JP2016157684A - Method for manufacturing carbon-coated polyanion based positive electrode active material particles, and intermediate particles for manufacturing carbon-coated polyanion based positive electrode active material particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyanion based active material with high conductivity by increasing the efficiency of carbon coating.SOLUTION: A method for manufacturing carbon-coated polyanion based positive electrode active material particles comprises: the step 1 of preparing polyanion based positive electrode active material particles (intermediate particles) with a polyoxyalkylene compound deposited thereon so that the weight ratio of carbon becomes 0.1-1.0%; the step 2 of mixing the intermediate particles with a carbon source; and the step 3 of carbonizing the carbon source. The steps are arranged in this order.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing carbon-coated polyanionic positive electrode active material particles suitably used as a positive electrode material for a lithium ion secondary battery, and an intermediate particle used in the production method.

  Lithium-ion secondary batteries are batteries that provide higher voltage and higher energy density than conventional nickel cadmium batteries and nickel metal hydride batteries, and can be made smaller and lighter. Widely used in mobile electronic devices. Lithium-ion secondary batteries are expected to be used further in the future for automotive applications such as electric vehicles and hybrid vehicles, and industrial applications such as electric tools, and there is a strong demand for higher capacity and higher output. Has been.

  A lithium ion secondary battery is configured by arranging a positive electrode and a negative electrode having an active material capable of reversibly removing and inserting lithium ions, and a separator separating the positive electrode and the negative electrode in a container and filling an electrolyte. .

The positive electrode is formed by applying an electrode agent containing a positive electrode active material for a lithium battery, a conductive additive, and a binder to a metal foil current collector such as aluminum and press-molding it. Current positive electrode active materials include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), or a ternary system in which cobalt is partially substituted with nickel / manganese (LiMn _x Ni _y Co _1-xy). A powder of a complex oxide of lithium and a transition metal such as O ₂ ) and spinel type lithium manganate (LiMn ₂ O ₄ ) is relatively well used. In addition, metal oxides such as V ₂ O ₅ and metal compounds such as TiS ₂ , MoS ₂ , and NbSe ₂ are also used as active materials.

  The negative electrode is formed by applying an electrode material containing an active material, a conductive additive and a binder to a metal foil current collector such as copper as in the case of the positive electrode, and in general, as an active material of the negative electrode, Lithium alloys such as metallic lithium, Li-Al alloy, Li-Sn, silicon compounds containing SiO, SiC, SiOC, etc. as basic constituent elements, conductive polymers such as lithium-doped polyacetylene and polypyrrole, and lithium ions in the crystal Intercalation compounds incorporated into the carbon material, carbon materials such as natural graphite, artificial graphite, and hard carbon are used.

In active materials currently in practical use, the theoretical capacity of the positive electrode is lower than the theoretical capacity of the negative electrode, and in order to increase the capacity of the lithium ion battery, it is essential to improve the capacity density of the positive electrode. Therefore, there is a demand for practical application of a polyanionic active material, which is a next-generation active material having a high capacity. Among the polyanionic active materials, the most advanced development is a phosphoric acid active material with high safety. Among phosphoric acid-based active materials, lithium iron phosphate (LiFePO ₄ ) containing iron, which is a resource-rich and inexpensive material, has begun to be put into practical use. Further, lithium manganese phosphate (LiMnPO ₄ ) having higher output energy has attracted attention as a next-generation active material. As other polyanion-based active materials, silicate-type active materials and fluorinated olivine-based active materials are attracting attention. The silicate type active material has a feature that the discharge capacity per weight is higher than that of the phosphoric acid type active material. The fluorinated olivine-based active material is characterized by a higher voltage than the phosphate-based active material. These are expected as active materials for the next generation.

  However, since the polyanionic positive electrode active material has very low electronic conductivity, it is difficult to put it into practical use. Therefore, a technique for imparting electronic conductivity to the polyanionic positive electrode active material is required.

  In order to improve the electronic conductivity in the positive electrode, a method of adding a conductive additive to the electrode agent is used. Examples of materials conventionally used as a conductive additive include graphite, acetylene black, and ketjen black. However, in the case of a positive electrode active material with particularly low conductivity, it is not sufficient to add a conductive additive, and a method for directly attaching the active carbon and a conductive carbon material as a conductive aid is required.

