KR20070119894A - Radical electrode active material having high density and electrochemical device using the same - Google Patents

Abstract

An electrode active material is provided to ensure high electroconductivity and energy improvement per unit volume and to ensure structural stability by fixing an electrochemically active radical to the surface of a matrix particle through chemical bonding. An electrode active material includes (a) a matrix particle, and (b) a radical having electrochemical activity which is fixed to a partial or all surface of the matrix particle through chemical bonding. The electrode active material has an energy per unit volume of 300 mAh/cm^3. An electrochemical device comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode, negative electrode, or both electrodes comprises the electrode active material.

Description

High-density radical electrode active material and electrochemical device using the same {RADICAL ELECTRODE ACTIVE MATERIAL HAVING HIGH DENSITY AND ELECTROCHEMICAL DEVICE USING THE SAME}

The present invention relates to a radical-containing high-density, high-conductivity electrode active material and a method for manufacturing the same, an electrode having an improved energy density per unit volume including the electrode active material, and an electrochemical device having improved performance.

Recently, Japan's NEC Electronics has adopted an organic radical polymer as a cathode active material for lithium ion batteries, demonstrating that this material is capable of ultra-fast charging and discharging, and has successfully commercialized it as a memory backup battery for computers (US). 6,866,964 B2).

Such an organic radical cathode active material includes a nitroxyl group containing radicals in a vinyl-based polymer backborn, and these radicals have a positive charge and thus store anions and simultaneously release electrons, thereby having an operating voltage of about 3.8 V. Can be used as The typical material is PTMA (poly tetrapyperidone methylacrylate). Scheme 1 shows a charge storage method of the organic radical cathode active material. In the reduction process, the anion binds to the positively charged nitrogen and the charge is stored as the anion is released during oxidation.

These organic radical cathode active materials have the advantage of very good speed characteristics, high initial efficiency of 90% or more, environmental stability, and easy processing because they are in the form of polymers. However, the charge / discharge capacity per mass is not so large as about 110 mAh / g, but also has a disadvantage in that the theoretical capacity per volume is very small, such as about 126 mAh / cc, since the density is about 1.15 g / cc because of its polymer form. For reference, the capacity of manganese-based cathode active materials on the market is higher than 400 mAh / cc. In addition, since the organic radical cathode active material is a nonconductor, there is a disadvantage in that an excessive amount of a conductive agent is added during electrode formation, and the concentration of cations and anions in the electrolyte is reduced during charging and discharging. The biggest problem among these disadvantages is the low conductivity and the small capacity per volume. Due to these problems, the commercialized battery is the main application of the computer as a memory backup battery. There is a limit to the application of this type of battery.

In addition, practically, the organic radical polymer cathode active material has a limitation in increasing the density. This is because it is difficult to improve the density by more than 10% even if it is crystallized as much as possible due to the matrix of the vinyl polymer. Therefore, solving the problems of low density and improved conductivity in such an organic radical battery is the most urgent problem.

In view of the above-described problems, the present inventors have applied chemical bonds instead of simply coating or covering a compound containing radically convertible functional groups on part or all of the surface of a dense, highly conductive matrix particle. By fixing through the physical properties of the carrier particles, the low-density and low-conductivity problems described above are fundamentally solved, thereby improving overall performance such as capacity per unit volume and the like, and also improving structural stability of the electrode active material. Completed.

Accordingly, an object of the present invention is to provide an electrode active material and a manufacturing method thereof, an electrode including the electrode active material and an electrochemical device having the electrode.

The present invention (a) carrier particles (matrix particle); And (b) an electrode active material comprising a radical having electrochemical activity fixed through chemical bonding to a part or all of the surface of the carrier particle, an electrode including the electrode active material, and the electrode. It provides an electrochemical device, preferably a lithium secondary battery.

In addition, the present invention comprises the steps of (a) fixing a compound containing a functional group capable of converting radicals on part or all of the surface of the carrier particles through chemical bonding; And (b) electrochemically activating a functional group convertible into a radical in the compound to generate a radical.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, a matrix particle having a high density, high conductivity, and a high surface area is introduced into a radical electrode active material resulting in low conductivity and low capacity-per-volume reduction due to the use of a low density polymer as a conventional backborn. It is done.

