JP2014232569A - Positive electrode active material for lithium ion secondary batteries, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vanadium lithium pyrophosphate positive electrode active material which is less expensive and exhibits a high discharge capacity and a high electrode potential when used as a positive electrode active material for a lithium ion secondary battery, and to provide a method for manufacturing such a positive electrode active material.SOLUTION: A positive electrode active material for lithium ion secondary batteries comprises Li, V, P, O, and as a main crystal, crystallized glass with a vanadium lithium pyrophosphate crystal precipitated. The vanadium lithium pyrophosphate crystal is expressed by the general formula LiVAPO(where 0<x≤2.5; 0≤y<1; and A is at least one element selected from Nb, Mg, Al, Ti, Zr, Fe, Sc, Cr, Mn, Co, and Ni).

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery used for portable electronic devices, electric vehicles, and the like, and a method for producing the same.

Lithium ion secondary batteries have established themselves as high-capacity and lightweight power supplies that are indispensable for portable electronic terminals and electric vehicles. Conventionally, inorganic metal oxides such as lithium cobaltate (LiCoO ₂ ) and spinel type lithium manganate (LiMn ₂ O ₄ ) have been used as the positive electrode active material of the lithium ion secondary battery.

  However, lithium cobaltate has been pointed out to be problematic in terms of safety because of its low cobalt reserves and high cost. In addition, lithium manganate has been subject to cycle deterioration due to distortion of crystal structure associated with elution of manganese at high temperatures and the yarn-teller effect of trivalent manganese ions.

In recent years, lithium iron phosphate (LiFePO ₄ ) has attracted attention and has been researched and developed at various institutions because it is advantageous in terms of cost, resources, and the like and has high safety.

However, since lithium iron phosphate has a low electrode potential of 3.4 V (vs. Li / Li ⁺ ), pyrophosphate lithium vanadium pyrophosphate (LiVP ₂ O ₇ ) using V instead of Fe is used. Attention (patent documents 1 and 2) has been noted. Note that LiVP ₂ O ₇ has a high electrode potential of 4.1 V (vs. Li / Li ⁺ ).

Japanese Patent Application Laid-Open No. 2002-246025 JP 2013-95613 A

A lithium ion secondary battery using LiVP ₂ O ₇ produced by a conventional manufacturing method (solid phase reaction method) as a positive electrode active material has low LiVP ₂ O ₇ crystal homogeneity and easily contains impurities. There was a problem that the capacity and electrode potential were low. Further, the conventional manufacturing methods have problems such as high manufacturing costs and limited to expensive raw materials such as liquid raw materials.

  The present invention has been made in view of such a current problem, and exhibits a high discharge capacity and a high electrode potential when used as a positive electrode active material for a lithium ion secondary battery, and is an inexpensive vanadium pyrophosphate. It aims at providing a lithium positive electrode active material and its manufacturing method.

The positive electrode active material for a lithium ion secondary battery of the present invention contains Li, V, P and O, and has a general formula of Li _x V _1-y A _y P ₂ O ₇ (0 <x ≦ 2.5) as a main crystal. 0 ≦ y <1, and A deposited at least one selected from Nb, Mg, Al, Ti, Zr, Fe, Sc, Cr, Mn, Co, and Ni) lithium vanadium pyrophosphate crystals It includes crystallized glass.

Further, as represented by mol% of oxide _equivalent, Li 2 O 10 to _50%, preferably contains _V 2 O 5 1 to 30% and _P 2 _O 5 _35~55%.

  Moreover, the positive electrode for lithium ion secondary batteries of this invention is characterized by including the said positive electrode active material for lithium ion secondary batteries.

  Furthermore, the lithium ion secondary battery of this invention is characterized by including the said positive electrode for lithium ion secondary batteries.

  The lithium secondary battery positive electrode active material manufacturing method of the present invention includes (1) a step of preparing a batch containing Li, V, P and O, (2) a step of melting the batch to obtain molten glass, and ( 3) It includes a step of quenching molten glass to obtain a precursor glass.

