WO2022039081A1

WO2022039081A1 - Additive for positive electrode of electrochemical device, composition for positive electrode of electrochemical device, positive electrode for electrochemical device, and electrochemical device including same

Info

Publication number: WO2022039081A1
Application number: PCT/JP2021/029609
Authority: WO
Inventors: 修志西村; 秀治岩崎
Original assignee: 株式会社クラレ
Priority date: 2020-08-17
Filing date: 2021-08-11
Publication date: 2022-02-24
Also published as: JP2023130538A

Abstract

The present invention pertains to an additive for a positive electrode of an electrochemical device including a porous carbon material which has a specific surface area of 2500-3300 m²/g, as measured by the BET method, and in which the minimum value for pore radius frequency distribution, represented by formula 1 below, is 1 or more when the pore radius is measured as being in the range of 0.5-2.5 nm by a water-vapor adsorption method. Formula 1: Pore radius frequency distribution＝ΔV/ΔLog r (In formula 1, "V" represents pore volume (cc/g) and "r" represents pore radius (Å).)

Description

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

This patent application claims priority under the Paris Convention for Japanese Patent Application No. 2020-137301 (filed on August 17, 2020), which is hereby referred to in its entirety. It shall be incorporated into the book.
The present invention relates to an additive for an electrochemical element positive electrode made of a porous carbon material and a composition for an electrochemical element positive electrode containing the additive. The present invention also relates to an electrochemical device having a positive electrode manufactured by using the composition for a positive electrode of an electrochemical device.

The demand for electrochemical elements such as lithium-ion secondary batteries, which are small and lightweight, have high energy density, and can be repeatedly charged and discharged, is rapidly expanding by taking advantage of their characteristics. 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. With the expansion and development of applications, these electrochemical devices are required to be further improved such as lower resistance, higher capacity, and improvement of mechanical properties and productivity.

Electrochemical elements such as lithium-ion secondary batteries are being developed for the purpose of increasing the capacity, and in particular, the positive electrode material has a great influence on the capacity (miniaturization) of the battery, so the capacity and high performance are increased. There is an urgent need to change. For example, in Patent Document 1, a positive electrode for a lithium ion secondary battery, which is excellent in short-time output characteristics at a low temperature, is studied. Further, in Patent Document 2, in a lithium ion secondary battery using a manganese-based positive electrode active material, a lithium secondary battery in which manganese ions are adsorbed and trapped in activated carbon is studied.

Further, in Patent Documents 3 and 4, a lithium ion secondary battery capable of reducing a decrease in battery capacity by removing water in the battery with a water adsorbent is studied.

Japanese Patent No. 4964404 Japanese Unexamined Patent Publication No. 2012-059690 Japanese Unexamined Patent Publication No. 2001-126766 Japanese Unexamined Patent Publication No. 2014-26819

On the other hand, in addition to the above-mentioned high capacity and high output characteristics, there is also a growing demand for cycle durability in lithium-ion secondary batteries. For example, an in-vehicle lithium-ion secondary battery is large and expensive, so it is difficult to replace it during use. Therefore, it must have at least the same durability as an automobile, and the discharge capacity drops even after repeated charging and discharging. Difficult, high cycle durability is required.

In view of the above problems, an object of the present invention includes an additive for an electrochemical element positive electrode capable of improving the conductivity of the positive electrode, reducing the electrode resistance, and suppressing the decrease in the discharge capacity when repeatedly charging and discharging. The present invention provides a composition for a positive electrode of an electrochemical element.

Still another object of the present invention is to provide an electrochemical device having a positive electrode produced by using the above composition and having excellent battery characteristics.

As a result of diligent studies by the present inventors, it has been found that the above-mentioned problems can be solved by an additive for a positive electrode of an electrochemical element made of a specific porous carbon material, and the present invention has been reached.
That is, the present invention includes the following aspects.

[1] The specific surface area by the BET method is 2500 to 3300 m ² / g, and the fineness represented by the following formula (1) when measured in the range of the pore radius of 0.5 to 2.5 nm by the steam adsorption method. An additive for the positive electrode of an electrochemical element containing a porous carbon material having a minimum pore radius frequency distribution of 1 or more.
Pore radius frequency distribution = ΔV / ΔLog r (1)
(In formula (1), V is the pore volume (cc / g) and r is the pore radius (Å).)
[2] The additive for the positive electrode of an electrochemical element according to [1], wherein the ash content of the porous carbon material is 0.5% by weight or less.
[3] The additive for an electrochemical element positive electrode according to [1] or [2], wherein the porous carbon material has an average particle size of 2 μm to 20 μm.
[4] The composition for an electrochemical element positive electrode containing the electrochemical element positive electrode additive according to any one of [1] to [3] and the positive electrode active material, and the electrochemical element positive electrode additive. The composition for an electrochemical element positive electrode having a content of 10% by weight or less based on the total weight of the positive electrode active material.
[5] The electrochemical element for the positive electrode of the electrochemical element according to [4], further comprising a binder in an amount of 0.5 to 10% by weight based on the total solid content of the composition for the positive electrode of the electrochemical element. Composition for positive electrode.
[6] The composition for an electrochemical element positive electrode according to [4] or [5], further comprising a conductive material in an amount of 1 to 10% by weight based on the total solid content of the composition for an electrochemical element positive electrode. Composition for positive electrode of electrochemical element.
[7] An electrochemical device having a positive electrode produced by using the composition for a positive electrode of an electrochemical device according to any one of [4] to [6].
[8] The electrochemical device according to [7], which operates at 2V to 5V.
[9] A lithium ion secondary battery having a positive electrode produced by using the composition for an electrochemical element positive electrode according to any one of [4] to [6].

According to the present invention, an electrochemical element positive electrode additive and an electrochemical element containing the same can reduce the electrode resistance by improving the conductivity of the positive electrode and suppress the decrease in the discharge capacity when repeatedly charging and discharging. A composition for a positive electrode can be provided. Further, it is possible to provide an electrochemical device having a positive electrode manufactured by using the above composition and having excellent battery characteristics.