  Patent Document 1 discloses a method of preparing a composite by mixing a raw material solution of lithium iron phosphate and a polymer serving as a carbon source, spray drying and firing. Patent Document 2 discloses a technique for imparting conductivity to lithium manganese phosphate particles by mixing and firing lithium manganese phosphate particles, lithium iron phosphate raw material, and polyvinyl alcohol. Non-Patent Document 1 discloses a method of imparting conductivity to lithium manganese silicate by mixing a raw material of lithium manganese silicate and sucrose, which is a carbon source, with a ball mill, followed by firing.

Japanese Patent No. 4043852 JP2012-185979

Y. Li, et. al. Journal of Power Sources 174 (2007) 528-532

  In the method described in Patent Document 1 or Patent Document 2, iron that is a carbonization catalyst is distributed on the surface and the active material surface is coated with carbon. However, this method is not a particle having a large amount of iron atoms on the surface. It cannot be applied and the active materials that can be used are limited. Moreover, in the method of adding iron in addition to the active material described in Patent Document 2, when iron is mixed, the discharge voltage decreases and the discharge capacity per weight decreases, and the battery performance deteriorates. Further, according to the method described in Non-Patent Document 1, carbonization of the carbon source occurs independently of the positive electrode active material, and it is impossible to uniformly coat the surface and sufficient conductivity cannot be obtained. .

  An object of the present invention is to obtain a highly conductive polyanionic active material by increasing the efficiency of carbon coating.

  In the present invention, intermediate particles in which a predetermined amount of a polyoxyalkylene compound is attached to polyanionic positive electrode active material particles are produced. Since the intermediate particles have an improved affinity between the carbon source and the particle surface, firing this can yield high-conductivity carbon-coated polyanionic positive electrode active material particles with high coating uniformity. it can.

That is, the present invention
Step 1: Polyanionic positive electrode active material particles (intermediate particles) to which a polyoxyalkylene compound represented by the general formula (1) described later is attached so that the carbon weight ratio is 0.1% to 1.0% ) Preparing;
Step 2: mixing the intermediate particles with a carbon source;
Step 3: Carbonizing the carbon source;
In this order is a method for producing carbon-coated polyanionic positive electrode active material particles.

  According to the present invention, it is possible to perform uniform carbon coating on polyanionic positive electrode active materials having various compositions, and the conductivity can be improved. As a result, high-capacity and high-power positive electrode active material particles can be obtained, and by using this for the positive electrode, the performance of the lithium ion secondary battery can be improved.

Example of peak fitting for determining the functionalization rate of the intermediate particles produced in Example 1

[Step 1]
In the present invention, first, polyanionic positive electrode active material particles (hereinafter, simply referred to as “active material particles”) to which a polyoxyalkylene compound is adhered so that the carbon weight ratio is 0.1% or more and 1.0% or less. Prepare).

The polyanionic positive electrode active material (hereinafter sometimes simply referred to as “active material”) in the present invention is selected from the group consisting of Li _x M _y AO _z (M is manganese, iron, vanadium, nickel, cobalt). A metal element, 0.5 <x <2, 0.5 <y <2, 3 <z <4, A is a compound represented by silicon, phosphorus, or boron. Examples of the polyanion positive electrode active material include a phosphoric acid positive electrode active material, a silicate positive electrode active material, a borate positive electrode active material, and lithium vanadium phosphate. Among the polyanionic positive electrode active materials, the positive electrode active materials that are effective are a phosphoric acid positive electrode active material and a silicate positive electrode active material. A phosphoric acid cathode active material is most suitable for the present invention.

The phosphoric acid-based positive electrode active material is Li _x M _y PO ₄ where A is phosphorus (where M is a metal element selected from the group consisting of manganese, iron, nickel, cobalt, 0.5 <x < 2, 0.5 <y <2). In particular, manganese is preferable as the metal element corresponding to M.

  In addition to the metals corresponding to Li and M, the phosphoric acid-based positive electrode active material may contain a metal having an element ratio of 10% or less with respect to phosphorus atoms. The metals included are not limited, but include manganese, iron, vanadium, nickel, cobalt, zinc, yttrium, magnesium, germanium, and the like. Further, a fluorinated olivine-based positive electrode active material in which fluorine is contained in the phosphoric acid-based positive electrode active material may be used.

The silicate-based positive electrode active material is Li _x M _y SiO ₄ (where M is a metal element selected from the group consisting of manganese, iron, vanadium, nickel, cobalt, 0.5 <x <2, 0. As the metal element corresponding to M indicating 5 <y <2), manganese and iron are particularly preferable.

