JP2013077517A - Secondary battery active material, secondary battery active material electrode, and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a cathode active material that can form a secondary battery having excellent high-rate charging performance; and a secondary battery using the cathode active material.SOLUTION: A secondary battery active material contains phosphoric acid vanadium lithium of Nasicon structure. The phosphoric acid vanadium lithium is phosphoric acid vanadium manganese lithium that a part of vanadium is replaced with manganese. The secondary battery active material contains each atom of lithium, vanadium, manganese, phosphor and oxygen. The secondary battery active material, in which the ratio of the atomic number of manganese to that of vanadium is not less than 0.5% nor more than 8%, is excellent in high-rate charging performance. Therefore, it is capable of improving the high-rate charging performance of a secondary battery comprised of a secondary battery electrode containing the secondary battery active material.

Description

  The present invention relates to an active material for a secondary battery, an electrode for an active material for a secondary battery, and a secondary battery using the same.

  In recent years, lithium secondary batteries with high energy density and low self-discharge and good cycle performance have attracted attention as power sources for portable devices such as mobile phones and notebook computers, and electric vehicles.

  Recently, polyanionic positive electrode active materials having excellent thermal stability have attracted attention. Since this polyanionic positive electrode active material is immobilized by covalently bonding oxygen to an element other than a transition metal, it does not release oxygen even at a high temperature. It is thought that the safety of the secondary battery can be dramatically improved.

As such a polyanionic positive electrode active material, lithium iron phosphate (LiFePO ₄ ) having an olivine structure has been actively studied. However, in addition to lithium insertion and desorption at a low potential of 3.4 V (vs. Li / Li ⁺ ), lithium iron phosphate has electrical conductivity unique to its crystal structure and lithium ion conductivity. Due to the low utilization factor of the active material derived from lowness and low high rate charge / discharge performance, the input / output performance is degraded as compared with conventional lithium-containing transition metal compounds. Then, examination of lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) having a reversible potential in the vicinity of about 4 V (vs. Li / Li ⁺ ) has been conducted. Lithium vanadium phosphate has a reversible potential of about 3.5 V (vs. Li ^/ Li ⁺ ) or higher, higher than lithium iron phosphate, and more electronic and ionic conductive than lithium iron phosphate. Because of its superiority, it is expected as a positive electrode active material that combines high safety and excellent output performance.

  However, in applications that require efficient recovery of regenerative energy, such as batteries for hybrid vehicles (HEV), excellent high-rate charging performance is required, but the current specifications for positive electrode active materials are not necessarily sufficient. I can't say that.

Patent Document 1 states that “a nominal general formula, Li _3-x M ′ _y M ″ _2-y (PO ₄ ) ₃ (where M ′ and M ″ are the same or different from each other, and at least M ′ and M ′ One of which includes a first electrode comprising an electrode active material having a plurality of oxidation states and represented by 0 ≦ y ≦ 2); a second counter electrode comprising an intercalation active material and an electrolyte; In the first condition, x = 0, and in the second condition, 0 <x ≦ 3, M ′ and M ″ are each a metal or a metalloid, and at least one of M ′ and M ″ is The lithium secondary battery which has an oxidation state larger than the oxidation state in 1st conditions. The invention of claim 1 is disclosed. According to Patent Document 1, “the lithium metal phosphate is desirably represented by the nominal general formula Li ₃ M′M” (PO ₄ ) ₃ . In some embodiments, metals M ′ and M ″ are the same, and in other embodiments, metals M ′ and M ″ are different from each other. Desirably, the phosphate is the compound Li ₃ M ₂ (PO ₄ ) ₃ , where M is a transition metal, most preferably V, Fe, Sr, Mn. Is described. The Examples of Patent Document, as _{Li 3 M'M "(PO 4)} 3 type electrode _{composition, Li 3 V 2 (PO 4} ) 3 is illustrated.

Patent Document 2 states that “the first state is the nominal general formula Li _3-x M ′ _y M” _2-y (PO ₄ ) ₃ , x = 0, 0 ≦ y ≦ 2, and the second The state is the nominal general formula Li _3-x M ′ _y M ″ _2-y (PO ₄ ) ₃ , 0 <x ≦ 3; M ″ is a transition metal and M ′ is a metal and metalloid group A lithium ion battery comprising: a first electrode having an active material that is a non-transition metal element selected from: a second electrode that is a counter electrode to the first electrode; and an electrolyte between the electrodes. The invention of claim 1 is disclosed. According to US Pat. No. 6,057,089, “lithium metal phosphate is preferably represented by the nominal general formula Li ₃ M′M” (PO ₄ ) ₃ In one aspect, the metals M ′ and M ″ are the same, and in another aspect, the metals M ′ and M ″ are different. Preferably, the phosphate is the compound Li ₃ M ₂ (PO ₄ ) ₃ where M is a transition metal and M is most preferably V, Fe, Cr, Ni, Co, and Mn. It is. The lithium metal phosphate is preferably a compound represented by the nominal general formula Li _3-x V ₂ (PO ₄ ) ₃ and exhibits a preferred composition and its ability to deintercalate lithium. The present invention solves the capacity problem posed by conventional cathode active materials. (Paragraph 0014). Examples of Patent Document 2 include Li ₃ V ₂ (PO ₄ ) ₃ , Li ₃ MnZr (PO ₄ ) ₃ , Li ₃ MnTi (PO ₄ ) ₃ , Li ₃ BMn (PO ₄ ) _{3 and the} like. Yes.

