KR20170102842A - Composite for Active Materials of Electrode and the Fabrication Method thereof - Google Patents

Abstract

The present invention relates to a composite for an electrode active material. In particular, the composite according to the present invention includes a transition metal oxide composed by electrostatic attraction, a branched water-soluble polymer having primary and secondary amine groups, and reduced graphene oxide (rGO). The present invention has low impedance, has high battery capacity, and prevents an initial capacity loss of a metal oxide.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite material for an electrode active material,

The present invention relates to a composite material for an electrode active material and a method for manufacturing the same, and more particularly, to a composite material for electrode active material having a low impedance, a high battery capacity, an initial capacity loss of a metal oxide is prevented, a stable cycle characteristic, To an electrode active material composite and a method of manufacturing the same.

Recently, as the interest in environmental problems grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, are being conducted.

Researches using a large lithium secondary battery as a power source for such electric vehicles and hybrid electric vehicles are being actively carried out, and some of them are in the commercialization stage. The electrical characteristics such as the capacity of the lithium secondary battery are strongly dependent on the electrochemical characteristics of the negative electrode and the positive electrode active material.

Currently, various materials are being studied as a cathode material for lithium secondary batteries, and research on hetero-composite materials based on oxides, metals, and carbonaceous materials is being carried out. However, the characteristics of the electrode are limited due to the limitation of the movement path of the charge formed through the reaction with lithium. In order to compensate this, the effect of improving the characteristics is secured by adding the carbon conductive material.

Korean Patent Publication No. 10-2012-0028071 discloses a method for producing a cathode active material for a lithium secondary battery by mixing at least one of nickel, cobalt and manganese with carbon and a solvent. However, in the case of the electrode manufacturing method by simple mixing with the electrode active material, there is a limit in the characteristics of the bonding between the active material and the conductive material. In order to solve this problem, an approach to induce hybridization from a synthesis step based on an oxide-based material has been proposed. However, there is a disadvantage that charge transfer between the hybridized materials is restricted due to limited connection between oxide-based materials.

The applicant of the present invention has provided an active material having an increased capacity and excellent charge / discharge cycle characteristics through hybridization between a conductive metal material of a one-dimensional form and an active material through the Korean Patent No. 1508480, and a method for manufacturing the same As a result, the inventors of the present invention have applied the present invention to an active material having improved capacity and charge-discharge cycle characteristics as well as improved high-rate characteristics.

Korean Patent Publication No. 10-2012-0028071 Korean Patent No. 10-1508480

The present invention provides a composite for an electrode active material having a low impedance, a high battery capacity, an initial capacity loss of the metal oxide is prevented, a stable cycle characteristic, and an improved rate characteristic, and a method for manufacturing the same.

The composite according to the present invention is a composite for an electrode active material and includes a transition metal oxide complexed by electrostatic attraction, a branched water-soluble polymer having primary and secondary amine groups, and reduced oxidized graphene (rGO).

The composite according to one embodiment of the present invention may satisfy at least one of the following properties (1) to (4).

(Relational expression 1)

R _SEI + R _CT ≤ 25Ω

In equation 1, R _SEI is the impedance of the half-cell is applied to the composite material as an anode active material measurement results, the negative electrode unit area (cm ²⁾ means a SEI (solid electrolyte interface) resistors each, and wherein R _CT are the same impedance measurements charge transfer Means the resistance (R _CT ).

(Relational expression 2)

0.8? Cap (30) / Cap (2)

Cap (30) represents the cell capacity (mAh / g) at 30 charge / discharge cycles in a charge / discharge cycle characteristic under a condition of 0.1 A / g of a half cell using the composite as the negative electrode active material, Cap ) Means the cell capacity (mAh / g) at the time of two charge / discharge cycles in the same charge-discharge cycle characteristic.

(Relational expression 3)

65? C (3000) / C (0.1)

In Equation 3, C (3000) is the cell capacity (mAh / g) when charging / discharging the half-cell (?) Applied with the composite as the anode active material and? g and the capacity (mAh / g) of the battery during charging and discharging.

(Relational expression 4)

700 mAh / g? C (0.1)

In Equation 4, C (0.1) is the capacity (mAh / g) of the battery when charging and discharging the half-cell to which the composite is applied as the negative electrode active material at 0.1 A / g.

The composite according to an embodiment of the present invention may contain 15 to 50 parts by weight of reduced oxidized graphene, based on 100 parts by weight of the transition metal oxide.

The composite according to an embodiment of the present invention may contain 2 to 15 parts by weight of a water-soluble polymer based on 100 parts by weight of the transition metal oxide.

The composite according to an embodiment of the present invention is characterized in that in a mixed solution containing an aqueous solvent, transition metal oxide, graphene oxide and a branched water-soluble polymer having primary and secondary amine groups, a water-soluble polymer having a positive charge and a negative charge The strip can be prepared by obtaining a precursor complexed by electrostatic attraction between the transition metal oxide and the graphene oxide and heat treating the precursor.

In a complex according to one embodiment of the present invention, the transition metal oxide may be a nanostructure selected from one or more of nanorods, nanoparticles, nanotubes, and nanowires.

In the complex according to one embodiment of the invention, the transition metal oxides are _{MnO 2, ZnO, SnO 2,} TiO 2, RuO 2, CoO, Co 3 O 4, CuO, Cu 2 O, NiO, Fe 3 O 4 or Or mixtures thereof.

In the complex according to an embodiment of the present invention, the water-soluble polymer may contain 200 to 500 amine groups per 1000 carbon atoms.

In the complex according to an embodiment of the present invention, the water-soluble polymer may have a weight average molecular weight of 1,000 to 50,000.

In the composite according to one embodiment of the present invention, the water-soluble polymer may be polyethyleneimine.

The present invention includes a secondary battery negative electrode active material containing the composite described above.

The present invention includes a negative electrode for a secondary battery comprising the above-described negative active material containing the composite.

The present invention includes a secondary battery having a negative electrode containing the above-described composite as a negative electrode active material. At this time, the secondary battery includes a lithium secondary battery.

