KR20150102662A - Preparing method of positive active material - Google Patents

Abstract

The present invention provides a method for producing a positive electrode material including: a first step of dissolving polymers in a mixed solution including oil, a surfactant, a cosurfactant, and a carbon supplying source; a second step of forming emulsion having a reversed micelle structure by adding a solution, obtained by dissolving a lithium salt compound and a manganese salt compound, into a solution obtained in the first step; a third step of producing a material in a gel phase by evaporating emulsion produced in the second step; a fourth step of producing precursors by heating the material in a gel phase; and a fifth step of obtaining powder by heating the precursors produced in the fourth step. Therefore, the positive electrode active material in which Li_2Mn_4O_3 having a layered structure is inserted in Li_4Mn_5O_1_2 having a spinel structure with excellent conductivity can be produced. The positive electrode active material including the produced Li_2Mn_4O_3/Li_4Mn_5O_1_2 complex is porous, has a high specific surface area, and thus increases mobility of lithium ions. The positive electrode active material is used for an positive electrode for a lithium ion battery and can enhance cycle properties and durability of the lithium ion battery.

Description

[0001] The present invention relates to a positive active material,

The present invention relates to a method for producing a positive electrode active material used in a lithium ion battery.

Lithium-ion batteries that supply electricity are energy storage devices that have a higher capacity or operating voltage than other batteries, and have excellent electrochemical properties such as energy density and circulation ability, and thus are used in various portable electronic devices. The anode of the lithium ion battery has a transition metal mixture in the main structure to reversibly intercalate / de-intercalate lithium ions. Lithium cobalt oxide (LiCoO ₂ ) is among the most common active materials among many oxidation transition metals. The amount of cobalt in the natural state is very small and as a result increases the production cost of the lithium ion battery.

Lithium manganese oxides are similar to lithium cobalt oxides and can replace cobalt. LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₄ O ₉ , LiMnO ₂ and Li _{1 + σ} Mn _{2- σ} O ₄ (0 << σ << 0.33) is considered. When lithium manganese oxide is used as a positive electrode active material of a lithium ion battery, it exhibits an electromotive force of about 3.0 to 4.0 V. Manganese oxide-based compounds are attractive in that they are low production cost and non-toxic, but various capacity problems of manganese with a valence of 3.5+ have been reported, and studies have been conducted to find alternative manganese oxides with higher battery cycles and valencies of 3.5+ .

Many studies have shown that the production of Li ₄ Mn ₅ O ₁₂ is difficult due to the high covalent valence of manganese atoms.

On the other hand, Korean Patent Laid-Open Publication No. 10-2013-0134949 discloses a lithium ion battery having a low life and excellent life characteristics by adding a material having a charging capacity larger than the discharge capacity to Li ₄ Mn ₅ O ₁₂ , And a method for manufacturing the same.

However, the above-mentioned invention also discloses the supply of an external lithium source to Li ₄ Mn ₅ O ₁₂ by adjusting the ratio of the lithium salt compound and the manganese salt compound to the porous Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ A method of manufacturing a cathode active material having an O ₁₂ structure has not been attempted.

An object of the present invention is to improve the cycle characteristics and lifetime of a lithium ion battery by preparing a porous cathode active material by using a low-priced lithium salt compound and a manganese salt compound as an electrode of a lithium ion battery.

The present invention relates to a process for preparing a polymer, which comprises dissolving a polymer in a mixed solution containing an oil, a surfactant, an auxiliary surfactant and a carbon source (first step); Adding a solution prepared by dissolving a lithium salt compound and a manganese salt compound in a solvent to a solution dissolved in the first step to form an emulsion of a reversed micelle structure (second step); Evaporating the emulsion produced in the second step to produce a gel form (step 3); Heating the gel-like substance to prepare a precursor (Step 4); And a step of heating the precursor prepared in step 4 to obtain a powder (step 5).

The polymer may also be a pluronic acid having a (PEO) ₂₀ - (PPO) ₇₀ - (PEO) ₂₀ structure.

The surfactant may also be n-butanol.

The auxiliary surfactant may also be lithium dodecylsulfate.

The carbon source may be any one selected from the group consisting of carbon black (carbon black), denka black, and ketjen black.

The lithium salt compound may be lithium nitrate (LiNO ₃ ).

The manganese salt compound may be manganese nitrate (Mn (NO ₃ ) ₂ ).

Also, the fourth step may be performed at a temperature of 300 to 400 DEG C for 8 to 10 hours.

