JP2006155941A - Method for producing electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for more efficiently producing an electrode active material mainly composed of a transition metal phosphate compound.
According to the present invention, the general formula: A _x M (PO ₄ ) _y (where 0 ≦ x ≦ 2, 0 <y ≦ 2, A is an alkali metal, and M is a transition metal); The manufacturing method of the electrode active material which has the phosphoric acid compound represented by these as a main component is provided. The method comprises preparing a molten composition comprising the source of M and a source of phosphorus (or a source of A if x <0) and slow cooling the melt. Including that. This method is suitable, for example, as a method for producing an electrode active material mainly composed of an olivine type lithium iron phosphate compound.
[Selection] Figure 3

Description

  The present invention relates to a method for producing an electrode active material suitable as a constituent material of a secondary battery. The present invention also relates to a non-aqueous electrolyte secondary battery using such an electrode active material.

  2. Description of the Related Art Secondary batteries that are charged and discharged when cations such as lithium ions move between both electrodes are known. A typical example of such a secondary battery is a lithium secondary battery (typically a lithium ion secondary battery). As an electrode active material of such a secondary battery, a material capable of occluding and releasing lithium ions can be used. Examples of the negative electrode active material include carbonaceous materials such as graphite. Examples of the positive electrode active material include oxides having lithium and a transition metal as constituent elements, such as lithium nickel oxide and lithium cobalt oxide.

Various materials have been studied as a positive electrode active material or a negative electrode active material of such a secondary battery. For example, Patent Document 1 describes a non-aqueous electrolyte secondary battery that includes an olivine-type iron phosphate complex represented by the formula LiFePO ₄ as a positive electrode active material. Patent Document 2 describes an electrode active material composed of a NASICON type iron phosphate complex represented by the formula Li ₃ Fe ₂ (PO ₄ ) ₃ . Patent documents 3-6 are mentioned as other conventional art literature about an electrode active material.

JP-A-9-134724 JP 2000-509193 A JP-A-9-134725 JP 2001-250555 A JP 2002-15735 A JP-A-8-83606

  In these conventional techniques, a crystalline iron phosphate complex for an electrode active material is produced by solid phase reaction (firing). In general, such a solid phase reaction takes a relatively long time. It would be beneficial to provide a method for more efficiently producing a phosphate-based electrode active material.

  Then, an object of this invention is to provide the method of manufacturing the electrode active material which has a transition metal phosphate compound as a main component more efficiently. Still another object of the present invention is to provide a secondary battery including such an electrode active material.

  The present inventor, instead of a conventional solid phase reaction method in which a raw material is reacted in a solid phase state in an electrode active material containing a transition metal phosphate compound as a main component, a composition in a molten state (liquid phase state) The present invention was completed by finding that an electrode active material can be produced more efficiently by slowly cooling from the molten state.

One invention disclosed herein is a general formula A _x M (PO ₄ ) _y (where 0 ≦ x ≦ 2, 0 <y ≦ 2, and A is one selected from alkali metals or An electrode active material mainly composed of a phosphoric acid compound (transition metal phosphate complex) represented by the following formula: M is two or more elements, and M is one or two or more elements selected from transition metals. It relates to a method of manufacturing. The manufacturing method is as follows. When x in the above general formula is not 0 (x ≠ 0), that is, when x is larger than 0 (0 <x), the source of M and phosphorus (P) in the general formula It includes preparing a molten composition (melt) containing a supply source and a supply source of A in the above general formula. In addition, when x in the general formula is 0 (x = 0), it includes preparing a molten composition (melt) including the M supply source and the phosphorus supply source. Such a melt includes, for example, the M source and the phosphorus source. When x is larger than 0, a solid raw material composition further including the A source is prepared. It can be prepared by melting (making it into a molten state) the composition. This manufacturing method further includes gradually cooling the melt. Here, “slow cooling” is a concept opposite to quenching, and means that the temperature is lowered relatively slowly.
According to such a production method (hereinafter, also referred to as “melting slow cooling method”), a material exhibiting characteristics useful as an electrode active material can be produced more efficiently (for example, in a shorter time).

In a preferred embodiment of the method disclosed herein, the molten composition (melt) and / or the raw material composition comprises substantially 1: 1: 1 of A, M and phosphorus. Contains by atomic ratio. The melt having such a composition (atomic ratio) has an electrode active mainly composed of a phosphoric acid compound in which both x and y in the general formula are substantially 1 (that is, x = y = 1). It is suitable for producing a substance (in other words, an electrode active material mainly composed of a phosphate compound having a composition corresponding to the olivine type).
In another preferred embodiment, the molten composition (melt) and / or the raw material composition does not substantially contain A, and M and phosphorus are substantially 1: 1. In an atomic ratio of The melt having such a composition (atomic ratio) is mainly composed of a phosphoric acid compound in which x in the general formula is substantially 0 and y is substantially 1 (that is, x = 0, y = 1). It is suitable for producing an electrode active material as a component (in other words, an electrode active material mainly composed of a phosphate compound having a composition corresponding to the olivine type).

