WO2010126185A1

WO2010126185A1 - Preparation method for olivine type cathode active material for lithium secondary battery, and lithium secondary battery using the same

Info

Publication number: WO2010126185A1
Application number: PCT/KR2009/002297
Authority: WO
Inventors: 김성배; 김창하; 김우성; 송기섭
Original assignee: 대정이엠 주식회사
Priority date: 2009-04-27
Filing date: 2009-04-30
Publication date: 2010-11-04
Also published as: WO2010126185A9; KR20100117895A

Abstract

The present invention relates to a method for preparing an olivine type cathode active material for a lithium secondary battery, and a lithium secondary battery using the same. The method for preparing an olivine type cathode active material for a lithium secondary battery of the present invention comprises: (S1) a step of preparing a specific manganese phosphate or phosphate iron manganese hydrate by coprecipitation; (S2) a step of press-molding a mixture comprising the manganese phosphate or manganese iron phosphate hydrate, lithium compound, and a carbon material to prepare a plasticizing precursor; and (S3) a step of plasticizing the plasticizing precursor. The preparation method of the present invention has an excellent reproducibility, and the cathode active material prepared has an improved capacity.

Description

Manufacturing method of olivine-type positive electrode active material for lithium secondary battery and lithium secondary battery using same

The present invention relates to a method for producing an olivine-type positive electrode active material for a lithium secondary battery capable of producing a high capacity olivine-type positive electrode active material with excellent reproducibility, and a lithium secondary battery using the same.

With the rapid development of the electronics, telecommunications, and computer industries, the rapid development of camcorders, mobile phones, notebook PCs, and the like, the demand for lithium secondary batteries as a power source capable of driving these portable electronic communication devices is increasing day by day. In particular, R & D is actively being conducted in Japan, Europe, and the United States as well as in Korea in relation to the application of electric vehicles, uninterruptible power supplies, power tools, and satellites as eco-friendly power sources.

Lithium cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of a lithium secondary battery. Currently, lithium nickel oxide (Li (Ni-Co-Al) O ₂ ) and lithium composite metal oxide (Li (Ni) are used as other layered positive electrode active materials. -Co-Mn) O ₂ ) and the like, in addition to the low-cost high-stable spinel lithium manganese oxide (LiMn ₂ O ₄ ) and olivine-type iron phosphate compound (LiFePO ₄ ) has been developed and commercialized.

Among these cathode active materials, lithium cobalt oxide and lithium nickel oxide have high energy density, but are mainly used as power sources for small household appliances such as mobile phones and notebook PCs due to problems of transition metal raw materials and safety issues. It is not suitable for large lithium secondary batteries such as electric vehicles.

Spinel-type lithium manganese oxide, which is currently being actively studied as a positive electrode active material for large lithium secondary batteries, has a low safety risk due to a rapid increase in terminal charge voltage and high thermal stability of the positive electrode active material itself in a charged state. Due to structural instability in the environment, aging due to the cycle progresses severely, and characteristics improvement is required to be applied as a power source of an electric vehicle requiring a lifespan characteristic of 10 years or more.

Currently, large-size lithium secondary batteries require high energy density and low price with excellent safety, long life, and olivine-type positive electrode active materials including iron attract attention. Lithium iron phosphate compound (LiFePO ₄ ), a typical olivine-type positive electrode active material, is a positive electrode active material having an electric capacity of about 150 to 160 mAh / g, but has an average operating voltage of 3.4 V, which is lower than other oxide-based positive electrode active materials, requiring high energy density. As a positive electrode active material for large lithium secondary batteries, it is not sufficient. On the other hand, lithium manganese phosphate compound (LiMnPO ₄ ), which is the same olivine compound, has a discharge voltage of 4.0 V similar to that of an oxide-based material, and thus, active research and development has recently been conducted to improve its characteristics. However, since LiMnPO ₄ is about 1000 times smaller in conductivity than LiFePO ₄ , it is known that LiMnPO ₄ is almost inert electrically when produced by a general method of manufacturing a positive electrode active material, so that discharge alone is almost impossible.

By the production process of LiMnPO ₄ it may include a solid phase method and a wet method, for the production of LiMnPO ₄ by the conventional method, only the high electric capacity of about 70 mAh / g even at a low current density of about 0.05C to FIG carbon composite material is It is obtained, and in general, the capacitance before and after 30 mAh / g is obtained. On the other hand, when manufacturing LiMnPO ₄ by the wet method, there are various reports, but it is reported that even up to 140 mAh / g depending on the manufacturing method.

However, compared to the wet method, since the solid state method is simple and the manufacturing process can be reduced and the production cost is generally adopted and used as a manufacturing process of the positive electrode active material, further research on the improved wet method continues.

