JP6437856B2 - Active material for nonaqueous electrolyte storage element - Google Patents

Description

  The present invention relates to an active material for a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element using the same.

Patent Document _1, Li 3 NbO ₄ and LiMeO ₂ (Me is Fe or Mn) is a solid solution of having a possible crystal structure belonging to the space group Fm-3m, the composition formula _{Li 1 + x Nb y Me z} A p O ₂ (Me is a transition metal containing Fe and / or Mn, 0 <x <1, 0 <y <0.5, 0.25 ≦ z <1, A is an element other than Nb and Me, 0 ≦ p ≦ A non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide represented by 0.2) as a positive electrode active material is described.

Non-Patent Document 1 discloses a solid solution of LiVO ₂ and Li ₂ TiO ₃ , having a crystal structure that can be assigned to the space group R-3m, and represented by a composition formula (1-x) LiVO ₂ · xLi ₂ TiO ₃ . A non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide as a positive electrode active material is described.

Non-Patent Document 2 describes a solid solution in which a part of V in LiVO ₂ is substituted with Cr, has a crystal structure that can be assigned to the space group R-3m, and is represented by a composition formula LiCr _x V _1-x O ₂ . A non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide as a positive electrode active material is described.

WO2014 / 156153

J. Power Sources, 174, 1007 (2007) J. Electrochem.Soc., 160, A279 (2013)

  However, the electrode containing the lithium transition metal composite oxide described in Patent Document 1 and Non-Patent Documents 1 and 2 has a problem that the discharge capacity is greatly reduced in the initial few cycles.

The present invention is an active material for a non-aqueous electrolyte storage element having a crystal structure that can be assigned to the space group Fm-3m and containing a lithium transition metal composite oxide represented by the composition formula (1).
_{Li 1 + x Nb y Me z} A p O 2 ··· (1)
(Me is a transition metal containing V, 0 <x <1, 0 <y <0.5, 0 <z <1, A is an element other than Nb, Me, O, 0 ≦ p ≦ 0.2)

  ADVANTAGE OF THE INVENTION According to this invention, the active material for nonaqueous electrolyte electrical storage elements which has high discharge capacity and the outstanding charging / discharging cycling performance can be provided.

1 is an external perspective view showing an embodiment of a nonaqueous electrolyte secondary battery according to the present invention. Schematic showing a power storage device configured by assembling a plurality of nonaqueous electrolyte secondary batteries according to the present invention X-ray diffraction pattern of active material for non-aqueous electrolyte storage element according to Example Charge / Discharge Curve of Nonaqueous Electrolyte Secondary Battery According to Example Charge / Discharge Curve of Nonaqueous Electrolyte Secondary Battery According to Example X-ray diffraction diagram of electrode for nonaqueous electrolyte storage element according to example

  The configuration and effects of the present invention will be described with a technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that 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 experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The active material for a nonaqueous electrolyte storage element according to the present invention is characterized in that the lithium transition metal composite oxide includes a solid solution of Li ₃ NbO ₄ —LiMeO ₂ (Me is a transition metal other than Nb). Therefore, it is understood that the valence of Nb is about +5 in the lithium transition metal composite oxide. In addition, the lithium transition metal composite oxide has a peak that can be assigned to the space group Fm-3m in the X-ray diffraction diagram. As described in the Examples section of the present specification, Li ₃ NbO ₄ has a peak that can be assigned to the space group I-43m, and LiVO ₂ has a peak that can be assigned to the space group R-3m. On the other hand, the non-aqueous electrolyte storage element active material according to the present invention, which is considered to contain both solid solutions, has a peak that can be assigned to the space group Fm-3m. The active material for a nonaqueous electrolyte electricity storage device according to the present invention may include a diffraction peak other than a peak that can be assigned to the space group Fm-3m. Among these, those having a peak that can be assigned to the space group Fm-3m and a peak that can be assigned to the space group R-3m are preferable.
Note that “−3” in the space groups “R-3m” and “Fm-3m” and “−4” in the space group “I-43m” represent the symmetrical elements of the 3-fold anti-axis and 4-fold anti-axis, respectively. “3” and “4” should be marked with a bar “−”.