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

[Additives for positive electrodes of electrochemical devices]
The additive for the positive electrode of the electrochemical element of the present invention has a specific surface area of 2500 to 3300 m ² / g by the BET method, and the pore radius is measured in the range of 0.5 to 2.5 nm by the steam adsorption method. It contains a porous carbon material having a minimum value of the pore radius frequency distribution represented by the formula (1) of 1 or more. By applying such a porous carbon material having specific pores as an additive for the positive electrode of an electrochemical element, it is possible to effectively suppress a decrease in electrode resistance and a decrease in battery capacity due to repeated charging and discharging.

(Porous carbon material)
The porous carbon material used in the present invention has a specific surface area of 2500 to 3300 m ² / g according to the BET method. When the specific surface area is smaller than the above lower limit, the electrolyte in the electrolytic solution cannot be sufficiently retained, and the resistance does not decrease sufficiently. From this viewpoint, the lower limit of the specific surface area needs to be 2500 m ² / g or more, preferably 2550 m ² / g or more, and more preferably 2600 m ² / g or more. On the other hand, if the specific surface area is larger than the above upper limit, the mechanical strength is lowered, which causes deterioration of battery performance such as powdering in the battery, release from the electrode during charging / discharging, and short circuit. From this viewpoint, the upper limit of the specific surface area needs to be 3300 m ² / g or less, preferably 3200 m ² / g or less, more preferably 3100 m ² / g or less, and more preferably 3000 m ² / g or less. The specific surface area is, for example, the lower limit or higher and the upper limit or lower by appropriately adjusting the type of the raw material of the porous carbon material; the activation conditions (atmosphere, temperature, time, etc.) in the method for producing the porous carbon material described later. Can be adjusted to.

The porous carbon material used in the present invention has the minimum value of the pore radius frequency distribution represented by the following formula (1) when the pore radius is measured in the range of 0.5 to 2.5 nm by the steam adsorption method. Is 1 or more.
Pore radius frequency distribution = ΔV / ΔLog r (1)
Here, r represents the pore radius (Å), V represents the pore volume (cc / g), and the formula (1) is a graph in which the logarithm of r is taken on the horizontal axis and the cumulative pore volume is taken on the vertical axis. Represents the inclination in. That is, the higher the numerical value of the pore radius frequency distribution represented by the equation (1), the narrower the pore distribution in the range. Since the pore distribution having a pore radius of 0.5 to 2.5 nm is narrow, the expansion and / or contraction of the electrode when the battery is repeatedly charged and discharged can be suppressed, and the expansion and / or expansion of the electrode can be suppressed. Alternatively, the decrease in discharge capacity caused by shrinkage can be suppressed. The reason for this is not limited to the following, but can be considered as follows.
Due to the narrow pore distribution in the pore radius range of 0.5 to 2.5 nm, when Li ions are adsorbed, they can be released again without suppressing the diffusion of Li ions. Further, since the pores in this range correspond to the size of heavy metal ions, the shuttle reaction caused by the heavy metal ions eluted in the electrolytic solution can be suppressed by adsorbing and retaining the heavy metals in the pores. can. As a result, it is possible to suppress the expansion and / or contraction of the electrode when the battery is repeatedly charged and discharged, and it is possible to suppress the decrease in discharge capacity caused by the expansion and / or contraction of the electrode and the deterioration of the electrode due to metal ions. For these reasons, the minimum value of the pore radius frequency distribution represented by the above formula (1) needs to be 1 or more, preferably 1.3 or more, and more preferably 1.8 or more. Further, the upper limit of the minimum value of the pore radius frequency distribution is not particularly limited, but is usually 5 or less.
The carbon material having such a pore distribution can be adjusted by adjusting the activation conditions according to the appropriate raw material.

Further, the porous carbon material used in the present invention has a large pore volume in the range of 0.5 to 2.5 nm, so that the electrolyte elutes from the positive electrode while maintaining the electrolyte in the vicinity of the positive electrode active material. The metal can be immobilized on the surface of the carbon material. From this viewpoint, the pore volume in the range of the pore radius of 0.5 to 2.5 nm is preferably 0.6 cm ³ / g or more, and more preferably 1.1 cm ³ / g or more. The upper limit of the pore volume in the range of the pore radius of 0.5 to 2.5 nm is not particularly limited, but is usually 4.0 cm ³ / g or less. The pore volume in the range of the pore radius of 0.5 to 2.5 nm is, for example, the type of the raw material of the porous carbon material in the method for producing the porous carbon material described later; activation conditions (atmosphere, temperature, time, etc.). Etc. can be adjusted to be equal to or higher than the lower limit. The pore volume having a pore radius in the range of 0.5 to 2.5 nm can be measured, for example, by pore distribution analysis by the DFT method by nitrogen adsorption measurement.

The heavy metal compound contained in the ash of the porous carbon material used in the present invention may diffuse in the positive electrode and precipitate during discharge, so a smaller content is preferable. From this viewpoint, the ash content is preferably 0.5% by weight or less, more preferably 0.48% by weight or less, further preferably 0.46% by weight or less, and 0.43% by weight or less. Is even more preferable, and 0.38% by weight or less is particularly preferable. The lower limit of the ash content is not particularly limited and may be 0% by weight or more. The ash content can be determined by measuring the ignition residue, for example, by the method described in Examples described later. Examples of the ash content that can be contained in the porous carbon material include nickel, iron, calcium, magnesium, and aluminum. In particular, nickel is preferably 100 ppm or less, more preferably 80 ppm or less. Further, iron is preferably 100 ppm or less, more preferably 50 ppm or less. The ash content can also be determined by, for example, IPC emission spectroscopic analysis. The ash content is adjusted to the above range by appropriately adjusting the type of the raw material of the porous carbon material; the cleaning conditions (type of acid, concentration, time, number of times, etc.) in the method for producing the porous carbon material described later, for example. be able to.

