JP2009302044A - Method for manufacturing inorganic particles, positive electrode of secondary battery using the same, and secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inorganic particles excellent in electron conductivity. <P>SOLUTION: A method for manufacturing inorganic particles includes a process (A) of adjusting solution of a raw material compound containing a constituent of the inorganic particles, a process (B) of forming first inorganic particles by spraying and thermolytically processing the solution of the raw material compound, a process (C) of forming composite particles containing a conductive material and inorganic particles by crushing and mixing the first inorganic particles and the conductive material in a wet method by using a planetary ball mill, and a process (D) of calcining the composite particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing inorganic particles excellent in electronic conductivity, a secondary battery positive electrode using the same, and a secondary battery.

In recent years, inorganic particles imparted with conductivity have been used in various fields. For example, for portable electronic devices such as mobile phones and laptop computers, lithium secondary batteries with high weight energy density and large volume energy density are required in order to satisfy the demands for miniaturization and weight reduction and to supply necessary power. The use of is expanding. In this lithium secondary battery, a positive electrode material in which particles such as lithium cobaltate (LiCoO ₂ ) and a conductive material are molded using a binder is used.

If the electronic conductivity of such inorganic particles is improved, it is effective for improving the performance of equipment using the inorganic particles. For example, in the lithium secondary battery using the lithium cobalt oxide (LiCoO ₂ ), the weight energy density and the volume energy density are improved, which is effective for further miniaturization and weight reduction.

Recently, as a substitute material for rare and a compound of expensive cobalt lithium cobaltate, lithium manganate with a spinel crystal structure _{(LiM x Mn 2-x O} 4, M = Mn, Al, Co, Mg, Ti, etc.), lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ) having an olivine type crystal structure are composed of abundant and inexpensive elements as resources, so their use is studied Has been. In particular, secondary batteries used for distributed large-scale power storage such as hybrid electric vehicles and nighttime power storage are required to be low-cost, and therefore, development of these alternative materials is being promoted. However, these alternative materials, for example, lithium iron phosphate, have a problem that only a low amount of electricity can be obtained because of its extremely low electronic conductivity compared to LiCoO ₂ .

  Therefore, in order to obtain a large amount of electricity, there is a demand for a method for improving the electronic conductivity of inorganic particles made of not only lithium cobaltate but also its alternative material such as lithium iron phosphate. Moreover, not only the material used for a lithium secondary battery but improving the electronic conductivity of the material is also effective for improving the performance of a gas sensor, a fuel cell, and a solar cell.

  By the way, in general, as a method for improving the electronic conductivity of a material, there is a method of increasing the reaction area involved in an electrochemical reaction by making the material finer and combining it with a conductive substance. Specifically, a solid phase reaction method, a hydrothermal synthesis method, a sol-gel method, a spray pyrolysis method, and the like have been proposed so far.

  The solid phase reaction method uses starting carbonates and oxides as starting materials, and these are refined and mixed using a ball mill or the like, and then fired in a high-temperature electric furnace to obtain the desired particles. It is a method (refer nonpatent literature 1). The hydrothermal synthesis method is a method in which raw material salt and conductive material are mixed in a liquid phase to produce fine particles in a subcritical or supercritical reaction field, and highly crystalline fine particles can be obtained at a relatively low temperature. (See Non-Patent Document 2). Furthermore, the sol-gel method is a method for producing particles using, for example, a hydrolysis polymerization reaction of a metal alkoxide (see Non-Patent Document 3). In the spray pyrolysis method, raw material salt and conductive material are mixed in a liquid phase and sprayed into a high-temperature reactor to rapidly heat and pyrolyze fine droplets to produce solid particles. This is a method for producing nanostructure ceramic particles in which fine particles having good crystallinity are aggregated by rapidly cooling the solid particles (Patent Document 1, Patent Document 2, Non-Patent Document 4, Non-Patent Document 5, Non-Patent Document 5, (See Patent Document 6).

JP 2004-14340 A JP 2004-259471 A

S. J. Kwon, C. W. Kim, W. T. Jeong, K. S. Lee, J. Power Sources, 137, 93-99 (2004) K. Dokko, K. Shiraishi, K. Kanamura, J. Electrochem. Society, 152, A2199-A2202 (2005) K.F.Hsu, S.Y.Tsay, B.J.Hwang, J. Mater. Chem., 14, 2690-2695 (2004) M.R.Yang, T.H.Teng, S.H.Wu, J. Power Sources, 159, 307-311 (2006) T.H.Teng, M.R.Yang, S.H.Wu, Y.P.Chiang, Solid State Communications, 142, 389-392 (2007) S. L. Bewlay, K. Konstantinov, G. X. Wang ,, S. X. Dou, H. H. Liu, Mater. Lett., 58, 1788-1791 (2004)

  However, in the solid phase reaction method, in order to obtain particles having a uniform composition and a single crystal structure, it is necessary to perform firing for a long time after sufficiently pulverizing the raw material. Therefore, finally, particles having relatively large crystal grains and a small specific surface area can be obtained. Furthermore, since the conductive substance is contained not only on the surface of the material but also inside, the conductivity of the obtained particles is not sufficiently improved.

  In addition, in the hydrothermal synthesis method, even if the raw material is prepared in a stoichiometric composition, the composition of the obtained particles is greatly deviated from the stoichiometric composition. Further, the conductive substance is contained not only on the surface of the particle but also inside. Therefore, there are relatively few conductive substances on the particle surface that contribute to electronic conductivity, and the conductivity of the resulting particles is not sufficiently improved.

  Furthermore, in the sol-gel method, since the raw material solution is prepared and synthesized in a liquid phase, composition control is easy, but the crystallinity of the particles is low, and thus the obtained particles must be fired at a high temperature. Thereby, grain growth of particles occurs. Moreover, since the synthesis process is a multistage operation, continuous synthesis is difficult. Furthermore, the conductive material is contained not only on the particle surface but also inside. Therefore, there are relatively few conductive substances on the particle surface that contribute to electronic conductivity, and the conductivity of the resulting particles is not sufficiently improved.

  Furthermore, since the spray pyrolysis method is a method of adding sucrose (carbon raw material) to the starting material, the obtained particles contain not only the particle surface but also the inside of the conductive material. . Therefore, there are relatively few conductive substances on the particle surface that contribute to electronic conductivity, and the conductivity of the resulting particles is not sufficiently improved. Moreover, in order to completely carbonize the carbon raw material added to the raw material solution, firing at a high temperature is required, which causes a problem of particle growth.

  Then, the subject of this invention solves the above-mentioned problem, and since the inorganic particle and the electroconductive substance are combined, the manufacturing method of the inorganic particle which can obtain the inorganic particle which shows the outstanding electronic conductivity is provided. There is.

  In order to solve the above-mentioned problems, the present inventors have intensively studied to produce amorphous or polycrystalline first inorganic particles having a uniform composition in a short time using a spray pyrolysis method. In addition, the inorganic particles having excellent crystallinity can be obtained by finely pulverizing with a conductive material and simultaneously mixing with a conductive material to synthesize composite particles of the first inorganic particles and the conductive material, followed by firing. It was found that it can be manufactured.

  Based on the above knowledge, the method for producing inorganic particles of the invention according to claim 1 is a method for producing inorganic particles, the step (A) of preparing a solution of a raw material compound containing constituents of the inorganic particles, A step (B) of forming a first inorganic particle by spray pyrolysis treatment of a solution of the raw material compound, and the first inorganic particle and the conductive substance are wet pulverized and mixed using a planetary ball mill to be conductive. It includes a step (C) of forming composite particles containing a substance and inorganic particles, and a step (D) of firing the composite particles.

  In this production method, inorganic particles having excellent electronic conductivity can be produced by a series of steps from the step (A) for preparing the raw material compound solution to the step (D) for firing the composite particles.

  The invention according to claim 2 is that, in the method for producing inorganic particles, the first inorganic particles are formed of an inorganic material including at least one selected from Fe, Mn, Co, and Ni and Li. Features.

  In this method for producing inorganic particles, the first inorganic particles are formed of an inorganic material containing at least one selected from Fe, Mn, Co, and Ni and Li, and are formed of a composite that is combined with a conductive material. Particles can be produced.

The invention according to claim 3 is characterized in that the first inorganic particles are formed of a phosphate containing lithium.
In this method for producing inorganic particles, composite particles containing a lithium-containing phosphate and a conductive substance can be produced.

The invention according to claim 4 is characterized in that the first inorganic particles are formed of a silicate containing lithium.
In this method for producing inorganic particles, composite particles containing a silicate containing lithium and a conductive substance can be produced.

