WO2014109534A1 - Electrode formulation, method for preparing the same, and electrode comprising the same - Google Patents

Electrode formulation, method for preparing the same, and electrode comprising the same Download PDF

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WO2014109534A1
WO2014109534A1 PCT/KR2014/000183 KR2014000183W WO2014109534A1 WO 2014109534 A1 WO2014109534 A1 WO 2014109534A1 KR 2014000183 W KR2014000183 W KR 2014000183W WO 2014109534 A1 WO2014109534 A1 WO 2014109534A1
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electrode
fibrous carbon
carbon material
active material
composite
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French (fr)
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Ju Suk Ryu
Sei Ung Park
Jong Ju Min
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Hanwha Chemical Corporation
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

An electrode formulation, method for preparing the same, and an electrode comprising the same are disclosed. The present invention provides an electrode formulation comprising an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound and a binder, and realizes a high-capacity battery by increasing the capacity of the electrode.

Description

ELECTRODE FORMULATION, METHOD FOR PREPARING THE SAME, AND ELECTRODE COMPRISING THE SAME
The present invention relates to an electrode formulation, a method for preparing the same, and an electrode comprising the same.
Recent research on energy storage materials has progressed in the direction of either improving output properties of a secondary battery for application to hybrid cars or improving fuel efficiency by utilizing a high power capacitor as an auxiliary output-apparatus. Secondary batteries for cars include nickel metal hydride batteries, lithium batteries, etc., and a supercapacitor is a capacitor having specific capacitance improved by 1,000 times or more as compared with conventional capacitive capacitors.
Electrochemical devices such as secondary batteries or supercapacitors utilize, as electrode-active material, transition metal compounds exhibiting electrochemical activity via oxidation-reduction reactions. To allow such electrode-active materials to effectively exhibit their theoretical capacities and voltage properties, it is necessary to control or complement electrochemical properties, such as electric conductivity, ionic conductivity, etc., and physicochemical properties, such as corrosion resistance, dispersibility, etc. For such purposes, numerous efforts have been made to date.
Examples of such efforts include the nanotization of the particles of transition metal compounds, the solid-solubilization of heteroelements, the formation of a protective film on particle surfaces, the incorporation of electrically conductive materials, etc. Carbon materials or ceramic materials which improve the electric conductivity of electrode materials while having high corrosion resistance and chemical resistance have been frequently used as materials for coating the surfaces of transition metal compound particles.
Particularly, since carbon materials have advantages including high electric conductivity, chemical and physical stability, etc., numerous methods either for mixing or combining carbon materials with transition metal compounds or for coating carbon materials on the surfaces of transition metal compound particles have been proposed to protect the transition metal compounds or improve their functions. Such carbon materials are simply mixed with transition metal compounds via mechanical mixing or coated on the surfaces of transition metal compound particles through chemical vapor deposition. In general, it has been known that coating the surfaces of individual particles with carbon materials is more effective than the mixing of carbon materials in providing surface protection and electric conductivity. The advantages of carbon materials include improved electric conductivity in electrode materials, the protection of transition metal compound particles from external physicochemical influences, the restriction of excessive growth of transition metal compound particles during heat treatment, and the like.
In addition, a carbon coating should have a thickness sufficient to provide physicochemical protection to transition metal compounds, and to ensure a sufficient thickness, carbon precursors should be used in large quantity. However, if carbon precursors are used in large quantity, they may be consumed not only in forming a carbon coating but also in forming carbon by-products, and thus increasing the possibility of causing problems such as decreased electrode density and low dispersibility.
In addition, if carbon material is coated on the surfaces of particles,　although electric conductivity is improved, the coated carbon material can interfere with the intercalation and deintercalation of ions which accompany electrochemical reactions of transition metal compounds.
As a method which can achieve effects comparable to those of the carbon coating of particles, the utilization of fibrous carbon materials, such as carbon fiber or carbon nanotubes (CNTs) has been proposed. Particularly, a proposal was made to improve electric conductivity by mixing with CNTs.
Korean Patent Application Laying-Open No. 10-2008-0071387 discloses a CNT composite having a structure in which CNTs, electrode materials for a lithium second battery, and carbon material which is formed from the carbonization of polymers are uniformly dispersed.
Korean Patent Registration No. 1,103,606 discloses an electrode-active material composite including a transition metal compound (electrode-active material) and a fibrous carbon material, wherein the composite is configured such that fibrous carbon material is aggregated more densely on the surface of the composite rather than at the inside or center thereof.
Meanwhile, in order to fabricate an electrode constituting a secondary battery, the electrode-active material composite is mixed with a binder and an electric conducting agent to prepare an electrode formulation, and then the electrode formulation is applied onto a current collector. In this case, for the purpose of improving electrical conductivity between electrode-active material particles or between an electrode-active material and a current collector, an electric conducting agent is added. Particularly, it is known that an electric conducting agent is required in order to prevent a binder region from acting as an electric nonconductor and to improve the electrical conductivity of cathode and anode active materials. However, the usage of an electric conducting agent causes a problem of reducing the capacity of a battery.
However, this conventional technology discloses an electrode formulation including an electrode-active material composite, a binder and an electric conducting agent, but does not disclose an electrode formulation including an electrode-active material and a binder while using a very small amount of an electric conducting agent or not using an electric conducting agent.
Accordingly, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electrode formulation, a method for preparing the same, and an electrode including the same by which the amount of a transition metal compound as a constituent of an electrode-active material composite increases, so the capacity and density of an electrode increase, thereby realizing a high-capacity battery.
In order to accomplish the above object, an aspect of the present invention provides an electrode formulation, including: 70 to 99.5 wt% of an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; and 0.5 to 30 wt% of a binder.
The electrode formulation may further include less than 5 wt% of an electric conducting agent.
In the electrode-active material composite, the fibrous carbon material may be non-uniformly dispersed in the aggregate.
In the electrode-active material composite, the fibrous carbon material may densely exist on the surface of the aggregate compared to the inside thereof.
In the electrode-active material composite, the fibrous carbon material densely exists in one side of the section of the aggregate compared to the other side thereof.
The fibrous carbon material may be a carbon fiber or a carbon nanotube.
All or a part of the primary particles may be electrically connected by the fibrous carbon material, and the fibrous carbon material may exist on the entire or partial surface of the aggregate of the primary particles in the form of a web.
The electrode-active material composite may include the transition metal compound and the fibrous carbon material at a weight ratio of 99.9: 0.1 to 80: 20.
The fibrous carbon material may include a non-functionalized fibrous carbon material and a surface-functionalized fibrous carbon material at a weight ratio of 1: 99 to 20: 80.
The binder may be at least one selected from the group consisting of cellulose, an ethylene polymer, an ethylene copolymer, a propylene polymer, a propylene copolymer, polyvinylpyrrolidone, polyvinylchloride, an ethylene-propylene-diene rubber (EPDM), a styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and a polyvinylidene fluoride copolymer.
The electric conducting agent may be at least one selected from the group consisting of graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, titanium oxide, nickel, and aluminum.
The electrode-active material composite may have an average particle diameter of 1 to 200μm.
The transition metal compound may be at least one selected from the group consisting of LiCoO2; LiMnO2; LiMn2O4; Li4Ti5O12; Li(Ni1-x-yCoxAly)O2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99); Li(Ni1-x-yMnxCoy)O2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99); and Li2-z(Fe1-x-yM1 xM2 y)zO2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99, 0<z<1, M1 and M2 are each independently Ti, Ni, Zn or Mn).
Further, the transition metal compound may be represented by Formula 1 below:
[Formula 1]
Li1-xM(PO4)1-y
wherein 0≤x≤0.15, 0≤y≤0.1, and M is represented by Formula 2 below:
[Formula 2]
MA aMB bMT tFe1-(a+b+t)
wherein MA is at least one selected from the group consisting of group 2 elements,MB is at least one selected from the group consisting of group 13 elements, MT is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, 0≤a≤1, 0≤b<0.575, 0≤t≤1, 0≤(a+b)<1, and 0≤(a+b+c)≤1.
The transition metal compound may be represented by Formula 3 below:
[Formula 3]
LiMPO4
wherein M is one or a combination of two or more selected from the group consisting of Fe, Mn, Ni, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo.
Another aspect of the present invention provides an electrode manufactured using the electrode formulation.
Still another aspect of the present invention provides a secondary battery comprising the electrode.
Still another aspect of the present invention provides a method of preparing an electrode formulation, comprising the steps of: (a) preparing a mixture in which at least one selected from a non-functionalized fibrous carbon material and a surface-functionalized fibrous carbon material and transition metal compound particles are dispersed; (b) drying and granulating the mixture to prepare an electrode-active material composite; and (c) mixing the electrode-active material composite with a binder to prepare an electrode formulation.
In the step (c) an electric conducting agent may be additionally mixed with the electrode-active material composite and the binder.
In the step (a) of preparing the mixture, the mixture may be dispersed therein with a non-functionalized fibrous carbon material, a surface-functionalized fibrous carbon material and transition metal compound particles, and the amount (based on weight) of the surface-functionalized fibrous carbon material may be greater than that of the non-functionalized fibrous carbon material.
Here, the mixture may include a dispersant in an amount of 10 to 500 parts by weight based on 100 parts by weight of the total amount of the fibrous carbon material.
The step (a) of preparing the mixture may include the steps of: dispersing the non-functionalized fibrous carbon material and the surface-functionalized fibrous carbon material in a dispersant to prepare a dispersion liquid; and mixing the dispersion liquid with the transition metal compound to prepare the mixture dispersed therein with the non-functionalized fibrous carbon material, the surface-functionalized fibrous carbon material and the transition metal compound.
The dispersant is at least one selected from the group consisting of water, alcohol, ketone, amine, ester, amide, alkyl halogen, ether and furan.
The present invention provides an electrode formulation including: an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; and a binder.