The method for producing an electrode active material according to the present invention comprises the steps of: a) preparing a mixed solution comprising oxidized graphene, transition metal oxide and a branched water-soluble polymer having primary and secondary amine groups; b) separating and recovering the solid phase from the mixed solution, and heat treating the mixed phase in an inert atmosphere to produce a complex of transition metal oxide-water soluble polymer-reduced graphene oxide (rGO).

In the method for producing an electrode active material according to an embodiment of the present invention, it is preferable that, by the electrostatic attraction between the water soluble polymer having a positive charge in the aqueous solvent and the negative charge transition metal oxide and the oxidized graphene, A composite precursor in which a transition metal oxide, a water-soluble polymer, and an oxide graphene are combined can be produced.

In the method for producing an electrode active material according to an embodiment of the present invention, a step of hydrothermally synthesizing a solution containing a transition metal precursor and a reducing agent may be used to prepare a transition metal oxide before step a).

In the method of manufacturing an electrode active material according to an embodiment of the present invention, step a) includes the steps of: a1) preparing a first mixed liquid in which graphene oxide and a transition metal oxide are dispersed; And a2) adding a branched water-soluble polymer having primary and secondary amine groups to the first mixed solution to prepare a second mixed solution.

In the method of manufacturing an electrode active material according to an embodiment of the present invention, the heat treatment may be performed at a temperature (300 C) lower than the decomposition temperature of the water-soluble polymer and in an inert atmosphere.

The transition metal oxide may be at least one selected from the group consisting of MnO ₂ , ZnO, SnO ₂ , TiO ₂ , RuO ₂ , CoO, Co ₃ O ₄ , CuO, Cu ₂ O, NiO, Fe ₃ O _4, or a mixture thereof, and may be one or more selected from nano-rods, nanoparticles, nanotubes, and nanowires.

In the method for producing an electrode active material according to an embodiment of the present invention, the mixed solution in step a) contains 15 to 50 parts by weight of the oxidized graphene and 50 to 150 parts by weight of the water-soluble polymer based on 100 parts by weight of the transition metal oxide .

The present invention includes an electrode comprising an electrode active material produced by the above-described manufacturing method.

The present invention includes a negative electrode for a secondary battery containing an electrode active material produced by the above-described production method.

The present invention includes a secondary battery having a negative electrode containing an electrode active material manufactured by the above-described manufacturing method. At this time, the secondary battery may be a lithium secondary battery.

The composite according to the present invention has a low impedance, an excellent electrochemical characteristic such as an improved rate characteristic and a high battery capacity, and has an advantage that its activity is stably maintained even in repeated electrochemical reactions.

The method for producing an electrode active material according to the present invention requires no surface modification and is highly compounded by mixing raw materials only in a water-based solvent. Thus, a high-quality electrode active material can be mass-produced in a short time by a simple and low- There is an advantage.

1 is a scanning electron microscope (SEM) image of the complex prepared in Example 1,
FIG. 2 is a graph showing the charge-discharge cycle characteristics of the half-cell produced in Example 3, Comparative Example 1 and Comparative Example 2,
FIG. 3 is a view showing an impedance measurement result and an equivalent electric circuit of the battery manufactured in Example 3,
4 is a graph showing the measurement of the rate characteristics of the battery manufactured in Example 3, Comparative Example 1, and Comparative Example 2. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a composite material for an electrode active material and a method for producing an electrode active material according to the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the technical and scientific terms used herein will be understood by those skilled in the art without departing from the scope of the present invention. Descriptions of known functions and configurations that may be unnecessarily blurred are omitted.

The composite according to the present invention is a composite for an electrode active material and includes a transition metal oxide complexed by an electrostatic attraction, a branched water-soluble polymer having primary and secondary amine groups, and a reduced graphene oxide (rGO) do.

The composite according to the present invention comprises a transition metal oxide, a branched water-soluble polymer having primary and secondary amine groups, and a reduced oxidized graphene, wherein the transition metal oxide, the water-soluble polymer, and the reduced graphene oxide There is a feature that complexation is made.

In detail, the composite of the present invention is characterized in that the surface of the active material or the conductive material is not modified, and the transition metal oxide and the oxide graphene, which have the original surface state in which the characteristics are not changed artificially, And they are combined and combined with each other by a human force.

More specifically, the complex of the present invention is a water-soluble polymer having an amine group and having a branching type water-soluble polymer containing primary and secondary amine groups having a positive charge in an aqueous solvent as well as a transition metal oxide having a negative charge in an aqueous solvent Graphene grains having a negative charge are combined with each other by electrostatic attraction.

A feature of using such a raw material of as-fabricated itself is that it does not require a long reflux process for surface modification in the manufacturing process, and the surface modification process, the surface condition, the modifier Etc., but these steps are unnecessary, so that it is possible to improve the productivity and the yield with the reduction of the manufacturing cost, the simplification of the development and the manufacturing process. Further, since the active material or the conductive material is not capped (or adsorbed) with a heterogeneous material for surface modification, the activity of the active material itself can be maintained, and the contact resistance is significantly And the electrical resistance (internal electrical resistance) of the composite itself can be remarkably reduced.

Furthermore, by the charge of the positive and negative charges provided in the branched water-soluble polymer having primary and secondary amine groups, the graphene oxide and the metal oxide, each having a negative surface potential, are not contained or enclosed in the water-soluble polymer, , The activity and the decrease in conductivity due to the complexation can be extremely effectively prevented.

In addition, rather than three-dimensionally complexing, microscopic two-dimensional hybridization between a water-soluble polymer charged with a positive charge and a negatively charged graphene and a metal oxide is carried out by an electrostatic attraction and a small amount of reduced A conductive network can be stably formed even with an oxidized graphene, and thus the content of the metal oxide having a relatively better electrochemical activity can be increased. However, it is a matter of course that the reduced oxidized graphene can act not only as a conductive member but also as an electrochemically active material.

