions and reducing ion diffusibility. Moreover, the technology described in Patent Document 2 does not take into consideration the case where the activated carbon contains other metals, for example, alkaline earth metals such as calcium, which cause fluorine-based binders such as PVDF to gel and significantly reduce coatability.

[0011] In addition, in the techniques described in Patent Documents 3 and 4, the moisture adsorbent provided inside the lithium ion secondary battery becomes an unnecessary member after adsorbing moisture. In other words, after adsorbing moisture, the moisture adsorbent itself does not contribute to improving the battery characteristics, so that an unnecessary member continues to exist inside the battery, which is not preferable from the viewpoint of improving the battery characteristics.

[0012] The activated carbon described in Patent Document 5 is used as a positive electrode active material of an electricity storage element in a positive electrode active material layer in a content of 15% by mass or more. The activated carbon described in Patent Document 6 is applied to an electric double layer capacitor, is used in both the positive and negative electrodes, and is used as an active material in an electrode for an electric double layer capacitor in a content of 80% by mass.

[0013] Furthermore, in the technology described in Patent Document 7, the modification of the fluorine-based binder resin has a problem that the number of monomers that can be copolymerized is small, the amount of copolymerization modification is limited, and the alkali resistance is limited, and the alkali resistance is also affected by additives in the positive electrode material. Therefore, there is a demand for a slurry stabilizer that is more stable, can prevent the gelation of the slurry, and can improve the coatability.

[0014] In view of the above problems, an object of the present invention is to provide an additive for electrochemical element positive electrodes capable of improving the conductivity of a positive electrode, reducing the electrode resistance, and increasing the lithium utilization efficiency, a slurry stabilizer for electrochemical element positive electrodes capable of preventing gelation of a slurry, improving the coatability, and improving battery characteristics, and a composition for electrochemical element positive electrodes containing the additive for electrochemical element positive electrodes.

[0015] It is still another object of the present invention to provide an electrochemical device having a positive electrode prepared using the above composition and having excellent battery characteristics. [Means for solving the problem]

[0016] As a result of extensive investigations, the present inventors have found that the above problems can be solved by an additive for a positive electrode of an electrochemical element, which comprises a specific activated carbon, and have thus completed the present invention. That is, the present invention includes the following aspects.

[0017] [1] BET specific surface area is 1300-2500 m 2 / g, and the pore volume of pores with diameters of 2 nm or more is 0.35 cm 3 / g or less, and the pore volume of pores with a diameter of less than 2 nm is 0.5 cm 3 / g or more and an ash content of 0.5 wt % or less. [2] The additive for a positive electrode of an electrochemical element according to [1], wherein the activated carbon has an oxygen content of 1.3% by weight or more and 3% by weight or less, and a hydrogen content of 0.33% by weight or more and 0.55% by weight or less. [3] The additive for a positive electrode of an electrochemical element according to [1] or [2], wherein the activated carbon has an average particle size of 2 μm to 20 μm. [4] A slurry stabilizer for a positive electrode of an electrochemical element, comprising the additive for a positive electrode of an electrochemical element according to any one of [1] to [3]. [5] A composition for an electrochemical element positive electrode, comprising the additive for an electrochemical element positive electrode according to any one of [1] to [3] and a positive electrode active material, wherein the content of the additive for an electrochemical element positive electrode is 10 wt % or less based on the total weight of the positive electrode active material. [6] The composition for an electrochemical element positive electrode according to [5], further comprising 0.5 to 10% by weight of a binder based on the total weight of the solid content of the composition for an electrochemical element positive electrode. [7] The composition for an electrochemical element positive electrode according to [5] or [6], further comprising 1 to 10% by weight of a conductive material based on the total weight of the solid content of the composition for an electrochemical element positive electrode. [8] An electrochemical device comprising a positive electrode for an electrochemical device having a layer made of the composition for a positive electrode of an electrochemical device according to any one of [5] to [7]. [9] The electrochemical device according to [8], which operates at 2 V to 5 V.

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

[0018] According to the present invention, it is possible to provide an additive for a positive electrode of an electrochemical element capable of improving the conductivity of the positive electrode, reducing the electrode resistance, and increasing the lithium utilization efficiency, a slurry stabilizer for a positive electrode of an electrochemical element capable of preventing the gelation of a slurry, improving the coatability, and improving the battery characteristics, and a composition for a positive electrode of an electrochemical element containing the additive for a positive electrode of an electrochemical element. It is also possible to provide an electrochemical element having a positive electrode prepared using the composition and having excellent battery characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] An embodiment of the present invention will now be described in detail, which is given by way of example only and is not intended to limit the invention, as defined by the claims.

[0020] [Additives for positive electrodes of electrochemical elements] The additive for the positive electrode of an electrochemical element of the present invention has a specific surface area of ​​1300 to 2500 m by the BET method. 2 / g, and the pore volume of pores with diameters of 2 nm or more is 0.35 cm 3 / g or less, and the pore volume of pores with a diameter of less than 2 nm is 0.5 cm 3 The electrochemical element positive electrode additive of the present invention is an activated carbon having such specific pores and low ash content, and therefore adsorbs metals eluted from the positive electrode, and reduces the risk of deposition and short circuit on the negative electrode, which is the counter electrode, and can suppress basification, which is a cause of coating defects during electrode production, and contribute to the manufacturing stability of the electrode. In addition, it is possible to improve the battery characteristics of the electrochemical element produced using this (particularly, reduction in electrode resistance and irreversible capacity). Furthermore, the electrochemical element positive electrode slurry stabilizer composed of such an electrochemical element positive electrode additive can prevent gelation of the electrochemical element positive electrode slurry, and can improve the battery characteristics of the electrochemical element produced using this.

[0021] (activated carbon) The activated carbon used in the present invention has a specific surface area of ​​1300 to 2500 m2 as measured by the BET method. 2 / g. If the specific surface area is too small, it is not preferable because it cannot sufficiently retain the electrolyte in the electrolyte solution and cannot contribute to a decrease in resistance. If the specific surface area is too large, it is not preferable because it reduces the mechanical strength, powders in the battery, or is separated from the electrode during charging and discharging, causing a short circuit and other deterioration in battery performance. The specific surface area is preferably 1400 m 2 / g or more, more preferably 1500m 2 / g or more. Also, preferably 2400m 2 / g or less, more preferably 2300m 2 / g or less, more preferably 2300m 2 / g, particularly preferably less than 2200m 2 That is, the specific surface area is preferably 1400 to 2400 m 2 / g, more preferably 1500 to 2300 m 2 / g, and more preferably 1500 to 2200 m 2 The specific surface area can be adjusted to fall within the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature, the activation time, and the like in the method for producing activated carbon described below.

