JP2004152753A - Manufacturing method of positive electrode active material for non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple manufacturing method of a positive electrode active material for a non-aqueous secondary battery which is made of a compound that contains lithium, nickel, and manganese, and has a layered structure. <P>SOLUTION: In the manufacturing method of the positive electrode active material for the non-aqueous secondary battery, a mixture of a metal compound which contains lithium, nickel, manganese, and boron, and is made of a compound that contains lithium, nickel, and manganese and has a layered structure, is calcinated. The compound which contains lithium, nickel, and manganese and has the layered structure is expressed in the X-ray diffraction in formula Li[Ni<SB>(x-y)</SB>Li<SB>(1/3-2x/3)</SB>Mn<SB>(2/3-x/3-y)</SB>Co<SB>2y</SB>] O<SB>2</SB>(provided that x is larger than 0 and 0.5 or less, y is 0 or more and 1/6 or less, and x > y), and is a compound identified as a compound having the layered structure. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a method for producing a positive electrode active material for a non-aqueous secondary battery.

A positive electrode active material is used for a nonaqueous secondary battery.
With the rapid progress of portable and cordless electronic devices, development of non-aqueous secondary batteries capable of realizing smaller, lighter, and larger capacities than conventional secondary batteries has been promoted. Among them, lithium secondary batteries have already been put to practical use as power sources for mobile phones, notebook computers, and the like. Further, enlargement and high output are being studied as power sources for automobiles and communication power backup.

  As a positive electrode active material for a non-aqueous secondary battery, for example, a spinel-type lithium manganese oxide has been conventionally used, but a positive electrode active material capable of producing a non-aqueous secondary battery with a larger capacity has been demanded. Was.

Under such circumstances, a composition formula of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ or LiNi _1/2 Mn _1/2 which is a compound containing lithium, nickel and manganese and having a layered structure. O ₂ (for example, see Non-Patent Document 1) and Li [Ni _x Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3)} ] O ₂ (0 ≦ x ≦ 1/2) _{), Li [Ni x Co 1-2x} Mn x] O 2 (0 <x ≦ 1/2) new compounds represented by (e.g., see non-Patent Document 2.) or the like solve the problems as described above It has been proposed and attracted attention as a positive electrode active material for non-aqueous secondary batteries that can be used. Here, the layered structure refers to a structure whose crystal structure is identified to be α-NaFeO ₂ type by X-ray diffraction (for example, see Non-Patent Document 3).

  Conventionally, composite hydroxides of nickel and manganese have been used to synthesize these compounds (for example, see Non-Patent Documents 1 to 3). However, since the divalent manganese in the composite hydroxide is easily oxidized to be trivalent, the control of the synthesis conditions of the composite hydroxide and the control of the atmosphere for the subsequent handling are strictly performed. And the production of the composite hydroxide was difficult. Therefore, a simple manufacturing method that does not require strict control of the atmosphere has been demanded.

Chemistry Letters, The Chemical Society of Japan, August 2001, p. 744 Proceedings of the 42nd Battery Symposium, November 21, 2001, Lecture No. 2I12 Electrochemical and Solid-State Letters, (USA), Electrochemical Society, Inc., December 2001, Vol. 4, p. A200-A203

  An object of the present invention is to provide a simple method for producing a positive electrode active material for a non-aqueous secondary battery, comprising a compound having a layered structure, containing lithium, nickel and manganese.

  The present inventors fired a mixture containing lithium, nickel and manganese, which is a mixture of metal compounds, containing lithium, nickel and manganese, and for a non-aqueous secondary battery comprising a compound having a layered structure. As a result of intensive studies on the method for producing the positive electrode active material, it was found that when a mixture containing boron was used as the mixture, it was not necessary to strictly control the atmosphere, and the positive electrode active material could be easily produced simply by firing. And completed the present invention.

  That is, the present invention provides a method for producing a positive electrode active material for a non-aqueous secondary battery comprising a compound having a layered structure, containing lithium, nickel and manganese, wherein the mixture of metal compounds comprises lithium, nickel and manganese. Provided is a production method for firing a mixture containing boron.

  According to the production method of the present invention, a nonaqueous secondary battery positive electrode active material having a layered structure containing lithium, nickel, and manganese can be easily produced, and a nonaqueous secondary battery using the same has a large capacity. Therefore, the present invention is extremely useful industrially.

