JP2015118879A - Positive electrode material for lithium ion secondary battery, and positive electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for a lithium ion secondary battery, which is excellent in heat resistance and porosity between electrodes, which has stability and high-output characteristics during charge and discharge, and which replaceably has densely-distributed lithium ions.SOLUTION: A positive electrode material for a secondary battery has hydrotreated zeolite. The positive electrode material for the lithium ion secondary battery has a lithium-transition metal oxide within a pore of the zeolite.

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery and a positive electrode for a lithium ion secondary battery using such a positive electrode material.

  In recent years, the use of secondary batteries with high energy density has been accelerated due to diversification of applications such as operating power sources for electronic devices and drive power sources for electrical devices. Currently, nickel-hydrogen batteries and nickel-cadmium batteries with relatively high capacity are the mainstream, but in the future, they will be used for hybrid cars, commercial use, household storage, etc., with high energy density, A highly efficient secondary battery that can be charged and discharged is required.

  Secondary batteries are strongly required to have properties such as storage life, charge / discharge cycle life, safety and reliability in addition to energy density and electric capacity (input and output). Furthermore, it is required to consider resource environment conservation such as reducing the use of rare resources such as rare metals, and electrode material costs.

Here, a lithium ion secondary battery can be cited as one that can meet such a demand. The electrode reaction of the lithium ion secondary battery is, for example, when lithium cobaltate is used as an active material, during discharge, lithium ions are extracted from the negative electrode (graphite), reach the positive electrode through the electrolyte phase, It is accommodated in a cobalt oxide (CoO ₂ ) structure, obtains electrons from an external circuit, and lithium cobalt oxide (LiCoO ₂ ) is generated. During charging, the reverse reaction causes lithium ions extracted from LiCoO ₂ to enter the negative electrode and be reduced to lithium (Li).

  As described above, lithium cobalt oxide is currently in practical use as an active material for lithium-ion secondary batteries capable of high-energy density and high-efficiency charging / discharging. However, because cobalt is a rare metal, it can be used as an alternative material. Lithium nickel oxide, lithium manganate, lithium vanadate and cobalt / lithium manganate, nickel / lithium manganate, iron / lithium phosphate and other secondary battery positive electrode materials such as spinel type and olipine type It is being considered.

These positive electrode materials for secondary batteries have high energy density. In other words, lead-acid batteries (Pb / PbO2), with respect to the energy density measured value of 30~45Wh / kg of nickel cadmium batteries (Cd / NiOOH), lithium cobaltate (LiCoO _2), the lithium nickel oxide (LiNiO ₂₎ Since it is 100 to 130 Wh / kg, which is about three times as high, it is used as a positive electrode for secondary batteries used in equipment that requires high electromotive force and large capacity.

Here, for example, lithium cobaltate has a laminated structure in which lithium (Li ⁺ ) layers and CoO ₆ octahedral layers are alternately stacked, and Li ⁺ is deintercalated during charging. It has also been pointed out that during overcharge, heat is generated and the crystal structure of cobalt acid (CoO ₂ ) is broken to generate oxygen and induce an oxidation reaction of the organic electrolyte.

  Lithium cobaltate can be easily obtained by mixing lithium hydroxide and a cobalt compound and firing in air. Furthermore, although there is an advantage that the characteristic change due to the starting material is small, there is a problem that only 50% of lithium ions can be used in the electrode reaction as shown in the following formula (1).

Other positive electrode active material materials are nickel-based, phosphate-based (olivine), manganese-based (layered, spinel), and the like. Ternary (Li (Ni-Mn-Co ,) VO 2) inverse spinel such as a high voltage positive electrode material has been studied.

  From the viewpoint of stability and safety of the positive electrode material, improvement in material properties such as melting temperature and heat resistance, porosity, pore size distribution, and heat shrinkage is required.