[0022] The activated carbon used in the present invention has a pore volume (mesopore volume) of 0.35 cm3 for pores with a diameter of 2 nm or more, as measured by pore distribution analysis using the DFT method using a nitrogen adsorption method. 3 / g or less. When the pore volume of the pore diameter of 2 nm or more is within this range, the electrolyte retention ability is excellent, and a sufficient electrolyte environment can be maintained around the positive electrode active material in the positive electrode, providing a fast ion transfer environment. This can improve the efficiency characteristics. In addition, such electrolyte retention ability can maintain the ion transfer environment around the active material while the charge / discharge cycle is proceeding, preventing the electrolyte from being depleted in the positive electrode, thereby improving the cycle life. On the other hand, when the pore volume of 2 nm or more is larger than the above range, it is not only economically undesirable because it significantly reduces the production yield of the activated carbon, but also increases the bulk density of the activated carbon, which leads to a decrease in the volume capacity as a positive electrode, which is undesirable. In addition, it is undesirable because it strongly adsorbs to anions in the battery, which leads to a decrease in the ion diffusion and therefore to a decrease in the battery output. The pore volume of pore diameter of 2 nm or more is 0.35 cm 3 / g or less, more preferably 0.33 cm 3 / g or less, more preferably 0.30 cm 3 / g or less, and particularly preferably 0.25 cm 3 / g or less. The lower limit is not particularly limited, but is 0.02 cm 3 / g or more is preferable, and 0.06 cm 3 The pore volume of 2 nm or more can be adjusted to fall within the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature, the activation time, and the like in the method for producing activated carbon described below.

[0023] The activated carbon used in the present invention has a pore volume of 0.5 cm3 for pores with diameters of less than 2 nm (micropore volume) as measured by pore distribution analysis using the DFT method with nitrogen adsorption. 3 / g or more. By having the pore volume of pores with diameters of less than 2 nm in the above range, Ni ions eluted from the positive electrode active material can be adsorbed, and the risk of precipitation on the negative electrode and short circuit can be reduced. In addition, Ni ions eluted from the positive electrode active material can be adsorbed, and gelation of the slurry can be easily prevented. Therefore, the pore volume of pores with diameters of less than 2 nm is 0.53 cm 3 / g or more is more preferable, and 0.55 cm 3 / g or more is more preferable. On the other hand, if the pore volume of the pores with a diameter of less than 2 nm is too large, Li ions are also adsorbed, and the Li utilization efficiency may decrease. Therefore, the pore volume of the pores with a diameter of less than 2 nm is preferably 1.5 cm 3 / g or less is preferable, and 1.0 cm 3 The pore volume of less than 2 nm can be adjusted to fall within the above range by, for example, appropriately adjusting the type of activated carbon precursor, the activation temperature, the activation time, etc. in the method for producing activated carbon described below.

[0024] The activated carbon used in the present invention has an ash content of 0.5% by weight or less. More preferably, it is 0.48% by weight or less, and even more preferably, it is 0.46% by weight or less. When the ash content is less than the upper limit, short circuits are unlikely to occur, and reactions with lithium ions that may cause an irreversible capacity increase are unlikely to occur. The heavy metal compounds contained in the ash may diffuse in the positive electrode and precipitate during discharge, so the lower the content, the more preferable it is. The lower limit of the ash content is not particularly limited, and may be 0% or more. The ash content can be determined by measuring the ignition residue, for example, by the method described in the Examples below. Examples of ash that can be contained in the activated carbon include nickel, iron, calcium, magnesium, and aluminum. 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, and the ash content can also be determined, for example, by IPC emission spectroscopy. The ash content can be adjusted to fall within the above range by appropriately adjusting, for example, the type of activated carbon precursor, the type and concentration of the acid used in acid washing in the method for producing activated carbon described below, the acid washing time, and the like.

[0025] The activated carbon used in the present invention preferably has an oxygen content of 1.3% by weight or more and 3% by weight or less. The method for measuring the oxygen content will be described later in the Examples. If the oxygen content is too low, the affinity for the electrolyte is low, which tends to hinder the electrolyte from penetrating into the electrode, which is undesirable. If the oxygen content is too high, not only is the electrochemical stability reduced, but the affinity with hydrophobic binders such as PVDF is reduced, which tends to reduce the electrode strength, which is undesirable. Therefore, the oxygen content is preferably 1.3 to 2.9% by weight, and more preferably 1.4 to 2.8% by weight. In addition, metals such as nickel eluted from the positive electrode active material may grow on the negative electrode due to charging and discharging during battery operation, which may break the separator and cause a short circuit, but by setting the oxygen content in the above range, the eluted nickel can be trapped and such a short circuit can be prevented. Furthermore, if the oxygen content is within the above range, the affinity with hydrophobic binders such as PVDF is not too high, so that gelation of the slurry due to hydrophobic interactions is unlikely to occur, making it easier to apply.

[0026] The activated carbon used in the present invention preferably has a hydrogen content of 0.33% by weight or more and 0.55% by weight or less. The method for measuring the hydrogen content will be described later in the Examples. If the hydrogen content is too low, it tends to be undesirable because it has low affinity for the electrolyte and may hinder the electrolyte from penetrating into the electrode. If the hydrogen content is too high, it is not only undesirable because it may reduce the electrochemical stability, but also undesirable because it reduces the affinity with hydrophobic binders such as PVDF, reducing the electrode strength. Therefore, hydrogen The content is in the range of 0.33 to 0.53% by weight, more preferably 0.34 to 0.52% by weight. The oxygen and hydrogen contents can be adjusted to the above ranges by, for example, appropriately adjusting the type of activated carbon precursor, and the activation temperature, activation time, activation atmosphere, etc. in the method for producing activated carbon described below.

[0027] The particle size of the activated carbon used in the present invention is preferably 2 μm to 20 μm in average particle size determined by a laser scattering method. Particles that are too large tend to be undesirable because they may inhibit the conductivity in the positive electrode, while particles that are too small tend to be undesirable not only economically but also because they contain fine powder, which cannot be suppressed by a binder or the like and is easily liberated from the electrode, which may cause a decrease in battery performance such as a short circuit.

[0028] (Activated carbon manufacturing method) In the present invention, the carbon precursor, which is the raw material of activated carbon, is not particularly limited, but examples thereof include coconut shells, coffee beans, tea leaves, sugar cane, fruits (e.g., mandarin oranges, bananas), straw, rice husks, broad-leaved trees, conifers, bamboo, and other plant materials, processed plant materials such as lignin and lignocellulose, thermosetting resins such as phenolic resins, furan resins, and melamine resins, and fossil fuels such as coal, coal pitch, and petroleum pitch. These raw materials may be used alone or in combination of two or more. Among these plant raw materials, plant-derived raw materials are preferred, and coconut shells are preferred, because they are easily available and can produce activated carbons with various properties.