The invention according to claim 5 is characterized in that, in the method for producing inorganic particles, the first inorganic particles are formed of a borate containing lithium.
In this method for producing inorganic particles, composite particles containing a borate containing lithium and a conductive substance can be produced.

The invention according to claim 6 is characterized in that, in the method for producing inorganic particles, the first inorganic particles are particles made of LiFePO ₄ .
In this method for producing inorganic particles, it is possible to produce composite particles having excellent electronic conductivity, including LiFePO ₄ and a conductive substance.

The invention according to claim 7 is characterized in that the first inorganic particles are formed of LiMnPO ₄ .
In this method for producing inorganic particles, composite particles having excellent electronic conductivity including LiMnPO ₄ and a conductive substance can be produced.

The invention according to claim 8 is characterized in that the first inorganic particles are formed by substituting a part of Mn of LiMnPO ₄ with one selected from Mg, Co, Ni, Fe and Zn. .
In this method for producing inorganic particles, electronic conductivity including an inorganic compound formed by replacing a part of Mn of LiMnPO ₄ with one selected from Mg, Co, Ni, Fe, and Zn, and a conductive substance. Composite particles having excellent properties can be produced.

The invention according to claim 9 is characterized in that, in the method for producing inorganic particles, the conductive substance is carbon black.
In this method for producing inorganic particles, inorganic particles having excellent electronic conductivity can be produced by using carbon black as the conductive material.

The invention according to claim 10 is characterized in that in the method for producing inorganic particles, the spray pyrolysis treatment of the step (B) of forming the first inorganic particles is performed at 300 to 800 ° C.
In this method for producing inorganic particles, amorphous or polycrystalline inorganic particles can be produced by performing spray pyrolysis at 300 to 800 ° C.

The invention according to claim 11 is the method for producing inorganic particles, wherein the rotational speed of the rotating base of the planetary ball mill in the step (C) of forming the composite particles is 100 to 1100 times / minute, and the rotational speed of the rotation of the mill pot. Is 200 to 2200 times / minute.
In this method for producing inorganic particles, the rotational speed of the rotating base of the planetary ball mill in the step (C) of forming the composite particles is 100 to 1100 times / minute, and the rotational speed of the rotation of the mill pot is 200 to 2200 times / minute. Thus, composite particles in which the first inorganic particles and the conductive material are combined can be obtained.

The invention according to claim 12 is characterized in that, in the method for producing inorganic particles, the ball diameter of the planetary ball mill in the step (C) of forming the composite particles is 100 to 10,000 μm.
In this inorganic particle manufacturing method, the ball diameter (diameter) of the planetary ball mill in the step (C) of forming the composite particle is 100 to 10,000 μm, whereby the first inorganic particle and the conductive material are combined. Composite particles can be obtained.

The invention according to claim 13 is characterized in that, in the method for producing inorganic particles, the firing temperature in the step (D) of firing the composite particles is 400 to 1200 ° C.
In this method for producing inorganic particles, the amorphous inorganic particles synthesized in the step (C) for forming the composite particles are crystallized by firing at a temperature of 400 to 1200 ° C. The crystallinity of the inorganic particles can be improved, and further, undecomposed substances can be removed.

The invention according to claim 14 is characterized in that, in the secondary battery positive electrode, inorganic particles produced by the production method according to any one of claims 1 to 13 are used.
By using the inorganic particles produced by the production method, a secondary battery positive electrode having a high capacity and excellent high-speed charge / discharge characteristics can be obtained.

The invention according to claim 15 is the secondary battery, wherein the secondary battery positive electrode according to claim 14 is used.
By using the secondary battery positive electrode, a secondary battery having a high capacity and excellent high-speed charge / discharge characteristics can be obtained.

According to the method for producing inorganic particles of the present invention, the material comprising the first inorganic particles and the conductive substance, and the material constituting the first inorganic particles is refined into particles of 100 nanometers or less, and they are electrically conductive. Composite particles excellent in electronic conductivity mixed uniformly with the substance can be obtained. In particular, the method of the present invention improves the electronic conductivity of particles made of LiFePO ₄ composed of abundant and inexpensive elements instead of lithium cobaltate (LiCoO ₂ ), and has high capacity and high-speed charge / discharge characteristics. Can be obtained.

It is the schematic which shows a spray pyrolysis apparatus. (A) is a conceptual diagram explaining a planetary ball mill, (b) is a conceptual diagram explaining operation | movement of the ground material and ball | bowl in the mill pot of a planetary ball mill. It is a powder X-ray-diffraction spectrum which shows the identification result of a crystal phase. 2 is a SEM photograph of inorganic particles obtained in Example 1. 4 is a SEM photograph of inorganic particles obtained in Comparative Example 1. 4 is a SEM photograph of inorganic particles obtained in Comparative Example 2. 2 is a TEM photograph of inorganic particles obtained in Example 1. FIG. 4 is a TEM photograph of inorganic particles obtained in Comparative Example 2. It is a figure which shows the initial stage charging / discharging curve of the charging / discharging cycle test in Example 1 and Comparative Example 1. FIG. It is a figure which shows the cycling characteristics in the various charging / discharging speed | velocity | rate in Example 1. FIG. It is a powder X-ray-diffraction spectrum which shows the identification result of a crystal phase. 4 is a SEM photograph of inorganic particles obtained in Example 3. 4 is a SEM photograph of inorganic particles obtained in Comparative Example 3. 4 is a TEM photograph of inorganic particles obtained in Example 3. It is a figure which shows the initial stage charge / discharge curve of the charging / discharging cycle test in Example 3 and Comparative Example 3. It is a figure which shows the cycle characteristic in the various charging / discharging speed | velocity in Example 3. FIG. It is a powder X-ray-diffraction spectrum which shows the identification result of a crystal phase. It is a powder X-ray-diffraction spectrum which shows the identification result of a crystal phase. It is a powder X-ray-diffraction spectrum which shows the identification result of a crystal phase. It is a figure which shows the initial stage charge / discharge curve of the charging / discharging cycle test in Example 13. It is a figure which shows the cycle characteristic in the charging / discharging speed | velocity in Examples 12-15. 4 is a SEM photograph of inorganic particles obtained in Example 4. 7 is a SEM photograph of inorganic particles obtained in Example 6.

Hereinafter, the method for producing inorganic particles excellent in electronic conductivity of the present invention (hereinafter referred to as “method of the present invention”) will be described in detail.
The method of the present invention includes a step (A) of preparing a solution of a raw material compound (hereinafter referred to as “raw material solution”), a step (B) of forming first inorganic particles, the first inorganic particles and a conductive substance. A step (C) of forming a composite particle containing a conductive substance and inorganic particles by wet pulverization and mixing using a planetary ball mill, and a step (D) of firing the composite particle It is.