  For example, in Patent Literature 1, ceramic particles such as alumina, silica, zirconia, and titania are mixed with the positive electrode material, and the fine particles adhere to the surface of the positive electrode active material layer. From the viewpoint of growth suppression, the stability of the positive electrode material is disclosed.

  Reference 2 reports that a positive electrode material obtained by spray-coating zirconium oxide particles on the surface of lithium cobalt oxide and firing at 823 K has increased thermal stability during charging. However, these conventional techniques cannot be said to be sufficient in terms of heat resistance and inter-electrode porosity.

JP 2007-305546 A

H. Miyashiro. J, Electrochemical Society 153 (2) A343-A353

  The present invention is excellent in heat resistance and inter-electrode porosity, has stability during charging / discharging and high output characteristics, and has a high density distribution of a positive electrode material for a lithium ion secondary battery, and such a positive electrode material. It is an object to provide an electrode for a lithium ion secondary battery and a lithium ion secondary battery

  In order to solve the above problems, a positive electrode material for a lithium ion secondary battery of the present invention is a positive electrode material for a secondary battery having a hydrogenated zeolite, and a lithium-transition metal is present in the pores of the zeolite. It has an oxide.

  In the positive electrode material for a lithium ion secondary battery of the present invention, in addition to the above configuration, the hydrogenated zeolite contains FAU (Y type), MFI (ZSM-5), BEA (β type), and ALPO ( One or more zeolites of SAPO) may be hydrotreated.

  In addition to the above-described structure, the positive electrode material for a lithium ion secondary battery of the present invention is obtained by impregnating the hydrogenated zeolite with an aqueous solution of a compound containing a transition metal and then heat-treating it in air. After being impregnated with an aqueous solution of a compound containing, a hydrogenated zeolite that has been heat-treated in air can be obtained.

  In the positive electrode material for a lithium ion secondary battery of the present invention, in addition to the above configuration, the transition metal includes a transition metal having an atomic number of 21 to 29, a transition metal having an atomic number of 39 to 47, and an atomic number of One or more selected from 57 to 79 transition metals can be used.

  In the positive electrode material for a lithium ion secondary battery of the present invention, in addition to the above configuration, the transition metal can be one or more selected from vanadium, manganese, iron, cobalt, and nickel.

  In the positive electrode material for a lithium ion secondary battery of the present invention, in addition to the above configuration, the heat treatment in the air can be performed at a temperature of 300 ° C. or higher and 700 ° C. or lower.

  The positive electrode for a lithium ion secondary battery of the present invention is characterized by having the above-described lithium ion secondary battery positive electrode material.

  The lithium ion secondary battery positive electrode material of the present invention is a positive electrode material for a secondary battery having a hydrogenated zeolite, and has a structure having a lithium-transition metal oxide in the pores of the zeolite. Because the rate is high and the active material is difficult to assemble, it has heat resistance and is stable against the heat generated when lithium moves through the pores (pore diameter: 0.3 nm to 1 nm) during charging. Become positive electrode material. Furthermore, since the lithium ion secondary battery positive electrode material of the present invention is a three-dimensional structure with a strong pore structure from a porous body skeleton, lithium ions can be easily moved even after repeated charge and discharge operations. High output is maintained and long cycle life can be realized.

It is a figure which shows the outline of the manufacturing method of the lithium ion secondary battery positive electrode material of this invention.

  The inventors of the present invention conducted ion exchange of the alkali metal of the zeolite structure with ammonia, nitric acid, hydrochloric acid, etc., and then hydrogenated (protonated) by a baking treatment, and formed solid acid sites (Bronsted acid portion and Lewis After introducing a transition metal and a lithium salt into the acid portion), we are studying a lithium transition metal oxide porous body formed by high-temperature firing, and measuring the electromotive force using the oxide porous body as a positive electrode material, The inventors have found that lithium ions move and have arrived at the present invention.

