KR102369513B1 - Method for preparing fluorophosphate-based secondary battery cathode active material, fluorophosphate-based secondary battery cathode active material manufactured through the method and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a method for preparing a fluorophosphate-based positive electrode active material of a secondary battery, a fluorophosphate-based positive electrode active material of a secondary battery obtained therethrough, and a secondary battery. The method according to the present invention includes the steps of: carrying out primary heat treatment of a mixture of a phosphate compound with a metal compound or metal phosphate hydrate to prepare a single phase of metal phosphate compound; analyzing the crystal phase of the resultant single-phase of metal phosphate compound; mixing the analyzed single phase of metal phosphate compound with a fluoride compound to prepare a mixture of the single phase of metal phosphate compound with the fluoride compound; drying the mixture of the single phase of metal phosphate compound with the fluoride compound; and carrying out secondary heat treatment of the dried mixture of the single phase of metal phosphate compound with the fluoride compound to obtain a single phase of fluorophosphate compound. According to the present invention, it is possible to obtain a fluorophosphate-based positive electrode active material of a secondary battery which forms single-phase crystals and shows improved conductivity, and thus provides a secondary battery with improved charge/discharge characteristics.

Description

Fluorophosphate-based secondary battery cathode active material manufacturing method, fluorophosphate-based secondary battery cathode active material and secondary battery manufactured through the same AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a method for manufacturing a fluorophosphate-based secondary battery cathode active material, a fluorophosphate-based secondary battery cathode active material and a secondary battery manufactured through the method, and more particularly, a single-phase XMePO ₄ F (X = Li, Na) It relates to a method for manufacturing a fluorophosphate-based positive electrode active material for a secondary battery that can be manufactured, and to a positive electrode active material for a fluorophosphate-based secondary battery manufactured through the same and a secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

A lithium transition metal composite oxide is used as a cathode active material for a lithium secondary battery, and among them, a lithium cobalt composite metal oxide of LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO ₂ has very poor thermal properties due to destabilization of the crystal structure due to lithium removal and is expensive, so there is a limit to its mass use as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxide (LiMnO ₂ or LiMn ₂ O ₄ etc.), lithium iron phosphate compound (LiFePO ₄ etc.) or lithium nickel composite metal oxide (LiNiO ₂ etc.), etc. have been developed. Among them, research and development of lithium-nickel composite metal oxide, which has a high reversible capacity of about 200 mAh/g, and is easy to realize a large-capacity battery, is being actively studied. However, LiNiO ₂ has poor thermal stability compared to LiCoO ₂ , and when an internal short circuit occurs in a charged state due to external pressure or the like, the positive active material itself is decomposed to cause rupture and ignition of the battery.

The existing LiFePO ₄ positive electrode active material has high thermal stability and excellent theoretical capacity, but has a problem in that electrochemical properties are deteriorated due to low electrical conductivity.

In order to solve this problem, XFePO ₄ F (X = Li, Na) positive electrode active material with added fluorine (F) is required. However, in the case of XFePO ₄ F positive electrode active material, Li ion deficiency occurs during synthesis at high temperature. Secondary phases such as Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₃ PO ₄ , FeF ₃ , FePO ₄ and the like are generated, making it difficult to prepare a single phase. For this reason, there is a problem in that it is necessary to additionally add Li ions in consideration of a situation in which Li ions are insufficient.

Therefore, there is a need for research on preparing a single-phase XFePO ₄ F cathode active material.

Republic of Korea Patent Publication No. 2207105, "Method for manufacturing a cathode active material for a secondary battery" Korean Patent Publication No. 2225821, "Method for manufacturing positive electrode active material and positive electrode active material"

An embodiment of the present invention is to provide a method for preparing a fluorophosphate-based secondary battery cathode active material capable of producing single-phase XMePO ₄ F (X = Li, Na), and a fluorophosphate-based secondary battery cathode active material manufactured through the same.

An embodiment of the present invention is to provide a secondary battery comprising a fluorophosphate-based secondary battery positive electrode active material with improved charge and discharge characteristics of a secondary battery by improving electrical conductivity by forming single-phase crystals of a fluorophosphate-based secondary battery positive active material do.

An embodiment of the present invention is to provide a secondary battery including a fluorophosphate-based secondary battery positive electrode active material capable of determining crystallographic and electromagnetic properties through Mossbauer measurement according to the temperature of a single-phase fluorophosphate-based secondary battery positive electrode active material. .

A method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the steps of: preparing a single-phase metal phosphate compound by performing primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate; analyzing the crystalline phase of the prepared single-phase metal phosphate compound; preparing a mixture of a single-phase metal phosphate compound and a fluoride compound by mixing the analyzed single-phase metal phosphate compound and a fluoride compound; drying the mixture of the single-phase metal phosphate compound and the fluoride compound; and preparing a single-phase fluorophosphate compound by subjecting the dried single-phase mixture of the metal phosphate compound and the fluoride compound to a secondary heat treatment.

The single-phase fluorophosphate compound may have a structure of Formula 1 below.

[Formula 1]

XFePO ₄ F (X = Li, Na)

The mixing time of the mixture of the phosphate compound and the metal compound may be 1 minute to 1 hour.

The phosphate compound is ammonium phosphate monobasic, ammonium phosphate dibasic, ammonium dihydrogen phosphate, di-ammonium hydrogen phosphate, and a third At least one of ammonium phosphate tribasic trihydrate may be included.

The single-phase metal phosphate compound may have a hexagonal structure.

The first heat treatment of the mixture of the phosphate compound and the metal compound or the metal phosphate hydrate to prepare a single-phase metal phosphate compound includes: calcining the mixture of the phosphate compound and the metal compound; and sintering a mixture of the calcined phosphate compound and the metal compound.

The calcination of the mixture of the phosphate compound and the metal compound may be performed at a temperature of 300°C to 400°C.

The step of sintering the mixture of the calcined phosphate compound and the metal compound may be performed at a temperature of 870°C to 900°C.

A mixing ratio of the mixture of the single-phase metal phosphate compound and the fluoride compound may be 1:1.05 or 1:1.1.

The mixture of the single-phase metal phosphate compound and the fluoride compound may be mixed using a defoaming and kneading device.

The second heat treatment of the dried single-phase mixture of the metal phosphate compound and the fluoride compound to prepare a single-phase fluorophosphate compound may be performed at a temperature of 575° C. to 650° C.

The fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention includes a single-phase fluorophosphate compound prepared by the method for preparing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, and the single-phase fluorophosphate compound has the structure of Formula 1 below.

[Formula 1]

XFePO ₄ F (X = Li, Na)

A secondary battery according to an embodiment of the present invention includes a positive electrode including a positive electrode active material for a fluorophosphate-based secondary battery according to an embodiment of the present invention; a negative electrode facing the positive electrode; and an electrolyte positioned between the positive electrode and the negative electrode.

According to an embodiment of the present invention, to provide a method for manufacturing a fluorophosphate-based secondary battery positive active material capable of producing single-phase XMePO ₄ F (X = Li, Na), and a fluorophosphate-based secondary battery positive active material manufactured through this method can

According to an embodiment of the present invention, by forming a single-phase crystal of a fluorophosphate-based secondary battery positive electrode active material, electrical conductivity is improved to provide a secondary battery comprising a fluorophosphate-based secondary battery positive electrode active material with improved charge and discharge characteristics can provide

According to an embodiment of the present invention, there is provided a secondary battery comprising a fluorophosphate-based secondary battery positive electrode active material capable of determining crystallographic and electromagnetic properties through Mossbauer measurement according to the temperature of a single-phase fluorophosphate-based secondary battery positive electrode active material can do.