A solid solution of Li ₃ NbO ₄ —LiMeO ₂ (Me is a transition metal containing V) is expressed by the following formula by arranging coefficients of oxygen.
aLiMeO _2. (1-a) Li _3/2 Nb _1/2 O ₂ (0 <a <1)
By transforming this, the following equation is obtained.
Li _{1+ (1-a) / 2} Nb _{(1-a) / 2} Me _a O ₂
Thus, following equation which _{Li 1 + x Nb y Me z} O 2
The range that y can take is 0 <y <0.5.
The above formula can be expressed by the following formula by adding the optional element A.
_{Li 1 + x Nb y Me z} A p O 2 ··· (1)
(Me is a transition metal containing V, 0 <x <1, 0 <y <0.5, 0 <z <1, A is an element other than Nb and Me, 0 ≦ p ≦ 0.2)
Here, according to the transformation process of the above equation, since x = y, 0 <x <0.5 is derived. However, it is generally performed that the Li raw material is added in excess of the theoretical composition ratio at the time of synthesis, the composition ratio of Li greatly varies due to charge and discharge, and the Li composition ratio becomes larger than at the time of synthesis at the end of discharge. Since there is a possibility, 0 <x <1 was written.

  In the above formula (1), the present inventors have a non-aqueous electrolyte electricity storage device having high discharge capacity and excellent charge / discharge cycle performance when Me includes V and the value of z is 0.3 or more. The present inventors have found that an active material can be obtained and have reached the present invention. From this viewpoint, the value of z is more preferably 0.4 or more. Further, the value of z is preferably 0.9 or less, and more preferably 0.8 or less. Moreover, y is preferably 0.05 or more, more preferably 0.1 or more, and further preferably 0.2 or more. Moreover, y is preferably 0.4 or less.

When the solid solution satisfies the relational expression of aLiMeO _2. (1-a) Li _3/2 Nb _1/2 O ₂ (0 <a <1), the relational expression of 2y + z = 1 and the relational expression of x = y are derived. It is burned. Therefore, practically, in the range of 0.8 ≦ 2y + z ≦ 1.2, it is possible to provide an active material for a nonaqueous electrolyte storage element having both a high discharge capacity and excellent charge / discharge cycle performance. The present invention can be implemented without departing from the technical idea of the present invention. Especially, it is more preferable that it is 0.9 <= 2y + z <= 1.1. Moreover, as an active material for a non-aqueous electrolyte storage element as a raw material before electrode preparation, practically, | xy | ≦ 0.2 is preferable, and 0 ≦ xy ≦ 0.03 is more preferable.

  In the composition formula (1), Me is essential for V. Although it does not limit as transition metals other than V which comprise Me, transition metals, such as Mn, Fe, Ni, Co, Cu, are preferable. The element ratio V / Me ratio of V constituting Me is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. Examples of the optional element A include, but are not limited to, alkali metals or alkaline earth metals such as Na and Ca, and elements such as Zn, In, and Al.

  The active material for nonaqueous electrolyte electricity storage elements of the present invention can be used as a positive electrode active material. Moreover, you may mix and use with another active material.

  The powder of the active material for a non-aqueous electrolyte electricity storage device of the present invention preferably has an average particle size of 100 μm or less. In particular, the thickness is desirably 30 μm or less for the purpose of improving the output characteristics of the nonaqueous electrolyte storage element. The average primary particle size of the lithium transition metal complex oxide is preferably 0.5 to 3 μm.

Next, a method for producing the active material for a nonaqueous electrolyte electricity storage device of the present invention will be described.
The active material for a non-aqueous electrolyte electricity storage device of the present invention basically includes a metal element (Li, Nb, Me) constituting the active material according to the composition of the target active material (lithium transition metal composite oxide). It can be obtained by adjusting the raw material to contain, and finally firing this raw material. However, with respect to the amount of the Li raw material, it is preferable that the Li raw material is excessively contained in an amount of about 1 to 5%, more preferably about 3%, in anticipation that part of the Li raw material disappears during firing.

