TW201420496A - Method for manufacturing LiFePO4 material - Google Patents

Abstract

The present invention provides a method for manufacturing LiFePO4 material, comprising: (A) providing a lithium precursor, an iron precursor, and a phosphorus precursor; (B) performing a dehydration process on at least one of the lithium precursor, the iron precursor, and the phosphorus precursor, at a temperature of about 300-800 DEG C for more than 2 hours, to obtain an anhydrous lithium precursor, an anhydrous iron precursor, and/or an anhydrous phosphor precursor; (C) mixing the lithium precursor and/or the anhydrous lithium precursor, the iron precursor and/or the anhydrous iron precursor, and the phosphorus precursor and/or the anhydrous phosphorus precursor, to obtain a precursor mixture containing lithium, iron, and phosphorus, wherein the precursor mixture is obtained from at least one of the anhydrous lithium precursor, the anhydrous iron precursor, and the anhydrous phosphor precursor; and (D) processing the precursor mixture into a lithium iron phosphate material.

Description

Method for preparing lithium iron phosphate material

The invention relates to a preparation method of a lithium iron phosphate material, in particular to a preparation method of a lithium iron phosphate material comprising a decrystallization water process.

In recent years, with the development of various portable electronic devices, the focus on energy storage technology has also increased. Among them, the battery is one of the main power sources of portable electronic devices, especially the portable electronic products such as the largest mobile phones and notebook computers, all of which use small secondary batteries as the power source. In addition to portable electronic devices, secondary batteries are currently used in electric vehicles.

Among the secondary batteries used today, lithium secondary batteries (or lithium ion batteries) developed in the early 1990s have become the focus of attention. In the early days, lithium-ion batteries used LiCoO ₂ as a cathode material. Because of their high working voltage and smooth charge and discharge voltage, they were widely used in portable products. Then, a lithium ion battery having an olivine structure LiFePO ₄ and a spinel structure LiMn ₂ O ₄ as a cathode material was developed. Compared with LiCoO ₂ as cathode material, LiFePO ₄ and LiMn ₂ O ₄ as cathode materials can have better safety, more charge and discharge times, lower cost, etc., and their safety performance and loop life. It is incomparable to other materials, and these are the most important technical indicators of power batteries.

Lithium iron phosphate (molecular formula: LiFePO ₄ , English: Lithium iron phosphate, also known as lithium iron phosphate, lithium iron phosphorus, referred to as LFP), is a cathode material for lithium ion batteries, also known as lithium iron phosphorus battery, featuring no Valuable elements such as cobalt, low raw material prices and abundant resources of phosphorus, lithium and iron in the earth, there will be no supply problems. The utility model has moderate working voltage, fast charging and long cycle life, and high stability under high temperature and high heat environment. At the same time, LiFePO _{4 is} more non-toxic and environmentally friendly, and has high temperature characteristics, so it is one of the most excellent cathode materials for lithium ion batteries.

However, the current lithium iron phosphate cathode material has a problem of poor conductivity, and this problem is a difficult point in the development of the lithium iron phosphate industry. In the past, there have been some studies on improving conductivity. For example, in the actual production process, the conductivity of the material is improved by adding an organic carbon source and a high-valent metal ion in the precursor, but the phosphoric acid obtained by these methods is obtained. The conductivity of lithium iron cathode materials still has a lot of room for improvement.

Therefore, there is an urgent need to develop a method for preparing a cathode material for a lithium iron phosphate battery, which can improve the charge and discharge efficiency of the battery and improve the conductivity.

The main object of the present invention is to provide a lithium iron monophosphate material which has a smaller particle size (between 1 and 35 μm ) and less pores (surface area 10 to 20 m ² / compared with a general lithium iron phosphate material). g), and a lower viscosity (1000 to 10000 cps), making subsequent processing easier, and the secondary battery made of it has a higher charge and discharge capacity given the same amount of electricity.

To achieve the above object, the present invention provides a method for preparing a lithium iron phosphate material, comprising the steps of: (A) providing a lithium precursor, an iron precursor And a phosphorus removal precursor; (B) performing a water removal process on at least one of the lithium precursor, the iron precursor, and the phosphorus precursor, wherein the temperature of the water removal process is between 300 and 800 °C, preferably between 400 and 650 ° C, and the time of the above water removal process is greater than 2 hours, preferably between 4 and 8 hours, to obtain a lithium precursor of decrystallization water, an iron precursor of decrystallization water, and / or a phosphorus precursor to the crystallization water; (C) a lithium precursor mixed with the lithium precursor and/or the above-mentioned decrystallization water, the iron precursor and/or the iron precursor of the above-mentioned decrystallization water, the phosphorus precursor And/or the phosphorus precursor of the above decrystallized water to obtain a mixed precursor containing lithium, iron, and phosphorus, wherein the source of the mixed precursor comprises the lithium precursor of the above decrystallized water, the above decrystallized water At least one of the iron precursor and the phosphorus precursor of the above decrystallized water; and (D) the above mixed precursor is made into a lithium iron phosphate material. The above-mentioned lithium precursor, iron precursor, and phosphorus precursor may be independently selected from one to three by water removal, that is, the three may be partially or completely treated by a water removal process.