In addition, this two-dimensional complexation can be achieved even when the electrode material is thickened for a high capacity, even if the graphene oxide and the metal oxide, which are reduced in the surface region of the water-soluble polymer, form irregularities around the water- layer by layer, so that the limitation of the moving speed of lithium ions hardly occurs and the moving distance of the lithium ions can be kept narrow, thereby realizing a high output battery.

As described above, due to such electrostatic attraction, the active material is not embedded in the water-soluble polymer, and the oxidized graphene and the metal oxide, which are reduced on the surface area of the water-soluble polymer having a positive charge, Thus, the metal oxide and the reduced oxide graphene are physically and stably bonded to each other through the water-soluble polymer, and open pores can be formed between the metal oxide and the metal oxide and the reduced oxide graphene. The bonding and open pores through the water-soluble polymer not only improve the specific surface area of the composite, but also prevent the composite from being destroyed by the volume change due to the desorption and insertion of lithium ions, and can have an improved lifetime.

As described above, since the composite includes a transition metal oxide complexed by electrostatic attraction, a branched water-soluble polymer having primary and secondary amine groups, and reduced Graphene Oxide (rGO), the present invention The composite according to one embodiment of the present invention can satisfy at least one of the following properties (1) to (4).

(Relational expression 1)

R _SEI + R _CT ≤ 25Ω

In equation 1, R _SEI is the impedance measurement results, the negative electrode unit area (cm ²⁾ (solid electrolyte interface) SEI per the resistance, and the R _CT are the same impedance measurement of the half-cell (?) Applied to the composite as an anode active material And the resultant charge transfer resistance (R _CT ).

(Relational expression 2)

0.8? Cap (30) / Cap (2)

Cap (30) represents the cell capacity (mAh / g) at 30 charge / discharge cycles in a charge / discharge cycle characteristic under a condition of 0.1 A / g of a half cell using the composite as the negative electrode active material, Cap ) Means the cell capacity (mAh / g) at the time of two charge / discharge cycles in the same charge-discharge cycle characteristic.

(Relational expression 3)

65? C (3000) / C (0.1)

In Equation 3, C (3000) is the cell capacity (mAh / g) when the composite is used as a negative electrode active material in a charge / discharge cycle of 3A / g and C Battery capacity (mAh / g) at discharge.

(Relational expression 4)

700 mAh / g? C (0.1)

In Equation 4, C (0.1) is the capacity (mAh / g) of the battery when charging and discharging the half-cell to which the composite is applied as the negative electrode active material at 0.1 A / g.

In detail, the half-cell to which the composite of the relational expressions 1 to 4 is applied as the negative electrode active material may be a coin-cell half-cell using metal lithium as a reference electrode. More specifically, the half cells of the relational expressions 1 to 4 were prepared by coating a paste prepared by mixing the composite, the conductive carbon and the binder in a weight ratio of 8: 1: 1 onto the aluminum current collector, drying the paste, A lithium reference electrode, an electrolytic solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) (1: 1 by volume) at a concentration of 1M, a coin cell type half- .

As can be seen from the relationship (1), the composite according to an embodiment of the present invention has a solid electrolyte interface ( _SEI ) resistance (R _SEI ) plus a charge transfer resistance (R _CT ) of 25 Ω or less, specifically, (Impedance). As is known, the smaller the R _SEI and the R _CT , the better the capacity and the high-rate characteristics can be obtained.

Furthermore, the composite according to one embodiment of the present invention satisfies the relationship (1), and the R _SEI is 2? To 10?, And the R _CT is 15? Or less, specifically 5? To 15 ?. An R _SEI of 2? To 10? Is a resistance region in which the battery can operate in a stable operation and the life of the battery due to repeated charge and discharge can be prevented. In addition, a remarkably small R _CT of 15 Ω or less, specifically 5 Ω to 15 Ω, enables a usable capacity to be stably maintained even at a high current (high C-rate), thereby improving capacity and high-rate characteristics. In particular, R _CT of 15 Ω or less, specifically 5 Ω to 15 Ω, means that the Li ion oxidation / reduction reaction occurs very smoothly at the interface of the electrode material. Such R _CT , due to the aforementioned electrostatic attraction, The most serious problem of oxides is that the conductivity is very stable and effective.

In Equation 1, the impedance measurement of the half-cell may be measured using a conventional electrochemical impedance spectroscopy (EIS), measured at a state of charge (SOC) of 10 to 80% And may be measured while varying the frequency from 0.01 Hz to 300 kHz with an amplitude of 10 mV. R _SEI and R _CT can, of course, be obtained by modeling the Nyquist plots obtained by SEI impedance measurements with well known equivalent electrical circuits.

As can be seen from the relational expression (2), the composite according to the embodiment of the present invention can have extremely excellent charge / discharge cycle characteristics, in which the battery capacity is hardly lowered even when repeatedly charging / discharging. In addition to the above-mentioned formula 2, the ratio between the initial capacity (twice charge / discharge) of the half-cell to which the composite was applied as the negative electrode active material and the capacity ratio during 30 charge / discharge cycles (charge / Can be 0.8 or more. That is, in the composite according to an embodiment of the present invention, the irreversible capacity decrease of the metal oxide can be remarkably reduced.

As can be seen from the relational expression 3 and the relational expression 4, the composite according to an embodiment of the present invention can have a very high-rate characteristic that a capacity of 65% or more is maintained even under a large current condition of 3 A / g, And can maintain a very high battery capacity of 550 mAh / g or more even under current conditions of 3 A / g.

As described above, the composite according to one embodiment of the present invention can satisfy at least one of physical properties defined by relational expression 1 to relational expression 4, more specifically, can satisfy two or more physical properties, and more specifically, All can be satisfied.

The above-mentioned complexes are obtained by mixing a water-soluble polymer having a positive charge and a transition metal oxide having a negative charge respectively in a mixed solution containing an aqueous solvent, a transition metal oxide, a graphene oxide and a branched water-soluble polymer having primary and secondary amine groups And a precursor compounded by the electrostatic attraction between the oxidized graphenes and heat-treating the precursor.