1 is a flowchart illustrating a method of manufacturing a fluorophosphate-based positive electrode active material for a secondary battery according to an embodiment of the present invention.
2 is a schematic diagram illustrating a process of insertion/desorption of lithium/sodium from an electrode in a secondary battery including a positive electrode active material for a fluorophosphate-based secondary battery according to an embodiment of the present invention.
3 is a graph showing the XRD analysis result of the metal phosphate compound prepared in the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention.
4 is a graph showing a room temperature Mossbauer spectrum of a metal phosphate compound prepared in the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention.
5 is a graph showing the XRD analysis results according to the synthesis temperature of the fluorophosphate-based secondary battery cathode active material (LiFePO4F(FePO4:LiF=1:1)) according to Comparative Example 1. Referring to FIG.
6 is a graph showing the XRD analysis results according to the synthesis temperature of the fluorophosphate-based secondary battery cathode active material (LiFePO4F(FePO4:LiF=1:1.05, 1:1.1)) according to Examples 1 and 2 of the present invention.
7 is a graph showing the XRD analysis result of a fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.
8 is a graph illustrating a room temperature Mossbauer spectrum of a fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.
9 is a graph showing the Mossbauer spectrum according to the temperature of the fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings and contents described in the accompanying drawings, but the present invention is not limited or limited by the embodiments.

The terminology used herein is for the purpose of describing the embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, "comprises" and/or "comprising" does not exclude the presence or addition of one or more other elements, steps, or elements mentioned.

As used herein, “embodiment”, “example”, “aspect”, “exemplary”, etc. are to be construed as advantageous in any aspect or design described as being preferred or advantageous over other aspects or designs. is not doing

Also, the term 'or' means 'inclusive or' rather than 'exclusive or'. That is, unless stated otherwise or clear from context, the expression 'x employs a or b' means any of natural inclusive permutations.

Also, as used herein and in the claims, the singular expression "a" or "an" generally means "one or more," unless stated otherwise or clear from the context that it relates to the singular form. should be interpreted as

The terms used in the description below have been selected as general and universal in the related technical field, but there may be other terms depending on the development and/or change of technology, customs, preferences of technicians, and the like. Therefore, the terms used in the description below should not be construed as limiting the technical idea, but as illustrative terms for describing the embodiments.

In addition, in a specific case, there is a term arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the corresponding description. Therefore, the terms used in the description below should be understood based on the meaning of the term and the content throughout the specification, rather than the simple name of the term.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly defined in particular.

Meanwhile, in the description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms used in this specification are terms used to properly express the embodiment of the present invention, which may vary according to the intention of a user or operator or customs in the field to which the present invention belongs. Accordingly, definitions of these terms should be made based on the content throughout this specification.

1 is a flowchart illustrating a method of manufacturing a fluorophosphate-based positive electrode active material for a secondary battery according to an embodiment of the present invention.

The method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the steps of preparing a single-phase metal phosphate compound by performing primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate (S110), the prepared single Analyzing the crystal phase of the metal phosphate compound (S120), mixing the analyzed single-phase metal phosphate compound and the fluoride compound to prepare a mixture of the single-phase metal phosphate compound and the fluoride compound (S130), single-phase metal Drying the mixture of the phosphate compound and the fluoride compound (S140) and the second heat treatment of the dried single-phase mixture of the metal phosphate compound and the fluoride compound to prepare a single-phase fluorophosphate compound (S150).

The method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises two steps (primary synthesis to prepare a single-phase metal phosphate compound and secondary synthesis to prepare a single-phase fluorophosphate compound) By preparing a single-phase fluorophosphate compound by a direct synthesis method (solid state reaction), the manufacturing process is simple and easy compared to other chemical synthesis methods (ionothermal, solvothermal, sol-gel, etc.).

In addition, although the fluorophosphate-based secondary battery positive active material is one of the materials lacking in prior research, the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention can prepare a single-phase fluorophosphate compound, preferably , the single-phase fluorophosphate compound may have the structure of Formula 1 below.

[Formula 1]

XFePO ₄ F (X = Li, Na)

First, the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the steps of preparing a single-phase metal phosphate compound by performing primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate (S110) (1) tea synthesis).

Preferably, the first heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate to prepare a single-phase metal phosphate compound (S110) uses a mixture of a phosphate compound and a metal compound as a starting material, or a metal phosphate hydrate can be used alone.

The mixture of the phosphate compound and the metal compound may be the first mixture.

When a mixture of a phosphate compound and a metal compound (first mixture) is used as a starting material, there is a process of mixing unlike in the case of using the metal phosphate hydrate alone, and when the heat treatment temperature and time are too low or too high, the secondary Phases may occur, but when mixed according to the equivalence ratio, the temperature and time according to the amount of heat treatment are not variable, unlike the metal phosphate hydrate used alone, and an optimal crystallized phase can be ensured through the heat treatment process.

Accordingly, when a mixture of a phosphate compound and a metal compound (the first mixture) is used as the starting material, the method may further include preparing a mixture of the phosphate compound and the metal compound by mixing the phosphate compound and the metal compound.

The mixing time of the mixture of the phosphate compound and the metal compound (the first mixture) may be from 1 minute to 1 hour, if the mixing time is less than 1 minute, it is highly unlikely that the mixture will be mixed properly, and if it exceeds 1 hour, a small amount in the mixing process of secondary phase materials can be synthesized.

In addition, when a mixture of a phosphate compound and a metal compound (a first mixture) is used as the starting material, the phosphate compound and the metal compound may be mixed in an equivalent ratio.

If the phosphate compound and the metal compound are not mixed in a reaction equivalent ratio, a secondary phase may exist during the heat treatment process.

According to the embodiment, since the phosphate compound has a rather large crystal solid state, the phosphate compound is pulverized and mixed, and then the phosphate compound and the metal compound are mixed to prepare a mixture of the phosphate compound and the metal compound You can proceed with the steps to

In addition, when a mixture of a phosphate compound and a metal compound (first mixture) is used as a starting material, the mixing time of the pulverized phosphate compound and the metal compound may be 30 minutes to 1 hour, and the mixing time is less than 30 minutes If it is, it may not be mixed properly, and if it exceeds 1 hour, a small amount of secondary phase material may be synthesized according to the loss rate in the mixing process.

The phosphate compound is ammonium phosphate monobasic, ammonium phosphate dibasic, ammonium dihydrogen phosphate, di-ammonium hydrogen phosphate and triphosphate. It may include at least one of ammonium phosphate tribasic trihydrate.

In the step of preparing a mixture of the phosphate compound and the metal compound by mixing the phosphate compound and the metal compound, ammonium phosphate dibasic or di-ammonium hydrogen phosphate is used as the phosphate compound. In this case, when exposed at room temperature for a long time, it is decomposed into ammonia and the loss rate is gradually increased, so it must be mixed quickly within 10 minutes.

In addition, as the temperature increases, it is decomposed into ammonia and ammonium phosphate monobasic to form a secondary phase when the final XFePO ₄ F positive electrode active material is generated. Preferably, ammonium monobasic acid A phosphate compound such as ammonium phosphate monobasic or ammonium dihydrogen phosphate may be used.

The metal compound may include at least one of iron (III) oxide (iron (III) oxide), iron (II, III) oxide, and iron oxalate dihydrate. there is.