Since the crystallization water does not participate in the reaction component, the main component of the former material is too low, so that the yield is lowered, and during the sintering reaction, the crystallization water reacts to form water vapor, which is an exhaust gas and causes many holes in the material. , resulting in low heat transfer efficiency and slow sintering reaction time. In addition, the lithium iron phosphate material that passes through the porous hole reduces the solidity of the powder (the tap density is about 0.9 to 1.0 g/ml). In order to overcome the influence of the above-mentioned crystallization water on the properties of the lithium iron phosphate material, the present invention utilizes a process for removing crystallization water to improve the lithium iron phosphate material, so that it has good electrical conductivity and processability, and can be used as a new generation lithium ion battery. The ideal cathode material.

The temperature and time of the water removal process may be any other suitable range, as long as the water of crystallization in the lithium, iron, and phosphorus precursors used in the present invention can be removed at the temperature and time, and is not limited thereto. The invention is described. However, if the temperature of the water removal process is too high (above 650 ° C), the precursor will react to form a different crystalline phase, which may not be easily reacted to form a lithium iron phosphate material; the temperature of the water removal process is too low (less than At 400 ° C), the crystal water of the precursor is not easily removed, so that the reaction time of the water removal reaction is too long, resulting in an excessive cost.

The effect of the interface after the removal of water improves the interface ratio, so that the solid-liquid ratio can be increased by more than 50%, and the sintering efficiency is improved from 70% to 80%, which increases the productivity and reduces the cost.

The lithium precursor used in the present invention may be at least one selected from the group consisting of LiOH, Li ₂ CO ₃ , LiNO ₃ , CH ₃ COOLi, Li ₂ C ₂ O ₄ , Li ₂ SO ₄ , LiCl, LiBr, LiI, LiH ₂ PO ₄ , The group consisting of Li ₂ HPO ₄ , Li ₃ PO ₄ , and a compound containing crystal water thereof is preferably lithium carbonate (Li ₂ CO ₃ ) and a compound containing the crystal water. The above list is only an example, and any other suitable lithium precursor may be used, and is not limited thereto.

The iron precursor used in the present invention may be at least one selected from the group consisting of FeCl ₂ , FeBr ₂ , FeI ₂ , FeSO ₄ , (NH ₄ ) ₂ Fe(SO ₄ ) ₂ , Fe ₂ O ₃ , Fe(NO ₃ ) ₃ , FeC. _a group consisting of ₂ O ₄ , (CH ₃ COO) ₂ Fe, FeCO ₃ , Fe ₃ (PO ₄ ) ₂ , FePO ₄ , and a compound containing crystal water thereof, preferably FePO ₄ and its crystal water-containing Compound. The above list is only an example, and any other suitable iron precursor may be used, and is not limited thereto.

The phosphorus precursor used in the present invention may be at least one selected from the group consisting of H ₃ PO ₄ , NaH ₂ PO ₄ , Na ₂ HPO ₄ , Mg ₃ (PO ₄ ) ₂ , (NH ₄ ) ₂ HPO _{4 ,} NH ₄ H ₂ PO _{4 .} a group consisting of LiH ₂ PO ₄ , Li ₂ HPO ₄ , Li ₃ PO ₄ , and a compound containing crystal water thereof, preferably ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) and its crystal water-containing Compound. The above list is only an example, and any other suitable phosphorus precursor may be used, and is not limited thereto.

According to the preparation method of the lithium iron phosphate material of the present invention, in the above step (B), the water removal process may be carried out in an environment in which a gas or a vacuum is required. The gas may include, but is not limited to, nitrogen, helium, neon, argon, helium, neon, carbon monoxide, methane, a mixed gas of nitrogen and hydrogen, or a combination thereof, and the gas may also be air. In one embodiment, the type of gas used in the water removal process may be selected in accordance with the type of lithium, iron, and phosphorus precursors used. Taking iron oxalate as an iron precursor as an example, since Fe ^{2+ in} iron oxalate is easily oxidized to Fe ³⁺ , the high temperature (300 to 800 ° C) of the present invention can be selected in an inert gas or vacuum environment. Water process.