  The source of M is a compound having M as a constituent element (hereinafter sometimes referred to as “M compound”), and the valence of M in the compound is the valence of M in the general formula. Higher numbers can also be selected. Further, as the M supply source, an M compound in which the valence of M is equal to the valence of M in the general formula may be selected. Alternatively, an M compound having a valence of M higher than the valence of M in the general formula and another M compound (that is, the valence of M is equal to or greater than the valence of M in the general formula) Or a low M compound). According to the manufacturing method disclosed herein, the choice of usable raw materials (sources of M or M compounds) can be expanded to low-reactive oxides and the like that could not be used in the conventional solid-phase baking method. Is possible. In particular, oxide raw materials are less expensive than ammonium salts, acetates, oxalates, etc., which are more reactive, and also have the merit of less generation of odorous and toxic reaction by-product gases. Have. Therefore, it is a very effective manufacturing method for shortening manufacturing time, reducing process cost, reducing raw material cost, and the like.

  In the case where an M compound having a higher valence of M than the valence of M in the general formula is used as a part or all of the raw material (M supply source or M compound), the composition in the molten state (melt) It is preferable to contain a reducing agent. By this, the desired phosphoric acid compound (compound represented by the said general formula) can be manufactured efficiently. As the reducing agent, for example, carbon powder can be preferably employed. Moreover, instead of using a reducing agent or in addition to using a reducing agent, the highest temperature reached by the melt (referred to as the temperature at which the temperature of the melt is highest during the manufacturing process; the same shall apply hereinafter). It is also effective to make the value relatively high.

The invention disclosed herein can be preferably applied to the production of an electrode active material whose main component is a phosphate compound in which M is mainly iron (Fe). For example, such a phosphate compound, wherein both x and y in the above general formula are substantially 1, an olivine type iron phosphorus represented by AFe ^II (PO ₄ ) Acid compound) or a phosphate compound (typically olivine-type iron phosphorus represented by Fe ^III (PO ₄ )) wherein x in the general formula is substantially 0 and y is substantially 1 It is suitable for the production of an electrode active material mainly composed of an acid compound. A particularly preferable application object is an iron phosphate compound in which both x and y in the general formula are substantially 1. According to the method disclosed herein, as a raw material (iron supply source) for producing an olivine-type iron phosphate compound having divalent iron in this way, a compound containing divalent iron as a constituent element (for example, Not only FeO) but also a compound containing trivalent iron as a constituent element (for example, Fe ₂ O ₃ ) can be preferably selected. When such a trivalent iron compound (Fe ₂ O ₃ or the like) is used as a part or all of the iron supply source, a reducing agent (carbon powder or the like) is contained in the melt, and the melting It is preferable to apply at least one of making the maximum temperature of the object relatively high. This makes it possible to more efficiently produce an electrode active material containing a desired iron phosphate compound as a main component.

The electrode active material obtained by any of the methods described above can be suitably used as a constituent material of a secondary battery (typically a lithium ion secondary battery). Such a secondary battery includes, for example, a first electrode (positive electrode or negative electrode) having any one of the electrode active materials described above, and a second electrode (a pair of the first electrode and the first electrode having a material that absorbs and releases cations). Electrode, ie, a negative electrode or a positive electrode), and a non-aqueous electrolyte or a solid electrolyte.
Another invention disclosed herein relates to a secondary battery. The secondary battery includes a positive electrode having an electrode active material obtained by any of the methods described above. In addition, a negative electrode including a material that occludes and releases alkali metal ions (preferably lithium ions) can be provided. Furthermore, a non-aqueous electrolyte or a solid electrolyte can be provided. According to the present invention, the secondary battery having such a configuration can be manufactured more efficiently.
Another aspect of the invention disclosed herein is a positive electrode active material for a secondary battery manufactured by any of the methods described above. A typical example of such an active material is a positive electrode active material for a secondary battery having a substantially crystalline phosphate compound represented by the above general formula as a main component.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The production method of the present invention can be applied to the production of an electrode active material containing a transition metal phosphorus compound represented by the general formula A _x M (PO ₄ ) _y as a main component (main component). M in the above general formula is one or more elements selected from transition metals. Specific examples of M include iron (Fe), vanadium (V), titanium (Ti), and the like. A in the above general formula is one or two or more (typically any one) selected from alkali metals such as lithium (Li), sodium (Na), and potassium (K). x is a number satisfying 0 ≦ x ≦ 2 (typically 0 <x ≦ 2). Y is a number satisfying 0 <y ≦ 2. Since the compound represented by the above general formula has a relatively small electrochemical equivalent, it can have a larger theoretical capacity. According to the method disclosed here, a useful electrode active material can be produced more efficiently.

  One preferable application object of the method disclosed herein (that is, an electrode active material suitable for manufacturing by applying the method) is mainly composed of a compound in which M in the general formula is mainly Fe. An electrode active material is mentioned. Of those, about 75% by number or more of M is preferably Fe, more preferably about 90% by number or more is Fe, and more preferably M is substantially Fe. As an electrode active material for use in a secondary battery that is charged / discharged by lithium ions moving back and forth between both electrodes, x in the above general formula is larger than 0, and A in the formula is mainly lithium (Li). What has a certain compound as a main component is preferable. In addition, as an electrode active material for use in a secondary battery that is charged / discharged by sodium ions moving back and forth between both electrodes, x in the above general formula is greater than 0, and A in the formula is mainly sodium (Na A compound having a compound as a main component is preferred.

The method disclosed herein is a compound represented by a compound (AM ^II (PO ₄ ) having a composition corresponding to the olivine type in which x and y in the general formula are substantially x = y = 1, such as LiFe ^II. It can be preferably applied to the production of an electrode active material containing (PO ₄ )) as a main component. Alternatively, a compound having a composition corresponding to an olivine type in which x and y in the above general formula are substantially x = 0 and y = 1 (a compound represented by M ^III (PO ₄ ), for example, Fe ^III (PO ₄ ) ) Can be preferably applied to the production of an electrode active material. In the production of such an olivine-type material (particularly, an olivine-type material in which M is mainly divalent), the effect of employing the method of the present invention can be exhibited particularly well.