In a complex according to one embodiment of the present invention, the transition metal oxide may be a nanostructure selected from one or more of nanorods, nanoparticles, nanotubes, and nanowires. Such nanostructures can be compounded more uniformly in the case of electrochemical activity increase by nano structure and increase of specific surface area, as well as complexation by electrostatic attraction force. In an aqueous solvent containing an aqueous solvent, the transition metal oxide may be in the form of nanorods, nano-particles, or the like so that the graphene oxide and the transition metal oxide both have a negative surface potential, It is preferable that the nanostructure is one or two or more nanostructures selected from a tube and a nanowire. Specifically, the transition metal oxide may be one or two or more nanostructures selected from nanorods, nanotubes and nanowires having an aspect ratio of 4 to 500, which is a major axis diameter / minor axis diameter, and may have an average minor axis diameter of 5 to 50 nm have. The dimension of such a nanostructure is advantageous for forming the above-described open pore structure while uniformly composing, and insertion and desorption of lithium ions can easily occur even if the active material layer is made thick, Is a dimension that can increase the contact point with the oxidized graphene. The transition metal oxide may be suitably designed as a material having electrochemical properties required for the application depending on the use of the electrode. Examples of the transition metal oxide include transition metal oxides such as MnO ₂ , ZnO, SnO ₂ , TiO _{2 , RuO 2, CoO, Co 3} O 4, CuO, Cu 2 O, NiO, Fe 3 O 4 or a mixture thereof. The oxidized graphene may have an average size of 200 nm to 3 μm and may be one that has been conventionally produced using known hummers or modified hummers.

The composite according to an embodiment of the present invention may contain 15 to 50 parts by weight, preferably 15 to 40 parts by weight, more preferably 15 to 25 parts by weight, based on 100 parts by weight of transition metal oxide, reduced oxidized graphene have. The amount of the reduced graphene graphene relative to the transition metal oxide is a condition capable of satisfying at least one of the physical properties according to the relational expressions 1 to 4 and is a condition in which a stable conductive network is formed in the composite, Is a content that may not occur.

The composite according to one embodiment of the present invention may contain a branched water-soluble polymer having 2 to 15 parts by weight of primary and secondary amine groups, based on 100 parts by weight of the transition metal oxide. When the transition metal oxide and the reduced graphene oxide are compounded via the branched water-soluble polymer having primary and secondary amine groups, when the number of the branched water-soluble polymer having primary and secondary amine groups is less than 2, stable combination is achieved There is a danger of not being able to hold the composite, and the mechanical stability of the composite is deteriorated. When the content of the branched water-soluble polymer having primary and secondary amine groups is more than 15 parts by weight, the improvement in complexation and mechanical stability is insignificant, while the content of the electrochemically active substance per unit mass of the composite unit is decreased So that the activity of the complex can be reduced.

The complex according to one embodiment of the present invention may contain a branched water-soluble polymer having primary and secondary amine groups, as described above. The amine group containing a primary amine group and a secondary amine group is a functional group which can easily act as a positive charge functional group in an aqueous solvent containing water and does not disturb the charge transfer in an electrochemical reaction. Positive charges provided by amine groups can cause electrostatic attraction between oxide graphene and transition metal oxide, each having a negative surface potential in an aqueous solvent containing water. Primary amines and secondary amines enable a more dense and uniformly complexed complex to be formed, and further, a branched water-soluble polymer having an amine group can include a tertiary amine together with a primary amine and a secondary amine . In addition, in the electrostatic attraction, the polymer providing positive charge has a structure branched from the main chain and the side chain, so that a stable space in which the metal oxide and the oxide graphene can be combined can be provided. Preferably, the branched water-soluble polymer having primary and secondary amine groups is a branched polymer having an amine group in both the main chain and the side chain. Since both the main chain and the side chain contain an amine group, the entire water-soluble polymer can uniformly exhibit positive charge and can increase the density of the positive charge even though stable combination is achieved without any spatial limitation. At this time, if the side chain is too long, the complexation in the side chain may be inhibited by the complexation in the side chain or the main chain. Accordingly, it is preferable that the side chain has a mean chain number of 2 to 8, preferably 2 to 6.

The branched water-soluble polymers having primary and secondary amine groups contain from 200 to 500 amine groups (including primary, secondary and tertiary amines) per 1000 carbon atoms (including both C in the main chain and side chain) , And an amine group formed on the main chain and the side chain). Preferably, the branched, water-soluble polymer having primary and secondary amine groups has an amine group at all terminal groups of the branched polymer and has 500 amine groups per 1000 carbon atoms (including both C in the main chain and side chain) It may be a water-soluble polymer.

As the water-soluble polymer is compounded, a water-soluble polymer having an excessively small molecular weight is not only difficult to provide a physically stable reaction site, but also may deteriorate mechanical stability. Accordingly, the water-soluble polymer having an amine group preferably has a weight average molecular weight of 1000 or more, more specifically 1000 to 50000 molecular weight.

In order to satisfy the physical properties required for use of the secondary battery active material, such as electrochemical and thermal stability, and to satisfy the physical properties of at least one of the relational expression 1, relational expression 2, relational expression 3 and relational expression 4, The branched water-soluble polymer having an amine group may be a branched polyethyleneimine having primary and secondary amine groups. Specifically, the main chain and the side chain may each be a branched polyethyleneimine having primary and secondary amine groups. More specifically, Is a mono-chain having an average carbon number of 2 to 8, preferably 2 to 6, in the side chain and has 200 to 500 amine groups (including primary, secondary and tertiary) groups per 1000 carbon atoms (including both C in the main chain and side chain) Including all tertiary amine groups, including amine groups formed in the main chain and side chains, more preferably all terminal groups are amine groups and contain 1000 carbon atoms (including both the main chain and the side chain C Hamham including an 500 amine groups (primary, secondary, and tertiary amines sugar), including both an amino group formed in the main chain and the side chain) can minutes yiminil branched polyethylene having a. At this time, the polyethyleneimine preferably has a weight average molecular weight of 1000 or more, more preferably a molecular weight of 1000 to 50,000.