When metal phosphate hydrate is used alone as a starting material, only the hydrate (H ₂ O) needs to be removed through a heat treatment process without a separate mixing process. This is low, and the heat treatment process to remove only the hydrate is relatively simple.

In addition, unlike the method of using a mixture of a phosphate compound and a metal compound (the first mixture), there is an advantage that only a heat treatment process is performed, but it is necessary to control the process for removing H ₂ O attached to the metal phosphate hydrate.

Since the metal phosphate hydrate before heat treatment has an amorphous form, if the heat treatment temperature and time are insufficient, a crystallized phase cannot be obtained because the amorphous crystallization time is insufficient. On the other hand, if the heat treatment temperature and time are exceeded, the mass loss increases do.

In addition, the heat treatment temperature and time may vary depending on the amount of the metal phosphate hydrate to be heat treated. For example, when a small amount of metal phosphate hydrate is heat treated, the heat treatment temperature and time must be reduced, and when a large amount of metal phosphate hydrate is heat treated, the heat treatment temperature and time must be relatively increased. Therefore, in order to obtain an optimal metal phosphate, an appropriate heat treatment temperature and time are required.

The metal phosphate hydrate may include at least one of iron(III) phosphate hydrate, iron(III) phosphate dihydrate, and iron(III) phosphate tetrahydrate. .

When a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate is first heat treated to prepare a single-phase metal phosphate compound (S110), when a mixture of a phosphate compound and a metal compound (first mixture) is used as a starting material, phosphate The first heat treatment of a mixture of a compound and a metal compound or a metal phosphate hydrate to prepare a single-phase metal phosphate compound ( S110 ) includes calcining a mixture of a phosphate compound and a metal compound and a calcined phosphate compound and a metal compound It may include the step of sintering the mixture of.

The step of calcining the mixture of the phosphate compound and the metal compound is a calcination step to remove ammonia and moisture (H ₂ O) generated during the reaction, and the mixture of the phosphate compound and the metal compound is calcined. The reaction temperature of the step of (calcination) may be 300 °C to 400 °C, and the reaction time may be 6 hours to 10 hours.

If the reaction temperature of the step of calcining the mixture of the phosphate compound and the metal compound is less than 300°C, the moisture and ammonia generated during the initial reaction are significantly left, which is added to the pellets in the step of sintering the mixture of the phosphate compound and the metal compound. This may result in cracks. On the other hand, when it exceeds 400° C., moisture and ammonia are removed, but there is a problem that there is a possibility that some secondary phases are formed.

If the reaction time of the step of calcining the mixture of the phosphate compound and the metal compound is less than 6 hours, there is a problem that there is insufficient time to sufficiently remove ammonia and moisture, and if it exceeds 10 hours, the reaction time is too long and some secondary phases are can be synthesized.

However, the reaction temperature and time of the step of calcining the mixture of the phosphate compound and the metal compound are not limited thereto, and a sufficient temperature and time to remove ammonia and moisture (H ₂ O) generated during the reaction. This may take more.

After performing the step of calcining the mixture of the phosphate compound and the metal compound, the calcined primary mixture is mixed again for 30 minutes to 1 hour, and then molded into pellets at a final reaction temperature of 870 ° C. to 900 ° C. for 8 hours The step of sintering the mixture of the phosphate compound and the metal compound may be performed by heat treatment for 12 hours.

After performing the step of calcining the mixture of the phosphate compound and the metal compound, the primary mixture in the calcined powder state is mixed again, and then formed into pellets to sinter the mixture of the phosphate compound and the metal compound. The reason is that when the pellets are heated to a temperature below the melting point of the primary mixture, the mixture solidifies and bonds to form a crystallized phase. If the step of sintering the mixture of the phosphate compound and the metal compound in the form of a powder rather than a pellet is performed, there is a problem in that a completely crystallized phase cannot be obtained.

The step of sintering the mixture of the phosphate compound and the metal compound is for sintering the calcined primary mixture, and if the reaction temperature of the step of sintering the mixture of the phosphate compound and the metal compound is less than 870° C., an amorphous or secondary phase is formed before the crystalline phase is formed. There is a problem that may exist, and when it exceeds 900° C., an additional secondary phase may be formed beyond crystalline phase formation.

If the reaction time of the step of sintering the mixture of the phosphate compound and the metal compound is less than 8 hours, there is a problem that amorphous or secondary phase formation exists due to insufficient time for phase formation, and when it exceeds 12 hours, additional new A secondary phase may form.

Both the calcination step and the sintering step may be performed in air, and the first synthesized single-phase metal phosphate compound may have a pale gray color.

When a metal phosphate hydrate is used as a starting material in the step S110 of preparing a single-phase metal phosphate compound by primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate, a mixture of a phosphate compound and a metal compound or a metal phosphate compound The step (S110) of preparing a single-phase metal phosphate compound by performing a primary heat treatment of the hydrate is to sufficiently remove moisture (H ₂ O) by heating it in air at 675 ° C. to 825 ° C. for 8 hours, whereby the primary synthesized single-phase metal A phosphate compound can be obtained.

When a metal phosphate hydrate is used as a starting material, if the reaction temperature in the step (S110) of preparing a single-phase metal phosphate compound by primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate is less than 675° C., moisture (H 2 O ) may not be sufficiently removed, and if it exceeds 825°C, there is a problem of causing mass loss. However, the reaction temperature of the step ( S110 ) of preparing a single-phase metal phosphate compound by performing primary heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate may vary flexibly depending on the number of hydrates attached thereto.

When a metal phosphate hydrate is used as a starting material, the reaction time of the step (S110) of preparing a single-phase metal phosphate compound by first heat-treating a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate may proceed about 8 hours, and , if the reaction time is short, there is a problem in that moisture is not sufficiently removed, and if the reaction time is too long, there may be mass loss. However, the reaction time may vary flexibly depending on the number of hydrates attached thereto.

In addition, when a metal phosphate hydrate is used as a starting material, the heat treatment temperature and reaction time are sufficiently flexible depending on the number of hydrates attached to the metal phosphate hydrate and the amount of metal phosphate hydrate to be heat treated as variables for obtaining a single phase metal phosphate. can be changed to

However, the reaction temperature and time are not limited thereto, and a sufficient temperature and time may be required to remove moisture (H ₂ O) generated during the reaction.

Preferably, the single-phase metal phosphate compound prepared by performing the first heat treatment of a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate to prepare a single-phase metal phosphate compound (S110) is iron phosphate (FePO ₄ ) can

In addition, the prepared single-phase metal phosphate compound may have a hexagonal structure.

Thereafter, in the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, a step (S120) of analyzing the crystalline phase of the prepared single-phase metal phosphate compound may be performed.

The step of analyzing the crystal phase of the prepared single-phase metal phosphate compound (S120) is to verify whether the firstly synthesized single-phase metal phosphate compound was synthesized as a single phase, and the analysis step of the single-phase metal phosphate compound was performed by Mossbauer spectroscopy. Alternatively, an X-ray diffraction method (XRD, X-Ray Diffraction) may be used, and if a single-phase metal phosphate compound having a hexagonal structure is not identified using Mossbauer spectroscopy or X-ray diffraction, the analyzed single-phase metal phosphate compound and mixing the fluoride compound to prepare a mixture of the single-phase metal phosphate compound and the fluoride compound ( S130 ) is not performed.