The inorganic particles produced by the method of the present invention are particles composed of an inorganic compound such as an oxide, sulfide, nitride or carbide containing one or more metal atoms or other elements. Specific examples of the inorganic compound include LiMn ₂ O ₄ , LiCoO ₂ , LiM _x Co _1-x O ₂ (M = Ni, Mn), LiMPO ₄ (M = Fe, Mn, Co, Ni), LiM ′ _x M “ _1-x PO ₄ (M ′, M” = Fe, Mn, Co, Ni, Mg, Zn, V), LiMBO ₃ (M = Fe, Mn, Co, Ni), Li ₂ MB ₂ O ₅ (M = Fe, Mn, Co, Ni), LiM ′ _x M ″ _1-x BO ₃ (M ′, M ″ = Mn, Co, Ni, Fe, Mg, Zn, V), Li ₂ M ′ _x M ″ _{1 -x SiO 4 (M ', M} "= Mn, Co, Ni, Fe, Mg, Zn, V), Li 2 M' x M" 1-x TiO 4 (M ', M "= Mn, Co, Ni , Fe, Mg, Zn, V), LiNiVO ₄ , LiCo _y Ni _1-y VO ₄ , LiM _x Mn _2−x O ₄ ( _{M = Co, Cr, Al,} Mg, Zn, Ni, Fe, V), LiNi x Mn 1-x O 2, LiNi 1-x-y Co x M y O 2 (M = Mn, Mg, Al, Ga _{, Fe), Li [Ni x} Co 1-2x Mn x] O 2, MnV 2 O 6, Li 4 Ti 5 O 12, CuO, CoO, Gd 2 O 3, Al 2 O 3, ZnO, ZrO 2, TiO ₂ , SnO ₂ , CeO ₂ , SiO ₂ , MgO, Fe ₂ O ₃ , NiO, Y ₂ O ₃ , PdO, PbO, Co ₃ O ₄ , Mn ₃ O ₄ , BaO, PuO, V ₂ O ₅ , MoO _{3 , WO 3, Eu 2 O 3} , YBa 2 Cu 3 O 7-x, YBa 2 Cu 4 O 8, La-Sr-Cu-O, Tl-Ca-BaCu-O, (Bi, Pb) -Sr-Ca _{-Cu-O, MRuO 3 (M} = Sr, _{a), M 2 Ru 2 O} 7-x (M = Bi, Pb, Y, Eu, Gd, Tb, Dy, Ho, Er, Tm), Bi 2 CaSr 2 Cu 2 O x, Bi 2 Ca 2 Sr 2 _{Cu 3 O x, ZnO-TiO} 2, ZrO 2 -SiO 2, MgAl 2 O 4, Co 2 Mo 3 O 8, CoMoO 4, CoAl 2 O 4, CuCr 2 O 4, PbCr 2 O 4, Pb (Zr, Ti) O ₃ , La _x Sr _1-x MnO ₃ , Ln _x Sr _1-x CoO ₃ (Ln = La, Nd, Gd), Ln _x Sr _1-x Co _y Fe _1-y O _3−δ (Ln) _{= La, Sm, Nd, Gd} ), La x Sr 1-x Ga y Mg 1-y O 3δ, Mullite (3Al 2 O 3 -2SiO 2), Mn-Zn ferrite, BaFe 12 O 19, Ba 0.86 _{a 0.14 TiO 3, BaTiO 3,} BaZn 1/3 Nb 2/3 O 3, PbMg 1/3 Nb 2/3 O 3, SrTiO 3, PbTiO 3, Zn 2 SiO 4, Zr x Sn 1-x TiO _{4, NiO-SDC (samaria-} doped ceria), NiO-CGO (gadorinia-doped ceria), Gd 3 Fe 5 O 12, BaFe 12 O 19, NiFe 2 O 4, SrTiO 3, LaAlO 3, Eu-doped Y 2 _{O 3, Eu-doped (YGd} ) 2 O 3, CdWO 4, ZnWO 4, CaWO 4, SrWO 4, LaPO 4, Ce-doped LaPO 4, Eu-doped LaPO 4, Ce-Tb-doped LaPO 4, Eu- _{doped (Gd x Y 1-x} ) _{O 3, Y 3 Al 5 O} 12, YAlO 3, Y 4 Al 2 O 9, Y 2 SiO 5, oxides such as _{Ce 1-x Tb x MgAl 11} O 19; ZnS, CdS, CuS, CuInS 2, CaLa sulfides such as _{2 S 4; Si 3 N 4} , BN, nitrides such as AlN; including carbides such as SiC and the like. Among these, the method of the present invention is performed by using LiFePO ₄ , LiM ′ _x M ″ _1-x PO ₄ (M ′, M ″ = Fe, Mn, Co, Ni, Mg, Zn, V), Li ₂ M ′ _x. M ″ _1-x SiO ₄ (M ′, M ″ = Mn, Co, Ni, Fe, Mg, Zn, V), Li ₂ M ′ _x M ″ _1-x TiO ₄ (M ′, M ″ = Mn, Co, Ni, Fe, Mg, Zn, V), LiMBO ₃ (M = Fe, Mn, Co, Ni), Li ₂ MB ₂ O ₅ (M = Fe, Mn, Co, Ni), LiM ′ _x M ″ _1-x BO ₃ (M ′, M ″ = Mn, Co, Ni, Fe, Mg, Zn, V), LiMn ₂ O ₄ , LiM _x Mn _2-x O ₄ (M = Co, Cr, Al, Mg) _{, Zn, Ni, Fe, V} ), LiNi x Mn 1-x O 2, LiNi 1-x-y Co x M y O 2 (M = Mn, M , _{Al, Ga, Fe),} and applied to the manufacture of _{Li [Ni x Co 1-2x Mn x} ] O 2, MnV 2 O 6, Li 4 Ti 5 O of ₁₂ like inorganic particles, excellent electron conductivity Inorganic particles can be produced. In particular, particles made of LiFePO ₄ having excellent electronic conductivity obtained by the method of the present invention are useful as a positive electrode material for a lithium secondary battery in place of LiCoO ₂ which is a rare and expensive cobalt compound.

  In the method of the present invention, the step (A) of preparing the raw material solution is a step of dissolving the raw material compound containing the constituent components of the first inorganic particles in a solvent.

  The raw material compound is not particularly limited as long as it contains the constituent components of the first inorganic particles. For example, lithium (Li), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), iron (Fe), aluminum (Al), magnesium (Mg), which are constituents of the compounds exemplified above ), Nitrates such as zinc (Zn), vanadium (V), titanium (Ti), yttrium (Y), organic acid salts such as acetate and formate, chlorides, oxychlorides, hydrates, etc. Can do. In addition, metal organic compounds such as metal alkoxide, metal acetylacetonate, and metal carboxylate, and metal complexes having various ligands can also be used. The composition ratio in the raw material solution is adjusted so that these raw material compounds have the stoichiometric ratio of the constituent components in the first inorganic particles.

  The concentration of the raw material compound in the raw material solution is preferably such that the total of the constituent components of the first inorganic particles in the raw material compound is 0.001 mol / L to 12.0 mol / L, and further 0.1 mol / L to 6 mol / L is preferable. When the total of the constituent components is 0.001 mol / L or less, it takes a long time to synthesize a certain amount of the first inorganic particles, and when it exceeds 12.0 mol / L, the raw material salt may not dissolve in the raw material solution. is there.

  In addition to the raw material compound, the raw material solution may contain a degradable additive in order to obtain finer particles in the spray pyrolysis treatment of the next step (B) for forming the first inorganic particles. . Examples of degradable additives include organic acids such as citric acid, lactic acid, succinic acid, malic acid, glycolic acid, and ascorbic acid, ammonium such as ammonium chloride, ammonium acetate, ammonium formate, ammonium nitrate, ammonium carbonate, ammonium sulfate, and urea. Compounds can be used. When adding a degradable additive to a raw material solution, the concentration of the degradable additive is preferably about 1 to 100 times the total concentration of the constituents contained in the raw material solution, and more preferably about 2 to 50 times. It is desirable that

  The solvent is not particularly limited as long as it dissolves the raw material compound and the degradable additive. For example, water or alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, ethylene oxide, triethanolamine, Nonaqueous solvents such as xylene and acetone can be used.

  Next, the step (B) of forming the first inorganic particles is a step of forming the first inorganic particles by spray pyrolysis treatment of the raw material solution prepared in the step (A) of preparing the raw material solution. In the present invention, the spray pyrolysis treatment means that the raw material solution is sprayed as fine droplets in an atmosphere maintained at a temperature higher than the temperature at which the thermal decomposition of the raw material compound occurs to evaporate the solvent and thermally decompose the raw material compound. It is the process which forms fine particle | grains comprised with the inorganic substance which consists of the said structural component while performing. By this spray pyrolysis, fine particles having excellent composition uniformity on the atomic scale and uniform dispersibility of trace component elements and excellent dispersibility can be obtained. The method for spraying the raw material solution as fine droplets is not particularly limited, and examples thereof include a method using an ultrasonic sprayer, a method using a two-fluid nozzle and a pressure nozzle, and a method using a rotating disk. The thermal decomposition can be performed, for example, by heating the sprayed droplets by gas burner heating, electric resistance heating, microwave heating, laser heating, or the like.

  In general, the diameter of the droplet in spraying the raw material solution is preferably about 0.1 to 500 μm. This has an advantage that first inorganic particles in which nano-sized primary particles are aggregated can be obtained.

Moreover, as a thermal decomposition temperature, although depending on the composition of the 1st inorganic particle to manufacture, the range of 300-800 degreeC is preferable. By making the thermal decomposition temperature 300 ° C. or higher, the raw material salt and additives can be decomposed to obtain amorphous or polycrystalline first inorganic particles, and by setting the thermal decomposition temperature to 800 ° C. or lower, There is an advantage that further thermal decomposition of the obtained first inorganic particles can be suppressed. _{Further, LiMPO 4 (M = Fe,} Mn) when manufacturing the first inorganic particles consisting of is preferably in the range of 400 to 800 ° C..

  Further, as the atmosphere in the spray pyrolysis treatment, air, oxygen, hydrogen, or a mixed gas of these and an inert gas such as nitrogen, argon, helium can be used.