Next, the present invention will be described in detail.
The production method of the present invention is a method for producing a positive electrode active material for a non-aqueous secondary battery comprising a compound having a layered structure, containing lithium, nickel and manganese, and is a mixture containing boron or a boron compound. It is characterized by firing a mixture containing boron in addition to lithium, nickel and manganese. In the present invention, boron is contained in the metal.

  In order to produce the mixture most simply, a lithium compound, a nickel compound, a manganese compound, and a boron compound may be mixed. Examples of the lithium compound, nickel compound and manganese compound include oxides, hydroxides, oxyhydroxides, carbonates, nitrates, acetates, chlorides, organometallic compounds, and alkoxides. Examples of the boron compound include various borates such as diboron trioxide, boric acid (orthoboric acid), metaboric acid, tetraboric acid, and lithium borate. Of these boron compounds, boric acid (orthoboric acid) is preferred because it is suitable for a dry mixing process. The content of boron or boron compound in the mixture is preferably 0.1 to 10 mol% based on the number of moles of lithium in the mixture. If the amount is less than 0.1 mol%, the formation of a compound having a layered structure may be insufficient, which is not preferable. On the other hand, when the content exceeds 10 mol%, the overvoltage when used in a battery is increased, and the discharge capacity at low temperatures may be reduced.

  Known methods can be used for mixing these metal compounds. Mixing can be performed either in a dry manner or in a wet manner, but the drying step can be omitted and simple dry blending can also be used, because lithium, nickel and manganese are contained and a compound having a layered structure can be obtained. The dry mixing can be performed by a known method generally used in industry such as a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a dry ball mill, and the like.

  As described above, the metal compound mixture containing lithium, nickel, manganese, and boron can be produced by mixing a lithium compound, a nickel compound, a manganese compound, and a boron compound. The production method is not particularly limited. For example, a production method of removing water from an aqueous solution containing lithium, nickel, manganese and boron, an aqueous solution containing nickel and manganese and an alkaline aqueous solution are dropped into water to obtain a precipitate containing nickel and manganese, and the precipitate and lithium A method in which a compound is mixed with a boron compound to produce the compound and the like can also be used.

  After compression-molding the mixture, if necessary, the mixture is kept at a temperature in the range of preferably 600 ° C. or more and 1200 ° C. or less, more preferably 800 ° C. or more and 1100 ° C. or less for 2 to 30 hours, and fired to obtain lithium And a nickel- and manganese-containing positive electrode active material for a non-aqueous secondary battery comprising a compound having a layered structure. At that time, it is preferable to quickly reach the holding temperature as long as the firing container is not damaged. As the firing atmosphere, any of an inert atmosphere such as nitrogen and argon; an oxidizing atmosphere such as air, oxygen, oxygen-containing argon and oxygen-containing nitrogen; and a reducing atmosphere such as hydrogen-containing nitrogen and hydrogen-containing argon are used. However, an oxidizing atmosphere is preferred. After the calcination, the particle size can be adjusted to a predetermined particle size by a known method that is generally used in industry such as a vibration mill, a jet mill, and a dry ball mill.

The positive electrode active material for a non-aqueous secondary battery according to the present invention contains a compound having a layered structure containing lithium, nickel, and manganese, and has a composition formula Li [Ni _(xy) Li _{(1 / 3- 2x / 3) Mn (2/} 3-x / 3-y) Co 2y] O 2 (I)
(0 <x ≦ 0.5, 0 ≦ y ≦ 1/6, x> y)
It is preferable that the compound is a compound identified as a compound represented by the formula: In the composition formula (I), it is preferable that y> 0, that is, Co is contained, since the cycle characteristics are improved. In addition, each site of lithium, nickel, manganese and cobalt is represented by Na, K, Mg, Ca, Sr, Ba, B, Al, Ga, In, Si, Zr, Sn, Ti, V, Cr, Fe, Cu, It may be substituted with Ag, Zn or the like within a range of 50 mol% of each site. In addition, even when oxygen is substituted with halogen, sulfur, or nitrogen within a range of 5 mol% or less, the crystal structure does not change, and the compound is identified as a compound represented by the composition formula (I) in X-ray diffraction. I just need.

