KR20010002210A - Positive active material for secondary battery and method of preparing thereof - Google Patents

Abstract

PURPOSE: An active anode material for a secondary lithium battery and a manufacturing method thereof are provided to improve a life feature in a higher temperature by controlling a shape of a primary particle of LixMnO2 or LixMn2O4 power. CONSTITUTION: In a method for manufacturing an active anode material for a secondary lithium battery, a lithium acetate solution and a manganese acetate solution are melted in a solvent by 1:2 mole rate. The solvent includes a methyl alcohol. An oxalic acid is added to the mixing solution and water is evaporated at 50 deg.C to obtain a gel-solution. The gel-solution is heated at 300 through 800 deg.C for 6 through 8 hours and slowly is cooled. A primary particle of the active anode material for a secondary lithium battery has a cylindrical or hexagonal shape. A particle size of the active anode material is less than 1 micrometer.

Description

A cathode active material for a lithium secondary battery and a manufacturing method thereof {POSITIVE ACTIVE MATERIAL FOR SECONDARY BATTERY AND METHOD OF PREPARING THEREOF}

Industrial use field

The present invention relates to a cathode active material for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a cathode active material for a lithium secondary battery with improved temperature life characteristics by controlling the shape of surface primary particles of a cathode active material for a lithium secondary battery, and a method for manufacturing the same. will be.

Conventional technology

As cordless portable devices such as video cameras, cellular phones, personal computers, and the like become smaller, lighter, and higher in functionality, demand for higher energy density is increasing for batteries used as driving power sources. In particular, the rechargeable lithium secondary battery is expected to have a high energy density, and research and development are being actively conducted at home and abroad.

In general, batteries include primary batteries used for single use, such as manganese batteries, alkaline batteries, mercury batteries, and silver oxide batteries, Ni-MH (nickel-metal hydride) batteries using lead-acid batteries, and metal hydrides as negative active materials, and nickel Rechargeable secondary batteries such as cadmium batteries, lithium metal batteries, lithium ion batteries (LIB), lithium group batteries such as lithium polymer batteries (LPB), and fuel cells , Solar cells and the like.

The dual primary battery has a problem of causing environmental pollution because it has a small capacity, a short lifespan, and is not recycled, whereas a secondary battery can be recharged and used for a long time, has excellent performance and efficiency, and generates waste. It is also excellent in environmental protection.

Lithium secondary batteries use a material capable of intercalation and deintercalation of lithium ions as a negative electrode and a positive electrode, and an organic electrolyte or polymer electrolyte capable of moving lithium ions between the positive electrode and the negative electrode. It is prepared by charging, and produces electrical energy by oxidation and reduction reaction when lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode.

Lithium secondary batteries use lithium metal or carbon as an anode material, and a chalcogenide compound of a metal capable of inserting and desorbing lithium ions is used as a cathode material. In the case of using lithium metal as a negative electrode material, there is a risk of explosion due to precipitation of lithium on a dendrite, and the charge and discharge efficiency of the lithium electrode is low, and thus the negative electrode material is being replaced with carbon material instead of lithium metal.

On the other hand, chromium oxide and manganese dioxide (MnO2) were initially used as anode materials. However, due to problems with charging and discharging efficiency and safety, a composite such as LiCoO2, LiMn2O4, LiNi1-xCoxO2 (0 <x <1), LiMnO2, etc. Metal oxides are being studied.

The development of manganese positive electrode active materials such as LiMnO2 and LiMn2O4 or cobalt positive electrode active materials such as LiCoO2 was mainly made, but the capacity was limited to 120 mAh / g and 160 mAh / g, respectively, based on 4.3 V. . In addition, LiCoO2 is widely used because it exhibits electrical conductivity of about 10 ⁻² to 1 S / cm, high battery voltage, and excellent electrode characteristics at room temperature, but has a problem of low stability at high rate charge and discharge.

On the other hand, research on the nickel-based positive electrode active material showing a discharge capacity of 20% or more higher than that of the cobalt-based positive electrode active material has been actively conducted.