According to the present invention, the electrical conductivity of the electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound is better than that of a conventional electrode-active material in which primary particles or an aggregate thereof are coated with a carbon material, and the fibrous carbon material can be brought into contact with the aggregates of the primary particles and can fill the pores between the aggregates of the primary particles, so that the electrical conductivity of the electrode formulation of the present invention can be exhibited even when an electric conducting agent is not added.
Further, the present invention provides an electrode formulation including: an electrode-active material composite including a fibrous carbon material and an aggregate of primary transition metal compound particles; a binder; and a small amount of an electric conducting agent.
According to the present invention, when this electrode formulation of the present invention is applied to an electrode, the amount of a transition metal compound in the electrode increases, so the capacity of a battery increases under the same electrode volume density, and the electrode includes a small amount of an electric conducting agent or does not include the electric conducting agent, with the result that the electrode density increases under the same electrode volume, thereby realizing a high-capacity battery.
Figure 1 is a sectional view showing an electrode-active material composite in which a fibrous carbon material densely exists on the surface of the aggregate compared to the inside thereof according to Preparation Example of composite A of the present invention.
Figure 2 is a sectional view showing an electrode-active material composite in which a fibrous carbon material densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof according to Preparation Example of composite B of the present invention.
Figure 3 is a SEM photograph at 500 magnification of the granular composite prepared in Preparation Example 1-1.
Figure 4 is a SEM photograph at 50,000 magnification of an outer side cross section of the granular composite including the surface prepared in Preparation Example 1-1.
Figure 5 is a SEM photograph of an inner side cross section obtained by cutting down the granular composite prepared in Preparation Example 1-1.
Figure 6 is a SEM photograph of a section of the composite prepared in Preparation Example 2-1.
Figure 7 is a SEM photograph of the section of the granular composite prepared in Preparation Example 2-1 and enlarged other parts thereof.
Figure 8 shows a SEM photograph at 1,000 times magnification of the composite prepared in Comparative Preparation Example 1 and a SEM photograph at 50.000 times magnification of the surface of said composite.
Figure 9 is shows a SEM photograph at 1,000 times magnification of the composite prepared in Comparative Preparation Example 2 and a SEM photograph at 50.000 times magnification of the surface of said composite.
Figure 10 is the crystal structures analysis by XRD of the composites prepared in Preparation Examples 1-1 and 1-11 to 1-22, and Comparative Preparation Examples 1, 3 and 4.
Figure 11 is the graph of the charge/discharge capacities of the secondary battery of the present invention using the composites (composite A) depending the content of the conductive agent.
Figure 12 is the graph of the charge/discharge capacities of the secondary battery of the present invention using the composites (composite B) depending the content of the conductive agent.
Hereinafter, preferred embodiments of the present invention will be described in detail. The present invention may be embodied in many different forms without departing from the spirit and significant characteristics of the invention. Therefore, the embodiments of the present invention are disclosed only for illustrative purposes and should not be construed as limiting the present invention. Further, in the description of the present invention, when it is determined that the detailed description of the related art would obscure the gist of the present invention the description thereof will be omitted.
1. Electrode formulation
The present invention provides an electrode formulation, including: 70 to 99.5 wt% of an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; and 0.5 to 30 wt% of a binder. Preferably, the present invention provides an electrode formulation, including: 90 to 99.5 wt% of an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; and 0.5 to 10 wt% of a binder.
The electrode formulation may further include an electric conducting agent in an amount of less than 5 wt%, preferably less than 4 wt%, more preferably less than 3 wt%, and most preferably less than 2 wt%, and may not include the electric conducting agent.
(1) Electrode-active material composite
The electrode-active material composite of the present invention may comprise an aggregate of primary particles of the transition metal compound and the fibrous carbon material.
"Primary particle" denotes an individual particle which is not aggregated with other particles.
"Surface region" of an aggregate denotes the region which defines the boundary between the aggregate and the outside. The surface region of an aggregate amounts to the surface region of the composite, and the inside of the aggregate amounts to the inside of the composite.
Referring to FIG. 1, the electrode-active material composite may be configured such that the fibrous carbon material is non-uniformly dispersed in the aggregate. Wherein the fibrous carbon materials may be present in the surface region of the aggregate at a higher density than in the inside region thereof. In the present invention, fibrous carbon materials are present in spaces between primary particles in the inside of an aggregate, and are also present in the surface region of the aggregate. They are present sparsely in the inside or in the center region but densely in the surface region of the aggregate.
Referring to FIG. 2, the electrode-active material composite may be configured such that the fibrous carbon material is non-uniformly dispersed in the aggregate in a different form from that in FIG. 1. Here, the electrode-active material composite may be configured such that the fibrous carbon material densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof. In this case, the fibrous carbon material may exist in the space between primary particles in the aggregate, and may densely exist in one side of the section (A-A') of the aggregate and sparsely exist in the other side thereof.
Fibrous carbon materials present in the inside of an aggregate serve as bridges electrically connecting at least a part of primary particles, and can form a network.
Fibrous carbon materials present in the surface region of an aggregate may form a web.
The electrode formulation of the present invention includes: an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; a binder; and an electric conducting agent. The electrode formulation of the present invention may include the electrode-active material composite in an amount of 70 to 99.5 wt%, preferably, 90 to 99.5 wt%, based on the total weight thereof.
When the amount of the electrode-active material composite is less than 70 wt%, the capacity of the electrode formulation is lowered, which is not preferable, and, when the amount thereof is more than 99.5 wt%, the performance of a battery is deteriorated, which is not preferable.
The transition metal compounds and the fibrous carbon materials constituting the composite can be present in a ratio of 99.9:0.1 to 80:20 by weight. Preferably, the fibrous carbon materials account for 0.5 to 10% by weight of the composite. If the amount of fibrous carbon materials is too small, electric connections between primary particles may be insufficient, or the external surface region of the composite cannot be sufficiently covered with the carbon materials, so that the fibrous carbon materials cannot, sufficiently improve the electric conductivity of the composite or cannot properly perform the function of protecting the composite against external influences. On the contrary, if fibrous carbon materials are present in an excessive amount, the amount of transition metal compounds as a constituent of the composite decreases, and then electrodes produced by utilizing such composites have problems in that they have a low electrode density and eventually have a low battery capacity and, further, the use of excessive carbon materials increases production costs.
The fibrous carbon materials include carbon fibers and carbon nanotubes (CNTs). As CNTs, single-walled, double-walled, thin multi-walled, multi-walled or roped forms or their mixtures can be used. The fibrous carbon materials used in the present invention have an average diameter of 0.5 to 200 nm, and preferably have an average aspect ratio of length to diameter of not less than 10.
In the electrode-active material composite in which a fibrous carbon material densely exists on the surface of the aggregate compared to the inside thereof, the fibrous carbon material existing on the surface of the aggregate may be a surface-functionalized fibrous carbon material, and the fibrous carbon material existing inside the aggregate may be a non-functionalized fibrous carbon material.
In the electrode-active material composite in which a fibrous carbon material densely exists in one side of the section of the aggregate compared to the other side thereof, the fibrous carbon material existing in one side of the aggregate may be a surface-functionalized fibrous carbon material, and the fibrous carbon material existing in the other side thereof may be a non-functionalized fibrous carbon material.
Surface functionalization means introducing a chemical functional group onto the surface.
In the present invention, a non-functionalized fibrous carbon material means a fibrous carbon material whose surface is not functionalized.
Introducing chemical functional groups into the surface of a carbon material can increase the dispersibility of the carbon material in a water-based or organic solvent-based solvent. A functional group which can be introduced for the functionalization of the surface of a fibrous carbon material can be the carboxyl group (-COOH), hydroxyl group (-OH), ether group (-COC-), carbohydrate groups (-CH) or the like. Surface functionalization can also be achieved by oxidizing a surface with an oxidant.
A surface-functionalized fibrous carbon material used in the present invention can comprise oxygen, nitrogen or hydrogen at 0.05 to 5% by weight. If the amount of oxygen, nitrogen and hydrogen is too small, the improvement of dispersion properties cannot be expected. On the other hand, if the amount is excessive, it may collapse the structure of the fibrous carbon material and increase resistance.
It is preferable that an electrode-active material composite where the fibrous carbon material is not uniformly dispersed in the aggregate according to the present invention comprises non-functionalized fibrous carbon materials and surface-functionalized fibrous carbon materials in a ratio of 1:99 to 20:80 by weight. Further, it is preferable that the ratio of the surface-functionalized fibrous carbon materials to the non-functionalized fibrous carbon materials by weight is higher in the surface region than in the inside of an aggregate or preferable that the fibrous carbon material densely exists in one side the section of the aggregate compared to the other side thereof.
In the present invention, any transition metal compound can be used as long as it allows reversible intercalation and deintercalation of alkali metal ions. Such transition metal compounds can be classified into spinel structure, layered structure and olivine structure depending on crystal structure.
Examples of the spinel structure compounds include LiMn2O4 and Li4Ti5O12, and examples of the layered structure compounds include LiCoO2; LiMnO2; Li(Ni1-x-yCoxAly)O2; Li(Ni1-x-yCoxAly)O2(x+y≤l, 0.01≤x≤0.99, 0.01≤y≤0.99); Li(Ni1-x-yMnxCoy)O2(x+y≤l, 0.01≤x≤0.99, 0.01≤y≤0.99); and Li2-z(Fe1-x-yM1 xM2 y)zO2(x+y≤l, 0.01≤x≤0.99, 0.01≤y≤0.99, 0<z<l, and each of M1 and M2 is Ti, Ni, Zn, or Mn).
In the present invention, a transition metal compound represented by the following chemical formula 1 can be used:
[Formula 1] Li1-xM(PO4)1-y
In above chemical formula 1, 0≤x≤0.15, 0≤y≤0.1, and M is represented by the following chemical formula 2.
