JP4747485B2 - Method for producing positive electrode active material for non-aqueous secondary battery - Google Patents

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 the non-aqueous secondary battery.
With the rapid progress of portable and cordless electronic devices, development of non-aqueous secondary batteries that are smaller, lighter, and have a larger capacity than conventional secondary batteries is underway. Among them, lithium secondary batteries have already been put into practical use as power sources for mobile phones, notebook computers, etc., and further studies have been made on increasing the size and increasing output as power sources for automobiles and communication power backup.

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

In such a situation, the composition formula 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 (see, for example, Non-Patent Document 1) and Li [Ni _x Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3)} ] O ₂ (0 ≦ x ≦ 1/2 ), A new compound represented by Li [Ni _x Co _1-2x Mn _x ] O ₂ (0 <x ≦ 1/2) (for example, see Non-Patent Document 2) and the like solve the above-mentioned problems. It has been proposed and attracted attention as a positive electrode active material for non-aqueous secondary batteries. Here, the layered structure refers to a structure whose crystal structure is identified as an α-NaFeO ₂ type by X-ray diffraction (see, for example, Non-Patent Document 3).

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

Chemistry Letters, Chemical Society of Japan, August 2001, p. 744 42nd Battery Symposium Proceedings, November 21, 2001, Lecture number 2I12 Electrochemical and Solid-State Letters, (USA), Electrochemical Society, Inc., December 2001, Vol. 4, p. A200-A203

  The objective of this invention is providing the simple manufacturing method of the positive electrode active material for non-aqueous secondary batteries which consists of a compound which contains lithium, nickel, and manganese and has a layered structure.

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

That is, the present invention relates to a method for producing a positive electrode active material for a non-aqueous secondary battery comprising lithium, nickel and manganese and having a layered structure, wherein a lithium compound, a nickel compound, a manganese compound and boric acid are mixed. The mixture of metal compounds obtained by firing is calcined , and the composition formula Li [Ni _(xy) Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3-y)} Co in X-ray diffraction is obtained. _2y ] O ₂ (where x is greater than 0 and less than or equal to 0.5, y is greater than 0 and less than or equal to 1/6, and x> y), and is identified as a compound having a layered structure. The present invention provides a method for producing a positive electrode active material for a non-aqueous secondary battery comprising producing a positive electrode active material for a non-aqueous secondary battery comprising a compound .

  According to the production method of the present invention, a non-aqueous secondary battery positive electrode active material having a layered structure containing lithium, nickel, and manganese can be easily produced, and a non-aqueous secondary battery using the non-aqueous secondary battery 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 lithium, nickel and manganese and having a layered structure, 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 included 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 preferable 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% with respect to 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. Moreover, when it exceeds 10 mol%, the overvoltage at the time of using for a battery will become large, and there exists a possibility that the discharge capacity in low temperature may fall especially.

  Known methods can be used for mixing these metal compounds. Mixing can be carried out either dry or wet. However, dry mixing is preferred because a compound having a layered structure containing lithium, nickel and manganese can be obtained by simple dry mixing which can omit the drying step. The dry mixing can be carried out by a publicly known method such as a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, or a dry ball mill.

  As described above, a 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 manufacturing method is not particularly limited. For example, a method for removing water from an aqueous solution containing lithium, nickel, manganese and boron, dropping an aqueous solution containing nickel and manganese and an aqueous alkaline solution into water to obtain a precipitate containing nickel and manganese, the precipitate and lithium A method of producing a mixture of a compound and a boron compound can also be used.

  After the mixture is compression-molded as necessary, the mixture is preferably sintered at a temperature range of 600 ° C. or higher and 1200 ° C. or lower, more preferably 800 ° C. or higher and 1100 ° C. or lower for 2 to 30 hours. And a positive electrode active material for a non-aqueous secondary battery comprising a compound having a layered structure containing nickel and manganese. At that time, it is preferable to rapidly reach the holding temperature as long as the baking 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 firing, the particle size can be adjusted to a predetermined particle size by a publicly known method such as a vibration mill, a jet mill, or a dry ball mill.