XRD can be used as the most general method for analyzing the crystal phase of a single-phase metal phosphate compound, but it is somewhat difficult to determine whether a small amount of secondary phase (Fe _{(1-x or 1+x)} PO ₄ +α) is possible. .

If a small amount of secondary phase is present in the metal phosphate compound, since the Fe ion state is changed, the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention uses Mossbauer spectroscopy to determine whether a secondary phase exists can be checked.

For example, the Fe ion value of iron phosphate (FePO ₄ ) exists in the Fe ³⁺ (ferric) state of one site so that a symmetric Mösbauer spectrum is measured, but when a secondary phase exists, Fe ³⁺ and Fe ²⁺ An asymmetrical spectrum in which (ferrous) is mixed or Fe ³⁺ states of two or more sites exist can be measured.

In addition, in the manufacture of a fluorophosphate-based secondary battery cathode active material, the possibility of forming a secondary phase in the final heat treatment of the cathode active material is very high, and there is a problem that the mixing ratio of the metal phosphate compound and the fluoride compound may vary, and the possibility of reproducibility of the cathode active material occurs. Since there is a problem of remarkably lowering, in the method of manufacturing a fluorophosphate-based positive electrode active material for a secondary battery according to an embodiment of the present invention, the metal phosphate compound must be formed as a single phase in order to increase the possibility of reproducibility.

The crystal structure of metal phosphate compounds (eg, iron phosphate, FePO ₄ ) is monoclinic and orthorhombic in addition to the hexagonal structure. A positive electrode active material can be obtained.

If monoclinic or orthorhombic iron phosphate is used, the structure of the final anodic material may be monoclinic or orthorhombic, but this is not a common case and is highly unlikely to be formed well.

Thereafter, the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the steps of preparing a mixture of a single-phase metal phosphate compound and a fluoride compound by mixing the analyzed single-phase metal phosphate compound and a fluoride compound ( S130) is performed.

The mixture of the single phase metal phosphate compound and the fluoride compound may be a second mixture.

The fluoride compound may include at least one of lithium fluoride (LiF) and sodium fluoride (NaF).

Since the fluoride compound may be evaporated at a high temperature, it may be mixed so that the ratio of fluoride to the single-phase metal phosphate compound exceeds 5% to 10% in consideration of evaporation at high temperature.

That is, if the mixing ratio of the single-phase metal phosphate compound and the fluoride compound is less than 1:1.05, the single-phase metal phosphate compound has a relatively high ratio of the single-phase metal phosphate compound because the fluoride compound evaporates at a high temperature compared to the single-phase metal phosphate compound, so the unreacted iron There is a problem in that phosphate is present, and when it exceeds 1:1.1, a fluoride compound remaining after the reaction exists, and other secondary phases (Li ₃ Fe ₂ (PO ₄ ) ₃ , FeF ₃ , etc.) may be formed.

The single phase metal phosphate compound and the fluoride compound may be mixed by adding a solvent, for example, the solvent may include at least one of ethanol, distilled water, and acetone, but the boiling point is relatively lower than that of ethanol. It is preferable to use ethanol having a low polarity and good solubility, while avoiding its use.

The mixture of the single phase metal phosphate compound and the fluoride compound (the second mixture) may be mixed with a defoaming and kneading device (foamless centrifugal stirrer) at 1500 rpm to 2000 rpm for 15 minutes to 30 minutes.

If the rotation speed of the degassing and kneading device is less than 1500 rpm, there is a problem that the mixture is not uniformly mixed, and when it exceeds 2000 rpm, the mixture is separated and not mixed.

If the mixing time of the single phase of the metal phosphate compound and the fluoride compound is less than 15 minutes, there is a problem that the mixture is not uniformly mixed, and because it is sufficiently uniformly mixed even after only 30 minutes, it is not unnecessarily mixed for more than 30 minutes.

When mixing using the mechanical milling method, a large amount of bubbles are generated while the compounds are mixed, but in the case of the stirring method using a defoaming and kneading device, the oxygen present in the bubbles in the mixture is removed while stirring and defoaming are performed simultaneously and the compound within a short time. can be mixed efficiently.

On the other hand, mechanical milling methods (e.g., ball mill, attrition mill, spex mill, etc.) require at least 12 to 24 hours of mixing time, but the defoaming and kneading device has the advantage of being able to mix for a short time of 15 to 30 minutes. there is.

In addition, in the case of mixing using the direct synthesis method, mixing is not performed well due to the difference in molecular weight between the metal phosphate (eg, iron phosphate) and the fluoride compound (eg, lithium/sodium ply) when mixing is performed by the mechanical milling method. Therefore, a single phase cannot be generated.

Therefore, in the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, a single-phase fluorophosphate compound is mixed using a degassing and kneading device by mixing a mixture of a single-phase metal phosphate compound and a fluoride compound (second mixture). It is possible to manufacture a cathode active material for a base secondary battery.

Thereafter, in the method of manufacturing a fluorophosphate-based positive electrode active material for a secondary battery according to an embodiment of the present invention, a step (S140) of drying a mixture of a single-phase metal phosphate compound and a fluoride compound is performed.

In the step of drying the mixture of the single-phase metal phosphate compound and the fluoride compound (S140), the single-phase mixture of the metal phosphate compound and the fluoride compound (second mixture) is transferred from the defoaming and kneading device to a glass Petri dish, and then the single phase A mixture of the metal phosphate compound and the fluoride compound (the second mixture) may be placed in a vacuum dryer and dried under a vacuum of 600 mmHg to 750 mmHg.

The internal temperature of the vacuum dryer may be 60 ℃ to 100 ℃, if the internal temperature is less than 60 ℃ there is a problem that the time to dry the mixture becomes too long, and the mixture is sensitive to oxidation, so it does not exceed 100 ℃.

In addition, in consideration of the boiling point and vacuum state of ethanol as a solvent, vacuum drying may be performed at 60° C. to 100° C.

The drying time may be 12 hours to 24 hours, and if the drying time is less than 12 hours, there is a problem that there is not enough time for the solvent to evaporate and moisture may remain, and if the drying time is not completely dried, the single-phase metal phosphate In the second heat treatment of the mixture of the compound and the fluoride compound, oxidation may occur in the mixture (the second mixture) of the single-phase metal phosphate compound and the fluoride compound by moisture.

In addition, considering the vacuum drying, drying the mixture in a vacuum lower than atmospheric pressure lowers the boiling point of the solvent, so it dries within a short time, so even if drying is performed within 24 hours, it is sufficient time for the mixture to be completely dried.

In addition, it must be carried out in a vacuum to prevent oxidation of Fe, and in the case of a general (atmospheric pressure) high temperature dryer, the possibility of secondary phase formation is high. may occur in some cases.

In addition, the internal temperature and drying time of the vacuum dryer of the mixture of the single-phase metal phosphate compound and the fluoride compound (second mixture) are not limited thereto, and the mixture of the single-phase metal phosphate compound and the fluoride compound (second mixture) is not It can be adjusted from the amount.

In the case of a mixture (second mixture) of a single-phase metal phosphate compound and a fluoride compound mixed in a defoaming and kneading device, it exists in a high-viscosity liquid state, and a drying step is performed to make it a powder-type mixture, and finally heat treatment You can grind it one last time to make it even more homogeneous.

In addition, it is possible to prevent the occurrence of cracking or oxidation of the pellets by the gas in the mixture in the final heat treatment process by removing the bubbles (gas) in the mixture through the degassing and kneading device and the drying step (S140).