[Formula 2] MA aMB bMT tFe1-(a+b+t)
In above chemical formula 2, MA is one or more elements selected from the group consisting of the Group 2 elements; MB is one or more elements selected from the group consisting of the Group 13 elements; MT is one or more elements selected from the group consisting of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, and Mo; 0≤a≤l; 0≤b≤0.575; 0≤t≤l; 0≤(a+b)≤l; and 0≤(a+b+c) ≤l.
In the present invention, a transition metal compound represented by the following chemical formula 3 can also be used
[Formula 3] LiMPO4
In the above chemical formula 3, M is one element or the combination of two or more elements selected from the group consisting of Fe, Mn, Ni, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo.
Such transition metal compounds can be prepared by any of the known solid state methods, coprecipitation methods, hydrothermal methods, supercritical hydrothermal methods, sol-gel methods, alkoxide methods, etc.
The size of primary particles as a constituent of a composite of the present invention is not specifically limited, but preferably is 0.01 to 5 μm.
The average particle size of the composites according to the present invention can be 1 to 200 μm, preferably 3 to 100 μm. If the size of composite is greater than 200 μm, it is difficult to obtain a coating having a desired thickness when preparing an electrode. On the contrary, if the size is less than 1 μm, process ability may deteriorate due to transport and weighing problems caused by powder scattering and flow ability decrease.
A composite according to the present invention can have various external shapes such as spherical, cylindrical, rectangular and atypical forms, but a spherical form is preferred in order to increase bulk density and filling rate when producing an electrode.
　 (2) Binder
The electrode formulation of the present invention may include a binder in an amount of 0.5 to 30 wt%, preferably, 0.5 to 10 wt%, based on the total weight of an electrode-active material composite, a binder and an electric conducting agent. When the amount of the binder is less than 0.5 wt%, the adhesion between a current collector and the electrode formulation is deteriorated, which is not preferable, and, when the amount thereof is more than 30 wt%, the resistance of the electrode formulation is increased, which is not preferable.
The binder is used in binding electrode-active material composites and binding the electrode-active material composite with a current collector.
The binder may be selected from the group consisting of cellulose, an ethylene polymer, an ethylene copolymer, a propylene polymer, a propylene copolymer, polyvinylpyrrolidone, polyvinylchloride, an ethylene-propylene-diene rubber (EPDM), a styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and a polyvinylidene fluoride copolymer. They may be used independently or in a combination of two or more, but are not limited thereto.
(3) Electric conducting agent
The electrode formulation of the present invention may further include an electric conducting agent in an amount of less than 5 wt%, preferably less than 3 wt%, and more preferably less than l w%, based on the total weight of an electrode-active material composite, a binder and an electric conducting agent.
When the amount of the electric conducting agent is 5 wt% or more, the capacity of a battery is decreased, which is not preferable.
Conventionally, an electric conducting agent was added for the purpose of improving the electrical conductivity between electrode-active material particles or the electrical conductivity between an electrode-active material and a metal current collector. Particularly, it is known that an electric conducting agent is necessarily required to prevent a binder region from acting as a nonconductor and to make up for the electrical conductivity of cathode and anode active materials. A conventional electrode formulation generally includes an electric conducting agent in an amount of 5 to 30 wt% based on the total weight of the electrode formulation. However, the usage of an electric conducting agent raises the problem of reducing the capacity of a battery. Further, a conventional technology discloses an electrode formulation including an electrode-active material composite, a binder and an electric conducting agent, but does not disclose an electrode formulation including an electrode-active material and a binder while using a very small amount of an electric conducting agent or not using an electric conducting agent.
As a conducting agent, there can be used any of those which are conductive and which do not cause a side reaction when the electrode is charged and discharged. Examples of the conducting agents are graphite materials such as natural graphite or artificial graphite; carbon black, acetylene black, ketjen black, etc.; fibrous carbon materials; conductive metal oxides such as titanium oxide, etc.; and conductive metal materials such as nickel, aluminum, etc.
(4) Dispersant
The electrode formulation of the present invention may further include a dispersant. An electrode-active composite and a binder are mixed with a dispersant and then stirred to prepare a paste, and then the paste is applied onto a current collector, pressed and then dried to fabricate a laminated electrode. Typical examples of the dispersant may include, but are not limited to, N-methylpyrrolidone, isopropyl alcohol, acetone, etc.
The present invention also provides an electrode produced by using said composite. An electrode can be fabricated by coating a current collector with an electrode material mixture. An electrode has a form which is produced by coating the surface of a conductive metal sheet such as aluminum foil with an electrode material mixture. A current collector has a thickness of 2 to 500 μm, and it is preferred if it does not cause a chemical side reaction when producing an electrode. Examples of the current collectors are those prepared by processing such materials as aluminum, stainless steel, nickel, titanium, silver, etc. into a sheet form. The surface of a current collector may be chemically etched or may be coated with a conductive material.
Further, an additive can be used for the purpose of inhibiting the expansion of an electrode. Such additives may be fibrous materials which do not cause any electrochemical side reaction, and can be, for example, olefin-based polymers or copolymers such as polyethylene, polypropylene, etc.; glass fibers, carbon fibers, etc.
The present invention provides secondary batteries, memory devices, or capacitors comprising an electrode prepared by using a transition metal compound-fibrous carbon material composite as an electrode-active material.
The composites of the present invention can be used in making lithium secondary batteries comprising a cathode, anode, separator membrane and a lithium salt-containing an aqueous or non-aqueous electrolytic solution. As the cathode of a lithium secondary battery, a current collector coated with the electrode formulation comprising composites of the present invention can be used. As the anode, a current collector coated with an anode-active material mixture can be used. A separator membrane physically separates an anode from a cathode, and provides a passage for lithium ion movement. As a separator membrane, one having high ion permeability and mechanical strength, and having thermal stability can be used. A non-aqueous electrolytic solution containing a lithium salt comprises an electrolytic solution and the lithium salt. As a non-aqueous electrolytic solution, a non-aqueous organic solvent, organic solid electrolyte, inorganic solid electrolyte, etc. can be used. As a lithium salt, one which can be easily dissolved in a non-aqueous electrolytic solution, for example, LiCl, LiBr, LiI, LiBF4, LiPF6, etc. can be used.
　 2. Preparation of electrode formulation
According to the present invention, an electrode formulation may be prepared by a process including the steps of: (a) preparing a mixture in which at least one selected from a non-functionalized fibrous carbon material and a surface-functional fibrous carbon material and transition metal compound particles are dispersed; (b) drying and granulating the mixture to prepare an electrode-active material composite; and (c) mixing the electrode-active material composite with a binder to prepare an electrode formulation.
(a) Preparation of mixture of transition metal compound and fibrous carbon material
A composite according to the present invention can be made by: preparing a mixture wherein non-functionalized fibrous carbon materials, surface-functionalized fibrous carbon materials, and transition metal compounds particles are dispersed, and wherein the weight of the surface-functionalized fibrous carbon materials is greater than that of the non-functionalized fibrous carbon materials.
Said mixture can comprise a dispersant in an amount of 10 to 500 wt% by weight with respect to 100 wt% by weight of the whole fibrous carbon materials.
The transition metal compounds and the fibrous carbon materials can be contained in a ratio of 99.9:0.1 to 80:20 by weight.
Surface functionalization may be achieved by the surface treatment of carbon materials with an oxidant such as oxygen, air, ozone, aqueous hydrogen peroxide or nitro compounds under sub-critical or supercritical conditions of 50 to 400 atm. Surface functionalization can also be achieved by treating the surfaces of carbon materials with a compound having such functional groups as carboxylic acid, carboxylic acid salt, amines, amine salt, quaternary amine, phosphoric acid, phosphoric acid salt, sulfuric acid, sulfuric acid salt, alcohol, thiol, ester, amide, epoxide, aldehyde or ketone at a temperature of 100 to 600 ℃ under a pressure of 50 to 400 atm. Such surface functionalization can be achieved by oxidizing the surfaces of fibrous carbon materials with carboxylic acid, nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, or aqueous hydrogen peroxide.
According to the present invention, the preparation of the composite may be performed by a process including the steps of: (i) dispersing the non-functionalized fibrous carbon material and the surface-functionalized fibrous carbon material in a dispersant to prepare a dispersion liquid; and (ii) mixing the dispersion liquid with the transition metal compound to prepare the mixture dispersed therein with the non-functionalized fibrous carbon material, the surface-functionalized fibrous carbon material and the transition metal compound.
In preparing a composite, the distribution of fibrous carbon materials in the inside and outside of the composites can vary depending on the degree of surface treatment of the fibrous carbon materials, the kind and amount of the dispersant, etc.
A dispersion of fibrous carbon materials can be prepared by mixing and dispersing fibrous carbon materials and a dispersant in the presence of an aqueous or non-aqueous dispersing medium.
As a dispersant, a hydrophobic or hydrophilic dispersant can be used. A hydrophilic dispersant disperses surf ace-functionalized fibrous carbon materials and a hydrophobic one is effective in dispersing non-functionalized fibrous carbon materials.
As a dispersant, polyacetal, acryl-based compound, methyl methacrylate, alkyl (C1~C10) acrylate, 2-ethylhexylacrylate, polycarbonate, styrene, alpha-methyl styrene, vinyl acrylate, polyesters, vinyl, polyphenylene ether resin, polyolefin, acrylonitrile-butadiene-styrene copolymer, polyarylate, polyamide, polyamideimide, polyarylsulfone, polyetherimide, polyethersulfone, polyphenylene sulfide, fluorine-based compound, polyimide, polyetherketone, polybenzoxazole, polyoxadiazole, polybenzothiazole, polybenzimidazole, polypyridine, polytriazole, polypyrrolidine, polydibenzofuran, polysulfone, polyurea, polyurethane, polyphosphazene, liquid crystal polymer, or copolymer thereof can be used.
In addition, a styrene/acryl-based water-soluble resin formed by polymerizing a styrene-based monomer with an acryl-based monomer can also be used as a dispersant.
