KR100984586B1 - Method of manufacturing lithium iron phosphate - Google Patents

Abstract

The present invention comprises the steps of (a) FeSO ₄ , FeCO ₃ , and FeO by mixing at least one Fe ²⁺ containing compound selected from the group consisting of lithium salt and phosphate to prepare a mixture; And (b) relates to a method for producing LiFePO ₄ comprising the step of firing the mixture of step (a) in an inert or reducing atmosphere. The present invention also relates to a secondary battery comprising the LiFePO ₄ and Manufacture of LiFePO ₄ as a cathode active material prepared by the above method.

LiFePO ₄ according to the present invention is an iron (Fe) precursor compound using an inexpensive Fe ²⁺ containing compound and using a solid state reaction (solid state reaction), mass production is easy, economical and the occurrence of side reactions It can be suppressed as much as possible. In addition, toxic by-products are not emitted, thereby improving safety.

Lithium iron phosphate composite oxide (LiFePO4), electrode active material, secondary battery

Description

Manufacturing Method of Lithium Iron Phosphate Composite Oxide (Li フ ｅＰＯ₄) {METHOD OF MANUFACTURING LITHIUM IRON PHOSPHATE}

1A is an X-ray diffraction analysis (XRD) pattern diagram of a LiFePO ₄ powder prepared according to Example 1. FIG.

1B is a SEM photograph of the LiFePO ₄ powder prepared according to Example 1. FIG.

Figure 2a is a graph showing the initial charge and discharge capacity at 0.1C of the battery prepared according to Example 2.

Figure 2b is a graph showing the initial charge and discharge capacity at 0.1C of a battery prepared according to Comparative Example 2.

3A is a graph showing high rate discharge characteristics (C-rate properties) of a battery manufactured according to Example 2. FIG.

3B is a graph showing high rate discharge characteristics (C-rate properties) of a battery manufactured according to Comparative Example 2. FIG.

4 is a graph showing charge and discharge capacity of the battery prepared according to Example 2 after 16 cycles under 1C conditions.

The present invention relates to a method for producing LiFePO ₄ (lithium iron phosphate composite oxide) which is economical, safe and easy to mass-produce, and a secondary battery comprising LiFePO ₄ produced thereby.

Recently, as miniaturization and light weight of electronic equipment have been realized and the use of portable electronic devices has become common, research on lithium secondary batteries having high energy density has been actively conducted. A lithium secondary battery is prepared by using a material capable of inserting and detaching lithium ions as a negative electrode and a positive electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions can be inserted and removed from the positive electrode and the negative electrode. Electrical energy is generated by oxidation and reduction reactions.

LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, etc. have been mainly studied as a cathode active material. However, LiCoO ₂ , which is currently widely used, has a high raw material price and causes environmental problems. In addition, LiNiO ₂ , which is studied as a substitute material for LiCoO ₂ , is difficult to manufacture and has low thermal stability, and LiMn ₂ O ₄ has disadvantages of rapid electrode degradation at high temperature and low electrical conductivity.

The new battery material, LiFePO _4, is environmentally friendly and contains iron, which is the most abundant metal, instead of using rare metals such as cobalt. In addition, the discharge voltage is 3.4 V (vs. Li / Li ⁺ ), and the theoretical capacity is 170 mAh / g, and the battery capacity is also excellent.

The LiFePO ₄ powder is prepared by a conventional solid phase reaction method, sol-gel method and the like. US 2002-0004169A1 discloses a method for synthesizing LiFePO ₄ using iron acetate, lithium carbonate and ammonium dihydrogen phosphate as reactants. However, when using the preparation method, toxic by-products such as acetic acid and ammonia are generated, which not only requires a large capacity gas collector but also a problem such as a large total volume of the precursor mixture and a high cost of iron acetate.

WO02 / 099913A1 discloses a method for the synthesis of LiFePO ₄ via solid state reaction of Fe (NO ₃ ) ₃ .9H ₂ O and LiH ₂ PO ₄ in a reducing atmosphere. However, LiH ₂ PO ₄ , one of the reactants, was not commercially accessible and therefore not suitable for mass production processes.