When the oxygen content in the porous carbon material used in the present invention is low, the carbon material tends to aggregate due to a difference in dispersibility with the active material when adjusting the electrode slurry, and it becomes difficult to obtain a stable slurry. From this viewpoint, the oxygen content in the porous carbon material is preferably 0.5% by weight or more, more preferably 0.6% by weight or more, still more preferably 0.7% by weight or more. Further, since oxygen in the porous carbon material becomes the starting point of decomposition of the electrolytic solution when the battery is charged and discharged, it is preferable that the oxygen content is low. From this viewpoint, the oxygen content in the porous carbon material is preferably 3.0% by weight or less, more preferably 2.8% by weight or less, and further preferably 2.6% by weight or less. .. The oxygen content in the porous carbon material is, for example, the lower limit thereof by appropriately adjusting the type of the raw material of the porous carbon material in the method for producing the porous carbon material described later; the activation conditions (atmosphere, temperature, time, etc.). The above and the above upper limit can be adjusted. The oxygen content can be determined by, for example, elemental analysis, fluorescent X-ray analysis, or the like.

The porous carbon material used in the present invention preferably has an average particle size of 2 μm to 20 μm, more preferably 2.3 μm to 18 μm, and 2.5 μm to 14 μm, which is determined by the laser scattering method. Is even more preferable. If it is within the above range, good coatability can be obtained, which is preferable. Particles that are too large may be unfavorable because they may hinder conductivity in the positive electrode, and particles that are too small are not only economically unfavorable, but also contain fine powder and cannot be suppressed by a binder or the like. It may be unfavorable because it may easily be released from the inside of the electrode and may cause deterioration of battery performance such as a short circuit. The average particle size is adjusted to the lower limit or higher and the upper limit or lower by appropriately adjusting the conditions of the raw material of the porous carbon material in the method for producing the porous carbon material described later; can do.

(Manufacturing method of porous carbon material)
The raw materials for the porous carbon material used in the present invention (hereinafter, may be simply referred to as raw materials) include coconut shells, palm coconuts, fruit seeds, sawdust, eucalyptus, pine and other plant-based materials, coal-based materials, and petroleum. Examples thereof include coke-based coke and carbonized products having a carbonized pitch, phenol resin, vinyl chloride resin, vinylidene chloride resin and the like. The shape and size of the raw material are not particularly limited, but crushed, granular, or columnar materials having a size of about 1 mm to 10 mm are generally used, but granular or powdered materials can also be used. Further, it is also possible to use a carbonized material as a raw material after molding by adding a binder to tar, pitch, phenol resin or the like. The shape of these molded bodies can be any shape such as granular, powdery, honeycomb or fibrous.

These raw materials are carbides in which the total content of alkali metals such as sodium, potassium and calcium and alkaline earth metals contained when heated and carbonized at 600 ° C. in an inert gas is 0.5% by weight or less. It is preferable to use. The inert gas here means a gas such as nitrogen, argon, and helium. The total content of alkali metals and alkali metals in the raw materials can be determined by the fluorescent X-ray method after heating and ashing the raw materials heated and carbonized at 600 ° C. in the above-mentioned inert gas at 850 ° C. in a muffle furnace. .. Further, the raw material preferably has a total content of alkali metals and alkaline earth metals of 0.01% by mass or more. As a result, it is easy to appropriately have pores in the first activation.

In the present invention, the above-mentioned raw material is preferably activated to obtain a porous carbon material, but in order to obtain the porous carbon material from the raw material, preferably, the above-mentioned carbide having a small amount of alkali metals is used as carbon dioxide gas. It is primarily activated at a temperature of 600 to 1200 ° C. in an atmosphere containing 2% by volume or less of water vapor and 2% by volume or more of carbon monoxide gas as the main component. Here, the fact that the carbon dioxide gas is the main component means that the carbon dioxide gas is the main component among the gases having an activating ability, and it is not possible to dilute the carbon dioxide gas with an inert gas such as nitrogen or argon. There is no problem. For example, the inert gas may occupy 50% by volume or more of the atmosphere at the time of activation. From the viewpoint of easy activation, the total amount of gas having an activating ability is preferably 20% by volume or more, more preferably 30% by volume or more, still more preferably 40% by volume or more in the atmosphere at the time of activation. The activation time of the primary activation is not particularly limited, but when a raw material having a particle size of 3 mm or more is used, the uniformity of the pores is impaired if it is performed in a very short time, so that it is more than 1 hour or more. It is preferable to activate for 1.5 hours or more, and it is preferable to activate for 1.5 hours or more regardless of the particle size. Usually, it is carried out in about 50 hours. The activation temperature is preferably 800 ° C to 1100 ° C.

According to the present invention, by primary activating the raw material in such a special atmosphere, a porous carbon material having a uniform pore size, a large specific surface area, and excellent adsorption of small molecule substances such as nitrogen can be produced. be able to. When using a raw material in which the total content of alkali metals and alkaline earth metals contained in the carbides when heated and carbonized at 600 ° C in an inert gas is 0.5% by weight or more, carbon dioxide gas is similarly used. It is activated at a temperature of 600 to 1200 ° C. in an atmosphere containing 2% by volume or less of water vapor and 2% by volume or more of carbon monoxide gas as the main component, and the weight loss due to activation of the raw material is 5 to 50%, preferably 10 to 10 to. When it reaches 30%, wash it with acid and water to reduce the total content of alkali metals and alkaline earth metals to 0.5% by weight or less, and put it in the activation furnace after drying or with water contained. After that, the primary activation is performed again at a temperature of 600 to 1200 ° C. in an atmosphere containing carbon dioxide gas as a main component, water vapor of 2% by volume or less, and carbon monoxide gas of 2% by volume or more.