In the fifth step, a powder which is heated at a temperature of 600 to 800 ° C. for 5 to 10 hours can be obtained.

According to the method for producing a cathode active material according to the present invention, a cathode active material having a layered structure of Li ₂ Mn ₄ O ₃ inserted into Li ₄ Mn ₅ O ₁₂ having a spinel structure with excellent conductivity can be produced. The prepared positive electrode active material containing Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite has a high specific surface area of porosity to improve the mobility of lithium ions and the positive electrode active material is used as a positive electrode for lithium ion batteries, The cycle characteristics and lifetime of the ion battery can be increased.

1 is a schematic view showing a step of forming a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex in an emulsion having an inverted micelle structure according to an embodiment of the present invention.
2 is an SEM and TEM image of a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite according to the Li / Mn content according to an embodiment of the present invention.
3 is a graph showing an XRD pattern of an electrode including a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite according to an embodiment of the present invention.
FIG. 4 shows the nitrogen adsorption / desorption isotherms of a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.
FIG. 5 illustrates the first and second charge / discharge curves of an electrode including a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.
6 is a graph showing the charge capacity versus cycle of an electrode containing a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.
7 is a graph showing Nyquist plots of an electrode containing a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention at frequencies between 100 and 0.01 kHz .

In studying lithium manganese oxide for replacing expensive lithium cobalt oxide used as a cathode active material of a lithium ion battery, the present inventors used a solution process to control the molar ratio of a lithium salt compound and a manganese salt compound, which are precursors, Of Li ₄ Mn ₅ O ₁₂ was inserted into Li ₂ Mn ₄ O ₃ , thereby completing the cathode active material.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a process for preparing a polymer, which comprises dissolving a polymer in a mixed solution containing an oil, a surfactant, an auxiliary surfactant and a carbon source (first step); Adding a solution prepared by dissolving a lithium salt compound and a manganese salt compound in a solvent to a solution dissolved in the first step to form an emulsion of a reversed micelle structure (second step); Evaporating the emulsion produced in the second step to produce a gel form (step 3); Heating the gel-like substance to prepare a precursor (Step 4); And a step of heating the precursor produced in the fourth step to obtain a powder (fifth step).

In the first step, the polymer may be a polymeric template having a structure of (PEO) ₂₀ - (PPO) ₇₀ - (PEO) ₂₀ wherein PEO is polyethylene glycol, and PPO Is polypropylene glycol.

The oil may be cyclohexane.

The oil may be used in conjunction with water to produce an emulsion for use in solution processes.

The surfactant may be n-butanol, and other surfactants may not have an inverted micellar structure.

The auxiliary surfactant may also be lithium dodecylsulfate.

An emulsion having an inverted micelle structure can be prepared using the above oil, surfactant, and cosurfactant. When the above conditions are not satisfied, an emulsion having an inverted micelle structure is not formed.

The carbon source may be any one selected from the group consisting of carbon black, denka black, and ketjen black.

When the carbon source is added, the electrical conductivity is improved, so that the cycle characteristics of the lithium ion battery can be increased.

Also, 10 to 20 g of pluronic acid, 9.5 to 10 g of n-butanol, 0.45 to 0.5 g of lithium dodecylsulfate, and 10 g of ketjen black were added to 80 to 100 g of the cyclohexane. 0.2 to 0.4 g may be mixed.

When the above conditions are exceeded, an emulsion having an inverted micellar structure can not be formed in a solution process.

To prepare a solution in which the lithium salt compound and the manganese salt compound were dissolved in the solvent in the second step, 20 ml of LiNO ₃ of 1.5 to 3.0 M and a solution of 1.0 M of LiNO ₃ were added to a 50 wt% nitric acid (HNO ₃ ) solution 10 ml of Mn (NO ₃ ) ₂ which is a manganese salt compound can be added.

If outside the above conditions can not be dissolved in a lithium salt compound and a manganese compound in a solvent, the precursor of the Li ₄ Mn layered on ₅ O ₁₂ spinel structure with the mol ralbi control of the lithium salt compound and a manganese compound Li ₂ MnO &lt; ₃ &gt; can not be formed due to the insertion of MnO.

Here, the molar ratio of the lithium salt compound LiNO ₃ to Mn (NO ₃ ) ₂ , which is the manganese salt compound, can be controlled by adding 1 mol of LiNO ₃ to 1 to 3 mol of Mn (NO ₃ ) ₂ .