Patent Document 3 states that “a lithium phosphate / vanadium composite compound represented by the following general formula (1).
Li _y (V _1−x M _x ) ₂ (PO ₄ ) ₃ (1)
Here, M is at least one cation selected from aluminum, titanium, and zirconium, and 0 <x ≦ 0.2, y is 3 when M is aluminum, When M is titanium or zirconium, y is 3-2x. The invention of claim 1 is disclosed. According to Patent Document 3, “the lithium phosphate / vanadium composite compound of the present invention is stabilized at a high temperature phase even at room temperature by replacing a part of vanadium with Zr, Ti and / or Al. Therefore, the positive electrode characteristics are remarkably improved by the high temperature phase stabilized at room temperature, that is, in the present invention, Li ₃ V ₂ is stabilized by stabilizing the high temperature phase having high ion conductivity and ion diffusibility at room temperature. (PO ₄ ) ₃ and Li ₃ Fe ₂ (PO ₄ ) ₃ are improved in low charge / discharge capacity ”(paragraph 0009). Examples of Patent Document 3 illustrate lithium phosphate / vanadium composite compounds in which a part of vanadium (5, 10, 15, 20 mol%) is substituted with Al, Ti, Zr.

Patent Document 4 describes that “manufacturing an aqueous solution containing at least one Li-containing meteorite or NASICON precursor compound and at least one carbon-containing monomer compound as a solute,
-In one step, precipitating the Li-containing meteorite or NASICON precursor compound and polymerizing the monomer compound;
Heat treating the resulting precipitate in a neutral or reducing environment such that a Li-containing meteorite or NASICON crystalline phase is formed and the polymer is decomposed to carbon;
A method for producing a carbon-coated Li-containing meteorite or NASICON powder comprising: (Claim 1) and “The crystal phase is Li _u M _v (XO ₄ ) _w [wherein u = 1, 2, or 3, v = 1 or 2, w = 1 or 3, M is Ti _a (wherein, a + b + c + d + e + f + g + h + i = 1) V b Cr c Mn d Fe e Co f Ni g Sc h Nb i represents, X is wherein represents a _{P x-1 S x (0} ≦ x ≦ 1).] and which is The method according to claim 1 is disclosed. According to Patent Document 4, “The present invention provides an improved solution process that guarantees the production of fine granular particles effectively coated with a conductive carbon layer. When used in Li-ion batteries, it shows very good performance when used in Li-ion batteries.The present invention requires a much smaller amount of total carbon in the electrode for similar electrode capacity and discharge rate. Similarly, the present invention provides a powder that provides higher capacity and discharge rate when the same amount of total carbon is used in the electrode. ”(Paragraph 0009) is there. Examples of Patent Document 4 illustrate lithium iron phosphate synthesized from a solution containing two types of carbon-containing monomers, citric acid and ethylene glycol.

Patent Document 5 states that “a nanometer-sized primary particle group of a crystal structure of a metal compound which is a cathode material and has one of an olivine structure and a NASICON structure and a particle size range of 10 to 500 nm; A micron-sized secondary particle group having a diameter range of 1 to 50 μm, and each micron-sized secondary particle group is composed of a nanometer-sized primary particle group of the crystal structure. (Claim 1) and "The metal compound has a composition formula of A _3x M _2y (PO ₄ ) ₃ , wherein A is a group consisting of Group IA, IIA and IIIA, and mixtures thereof. And M represents at least one second metal component selected from the group consisting of Group IIA and IIIA, transition elements, and mixtures thereof; <x ≦ 1.2, 0 <y ≦ 1.6 The cathode material according to claim 1, characterized in that the invention of claim 5 is disclosed. According to Patent Document 5, “compared with the conventional cathode material, each of which includes a nanometer-sized primary particle group having a crystal structure of a metal compound and a secondary particle group having a micron size with a particle size range of 1 to 50 μm. The cathode material of the present invention has an improved specific surface area and capacity "(paragraph 0033). Examples of Patent Document 5 include LiFePO ₄ , LiFe _0.98 Mg _0.01 Al _0.01 PO _{4, and the} like.