The method for preparing a lithium iron phosphate material according to the present invention, wherein the step (D) may include, but is not limited to, a polishing process, a granulation process, and a sintering process. In one embodiment of the present invention, after the above-mentioned lithium, iron, and phosphorus mixed precursor is subjected to a polishing process at room temperature, the granulation process is subsequently carried out using a spray granulator having a plurality of nozzle heads. By means of the nozzle head design of the spray granulation device, the flow rate, the air volume and the spray pressure are controlled, and a granular mixture of lithium metal phosphate having a uniform size of nanometer, submicron or micrometer can be directly obtained. Next, proceed under nitrogen In the sintering process, the sintering step can be carried out at a temperature of 650 to 850 ° C, preferably 700 ° C. Further, the sintering step is carried out for 3 to 10 hours, preferably 8 hours. After sintering, the granular mixture further forms a porous lithium metal phosphate salt, and its porosity can contribute to increase porosity and reduce the moving distance of lithium ions to improve the efficiency of rapid charge and discharge. Finally, the porous lithium metal phosphate salt obtained by the above preparation method can be packaged and shipped for subsequent production.

Since the preparation method of the lithium iron phosphate material of the present invention comprises the above water removal process, the lithium water in the lithium precursor, the iron precursor, and the phosphorus precursor can be removed, so that the lithium iron phosphate obtained after the subsequent grinding process is coarse. The material may have a particle size of 0.1 to 5 μm, preferably 0.7 to 1 μm. (The particle size of the lithium iron phosphate coarse material obtained when the water of crystallization is not removed is 0.5 to 8 μm, preferably 1 to 2 μm.), and the viscosity of the crude material can be lowered to have a viscosity of 1000 to 10000 cps. Preferably, it is 2500~5000 cps. Finally, since the crude material of the iron phosphite treated by the decrystallization water has less pores, the surface area is reduced from 30 to 60 m ² /g (not water removed) to 6 to 15 m ² /g (water removal), and the surface area reduction powder is reduced. Body coating, reducing powder loss; in addition, at the same solid-liquid ratio, the reduction of surface area, reducing the viscosity of the slurry, easier to carbon recovery, so the surface area of the lithium iron phosphate material after sintering 20~30 m ² /g (not water removal) reduced to 10~20m ² /g (water removal), the reduction of surface area can improve the material processability, so the purity of one lithium iron phosphate material obtained through the above sintering process is pure. Up to 97%.

In an embodiment of the present invention, in the step (C) of the method for preparing the lithium iron phosphate material, a small amount of a doped metal compound may be added as needed. To increase the conductivity of the formed lithium iron phosphate material. Wherein, the doping metal may be at least one selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, A group consisting of Ga, In, Be, Mg, Ca, Sr, B, and Nb. Preferably, the doping metal compound is a metal sulfate, a metal carbonate, a metal nitrate, a metal oxalate, a metal acetate, a chloride, a bromide or an iodide salt of the above metal element. More preferably, the doping metal compound is a sulfate metal salt of the above metal element. Most preferably, the doping metal compound is a metal sulfate of Mn, Cr, Co, Cu, Ni, Zn, Al, or Mg.

In an embodiment of the present invention, in the step (C) of the method for preparing the lithium iron phosphate material, a small amount of carbon material may be further added as needed to coat the surface of the synthesized lithium iron phosphate material with carbon to increase The conductivity of the formed lithium iron phosphate material. Among them, the carbon material can be any sugar such as sucrose.

Further, the lithium iron phosphate material of the lithium ion battery of the present invention can be used as a cathode material by a method known in the art or developed in the future to produce a lithium ion battery. The preparation method of the lithium ion battery in an embodiment will be briefly described below, but the present invention is not limited thereto.

Wherein, the process of the anode is formed by coating a carbon material on an anode current collector, followed by drying and pressing; and the process of the cathode is by coating a cathode active material (ie, the phosphoric acid of the invention) The lithium iron material is placed on a cathode current collector, which is then dried and pressed. Then, a separator is inserted between the cathode and the anode, and then an electrolyte containing a lithium salt is injected. After encapsulation, a lithium ion battery is obtained.