Further, as a dispersant, there can be used a polymer formed by subjecting a styrene-based monomer selected from styrene and mixture of styrene and alpha-methyl styrene, and an acryl-based monomer to continuous bulk polymerization in di ethylene glycol mono ethyl ether or a mixed solvent of di propylene glycol mono ethyl ether and water, at a reaction temperature of 100 to 200 ℃. In this case, a styrene-based monomer and a acryl-based monomer can be present in a ratio of 60:40 to 80:20 by weight, wherein the styrene-based monomer can comprise either styrene only or styrene and alpha-methyl styrene at a mixing ratio of 50:50 to 90:10 by weight, and the acryl-based monomer can comprise either acrylic acid only or acrylic acid and alkyl acrylate monomer in a mixing ratio of 80:20 to 90:10 by weight.
As a dispersant, there can also be used a polymer having a weight average molecular weight of 1,000 to 100,000 and prepared by polymerizing 25 to 45 wt% of styrene, 25 to 45 wt% of alpha-methyl styrene, and 25 to 35 wt% of acrylic acid, with respect to the total weight of the polymer, in the presence of a mixed solvent of di ethylene glycol mono ethyl ether and water.
A dispersant can be included in an amount of 10 to 500 wt% by weight with respect to 100 wt% by weight of the fibrous carbon materials, and the mixing ratio of a hydrophobic dispersant and a hydrophilic dispersant is preferably within a ratio of 5:95 to 30:70.
As a dispersing medium, water, alcohol, ketone, amine, ester, amide, alkyl halogen, ether or furan can be used.
(b) Preparation of electrode-active material composite
According to the present invention, an electrode-active material composite is prepared by drying and granulating the mixture of a transition metal compound. In this case, the drying may be spray drying, fluidized-bed drying or the like. If necessary, after the granulation of the mixture, the granulated mixture may be heat-treated at 300 ~ 1,200 ℃, thus enhancing the crystallinity of the transition metal compound and improving the electrochemical characteristics of the electrode-active material composite. In the heat treatment (or calcinations) of the granulated mixture, the fibrous carbon material existing in the gap between primary particles serves to prevent interparticle contact, and the carbon material web existing on the surface of the electrode-active material composite serves to prevent the aggregation of electrode-active material composite particles, thereby suppressing the growth of particles.
(c) Preparation of electrode formulation
The electrode formulation of the present invention may be prepared by mixing an electrode-active material composite with a binder. Further the electrode formulation may be prepared by mixing an electric conducting agent with an electrode-active material composite and a binder.
The binder is used in binding electrode-active material composites and binding the electrode-active material composite with a current collector. The binder is added in an amount of 0.5 to 30 wt% based on the total weight of an electrode-active material composite, a binder and an electric conducting agent.
The binder may be selected from the group consisting of cellulose, an ethylene polymer, an ethylene copolymer, a propylene polymer, a propylene copolymer, Polyvinyl- pyrrolidone, polyvinylchloride, an ethylene-propylene-diene rubber (EPDM), a styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVdF), and a polyvinylidenefluoride copolymer. They may be used independently or in a combination of two or more, but are not limited thereto.
The electrode-active composite and the binder are mixed with a dispersant, or the electrode-active composite, the binder and the electric conducting agent are mixed with a dispersant and then stirred to prepare a paste, and then the paste is applied onto a current collector, pressed and then dried to fabricate a laminated electrode. Typical examples of the dispersant may include, but are not limited to, N-methylpyrrolidone, isopropyl alcohol, acetone, etc.
The present invention is explained in more detail by the following Examples. However, these Examples are provided only to assist the understanding of the present invention. It is not intended that the scope of the present invention is limited in any manner by these Examples.
[Examples]
[Preparation]
Preparation of electrode-active material composites
1. Preparation Examples 1-1 to 1-24: electrode-active material composites (composite A) each in which fibrous carbon material densely exists on the surface thereof
Electrode-active material composites of Preparation Examples 1-1 to 1-10 (LiFePO4), Preparation Example 1-11 (LiMPO4, M is a combination of Fe, Mn and Co), Preparation Examples 1-12 (Olivine-structured LiMPO4, M is an combination of Mn and Fe), Preparation Example 1-13 (Olivine-structured LiMPO4, M is Mn), Preparation Example 1-14 (Olivine-structured LiMPO4, M is a combination of Co and Fe), Preparation Example 1-15 (Olivine-structured LiMPO4, M is Co), Preparation Example 1-16 (Olivine-structured LiMPO4, M is a combination of Ni and Fe), Preparation Example 1-17 (Olivine-structured LiMPO4, M is Ni), Preparation Example 1-18 (Olivine-structured LiMPO4, M is a combination of Mn, Co and Ni), Preparation Example 1-19 (Olivine-structured LiMPO4, M is a combination of Mn, Co, Ni, and Fe), Preparation Example 1-20 (Olivine-structured LiMPO4, M is a combination of Mg and Fe), Preparation Example 1-21 (Olivine-structured LiMPO4, M is a combination of Mg and Mn), Preparation Example 1-22 (Olivine-structured LiMPO4, M is a combination of Al, Mn, and Fe), Preparation Example 1-23 (3-component Li(NiMnCo)O2) and Preparation Example 1-24 (Spinel-structured lithium titanate (Li4Ti5O12)) were prepared in the same method as those disclosed in Korean Patent Registration No. 10-1103606, filed by the present inventors, and International Publication No. WO2012-086976 and the details are described in Table 1.
2. Preparation Examples 2-1 to 2-24: electrode-active material composites (composite B) each in which fibrous carbon material densely exists on one side thereof
The electrode-active material composites of Preparation Examples 1-1 to 1-24 were respectively pulverized by jet mill to prepare electrode-active material composites of Preparation Examples 2-1 to 2-24, each in which a fibrous carbon material densely exists in one side of the section of the composite compared to the other side thereof.
3. Comparative Preparation Examples 1 to 6
[Comparative Preparation Example 1] Preparation of LiFePO 4 powder coated with carbon
1 kg of LiFePO4 powder and 80 g of sucrose were added to 9 kg of distilled water and stirred for 30 minutes, and then dried by means of a spray dryer. The dried powder was calcined for 10 hours at 700℃ under an argon (Ar) atmosphere to prepare LiFePO4 composite powder uniformly coated with carbon.
Said LiFePO4 composite powder coated with carbon had a carbon content of 2.2%, and was identified as having an average particle size of 21.0㎛ as determined by a laser diffraction particle size analyzer.
[Comparative Preparation Example 2] Preparation of a composite comprising LiFePO 4 particles coated with carbon and carbon nanotubes
27.0 g of surface-functionalized carbon nanotubes including 1.27 wt% of oxygen and 0.21 wt% of hydrogen, 3.0 g of non-functionalized carbon nanotubes, 21.6 g of a styrene-acrylate copolymer, 2.4 g of an acrylate polymer and 970 g of distilled water were mixed and dispersed by a homogenizer to prepare a carbon nanotube dispersed solution in which the combination ratio of surface-functionalized carbon nanotubes is different from that of non-functionalized carbon nanotubes.
1 kg of LiFePO4 powder and 80 g of sucrose were mixed with 666.6 g of the carbon nanotube dispersed solution and 9 kg of distilled water was added thereto, and the mixture was then stirred for 1 hour and spray-dried at a temperature of 180 ℃ to produce granular powder.
The resulting granular powder was calcined for 10 hours at 700 ℃ under an argon (Ar) atmosphere to obtain composite powder comprising LiFeP04 particles coated with carbon and carbon nanotubes (CNTs).
Said composite had a carbon content of 2.3%, and was identified as having an average particle size of 22.2 μm as determined by a laser diffraction particle size analyzer.
[Comparative Preparation Example 3] Preparation of LiFePO 4 (M is a combination of Mn and Fe)
0.6 mol of manganese sulfate (MnSO4) and 0.4 mol of ferrous sulfate (FeSO4) as precursors of the metal M, 1 mol of phosphoric acid as a phosphoric acid compound, and 27.8 g of sugar as a reducing agent were dissolved in 1.6 L of water to prepare a first solution. 1.5 mol of ammonia as an alkalizing agent and 2 mol of lithium hydroxide as a lithium precursor were dissolved in 1.2 L of water to prepare a second solution.
The first solution and the second solution were processed in the order of the following steps (a), (b), and (c) to prepare anion-deficient lithium manganese iron phosphate.
Step (a): The first solution and the second solution were continuously pumped under pressure of 250 bars at normal temperature into a mixer to be mixed therein to produce a slurry comprising the precursor of lithium transition metal phosphate compound.
Step (b): Ultra-pure water heated to 450 °C was pressurized under 250 bars and pumped into the precursor slurry of step (a) to be mixed in a mixer. The mixed solution was transferred to a reactor maintained at 380 °C, 250 bars and left therein for 7 seconds to continuously synthesize an anion-deficient lithium transition metal phosphate compound having low crystallinity, which was then cooled and concentrated. The resulting concentrate was mixed with sucrose, which was a carbon precursor, and was in an amount of 10% relative to the lithium transition metal phosphate compound in the concentrate, and then dried via a spray dryer to form granules.
Step (c): The dry granules formed through the spray-drying in step (b) were calcined in a calcinations furnace under an argon (Ar) atmosphere at 700 °C for 10 hours to prepare a lithium transition metal phosphate compound whose particle surface was coated with carbon.
Said lithium transition metal phosphate compound coated with carbon was confirmed as having an olivine structure by means of XRD analysis. In addition, said lithium transition metal phosphate compound was identified to be Li0.9(Mn0.4Fe0.6)(PO4)0.96 from the molar ratios of the constituent elements analyzed by ICP-AES.