Japanese Patent No. 4292317 Japanese translation of PCT publication No. 2002-530835 Japanese Patent No. 2949229 JP 2005-530676 Gazette JP 2007-294461 A

Patent Document 1 describes that part or all of vanadium of lithium vanadium phosphate having a NASICON type crystal structure may be manganese. However, as in the present invention, vanadium phosphate is used. It is not described that high-rate charging performance is improved by including manganese in lithium, and there is no description on the optimum amount of manganese to be included in lithium vanadium phosphate.
Patent Document 2 exemplifies compounds employing various elements at the vanadium site of lithium vanadium phosphate. However, examples where lithium vanadium phosphate is partially replaced by manganese are not described, and all the exemplified compounds are in a 1: 1 molar ratio at the vanadium site. In the above document, the inclusion of manganese in lithium vanadium phosphate improves the high rate charging performance and the optimum amount of manganese to be contained in lithium vanadium phosphate is not described. I can't even find it.
Patent Document 3 describes that a part of vanadium of lithium vanadium phosphate is replaced with zirconium, titanium, or aluminum, so that a high-temperature phase having high ion conductivity and ion diffusibility is stabilized at room temperature. Describes that the discharge capacity of lithium vanadium phosphate is improved. However, it is not described that lithium is contained in lithium vanadium phosphate.
Patent Document 4 is a method for producing a carbon-coated NASICON powder. As a compound having a NASICON crystal phase, Li ₃ Fe ₂ (PO ₄ ) ₃ is described, but a specific description of lithium vanadium phosphate is described. There is nothing. Moreover, the knowledge regarding the element substitution of the compound which has a NASICON crystal phase is not described.
In Patent Document 5, although there is a description on the general formula, there is no specific description about lithium vanadium phosphate or including manganese in lithium vanadium phosphate.

  This invention is made | formed in view of the said subject, and provides the active material for secondary batteries which can provide the secondary battery excellent in the high-rate discharge performance, and a secondary battery using the same. It is aimed.

  The configuration and effects of the present invention are as follows. However, the action mechanism described in this specification includes estimation, and its correctness does not limit the present invention.

The present invention is an active material for a secondary battery containing lithium vanadium phosphate having a NASICON structure, wherein the lithium vanadium phosphate is lithium vanadium phosphate in which a part of vanadium is substituted with manganese, and The secondary battery active material contains lithium, vanadium, manganese, phosphorus, and oxygen atoms, and the ratio of the number of manganese atoms to vanadium is 0.5% or more and 8% or less. It is an active material for secondary batteries.
Thus, the ratio of the number of vanadium and manganese atoms contained in the active material for a secondary battery containing lithium vanadium phosphate having a NASICON structure is such that the ratio of manganese to vanadium is 0.5% or more and 8% or less. By doing so, the high rate charging performance of the active material for the secondary battery is improved.
Here, lithium vanadium phosphate having a NASICON structure is generally known to have a monoclinic crystal structure (space group P2 ₁ / n). Sometimes take. It is also known that an orthorhombic or rhombohedral crystal structure is obtained by substituting a part of vanadium with a specific element. The lithium vanadium phosphate in the present invention has a monoclinic crystal structure.

The present invention is characterized in that the lithium vanadium phosphate is represented by the general formula _{Li x V 2-y Mn y} (PO 4) 3 (0 ≦ x ≦ 5,0.01 ≦ y ≦ 0.16) And an active material for a secondary battery.
Thus, by replacing a part of vanadium of lithium vanadium phosphate with manganese, the high rate charging performance of the active material for the secondary battery is improved.

In the present invention, the lithium vanadium phosphate is represented by the general formula Li _x V _{2 -y} Mn _y (PO ₄ ) ₃ (0 ≦ x ≦ 5, 0.01 ≦ y ≦ 0.10). Is an active material for a secondary battery.
Thus, by replacing a part of vanadium of lithium vanadium phosphate with manganese, the high rate charging performance of the active material for the secondary battery is improved.

Furthermore, the active material for secondary batteries of this invention is a secondary battery active material characterized by containing the manganese compound which has a crystal structure different from the said lithium vanadium phosphate.
Here, the lithium vanadium phosphate and the manganese compound coexist in secondary particles of the active material for secondary battery.

Moreover, the active material for secondary batteries of this invention is an active material for secondary batteries characterized by having a carbonaceous compound on the surface or inside of the active material particles.
The active material particles of the active material for the secondary battery refer to primary particles, secondary particles, or higher order particles, and a carbonaceous compound such as carbon adheres to the surface or inside of the particles. It is provided in the form of a coating or the like.

  Moreover, this invention is an electrode for secondary batteries containing the said active material for secondary batteries.