The positive electrode active material for a non-aqueous secondary battery in the present invention is composed of a compound containing lithium, nickel, and manganese and having a layered structure. In X-ray diffraction, the 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)
If in a represented compound is identified as a compound that having a layered structure is preferable. In the composition formula (I), y> 0, that is, containing Co is preferable because cycle characteristics are improved. Further, each site of lithium, nickel, manganese and cobalt is changed to Na, K, Mg, Ca, Sr, Ba, B, Al, Ga, In, Si, Zr, Sn, Ti, V, Cr, Fe, Cu, Substitution within 50 mol% of each site may be performed with Ag, Zn, or the like. 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 is a compound identified as a compound represented by the composition formula (I) in X-ray diffraction. I just need it.

A preferred configuration for producing a battery will be described below by taking as an example the case where the positive electrode active material for a non-aqueous secondary battery of the present invention is used for the positive electrode of a lithium secondary battery.
A positive electrode of a lithium secondary battery which is one embodiment of the present invention includes a positive electrode mixture containing the active material for a non-aqueous secondary battery of the present invention, and further containing a carbonaceous material, a binder and the like as a conductive material. It can be produced by carrying it on a current collector.
Further, the non-aqueous solution of the present invention, such as lithium cobaltate, lithium nickelate, spinel-type lithium manganese oxide, olivine-type lithium iron phosphate, and some of those constituent elements substituted with other elements as necessary. You may mix active materials other than the active material for secondary batteries.

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

  As the binder, a thermoplastic resin is usually used. Specifically, polyvinylidene fluoride (hereinafter sometimes referred to as PVDF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), and tetrafluoroethylene. -Hexafluoropropylene / vinylidene fluoride copolymer, hexafluoropropylene / vinylidene fluoride copolymer, tetrafluoroethylene / perfluorovinyl ether copolymer, and the like. These may be used alone or in combination of two or more.

  Further, a fluororesin and a polyolefin resin are used as binders, so 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. Use in combination with the positive electrode active material of the invention is preferable because it has excellent binding properties with the current collector and can further improve the 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 is easily processed into a thin film and is inexpensive. Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure molding, or a method of pasting using a solvent or the like, and applying and drying and pressing on the positive electrode current collector. .

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

  The shape of the carbonaceous material may be, 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 the chalcogen compounds such as oxides and sulfides used as the negative electrode include oxides of Group 13, 14, and 15 elements of the periodic table. Also in these cases, 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 it can be easily processed into a thin film. The negative electrode current collector is loaded with a mixture containing the negative electrode active material by pressure molding, or pasted using a solvent, and fixed on the negative electrode current collector by coating, drying and pressing. The method of doing is mentioned.

  Examples of the separator used in the lithium secondary battery according to one embodiment of the present invention include a porous film, a nonwoven fabric, a woven fabric made of a material such as polyolefin resin such as polyethylene and polypropylene, fluororesin, nylon, and aromatic aramid. A material having a form such as cloth can be used. The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced, and is preferably about 10 to 200 μm.

As the electrolyte used in the lithium secondary battery which is one embodiment of the present invention, for example, a known one selected from a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent or a solid electrolyte is used. Can do. Examples of the lithium salt 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 lower aliphatic carboxylic acid lithium salts, 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 which is one embodiment of the present invention include propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3. Carbonates such as -dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3 -Ethers such as tetrafluoropropyl difluoromethyl 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 sulfite, propylene sulfite, Sulfur-containing compounds such as dimethyl sulfite and diethyl sulfite, or those obtained by further introducing a fluorine substituent into the above organic solvent can be used. Usually, two or more of these are mixed and used. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable.

  The mixed solvent of cyclic carbonate and non-cyclic 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 the negative electrode active material. In addition, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable.

Further, in view of particularly excellent safety improving effect is obtained, it is preferable to use an electrolyte containing an organic solvent having a lithium salt and / or fluorine substituent containing fluorine such as LiPF _6. A mixed solvent containing ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate has excellent high-current discharge characteristics, preferable.

