KR20120012628A - Surface-modified cathode active material for a lithium secondary battery and the fabrication method thereof - Google Patents

Abstract

PURPOSE: A manufacturing method of a positive electrode active material is provided to manufacture LMO powder in which nano-sized ITO crystals are uniformly coated on the surface of LMO powder without cohesion, thereby manufacturing powders having simple processes and remarkably improved characteristics. CONSTITUTION: A manufacturing method of a positive electrode active material comprise: a step of forming ITO sol by mixing indium acetate and tin chloride in solvent; a step of forming a ITO layer on the surface of a positive electrode active material by mixing the ITO sol and the positive electrode active material and drying the mixture; and a step of forming positive electrode active material powder in which nano ITO particles are coated by crystallizing the ITO by high-temperature heat treating the positive electrode active material.

Description

Surface-Modified Cathode Active Material for Lithium Secondary Battery and Its Manufacturing Method {SURFACE-MODIFIED CATHODE ACTIVE MATERIAL FOR A LITHIUM SECONDARY BATTERY AND THE FABRICATION METHOD THEREOF}

The present invention relates to a positive electrode active material for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a positive electrode active material and a method of manufacturing the surface of the positive electrode active material is surface-modified with nanoparticles, etc. to improve the performance of the secondary battery.

With the spread of portable devices, demand for lithium secondary batteries is expected to increase. Compared to LiCoO ₂ and Li (Co _x Ni _y Mn _(1-xy) ) O _{2 which} are widely used at present, lithium manganese spinel oxide (LiMn ₂ O ₄ , LMO), an Mn-based cathode active material, is easy to synthesize and Inexpensive, excellent stability and harmless to the human body, but the theoretical capacity of 148 mAh / g has a lower problem than lithium cobalt oxide (LCO). In particular, due to the phenomenon that the capacity is rapidly falling as the charge and discharge continues at a high temperature (55 ℃) it is not widely used.

This dose causes the elution of Mn ^{+ 2} in the ^{reduction, Jahn-Teller distortion of Mn 3} +, there are electrolytes such as decomposition of the electrode. In particular, from being identified as the main reason it is that Mn ^{2 +} are eluted into the electrolyte. This phenomenon occurs at the interface between the electrode and the electrolyte during the charge and discharge of the battery. As a way to reduce the contact between the Mn ^{+ 2} and the electrolyte, a method for coating the positive electrode active material surface with an oxide or non-oxide it has been reported a lot. According to "A review of recent developments in the surface modification of LiMn ₂ O ₄ as cathode material of power lithium-ion battery (Ionics (2009) 15, 779-784), oxide coating materials include alumina, MgO, ZnO, CeO ₂ , silica, ZrO ₂ , SnO ₂ , AlPO ₄ as a non-oxidation system, Ag, Au as a metal, LiCoO ₂ as an electrode material, etc. are proposed, and carbon materials, SrF ₂ , BiOF, Li ₂ O— 2B ₂ O _{3 was} also tried.

Through surface modification, the cycle characteristics of the LMO can be improved. In the case of coating a conductive material, it is considered that the low resistance of the interface contributes to the improvement of properties in addition to the interface reaction with the electrolyte. In Korean Patent 10-2008-0005995, LiCoO _2- based electrode material was used for LMO powder coating as a slurry, and a coating amount of 0.5 to 12 wt% is proposed. In the case of indium tin oxide (ITO), an oxide and a conductive material, in US 6,534,217, ITO powder was mixed with LMO powder, heat treated at 700 ° C, and then pulverized, and the amount of ITO was improved by using 4 to 10 mol%. I was. Korean Patent No. 10-2005-0048452 proposes a method of coating ITO on an LMO surface using an alcohol solution of indium nitrate and butoxytin, and a cathode active material coated with ITO. In Korean Patent 10-2005-0048453, A surface modification method is proposed in which a chelating compound is added to an aqueous solution of tin salt, or a hydroxide precipitate of an aqueous solution of indium salt and tin salt is coated on the surface of the positive electrode active material.

Such conventional methods have a problem that the surface of the positive electrode active material cannot be uniformly coated even when a relatively large amount of ITO precursor is used. Therefore, the effective surface modification is not made, it is required to develop a simple process for coating the surface of the positive electrode active material with ITO.

An object of the present invention is to improve the thermal stability by coating the surface of the LMO powder with high electrical conductivity ITO nanoparticles without fear of introducing impurities through a simple process in a non-aqueous system, to improve the thermal stability, It is to improve the characteristics.

The method of manufacturing a cathode active material for a secondary battery of the present invention comprises the steps of: (1) mixing an indium acetate and tin chloride in a solvent to form an ITO sol, (2) mixing and drying the ITO sol and a cathode active material to form a surface of the cathode active material. Forming an ITO film in (3) and forming a cathode active material powder coated with nano ITO particles by crystallizing ITO by high temperature heat treatment of the cathode active material having the ITO film formed through the step (2).