  Furthermore, the present invention is a secondary battery comprising the secondary battery electrode, a counter electrode paired with the electrode, and an electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the active material for secondary batteries excellent in high-rate charging performance, the electrode for secondary batteries containing the active material for secondary batteries, and the secondary excellent in high-rate charging performance using them. A secondary battery can be provided.

In the active material for a secondary battery containing lithium vanadium phosphate having a NASICON structure according to the present invention, a part of vanadium of the lithium vanadium phosphate is substituted with manganese. Such a manganese-substituted lithium vanadium phosphate is superior in the high-rate charging performance of the active material for the secondary battery in order to improve the high-rate charging performance as compared with lithium vanadium phosphate not replacing manganese. It becomes possible. Further, if the ratio of the number of manganese atoms to vanadium contained in the secondary battery active material is 0.5% or more, the effect of the present invention is exhibited, which is preferable. Further, when the ratio of the number of atoms exceeds 8%, the charge / discharge capacity of the active material for secondary battery is remarkably reduced. Therefore, the ratio is preferably 8% or less.
In the active material for secondary battery of the present invention, a manganese compound having a crystal structure different from that of lithium vanadium phosphate may be present. The manganese compound tends to increase in abundance as the ratio of the number of atoms of manganese increases. The manganese compound is considered to be lithium manganese phosphate having an orthorhombic crystal structure, as will be described later in Examples. This lithium manganese phosphate has a larger theoretical capacity than lithium vanadium phosphate when the charge potential of the positive electrode is 4.3 V (vs. Li ^/ Li ⁺ ) as in the examples described later. From the above, it is preferable to increase the charge / discharge capacity of the active material for a secondary battery.

Lithium vanadium phosphate contained in the active material for a secondary battery according to the present invention is represented by the general formula _{Li x V 2-y Mn y} (PO 4) 3 (0 ≦ x ≦ 5,0.01 ≦ y ≦ 0. 16). Here, it is preferable that the value of y is 0.01 or more because the effect of the present invention is exhibited. On the other hand, if the amount of substitution of manganese is too large, the charge / discharge capacity of the secondary battery active material containing lithium vanadium phosphate is reduced, and therefore y is preferably 0.16 or less. Moreover, when y is in the range of 0.01 ≦ y ≦ 0.10, it is more preferable because the discharge capacity is relatively maintained. Furthermore, in the range of 0.02 ≦ y ≦ 0.08, the active material for a secondary battery containing lithium vanadium phosphate is excellent in high rate charge / discharge performance and maintains high charge / discharge capacity. Is particularly preferable.

The method for synthesizing the active material for a secondary battery containing lithium vanadium phosphate having a NASICON structure according to the present invention is not particularly limited. Specific examples include a solid phase method, a liquid phase method, a sol-gel method, a hydrothermal method, and the like, among which the liquid phase method and the sol-gel method are preferable. For example, a raw material containing lithium, vanadium, manganese, phosphorus and oxygen is dissolved in a solvent to prepare a precursor solution without a precipitate, and the precursor solution is dried to obtain a precursor powder. What is manufactured by baking in inert atmosphere or reducing atmosphere at temperature is preferable.
It is preferable that a carbon source coexists in the precursor solution. The coexistence of the carbon source makes it possible to provide a conductive carbonaceous compound on the surface or inside of the synthesized secondary battery active material and lithium vanadium phosphate particles contained therein. The carbon source coexisting in the precursor solution is not particularly limited as long as it is soluble in the same solvent as the precursor solution. Citric acid, sucrose, lactose monohydrate, maltose monohydrate, ascorbine An acid, ethylene glycol, polyvinyl alcohol, etc. are mentioned.
The method for drying the precursor solution is not particularly limited, and an existing drying device such as a slurry dryer or a spray dryer can be used. Further, the precursor powder can be obtained by evaporating and removing the solvent while stirring and heating the precursor solution in a container such as a beaker.
As the firing temperature, a temperature at which lithium vanadium phosphate is generated and the carbon source is carbonized by thermal decomposition is required. If the temperature is too low, a compound such as LiVOPO ₄ different from the NASICON structure is generated, If the temperature is too high, the performance of the secondary battery active material deteriorates, and therefore the firing temperature is preferably 600 ° C to 950 ° C. More preferably, it is 650 degreeC-850 degreeC.

  The carbon source when synthesizing the active material for the secondary battery according to the present invention is larger than the carbon consumed for the reduction reaction of vanadium in the firing step, and the total mass of the active material for the secondary battery is It is preferable that 0.5% by mass or more of carbon is included. In addition, if there is too much carbon contained in the active material for the secondary battery, it will lead to a decrease in the tap density. It is preferable that it is below mass%.