As a method for producing a lithium transition metal composite oxide having a target composition, a so-called “solid phase method” in which each salt of Li, Nb, and Me is mixed and fired, or Nb and Me in one particle in advance. "Coprecipitation method", in which a coprecipitation precursor present in the solution is prepared, and Li salt is mixed and calcined to this, in addition to this, "evaporation to dryness method", "spray dry method", etc. .
In the present invention, the “solid phase method” is employed as described later in the Examples. By adopting the “solid phase method”, a special apparatus is not required, the synthesis process can be simplified, and the synthesis cost of the active material can be reduced, which is preferable.

  The firing temperature in the synthesis by the above-mentioned “solid phase method” is not particularly limited as long as it is a temperature at which the target lithium transition metal composite oxide is formed, but it should be not less than the temperature at which the lithium salt used as a raw material melts. In this case, since the crystallization proceeds, the charge / discharge capacity increases, which is preferable. Specifically, although it depends on the type of lithium salt used, the firing temperature is preferably 500 ° C. or higher. Furthermore, it is more preferable to set it at 800 ° C. or higher for the purpose of appropriately increasing the crystallinity of the produced lithium transition metal composite oxide and improving the charge / discharge characteristics.

  The lithium transition metal composite oxide produced by the above-described method can use a pulverizer or a classifier to obtain powder in a predetermined shape. 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 or a sieve is used. At the time of pulverization, wet pulverization in which an organic solvent such as water, acetone or hexane coexists can be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  Moreover, in this invention, you may equip the surface of the particle | grains of the active material for nonaqueous electrolyte electrical storage elements with the electroconductive substance in order to supplement the electronic conductivity of lithium transition metal complex oxide. The conductive substance is not particularly limited as long as it has better electronic conductivity than the lithium transition metal composite oxide. Examples thereof include graphitic carbon such as metal, metal oxide, and acetylene black, carbon nanotubes, carbon derived from pyrolysis of organic substances, and conductive polymers. In the present invention, graphitic carbon is preferable.

  As a method for providing the conductive material on the surface of the active material particle for the nonaqueous electrolyte storage element, a method of physically bonding the conductive material to the surface of the active material particle, such as mechanofusion, is preferable. In the present invention, as described in Examples described later, after the active material for a nonaqueous electrolyte electricity storage element is fired, a pulverizing step using a ball mill is provided. By allowing a conductive substance to coexist in this step, the conductive substance can be provided on the surface of the particles.

  As a method for providing a conductive material on the surface of particles of the active material for a non-aqueous electrolyte storage element, there is a method using thermal decomposition of an organic compound. In this method, the active material for non-aqueous electrolyte storage element after firing and the organic compound are mixed and heated in an inert or reducing atmosphere, exceeding the thermal decomposition temperature of the organic matter, so that the non-aqueous electrolyte storage element use The surface of the active material particles can be coated with carbon. However, depending on the type of transition metal contained in the lithium transition metal composite oxide, care should be taken because the composition of the target lithium transition metal composite oxide may change due to reduction to the metal during heating. is there.

The negative electrode material used for the negative electrode of the non-aqueous electrolyte secondary battery according to the present invention is not limited, and any negative electrode material that can occlude and release lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure typified by Li [Li _1/3 Ti _5/3 ] O ₄ ; alloy-based materials such as Si, Sb, and Sn; lithium metal; lithium -Lithium alloys such as silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium; lithium composite oxides such as lithium-titanium; silicon oxide; alloys capable of inserting and extracting lithium Carbon materials such as graphite, hard carbon, low-temperature calcined carbon, and amorphous carbon can be used.

  The powder of the negative electrode material desirably has an average particle size of 100 μm or less. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is 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 or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite such as scaly graphite, scaly graphite, and earth graphite; artificial graphite; carbon black; acetylene black; Chain black; carbon whisker; carbon fiber; metal powder such as copper, nickel, aluminum, silver, and gold; metal fiber; conductive materials such as conductive ceramic materials can be used alone or in combination of two or more. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing it into ultrafine particles of 0.1 to 0.5 μm because the required amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  The filler may be any material as long as it does not adversely affect the performance of the storage element. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode contain the main constituent (positive electrode active material or negative electrode material), and prepare a coating solution using an organic solvent such as N-methylpyrrolidone or toluene or water as a dispersion solvent, and the positive electrode current collector or the negative electrode It is preferably produced by applying to a current collector and removing the dispersion solvent by heating. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  The non-aqueous solvent contained in the non-aqueous electrolyte used in the non-aqueous electrolyte electricity storage device according to the present invention is not limited, and non-aqueous solvents generally proposed for use in lithium batteries and the like can be used. Examples of the nonaqueous solvent used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2- Ethers such as dimethoxyethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or the like A single derivative or a mixture of two or more thereof can be exemplified, but the invention is not limited to these.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ , NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, Examples thereof include organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more.