Further, the precursor glass, in mol% of the oxide _equivalent, Li 2 O 10 to _50%, preferably contains _V 2 O 5 1 to 30% and _P 2 _O 5 _35~55%.

  Further, (4) a step of pulverizing the obtained precursor glass to obtain a precursor glass powder, and (5) a step of firing the precursor glass powder at a glass transition temperature to 900 ° C. to obtain a crystallized glass powder. It is preferable.

  Furthermore, in the step (5), it is preferable to add an organic compound and / or conductive carbon to the glass powder and perform firing in an inert or reducing atmosphere.

  According to the present invention, it is possible to obtain a lithium vanadium pyrophosphate positive electrode active material that exhibits a high discharge capacity and a high electrode potential when used as a positive electrode active material for a lithium ion secondary battery at a lower cost than in the past. Become.

The positive electrode active material for a lithium ion secondary battery of the present invention contains Li, V, P and O, and has a general formula of Li _x V _1-y A _y P ₂ O ₇ (0 <x ≦ 2.5) as a main crystal. 0 ≦ y <1, and A deposited at least one selected from Nb, Mg, Al, Ti, Zr, Fe, Sc, Cr, Mn, Co, and Ni) lithium vanadium pyrophosphate crystals It includes crystallized glass. With the above structure, a positive electrode active material having a high discharge capacity and a high electrode potential can be obtained.

Further, as represented by mol% of oxide _equivalent, Li 2 O 10 to _50%, preferably contains _V 2 O 5 1 to 30% and _P 2 _O 5 _35~55%. The reason for limiting the composition as described above will be described below.

Li ₂ O is the main component of the lithium vanadium pyrophosphate crystal. The content of Li ₂ O is preferably 10 to 50%, more preferably 20 to 45%, and particularly preferably 22 to 43%. If the content of Li ₂ O is too large, the amount of Li ions in the crystal becomes too large and Li ions themselves interfere with the diffusion of other Li ions, resulting in a decrease in the diffusion rate of Li ₂ O insertion / desorption. This is not preferable because the discharge capacity is lowered. When the Li 2 _O content is too small, heterogeneous crystals are liable to occur, the proportion of pyrophosphate lithium vanadium-based crystal tends to decrease.

P ₂ O _{5 is} also a main component of the lithium vanadium pyrophosphate crystal. The content of P ₂ O ₅ is preferably 35 to 55%, more preferably 37 to 52%, and particularly preferably 40 to 50%. When the content of P ₂ O ₅ is too low or too high, lithium vanadium pyrophosphate crystals are hardly formed when the obtained precursor glass is heat-treated.

V ₂ O _{5 is} also a main component of the lithium vanadium pyrophosphate crystal. The content of V ₂ O ₅ is preferably 1 to 30%, more preferably 5 to 30%, further preferably 15 to 27%, and particularly preferably 20 to 27%. . When the content of V ₂ O ₅ is too low or too high, lithium vanadium pyrophosphate crystals are hardly formed when the obtained precursor glass is heat-treated.

The positive active material for a lithium ion secondary battery of the present _{invention, Nb 2 O 5, MgO,} Al 2 O 3, TiO 2, ZrO 2, Fe 2 O 3, Sc 2 O 3, Cr 2 O 3, MnO ₂ , at least one oxide selected from the group of CoO and NiO may be contained. By containing these components, these components are taken into the lithium vanadium pyrophosphate crystal, and it becomes easier to produce a lithium vanadium pyrophosphate crystal having a higher electron conductivity, so that high-speed charge / discharge characteristics are easily improved. . The total content of the above components is preferably 0 to 25%, particularly preferably 0.2 to 10%. If the content of the above component is too large, different types of crystals are formed, and the deposition rate of lithium vanadium pyrophosphate crystals tends to decrease, so the discharge capacity tends to decrease.

In addition to the above components, for example, SiO ₂ , B ₂ O ₃ , GeO ₂ , Ga ₂ O ₃ , Sb ₂ O ₃ or Bi ₂ O ₃ may be contained. By further containing these components, the glass forming ability is improved, and a homogeneous precursor glass is easily obtained. The total content of the above components is preferably 0 to 25%, particularly preferably 0.2 to 10%. When there is too much content of the said component, the precipitation rate of a lithium vanadium pyrophosphate crystal will fall easily.