  The spray pyrolysis time is adjusted according to the composition of the first inorganic particles to be produced. Usually, it is preferably 5 seconds or more, and more preferably 20 seconds or more. By setting it to 5 seconds or more, there is an advantage that the raw material salt and the additive are decomposed and finally the first inorganic particles as the target object of amorphous or polycrystalline substance can be obtained.

Next, the step (B) of forming the first inorganic particles using the spray pyrolysis apparatus MP shown in FIG. 1 will be specifically described.
The spray pyrolysis apparatus MP shown in FIG. 1 has, as a droplet generator, an ultrasonic sprayer 5 for generating droplets of a raw material solution in a mist state, and an ultrasonic sprayer that stores the raw material solution stored in the raw material solution tank 7. And a constant temperature water circulation system including a constant temperature bath 9, a refrigerator 10 and a pump 8.

  The ultrasonic atomizer 5 includes a gas cylinder 1 for supplying an atmospheric gas (carrier gas) and a packed column 2 in order to introduce droplets generated by the ultrasonic atomizer 5 into a thermal decomposition reactor 11 described later. A droplet introducing means comprising a filter 3 and a flow meter 4 is connected. A gas thermometer T11 for measuring the temperature of the atmospheric gas introduced into the ultrasonic sprayer 5 is disposed in the middle of the flow path from the filter 3 to the flow meter 4.

  Further, the spray pyrolysis apparatus MP has a pyrolysis reaction furnace 11 as a pyrolysis section, and this pyrolysis reaction furnace 11 is a cylindrical space for preheating the mist droplets introduced from the ultrasonic sprayer 5. And a reaction tube 112 having a cylindrical space connected to the preheating tube 111 and performing thermal decomposition. Around the preheating tube 111 and the reaction tube 112, a heater 12 for adjusting the temperature in the preheating tube 111 and the reaction tube 112 is disposed. Further, temperature controllers TC1, TC2, TC3, TC4, TC5, and TC6 for measuring and controlling the temperature of each part are arranged in the preheating tube 111 and the reaction tube 112. Thereby, the temperature inside the preheating tube 111 and the reaction tube 112 is adjusted appropriately. The mist droplets introduced from the ultrasonic sprayer 5 are introduced into the preheating tube 111 and the reaction tube 112, and the solvent evaporates from the surface of the droplets in the section of the preheating tube 111, so that the solute is precipitated. The first inorganic particles are generated through the pyrolysis process in the section of the reaction tube 112 through the drying process.

  At this time, the temperature in the preheating tube 111 and the reaction tube 112 is adjusted to about 300 ° C to 800 ° C. Further, the atmospheric gas containing droplets flowing through the preheating tube 111 and the reaction tube 112 is usually adjusted to a flow rate of about 0.5 L / min to 4.0 L / min. This flow rate can be adjusted by adjusting the flow rate of the atmospheric gas from the gas cylinder 1. The TC 7 is a temperature controller for measuring and controlling the temperature at the outlet of the reaction tube 112 of the pyrolysis reactor 11.

  A diffusion electrostatic collector 14 is disposed at the outlet of the reaction tube 112 of the pyrolysis reactor 11. The diffusion type electrostatic collector 14 removes acidic exhaust gas such as NOx contained in the exhaust gas derived from the direct current voltage power source 13 for applying a direct current voltage and the reaction tube 112 of the thermal decomposition reactor 11. For this purpose, a cooling trap 15, a filter 16 for collecting uncollected particles, and a vacuum pump 18 are connected. The TC 8 is a temperature controller for measuring and controlling the temperature in the diffusion type electrostatic collector 14. A flow meter 17 for measuring the flow rate of the exhaust gas derived from the filter 16 is disposed, and a gas thermometer T12 for measuring the temperature of the exhaust gas derived from the filter 16 is disposed. In this diffusion type electrostatic collector 14, first inorganic particles generated by pyrolysis of the dry particles in the reaction tube 112 of the pyrolysis reactor 11 can be obtained.

  In the production of the first inorganic particles in the spray pyrolysis apparatus MP, first, the composition ratio, concentration, etc. of the constituent components are prepared by the step (A) of preparing the raw material solution, and the raw material solution stored in the raw material solution tank 7 is used. Then, it is supplied to the ultrasonic sprayer 5 by the microtube pump 6. And the raw material solution supplied to the ultrasonic sprayer 5 is formed in a mist-like droplet. The mist-like droplets are introduced into the thermal decomposition reactor 11 together with the atmospheric gas by droplet introducing means including the gas cylinder 1, the packed column 2, the filter 3, and the flow meter 4. The droplets introduced into the pyrolysis reactor 11 are evaporated, crystallized, dried and pyrolyzed through the preheating tube 111 and the reaction tube 112 to generate first inorganic particles. The generated first inorganic particles are collected by the diffusion electrostatic collector 14. Thereby, the 1st inorganic particle which consists of a component of a raw material compound is obtained.

  In the method of the present invention, in the step (C) of forming the composite particles, the first inorganic particles obtained in the step (B) of forming the first inorganic particles and the conductive material are used using a planetary ball mill. This is a step of forming composite particles including a conductive substance and inorganic particles by pulverizing and mixing in a wet process.

  FIG. 2A shows a schematic diagram of a planetary ball mill used in the step (C) of forming composite particles. A planetary ball mill 21 shown in FIG. 2A includes a rotating base 22 that rotates in the direction of arrow A, and a plurality of rotating bases 22 that are rotatably supported by bearings (not shown) on the rotating base 22 and that rotate in the direction of arrow B. It is an apparatus having a mill pot 23. In this planetary ball mill 21, in each mill pot 23, the first inorganic particles 25 obtained in the step (B) of forming the first inorganic particles, a conductive material, a wet medium, and a ball 24 as a grinding medium, Then, the mill pot 23 is supported on the turntable 22. Then, by meshing the sun gear provided on the central axis of the turntable 22 and the planetary gear provided on the rotary shaft of each mill pot 23, each mill pot 23 revolves around the central axis in the direction of arrow A. Rotates around the rotation axis in the direction of arrow B. As a result, in each mill pot 23, as shown in FIG. 2B, the first inorganic particles 25 and the conductive material collide with the balls 24 and are pulverized while being subjected to centrifugal force due to revolution and rotation. Received and mixed. Then, the first inorganic particles 25 obtained in the step (B) of forming the first inorganic particles are pulverized to become finer and mixed with a conductive substance to form composite particles.

  The wet pulverization and mixing by the planetary ball mill can be performed at a rotation speed of the turntable 22 of about 100 to 1100 times / minute and a rotation speed of the mill pot 23 of about 200 to 2200 times / minute. Since composite particles in which particles and a conductive material are combined can be obtained, the rotational speed of the turntable 22 is 600 to 1100 times / minute, and the rotational speed of the mill pot rotation is 1200 to 2200 times / minute. Is preferred. Moreover, the ratio of the total volume of the first inorganic particles and the conductive material / the volume of the balls 24 charged in each mill pot 23 is usually adjusted to about 0.2 to 3. The ratio of the total mass of the first inorganic particles and the conductive material / the mass of the balls 24 charged in each mill pot 23 is usually adjusted to about 0.0125 to 0.1. Further, examples of the wet medium include water, alcohol-based media such as methanol and ethanol, water and mixed media thereof, N-methyl-2pyrrolidone, methyl ethyl ketone, toluene, ethylene glycol, and the like. It can be used at a ratio of 1: 1 to 1:50 with respect to the volume added with 24. Further, as the balls 24 used as the grinding medium, zirconia balls, alumina balls, silicon nitride balls, etc. are used, and those having a spherical diameter of about 100 to 10,000 μm are used. The spherical diameter of the ball 24 is preferably about 0.5 to 1 mm.

  Examples of the conductive substance used include carbon black such as acetylene black and ketjen black, platinum, copper, and a conductive polymer. Among these, carbon black is preferable because it is inexpensive and has good electronic conductivity. The conductive substance and the first inorganic particles can be used at a ratio of 1/99 to 50/50 in terms of the mass ratio of conductive substance / first inorganic particles.

  In the step (C) of forming the composite particles, the wet pulverization / mixing by the planetary ball mill is usually performed for about 0.2 to 36 hours, thereby combining the first inorganic particles and the conductive material. Body particles can be obtained.

