JP5182626B2 - Positive electrode active material and non-aqueous electrolyte battery - Google Patents

Description

The present invention is a positive electrode active material containing iron phosphate lithium compound having an olivine-type crystal structure, and a nonaqueous electrolyte battery obtained by using the positive electrode active material.

Conventionally, a non-aqueous electrolyte battery represented by a lithium ion battery has been widely used as a battery for consumer use such as a portable communication device whose size and weight are being reduced. In such applications, the nonaqueous electrolyte battery is required to have characteristics such as high voltage and high energy density, and therefore, transition metal oxide materials such as LiCoO ₂ have been frequently used as the positive electrode active material.

  2. Description of the Related Art In recent years, studies have been actively conducted on the use of nonaqueous electrolyte batteries as batteries for industrial applications that require high capacity and high output, such as for HEV (hybrid vehicles) and power storage. In such applications, miniaturization of equipment is not an issue, but many batteries are often used together, and replacement of batteries requires labor costs, etc. Polyanion having an olivine-type crystal structure typified by lithium iron phosphate as a positive electrode active material because it has a long life in terms of charge / discharge cycle performance rather than characteristics such as density and high safety is required. Mold materials are attracting attention and are being studied.

  However, a polyanionic material having an olivine type crystal structure as a positive electrode active material used in the battery for industrial use has a problem in high output performance. That is, in the battery for industrial use, as described above, the high energy density performance is not necessarily important. Therefore, the capacity of the active material can be dealt with by increasing the active material provided in the battery. However, in terms of high output performance, specifically, it is required that the discharge capacity obtained at the high rate discharge does not greatly decrease with respect to the discharge capacity obtained at the low rate discharge.

For the purpose of “providing a high-capacity and inexpensive lithium secondary battery excellent in charge / discharge cycle characteristics” (paragraph 0011), the following Patent Document 1 describes “represented by a composition formula LiFe _1-x M _x PO ₄ . (Claim 1), "When an element lighter than Fe, such as Al or Mg, is used as the element M, an electrode material having a high energy density can be synthesized" (paragraph 0017). (Example 3) Aluminum acetate and magnesium acetate are used as raw materials corresponding to the substitution element M, and the element ratio of Li: Fe: Al: Mg: P is 1: 0.9. : 0.05: 0.05: 1, except that the electrode material of the present invention was obtained in the same manner as in Example 1. From the X-ray diffraction pattern of the obtained electrode material, a single crystal was obtained. I found that it was obtained in the phase (Paragraph 0028).

Further, Patent Document 2, _{"Li x Fe 1-y M y} PO 4 carbon composite material (wherein a 0.05 ≦ x ≦ 1.2,0 ≦ y ≦ 0.8, M is Mn, Cr, Co, Cu, Ni, V, Mo, TI, Zn, Al, Ga, Mg, B, and Nb) are reliably single-phase synthesized to provide excellent battery performance. “Providing a manufacturing method of a positive electrode active material to be realized” (paragraph 0014) “Synthesizing LiFe _0.3 Al _0.7 PO ₄ carbon composite as a positive electrode active material” (paragraph 0137) The production (Example 14) is described.

Patent Document 3, in order to improve the production efficiency of the Li _x A _y D _z A positive active material for PO ₄ as main components, _{"Li x A y D z PO 4} ( where, A is One selected from Co, Ni, Mn, Fe, Cu, Cr, D is Mg, Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, One or more selected from Al, Ga, In, Si, B and rare earth elements and different from A, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5) In the method of continuously producing a positive electrode active material for a lithium battery represented by the above, one or more of the lithium (Li) component, the A component, and the D component that are raw materials of the LixAyDzPO4 are used at room temperature. A phosphorus compound insoluble in a solvent containing water as a main component under normal pressure, The lithium (Li) component, the A component and the D component are added to form a slurry having a temperature (1), and then the slurry is maintained at a temperature (2) higher than the temperature (1) to precipitate crystal nuclei, And a method for producing a positive electrode active material for a lithium battery, characterized in that crystal nuclei in the slurry are grown at a temperature (3). ”(Claim 1) In addition to the metal salt, for example, it may be a phosphorus compound that is insoluble in a solvent containing water as a main component and contains D. For example, aluminum phosphate (AlPO ₄ ), magnesium phosphate (Mg ₃ (PO ₄ )) ₂ ), (ortho) manganese phosphate (II) (Mn ₃ (PO ₄ ) ₂ ), (ortho) manganese phosphate (III) (MnPO ₄ ), etc. ”(paragraph 0038) There is.