Lithium secondary batteries using nickel-based positive electrode active materials are highly likely to form high capacity batteries due to the characteristics of large discharge capacity, but low life characteristics and structural instability of materials such as LiNi1-xCoxO2 (0 <x <1) active materials Due to the development of a nickel-based positive electrode active material to overcome these disadvantages is required.

In case of LiNiO2, the charge / discharge capacity is higher than 200 mAh / g when discharged at 0.1 C based on 4.3 V charging, and the initial discharge capacity is about 180 mAh / g when discharged at 1.0 C. Due to the instability of the structure that changes from monoclinic) structure to hexagonal structure, the capacity during the continuous charging and discharging is drastically reduced, and it is impossible to use in actual batteries due to poor life characteristics and it is difficult to synthesize.

Meanwhile, manganese-based active materials such as LiMnO 2 and LiMn 2 O 4 are easy to synthesize, are relatively inexpensive, and have the least pollution to the environment.

However, LixMnO2 or LixMn2O4 (0 <x) obtained by mixing Li2CO3 and MnO2, which is a conventional manufacturing method, and then adding a solvent such as ethanol or water and then grinder-mixing the mixture in a mortar stirrer at about 700 to 900 ° C ≤1.5), the capacity is small and the discharge capacity decreases rapidly at high rate charge and discharge, and the capacity decrease rate is small as the cycle progresses at room temperature, but when continuously charged and discharged at high temperature, manganese is eluted into the electrolyte and Mn ³⁺ is Mn. ^{Disproportionation} of ⁴⁺ and Mn ²⁺ causes the battery life to deteriorate rapidly within the first 10 cycles.

The present invention is to provide a cathode active material for a lithium secondary battery that improves the life characteristics at high temperature by controlling the shape of the primary particles of LixMnO2 or LixMn2O4 (0 <x ≤ 1.5) powder to solve the above problems.

Another object of the present invention is to provide a method for producing the same.

Figure 1 shows a SEM photograph of the positive electrode active material powder prepared in Example 1.

Figure 2 shows a SEM photograph of the positive electrode active material powder prepared in Comparative Example 1.

Figure 3 shows a SEM photograph of the positive electrode active material powder prepared in Comparative Example 2.

Figure 4 is a graph showing the charge and discharge characteristics evaluation for the positive electrode active material powder prepared in Example 1 and the charge and discharge characteristics evaluation for the positive electrode active material powder prepared by Comparative Examples 1 and 2.

In order to achieve the above object, the present invention, by controlling the shape of the primary particles, LixMnO2 or LixMn2O4 (0 <x≤1.5), which is a positive electrode active material for lithium secondary batteries whose spherical particles are round ellipses or hexagonal shapes of primary particles ).

In addition, the lithium acetate (Li-acetate) solution and manganese acetate (Mn-acetate) solution is dissolved in a solvent such as methanol solution in a 1: 2 molar ratio, this mixed solution is added to the water at 50 ℃ by adding oxalic acid (oxalic acid) LixMnO2 or LixMn2O4, which is a positive electrode active material for a lithium secondary battery, includes evaporating a gel-solution to obtain a gel-solution, and thermally cooling the gel-solution at 300 to 800 ° C. for 6 to 8 hours. 0 <x≤1.5) is provided.

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

LixMnO2 or LixMn2O4 (0 <x≤1.5) prepared in a round ellipse or hexagon in the shape of primary particles has a large particle size distribution because of the large particle size of the cathode active material. As a result, the primary particle shape is mainly octahedral. In this case, after prolonged charging and discharging at high temperature, the battery life within the initial 10 cycles is due to the disproportionation reaction of Mn ³⁺ into Mn ⁴⁺ and Mn ²⁺ due to the instability of the particles. This deteriorates sharply.

However, in the form of the powder made of the sol-solution, the octagonal shape disappears, mainly round, and other hexagons form, and the particle size distribution is small, resulting in stable particle shape, and thus the cathode active material can achieve structural stability. It is possible to provide a positive electrode active material for a lithium secondary battery with a small drop in capacity even during long time charge and discharge at high temperatures.