  The positive electrode active material of the present invention is in a powder form, and the average particle size is preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm, and particularly preferably 0.5 to 10 μm. preferable. When the average particle diameter of the positive electrode active material is too small, the cohesive force between the positive electrode active material particles becomes strong, and it becomes difficult to disperse when formed into a paste. As a result, the internal resistance of the battery increases and the discharge voltage tends to decrease. In addition, the electrode density tends to decrease and the discharge capacity per unit volume of the battery tends to decrease. On the other hand, if the average particle size of the positive electrode active material is too large, the specific surface area of the positive electrode active material tends to be small, and the conductivity of lithium ions at the interface between the positive electrode active material and the electrolyte tends to decrease. Moreover, there exists a tendency to be inferior to the surface smoothness of an electrode.

  In the present invention, the average particle diameter means D50 (volume-based average particle diameter), which is a value measured by a laser diffraction scattering method.

  The XRD integral intensity derived from the lithium vanadium pyrophosphate crystal calculated from the powder X-ray diffraction pattern is preferably 1200 cps · deg or more, 1400 cps · deg or more, particularly 1500 cps · deg or more. When the XRD integral intensity derived from the lithium vanadium pyrophosphate crystal is too small, the discharge capacity tends to decrease.

  The XRD integral intensity derived from lithium vanadium pyrophosphate crystals is derived from lithium vanadium pyrophosphate crystals in the diffraction line profile of 10-60 ° with 2θ values obtained by powder X-ray diffraction measurement (XRD measurement) using CuKα rays. It is calculated | required from the crystalline diffraction line of this. Specifically, from the total scattering curve obtained by subtracting the background from the diffraction line profile, the integral obtained by peak-separating the crystalline diffraction line derived from the lithium vanadium pyrophosphate crystal detected at 10 to 60 ° It is obtained from the sum of strength.

  The XRD measurement was performed with a powder X-ray diffractometer (RINT2100 manufactured by Rigaku), using a Kα ray generated by a Cu target at a voltage of 40 KV and a current value of 40 mA, in a range of 2θ = 10 to 60 °, 1 ° / The measurement was performed under the conditions of a scanning speed of 1 minute and a sampling interval of 0.01 °. When the peak intensity of the crystal was 100 cps or less, it was determined that the peak was noise.

  The crystallinity of the lithium vanadium pyrophosphate crystal in the positive electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. If the crystallinity of the lithium vanadium pyrophosphate crystal is too low, the discharge capacity tends to decrease. In addition, although it does not specifically limit about an upper limit, In reality, it is 99 mass% or less.

  The crystallinity of the lithium vanadium pyrophosphate crystal is separated into a crystalline diffraction line and an amorphous halo in a diffraction line profile of 10 to 60 ° with 2θ values obtained by powder X-ray diffraction measurement using CuKα rays. Is required. Specifically, the integrated intensity obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 45 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile is Ia, 10 Ic is the sum of integral intensities obtained by peak separation of crystalline diffraction lines derived from lithium vanadium pyrophosphate crystals detected at -60 °, and Io is the sum of integral intensities obtained from other crystal diffraction lines. In this case, the crystal content Xc is obtained from the following formula.

    Xc = [Ic / (Ic + Ia + Io)] × 100 (%)

  As the crystallite size of the lithium vanadium pyrophosphate crystal is smaller, the average particle diameter of the positive electrode active material particles can be reduced, and the electrical conductivity can be improved. Specifically, the crystallite size of the lithium vanadium pyrophosphate crystal is preferably 100 nm or less, and particularly preferably 80 nm or less. The lower limit is not particularly limited, but is actually 1 nm or more, and further 10 nm or more. The crystallite size is determined according to Scherrer's equation from the analysis result of powder X-ray diffraction.