[0029] The coconut shell is not particularly limited, but examples thereof include coconut shells of palm (oil palm), coconut, salak, and oat palm. These coconut shells may be used alone or in combination of two or more. Coconut and palm shells are biomass wastes generated in large quantities after coconuts are used as food, detergent raw materials, biodiesel oil raw materials, and the like, and are particularly preferred from the viewpoint of easy availability.

[0030] The activated carbon used in the present invention is preferably produced by carbonizing a plant-derived carbon precursor, subjecting it to primary activation, washing, and further subjecting it to high-level activation.

[0031] The carbonization and activation methods are not particularly limited, and may 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, or a rotary kiln.

[0032] In the method for producing activated carbon used in the present invention, a carbon precursor derived from a plant is first carbonized. The carbonization method is not particularly limited, but includes a method of carbonizing the precursor at a temperature of about 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 mixed gas of these inert gases, or a mixed gas of these inert gases with other gases that mainly contain these inert gases.

[0033] After the carbon precursor is carbonized, primary activation is performed. There are gas activation and chemical activation methods as activation methods, but in the present invention, gas activation is preferred from the viewpoint of leaving less 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.).

[0034] In the primary activation, from the viewpoint of efficiently proceeding with the activation, a mixture of inert gas and water vapor similar to that used in carbonization is preferred, and the partial pressure of the water vapor is preferably in the range of 10 to 60%. If the partial pressure of the water vapor is 10% or more, the activation can be easily proceeded sufficiently, and if it is 60% or less, a rapid activation reaction is suppressed, and the reaction can be easily controlled.

[0035] The total amount of activation gas supplied in the primary activation is preferably 50 to 10,000 parts by weight, more preferably 100 to 5,000 parts by weight, and further preferably 200 to 3,000 parts by weight, relative to 100 parts by weight of the carbon precursor. When the total amount of activation gas supplied is within the above range, the activation reaction can proceed more efficiently.

[0036] The activation temperature in the primary activation is usually 700 to 1100°C, preferably 800 to 1000°C. The activation time and the heating rate are not particularly limited, and it goes without saying that they vary depending on the type, shape, size, and desired pore size distribution of the plant-derived carbon precursor selected. In addition, if the activation temperature in the primary activation is increased or the activation time is extended, the BET specific surface area of ​​the obtained activated carbon tends to increase. Therefore, in order to obtain activated carbon having a BET specific surface area in the desired range, it is necessary to adjust the activation temperature and activation time.

[0037] 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.

[0038] Next, it is preferable to wash the activated carbon obtained after the primary activation to reduce the ash content. The washing can be performed by immersing the activated carbon obtained after the primary activation in a washing solution containing an acid. Examples of the washing solution include mineral acids and organic acids. Examples of the mineral acids include hydrochloric acid and sulfuric acid. Examples of the 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 viewpoint of washability, the acid used in the washing solution is preferably a mineral acid, and more preferably hydrochloric acid. In addition, after washing with an acid, it is preferable to further wash with water or the like to remove excess acid, and this operation can reduce the load on the activation equipment after the secondary activation.

[0039] The cleaning solution can usually be prepared by mixing an acid with an aqueous solution. The aqueous solution can be water or a mixture of water and a water-soluble organic solvent. The water-soluble organic solvent can be, for example, an alcohol such as methanol, ethanol, propylene glycol, or ethylene glycol.

[0040] The concentration of the acid in the cleaning solution is not particularly limited, and may be appropriately adjusted depending on the type of acid used. The acid concentration in the cleaning solution 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 cleaning solution. If the acid concentration in the cleaning solution is within the above range, it is preferable because impurities contained in the activated carbon can be efficiently removed.

[0041] The temperature of the cleaning solution when the activated carbon is immersed is not particularly limited, but is preferably 0 to 98° C., more preferably 10 to 95° C., and further preferably 15 to 90° C. If the temperature of the cleaning solution when the activated carbon is immersed is within the above range, it is desirable because cleaning can be performed for a practical time with reduced load on the device.

[0042] The method for washing the activated carbon is not particularly limited as long as it can immerse the activated carbon in the washing liquid, and may be a method in which the washing liquid is continuously added, retained for a predetermined time, and immersed while removing the liquid, or a method in which the activated carbon is immersed in the washing liquid, retained for a predetermined time, drained, and then new washing liquid is added and the immersion-draining process is repeated. In addition, the washing liquid may be entirely renewed, or may be partially renewed. The time for immersing the activated carbon in the washing liquid may be appropriately adjusted depending on the acid used, the concentration of the acid, the treatment temperature, etc.

[0043] The washing time is not particularly limited, but from the viewpoints of the economic efficiency of the reaction equipment and the structure retention of the activated carbon, it is preferably 0.05 to 4 hours, more preferably 0.1 to 3 hours.

[0044] When immersing the activated carbon in the washing solution, the weight ratio between the washing solution and the activated carbon may be appropriately adjusted depending on the type, concentration, temperature, etc. of the washing solution used. The weight of the activated carbon to be immersed relative to the weight of the washing solution is usually 0.1 to 50% by weight, preferably 1 to 20% by weight, and more preferably 1.5 to 10% by weight. Within the above range, impurities dissolved in the washing solution are unlikely to precipitate from the washing solution, redeposition to the activated carbon is easily suppressed, and the volume efficiency is appropriate, which is desirable from the viewpoint of economy.

[0045] The atmosphere in which the cleaning is carried out is not particularly limited and may be appropriately selected depending on the method used for cleaning. In the present invention, cleaning is usually carried out in an air atmosphere.

[0046] In the present invention, it is preferable to carry out secondary activation of the activated carbon obtained after washing. The secondary activation can be carried out under the same condition range as the primary activation. Similarly, in the secondary activation, if the activation temperature is increased or the activation time is extended, the BET specific surface area of ​​the obtained activated carbon tends to increase. Therefore, in order to obtain activated carbon having a BET specific surface area in the desired range, the activation temperature and activation time may be adjusted.

[0047] After the secondary activation, a tertiary activation or a higher activation may be carried out. Also, washing may be carried out between each activation after the secondary activation. From the viewpoint of economic efficiency, it is preferable to carry out the secondary activation or the tertiary activation. In the present invention, the tertiary activation and the higher activation may be carried out under the same condition range as the primary activation.

[0048] The activated carbon obtained after the secondary activation or a higher activation may be further washed to remove ash and metal impurities contained in the activated carbon. The activated carbon obtained after the secondary activation or a higher activation may be heat-treated in an inert gas atmosphere or a vacuum atmosphere at 500°C to 1500°C, preferably 800°C or less, to heat-remove residues after washing, remove unnecessary surface functional groups, and increase the crystallization of the carbon to increase electrical conductivity. The heat-treatment time is not particularly limited, but is usually in the range of 10 minutes to 3 hours.