For example, Japanese Laid-Open Patent Publication No. 2008-184346 discloses a method for producing LiMnPO ₄ powder having a size of 200 to 500 nm using an excess of Li ₃ PO ₄ . However, it is almost impossible to use industrially in the form of using about 40 times Li ₃ PO ₄ .

In addition, Japanese Patent Application Laid-Open No. 2007-119304 discloses a method for producing LiMnPO ₄ at low temperature under pressurized conditions through precipitation and reduction of Mn (OH) ₂ . However, the obtained electrolytic capacity of the LiMnPO ₄ positive electrode active material is about 40 mAh / g, which is insufficient in industrial use.

In addition, Japanese Laid-Open Patent Publication No. 2007-48612 discloses a method for producing LiMnPO ₄ by firing a raw material mixture recovered by spray drying after preparing a raw material mixture. The obtained capacitance of the LiMnPO ₄ positive electrode active material was 92mAh / g at 0.25C current density, while LiMnPO ₄ composited with 15% carbon had 130mAh / g at 0.12C current density, but the proportion of the positive electrode active material occupying at the positive electrode It is difficult to say that the proportion of the positive electrode active material is so low that the electrochemical property of the positive electrode active material itself is sufficiently improved to about 63%.

In addition, Japanese Patent Application Laid-Open No. 2007-35358 proposes an olivine-type positive electrode active material and a manufacturing method of several nm in order to improve the problem of using a nanometer-sized fine active material. However, the electrochemical characteristics of the obtained positive electrode active materials of LiFePO ₄ and LiFe _0.5 Mn _0.5 PO ₄ are not sufficient, such as 123 mAh / g and 80 mAh / g, respectively, at 0.1C current density.

On the other hand, Korean Patent Laid-Open Publication No. 10-2003-0006177 proposes a method for producing a positive electrode active material of LiFePO ₄ by producing iron phosphate hydrate by the precipitation method. However, it does not suggest raw materials other than iron phosphate hydrate.

In addition, Korean Patent No. 10-0805910 proposes a method for synthesizing an olivine-type positive active material having a specific surface area and suppressing a high volumetric energy density. Here, when preparing the iron phosphate hydrate, a process of continuously obtaining the iron phosphate hydrate slurry by supplying the aqueous solution of the raw material and the ammonia water at a constant speed is proposed. However, when ammonia water is used in the case of manganese phosphate hydrate or manganese phosphate-iron hydrate other than iron, there is a problem in that excellent electrochemical properties are not obtained due to plate crystal growth. In addition, it is proposed to increase the size of the secondary particles to increase the volume energy density of the positive electrode according to the increase in the tap density, but does not suggest a high rate charge-discharge characteristic change according to the increase in the secondary particle size.

As described above, when the LiMnPO ₄ is manufactured by the solid phase method, the manufacturing process is simple, but it is difficult to obtain excellent electrochemical properties, and when the wet method is used, good electrochemical properties are obtained, but the manufacturing process is complicated. Therefore, there is an urgent need for a new production method capable of industrially producing an olivine-type positive electrode active material having excellent battery characteristics with excellent reproducibility.

Therefore, the problem to be solved by the present invention is a method for preparing a positive electrode active material and a olivine-type positive electrode active material for a lithium secondary battery having excellent reproducibility and productivity, a simple manufacturing process, and a positive electrode active material prepared therefrom and a lithium secondary using the same It is to provide a battery positive electrode and a lithium secondary battery.

In order to solve the above problems, the manufacturing method of the olivine-type positive electrode active material for a lithium secondary battery of the present invention, (S1) step of preparing a manganese phosphate or manganese phosphate-iron hydrate represented by the formula (1) by the coprecipitation method; (S2) pressure-molding the mixture containing the manganese phosphate or manganese phosphate-iron hydrate, a lithium compound, and a carbon material to prepare a calcination precursor; And (S3) calcining the calcining precursor:

Formula 1

In Formula 1, 0 ≦ x ≦ 0.4, and 6 ≦ a <8.

The inventors of the present invention, when the manganese phosphate or manganese phosphate-iron hydrate represented by the formula (1) is prepared in the exact equivalent ratio by using the coprecipitation method and used in the production of a positive electrode active material, it is superior to LiMnPO ₄ or LiMnFePO ₄ prepared by the same It was found that chemical properties are expressed. In addition, it was found that by going through the pressure forming step, the possibility of direct contact with each reactant can be increased to induce a smooth solid state reaction and increase productivity.

In addition, the olivine-type positive electrode active material for a lithium secondary battery manufactured by the manufacturing method of the present invention may be represented by the following Chemical Formula 2:

Formula 2

In

Chemical Formula

2, 0 ≦ x ≦ 0.4.