Next, in the method of the present invention, a step (D) of firing the composite particles obtained in the step (C) of forming composite particles is performed.
The firing in the step (D) of firing the composite particles is not particularly limited, and the composite particles or aggregates obtained in the step (C) of forming the composite particles are usually about 400 to 1200 ° C. Preferably, it is carried out by firing at a firing temperature of about 500 to 900 ° C. for about 0.5 to 8 hours in a mixed gas atmosphere of air, oxygen, hydrogen or an inert gas such as nitrogen, argon or helium. it can. The heating rate and cooling rate during firing are usually adjusted to about 1 to 10 ° C./min.

The firing furnace used for firing is not particularly limited, and for example, an electric resistance heating furnace or a microwave firing furnace can be used.
The inorganic particles after firing have a particle size of about 0.01 to 20 μm.

Since the inorganic particles produced by the method of the present invention are excellent in electronic conductivity, they can be suitably used for various applications. In particular, the LiFePO ₄ particles combined with carbon produced by the method of the present invention are excellent in electronic conductivity, and are composed of abundant and inexpensive elements as resources, so they are rare and expensive cobalt compounds. It is useful as a positive electrode material for a lithium secondary battery in place of some lithium cobalt oxide.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples.

(Example 1)
Preparation of raw material solution Lithium formate monohydrate, iron chloride tetrahydrate, and phosphoric acid were used as raw material salts. These were dissolved in distilled water at a stoichiometric ratio (Li: Fe: P = 1: 1: 1) so that the total number of moles (Li + Fe + P) was 0.6 mol / L. In addition, 0.05 mol / L hydrochloric acid was added for pH adjustment.

Production of First Inorganic Particles First inorganic particles were produced using a spray pyrolysis apparatus MP having a structure shown in FIG.
First, the raw material solution stored in the raw material solution tank 7 was supplied to the ultrasonic sprayer 5 (medical ultrasonic nebulizer (manufactured by OMRON Corporation, NE-U12 type)) by the microtube pump 6. And the raw material solution supplied to the ultrasonic sprayer 5 was formed into the mist-like droplet with the ultrasonic wave of frequency 1.7MHz. The generated mist-like droplets are introduced into the ultrasonic sprayer 5 by a droplet introducing means including a gas cylinder 1, a packed column 2, a filter 3, and a flow meter 4, and the amount is 1 L / min (room temperature). It was accompanied by nitrogen gas and introduced into the pyrolysis reactor 11. At this time, the supply speed of the mist droplets to the pyrolysis reactor 11 was 30 ml / h. The pyrolysis reactor 11 has a pyrolysis reaction section (reaction tube 112) set at 500 ° C. and having an inner diameter of 20 mm and a length of 1105 mm. The droplets supplied to the thermal decomposition reactor 11 are subjected to a preheating tube 111 in which the solvent evaporates from the droplet surface, and a solute deposition and drying process is performed in the section of the reaction tube 112 through a pyrolysis process. Finally, the first inorganic particles made of the target LiFePO ₄ were obtained at the outlet of the thermal decomposition reactor 11. The generated first inorganic particles were collected in the diffusion type electrostatic collector 14. The particles were collected at an applied voltage of 9 kV. The exhaust gas was cooled with liquid nitrogen, and the acidic exhaust gas contained therein was removed, and then discharged out of the system.

Production and firing of composite particles The first inorganic particles (LiFePO ₄ ) were wet micronized using a planetary ball mill and composited with carbon. As the carbon, acetylene black was used. In a planetary ball mill, a zirconia pot is used, and 40 g of zirconia balls, 1.0 g of a sample (LiFePO ₄ / acetylene black = 90/10 mass ratio), and 2 ml of ethanol as a wet medium are rotated. The mixture was pulverized and mixed wet for several hours at several 800 times / minute and 1600 rotations / minute of the mill pot to obtain composite fine particles in which LiFePO ₄ and acetylene black were combined. Further, the composite fine particles were baked at 500 ° C. for 4 hours in a nitrogen atmosphere containing 3% hydrogen to obtain inorganic particles in which LiFePO ₄ and acetylene black were combined.

(Example 2)
First inorganic particles made of LiFePO ₄ precursor are produced by spray pyrolysis under the same raw material solution and the same conditions as in Example 1, and further combined with carbon under the same conditions, and at 600 ° C. for 4 hours. By firing, LiFePO ₄ composite particles having a single-phase olivine structure were obtained.

(Comparative Example 1)
A LiFePO ₄ precursor was synthesized by spray pyrolysis under the same raw material solution and the same conditions as in Example 1, and further calcined under the same conditions to obtain LiFePO ₄ particles having a single-phase olivine structure.

(Comparative Example 2)
First inorganic particles were synthesized by spray pyrolysis under the same raw material solution and the same conditions as in Example 1, and subjected to primary firing at 600 ° C. for 4 hours in a nitrogen gas atmosphere containing 3% hydrogen. LiFePO ₄ having a phase olivine structure was obtained. Further, in a planetary ball mill, a zirconia pot was used, and 40 g of zirconia balls and 1.5 g of a sample (a mass ratio of LiFePO ₄ / acetylene black = 90/10) were added thereto, and the rotational speed of the turntable was 400 times / minute, Grinding and coating were carried out in a dry process at a mill pot rotational speed of 800 times / minute for 12 hours to obtain LiFePO ₄ fine particles coated with carbon. Furthermore, it was subjected to secondary firing at 500 ° C. for 4 hours in a nitrogen atmosphere containing 3% hydrogen to obtain LiFePO ₄ inorganic particles whose surfaces were coated with carbon.

  With respect to the fine particles obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the structure of the fine particles, the measurement of the specific surface area and the identification of the crystal phase were performed according to the following method. As a positive electrode active material, a charge / discharge cycle test of a lithium secondary battery was performed.

Structure of composite particle The structure of the composite particle was observed using a field emission scanning electron microscope (FE-SEM, manufactured by Hitachi, S-800) and a transmission electron microscope (TEM, manufactured by JEOL, JEM-200CX). did.

Specific surface area BET method (manufactured by Shimadzu Corporation, Flowsorb II2300) was used. For the measurement, a particle sample of 150 to 250 mg dried at 200 ° C. for about 30 minutes was used. The measurement was performed 3 to 5 times, and the average value at the time of desorption was used.

Identification of Crystal Phase The crystal phase of the fine particles was identified using a powder X-ray diffractometer (manufactured by Philips, PW1700 system). The measurement was performed under the following conditions for a particle sample of about 50 to 80 mg using CuKα1 and CuKα2 wires.
Voltage: 40 kV
Current: 30 mA
Time constant: 0.5 s
Scanning speed: 0.04 degrees / s
Measurement range: 4 degrees ≤ 2θ ≤ 70 degrees

Evaluation of lithium secondary battery Using the fine particles obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2, a positive electrode of a lithium secondary battery was produced. First, fine particles obtained in each example as an active material, acetylene black as a conductive material, polyvinylidene fluoride (PVDF, KF polymer # 1100) as a binder (binder) in 80% by mass (composite carbon). Excluded): 20 (including complexed carbon): Dispersed and mixed in an NMP (N-methyl-2-pyrrolidinone) solution at a ratio of 10 and applied to an aluminum foil by a doctor blade method to form a film. This was dried and rolled to obtain a positive electrode.

Using the positive electrode of the obtained lithium secondary battery, CR2032-type coin cells, which are lithium secondary batteries, were respectively produced. At this time, metallic lithium is used for the negative electrode, and EC (ethylene carbonate) and DEC (diethyl carbonate) are mixed in a ratio of 1: 1 (volume basis) to the electrolytic solution, and LiClO ₄ is dissolved to 1 mol / L. The separator was made of Celgard 2400 # as the separator, and stainless steel was used as the positive electrode current collector plate (positive electrode can) and negative electrode current collector plate (negative electrode terminal).
The material of the secondary battery negative electrode is not limited to metallic lithium, and a carbon material, Li alloy, Li ₄ Ti ₅ O ₁₂ or the like may be used. Moreover, the substance which comprises electrolyte solution is not limited to EC (ethylene carbonate) and DEC (diethyl carbonate), You may use another carbonate, fatty acid ester, a nitrogen compound, sulfide, an aprotic solvent, etc. Further, a solid electrolyte may be used instead of the electrolytic solution and the separator.

  About the obtained lithium secondary battery, charging / discharging was repeated with various charging / discharging speed | rates, and the discharge capacity was measured.