It is preferable to wash the raw material carbonaceous material after the primary activation to reduce alkali metals and / or alkaline earth metals. The washing can be performed by immersing the activated carbon obtained after the primary activation in a washing liquid containing an acid. As the acid, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid and carbonic acid, or organic acids such as formic acid and acetic acid are suitable. It is generally used in an aqueous solution, the concentration of which is usually 1 to 30% by weight. In addition, the cleaning effect can be further enhanced by removing salts and acids remaining in the raw material by washing with water or warm water after pickling, and at the same time, corrosion of the device and waste gas when shifting to the later activation process. It is also suitable in terms of processing. In that case, the amount of water is not particularly limited, but it is practical to carry out the process at 10 to 50 times the weight of the raw material carbonaceous material. The atmosphere for cleaning 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.

The raw carbonaceous material that has been washed is secondarily activated. It is preferable to perform secondary activation after drying, but it is also possible to omit drying and immediately put it in an activation furnace for activation. The drying conditions here may be the same as those for drying the porous carbonaceous material described later. In the secondary activation step of the present invention, it is important to use carbon dioxide gas as the oxidizing gas, to have an atmosphere containing 2% by volume or more of carbon monoxide gas and 2% by volume or less of water vapor. It is permissible to dilute the carbon dioxide with an inert gas such as argon.

The secondary activation temperature is 600 to 1200 ° C, preferably 800 to 1100 ° C. Further, if the activation time is too short, activation spots occur inside and outside the particles and the uniformity of the pores is impaired. Therefore, when the particle size of the raw material is less than 1 mm, it is 30 minutes or more after reaching a predetermined temperature and 3 mm or more. It is preferably activated for 1 hour or more, and preferably for 1.5 to 30 hours regardless of the particle size. The maximum activation time is not particularly limited from the viewpoint of the performance of the porous carbon material, but it is preferably carried out within 30 hours from the viewpoint of industry. The activation furnace may be of any type as long as the reaction is uniformly carried out, and various types can be used. Usually, a flow furnace, a multi-stage furnace, a rotary furnace and the like are suitable. The activation method may be either a batch method or a continuous method. Further, the conditions for the primary activation and the conditions for the secondary activation may be the same.

Further cleaning may be performed after the secondary activation, in which case the cleaning can be performed in the same manner as the cleaning after the primary activation.

It is preferable that the porous carbon material thus obtained is then pulverized. The pulverization method is not particularly limited, but a known pulverization method such as a ball mill, a roll mill or a jet mill, or a combination thereof can be adopted.

In the present invention, the porous carbon material obtained by pulverization may be classified and used. For example, by excluding particles having a particle diameter of 1 μm or less, it becomes possible to obtain porous carbon material particles having a narrow particle size distribution width. By removing such fine particles, it is possible to reduce the amount of binder in the electrode configuration. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. Examples of the wet classifier include a classifier using principles such as gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of the dry classifier include classifiers that utilize principles such as sedimentation classification, mechanical classification, and centrifugal classification. From the viewpoint of economy, it is preferable to use a dry classifier.

The obtained porous carbon material may be dried. Drying is an operation for removing the moisture or the like adsorbed on the porous carbon material. For example, by heating the porous carbon material, the moisture or the like adsorbed on the porous carbon material can be removed. can. In addition to or instead of heating, drying can be performed by means such as depressurization, decompression heating, and freezing to remove water and the like adsorbed on the porous carbon material.

The drying temperature is preferably 100 to 330 ° C., more preferably 110 to 300 ° C., and further preferably 120 to 250 ° C. from the viewpoint of removing water adsorbed on the porous carbon material. preferable.

The drying time depends on the drying temperature to be adopted, but from the viewpoint of removing the water adsorbed on the porous carbon material, it is preferably 0.1 hours or more, more preferably 0.5 hours or more, still more preferably 1. It's more than an hour. Further, from the viewpoint of economic efficiency, it is preferably 24 hours or less, more preferably 12 hours or less, still more preferably 6 hours or less.

Drying can be performed under normal pressure or reduced pressure atmosphere. When the drying is carried out at normal pressure, it is preferably carried out in an atmosphere of an inert gas such as nitrogen gas or argon gas or in an air atmosphere having a dew point of −20 ° C. or lower.

The porous carbon material obtained as described above can be preferably used as an additive for the positive electrode of an electrochemical device of the present invention.

[Composition for positive electrode of electrochemical device]
The composition for a positive electrode of an electrochemical element of the present invention contains the above-mentioned additive for a positive electrode of an electrochemical element and a positive electrode active material. Further, the composition for a positive electrode of an electrochemical device of the present invention may optionally contain other components other than the above.

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, still more preferably 6% by weight or less, based on the total weight of the positive electrode active material. This is because if the content of the additive for the positive electrode of the electrochemical device is large, the weight of the positive electrode active material is relatively reduced, so that the capacity may be reduced. Further, if the content of the additive for the positive electrode of the electrochemical element is small, the effect of reducing the electrode resistance, which is the object of the present invention, and suppressing the electrode expansion during repeated charging and discharging may be insufficient, so that the weight is 0.5. % Or more is preferable, and 1% by weight or more is more preferable.

Further, the mixing ratio of the additive for the positive electrode of the electrochemical device and the positive electrode active material described later may be 1:99 to 10:90 in terms of weight ratio. When the mixing ratio of the electrochemical device positive electrode additive and the positive electrode active material is included in this range, excellent output characteristics and capacity characteristics can be obtained.

(Positive electrode active material)
The positive electrode active material to be blended in the composition for the positive electrode of the electrochemical element is not particularly limited, and a known positive electrode active material can be used. For example, lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), Co-Ni-Mn lithium-containing composite oxide, Ni-Mn-Al. Lithium-containing composite oxide, Ni-Co-Al lithium-containing composite oxide, olivine-type lithium iron phosphate (LiFePO ₄ ), olivine-type lithium manganese phosphate (LiMnPO ₄ ), Li _{1 + x} Mn _2-x O ₄ (0) Metals such as Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ and LiNi _0.5 Mn _1.5 O ₄ represented by <X <2). Examples thereof include organic radicals such as oxides, sulfur, compounds and polymers having a nitroxyl radical, compounds and polymers having an oxyradic, compounds and polymers having a nitrogen radical, and compounds and polymers having a fluvalene skeleton.