The positive electrode active material prepared according to the manufacturing method of the present invention has better electrochemical properties than the positive electrode active material prepared by the conventional method.

The above-described positive electrode active material for a lithium secondary battery can be used in the production of a lithium secondary battery positive electrode and a lithium secondary battery including such a positive electrode.

In the method for producing an olivine-type positive electrode active material for a lithium secondary battery of the present invention, it is possible to manufacture a positive electrode active material having excellent electrochemical properties with a superior reproducibility and productivity by a simpler manufacturing method than before.

In addition, the olivine-type positive electrode active material prepared according to the present invention has better electrochemical properties than the positive electrode active material prepared by the conventional method.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a SEM photograph of a sintered precursor prepared according to Examples and Comparative Examples of the present invention. (A: Example 1, b: Example 2, c: Example 3, d: Comparative Example 1)

2 is a SEM photograph of the positive electrode active material prepared according to Examples and Comparative Examples of the present invention. (a: Example 1, b: Example 2, c: Example 3, d: Comparative Example 1)

3 is an X-ray diffraction pattern of the positive electrode active material prepared according to Examples 1-3 and Comparative Examples 1-2 of the present invention.

4 is an X-ray diffraction pattern of the positive electrode active material prepared according to Example 3 and Comparative Examples 3 to 4 of the present invention.

5 is a graph showing an initial charge and discharge curve of the positive electrode active material prepared according to Example 1, Comparative Example 2 and Comparative Example 4.

6 is a graph showing the initial charge and discharge curves of the positive electrode active material prepared according to Example 2, Example 3, Comparative Example 1 and Comparative Example 3.

7 is a graph showing an initial charge and discharge curve of the cathode active material of the present invention prepared according to Examples 4 to 8.

8 is a graph showing the discharge capacity ratio up to the 3.6 V point of the initial discharge capacity of the positive electrode active material of the present invention prepared according to Examples and Comparative Examples.

Hereinafter, the manufacturing method of the present invention will be described in detail. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

First, manganese phosphate or manganese phosphate-iron hydrate represented by Chemical Formula 1 is prepared by coprecipitation (step S1).

In preparing the olivine-type positive electrode active material according to the present invention, when using manganese phosphate or manganese phosphate-iron hydrate represented by the formula (1), the influx of impurities contained in each metal salt is limited, composition control at the molecular level This becomes possible, and the olivine type positive electrode active material of uniform crystal structure can be manufactured. In Formula 1, if x is out of the range, there is a problem that the operating voltage rise of the lithium manganese phosphate-iron cathode active material is limited. In Chemical Formula 1, more preferably 0 ≦ x ≦ 0.2.

The manganese phosphate or manganese phosphate-iron hydrate according to the present invention needs to be prepared in the correct equivalent ratio. Therefore, manganese phosphate or manganese phosphate-iron hydrate is prepared by coprecipitation which allows precise control of the equivalence ratio of the reactants. Coprecipitation can use any method used in the art without limitation.

More specifically, manganese metal salts, iron metal salts, and phosphate compounds are continuously added as a raw material reactant in a coprecipitation environment, and a slurry containing metal phosphate is continuously taken in the form of a reactant, followed by washing with water, filtration, and drying. To prepare manganese phosphate or manganese phosphate-iron hydrate represented by. As the metal salt, sulfate, nitrate, acetate, and the like may be used, and phosphoric acid may be used as the phosphorus compound, but is not limited thereto.

Next, pressure-molding the mixture containing the manganese phosphate or manganese phosphate-iron hydrate, a lithium compound and a carbon material to prepare a firing precursor (step S2).

The lithium compound is a raw material for producing an olivine-type positive electrode active material by reacting with the manganese phosphate or manganese phosphate-iron hydrate. Examples of the lithium compound usable in the present invention include LiOH.H ₂ O, Li ₂ CO ₃ , Li ₃ PO ₄ , and the like. Preferably Li ₃ PO ₄ can be used.

On the other hand, the carbon material is fired together in the production of the positive electrode active material in order to increase the conductivity of the olivine-type positive electrode active material. As a method of adding a carbon material, for example, carbon materials such as acetylene black and Ketjen black, carbon materials such as graphite, graphite and graphite are added directly, or an organic compound serving as a carbon source is dissolved in a solvent and then the solvent is removed to remove the carbon source. There exists a method of using the form which the organic compound to become uniformly disperse | distributed.

In the present invention, it is preferable to use an organic compound that is dissolved at a specific temperature range and is pyrolyzed in a subsequent calcination step. For example, organic acids such as adipic acid, ascorbic acid, stearic acid, citric acid, and mixtures thereof are preferable.