In Non-Patent Document 1, Al (OC ₂ H ₅ ) ₃ which is a metal alkoxide is added as a dopant (Al ³⁺ ) together with Li ₂ CO ₃ , NH ₄ H ₂ PO ₄ and FeC ₂ O ₄ .2H ₂ O, It describes that the material was synthesized by solid phase reaction. Further, it is described that, prior to firing, the raw material was crushed for 24 hours using a zirconia ball mill using acetone as a solvent, dried and further pulverized. In addition, there is no description about the temperature-fall rate after baking.

Patent Document 4 describes that Li (Al _0.002 Fe _0.998 ) PO ₄ (Sample 2a1) and (Li _0.99 Al _0.01 ) FePO ₄ (Sample 2b6) were synthesized (Table 5). In the “XRD / TEM / STEM observation” column, “dopant soluble” is described, and in the “microphase (by XRD)” column, “not detected” is described. Moreover, the figure seen as the X-ray diffraction pattern of this sample is described in "FIG. 6-B".
In addition, synthesis materials of these samples include NH ₄ H ₂ PO ₄ , Li ₂ CO ₃ and FeC ₂ O ₄ .2H ₂ O (Table 2), together with “aluminum ethoxide to prepare Al-doped samples, "Al (OC ₂ H ₅ ) ₃ was used as a dopant salt" (paragraph 0090). In addition, it is described that the heat treatment conditions during the synthesis of “Sample 2b6” were “350 ° C., 20 hours, Ar” after “350 ° C., 10 hours, Ar” (Table 8) under 1 atm.

Patent Document 5 states that “when a lithium-containing composite oxide powder such as LiNiO ₂ or LiMn ₂ O ₄ is used as a positive electrode active material of a lithium ion secondary battery, the charge / discharge cycle proceeds at a high voltage. There are problems with cycle characteristics and stability, such as a decrease in discharge capacity and capacity deterioration during high-temperature storage, and problems such as insufficient battery voltage and cycle characteristics even when room temperature molten salt is used as the electrolyte. ” In order to solve the paragraph 0012), “a positive electrode is formed in a lithium ion secondary battery in which a mixture of an ambient temperature molten salt and a lithium salt as an electrolyte is interposed between a negative electrode material using lithium and a positive electrode material. The positive electrode active material particles to be represented by the general formula LixMOy (M in the formula is mainly composed of a transition metal and contains at least one of Co, Mn, Ni, V, and Fe. Also, the values of x and y in the formula Is a lithium-containing composite oxide powder represented by the following formula: x = 0.02 to 2.2 and y = 1.4 to 3. The surface of the positive electrode active material particles is positive electrode active material particles. A lithium ion secondary battery using a room temperature molten salt, characterized in that at least a part of the surface is covered with a deposit having ion conductivity and electron conductivity that does not easily change in valence on the surface of the battery. The invention of claim 1) is described, and the deposit is “Al ₂ O ₃ , TiO ₂ , ZrO ₂ , B ₂ O ₃ , SiO ₂ , AlPO ₄ , or a mixture of two or more thereof” ( (Claim 7), LiMPO ₄ (M = Mn, Fe, Co, Ni) or the like (Claim 5). Further, in the examples, a battery using “positive electrode active material: LiCoO ₂ coated with 3 wt% of ZrO ₂ ” on the positive electrode is described.