(Results and discussion on LiFePO ₄ )
With respect to LiFePO ₄ , the specific surface area measurement results for the above-described Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below, and the results of crystal phase identification are shown in FIG. Moreover, the SEM photograph of the composite particle obtained in Example 1 is shown in FIG. 4, that of Comparative Example 1 is shown in FIG. 5, and that of Comparative Example 2 is shown in FIG. Regarding the TEM photographs, those of Example 1 are shown in FIG. 7, and those of Comparative Example 2 are shown in FIG. Furthermore, FIG. 9 shows the initial charge / discharge curves of the charge / discharge cycle tests of Example 1 and Comparative Example 1, and FIG. 10 shows the cycle characteristics of Example 1 at various charge / discharge rates.

First, from the identification result of the crystal phase by powder X-ray diffraction shown in FIG. 3, in any case of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, lithium iron phosphate having a single-phase olivine structure It can be seen that LiFePO ₄ could be synthesized.

  Further, when these particle diameters were examined using a scanning electron microscope (SEM), as is apparent from FIGS. 4, 5, and 6, in Example 1, many particles of about 100 nm or less are observed. In Comparative Example 1, particles of about 1 to 3 μm are formed, and in Comparative Example 2, particles of about 400 nm or more form single or aggregates.

  Further, Example 1 and Comparative Example 2 were examined in more detail using a transmission electron microscope (TEM). As is apparent from FIGS. 7 and 8, in Example 1, the particle diameter of the primary particles was 20 nm. It was revealed to be in the range of ˜90 nm. On the other hand, in Comparative Example 2, it was revealed that the particle diameter of the primary particles was 400 nm or more. Thus, it became clear that the size of the primary particles is greatly different between the example and the comparative example.

Furthermore, measurement of the specific surface area of these samples, as shown in Table 1, 66.3m ² / g in Example 1, in contrast to Example 2, 64.5m ² / g, Comparative Example 1 2 9.9 m ² / g and 46.5 m ² / g in Comparative Example 2, and Examples 1 and 2 showed a very large specific surface area by wet grinding and compounding with carbon. From this result, Examples 1 and 2 are expected to be excellent in battery characteristics since the reaction area involved in the electrode reaction is large.

In order to support this prediction, a lithium secondary battery was fabricated using the synthesized material as the positive electrode active material, and the battery characteristics were evaluated.
FIG. 9 shows initial charge / discharge curves of Example 1 and Comparative Example 1. In Example 1, a large plateau is observed around 3.4 V, which is peculiar to lithium iron phosphate. Also, the initial discharge capacity is 163 mAh / g, which is a high discharge capacity corresponding to 96% of the theoretical capacity, and no initial irreversible capacity is seen. In contrast, in Comparative Example 1, the initial discharge capacity was 82 mAh / g. As is clear from this result, the material is refined to a few tens of nanometers by a wet process using a planetary ball mill, and they are uniformly mixed with a conductive substance to form composite particles. It can be seen that the improved battery characteristics are exhibited.

  FIG. 10 shows the cycle characteristics of Example 1 at various charge / discharge rates. Under the condition of 1C, the capacity deterioration after 100 cycles is 0% with respect to the initial discharge capacity, the capacity deterioration after 100 cycles at 3C is 1.2% with respect to the initial discharge capacity, and the capacity deterioration after 100 cycles at 10C is initial. The discharge capacity was 3.1%. Thus, it was confirmed that Example 1 was extremely excellent in cycle characteristics.

  Next, Table 2 shows initial discharge capacities obtained at various charge / discharge rates in Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

As shown in Table 2, in Example 1, 163 mAh / g at 0.1 C (10 hours charging, 10 hours discharging), 153 mAh / g at 1 C (1 hour charging, 1 hour discharging), 3C (20 minutes charging, 20 Min discharge) 135 mAh / g at 5 C (12 minutes charge, 12 minutes discharge) 118 mAh / g at 10 C (6 minutes charge, 6 minutes discharge) 97 mAh / g at 15 C (4 minutes charge, 4 minutes discharge) 53 mAh The battery characteristics were 24 mAh / g at 20 C (3 minutes charge, 3 minutes discharge). That is, when LiFePO ₄ is refined and compounded with carbon, the initial discharge capacity is 2.0 times under the condition of 0.1 C, compared with the material not performing it (Comparative Example 1), and under the condition of 3 C or more, Comparative Example 1 did not operate as a battery, whereas Example 1 exhibited a very large discharge capacity.

  Further, for Example 2 fired at 600 ° C., the initial discharge capacity was 153 mAh / g under the conditions of 0.1 C, 138 mAh / g at 1 C, 123 mAh / g at 5 C, 110 mAh / g at 10 C, 81 mAh / 15 at 15 C. g, 74 mAh / g at 20C.

  On the other hand, the material (Comparative Example 1) that was not pulverized and combined with carbon was 82 mAh / g at 0.1C.

Further, the material (Comparative Example 2), which is dry-ground and coated with carbon on the surface (Comparative Example 2), shows a capacity similar to that of Example 1 up to 3C, and an initial discharge capacity larger than that of Example 2. However, in the high-speed charge / discharge conditions of 5C or more, Examples 1 and 2 show a larger discharge capacity. In particular, at 15 C or higher, Comparative Example 2 did not operate as a battery, but Example 2 exhibited extremely excellent battery characteristics of 81 mAh / g and 20 mA at 74 mAh / g.
As described above, Examples 1 and 2 have the same number of steps in the low-speed charge / discharge conditions of 3C or less, although the number of firing steps is less than that of Comparative Example 2 and the manufacturing process is simplified with energy saving. Battery performance is extremely excellent under high-speed charge / discharge conditions of 5C or higher.

(Example 3)
First inorganic particles composed of a LiFePO ₄ precursor were produced by spray pyrolysis under the same raw material solution and the same conditions as in Example 1.

Production and firing of composite particles The first inorganic particles (LiFePO ₄ ) were wet micronized using a planetary ball mill and composited with carbon. As the carbon, acetylene black was used. In a planetary ball mill, a zirconia pot is used, and 40 g of zirconia balls, a sample of 0.5 g (LiFePO ₄ / acetylene black = 90/10 mass ratio), 1 ml of ethanol as a wet medium, and a rotating table is rotated. The mixture was pulverized and mixed wet for several hours at several 800 times / minute and 1600 rotations / minute of the mill pot to obtain composite fine particles in which LiFePO ₄ and acetylene black were combined. Further, the composite fine particles were fired at 600 ° C. for 4 hours in a nitrogen atmosphere containing 3% hydrogen to obtain inorganic particles in which LiFePO ₄ and acetylene black were combined.

(Comparative Example 3)
A LiFePO ₄ precursor was synthesized by spray pyrolysis under the same raw material solution and the same conditions as in Example 3, and further calcined under the same conditions to obtain LiFePO ₄ particles having a single-phase olivine structure.

  With respect to the fine particles obtained in Example 3 and Comparative Example 3, the structure of the fine particles, the measurement of the specific surface area and the identification of the crystal phase were performed according to the following method, and further used as the positive electrode active material of the lithium secondary battery. A charge / discharge cycle test of the secondary battery was performed.

Structure of Composite Particles The structure of the composite particles was determined using a field emission scanning electron microscope (FE-SEM, manufactured by Hitachi, S4500) and a high-resolution transmission electron microscope (TEM, manufactured by JEOL, JEM-3010). Observed.

Specific surface area The specific surface area was measured by the same method (conditions) as that used for the fine particles obtained in Example 1 above.

Identification of Crystal Phase The crystal phase of the fine particles was identified using a powder X-ray diffractometer (manufactured by Rigaku Corporation, Ultima IV, D / teX Ultra). The measurement was performed under the following conditions using a CuKα ray for a particle sample of about 50 to 80 mg.
Voltage: 40 kV
Current: 40 mA
Measurement range: 10 degrees ≤ 2θ ≤ 80 degrees

Evaluation of lithium secondary battery Using the fine particles obtained in the above Example 1 and the like, the same method (conditions) as the method for producing the positive electrode of the lithium secondary battery and the lithium secondary battery was compared with Example 3. Using the fine particles obtained in Example 3, a positive electrode of a lithium secondary battery and a lithium secondary battery were produced.

  About the obtained lithium secondary battery, charging / discharging was repeated with various charging / discharging speed | rates, and the discharge capacity was measured.

(Results and discussion on LiFePO ₄ )
Table 3 below shows the measurement results of the specific surface area of Example 3 and Comparative Example 3 related to LiFePO ₄ . The results of identification of the crystal phase of the composite particles obtained in Example 3 are shown in FIG. Further, an SEM photograph of the composite particles obtained in Example 3 is shown in FIG. 12, and that of Comparative Example 3 is shown in FIG. As for the TEM photograph, that of Example 3 is shown in FIG. Furthermore, FIG. 15 shows the initial charge / discharge curves of the charge / discharge cycle tests of Example 3 and Comparative Example 3, and FIG. 16 shows the cycle characteristics of Example 3 at various charge / discharge rates.