Further, the method disclosed herein is a compound (A ₃ M ^III ₂ (PO ₄ ) ₃ having a composition corresponding to a NASICON type in which x and y in the general formula are substantially x = y = 1.5. The present invention can also be preferably applied to the production of an electrode active material containing as a main component a compound represented, for example, Li ₃ Fe ^III ₂ (PO ₄ ) ₃ ). The advantage by adopting the method of the present invention can be appropriately exerted also in the production of such NASICON type materials.

When the method disclosed herein is applied to the production of an electrode active material whose main component is x in the above general formula (ie, 0 <x), the M supply source and phosphorus A molten composition (melt) including the supply source of (P) and the supply source of A is prepared. Typically, the atomic ratio (molar ratio) of M, P and A in the melt is determined based on the target electrode active material (transition metal phosphate compound represented by the general formula A _x M (PO ₄ ) _y ). The atomic ratio corresponding to. For example, a solid raw material composition containing M, P and A at an atomic ratio corresponding to the target product may be prepared and the composition may be melted. In general, it is appropriate that the atomic ratio of M, P and A is approximately the same between the melt and / or the raw material composition and the target product.

As the supply source of M, the supply source of P, and the supply source of A, compounds having any one of M, P and A as constituent elements can be used. That is, as the M supply source, a compound having M as a constituent element (M compound) can be used. As the M compound, for example, an M oxide or a compound that can be converted into an oxide by heating (such as M carbonate, bicarbonate, acetate, oxalate, halide, hydroxide, etc.) is preferably used. Can do. As the P supply source, a phosphorus compound having P as a constituent element can be preferably used. For example, it is preferable to use an oxide of phosphorus or a compound that can be converted into an oxide 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 ). it can. As a supply source of A, a compound having A as a constituent element (A compound) can be used. For example, a salt of A (A carbonate, bicarbonate, acetate, oxalate, halide, hydroxide, etc.) can be used. Each source can be composed of one or more compounds. When A is mainly lithium, one or more selected from lithium salts such as lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) can be used as a lithium supply source.
Note that by selecting a compound that can function as a flux (for example, Li ₂ CO ₃ ) as the supply source of A, the melting point of the melt can be lowered.

  Alternatively, a compound having two or more of M, P and A as constituent elements may be used as the M supply source, the P supply source, and the A supply source. For example, a compound having P and A as constituent elements can be used as the P supply source and the A supply source, and a compound having M as the constituent element can be used as the M supply source. Furthermore, a compound having all of M, P and A as constituent elements may be used as a common source of M, P and A. For example, one or two or more types of phosphoric acid compounds represented by the above general formula (which may be crystalline or amorphous, and may include crystalline and amorphous) may be represented by M, P and It can also be used as a source of A. Since it is easy to adjust the atomic ratio of each element (M, P and A), etc., usually a raw material composition and / or a compound having any one of M, P and A as a constituent element is used. It is preferable to prepare a melt (a composition in a molten state).

The source of M is a compound in which the valence of M in the compound used as the source is equal to the valence of M in the target product (that is, the valence of M in the compound represented by the general formula) Can be selected. For example, when the production of an olivine type material represented by AM ^II (PO ₄ ) is intended, a compound in which M is divalent (M source) can be preferably selected. For example, when the production of a NASICON type material represented by A ₃ M ^III ₂ (PO ₄ ) ₃ is intended, a compound in which M is trivalent can be preferably selected. Here, for example, an electrode active mainly composed of an element (for example, iron) in which M is more trivalent than divalent, such as iron, and the valence of M in the above general formula is mainly 2. When the production of the material is intended, the production process of the electrode active material is performed under reducing conditions in order to prevent the divalent M source (for example, FeO) from being oxidized and becoming trivalent. be able to.

Further, as the M supply source, a compound in which the valence of M in the supply source is higher than the valence of M in the target product may be selected. According to the method disclosed herein, M is an element (for example, iron (Fe), manganese (Mn), etc.) that tends to be more stable when trivalent than divalent. If a value (e.g., AM ^II (if intended for the manufacture of olivine type material represented by PO ₄₎₎ also in the trivalent M source (e.g., if M is iron Fe ₂ O ₃ etc.) can be preferably selected. In other words, according to the method of the present invention, an electrode having an olivine type composition represented by a material having divalent M as a constituent element (for example, AM ^II (PO ₄ ) using a trivalent M source. Active material) can be produced. This is important, for example, in the production of an electrode active material substantially composed of an olivine type material in which M in the above general formula is mainly divalent iron (Fe). This is because Fe ₂ O ₃ as a trivalent iron supply source is obviously cheaper than FeO as a divalent iron supply source. In addition, the effect by adopting the present invention (the effect of reducing raw material costs) is the case where a part of FeO as an iron supply source is replaced with Fe ₂ O ₃ (that is, a divalent iron supply source and a trivalent iron source). (When used in combination with an iron supply source).

On the other hand, when producing an electrode active material whose main component is a compound (M (PO ₄ ) _y ) in which x in the general formula is substantially 0, supply of M and supply of phosphorus (P) A molten composition (melt) containing a source is prepared. As the M supply source and the P supply source, compounds similar to those exemplified for the case of x <0 can be appropriately selected and used. For example, when the production of an olivine type material represented by M ^III (PO ₄ ) (ie, y = 1) is intended, a compound in which M is trivalent is preferably selected as a source of M. it can.