As described above, the composite according to the present invention is a composite for an electrode active material, and the electrode of the electrode active material includes an electrode of an energy storage device including a secondary battery, a supercapacitor, a fuel cell, and the like.

In detail, the composite according to the present invention may be a composite for a secondary battery electrode active material, and the secondary battery may include a lithium secondary battery. At this time, the lithium secondary battery may include a lithium ion battery or a lithium polymer battery.

The present invention includes a negative active material for a lithium secondary battery containing the above-described complex. At this time, the negative electrode active material may be in powder form.

The present invention includes a negative electrode for a lithium secondary battery containing the above-described complex as a negative electrode active material. At this time, the negative electrode may include a collector and an active material layer positioned on the collector, and the active material layer may include the above-described complex, binder, and conductive material. The binder of the active material layer may be a binder used in a conventional lithium secondary battery. Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trichlorethylene copolymer, polymethyl methacrylate, poly But are not limited to, acrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpolylane, Styrene-butadiene copolymer, polyimide, polytetrafluoroethylene, or a mixture thereof, and the like can be used as a binder resin, and examples of the binder resin include polyvinyl alcohol, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, However, It is needless to say that it can not be limited by the binder (binder) of the quality layer.

The collector of the negative electrode may also be a collector in a conventional lithium secondary battery. In one example, the current collector may be in the form of a foam, a film, a mesh, a felt or a porous foil of a conductive material, and may be formed of graphite, graphene, titanium, copper, Platinum, aluminum, nickel, silver, gold, or carbon nanotubes. However, it goes without saying that the present invention can not be limited by the current collector of the electrode.

The conductive material may also be a conductive material conventionally used for improving the conductivity of the active material layer in a conventional lithium secondary battery. For example, carbon black, acetylene black, carbon nanotubes and the like can be mentioned, but it is needless to say that the present invention can not be limited by the conductive material added to the active material layer.

The present invention includes a lithium secondary battery provided with a negative electrode including the aforementioned composite.

The lithium secondary battery may include a positive electrode, the above-described negative electrode, and a separator formed between the positive electrode and the negative electrode, and may include a non-aqueous electrolyte or a polymer electrolyte.

The positive electrode may be provided with a positive electrode active material conventionally used in a lithium secondary battery. The positive electrode active material may be a material capable of reversibly intercalating lithium ions, and a positive electrode active material used in a conventional lithium secondary battery may suffice. As a non-limiting example, the cathode active material may be a layered oxide represented by LiCoO ₂ , an oxide of a spinel structure represented by LiMn ₂ O ₄ , a phosphate-based material of an olivine structure typified by LiFePO ₄ , Li _{1 + x} (Mn _a Ni _b Co _c O _{2 + y} (real number 0? _x ? 0.5, real number 0.5? a? 0.75, real number 0.2? _b ? 0.25, real number 0? _c ? 0.3, real number 0? _y ? 0.5 (Li excess) -manganese-nickel-cobalt composite oxide represented by Li (Ni _a Co _b M _c ) O ₂ (real number of 0.7? A? 1, real number of 0? B + c? Lt; = c < = 0.1, M = a transition metal except Ni and Co).

The positive electrode may be manufactured by applying a slurry containing a positive electrode active material and a binder (binder) to the current collector, followed by pressing to form a positive electrode active material layer on the current collector. In this case, it is needless to say that the current collector and the binder may be similar or identical to the above-mentioned materials at the cathode.

The electrolytic solution may be an electrolytic solution containing an organic solvent and a lithium salt ordinarily used for a lithium secondary battery. As a specific, non-limiting example, a lithium salt is a lithium salt whose anion is F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^{- _{CF 3) 2 PF 4 -,}} (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 ^{_{CF 2 SO 3 -, (CF}} 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) _{^{3 C -, (CF 3 SO}} 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N ^- . ≪ / RTI > Specific examples of the organic solvent include, but are not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) Examples of the organic solvent include ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran ≪ RTI ID = 0.0 > and / or < / RTI >

The separator may be a separator which is conventionally used for preventing a short circuit between a cathode and an anode in a conventional secondary battery. As a non-limiting example of a lithium secondary battery, the separation membrane may be a material selected from one or more of polyethylene, polypropylene, polyolefin, and polyester, and may be a microporous membrane structure. In this case, the microporous membrane may be coated with an inorganic material, and may have a laminated structure in which a plurality of organic films such as a polyethylene membrane, a polypropylene membrane, and a nonwoven fabric are laminated for the purpose of preventing overcurrent, have.

The secondary battery may include a coin-cell type, a pouch type, a jelly-roll type, or a stack type secondary battery.

Hereinafter, a method for producing the composite as the electrode active material will be described in detail.

The method for producing an electrode active material according to the present invention comprises the steps of: a) preparing a mixed solution comprising oxidized graphene, transition metal oxide and a branched water-soluble polymer having primary and secondary amine groups; And b) separating and recovering the solid phase from the mixed solution and heat treating the mixture in an inert atmosphere to produce a composite of transition metal oxide-water-soluble polymer-reduced graphene oxide (rGO); .

The solvent of the mixed solution is preferably an aqueous solvent, and water is better in terms of process cost reduction, safety and environment, and transition metal oxide and oxidized graphene are preferable to have a stable negative surface potential. That is, the present invention relates to a process for producing a polymer electrolyte membrane, which comprises only graft-type water-soluble polymers having a grafted oxide (graft), a grafted (or sold) state transition metal oxide and a primary and secondary amine group A simple, commercial, and fast method of mixing with water at an extremely low cost can be used to make a composite between the oxidized graphene and the transition metal oxide and the water soluble polymer.

In step (a), a complex precursor in which a transition metal oxide, a water-soluble polymer and a graphene oxide are combined is formed by electrostatic attraction between a water-soluble polymer having a positive charge in an aqueous solvent and a negative charge transition metal oxide and a graphene oxide respectively .