First, from the identification result of the crystal phase by powder X-ray diffraction shown in FIG. 11, it can be seen that in Example 3, lithium iron phosphate LiFePO ₄ having a single-phase olivine structure could be synthesized.

  Further, when these particle sizes were examined using a scanning electron microscope (SEM), as is apparent from FIGS. 12 and 13, in Example 3, very small particles of about 100 nm or less were observed. In Comparative Example 3, many particles of 1 μm or more are observed.

Further, when Example 3 was examined in more detail using a transmission electron microscope (TEM), from FIG. 14, in Example 3, the surface of LiFePO ₄ nanoparticles was covered with a carbon layer of about several nanometers. Is observed. That is, it can be seen that nanocarbon-coated LiFePO ₄ particles in which carbon is coated on the surface of lithium iron phosphate LiFePO ₄ having a thickness of 100 nm or less on a several nanometer scale are synthesized.

Furthermore, when the specific surface areas of these samples were measured, as shown in Table 3, it was 51 m ² / g in Example 3, while it was 2.5 m ² / g in Comparative Example 3, and was wet-ground. In Example 3, the composite surface treatment with carbon and carbon showed a very large specific surface area. From this result, it is expected that Example 3 is excellent in battery characteristics since the reaction area involved in the electrode reaction is large.

In order to support this prediction, a lithium secondary battery was fabricated using the synthesized material as the positive electrode active material, and the battery characteristics were evaluated.
FIG. 15 shows initial charge / discharge curves of Example 3 and Comparative Example 3. In Example 3, a large plateau is observed around 3.4 V, which is peculiar to lithium iron phosphate. Also, the initial discharge capacity is 165 mAh / g, which is a high discharge capacity corresponding to 97% of the theoretical capacity, and no initial irreversible capacity is seen. In contrast, in Comparative Example 3, the initial discharge capacity was 100 mAh / g. As is clear from this result, the material is refined to a few tens of nanometers by wet using a planetary ball mill, and the surface is coated with carbon at a few nanoscales to improve the electronic conductivity of the material, It can be seen that the battery characteristics are extremely excellent.

  FIG. 16 shows the cycle characteristics of Example 3 at various charge / discharge rates. Under the conditions of 5C to 60C, the capacity deterioration after 100 cycles was less than 0.3% with respect to the initial discharge capacity. Thus, it was confirmed that Example 3 was extremely excellent in cycle characteristics.

  Next, Table 4 shows initial discharge capacities obtained at various charge / discharge rates in Example 3 and Comparative Example 3.

  As shown in Table 4, in Example 3, 165 mAh / g at 0.1 C, 155 mAh / g at 1 C, 130 mAh / g at 5 C, 118 mAh / g at 10 C, 105 mAh / g at 20 C, 30 C (2 minute charge, 2 (Battery discharge) was 95 mAh / g, and 60 C (1 minute charge, 1 minute discharge) was 75 mAh / g.

In contrast, the material that was not pulverized and combined with carbon (Comparative Example 3) was 100 mAh / g at 0.1 C and 40 mAh / g at 1 C.
In this way, LiFePO ₄ is refined and the surface thereof is coated with carbon on the order of several nanoscales, so that the initial discharge capacity is 1. Under the conditions of 7 times, 1C, 3.9 times, and further 5C or more, Comparative Example 3 did not operate as a battery, whereas Example 3 showed a very large discharge capacity.

(Examples 4 to 15)
Preparation of Raw Material Solution As the raw material salt, one kind of nitrate and phosphoric acid selected from lithium, manganese, and magnesium, or cobalt, nickel, iron, and zinc were used. These were dissolved in distilled water at a stoichiometric ratio (Li: M (Mg, Co, Ni, Fe, Zn): Mn: P = 1: x: 1-x: 1), and the total number of moles (Li + M + Mn + P) was 0. It was prepared to be 6 mol / L.
In Examples 4 and 12, x = 0, Examples 5 and 13, M = Mg, x = 0.04, Examples 6 and 14, M = Mg, x = 0. .08, Example 7, and Example 15 are M = Mg, x = 0.12, Example 8 is M = Co, x = 0.08, Example 9 is M = Ni, x = 0. 08, Example 10 is M = Fe, x = 0.08, and Example 11 is M = Zn, x = 0.08.

Production of first inorganic particles The structure of the basic apparatus is the same as that of the apparatus used in Example 1 (FIG. 1), but in Examples 4 to 15, a horizontal spray pyrolysis apparatus was used. The pyrolysis reactor of this spray pyrolysis apparatus has an inner diameter of 90 mm and a length of 1800 mm. Further, a nitrogen gas containing 3% hydrogen was used as the carrier gas, and the gas flow rate was 2 dm ³ / min (room temperature). The pyrolysis reactor was set at 400 ° C.
The production of the other first inorganic particles is the same method (conditions) as the method of producing the first inorganic particles in Example 1 above.

Production and firing of composite particles The first inorganic particles (LiM _x Mn _1-x PO ₄ ) were wet micronized using a planetary ball mill and composited with carbon. As the carbon, acetylene black was used. In a planetary ball mill, using a zirconia pot, 40 g of zirconia balls (diameter 1 mm or 0.5 mm) and 1.0 g of a sample (LiM _x Mn _1-x PO ₄ / acetylene black = 90/10 mass ratio) Then, 2 ml of ethanol is added as a wet medium, and the mixture is pulverized and mixed in a wet manner for 6 hours at a rotational speed of a rotary table of 800 times / minute and a rotational speed of a mill pot of 1600 times / minute, and LiM _x Mn _1-x PO ₄ and acetylene Composite fine particles in which black was combined were obtained. Furthermore, the composite fine particles were fired at 500 ° C. for 4 hours in a nitrogen atmosphere containing 3% of hydrogen to obtain inorganic particles in which LiM _x Mn _1-x PO ₄ and acetylene black were combined.
In Examples 4 to 11, the diameter of the zirconia ball is 1 mm, and in Examples 12 to 15 is 0.5 mm.

(Comparative Example 4)
A LiMnPO ₄ precursor was synthesized by spray pyrolysis under the same raw material solution and the same conditions as in Example 4, and further calcined under the same conditions to obtain LiMnPO ₄ particles having a single-phase olivine structure.

  For the fine particles obtained in Examples 4 to 15 and Comparative Example 4, the specific surface area was measured and the crystal phase was identified according to the following method. Further, the fine secondary particles were used as a positive electrode active material for a lithium secondary battery. A charge / discharge cycle test of the battery was performed.

Specific surface area The specific surface area was measured by the same method (conditions) as that used for the fine particles obtained in Example 1 above.

Identification of Crystal Phase The crystal phase of the fine particles was identified using a powder X-ray diffractometer (manufactured by Philips, PW1700 system). The measurement was performed under the following conditions for a particle sample of about 50 to 80 mg using CuKα1 and CuKα2 wires.
Voltage: 40 kV
Current: 30 mA
Time constant: 0.5 s
Scanning speed: 0.04 degrees / s
Measurement range: 4 degrees ≤ 2θ ≤ 70 degrees

Evaluation of Lithium Secondary Battery Examples 4 to 15 were performed in the same manner (conditions) as the method for producing the positive electrode of the lithium secondary battery and the lithium secondary battery using the fine particles obtained in Example 1 and the like. And the positive electrode of a lithium secondary battery and the lithium secondary battery which used the microparticles | fine-particles obtained by the comparative example 4 were produced.

  About the obtained lithium secondary battery, charging / discharging was repeated with various charging / discharging speed | rates, and the discharge capacity was measured.

(Results and discussion on LiM _x Mn _1-x PO ₄ )
Table 5 below shows the measurement results of the specific surface area of Examples 4 to 15 and Comparative Example ₄ related to LiM _x Mn _1-x PO ₄ . The results of identification of the crystal phase of the composite particles obtained in Comparative Example 4 and Examples 4 to 15 are shown in FIGS. Furthermore, FIG. 20 shows the initial charge / discharge curve of the charge / discharge cycle test of Example 13, and FIG. 21 shows the cycle characteristics at the charge / discharge rates of Examples 12-15.