Method of manufacturing a positive electrode for a secondary battery of the present invention comprises the steps of forming a slurry by mixing a positive electrode active material, a conductive material and a binder prepared by the above method and applying the slurry to a thin film and vacuum drying to form a positive electrode The method of manufacturing a secondary battery according to the present invention includes forming a positive electrode and a counter electrode manufactured by the above method, and forming an electrolyte and a separator between the positive electrode and the counter electrode.

According to the production method of the present invention, the non-aqueous ITO sol is simply mixed with LMO powder, dried, and heat treated to produce LMO powder in which nano-sized ITO crystals are evenly coated on the surface of the LMO powder without aggregation. Simple and greatly improved powders can be obtained.

According to the manufacturing method of the present invention, by coating the surface of the positive electrode active material of the lithium secondary battery with ITO nanoparticles of a material having high electrical conductivity, the reaction between the positive electrode active material and the electrolyte is suppressed, thereby stabilizing the structure of the positive electrode active material, the positive electrode By improving the electronic conductivity of the active material, it is possible to improve high rate characteristics, life characteristics and thermal stability of the battery using the same. In addition, there is an advantage in that the coating process is simple and the amount of ITO used is small.

1 is a field emission scanning microscope (FESEM) photograph of LiMn ₂ O ₄ raw material powder.
2 is a field scanning microscope photograph of LiMn ₂ O ₄ powder coated with 0.5% by weight of ITO prepared in Example 2. FIG.
3 is a graph showing charge and discharge life characteristics at room temperature of each of the batteries prepared in Comparative Example 1, Example 1, and Example 2. FIG.
4 is a graph showing charge and discharge life characteristics at room temperature of each of the batteries prepared in Comparative Examples 1, 2, and 3;
5 is a graph showing charge and discharge life characteristics at 55 ° C. of the batteries prepared in Example 2 and Comparative Example 1. FIG.
Figure 6 is a graph showing the charge and discharge life characteristics according to the C-rate of the battery prepared in Example 2 and Comparative Example 1.
7 is a graph of charge and discharge life characteristics at 55 ° C. of a full cell using Comparative Examples 1, 2 and 3 as the positive electrode.

The method of manufacturing a cathode active material for a secondary battery of the present invention comprises the steps of: (1) mixing an indium acetate and tin chloride in a solvent to form an ITO sol, (2) mixing and drying the ITO sol and a cathode active material to form a surface of the cathode active material. Forming an ITO film in (3) and forming a cathode active material powder coated with nano ITO particles by crystallizing ITO by high temperature heat treatment of the cathode active material having the ITO film formed through the step (2).

The positive electrode active material mixed with the ITO sol is spinel Li [Mn _2-x M _x ] O ₄ having a cubic structure (M is Co, Ni, Mg or Al, and 0 ≦ _x ≦ 0.1), or spinel Li having a cubic structure. [Ni _0.5 Mn _1.5-x M _x ] O ₄ (M is Co, Ni, Mg or Al and 0 ≦ _x ≦ 0.1) or LiM _x Fe _{1 - x} PO ₄ (M is Mn, Co or Ni, and 0 ≦ x ≦ 1).

Step (1) comprises the steps of (a) dispersing the indium compound and tin chloride compound in a propionic acid and butanol mixed solvent and heating to prepare a first indium tin oxide sol, (b) an indium compound in a dimethylformamide and butanol mixed solvent and Dispersing the tin chloride compound and adding nitric acid, followed by heating and rapid cooling to prepare a second indium tin oxide sol and (c) adding the first indium tin oxide sol to the second indium tin oxide sol while stirring To form a mixed indium tin oxide sol.

After step (3), (4) may further comprise a post-heat treatment of the positive electrode active material powder coated with the nano ITO particles.

As the solvent, at least one selected from the group consisting of ethanol, propanol, isopropanol, butanol, acetylacetone, ethyl acetate, dimethylformamide, ethanolamine, propionic acid and ethylene glycol can be used.

ITO sol may have a concentration of ITO in the solution of 0.1 to 4% by weight.

In step (2), the mixing ratio of ITO sol and LMO may be mixed in a weight ratio of 1:10 to 1: 1.

The heat treatment of step (3) may be made at 400 to 700 ° C. under air or inert gas atmosphere, and the post heat treatment of step (4) may be made at 200 to 400 ° C. under reducing atmosphere.

On the other hand, the secondary battery positive electrode manufacturing method of the present invention is a step of forming a slurry by mixing the positive electrode active material prepared by the above method with a conductive material and a binder and applying the slurry to a thin film and vacuum drying to form a positive electrode It is made to include.