  The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention includes (1) a step of preparing a batch containing Li, V, P and O, (2) a step of melting the batch to obtain molten glass, And (3) a step of quenching the molten glass to obtain a precursor glass. By producing the positive electrode active material by such a melting method, it is easy to obtain a positive electrode active material in which each component is uniformly dispersed.

  What is necessary is just to adjust a melting temperature suitably so that a raw material batch may be fuse | melted uniformly. Specifically, it is preferably 700 ° C. or higher, and particularly preferably 900 ° C. or higher. Although an upper limit is not specifically limited, Since it will lead to an energy loss when too high, it is preferable that it is 1500 degrees C or less, and it is especially preferable that it is 1400 degrees C or less.

  Moreover, as a process for obtaining the precursor glass, a sol-gel process, a chemical vapor synthesis process such as spraying a solution mist into a flame, a mechanochemical process, and the like can be applied.

Further, the precursor glass, in mol% of the oxide _equivalent, Li 2 O 10 to _50%, preferably contains _V 2 O 5 1 to 30% and _P 2 _O 5 _35~55%.

  Furthermore, the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention includes (4) a step of pulverizing the obtained precursor glass to obtain a precursor glass powder, and (5) a glass of the precursor glass powder. It is preferable to manufacture by the method of including the process of baking by transition temperature -1000 degreeC, and obtaining crystallized glass powder.

  The method for pulverizing the precursor glass is not particularly limited, and a general pulverizing apparatus such as a ball mill, a bead mill, or an attritor can be used.

  The smaller the average particle size of the precursor glass powder, the larger the specific surface area of the positive electrode active material as a whole, and it becomes easier to exchange ions and electrons.

The heat treatment temperature of the precursor glass powder is not particularly limited because it varies depending on the composition of the precursor glass, but at least the crystallization temperature or higher (specifically, 450 ° C. or higher, preferably 500 ° C. or higher, more preferably It is appropriate to perform the heat treatment at 600 ° C. or higher. If the heat treatment temperature is too low, crystal precipitation becomes insufficient and the discharge capacity may be reduced. Alternatively, different types of crystals such as β-LiVOPO ₄ are likely to be precipitated, and lithium ion conductivity may be reduced. On the other hand, the upper limit of the heat treatment temperature is preferably 900 ° C., more preferably 850 ° C., and particularly preferably 800 ° C. If the heat treatment temperature is too high, the precipitated lithium vanadium pyrophosphate crystal may be dissolved. Here, the “crystallization temperature” refers to a crystallization peak temperature measured with a differential thermal analysis (DTA) apparatus, and refers to a value measured at a heating rate of 10 ° C./min.

The heat treatment time is appropriately adjusted so that the crystallization of the precursor glass powder proceeds sufficiently. Specifically, it is preferably 1 to 20 hours, 5 to 15 hours, particularly 8 to 12 hours. If the heat treatment time is too short, the valence of vanadium in the glass becomes difficult to become trivalent, and different types of crystals such as β-LiVOPO ₄ tend to precipitate.

  Furthermore, in the step (5), it is preferable to add an organic compound and / or conductive carbon to the glass powder and perform firing in an inert or reducing atmosphere. Thereby, the surface of the positive electrode active material particles can be covered with the carbon-containing layer. Furthermore, since the organic compound and / or the conductive carbon exhibit a reducing action when fired, the valence of vanadium in the glass tends to change to trivalent during crystallization, and the lithium vanadium pyrophosphate crystal It can be selectively obtained at a high rate.

  Examples of the conductive carbon include graphite, acetylene black, and amorphous carbon. Note that it is preferable that the amorphous carbon does not substantially detect a C—O bond peak or a C—H bond peak that causes a decrease in conductivity of the positive electrode active material in the FT-IR analysis. Examples of the organic compound include carboxylic acids such as aliphatic carboxylic acids and aromatic carboxylic acids, glucose and organic binders, surfactants, and the like.