  The melt is typically prepared by mixing a source of M and a source of P and a source of A when x is larger than 0 to prepare a solid raw material composition, It can be prepared by melting the raw material composition. For example, a raw material composition can be prepared by mixing M source powder, P source powder, and A source powder. The average particle size and particle size distribution of each supply source used here are not particularly limited. This is because, since the raw material composition is once melted, the influence of the properties of the raw material composition on the product can be suppressed as compared with the conventional solid phase reaction method. The mixing state of each of these sources (typically in powder form) is preferably relatively uniform, and more preferably substantially uniform. However, since the raw material composition is once melted, an electrode active material having practically sufficient uniformity can be produced even when the uniformity of the raw material composition is not so high. As described above, the method disclosed herein (melting and slow cooling method) can facilitate the management of production conditions as compared with, for example, a conventional solid-phase reaction method. For example, it is easy to manage properties of raw materials to be used (a supply source of each element, etc.), uniformity of a raw material composition (mixed state of each supply source), and the like. This is advantageous from the viewpoint of increasing manufacturing efficiency.

The method for melting (heating) such a raw material composition is not particularly limited. Known heating means such as induction heating or microwave heating can be appropriately employed.
The heating rate (temperature increase rate) when melting the raw material composition is not particularly limited. An appropriate heating rate can be adopted according to the ability of the heating means used. However, if the heating rate is too low, the production efficiency tends to decrease. From this point of view, the heating rate is usually preferably about 60 ° C./h or more, and more preferably about 150 ° C./h or more.

  The maximum attainable temperature of the molten composition (melt) is not particularly limited as long as the molten state of the composition is realized. For example, the temperature can be about 800 to 2000 ° C. (preferably about 850 to 1800 ° C., more preferably about 900 to 1600 ° C.) and can realize a molten state. The lower limit temperature at which such a molten state can be realized may vary depending on the composition of the target product (for example, the types of A and M, the values of x and y, etc.). For example, when A is mainly lithium and M is mainly Fe, the maximum temperature reached is preferably about 850 to 1800 ° C, and more preferably about 900 to 1600 ° C.

  Note that an olivine-type material in which M is more divalent than trivalent (for example, iron) and M is mainly divalent (typically, x and y in the above general formula are In the case where the production of an electrode active material mainly composed of a compound that is almost 1) is intended, it is preferable that the maximum temperature reached is relatively high. For example, the manufacturing conditions may be set so that the highest temperature reaches about 400 ° C. or higher (typically about 400 to 800 ° C.) higher than the lower limit temperature at which the molten state can be realized. Preferably, the temperature is more preferably about 600 ° C. or higher (typically about 600 to 800 ° C.).

  The time (melting time) from when the raw material composition is melted to when cooling (slow cooling) is started is not particularly limited. From the viewpoint of production efficiency and energy cost, it is usually appropriate to set the melting time to about 24 hours or less (typically about 5 minutes to 24 hours), and about 6 hours or less (typically About 5 minutes to 6 hours) is preferable. Further, the time for keeping the melt at the maximum temperature is not particularly limited. From the standpoint of enhancing the uniformity of the target object, it is usually appropriate to set the holding time to about 30 seconds or more (for example, about 30 seconds to 2 hours), and about 1 minute or more (for example, about 1 minute to 1). Time). Alternatively, temperature lowering (cooling or slow cooling) may be started immediately after heating to the highest temperature.

  In addition, the method of preparing the composition in a molten state is not limited to the method of melting the solid raw material composition mixed (prepared) in advance as described above. For example, each solid supply source may be prepared separately, and mixed while sequentially melting them. Specifically, for example, a solid M supply source may be melted, a solid A supply source may be added to the molten M supply source, and then a solid P supply source may be added. Alternatively, each supply source may be melted individually, and the molten sources may be mixed.

The molten composition (melt) can contain a reducing agent. In particular, an M compound having a higher valence of M than the valence of M in the general formula (for example, divalent) (for example, an M compound having trivalent M as a constituent element) is part or all of the M supply source. When using as, it is preferable to contain a reducing agent in this melt. In addition, for example, when M is an element (for example, iron) that tends to be more stable than trivalent than trivalent (for example, iron) and M is mainly divalent, M source In the case of using a trivalent M compound (for example, Fe ₂ O ₃ ) as well as using a divalent M compound (for example, FeO) as an M supply source, a reducing agent should be included in the melt. Better results can be achieved. For example, the event that M is oxidized to become trivalent can be better prevented.
As the reducing agent, a carbon material (for example, carbon powder such as acetylene black, ketjen black, graphite precursor) can be preferably used. Examples of other reducing agents that can be used in the method disclosed herein include saccharides and polypropylene.

  The means for incorporating such a reducing agent into the melt is not particularly limited. For example, a raw material composition may be prepared by mixing a powdery reducing agent (carbon powder or the like) together with the powder of each supply source, and the raw material composition may be melted. Alternatively, the reducing agent may be added thereto after melting each supply source. The amount of the reducing agent to be contained in the melt is not particularly limited, but if it is too small, the effect of using the reducing agent may not be sufficiently exhibited. On the other hand, if the amount of the reducing agent used is too large, the performance of the target product (battery performance, etc.) may be unintentionally affected. Considering these circumstances, the amount of reducing agent used can be set to, for example, about 2 g per 100 g of melt.