In this case, the carrier particles have a form in which some or all of the surface of the particles come into contact with radicals having an electrochemical activity, and are fixed through chemical bonding instead of simply contacting by coating or cover. Differentiate.

The characteristics of the electrode active material including radicals chemically fixed to the carrier particles will be described in more detail as follows.

1) Since the conventional organic radical electrode active material is introduced in the form of containing radicals in the polymer matrix, which is low density and insulator, the theoretical capacity per volume itself is very small, and an excessive amount of conductive agent is used in manufacturing the electrode, for example 30 per 100 parts by weight of the electrode material. The use of parts in parts by weight is essential. In particular, an organic radical battery stores anions and cations in the positive and negative electrodes, respectively, during charging, and is discharged again when discharged. In this case, the radicals are combined (reduced) with anions by charging. The charge is stored, and the negative ions are released (oxidized) by the discharge. As the concentration of cations and anions in the electrolyte caused by the charging of the battery itself is reduced, the overall conductivity is reduced. Therefore, the low conductivity of the electrode active material included in the insulator polymer matrix may limit the commercial application of the radical battery. do.

Thus, in the present invention, by using a carrier having a high density, high conductivity, and a high surface area instead of the conventional low density and nonconducting polymer matrix, not only can the conductive material be significantly reduced, but also high electron conductivity can be exhibited. The density can be raised significantly. In fact, it can be confirmed through the present experimental example that it represents 300mAh / cm ³ or more improved by about 3 times compared with the conventional organic radical cathode active material.

2) In addition, in the present invention, the radical having electrochemical activity is fixed to the surface of the carrier through chemical bonding, thereby improving performance of the battery such as cycle characteristics, life characteristics, and the like through structural structural improvement of the electrode active material.

3) In addition, when preparing an electrode including a conventional radical, by introducing a chemically labile radical directly into the electrode, the radical and the carrier are used in the present invention, compared to the problem of difficulty in handling the radical and adding an economic cost thereof. When chemically immobilized, novel chemical immobilization methods which eliminate the use of additives such as separate fixatives, adjuvants and the like and eliminate the difficulties of radical handling, such as (a) the first polar functional groups present on the surface of the carrier particles and (b) By fixing through a chemical reaction with a second polar functional group present in the compound containing a functional group capable of converting into radicals, it is possible to secure the simplicity of the manufacturing process and to improve the economics. In addition, a compound having a radical-convertible functional group chemically fixed to a carrier may be provided with an energy supply and / or an oxidizing (reducing) agent corresponding to an excited energy state or higher of an excited electron state. Another advantage is that radicals can be easily generated through radical generating electroactivation methods such as reactions.

According to the present invention, a carrier to which a radical having electrochemical activity is fixed is in the form of particles, and is not particularly limited as long as it is electrochemically stable. That is, the carrier particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range of the battery to be applied (for example, 0 to 5 V on the basis of Li / Li ⁺ ).

The size of the carrier particles is not particularly limited, but may range from 5 to 100 nm. In addition, the density of the carrier particles is not particularly limited so long as it is higher than the density (1.15 g / cc) of the conventional polymer matrix, and preferably in the range of ³ g / cm ³ or more.

The carrier particles according to the invention are preferably as conductive as possible, in which the conductivity range is not particularly limited. For example, it may have a conductivity range of about several tens of mS / cm ² to several hundred S / cm ² . In addition, in order to easily chemically fix a compound having a radical convertible functional group on the carrier particle, a conventional polar functional group known in the art (e.g., a first polarity), if possible, on part or all of the surface of the carrier particle. Functional groups), and non-limiting examples of the polar functional groups include a carboxyl group, a carbonyl group, a hydroxy group, a hydroxyl group, and the like.

The material of the carrier particles is not particularly limited, but may be composed of a carbon material, a (semi) metal, a (semi) metal oxide, other inorganic substances, or a mixture thereof. Non-limiting examples thereof include titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), zeolite, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), activated carbon, graphite, activated carbon Fiber or exfoliated graphite. In addition, the carrier particles preferably have a surface area as high as possible in order to chemically fix a large amount of radicals having electrochemical activity on the surface of the particles, and thus may have a porosity structure. In one example, the carrier may have a surface area in the range of several hundreds to 2000 m ² / g. At this time, in addition to the surface area, the porosity and pore size is not particularly limited, and can be adjusted within a range conventional in the art.