JP 2001-307726 A JP 2003-117849 A JP 2006-331992 A JP-T-2005-514304 JP 2007-005267 A Sung-Yoon Chung, Jason T. Bloking & Yet-Ming Chiang, "Electronically conductive phospho-olivines as lithium storage electrodes", nature materials, 2002, vol.1 pp123-128.

  However, any of the conventional batteries as described above has a low ratio of the discharge capacity obtained at the high rate discharge to the discharge capacity obtained at the low rate discharge, and is sufficient as, for example, a battery for industrial use as described above. It has a problem that it does not have a good performance.

  In view of the above-described problems of the prior art, the present invention provides a positive electrode for a non-aqueous electrolyte battery that can increase the ratio of the discharge capacity obtained during high rate discharge to the discharge capacity obtained during low rate discharge. An object is to provide an active material and a non-aqueous electrolyte battery using the active material.

  The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention. The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or examples are merely examples in all respects, and the present invention should not be construed as being limited thereto. The scope of the present invention is defined by the scope of claims, and is not limited to the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention contains grain boundaries of the primary particles AlPO ₄ is present in at least a portion of the polycrystalline body of lithium iron phosphate compounds which have a olivine crystal structure, Fe element, a transition metal other than Fe Element ratio of element M, Al element, and P element is [(Fe _1−x M _x ) _1−y Al _y ]: P = 1: 1 (x is 0 or more and less than 1 and y is 0.007. providing a positive electrode active material of a nonaqueous electrolyte for batteries, which is a more less than 0.05).

The present invention also provides the positive electrode active material for a non-aqueous electrolyte battery having a diffraction peak due to AlPO ₄ at 2θ = 26 ° to 27 ° in X-ray diffraction using CuKα rays .

Further, the present invention is characterized in that primary particles in which AlPO ₄ is present in at least part of the crystal grain boundaries are produced by firing aluminum isopropoxide, which is an Al raw material, together with other active material raw materials. A positive electrode active material for the non-aqueous electrolyte battery is provided.

  Furthermore, the present invention provides a non-aqueous electrolyte battery comprising any one of the positive electrode active materials described above.

  In the present invention, the X-ray diffraction using CuKα rays means that the diffraction peak is at 2θ = 26 ° to 27 °. The maximum peak intensity measured in the range of 2θ = 15 ° to 60 ° using CuKα rays. On the X-ray diffractogram with full scale on the vertical axis, at least the peak can be visually recognized, or the waveform processing device can clearly distinguish it from the background noise and recognize the peak, preferably the maximum diffraction peak On the other hand, it has a peak intensity of at least 0.5%.

Further, in the present invention, a part of PO ₄ in the crystal (polyanion) may be SiO ₄ is not a solid solution, that solid solution of a Si0 ₄ is not intended to excluded from the scope.

  According to the nonaqueous electrolyte battery using the positive electrode active material for a nonaqueous electrolyte battery according to the present invention, the ratio of the discharge capacity obtained during high rate discharge to the discharge capacity obtained during low rate discharge can be increased.

Positive electrode active material according to the present invention are those which contain primary particles Al compound to at least a portion of the grain boundaries in the polycrystalline body of lithium iron phosphate compounds which have a olivine crystal structure is present.
The primary particles are configured such that AlPO ₄ as an Al compound exists in at least a part of the crystal grain boundary.

  The positive electrode active material is usually in a state where a part of primary particles, which is the smallest unit of particles, aggregates to form secondary particles. When the secondary particles are pulverized using a mortar or the like, some of them have a property of loosening into primary particles, and the primary particles have a property of easily agglomerating into secondary particles by mixing a solvent or the like. Most of the primary particles are polycrystalline.

The polycrystalline body is iron phosphate lithium compound, Fe elements, a portion of which those can be substituted by a transition metal element other than Fe. As the transition metal element, any transition metal element other than Fe can be used alone or in combination of two or more. Preferable examples of the transition metal element include Co, Mn, V and the like.

In addition to LiFePO ₄ , lithium iron phosphate compounds having such an olivine type crystal structure include those in which Fe element is replaced by a transition metal element other than Fe , specifically, LiFe _0.9 Co _0.1 PO ₄ , LiFe _0.5 Mn _0.5 PO ₄ , LiFe _0.1 V _0.9 PO ₄ and mixtures thereof.