  The target product is obtained by slowly cooling and solidifying the molten composition (melt). Such slow cooling may be performed while being controlled so as to achieve a predetermined temperature profile, or may be allowed to cool the melt naturally. The predetermined temperature profile may be one that gradually decreases the temperature at a constant rate, one that gradually decreases the temperature, or a temperature profile that combines these. Usually, it is easy and preferable to lower the temperature at a constant rate (temperature decrease rate). In this case, the temperature lowering rate 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. As a general tendency, an object having higher crystallinity can be obtained by slowing the temperature lowering rate. On the other hand, excessively slowing the temperature lowering rate can lead to a decrease in manufacturing efficiency. From this point of view, it is usually appropriate to set the temperature drop rate to about 6 ° C./h or more, preferably about 30 ° C./h or more, and more preferably about 60 ° C./h or more. Even in the case where the temperature is lowered stepwise, it is preferable that the average cooling rate from the start of slow cooling to the end of slow cooling be within the above range.

  In one embodiment of the method disclosed herein, at least the composition in the molten state from the molten state (typically from when the composition is at a maximum temperature) to solidification. Slowly cool the product (melt). Typically, it is slowly cooled until the temperature of the melt is at least about 300 ° C. or less (preferably about 100 ° C. or less). The melt may be gradually cooled until it reaches a room temperature (for example, about 60 ° C. or lower, preferably about 40 ° C. or lower).

Note that when M in the above general formula is an element whose valence is higher than the valence of M in the general formula (for example, M in the general formula is mainly divalent and M is In the case of iron), at least a part of the manufacturing process described above is performed in a non-oxidizing atmosphere (typically, an inert gas atmosphere such as argon or an atmosphere containing a reducing gas such as hydrogen (H ₂ ) gas). ). Usually, it is preferable to perform at least from the start of slow cooling (temperature decrease) to the end of slow cooling in a non-oxidizing atmosphere. More preferably, the step from melting the solid raw material composition to the end of slow cooling is performed in a non-oxidizing atmosphere, and the step from preparing the raw material composition to the end of slow cooling is performed in a non-oxidizing atmosphere. Further preferred.

  The electrode active material obtained by any of the manufacturing methods described above can be substantially crystalline as a typical example. For example, it may be an electrode active material substantially composed of such a crystalline transition metal phosphate compound. In a preferred embodiment, the electrode active material may be composed mainly of a crystalline olivine type transition metal phosphate compound or a crystalline NASICON type transition metal phosphate compound. Alternatively, an electrode active material that is mainly crystalline but partially includes an amorphous portion may be used. It is confirmed by, for example, an X-ray diffraction pattern that the electrode active material is crystalline (at least mainly crystalline) and has a predetermined crystal structure (olivine type, NASICON type, etc.). Can do. The X-ray diffraction pattern can be obtained by an ordinary method using, for example, an X-ray diffraction apparatus (model number “Rigaku RINT 2100HLR / PC”) available from Rigaku Corporation.

According to the method disclosed herein, a material (or an electrode active material substantially composed of the material) substantially composed of an olivine single-phase transition metal phosphate compound can be produced. Here, the term “olivine single phase” means that the material does not substantially contain trivalent M (for example, Fe) when the production of an olivine type material represented by AM ^II (PO ₄ ) is intended. That means. For example, it means that the presence of trivalent Fe is not confirmed at least in the X-ray diffraction profile of the material. According to one preferred embodiment, such an olivine single-phase alkali metal iron phosphate compound (typically a lithium iron phosphate compound or the like) is used as a starting material from a divalent iron source (eg, FeO). In addition to the case of using a trivalent iron source (for example, Fe ₂ O ₃ ), it can be efficiently produced.

  An electrode active material manufactured by applying the method disclosed herein can function as an electrode active material of a secondary battery by insertion / extraction of various cations. The cations that can be inserted into or desorbed from the active material include alkali metal ions such as lithium ion, sodium ion, potassium ion, and cesium ion, alkaline earth metal ions such as calcium ion and barium ion, magnesium ion, aluminum ion, silver Ions, zinc ions, tetrabutylammonium ions, tetraethylammonium ions, tetramethylammonium ions, triethylmethylammonium ions, triethylammonium ions and other ammonium ions, imidazolium ions, imidazolium ions such as ethylmethylimidazolium ions, pyridinium Ion, hydrogen ion, tetraethylphosphonium ion, tetramethylphosphonium ion, tetraphenylphosphonium ion, triphenyl Sulfonium ions, triethyl sulfonium ions, and the like. Of these, preferred are alkali metal ions, and lithium ions are particularly preferred.

  When the electrode active material manufactured by applying the method disclosed herein is used for the positive electrode of a battery, the active material of the negative electrode that is the counter electrode is lithium (Li), sodium (Na), magnesium (Mg), A metal such as aluminum (Al) or an alloy thereof, or a carbon material capable of occluding and releasing cations can be used.

  The electrode having the electrode active material can be suitably used as an electrode for secondary batteries having various shapes such as a coin shape, a cylindrical shape, and a square shape. For example, this electrode active material can be compression molded to form an electrode in the form of a pellet. A plate-like or sheet-like electrode can be formed by attaching the electrode active material to a current collector made of a conductive material such as metal. In addition to the electrode active material according to the present invention, such an electrode can contain one or more materials similar to those of a general electrode active material, if necessary. Typical examples of such a material include a conductive material and a binder. As the conductive material, a carbon material such as acetylene black (AB) can be used. As the binder, organic polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) can be used.