In the manufacturing method according to an embodiment of the present invention, the step a) comprises: a1) preparing a first mixed solution in which graphene oxide and a transition metal oxide are dispersed; And a2) adding a branched water-soluble polymer having primary and secondary amine groups to the first mixed solution to prepare a second mixed solution.

That is, after the dispersion phase of the oxide graphene and the transition metal oxide having a negative surface charge in the aqueous solvent is first prepared, the water-soluble branched polymer having the primary and secondary amine groups may be added to proceed the complexing. When the electrode active material is prepared by such a dispersion step and a complexing step, fine graining is prevented by the repulsive force of each other as the oxide graphene and the transition metal oxide both have a negative surface potential in the dispersion step, Can be formed. In this case, a mixing method commonly used in the related art may be used for forming a homogeneous dispersed phase in the first mixed liquid, for example, a dispersed phase can be formed more quickly and uniformly by applying ultrasonic waves. The application condition of the ultrasonic waves may be a range that is easy to form the dispersed phase, and may be applied at a frequency of 15 k to 20 kHz and an intensity of 670 to 2000 W, for example. However, Of course not.

When a branched water-soluble polymer having primary and secondary amine groups having positive electric charges is introduced into a first mixture liquid in which graphene oxide and transition metal oxide have negative surface potentials and are dispersed very homogeneously, The graphene oxide and the transition metal oxide can be more homogeneously compounded on the water-soluble polymer. When the water-soluble polymer is added to the first solution, the water-soluble polymer is dissolved in the same solvent or miscible solvent as the solvent of the first solution to form a water-soluble polymer liquid in a dissolved state Is added to the first solution to prepare the second solution.

When a water-soluble polymer, preferably a water-soluble polymer liquid, is added to the first mixture to produce a second mixture, the second mixture may be stirred. Stirring may be carried out at a low speed stirring rate of 1000 rpm or less, substantially 400 to 1000 rpm, without interfering with the complexity and shortening the time required for the complexing by the electrostatic attraction.

The content of the transition metal oxide and the graphene oxide in the mixed liquid (including the first mixed liquid) can form a dispersed phase uniformly, and the fluidity can be guaranteed. As a specific example, the mixed liquid may contain 0.5 to 5% by weight of the solid phase (transition metal oxide and the graphene oxide), but it goes without saying that the present invention can not be limited by the solid phase content in the mixed liquid.

In the manufacturing method according to an embodiment of the present invention, the transition metal oxide may be a nanostructure selected from one or more of nano-rods, nanoparticles, nanotubes, and nanowires. In the nanorods, nanotubes, It is better to have one or more selected nanostructures. Specifically, the transition metal oxide may be one or two or more nanostructures selected from nanorods, nanotubes and nanowires having an aspect ratio of 4 to 500, which is a major axis diameter / minor axis diameter, and may have an average minor axis diameter of 5 to 50 nm have.

The transition metal oxide may be suitably designed as a material having electrochemical properties required for the application depending on the use of the electrode. Examples of the transition metal oxide include transition metal oxides such as MnO ₂ , ZnO, SnO ₂ , TiO _{2 , RuO 2, CoO, Co 3} O 4, CuO, Cu 2 O, NiO, Fe 3 O 4 or a mixture thereof.

The oxidized graphene may have an average size of 200 nm to 3 μm and may be one that has been conventionally produced using known hummers or modified hummers.

The branched water-soluble polymer having primary and secondary amine groups may be a branched polymer having an amine group in both the main chain and the side chain, and each of the main chain and the side chain may contain both a primary amine group and a secondary amine group . At this time, the carbon number of the side chain may be a single chain having 2 to 8 carbon atoms. Further, the branched water-soluble polymer may further contain a tertiary amine together with primary and secondary amine groups.

The branched water-soluble polymer having primary and secondary amine groups may be a branched polymer having 200 to 500 amine groups per 1000 carbon atoms, and all terminal groups may be amine groups. And may have a weight average molecular weight of 1000 or more, more specifically 1000 to 50000 molecular weight. Further, the branched water-soluble polymer having primary and secondary amine groups may be a polymer having a thermal decomposition temperature of more than 150 ° C., specifically more than 300 ° C., so as to have thermal stability upon reduction heat treatment of the graphene oxide .

As a preferred example, the branched water-soluble polymer having primary and secondary amine groups may be a branched polyethyleneimine having primary and secondary amine groups, and specifically, a branched polyethyleneimine having primary and secondary amine groups Lt; / RTI > polyethylene imine. More specifically, it may be a branched chain polyethyleneimine having 2 to 8 carbon atoms in the side chain and having 200 to 500 amine groups per 1000 carbon atoms, and may be a branched polyethyleneimine in which all terminal groups are amine groups. At this time, it is preferable that the polyethyleneimine has a weight average molecular weight of 1000 or more, specifically 1000 to 50,000.

In the manufacturing method according to the embodiment of the present invention, the amount of the mixed liquid (including the first mixed liquid) is 15 to 50 parts by weight, preferably 15 to 40 parts by weight, more preferably 15 to 40 parts by weight, 25 parts by weight of graphene oxide.

In the production method according to an embodiment of the present invention, the mixed solution (including the second mixed solution) may contain 50 to 150 parts by weight of the water-soluble polymer based on 100 parts by weight of the transition metal oxide. This is because an excessive amount of the water-soluble polymer is added to the water-soluble polymer required for complexing with the transition metal oxide and the graphene oxide, and then the excess water-soluble polymer not combined is removed during solid-phase separation and recovery in the step b). As a result, complexing is performed in a state in which a sufficient amount of electric charge is present, so that the electrode active material can be manufactured stably and reproducibly and the electrode active material can be manufactured more quickly.

 The solid-phase separation step of step b) may be any known method capable of separating and recovering the solid phase from the dispersion phase in which the solid phase is dispersed in the liquid phase. As a specific example, the solid phase can be separated by centrifugation, but it is needless to say that the present invention can not be limited by the solid phase separation and recovery method.