[0049] The activated carbon thus obtained is then preferably pulverized. The pulverization method is not particularly limited, but any known pulverization method such as a ball mill, a roll mill, or a jet mill, or a combination of these methods can be used.

[0050] In the present invention, the activated carbon obtained by pulverization may be classified before use. For example, by removing particles having a particle size of 1 μm or less, activated carbon particles having a narrow particle size distribution width can be obtained. By removing such fine particles, it is possible to reduce the amount of binder when constructing an electrode. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From the viewpoint of economy, it is preferable to use a dry classification device.

[0051] The obtained activated carbon may be dried. Drying is an operation for removing moisture and the like adsorbed to the activated carbon, and for example, the activated carbon may be heated to remove the moisture and the like adsorbed to the activated carbon. In addition to or instead of heating, drying may be performed by means of, for example, reduced pressure, reduced pressure heating, freezing, or the like to remove the moisture and the like adsorbed to the activated carbon.

[0052] The drying temperature is preferably from 100 to 330°C, more preferably from 110 to 300°C, and even more preferably from 120 to 250°C, from the viewpoint of removing the moisture adsorbed on the activated carbon.

[0053] The drying time depends on the drying temperature employed, but from the viewpoint of removing the moisture adsorbed on the activated carbon, it is preferably 0.1 hours or more, more preferably 0.5 hours or more, and even more preferably 1 hour or more, and from the viewpoint of economy, it is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less.

[0054] The drying can be carried out under normal pressure or reduced pressure. When the drying is carried out under normal pressure, it is preferable to carry out the drying under an inert gas atmosphere such as nitrogen gas or argon gas, or under an air atmosphere with a dew point of -20°C or lower.

[0055] The activated carbon obtained as described above can be preferably used as an additive for the positive electrode of an electrochemical element of the present invention. The additive for the positive electrode of an electrochemical element of the present invention can also be preferably used as a slurry stabilizer for the positive electrode of an electrochemical element. Therefore, the present invention also includes a slurry stabilizer for the positive electrode of an electrochemical element, which is composed of the additive for the positive electrode of an electrochemical element.

[0056] [Composition for positive electrodes of electrochemical elements] The composition for a positive electrode of an electrochemical element of the present invention contains the additive for a positive electrode of an electrochemical element and the positive electrode active material described above. The composition for a positive electrode of an electrochemical element of the present invention may also contain other components in addition to those described above.

[0057] The content of the additive for the positive electrode of the electrochemical element is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 6% by weight or less, based on the total weight of the positive electrode active material. The lower limit of the content of the additive for the positive electrode of the electrochemical element is not particularly limited, but is preferably 0.5% by weight or more, and more preferably 1% by weight or more.

[0058] The mixing ratio of the electrochemical element positive electrode additive to the positive electrode active material described below may be 1:99 to 10:90 by weight. When the mixing ratio of the electrochemical element positive electrode additive to the positive electrode active material is within this range, the output characteristics and capacity characteristics tend to be good.

[0059] [Slurry for electrochemical element positive electrodes] The slurry for electrochemical element positive electrode contains the above-mentioned slurry stabilizer for electrochemical element positive electrode of the present invention, a positive electrode active material, and a solvent. The slurry for electrochemical element positive electrode is unlikely to gel and is stable, so that it has excellent coatability and can easily form an electrochemical element positive electrode on a current collector. The slurry for electrochemical element positive electrode may also contain other components other than those described above.

[0060] In the slurry for electrochemical element positive electrode, the content of the slurry stabilizer for electrochemical element positive electrode is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 6% by weight or less, based on the total weight of the positive electrode active material. When the content of the slurry stabilizer for electrochemical element positive electrode is within the above range, the amount of solvent during slurry preparation can be reduced, that is, the solid content in the slurry can be increased, and the time required to remove the solvent can be shortened and the equipment can be made smaller, along with coating stability. In addition, the lower limit of the content of the slurry stabilizer for electrochemical element positive electrode is not particularly limited, but is preferably 0.5% by weight or more, and more preferably 1% by weight or more.

[0061] The mixing ratio of the slurry stabilizer for electrochemical element positive electrodes to the positive electrode active material described below may be 1:99 to 10:90 by weight. When the mixing ratio of the slurry stabilizer for electrochemical element positive electrodes to the positive electrode active material is within this range, the output characteristics and capacity characteristics tend to be good.

[0062] (Cathode active material) The positive electrode active material to be mixed in the electrochemical element positive electrode composition or the electrochemical element positive electrode slurry is not particularly limited, and any known positive electrode active material can be used. For example, lithium-containing cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxide of Co-Ni-Mn, lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li 1+x Mn 2-xLithium-excess spinel compounds represented by O4 (0 < X < 2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4 and other metal oxides, sulfur, compounds and polymers having nitroxyl radicals, compounds and polymers having oxyradicals, compounds and polymers having nitrogen radicals, organic radicals such as compounds and polymers having a fulvalene skeleton, etc. can be mentioned.

[0063] These 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, etc., lithium-containing cobalt oxide (LiCoO2) as a positive electrode active material; lithium-containing nickel oxide (LiNiO2); lithium-containing composite oxide of Co-Ni-Mn, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.; lithium-containing composite oxide of Ni-Co-Al, for example LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc. are preferably used.

[0064] Note that the particle size of the positive electrode active material is not particularly limited and can be the same as that of the conventionally used positive electrode active material. Usually, the range of 0.1 μm to 40 μm, more preferably 0.5 μm to 20 μm is used.

[0065] In the composition for the positive electrode of the electrochemical element of the present invention, the content of the positive electrode active material may be 40 to 90% by weight based on the total weight of the solid content of the composition.

[0066] (Solvent) The composition for electrochemical element positive electrode of the present invention may contain a solvent. As the solvent used in the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode, for example, an organic solvent can be used, and among them, a polar organic solvent capable of dissolving the binder described later is preferable. Specifically, the organic solvent that can be used includes acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, N,N-dimethylacetamide, dimethylformamide, dimethylsulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, etc. Among these, N-methylpyrrolidone (NMP) is most preferable from the viewpoints of ease of handling, safety, ease of synthesis, etc. These organic solvents may be used alone or in combination of two or more.

[0067] The amount of the solvent used is such that the solid content concentration in the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode is preferably in the range of 1 to 80% by weight, more preferably 5 to 70% by weight, and further preferably 10 to 60% by weight. By setting the solid content concentration in the above range, the positive electrode active material, the additive for electrochemical element positive electrode or the slurry stabilizer for electrochemical element positive electrode, and other components contained therein can be uniformly dispersed, which is preferable.