Hereinafter, a preferred configuration for producing a battery will be described by taking as an example a case where the positive electrode active material for a nonaqueous secondary battery of the present invention is used for a positive electrode of a lithium secondary battery.
The positive electrode of a lithium secondary battery, which is one of the embodiments of the present invention, contains a positive electrode mixture containing the active material for a non-aqueous secondary battery of the present invention, and further contains a carbonaceous material as a conductive material, a binder, and the like. It can be manufactured by being supported on a current collector.
Further, if necessary, the non-aqueous water of the present invention such as lithium cobaltate, lithium nickelate, spinel lithium manganese oxide, olivine lithium iron phosphate, and those in which some of their constituent elements are replaced by other elements. An active material other than the secondary battery active material may be mixed.

  Examples of the carbonaceous material include natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, or for example, a mixture of artificial graphite and carbon black may be used.

  As the binder, a thermoplastic resin is usually used, and specifically, polyvinylidene fluoride (hereinafter, sometimes referred to as PVDF), polytetrafluoroethylene (hereinafter, sometimes referred to as PTFE), and tetrafluoroethylene. • Propylene hexafluoride / vinylidene fluoride copolymer, propylene hexafluoride / vinylidene fluoride copolymer, ethylene tetrafluoride / perfluorovinyl ether copolymer, and the like. Each of these may be used alone, or two or more of them may be used in combination.

  Further, a fluororesin and a polyolefin resin are used as binders such that the ratio of the fluororesin in the positive electrode mixture is 1 to 10% by weight and the ratio of the polyolefin resin is 0.1 to 2% by weight. When used in combination with the positive electrode active material of the present invention, it is preferable because it has excellent binding properties to the current collector and can further improve safety against external heating.

  As the positive electrode current collector, Al, Ni, stainless steel, or the like can be used, but Al is preferable because it can be easily processed into a thin film and is inexpensive. Examples of a method for supporting the positive electrode mixture on the positive electrode current collector include a method of pressure molding, a method of forming a paste using a solvent or the like, and a method of applying a paste on the positive electrode current collector, followed by drying and pressing to fix the mixture. .

  As the negative electrode of the lithium secondary battery which is one of the embodiments of the present invention, for example, a lithium metal, a lithium alloy, a material capable of doping / dedoping lithium ions, or the like can be used. Materials capable of doping / dedoping lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds; a lower potential than the positive electrode And chalcogen compounds such as oxides and sulfides which can be doped and dedoped with lithium ions.

  The shape of the carbonaceous material may be any of, for example, a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder. A thermoplastic resin can be added as a binder. Examples of the thermoplastic resin include PVDF, polyethylene, and polypropylene.

  Examples of chalcogen compounds such as oxides and sulfides used as the negative electrode include oxides of elements of Groups 13, 14, and 15 of the periodic table. Also in these, a carbonaceous material can be added as a conductive material and a thermoplastic resin can be added as a binder, if necessary.

  As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and is easily processed into a thin film. As a method of supporting the mixture containing the negative electrode active material on the negative electrode current collector, a method of pressure molding, or a method of forming a paste using a solvent or the like, applying the mixture on the negative electrode current collector, drying, and then pressing and fixing is performed. Method.

  Examples of the separator used in the lithium secondary battery that is one of the embodiments of the present invention include, for example, a porous film, a nonwoven fabric, and a woven fabric made of a material such as polyolefin resin such as polyethylene and polypropylene, a fluorine resin, nylon, and aromatic aramid. A material having a form such as cloth can be used. From the viewpoint that the volume energy density of the battery increases and the internal resistance decreases, the thickness of the separator is preferably as thin as possible while maintaining the mechanical strength, and is preferably about 10 to 200 μm.

As the electrolyte used in the lithium secondary battery which is one of the embodiments of the present invention, for example, a nonaqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent, or a known electrolyte selected from solid electrolytes may be used. Can be. Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lithium aliphatic carboxylate, LiAlCl ₄ , LiB (C ₂ O ₄ ) _{2 and the} like can be mentioned.

  Examples of the organic solvent used in the lithium secondary battery according to an embodiment of the present invention include propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and 4-trifluoromethyl-1,3. Carbonates such as dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3 Ethers such as tetrafluoropropyldifluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfolane, dimethyl sulfoxide, 1,3-propane sultone, ethylene sulphite, propylene sulphite; Sulfur-containing compounds such as dimethylsulfite and diethylsulfite, or those obtained by further introducing a fluorine substituent into the above-mentioned organic solvent can be used. Usually, two or more of these are used as a mixture. Among them, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate, or a mixed solvent of a cyclic carbonate and an ether is more preferable.

  The mixed solvent of cyclic carbonate and acyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as an active material of the negative electrode. And a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferred.