Radical chemically immobilized on a carrier particle in accordance with the present invention refers to a species that does not form a pair of electrons, i.e., has an unpaired electron, and thus the spin nuclear momentum is not zero. It has various magnetic properties such as paramagnetic, and is generally produced by chemical bond decomposition in a molecule by pyrolysis, photolysis, radiation decomposition or electron transfer. In addition to the very high chemical reactivity, the presence of such radicals is measured in the electron spin spectrum (ESR).

The kind of radicals is not particularly limited, and non-limiting examples thereof include carbon radicals, boron radicals, sulfur radicals, oxy radicals, nitroxy radicals, hydroxy radicals, or hydrazyls. Radicals, etc. Further, the spin concentration range of the generated radicals is preferably 10 ²⁰ spin / g or more on the ESR spectrum, but is not limited thereto.

Radicals immobilized on the carrier particles according to the present invention are not particularly limited and may be generated from a compound having a functional group convertible into radicals. In particular, in order to be easily fixed through chemical bonding on the surface of the carrier described above, (i) a functional group convertible to radicals; And (ii) a second polar functional group capable of chemically reacting with the first polar functional group on the surface of the carrier.

The second polar functional group is not particularly limited as long as it is a functional group capable of chemical reaction with the first polar functional group on the carrier, and non-limiting examples thereof include a hydroxy group (-OH), an amine group (-NH ₂ ), and the like. In particular, the second polar functional group is preferably separated from the radical convertible functional group, if possible, for ease of chemical bonding with the first polar functional group. For example, in the case of a cyclic compound, the second polar functional group is separated from the radical convertible functional group. It is appropriate to exist at the location. However, it is not limited thereto.

Compounds containing functional groups that can be converted to radicals are substituted or unsubstituted linear, cyclic, including one or more functional groups selected from the group consisting of boron, sulfur, oxy, nitoxy groups, hydroxy groups and hydrazyl groups, NH groups (cyclic) or a compound having a mixed structure thereof, and examples of the substituent include a hydrogen atom, a lower alkyl group or an aralkyl group having 1 to 7 carbon atoms, a lower alkoxy group, a halogen atom, a cyan group, a phenyl group, a nitro group, an amino group, Ureido groups, carboxylic acid groups, isocyanate groups, glycidyl groups, hydroxyl groups, and the like, and may include heteroatoms such as nitrogen, oxygen, and sulfur. Non-limiting examples thereof include organic peroxides, azo compounds, sulfur containing organic compounds, boron containing compounds and the like. In this case, the lower means an atomic group or a compound having 6 or less carbon atoms, preferably 5 or less carbon atoms, and the lower alkyl group is a linear or branched lower saturated aliphatic hydrocarbon, for example, methyl, ethyl, n -propyl, iso Propyl, n -butyl, s -butyl, isobutyl, t -butyl and n -pentyl groups. In addition, the compound containing a functional group capable of converting into a radical may be a monomer capable of forming a conventional polymer or cross-linking polymer having a network structure on the surface of a carrier particle. .

Unlike the conventional radical electrode active material, the electrode active material of the present invention, which is composed of a compound including a functional group convertible to a radical and a radical, is fixed through chemical bonding, for example, (a) the surface of the carrier particle It can be immobilized on a carrier particle through a chemical reaction with a first polar functional group present in the phase and (b) a second polar functional group present in the compound comprising a functional group convertible into radicals. In this case, the chemical bonds include conventional chemical bonds known in the art, such as condensation reactions, and the like, and hydrogen bonds having a polar working period are also included in the scope of the present invention.

According to the present invention, an electrode active material in which radicals having an electrochemical activity on a carrier particle are chemically fixed may be prepared as follows, but is not limited thereto.

Firstly, 1) a compound comprising a functional group convertible to radicals is fixed to a part or all of the surface of the carrier particle through chemical bonding.

The step can be carried out according to conventional methods known in the art, and in one preferred embodiment thereof, as described above, (i) convertible to radicals and (ii) radicals present on the surface of the carrier particles. It is through the chemical reaction with the 2nd polar functional group which exists in the compound containing a functional group.