In addition, EP 1391424 A2 proposed a method for producing LiFePO ₄ , but according to this, toxic gases such as carbon monoxide and ammonia were obtained as by-products, and high temperatures in the range of 750 to 800 ° C. were required. In addition, the discharge capacity of the manufactured LiFePO ₄ was only about 121mAh / g under a current density of 0.2mA / cm ² .

Therefore, there is a need for a new production method suitable for mass production, while having good reproducibility, simple manufacturing process, and less use of non-use in the production of LiFePO ₄ .

The present invention provides a low-cost Fe ²⁺ compound and a lithium in place of an expensive iron oxalate (FeC ₂ O ₄ .2H ₂ O) or iron acetate (Fe (CH ₃ COO) ₂ ) as an iron (Fe) precursor compound. By using salts and phosphates and using a solid state reaction, it is desired to provide a method for producing LiFePO ₄ that suppresses side reactions and by-products, facilitates mass production, and is economical. In addition, the present invention is to provide a LiFePO ₄ produced by the above method and a secondary battery using the same as a cathode active material.

The present invention comprises the steps of (a) FeSO ₄ , FeCO ₃ , and FeO by mixing at least one Fe ²⁺ containing compound selected from the group consisting of lithium salt and phosphate to prepare a mixture; And (b) it provides a method for producing LiFePO ₄ comprising the step of firing the mixture of step (a) in an inert or reducing atmosphere.

Further, the present invention provides a secondary battery comprising the LiFePO ₄ and Manufacture of LiFePO ₄ as a cathode active material prepared by the above method.

Hereinafter, the present invention will be described in detail.

The method for preparing LiFePO ₄ according to the present invention is characterized by using a Fe ²⁺ -containing compound as an iron (Fe) precursor compound, and using a conventional solid state reaction known in the art. Solid state reactions are the most basic method for synthesizing powders.

In order to reduce Fe ³⁺ to Fe ²⁺ , a carbon or a hydrogen mixed gas is further required, and therefore Fe ²⁺ -containing compound is preferable as the iron precursor compound. In particular, the manufacturing method of the present invention is a Fe ^{2 +} containing compound FeSO ₄ , FeCO ₃ , Fe instead of expensive iron oxalate (FeC ₂ O ₄ · 2H ₂ O) or iron acetate (Fe (CH ₃ COO) ₂ ) Inexpensive compounds such as FeO are used.

The manufacturing method of the present invention may further include the step of removing the gas generated in the firing step (c) after the firing step (b). Specifically, the gas generated in the firing of step (b) can be removed using CaO. For example, when FeSO ₄ is used as the Fe ²⁺ -containing compound, SO ₂ or SO ₃ gas may be generated during the firing process, and the gas may be passed through a tube containing CaO, or CaO may be administered to the gas. The gas generated can be removed by changing to CaSO ₃ or CaSO ₄ . In addition, gas may be removed through adsorption using activated carbon, metal oxides, or zeolites instead of CaO. The said gas removal material can be used individually or in mixture of 2 or more types.

In the production method of the present invention, a lithium salt commonly used as a lithium (Li) precursor compound may be used. Non-limiting examples of lithium salts include lithium chloride, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium sulfate, lithium oxide, lithium aluminum oxide, and the like. These lithium salts may be used alone or in combination of two or more thereof. have.

In addition, as the phosphoric acid (PO ₄ ) precursor compound, a phosphate commonly used may be used. Non-limiting examples of phosphates include ammonium phosphate, ammonium dihydrogen phosphate, lithium phosphate, iron phosphate, phosphoric acid, phosphates (P ₂ O ₅ , P ₄ O ₁₀ ), diammonium hydrogen phosphate, and the like. Or two or more types can be mixed and used.

In the preparation method of the present invention, in the preparation of the mixture of step (a), Fe ²⁺ : Li ⁺ : PO ₄ ^3- the Fe ^{2 +} containing compound, lithium salt such that the stoichiometric ratio of 1 ~ 1.1: 1: 1 And phosphate salts. I.e., Fe ²⁺ Fe ²⁺ containing compound: Lithium salt of Li ^+: preferably from 1: PO ₄ ^3- is mole (mole) ratio of 1 ~ 1.1 phosphate: 1. If the mixing ratio is exceeded, the generation of unwanted reaction by-products increases or unreacted substances remain.