The mixing ratio of the positive electrode active material, the conductive material and the binder may be 70 to 97% by weight of the positive electrode active material, 2 to 20% by weight of the conductive material, and 1 to 10% by weight of the binder.

The conductive material mixed to impart the electrical conductivity to the positive electrode active material is influenced by the particle size of the positive electrode active material, generally 2 to 20% by weight. On the other hand, the binder as a binder for improving the adhesion between the positive electrode active material and the current collector is mixed in a weight ratio of 1 to 10%. Substantial mixing involves putting them into a dispersant and stirring to prepare a paste, which is then applied to a current collector of a metal material, compressed and dried to produce a laminate-shaped positive electrode.

Carbon black is generally used as a conductive material, and acetylene black series (Chevron Chemical Company, Gulf Oil Company, etc.) and Ketzen Black ( Ketjen Black) EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Treem (MMM)).

As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and its copolymer or cellulose are generally used. As a dispersant for forming a paste, isopropyl alcohol, N-methylpyrrolidone is generally used. (NMP) or acetone or the like is used.

In addition, the method of manufacturing a secondary battery of the present invention comprises the steps of forming a positive electrode and a counter electrode manufactured by the above method and forming an electrolyte and a separator between the positive electrode and the counter electrode.

Example

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, this is only one embodiment of the present invention and the present invention is not limited thereto.

Example 1

The ITO sol used here is a mixture of ITO sol (Korean Patent 10-2010-0041416) developed by the present inventors, and the concentration of ITO [(In _0.9 Sn _0.1 ) O _2-x ] of 2.0 wt% in the mixed organic solvent. Is a clear solution. 50 g of LMO (Citic Guoan Mengguli Power Source, China, average particle size 11.31 μm) was mixed with 12.5 g of ITO sol by milling for 2 hours, dried, and then heat-treated at 520 ° C. for 3 hours in an air atmosphere to form ITO-coated LMO. Powder was prepared.

A slurry made by mixing ITO-coated LMO powder, acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) with a binder in a weight ratio of 90: 5: 5 was uniformly mixed in an aluminum foil with a thickness of 20 μm or less. It was applied and dried in vacuo at 120 ℃ to prepare a positive electrode.

Coin cell according to a general manufacturing method using a prepared positive electrode, a lithium foil as a counter electrode, a porous polyethylene membrane as an separator, and an electrolyte made of 1 mol of LiPF ₆ in a solvent in which ethylene carbonate and diethyl carbonate were mixed in the same volume. Was prepared. The manufactured coin cell was subjected to electrochemical analysis (charge / discharge characteristic evaluation) at 0.5 mA / cm ² , 0.5 C, 3.4 to 4.3 V using an electrochemical analysis device.

Example 2

The ITO-coated LMO powder prepared in Example 1 was subjected to post-heat treatment (reduction treatment) at 300 ° C. for 30 minutes under a 4% H ₂ / Ar flow (containing H ₂ 4% in Ar gas) atmosphere (reduction atmosphere). The conditions were the same as those in Example 1 except that the post-heat treatment was performed. Using this powder, a battery was produced by the method described in Example 1 and subjected to performance experiments.

Example 3

Same as Example 2, except that a 2% by weight ITO sol corresponding to 0.8% by weight ITO relative to LMO was used.

Comparative Example 1

The LMO powder purchased was dried in an oven at 110 ° C. without surface modification, and coin cells were produced in the same manner as in Example 1, and the battery characteristics were examined in the same manner as in Example 1.

1 is a field emission scanning microscope (FESEM) picture of the LiMn ₂ O ₄ raw material powder, Figure 2 is a field emission scanning microscope picture of LiMn ₂ O ₄ powder coated with 0.5% by weight of ITO prepared in Example 2. Looking at Figure 2, unlike in Figure 1, it can be seen that the ITO particles of about 20 nm size is coated on the surface of the LMO. That is, it can be seen that sufficient coating is achieved even with 0.5% by weight of ITO.

FIG. 3 shows Comparative Examples 1 (without coating), Example 1 (with 0.5 wt% ITO coated and heat treated at 520 ° C.) and Example 2 (post heat treatment at 300 ° C. under a reducing atmosphere after the same treatment as Example 1 It is a graph showing the charge and discharge life characteristics at room temperature of each battery manufactured in one case). The characteristics were superior to Comparative Example 1, which was not coated, and the reduction treatment through post-heat treatment was better than that of simple heat treatment.

4 is prepared in Comparative Example 1 (without coating), Example 2 (with 0.5 wt% ITO coating, heat treated and post-heat treated) and Example 3 (with 0.8 wt% ITO coated, heat treated and post-heat treated) It is a graph showing the charge and discharge life characteristics of the batteries at room temperature. It can be seen that the charge and discharge characteristics were greatly improved by the ITO coating. In the uncoated LMO powder, the battery capacity starts to drop from 130 cycles and drops sharply at about 160, whereas the surface coated with ITO according to the present invention maintains a high capacity even at 200 cycles, and has an ITO content of 0.5. In the case of mass%, it was better than in the case of 0.8% by weight.