The ratio of the transition metal element substituting for the Fe element is preferably 0 atomic percent or more and less than 10 atomic percent, and more preferably 0 atomic percent or more and less than 5 atomic percent.
If the amount of the transition metal element is within the above range, the reversible potential associated with the lithium insertion / elimination reaction does not become too high, and the lithium iron phosphate compound has a relatively low reversible potential of around 3.4 V. Can be used. Therefore, the possibility of causing oxidative decomposition of the electrolytic solution can be reduced, and a nonaqueous electrolyte battery excellent in charge / discharge cycle performance can be obtained at both low rate discharge and high rate discharge.

Further, in the present invention, the Al compound, together with crystals constituting the polycrystal has been included in the primary particles, in other words, so as to present at least part of the crystal grain boundary which constitutes the primary particles Is distributed.

As the Al compound, but are not particularly limited, for _{example, AlPO 4, Al 2 O 3} , AlP, Al (PO 3) 3, LiAlO 2, Al (OH) 3, Al 4 C 3, AlLiO 2 , Li ₃ Al ₂ (PO ₄ ) _{3 and the} like. Among them, AlPO ₄ is preferable from the viewpoint of increasing the ratio of the discharge capacity obtained at the high rate discharge to the discharge capacity obtained at the low rate discharge.
In the present invention, LiFe _1-z Al _z PO ₄ is not regarded as an Al compound existing at the crystal grain boundary.

In addition, the Al compound can be suitably generated in at least a part of the crystal grain boundary by firing an Al raw material as described later together with another active material raw material.
Moreover, it is preferable to contain this Al compound in the said positive electrode active material in the ratio of 1-9 mass parts with respect to 100 mass parts of crystal | crystallization which comprises the said polycrystal , and the ratio of 1-4 mass parts is also the same. More preferably, it is contained in the positive electrode active material.

  The presence or absence of the Al compound can be confirmed by X-ray diffraction using CuKα rays as shown in the Examples, and the Al content can be measured by ICP emission spectroscopic analysis as shown in the Examples. Can do.

Specifically, when an X-ray diffraction measurement using CuKα rays is performed by the method shown in the following examples and a diffraction peak is present in the range of 2θ = 26 ° to 27 °, the Al compound, particularly AlPO _{4 is used.} Is considered to exist.
In the positive electrode active material of the present invention, the peak intensity of the diffraction peak observed in the range of 2θ = 26 ° to 27 ° on the diffraction diagram obtained by the X-ray diffraction has an olivine structure (020 ) The peak intensity at 2θ = 17.0-17.5 ° measured corresponding to the plane is preferably 3% to 12%, more preferably 3% to 5%.
In the present specification, the peak intensity on the X-ray diffraction diagram indicates the peak integrated intensity (cps) corresponding to the peak area.

Thus, the olivine-type primary particles, wherein the Al compound to at least a part of the crystal grain boundary is configured to reside in the polycrystalline body of lithium iron phosphate compound crystal structure to have a the generation of the primary particles In the process, the crystal growth of the phase having the crystal structure is suppressed, and a plurality of crystal grains are present. Therefore, the surface area of the phase having the crystal structure is increased compared to the conventional one, and as a result, the electrochemical reactivity is increased. Therefore, the positive electrode active material is configured using the primary particles having such a configuration. Therefore, it is considered that the ratio of the discharge capacity obtained at the high rate discharge to the discharge capacity obtained at the low rate discharge becomes high.

The element ratio of Fe element (including a portion substituted by a transition metal element) and Al element contained in the positive electrode active material according to the present invention is Fe: Al = 1-y: y (provided that y Is preferably 0.007 or more and less than 0.05.
Here, the ratio of the number of elements does not indicate the amount of Al dissolved in the phase having the olivine type crystal structure, but the whole positive electrode active material, more specifically, the crystal having the olivine type crystal structure. This means the ratio of the LiFe _1-x Al _x PO ₄ phase formed by dissolving Al in the crystal having the structure and the positive electrode active material including the Al compound.