In addition, the mixture of step (a) may be mixed by ball milling.

In the production method of the present invention, LiFePO ₄ may be obtained by calcining the mixture of step (a) under inert or reducing dusting.

Before firing the mixture containing the Fe ²⁺ compound, the lithium salt, and the phosphate in an inert atmosphere, the mixture may be calcined by adding and mixing a conductive carbon material or an organic material which is a precursor of carbon.

Iron generally has the property of being easily oxidized because Fe ³⁺ is more stable than Fe ²⁺ . Therefore, in order to reduce the iron compound in the production of LiFePO ₄ , such a conductive carbon material can be used. The conductive carbon material serves to reduce iron ions, and since a small amount of carbon material remaining after the reaction exists in an initial carbon state, it serves as a conductive component in the final product.

Conductive carbon materials that can be used are carbon black, acetylene black series (Chevron Chemical Company or Gulf Oil Company), and ketjen black EC series. (Armak company), Vulcan XC-72 (manufactured by Cabot company), and Carbon Super-P (manufactured by MMM). In addition, organic materials as carbon precursors that can be used include substances such as sucrose, organic acids, resins, pitches, and resorcinol-formaldehyde. These substances can be used individually or in mixture of 2 or more types. In addition, the conductive carbon material or the precursor of carbon may be added and mixed in a ratio of 0.1 to 20 parts by weight based on 100 parts by weight of the mixture containing iron, lithium salt and phosphate.

The firing time and temperature of the mixture containing the Fe ²⁺ containing compound, lithium salt and phosphate are not particularly limited, but are preferably in the range of 5 to 40 hours and 450 to 850 ° C. If lower than 450 ℃ crystalline material is difficult to form, if higher than 850 ℃ particles are too coarse, there is a problem that the physical properties are lowered.

In addition, the atmosphere at the time of baking is suitable with a normal inert or reducing atmosphere, and nitrogen gas mixed with 0-5% (volume ratio) of hydrogen is especially preferable. This is to prevent oxidation of iron (Fe ²⁺ ).

The present invention provides LiFePO ₄ prepared by the above-described method.

The present invention also provides a secondary battery comprising LiFePO ₄ prepared by the above method as a cathode active material. The secondary battery of the present invention can be produced by a conventional method known in the art, including a positive electrode prepared by using the LiFePO ₄ of the present invention as a positive electrode active material. For example, a porous separator may be inserted between the positive electrode and the negative electrode to add an electrolyte solution. The secondary battery includes a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

In the secondary battery of the present invention, the electrode can be prepared by conventional methods known in the art. For example, using LiFePO ₄ prepared according to the manufacturing method of the present invention as a positive electrode active material, a slurry is prepared by mixing and stirring a binder, a solvent, a conductive material, and a dispersant, if necessary, and then a slurry on a current collector of a metallic material. The positive electrode can be prepared by applying, compressing and drying.

With respect to the electrode active material, the binder may be suitably used in 1 to 10 weight ratio, and the conductive material in 1 to 30 weight ratio.

As the negative electrode active material, a carbon material capable of occluding and releasing lithium ions, a carbon-silicon composite, a lithium metal, or an alloy thereof may be used, and other TiO ₂ which may occlude and release lithium and have a potential of less than ₂ V for lithium. , Metal oxides such as SnO ₂ Li ₄ Ti ₅ O ₁₂ may be used. In particular, carbon materials, such as graphite, are preferable.

Examples of binders that can be used include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and the like.

Generally, carbon black may be used as the conductive material, and acetylene black series (Chevron Chemical Company or Gulf Oil Company) may be used as a conductive material. ), Ketjen Black EC series (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and carbon super-P (MMM) Company products).

Examples of the solvent include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide or water, and these solvents may be used alone or in combination of two or more thereof. . The amount of the solvent used is sufficient to dissolve and disperse the electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the slurry of the electrode active material can be easily adhered and is not reactive in the voltage range of the battery. Representative examples include meshes, foils, and the like, which are manufactured by aluminum, copper, gold, nickel or an aluminum alloy or a combination thereof.

The electrolyte may include a nonaqueous solvent and an electrolyte salt.

