KR20070086541A - Method of producing electrode active material - Google Patents

Abstract

An object of the present invention is to provide a method of more efficiently producing an electrode active material whose main component is a transition metal phosphate compound. According to the present invention, a method of producing an electrode active material is provided in which the main component thereof is a phosphate compound represented by the general formula: AxM(PO4) y (here, 0 <= x <= 2, 0 < y <= 2, A is an alkali metal, and M is a transition metal). This method comprises preparing a composition in the melted state that contains a source of M and a source of phosphorus (and also a source of A when 0 < x). This method is suitable as a method of producing an electrode active material whose main component is, for example, an olivine-type lithium iron phosphate compound.

Description

METHOD OF PRODUCING ELECTRODE ACTIVE MATERIAL}

The present invention provides a general formula A _x M (PO ₄ ) _y which can be used as an electrode active material of a secondary battery, where 0 ≤ x ≤ 2, 0 <y ≤ 2, A is one element or two or more selected from alkali metals Elements, and M is one element or two or more elements selected from transition metals). The invention also relates to a non-aqueous electrolyte secondary battery using an electrode active material.

Secondary batteries are known that are charged and discharged by cations, such as lithium ions, that move between a pair of electrodes. Typical examples of this type of secondary battery are lithium secondary batteries (generally lithium ion batteries). A material capable of storing / releasing cations can be used as an electrode active material of a secondary battery. In the present description and claims, the term electrode active material means a material used to form an electrode of a secondary battery. The electrode may comprise conductive material (s) and binder (s) in addition to the electrode active material. Typically, the electrode active material is used with a metal piece connected to the end of the secondary battery. In general, the electrode active material is in the form of a powder and a paste comprising the electrode active powder is coated onto the metal fragment. The paste may include conductive powders and binder (s) in addition to the electrode active powder. Electrode active powder may be compressed to form an electrode.

Various materials have been studied as anode active materials and cathode active materials of this type of secondary batteries. For example, Japanese Patent Application Laid-open No. H9-134724 discloses a non-aqueous electrolyte secondary battery comprising an olivine-type iron phosphate compound represented by the general formula LiFePO ₄ as an anode active material. In addition, Japanese Patent Application Laid-Open No. 2000-509193 discloses an electrode active material composed of a Nasicon-type iron phosphate compound represented by the general formula Li ₃ Fe ₂ (PO ₄ ) ₃ . Other prior art references relating to electrode active materials include Japanese Patent Application Laid-Open Nos. H9-134725, 2001-250555, 2002-15735, and H8-83606.

Intensive studies have shown that the general formula A _x M (PO ₄ ) _y (where 0 ≦ x ≦ 2, 0 <y ≦ 2, A is one or more elements selected from alkali metals, and M is a transition metal) Phosphate compounds (compounds of transition metals and phosphates or compounds of alkali metals, transition metals and phosphates) represented by one element or two or more elements selected from them have been found to be used as electrode active materials of secondary batteries. In the following, the definitions of x, y, A and M may be omitted when the above definition is applied.

In the prior art, phosphate compounds suitable for the electrode active material are prepared by solid state reaction (baking). This type of solid state reaction generally requires a long time. It would be useful if a more effective method of preparing the phosphate compound was provided.

It is therefore an object of the present invention to provide a more effective method for preparing phosphate compounds represented by the general formula A _x M (PO ₄ ) _y which can be employed as the electrode active material.

Another object of the present invention is to provide a secondary battery comprising this type of electrode active material.

The inventors of the present invention can prepare a phosphate compound represented by the general formula A _x M (PO ₄ ) _y with better efficiency by slow cooling the composition of the molten raw materials from the molten state (liquid state) to the solid state. I found out that I could.

One invention disclosed herein is a general formula A _x M (PO ₄ ) _y (where 0 ≦ x ≦ 2, 0 <y ≦ 2, A is one element or two or more elements selected from alkali metals, and M is a transition A method for producing a phosphate compound (a compound of transition metals and phosphates or a compound of alkali metals, transition metals and phosphates) represented by one element or two or more elements selected from metals. The manufacturing method includes preparing a raw material composition in a molten state. The raw material is a source of A in A _x M (PO ₄ ) _y , a source of M in A _x M (PO ₄ ) _y and a source of phosphorus (P), provided that A _x M (PO ₄ ) _y in x Is not 00 (x ≠ 0), that is, x is greater than 00 (0 <x). When x is 00 in A _x M (PO ₄ ) _y (x = 0), the raw material includes a source of M and a source of phosphorus (P) in A _x M (PO ₄ ) _y . A molten composition of this type is for example a mixture of a solid raw material comprising a source of M and a solid raw material comprising a source of phosphorus and a solid raw material comprising a source of A when x is greater than 00 and then the raw material is mixed. It can be produced by heating to a molten state. The preparation method also includes a slow slow cooling of the molten composition. Here, "slow cooling" is a concept opposite to quenching, which means decreasing the temperature relatively slowly. There can be no obvious boundary between slow cooling and quenching. Non-crystalline phosphates are produced when the molten compound cools rapidly while crystalline phosphates are produced when the molten compound cools slowly. That is, quick cooling (quenching) in which the cooling rate is faster than the predetermined rate grows non-crystalline phosphate, and slow cooling in which the cooling rate is slower than the predetermined rate grows the crystalline phosphate.

Non-crystalline phosphate and crystalline phosphate can be distinguished by X-ray diffraction pattern. Non-crystalline phosphate shows no peaks in the X-ray diffraction pattern, while crystalline phosphate shows peaks corresponding to the crystal structure of the crystalline phosphate in the X-ray diffraction pattern.

According to this preparation method, a compound showing properties useful as an electrode active material can be produced with better efficiency (ie, in a shorter time).

In one preferred aspect of this method, the molten composition and / or raw materials for forming the molten composition comprise A, M and phosphorus in an atomic ratio of substantially 1: 1: 1. Molten compositions having this atomic ratio are suitable for preparing phosphate compounds in which both x and y are substantially 1 in A _x M (PO ₄ ) _y . In other words, a molten composition having such an atomic ratio is suitable for preparing a phosphate compound represented by the general formula AMPO ₄ corresponding to the olivine form. The olivine type AMPO ₄ has better properties for the electrode active material.