The composite precursor in which the separated and recovered solid phase, that is, the transition metal oxide, the water-soluble polymer, and the oxide graphene are complexed can be heat-treated to reduce the oxidation graphene and improve the mechanical strength of the composite precursor. The heat treatment may be performed in an inert atmosphere, and the inert atmosphere may mean a gas atmosphere selected from one or more of argon, nitrogen and helium. The heat treatment may be performed at a temperature lower than the pyrolysis temperature of the water-soluble polymer of the complex precursor to a temperature of 150 ° C or higher. In the case of polyethyleneimine, which is an example of the preferred water-soluble polymer described above, the heat treatment temperature may be from 150 to 300 캜.

By the above-described heat treatment, a composite in which a transition metal oxide, a water-soluble polymer, and a reduced graphene oxide are combined can be produced.

The method according to an embodiment of the present invention may further include hydrothermally synthesizing a solution containing a transition metal precursor and a reducing agent to prepare a transition metal oxide before step a).

The transition metal precursor may be any material that can produce the desired transition metal oxide by an oxidizing agent, and may be selected in view of the use of the transition metal oxide. Examples thereof include transition metal sulfides, transition metal halides, metal salts such as transition metal oxides, metal salt hydrates, or mixtures thereof. The transition metal of the transition metal precursor may be one or more selected from among Mn, Zn, Sn, Ti, Ru, Co, Cu, Ni and Fe. The transition metal precursor may be MnSO ₄ .H ₂ O, C ₄ H ₆ MnO ₄ .4H ₂ O, MnN ₂ O ₆ .4H ₂ O, or mixtures thereof, but are not limited thereto.

The oxidizing agent is not limited as long as it can oxidize the transition metal precursor, and examples thereof include KMnO ₄ , NaMnO ₄ , and mixtures thereof. At this time, the oxidizing agent may be added in an amount of 0.5 to 1 mol based on 1 mol of the transition metal precursor.

The hydrothermal reaction may be performed by applying microwave at 100 to 200 ° C for 5 to 120 minutes, preferably at 130 to 150 ° C for 15 to 60 minutes. By applying microwaves, the surface of the metal rises rapidly to a high temperature, which makes it possible to manufacture metal oxides in a very short time. At this time, the microwave may be applied at 400 to 1000 W.

However, as is known, pure metal oxides that do not undergo an artificial surface treatment have negative surface potentials in aqueous solvents and oxidized grains also have negative surface potentials. Accordingly, a metal oxide may be prepared and used so as to have a more preferable shape and dimensions, but a commercially available metal oxide or graphene oxide may be used.

(Production example)

1.5365 g of manganese precursor MnSO ₄ .H ₂ O and 0.9578 g of oxidizing agent KMnO _{4 were} added to 50 ml of distilled water and stirred at room temperature for 10 minutes to prepare a mixture. Thereafter, the mixture was irradiated with microwaves (400 W) at 180 캜 for 10 minutes, sufficiently dried in an oven at 120 캜 and pulverized to prepare MnO ₂ nanorods having an average diameter of 25 nm and an average length of 500 nm.

The oxidized graphene was synthesized using the Hummers method. The average size of the graphene oxide was 1.5 μm.

The prepared manganese oxide nanorods were dispersed in water and the surface potential (Zeta potential) was measured. As a result, it was confirmed that the surface potential of -23 mV was observed. The surface potential of the graphene oxide was measured to have a surface potential of -37 mV Respectively.

(Example 1)

The weight of the manganese oxide nano-rods and the graphene oxide prepared in Preparation Example was quantified to be 80:20, and the mixture was poured into distilled water. The mixture was dispersed using an ultrasonic mixer (Sonic Dismember 550, Fisher Scientific) Solid phase). A polyethyleneimine aqueous solution was added to the first mixed solution so that the weight ratio of manganese oxide: polyethyleneimine was 100: 75, and the mixture was stirred at 600 rpm for 30 minutes to prepare a second mixed solution. At this time, the polyethyleneimine had a weight average molecular weight of 1300, 500 amines (primary, secondary and tertiary amines) per 1000 carbon atoms, all terminal functional groups were amine groups, 2 to 6 carbon atoms had side chains, The thermal decomposition temperature was 250 占 폚.

The solid phase (complex precursor) was collected and dried from the second mixed solution through centrifugation, and then heat-treated at 200 ° C for 1 hour in an argon atmosphere to prepare a composite.

(Example 2)

Except that the first mixed solution was prepared in the same manner as in Example 1 except that the weight ratio of the manganese oxide nano-rod and the graphene oxide was 70:30, to prepare a composite.

(Example 3)

(Composite): 1 (super P) was prepared by mixing the composite prepared in Example 1, carbon-based material Super P (Timcal Graphite & Carbon, BET 20 m ² / g, average particle size 40 nm) and polyvinylidene difluoride (PVDF) : 1 (PVDF), and a paste was prepared using N-methylpyrrolidone (NMP) solvent. The paste thus prepared was applied to a Cu current collector using a bar coating method, dried at 80 ° C. for 15 minutes, and then dried in a 120 ° C. vacuum oven overnight to prepare an active material layer. Using a roll press Followed by pressing to produce a negative electrode.

The prepared cathode was cut into a circular disk having a diameter of 12 mm, and then Li metal was used as a reference electrode and 1M LiPF ₆ -ethylene carbonate (EC) / diethyl carbonate (DEC) (1: 1 volume ratio) A 2032 type coin cell was prepared using a polypropylene membrane (PP membrane, Celgard 24010 Microporous membrane, Celgard) as a separator.

(Example 4)

A coin cell was prepared in the same manner as in Example 4, except that the composite prepared in Example 2 was used instead of the composite prepared in Example 1.

(Comparative Example 1)

The same procedure as in Example 1 was carried out except that the first mixed solution was prepared so that the weight ratio of the manganese oxide nano-rods and the graphene oxide was 80:20 without adding the water-soluble polymer, and then the first mixed solution was immediately centrifuged, After the separation and recovery, the mixture was heat-treated in the same manner as in Example 1 to prepare a composite.