In addition, it is preferable to use an electrolyte containing a lithium salt containing fluorine such as LiPF ₆ and / or an organic solvent having a fluorine substituent, since a particularly excellent effect of improving safety can be obtained. The mixed solvent containing dimethyl carbonate and ethers having a fluorine substituent such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether has excellent high-current discharge characteristics. preferable.

As the solid electrolyte, for example, a polymer electrolyte such as a polyethylene oxide polymer compound and a polymer compound containing at least one polyorganosiloxane chain or polyoxyalkylene chain can be used. Further, a so-called gel type in which a non-aqueous electrolyte solution is held in a polymer can also be used. A sulfide electrolyte such as Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—P ₂ S ₅ , Li ₂ S—B ₂ S ₃ , or Li ₂ S—SiS ₂ —Li ₃ PO ₄ ; When an inorganic compound electrolyte containing a sulfide such as Li ₂ S—SiS ₂ —Li ₂ SO ₄ is used, safety may be improved in some cases.

  The shape of the nonaqueous secondary battery of the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a square type, and the like.

  Instead of using a metal hard case also serving as a negative electrode or a positive electrode terminal as a package, a bag-like package made of a laminated sheet containing aluminum or the like may be used.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Unless otherwise specified, preparation of electrodes for a charge / discharge test and a flat battery, and powder X-ray diffraction measurement were performed by the following methods.

(1) Preparation of Flat Battery for Charge / Discharge Test A 1-methyl-2-pyrrolidone (hereinafter, sometimes referred to as NMP) solution of PVDF as a binder is mixed with a mixture of a positive electrode active material and acetylene black as a conductive material. Active material: conductive material: binder = 86: 10: 4 (weight ratio) and kneaded to form a paste. The paste is applied to a # 100 stainless steel mesh serving as a positive electrode current collector, and the paste is applied. Vacuum drying was performed at 8 ° C. for 8 hours to obtain a positive electrode.

In the obtained positive electrode, ethylene carbonate (hereinafter, sometimes referred to as EC), dimethyl carbonate (hereinafter, sometimes referred to as DMC), and ethyl methyl carbonate (hereinafter, sometimes referred to as EMC) are used as electrolytes. LiPF ₆ dissolved in a 30:35:35 (volume ratio) mixed solution at a concentration of 1 mol / liter (hereinafter sometimes referred to as LiPF ₆ / EC + DMC + EMC), a polypropylene porous membrane as a separator, and A flat battery was produced by combining metallic lithium as the negative electrode.

(2) X-Ray Powder Diffraction Measurement The measurement was performed under the following conditions using a RINT type manufactured by Rigaku Corporation.
X-ray: CuKα
Voltage-current: 40kV-140mA
Measurement angle range: 2θ = 10 to 90 °
Slit: DS-1 °, RS-0.3mm, SS-1 °
Step: 0.02 °

Example 1
(1) Synthesis of positive electrode active material First, lithium hydroxide (manufactured by Honjo Chemical Co., Ltd.), nickel hydroxide (manufactured by Tanaka Chemical Laboratory Co., Ltd., nickel content: 61.8% by weight), manganese carbonate (Wako Pure Chemical Industries, Ltd.) company, Ltd., special grade reagent, manganese content 46.4% by weight), boric acid (H ₃ BO _3: manufactured by Wako Pure Chemical Industries, Ltd., guaranteed reagent) is the molar ratio of each element Li: Ni: Mn: B = After weighing so as to be 1.0: 0.5: 0.5: 0.02, they were mixed well in a mortar. The obtained mixed powder is placed in a box furnace, and is baked at 1000 ° C. for 15 hours in the air to obtain a positive electrode active material E1 for a nonaqueous secondary battery (x = 0 in the composition formula (I)). _0.5 , y = 0, which is a compound represented by the composition formula Li [Ni _0.5 Mn _0.5 ] O ₂ ). The result of the powder X-ray diffraction measurement of E1 is shown in FIG. E1 was confirmed to have the same layered structure as reported by Ohzuku et al. (Non-Patent Document 1).

(2) Charge / discharge performance evaluation when a positive electrode active material of a lithium secondary battery was used A flat battery was manufactured using E1, and a charge / discharge test using constant current / constant voltage charge and constant current discharge was performed under the following conditions. .
Maximum charging voltage 4.3V, charging time 8 hours, charging current 0.5mA / cm ²
Minimum discharge voltage 3.0 V, discharge current 0.5 mA / cm ²
FIG. 2 shows the change in discharge capacity. The discharge capacities at the 10th and 20th cycles were 127 and 124 mAh / g, respectively, indicating high capacity and good cycle characteristics.