A solution prepared by dissolving a lithium salt compound and a manganese salt compound in the solvent may be added to the solution prepared in the first step to form an emulsion having an inverted micelle structure.

When the emulsion of the reversed micelle structure is formed, the lithium salt compound LiNO ₃ and the manganese salt compound Mn (NO ₃ ) ₂ added in the cyclohexane atmosphere form Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex, Can be penetrated into the hydrophilic head of FIG.

When the reversed micelle structure can not be formed, Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex can not be formed even when LiNO ₃ , which is a lithium salt compound, and Mn (NO ₃ ) ₂ , a manganese salt, are added.

The reversed micelle structure is a structure in which the hydrophilic head coheses inward and the minor nonpolar tail faces outward. The block copolymer polymer in which the polypropylene oxide is located on the inner side and the polyethylene oxide is located on the outer side is the surfactant n - Can be expanded by butanol to adjust the size of the micelle.

The Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite may be represented by the formula xLi ₂ MnO ₃ (1-x) Li _{1 + σ} Mn ₂ -σ O ₄ (0 <x <<?<0.67).

In the third step, the emulsion may be stirred for 15 to 20 hours and then slowly evaporated at 130 DEG C to prepare a gel.

When the above conditions are exceeded, the gel is not formed or solidifies to form a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex.

In the fourth step, the gel prepared in the third step may be heated at 300 to 400 ° C. for 8 to 10 hours to prepare a precursor.

When the above conditions are exceeded, the carbon supply source Ketjenblack can be agglomerated.

In the fifth step, the precursor prepared in the fourth step may be heated at 600 to 800 ° C for 5 to 10 hours to prepare a powdery cathode active material.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

&Lt; Example 1 > Preparation of cathode active material

To 80 g of cyclohexane (Aldrich) was added a mixed solution of 0.45 g of lithium dodecylsulfate (LDS, Adlrich), 9.6 g of n-butanol, 0.2 g of ketjen black and a residual amount of water to 10.0 (PEO) ₂₀ - (PPO) ₇₀ - (PEO) ₂₀ , Aldrich) was added thereto, and the mixture was stirred until it became transparent.

20 ml of 1.5 M LiNO ₃ dissolved in 45 wt% nitric acid (HNO ₃ ) diluted in 30 ml of an aqueous solution of 10 ml of 1.0 M Mn (NO ₃ ) was added to the prepared non-aqueous mixture to prepare an emulsion.

The prepared emulsion was stirred for 20 hours and then evaporated at 130 ° C to obtain a brown gel.

The gel was heated at 300 占 폚 for 6 hours to obtain a precursor, and the precursor was heated again at 600 占 폚 for 10 hours to obtain a powder.

The powder was repeatedly washed with acetone and dried in an oven at 60 &lt; 0 &gt; C to remove residual surfactant to remove residual reactants.

&Lt; Example 2 >

A lithium coin cell was fabricated to confirm the electrochemical performance of the prepared cathode active material.

The electrode was prepared by mixing 80 wt% of the cathode active material prepared in Example 1, 10 wt% of a conductive material, Alfa Aesar, and 1 wt% of a binder polyvinyl alcohol, in 1-methyl-2-pyrrolidone, After the slurry mixture was prepared by adding polyvinylidene difluoride (Alfa Aesar), the mixture was deposited on the surface of aluminum foil as a current collector and dried at 100 ° C for 12 hours.

The electrode manufactured to a size of 1.32 cm 2 was dried in a vacuum oven at 70 ° C. and the electrode manufactured using lithium foil (FMC Corporation) as a counter electrode was evaluated.

The coin cell is provided inside a glove box (<5 ppm, H ₂ O and O ₂ ) filled with argon (Ar), and the anode and the cathode inside the cell are separated from each other by a porous polypropylene membrane .

Electrolyte solution is ethylene carbonate (ethylene carbonate) of 1.4 M LiPF ₆ contained in: a flow of ethylene carbonate (fluoro-ethylene carbonate): dimethyl carbonate (dimethyl carbonate): ethyl methyl carbonate (ethylmethyl carbonate), each of 1: 1: 6: 2 was used.

&Lt; Experimental Example 1 > Properties of the cathode active material

The electrode size and shape were measured using a scanning electron microscope (FE-SEM, JSM-6700F, Eindhoven) and a field emission transmission electron microscope (FE-TEM, Tecnai G2 F30 operating voltage 300 kV).