Finally, the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the steps of preparing a single-phase fluorophosphate compound by performing secondary heat treatment on a mixture of a dried single-phase metal phosphate compound and a fluoride compound (S150) ) is carried out.

First, the dried single-phase mixture of the metal phosphate compound and the fluoride compound (the second mixture) is pulverized for 30 minutes, and then the mixture of the single-phase metal phosphate compound and the fluoride compound dried by molding into pellets is subjected to secondary heat treatment To prepare a single-phase fluorophosphate compound (S150) (secondary synthesis) may proceed.

In the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, a mixture of a single-phase metal phosphate compound and a fluoride compound (second mixture) is molded into pellets so that the mixture in the form of pellets is hardened at a high temperature. Since the crystallized phase is formed while being combined, a relatively amorphous phase can be obtained if the secondary heat treatment step is performed in the form of a powder.

The step of preparing a single-phase fluorophosphate compound by performing secondary heat treatment on a mixture of the dried single-phase metal phosphate compound and the fluoride compound (S150) is a mixture of the dried single-phase metal phosphate compound and the fluoride compound (second mixture). Sintering may be carried out at 575 ° C. to 650 ° C. for 1.5 hours to 2 hours.

If the reaction temperature of the step (S150) of preparing a single-phase fluorophosphate compound by secondary heat treatment of a mixture of a dried single-phase metal phosphate compound and a fluoride compound is less than 575° C., the starting material is insufficient to form a phase. There is a problem of not reacting (the starting material (FePO ₄ ) is still present), and when it exceeds 650° C., Li ₃ Fe ₂ (PO ₄ ) ₃ in a mixture of a single-phase metal phosphate compound and a fluoride compound (second mixture) Alternatively, a secondary phase such as Li ₃ PO ₄ , FeF ₃ and the like begins to decompose may be formed.

The method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention comprises the second heat treatment of a mixture of a dried single-phase metal phosphate compound and a fluoride compound to prepare a single-phase fluorophosphate compound (S150) Reaction of Depending on the temperature, the crystallographic properties can be controlled.

If the reaction time of the step (S150) of preparing a single-phase fluorophosphate compound by secondary heat treatment of a mixture of a dried single-phase metal phosphate compound and a fluoride compound is less than 1.5 hours, the final synthetic material is not sufficient to form a phase There is a problem that it cannot be made, and if it exceeds 2 hours, oxidation in the surface may occur.

The synthesis atmosphere of the step (S150) of preparing a single-phase fluorophosphate compound by secondary heat treatment of a mixture of a dried single-phase metal phosphate compound and a fluoride compound is argon, nitrogen, or an argon-nitrogen mixed gas (argon 95%-hydrogen 5 %) can be

In the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, a second heat treatment is performed on a mixture of a dried single-phase metal phosphate compound and a fluoride compound to prepare a single-phase fluorophosphate compound (S150). After that, the step of verifying the single-phase fluorophosphate compound may be performed.

The step of verifying the single-phase fluorophosphate compound may use Mossbauer spectroscopy or XRD.

Preferably, the step of verifying the single-phase fluorophosphate compound can be verified by confirming that a single doublet-shaped spectrum is exhibited through Mösbauer spectroscopy with higher resolution than XRD.

If a secondary phase exists in the primary synthesized single-phase metal phosphate compound (eg, iron phosphate), an asymmetric doublet spectrum of Fe _x PO ₄ material or a metal compound as a starting material (eg, Fe) A spectrum in the form of six lines for ₂ O ₃ ) can be observed.

That is, in the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, the presence or absence of a secondary phase of a metal phosphate compound, which is a primary synthesized material, is checked by Mossbauer spectroscopy or XRD, and the secondary synthesized material is A single-phase fluorophosphate compound can be synthesized by verifying the presence or absence of a secondary phase using Mossbauer spectroscopy.

Therefore, the fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention includes a single-phase fluorophosphate compound prepared by the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, and a single-phase fluorophosphate The compound has the structure of Formula 1 below.

[Formula 1]

XFePO ₄ F (X = Li, Na)

The positive electrode active material for a fluorophosphate-based secondary battery according to an embodiment of the present invention has a single phase, so that electrical conductivity is improved, thereby improving charge/discharge characteristics of the secondary battery.

The cathode active material used in secondary batteries is being studied based on actual commercial use. However, in the case of a positive electrode active material having a secondary phase, reproducibility for commercial application is insufficient. For example, it is somewhat difficult to reproduce the same type of secondary phase material and ratio as it is every time through a heat treatment process.

Therefore, the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention can increase the commercial application potential by securing the reproducibility of the single-phase fluorophosphate compound manufacturing.

In particular, the method for manufacturing a fluorophosphate-based positive electrode active material for a secondary battery according to an embodiment of the present invention can prepare a single phase of a fluorophosphate compound, which has not been solved in conventional studies, by using a direct synthesis method.

According to the embodiment, the method of manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention may be utilized for manufacturing other positive electrode active materials in addition to single-phase XFePO ₄ F (X = Li, Na) using the same manufacturing method. can

2 is a schematic diagram illustrating a process of insertion/desorption of lithium/sodium from an electrode in a secondary battery including a positive electrode active material for a fluorophosphate-based secondary battery according to an embodiment of the present invention.

A secondary battery according to an embodiment of the present invention is a positive electrode 110 including a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, a negative electrode 120 and a positive electrode 110 positioned opposite to the positive electrode 110 and an electrolyte 130 positioned between the anode 120 .

A secondary battery refers to a battery in which a positive electrode 110 and a negative electrode 120 can repeatedly perform a charge/discharge process.

Therefore, in the secondary battery, the process of insertion and extraction of ions in the battery should be smooth. The secondary battery including the positive electrode active material of the fluorophosphate-based secondary battery according to the embodiment of the present invention uses fluorine ( By using the single-phase XFePO ₄ F (X = Li, Na) to which F) is added as the positive electrode active material, the electrical conductivity of the positive electrode 110 may be improved, thereby improving the charge/discharge characteristics of the secondary battery.

The secondary battery according to the embodiment of the present invention may include the positive electrode 110 .

The positive electrode 110 includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. In this case, the positive electrode active material layer may include a positive electrode active material in the secondary battery according to an embodiment of the present invention. In the secondary battery according to the embodiment of the present invention, the specific content of the positive electrode active material is the same as described above, and thus a detailed description thereof will be omitted.

In particular, the cathode active material is very important to play a large role in determining the capacity, output, and lifespan of the battery.

Therefore, the secondary battery according to the embodiment of the present invention is a single-phase XFePO ₄ F (X = Li, Na) positive electrode to which fluorine (F), which is a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, is added as a positive electrode active material By using the active material, the electrical conductivity of the positive electrode 110 may be improved, thereby improving the capacity, output, and lifespan of the battery of the secondary battery.

The positive electrode 110 may be manufactured according to a typical method of manufacturing the positive electrode 110 except that the secondary battery according to an embodiment of the present invention uses a positive electrode active material. For example, the positive electrode 110 is prepared by dissolving or dispersing the components constituting the positive electrode active material layer, that is, the positive electrode active material, the conductive material and/or the binder, in a solvent, and the positive electrode mixture is used as a positive electrode current collector. After coating on at least one surface of the, drying, rolling, or by casting the positive electrode composite material on a separate support, and then peeling from the support, it can be prepared by laminating the obtained film on the positive electrode current collector.

At this time, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, Those surface-treated with titanium, silver, etc. can be used.