  The addition amount of the organic compound and / or conductive carbon, or both, is preferably 0.01 to 50 parts by mass, more preferably 0.1 to 50 parts by mass with respect to 100 parts by mass of the precursor glass. Preferably, it is 1-30 mass parts, More preferably, it is 5-20 mass parts. When the addition amount of the organic compound and / or the conductive carbon is too small, it becomes difficult to sufficiently cover the surface of the positive electrode active material particles with the carbon-containing layer. When the addition amount of the organic compound and / or the conductive carbon is too large, the thickness of the carbon-containing layer is increased, the movement of lithium ions is hindered, and the discharge capacity tends to decrease.

  The positive electrode active material for a lithium ion secondary battery of the present invention preferably has a carbon content of 0.01 to 20% by mass, 0.05 to 20% by mass, and more preferably 1 to 20% by mass. Preferably, it is 2-15 mass%, More preferably, it is 3-12 mass%. When the carbon content is too small, the coating with the carbon-containing layer becomes insufficient, and the electron conductivity tends to be inferior. On the other hand, when the carbon content is too large, the content of the positive electrode active material particles is relatively small, and the discharge capacity per unit mass of the positive electrode active material tends to be small.

Cathode active material for a lithium ion secondary battery of the present invention, the ratio of the peak intensity D of 1300～1400Cm ^-1 to the peak intensity G of 1550～1650Cm ^-1 in Raman spectroscopy (D / G) is less than or equal to 1 Is preferable, and 0.8 or less is particularly preferable. Furthermore, the ratio (F / G) of the peak intensity F of 800 to 1100 cm ⁻¹ with respect to the peak intensity G is preferably 0.5 or less, and particularly preferably 0.1 or less. When these peak intensity ratios satisfy the above range, the electron conductivity of the positive electrode active material tends to increase.

The positive electrode active material for a lithium ion secondary battery of the present invention preferably has a specific surface area of 5 m ² / g or more, particularly preferably 10 m ² / g or more. When the specific surface area of the positive electrode active material satisfies the above range, the contact area between the positive electrode active material and the electrolyte is increased, and exchange of lithium ions and electrons is facilitated, and the discharge capacity can be improved. On the other hand, the upper limit is not particularly limited, but if it is too large, moisture tends to be adsorbed on the surface of the positive electrode active material, which may cause ignition during charging and discharging. Therefore, the specific surface area of the positive electrode active material is preferably 100 m ² / g or less, more preferably 80 m ² / g or less, and particularly preferably 60 m ² / g or less.

  The positive electrode active material for a lithium ion secondary battery of the present invention preferably has a tap density of 0.3 g / ml or more, particularly preferably 0.5 g / ml or more. If the tap density is too small, the electrode density decreases and the discharge capacity per unit volume of the battery tends to decrease. The upper limit is approximately a value corresponding to the true specific gravity. However, in consideration of powder agglomeration, the upper limit is practically 5 g / ml or less. In the present invention, the tap density is a value measured under tapping conditions of tapping stroke: 10 mm, tapping frequency: 250 times, tapping speed: 2 times / 1 second.

  The positive electrode for a lithium ion secondary battery of the present invention is made into a slurry by adding a conductive additive and a binder to the positive electrode active material described above and suspending them in a solvent such as water or N-methylpyrrolidone. The slurry is applied to a current collector such as an aluminum foil, dried and pressed to form a strip.

  A conductive support agent is a component added in order to achieve rapid charging / discharging. Specific examples include highly conductive carbon black such as acetylene black and ketjen black, graphite, coke and the like. Among them, it is preferable to use highly conductive carbon black that exhibits excellent conductivity when added in a very small amount.

  Examples of the binder include thermoplastic linear polymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-based rubber, and styrene-butanediene rubber (SBR); thermosetting polyimide, polyamide Thermosetting resins such as imide, polyamide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, polyurethane; carboxymethylcellulose (including carboxymethylcellulose salts such as carboxymethylcellulose sodium; the same shall apply hereinafter), hydroxypropylmethylcellulose , Cellulose derivatives such as hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose and hydroxymethylcellulose, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone And water-soluble polymers such as copolymers thereof.

  The compounding ratio of the positive electrode active material, the conductive assistant and the binder is preferably in the range of 70 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive assistant and 2 to 10% by weight of the binder.