In another preferred aspect, the molten composition and / or raw materials for forming the molten composition do not comprise A. The molten composition and / or raw materials comprise M and phosphorus in an atomic ratio of substantially 1: 1. The molten composition having this atomic ratio is suitable for the general formula A _x M (PO ₄₎ in the _y and x is 0 y in the general formula A _x M (PO _{4) y} manufacturing the substantially equal to one phosphate compound. In other words, a molten composition having such an atomic ratio is suitable for preparing a phosphate compound represented by the general formula MPO ₄ corresponding to the olivine form. Olivine type MPO ₄ also has better properties for electrode active materials.

The source of M may be a compound having M as a constituent element (hereinafter also referred to as "M compound"). The M compound may be selected from compounds in which the valence number of M is greater than the valence number of M in A _× M (PO ₄ ) _y . In addition, the M compound may be selected from compounds in which the valence number of M is equal to the valence number of M in A _x M (PO ₄ ) _y . Alternatively, in the number of valence of M, A _x M (PO _{4) y} large M compound than the valence of M in the number of valence of M, A _x M (PO _{4) y} may be used with the M compound than can the valence of M . According to the manufacturing methods disclosed herein, the selection for the source of M can be extended to low reactivity oxide compounds that cannot be used in conventional solid state baking methods. In particular, the advantage of oxide raw materials is that oxide raw materials are generally cheaper than more reactive materials such as ammonium salts, acetates, oxalates and the like. In addition, oxide raw materials generate little to no reactive or byproduct gases that are malodorous or toxic. Therefore, the manufacturing method disclosed herein is extremely effective in shortening the manufacturing time, reducing the manufacturing cost, reducing the raw material cost.

When a M compound having a cost number of M greater than the valence number of A _x M (PO ₄ ) _y is used as part or all of the source of M, the composition in the molten state (molten composition) preferably includes a reducing agent. Do. In this way, the desired phosphate compound A _x M (PO ₄ ) _y can be produced with good efficiency. For example, carbon powder can be used as the reducing agent. It is also useful to increase the maximum temperature of the molten composition instead of or in addition to using a reducing agent (hereinafter the maximum temperature means the highest temperature of the molten composition during the manufacturing process).

The invention disclosed herein can be applied to prepare an electrode active material whose main component is a phosphate compound in which M is mainly iron (Fe). For example, the present invention is suitable for the preparation of iron phosphate compounds A _x Fe ^II (PO ₄ ) _y (generally, olivine-type iron phosphate compounds represented by AFe ^II (PO ₄ )) in which x and y are both 1. . The invention is also suitable for the preparation of iron phosphate compounds A _x Fe ^III (PO ₄ ) _y (generally, olivine-type iron phosphate compounds represented by Fe ^III (PO ₄ )) with x being 0 and y being 1. Particularly preferred applications are iron phosphate compounds in which both x and y are substantially 1 in A _x M (PO ₄ ) _y . According to the method disclosed herein, a compound containing bivalent iron as a component (for example, FeO) is used as a raw material (source of iron) for the preparation of the olivine-type phosphate compound having the above-described divalent iron. In addition to being selected, compounds containing trivalent iron as constituents (eg Fe ₂ O ₃ ) may also be selected as raw materials. When trivalent iron oxides (such as Fe ₂ O ₃ ) are used as part of iron or as a full source of iron, a reducing agent (carbon powder) is added to the molten composition and / or the maximum temperature of the molten composition is relatively It is desirable to increase. In this way, an electrode active material whose main component is the desired iron phosphate compound can be produced with excellent efficiency.

The electrode active material obtained by any of the above methods can be suitably used as a constituent material of a secondary battery (generally, a lithium ion secondary battery). The secondary battery described above may comprise, for example, a first electrode (anode or cathode) having any of the electrode active materials described above, a second electrode having a material to store / discharge cations (an electrode opposite to the first electrode, e.g. Cathode or anode), and non-aqueous-type electrolytes or solid electrolytes.

Another invention disclosed herein relates to a secondary battery. This secondary battery comprises an anode having an electrode active material obtained by any of the methods described above. In addition, the secondary battery includes a cathode having a material for storing / discharging alkali metal ions. For example, if the battery of the present invention is a lithium secondary battery, the battery of the present invention will include a cathode having a material that stores / discharges lithium ions. According to the present invention, the secondary battery having the above-described configuration can be manufactured with excellent efficiency.

Another aspect of the invention disclosed herein is an anode active material for a secondary battery produced by any of the methods described above. Typical examples of the active material of the present invention are anode active materials for secondary batteries in which the substantially crystalline phosphate compound represented by A _x M (PO ₄ ) _y is a main component.

Preferred embodiments of the present invention will be described below. It is noted that contents other than those specifically mentioned in the specification, essential for practicing the present invention, will be understood as contents which can be designed by those skilled in the art based on the prior art in this field. The invention can be carried out on the basis of the details disclosed herein and the general technical knowledge in this field.

The production method of the present invention can be applied to the preparation of an electrode active material whose main component is a transition metal phosphate compound represented by the general formula A _x M (PO ₄ ) _y . M in A _x M (PO ₄ ) _y is one element or two or more elements selected from transition metals. Specific examples of M include iron (Fe), vanadium (V), titanium (Ti) and the like. In A _x M (PO ₄ ) _y , A is one element or two or more elements (generally one element) selected from alkali metals such as lithium (Li), sodium (Na), potassium (K) and the like. “x” is a number that satisfies 0 ≦ x ≦ 2 (generally 0 <x ≦ 2, but x may be zero). Further, "y" is a number that satisfies 0 <y ≤ 2 (y cannot be 0). Since the electrochemical equivalent of the compound represented by A _x M (PO ₄ ) _y is relatively small, a large theoretical capacity can be achieved. According to the production method of the present invention, useful electrode active materials of this type can be produced with good efficiency.