  In the active material for a secondary battery containing the lithium vanadium phosphate, it does not prevent lithium, vanadium, manganese, phosphorus, and oxygen from being partially substituted with other elements. As other elements to be substituted, for example, in the case of lithium, alkali metal or alkaline earth metal such as sodium, potassium and magnesium, and in the case of vanadium or / and manganese, scandium, titanium, chromium, iron, cobalt, nickel In the case where the metal such as zirconium, indium and aluminum is phosphorus, silicon, boron, sulfur and the like are used, and in the case where oxygen is used, fluorine, chlorine and the like are mentioned. Further, for the purpose of improving the performance of the active material for secondary batteries containing lithium vanadium phosphate, impurities may be intentionally coexisted within a range not impairing the effects of the present invention, and further, a synthesis step, etc. In this case, impurities may be mixed unintentionally.

  The active material for a secondary battery containing lithium vanadium phosphate contains a lithium atom, a vanadium atom, a manganese atom, a phosphorus atom, and the amount thereof is determined by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis. Can be confirmed. Further, the fact that metal atoms are in solid solution and the crystal structure thereof can be confirmed by powder X-ray diffraction analysis (XRD). In addition, transmission electron microscope observation (TEM), energy dispersive X-ray spectroscopy (EDX), scanning electron microscope X-ray analysis (EPMA), high resolution electron microscope analysis (HRAEM), electron energy loss spectroscopy (EELS), etc. It is possible to perform detailed analysis by using together the analytical instrument.

In the present invention, the active material for a secondary battery containing the lithium vanadium phosphate is preferably used as a powder having a secondary particle average particle size of 100 μm or less. In particular, the average particle size of the secondary particles is more preferably 0.1 to 50 μm, and the particle size of the primary particles constituting the secondary particles is preferably 1 to 500 nm. Further, the BET specific surface area of the powder particles by the flow method nitrogen gas adsorption method is preferably large to some extent in order to improve the high rate charge / discharge performance of the electrode, and is preferably 1 to 100 m ² / g. More preferably, it is 5-50 m < ² > / g. 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 water or an organic solvent such as alcohol or hexane coexists may be used. The classification method is not particularly limited, and a sieve or an air classifier can be used as necessary.

  In preparing a lithium secondary battery electrode using the secondary battery active material containing lithium vanadium phosphate according to the present invention, in addition to the secondary battery active material containing lithium vanadium phosphate, polyvinylidene fluoride is used. Well-known binders such as silicon butadiene rubber, polytetrafluoroethylene, and carboxymethyl cellulose, and well-known conductive agents such as acetylene black, ketjen black, and carbon nanofiber can be used in a well-known formulation. Even if the acetylene black or the like is mixed in the secondary battery electrode using the secondary battery active material of the present invention, the fibrous carbon included in the secondary battery active material of the present invention and Carbon such as acetylene black is a scanning electron microscope (SEM), transmission electron microscope observation (TEM), focused ion beam (FIB), scanning ion microscope (SIM), energy dispersive X-ray spectroscopy (EDX) By using together, it is possible to discriminate.

  When the secondary battery active material containing lithium vanadium phosphate of the present invention is used in a non-aqueous electrolyte, it is preferable that the amount of water contained in the electrode is small, specifically less than 1000 ppm. preferable. As a means for reducing the amount of moisture, a method of drying the electrode in a high temperature / depressurized environment and a method of electrochemically decomposing moisture contained in the electrode are suitable.

  The thickness of the electrode mixture layer is preferably 10 to 500 μm in view of the energy density of the battery.

The counter electrode of the battery of the present invention is not limited in any way, but lithium metal, lithium alloy (lithium metal such as lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloy) Alloys), alloys capable of inserting and extracting lithium, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), metal oxides, lithium metal oxides (Li ₄ Ti ₅ O ₁₂₎ Etc.), polyphosphate compounds, polyanion compounds, lithium transition metal composite oxides, and the like. These can be used according to the kind of electrolyte used for the secondary battery.

  In general, the secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte containing an electrolyte salt in a solvent. Generally, a separator and an outer package for packaging them between the positive electrode and the negative electrode. Is provided.

  Solvents include cyclic carbonates such as propylene carbonate and ethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; formic acid Chain esters such as methyl, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme, etc. Ethers such as acetonitrile, nitriles such as benzonitrile, dioxolane or derivatives thereof, and non-aqueous solvents and water consisting of ethylene sulfide, sulfolane, sultone or derivatives thereof alone or a mixture of two or more thereof You can It is not limited.

Examples of the electrolyte salt include ionic compounds such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiN (CF ₃ SO ₂ ) _2. It can be used alone or in combination of two or more. It is also possible to include an electrolyte salt other than lithium, for example, NaClO _4, and the like. The concentration of the electrolyte salt in the electrolyte is preferably 0.5 mol / l or more and 5 mol / l or less, more preferably 1 mol / l or more and 2.5 mol / l, in order to reliably obtain a secondary battery having high battery performance. It is as follows.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following embodiments.