[Comparative Example 4] Preparation of LiMPO 4 (M is a combination of Mn, Ni, Co and Fe)
0.25 mol of manganese sulfate, 0.25 mol of cobalt nitrate, 0.25 mol of nickel nitrate, 0.25 mol of ferrous sulfate, 1 mol of phosphoric acid, and 27.8 g of sugar were dissolved in 1.6 L of water to prepare a first solution. 1.5 mol of ammonia and 2 mol of lithium hydroxide were dissolved in 1.2 L of water to prepare a second solution.
The first solution and the second solution were processed in the order of the following steps (a), (b), and (c) by using the same reaction apparatus as used in Example 1, to prepare Li(FeMnNiCo)PO4.
Step (a): The first solution and the second solution were continuously pumped under pressure of 250 bars at normal temperature into a mixer to mixed therein to produce a slurry comprising a precursor of a lithium transition metal phosphate compound.
Step (b): Ultra-pure water heated to 450 °C was pressurized under 250 bars and pumped into the precursor slurry of step (a) to be mixed in a mixer. The mixed solution was transferred to a reactor maintained at 380 °C, 250 bars and left therein for 7 seconds to continuously synthesize a low-crystallizing, anion-deficient lithium transition metal phosphate compound, which was then cooled and concentrated. The resulting concentrate was mixed with sucrose, which was a carbon precursor and was in an amount of 10% relative to the lithium transition metal phosphate compound in the concentrate, and then dried via a spray dryer to form granules.
Step (c): The dry granules formed through the spray-drying in step (b) were calcined in a calcination furnace under an argon (Ar) atmosphere at 700℃ for 10 hours to prepare a lithium transition metal phosphate compound whose particle surface was coated with carbon.
Said lithium transition metal phosphate compound coated with carbon was confirmed as having an olivine structure by means of XRD analysis. In addition, said lithium transition metal phosphate compound was also identified to be Li0.90(Mn0.25 Co0.25Ni0.25Fe0.25)(PO4)0.97 from the molar ratios of the constituent elements analyzed by ICP-AES.
[Comparative Preparation Example 5] Preparation of Li(MnNiCo)O 2
0.25 mol of manganese sulfate, 0.25 mol of cobalt nitrate, and 0.25 mol of nickel nitrate as precursors of the metal M were dissolved in 1.6 L of water to prepare a first solution. 1.5 mol of ammonia as an alkalizing agent and 2 mol of lithium hydroxide as a lithium precursor were dissolved in 1.2 L of water to prepare a second solution.
The first solution and the second solution were processed in the order of the following steps (a), (b) , and (c) by using the same reaction apparatus as used in Example 1, to prepare lithium manganese nickel cobalt phosphate.
Step (a): Said two aqueous solutions were continuously pumped under pressure of 250 bars at normal temperature into a mixer to be mixed therein to produce a slurry comprising the precursor of a lithium transition metal phosphate compound.
Step (b): Ultra-pure water heated to 450 °C was pressurized under 250 bars and pumped into the precursor slurry of step (a) to be mixed in a mixer. The mixed solution was transferred to a reactor maintained at 380 °C, 250 bars and left therein for 7 seconds to continuously synthesize lithium transition metal oxide, which was then cooled and concentrated to a slurry having a solid content of 30%. The resulting concentrate was spray-dried at 180 °C to form granules.
Step (c): The dry granules formed through the spray-drying in step (b) were calcined under an oxidizing atmosphere at 900 ℃ for 12 hours to prepare granular composite powder.
Said granular composite was confirmed as having a layered structure by means of XRD analysis. In addition, said granular composite was identified to be Li(Mn0.33Ni0.33Co0.33)O2 from the molar ratios of the constituent elements analyzed by ICP-AES.
[Comparative Preparation Example 6] Preparation of Li 4 Ti 5 O 12
40 g of Li2Co3, 79.9 g of TiO2, 500 g of distilled water,and 7.4 g of sucrose were introduced together with 200 g of zirconia balls having a diameter of 10 mm into a cylindrical Teflon vessel with 1.0 L volume, mixed for 12 hours by a ball mill, and then spray-dried at temperature of 180 °C, and calcined for 4 hours in a calcination furnace under atmospheric conditions at a temperature of 750 °C to prepare granular composite powder.
Said granular composite was confirmed as having a spinel structure by means of XRD analysis. In addition, the granular composite was identified to be Li4Ti5O12 from the molar ratios of the constituent elements analyzed by ICP-AES, and identified as having a carbon content of 2.2 wt%.
Shape of electrode-active material composite
FIG. 1 is a sectional view showing an electrode-active material composite in which a fibrous carbon material densely exists on the surface of the aggregate compared to the inside thereof according to Preparation Example of the present invention. FIG. 2 is a sectional view showing an electrode-active material composite in which a fibrous carbon material densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof according to Preparation Example of the present invention.
In the electrode-active material composite of the present invention, a fibrous carbon material densely exists on the surface of the aggregate compared to the inside thereof, or densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof. For this reason, when an electrode is fabricated by applying the electrode-active material composite to a current collector and then rolling the composite, adjacent electrode-active material composites are electrically continuously connected with each other by a fibrous carbon material to greatly increase the electrical conductivity of the electrode-active material composite, thereby remarkably improving the efficiency of a battery. Further, in this case, the contact area of an electrode-active material and a current collector through the medium of a fibrous carbon material is increased to increase the adhesion there between, thereby improving the lifespan and stability of an electrode.
The composites prepared in comparative Example 1-1, Comparative Example 1, and comparative Example 2 were each analyzed by a scanning electron microscope (SEM) for the determination of their powder shapes.
In the case of the powder prepared in Example 1-1, a granule was cut down for the observation of the inner cross section of the granule.
FIG. 3 is a SEM photograph at 500 magnification of the shape of the granular composite powder of Preparation Example 1-1; FIG. 4 is a SEM photograph of an outer cross section of the granule including the surface of Preparation Example 1-1 and FIG. 5 is a SEM photograph of an inner side cross section of the granule obtained by cutting down the granule with fast ion bombardment (FIB) of Preparation Example 1-1. From the figures, it is confirmed that the external surface of the composite is covered with dense carbon nanotube (CNT) web, and the inside of the composite has a network structure wherein LiFePO4 primary particles are connected by CNTs.
FIG. 6 is an electron microscope photograph of aggregates of the electrode-active material composite of Preparation Example 2-1. FIG. 7 is a scanning electron microscope photograph of the section of the granulated electrode-active material composite of Preparation Example 2-1 and enlarged other part thereof, wherein a fibrous carbon material densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof.
FIG. 8 is a SEM photograph of LiFePO4 primary particles coated with carbon according to Comparative Preparation Example 1. Figure 9 is a SEM photograph of composites which have carbon coatings and CNTs of Comparative Preparation Example 2, from which it is confirmed that CNTs densely cover the external surfaces of the granules.
Compositions and crystal structures of the composites
The composites prepared in Preparation Example 1-1 to 1-24 and Comparative Preparation Examples 1 to 6 were assayed to determine the compositional ratios of respective elements by ICP-AES, and the results are shown in the following Table 1.
Further, the crystal structures of the composites prepared in Preparation Examples 1-1 and 1-11 to 1-22, and Comparative Preparation Examples 1, 3 and 4 were analyzed by XRD analysis, and are shown in Figure 10. As can be confirmed from each graph of Figure 10, the composites prepared in Preparation Examples 1-1 and 1-11 to 1-22, and Comparative Preparation Examples 1, 3, and 4 have the pure olivine crystal structure and do not comprise any impurity phase.
Table 1
Chemical Formula Crystal Phase Atomic mole ratio (by ICP-AES)
Li Fe P Mn Ni Co Ti Mg Al
Prep. Ex. 1-1~1-10 LiFePO4 olivine 0.98 1.00 1.00
Prep. Ex. b1-11 Li(FeMnNiCo) PO4 olivine 1.00 0.25 1.00 0.25 0.25 0.25
Prep. Ex. 1-12 Li(FeMn)PO4 olivine 0.90 0.50 0.96 0.50
Prep. Ex. 1-13 LiMnPO4 olivine 0.91 0.97 1.00
Prep. Ex. 1-14 Li(FeCo)PO4 olivine 0.91 0.50 0.97 0.50
Prep. Ex. 1-15 LiCoPO4 olivine 0.90 0.97 1.00
Prep. Ex. 1-16 Li(FeNi)PO4 olivine 0.92 0.50 0.97 0.50
Prep. Ex. 1-17 LiNiPO4 olivine 0.93 0.98 1.00
Prep. Ex. 1-18 Li(MnNiCo)PO4 olivine 0.89 0.96 0.33 0.33 0.33
Prep. Ex. 1-19 Li(FeMnNiCo) PO4 olivine 0.90 0.25 0.97 0.25 0.25 0.25
Prep. Ex. 1-20 Li(MgFe)PO4 olivine 0.88 0.93 0.96 0.07
Prep. Ex. 1-21 Li(MgMn)PO4 olivine 0.92 0.97 0.90 0.10
Prep. Ex. 1-22 Li(AlFeMn)PO4 olivine 0.85 0.19 0.98 0.78 0.03
Prep. Ex. 1-23 Li(NiMnCo)PO4 layered 1.00 0.33 0.33 0.33
Prep. Ex. 1-24 Li4Ti5O12 spinel 0.80 1.00
Comp.Prep. Ex.1 LiFePO4 olivine 0.98 1.00 1.00
Comp.Prep. Ex.2 LiFePO4 olivine 0.98 1.00 1.00
Comp.Prep. Ex.3 Li(FeMn)PO4 olivine 0.90 0.50 0.96 0.50
Comp.Prep. Ex.4 Li(FeNiMnCo) PO4 olivine 1.00 0.25 1.00 0.25 0.25 0.25
Comp.Prep. Ex.5 Li(NiMnCo)O2 layered 1.00 0.33 0.33 0.33
Comp.Prep. Ex.6 Li4Ti5O12 spinel 0.80 1.00
The element composition analyses of the electrode-active material composites prepared in Preparation Examples 2-1 to 1-24 using inductively-coupled plasma atomic emission spectrometry (ICP-AES) were carried out. The results thereof are the same as those of electrode-active material composites of Preparation Examples 1-1 to 1-24.