Electrode active materials preparable by the methods disclosed herein include electrode active materials whose main component is a compound in which M is mainly Fe in A _x M (PO ₄ ) _y . Preferably, at least about 75% of M in A _x M (PO ₄ ) _y is Fe. More preferably, at least about 90% of M in A _x M (PO ₄ ) _y is Fe. Even more preferably, substantially all of M in A _x M (PO ₄ ) _y is Fe. Electrode active materials used in secondary batteries that store / discharge electricity by lithium ions moving between a pair of electrodes are A _x M (PO ₄ ) _y where x is greater than 0 and A is mainly lithium ( Preferred are substances in which Li) is the main component. In addition, an electrode active material used in a secondary battery that stores / discharges electricity by sodium ions moving between a pair of electrodes has x greater than 0 in A _x M (PO ₄ ) _y and A is mainly sodium (Na). Preference is given to substances in which the compound is a major component.

The method disclosed herein is a compound represented by AM ^II (PO ₄ ) in the form of olivine in which x and y are substantially x = y = 1 in A _x M (PO ₄ ) _y , for example LiFe ^II ( PO ₄ )) can be applied in the preparation of an electrode active material as a main component. Optionally, the method disclosed herein is a compound represented by M ^III (PO ₄ ) having an olivine form in which x and y are substantially x = 0, y = 1 in A _x M (PO ₄ ) _y , eg For example, Fe ^III (PO ₄ )) can be applied to the preparation of the electrode active material as a main component. In the preparation of the olivine-type material described above (especially the olivine-type material in which M is mainly divalent), particularly good effects will be obtained by adopting the method of the present invention.

In addition, the method disclosed herein is a compound (A ₃ M ^III ₂ (PO ₄ ) ₃ ) having a nazicon form in which x and y are substantially x = y = 1.5 in A _x M (PO ₄ ) _y , wherein the main component is It may be applied to the preparation of the electrode active material. Compounds represented by A ₃ M ^III ₂ (PO ₄ ) ₃ include, for example, Li ₃ Fe ^III ₂ (PO ₄ ) ₃ ). The effect of adopting the method of the present invention will be suitably shown in the preparation of the Nazicon form of the material described above.

When the method disclosed herein is applied to the preparation of an electrode active material in which x is greater than zero (i.e. 0 <x) in A _x M (PO ₄ ) _{y the} main component is a source of M, P (phosphorus) A molten composition (melt) will be prepared comprising a source and a source of A. In general, the atomic ratio (molar ratio) of M, P and A in the melt is the atomic ratio corresponding to the electrode active material (A _x M (PO ₄ ) _y ) (target compound) to be produced. For example, a solid composition of raw materials comprising M, P and A in an atomic ratio corresponding to a target compound may be prepared, and the composition of the raw materials may be melted. In general, it is suitable that the atomic ratios of M, P and A are substantially matched between the melt of raw materials and / or the composition of raw materials and the target compound.

Compounds having any one of M, P and A as components can be used as the source of M, the source of P, and the source of A, respectively. In other words, a compound having M as a component (M compound) can be used as a source of M. Oxides of M or compounds which produce oxides of M by heating (carbonates of M, hydrogen carbonate, acetates, oxalates, halides, hydroxides, etc.) can be used, for example, as M compounds. Phosphorus compounds having P as a component can be used as the source of P. For example, an oxide of phosphorus or a compound that produces an oxide of phosphorus by heating (an oxide such as P ₂ O ₅ , an ammonium salt such as NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO _4, etc.) may be used. Compounds having A as a component (Compound A) can be used as a source of A. For example, salts of A (carbonates, hydrogen carbonates, acetates, oxalates, halides, hydroxides, etc.) can be used. Each source consists of one compound or two or more compounds. When A is mainly lithium, the source of lithium may be one compound or two or more compounds selected from lithium salts such as lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH) and the like.

Note that the melting point of the melt can be reduced by selecting a compound (eg Li ₂ CO ₃ ) that functions as a source of A as well as a flux.

Optionally, a compound having any two or more of M, P and A as components may be used as the source of M, the source of P and the source of A. For example, a compound having P and A as components may be used as a source of P and a source of A, and a compound having M as a component may be used as a source of M. In addition, compounds having M, P and A as components can be used as a common source of M, P and A. For example, one form or two or more forms of phosphorus compounds represented by A _x M (PO ₄ ) _y may be used as the source of M, P and A. A _x M (PO ₄ ) _y used as a source may be crystalline or non-crystalline, or a mixture of crystalline and non-crystalline. Since the atomic ratio of each element (M, P and A) can be easily controlled, the composition and / or melt of the raw materials using three or more kinds of compounds each having one element of M, P and A (the molten state It is generally preferred to produce a composition of the raw materials of).

The compound may be selected as a source of M such that the valence number of M in the compound is equal to the valence number of M in A _x M (PO ₄ ) _y . For example, to prepare the olivine-type electrode active material represented by AM ^II (PO ₄ ), a compound of M divalent can be selected. ^{_{A 3 M Ⅲ 2 (PO 4}} ) born cone represented by the ₃ - to produce the electrode active material, M is selected to be a trivalent compound. When M is an element (e.g. iron) that tends to be more stable in the trivalent state than in the divalent state and the target material is an electrode active material with a predominantly 2 valence number of M in A _x M (PO ₄ ) _y , In order to prevent the divalent M source (eg FeO) from oxidizing and becoming trivalent, the step of preparing the electrode active material can be carried out in a reducing condition.