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, lithium-containing cobalt oxide (LiCoO ₂ ); lithium-containing nickel oxide (LiNiO ₂ ); and Co-Ni-Mn lithium as the positive electrode active material. Containing composite oxides, such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ etc .; Lithium-containing composite oxides of Ni—Co—Al, such as LiNi _0.8 Co _0.1 Al _0.1 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , etc. can be used. preferable.

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.

In the composition for a positive electrode of an electrochemical element of the present invention, the content of the positive electrode active material is preferably 35 to 95% by weight, more preferably 40 to 90% by weight, based on the total solid content of the composition. good.

(solvent)
The composition for a positive electrode of an electrochemical device of the present invention may contain a solvent. As the solvent, 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, as the organic solvent, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, N, N-dimethylacetamide, dimethylformamide, dimethylsulfoxide, methylformamide, methylethylketone, furfural, ethylenediamine and the like can be used. can. Among these, N-methylpyrrolidone (NMP) is most preferable from the viewpoint of ease of handling, safety, and ease of synthesis. These organic solvents may be used alone or in combination of two or more.

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

(binder)
The composition for a positive electrode of an electrochemical element of the present invention preferably contains a binder for satisfactorily adhering positive electrode active material particles to each other and satisfactorily adhering positive electrode active material to a current current collector. Examples of binders include, for example, 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, realized styrene-butadiene rubber, epoxy resin, nylon and the like may be used, but the present invention is not limited thereto. These may be used alone or in combination of two or more.
In the composition for the positive electrode of the electrochemical element of the present invention, the content of the binder is preferably 0.5 to 10% by weight with respect to the total weight of the solid content in the composition for the positive electrode of the electrochemical element. It is more preferably 7% by weight. When the content of the binder is within the above range, it is easy to suppress the breakage of the electrode due to the expansion and contraction of the active material during charging and discharging while suppressing the increase in electrical resistance.

(Conductive material)
The composition for a positive electrode of an electrochemical element of the present invention may further contain a conductive material in order to further enhance the conductivity of the positive electrode formed on the current collector. As the conductive material, any electronically conductive material that does not cause a chemical change can be used in the electrochemical element to be constructed. Specific examples of conductive materials include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber, metal powder such as copper, nickel, aluminum, and silver, and metal fiber. Alternatively, one kind or a mixture of two or more kinds of conductive materials such as a polyphenylene derivative may be used.
In the composition for the positive electrode of the electrochemical element of the present invention, the content of the conductive material is preferably 1 to 10% by weight with respect to the total solid content of the composition for the positive electrode of the electrochemical element, and is preferably 1 to 7% by weight. % Is more preferable. When the content of the conductive material is within the above range, the electric capacity of the electrode material can be suitably drawn out without significantly reducing the battery capacity of the positive electrode and by reducing the resistance.

(Manufacturing method of composition for electrochemical device positive electrode)
The method for producing the composition for the positive electrode of the electrochemical element of the present invention can be produced by mixing the above-mentioned additive for the positive electrode of the electrochemical element, the positive electrode active material, and if necessary, a solvent and other components. The mixing method is not particularly limited, 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.

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. A temperature that is too low is not preferable because the viscosity is high and coating may not be possible, and a temperature that is too high is not preferable from the viewpoint of safety and equipment operability such as volatilization of organic solvent and accompanying viscosity change. be.

[Electrochemical element]
Such a composition for a positive electrode of an electrochemical device according to an embodiment of the present invention can be usefully used for an electrochemical device. The present invention also includes an electrochemical device having a positive electrode manufactured by using the above-mentioned composition for an electrochemical device positive electrode. By containing the above-mentioned additive for the positive electrode of the electrochemical element, the electrochemical element of the present invention can improve the conductivity of the positive electrode, reduce the electrode resistance, and suppress the electrode expansion during repeated charging and discharging. can. The electrochemical element of the present invention preferably operates at 2V to 5V, and examples thereof include a lithium ion secondary battery and a capacitor.

For example, when the electrochemical element 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.

(Positive electrode)
The positive electrode is produced by using the composition for a positive electrode of an electrochemical element 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 an electrochemical element positive electrode of the present invention to the current collector.

The method for applying the composition for the positive electrode of the electrochemical device on the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, 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 and the like can be used. At this time, the composition for the positive electrode of the electrochemical device 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 after application and before drying can be appropriately set according to the thickness of the positive electrode active material layer obtained by drying.

As the current collector to which the composition for the positive electrode of the electrochemical element is applied, a material having electrical conductivity and having electrochemical durability is used. Specifically, as the current collector, a current collector made of aluminum or an aluminum alloy can be used. At this time, 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 have heat resistance and are electrochemically stable.

The method for drying the composition for the positive electrode of the electrochemical element on the current collector is not particularly limited, and a known method can be used, for example, drying with warm air, hot air, low humidity air, vacuum drying, infrared rays or an electron beam. A drying method by irradiation such as is mentioned. By drying the composition for the positive electrode of the electrochemical element on the current collector in this way, it is possible to form a positive electrode active material layer on the current collector and obtain a positive electrode having the current collector and the positive electrode active material layer. can.

In particular, in order to maintain the metal trapping power of the added porous carbon material, it is preferable to sufficiently perform the drying step at the time of producing the positive electrode, and the current collector (for example, aluminum foil) is not affected and the area is not affected. It is preferable to perform drying within a range in which water adsorbed on the surfaces of the positive electrode active material and the porous carbon material can be volatilized. It is preferably carried out at a drying temperature of 70 to 200 ° C., more preferably 100 ° C. or higher and 160 ° C. or lower under atmospheric pressure or reduced pressure in the range of 20 minutes to 24 hours, preferably 1 hour to 12 hours.