Carbon content, specific surface area, particle size, and powder resistance of powder
(1)electrode-active material composites (composite A) each in which fibrous carbon material densely exists on the surface thereof
Regarding the granular composites prepared in Preparation Examples 1-1 to 1-24 and Comparative Preparation Examples 1-6, carbon content was measured by elementary analysis, the average particle size of the granules was measured by a laser diffraction particle size analyzer, and the specific surface area of powder was measured by the BET method. For the determination of the electric conductive properties of the powder, volume resistance was measured depending on compressive strength by a powder resistant tester. The results are shown in the following Table 2.
Table 2
CNT ratio Carbon Contents (wt%) Average Particle Size (μm) Specific Surface Area (m2/g) Powder resistant tester
n- CNT* s- CNT** 4KN 8KN 12KN 16KN 20KN
12.73 MPa 25.46 MPa 38.19 MPa 50.92 MPa 63.66MPa
Prep. Ex. 1-1 1 99 2.1 16.00 15.40 5.190 E+01 3.767 E+01 2.297 E+01 2.297 E+01 1.989 E+01
Prep. Ex. 1-2 5 95 2.2 17.50 15.20 5.490 E+01 4.812 E+01 3.867 E+01 2.997 E+01 2.189 E+01
Prep. Ex. 1-3 10 90 2.0 19.00 15.90 6.190 E+01 4.0512 E+01 3.767 E+01 3.297 E+01 2.589 E+01
Prep. Ex. 1-4 15 85 2.0 20.00 15.10 6.590 E+01 4.912 E+01 4.261 E+01 3.697 E+01 3.189 E+01
Prep. Ex. 1-5 20 80 2.0 21.30 15.80 7.390 E+01 5.712 E+01 4.967 E+01 4.097 E+01 3.389 E+01
Prep. Ex. 1-6 10 90 0.5 20.40 12.80 6.570 E+02 4.892 E+02 3.947 E+02 3.287 E+02 2.909 E+02
Prep. Ex. 1-7 10 90 1.0 20.30 13.60 3.190 E+02 2.512 E+02 1.547 E+02 8.597 E+01 7.489 E+01
Prep. Ex. 1-8 10 90 2.5 20.50 16.70 5.290 E+01 3.812 E+01 2.767 E+01 1.897 E+00 1.089 E+01
Prep. Ex. 1-9 10 9 3.0 20.40 18.30 1.190 E+01 9.116 E+00 7.670 E+00 6.968 E+00 6.893 E+00
Prep. Ex. 1-10 10 90 3.0 20.70 22.20 6.987 E+00 4.116 E+00 3.270 E+00 2.682 E+00 1.893 E+00
Prep. Ex. 1-11 10 90 2.0 20.70 15.60 6.390 E+01 4.713 E+01 4.367 E+01 3.497 E+01 3.089 E+01
Prep. Ex. 1-12 10 90 2.0 20.50 15.45 5.890 E+01 4.412 E+01 4.067 E+01 3.366 E+01 2.854 E+01
Prep. Ex. 1-13 10 90 2.0 20.20 15.22 7.535 E+01 5.456 E+01 4.887 E+01 4.197 E+01 3.631 E+01
Prep. Ex. 1-14 10 90 2.0 19.90 14.99 6.390 E+01 4.319 E+01 3.964 E+01 3.019 E+01 2.921 E+01
Prep. Ex. 1-15 10 90 2.0 18.70 16.23 6.879 E+01 4.772 E+01 4.134 E+01 3.646 E+01 3.024 E+01
Prep. Ex. 1-16 10 90 2.0 21.40 15.78 5.490 E+01 4.014 E+01 3.746 E+01 3.139 E+01 2.639 E+01
Prep. Ex. 1-17 10 90 2.0 20.80 15.44 8.790 E+01 6.512 E+01 5.487 E+01 4.278 E+01 3.525 E+01
Prep. Ex. 1-18 10 90 2.0 21.20 14.99 7.770 E+01 6.142 E+01 5.387 E+01 4.024 E+01 3.821 E+01
Prep. Ex. 1-19 10 90 2.0 19.50 16.12 7.160 E+01 6.212 E+01 5.147 E+01 3.966 E+01 3.345 E+01
Prep. Ex. 1-20 10 90 2.0 21.30 14.89 3.490 E+01 2.457 E+01 1.967 E+01 1.195 E+01 4.651 E+01
Prep. Ex. 1-21 10 90 2.0 19.90 15.20 4.485 E+01 3.279 E+01 2.667 E+01 1.833 E+01 1.065 E+01
Prep. Ex. 1-22 10 90 2.0 21.00 15.43 5.290 E+01 4.125 E+01 3.428 E+01 2.546 E+01 1.622 E+01
Prep. Ex. 1-23 10 90 2.0 22.20 9.75 6.590 E+01 4.912 E+01 4.267 E+01 3.697 E+01 3.189 E+01
Prep. Ex. 1-24 10 90 2.0 26.40 13.71 4.190 E+01 3.116 E+01 2.670 E+01 2.463 E+01 2.393 E+01
Comp. Prep. Ex.1 2.0 21.00 14.37 5.590 E+03 4.712 E+03 3.867 E+03 3.167 E+03 2.769 E+03
Comp. Prep. Ex.2 4.3 22.20 19.45 4.190 E+00 3.116 E+00 2.670 E+00 2.468 E+00 2.393E+00
Comp. Prep. Ex.3 2.0 19.80 13.80 5.270 E+03 4.312 E+03 3.647 E+03 2.897 E+03 2.089 E+03
Comp. Prep. Ex.4 2.0 20.60 14.13 7.490 E+03 5.812 E+03 4.167 E+03 3.997 E+03 3.289 E+03
Comp. Prep. Ex.5 0.0 21.80 8.43 6.897 E+02 4.116 E+02 3.670 E+02 2.968 E+02 2.191 E+02
Comp. Prep. Ex.6 2.2 25.45 6.21 4.319 E+01 3.212 E+01 2.467 E+01 1.247 E+01 9.393 E+00
*n-CNT: non-functionalized CNT
**s-CNT: surface-functionalized CNT
As can be seen from Table 2, LiFePO4-carbon nanotube composites (Preparation Examples 1-1 to 1-10 and Comparative Preparation Example 2) have a significantly lower volume resistance than Comparative Preparation Example 1 which adopted only carbon coating.
Further, the transition metal phosphate compound-carbon nanotube composites prepared in Preparation Examples 1-12 and 1-19 of the present invention have a significantly lower volume resistance than Comparative Preparation Examples 3 and 4 which simply adopts a carbon coating.
Further, the ternary-system lithium transition metal compound-carbon nanotube composites prepared in Preparation Example 1-23 of the present invention have a significantly lower volume resistance than Comparative Preparation Example 5.
Further, the lithium titanate-carbon nanotube composites having a spinel structure as prepared in Preparation Example 1-24 of the present invention have a significantly lower volume resistance than Comparative Preparation Example 6 which simply adopts a carbon coating.
(2) Electrode-active material composite (composite B) in which fibrous carbon material densely exists in one side of the section (A-A') of the aggregate compared to the other side thereof
The carbon contents of the granulated electrode-active material composites prepared in Preparation Examples 2-1 to 2-24 were measured using element analysis, the average particle diameters thereof were measured using a laser diffraction type particle size analyzer, and the specific surface areas of powder thereof were measured using Brunauer-Emmett-Teller(BET) method. Further, in order to evaluate the electrical conductivity of power thereof, the volume resistances of powder thereof according to compressive strength were measured using a power resistance meter. The results thereof are given in Table 3.