In summary, the present invention adds a step of removing the crystal water in the lithium, iron, and phosphorus precursors before the general process of the general lithium iron phosphate process, and the lithium iron phosphate material obtained is only passed through the general lithium iron phosphate. The general process-processed lithium iron phosphate material has a smaller particle size (between 1 and 35 μm , preferably between 1.5 and 3 μm ) and fewer pores, with a surface area of 20 to 40 m ² / g (not water removed) is reduced to 6-20 m ² /g (water removal), preferably 10-15 m ² /g. And a lower viscosity (1000~10000 cps, preferably 2500~5000 cps), which makes the subsequent processing process easier, and the secondary battery made thereof has a higher power given the same amount of electricity. The charging and discharging capacity can meet the needs of frequent charging and discharging, and has the advantages of non-toxicity, no pollution, good safety performance, wide source of raw materials, low price and long service life. It is an ideal cathode material for a new generation of lithium ion batteries.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily appreciate the other advantages and advantages of the present invention. The present invention may be embodied or applied in various other specific embodiments. The details of the present invention can be variously modified and changed without departing from the spirit and scope of the invention.

Example 1

The iron phosphate containing crystal water was subjected to calcination at different temperatures to remove water, and exhibited a weight loss rate, a change in tap density (Tap) and a change in specific surface area (BET). The use parameters and results are shown in Table 1 below.

Mix lithium carbonate (Li ₂ CO ₃ ) and dehydrated iron phosphate (FePO ₄ ) in a ratio of 1:1, and add vitamin C or glucose (about 10 to 15% molar percentage) at room temperature Grinding is carried out to form a mixture. Next, using the nozzle heads of the spray granulation apparatus of the present invention, the flow rate is 0.3 L/min, the air volume is 120 m ³ /min, and the spray pressure is 8 kg/cm ² , and the hot air temperature of the spray granulator is 230 ° C and an outlet temperature of 110 ° C to produce a granular mixture. Then, the above granular mixture was sintered at a temperature of 750 ° C for 8 hours under a nitrogen atmosphere, and the porous lithium iron phosphate (LiFePO ₄ ) particles obtained in the present example were observed by a scanning electron microscope (SEM). The product of the present example does have a porous pore structure, and the lattice structure is confirmed by XRD instrumental analysis, and the purity of the LiFePO ₄ phase can reach 99.5% or more.

The above porous lithium iron phosphate (LiFePO ₄ ) particles were analyzed by a laser particle size analyzer, wherein the particle size distribution of the porous lithium metal phosphate salt was a multi-Gaussian distribution. The Gaussian distribution of the particle size is analyzed semi-quantitatively, wherein about 4.5% is distributed at about 0.3 μm, about 45.6% is distributed at about 1.5 μm, about 17.9% is distributed at about 2.9 μm, and about 32.0% is distributed at 3.8 μm. Left and right, and has a high porosity, resulting in a surface area of 10 to 15 m ² /g.

In this embodiment, lithium carbonate (Li ₂ CO ₃ ) is used as the lithium-containing precursor; iron phosphate (FePO ₄ ) is used as the iron source and the phosphorus source; and vitamin C and glucose are used as the carbon source. However, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or a combination thereof may be selected as the phosphoric acid precursor according to actual needs; lithium hydroxide (LiOH), lithium chloride (LiCl), or the above-mentioned group cooperation, is a lithium-containing precursor; iron nitrate (Fe(NO ₃ ) ₃ ), iron oxide (Fe ₂ O ₃ ), iron oxalate (FeC ₂ O ₄ ), iron sulfate (Fe _{2 )} (SO ₄ ) ₃ ), iron powder, or a combination thereof as an iron source; and, a saccharide, citric acid, polyethylene, polypropylene, a benzene ring-containing polymer, a linear hydrocarbon, or a combination thereof Etc. as a carbon source.

Example 2

The ferrous oxalate (FeC ₂ O ₄ ^* 2H ₂ O) containing crystal water was subjected to calcination at 300 ° for 5 hours to remove water, and exhibited a 19 to 21% weight loss rate.

Mixing ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), lithium carbonate (Li ₂ CO ₃ ), and ferrous oxalate (FeC ₂ O ₄ ) after water removal at a ratio of 1:0.5:1, and adding vitamin C Glucose (about 10% molar percentage) was milled at room temperature to form a mixture. Next, using the nozzle heads of the spray granulator of the present invention, the flow rate is 0.3 L/min, the air volume is 120 m ³ /min, and the spray pressure is 8 kg/cm ² , and the hot air temperature of the spray granulator is 230. °C, and the outlet temperature was 110 ° C to prepare a granular mixture. Then, the above granular mixture was sintered at a temperature of 650 ° C for 10 hours under a nitrogen atmosphere, and the porous lithium iron phosphate (LiFePO ₄ ) particles obtained in the present example were observed by a scanning electron microscope (SEM). The product of the present example does have a porous pore structure, and the lattice structure is confirmed by XRD instrumental analysis, and the purity of the LiFePO ₄ phase can reach 98.5% or more.