The content of additional carbon added to the positive electrode active material according to the present invention can be controlled by the amount of carbon source added, and preferably 2 parts by weight to 30 parts by weight with respect to 100 parts by weight of the positive electrode active material. If the carbon content is less than 2 parts by weight, the capacity improvement effect due to the conductivity is not sufficient, and if it is more than 30 parts by weight, the amount of the positive electrode active material is reduced, which is not preferable because of the reduction of the electric capacity when the positive electrode is configured.

On the other hand, in the present invention, "plastic precursor" means a molded article having a predetermined shape by continuously tableting a mixture containing manganese phosphate or manganese phosphate-iron hydrate, a lithium compound, and a carbon material using a high pressure molding machine.

The high pressure molding machine is not limited so long as it is a molding machine capable of molding a mixture of the raw material compound in powder form at a constant pressure into a high density and constant shape. The fired precursor produced by the high pressure molding machine preferably has a density of 1 to 5 g / cc. If the density is less than 1 g / cc, it is difficult to mold to a certain shape or take a long time, so that the productivity is not greatly improved. As the density of the firing precursor is low, the productivity improvement effect due to the densification is not large, and the contact of raw materials is limited. It is not preferable because uniform firing does not proceed efficiently. Density of more than 5 g / cc is undesirable because the molding time for high density is long and additional equipment or energy is required to apply high pressure.

The reason why the raw material mixture precursor molded at such a high density is used is as follows. Lithium compounds (LiOH · H ₂ O, Li ₂ CO ₃ ), which are used to fire general layered positive electrode active materials, are melted before and after 450 to 600 ° C., so that they may be uniformly mixed by a conventional solid phase mixing method. Firing is possible, but in the case of a lithium compound having a melting point higher than the firing temperature of the firing step described below (for example, Li ₃ PO ₄ usable in the present invention has a melting point of 837 ° C.), the solid phase reaction does not proceed smoothly. do.

Therefore, when the firing proceeds in the densified precursor state as described above, a smooth solid state reaction may be performed through direct contact between manganese phosphate or manganese phosphate-iron hydrate and a lithium compound. In addition, although most of the raw material compounds are nanometer-sized fine powders, the density of the mixture is remarkably low, and thus the amount of the raw material compounds to be injected into the ceramic firing vessel used for firing is small. Because it can be put a lot, the yield can be improved.

Optionally, in the process of forming at a high density, a thermoplastic polymer may be used as the binder. The thermoplastic polymer acts as a releasing agent for smoothly desorbing the precursor formed in the mold or jig and is thermally decomposed in the sintering step described later to serve as an additional carbon source. The amount of the thermoplastic polymer added is added to maintain the above-described content range of the carbon material, and is 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the positive electrode active material. If it is less than 0.1 part by weight, the release effect and carbon coating amount of the addition is small, it is not preferable. If it is more than 10 parts by weight, the release effect is sufficient, but in the sintering step to be described later inadequate gas generation and carbon contained more than necessary If configured as, there is a risk that leads to a reduction in capacitance is not preferable.

Next, the firing precursor is fired (step S3).

It is preferable to make baking temperature into the temperature range of 500-700 degreeC, for example. If the calcination temperature is less than 500 ° C., the olivine-type lithium composite metal compound is less likely to be produced. If the calcination temperature is more than 700 ° C., crystals grow more than necessary or some decomposition occurs, which is not preferable. Moreover, it is preferable to advance baking environment under inert atmosphere, such as nitrogen gas and argon gas. In particular, since iron contained in the firing precursor is divalent, it is not necessary to use a reducing gas such as hydrogen gas. In addition, it is preferable to make baking time into 5 to 24 hours, for example. If the firing time is less than 5 hours, there is a fear that it may not be obtained in a uniform olivine phase, and if it is more than 24 hours, productivity may be reduced industrially.

The olivine-type positive electrode active material of the present invention may be manufactured through the above manufacturing steps, and the prepared olivine-type positive electrode active material for lithium secondary battery of the present invention is represented by Chemical Formula 2. When x is outside the above range in Chemical Formula 2, the operation voltage rise is limited because it is similar to the lithium iron phosphate compound as described above. In Chemical Formula 2, more preferably 0 ≦ x ≦ 0.2.

The olivine-type positive electrode active material thus prepared is a form in which nanometer-level fine primary particles are aggregated, and the size and shape of the primary particles vary depending on the composition ratio of the metal phosphate and the coprecipitation environment.

The olivine-type positive electrode active material for a lithium secondary battery of the present invention, which may be manufactured by the above method, may be bonded to at least one surface of a positive electrode current collector using a binder to form a positive electrode of a lithium secondary battery. The binder resin and the positive electrode current collector may be used without limitation those conventionally used in the art.