After the drying step, the positive electrode active material layer may be pressure-treated by using a die press or a roll press. The pressure treatment can improve the adhesion between the positive electrode active material layer and the current collector.

(Negative electrode)
The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer contains a negative electrode active material. The process of manufacturing a negative electrode is a process widely known in the art.

The negative electrode active material includes a substance capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, a lithium metal alloy, a lithium-doped and de-doped substance, or a transition metal oxide. ..

As a substance capable of reversibly intercalating / deintercalating the above lithium ions, crystalline carbon, amorphous carbon, or both of them may be used. 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 or hard carbon. Examples include carbon, mesophase-pitch carbide, and calcined coke.

As the alloy of the 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. ..

Examples of the substance that can be doped and dedoped with lithium include alloys such as Si and SiMg, SiO _x (0 <x <2), Sn, SnO ₂ and the like.

The content of the negative electrode active material in the negative electrode active material layer may be 70% by weight to 100% by weight with respect to the total weight of the negative electrode active material layer. The negative electrode active material layer may be composed of only the negative electrode active material.

The negative electrode active material layer may also contain a binder, and may optionally further contain a conductive material. The content of the binder in the negative electrode active material layer may be 1% by weight to 5% by weight with respect to the total weight of the negative electrode active material layer. When the conductive material is further contained, 90% by weight to 98% by weight of the negative electrode active material, 1% by weight to 10% by weight of the binder, and 1% by weight to 10% by weight of the conductive material may be used.

The binder plays a role of adhering the negative electrode active material particles to each other well and also adhering the negative electrode active material to the current current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, and polyamideimide. Polyimide or a combination thereof can be mentioned.

Examples of the water-soluble binder include styrene-butadiene rubber, realized styrene-butadiene rubber, polyvinyl alcohol, cellulose, sodium polyacrylate, propylene and an olefin copolymer having 2 to 8 carbon atoms, (meth) acrylic acid and (meth) acrylic acid. Meta) A copolymer of acrylic acid alkyl ester or a combination thereof can be mentioned.

When a water-soluble binder is used as the negative electrode binder, a cellulosic compound capable of imparting viscosity may be further used as a thickener. Examples of the cellulosic compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof, and the content of such a thickener used is 0.1 part by weight to 100 parts by weight with respect to 100 parts by weight of the binder. It may be a department.

The above-mentioned conductive material is used for imparting conductivity to an electrode, and any electronic conductive material that does not cause a chemical change can be used in a constituent battery, and an example thereof. As carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; metal powder such as copper, nickel, aluminum, silver or metal-based material such as metal fiber; polyphenylene derivative, etc. Conductive polymers; or conductive materials containing mixtures thereof may be used.

The current collector is 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 a combination thereof. You may use the one.

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

The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or non-protonic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylmethylcarbonate. (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and the like may be used, and as the ester solvent, n-methyl acetate, n-ethyl acetate, n-propyl acetate and the like may be used. , Dimethylacetate, methylpropionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like may be used. As the ether, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like may be used, and as the ketone solvent, cyclohexanone and the like may be used. Further, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol or the like may be used, and as the non-protonic solvent, R-CN (R is a linear or branched form having 2 to 20 carbon atoms). , Or a ring-structured hydrocarbon group, 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.

The above-mentioned non-aqueous organic solvent may be used alone or in combination of two or more kinds, or the mixing ratio when two or more kinds are mixed and used may be appropriately adjusted according to the target battery performance. good.

Further, in the case of the above-mentioned carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of 1: 1 to 1: 9, the performance of the electrolytic solution can be shown more predominantly.

The lithium salt is dissolved in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium ion secondary battery and promote the movement of lithium ions between the positive electrode and the negative electrode. It is a substance that plays a role. Typical examples of such lithium salts are, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ . N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl , LiI and LiB (C ₂ O ₄ ) ₂ (lithium bisoxalatoborate (LiBOB)) and the like. These may be used alone or in admixture of two or more. The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte tends to be low and the electrolyte performance tends to deteriorate, and if it exceeds 2.0 M, the viscosity of the electrolyte increases and the mobility of lithium ions Tends to decrease.

The electrolyte may further contain a vinylene carbonate or an ethylene carbonate compound as a life improving agent in order to improve the battery life.

Typical examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, and fluoroethylene carbonate. When such a life-improving agent is further used, the amount used may be appropriately adjusted.

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 having two or more layers thereof may be used, and a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / A mixed multilayer film such as a polyethylene / polypropylene three-layer separator may be used.

Hereinafter, examples and comparative examples will be described. However, the following examples are only one example, and the idea of the present invention is not limited to the following examples.

(Specific surface area by nitrogen adsorption BET method)
The approximate expression derived from the BET equation is described below.

Using the above approximate expression, the amount of adsorption (v) actually measured at a predetermined relative pressure ( _p / p ₀ ) at a liquid nitrogen temperature by the multipoint method by nitrogen adsorption is substituted to obtain vm, and the following equation is obtained. The specific surface area of the sample (SSA: unit is m ² / g) was calculated.

In the above formula, v _m is the adsorption amount (cm ³ / g) required to form a single molecule layer on the sample surface, v is the measured adsorption amount (cm ³ / g), and p ₀ is the saturated vapor pressure. p is the absolute pressure, c is the constant (reflecting the heat of adsorption), N is the Avogadro number 6.022 × 10 ²³ , and a (nm ² ) is the area occupied by the adsorbent molecule on the sample surface (molecular occupied cross-sectional area).

Specifically, using "Autosorb-iQ-MP" manufactured by Kantachrome, the amount of nitrogen adsorbed on the carbon material at the liquid nitrogen temperature was measured as follows. A carbon material as a measurement sample is filled in a sample tube, the sample tube is cooled to -196 ° C., the pressure is reduced once, and then nitrogen (purity 99.999%) is adsorbed on the measurement sample at a desired relative pressure. rice field. The amount of nitrogen adsorbed on the sample when the equilibrium pressure was reached at each desired relative pressure was defined as the adsorbed gas amount v.