The above porous lithium iron phosphate (LiFePO ₄ ) particles were analyzed by a laser particle size analyzer, wherein the particle size distribution of the porous lithium metal phosphate salt was a multi-Gaussian distribution. The Gaussian distribution of the particle size is analyzed semi-quantitatively, wherein about 4.5% is distributed at about 0.3 μm, about 45.6% is distributed at about 1.5 μm, about 17.9% is distributed at about 2.9 μm, and about 32.0% is distributed at 3.8 μm. It has a high porosity and a surface area of 6 to 20 m ² /g (water removal).

In this embodiment, ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) is used as a phosphoric acid precursor; lithium carbonate (Li ₂ CO ₃ ) is used as a lithium-containing precursor; and ferrous oxalate (FeC ₂ O ₄ ) is used as an iron source. And, as a carbon source, vitamin C. However, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or a combination thereof may be selected as the phosphoric acid precursor according to actual needs; lithium hydroxide (LiOH), lithium chloride (LiCl), or the above-mentioned group cooperation, is a lithium-containing precursor; iron nitrate (Fe(NO ₃ ) ₃ ), iron oxide (Fe ₂ O ₃ ), iron phosphate (FePO ₄ ), iron sulfate (Fe ₂ (SO) ₄ ) ₃ ), iron powder, or a combination thereof as an iron source; and, as a saccharide, citric acid, polyethylene, polypropylene, a benzene ring-containing polymer, a linear hydrocarbon, or a combination thereof Carbon source.

Example 3

The iron phosphate (FePO ₄ ^* 2H ₂ O) containing crystal water was subjected to calcination at 500 ° for 8 hours to remove water, and exhibited a 19 to 21% weight loss rate.

Ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), lithium carbonate (Li ₂ CO ₃ ), dehydrated iron phosphate (FePO ₄ ), and manganese sulfate (MnCO ₃ ) in a 1:1:1:1 equivalent Mix in proportions and add vitamin C and glucose (about 10% molar percentage) and grind at room temperature to form a mixture. Next, using the nozzle heads of the spray granulator of the present invention, the flow rate is 0.3 L/min, the air volume is 120 m ³ /min, and the spray pressure is 8 kg/cm ² , and the hot air temperature of the spray granulator is 230. °C, and the outlet temperature was 110 ° C to prepare a granular mixture. Then, the above granular mixture was sintered at a temperature of 650 ° C for 10 hours under a nitrogen atmosphere, and the porous lithium iron phosphate (LiFe _0.5 Mn _0.5 PO obtained in the present example) was observed by a scanning electron microscope (SEM). ₄ ) Particles confirming that the product of this example does have a surface area of 10 to 15 m ² /g.

The above-mentioned polyporous lithium iron phosphate manganese (LiFe _0.5 Mn _0.5 PO ₄ ) particles were analyzed by a laser particle size analyzer, wherein the particle size distribution of the porous lithium metal phosphate salt was a multi-Gaussian distribution. The Gaussian distribution of the particle size is analyzed semi-quantitatively, wherein about 30.8% is distributed around 0.7 μm, about 58.1% is distributed at about 2.6 μm, and about 11.1% is distributed at about 4.3 μm, and has a porosity of 65%. .

In this embodiment, ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) is used as a phosphoric acid precursor; lithium carbonate (Li ₂ CO ₃ ) is used as a lithium-containing precursor; and ferrous oxalate (FeC ₂ O ₄ ) is used as an iron source. Manganese sulfate (MnSO ₄ ) is used as a source of manganese; and vitamin C is used as a carbon source. However, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or a combination thereof may be selected as the phosphoric acid precursor according to actual needs; lithium hydroxide (LiOH), lithium chloride (LiCl), or the above-mentioned group cooperation, is a lithium-containing precursor; iron nitrate (Fe(NO ₃ ) ₃ ), iron oxide (Fe ₂ O ₃ ), iron phosphate (FePO ₄ ), iron sulfate (Fe ₂ (SO) ₄ ) ₃ ), iron powder, or a combination of the above as iron source; manganese nitrate (Mn(NO ₃ ) ₂ ), manganese acetate (Mn(CH ₃ COO) ₂ ), manganese carbonate (MnCO ₃ ), manganese chloride (MnCl ₂ ), manganese oxide (MnO), or a combination thereof, as a manganese source; and a sugar, citric acid, polyethylene, polypropylene, a benzene ring-containing polymer, a linear hydrocarbon, or the like Combinations and the like serve as a carbon source. In addition, the iron source and the manganese source may be different in proportion to each other to form a porous lithium iron iron manganese having a molecular formula of LiFe _1-x Mn _x PO ₄ , wherein x may be 0.2 to 0.8.