In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

At least one surface of the positive electrode current collector includes the positive electrode active material for a fluorophosphate-based secondary battery according to an embodiment of the present invention, and a positive electrode active material layer optionally further comprising at least one of a conductive material and a binder may be positioned as needed. .

The cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the cathode active material layer.

The positive electrode active material constituting the positive electrode 110 occupies the largest proportion in the cost of the secondary battery, and is a material that plays the largest role in characteristics such as capacity and driving voltage of the battery. Therefore, if the content of the cathode active material is less than 80% by weight, there is a problem of lowering the performance of the battery due to a decrease in the capacity and energy density of the battery, and if it exceeds 99% by weight, the content of the conductive material and the binder is relatively reduced. As a result, there is a problem in that the performance of the battery is reduced.

The conductive material is a fine carbon powder added in a small amount for the purpose of improving electron conductivity by forming an electron conduction channel in the composite electrode. In particular, it is absolutely necessary to prevent the binder region from acting as an electronic insulator and to compensate for insufficient electron conductivity of the positive electrode active material.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. For example, the conductive material may be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used.

Preferably, a carbon-based material is mainly used as the conductive material, and for example, VGCF showing the highest conductivity or graphite fine powder advantageous in fairness such as mixing/coating is used, but VGCF has a high unit cost. Since a large amount of graphite fine powder is required for conductivity, it can generally be mixed with carbon black.

The conductive material may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer, and if the content is less than 1% by weight, the amount of the conductive material is not sufficient, resulting in not being able to perform the role of the conductive material properly, so that the positive electrode active material There is a problem in that a non-reactive part is generated, which leads to a decrease in the capacity of the secondary battery, and a potential distribution occurs during charging and discharging, thereby reducing the utilization rate of the powder active material.

On the other hand, if the content exceeds 30% by weight, there is a problem in that the loss of the positive electrode active material occurs due to the excessively included conductive material.

The binder serves to bind the positive electrode active material and the conductive material powder to the metal current collector, which is the current collector. Basically, the binder is an insulator and can maintain the structure of the electrode.

The binder should maintain binding force without being dissolved in the electrolyte, the coating processability (viscosity and dispersibility) of the mixture slurry should be excellent, and should have high heat resistance and oxidation resistance properties.

For example, the binder is polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose Woods (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

The binder may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer, and if the content is less than 1% by weight, it does not play a role in binding the positive electrode active material and the conductive material powder, so there is concern about a decrease in the fixing force of the metal current collector And, when the content exceeds 30 wt%, resistance in the positive electrode 110 increases to shorten the life of the electrode, and there is a problem in that the energy density is decreased due to a relative decrease in the ratio of the positive electrode active material. Therefore, it is necessary to stably apply the anode material and the conductive material powder using an appropriate amount of binder.

In addition, the solvent used in the preparation of the positive electrode composite material may be a solvent generally used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N- methyl pyrrol Money (NMP), acetone (acetone), water, etc. may be used alone or a mixture thereof. The amount of the solvent used may be appropriately adjusted in consideration of the application thickness of the slurry, the production yield, the viscosity, and the like.

The secondary battery according to an embodiment of the present invention may include a negative electrode 120 positioned to face the positive electrode 110 .

The negative electrode 120 may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

The negative electrode 120 may be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode 120 prepares a negative electrode mixture by dissolving or dispersing the components constituting the negative electrode active material layer, that is, the negative electrode active material, a conductive material and/or a binder, in a solvent, and using the negative electrode mixture as a negative electrode current collector It can be prepared by coating on at least one side of the substrate, followed by drying and rolling, or by casting the negative electrode mixture on a separate support and then laminating the film obtained by peeling from the support on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon on the surface of copper or stainless steel. , nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used.

In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOv (0<v<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used.

In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The binder and the conductive material may be the same as those described above for the positive electrode.

The secondary battery according to an embodiment of the present invention may include a negative electrode 120 and an electrolyte 130 positioned between the positive electrode 110 and the negative electrode 120 .

The electrolyte 130 may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a secondary battery.

Specifically, the electrolyte 130 may include an organic solvent and a lithium salt.

In the secondary battery according to the embodiment of the present invention, in addition to the positive electrode 110 , the negative electrode 120 , and the electrolyte 130 , the secondary battery is at least any one of a separator 140 , an exterior material, a battery container, a sealing member, a tab, and a safety element. More may be included.

The separator 140 separates the negative electrode 120 and the positive electrode 110 and provides a passage for lithium ions to move, and as long as it is used as the separator 140 in a secondary battery, it can be used without particular limitation, and in particular, the ions of the electrolyte It is preferable to have low resistance to movement and to have excellent electrolyte moisture content.

Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or A laminate structure of two or more layers thereof may be used.

In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

Example 1: LiFePO ₄ F (FePO ₄ :LiF=1:1.05)

To prepare a LiFePO4F cathode active material, firstly, Fe ₂ O3 and (NH ₄ )H ₂ PO ₄ material were mixed in a 1:1 ratio (based on 1 g of FePO4 material, Fe2O3 (99%); 0.5348 g, ( NH ₄ )H ₂ PO ₄ (99.99%); 0.7628 g, a value corrected for purity), calcined at 350° C. for 12 hours, re-ground into pellets, and then at 870° C. for 10 hours Sintered in air to finally prepare FePO ₄ material (10 g basis, Fe ₂ O ₃ (99%); 5.3477 g, (NH ₄ )H ₂ PO ₄ (99.99%); 7.6279 g, purity (purity) Corrected value (per gram, each starting material counted in multiples).

Secondarily, FePO ₄ and LiF prepared previously were mixed in a ratio of 1:1.05 and dissolved in ethanol (based on 1 g of LiFePO ₄ F material, 5 mL) (LiFePO ₄ F 1 g based, FePO ₄ (100%); 0.8532 g, LiF (99.98%); 0.1541 g, purity corrected value), and mixed for 15 minutes at 1500 rpm using a defoaming and kneading device (10 g basis, FePO ₄ (100%); 8.5325 g, LiF (99.98) %, greater than 5%): 1.5412 g, corrected for purity (per g, each starting material counted in multiples). The defoamed mixture was dried in a vacuum dryer at 80° C. for 18 hours.

The dried mixture was ground again to form pellets, and then heat-treated at 590° C. for 1.5 hours at 2° C. temperature increase rate in an argon (Ar) atmosphere tube electric furnace to finally prepare a LiFePO ₄ F cathode active material.

Example 2: LiFePO ₄ F (FePO ₄ :LiF=1:1.1)

In order to prepare 1 g of the LiFePO 4 F cathode active material, 0.8532 g of FePO ₄ and 0.1615 g of LiF were mixed and mixed in a mixing ratio of 1:1.1, except that the mixture was prepared in the same manner as in Example 1.

The purity of the prepared FePO ₄ material is 100%, the purity of the LiF material is corrected for 99.98%, and when you want to obtain a multiple of the amount of LiFePO ₄ F cathode active material, the amount of FePO ₄ and LiF material is It can be mixed in multiples.

Comparative Example: LiFePO ₄ F (FePO ₄ :LiF=1:1)

In order to prepare 1 g of the LiFePO 4 F cathode active material, 0.8532 g of FePO ₄ and 0.1468 g of LiF were mixed and mixed so as to have a mixing ratio of 1:1. It was prepared in the same manner as in Example 1.

It is a value corrected by 100% of the purity of the manufactured _FePO4 material and 99.98% of the purity of _the LiF material. It can be mixed and stretched.