When the positive electrode active material satisfies such an element ratio, the amount of crystal phase having an olivine-type crystal structure is reduced according to the reduction ratio (value of y) of iron and transition metal, and at the same time, excess phosphorus (P) is considered to generate Al compounds such as AlPO ₄ together with Al and increase the electrochemical reactivity by the action as described above.

The positive electrode active material for a non-aqueous electrolyte battery according to the present invention includes a solid phase method that includes a step of mixing raw materials and a step of firing the mixed raw materials, and a sol-gel method that includes a step of gelling a solution containing a metal compound. , Coprecipitation method in which metal ions are precipitated in an aqueous solution and then pyrolyzed the filtrate, hydrothermal method in which an aqueous solution of the raw material is introduced into a sealed container and then heated from the outside of the container As long as the active material obtained after the synthesis contains an olivine-structured LiFePO ₄ skeleton, it may be synthesized by any method.
Therefore, the raw materials are also, for example, iron oxalate, iron nitrate, iron oxide, iron acetate as the Fe source, lithium carbonate, lithium hydroxide as the Li source, and ammonium dihydrogen phosphate, phosphoric acid as the PO ₄ source. A material suitable for the synthesis method such as lithium can be used.

  The Al source is preferably an aluminum isopropoxide, aluminum oxalate, aluminum hydroxide, or the like that does not interfere with the skeleton formation of the olivine type crystal structure during synthesis, and aluminum isopropoxide is particularly preferable.

When mixing the raw materials of the positive electrode active material, it is preferable to mix the raw materials so as to have the element ratio as described above. Specifically, Fe element, transition metal element M other than Fe, Al element, and The element ratio of P element is [(Fe _1−x M _x ) _1−y Al _y ]: P = 1: 1 (where x is 0 or more and less than 1 and y is 0.007 or more and 0.05). Less) .
By blending the raw material at such an element ratio, crystals such as those described in Patent Document 4 and Non-Patent Document 1 in which Al element is dissolved so as to replace Li element (specifically, (Li _0.99 Al _0.01) FePO _{4 and, Li 1-x Al x FePO} 4) and not.

As conditions for the synthesis, in order to avoid the formation of iron (III), the atmosphere should be an inert gas atmosphere such as nitrogen or argon, or an atmosphere containing a reducing gas such as hydrogen in the inert gas. Is preferred.
Further, in the step of mixing the raw materials before firing, it is preferable to mix so as not to cause mechanical alloying. For example, when the raw materials are pulverized and mixed by a ball mill, the rotational speed is 150 to 200 rpm, the pulverization time is 0. It is preferable to carry out for 5 to 3 hours.
Furthermore, if the temperature-decreasing rate after firing is too fast, as described in Non-Patent Document 1, Al is dissolved so as to replace Li in the crystal structure of LiFe _1-x Al _x PO ₄ and Li ₃ PO ₄ is presumed to occur, it is preferable that the temperature drop after firing is carried out gently so that this does not occur. Specifically, it does not exceed − (minus) 1 ° C./min. It is preferable to cool down slowly.

The positive electrode active material for a non-aqueous electrolyte battery according to the present invention is preferably used as a powder having an average particle size of 100 μm or less. In particular, in order to effectively bring out the effects of the present invention, it is preferable that the particle size is small, and the particle size of the primary particles configured as a polycrystalline body in which an Al compound is present in at least a part of the crystal grain boundary is 50. More preferably, the average particle diameter of secondary particles formed by agglomeration of the primary particles is 0.5 to 20 μm.
The specific surface area of the powder particles, better well great in order to improve the high rate performance of the positive electrode is preferably ^{1~100m 2 / g, 10~100m 2 /} g is more preferable.
In order to obtain the powder in a predetermined shape, a pulverizer or a classifier can be used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like can be used. At the time of pulverization, wet pulverization in which an organic solvent such as water or alcohol or hexane coexists may be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like can be used dry or wet as necessary.