  First, it can be seen from the results of crystal phase identification by powder X-ray diffraction shown in FIGS. 17 to 19 that lithium manganese phosphate having a single-phase olivine structure was synthesized in Comparative Example 4 and Examples 4 to 15.

Moreover, when the specific surface area of those samples was measured, as shown in Table 5, in Examples 4 to 15, it was at least 35.9 m ² / g, whereas in Comparative Example 4, it was 4.0 m ² / g. In Examples 4 to 15, Examples 4 to 15 exhibited extremely large specific surface areas by wet grinding and compounding with carbon. From these results, it is expected that Examples 4 to 15 are excellent in battery characteristics because the reaction area involved in the electrode reaction is large.

In order to support this prediction, a lithium secondary battery was fabricated using the synthesized material as the positive electrode active material, and the battery characteristics were evaluated.
FIG. 20 shows an initial charge / discharge curve of Example 13 as an example. In Example 13, a large plateau is observed around 4 V, which is characteristic of lithium manganese phosphate. In addition, the initial discharge capacity is 126 mAh / g at a charge / discharge rate of 0.05 C, and a high discharge capacity corresponding to 73% of the theoretical capacity is 115 mAh / g at a charge / discharge rate of 0.1 C, and 68% of the theoretical capacity. It had a high discharge capacity corresponding to. As is clear from this result, it can be seen that by using a planetary ball mill to refine the material in a wet process and to combine it with carbon, the electronic conductivity is improved and excellent battery characteristics are exhibited.

  FIG. 21 shows the cycle characteristics at the charge / discharge rate (0.1 C) for Examples 12 to 15. In any of the examples, only a slight capacity decrease is observed in about 10 cycles. As described above, Examples 12 to 15 were confirmed to be extremely excellent in cycle characteristics.

  Next, Table 6 shows initial discharge capacities obtained at various charge / discharge rates in Examples 4 to 15 and Comparative Example 4.

As shown in Table 6, in Example 4, the discharge capacity was 60 mAh / g at 0.05 C (20 hours charge, 20 hours discharge) and 53 mAh / g at 0.1 C. In contrast, the material that was not pulverized and combined with carbon (Comparative Example 4) did not operate as a secondary battery under any charge / discharge conditions.
That is, LiMnPO ₄ can be refined and combined with carbon to be used as a positive electrode material for a lithium secondary battery.

Further, a material obtained by replacing a part of manganese of lithium manganese phosphate with magnesium was further pulverized in a wet manner and combined with carbon to improve the discharge capacity.
Specifically, for LiMg _0.04 Mn _0.96 PO ₄ , 0.05 mA at 80 mAh / g, 0.1 C at 62 mAh / g (Example 5), and LiMg _0.08 Mn _0.92 PO ₄ , 0.05 mA at 106 mAh / g, 0.1 C at 92 mAh / g (Example 6), LiMg _0.12 Mn _0.88 PO ₄ at 0.05 C at 94 mAh / g, 0.1 C at 89 mAh / g (implemented) Example 7).

Furthermore, further improvement of the discharge capacity was observed by wet grinding and compounding with carbon of a material in which a part of manganese of lithium manganese phosphate was replaced with one selected from cobalt, nickel, iron and zinc. It was.
Specifically, LiCo _0.08 Mn _0.92 PO ₄ is 94 mAh / g at 0.05 C, 84 mAh / g at 0.1 C (Example 8), and LiNi _0.08 Mn _0.92 PO ₄ is 0.05 mA at 85 mAh / g, 0.1 C at 77 mAh / g (Example 9), LiFe _0.08 Mn _0.92 PO ₄ at 0.05 C at 85 mAh / g, 0.1 C at 66 mAh / g (implemented) In Example 10), LiZn _0.08 Mn _0.92 PO ₄ , it was 77 mAh / g at 0.05 C and 66 mAh / g at 0.1 C (Example 11).

Furthermore, when performing pulverization and compounding with carbon in a wet manner, by using a zirconia ball having a diameter of 0.5 mm, LiMnPO ₄ is 90 mAh / g at 0.05 C and 77 mAh / g at 0.1 C ( Example 12), LiMg _0.04 Mn _0.96 PO ₄ was 0.05 mA at 126 mAh / g, 0.1 C at 115 mAh / g, 0.5 C at 75 mAh / g (Example 13), LiMg _0.08 For Mn _0.92 PO ₄ , 0.05 mA at 120 mAh / g, 0.1 C at 110 mAh / g, 0.5 C at 73 mAh / g (Example 14), LiMg _0.12 Mn _0.88 PO ₄ at 0 It was 109 mAh / g at 0.05 C, 98 mAh / g at 0.1 C, and 61 mAh / g at 0.5 C (Example 15).
That is, when the case of using a zirconia ball having a diameter of 0.5 mm (Examples 12 to 15) and the case of a diameter of 1 mm (Examples 4 to 7) are compared, in the case of a diameter of 0.5 mm, the discharge capacity is further improved. It was observed.

As an example, SEM photographs of the composite particles obtained in Example 4 and Example 6 are shown in FIGS. Observation was performed using the same apparatus as that used in Example 3 above. As a result, as is apparent from FIGS. 22 and 23, in Example 4 and Example 6, very small particles of about 100 nm or less are observed.
From this, it can be seen that LiM _x Mn _1-x PO _{4 of} 100 nm or less was synthesized by wet grinding using a planetary ball mill and composite treatment with carbon, similar to the above LiFePO _4. This is the difference in specific surface area.

MP spray pyrolysis apparatus 1 Gas cylinder 2 Packed column 3 Filter 4 Flow meter 5 Ultrasonic sprayer 6 Microtube pump 7 Raw material solution tank 8 Pump 9 Constant temperature bath 10 Refrigerator 11 Pyrolysis reactor 111 Preheating tube 112 Reaction tube 12 Heater 13 DC Voltage power source 14 Diffusion type electrostatic collector 15 Cooling trap 16 Filter 17 Flow meter 18 Vacuum pump 21 Planetary ball mill 22 Turntable 23 Mill pot 24 Ball 25 First inorganic particles TC1, TC2, TC3, TC4, TC5, TC6, TC7, TC8 Temperature controller T11, T12 Gas thermometer

Claims (15)

A method for producing inorganic particles,
A step (A) of preparing a solution of a raw material compound containing the constituents of the inorganic particles;
A step (B) of forming a first inorganic particle by spray pyrolysis treatment of the solution of the raw material compound;
The first inorganic particles and the conductive material are wet pulverized and mixed using a planetary ball mill to form composite particles containing the conductive material and the inorganic particles (C);
A step (D) of firing the composite particles;
The manufacturing method of the inorganic particle characterized by including.   The method for producing inorganic particles according to claim 1, wherein the first inorganic particles are formed of an inorganic material including at least one selected from Fe, Mn, Co, and Ni and Li.   The method for producing inorganic particles according to claim 1 or 2, wherein the first inorganic particles are formed of a phosphate containing lithium.   The method for producing inorganic particles according to claim 1 or 2, wherein the first inorganic particles are formed of a silicate containing lithium.   The method for producing inorganic particles according to claim 1 or 2, wherein the first inorganic particles are formed of a borate containing lithium. The method for producing inorganic particles according to claim 1, wherein the first inorganic particles are formed of LiFePO ₄ . The method for producing inorganic particles according to claim 1, wherein the first inorganic particles are formed of LiMnPO ₄ . 2. The inorganic particle according to claim 1, wherein the first inorganic particle is formed by substituting a part of Mn of LiMnPO ₄ with one selected from Mg, Co, Ni, Fe, and Zn. Manufacturing method.   The method for producing inorganic particles according to any one of claims 1 to 8, wherein the conductive substance is carbon black.   The method for producing inorganic particles according to any one of claims 1 to 9, wherein the spray pyrolysis treatment in the step (B) of forming the first inorganic particles is performed at 300 to 800 ° C.   The rotating speed of the rotating base of the planetary ball mill in the step (C) of forming the composite particles is 100 to 1100 times / min, and the rotating speed of the mill pot is 200 to 2200 times / min. The manufacturing method of the inorganic particle of any one of Claims 1-10.   The method for producing inorganic particles according to any one of claims 1 to 11, wherein the ball diameter of the planetary ball mill in the step (C) of forming the composite particles is 100 to 10000 µm. .   The method for producing inorganic particles according to any one of claims 1 to 12, wherein a firing temperature in the step (D) of firing the composite particles is 400 to 1200 ° C.   A secondary battery positive electrode using inorganic particles produced by the production method according to any one of claims 1 to 13. A secondary battery using the secondary battery positive electrode according to claim 14.