  In addition to the metal corresponding to Li and M, the silicate-based positive electrode active material may contain a metal having an element ratio of 10% or less with respect to the silicon atom. The metals included are not limited, but include manganese, iron, vanadium, nickel, cobalt, zinc, yttrium, magnesium, germanium, and the like.

The borate-based positive electrode active material refers to Li _x M _y BO ₃ (where M is a metal element selected from manganese and iron, 0.5 <x <2, 0.5 <y <2). In addition to the metal corresponding to Li and M, the borate-based positive electrode active material may contain a metal having an element ratio of 10% or less with respect to the boron atom. The metals included are not limited, but include manganese, iron, vanadium, nickel, cobalt, zinc, yttrium, magnesium, germanium, and the like.

Lithium vanadium phosphate refers to Li ₃ V ₂ (PO ₄ ) ₃ . Although the crystal system is different from the active material containing other phosphates, it is mentioned as an active material suitable for the present invention.

  Further, when manganese and phosphoric acid are contained in the polyanionic positive electrode active material, it is preferable that manganese chemically bonded to the phosphate ester is contained. Here, the phosphate ester refers to a compound in which an organic component such as an alkyl group is bonded to phosphoric acid. Examples of such compounds are shown in the following formula. When there is a substance in which phosphoric acid and manganese are chemically bonded via an organic component, the organic component is likely to appear on the surface when firing at a high temperature, and the affinity with a carbon source described later is improved.

  Since the polyanionic positive electrode active material generally has low conductivity, it is preferable that the crystallite size is small in order to improve efficiency during charging and discharging. However, if it is too small, the influence of the surface becomes too large and the crystal structure is destroyed. Therefore, it is preferable to use particles having a crystallite size of 10 nm to 60 nm as the polyanionic positive electrode active material particles. The crystallite size is more preferably 20 nm or more and 55 nm or less, and further preferably 30 nm or more and 50 nm.

  In the present invention, a polyoxyalkylene compound is attached to such polyanionic positive electrode active material particles.

  The polyoxyalkylene compound in the present invention is a molecule having a structure represented by the following general formula (1).

[In General Formula (1), R represents a hydrogen atom or a methyl group, and each structural unit may be the same or different. X and Y represent a hydrogen atom or an arbitrary substituent. n represents an integer of 2 or more. ]
The polyoxyalkylene compound in the present invention is a polyoxyethylene compound in which R is hydrogen in the general formula (1), a polyoxypropylene compound in which R is a methyl group, or a co-polymerization of a polyoxyethylene compound and a polyoxypropylene compound. Refers to coalescence. Examples of the polyoxyethylene compound include polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene aryl ether, polyoxyethylene fatty acid ester or derivatives thereof. Examples of the polyoxypropylene compound include polypropylene glycol, polyoxypropylene alkyl ether, polyoxypropylene aryl ether, polyoxypropylene fatty acid ester or derivatives thereof. In the above, polyethylene glycol and polypropylene glycol are preferable because the terminal of the polar group is better in adhesion to the particle surface. Further, from the viewpoint of affinity with a carbon source, a polyoxyethylene compound is preferable to a polyoxypropylene compound, and polyethylene glycol is particularly preferable.

  Further, from the viewpoint of affinity with the polyanionic positive electrode active material particles, when phosphoric acid is contained in the polyanionic positive electrode active material, X or Y in the general formula (1) is a polyphosphoric acid ester group. Oxyethylene compounds are preferred. When silicic acid is contained in the polyanionic positive electrode active material, a polyoxyethylene compound in which X or Y in the general formula (1) is a silicate group is preferable.

  The weight average molecular weight of the polyoxyalkylene compound is preferably 1000 or less, and more preferably 500 or less. More preferably, both a polyoxyalkylene compound having a weight average molecular weight of 300 or more and a polyoxyalkylene compound having a weight average molecular weight of 200 or less are contained. Preferable specific examples of the polyoxyalkylene compound having a weight average molecular weight of 300 or more include polyethylene glycol having a weight average molecular weight within the range. Specific examples of the polyoxyalkylene compound having a weight average molecular weight of 200 or less include diethylene glycol, triethylene glycol, tetraethylene glycol, and derivatives thereof.