In general, lithium iron phosphate is known to have a lower electronic conductivity than LiCoO _{2 and the} like, and after applying a carbon coating treatment to a lithium iron phosphate material in advance, as a positive electrode active material for a non-aqueous electrolyte battery The method used is known. In Examples to be described later, in order to confirm the effects of the present invention in detail, a positive electrode plate was prepared and evaluated without intentionally performing a carbon coating treatment. In manufacturing a water electrolyte battery, it is preferable to apply a prescription such as carbon coating using a known technique.

  A well-known thing can be used by a well-known prescription about the electrically conductive agent and binder further mixed with an electrode mixture.

  The amount of water contained in the positive electrode containing the positive electrode active material of the present invention is preferably as small as possible, specifically less than 5000 ppm.

  Moreover, the thickness of the electrode mixture layer is preferably 20 to 500 μm in view of the energy density of the battery.

  As one embodiment of the nonaqueous electrolyte battery according to the present invention, a positive electrode, a negative electrode, and an electrolyte salt are composed of a nonaqueous electrolyte containing a nonaqueous solvent, and a separator and these are packaged between the positive electrode and the negative electrode The thing provided with the exterior body can be mentioned.

  Non-aqueous solvents include cyclic carbonates such as propylene carbonate and ethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate; diethyl carbonate; chain carbonates such as ethyl methyl carbonate; methyl formate Chain esters such as methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme, etc. Ethers; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof can be used alone or as a mixture of two or more thereof, but are not limited thereto. It is not a thing.

Examples of the electrolyte salt include ionic compounds such as LiClO ₄ , LiBF ₄ , LiPF ₆ , and LiBOB. These ionic compounds can be used alone or in admixture of two or more. The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.5 mol / l to 5 mol / l, more preferably 1 mol / l to 2.5 mol / l in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. preferable.

  Hereinafter, the present invention will be described more specifically by illustrating test examples.

(Test Example 1)
A molar ratio of iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) is 2. It weighed so that it might be set to 0: 1.0: 2.0, it injected | thrown-in to the ball mill container with 2-propanol as a solvent for mixing, and it mixed at the rotational speed of 180 rpm for 2 hours, and obtained the mixture of the precursor. Next, after transferring the mixture to a ceramic container, it was placed in a chamber-type tabletop vacuum gas replacement furnace (manufactured by Denken, model number: KDF75), and in a nitrogen gas stream (2 liters / minute) at 350 ° C. for 2 hours. Subsequently, the temperature was raised to 700 ° C., and after further firing for 2 hours, the temperature was lowered by natural cooling (average 50 ° C./hour). In this way, an iron phosphate compound (LiFePO ₄ ) having an olivine type crystal structure phase was obtained.

(Test Example 2)
Iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide [( CH ₃ ) ₂ CHO] ₃ Al was mixed in a molar ratio of 1.99: 1.00: 2.00: 0.01 in the same manner as in Test Example 1, but with an olivine type crystal structure phase. Thus, an iron phosphate compound in which the number of Al atoms was 0.005 (0.5 atomic%) relative to the total number of Fe and Al atoms (Fe + Al) was obtained.

(Test Example 3)
First, iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide An olivine type crystal was obtained in the same manner as in Test Example 1 except that [(CH ₃ ) ₂ CHO] ₃ Al was mixed so that the molar ratio was 1.986: 1.000: 2.000: 0.014. An iron phosphate compound having a structural phase and having an Al atom number of 0.007 (0.7 atomic%) with respect to the total amount of Fe and Al atoms (Fe + Al) was obtained.

(Test Example 4)
Iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide [( CH ₃ ) ₂ CHO] ₃ Al was mixed in a molar ratio of 1.98: 1.00: 2.00: 0.02 in the same manner as in Test Example 1, but with an olivine type crystal structure phase. An iron phosphate compound in which the number of Al atoms is 0.01 (1 atomic%) relative to the total number of Fe and Al atoms (Fe + Al) is obtained.