  In the lithium ion secondary battery positive electrode material of the present invention, a transition metal element is introduced into a zeolite three-dimensional porous body having a pore structure of 6, 8, 10, 12-membered ring made of an alkali metal, silica and aluminum. By forming a lithium-transition metal oxide in the porous body, it becomes a positive electrode material having excellent stability during charging and discharging and high output characteristics, and having high density of exchangeable lithium ions.

As the zeolite used in the present invention, for example, 4 kinds of about 10 kinds of zeolites used industrially can be suitably used. Its general composition is xM ₂ /nO.Al ₂ O ₃ .ySiO ₂ .zH ₂ O (wherein M is sodium or potassium, x is 2 to 2.5, n is a cation valence, y is An integer of 2 or more, z is an integer of 0 or more).

  Examples of these four types of zeolites are Y-type (FAU), ZSM-5 (MFI), beta-type (BAE) aluminosilicate compounds, and phosphate-type silicoaluminophosphate (SAPO). In addition, zeolites belonging to the structure codes of LTA, FER, MOR, LTL, and MWW may be used.

  Moreover, you may use the zeolite prepared by the hydrothermal synthesis method by the International Zeolite Association (International Zeolite Association).

  Before using zeolite, in the case of a zeolite using a template in the hydrothermal synthesis method, the residual template and moisture are removed by heat treatment in air at 500 ° C. for 2 hours, and the X-ray diffraction results are diffracted. The pattern is compared with the data pattern of the International Zeolite Society, and the structure is confirmed from the diffraction angle and d value.

  Next, the preparation method of the lithium ion secondary battery positive electrode material of this invention is demonstrated.

  If necessary, the cation of the zeolite after the above heat treatment at 500 ° C. is treated in an ammonium nitrate aqueous solution or nitric acid at a temperature of 50 ° C. or more and 2 hours or more and 5 hours or less, and the cation is ionized. Exchange and dealumination treatment (see reaction transition from upper to middle in FIG. 1), wash with water, dry, and again at 350 ° C. or higher, eg, 3 Bronsted acid or Lewis acid at 500 ° C. A hydrogenated zeolite having is prepared.

  Next, the hydrogenated zeolite is impregnated in an aqueous solution of, for example, 0.2 mol / L (liter) or more and 5 mol / L or less of a compound containing, for example, iron, cobalt, and manganese as the transition metal (see FIG. 1) (corresponding to “metal salt” in the middle stage of 1), the transition metal and the zeolite are combined and reacted with stirring under the conditions of 50 ° C. or more and 1 hour or more and 5 hours or less, then washed and dried, for example, 300 ° C. or more. A transition metal oxide-supported zeolite (transition metal oxide-supported hydrogenated zeolite) (corresponding to the left side of the lower part of FIG. 1) is prepared by heat treatment in air at 600 ° C. or lower for 2 hours to 5 hours. .

  The transition metal is not limited to those described above, and may be one or more of other transition metals such as vanadium, chromium, yttrium, zirconium, niobium, molybdenum, gallium, and indium. Any metal salt such as nitrate, sulfate, hydrochloride, acetate, or oxalate may be used.

  Furthermore, 1 mol / L or more and 5 mol / L or less of an aqueous solution of lithium salt such as lithium nitrate or lithium acetate or lithium hydroxide (lithium compound, corresponding to “lithium salt” in the left side of FIG. 1) The above-mentioned transition metal oxide-supported zeolite is added to, for example, after reacting lithium and the transition metal oxide with stirring under conditions of 50 ° C. or more and 1 hour or more and 5 hours or less, after washing and drying, 300 ° C. The hydrogenated zeolite (hereinafter referred to as “lithium-transition metal oxide zeolite”) in which the lithium-transition metal oxide is chemically fixed by performing a heat treatment in air of 700 ° C. or less and 2 hours or more and 5 hours or less. (Refer to the lower right diagram in FIG. 1).