(Pore radius frequency distribution)
The adsorption isotherm of water vapor was measured using a Bell Soap 28SA type measuring instrument manufactured by Nippon Bell Co., Ltd. The carbon material as the measurement sample was filled in the sample tube, the sample tube was once depressurized at 25 ° C., and then saturated water vapor was adsorbed on the measurement sample at a desired relative pressure. Based on the obtained adsorption isotherm, the pore radius frequency distribution represented by the above formula (1) was calculated in the range where the pore radius of the porous carbon material was 0.5 to 2.5 nm.

(Average particle size by laser scattering method)
The average particle size (particle size distribution) of the plant-derived raw material and the carbon material was measured by the following method. The sample was put into an aqueous solution containing 5% by weight of a surfactant (“Toriton X100” 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 measurement was performed using a particle size / particle size distribution measuring device (“Microtrack MT3300EXII” manufactured by Microtrack Bell Co., Ltd.). D50 is a particle size having a cumulative volume of 50%, and this value was used as the average particle size.

(Measurement method of ash content)
Weigh the alumina crucible that has been air-baked at 900 ° C. and allowed to cool in a desiccator containing silica gel. After vacuum drying in a constant temperature dryer adjusted to 120 ° C. for 8 to 10 hours, 20 g of the carbon material allowed to cool in a desiccator containing silica gel as a desiccant was placed in an alumina crucible having a volume of 50 ml, and the weight of the crucible + carbon material was reduced to 0. Accurately weighed up to 1 mg. The alumina crucible containing the sample was placed in an electric furnace, and with dry air introduced into the electric furnace at 20 L / min, the temperature was raised to 200 ° C in 1 hour and then to 700 ° C over 2 hours. It was kept at 700 ° C. for 14 hours and incinerated. After the completion of ashing, the mixture was allowed to cool in a desiccator containing silica gel, the weight of the crucible + ash was accurately weighed to 0.1 mg, and the ash content was calculated from the following formula.

(Composition for positive electrode of lithium ion secondary battery)
30 parts by weight of N-methylpyrrolidone solution in which 3 parts by weight of polyfluorinated vinylidene (KF polymer 7200 manufactured by Kureha Co., Ltd.) is dissolved, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (Nippon Kagaku Kogyo Co., Ltd.) , "Celseed C-5H") 93 parts by weight, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Black") 2 parts by weight as a conductive material, 2 parts by weight of carbon material produced in Examples and Comparative Examples described later. And mixed, stirring and dispersing with a homomixer (4500 rpm) manufactured by Primix Co., Ltd. while appropriately adding N-methylpyrrolidone so that the solid content concentration of the composition becomes 50% by weight, and the positive electrode of the lithium ion secondary battery. The composition for use was obtained.

(Positive electrode for lithium-ion secondary battery)
The above composition for a positive electrode of a lithium ion secondary battery is coated on an aluminum foil (“1N30-H”, manufactured by Fuji Kako Paper) of a current collector using a bar coater (“T101”, manufactured by Matsuo Sangyo). After primary drying at 80 ° C. for 30 minutes in a hot air dryer (manufactured by Yamato Kagaku), rolling treatment was performed using a roll press (manufactured by Hosen). Then, after punching as a positive electrode for a lithium ion secondary battery (φ14 mm), a positive electrode for a lithium ion secondary battery was produced by secondary drying under a reduced pressure condition at 120 ° C. for 3 hours. For the water content at this time, take a prepared and dried electrode (φ14 mm), heat it to 250 ° C with a Karl Fischer (manufactured by Mitsubishi Chemical Analytech), measure the water content under a nitrogen stream, and measure the water content. Was controlled to be 20 ppm or less so that the added carbon material could exert an action other than water absorption.

(Manufacturing of lithium-ion secondary battery)
The positive electrode for the lithium ion secondary battery was transferred to a glove box (manufactured by Miwa Seisakusho) in an argon gas atmosphere. For the negative electrode, a laminated body made of a metallic lithium foil (thickness 0.2 mm, φ16 mm) was used as the negative electrode active material layer, and a stainless steel foil (thickness 0.2 mm, φ17 mm) was used as the current collector. In addition, a polypropylene-based solvent (Celguard # 2400, manufactured by Polypore) is used as a separator, and the electrolyte is lithium hexafluorophosphate (LiPF ₆ ) in ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in vinylene carbonate (VC). A coin-type lithium ion secondary battery (2032 type) was prepared by injecting using a mixed solvent system (1M-LiPF ₆ , EC / EMC = 3/7% by volume, VC2% by weight) to which the above was added.

[Example 1]
Carbides obtained by carbonizing coconut shells having a total content of alkali metals and alkaline earth metals of 0.01% by weight or more and 0.5% by weight or less at 600 ° C. are crushed to a size of 1 to 3 mm. As shown in Table 1 below, a batch-type flow activator with an inner diameter of 50 mm is used as a raw material, and the atmosphere is such that carbon dioxide gas is the main component, water vapor is 2% by volume or less, and carbon monoxide gas is 2% by volume or more. Was activated at 900 ° C. Then, pickling with hydrochloric acid (concentration: 0.5 regulation, diluted solution: ion-exchanged water) at a temperature of 85 ° C. for 30 minutes, and then thoroughly washing with ion-exchanged water to remove residual acid, 80. After drying at ° C. for 3 hours, secondary activation was carried out under the same conditions as those shown in Table 1 below (primary activation). Various physical properties of the porous carbon material obtained by finely grinding this granular porous carbon material so that the average particle size became 6 μm were measured.