In addition, the compound may be selected as a source of M where the valence number of M of the source is greater than the valence number of M of the target material. According to the methods disclosed herein, it is still possible to select a trivalent M source, even if M tends to be more stable in the trivalent state than in the divalent state and M of the target material is predominantly divalent. For example, when the target material is an olivine-type material represented by LiFe ^II (PO ₄ ) containing _divalent Fe, Fe ₂ O ₃ including _trivalent Fe may be used as a source of Fe. In other words, according to the method of the present invention, a trivalent M source is used to prepare a material having divalent M as a component (eg, olivine-type electrode active material represented by AM ^II (PO ₄ )). Can be. This is important, for example, in the preparation of electrode active materials substantially composed of olivine-like material in which M is predominantly divalent iron (Fe) in A _x M (PO ₄ ) _y . This is because Fe ₂ O ₃ is certainly cheaper to use as an iron source than FeO. Even if a portion of FeO as an iron source is replaced by Fe ₂ O ₃ , the effect (reduction of raw material cost) due to the adoption of the present invention will be adequately exhibited.

On the other hand, when an electrode active material is prepared in which A _x M (PO ₄ ) _y is a compound (M (PO ₄ ) _y ) whose x is substantially zero, the above-mentioned source of M and phosphorus (P) A molten state (melt) composition comprising a source must be prepared. When 0 <x, compounds such as those described above may be appropriately selected and used as the M source and P source. For example, when preparing an olivine-type material represented by M ^III (PO ₄ ) (ie y = 1), a compound in which M is trivalent can be selected.

The melt described above can be prepared by mixing together a raw material having a source of M and a raw material having a source of P and a raw material having a source of A when x is greater than 0 and heating the composition of the mixed raw materials. For example, the powdered M source, powdered P source and powdered A source can be mixed together to prepare a composition of the raw material. The average particle diameter and particle size distribution of each source are not particularly limited. This is because the composition of the raw materials will melt and thus the impact that the quality of the composition of the raw materials will have on the final product will be limited. It is desirable for the mixed state of each of these sources (generally powdered) to be relatively uniform. More preferably, the mixed state is substantially uniform. However, since the composition of the raw materials is melted, an electrode active material having sufficient uniformity for practical use can be produced even if the uniformity of the raw materials is not so great. Thus, the production parameters of the process will be easier to manage than, for example, in conventional solid state reaction processes. For example, it will be easy to manage the quality of the raw materials to be used (sources of each element, etc.), and the uniformity of the composition of the raw materials (mixed state of each source). This is useful for increasing manufacturing efficiency.

The melting (heating) method of the composition of the raw materials is not particularly limited. Known heating means, such as induction heating, heating by microwaves, and the like may be appropriately adopted.

The heating rate (temperature increase rate) for melting the raw material composition is not particularly limited. Appropriate heating rates may be employed depending on the capabilities of the heating means to be used and the like. However, if the heating rate is too slow, the manufacturing efficiency can be reduced. In this respect, it is generally preferred that the heating rate be at least about 60 ° C./h, and more preferably at least about 150 ° C./h.

The maximum temperature of the composition (melt) in the molten state is not particularly limited as long as the molten state of the composition is obtained. For example, it is about 800 to 2000 ° C. (preferably about 850 to 1800 ° C., more preferably about 900 to 1600 ° C.) and is the temperature at which the molten state can be achieved. The lowest temperature at which the molten state can be achieved will depend on the composition of the raw materials (eg, the form of A and M, the values of x and y, etc.). For example, when A is predominantly lithium and M is predominantly Fe, the maximum temperature is preferably about 850-1800 ° C., more preferably about 900-1600 ° C.

Olivine-like material in which M is a tendency to be more stable in the trivalent state than in the divalent state and M is predominantly divalent (generally, compounds where both x and y are substantially 1 in A _x M (PO ₄ ) _y In the case of producing an electrode active material which is a main component thereof, it is preferable that the maximum temperature described above is relatively increased. For example, the manufacturing parameters are preferably set such that the maximum temperature is at least about 400 ° C. (typically between about 400 and 800 ° C.) higher than the minimum temperature at which the molten state can be achieved, and at least about 600 ° C. (typically More preferably between about 600 and 800 ° C.).

The amount of time (melt time) for which the composition of the raw materials is kept in the molten state is not particularly limited. In terms of manufacturing efficiency, energy cost, etc., the melting time is generally about 24 hours or less (generally about 5 minutes to 24 hours), preferably about 6 hours or less (generally about 5 minutes to 6 hours) is generally suitable. Do. In addition, the period in which the melt is maintained at the above-mentioned maximum temperature (hold time) is also not particularly limited. In terms of increased uniformity, etc. of the target material, the retention time is at least about 30 seconds (eg, about 30 seconds to 2 hours) and preferably at least 1 minute (eg, about 1 minute to 1 minute). Time) is generally suitable. Optionally, temperature reduction (cooling or slow cooling) may be initiated immediately after heating the composition to the maximum temperature.

Note that the method of preparing the composition in the molten state is not limited to the above-described method in which the pre-mixed (prepared) composition of the solid raw materials is melted. For example, each solid source can be made separately and then melted separately and the separately melted raw materials can be mixed together to form a molten composition of the raw materials. More specifically, each source may be melted separately and the sources in the molten state may be mixed together. Optionally, the solid (M) source can be molten, and then the solid (A) source can be added to the molten M source, followed by the solid (P) source.

Reducing agents may be included in the melt compositions described above. In particular, M compounds having a valence number of M in A _x M (PO ₄ ) _y greater than the valence number of M (eg, divalent) (eg, M compounds in which M is trivalent) are all M sources or portions thereof. When used as, it is preferred that a reducing agent be added to the molten composition. In addition, an M compound (eg, an M compound of which M is divalent) such that the valence number of M is equal to the valence number of M (eg, divalent) in A _x M (PO ₄ ) _y is the total M source or portion thereof. When used as, it is preferred that a reducing agent be added to the molten composition. In particular, when M is a more stable element than the divalent state (eg iron), it is preferred that a reducing agent is added to the molten composition. The reducing agent can better prevent the phenomenon that the divalent M of the M compound is oxidized to trivalent M.

Preferably, carbonaceous materials (eg, acetylene black, ketjen black, graphite precursors, etc.) may be used. Examples of other reducing agents that can be used in the methods disclosed herein include saccharides, polypropylene, and the like.