(Test Example 5)
Iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide [( CH ₃ ) ₂ CHO] ₃ Al was mixed in a molar ratio of 1.94: 1.00: 2.00: 0.06 in the same manner as in Test Example 1, but with an olivine type crystal structure phase. And an iron phosphate compound in which the number of Al atoms was 0.03 (3 atomic%) relative to the total number of Fe and Al atoms (Fe + Al) was obtained.

(Test Example 6)
Iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide [( CH ₃ ) ₂ CHO] Al was mixed in a molar ratio of 1.9: 1.0: 2.0: 0.1 in the same manner as in Test Example 1 except that the olivine-type crystal structure phase was changed. And an iron phosphate compound in which the number of Al atoms is 0.05 (5 atomic%) relative to the total number of Fe and Al atoms (Fe + Al).

(Test Example 7)
Iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), lithium carbonate (Li ₂ CO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and aluminum isopropoxide [( CH ₃ ) ₂ CHO] Al was mixed in a molar ratio of 1.6: 1.0: 2.0: 0.4 in the same manner as in Test Example 1 except that the olivine type crystal structure phase was changed. Thus, an iron phosphate compound in which the number of Al atoms is 0.2 (20 atomic%) relative to the total number of Fe and Al atoms (Fe + Al) was obtained.

When the active material obtained by the TEM observation test example was observed with a transmission electron microscope (TEM), it was confirmed that the primary particles were polycrystalline. Further, in the active materials obtained in Test Examples 2 to 7, it was confirmed that another compound different from the crystal phase was present in a part of the crystal grain boundary of the polycrystal.

Structural analysis Furthermore, about each compound obtained by the test example, the structural analysis by X-ray diffraction measurement was performed.
Specifically, after pulverizing the obtained active material with a mortar, using a powder X-ray diffractometer (RINT2400, manufactured by Rigaku Corporation), a gonio radius of 185 mm, a divergence slit of 1 deg., A scattering slit of 1 deg. The measurement was performed under the conditions of 15 mm, an X-ray source CuKα ray, a tube voltage of 50 kV, and a tube current of 200 mA. The diffraction angle was 2θ = 15.0 to 85.0 °, the scan speed was 4.000 ° / min., And the scan step was 0.020 °.

As a result, peaks attributable to olivine crystal structure is observed in any of the results of Test Example, it was confirmed that the iron phosphate lithium compound having an olivine-type crystal structure is present.
Specifically, for example, in the diffraction pattern of Test Example 1 shown in FIG. 1, a peak (indicated by * in the figure) due to the olivine type crystal structure is observed, and the diffraction of Test Example 6 shown in FIG. In the diffractograms of Test Example 4 shown in FIG. 3 and FIG. 3, in addition to the peak attributed to the olivine type crystal structure, a peak not attributed to the olivine type crystal structure in the range of 2θ = 26 ° to 27 ° (▼ in the figure) Was observed).
In the diffraction diagram of Test Example 1 in which no Al raw material is added (FIG. 1), no peak is observed in such a range of 2θ = 26 ° to 27 °. Therefore, the peak has other olivine type crystal structure. It is estimated that it originates in a compound, specifically, an Al compound.

Mass Spectrometry Further, the obtained active material was measured by ICP emission spectroscopic analysis.
Specifically, first, 0.2 g of the synthesized active material was boiled for 30 minutes in 20 ml of 5 mol / l hydrochloric acid aqueous solution, and then this solution was diluted to 100 ml with water to prepare a measurement solution. Next, this solution was subjected to a plasma output of 1150 W, a nebulizer flow rate of 28.0 psi, and an auxiliary gas flow rate of 0.51 min ⁻¹ using a CID high-frequency plasma emission spectroscopic analyzer (manufactured by Nippon Jarrel Ash, IRIS-AP) The measurement was performed.
As a result, it was confirmed that the amount of Al element as shown in Table 1 was contained in the active material of the test example.