(Synthesis of active material for secondary battery containing lithium vanadium phosphate)
Example 1
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O) (manufactured by Nacalai Tesque Co., Ltd.) was dissolved in ion-exchanged water as a manganese source to prepare an aqueous manganese acetate solution. Separately, lithium hydroxide monohydrate (LiOH.H ₂ O) (manufactured by Nacalai Tesque Co., Ltd.) was dissolved in ion-exchanged water as a lithium source. While stirring this lithium hydroxide aqueous solution with a stirrer, vanadium pentoxide (V ₂ O ₅ ) (Taiyo Mining Co., Ltd., VT-2) as a vanadium source was added and dissolved, and then prepared in advance. The aqueous manganese acetate solution was mixed. Further, after confirming that citric acid monohydrate (C ₆ H ₈ O ₇ .H ₂ O) (manufactured by Nacalai Tesque Co., Ltd.) as a carbon source was added and dissolved, diphosphoric acid as a phosphoric acid source A precursor solution was prepared by adding ammonium hydrogen (NH ₄ H ₂ PO ₄ ) (manufactured by Nacalai Tesque). The molar ratio of each raw material in the precursor _{solution, LiOH · H 2 O: V} 2 O 5: Mn (CH 3 COO) 2 · 4H 2 O: C 6 H 8 O 7 · H 2 O: NH 4 H 2 PO ₄ = 3.03: 0.995: 0.01: 1.5: 3, and the lithium hydroxide concentration was 1 mol / l. The precursor solution was evaporated to dryness while being heated and stirred on a 150 ° C. hot plate with a magnetic stirrer. The obtained dried precursor was pulverized in an automatic mortar for 1 hour to obtain a precursor powder. This precursor powder was put in an alumina bowl (outside dimension 90 × 90 × 50 mm), and using an atmosphere substitution type firing furnace (a tabletop vacuum gas substitution furnace KDF-75 manufactured by Denken Co., Ltd., internal volume 2400 cm ³ ), Temporary calcination and calcination were continuously performed under the flow of nitrogen gas (flow rate: 1.0 l / min). The calcination temperature was 350 ° C., and the calcination time (time for maintaining the calcination temperature) was 3 hours. After the pre-baking, the process was shifted to baking without lowering the temperature in the furnace, and baking was performed at a baking temperature of 850 ° C. and a baking time (time for maintaining the baking temperature) for 6 hours. The rate of temperature rise was 5 ° C./min through pre-firing and firing, and the temperature was naturally cooled. The fired product was taken out in a state where the furnace temperature was 50 ° C. or lower in order to prevent the oxidation. Nitrogen gas was always flown at a constant flow rate until the powder was taken out after the powder was introduced into the furnace. The fired product taken out from the firing furnace was pulverized for 1 hour using an automatic mortar to produce an active material for a secondary battery containing 0.5% manganese. This is designated as active material a1 of the present invention.

(Example 2)
In the production of an active material for a secondary battery, the molar ratio of each raw material in the precursor solution is set to LiOH.H ₂ O: V ₂ O ₅ : Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O. ₇ · H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 0.99: 0.02: 1.5: 3, except that manganese was 1% in the same manner as in Example 1. The active material for secondary batteries to contain was produced. This is designated as active material a2 of the present invention.

(Example 3)
In the production of an active material for a secondary battery, the molar ratio of each raw material in the precursor solution is set to LiOH.H ₂ O: V ₂ O ₅ : Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O. ₇ · H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 0.98: 0.04: 1.5: 3, except that manganese was 2% in the same manner as in Example 1. The active material for secondary batteries to contain was produced. This is designated as active material a3 of the present invention.

Example 4
In the production of an active material for a secondary battery, the molar ratio of each raw material in the precursor solution is set to LiOH.H ₂ O: V ₂ O ₅ : Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O. ₇ · H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 0.96: 0.08: 1.5: 3, except that manganese was 4% in the same manner as in Example 1. The active material for secondary batteries to contain was produced. This is designated as an active material a4 of the present invention.

(Example 5)
In the production of an active material for a secondary battery, the molar ratio of each raw material in the precursor solution is set to LiOH.H ₂ O: V ₂ O ₅ : Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O. ₇ · H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 0.95: 0.10: 1.5: 3, except that manganese was 5% in the same manner as in Example 1. The active material for secondary batteries to contain was produced. This is designated as active material a5 of the present invention.

(Example 6)
In the production of an active material for a secondary battery, the molar ratio of each raw material in the precursor solution is set to LiOH.H ₂ O: V ₂ O ₅ : Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O. ₇ · H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 0.92: 0.16: 1.5: 3, except that manganese was 8% in the same manner as in Example 1. The active material for secondary batteries to contain was produced. This is designated as active material a6 of the present invention.