[0068] (binder) The electrochemical element positive electrode composition or the electrochemical element positive electrode slurry preferably contains a binder for adhering the positive electrode active material particles to each other well and for adhering the positive electrode active material to the current collector well. Examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. These may be used alone or in combination. In the composition for electrochemical element positive electrodes or the slurry for electrochemical element positive electrodes, the content of the binder may be 0.5 to 10% by weight, or 1 to 7% by weight, based on the total weight of solids in the composition or slurry.

[0069] (Conductive material) The composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode may further contain a conductive material in order to further increase the conductivity of the positive electrode formed on the current collector. Any conductive material that does not cause chemical changes in the electrochemical element may be used as the conductive material. Specific examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers, metal powders and metal fibers such as copper, nickel, aluminum, and silver, and conductive materials such as polyphenylene derivatives may be used in combination of one or more types. In the composition for electrochemical element positive electrodes or the slurry for electrochemical element positive electrodes, the content of the conductive material may be 1 to 10% by weight, or 1 to 7% by weight, based on the total weight of solids in the composition.

[0070] (Method of manufacturing a composition for electrochemical element positive electrode) The composition for the positive electrode of an electrochemical element can be produced by mixing the additive for the positive electrode of an electrochemical element, the positive electrode active material, and, if necessary, a solvent and other components. There is no particular limitation on the mixing method, and for example, a general mixing device such as a disperser, a mill, or a kneader can be used. For example, it is preferable to stir for 20 minutes or more and 120 minutes or less.

[0071] 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. If the temperature is too low, the viscosity becomes too high and coating becomes impossible, which is undesirable, while if the temperature is too high, it is undesirable from the viewpoints of safety and operability of the equipment, due to the volatilization of the organic solvent and the associated viscosity changes.

[0072] (Method for producing slurry for electrochemical element positive electrode) The method for producing the slurry for the positive electrode of an electrochemical element is the same as the method for producing the slurry for the positive electrode of an electrochemical element described above, which can be produced by mixing the slurry stabilizer for the positive electrode of an electrochemical element, the positive electrode active material, and other components as necessary in a solvent. There is no particular limitation on the mixing method, and for example, a general mixing device such as a disper, a mill, or a kneader can be used. For example, it is preferable to stir for 20 minutes or more and 120 minutes or less.

[0073] 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. If the temperature is too low, the viscosity becomes too high and coating becomes impossible, which is undesirable, while if the temperature is too high, it is undesirable from the viewpoints of safety and operability of the equipment, due to the volatilization of the organic solvent and the associated viscosity changes.

[0074] [Electrochemical element] The composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode according to the embodiment of the present invention can be usefully used in electrochemical elements. The present invention also includes an electrochemical element having a positive electrode prepared using the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode. The electrochemical element of the present invention contains the additive for electrochemical element positive electrode, and thus the conductivity of the positive electrode is improved and the electrode resistance can be reduced. In addition, the lithium utilization efficiency can be improved and the irreversible capacity can be reduced. The electrochemical element of the present invention is preferably one that operates at 2V to 5V, and examples thereof include a lithium ion secondary battery or a capacitor.

[0075] 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.

[0076] (positive electrode) The positive electrode is prepared using the composition for electrochemical element positive electrodes or the slurry for electrochemical element positive electrodes of the present invention, and includes a current collector and a positive electrode active material layer. The positive electrode active material layer is formed by applying the composition for electrochemical element positive electrodes or the slurry for electrochemical element positive electrodes of the present invention to the current collector.

[0077] The method of applying the electrochemical element positive electrode composition or the electrochemical element positive electrode slurry on the current collector is not particularly limited, and a known method can be used. Specifically, the application method can be a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like. In this case, the electrochemical element positive electrode composition or the electrochemical element positive electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the composition film on the current collector before drying after application can be appropriately set according to the thickness of the positive electrode active material layer obtained by drying. The positive electrode active material layer may be formed on the current collector not as a composition or slurry containing a solvent, but only with the solid content of the electrochemical element positive electrode composition. The molding method is not particularly limited, and the material can be dry-mixed while applying mechanical crushing energy using a ball mill, a bead mill, a jet mill, or the like, and then formed into a film on a current collector in the powder state by an aerodeposition method or a cold spray method to form an electrode, or the material can be kneaded with a polymer binder, pressurized and stretched to form a film, and then formed into an electrode on a current collector.

[0078] As the current collector to which the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode is applied, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, a current collector made of aluminum or an aluminum alloy can be used. In this case, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat resistant and electrochemically stable.

[0079] The method for drying the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode on the current collector is not particularly limited and may be a known method, for example, drying with warm air, hot air, or low humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. By drying the composition for electrochemical element positive electrode or the slurry for electrochemical element positive electrode on the current collector in this manner, a positive electrode active material layer can be formed on the current collector, and a positive electrode including the current collector and the positive electrode active material layer can be obtained.

[0080] In particular, in order to maintain the metal capturing power of the added activated carbon, it is preferable to perform the drying process sufficiently during the production of the positive electrode, and it is preferable to perform drying within a range in which the current collector (e.g., aluminum foil) is not affected and the water adsorbed on the positive electrode active material and the activated carbon surface can be evaporated. Preferably, the drying is performed at a temperature of 100°C to 160°C under atmospheric pressure or reduced pressure for 1 to 12 hours.

[0081] After the drying step, the positive electrode active material layer may be subjected to a pressure treatment using a mold press, a roll press, etc. The pressure treatment can improve the adhesion between the positive electrode active material layer and the current collector.

[0082] (Negative electrode) The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer including a negative electrode active material. The process for producing the negative electrode is a process well known in the art.

[0083] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0084] The material capable of reversibly intercalating / deintercalating lithium ions may be crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, scaly, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0085] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Mg, Ca, Sr, Si, Sb, In, Zn, Ge, Al and Sn may be used.

[0086] The above-mentioned lithium-doped and dedoped materials include Si, alloys such as SiMg, SiO x (0 <x<2)、Sn、SnO2などがあげられる。

[0087] The content of the negative electrode active material in the negative electrode active material layer may be 70% by weight to 100% by weight based on the total weight of the negative electrode active material layer. The negative electrode active material layer may be made of only the negative electrode active material.

[0088] The negative electrode active material layer may also include a binder, and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer further includes a conductive material, the negative electrode active material may be used in an amount of 80 wt% to 98 wt%, the binder may be used in an amount of 1 wt% to 10 wt%, and the conductive material may be used in an amount of 1 wt% to 10 wt%.

[0089] The binder serves to adhere the negative electrode active material particles to each other and to the current collector well. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0090] The non-water-soluble binder includes polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0091] Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and an olefin having 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and an alkyl (meth)acrylate ester, or a combination thereof.