The means for adding this type of reducing agent to the molten composition is not particularly limited. For example, each powdered source may be mixed with a powdered reducing agent (such as carbon powder) to prepare a raw material composition, and then the mixture of raw materials may be melted. Optionally, a reducing agent may be added after each source has melted. The amount of the reducing agent added to the molten composition is not particularly limited, but when added in a small amount, the effect of using the reducing agent may not be effectively exhibited. On the other hand, if too many reducing agents are used, unintended effects on the properties of the target material may occur and battery performance may be degraded. The amount of reducing agent may, for example, be about 2 g per 100 g of the molten composition.

The target material will be obtained by slow cooling and hardening the molten composition. Slow cooling may be performed while managing slow cooling to achieve a predetermined temperature profile, or the molten composition may be naturally cooled. The predetermined temperature profile may be a temperature profile in which the temperature is gradually reduced at a fixed rate, a temperature profile in which the temperature is reduced in steps, or a temperature profile in which they are combined. In general, it is easy for the temperature to decrease at a fixed rate (temperature decreasing rate), and is therefore preferable. The rate of temperature reduction in such a situation can be, for example, about 600 ° C./h or less, preferably about 450 ° C./h or less, and more preferably about 300 ° C./h or less. When the rate of temperature decrease is slow, the target material tends to be highly crystalline. On the other hand, excessively slowing the rate of temperature reduction can result in a reduction in manufacturing efficiency. In this respect, it is generally suitable that the rate of temperature reduction is at least about 6 ° C./h, preferably at least about 30 ° C./h, more preferably at least about 60 ° C./h. Even when the temperature is gradually decreased, it is preferable that the average temperature decrease rate is within the above range from the slow cooling start to the slow cooling completion.

In one aspect of the methods disclosed herein, the molten composition is slowly cooled from the temperature at which the composition is in the molten state (generally from the maximum temperature) to the temperature at which the composition cures. Generally, slow cooling will be performed until the temperature of the composition is lowered to at least about 300 ° C. or less (preferably about 100 ° C. or less). Slow cooling will preferably be performed until the temperature of the composition is approximately room temperature (eg, about 60 ° C. or less, preferably about 40 ° C. or less).

A _x M (PO ₄₎ in the _y The M A _x M (PO ₄₎ when the _y of the M number of atoms greater than the number of atoms when having a characteristic that the more stable (e. G., A _x M (PO ₄₎ from _y If M is predominantly divalent and M is iron, then at least a portion of the manufacturing process described above is in a non-oxidizing atmosphere (generally an inert gas atmosphere such as argon or an atmosphere comprising a reducing gas such as hydrogen (H ₂ )). Can be implemented. In general, it is preferred that the process from the onset of slow cooling (temperature reduction) to the completion of slow cooling of the molten composition is carried out in a non-oxidizing atmosphere. More preferably, the process from melting of the solid raw materials to the completion of the slow cooling is carried out in a non-oxidizing atmosphere, and even more preferably, the process from the preparation of the raw materials to completion of the slow cooling is carried out in a non-oxidizing atmosphere.

Electrode active materials obtained by any of the above-described manufacturing methods are generally substantially crystalline. For example, the electrode active material thus prepared is a crystalline transition metal phosphate compound as discussed above. In a preferred aspect, the electrode active material may be a material whose main component is a crystalline transition metal phosphate compound having an olivine-type structure or a crystalline transition metal phosphate compound having a nazicon-type structure. Optionally, the electrode active material may be a material that is predominantly crystalline but includes non-crystalline portions. The fact that the electrode active material is crystalline (at least mainly crystalline), and that the electrode active material has a defined crystalline structure (olivine type, Nazicon type, etc.) can be confirmed, for example, by an X-ray diffraction pattern. have. X-ray diffraction patterns can generally be made by X-ray diffraction apparatus.

According to the methods described herein, a material made of a substantially olivine single phase transition metal phosphate compound (or an electrode active material formed substantially from this material) can be prepared. At this time, "single phase as olivine" is intended to produce an olivine-type material, for example denoted AM ^II (PO ₄ ), which material substantially comprises trivalent M (eg trivalent Fe). I will not. The "single phase of olivine" is obtained when the presence of trivalent Fe in the X-ray diffraction profile of this material cannot be identified. According to a preferred aspect, the single phase alkali metal, transition metal and phosphate compounds (generally lithium iron phosphate compounds, etc.) of the olivines described above can be produced with good efficiency. Lithium iron phosphate compounds and the like can be prepared as _divalent iron sources (eg FeO) as well as trivalent iron sources (eg Fe ₂ O ₃ ).

Electrode active materials prepared by the methods disclosed herein can act as electrode active materials in secondary batteries that generate voltage by storing / emitting various types of cations. Cations that can be stored / released by this type of active material include alkali metal ions such as lithium ions, sodium ions, potassium ions, cesium ions and the like; Alkaline earth metal ions such as calcium ions, barium ions and the like; Magnesium ions; Aluminum ions; Silver ions; Zinc ions; Ammonium ions such as tetrabutylammonium ion, tetraethylammonium ion, tetramethylammonium ion, triethylmethylammonium ion, triethylammonium ion and the like; Imidazolium ions such as imidazolium ions and ethylmethyl imidazolium; Pyridinium ions; Hydrogen ions; Tetraennium ions; Tetramethylphosphonium ions; Tetraphenylphosphonium ions; Triphenylsulfonium ions; Triethylsulfonium ion; Etc. are included. Of these, alkali metal ions are preferred, and lithium ions are particularly preferred.

When the electrode active material prepared by the method disclosed herein is used in the anode of a secondary battery, lithium (Li), sodium (Na), magnesium (Mg), aluminum (Al), which can store / release cations Metals such as these, or alloys thereof, carbonaceous materials and the like can be used as the active material of the cathode.