(Comparative Example 1)
In the production of the secondary battery active material, manganese acetate tetrahydrate was not used as a raw material, that is, the molar ratio of each raw material in the precursor solution was determined as LiOH.H ₂ O: V ₂ O ₅ : Except that Mn (CH ₃ COO) ₂ .4H ₂ O: C ₆ H ₈ O ₇ .H ₂ O: NH ₄ H ₂ PO ₄ = 3.03: 1: 0: 1.5: 3 In the same manner as in Example 1, a secondary battery active material not containing manganese was produced. This is referred to as a comparative active material b1.

(XRD measurement)
The active materials for secondary batteries obtained in Examples 1 to 6 and Comparative Example 1 were subjected to X-ray diffraction measurement using an X-ray diffraction apparatus (manufactured by Rigaku, model name: MiniFlex II) using a CuKα radiation source. .

(Preparation of positive electrode)
The active material for a secondary battery of Example 1, acetylene black as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were contained at a mass ratio of 84: 8: 8, and N-methyl-2-pyrrolidone ( A positive electrode paste using NMP) as a solvent was prepared. The positive electrode paste is applied to both surfaces of an aluminum mesh current collector with an aluminum terminal attached, and after removing NMP at 80 ° C., the coated portions are overlapped with each other so that the projected area of the coated portion is halved. Were pressed so that the thickness after bending was 400 μm, and the positive electrode of the present invention was obtained. The application area after bending is 2.25 cm ² and the application mass is about 0.074 g. The positive electrode was used under reduced pressure drying at 150 ° C. for 5 hours or more to remove moisture in the electrode plate.

(Preparation of negative electrode)
A stainless steel (product name: SUS316) mesh current collector attached with a stainless steel (product name: SUS316) terminal was bonded to both sides of a 300 μm-thick lithium metal foil and pressed to form a negative electrode.

(Production of reference electrode)
A reference electrode was prepared by attaching a lithium metal piece to the tip of a current collector rod made of stainless steel (product name: SUS316).

(Preparation of electrolyte)
In a mixed solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 1: 1, LiPF ₆ which is a fluorine-containing electrolyte salt is dissolved at a concentration of 1.0 mol / l, and a non-aqueous electrolyte is obtained. Was made. The amount of water in the non-aqueous electrolyte was less than 50 ppm.

(Battery assembly)
A glass lithium ion secondary battery was assembled in an Ar box having a dew point of −40 ° C. or lower. Each of the positive electrode, the negative electrode, and the reference electrode was sandwiched between gold-plated clips whose conductors were previously fixed to the lid portion of the container, and then fixed so that the positive and negative electrodes were opposed to each other. The reference electrode was fixed at a position on the back side of the positive electrode when viewed from the negative electrode. Next, a polypropylene cup containing a certain amount of electrolyte was placed in a glass container, and a battery was assembled by covering the positive electrode, the negative electrode, and the reference electrode so as to be immersed therein. This battery is referred to as a battery A1 of the present invention.

  Similarly, a positive electrode was produced using each of the secondary battery active materials of Examples 2 to 6 and Comparative Example 1, and a lithium secondary battery was assembled according to the above procedure. The lithium secondary batteries using the positive electrodes using the present active materials a2 to a6 and the comparative active material b1 are referred to as present invention batteries A2 to A6 comparative batteries B1, respectively.

(Initial activation)
Invention batteries A1 to A6 and comparative battery B1 produced as described above were subjected to an initial activation step in which charging and discharging were performed for 3 cycles at a temperature of 25 ° C. The charging conditions were a constant current and constant voltage charging with a current of 0.78 mA, a charging voltage of 4.3 V, and 15 hours, and the discharging conditions were constant current discharging with a current of 0.78 mA and a discharge end voltage of 2.7 V. The current value of 0.78 mA corresponds to 0.1 CmA when the discharge capacity per gram of the active material for a secondary battery is 130 mAh.

(High rate charge capacity test)
Following the initial activation step, the batteries A1 to A6 of the present invention and the comparative battery B1 were charged at a constant current of 39 mA and a charging voltage of 4.3 V at a temperature of 25 ° C. A constant current discharge at 8 mA and a final discharge voltage of 2.7 V was performed. The charge current value of this high rate charge capacity test corresponds to 5 CmA when the discharge capacity per gram of active material is 130 mAh.
The discharge capacity at the third cycle of the initial activation step was recorded as “0.1 CmA discharge capacity”, and the value of the charge capacity obtained during the high rate charge capacity test was recorded as “5 CmA charge capacity”. The values are shown in Table 1.