Further, by using a mixture of LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced, The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / L to 5 mol / L, more preferably 0.5 mol / L in order to reliably obtain a non-aqueous electrolyte storage element having high storage element characteristics. -2.5 mol / L.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene; polyester resins typified by polyethylene terephthalate and polybutylene terephthalate; polyvinylidene fluoride; vinylidene fluoride-hexa Fluoropropylene copolymer; vinylidene fluoride-perfluorovinyl ether copolymer; vinylidene fluoride-tetrafluoroethylene copolymer; vinylidene fluoride-trifluoroethylene copolymer; vinylidene fluoride-fluoroethylene copolymer; Vinylidene fluoride-hexafluoroacetone copolymer; vinylidene fluoride-ethylene copolymer; vinylidene fluoride-propylene copolymer; vinylidene fluoride-trifluoropropylene copolymer; vinylidide fluoride - tetrafluoroethylene - hexafluoropropylene copolymer; a vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  FIG. 1 is a schematic view of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The configuration of the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

  In addition, since the raw material used for the active material for nonaqueous electrolyte electrical storage elements which concerns on this invention, and its synthesis | combination contains trivalent vanadium (V), it is easy to be oxidized. Therefore, the active material synthesis step and the electrode preparation step are preferably performed in an inert atmosphere such as nitrogen or argon.

Example 1
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Nacalai Tesque), niobium pentoxide (Nb ₂ O ₅ ) (manufactured by high purity chemical) and vanadium trioxide (V ₂ O ₃ ) (manufactured by high purity chemical) Was measured so that the molar ratio of Li: Nb: V was 135: 35: 30, and zirconia having an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls (product name: YTZ balls) having a diameter of 5 mm. It was put into the pot made. The starting material charge was about 18 g. Add 10 mL of acetone to the pot, cover it, set it on a planetary ball mill (FRISCH, model number pulverisete 5), mix for 9 minutes at a revolution speed of 300 rpm, and then put a pause for 1 minute. Repeated 6 times. The mixture was dried at 75 ° C. for 3 hours or longer in a dryer to prepare a mixed powder having a Li: Nb: V molar ratio of 135: 35: 30. This mixed powder is placed in an alumina crucible (model number: 1-7745-07) with a capacity of 30 mL and placed in a tabletop vacuum / gas replacement furnace (model number: KDF75), and heated in a nitrogen stream under normal pressure. The temperature was raised from room temperature to 1050 ° C. over about 100 min at a rate of 10 ° C./min, and held at 1050 ° C. for 5 min. The baked powder was taken out and pulverized for several minutes in a smoked automatic mortar to make the particle size uniform. In this way, a lithium transition metal composite oxide according to Example 1 represented by the composition formula Li _1.35 Nb _0.35 V _0.3 O ₂ was produced.

(Examples 2 to 4)
In the mixed powder preparation process, the molar ratio of Li: Nb: V was 130: 30: 40 for Example 2, 125: 25: 50 for Example 3, and 120: 20: 60 for Example 4. In the same manner as in Example 1, except that lithium carbonate, niobium pentoxide, and divanadium trioxide were weighed so that Lithium transition metal composite oxides according to Examples 2 to 4 were produced.

(Example 5)
In the preparation process of the mixed powder, lithium carbonate, niobium pentoxide, divanadium trioxide, and dimanganese trioxide (so that the molar ratio of Li: Nb: V: Mn is 130: 30: 30: 10 ( (Mn ₂ O ₃ ) (manufactured by Kojundo Chemical Co., Ltd.) and the composition formula Li _1.3 Nb _{0. A} lithium transition metal composite oxide according to Example 5 represented by ₃₀ V _0.3 Mn _0.1 O ₂ was produced.