The electrode having the above electrode active material can be suitably used as an electrode of a secondary battery having various forms such as coin, cylinder, square, and the like. For example, the electrode active material may be compression-molded to form the electrode in the form of a plate or the like. Further, by attaching the above-mentioned electrode active material to a collector made of a conductive material such as a metal sheet, a plate-type electrode or a sheet-type electrode can be formed. In addition to the electrode active material according to the invention, this type of electrode may comprise one or two or more of the same type of material in the electrode with the standard electrode active material as required. Representative examples of this type of material include conductive materials and binders. Carbonaceous materials such as acetylene black (AB) and the like may be used as the conductive material. Organic polymers such as polyfluorovinylidene (PVDF), polytetrafluoroethylene (PTFE), polyfluorovinylidene-hexafluoropropylene copolymer (PVDF-HFP) and the like can be used as the binder.

As the non-aqueous electrolyte, a compound having an electrolyte including a non-aqueous solvent and a cation that can be stored / released by the electrode active material (supporting electrolyte) can be used.

Aprotic solvents with carbonates, esters, ethers, nitriles, sulfones, lactones, and the like can be used as, but are not limited to, non-aqueous solvents that form non-aqueous electrolytes. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, Propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxoran (1,3-dioxoran), nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane (sulfolane), γ-butyrolactone, and the like. Only one form may be selected from these non-aqueous solvents or a mixture of two or more forms may be used.

In addition, as a supporting electrolyte for forming a non-aqueous electrolyte, a compound containing a cation that can be stored / released by an electrode active material, for example, LiPF ₆ , LiBF ₄ , LiN when a lithium ion secondary battery is used One or more forms selected from lithium compounds (lithium salts) such as (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiClO _4, etc. may be used. Can be.

1 is an X-ray profile of sample 1. FIG.

2 is an X-ray profile of Sample 2. FIG.

3 is an X-ray profile of Sample 3. FIG.

4 is an X-ray profile of Sample 4. FIG.

5 is an X-ray profile of sample 5. FIG.

6 is an X-ray profile of Sample 6.

7 is an X-ray profile of Sample 7.

8 is a charge / discharge profile of Sample 1. FIG.

9 is a graph showing the cycle characteristics of Sample 1.

10 is a graph showing the rate (rate) characteristics of Sample 1.

11 is a charge / discharge profile of Sample 2. FIG.

12 is a graph showing the cycle characteristics of Sample 2.

FIG. 13 is a graph showing the speed characteristic of Sample 2. FIG.

14 is a charge / discharge profile of Sample 3. FIG.

15 is a graph showing the cycle characteristics of Sample 3.

16 is a graph showing the velocity characteristics of Sample 3.

17 is a charge / discharge profile of Sample 5. FIG.

18 is a graph showing the cycle characteristics of Sample 5.

19 is a cross-sectional view schematically showing the structure of a measuring cell.

Some embodiments of the invention will be described below, but the invention is in no way limited to these embodiments.

Experimental Example 1

This experimental example is an experimental example in which a Fe source having a divalent Fe (FeO) was used to prepare an electrode active material sample whose main component was a phosphate compound having a divalent iron.

FeO, P ₂ O ₅ and LiOH were mixed together in a molar ratio of 1: 0.5: 1. This mixture (raw composition) was heated to a maximum temperature of 1100 ° C. at an increasing rate of 200 ° C./h in an Ar atmosphere to dissolve it, and this temperature was maintained for 15 minutes. This molten composition (melt) was then slowly cooled to 200 ° C./h from 1100 ° C. molten state to room temperature. The resulting product was milled by standard methods to obtain a sample (the product obtained and the milled product referred to below as “sample 1”) and powder X-ray diffraction (XRD) measurements were made. An X-ray diffraction apparatus (model number "Rigaku RINT 2100HLR / PC") available from Rigaku Corporation was used for the measurement. The results are shown in FIG. As shown in FIG. 1, only X-ray diffraction profiles with olivine-like properties were observed. From this, it was confirmed that Sample 1 obtained by this Experimental Example was substantially crystalline and of olivine (LiFePO ₄ ) single phase.

Experimental Example 2

This experimental example is another experimental example in which a Fe source having a divalent Fe (FeO) was used to prepare an electrode active material sample whose main component was a phosphate compound having a divalent iron.

FeO, P ₂ O ₅ and Li ₂ CO ₃ were mixed together in a molar ratio of 1: 0.5: 0.5. Sample 2 was obtained in the same manner as in Experimental Example 1, except that this mixture was used as raw material composition and the fact that the 1100 ° C. maximum temperature was maintained for 30 minutes. The result of the XRD measurement performed on Sample 2 in the same manner as in Experimental Example 1 is shown in FIG. 2. As shown in FIG. 2, only X-ray diffraction profiles with olivine-like properties were observed, and Sample 2 was found to be substantially crystalline and olivine (LiFePO ₄ ) single phase. From this, Sample 2 was found to be substantially crystalline and olivine (LiFePO ₄ ) single phase.

Experimental Example 3

This experimental example is an experimental example in which a Fe source (Fe ₂ O ₃ ) having trivalent Fe was used to prepare an electrode active material sample whose main component is a phosphate compound having divalent iron.

Fe ₂ O ₃ , P ₂ O ₅ and Li ₂ CO ₃ were mixed together in a molar ratio of 1: 1: 1, and carbon powder (acetylene black, hereinafter also referred to as “AB”) was also mixed therein as a reducing agent. The amount of AB mixed therein was ₂ parts by mass relative to a total of 100 parts by mass of Fe ₂ O ₃ , P ₂ O _5, and Li ₂ CO ₃ . It was heated to a maximum temperature of 1100 ° C. and melted as in Experimental Example 1, and the maximum temperature was maintained for 30 minutes. This melt (including AB as reducing agent) was then slowly cooled at a rate of reduction of 200 ° C./h from the molten state of 1100 ° C. to nearly room temperature. The resulting product was milled by standard method to obtain Sample 3 and XRD measured in the same manner as in Experimental Example 1. The results are shown in FIG. As shown in FIG. 3, only X-ray diffraction profiles with olivine-like properties were observed and Sample 3 was found to be substantially crystalline and olivine (LiFePO ₄ ) single phase.