As the solid electrolyte, for example, a polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound including at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the nonaqueous electrolyte solution in the polymer | macromolecule can also be used. Sulfide electrolytes 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.

  The shape of the non-aqueous 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.

  Moreover, you may use the bag-shaped package which consists of a laminated sheet etc. which contain aluminum, without using the metal hard case which serves as a negative electrode or a positive electrode terminal as an exterior.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these. Unless otherwise specified, the electrode for charge / discharge test and the production of the flat battery and the powder X-ray diffraction measurement were performed by the following methods.

(1) Production 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 added to a mixture of a positive electrode active material and acetylene black of a conductive material. Active material: conductive material: binder = 86: 10: 4 (weight ratio) is added and kneaded to obtain a paste. The paste is applied to a # 100 stainless steel mesh as a positive electrode current collector and 150 Vacuum drying was performed at 0 ° C. for 8 hours to obtain a positive electrode.

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

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

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

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

Comparative Example 1
(1) Synthesis of positive electrode active material A positive electrode active material C1 for a nonaqueous 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 addition to the layered structure similar to that reported by Ohzuku et al., Diffraction lines of NiO and Li ₂ MnO ₃ were observed in C1.

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

Example 2
(1) Synthesis of positive electrode active material First, nickel hydroxide (OM Group, Inc., plain grade, nickel content 61.1% by weight), manganese dioxide (High Purity Chemical Laboratory, Inc.) Manufactured, purity 99%), tribasic cobalt oxide (manufactured by Shodo Chemical Industry Co., Ltd., product name cobalt oxide HCO, cobalt content 73.0%), the molar ratio of each element is Ni: Mn: Co = 0.4 : Weighed so as to be 0.4: 0.2, and then mixed by a dry ball mill using alumina balls. Thereafter, lithium hydroxide (Honjo Chemical Co., Ltd.), the mixture, boric acid (H ₃ BO ₃ : Wako Pure Chemical Industries, Ltd., reagent special grade) are mixed at a molar ratio of each element of Li: Ni: Mn: Co: B = 1.0: 0.4: 0.4: 0.2: 0.02 was weighed and mixed well in a mortar. The obtained mixed powder was placed in a box furnace and calcined by holding at 1000 ° C. for 15 hours in air, whereby positive electrode active material E2 for non-aqueous secondary battery (x = 0 in composition formula (I)) .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 powder X-ray diffraction measurement result of E2 is shown in FIG. It was confirmed that E2 has the same layered structure as that reported by Ohzuku et al.
(2) Evaluation of Charge / Discharge Performance when Using as Positive Electrode Active Material of Lithium Secondary Battery A flat battery was prepared using E2, and a charge / discharge test was conducted in the same manner as in Example 1.
The change in discharge capacity is shown in FIG. The discharge capacities at the 10th and 20th cycles were 139 and 138 mAh / g, respectively, indicating a high capacity and good cycle characteristics.

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

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

Claims (5)

Obtained by mixing a lithium compound, a nickel compound, a manganese compound, and boric acid in a method for producing a positive electrode active material for a non-aqueous secondary battery comprising a compound containing lithium, nickel, and manganese and having a layered structure by calcining a mixture of metal compounds, in X-ray diffraction, the composition formula _{Li [Ni (xy) Li (} 1 / 3-2x / 3) Mn (2/3-x / 3-y) Co 2y] O 2 ( However, x is greater than 0 and less than or equal to 0.5, y is greater than 0 and less than or equal to 1/6, and x> y.)) A method for producing a positive electrode active material for a non-aqueous secondary battery, comprising producing a positive electrode active material for a secondary battery . The method according to claim 1, wherein the content of boric acid in the mixture is 0.1 to 10 mol% with respect to the number of moles of lithium in the mixture.   The method according to claim 1 or 2, wherein the mixture of metal compounds is a mixture obtained by dry mixing.   A positive electrode active material for a non-aqueous secondary battery, which is 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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