3 is a graph showing the XRD analysis result of the metal phosphate compound prepared in the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention.

3 is an X-ray diffraction (XRD) analysis method as an analysis method in the step (S130) of analyzing the crystal phase of a single-phase metal phosphate compound prepared in the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention. It specifies the technology to be used.

In FIG. 3 , Yobs. is measured data, Ycalc. is a calculated value assuming a crystal structure from the measured data, Yobs.-Ycalc. is a difference from a calculated value assuming a crystal structure from the measured data, and the Bragg position ( Bragg position) indicates the position of the diffraction line by the crystal structure.

Referring to FIG. 3 , iron phosphate (FePO ₄ ), which is a metal phosphate compound synthesized in the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, is a hexagonal system having a P3121 space group (hexagonal, a=b). ≠c, α = β =90 ^o , γ =120 ^o ), it can be seen that the lattice constants are a = 5.0340 Å, c = 11.2449 Å, V = 246.778 Å ³ .

Accordingly, it can be seen that iron phosphate (FePO ₄ ), which is a metal phosphate compound synthesized in the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, has a single phase and has a hexagonal structure.

4 is a graph showing a room temperature Mossbauer spectrum of a metal phosphate compound prepared in the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention.

4 illustrates a technique using Mossbauer spectroscopy as an analysis method in the step (S130) of analyzing the crystalline phase of a single-phase metal phosphate compound prepared in the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention. did it

Referring to FIG. 4 , iron phosphate (FePO ₄ ), which is a metal phosphate compound prepared in the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, is one doublet-shaped spectrum at room temperature. It can be seen that isomer shift ( δ ) and electric quadrupole splitting ( ΔE _Q ) are 0.14 mm/s and 0.59 mm/s, respectively.

The Mösbauer parameter of the hexagonal structure of iron phosphate (FePO ₄ ) is the orthorhombic (a≠b≠c, α = β = γ= 90 ^o ) Mösbauer parameter of the iron phosphate (FePO ₄ ) with the structure ( δ = 0.31 mm/s, Δ E _Q = 1.51 mm/s, [J. Korean Phys. Soc. 62, 1922, (2013)]), it can be seen that it has a hexagonal structure.

Therefore, in the method of manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention, in step S130, a single-phase metal phosphate compound is analyzed through Mossbauer spectroscopy, and in step S120, if single-phase iron phosphate (hexagonal structure) is not obtained, do not proceed to step S140.

The crystal structure of the prepared iron phosphate (FePO4) is monoclinic and orthorhombic in addition to the hexagonal structure. However, if the hexagonal iron phosphate is used, it is possible to obtain a triclinic final positive electrode active material.

If the prepared iron phosphate (FePO ₄ ) has an orthorhombic structure, the structure of the final anode material may be monoclinic or orthorhombic, but this is not a common case and is highly unlikely to be formed well.

5 is a graph showing the XRD analysis results according to the synthesis temperature of the fluorophosphate-based secondary battery cathode active material (LiFePO4F(FePO4:LiF=1:1)) according to Comparative Example 1. Referring to FIG.

Referring to FIG. 5 , in the method of manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention, when the mixing ratio of the single-phase metal phosphate compound and the fluoride compound is 1:1 according to the equivalence ratio, 575 ° C. From the XRD data of a mixture of a single-phase metal phosphate compound and a fluoride compound synthesized at to 650° C., it can be seen that a secondary phase exists in the 15 ^o to 30 ^o section.

More specifically, a representative secondary phase is Li ₃ Fe ₂ (PO ₄ ) ₃ material, and FePO ₄ , a primary synthetic material that does not react in a mixture of a single-phase metal phosphate compound and fluoride compound synthesized at 575 ° C., is present. can see.

Therefore, the method for manufacturing a fluorophosphate-based secondary battery cathode active material according to an embodiment of the present invention is not suitable because it cannot be prepared as a single phase when the mixing ratio of the single-phase metal phosphate compound and the fluoride compound is reacted according to the equivalence ratio. it can be seen that

6 is a graph showing the XRD analysis results according to the synthesis temperature of the fluorophosphate-based secondary battery cathode active material (LiFePO4F(FePO4:LiF=1:1.05, 1:1.1)) according to Examples 1 and 2 of the present invention.

6 is a single-phase metal phosphate mixed by adding more than 5% or 10% of a fluoride compound to a single-phase metal phosphate compound primarily synthesized in the method for manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention; A mixture of the compound and the fluoride compound was finally synthesized at 575 °C to 650 °C.

Referring to FIG. 6 , it can be confirmed that the secondary phase is present in the mixture of the single-phase metal phosphate compound and the fluoride compound according to the mixing ratio.

That is, it can be seen that although the intensity of the secondary phase is relatively lowered compared to FIG. 5 in which the fluoride compound is added in an equivalent ratio to the metal phosphate compound of the single phase, it is still present.

However, it can be seen that the secondary phase does not exist in the XRD data of a mixture (590/1.05) of a single-phase metal phosphate compound and a fluoride compound synthesized secondarily at 590° C. by adding more than 5% of the fluorite compound.

In addition, if the secondary synthesized mixture of single-phase metal phosphate compound and fluoride compound (590/1.05) is precisely analyzed, the secondary synthesized single-phase mixture of metal phosphate compound and fluoride compound (590/1.05) does not exist. /1.05) shows a secondary phase in the first synthesis step and the second synthesis step, and is not brownish yellow, but pale yellow.

Conventionally, the mixture is finally synthesized in a gas atmosphere to prevent Fe oxidation in the secondary synthesis step, but Fe oxidation occurs on the pellet surface of the secondary mixture that is not properly mixed, so that the surface of the pellet is red, brown, or reddish brown. It is colored, and since the inside of the pellet is yellow, when the pellet is finally pulverized, it shows a brownish yellow color.

Therefore, in the case of XRD measurement data of a mixture of a metal phosphate compound and a fluoride compound of a single phase synthesized secondary, a secondary phase is clearly present in the interval of 15 ^o to 30 ^o .

7 is a graph showing the XRD analysis result of a fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.

공간군을 가지는 삼사정계(triclinic, a≠b≠c, α≠β≠γ) 구조로 확인되었으며, 격자 상수는 a = 5.2973 Å, b =7.2539 Å, c = 5.1506 Å, α = 107.92 ^o, β = 98.52 ^o, γ = 107.35 ^o, V = 173.34 ų 분석되었다.Referring to FIG. 7 , the XRD data measured in the range of 10 ^o to 80 ^o of the secondary synthesized mixture of a single-phase metal phosphate compound and a fluoride compound (590/1.05) was subjected to Rietveld refinement using the Fullprof program. ) through the analysis result,

It was confirmed as a triclinic (a≠b≠c, α≠β≠γ) structure with space groups, and the lattice constants were a = 5.2973 Å, b =7.2539 Å, c = 5.1506 Å, α = 107.92 ^o , β = 98.52 ^o , γ = 107.35 ^o , V = 173.34 Å ³ analyzed.

Therefore, from these results, it can be seen that the finally synthesized LiFePO ₄ F exhibits a single phase.

8 is a graph illustrating a room temperature Mossbauer spectrum of a fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.

In FIG. 8, a mixture (590/1.05) of a single-phase metal phosphate compound and a fluoride compound synthesized secondarily at 590° C. was used.

Referring to FIG. 8 , the crystal structure of single-phase LiFePO ₄ F prepared by the method of manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention is Fe1 (A) and Fe(B) octahedral FeF ₂ O There are two crystallographically independent Fe sites forming _four chains.