[0092] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further used as a thickener. Examples of the cellulose-based compound include carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose and alkali metal salts thereof, and the content of such a thickener may be 0.1 to 100 parts by weight per 100 parts by weight of the binder.

[0093] The conductive material is used to impart electrical conductivity to the electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Examples of the conductive material that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0094] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0095] (electrolyte) The electrolyte preferably contains at least a non-aqueous organic solvent and a lithium salt.

[0096] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0097] As the non-aqueous organic solvent, carbonate, ester, ether, ketone, alcohol, or aprotic solvent may be used. As the 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. may be used, and as the ester solvent, n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. may be used. As the ether, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used, and as the ketone solvent, cyclohexanone, etc. may be used. Furthermore, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and as the aprotic solvent, nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 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. may be used.

[0098] The non-aqueous organic solvents may be used alone or in combination of two or more. When two or more are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance.

[0099] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate in a volume ratio of 1:1 to 1:9, which can provide better electrolyte performance.

[0100] The lithium salt is a substance that is dissolved in an organic solvent and acts as a lithium ion source in a battery to enable basic operation of a lithium ion secondary battery and promotes 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+1 Examples of the lithium salt include lithium bis(oxalatoborate) (LiBOB) and lithium bis(oxalatoborate). These may be used alone or in combination. The lithium salt concentration is preferably within the range of 0.1 to 2.0M. If the lithium salt concentration is less than 0.1M, the electrolyte conductivity tends to decrease and the electrolyte performance tends to decrease, whereas if the lithium salt concentration is more than 2.0M, the electrolyte viscosity tends to increase and the mobility of lithium ions tends to decrease.

[0101] The electrolyte may further contain a vinylene carbonate or ethylene carbonate based compound as a life enhancer to improve the battery life.

[0102] Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life improver is further used, the amount used may be appropriately adjusted.

[0103] In the lithium ion secondary battery of the present invention, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, or 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.

[0104] A lithium ion secondary battery is generally formed by opposing the above-mentioned positive electrode and negative electrode (with a separator interposed between them as necessary) and immersing them in an electrolyte solution. EXAMPLES

[0105] Examples and comparative examples will be described below, but the following examples are merely examples and the concept of the present invention is not limited to the following examples.

[0106] (Specific surface area by nitrogen adsorption BET method) Below is an approximate formula derived from the BET formula.

number

[0107] Using the above approximation formula, the amount of adsorption (v) measured at a given relative pressure (p / p0) by the multipoint method using nitrogen adsorption at liquid nitrogen temperature is substituted to obtain v m The specific surface area (SSA: unit is m 2 / g) was calculated.

number

[0108] In the above formula, v m is the amount of adsorption (cm) required to form a monolayer on the sample surface. 3 / g), v is the measured adsorption amount (cm 3 / g), p0 is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the heat of adsorption), and N is Avogadro's number 6.022 × 10 23 , a(nm 2 ) is the area that the adsorbate molecule occupies on the sample surface (molecular occupancy cross-sectional area).

[0109] Specifically, the amount of nitrogen adsorbed by activated carbon at liquid nitrogen temperature was measured using Quantachrome's "Autosorb-iQ-MP" as follows. The activated carbon, which was the measurement sample, was filled into a sample tube, and the sample tube was cooled to -196°C, and the pressure was reduced once, and then nitrogen (purity 99.999%) was adsorbed onto the measurement sample at the desired relative pressure. The amount of nitrogen adsorbed into the sample when equilibrium pressure was reached at each desired relative pressure was taken as the amount of adsorbed gas v.

[0110] (Pore volume) The adsorption isotherm obtained by measuring the amount of adsorbed nitrogen as described above was analyzed by the NL-DFT method, and the volume of pores having a pore diameter of less than 2 nm was calculated as the micropore volume, and the volume of pores having a pore diameter of 2 nm or more and 50 nm or less was calculated as the mesopore volume.

[0111] (Elemental analysis) Elemental analysis was performed based on the inert gas dissolution method using an oxygen / nitrogen / hydrogen analyzer EMGA-930 (Horiba, Ltd.). The detection methods of this device are oxygen: inert gas fusion-non-dispersive infrared absorption (NDIR), nitrogen: inert gas fusion-thermal conductivity (TCD), hydrogen: inert gas fusion-non-dispersive infrared (NDIR), and calibration is performed with (oxygen / nitrogen) Ni capsule, TiH2 (H standard sample), and SS-3 (N, O standard sample). As pretreatment, 20 mg of the sample whose moisture content was measured at 250℃ for about 10 minutes was placed in a Ni capsule and degassed for 30 seconds in the elemental analyzer before measurement. Three samples were analyzed in the test, and the average value was used as the analytical value.

[0112] (Average particle size by laser scattering method) The average particle size (particle size distribution) of plant-derived char and activated carbon was measured by the following method: The sample was placed in an aqueous solution containing 5% by weight of a surfactant ("ToritonX100" manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution was measured using a particle size / particle size distribution measuring device (Microtrack MT3300EXII, manufactured by Microtrack Bell Co., Ltd.). D50 is the particle size at which the cumulative volume becomes 50%, and this value was used as the average particle size.

[0113] (Method of measuring ash content) The weight of the alumina crucible was measured after baking at 900°C and cooling in a desiccator containing silica gel. After vacuum drying for 8-10 hours in a thermostatic dryer adjusted to 120°C, 20g of activated carbon was placed in an alumina crucible with a volume of 50 ml, and the weight of the crucible + activated carbon was accurately measured to the nearest 0.1 mg. The alumina crucible containing the sample was placed in an electric furnace, and while introducing dry air into the electric furnace at 20 L / min, the temperature was raised to 200°C in 1 hour, and then raised to 700°C over 2 hours, and the sample was kept at 700°C for 14 hours for incineration. After incineration, the sample was cooled in a desiccator containing silica gel, and the weight of the crucible + ash was accurately measured to the nearest 0.1 mg, and the ash content was calculated using the following formula.

number

[0114] (Composition for lithium ion secondary battery positive electrode or slurry for lithium ion secondary battery positive electrode) 30 parts by weight of N-methylpyrrolidone solution containing 3 parts by weight of polyvinylidene fluoride (KF Polymer 7200, manufactured by Kureha Corporation), LiNi 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 Denki Kagaku Kogyo Co., Ltd., "Denka Black") as a conductive material, and 2 parts by weight of the activated carbon prepared in the Examples and Comparative Examples described below were added and mixed, and stirred and dispersed in a homogenizer manufactured by Primix Corporation (4,500 rpm) while adding N-methylpyrrolidone appropriately so that the solid content concentration of the composition became 50% by weight, thereby obtaining a composition for lithium ion secondary battery positive electrode or a slurry for lithium ion secondary battery positive electrode.