Example 4

The ferrous oxalate (FeC ₂ O ₄ ^* 2H ₂ O) containing crystal water was subjected to calcination at 300 ° for 5 hours to remove water, and exhibited a 19 to 21% weight loss rate.

Ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), lithium carbonate (Li ₂ CO ₃ ), ferrous iron oxalate (FeC ₂ O ₄ ), and manganese sulfate (MnCO ₃ ) at 1:0.5:0.5: The equivalent ratio of 0.5 was mixed, and vitamin C and glucose (about 10% molar percentage) were added and ground at room temperature to form a mixture. Next, using the nozzle heads of the spray granulator of the present invention, the flow rate is 0.3 L/min, the air volume is 120 m ³ /min, and the spray pressure is 8 kg/cm ² , and the hot air temperature of the spray granulator is 230. °C, and the outlet temperature was 110 ° C to prepare a granular mixture. Then, the above granular mixture was sintered at a temperature of 650 ° C for 10 hours under a nitrogen atmosphere, and the porous lithium iron phosphate (LiFe _0.5 Mn _0.5 PO obtained in the present example) was observed by a scanning electron microscope (SEM). ₄ ) Particles, confirming that the product of this example does have a high fine porosity, resulting in a surface area of 10 to 15 m ² /g.

The above porous lithium iron phosphate manganese (LiFe _0.5 Mn _0.5 PO ₄ ) particles were analyzed by a laser particle size analyzer, wherein the particle size distribution of the porous lithium metal phosphate salt was a multi-Gaussian distribution. The Gaussian distribution of the particle size is analyzed semi-quantitatively, wherein about 30.8% is distributed around 0.7 μm, about 58.1% is distributed at about 2.6 μm, and about 11.1% is distributed at about 4.3 μm, and has a porosity of 65%. .

In this embodiment, ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) is used as a phosphoric acid precursor; lithium carbonate (Li ₂ CO ₃ ) is used as a lithium-containing precursor; and ferrous oxalate (FeC ₂ O ₄ ) is used as an iron source. Manganese sulfate (MnSO ₄ ) is used as a source of manganese; and vitamin C is used as a carbon source. However, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or a combination thereof may be selected as the phosphoric acid precursor according to actual needs; lithium hydroxide (LiOH), lithium chloride (LiCl), or the above-mentioned group cooperation, is a lithium-containing precursor; iron nitrate (Fe(NO ₃ ) ₃ ), iron oxide (Fe ₂ O ₃ ), iron phosphate (FePO ₄ ), iron sulfate (Fe ₂ (SO) ₄ ) ₃ ), iron powder, or a combination of the above as iron source; manganese nitrate (Mn(NO ₃ ) ₂ ), manganese acetate (Mn(CH ₃ COO) ₂ ), manganese carbonate (MnCO ₃ ), manganese chloride (MnCl ₂ ), manganese oxide (MnO), or a combination thereof, as a manganese source; and a sugar, citric acid, polyethylene, polypropylene, a benzene ring-containing polymer, a linear hydrocarbon, or the like Combinations and the like serve as a carbon source. In addition, the iron source and the manganese source may be different in proportion to each other to form a porous lithium iron iron manganese having a molecular formula of LiFe _1-x Mn _x PO ₄ , wherein x may be 0.2 to 0.8.

Comparative example

Lithium carbonate (Li ₂ CO ₃ ) and iron phosphate (FePO ₄ ‧2H ₂ O) containing 2 crystal waters are mixed in a ratio of 1:1, and vitamin C or glucose (about 10 to 15% molar) is added. Percent), ground at room temperature to form a mixture. Next, using the nozzle heads of the spray granulator of the present invention, the flow rate is 0.3 L/min, the air volume is 120 m ³ /min, and the spray pressure is 8 kg/cm ² , and the hot air temperature of the spray granulator is 230. °C, and the outlet temperature was 110 ° C to prepare a granular mixture. Then, the above granular mixture was sintered at a temperature of 750 ° C for 8 hours under a nitrogen atmosphere, and the porous lithium iron phosphate (LiFePO ₄ ) particles obtained in the present example were observed by a scanning electron microscope (SEM). The product of the present example does have a porous pore structure, and the lattice structure is confirmed by XRD instrumental analysis, and the purity of the LiFePO ₄ phase can reach 98.5% or more.