Experimental Example 4

This experimental example is another experimental example in which a Fe source having trivalent Fe (Fe ₂ O ₃ ) was used to prepare an electrode active material sample whose main component was a phosphate compound having divalent iron.

The raw material composition was prepared in the same manner as in Experimental Example 3, except that AB was not used as the reducing agent. This raw composition was used, heated (200 ° C./h increase rate, 1000 ° C. maximum temperature, 30 min hold time), cooled (200 ° C./h decrease rate), and Experimental Example to obtain Sample 4. Milled in the same manner as in 3. XRD measurements were performed on Sample 4 in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in FIG. 4, Sample 4 obtained by the production parameter of the present experimental example contained a trivalent Fe compound, and was not olivine (LiFePO ₄ ) single phase.

Experimental Example 5

This experimental example is another experimental example in which a Fe source having a divalent Fe (FeO) was used to prepare an electrode active material sample whose main component was a phosphate compound having a divalent iron.

FeO, P ₂ O ₅ and LiOH were mixed together in a molar ratio of 1: 0.5: 1. This mixture (raw composition) was heated to 1500 ° C. (maximum temperature) at a rate of 200 ° C./h in an Ar atmosphere to dissolve it, and this temperature was maintained for 5 minutes. This melt was then cooled (slow cooling) at a rate of 200 ° C./h from 1500 ° C. molten state to near room temperature. The resulting product was milled by standard methods to obtain sample 5 and powder X-ray diffraction (XRD) measurements. The result is shown in FIG. As shown in FIG. 5, only X-ray diffraction profiles with olivine-like properties were observed and Sample 5 was found to be substantially crystalline and olivine (LiFePO ₄ ) single phase. Therefore, even when the maximum temperature rose from 1100 ° C to 1500 ° C, a sample made of the olivine single phase as in Experimental Example 1 was obtained.

Experimental Example 6

This experimental example is another experimental example in which a Fe source having trivalent Fe (Fe ₂ O ₃ ) was used to prepare an electrode active material sample whose main component was a phosphate compound having divalent iron.

The raw material composition was prepared in the same manner as in Experimental Example 3, except that AB was not used as the reducing agent. This mixture (raw composition) was used, heated (200 ° C./h increase rate, maximum temperature 1500 ° C., hold time of 5 minutes), cooled (200 ° C./h decrease rate), and sample 6 was obtained. And milled in the same manner as in Experiment 5. XRD measurements were performed on Sample 6 in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in FIG. 6, an X-ray profile with olivine-like properties was observed and sample 6 was found to be substantially crystalline and olivine (LiFePO ₄ ) single phase. Therefore, even when Fe ₂ O ₃ was used as the Fe source, a sample made of olivine single phase without using a reducing agent was obtained by raising the melting temperature (maximum temperature) from 1100 ° C. to 1500 ° C.

Experimental Example 7

This experimental example is another experimental example in which a Fe source having trivalent Fe (Fe ₂ O ₃ ) was used to prepare an electrode active material sample whose main component was a phosphate compound having trivalent iron.

Fe ₂ O ₃ and P ₂ O ₅ were mixed together in a molar ratio of 1: 1. This mixture (raw composition) was used, heated (increase rate of 200 ° C./h, maximum temperature of 1500 ° C., hold time of 5 minutes), cooled (rate of reduction of 200 ° C./h), and obtain sample 7. And milled in the same manner as in Experiment 6. XRD measurements were performed on Sample 7 in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in FIG. 7, an X-ray profile with olivine-like properties was observed and sample 7 was found to be substantially crystalline and olivine (LiPO ₄ ) single phase.

(Characteristic test of sample 1)

Sample 1 obtained by Experimental Example 1 was used to make a measurement cell.

In other words, sample 1 was milled until it could not be felt at the fingertips, thereby preparing it as an electrode active material (for convenience, the milled product is referred to below as “sample 1”). About 0.25 g of electrode active material was mixed with about 0.089 g of acetylene black (AB) as the conductive material (mass ratio: about 70:25). A planetary ball mill was used to mix the electrode active material and AB. To this mixture (mixture of electrode active material and AB) about 0.018 g of polytetrafluoroethylene (PTFE) was added and mixed as binder (mass ratio of electrode active material: AB: PTFE: about 70: 25: 5). This mixture was compression molded into a plate shape having a diameter of about 1.0 cm and a thickness of about 0.5 mm, and test electrodes were prepared.

Lithium foil having a diameter of 1.5 mm and a thickness of 0.15 mm was used as the counter electrode. A porous polyethylene sheet having a diameter of 22 mm and a thickness of 0.02 mm was used as a separator. In addition, a non-aqueous electrolyte was used in which LiPF ₆ was dissolved at a concentration of about 1 mol / liter in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1. These elements were combined in a stainless steel container, and as shown in FIG. 19, a coin-type battery cell having a thickness of 2 mm and a diameter of 32 mm (type 2032) was constructed. In Fig. 19, reference numeral 1 denotes a positive electrode (test electrode), reference numeral 2 denotes a negative electrode (counter electrode), reference numeral 3 denotes a separator and an electrolyte solution (non-aqueous electrolyte). 4 denotes a gasket, 5 denotes a positive electrode container, and 6 denotes a negative electrode cover. The cell in which Sample 1 was used as the electrode active material and a planetary ball mill was used to mix the electrode active material with AB is referred to as "cell 1-B" below.

In addition, test electrodes were prepared and cells were constructed in the same manner as the test electrodes and cells described above except that a stone mill was used instead of the planetary ball mill to mix the electrode active material, AB and PTFE together. Sample 1 was used as electrode active material and the stone mill was used to mix the electrode active material with AB is referred to hereinafter as "cell 1-S".