  As the current collector, for example, an aluminum foil or an aluminum alloy foil can be used. Examples of the aluminum alloy include alloys made of aluminum and elements such as magnesium, zinc, and silicon.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this Example.
Example 1
(1) Preparation of precursor glass Using lithium metaphosphate (LiPO ₃ ), lithium carbonate (Li ₂ CO ₃ ), vanadium pentoxide (V ₂ O ₅ ), and orthophosphoric acid (H ₃ PO ₄ ) as raw materials, mol% The raw material powder was prepared so that Li ₂ O 25.0%, P ₂ O ₅ 50.0%, V ₂ O ₅ 25.0%, and melted in the air atmosphere at 1300 ° C. for 1 hour. went. Then, molten glass was poured into a pair of rolls, and a precursor glass was produced by forming into a film shape while rapidly cooling. When the obtained precursor glass was pulverized with a mortar and the powder X-ray diffraction pattern was confirmed, no crystalline peak was confirmed, and only halo, which was an amorphous-derived diffraction line, was confirmed.

(2) Preparation of precursor glass powder The precursor glass was pulverized with a ball mill for 20 hours to obtain a precursor glass powder having an average particle diameter of 0.8 μm.

(3) Preparation of positive electrode active material for lithium ion secondary battery 8 parts by mass of polyoxyethylene nonylphenyl ether (corresponding to 5 parts by mass in terms of graphite) as a carbon source and 54 as a solvent with respect to 100 parts by mass of the precursor glass powder. The slurry was made by mixing parts by mass of ethanol, formed by a known doctor blade method, and then dried at 80 ° C. for about 1 hour. Next, the obtained molded body was powdered with a mortar and then heat treated at 600 ° C. for 10 hours in a nitrogen atmosphere to obtain a positive electrode active material. When the powder X-ray diffraction pattern was confirmed, a diffraction line derived from a lithium vanadium pyrophosphate crystal was confirmed.
(4) Battery characteristic evaluation of positive electrode active material for lithium ion secondary battery The discharge capacity and average discharge voltage at 0.1 C rate of the obtained positive electrode active material were evaluated as follows.

With respect to the positive electrode active material for a lithium ion secondary battery, PVDF is used as a binder, ketjen black is used as a conductive auxiliary, and the positive electrode active material: binder: conductive auxiliary = 80: 10: 10 (mass ratio). These were weighed and dispersed in N-methylpyrrolidone (NMP), and then sufficiently stirred with a rotation / revolution mixer to form a slurry. Next, using a doctor blade with a gap of 100 μm, the obtained slurry was coated on a 20 μm-thick aluminum foil as a positive electrode current collector, dried at 80 ° C. in a dryer, and then between a pair of rotating rollers The electrode sheet was obtained by pressing at 1 t / cm ² . The electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried at 140 ° C. for 6 hours to obtain a circular positive electrode.

Next, the obtained positive electrode was placed on the bottom lid of the coin cell with the aluminum foil surface facing down, and then a separator made of a polypropylene porous film having a diameter of 16 mm and dried under reduced pressure at 60 ° C. for 8 hours (Hoechst Cera A test battery was produced by stacking Celgard # 2400) manufactured by Needs Co., Ltd. and metallic lithium as a counter electrode. As the electrolytic solution, 1M LiPF ₆ solution / EC (ethylene carbonate): DEC (diethyl carbonate) = 1: 1 (volume ratio) was used. The test battery was assembled in an environment with a dew point temperature of −40 ° C. or lower.

  A charge / discharge test was performed using the obtained test battery, and a discharge capacity and an average discharge voltage were measured. The results are shown in Table 1.

In the charge / discharge test, charging (releasing lithium ions from the positive electrode active material) is performed by CC (constant current) charging from 2.5 V to 4.6 V, and discharging (occluding lithium ions in the positive electrode active material). ) Was performed by discharging from 4.6V to 2.5V.
(Example 2)
Lithium metaphosphate (LiPO ₃ ), lithium carbonate (Li ₂ CO ₃ ), vanadium pentoxide (V ₂ O ₅ ), and orthophosphoric acid (H ₃ PO ₄ ) are used as raw materials, and Li ₂ O 27.0% in mol%. , P ₂ O ₅ 48.7%, V ₂ O ₅ 24.3%, and the raw material powder was prepared and melted in the air atmosphere at 1300 ° C. for 1 hour. Then, molten glass was poured into a pair of rolls, and a precursor glass was produced by forming into a film shape while rapidly cooling.