The above porous lithium iron phosphate (LiFePO ₄ ) particles were analyzed by a laser particle size analyzer, wherein the particle size distribution of the porous lithium metal phosphate salt was a multi-Gaussian distribution. The Gaussian distribution of the particle size is analyzed semi-quantitatively, wherein about 4.5% is distributed at about 0.3 μm, about 45.6% is distributed at about 1.5 μm, about 17.9% is distributed at about 2.9 μm, and about 32.0% is distributed at 3.8 μm. Left and right, and high porosity, resulting in a surface area of 20 ~ 40 m2 / g.

In this embodiment, lithium carbonate (Li ₂ CO ₃ ) is used as the lithium-containing precursor; iron phosphate (FePO ₄ ) is used as the iron source and the phosphorus source; and vitamin C and glucose are used as the carbon source. However, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or a combination thereof may be selected as the phosphoric acid precursor according to actual needs; lithium hydroxide (LiOH), lithium chloride (LiCl), or the above-mentioned group cooperation, is a lithium-containing precursor; iron nitrate (Fe(NO ₃ ) ₃ ), iron oxide (Fe ₂ O ₃ ), iron oxalate (FeC ₂ O ₄ ), iron sulfate (Fe _{2 )} (SO ₄ ) ₃ ), iron powder, or a combination thereof as an iron source; and, a saccharide, citric acid, polyethylene, polypropylene, a benzene ring-containing polymer, a linear hydrocarbon, or a combination thereof Etc. as a carbon source.

1A is a graph showing the particle diameter of a lithium iron phosphate coarse material obtained after a polishing process without a water removal process according to a comparative example of the present invention. 1B is a view showing the particle diameter of a lithium iron phosphate coarse material obtained after a water removal process and a polishing process according to an embodiment of the present invention.

2A is a view showing an X-ray diffraction pattern of a lithium iron phosphate material obtained after a grinding, granulating, and sintering process without a water removal process according to a comparative example of the present invention. 2B is an X-ray diffraction pattern showing a lithium iron phosphate material obtained after a water removal process and a grinding, granulating, and sintering process, in accordance with an embodiment of the present invention. The purity of the compound can be seen from the X-ray diffraction pattern. The purity of the lithium iron phosphate material obtained after the grinding, granulating, and sintering processes in Fig. 2A without water removal process can reach 98.51%; Figure 2B The lithium iron phosphate material obtained after the grinding, granulating, and sintering processes without the water removal process has a purity of 98.52%.

3A is a graph showing the electrical properties of a lithium iron phosphate material obtained after a grinding, granulating, and sintering process without a water removal process according to a comparative example of the present invention. 3B is a graph showing the electrical properties of a lithium iron phosphate coarse material obtained after a water removal process and a grinding, granulating, and sintering process, in accordance with an embodiment of the present invention.

According to the results obtained by the examples and the comparative examples of the present invention, the present invention adds a step of removing the crystal water in the lithium, iron, and phosphorus precursors before the general process of the general lithium iron phosphate process. The lithium iron material has a smaller particle size (up to 0.1 to 5 μm, preferably 0.7 to 1 μm) and less pores, surface area than the comparative example processed by the general process of general lithium iron phosphate. Reduced from 30~60 m ² /g (without water removal) to 6~15m ² /g (water removal), and lower viscosity (cps less than 3000), making subsequent processing easier and more A secondary battery was charged and discharged under the same amount of current of 0.1 C, and the difference in charge and discharge capacity was compared. The 0.1 C gram capacity of Example 1 was 156 mAh/g, and the comparative electrode capacity was only 141 mAh. /g (the higher the amount of electricity supplied, the larger the difference between the charge and discharge capacity of the embodiment and the comparative example. See Table 2, for example, 8 Coulomb, the charge and discharge capacity of the example can be more than 1.8 times that of the comparative example, and the conductivity Increased by more than 80%), so the lithium iron phosphate material obtained by the present invention can be used as The ideal cathode material for a new generation of lithium-ion batteries.

While the invention has been described above in terms of several preferred embodiments, it is not intended to limit the scope of the present invention, and any one of ordinary skill in the art can make any changes without departing from the spirit and scope of the invention. And the scope of the present invention is defined by the scope of the appended claims.

1A is a graph showing the particle diameter of a lithium iron phosphate coarse material obtained after a polishing process without a water removal process according to a comparative example of the present invention.

1B is a view showing the particle diameter of a lithium iron phosphate coarse material obtained after a water removal process and a polishing process according to an embodiment of the present invention.