Subsequently, the fabricated Cell 1-B and Cell 1-S (ie, cell constructions) were both left as is for about 12 hours and then constant current charge / charge on these cells. Discharge test was performed. Test parameters were voltage control (cell voltage) of 4.5-2.5 V and current density of 0.2 mA / cm ² . The charge / discharge profile obtained by the primary charge / discharge cycle is shown at the top of FIG. 8. The result is that cell 1-B (thick lines in the drawing) where planetary ball mills are used for mixing is superior to cell 1-S (thin lines in the drawing) where stone mills are used for mixing (lithium ion usage ratio). ). Thus, only the results of cell 1 -B of the second cycle are shown at the bottom of FIG. 8.

Note that Li is lost due to volatility in the melt process, so the initial charge capacity is slightly lower than the discharge capacity. However, this does not mean that the site is lost, but rather that the charging capacity of the missing Li recovers after the second cycle.

Cycle test of cell 1-B was performed. In other words, the charge / discharge cycles were repeated in cell 1-B at the test parameters described above (voltage control of 4.5 to 2.5 V and current density of 0.2 mA / cm ² ), and the specific capacity of each cycle was Was measured. The obtained result (cycle characteristic) is shown in FIG.

In addition, the discharge capacities of the cells 1-B of the first cycle were measured at discharge rates of 0.1 mA / cm ² , 0.2 mA / cm ² , 0.5 mA / cm ² and 1.0 mA / cm ² . The obtained result (ratio characteristic) is shown in FIG.

(Characteristic test of sample 2)

A measurement cell was prepared in the same manner as Cell 1-B except that Sample 2 was used as the electrode active material instead of Sample 1 (ie, a planetary ball mill was used to mix the electrode active material and AB). This measurement cell will hereinafter be referred to as "cell 2-B".

The constant current charge / discharge test and cycle test were performed on cell 2-B using the same test parameters as in test 1 above. The results obtained are shown in FIGS. 11 and 12, respectively. In addition, the discharge capacities of the cell 2-B of the first cycle were measured at discharge rates of 0.1 mA / cm ² , 0.2 mA / cm ² , 0.5 mA / cm ^2, and 1.0 mA / cm ² . The result is shown in FIG.

(Characteristic test of sample 3)

A measurement cell was prepared in the same manner as Cell 1-B except that Sample 3 was used instead of Sample 1 as the electrode active material (ie, a planetary ball mill was used to mix the electrode active material and AB). This measuring cell will hereinafter be referred to as "cell 3-B".

Constant current charge / discharge tests and cycle tests were performed on cell 3-B using the same test parameters as in test 1 above. The results obtained are shown in FIGS. 14 and 15, respectively. In addition, the discharge capacities of cell 3-B of the first cycle were 0.1 mA / cm ² , 0.2 mA / cm ² , and 0.5 mA / cm ^2. It was measured at the discharge rate of. The result is shown in FIG.

(Characteristic test of sample 5)

A measurement cell was prepared in the same manner as Cell 1-S except that Sample 5 was used instead of Sample 1 as the electrode active material (ie, a stone mill was used to mix the electrode active material and AB). This measurement cell will hereinafter be referred to as "cell 5-S".

The constant current charge / discharge test and cycle test were performed on cell 5-S using the same test parameters as in test 1 above. The results obtained are shown in FIGS. 17 and 18, respectively.

These tests confirmed that all of Samples 1, 2, 3 and 5 obtained in the above experimental examples exhibited various useful properties as electrode active materials for lithium secondary batteries (generally, lithium ion secondary batteries).

Preferred embodiments of the invention have been described in detail above. However, these are merely examples and do not limit the scope of the present claims. The technology disclosed in the claims includes various modifications and variations of the above mentioned aspects. In addition, the technical components described in this specification or the drawings show technical utility independently or in various combinations, and are not limited by the combinations disclosed in the claims when applied. In addition, the techniques described in this specification or the drawings have technical utility by achieving a plurality of objects at the same time and achieving one of them.

Claims (12)

General formula A _x M (PO ₄ ) _y (where 0 ≦ x ≦ 2, 0 <y ≦ 2, A is one element or two or more elements selected from alkali metals, and M is one element selected from transition metals or In the method for producing a phosphate compound represented by two or more elements), Preparing a composition in a molten state, wherein the molten composition comprises a source of A in formula, a source of M in formula and a source of phosphorus when x in the formula is greater than 0; And And slowly cooling the composition from the molten state to the solid state. The method of claim 1, The step of preparing the molten composition is: A process for producing a phosphate compound, comprising the step of preparing a composition in a molten state comprising a source of M and a source of phosphorus in the general formula when x is zero in the general formula. The method of claim 1, The step of preparing the molten composition is: Mixing a solid raw material comprising a source of A in the general formula, a solid raw material including a source of M in the general formula, and a source of phosphorus when x is greater than 0 in the general formula; And And heating the mixture of the solid raw materials to a molten state. The method of claim 3, wherein The step of preparing the molten composition is: When x in the general formula is 0, a method for producing a phosphate compound comprising the step of mixing a solid raw material comprising a source of M, and a solid raw material comprising a source of phosphorus in the general formula. The method according to claim 1 or 3, Wherein said molten composition comprises said A, said M and said phosphorus in an atomic ratio of substantially 1: 1: 1. The method according to claim 2 or 4, And wherein said molten composition comprises said M and phosphorus in an atomic ratio of substantially 1: 1. The method according to any one of claims 1 to 6, The source of M comprises a compound having M as a component, the valence number of M of the compound being greater than the valence number of M in the general formula, and the molten composition comprises a reducing agent Manufacturing method. The method according to any one of claims 1 to 7, The phosphate compound represented by the above formula is a olivine-type iron phosphate compound wherein M is mainly divalent iron in the above formula. The method of claim 8, The molten composition comprises a reducing agent and Fe ₂ O ₃ as a source of M. The method according to claim 7 or 9, Carbon powder is used as said reducing agent, The manufacturing method of the phosphate compound characterized by the above-mentioned. In a secondary battery, An anode having a phosphate compound prepared by the method as defined in any one of claims 1 to 10; A cathode having a substance for storing / discharging alkali metal ions; And A secondary battery comprising a non-aqueous electrolyte or a solid electrolyte. The method of claim 11, The secondary battery, wherein the alkali metal ions are lithium ions.

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