In Example 3, a coin cell was prepared in the same manner as in Example 3, using the composite prepared in Comparative Example 1, instead of the composite prepared in Example.

(Comparative Example 2)

In Example 3, a coin cell was prepared in the same manner as in Example 3, except that the manganese oxide prepared in Preparation Example was used instead of the composite prepared in Example.

(CC: 100 mA / g, 0.01 V CUT-OFF, charging condition: CC) using a charge-discharge tester (TOSCAT-3100, Toyo Co. Ltd) , 100 mA / g, 3 V CUT-OFF).

1 is a scanning electron microscope (SEM) image of the complex prepared in Example 1. Fig. As can be seen from FIG. 1, it can be seen that the polymer, the metal oxide nano-rod and the reduced oxide graphene are uniformly compounded, and the metal oxide nano-rod and the reduced oxide graphene are not embedded or enclosed in the polymer, It can be seen that a composite in which the polymer films having the metal oxide nanorods and the reduced graphene grains dispersed and bound on the surface are overlapped with each other irregularly is produced. The polyethyleneimine was removed from the resulting composite by using thermal parallax analysis, and the weight decreased. As a result, it was confirmed that the composite contained 5 wt% of polyethyleneimine.

Table 1 below shows the relationship between the cell capacity at the time of first charge-discharge, the cell capacity at the time of the second charge-discharge, and the cell capacity at the second charge- The battery capacity of the battery is measured.

(Table 1)

Figure 2 is a third embodiment (Fig. 2 of the MnO ₂ -PEI-GRO), Comparative Example 1 (Fig. 2 of the MnO ₂ -GRO) and Comparative Example 2 (Fig. 2 of the MnO ₂₎ the half-cell prepared as described above in Charge / discharge cycle characteristics in which the charge / discharge cycle is repeatedly performed under the conditions shown in FIG.

As shown in Table 1 and FIG. 2, in the case of the composite prepared according to one embodiment of the present invention, it was found that the capacity decrease, which is a problem of the metal oxide active material, was remarkably reduced, g < / RTI >

3 is a view showing an impedance measurement result of the battery manufactured in Example 3 and an equivalent electric circuit. Impedance measurements were made at 0.42 V and measured by varying the frequency from 0.01 Hz to 300 kHz with an amplitude of 10 mV. As can be seen in FIG. 3, it can be seen that R _SEI of 5.9? And remarkably low R _CT of 12.4?.

4 is a graph showing the measurement of the rate characteristics of the battery produced in Example 3, Comparative Example 1, and Comparative Example 2. Fig. At this time, 'numerical value A / g' shown in the figure means a current condition in which charge / discharge is performed. As can be seen from FIG. 4, the secondary battery including the electrode active material according to an embodiment of the present invention has a higher capacity than the lithium secondary battery of the comparative example, and the rate characteristics are remarkably improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Those skilled in the art will recognize that many modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (12)

A complex for an electrode active material comprising a transition metal oxide complexed by electrostatic attraction, a branched water-soluble polymer having primary and secondary amine groups, and reduced oxidized graphene (rGO). The method according to claim 1,
Wherein at least one of the following relational expressions 1 to 4 physical properties is satisfied.
(Relational expression 1)
R _SEI + R _CT ≤ 25Ω
(In the equation 1, R _SEI is the impedance measurement result of the half-cell is applied to the composite material as an anode active material, it means that the negative electrode per unit area (solid electrolyte interface (SEI per cm ²⁾⁾ resistance, and the R _CT are the same impedance measurements charge Movement resistance (R _CT )
(Relational expression 2)
0.8? Cap (30) / Cap (2)
(30) represents the cell capacity (mAh / g) at 30 charge / discharge cycles in the charge / discharge cycle characteristics under the condition of 0.1 A / g of the half cell using the composite as the negative electrode active material, and Cap 2) represents the cell capacity (mAh / g) at the time of two charge-discharge cycles in the same charge-discharge cycle characteristic)
(Relational expression 3)
65? C (3000) / C (0.1)
C (3000) is the cell capacity (mAh / g) when the composite is used as a negative electrode active material in a charge / discharge cycle of 3A / g, / g and the capacity (mAh / g) of the battery during charging and discharging)
(Relational expression 4)
700 mAh / g? C (0.1)
(In the relational expression 4, C (0.1) is the cell capacity (mAh / g) when charging and discharging the half-cell to which the composite is applied as the negative electrode active material at 0.1 A / g) The method according to claim 1,
15 to 50 parts by weight of reduced graphene graphene based on 100 parts by weight of the transition metal oxide. The method according to claim 1,
Based on 100 parts by weight of the transition metal oxide, 2 to 15 parts by weight of a water-soluble polymer. The method according to claim 1,
The composite is composed of a water-soluble polymer having a positive charge in a mixed solution containing an aqueous solvent, a transition metal oxide, a graphene oxide and a water-soluble polymer, and an electrostatic attraction between the transition metal oxide and the oxide graphene, A composite prepared by obtaining a precursor and heat treating. The method according to claim 1,
Wherein said transition metal oxide is a nanostructure selected from one or more of nanorods, nanoparticles, nanotubes, and nanowires. The method according to claim 1,
Wherein the transition metal oxide is a composite of MnO ₂ , ZnO, SnO ₂ , TiO ₂ , RuO ₂ , CoO, Co ₃ O ₄ , CuO, Cu ₂ O, NiO, Fe ₃ O ₄ or a mixture thereof. The method according to claim 1,
Wherein the water-soluble polymer has 200 to 500 amine groups per 1000 carbon atoms. The method according to claim 1,
Wherein the water-soluble polymer has a weight average molecular weight of 1,000 to 50,000. The method according to claim 1,
Wherein the water-soluble polymer is a polyethyleneimine. A secondary battery negative electrode active material containing the composite according to any one of claims 1 to 10. A secondary battery comprising a negative electrode comprising the negative electrode active material of claim 11.

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