(Examples 6 to 10)
In the mixed powder preparation step, the molar ratio of Li: Nb: V was 115: 15: 70 for Example 6, 110: 10: 80 for Example 7, and 120: 30: 50 for Example 8. , Except that lithium carbonate, niobium pentoxide and divanadium trioxide were weighed out to be 125: 15: 60 for Example 9 and 130: 10: 60 for Example 10. In the same procedure as in Example 1, lithium transition metal composite oxides according to Examples 6 to 10 represented by the respective composition formulas shown in Table 1 were produced.

(Comparative Example 1)
Lithium carbonate, niobium pentoxide and dimanganese trioxide were weighed so that the molar ratio of Li: Nb: Mn was 130: 30: 40 in the mixed powder preparation process, and an argon stream A lithium transition metal composite oxide according to Comparative Example 1 represented by the composition formula Li _1.30 Nb _0.30 Mn _0.4 O ₂ in the same procedure as in Example 1 except that it was fired in Was made.

(Comparative Example 2)
In the mixed powder preparation step, lithium carbonate, niobium pentoxide, dimanganese trioxide and ferric trioxide (so that the molar ratio of Li: Nb: Mn: Fe is 1215: 215: 380: 190 ( Fe ₂ O ₃ ) (manufactured by Nacalai Tesque) and compositional formula Li _1.215 Nb _{0.215 in} the same procedure as in Example 1 except that it was fired in an argon stream. A lithium transition metal composite oxide according to Comparative Example 2 represented by Mn _0.38 Fe _0.19 O ₂ was produced.

(Comparative Example 3)
In the mixed powder preparation process, lithium carbonate and niobium pentoxide were weighed so that the molar ratio of Li: Nb was 30:10, and in the firing process, Under the same conditions as in Example 1 except that the temperature was raised from room temperature to 950 ° C. over about 600 min at a temperature rising rate of 1.5 ° C./min and maintained at 950 ° C. for 240 min, the composition formula Li ₃ A lithium transition metal composite oxide according to Comparative Example 3 represented by NbO ₄ was produced.

(Comparative Example 4)
In the mixed powder preparation step, the same procedure as in Example 1 was performed except that lithium carbonate and divanadium trioxide were weighed so that the molar ratio of Li: V was 10 :: 10. A lithium transition metal composite oxide according to Comparative Example 4 represented by the composition formula LiVO ₂ was produced.

(Comparative Example 5)
Except that lithium carbonate, niobium pentoxide and divanadium trioxide were weighed so that the molar ratio of Li: Nb: V was 140: 40: 20 in the mixed powder preparation process. In the same procedure as in Example 1, a lithium transition metal composite oxide according to Comparative Example 5 represented by the composition formula Li _1.40 Nb _0.40 V _0.2 O ₂ was produced.

  The value of 2y + z is 1.0 for Examples 1 to 7, 1.1 for Example 8, 0.9 for Example 9, and 0.8 for Example 10. It is.

(X-ray diffraction measurement)
Powder X-ray diffraction measurement was performed using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). The radiation source is CuKα ray, the tube voltage and tube current are 30 kV and 15 mA, respectively, and the diffraction X-ray passes through a Kβ filter having a thickness of 30 μm and is detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2). The sampling width is 0.01 °, the scanning speed is 5 ° / min, the divergence slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. The obtained X-ray diffraction diagram and X-ray diffraction data were analyzed using integrated powder X-ray analysis software “PDXL” (manufactured by Rigaku).