As the non-aqueous electrolyte used for the secondary battery, a non-aqueous solvent and a compound containing a compound (supporting electrolyte) containing a cation that can be inserted into and removed from the electrode active material can be used.
As the non-aqueous solvent constituting the non-aqueous electrolyte, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used without particular limitation. 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, Examples include 3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. Only 1 type selected from such a non-aqueous solvent may be used, and 2 or more types may be mixed and used for it.
In addition, as the supporting electrolyte constituting the non-aqueous electrolyte, a compound containing a cation inserted / extracted from the electrode active material, for example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO _{2 in} the case of a lithium ion secondary battery). ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiClO _4, or one or more selected from lithium compounds (lithium salts) can be used.

  Hereinafter, some specific examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the specific examples.

<Experimental example 1>
In this experimental example, a sample for an electrode active material mainly composed of a phosphoric acid compound having divalent iron was manufactured using an Fe supply source (FeO) having divalent Fe.
FeO, P ₂ O ₅ and LiOH were mixed at a molar ratio of 1: 0.5: 1. This mixture (raw material composition) was melted by heating to 1100 ° C. (maximum temperature reached) at a rate of temperature increase of 200 ° C./h in an Ar atmosphere, and held at that temperature for 15 minutes. Subsequently, the melt was cooled (slowly cooled) from a melted state at 1100 ° C. to a temperature of about room temperature at a temperature lowering rate of 200 ° C./h. Powder X-ray diffraction (XRD) measurement was performed on a sample obtained by pulverizing the resultant product by a conventional method (hereinafter, the resulting product and the pulverized product are referred to as “Sample 1”). An X-ray diffractometer (model number “Rigaku RINT 2100HLR / PC”) available from Rigaku Corporation was used for the measurement. The result is shown in FIG. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed. From this, it was confirmed that Sample 1 obtained in this experimental example is substantially crystalline and has a single phase of olivine (LiFePO ₄ ).

<Experimental example 2>
This experimental example is another example in which a sample for an electrode active material containing a divalent iron-containing phosphate compound as a main component is manufactured using an Fe supply source (FeO) having divalent Fe.
FeO, P ₂ O ₅ and Li ₂ CO ₃ were mixed at 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 a raw material composition and the time for maintaining the maximum temperature (here, 1100 ° C.) was 30 minutes. FIG. 2 shows the result of XRD measurement performed on Sample 2 in the same manner as in Experimental Example 1. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed, and it was confirmed that this sample 2 was substantially crystalline and was a single phase of olivine (LiFePO ₄ ).

<Experimental example 3>
The present experimental example is an example in which a sample for an electrode active material mainly composed of a phosphoric acid compound having divalent iron is manufactured using an Fe supply source (Fe ₂ O ₃ ) having trivalent Fe.
Fe ₂ O ₃ , P ₂ O ₅ and Li ₂ CO ₃ are mixed at a molar ratio of 1: 1: 1, and carbon powder as a reducing agent (acetylene black, hereinafter sometimes referred to as “AB”). .) Was mixed. The mixing amount of AB was 2 parts by mass with respect to 100 parts by mass of the total mass of Fe ₂ O ₅ , P ₂ O ₅ and Li ₂ CO ₃ . This was heated to the highest temperature reached (here, 1100 ° C.) in the same manner as in Experimental Example 1 and melted and held at that temperature for 30 minutes. Next, the melt (containing AB as a reducing agent) was cooled (slowly cooled) from a melted state at 1100 ° C. to a temperature of about room temperature at a temperature decreasing rate of 200 ° C./h. XRD measurement was performed in the same manner as in Experimental Example 1 for Sample 3 obtained by pulverizing the resulting product by a conventional method. The result is shown in FIG. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed, and it was confirmed that this sample 3 was substantially crystalline and was olivine (LiFePO ₄ ) single phase.

<Experimental example 4>
This experimental example is another example in which a sample for an electrode active material mainly composed of a phosphoric acid compound having divalent iron was manufactured using an Fe supply source (Fe ₂ O ₃ ) having trivalent Fe. is there.
A raw material composition was prepared in the same manner as in Experimental Example 3 except that AB as a reducing agent was not used. Using this raw material composition, heating (temperature increase rate 200 ° C./h, maximum attained temperature 1100 ° C., holding time 30 minutes), cooling (temperature decrease rate 200 ° C./h) and pulverization were performed in the same manner as in Experimental Example 3. Sample 4 was obtained. This sample 4 was subjected to XRD measurement in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in the figure, Sample 4 obtained under the production conditions of this Experimental Example contained a trivalent Fe compound and was not an olivine (LiFePO ₄ ) single phase.

<Experimental example 5>
This experimental example is another example in which a sample for an electrode active material containing a divalent iron-containing phosphate compound as a main component is manufactured using an Fe supply source (FeO) having divalent Fe.
FeO, P ₂ O ₅ and LiOH were mixed at a molar ratio of 1: 0.5: 1. This mixture (raw material composition) was melted by heating to 1500 ° C. (maximum temperature reached) at a rate of temperature increase of 200 ° C./h in an Ar atmosphere and held at that temperature for 5 minutes. The melt was cooled (slow cooling) from a molten state at 1500 ° C. to a temperature of about room temperature at a rate of temperature decrease of 200 ° C./h. Powder X-ray diffraction (XRD) measurement was performed on Sample 5 obtained by pulverizing the resultant product by a conventional method. The result is shown in FIG. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed, and it was confirmed that this sample 5 was substantially crystalline and was olivine (LiFePO ₄ ) single phase. Thus, even when the melting temperature (maximum temperature reached) was raised from 1100 ° C. to 1500 ° C., good results (samples consisting of an olivine single phase) were obtained as in Experimental Example 1.