  The lithium-transition metal oxide zeolite of the present invention is formed by kneading with carbon black, polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), etc., and coating the aluminum foil or aluminum pore thin plate. Can be used.

When the lithium-transition metal oxide zeolite which is the positive electrode material of the lithium ion secondary battery of the present invention is incorporated in a lithium secondary battery, the lithium ions in the pores of the zeolite are charged during charging (in a negative electric field). The pores are sequentially moved to the high energy side, and supplied to the negative electrode through an electrolyte such as carbon black and lithium hexafluorophosphate (LiPF ₆ ) adjacent to the opening of the pore. At the time of discharging, the reverse movement of lithium ions from the negative electrode to the positive electrode proceeds.

  As mentioned above, although this invention was demonstrated and mentioned with preferable embodiment, the positive electrode material for lithium ion secondary batteries of this invention and the positive electrode for lithium ion secondary batteries are not limited to the structure of said form. Absent.

  A person skilled in the art can appropriately modify the positive electrode material for a lithium ion secondary battery and the positive electrode for a lithium ion secondary battery of the present invention according to conventionally known knowledge. As long as the modification includes the positive electrode material for a lithium ion secondary battery and the positive electrode for a lithium ion secondary battery of the present invention, it is, of course, included in the category of the present invention.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  In the examples, four types of zeolite, commercially available FAU (Y type), MFI (ZSM-5), BAE (β type), and ALPO (SAPO-34) were used. These zeolites were hydrotreated by heating in air at 500 ° C. and cation exchange in nitric acid at 50 ° C. for 3 hours, and again by heating in air at 500 ° C. for 2 hours.

  The structural analysis of the above hydrogenated zeolite uses X-ray diffraction (X-ray diffraction analyzer manufactured by Rigaku Corporation, RINT2200 (Cu source)), and is compared with the data pattern of the International Zeolite Association. It was identified.

  The transition metal oxide is prepared by adding the above-mentioned hydrogenated zeolite to a 0.2 molar aqueous solution of transition metal salts, and subjecting the transition metal and zeolite to a binding reaction while stirring at 50 ° C. for 2 hours, washing and drying. Then, a hydrogenated zeolite (lithium-transition metal oxide zeolite) in which the transition metal oxide was chemically fixed was prepared by performing a heat treatment in air at 500 ° C. for 2 hours.

  Next, the above-mentioned hydrogenated zeolite in which the transition metal oxide is chemically fixed is added to a 1 mol / L lithium nitrate aqueous solution, and the lithium salt and the transition metal oxide are stirred at 50 ° C. for 2 hours. After the porous zeolite was bonded, it was washed and dried, and then calcined at 500 ° C. for 2 hours to prepare a lithium-transition metal oxide zeolite.

<Example 1>
As FAU (Y-type) zeolite, one having a chemical composition of Na ₅₈ Al ₅₈ Si ₁₃₄ O ₃₈₄ is used, and transition metals are introduced into the Y-type lithium-transition metal by introducing iron, cobalt and manganese, respectively. An oxide zeolite was prepared.

<Example 1a (iron)>
Y-type zeolite hydrogenated in an aqueous solution of iron (III) nitrate (III) 0,2 mol / L as a transition metal is put in a half of the mass of the solution, and the transition metal and the zeolite are combined. After drying (150 ° C., 5 hours), heat treatment was performed in air (500 ° C., 2 hours) to prepare a hydrogenated zeolite in which iron oxide was chemically fixed. Next, the zeolite in which iron oxide is fixed in a 1 mol / L lithium nitrate solution is mixed so that the zeolite becomes 1 with respect to the solution 2 in a weight ratio, and then dried (150 ° C., 5 hours). A hydrogenated zeolite (Example 1a) on which lithium-iron oxide was fixed was obtained by heat treatment in air (500 ° C., 2 hours).