The nonaqueous solvent is not particularly limited as long as it is normally used as a nonaqueous solvent for nonaqueous electrolyte, and cyclic carbonate, linear carbonate, lactone, ether, ester or ketone can be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC) and dipropyl carbonate. (DPC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like. There is this. In addition, examples of the ester include methyl acetate, ethyl acetate, methyl propionate, methyl pivalate, and the like, and the ketone includes polymethylvinyl ketone. These nonaqueous solvents can be used individually or in mixture of 2 or more types.

The electrolyte salt is not particularly limited as long as it is usually used as an electrolyte salt for nonaqueous electrolyte. Electrolytic salt, non-limiting example, A ⁺ B ^- A salt of the structure, such as, A ⁺ comprises a Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ) ₃ ^- and a salt containing the same anion ion or a combination thereof. In particular, lithium salts are preferred. These electrolyte salts can be used individually or in mixture of 2 or more types.

The secondary battery of the present invention may include a separator. The separator can be used is not particularly limited, it is preferable to use a porous separator, non-limiting examples include a polypropylene-based, polyethylene, or polyolefin-based porous separator.

The secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the following examples are merely to illustrate the present invention and the present invention is not limited by the following examples.

(Example 1)

The Fe ²⁺ -containing compound was mixed with FeSO ₄ , lithium salt, Li ₂ CO _3, and phosphate (NH ₄ ) ₂ HPO ₄ in a molar ratio of 1: 0.5: 1. 5 parts by weight of Ketjen Black was added to 100 parts by weight of the mixture, and they were placed in a stainless steel container having stainless steel balls and mixed uniformly using a planetary ball miller to prepare a mixture.

The mixture was placed in a ceramic crucible and pretreated for 5 hours in an electric furnace at 350 ° C. and then calcined at 750 ° C. for 8 hours, at which time firing was carried out under a reducing atmosphere of N ₂ /2% H ₂ mixed gas. LiFePO ₄ containing carbon was obtained through the firing process, and the average particle diameter thereof was 0.3 to 0.5 μm, and the carbon content was 2.5 wt%.

SO ₂ gas generated during firing was removed by adsorption on activated carbon.

(Example 2)

LiFePO ₄ prepared in Example 1 was used as a cathode active material. After mixing 88 parts by weight of the prepared LiFePO _{4 with} 6 parts by weight of acetylene black as a conductive agent and 6 parts by weight of PVDF with a binder and added to NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry, this is aluminum (Al) The positive electrode was prepared by applying and drying on a current collector.

1 M LiPF ₆ / ethylene carbonate (EC): ethyl methyl carbonate (EMC) (v: v = 1: 2) was used as an electrolyte, and a lithium coin was used together with a cathode prepared by the above method using lithium foil as a negative electrode. Halfcells were prepared.

(Comparative Example 1)

The Fe ²⁺ containing compounds with Li ₂ CO _3, and phosphate as Fe ₂ O ₃ and a lithium salt (NH _{4) 2} HPO ₄ mol (mole) ratio of 1: 1: 1 as a mixture of 2, the gases generated during firing Except not removing, LiFePO ₄ containing carbon was obtained in the same manner as in Example 1, and the carbon content thereof was 9% by weight.

(Comparative Example 2)

A coin half paper was manufactured in the same manner as in Example 2, except that LiFePO ₄ prepared in Comparative Example 1 was used as the cathode active material.

Experiment 1: Analysis of LiFePO ₄

In order to analyze the LiFePO ₄ prepared in Example 1 was carried out the following experiment.

As a result of X-ray diffraction analysis (XRD: X-ray Diffraction), the LiFePO ₄ powder prepared in Example 1 was found to be a single phase, and coincident in all ranges with the peak of the standard LiFePO ₄ compound.

In addition, since LiFePO ₄ is charged and discharged in lithium, insertion / desorption occurs in the vertical direction of the (010) plane, and thus, LiFePO ₄ having a well-developed crystal in the (010) plane direction may have excellent physical properties. X-ray diffraction analysis of the LiFePO ₄ and the crystal structure based on this result showed that the relative magnitude of the peak characterized from the (020) plane was very large, and from this the LiFePO ₄ of the well developed (010) plane was obtained. It was found that to get.

As a result of analyzing by SEM (Scanning electron microscope), the average particle size of LiFePO ₄ powder was found to be about 300 ~ 500nm.