In addition, the positive electrode for a lithium secondary battery of the present invention may be manufactured as a lithium secondary battery together with a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode. As the negative electrode, the separator and the electrolyte, those conventionally used in the art may be used without limitation.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

실시예 1Example 1

<인산 망간의 제조><Manufacture of Manganese Phosphate>

Ion exchange water purified from manganese sulfate (MnSO ₄ · H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O), and phosphoric acid (H ₃ PO ₄ ) so that the molar ratio of manganese, iron, and phosphorus is 1.0: 0.0: 1.0 It was dissolved in to prepare a metal aqueous solution and sodium hydroxide (NaOH) aqueous solution.

After adding the prepared aqueous metal solution at room temperature, the sodium hydroxide aqueous solution was added at a rate of 200 ml / min, and when the pH of the reaction solution reached the range of 5.9, manganese phosphate (Mn ₃ (PO ₄ ) ₂ · 6H ₂ O) precipitation of hydrates occurs. From then on, while maintaining the pH in the reactor at a steady state, a slurry containing manganese phosphate hydrate was continuously prepared by supplying an aqueous metal solution and an aqueous sodium solution at a constant rate. The slurry was washed with water using a centrifugal filter and filtered, and the obtained manganese phosphate hydrate powder was dried at 80 DEG C for at least 24 hours to prepare manganese phosphate hydrate.

<소성 전구체의 제조><Production of Plastic Precursor>

Stearic acid (SA, C ₁₈ H ₃₆ O ₂ ) and polyethylene glycol (PEG) were uniformly ground and mixed with the obtained manganese phosphate hydrate, lithium phosphate (Li ₃ PO ₄ ) and a carbon source, and then 30 mm in diameter and 120 mm in length. 30 g was put into the mold of, and pressure-molded by the pressure of 10 atmospheres to produce a cylindrical plastic precursor. The bulk density of the raw mixture was 1.42 g / cc. Carbon source SA and PEG were added in an amount of 3 parts by weight based on the final positive electrode active material. The resulting fired precursor was molded into a cylindrical shape of 30 mm diameter and 20 mm length with a density of 2.83 g / cc.

<양극 활물질의 제조><Production of Anode Active Material>

The calcined precursor obtained was calcined at 550 ° C. for 10 hours using a calcining furnace capable of temperature control. Thereafter, a LiMnPO ₄ positive electrode active material having an average particle diameter adjusted by pulverization and classification was prepared.

After that, characteristics of the obtained positive electrode active material were evaluated, and the results are summarized in Tables 1 and 2.

실시예 2Example 2

An aqueous metal solution prepared by adjusting manganese sulfate (MnSO ₄ H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O), and phosphoric acid (H ₃ PO ₄ ) so that the molar ratio of manganese, iron, and phosphorus is 0.8: 0.2: 1.0 A manganese phosphate-iron hydrate ((Mn _0.8 Fe _0.2 ) ₃ (PO ₄ ) ₂ .6.4H ₂ O) was prepared in the same manner as in Example 1 to prepare a LiMn _0.8 Fe _0.2 PO ₄ cathode active material.

실시예 3Example 3

A metal solution prepared by adjusting manganese sulfate (MnSO ₄ H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O), and phosphoric acid (H ₃ PO ₄ ) so that the molar ratio of manganese, iron, and phosphorus is 0.6: 0.4: 1.0 A manganese phosphate-iron hydrate ((Mn _0.6 Fe _0.4 ) ₃ (PO ₄ ) ₂ .6.8H ₂ O) was prepared in the same manner as in Example 1 to prepare a LiMn _0.6 Fe _0.4 PO ₄ positive electrode active material.

실시예 4 ~ 8Examples 4-8

The molar ratios of manganese, iron and phosphorus in manganese sulfate (MnSO ₄ H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O) and phosphoric acid (H ₃ PO ₄ ) are 0.81: 0.19: 1.0 and 0.82: 0.18: 1.0, respectively. , Except that the aqueous metal solution adjusted to 0.83: 0.17: 1.0, 0.84: 0.16: 1.0, 0.85: 0.15: 1.0 was prepared in the same manner as in Example 1 to prepare manganese phosphate-iron hydrate, respectively, LiMn _0.81 Fe _0.19 PO ₄ , LiMn _0.82 Fe _0.18 PO ₄ , LiMn _0.83 Fe _0.17 PO ₄ , LiMn _0.84 Fe _0.16 PO ₄ , LiMn _0.85 Fe _0.15 PO ₄ positive electrode active material was prepared.