5 is a graph showing charge and discharge life characteristics at 55 ° C. of the batteries prepared in Example 2 and Comparative Example 1. FIG. 92% coated at 100 cycles, the charge and discharge characteristics are significantly higher than 75% of the uncoated.

Figure 6 is a graph showing the charge and discharge life characteristics according to the C-rate of the battery prepared in Example 2 and Comparative Example 1. As the filling speed increases, the capacity decreases. The uncoated powder starts to fall from 2C at a rapid rate and drops rapidly from 4C, but the coated powder shows about 90% improvement even at 5C.

7 is a graph of charge and discharge life characteristics at 55 ° C. of a full cell using Comparative Examples 1, 2 and 3 as the positive electrode. 7 shows that the capacity reduction rate occurs rapidly in the case of LMO powder which is not coated in comparison with the cycle characteristics in the full cell, but drops rapidly after 100 cycles, but the coated one shows a gentle decrease rate, 0.5 wt% In case of ITO coating, the decreasing slope is more gentle than that in case of 0.8 wt%, and it can be confirmed that the characteristics are good.

Claims (12)

(1) mixing indium acetate and tin chloride in a solvent to form an ITO sol;
(2) mixing and drying the ITO sol and the positive electrode active material to form an ITO film on the surface of the positive electrode active material; And
(3) high temperature heat treatment of the positive electrode active material having the ITO film formed through the step (2) to crystallize the ITO to form a positive electrode active material powder coated with nano ITO particles;
Method for producing a cathode active material for a secondary battery comprising a. The spinel of claim 1, wherein the cathode active material is a spinel Li [Mn _{2 - x} M _x ] O ₄ having a cubic structure (M is Co, Ni, Mg, or Al, and 0 ≦ _x ≦ 0.1), and a spinel having a cubic structure. _{Li [Ni 0 .5 Mn 1 .5} -x M x] O 4 (M is Co, Ni, Mg or Al and 0≤x≤0.1) or _{LiM x Fe 1 -x PO 4 (} M having Olivine structure The manufacturing method of the positive electrode active material for secondary batteries whose Mn, Co or Ni, and 0 <= ≤ <1). The method of claim 1, wherein step (1) comprises:
(a) dispersing and heating an indium compound and a tin chloride compound in a propionic acid and butanol mixed solvent to prepare a first indium tin oxide sol;
(b) dispersing an indium compound and a tin chloride compound in a mixed solvent of dimethylformamide and butanol, adding nitric acid, and then heating and rapidly cooling to prepare a second indium tin oxide sol; And
(c) adding the first indium tin oxide sol to the second indium tin oxide sol while stirring to produce a mixed indium tin oxide sol.
Method for producing a cathode active material for a secondary battery comprising a. The process according to claim 1, wherein after step (3):
(4) The method of manufacturing a cathode active material for a secondary battery further comprising the step of post-heat treatment of the cathode active material powder coated with the nano ITO particles. The method of claim 1,
The solvent is at least one selected from the group consisting of ethanol, propanol, isopropanol, butanol, acetylacetone, ethyl acetate, dimethylformamide, ethanolamine, propionic acid and ethylene glycol. The method of claim 1,
ITO concentration of the ITO sol is 0.1 to 4% by weight of the manufacturing method of the positive electrode active material for a secondary battery. The method of claim 1,
The mixing ratio of the ITO sol and LMO in step (2) is 1: 10 to 1: 1 by weight ratio method for producing a positive electrode active material for secondary batteries. The method of claim 1,
The heat treatment of step (3) is a method of manufacturing a positive electrode active material for secondary batteries which is made of 400 to 700 ℃ under air or inert gas atmosphere. The method of claim 4, wherein
The post-heat treatment of step (4) is a method for producing a positive electrode active material for secondary batteries which consists of 200 to 400 ℃ in a reducing atmosphere. A method of manufacturing a slurry comprising: mixing a positive electrode active material, a conductive material, and a binder prepared by the method of any one of claims 1 to 9 to form a slurry; And
Applying the slurry to a thin film and vacuum drying to form an anode
Method for producing a positive electrode for a secondary battery comprising a. The method of claim 10,
The cathode active material is 70 to 97% by weight, the conductive material is 2 to 20% by weight, the binder is a method for producing a positive electrode for secondary batteries. Forming a positive electrode and a counter electrode prepared by the method of claim 10; And
Forming an electrolyte and a separator between the anode and the counter electrode
Method of manufacturing a secondary battery comprising a.

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