As a result, in the lithium transition metal composite oxide according to Example 1, a peak attributable to the space group Fm-3m and a peak attributable to the space group I-43m were observed, and the lithium transition metal composite oxide according to the example 2 was observed. In the oxide, a peak that can be assigned to the space group Fm-3m is observed, and the lithium transition metal composite oxides according to Example 3, Example 4, Example 6, and Example 7 belong to the space group Fm-3m. A possible peak and a peak that can be assigned to the space group R-3m are observed, and the lithium transition metal composite oxide according to Example 5 can be assigned to the peak that can be assigned to the space group Fm-3m and Li ₃ VO _4. A weak impurity peak is observed, and the lithium transition metal composite oxide according to Example 8 has a peak that can be assigned to the space group Fm-3m, a peak that can be assigned to the space group R-3m, and an impurity peak that can be assigned to LiNbO _3. In the lithium transition metal composite oxide according to Example 9, the peak that can be assigned to the space group Fm-3m, the peak that can be assigned to the space group R-3m, and the weak impurity that can be assigned to Li ₃ VO ₄ A peak is observed, and the lithium transition metal composite oxide according to Example 10 has a peak that can be assigned to the space group Fm-3m, a peak that can be assigned to the space group R-3m, and an impurity peak that can be assigned to Li ₃ VO _4. Was observed. Here, the peaks that can be assigned to the space group Fm-3m are derived from the NaCl type structure in which cations are irregularly arranged, and the peaks that can be assigned to the space group R-3m are regularly arranged in cations. It is interpreted to be derived from the α-NaFeO ₂ type structure. Moreover, the lithium transition metal composite oxide according to Comparative Example 1 and Comparative Example 2 has a peak that can be assigned to the space group Fm-3m, and the lithium transition metal composite oxide according to Comparative Example 3 has the space group I- A peak that can be assigned to 43 m is observed, and the lithium transition metal composite oxide according to Comparative Example 4 has a peak that can be assigned to the space group R-3m and a weak impurity peak that can be assigned to LiV ₂ O _4. In the lithium transition metal composite oxide according to Example 5, a peak attributable to the space group Fm-3m and a peak attributable to the space group I-43m were observed. FIG. 3 shows X-ray diffraction patterns of lithium transition metal composite oxides according to Examples 1 to 10.

(Preparation of non-aqueous electrolyte secondary battery)
Using each of the lithium transition metal composite oxides of Examples 1 to 10 and Comparative Examples 1 to 5 as the positive electrode active material of the non-aqueous electrolyte battery, a non-aqueous electrolyte secondary battery was produced by the following procedure, and the battery characteristics were evaluated.

Weighing 2.275 g of the positive electrode active material and 0.700 g of acetylene black (AB), respectively, and a zirconia pot with an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls (product name: YTZ balls) with a diameter of 5 mm It was thrown into. Add 10 mL of acetone to the pot, cover it, set it on a planetary ball mill (FRISCH, model number pulverisete 5), mix for 9 minutes at a revolution speed of 300 rpm, and then put a pause for 1 minute. Repeated 6 times. This mixture was dried at 75 ° C. for 3 hours or longer to prepare a mixed powder. This mixed powder and polyvinylidene fluoride (PVdF) were mixed so that the mass ratio of the positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) was 65:20:15. This mixture was kneaded and dispersed by adding N-methylpyrrolidone as a dispersion medium to prepare a coating solution. In addition, about PVdF, it converted into solid mass by using the liquid by which solid content was melt | dissolved and dispersed. The coating solution was applied to an aluminum foil current collector with a thickness of 20 μm, and then dried for 60 minutes on a hot plate at 80 ° C. to evaporate the dispersion medium, and a positive electrode plate was produced by performing a roll press. . The thickness of the mixture layer after pressing was 18 μm, and the coating weight was 2.5 mg / cm ² .

  Lithium metal was used for the negative electrode in order to observe the single behavior of the positive electrode. This lithium metal was adhered to a nickel foil current collector. However, the capacity of the non-aqueous electrolyte secondary battery was adjusted to be sufficiently positive electrode regulated.

As an electrolytic solution, LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent having a volume ratio of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) of 30:35:35. It was. As the separator, a microporous membrane made of polypropylene was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package. The electrode was accommodated in this exterior body so that the open ends of the positive electrode terminal and the negative electrode terminal were exposed to the outside. The fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed except for the portion to be the injection hole. After injecting a sufficient amount of the above electrolyte from the injection hole into the battery in the same amount for each battery, the injection hole is heat sealed while decompressing the battery. A secondary battery was produced.