  As can be seen from FIG. 1, in the XRD profile of the secondary battery active material a4 having a manganese content of 4%, a shift is observed in some of the peaks, but the profile is almost the same as that of b1 not containing manganese. As a result, no impurity peak exists. Although not shown in this figure, the same XRD profile as that of a4 is observed in the active materials for secondary batteries a1 to a3 and a5 having a manganese content of 5% or less. It was not confirmed. From this, it is considered that the active materials for secondary batteries a1 to a4 have manganese dissolved in lithium vanadium phosphate, that is, manganese is partially substituted for vanadium of lithium vanadium phosphate. It is done. On the other hand, a peak that does not exist in the profile b1 is observed in the XRD profile of the active material for secondary battery a6 having a manganese content of 8. Analysis of this peak revealed that it was lithium manganese phosphate having a crystal structure different from that of lithium vanadium phosphate. Therefore, it is considered that the active materials for secondary batteries a5 and a6 contain lithium manganese phosphate as an impurity in addition to the lithium vanadium phosphate.

Further, as can be seen from Table 1, the batteries A1 to A6 of the present invention have a high high rate charge capacity as compared with the comparative battery B1. This difference in battery performance is considered to be derived from the active material for secondary battery contained in the positive electrode. The active materials for secondary batteries of Examples 1 to 6 contain manganese, and as described above, all or part of the manganese is obtained by replacing a part of vanadium of lithium vanadium phosphate with manganese. Yes. It is considered that lithium vanadium phosphate in which a part of vanadium is substituted with manganese has a higher rate of charge performance than lithium vanadium phosphate not containing manganese. As described above, the reason why lithium vanadium phosphate in which a part of vanadium is replaced by manganese is excellent in the high rate charging performance is not clear, but a part of the vanadium site is replaced by manganese having a large ionic radius. This improves the diffusion coefficient of lithium ions such that the crystal grows in a specific lattice plane direction and the diffusion path of lithium ions expands, or the diffusion path of lithium ions is more linearly connected. It is considered that the effect of the invention is exhibited.
On the other hand, the comparative battery B1 has the largest discharge capacity, the capacity decreases in order from the present invention battery A1, and is the smallest in the present invention battery A6. From this result, it can be seen that the discharge capacity tends to decrease as the manganese content in the secondary battery active material increases. This is considered to be related to the manganese substitution amount of lithium vanadium phosphate contained in the active material for secondary batteries. That is, it is presumed that manganese substituted with lithium vanadium phosphate does not participate in lithium ion insertion / extraction reactions. Therefore, it is considered that the discharge capacity decreases because the manganese substitution amount of lithium vanadium phosphate increases as the proportion of manganese contained in the active material for secondary batteries increases.
From these results, it is preferable that the ratio of the number of manganese atoms to vanadium is contained in the active material for a secondary battery in a ratio of 0.5% or more and 8% or less. In addition, since the discharge capacity is relatively maintained, the ratio of the number of manganese atoms to vanadium contained in the secondary battery active material is more preferably 0.5% or more and 5% or less. preferable. Further, if the ratio of the number of manganese atoms to vanadium contained in the secondary battery active material is 1% or more and 4% or less, it is particularly preferable because both the discharge capacity and the high rate charge performance are excellent.

Since the active material for a secondary battery of the present invention is excellent in high rate charging performance, a secondary battery excellent in high rate charging performance and input performance can be provided. Since the secondary battery of the present invention is excellent in high-rate charging performance and input performance, it is suitable for application to fields in which high regenerative charging capability is particularly required in industrial batteries such as hybrid vehicles and electric vehicles that are expected to be developed in the future. It is suitable and has a great potential for industrial use.

XRD profiles of secondary battery active materials of Examples 4 and 6 and Comparative Example 1

Claims (7)

A secondary battery active material containing lithium vanadium phosphate having a NASICON structure, wherein the secondary battery active material contains lithium, vanadium, manganese, phosphorus and oxygen atoms, and manganese atoms relative to vanadium An active material for a secondary battery, wherein the number ratio is 0.5% or more and 8% or less. The lithium vanadium phosphate can claims, characterized by being represented by the general formula _{Li x V 2-y Mn y} (PO 4) 3 (0 ≦ x ≦ 5,0.01 ≦ y ≦ 0.16) The active material for secondary batteries as described in 1. The lithium vanadium phosphate can claims, characterized by being represented by the general formula _{Li x V 2-y Mn y} (PO 4) 3 (0 ≦ x ≦ 5,0.01 ≦ y ≦ 0.10) The active material for secondary batteries as described in 1. The active material for secondary batteries according to any one of claims 1 to 3, wherein the active material for secondary batteries contains a manganese compound having a crystal structure different from that of the lithium vanadium phosphate. The active material for a secondary battery according to any one of claims 1 to 4, wherein the active material for a secondary battery includes a carbonaceous compound on the surface or inside of the active material particles. The electrode for secondary batteries containing the active material for secondary batteries in any one of Claims 1-5. The secondary battery provided with the electrode which consists of an active material for secondary batteries of Claim 6, the counter electrode which makes a pair with the electrode, and electrolyte.