(Experiment 2: Evaluation of Initial Capacity of Battery)

Experiments were conducted for the initial capacity evaluation of the batteries using the batteries prepared in Example 2 and Comparative Example 2.

The current density was 0.1C, and the charge and discharge region was experimented with 4.2 V ( vs. Li / Li ⁺ ) at 2.7 V.

As a result of the experiment, the initial charge and discharge efficiency of the battery prepared in Example 2 using LiFePO ₄ prepared in Example 1 as the positive electrode active material showed an efficiency equivalent to the initial charge and discharge efficiency of the battery prepared in Comparative Example 2 (Fig. 2a and 2b).

(Experiment 3: C-rate evaluation of battery)

The cells prepared in Example 2 and Comparative Example 2 were used, and the cells were cycled at discharge rates of 0.1C, 0.2C, 0.5C, and 1C.

As a result of the experiment, the battery prepared in Example 2 showed a high rate discharge (C-rate) characteristics by showing a discharge rate comparable to the battery prepared in Comparative Example 2 (see FIGS. 3A and 3B).

(Experiment 4: Cycle Characteristic Evaluation)

The batteries prepared in Example 2 and Comparative Example 2 were used. The current density was 1C, and the charge / discharge region was experimented with 3.0 V at 4.2 V ( vs. Li / Li ⁺ ).

As a result of the experiment, the battery prepared in Example 2 was cycled up to 16 times, there was almost no difference in the charge-discharge capacity of the battery, it was confirmed that the reversibility has a long life characteristics (see Figure 4).

LiFePO ₄ according to the present invention is an iron (Fe) precursor compound using an inexpensive Fe ²⁺ containing compound and using a solid state reaction (solid state reaction), mass production is easy, economical and the occurrence of side reactions It can be suppressed as much as possible. In addition, toxic by-products are not emitted, thereby improving safety.

Claims (14)

(a) preparing a mixture by mixing at least one Fe ²⁺ containing compound selected from the group consisting of FeSO ₄ , FeCO ₃ , and FeO with lithium salts and phosphates; (b) calcining the mixture of step (a) under an inert or reducing atmosphere; And (c) using the at least one selected from the group consisting of CaO, activated carbon, zeolite and metal oxide to remove the gas generated in the firing of step (b); Method for producing LiFePO ₄ comprising a. delete delete The method of claim 1, wherein the lithium salt is LiFePO ₄ characterized in that at least one selected from the group consisting of lithium chloride, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium sulfate, lithium oxide and lithium aluminum oxide. Way. The method of claim 1 wherein the phosphate is ammonium phosphate, dihydrogen phosphate ammonium, method of producing a lithium phosphate, iron phosphate, phosphoric acid, characterized in that at least one member selected from phosphate and hydrogen phosphate group consisting of 2 ammonium LiFePO _4. The method of claim 1, wherein the mixture of step (a) comprises the Fe ^{2 +} -containing compound, lithium salt and phosphate such that Fe ²⁺ : Li ⁺ : PO ₄ ^3- is 1 to 1.1: 1: 1 in a stoichiometric ratio. Method for producing LiFePO ₄ characterized in that the mixture. 2. The method of claim 1, wherein (a) the mixture of step method for producing LiFePO _4, characterized in that the mixture to ball milling. The method for producing LiFePO ₄ according to claim 1, wherein a conductive carbon material or a precursor of carbon is added to and mixed with the mixture of step (a). 9. The method of claim 8, wherein the production of the conductive carbon material is carbon black, Kane teujen black, LiFePO _4, characterized in that at least one member selected from the group consisting of acetylene black and carbon super -P. The method of claim 8 wherein the precursor of carbon is a process for producing a sucrose, organic acids, resin, pitch, and LiFePO _4, characterized in that at least one member selected from the group consisting of resorcinol-formaldehyde. The method of claim 8, wherein the conductive carbon material or precursor of carbon is iron, lithium salt and phosphate mixture was added to 100 parts by weight ratio of 0.1 to 20 parts by weight of the preparation includes a method for the preparation of LiFePO _4, characterized in that the mixture. The method of claim 1 wherein the production of LiFePO ₄ for the baking of step (b) is characterized in that formed at 450 ~ 850 ℃. delete delete

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