(Charge / discharge cycle test A)
The nonaqueous electrolyte secondary battery produced as described above was transferred to a thermostat set at 25 ° C., and charge / discharge of 4 cycles was performed. Charging was constant current constant voltage (CVCC) charging, and discharging was constant current (CC) discharging. The constant current value for charging and discharging was 10 mA / g with respect to the mass of the positive electrode active material contained in the positive electrode plate. The charge upper limit voltage and the discharge end voltage were 4.8 V and 1.5 V, and the charge end condition was the time when the charging current was attenuated to 2 mA / g, or the time when 3 hours had passed after reaching the charge upper limit voltage. In all cycles, a 10 minute rest period was set after charging and discharging.

  As a result of the charge / discharge cycle test A, the battery of Comparative Example 4 was not subjected to the subsequent tests because the charge voltage did not reach 4.8 V in the charging process of the first cycle. For all Examples and Comparative Examples except Comparative Example 4, the discharge capacity (mAh / g) per second active material mass, and the value obtained by dividing the discharge capacity of the fourth cycle by the discharge capacity of the second cycle Table 1 shows the capacity retention ratio (%).

  As can be seen from Table 1, the batteries of Comparative Examples 1 to 3 have a capacity maintenance rate (%) of 95% or less, whereas the batteries of Examples 1 to 10 and Comparative Example 5 have a capacity maintenance rate (%). It was 96% or more. Among them, the composition ratio of vanadium is high, and both the peak attributable to the space group Fm-3m and the peak attributable to the space group R-3m were observed. In Examples 7 and 9, the discharge capacity was particularly high. The battery of Comparative Example 5 had a capacity retention rate (%) of 100% or more, but the discharge capacity was small.

  Tests described below that the non-aqueous electrolyte storage element active material according to the example has excellent discharge capacity and excellent charge / discharge cycle performance compared to the conventional non-aqueous electrolyte storage element active material Further details will be described based on the results.

(Charge / discharge cycle test B)
Using the lithium transition metal composite oxide of Example 2, a non-aqueous electrolyte secondary battery was newly produced in the same procedure as described above, transferred to a constant temperature bath set at 25 ° C., and a 4-cycle charge / discharge cycle test was performed. went. The charging conditions and the discharging conditions are the same as those in the charge / discharge cycle test A for Example 2-1, the charging upper limit voltage is 4.2 V for Example 2-2, and the charging termination condition is charged. The charge / discharge cycle test A is the same as that described above except that the current is reduced to 2 mA / g.

Using the lithium transition metal composite oxide of Comparative Example 1, a non-aqueous electrolyte secondary battery was newly produced in the same procedure as described above, transferred to a thermostat set at 25 ° C., and subjected to a charge / discharge cycle test of 4 cycles. It was. The charging conditions and the discharging conditions are the same as those in the charge / discharge cycle test A for Comparative Example 1-1, and Comparative Example 1-2, Comparative Example 1-3, Comparative Example 1-4, Comparative Example 1-5, and Comparative Example Regarding Example 1-6, the charging upper limit voltage was set to 4.4 V, 4.35 V, 4.3 V, 4.25 V and 4.2 V, respectively, and the charging end condition when the charging current was attenuated to 2 mA / g The charge / discharge cycle test A is the same as that described above.

  For the charge / discharge cycle test B, the discharge capacity (mAh / g) per second active material mass and the capacity retention rate (%), which is the value obtained by dividing the discharge capacity of the fourth cycle by the discharge capacity of the second cycle, It shows in Table 2.

In the conventional solid solution of Li ₃ NbO ₄ and LiMeO ₂ (Me is Fe or Mn), when the end-of-charge voltage is set low, as can be seen from the results of Comparative Examples 1-4 to 1-6, the high capacity is maintained. Although the rate is high, the discharge capacity is low. This is because the Mn oxidation-reduction reaction is used without using the O (oxygen) oxidation-reduction reaction, and thus the capacity retention rate is high. However, since the number of reaction electrons of Mn is small, the discharge capacity is considered low. Further, when the end-of-charge voltage is set high, as can be seen from the results of Comparative Examples 1-1 to 1-3, the capacity retention rate is low, although a high discharge capacity is exhibited. This uses a redox reaction of O in addition to a redox reaction of Mn, and thus exhibits a high discharge capacity, but is considered to have a low capacity retention rate. On the other hand, in the solid solution of Li ₃ NbO ₄ and LiMeO ₂ (Me is a transition metal containing V) according to the present invention, as can be seen from the results of Examples 2-1 and 2-2, the oxidation of O Providing an active material for non-aqueous electrolyte electricity storage devices that uses an oxidation-reduction reaction of V without using a reduction reaction and has a large number of reactive electrons of V, so it has both excellent discharge capacity and excellent charge / discharge cycle performance. It is considered possible.