The carrier may already have polar functional groups on the surface without special treatment, or may impart polar functional groups to the surface through acid treatment or oxidation treatment in the atmosphere (see Scheme 2 (1) below). For example, it can be used by dispersing in a solvent such as water, alcohol or ketone.

As such, when the first polar functional group present on the surface of the carrier particle and the second polar functional group present in the compound including the radical-converting functional group are chemically reacted under appropriate conditions, the chemical bond as shown in (3) It will be fixed through. At this time, the type of chemical reaction and its conditions are not particularly limited, and can be adjusted within the conventional conditions known in the art.

2) The radicals in the compound are converted electrochemically into functional groups to generate radicals (see Scheme 2 (4)).

At this time, the electrochemically active method of generating radicals is not particularly limited, and for example, may provide energy corresponding to an excited energy state or higher of a radical and / or an oxidizing (reducing) agent. It can be made by the reaction of. The oxidizing agent (reducing agent) may be used a conventional oxidizing agent (reducing agent) known in the art, for example mCPBA.

The electrode active material having the electrochemically active radicals fixed on the carrier particles prepared as described above has an energy per unit volume of 300 mAh / cm ³ or more when a carrier having a density of 3 g / cm ³ or more is used. 3 times the capacity increase is shown. In addition, despite the use of a small amount of a conductive agent compared to the conventional organic radical cathode material, it is possible to improve the overall performance due to excellent electronic conductivity. In this case, the electrochemical reaction potential of the radicals are different from each other depending on the type of the radical, for example, the electrochemical reaction potential of the nitrooxy radical may represent about 3.75 V (vs. Li / Li ⁺ ).

The present invention provides an electrode comprising the electrode active material described above. In this case, the electrode active material may be used for both the positive electrode, the negative electrode, or the positive electrode, but the positive electrode used as the positive electrode active material in terms of energy density is preferable.

When using an electrode active material in which radicals are chemically fixed on the carrier particles as the electrode active material of either the positive electrode or the negative electrode, the following materials may be used as the active material of the other electrode.

When introducing the electrode active material of the present invention as a negative electrode active material, non-limiting examples of the positive electrode active material that can be used can be used a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, for example lithium manganese oxide, lithium cobalt oxide And lithium intercalation materials such as a composite oxide formed by lithium nickel oxide, lithium iron oxide, or a combination thereof. In addition, when introducing the electrode active material of the present invention into the positive electrode active material, non-limiting examples of the negative electrode active material that can be used can be used a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, for example lithium metal or lithium alloy , Lithium adsorbents such as carbon, petroleum coke, activated carbon, graphite, metal oxides, conductive polymers or other carbons. In addition, when the electrode active material of the present invention is applied to the energy storage element of the adsorption-and-desorption method by the method in which charge absorbs and desorbs on the positive electrode surface to store energy, it is applicable to both the positive electrode and the negative electrode.

The electrode including the electrode active material of the present invention may be prepared in the form of the electrode active material described above bound to the electrode current collector according to a conventional method known in the art, and if necessary, a binder and / or a conductive agent may be used. Can be.

In addition, the present invention is an electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode, the negative electrode and the positive electrode is characterized in that the electrode is made from the electrode active material is chemically fixed on the carrier particles described above Provides an electrochemical device.

Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary, fuel cells, solar cells, or capacitors, which are energy storage devices of a desorption type. have. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery among the secondary batteries is preferable.

In particular, the conventional lithium secondary battery exhibits a battery voltage due to the electrochemical potential difference of lithium generated when lithium ions are occluded and desorbed into crystals of a positive electrode and a negative electrode. By combining at the surface, a surface reaction similar to that of conventional supercapatiors occurs. In this case, when a radical material is used as the cathode active material, charge / discharge is performed in such a manner that an anion reacts with the radical during charging and charge is stored, and during discharge, the combined anion is released into the electrolyte. Conversely, when the radical material is applied to the cathode, cations react with the radicals during charging to store charges. The difference in reaction with the electrode active material in such a conventional lithium ion battery is to indicate an increase in the charge storage and release rate of the battery composed of the radical material.

The electrochemical device may be manufactured according to conventional methods known in the art, and for example, an electrochemical device may be manufactured by injecting an electrolyte after assembling a separator between a pair of electrodes such as an anode and a cathode. Can be.