비교예 1Comparative Example 1

An aqueous metal solution prepared by adjusting manganese sulfate (MnSO ₄ H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O), and phosphoric acid (H ₃ PO ₄ ) so that the molar ratio of manganese, iron, and phosphorus is 0.4: 0.6: 1.0 Manganese phosphate-iron hydrate ((Mn _0.4 Fe _0.6 ) ₃ (PO ₄ ) ₂ .7.2H ₂ O) was prepared in the same manner as in Example 1, except that the firing temperature was 600 ° C. In the same manner as the LiMn _0.4 Fe _0.6 PO ₄ positive electrode active material was prepared.

비교예 2Comparative Example 2

An aqueous metal solution in which manganese sulfate (MnSO ₄ · H ₂ O), iron sulfate (FeSO ₄ · 7H ₂ O), and phosphoric acid (H ₃ PO ₄ ) is adjusted so that the molar ratio of manganese, iron, and phosphorus is 0.0: 1.0: 1.0 LiFePO ₄ positive electrode active material was prepared in the same manner as in Example 1, except that iron phosphate hydrate (Fe ₃ (PO ₄ ) ₂ .8H ₂ O) was prepared in the same manner as in Example 1, and the firing temperature was set to 650 ° C. Was prepared.

비교예 3Comparative Example 3

The manganese phosphate compound (Mn ₃ (PO ₄ ) ₂ .6H ₂ O) obtained in Example 1 and the iron phosphate hydrate (Fe ₃ (PO ₄ ) ₂ .8H ₂ O) obtained in Comparative Example 2 were used except for using a raw material compound. In the same manner as in Example 3, a LiMn _0.6 Fe _0.4 PO ₄ positive electrode active material was prepared.

비교예 4Comparative Example 4

It produced and evaluated similarly to Example 1 except having baked in the powder state without shape | molding with a press molding machine.

특성평가Characteristic evaluation

1. 분체 특성1. Powder Characteristics

(1) 평균입경 및 밀도(1) Average particle diameter and density

The average particle diameter and bulk density (molding density) of the fired precursors prepared according to the Examples and Comparative Examples were measured, and the results are shown in Table 1, and the average particle diameter and the tap density of the positive electrode active materials prepared from the fired precursors were measured. The results are shown in Table 2.

The average particle size was measured using a particle size distribution analyzer (Malvern, Mastersizer 2000E) and dispersed using ultrasonic waves to obtain an average particle diameter D ₅₀ by laser scattering. The bulk density was measured from the volume after 5 strokes using a 100 ml measuring cylinder, and the tap density was measured from the volume change before and after 500 strokes. In addition, the molding density was measured from the volume change after molding.

Table 1

division	Furtherance	Molding	Average particle size (d ₅₀ -㎛)	Density (g / cc)
Example 1	Mn ₃ (PO ₄ ) ₂ · 6H ₂ O	Molded body	0.34	2.83
Example 2	_{_{_{(Mn 0.8 Fe 0.2) 3 (}}} PO 4) 2 · 6.4H 2 O	Molded body	0.67	3.21
Example 3	_{_{_{(Mn 0.6 Fe 0.4) 3 (}}} PO 4) 2 · 6.8H 2 O	Molded body	0.58	2.94
Comparative Example 1	_{_{_{(Mn 0.4 Fe 0.6) 3 (}}} PO 4) 2 · 7.2H 2 O	Molded body	0.65	3.05
Comparative Example 2	Fe ₃ (PO ₄ ) ₂ · 8H ₂ O	Molded body	0.45	3.45
Comparative Example 3	0.6Mn ₃ (PO ₄ ) ₂ · 6H ₂ O + 0.4 Fe ₃ (PO ₄ ) ₂ · 8H ₂ O	Molded body	0.38	2.94
Comparative Example 4	Mn ₃ (PO ₄ ) ₂ · 6H ₂ O	powder	0.34	1.42

TABLE 2

division	Furtherance	Average particle size (d ₅₀ -㎛)	Tap density (g / cc)
Example 1	LiMnPO ₄	5.52	1.65
Example 2	LiMn _0.8 Fe _0.2 PO ₄	2.78	2.00
Example 3	LiMn _0.6 Fe _0.4 PO ₄	1.86	1.69
Comparative Example 1	LiMn _0.4 Fe _0.6 PO ₄	3.21	2.02
Comparative Example 2	LiFePO ₄	1.86	1.68
Comparative Example 3	LiMn _0.6 Fe _0.4 PO ₄	4.30	1.05
Comparative Example 4	LiMnPO ₄	3.91	1.07

As shown in Table 2, when the average particle diameter of the positive electrode active material particles is viewed, the olivine-type positive electrode active materials prepared in Examples and Comparative Examples are regarded as secondary particles in which fine particles are aggregated, not nanometer-sized fine particles.