X-ray diffraction (XRD) was performed to analyze the structure. X-ray diffractometer (D2 PHASER, Bruker AXS) used a nickel (Ni) filter and Cu (λ = 0.15418 ㎚) as the source and the source was adjusted to 10 mA at 30 kV.

And scanned from 10 to 80 degrees at a 2 [theta] angle of 0.5 [deg.] / Min. Nitrogen adsorption and desorption characteristics were recorded (ASAP 2020). The specific surface area was measured according to the BET method in the range of the relative pressure (P / P ₀ ) of the adsorption isotherm from 0.05 to 0.30, and the pore distribution was determined using the Barrette Joyner Halenda (BJH) method in the desorption isotherm Respectively.

The content of lithium and manganese contained in the cathode material was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES, Optima-4300 DV, PerkinElmer) after dissolution.

The chemical composition of the surface was measured by X-ray photoelectron spectroscopy (XPS, Thermo VG, U.K.) using monochromatic aluminum (Al) X-ray as source (Al Kα Line: 1486.6 eV).

1 is a schematic view showing a step of forming a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex in an emulsion having an inverted micelle structure according to an embodiment of the present invention.

When the emulsion of the reversed micelle structure is formed, the lithium salt compound LiNO ₃ added in the cyclohexane atmosphere and the manganese salt compound Mn (NO ₃ ) _{2 form} the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex .

2 is an SEM and TEM image of a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite according to the Li / Mn content according to an embodiment of the present invention.

The composite changed the molar ratio of Li / Mn from 1.5 to 3.0. Figures 2 (a) and 2 (e) show 1.5, 2 (b) and 2 (f) show 1.9, 2 (c) and 2 (g) show 2.5 and 2 (d) and 3 (h) show 3.0.

It was confirmed that uniform spherical particles of 600 to 800 nm were formed in all the samples. As the molar ratio of Li / Mn increased, the sample changed from dark reddish brown to bright reddish brown.

2 (e) to 2 (h) are TEM images of the sample. It was confirmed that the particles were composed of small nanoparticles of 40 nm or less and all the samples were layered on the spinel crystal structure.

Especially, when the molar ratio of Li / Mn was 1.9, it was confirmed that the spinel structure and the layered portion were structurally well integrated in the nano-range (FIGS. 2 (b) and 2 (f)).

&Lt; Experimental Example 2 > Properties of manufactured electrode

3 is a graph showing an XRD pattern of an electrode including a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite according to an embodiment of the present invention.

The spinel crystal structure of Li ₄ Mn ₅ O ₁₂ has a cube filled with oxygen mesh and FD-3 space group of manganese in the octahedron of the common side. Li ₂ Mn ₄ O ₃ has a layered structure having monoclinic unit cells and a C2 / m space group.

The Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex having a Li / Mn molar ratio of 1.5 was predominant in the spinel crystal structure of Li ₄ Mn ₅ O ₁₂ , but as the Li / Mn molar ratio increased from 1.5 to 3.0 In the XRD pattern, the layered Li ₂ Mn ₄ O ₃ showed a clear peak at 21.7 °.

From the above results, it can be seen that the ratio of the layered Li ₂ Mn ₄ O _{3 to} the Li ₄ Mn ₅ O ₁₂ of the spinel crystal structure in the preparation of the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite .

(002) of Li ₂ Mn ₄ O ₃ at (111) and 18.705 ° of Li ₄ Mn ₅ O ₁₂ overlapped at about 18.7 ° at 18.817 ° in FIG. 3 (b).

The peaks of Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composites prepared with molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0 were 18.813 °, 18.777 °, 18.754 ° and 18.724 °, respectively , And the phase transition from Li ₄ Mn ₅ O ₁₂ of the spinel crystal structure to the layered Li ₂ Mn ₄ O ₃ predominantly changes with increasing molar ratio of Li / Mn.

Table 1 shows the values of spinel lattice constant for Li ₄ Mn ₅ O ₁₂ a = 8.1616 Å.

<Table 1>

As the spinel lattice constant increases from a = 8.1616 to 8.198 Å, the spinel fraction of the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite decreases as the molar ratio of Li / Mn increases.

On the other hand, the lattice constant of the layered portion close to the reference value indicates that the layer portion of the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite increases as the molar ratio of Li / Mn increases.