[0115] (Positive electrode for lithium-ion secondary batteries) The lithium ion secondary battery positive electrode composition or the lithium ion secondary battery positive electrode slurry was applied to an aluminum foil current collector ("1N30-H", Fuji Kakoshi) using a bar coater ("T101", Matsuo Sangyo Co., Ltd.), and then primary dried at 80 ° C. for 30 minutes with a hot air dryer (Yamato Scientific Co., Ltd.), followed by rolling using a roll press (Hosen Co., Ltd.). After that, the lithium ion secondary battery positive electrode (φ14 mm) was punched out, and secondary dried at 120 ° C. for 3 hours under reduced pressure to prepare a lithium ion secondary battery positive electrode. The water content at this time was measured by taking the prepared and dried electrode (φ14 mm), heating it to 250 ° C. with a Karl Fischer (Mitsubishi Chemical Analytech Co., Ltd.), and measuring the water content under a nitrogen stream, and controlling the water content to be 20 ppm or less, so that the added activated carbon could exert functions other than water absorption.

[0116] (Production of lithium-ion secondary batteries) The positive electrode for the lithium ion secondary battery was transferred to a glove box (manufactured by Miwa Seisakusho) under an argon gas atmosphere. For the negative electrode, a laminate consisting of a metallic 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 was used. In addition, a polypropylene-based separator (Celgard #2400, manufactured by Polypore) was used, and the electrolyte was injected using a mixed solvent system (1M-LiPF6, EC / EMC=3 / 7 volume%, VC2 weight%) of lithium hexafluorophosphate (LiPF6) with vinylene carbonate (VC) added to ethylene carbonate (EC) and ethyl methyl carbonate (EMC), to prepare a coin-type lithium ion secondary battery (2032 type).

[0117] 1. Additives for the positive electrodes of lithium-ion secondary batteries [Example 1] Char made from Philippine coconut shells (specific surface area: 370 m 2 The carbon black was subjected to primary activation for 2 hours at 850°C using propane combustion gas and water vapor (water vapor partial pressure: 25%) for 100g / g. The carbon black was then pickled for 30 minutes at 85°C using hydrochloric acid (concentration: 0.5 normal, diluent: ion-exchanged water), and then thoroughly washed with ion-exchanged water to remove residual acid, and dried to obtain primary activated granular activated carbon. Further, heat treatment was performed at 700°C for 1 hour in a nitrogen atmosphere. The granular activated carbon was then pulverized to an average particle size of 6 μm to obtain activated carbon.

[0118] [Example 2] The primary activation granular activated carbon was obtained by washing with acid water and drying in the same manner as in Example 1. This granular activated carbon was further subjected to secondary activation using propane combustion gas (water vapor partial pressure 15%) at 970°C for 2 hours to obtain granular activated carbon. The obtained secondarily activated granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere 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.

[0119] [Example 3] The activation time in Example 1 was extended to 3 hours, and the specific surface area was increased to 1810 m2 / g of primary activation granular activated carbon. This granular activated carbon was further subjected to secondary activation at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The obtained secondarily activated granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere to obtain secondary washed granular activated carbon, and the activated carbon was obtained in the same manner as in Example 1.

[0120] [Example 4] The same procedure as in Example 1 was repeated except that the mixture was prepared and discharged into a nitrogen flow container with a purity of 99.99% when the mixture was discharged for heat treatment, and cooled to 200° C. or less under a nitrogen gas atmosphere. This granular activated carbon was pulverized to an average particle size of 6 μm to obtain activated carbon.

[0121] [Example 5] Primary activation granular activated carbon was obtained in the same manner as in Example 1. This granular activated carbon was further subjected to secondary activation using propane combustion gas + steam (steam partial pressure 15%) at 970°C until the specific surface area reached the following: specific surface area of ​​2252 m 2 / g of secondarily activated granular activated carbon was obtained. The obtained secondarily activated granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere to obtain secondarily washed granular activated carbon. This granular activated carbon was finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0122] [Example 6] The procedure of Example 1 was repeated to obtain activated carbon, except that the granular activated carbon was pulverized to an average particle size of 2.4 μm.

[0123] [Comparative Example 1] Activated carbon was obtained in the same manner as in Example 1, except that the acid washing was not carried out.

[0124] [Comparative Example 2] An activated carbon was obtained in the same manner as in Example 1, except that the primary activation temperature was 920°C.

[0125] The physical properties of the activated carbons obtained in the examples and comparative examples are shown in Table 1.

[0126] [Table 1]

[0127] [Examples 7 to 12 and Comparative Examples 3 to 4] Using the activated carbon obtained in Examples 1 to 6 and Comparative Examples 1 to 2, lithium ion secondary batteries were produced according to the above description. The obtained lithium ion secondary batteries were subjected to a charge / discharge test using a charge / discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT") to measure the DC resistance before initial charging, and then a charge / discharge test was performed. The DC resistance was measured when 0.5 mA was applied for 3 seconds. Lithium doping was performed at a rate of 70 mA / g relative to the weight of the active material, and doping was continued until the lithium potential reached 1 mV. A constant voltage of 1 mV was further applied to the lithium potential for 8 hours to terminate the doping. The capacity (mAh / g) at this time was taken as the charge capacity. Next, dedoping was performed at a rate of 70 mA / g relative to the weight of the active material until the lithium potential reached 2.5 V, and the capacity discharged at this time was taken as the discharge capacity. The percentage of the discharge capacity / charge capacity was taken as the charge / discharge efficiency (initial charge / discharge efficiency), which was used as an index of the utilization efficiency of lithium ions in the battery. The irreversible capacity was calculated by subtracting the discharge capacity from the charge capacity. The results are shown in Table 2.

[0128] [Comparative Example 5] A lithium ion secondary battery was fabricated and its characteristics were measured in the same manner as in Example 7, except that no activated carbon was added. The results are shown in Table 2.

[0129] [Table 2]

[0130] From the results in Table 2, it was found that when the additive for electrochemical element positive electrodes of the present invention was used, the DC resistance was low and the conductivity of the positive electrode was improved. In addition, the initial charge / discharge efficiency was high and the irreversible capacity was low, indicating that the utilization efficiency of lithium ions in the battery was improved. On the other hand, when the activated carbon of Comparative Example 1, in which the ash content does not satisfy the range of the present invention, was used, the lithium ion secondary battery shorted out and the battery characteristics could not be measured. In addition, when the activated carbon of Comparative Example 2, in which the specific surface area and pore volume do not satisfy the range of the present invention, was used, the lithium ion secondary battery shorted out and the battery characteristics could not be measured. 5 The DC resistance was higher than that of the conventional battery, and the initial charge / discharge efficiency and other battery characteristics were also inferior.