On the other hand, when the tap densities of Example 1, Comparative Example 4, and Example 3 and Comparative Example 3 having the same composition of the positive electrode active material, the tap densities of Examples 1 and 3 are larger than the comparative examples, It can be seen that the positive electrode active material of the example prepared from the single calcined precursor has excellent powder characteristics compared to the positive electrode active material of the comparative example.

(2) SEM 사진 평가(2) SEM photo evaluation

SEM (HP, 8564E) photographs were taken to confirm average particle diameters of the phosphate compounds of Mn and Fe and the positive electrode active materials obtained in Examples and Comparative Examples. Calcined precursor, c: calcined precursor of Example 3, d: calcined precursor of Comparative Example 1) and FIG. 2 (a: positive electrode active material of Example 1, b: positive electrode active material of Example 2, c: positive electrode of Example 3 Active material, d: positive electrode active material of Comparative Example 1).

As shown in FIG. 1, it can be seen that as the iron content increases, primary particles (fine particles) grow and form as needles. In addition, as shown in Figure 2, it can be seen that the shape of the metal phosphate as a raw material and the size of the primary particles (fine particles) are maintained as it is.

(3) X-선 회절분석(3) X-ray diffraction analysis

In order to confirm the crystal structure of the positive electrode active material obtained according to the Examples and Comparative Examples, X-ray diffraction analysis was performed, and the results are shown in FIG. 3. In addition, X-ray diffraction patterns of the positive electrode active material obtained from Example 3, Comparative Example 3, and Comparative Example 4 having the same composition but completely different manufacturing methods are shown in FIG. 4.

Looking at Figure 3, it can be confirmed that the positive electrode active material was prepared according to the embodiment and the comparative example. In addition, as the substitution amount of Fe increases, the diffraction angle 2θ shifted to the right side according to the difference in the ion radius of Mn and Fe ions.

However, referring to FIG. 4, it can be seen that there is a difference in firing completeness of Comparative Example 3, which has the same positive electrode active material composition as Comparative Example 4, which has undergone a direct firing step in powder form without introducing a firing precursor, compared to Example 3. Specifically, in the case of firing using a mixed powder of a raw material compound (Comparative Example 3) and in the case of powder firing (Comparative Example 4) as compared with the case of using the press-formed product as a firing precursor, impurities, that is, unreacted Li _It was confirmed that ₃ PO ₄ remained significantly, it was confirmed that the crystallinity is insufficient. In addition, it was confirmed that the crystallinity was more excellent in the case of using a composite phosphate of Mn and Fe than when the raw material compounds of Mn and Fe were mixed and calcined.

2. 전기화학적 특성2. Electrochemical Properties

In order to evaluate the initial specific capacity and initial efficiency of the olivine positive electrode active material obtained in Examples 1 to 8 and Comparative Examples 1 to 4, it was mixed with NMP solution in which teflonized acetylene black and binder PVDF were dissolved as a positive electrode active material and a conductive material. To prepare a slurry. The mass ratio of the positive electrode active material, the conductive material and the binder in the slurry was 80:10:10. The slurry was applied onto a 30 μm Al current collector, dried, compressed to a constant thickness, and punched out to a diameter of 13 mm to prepare a positive electrode.

Using the obtained positive electrode and lithium foil as a negative electrode, the coin type battery of the 2032 standard was manufactured through the 20-micrometer-thick separator. At this time, a 1.2 mol LiPF ₆ solution of a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 3) was used as the electrolyte. The battery was charged with a current density of 0.2 C in a voltage range of 25 ° C., 2.0 to 4.5 V (2.0 to 4.0 V in Comparative Example 2) using a charge / discharge cycle device, and charging was performed under constant current-constant voltage conditions (end of charge 0.02 C). ), The discharge was measured in the charge and discharge capacity under constant current conditions and the results are shown in Table 3.

The initial charge and discharge curves of the positive electrode active material prepared according to Example 1, Comparative Example 2 and Comparative Example 4 and the initial charge and discharge curves of the positive electrode active material prepared according to Example 2, Example 3, Comparative Example 1 and Comparative Example 3 5 and 6, respectively.

In addition, the initial charge and discharge capacity of the positive electrode active material prepared according to Examples 4 to 8 were evaluated in the same manner as above, and the results are shown in Table 4, and the initial charge and discharge curves are shown in FIG. 7.