<Example 1b (cobalt)>
Hydrogenated zeolite in which lithium-cobalt oxide is fixed in the same manner as in Example 1a, except that an aqueous solution of cobalt nitrate 0.3 mol / L was used instead of an aqueous solution of iron nitrate (III) 0.2 mol / L. (Example 1b) was obtained.

<Example 1c (manganese)>
A hydrogenated zeolite in which lithium-manganese oxide was fixed in the same manner as in Example 1a, except that an aqueous solution of 0.2 mol / L manganese acetate was used instead of an aqueous solution of 0.2 mol / L iron (III) nitrate. (Example 1c) was obtained.

<Comparative Example 1>
Y-type hydrogenated zeolite is mixed with 1 mol / L lithium nitrate aqueous solution, dried (150 ° C., 5 hours), heat-treated in air (500 ° C., 2 hours), and treated with lithium nitrate-treated Y-type zeolite ( Comparative Example 1) was prepared.

<Example 2>
As the MFI (ZSM-5 type) zeolite, one having a chemical composition of Na ₇ Al ₇ Si ₈₉ -nO ₁₉₂ is used, and transition metals are introduced as MFI type lithium-transition by introducing iron, cobalt and manganese, respectively. A metal oxide zeolite was prepared.

<Example 2a>
Lithium-iron oxide was fixed in the same manner as in Example 1a except that hydrogenated MFI (ZSM-5 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 2a) was obtained.

<Example 2b>
Lithium-cobalt oxide was fixed in the same manner as in Example 1b except that hydrogenated MFI (ZSM-5 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 2b) was obtained.

<Example 2c>
Lithium-manganese oxide was fixed in the same manner as Example 1c except that hydrogenated MFI (ZSM-5 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 2c) was obtained.

<Comparative Example 2>
In the same manner as in Comparative Example 1, except that a hydrogenated MFI (ZSM-5 type) zeolite was used instead of the hydrogenated FAU (Y type) zeolite, a lithium nitrate treated MFI type zeolite ( Comparative Example 2) was prepared.

<Example 3>
A BEA (β-type) zeolite having a chemical composition of <Na ₇ Al ₇ Si ₅₇ O ₁₂₈ > is used, and the transition metals are β-type lithium-transition metal by introducing iron, cobalt, and manganese, respectively. A zeolite with fixed oxide was prepared.

<Example 3a>
Hydrogenation in which lithium-iron oxide was fixed in the same manner as in Example 1a, except that hydrogenated BEA (β-type) zeolite was used instead of hydrogenated FAU (Y-type) zeolite. Zeolite (Example 3a) was obtained.

<Example 3b>
Hydrogenation in which lithium-cobalt oxide was fixed in the same manner as in Example 1b, except that hydrogenated BEA (β-type) zeolite was used instead of hydrogenated FAU (Y-type) zeolite. Zeolite (Example 3b) was obtained.

<Example 3c>
Hydrogenation in which lithium-manganese oxide was fixed in the same manner as in Example 1c, except that hydrogenated BEA (β-type) zeolite was used instead of hydrogenated FAU (Y-type) zeolite. Zeolite (Example 3c) was obtained.

<Comparative Example 3>
MFI type zeolite treated with lithium nitrate (Comparative Example) in the same manner as in Comparative Example 1 except that hydrogenated BEA (β type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. 3) was produced.

<Example 4>
As the CHA (SAPO-34 type) zeolite, one having a chemical composition of Na ₇ Al ₇ Si ₅₇ O ₁₂₈ is used, and transition metals are introduced into the SAPO-34 type lithium by introducing iron, cobalt and manganese, respectively. A zeolite having a transition metal oxide immobilized thereon was prepared.

<Example 4a>
Lithium-iron oxide was fixed in the same manner as in Example 1a, except that hydrogenated CHA (SAPO-34 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 4a) was obtained.

<Example 4b>
Lithium-cobalt oxide was fixed in the same manner as in Example 1b except that hydrogenated CHA (SAPO-34 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 4b) was obtained.