<Experimental example 6>
This experimental example is another example in which a sample for an electrode active material mainly composed of a phosphoric acid compound having divalent iron was manufactured using an Fe supply source (Fe ₂ O ₃ ) having trivalent Fe. is there.
A raw material composition was prepared in the same manner as in Experimental Example 3 except that AB as a reducing agent was not used. Using this mixture (raw material composition), heating (temperature increase rate 200 ° C./h, maximum temperature reached 1500 ° C., holding time 5 minutes), cooling (temperature decrease rate 200 ° C./h) and pulverization were performed in the same manner as in Experimental Example 5. To obtain a sample 6. The sample 6 was subjected to XRD measurement in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed, and it was confirmed that this sample 6 was substantially crystalline and was a single phase of olivine (LiFePO ₄ ). Thus, even when Fe ₂ O ₃ is used as the Fe supply source, by raising the melting temperature (maximum temperature reached) from 1100 ° C. to 1500 ° C., good results without using a reducing agent (olivine single phase) Sample) was obtained.

<Experimental example 7>
This experimental example is another example in which a sample for an electrode active material mainly composed of a phosphoric acid compound having trivalent iron was manufactured using an Fe supply source (Fe ₂ O ₃ ) having trivalent Fe. is there.
Fe ₂ O ₃ and P ₂ O ₅ were mixed at a molar ratio of 1: 1. Using this mixture (raw material composition), heating (temperature increase rate 200 ° C./h, maximum temperature reached 1500 ° C., holding time 5 minutes), cooling (temperature decrease rate 200 ° C./h) and pulverization were performed in the same manner as in Experimental Example 6. A sample 7 was obtained. The sample 7 was subjected to XRD measurement in the same manner as in Experimental Example 1. The result is shown in FIG. As shown in the figure, only the X-ray profile peculiar to the olivine type was observed, and it was confirmed that this sample 7 was substantially crystalline and was olivine (FePO ₄ ) single phase.

<Characteristic test of sample 1>
A measurement cell was prepared using Sample 1 obtained in Experimental Example 1.
That is, as an electrode active material, a material obtained by pulverizing the sample 1 to such an extent that it cannot be felt by the fingertip (for convenience, this pulverized product is also referred to as “sample 1”, the same shall apply hereinafter). About 0.25 g of the electrode active material and about 0.089 g of acetylene black (AB) as a conductive material were mixed (mass ratio of about 70:25). A planetary ball mill was used for mixing the electrode active material and AB. To this mixture (mixture of electrode active material and AB), about 0.018 g of polytetrafluoroethylene (PTFE) as a binder was further added and mixed (mass ratio of electrode active material: AB: PTFE: about 70: 25: 5). This mixture was compression-molded into a disc shape (pellet shape) having a diameter of about 1.0 cm and a thickness of about 0.5 mm to produce a test electrode.

As the counter electrode, a lithium foil having a diameter of 1.5 mm and a thickness of 0.15 mm was used. As the separator, a porous polyethylene sheet having a diameter of 22 mm and a thickness of 0.02 mm was used. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ 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 was used. These constituent elements were assembled in a stainless steel container to construct a coin-type cell having a thickness of 2 mm and a diameter of 32 mm (2032 type) as shown in FIG. In FIG. 19, reference numeral 1 is a positive electrode (test electrode), reference numeral 2 is a negative electrode (counter electrode), reference numeral 3 is a separator and electrolyte solution (non-aqueous electrolyte), reference numeral 4 is a gasket, and reference numeral 5 is a positive electrode container. Reference numeral 6 denotes a negative electrode lid. Hereinafter, the above cell produced using Sample 1 as the electrode active material and using a planetary ball mill for mixing the electrode active material and AB is referred to as “cell 1-B”.

  Further, a test electrode and a cell were constructed in the same manner as described above except that an electrode active material, AB and PTFE were mixed using a stone mill instead of a planetary ball mill. The cell prepared using the sample 1 as the electrode active material and using a machine that is difficult to mix the electrode active material and AB is referred to as “cell 1-S”.

Each of the cells 1-B and 1-S was allowed to stand for about 12 hours after production (that is, cell construction), and then a constant current charge / discharge test was performed on these cells. The test conditions were a voltage regulation of 4.5 to 2.5 V (cell voltage) and a current density of 0.2 mA / cm ² . A charge / discharge profile obtained by charge / discharge in the first cycle is shown in the upper part of FIG. As a result, the cell 1-B (thick line in the figure) mixed using a planetary ball mill has better performance (lithium ion) than the cell 1-M (thin line in the figure) mixed using a rough machine. Utilization rate). Therefore, for the second cycle, only the results for cell 1-B are shown in the lower part of FIG.
Here, the initial charge capacity is slightly less than the discharge capacity because the Li component volatilizes and disappears in the melting process, but the site does not disappear, and the charge capacity for the Li deficiency is from the second cycle onwards. It has recovered.