2A is a view showing an X-ray diffraction pattern of a lithium iron phosphate material obtained after a grinding, granulating, and sintering process without a water removal process according to a comparative example of the present invention.

2B is an X-ray diffraction pattern showing a lithium iron phosphate material obtained after a water removal process and a grinding, granulating, and sintering process, in accordance with an embodiment of the present invention.

3A is a graph showing the electrical properties of a lithium iron phosphate material obtained after a grinding, granulating, and sintering process without a water removal process according to a comparative example of the present invention.

3B is a graph showing the electrical properties of a lithium iron phosphate coarse material obtained after a water removal process and a grinding, granulating, and sintering process, in accordance with an embodiment of the present invention.

Claims (11)

A method for preparing a lithium iron phosphate material, comprising the steps of: (A) providing a lithium precursor, an iron precursor, and a phosphorus precursor; (B) the lithium precursor, the iron precursor, and the phosphorus At least one of the precursors is subjected to a water removal process, wherein the temperature of the water removal process is between 300 and 800 ° C, and the time of the water removal process is greater than 2 hours to obtain a lithium precursor of decrystallization water, Dephosphorizing the iron precursor of water, and/or a phosphorus precursor of decrystallization water; (C) mixing the lithium precursor and/or the lithium precursor of the decrystallized water, the iron precursor and/or the decrystallization a water precursor, a phosphorus precursor, and/or a phosphorus precursor of the decrystallized water to obtain a mixed precursor containing lithium, iron, and phosphorus, wherein the source of the mixed precursor includes the At least one of a lithium precursor of crystallization water, an iron precursor of the decrystallized water, and a phosphorus precursor of the decrystallized water; and (D) the mixed precursor is made into a lithium iron phosphate material. The method for preparing a lithium iron phosphate material according to claim 1, wherein in the step (B), the water removal process is further performed in a gas atmosphere, the gas includes: nitrogen gas, helium gas, Helium, argon, helium, neon, carbon monoxide, methane, a mixture of nitrogen and hydrogen, air, or a combination thereof. The method for preparing a lithium iron phosphate material according to claim 1, wherein the step (D) comprises: a polishing process, a granulation process, and a sintering process. The method for preparing a lithium iron phosphate material according to claim 1, wherein the lithium precursor is at least one selected from the group consisting of LiOH, Li ₂ CO ₃ , LiNO ₃ , CH ₃ COOLi, Li ₂ C ₂ O ₄ , Li ₂ A group consisting of SO ₄ , LiCl, LiBr, LiI, LiH ₂ PO ₄ , Li ₂ HPO ₄ , Li ₃ PO ₄ , and a compound containing crystal water. The method for preparing a lithium iron phosphate material according to claim 1, wherein the iron precursor is at least one selected from the group consisting of FeCl ₂ , FeBr ₂ , FeI ₂ , FeSO ₄ , (NH ₄ ) ₂ Fe(SO ₄ ) ₂ , Fe ₂ O ₃ , Fe(NO ₃ ) ₃ , FeC ₂ O ₄ , (CH ₃ COO) ₂ Fe, FeCO ₃ , Fe ₃ (PO ₄ ) ₂ , FePO ₄ , and compounds containing crystal water Group of. The method for preparing a lithium iron phosphate material according to claim 1, wherein the phosphorus precursor is at least one selected from the group consisting of H ₃ PO ₄ , NaH ₂ PO ₄ , Na ₂ HPO ₄ , and Mg ₃ (PO ₄ ) _{2 .} a group consisting of (NH ₄ ) ₂ HPO _{4 ,} NH ₄ H ₂ PO ₄ , LiH ₂ PO ₄ , Li ₂ HPO ₄ , Li ₃ PO ₄ , and a compound containing water of crystallization. The method for preparing a lithium iron phosphate material according to claim 1, wherein in the step (B), the temperature of the water removal process is between 400 and 650 °C. The method for preparing a lithium iron phosphate material according to claim 1, wherein in the step (B), the water removal process has a time of 4 to 8 hours. The method for preparing a lithium iron phosphate material according to the third aspect of the invention, wherein the material of the lithium iron phosphate coarse material obtained by the polishing process has a particle size of 0.1 to 5 μm, preferably 0.7 to 1 μm. The method for preparing a lithium iron phosphate material according to claim 3, wherein the viscosity of the lithium iron phosphate crude material obtained by the polishing process is between 1000 and 10000 cps, preferably between 2,500 and 5,000 cps. The method for preparing a lithium iron phosphate material according to claim 3, wherein the purity of the lithium iron phosphate crude material obtained by the sintering process is 97% or more.