The Mn 2P _3/2 spectrum was measured to clearly confirm the covalent valence of the manganese element of the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite produced. A narrow peak at 642 eV, a shoulder peak distinct at 643 eV, and a broad and distinct shoulder peak between 644 and 647 eV.

The results were confirmed to fit the spectrum of Mn ⁴⁺ .

Table 2 shows Li ₂ Mn ₄ O ₃ and Shows a Li ₂ Mn ₄ O ICP-AES value of ₃ / Li ₄ Mn ₅ O ₁₂ weight percent (wt%) for Li and Mn in the composite material for Li ₄ based on the Mn ₅ O _12.

<Table 2>

Based on Li ₂ Mn ₄ O ₃ and And the weight ratio of Li: Mn of Li ₄ Mn ₅ O ₁₂ was set to 9.186: 90.814 and 20.166: 79.834, respectively. The weight ratio of Li: Mn in the Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite was adjusted to 10.214: 89.786, 12.033: 87.967, 16.582: 83.418 and 18.653: 81.347, respectively.

The results showed that the phase transition from Li ₄ Mn ₅ O ₁₂ to Li ₂ Mn ₄ O ₃ was increased with increasing molar ratio of Li / Mn. According to the position of the peak identified in the XRD pattern and the value of Li / Mn determined from the ICP-AES value, it was confirmed that Li ₄ Mn ₅ O ₁₂ to Li ₂ Mn ₄ O ₃ as a function of molar ratio of Li / And that the relative ratios can be adjusted.

FIG. 4 shows the nitrogen adsorption / desorption isotherms of a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.

(A) shows a case where the molar ratio of Li / Mn is 1.5, (b) is 1.9, (c) is 2.5, and (d) is 3.0.

Referring to the drawings, the isotherm curves of the composite are shown at relative pressures (P / P ₀ ) from 0.6 to 0.8 Which is defined as a classical IV classification with a typical H1 hysteretic loop representing the porous material.

Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composites prepared with molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0 respectively showed specific surface areas of 16.2, 20.4, 18.9 and 16.8 ㎡ g ^-1 And porosity, which is very favorable for lithium ion mobility.

It was confirmed that mesopores with a narrow pore diameter and within 2.5 ㎚ were found in all samples.

FIG. 5 shows the first and second charge / discharge curves of an electrode containing a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.

(B) and (f) are 1.9, (c) and (g) are 2.5, (d) and (g) are 3.0 .

Electrodes containing Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complexes prepared at molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0, respectively, at a current density of 0.1 C were 199.84, 269.41 , 184.78, and 182.01 mAh g &lt; ^{-1 &} gt ;, respectively.

The discharge curves of the lithium cell including the anode prepared according to the properties of the composite of the spinel crystal structure of Li ₄ Mn ₅ O ₁₂ and the layered structure of Li ₂ Mn ₄ O ₃ were classified into four main parts, V, a layered portion of 3.8 to 2.8 V, a 2.8 to 2.7 V spinel and a 2.7 to 2.0 V layered / spinel portion.

Table 3 compares the discharge capacity of the electrode containing the controlled Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex to the four parts.

<Table 3>

Electrodes containing composites prepared with molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0, respectively, in the layered portions between 3.8 and 2.8 V showed 21.41, 28.26, 44.15 and 52.55% capacities.

On the other hand, the electrode containing the complex prepared with molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0 at spinel portions between 3.8 and 2.8 V showed capacities of 16.41, 15.21, 8.66 and 4.17%, respectively.

The results show that as the Li / Mn molar ratio increases, the contribution of the spinel moiety decreases, while the proportion of the layered moiety increases, consistent with the XRD and ICP-AES analyzes.

5 (e) to 5 (h) are graphs showing the relationship between the range of between 4.8 and 2.0 V at an anode which is a counter electrode of Li / Li ⁺ in a lithium coin cell including a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex, s ^-1 . &lt; / RTI &gt;

Representative reduction peaks were observed at 4.0 and 2.7 V, and especially the layered portion was found to have a reduction region between 3.8 and 2.8 V, and as the molar ratio of Li / Mn increased from 1.5 to 3.0, The reduction peak corresponding to the discharge was clearly observed in the potential range.

6 is a graph showing the charge capacity versus cycle of an electrode containing a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ complex according to an embodiment of the present invention.

(A) shows the molar ratio of Li / Mn is 1.5 (b) is 1.9, (c) is 2.5, and (d) is 3.0.