Table 3
CNT ratio Carbon Contents (wt%) Average Particle Size(μm) Specific Surface Area (m2/g) Powder resistant tester
n- CNT* s- CNT** 4KN 8KN 12KN 16KN 20KN
12.73MPa 25.46 MPa 38.19 MPa 50.92MPa 63.66MPa
Prep.Ex. 2-1 1 99 2.1 5.80 15.1 5.412E+01 3.942E+01 3.548E+01 2.930E+01 2.479E+01
Prep.Ex. 2-2 5 95 2.2 5.80 15.4 5.872E+01 4.712E+01 3.674E+01 2.958E+01 2.503E+01
Prep.Ex. 2-3 10 90 2.0 5.90 15.9 6.075E+01 4.622E+01 3.512E+01 3.399E+01 2.876E+01
Prep.Ex. 2-4 15 85 2.0 5.60 15.2 6.497E+01 5.144E+01 4.447E+01 3.727E+01 3.153E+01
Prep.Ex. 2-5 20 80 2.0 6.00 15.7 7.215E+01 5.517E+01 4.965E+01 4.100E+01 3.469E+01
Prep.Ex. 2-6 10 90 0.5 6.20 12.8 6.971E+01 5.078E+01 4.570E+01 3.774E+01 3.193E+01
Prep.Ex. 2-7 10 90 1.0 6.00 13.7 4.001E+01 2.915E+01 2.623E+01 2.166E+01 1.833E+01
Prep.Ex. 2-8 10 90 2.5 6.10 16.7 2.212E+01 1.611E+01 1.450E+01 1.197E+01 1.013E+01
Prep.Ex. 2-9 10 90 3.0 5.50 18.2 7.342E+00 5.348E+00 4.813E+00 3.975E+00 3.363E+00
Prep.Ex. 2-10 10 90 5.0 5.40 22.1 2.120E+00 1.544E+00 1.390E+00 1.148E+00 1.001E+00
Prep.Ex. 2-11 10 90 2.0 6.20 15.7 6.122E+01 4.460E+01 4.013E+01 3.314E+01 2.891E+01
Prep.Ex. 2-12 10 90 2.0 5.80 15.4 5.812E+01 4.234E+01 3.810E+01 3.146E+01 2.744E+01
Prep.Ex. 2-13 10 90 2.0 5.50 15.5 7.465E+01 5.438E+01 4.894E+01 4.041E+01 3.525E+01
Prep.Ex. 2-14 10 90 2.0 6.00 15.2 6.251E+01 4.554E+01 4.098E+01 3.384E+01 2.952E+01
Prep.Ex. 2-15 10 90 2.0 5.70 16.1 6.685E+01 4.870E+01 4.382E+01 3.619E+01 3.156E+01
Prep.Ex. 2-16 10 90 2.0 5.70 15.9 5.632E+01 4.103E+01 3.692E+01 3.049E+01 2.659E+01
Prep.Ex. 2-17 10 90 2.0 5.80 15.2 9.001E+01 6.557E+01 5.901E+01 4.873E+01 4.250E+01
Prep.Ex. 2-18 10 90 2.0 5.90 14.8 8.012E+01 5.836E+01 5.252E+01 4.337E+01 3.783E+01
Prep.Ex. 2-19 10 90 2.0 6.50 15.1 7.425E+01 5.409E+01 4.868E+01 4.020E+01 3.506E+01
Prep.Ex. 2-20 10 90 2.0 5.40 16.3 3.712E+01 2.704E+01 2.433E+01 2.009E+01 1.753E+01
Prep.Ex. 2-21 10 90 2.0 5.60 14.7 4.522E+01 3.294E+01 2.964E+01 2.448E+01 2.135E+01
Prep.Ex. 2-22 10 90 2.0 5.60 15.3 5.416E+01 3.945E+01 3.551E+01 2.932E+01 2.557E+01
Prep.Ex. 2-23 10 90 2.0 5.30 15.3 6.923E+01 5.043E+01 4.538E+01 3.748E+01 3.269E+01
Prep.Ex. 2-24 10 90 2.0 5.60 10.1 4.312E+01 3.141E+01 2.827E+01 2.334E+01 2.036E+01
Preparation of electrode formulation
Example 1
95 parts by weight of the electrode-active material composite prepared in Preparation Examples1-1 and 5 parts by weight of polyvinylidene fluoride (binder, PVDF) were added to 53 parts by weight of N-methyl pyrrolidinone (NMP), and then mixed in a mortar to prepare an electrode formulation for a cathode mixture slurry.
Examples 2 to 24
Electrode formulations of Examples 2 to 24 were prepared in the same manner as in Example 1 according to the composition ratio given in Table 4 below.
Comparative Example 1
90 parts by weight of the electrode-active material composite of Preparation Example 1-1, 5 parts by weight of Denka black (electric conducting agent) and 5 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed with 53 parts by weight of N-methyl pyrrolidinone (NMP) to prepare an electrode formulation which is a cathode mixture slurry.
Comparative Examples 2 to 23
Electrode formulations of Comparative Examples 2 to 23 were prepared in the same manner as in Comparative Example 1 according to the composition ratio given in Table 4 below.
Table 4
Electrode-formulation Electrode-active material composite Electric Conducting Agent(Denka black)/part by weight Binder(PVDF)/part by weight
Parts by weight Part by weight
Ex. 1 Prep.Ex. 1-1 95 0 5
Ex. 2 Prep.Ex. 1-1 93 2 5
Ex. 3 Prep.Ex. 1-3 95 0 5
Ex. 4 Prep.Ex. 1-3 94.5 0.5 5
Ex. 5 Prep.Ex. 1-3 94 1 5
Ex. 6 Prep.Ex. 1-3 93 2 5
Ex. 7 Prep.Ex. 1-3 92 3 5
Ex. 8 Prep.Ex. 1-3 91 4 5
Ex. 9 Prep.Ex. 1-5 95 0 5
Ex. 10 Prep.Ex. 1-12 95 0 5
Ex. 11 Prep.Ex. 1-18 95 0 5
Ex. 12 Prep.Ex. 1-24 95 0 5
Ex. 13 Prep.Ex. 2-1 95 0 5
Ex. 14 Prep.Ex. 2-1 93 2 5
Ex. 15 Prep.Ex. 2-3 95 0 5
Ex. 16 Prep.Ex. 2-3 94.5 0.5 5
Ex. 17 Prep.Ex. 2-3 94 1 5
Ex. 18 Prep.Ex. 2-3 93 2 5
Ex. 19 Prep.Ex. 2-3 92 3 5
Ex. 20 Prep.Ex. 2-3 91 4 5
Ex. 21 Prep.Ex. 2-5 95 0 5
Ex. 22 Prep.Ex. 2-12 95 0 5
Ex. 23 Prep.Ex. 2-18 95 0 5
Ex. 24 Prep.Ex. 2-24 95 0 5
Comp. Ex. 1 Prep.Ex. 1-3 90 5 5
Comp. Ex. 2 Prep.Ex. 1-3 88 7 5
Comp. Ex. 3 Prep.Ex. 1-3 85 10 5
Comp. Ex. 4 Prep.Ex. 1-3 80 15 5
Comp. Ex. 5 Prep.Ex. 1-3 75 20 5
Comp. Ex. 6 Prep.Ex. 1-5 90 5 5
Comp. Ex. 7 Prep.Ex. 1-12 90 5 5
Comp. Ex. 8 Prep.Ex. 1-18 90 5 5
Comp. Ex. 9 Prep.Ex. 1-24 90 5 5
Comp. Ex. 10 Prep.Ex. 2-3 90 5 5
Comp. Ex. 11 Prep.Ex. 2-3 88 7 5
Comp. Ex. 12 Prep.Ex. 2-3 85 10 5
Comp. Ex. 13 Prep.Ex. 2-3 80 15 5
Comp. Ex. 14 Prep.Ex. 2-3 75 20 5
Comp. Ex. 15 Prep.Ex. 2-5 90 5 5
Comp. Ex. 16 Prep.Ex. 2-12 90 5 5
Comp. Ex. 17 Prep.Ex. 2-18 90 5 5
Comp. Ex. 18 Prep.Ex. 2-24 90 5 5
Comp. Ex. 19 Comp.Prep.Ex. 1 95 0 5
Comp. Ex. 20 Comp.Prep.Ex. 2 95 0 5
Comp. Ex. 21 Comp.Prep.Ex. 3 95 0 5
Comp. Ex. 22 Comp.Prep.Ex. 5 95 0 5
Comp. Ex. 23 Comp.Prep.Ex. 6 95 0 5
Fabrication of electrode and coin cell and evaluation of charge-discharge characteristics thereof
Electrodes and coin half cells for a lithium secondary battery were fabricated using the electrode formulations of Examples 1 to 24 and Comparative Examples 1 to 23, and the electrode characteristics and electrochemical characteristics thereof were measured and compared.
The resulting slurry was applied to one side of aluminum foil, dried and then rolled through a pressing process to produce a cathode plate.
Said cathode plate was punched into a circular specimen having a diameter of 1.2 cm and used as the cathode, and a lithium metal film was used as the anode. 1 mol of LiPF6 was dissolved in a solvent mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a mixing ratio of 1:2 by volume to be used as the electrolyte, and a Celgard 2400 film was used as the separator membrane to prepare a lithium secondary battery.
(1) Charge-discharge characteristics of lithium secondary batteries fabricated using the electrode formulations of Examples 1 to 24 and Comparative Examples 1 to 23 including the electrode-active material composites (composite A)
The charge/discharge capacities depending on C-rates (0.1C, 0.2C, and 1.0C,) were measured in the range of 2.0 to 4.1 V by a Maccor series 4000 battery tester, and the results are shown in the following Table 5 and FIG. 11.
Referring to Table 5 and FIG. 11, it can be ascertained that, in the case of the electrode formulation using the electrode-active material composite (composite A), when the electrode formulation further including less than 5 wt% of an electric conducting agent is applied to an electrode, the amount of a transition metal compound as a constituent of the electrode-active material composite increases, so the volume capacity of the electrode increases, and thus the charge-discharge effects of a lithium secondary battery are remarkably improved compared to when the case of the electrode formulation including 5 wt% or more of the electric conducting agent is used, thereby realizing a high-capacity lithium secondary battery.
Table 5
part by weight Electric Conducting Agent(Denka black)/part by weight Binder (PVDF)/ part by weight Specific discharge Capacity (mAh/cc)
0.1 C 0.2 C 1.0 C
Ex. 1 95 0 5 273.4 268.1 241.5
Ex. 2 93 2 5 272.4 267.3 246.7
Ex. 3 95 0 5 272.8 270.6 246.8
Ex. 4 94.5 0.5 5 272.3 268.8 247.5
Ex. 5 94 1 5 272.2 265.6 245.4
Ex. 6 93 2 5 270.7 265.5 245.0
Ex. 7 92 3 5 266.4 261.3 244.4
Ex. 8 91 4 5 264.0 258.7 239.7
Ex. 9 95 0 5 273.5 269.5 244.7
Ex. 10 95 0 5 245.2 240.1 224.4
Ex. 11 95 0 5 238.7 236.1 227.9
Ex. 12 95 0 5 332.7 326.4 315.4
Comp. Ex. 1 90 5 5 257.0 252.0 240.4
Comp. Ex. 2 88 7 5 247.2 245.3 234.9
Comp. Ex. 3 85 10 5 239.3 234.9 226.7
Comp. Ex. 4 80 15 5 223.1 222.4 209.6
Comp. Ex. 5 75 20 5 210.0 207.7 198.9
Comp. Ex. 6 90 5 5 255.8 252.0 232.4
Comp. Ex. 7 90 5 5 232.3 227.5 212.5
Comp. Ex. 8 90 5 5 226.1 223.7 215.9
Comp. Ex. 9 90 5 5 315.2 309.2 298.8
Comp. Ex. 20 95 0 5 258.7 256.0 250.7
Comp. Ex. 21 95 0 5 245.2 238.4 185.9
Comp. Ex. 22 95 0 5 233.5 218.6 157.9
Comp. Ex. 23 95 0 5 302.1 289.6 231.5
(b) Charge-discharge characteristics of lithium secondary batteries fabricated using the electrode formulations of Examples 1 to 24 and Comparative Examples 1 to 23 including the electrode-active material composites (composite B)
The charge-discharge characteristics of a lithium secondary battery fabricated using the electrode formulation including the electrode-active material composites (composite B) were measured within the voltage range of 2.0 to 4.1V according to c-rates (0.1C, 0.2C and 1.0C) using a Maccor series 4000 charge-discharge tester, and the results thereof are shown in Table 6 and FIG. 12. Referring to Table 6 and FIG. 12, it can be ascertained that, in the case of electrode formulation using the electrode-active material composite (composite B), when the electrode formulation further including less than 5 wt% of an electric conducting agent is applied to an electrode, the amount of a transition metal compound as a constituent of the electrode-active material composite increases, so the volume capacity of the electrode increases, and thus the charge-discharge effects of a lithium secondary battery are remarkably improved compared to when the case of the electrode formulation including 5 wt% or more of the electric conducting agent is used, thereby realizing a high-capacity lithium secondary battery.