Comparative Example 1
(1) Synthesis of positive electrode active material A positive electrode active material C1 for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that boric acid was not added. The result of the powder X-ray diffraction measurement of C1 is shown in FIG. In C1, diffraction lines of NiO and Li ₂ MnO ₃ were observed in addition to the same layer structure as reported by Ohzuku et al.

(2) Evaluation of Charge / Discharge Performance When Using Positive Electrode Active Material of Lithium Secondary Battery A flat battery was manufactured using C1, and a charge / discharge test was performed in the same manner as in Example 1.
FIG. 2 shows the change in discharge capacity. The discharge capacity at the 10th and 20th cycles was as low as 84 and 83 mAh / g, respectively.

Example 2
(1) Synthesis of Positive Electrode Active Material First, nickel hydroxide (OM Group, Inc., manufactured by OM Group, Inc., plain grade, nickel content: 61.1% by weight), manganese dioxide (Kojundo Chemical Laboratory Co., Ltd.) (Purity: 99%), cobalt trioxide (manufactured by Seido Chemical Co., Ltd., product name: cobalt oxide HCO, cobalt content: 73.0%). : 0.4: 0.2 and then mixed in a dry ball mill using alumina balls. Then, lithium hydroxide (manufactured by Honjo Chemical Co., Ltd.), the mixture, and boric acid (H ₃ BO ₃ : manufactured by Wako Pure Chemical Industries, Ltd., special grade) were used in a molar ratio of each element of Li: Ni: Mn: Co: B. = 1.0: 0.4: 0.4: 0.2: 0.02, and then mixed well in a mortar. The obtained mixed powder is placed in a box furnace, and calcined at 1000 ° C. for 15 hours in the air, whereby a positive electrode active material E2 for a non-aqueous secondary battery (x = 0 in the composition formula (I)) is obtained. 0.5, y = 0.1, which is a compound represented by the composition formula Li [Ni _0.4 Mn _0.4 Co _0.2 ] O ₂ ). The results of the powder X-ray diffraction measurement of E2 are shown in FIG. E2 was confirmed to have the same layered structure as reported by Ohzuku et al. (Non-Patent Document 1).
(2) Evaluation of Charge / Discharge Performance When Using Positive Electrode Active Material of Lithium Secondary Battery A flat battery was manufactured using E2, and a charge / discharge test was performed in the same manner as in Example 1.
FIG. 4 shows the change in the discharge capacity. The discharge capacities at the 10th and 20th cycles were 139 and 138 mAh / g, respectively, indicating high capacity and good cycle characteristics.

Comparative Example 2
A positive electrode active material C2 for a non-aqueous secondary battery was obtained in the same manner as in Example 2 except that boric acid was not added. The result of the powder X-ray diffraction measurement of C2 is shown in FIG. In C2, diffraction lines of NiO and Li ₂ MnO ₃ were recognized in addition to the same layered structure as reported by Ohzuku et al.

The figure which shows the powder X-ray diffraction measurement result in Example 1 and Comparative Example 1. FIG. 4 is a diagram showing a cycle change of a discharge capacity in Example 1 and Comparative Example 1. The figure which shows the powder X-ray diffraction measurement result in Example 2 and Comparative Example 2. FIG. 9 is a diagram showing a cycle change of a discharge capacity in Example 2.

Claims (5)

  A method for producing a positive electrode active material for a non-aqueous secondary battery comprising a compound having a layered structure, containing lithium, nickel, and manganese, wherein the mixture of metal compounds contains lithium, nickel, manganese, and boron. A production method characterized by firing the mixture. A compound containing lithium, nickel, and manganese and having a layered structure can be _analyzed by X-ray diffraction to _find a composition represented by the composition formula Li [Ni _(xy) Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3-y )} Co _2y ] O ₂ (where x is greater than 0 and 0.5 or less, y is 0 or more and 1/6 or less, and x> y) and identified as a compound having a layered structure. 2. The method according to claim 1, wherein the compound is a compound.   The method according to claim 1, wherein the mixture of metal compounds is a mixture obtained by dry mixing.   A positive electrode active material for a non-aqueous secondary battery obtained by the production method according to claim 1. A non-aqueous secondary battery comprising the positive electrode active material for a non-aqueous secondary battery according to claim 4.

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