Therefore, the room temperature Mösbauer spectrum was obtained for two Fe sites; Two doublets with Fe1(A) and Fe(2) were analyzed, and the ratio of the two doublets determined by fitting matches the ratio derived from the single-phase LiFePO ₄ F crystal structure. was analyzed 1:1.

9 is a graph showing the Mossbauer spectrum according to the temperature of the fluorophosphate-based secondary battery cathode active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.

In FIG. 9, a mixture (590/1.05) of a single-phase metal phosphate compound and a fluoride compound synthesized secondarily at 590° C. was used.

Table 1 is a table showing Mossbauer parameter values according to temperature of a fluorophosphate-based secondary battery positive active material (single-phase LiFePO ₄ F) according to an embodiment of the present invention.

[Table 1]

9 and Table 1, the neil temperature of the single-phase LiFePO ₄ F prepared by the method of manufacturing a fluorophosphate-based secondary battery positive active material according to an embodiment of the present invention (antiferromagnetic behavior, but thermal vibration as the temperature increases) It can be seen that the temperature exhibiting paramagnetic behavior) is 73 K.

Also, below the Neil temperature (73 K), two sets of six-line spectra can be seen.

The Mossbauer effect is that when an atomic nucleus emitting/absorbing gamma rays is confined in a solid and the solid premise absorbs the bounce momentum, the bounce energy becomes practically zero, which means the emission or absorption of such non-rebound gamma rays.

9 is a result of measuring the Mössbauer spectrum in a temperature range of 4.2 K to 73 K.

The LiFePO ₄ F cathode material has two crystallographically unique Fe ³⁺ sites, but these two sites are very similar, and two fluorides of similar bond length and four Since it has two oxygen ligands, it is difficult to distinguish them.

Therefore, in order to clearly distinguish the two sites (Fe1(A), Fe2(B)), a Mösbauer temperature experiment was performed. The Mösbauer spectrum was identified as two sets of six absorption lines for Fe1(A) and Fe2(B), and was analyzed based on the nonlinear least-squares method using Lorentz linearity.

From the velocity, which is the position of the resonance absorption line obtained through analysis, magnetic hyperfine field (H _hf ) at each temperature, electric quadrupole splitting (ΔE _Q ), isomer shift ( δ ) ) was calculated, and it is shown in [Table 1].

The magnetic dipole moment of an atomic nucleus disrupts the energy level of the nucleus by interaction with the magnetic field existing in the nucleus (Zeeman), but causes the effect, and the interaction Hemiltonian at this time can be obtained. According to the energy level of the 57Fe nucleus and the six transitions for the case where the electric quadrupole interaction is significantly smaller than the magnetic dipole interaction, the position of the Mösbauer resonance absorption line of each transition can be known, and the size of this energy level can be determined. The nuclear magnetic field can be calculated by observation, which is called an ultrafine magnetic field.

Since the actual nucleus has a distorted structure, it interacts with the quadrupole moment of the nucleus and the electric field caused by the electric field tensor. The contribution of the ligand lattice by the charges of atoms or ions around the nucleus and the contribution of valence electrons to the electron complement distribution in the valence orbital within the nucleus affects the electric field gradient.

If this interaction is described using the Hemiltonian operator and the perturbation energy is obtained by diagonalizing the matrix elements, the quadrupole split value can be obtained, and information on the electric field gradient acting on the nucleus can be obtained from this value.

The isomer shift value is generally calculated to confirm the valence state of an atom. For example, if the valence of Fe in a material decreases, the isomer shift value increases. In the case of the LiFePO ₄ F cathode active material, the isomer shift value from 4.2 K to room temperature was analyzed to be 0.31 to 0.43 mm/s, which means that both Fe1(A) and Fe2(B) sites are Fe ³⁺ .

Accordingly, as shown in FIG. 9 , the doublet exhibits paramagnetic behavior at the Neal temperature, and appears as six absorption lines due to antiferromagnetic alignment below the Neil temperature.

As described above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations from these descriptions are provided by those skilled in the art to which the present invention pertains. This is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the following claims as well as the claims and equivalents.

Claims (13)

preparing a single-phase metal phosphate compound by first heat-treating a mixture of a phosphate compound and a metal compound or a metal phosphate hydrate;
analyzing the crystalline phase of the prepared single-phase metal phosphate compound using Mossbauer spectroscopy;
preparing a mixture of a single-phase metal phosphate compound and a fluoride compound by mixing the analyzed single-phase metal phosphate compound and a fluoride compound;
drying the mixture of the single-phase metal phosphate compound and the fluoride compound in a vacuum dryer; and
preparing a single-phase fluorophosphate compound by performing secondary heat treatment on a mixture of the dried single-phase metal phosphate compound and a fluoride compound;
A method of manufacturing a fluorophosphate-based secondary battery cathode active material comprising a.
The method of claim 1,
The single-phase fluorophosphate compound is a method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that it has a structure of the following formula (1).
[Formula 1]
XFePO ₄ F (X = Li, Na)
According to claim 1,
The mixing time of the mixture of the phosphate compound and the metal compound is a method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that from 1 minute to 1 hour.
According to claim 1,
The phosphate compound is ammonium phosphate monobasic, ammonium phosphate dibasic, ammonium dihydrogen phosphate, di-ammonium hydrogen phosphate, and a third A method of manufacturing a positive electrode active material for a fluorophosphate-based secondary battery, comprising at least one of ammonium phosphate tribasic trihydrate.
The method of claim 1,
The single-phase metal phosphate compound is a method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that it has a hexagonal structure.
According to claim 1,
The first heat treatment of a mixture of the phosphate compound and the metal compound or the metal phosphate hydrate to prepare a single-phase metal phosphate compound comprises:
calcining a mixture of the phosphate compound and the metal compound; and
sintering the mixture of the calcined phosphate compound and the metal compound;
A method of manufacturing a fluorophosphate-based secondary battery cathode active material comprising a.
7. The method of claim 6,
The step of calcining the mixture of the phosphate compound and the metal compound,
A method of manufacturing a positive electrode active material for a fluorophosphate-based secondary battery, characterized in that it is carried out at a temperature of 300°C to 400°C.
7. The method of claim 6,
The step of sintering the mixture of the calcined phosphate compound and the metal compound,
A method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that it proceeds at a temperature of 870 ° C to 900 ° C.
According to claim 1,
The mixing ratio of the single-phase metal phosphate compound and the fluoride compound is 1:1.05 and 1:1.1.
According to claim 1,
A method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that the mixture of the single-phase metal phosphate compound and the fluoride compound is mixed using a defoaming and kneading device.
According to claim 1,
The second heat treatment of a mixture of the dried single-phase metal phosphate compound and the fluoride compound to prepare a single-phase fluorophosphate compound comprises:
A method of manufacturing a fluorophosphate-based secondary battery cathode active material, characterized in that it is carried out at a temperature of 575°C to 650°C.
A fluorophosphate-based secondary battery positive active material comprising a single-phase fluorophosphate compound prepared by the method according to claim 1,
The single-phase fluorophosphate compound is a fluorophosphate-based secondary battery cathode active material, characterized in that it has a structure of the following formula (1).
[Formula 1]
XFePO ₄ F (X = Li, Na)
A positive electrode comprising the positive active material of the fluorophosphate-based secondary battery according to claim 12;
a negative electrode facing the positive electrode; and
A secondary battery comprising an electrolyte positioned between the positive electrode and the negative electrode.

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