A cycle test of the cell 1-B was performed. That is, for the cell 1-B, the charge / discharge cycle was repeated under the above conditions (voltage regulation 4.5 to 2.5 V, current density 0.2 mA / cm ² ), and the specific capacity for each cycle was measured. . The obtained results (cycle characteristics) are shown in FIG.
Furthermore, per the cell ^{1-B, 0.1mA / cm 2} , 0.2mA / cm 2, at each discharge rate of 0.5 mA / cm ² and 1.0 mA / cm ^2, the discharge capacity of each first cycle It was measured. The obtained results (rate characteristics) are shown in FIG.

<Characteristic test of sample 2>
A measurement cell was produced in the same manner as in the cell 1-B except that the sample 2 was used as the electrode active material instead of the sample 1 (that is, using a planetary ball mill for mixing the electrode active material and AB). . Hereinafter, this measurement cell is referred to as “cell 2-B”.
About this cell 2-B, the constant current charging / discharging test and the cycle test were done on the test conditions similar to the said test 1. FIG. The obtained results are shown in FIGS. 11 and 12, respectively. Furthermore, per the cell ^{2-B, 0.1mA / cm 2} , 0.2mA / cm 2, at each discharge rate of 0.5 mA / cm ² and 1.0 mA / cm ^2, the discharge capacity of each first cycle It was measured. The obtained result is shown in FIG.

<Characteristic test of sample 3>
A measurement cell was prepared in the same manner as in the cell 1-B except that the sample 3 was used as the electrode active material instead of the sample 1 (that is, using a planetary ball mill for mixing the electrode active material and AB). . Hereinafter, this measurement cell is referred to as “cell 3-B”.
About this cell 3-B, the constant current charging / discharging test and the cycle test were done on the test conditions similar to the said test 1. FIG. The obtained results are shown in FIGS. 14 and 15, respectively. Further, for the cell 3-B, the discharge capacity at the first cycle was measured at each discharge rate of 0.1 mA / cm ² , 0.2 mA / cm ² and 0.5 mA / cm ² . The obtained results are shown in FIG.

<Characteristic test of sample 5>
A measurement cell is produced in the same manner as in the cell 1-S except that the sample 5 is used as the electrode active material instead of the sample 1 (that is, using a machine that is difficult to mix the electrode active material and AB). did. Hereinafter, this measurement cell is referred to as “cell 5-S”.
About this cell 5-S, the constant current charging / discharging test and the cycle test were done on the test conditions similar to the said test 1. FIG. The obtained results are shown in FIGS. 17 and 18, respectively.
As a result of these tests, Samples 1, 2, 3 and 5 obtained in the above experimental examples all show various characteristics useful as electrode active materials for lithium secondary batteries (typically lithium ion secondary batteries). Confirmed to get.

  The preferred embodiments of the present invention have been described in detail above, but these are only examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the above-described embodiments. In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

2 is an X-ray profile of Sample 1. 2 is an X-ray profile of Sample 2. 3 is an X-ray profile of Sample 3. It is an X-ray profile of sample 4. It is an X-ray profile of sample 5. 7 is an X-ray profile of Sample 6. It is an X-ray profile of Sample 7. 2 is a charge / discharge profile of Sample 1. 3 is a graph showing cycle characteristics of Sample 1. 3 is a graph showing rate characteristics of Sample 1. 2 is a charge / discharge profile of Sample 2. 6 is a graph showing cycle characteristics of Sample 2. 6 is a graph showing rate characteristics of Sample 2. 3 is a charge / discharge profile of Sample 3. 5 is a graph showing cycle characteristics of Sample 3. 5 is a graph showing rate characteristics of Sample 3. 5 is a charge / discharge profile of Sample 5. 6 is a graph showing cycle characteristics of Sample 5. It is sectional drawing which shows the structure of the cell for a measurement typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator and non-aqueous electrolyte

Claims (8)

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 1 or two or more elements selected from transition metals)), and a method for producing an electrode active material mainly comprising a phosphate compound represented by
A molten composition comprising a source of M and a source of phosphorus (P) in the general formula, and when x in the general formula is greater than 0, further comprises a source of A in the general formula And
Slow cooling the molten composition;
An electrode active material manufacturing method comprising: To prepare the molten composition,
Providing a solid raw material composition comprising a source of M and a source of phosphorus, and further comprising the source of A when x is greater than 0; and
Melting the raw material composition;
The method of claim 1, wherein The molten composition is:
Contains A, M and phosphorus in a substantially 1: 1: 1 atomic ratio, or
The method according to claim 1 or 2, wherein the A is substantially not contained, and the M and phosphorus are contained in a substantially 1: 1 atomic ratio. The source of M includes a compound having M as a constituent element, wherein the M valence in the compound is higher than the valence of M in the general formula; and
A reducing agent is included in the molten composition;
The method as described in any one of Claims 1-3. The phosphate compound represented by the general formula is an olivine-type iron phosphate compound in which M in the general formula is mainly divalent iron (Fe),
Fe ₂ O ₃ is used as the source of M, and
A reducing agent is included in the molten composition;
The method as described in any one of Claims 1-3.   The method according to claim 4 or 5, wherein carbon powder is used as the reducing agent. A positive electrode having an electrode active material obtained by the method according to any one of claims 1 to 6;
A negative electrode having a material that occludes and releases alkali metal ions;
A non-aqueous electrolyte or a solid electrolyte;
A secondary battery comprising:   The secondary battery according to claim 7, wherein the alkali metal ion is a lithium ion.

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