Furthermore, it was found that the peak intensity observed in the range of 2θ = 26 ° to 27 ° by the X-ray diffraction method is generally correlated with the Al content (atomic%) measured by the ICP emission spectroscopic analysis. did.
Al compound having a peak in the 2θ = 26 ° ~27 °, since considered to be AlPO _4, Al element contained in the active material in Test Example 2-7 are all present as AlPO _4, the AlPO _As observed by TEM, ₄ is presumed to exist at the grain boundary.

Using the compounds obtained in Test Examples 1 to 7 for high rate discharge capacity ratio as positive electrode active materials, N-methylpyrrolidone as a solvent, and through a mixer mixing step, the positive electrode active material, acetylene black and polyvinylidene fluoride A positive electrode paste containing (PVdF) at a mass ratio of 80: 8: 12 was obtained. The positive electrode paste was applied to an aluminum mesh as a base material, and then vacuum dried at 150 ° C. to prepare a positive electrode plate. Using the obtained positive electrode plate, using a Li plate as a counter electrode and a reference electrode, LiClO ₄ was dissolved at a concentration of 1 mol / l in a 1: 1 solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) as an electrolytic solution. Using this, a tripolar glass cell was produced in a glove box under an argon atmosphere to obtain a nonaqueous electrolyte battery for evaluation.

Seven types of nonaqueous electrolyte batteries for evaluation corresponding to each of Test Examples 1 to 7 were charged at a current of 0.2 ItmA and then discharged at a current of 0.1 ItmA. Further, after charging with a current of 0.2 ItmA, discharging was performed with a current of 2.0 ItmA. Here, all the charging is constant current constant voltage charging, and the charging potential is 3.8 V (vs. Li ^/ Li ⁺ ) and the charging time is 7.5 hours. Moreover, all discharges are constant current discharges, and the discharge end voltage is 2.0 V (vs. Li ^/ Li ⁺ ). Moreover, all these tests were implemented on 25 degreeC conditions. The ratio of the discharge capacity obtained during 2.0 ItmA discharge to the discharge capacity obtained during 0.1 ItmA discharge is shown in Table 1 and FIG. 4 as a “high rate discharge capacity ratio (%)”.

  As shown in Table 1 and FIG. 4, when the amount of Al (atomic%) with respect to the total amount of Al and Fe is 0.7%, 1%, and 3%, the discharge rate is particularly high at 65% or more. It can be seen that the capacity ratio is obtained and the high rate discharge characteristics are remarkably improved.

2 is an X-ray diffraction diagram for the compound obtained in Test Example 1. FIG. In the figure, * indicates a peak derived from the olivine type crystal structure. 6 is an X-ray diffraction diagram for the compound obtained in Test Example 6. FIG. In the figure, * represents a peak derived from the olivine type crystal structure, and ▼ represents a peak not derived from the olivine type crystal structure. 6 is an X-ray diffraction diagram for the compound obtained in Test Example 4. FIG. In the figure, ▼ indicates a peak not derived from the olivine type crystal structure. It is the graph which showed the high rate discharge capacity ratio of the nonaqueous electrolyte battery of this invention.

Claims (4)

Containing grain boundaries of the primary particles AlPO ₄ is present in at least a portion of the polycrystalline body of lithium iron phosphate compounds which have a olivine crystal structure,
The ratio of Fe element, transition metal element M other than Fe, Al element, and P element is [(Fe _1−x M _x ) _1−y Al _y ]: P = 1: 1 (x is 0 or more and less than 1) And y is 0.007 or more and less than 0.05) . A positive electrode active material for a non-aqueous electrolyte battery. The positive electrode active material for a nonaqueous electrolyte battery according to claim 1, which has a diffraction peak caused by AlPO ₄ at 2θ = 26 ° to 27 ° in X-ray diffraction using CuKα rays. By baking aluminum isopropoxide is Al raw material together with other raw active material, according to AlPO ₄ claim 1 or 2 ing to primary particles present is generated at least a portion of the grain boundaries Positive electrode active material for non-aqueous electrolyte battery. Nonaqueous electrolyte battery characterized by being constituted by using a positive electrode active material according to any one of claims 1-3.

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