Table 6
part by weight Electric Conducting Agent(Denka black)/part by weight Binder (PVDF)/ part by weight Specific discharge Capacity (mAh/cc)
0.1 C 0.2 C 1.0 C
Ex. 13 95 0 5 253.2 235.1 218.0
Ex. 14 93 2 5 253.1 234.8 214.0
Ex. 15 95 0 5 259.7 255.4 231.1
Ex. 16 94.5 0.5 5 259.1 254.0 229.9
Ex. 17 94 1 5 258.3 254.0 229.8
Ex. 18 93 2 5 257.1 252.3 232.7
Ex. 19 92 3 5 254.4 249.6 230.2
Ex. 20 91 4 5 251.6 246.8 227.7
Ex. 21 95 0 5 256.5 256.0 249.0
Ex. 22 95 0 5 232.9 228.1 213.1
Ex. 23 95 0 5 226.8 224.3 216.5
Ex. 24 95 0 5 316.0 310.1 299.6
Comp. Ex. 10 90 5 5 244.1 237.8 223.7
Comp. Ex. 11 88 7 5 239.5 233.3 212.5
Comp. Ex. 12 85 10 5 231.8 223.1 208.3
Comp. Ex. 13 80 15 5 218.4 215.6 196.0
Comp. Ex. 14 75 20 5 203.4 202.1 181.1
Comp. Ex. 15 90 5 5 243.0 239.4 226.5
Comp. Ex. 16 90 5 5 223.5 214.8 198.1
Comp. Ex. 17 90 5 5 214.8 212.5 205.1
Comp. Ex. 18 90 5 5 299.4 293.7 283.8
Comp. Ex. 20 95 0 5 255.4 236.9 188.2
Comp. Ex. 21 95 0 5 232.9 226.4 176.6
Comp. Ex. 22 95 0 5 221.8 213.1 94.4
Comp. Ex. 23 95 0 5 289.6 273.0 216.8
Although the preferred embodiment of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
According to the present invention, the electrical conductivity of the electrode-active material composite including a fibrous carbon material and an aggregate of primary transition metal compound particles is better than that of a conventional electrode-active material in which primary particles or an aggregate thereof are coated with a carbon material, and the fibrous carbon material can be brought into contact with the aggregates of the primary particles and can fill the pores between the aggregates of the primary particles, so that the electrical conductivity of the electrode formulation of the present invention can be exhibited even when an electric conducting agent is not added.

Claims (23)

  1. An electrode formulation, comprising:
    70 to 99.5 wt% of an electrode-active material composite including a fibrous carbon material and an aggregate of primary particles of transition metal compound; and
    0.5 to 30 wt% of a binder.
  2. 　　 　The electrode formulation of claim 1, further comprising less than 5 wt% of an electric conducting agent.
  3. 　　　　The electrode formulation of claim 1, wherein, in the electrode-active material composite, the fibrous carbon material is non-uniformly dispersed in the aggregate.
  4. 　　　　The electrode formulation of claim 3, wherein, in the electrode-active material composite, the fibrous carbon material densely exists on the surface of the aggregate compared to the inside thereof.
  5. 　　 The electrode formulation of claim 3, wherein, in the electrode-active material composite, the fibrous carbon material densely exists in one side of the section of the aggregate compared to the other side thereof.
  6. 　　　 The electrode formulation of claim 1, wherein the fibrous carbon material is a carbon fiber or a carbon nanotube.
  7. 　　　 The electrode formulation of claim 1, wherein all or a part of the primary particles are electrically connected by the fibrous carbon material, and the fibrous carbon material exists on the entire or partial surface of the aggregate of the primary particles in the form of a web.
  8. 　　　 The electrode formulation of claim 1, wherein the electrode-active material composite includes the transition metal compound and the fibrous carbon material at a weight ratio of 99.9: 0.1 to 80: 20.
  9. 　　　 The electrode formulation of claim 3, wherein the fibrous carbon material includes a non-functionalized fibrous carbon material and a surface-functionalized fibrous carbon material at a weight ratio of 1: 99 to 20: 80.
  10. 　　　The electrode formulation of claim 1, wherein the binder is at least one selected from the group consisting of cellulose, ethylene polymer, ethylene copolymer, propylene polymer, propylene copolymer, polyvinylpyrrolidone, polyvinylchloride, ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride copolymer.
  11. 　　　 The electrode formulation of claim 2, wherein the electric conducting agent is at least one selected from the group consisting of graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, titanium oxide, nickel, and aluminum.
  12. 　　　 The electrode formulation of claim 1, wherein the electrode-active material composite has an average particle diameter of 1 to 200 μm.
  13. 　　　 The electrode formulation of claim 1, wherein the transition metal compound is at least one selected from the group consisting of LiCoO2; LiMnO2; LiMn2O4; Li4Ti5O12; Li(Ni1-x-yCoxAly)O2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99); Li(Ni1-x-yMnxCoy)O2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99); and Li2-z(Fe1-x-yM1 xM2 y)zO2 (x＋y≤1, 0.01≤x≤0.99, 0.01≤y≤0.99, 0<z<1, M1 and M2 are each independently Ti, Ni, Zn or Mn).
  14. 　　　　The electrode formulation of claim 1, wherein the transition metal compound is represented by Formula 1 below:
    　　　　[Formula 1]
    　　　 Li1-xM(PO4)1-y
    　　　　wherein 0≤x≤0.15, 0≤y≤0.1, and M is represented by Formula 2 below:
    　　　　[Formula 2]
    　　　 MA aMB bMT tFe1-(a+b+t)
    　　　 wherein MA is at least one selected from the group consisting of group 2 elements,MB is at least one selected from the group consisting of group 13 elements, MT is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, 0≤a≤1, 0≤b<0.575, 0≤t≤1, 0≤(a+b)<1, and 0≤(a+b+c)≤1.
  15. The electrode formulation of claim 1, wherein the transition metal compound is represented by Formula 3 below:
    [Formula 3]
    LiMPO4
    wherein M is one or a combination of two or more selected from the group consisting of Fe, Mn, Ni, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo.
  16. An electrode manufactured using the electrode formulation of claim 1.
  17. 　A secondary battery comprising the electrode of claim 16.
  18. 　　A method of preparing an electrode formulation, comprising the steps of:
    (a) preparing a mixture in which at least one selected from a non-functionalized fibrous carbon material and a surface-functionalized fibrous carbon material and transition metal compound particles are dispersed;
    (b) drying and granulating the mixture to prepare an electrode-active material composite; and
    (c) mixing the electrode-active material composite with a binder to prepare an electrode formulation.
  19. 　 The method of claim 18, wherein, in the step (c), an electric conducting agent is additionally mixed with the electrode-active material composite and the binder.
  20. 　　　 The method of claim 18, wherein, in the step (a) of preparing the mixture, the mixture is dispersed therein with a non-functionalized fibrous carbon material, a surface-functionalized fibrous carbon material and transition metal compound particles, and the amount (based on weight) of the surface-functionalized fibrous carbon material is greater than that of the non-functionalized fibrous carbon material.
  21. 　　　 The method of claim 18, wherein the mixture includes a dispersant in an amount of 10 to 500 parts by weight based on 100 parts by weight of the total amount of the fibrous carbon material.
  22. 　　　 The method of claim 21, wherein the step (a) of preparing the mixture includes the steps of:
    dispersing the non-functionalized fibrous carbon material and the surface-functionalized fibrous carbon material in a dispersant to prepare a dispersion liquid; and
    mixing the dispersion liquid with the transition metal compound to prepare the mixture dispersed therein with the non-functionalized fibrous carbon material, the surface-functionalized fibrous carbon material and the transition metal compound.
  23. 　　　 The method of claim 22, wherein the dispersant is at least one selected from the group consisting of water, alcohol, ketone, amine, ester, amide, alkyl halogen, ether and furan.
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EP3086388A1 (en) * 2015-04-24 2016-10-26 Samsung Electronics Co., Ltd. Complex for anode active material, anode including the complex, lithium secondary battery including the anode, and method of preparing the complex
CN106067544A (en) * 2015-04-24 2016-11-02 三星电子株式会社 Complex for negative active core-shell material, the negative pole containing complex, include the lithium secondary battery of negative pole and prepare the method for complex
US10263245B2 (en) 2015-04-24 2019-04-16 Samsung Electronics Co., Ltd. Complex for anode active material, anode including the complex, lithium secondary battery including the anode, and method of preparing the complex
CN106067544B (en) * 2015-04-24 2020-12-11 三星电子株式会社 Composite for negative active material, method of preparing the same, negative electrode, and lithium secondary battery
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