Identifying the characteristics for 25 cycles at a charge rate of 0.1 C, the initial stage between the first and fifth cycles indicated the active phase in the cycle reaction.

The first discharge capacities of the electrodes prepared with molar ratios of Li / Mn of 1.5, 1.9 and 2.5 were 199.84, 269.27 and 184.78 mAh g ^-1 , respectively. The storage capacities after 72 cycles were 72.36, 84.47, and 99.50% Respectively.

6 (d), when the molar ratio of Li / Mn was 3.0, the first and the fifteenth discharge capacities were confirmed to be 180.01 and 190.12 mAh g ^-1 , respectively, and it was confirmed that the initial capacity was exceeded after 25 cycles .

7 is a graph showing a Nyquist plot of a Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ composite according to an embodiment of the present invention at frequencies between 100 and 0.01 kHz.

The impedance spectrum of the battery cell consisted of two pressed semicircles and a straight line in the low frequency region in the high - to - mid frequency region. The diameter values of the semicircle on the Z real axis are related to the charge transfer resistance (R _ct ), and the molar ratios of Li / Mn are respectively Li ₂ Mn ₄ O ₃ / Li prepared at 1.5, 1.9, 2.5 and 3.0 The R _ct values of the electrode containing ₄ Mn ₅ O ₁₂ complex were 130, 128, 157 and 198 Ω, respectively.

The straight line in the lower frequency range is due to the lithium diffusion and the diffusion of the lithium ions into the electrode material.

Table 4 shows the R _ct , And the bug impedance constant (? W) and the diffusion constant (D).

<Table 4>

<Formula 1>

Using the formula 1 (2), the electrodes prepared with molar ratios of Li / Mn of 1.5, 1.9, 2.5 and 3.0, respectively, were 4.05 ㅧ ^10-14 , 4.56 ㅧ ^10-14 , 2.27 ㅧ ^10-14, and 2.33 ㅧ The diffusion coefficient of lithium ion at 10 ^-14 cm ² s ^-1 was obtained and the fastest diffusion of lithium ion was confirmed when the molar ratio of Li / Mn was 1.9.

As a result, it was confirmed that the electrode manufactured by the high lithium ion diffusion coefficient of the electrode having a wide specific surface area, low migration resistance and porous nanostructure had a very effective lithium intercalation property.

As described above, according to the method for preparing a cathode active material according to the present invention, meso pores of Li ₂ Mn ₄ O ₃ / Li ₄ Mn ₅ O ₁₂ Complex can be produced. The proportion of Li ₂ Mn ₄ O ₃ having a layered structure to Li ₄ Mn ₅ O ₁₂ having a spinel crystal structure can be precisely controlled by controlling Li / Mn molar ratio, which is a precursor, and an electrode is manufactured using the composite as a cathode active material Since it has a large specific surface area and mesopores, the mobility of lithium ions can be increased, thereby increasing the cycle characteristics and lifetime of the lithium ion battery.

While the invention has been described with reference to a limited number of embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (9)

Dissolving the polymer in a mixed solution containing an oil, a surfactant, a cosurfactant and a carbon source (first step);
Adding a solution prepared by dissolving a lithium salt compound and a manganese salt compound in a solvent to a solution dissolved in the first step to form an emulsion of a reversed micelle structure (second step);
Evaporating the emulsion produced in the second step to produce a gel form (step 3);
Heating the gel-like substance to prepare a precursor (Step 4); And
And a step of heating the precursor produced in the fourth step to obtain a powder (fifth step). The method of claim 1, wherein the polymer is a pluronic acid having a structure of (PEO) ₂₀ - (PPO) ₇₀ - (PEO) ₂₀ .
PEO is polyethylene glycol and PPO is polypropylene glycol. The method of claim 1, wherein the surfactant is n-butanol. The method of claim 1, wherein the auxiliary surfactant is lithium dodecylsulfate. The method of claim 1, wherein the carbon source is any one selected from the group consisting of activated carbon, denka black, and ketjen black. The method of claim 1, wherein the lithium salt compound is lithium nitrate (LiNO ₃ ). The method of claim 1, wherein the manganese salt compound is manganese nitrate (Mn (NO ₃ ) ₂ ). The method of claim 1, wherein the fourth step is performed at a temperature of 300 to 400 ° C for 8 to 10 hours. The method for producing a cathode active material according to claim 1, wherein the fifth step is a step of obtaining a powder heated at a temperature of 600 to 800 ° C for 5 to 10 hours.

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