The shape of the primary particles of this active material is preferably a spinel system having a round ellipse shape or a hexagonal shape.

In addition, when the particle shape is a round ellipse or hexagon, the disproportionation reaction of Mn ³⁺ to Mn ⁴⁺ and Mn ²⁺ hardly occurs, so that the capacity decrease can be reduced.

At this time, the particle size is preferably 1 micron or less.

On the other hand, in order to prepare the LixMnO2 or LixMn2O4 (0 <x ≤ 1.5) as a starting material, a lithium acetate solution and a manganese acetate solution is dissolved using a solvent in a molar ratio of 1: 2. The solvent may be a suitable solvent such as methanol, ethanol, water, acetone.

Oxalic acid is added to the mixed solution prepared as described above to 5 to 10% by weight to evaporate water or solvent at 50 ℃ to obtain a gel-solution.

When the gel solution is heat-treated at 300 to 800 ° C. for 6 to 8 hours and then slowly cooled, LixMnO 2 or LixMn 2 O 4 (0 <x ≦ 1.5), which is a cathode active material for lithium secondary batteries having rounded ellipses or hexagons, may be prepared. .

Hereinafter, preferred examples are provided to aid in understanding the present invention.

However, these examples are only presented to aid the understanding of the present invention, and the present invention is not limited to the following embodiments.

Example 1

Lithium acetate and manganese acetate were dissolved in methanol solution in a molar ratio of 1: 2. A small amount of oxalic acid was added to this mixed solution, and then water was evaporated to obtain a gel-solution.

After heat-treating this gel-solution for 15 hours at 750 degreeC, it cooled slowly and obtained LiMn2O4 which is a positive electrode active material for lithium secondary batteries.

Comparative Example 1

Li 2 CO 3 and MnO 2 are uniformly mixed in a molar ratio of 1: 2. The mixture was calcined at 750 ° C. for 24 hours and then slowly cooled to room temperature to obtain LiMn 2 O 4 powder.

These powders were sieveed using a sieve group with an average particle size of 25 microns to obtain LiMn 2 O 4 powder, which is a cathode active material for a lithium secondary battery.

Comparative Example 2

LiMn 2 O 4 powder, which is a cathode active material for a lithium secondary battery, was manufactured in the same manner as in Comparative Example 1, except that the average particle size was 50 microns when sieving.

FIGS. 1,2 and 3, which are SEM photographs showing the shape of surface particles, show the shape of the particles of the powders prepared in Example 1 and Comparative Examples 1,2.

As shown in FIG. 1, the cathode active material powder synthesized in Example 1 shows a small particle size distribution in the upper figure of FIG. 1, and the particle shape of the cathode active material is mainly spherical in the lower figure of FIG. 1. I can see that there is.

FIG. 2 shows the contrast between the larger and smaller particles in the top picture of FIG. 2. In the middle and bottom pictures of FIG. 2, which are enlarged pictures, the middle picture of FIG. The bottom figure of FIG. 2 which shows the square or the octagon of which the shape is almost angled but the size of the particle is small shows that the shape is spherical.

FIG. 3 shows the shape of particles having a large particle size distribution in the top picture of FIG. 3, and the shape of the shape is angled in the middle and bottom pictures of FIG. 3.

Therefore, it can be said that in the present invention, the cathode active material having a small particle size and a small particle size distribution mainly exhibits a spherical shape. As a result of the SEM photograph, the positive electrode active material powder prepared using the gel-solution of Example 1, as shown in FIG. 1, the shape of the powder is completely round and made of small particles.

Charge / discharge characteristic evaluation

The LiMn 2 O 4 powders prepared by the methods of Example 1 and Comparative Examples 1 and 2 were configured with a half cell to evaluate charge and discharge characteristics.

The half cell was PVDF as a binder, and the weight ratio of the powder LixMn2O4: PVDF: carbon black was mixed in a ratio of 92: 4: 4, and then mixed until a uniform paste was added with a certain amount of NMP.