[Examples 2 to 3, Comparative Examples 1 to 3]
In each of Examples 2 to 3 and Comparative Examples 1 to 3, the same conditions as in Example 1 were carried out except that the activation conditions were changed to the conditions shown in Table 1 below (primary activation and secondary activation were performed under the same conditions, respectively). rice field).

[Comparative Example 4]
100 g (100 parts by weight of dry solid content) of pine shavings (48% by weight) and 97.8 g [160 parts by weight of dry solid content (concentration 100% by weight)] phosphoric acid aqueous solution (concentration 85) Weight%) was mixed [weight ratio of phosphoric acid to shavings (phosphoric acid / shavings) = 1.6]. The mixture was heated with stirring in a circulation dryer set at 175 ° C.
The obtained mixture was put into a rotary kiln, heated to 300 ° C. in air at 4 ° C./min, and kept for 3 hours for oxidation.
Next, the circulating gas was switched from air to nitrogen, the temperature was raised to 500 ° C. at 4 ° C./min under nitrogen, and the gas was kept for 2 hours for activation.
Activated carbon was obtained by washing the activated pellets with water and drying them. The obtained activated carbon was subjected to a ball mill crusher to have an average particle size of 5.6 μm. Various physical properties of the porous carbon material obtained in Comparative Example 4 were measured. The measurement results are shown in Table 1.

[Examples 4 to 6 and Comparative Examples 5 to 8]
(Measurement of initial charge / discharge capacity / efficiency of lithium-ion secondary battery when applying positive electrode)
Using the porous carbon materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4, lithium ion secondary batteries were prepared according to the above description. The obtained lithium ion secondary battery was subjected to a charge / discharge test using a charge / discharge test device (“TOSCAT” manufactured by Toyo System Co., Ltd.). Lithium was doped at a rate of 70 mA / g relative to the weight of the active material and doped until it reached 1 mV with respect to the lithium potential. Further, a constant voltage of 1 mV was applied to the lithium potential for 8 hours to complete 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 with respect to the weight of the active material until it reached 2.5 V with respect to the lithium potential, and the capacity discharged at this time was defined as the discharge capacity. The charge / discharge efficiency (initial charge / discharge efficiency) was defined as the percentage of discharge capacity / charge capacity, and was used as an index of the utilization efficiency of lithium ions in the battery. In addition, the irreversible capacity was calculated by subtracting the discharge capacity from the charge capacity. Further, charging / discharging was repeated 100 times under the same conditions, and the value obtained by dividing the discharge capacity obtained at the time of the 100th charging / discharging by the initial capacity was defined as the capacity retention rate.

(Measurement of impedance)
Using the electrode produced above, using an electrochemical measuring device (“1255WB type high-performance electrochemical measuring system” manufactured by Solartron), an amplitude of 10 mV centered on 0 V is applied at 25 ° C, and a frequency of 10 MHz to 1 MHz is applied. The constant voltage AC impedance was measured at the frequency, and the real resistance at a frequency of 1 kHz was taken as the impedance resistance.

(Measurement of electrode expansion rate)
The coin cell having the above configuration was charged at a rate of 70 mA / g with respect to the weight of the active material, and was doped until it reached 1 mV with respect to the lithium potential. Further, a constant voltage of 1 mV was applied to the lithium potential for 8 hours. Then, the electric discharge was performed at a rate of 70 mA / g with respect to the weight of the active material until it reached 2.5 V with respect to the lithium potential. After repeating this charge / discharge cycle 5 times, the coin cell was disassembled in a glove box under an argon atmosphere to take out the negative electrode, and the taken out negative electrode was washed with diethyl carbonate and then dried. The negative electrode thickness (D) after drying was measured, and the ratio to the negative electrode thickness (C) measured before charging / discharging [percentage of "thickness (D) / thickness (C)"] was determined and used as the electrode expansion rate. The negative electrode thickness (C) and the negative electrode thickness (D) are the negative electrode thicknesses obtained by measuring the total thickness of the mixture layer and the aluminum foil at several points and subtracting the aluminum foil thickness from each total thickness. It is an average value.

Table 2 shows the results obtained by the above measurements.

As shown in Table 2, the examples showed lower impedance than the comparative examples, and had a high capacity retention rate after being charged and discharged 100 times.

Claims

The specific surface area by the BET method is 2500 to 3300 m 2 / g, and the pore radius frequency represented by the following formula (1) when measured in the range of 0.5 to 2.5 nm by the water vapor adsorption method. An additive for the positive electrode of an electrochemical element containing a porous carbon material having a minimum distribution value of 1 or more.
Pore radius frequency distribution = ΔV / ΔLog r (1)
(In formula (1), V is the pore volume (cc / g) and r is the pore radius (Å).)
The additive for the positive electrode of an electrochemical element according to claim 1, wherein the ash content of the porous carbon material is 0.5% by weight or less.
The additive for an electrochemical element positive electrode according to claim 1 or 2, wherein the porous carbon material has an average particle size of 2 μm to 20 μm.
The composition for an electrochemical element positive electrode containing the electrochemical element positive electrode additive according to any one of claims 1 to 3 and the positive electrode active material, and the content of the electrochemical element positive electrode additive is described above. A composition for a positive electrode of an electrochemical element, which is 10% by weight or less based on the total weight of the positive electrode active material.
The composition for an electrochemical element positive electrode according to claim 4, further comprising a binder in an amount of 0.5 to 10% by weight based on the total solid content weight of the electrochemical element positive electrode composition. thing.
The composition for an electrochemical element positive electrode according to claim 4 or 5, further comprising a conductive material in an amount of 1 to 10% by weight based on the total solid content of the composition for an electrochemical element positive electrode, for an electrochemical element positive electrode. Composition.
An electrochemical device having a positive electrode produced by using the composition for a positive electrode of an electrochemical device according to any one of claims 4 to 6.
The electrochemical device according to claim 7, wherein the electrochemical device operates at 2V to 5V.
A lithium ion secondary battery having a positive electrode produced by using the composition for an electrochemical element positive electrode according to any one of claims 4 to 6.