(Charge / discharge cycle test C)
Using the lithium transition metal composite oxide of Example 2, a non-aqueous electrolyte secondary battery was newly produced in the same procedure as described above, the charge upper limit voltage was set to 4.8 V or 4.2 V, and the above charge / discharge cycle test A charge / discharge cycle test of 10 cycles was performed under the same charge / discharge conditions as B. Fig. 4 shows the charge and discharge curves for the second and tenth cycles of the battery with a charge upper limit voltage of 4.8V, and Fig. 4 shows the charge and discharge curves for the second and tenth cycles of the battery with a charge upper limit voltage of 4.2V. As shown in FIG.

  Each battery after the charge / discharge cycle test was disassembled in a glove box maintained in an argon atmosphere, the positive electrode was taken out, washed with dimethyl carbonate (DMC), and then sufficiently dried. This is installed in a dedicated apparatus (general-purpose atmosphere separator) (manufactured by Rigaku) for maintaining an argon atmosphere, and powder X-ray diffraction measurement is performed using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). It was. The radiation source is CuKα ray, the tube voltage and tube current are 30 kV and 15 mA, respectively, and the diffraction X-ray passes through a Kβ filter having a thickness of 30 μm and is detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2). The sampling width is 0.01 °, the scanning speed is 2 ° / min, the divergence slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. The obtained X-ray diffraction diagram and X-ray diffraction data were analyzed using integrated powder X-ray analysis software “PDXL” (manufactured by Rigaku).

  The upper part of FIG. 6 is an X-ray diffraction diagram of the positive electrode plate taken out from the battery after 10 cycles of charge / discharge cycle tests with the end-of-charge voltage and end-of-discharge voltage set to 4.8 V and 1.5 V. FIG. 3 is an X-ray diffraction diagram of a positive electrode plate taken out from a battery after a 10-cycle charge / discharge cycle test in which a charge end voltage and a discharge end voltage are 4.2 V and 1.5 V, respectively. Here, peaks derived from aluminum used for the positive electrode current collector appear around 38 °, 65 °, and 78 °. The peaks derived from the active material are peaks at around 37 °, around 43 °, around 63 °, around 75 °, and around 79 °. The electrodes after the charge / discharge cycle all showed the same X-ray diffraction pattern as the active material used therein, and the crystal structure that can be assigned to the space group Fm-3m was maintained even after the charge / discharge cycle. . Accordingly, the active material for a non-aqueous electrolyte storage element according to the present invention is considered to undergo a reversible charge / discharge cycle while maintaining a crystal structure that can be assigned to the space group Fm-3m, and thus exhibits a high capacity retention rate. it is conceivable that.

  The active material for a non-aqueous electrolyte storage element of the present invention is excellent in energy density and discharge capacity, and is therefore effectively used for a non-aqueous electrolyte storage element such as a power source for electric vehicles, a power source for electronic devices, and a power storage power source. it can.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (4)

The active material for nonaqueous electrolyte electrical storage elements which contains the lithium transition metal complex oxide which has a peak which can be assigned to space group Fm-3m, and is represented by a composition formula (1) in an X-ray diffraction diagram.
_{Li 1 + x Nb y Me z} A p O 2 ··· (1)
(Me is a transition metal containing V, element ratio V / Me ratio of V constituting Me is 0.5 or more, 0 <x <1, 0 <y ≦ 0.35 , 0.3 ≦ z <1, A Is an element other than Nb, Me, O, 0 ≦ p ≦ 0.2)   The active material for a nonaqueous electrolyte electricity storage element according to claim 1, wherein 0.8 ≦ 2y + z ≦ 1.2.   The electrode for nonaqueous electrolyte electrical storage elements containing the active material for nonaqueous electrolyte electrical storage elements of Claim 1 or 2.   A nonaqueous electrolyte storage element comprising the electrode for a nonaqueous electrolyte storage element according to claim 3.