There is no electrolyte which can be used in the present invention is no particular limitation if only to have ion conductivity, A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, a cation an alkali metal such as K ⁺ or a combination thereof including ions consisting of and B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 ^{_{SO 2) 2 -, C (}} CF 2 SO 2) 3 - salts comprising the anions or an ion composed of a combination of propylene carbonate (PC like), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl Carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC) , Dissolved or dissociated in an organic solvent consisting of gamma butyrolactone (γ-butyrolactone) or mixtures thereof Can. As the electrolyte salt, a (CH ₃ ) ₄ N salt, a (C ₂ H ₅ ) ₄ N salt, or the like may be used.

As the separator, conventional microporous separators known in the art such as polyolefin-based and / or cellulose-based separators may be used to prevent contact between the two electrodes.

The invention is explained in more detail based on the following examples and experimental examples. However, Examples and Experimental Examples are for illustrating the present invention and are not limited to these.

In the present invention, by fixing a radical having electrochemical activity on the surface of the carrier having a high density, high conductivity and high surface area through chemical bonding, it is possible to realize high conductivity and energy improvement per unit volume, as well as to provide structural characteristics of the electrode active material. Stability can be attained.

Claims (19)

(a) matrix particles; And (b) radicals having fixed electrochemical activity through chemical bonding to some or all of the surface of the carrier particles; Electrode active material comprising a. The electrode active material according to claim 1, wherein the carrier particle has a first polar functional group on its surface. The electrode active material of claim 1, wherein the carrier particles have a size in the range of 5 to 100 nm. The electrode active material according to claim 1, wherein the carrier particles have a density of 3 g / cm ³ or more. The electrode active material according to claim 1, wherein the carrier particles have conductivity. The electrode active material according to claim 1, wherein the material of the carrier particles is at least one member selected from the group consisting of carbon materials, (semi) metals, (semi) metal oxides, and inorganic substances. The method of claim 1, wherein the radical comprises (i) a functional group convertible to a radical; And (ii) a compound containing a second polar functional group. The electrode active material according to claim 1, wherein the spin concentration of the radical is 10 ²⁰ spin / g or more on the ESR spectrum. The method of claim 1, wherein the electrode active material is subjected to a chemical reaction between (a) a first polar functional group present on the surface of the carrier particle and (b) a second polar functional group present in the compound comprising a functional group convertible to radicals. Electrode active material characterized in that the fixing on the carrier particles. The method of claim 1, wherein the radical is selected from the group consisting of carbon radicals, boron radicals, sulfur radicals, oxy radicals, nitroxy radicals, hydroxy radicals and hydrazyl radicals. Electrode active materials. The method of claim 7, wherein the compound is substituted or unsubstituted linear comprising at least one functional group selected from the group consisting of carbon, boron, sulfur, oxy, nitoxy group, hydroxy group, NH group and hydrazyl group, An electrode active material which is a compound having a cyclic or a mixed structure thereof. The electrode active material according to claim 1, wherein the energy per unit volume of the electrode active material is 300 mAh / cm ³ or more. An electrode comprising the electrode active material of any one of claims 1 to 12. The electrode of claim 13, wherein the electrode is an anode. An electrochemical device comprising an anode, a cathode, a separator, and an electrolyte, wherein the anode, the cathode, or the positive electrode is an electrode including the electrode active material of any one of claims 1 to 12. The electrochemical device of claim 15, wherein the electrochemical device is a lithium secondary battery. (a) immobilizing a compound comprising a functional group convertible into radicals on part or all of the surface of the carrier particle through chemical bonding; And (b) electrochemically activating a functional group convertible to a radical in the compound to generate a radical The manufacturing method of the electrode active material in any one of Claims 1-12 containing. 18. The chemical reaction of claim 17, wherein step (a) comprises (i) a first polar functional group present on the surface of the carrier particle and (ii) a second polar functional group present in the compound comprising a radical convertible functional group. Method for producing characterized in that the fixing on the carrier particles through. 18. The method of claim 17, wherein the electrochemical activity of generating radicals in step (b) comprises: (i) supplying energy corresponding to or above the excited energy state of the radicals and (ii) oxidation A production method characterized by at least one method selected from the group consisting of reaction with a (reduction) agent.