The paste was coated on an aluminum foil at a thickness of 300 microns by using a doctor-blade machine, followed by evaporation of NMP at 150 ° C., and compression to a constant pressure to prepare a cathode paste.

The cathode paste prepared to construct the lithium battery was cut into circles and then attached to a coin battery cap. The negative electrode lithium foil was also cut to the same size as the positive electrode and then pressed into a nickel foil in a coin battery cap.

Celgard was used as a separator and ethylene carbonate / dimethyl carbonate and LiPF6 were used as electrolytes.

The cathode active materials prepared as described above were evaluated for charge and discharge characteristics at 50 ° C. for 20 cycles.

4A, 4B and 4C are graphs showing charge and charge characteristic evaluations of the positive electrode active materials prepared in Example 1 and Comparative Examples 1 and 2;

In FIG. 4A, the capacity decrease after 20 cycles of charge and discharge shows a decrease of about 1/3 from about 120 mAh / g to about 80 mAh / g. However, in FIGS. 4B and 4C, the capacity decrease is about 60 at about 120 mAh / g. The mAh / g roll shows a decrease of almost 1/2.

Thus, it was shown by Example 1 that the LiMn 2 O 4 powder prepared using the gel-solution had better high temperature life characteristics than the powders prepared by Comparative Examples 2 and 3. This is believed to be attributable to the small particle size distribution of the powder prepared in Example 1 and its shape being spherical or hexagonal.

In addition, even when the charge and discharge characteristics were evaluated for 5 cycles and 10 cycles, the capacity decrease of the positive electrode active material powder prepared in Example 1 was smaller than that of the powders prepared in Comparative Examples 2 and 3.

The LixMnO2 or LixMn2O4 (0 <x≤1.5) positive electrode active material prepared so that the particle size distribution has a small particle size of less than 1 micron and has a spherical or hexagonal shape by controlling the particle shape prepared in the present invention is high temperature In the case of long-term use, the capacity decrease is smaller than that of conventional materials, and thus it is possible to provide a cathode active material for a lithium secondary battery having excellent life characteristics at high temperature and a long time.

In addition, the LixMnO2 or LixMn2O4 (0 <x≤1.5) powder having improved high temperature capacity characteristics as described above may be provided using a gel-solution to provide a method of manufacturing a cathode active material for a lithium secondary battery.

Claims (9)

The positive electrode active material for lithium secondary batteries, characterized in that the shape of the primary particles is a spinel type having a round ellipse or hexagonal shape. The method of claim 1, The cathode active material for a lithium secondary battery is LixMnO 2 or LixMn 2 O 4 (0 <x ≦ 1.5). The method of claim 1, The cathode active material for a lithium secondary battery having a particle size of the cathode active material is 1 micron or less. In the method of manufacturing the positive electrode active material for a lithium secondary battery, (a) dissolving a lithium acetate (Li-acetate) solution and a manganese acetate (Mn-acetate) solution in a solvent; (b) adding oxalic acid to the mixed solution and evaporating water to obtain a gel-solution; (c) slow cooling the gel-solution after heat treatment. Method for producing a positive electrode active material for lithium secondary batteries comprising a. The method of claim 4, wherein The positive electrode active material for lithium secondary batteries is LixMnO2 or LixMn2O4 (0 <x≤1.5) The manufacturing method of the positive electrode active material for lithium secondary batteries. The method of claim 4, wherein The manufacturing method of the positive electrode active material for lithium secondary batteries which is a spinel type which has a round ellipse form or a hexagonal form of a primary particle. The method of claim 4, wherein The particle size of the positive electrode active material is a method for producing a positive electrode active material for lithium secondary batteries of 1 micron or less. The method of claim 4, wherein A method of manufacturing a cathode active material for a lithium secondary battery, comprising the step of (b) evaporating water at 50 ° C. to obtain a gel-solution. The method of claim 4, wherein In (c), the heat treatment temperature is 300 to 800 ° C. A method for producing a cathode active material for a lithium secondary battery.