<Example 4c>
Lithium-manganese oxide was fixed in the same manner as in Example 1c, except that hydrogenated CHA (SAPO-34 type) zeolite was used instead of hydrogenated FAU (Y type) zeolite. Hydrogenated zeolite (Example 4c) was obtained.

<Comparative Example 4>
In the same manner as in Comparative Example 1, except that hydrogenated CHA (SAPO-34) zeolite was used instead of hydrogenated FAU (Y type) zeolite, lithium nitrate-treated CHA (SAPO-) was used. 34 type) zeolite (Comparative Example 4) was prepared.

<Preparation of positive electrode>
55 parts by mass of each zeolite prepared in Examples 1 to 4 and Comparative Examples 1 to 4, 2 parts by mass of carbon black, 22 parts by mass of polyvinylidene fluoride (PVDF), and n-methyl-2-pyrrolidone (NMP) 21 Mass parts were kneaded, applied to a commercially available aluminum foil of 2.2 cm ² and then compression molded to produce positive electrodes.

<Measurement of electromotive force>
The voltage of the produced positive electrode was measured using a three-electrode cell. At this time, a platinum electrode as an auxiliary electrode, silver / silver chloride (Ag / AgCl, 0.199V (25 ° C.)) as a reference electrode, and each of the positive electrode materials prepared above as a working electrode and an electrolyte Used a mixed solvent solution of lithium hexafluorophosphate (LiPF ₆ ) in ethylene carbonate and dimethyl carbonate.

  As an external voltage, 3.0 V was applied to the auxiliary electrode and the working electrode, and the voltage between the working electrode and the reference electrode was measured. The voltage was calculated by the following formula (2).

[Equation 1]
V = {(A)-(C)}-{(B)-(C)} (2)
(Wherein (A) is the platinum electrode voltage, (B) is the reference electrode voltage, (C) is the working electrode voltage,
V is voltage (potential difference)

  Measured electromotive force of a positive electrode having the lithium-transition metal oxide zeolite of the above example as a lithium ion secondary battery positive electrode material, and lithium nitrate-treated zeolite of Comparative Examples 1 to 4 as a lithium ion secondary battery positive electrode material Table 1 shows the measured electromotive force values of the positive electrodes.

  From Table 1, it is understood that according to the lithium ion secondary battery positive electrode material of the present invention, a high potential difference (voltage) can be obtained with respect to the comparative example by the three-electrode cell measurement.

Claims (7)

  A positive electrode material for a secondary battery having a hydrogenated zeolite, wherein the positive electrode material for a lithium ion secondary battery has a lithium-transition metal oxide in the pores of the zeolite.   The hydrotreated zeolite is a zeolite obtained by hydrotreating at least one of FAU (Y type), MFI (ZSM-5), BEA (β type), and ALPO (SAPO). The lithium ion secondary battery positive electrode material according to claim 1.   The hydrotreated zeolite was impregnated with an aqueous solution of a compound containing a transition metal and then heat-treated in air, and then impregnated with an aqueous solution of a compound containing lithium and then heat-treated in air. 3. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the positive electrode material is a hydrogenated zeolite. 4.   The transition metal is at least one selected from transition metals having an atomic number of 21 to 29, transition metals having an atomic number of 39 to 47, and transition metals having an atomic number of 57 to 79. The lithium ion secondary battery positive electrode material according to any one of claims 1 to 3.   The lithium ion secondary battery positive electrode material according to claim 4, wherein the transition metal is one or more selected from vanadium, manganese, iron, cobalt, and nickel.   The lithium ion secondary battery positive electrode material according to claim 1, wherein the heat treatment in air is performed at a temperature of 300 ° C. or higher and 700 ° C. or lower.   A positive electrode for a lithium ion secondary battery comprising the lithium ion secondary battery positive electrode material according to any one of claims 1 to 6.

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