TABLE 3

division	1 ^st charging capacity (mAh / g)	1 ^st discharge capacity (mAh / g)	1 ^st efficiency (%)	Constant voltage charge rate (%)	3.6V discharge capacity ratio (%)
Example 1	117.7	109.1	92.7	14.7	66.1
Example 2	122.4	118.2	96.6	6.9	59.2
Example 3	136.8	133.9	97.9	6.7	55.7
Comparative Example 1	139.0	134.7	96.9	5.4	36.4
Comparative Example 2	150.0	146.6	97.7	3.8	0.0
Comparative Example 3	127.0	113.3	89.2	28.0	49.2
Comparative Example 4	57.2	47.0	82.2	62.9	54.7

Table 4

division	Furtherance		1 ^st charging capacity (mAh / g)	1 ^st discharge capacity (mAh / g)	1 ^st efficiency (%)	Constant voltage charge rate (%)	3.6V discharge capacity ratio (%)
Example 4	LiMn _0.81 Fe _0.19 PO ₄	122.7	118.1	96.2	9.1	66.9
Example 5	LiMn _0.82 Fe _0.18 PO ₄	123.3	118.4	96.0	9.5	70.5
Example 6	LiMn _0.83 Fe _0.17 PO ₄	124.6	120.4	96.6	10.2	71.8
Example 7	LiMn _0.84 Fe _0.16 PO ₄	136.2	131.3	96.4	13.2	72.4
Example 8	LiMn _0.85 Fe _0.15 PO ₄	137.9	132.8	96.3	13.1	72.7

As can be seen from Table 3, the positive electrode active material prepared by using the press-molded body as the firing precursor according to Example 1 of the present invention has excellent electrochemical properties compared to the positive electrode active material prepared by using the powder precursor according to Comparative Example 4 I could see that. In addition, it was found that the positive electrode active material of Example 3 has excellent electrochemical properties compared to the positive electrode active material of Comparative Example 3 prepared by simply mixing phosphate of Mn and Fe.

As can be seen from Table 3, the capacity ratio of 3.6 V or more of discharge area was determined according to the Mn content. When Mn was 100%, the discharge capacity ratio of 66.1% was obtained, and the Fe substitution amount was 20%, 40%, 60 The percentage increased to 59.2%, 55.7% and 36.4%, respectively. In the case of 100% substitution with Fe (Comparative Example 2), the 3.6V discharge capacity ratio was 0%.

Furthermore, as can be seen from Examples 4 to 8 and FIG. 7, when the composite phosphate of Mn and Fe of the present invention is used as a raw material, it is possible to control the content of Fe in 0.1 mol units, thereby preparing a cathode active material having an accurate equivalent ratio. Since it is possible, the manufacturing method of this invention is excellent in reproducibility.

In addition, the 3.6V discharge capacity ratio according to the substitution amount of Fe is shown in Fig. 8, preferably when the molar ratio of Fe is 0.2 or less, more preferably 0.14 to 0.15, more excellent electrochemical properties are obtained You can see that.

Claims

(S1) preparing manganese phosphate or manganese phosphate-iron hydrate represented by Formula 1 by coprecipitation;

(S2) pressure-molding the mixture containing the manganese phosphate or manganese phosphate-iron hydrate, a lithium compound, and a carbon material to prepare a calcination precursor; And

(S3) calcining the calcined precursor

Method for producing an olivine-type positive electrode active material for a lithium secondary battery comprising:

[Formula 1]

In Formula 1, 0 ≦ x ≦ 0.4, and 6 ≦ a <8.
The method of claim 1,

In the step (S2), the lithium compound is any one selected from the group consisting of lithium hydroxide, lithium carbonate and lithium phosphate or a mixture of two or more thereof.
The method of claim 1,

The carbon material is any one selected from the group consisting of adipic acid, ascorbic acid, stearic acid and citric acid or a mixture of two or more thereof.
The method of claim 1,

Before the pressing in the step (S2), the mixture is a method for producing an olivine-type positive active material for a lithium secondary battery, characterized in that it further comprises a thermoplastic polymer binder.
The method of claim 1,

The firing precursor in the step (S2) has a density of 1 ~ 5 g / cc olivine-type positive electrode active material for a lithium secondary battery characterized in that it has a density.
The method of claim 1,

Firing in the step (S3) is a manufacturing method of an olivine-type positive electrode active material for a lithium secondary battery, characterized in that carried out at a temperature of 500 ~ 700 ℃.
An olivine-type positive electrode active material for a lithium secondary battery prepared by the method of claim 1 and represented by the following Chemical Formula 2:

[Formula 2]

In Chemical Formula 2, 0 ≦ x ≦ 0.4.
A positive electrode current collector; And a positive electrode active material layer formed on at least one surface of the positive electrode current collector and including a positive electrode active material and a binder.

The cathode of a lithium secondary battery, wherein the cathode active material is a cathode active material manufactured by the method of any one of claims 1 to 6.
In a lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode,

Lithium secondary battery, characterized in that the positive electrode is a positive electrode according to claim 8.