  A positive electrode active material was produced in the same manner as in Example 1 using the obtained precursor glass. When the powder X-ray diffraction pattern was confirmed, a diffraction line derived from a lithium vanadium pyrophosphate crystal was confirmed.

The discharge capacity and average discharge voltage at 0.1 C rate of the obtained positive electrode active material were measured by the same method as in Example 1. The results are shown in Table 1.
(Comparative Example 1)
Lithium carbonate (Li ₂ CO ₃ ), vanadium pentoxide (V ₂ O ₅ ), and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) are used as raw materials, and Li ₂ O 25.0% in mol%, P _The raw material powder was prepared so as to be 2O ₅ 50.0% and V ₂ O ₅ 25.0%, pulverized and mixed by a ball mill, pelletized, and then subjected to solid phase reaction at 300 ° C. for 8 hours in an argon atmosphere. . Then, the positive electrode active material was produced by repeating each process of the grinding | pulverization by a ball mill, pelletization, and solid-phase reaction for 8 hours at 300 degreeC in argon atmosphere. When the powder X-ray diffraction pattern was confirmed, a diffraction line derived from a lithium vanadium pyrophosphate crystal was confirmed.

  The discharge capacity and average discharge voltage at 0.1 C rate of the obtained positive electrode active material were measured by the same method as in Example 1. The results are shown in Table 1.

As described above, the positive electrode active materials prepared in Examples 1 and 2 had a discharge capacity at a 0.1 C rate as high as 110 to 115 mAhg ⁻¹ and an average voltage as high as 4.1 V. On the other hand, since the positive electrode active material produced in Comparative Example 1 is produced by a solid-phase reaction and is not crystallized glass, the discharge capacity at a 0.1 C rate is as low as 70 mAhg ⁻¹ and the average voltage is 3. It was as low as 8V.

Claims (8)

It contains Li, V, P and O, and has the general formula Li _x V _1-y A _y P ₂ O ₇ (0 <x ≦ 2.5, 0 ≦ y <1, A is Nb, Mg, Al Lithium ion secondary, characterized in that it comprises a crystallized glass in which lithium vanadium pyrophosphate crystals represented by the formula: Ti, Zr, Fe, Sc, Cr, Mn, Co, Ni) are precipitated. Positive electrode active material for batteries. As represented by mol% based on oxides _basis, lithium ions according to claim 1, characterized in that it contains _{Li 2 O 10~50%, V 2} O 5 1~30% and _P 2 _O 5 35 to 55% Positive electrode active material for secondary battery.   The positive electrode for lithium ion secondary batteries containing the positive electrode active material for lithium ion secondary batteries of Claim 1 or 2.   The lithium ion secondary battery containing the positive electrode for lithium ion secondary batteries of Claim 3.   (1) preparing a batch containing Li, V, P and O, (2) melting the batch to obtain molten glass, and (3) quenching the molten glass to obtain precursor glass. The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by the above-mentioned. Claim wherein the precursor glass, which by mol% of oxide _equivalent, Li 2 O 10 to _50%, characterized in that it contains _V 2 O 5 1 to 30% and _P 2 _O 5 35 to 55% 5. A method for producing a positive electrode active material for a lithium ion secondary battery according to 5.   Further, (4) a step of pulverizing the obtained precursor glass to obtain a precursor glass powder, and (5) a step of firing the precursor glass powder at a glass transition temperature to 900 ° C. to obtain a crystallized glass powder. The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 5 or 6 characterized by the above-mentioned. 8. The positive electrode for a lithium secondary battery according to claim 7, wherein in the step (5), an organic compound and / or conductive carbon is added to the glass powder and firing is performed in an inert or reducing atmosphere. A method for producing an active material.