[0131] 2. Slurry stabilizer for positive electrodes of lithium-ion secondary batteries [Example 13] Char made from Philippine coconut shells (specific surface area: 370 m 2 The activated carbon (1.0 g / g) was subjected to primary activation at 850°C for 2 hours using propane combustion gas + steam (steam partial pressure: 25%). It was then pickled at 85°C for 30 minutes using hydrochloric acid (concentration: 0.5 normal, diluent: ion-exchanged water), and then thoroughly washed with ion-exchanged water to remove residual acid, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere. This granular activated carbon was then finely pulverized to an average particle size of 6 μm to obtain activated carbon.

[0132] [Example 14] The primary activation granular activated carbon was obtained by washing with acid water and drying in the same manner as in Example 13. This granular activated carbon was further subjected to secondary activation at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The obtained secondary activation granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere 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.

[0133] [Example 15] The activation time of Example 13 was extended by 3 hours, and the specific surface area was increased to 1810 m 2 / g of primary activation granular activated carbon. This granular activated carbon was further subjected to secondary activation at 970°C using propane combustion gas (water vapor partial pressure 15%) to obtain granular activated carbon. The obtained secondary activation granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere to obtain secondary washed granular activated carbon, and the activated carbon was obtained in the same manner as in Example 13.

[0134] [Example 16] The same procedure was followed as in Example 13, except that the granular activated carbon was discharged into a nitrogen flow container with a purity of 99.99% and cooled to 200°C or less under a nitrogen gas atmosphere when discharged from the heat treatment. The granular activated carbon was pulverized to an average particle size of 6 μm to obtain activated carbon.

[0135] [Example 17] Primary activation granular activated carbon was obtained in the same manner as in Example 13. This granular activated carbon was further subjected to secondary activation using propane combustion gas + steam (steam partial pressure 15%) at 970°C until the specific surface area reached the following: specific surface area of ​​2252 m 2 / g of secondary activation granular activated carbon. The obtained secondary activation granular activated carbon was further washed with acid water, dried, and then heat-treated at 700°C for 1 hour in a nitrogen atmosphere 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.

[0136] [Example 18] The same procedure as in Example 13 was carried out, except that the granular activated carbon was pulverized to an average particle size of 2.4 μm, to obtain activated carbon.

[0137] [Comparative Example 6] An activated carbon was obtained in the same manner as in Example 13, except that the heat treatment temperature was 830°C.

[0138] [Comparative Example 7] An activated carbon was obtained in the same manner as in Example 13, except that the primary activation temperature was 920°C.

[0139] [Comparative Example 8] An activated carbon was obtained in the same manner as in Example 14, except that the secondary activation temperature was 870°C.

[0140] The physical properties of the activated carbons obtained in the Examples and Comparative Examples are shown in Table 3.

[0141] [Table 3]

[0142] [Examples 19 to 24 and Comparative Examples 9 to 12] Using the activated carbon obtained in Examples 13 to 18 and Comparative Examples 6 to 8, a slurry for a lithium ion secondary battery positive electrode and a lithium ion secondary battery were prepared according to the above description. A charge / discharge test was performed on the obtained lithium ion secondary battery using a charge / discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). Lithium doping was performed at a rate of 70 mA / g relative to the active material mass, and doping was performed until the lithium potential reached 1 mV. A constant voltage of 1 mV was further applied to the lithium potential for 8 hours to terminate the doping. The capacity (mAh / g) at this time was taken as the charge capacity. Next, dedoping was performed at a rate of 70 mA / g relative to the active material mass until the lithium potential reached 2.5 V, and the capacity discharged at this time was taken as the discharge capacity. The percentage of the discharge capacity / charge capacity was taken as the charge / discharge efficiency (initial charge / discharge efficiency), and was used as an index of the utilization efficiency of lithium ions in the battery. The charge / discharge efficiency was calculated as the irreversible capacity by subtracting the discharge capacity from the charge capacity. The results obtained are shown in Table 4.

[0143] (Coatability evaluation) The coating properties of the lithium ion secondary battery positive electrode composition obtained above were evaluated as follows. After the coated electrode was dried with hot air at 80°C for 30 minutes as described above, the coated surface was evaluated as having absolutely no bubbles or agglomerates, as follows: ⊚; no agglomerates but bubbles; △; slight agglomerates; and ×; agglomerates everywhere. The results are shown in Table 4.

[0144] [Comparative Example 12] A lithium ion secondary battery was produced and its characteristics were measured in the same manner as in Example 19, except that no activated carbon was added. The results are shown in Table 4.

[0145] [Table 4]

[0146] From the results in Table 4, it was found that when the slurry stabilizer for electrochemical element positive electrodes of the present invention was used, the slurry coatability was excellent, and the lithium ion secondary battery produced using the same had excellent battery characteristics. On the other hand, when activated carbon not satisfying the range of the present invention was used, or when activated carbon was not contained as a slurry stabilizer, the slurry coatability was poor, and the battery characteristics of the obtained lithium ion secondary battery were also poor.

Claims

1. BET specific surface area is 1300-2500m ２ / g, and the volume of pores with a diameter of 2 nm or more is 0.35 cm ３ / g or less, and the volume of pores with a pore diameter of less than 2 nm is 0.5 cm ３ / g or more and an ash content of 0.5 wt % or less, wherein the electrochemical element is a non-aqueous electrolyte secondary battery.

2. 2. The additive for a positive electrode of an electrochemical element according to claim 1, wherein the activated carbon has an oxygen content of 1.3% by weight or more and 3% by weight or less, and a hydrogen content of 0.33% by weight or more and 0.55% by weight or less.

3. 3. The additive for a positive electrode of an electrochemical element according to claim 1, wherein the activated carbon has an average particle size of 2 μm to 20 μm.

4. A slurry stabilizer for electrochemical element positive electrodes, comprising the additive for electrochemical element positive electrodes according to any one of claims 1 to 3.

5. A composition for a positive electrode of an electrochemical element, comprising the additive for a positive electrode of an electrochemical element according to any one of claims 1 to 3 and a positive electrode active material, wherein the content of the additive for a positive electrode of an electrochemical element is 10 wt % or less based on the total weight of the positive electrode active material.

6. 6. The composition for a positive electrode of an electrochemical element according to claim 5, further comprising a binder in an amount of 0.5 to 10% by weight based on the total weight of the solid content of the composition for a positive electrode of an electrochemical element.

7. 7. The composition for a positive electrode of an electrochemical element according to claim 5, further comprising a conductive material in an amount of 1 to 10% by weight based on the total weight of the solid content of the composition for a positive electrode of an electrochemical element.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode for an electrochemical element having a layer made of the composition for an electrochemical element positive electrode according to any one of claims 5 to 7.

9. 9. The nonaqueous electrolyte secondary battery according to claim 8, which operates at 2 V to 5 V.

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