  The polyoxyalkylene compound does not easily leave the polyanionic positive electrode active material even when heated, and has an effect of increasing the affinity between the active material and the polar organic material. For this reason, the affinity between the active material and the organic substance serving as the carbon source is increased, and when the carbon source is carbonized, it becomes easy to adhere to the surface of the polyanionic positive electrode active material particles, so the carbon coverage of the active material particles is increased. It becomes possible.

  In the present invention, first, polyanionic positive electrode active material particles to which a polyoxyalkylene compound is attached are prepared. In the present specification, the polyanionic positive electrode active material particles to which the polyoxyalkylene compound is prepared, which are prepared in this step, are referred to as “intermediate particles”.

  In the present invention, the fact that the polyoxyalkylene compound is attached to the surface of the polyanionic positive electrode active material particles can be analyzed by the TOF-SIMS method. In the TOF-SIMS method, the sample surface is irradiated with pulsed ions (primary ions) in an ultra-high vacuum, and the ions (secondary ions) emitted from the sample surface are subjected to mass spectrometry, thereby performing sample analysis. It is possible to analyze these substances. In the TOF-SIMS method, local analysis is also possible. When there is a mixture other than polyanionic positive electrode active material particles, only the surface portion of the polyanionic positive electrode active material particles is analyzed to adhere to the surface. It is possible to confirm that

  In the present invention, the adhesion amount of the polyoxyalkylene compound is adjusted so that the carbon weight ratio when the elemental analysis of the intermediate particles is performed is 0.1% or more and 1% or less. When there are too few polyoxyalkylene compounds, the adhesiveness with respect to a carbon source will become low. On the other hand, when the adhesion amount of the polyoxyalkylene compound increases, adhesion between particles occurs during firing, and the crystallite size increases. In general, a polyanionic positive electrode active material having a large crystallite size makes it difficult to charge and discharge inside the particles, and the battery characteristics deteriorate. Further, since the polyoxyalkylene compound itself has a low carbonization efficiency, if it is too much, bad quality carbon will increase and the conductivity will be lowered. For this reason, the polyoxyalkylene compound needs to adhere to the extent that it has an affinity for carbon, but is preferably as small as possible. From such a viewpoint, the carbon weight ratio of the intermediate particles is preferably 0.2% to 0.8%, more preferably 0.3% to 0.6%.

  The carbon weight ratio of the intermediate particles can be quantified by a carbon-sulfur analyzer. In the carbon-sulfur analyzer, the composite is heated in air by high frequency, the contained carbon is completely oxidized, and the generated carbon dioxide is detected by infrared rays. An example of the measuring device is a carbon-sulfur analyzer EMIA-810W manufactured by Horiba.

  When manganese and phosphoric acid are contained in the polyanionic positive electrode active material, it is preferable that manganese chemically bonded to the above-described phosphate ester is present on the surface of the intermediate particle. When manganese chemically bonded to phosphate ester is present on the surface of the intermediate particles, when firing with the carbon source, the carbon source is strongly adsorbed on the surface of the active material particles to advance the bonding between the organic substance and the inorganic substance. Coat efficiency is improved.

  The presence of manganese chemically bonded to phosphate ester on the surface of the intermediate particle means that when the liquid obtained by repeatedly washing and extracting the intermediate particle with water is analyzed with a high performance liquid chromatograph mass spectrometer, This can be confirmed by detecting chemically bonded manganese.

  The method for preparing the intermediate particles is not limited, but a method of removing the solvent after contacting the polyanionic positive electrode active material particles with the polyoxyalkylene compound solution is preferable. The polyoxyalkylene compound aqueous solution and the polyanionic positive electrode The method of lyophilizing or filtering / drying after mixing the active material particles is particularly preferred. As other methods, polyoxyalkylene compounds and polyanionic positive electrode active material particles are used in an apparatus such as a blender, a mortar, a rotary ball mill, a planetary ball mill, a hybridizer, and a multiplex (Paurec, MP-25). Then, after mixing, there is a method of washing as necessary.

  The intermediate particles preferably have a surface carbon functionalization rate of 0.4 to 0.7. The higher the functionalization rate of carbon, the greater the affinity with the carbon source on the surface, but if it is too high, the conductivity of carbon on the surface will be low. Therefore, the functionalization rate of the carbon component on the surface is preferably 0.5 or more and 0.6 or less.

The functionalization rate is determined by X-ray photoelectron spectroscopy. In X-ray photoelectron spectroscopy, when a sample containing carbon is measured, a peak derived from carbon is detected in the vicinity of 284 eV, but it is known that when carbon is bonded to oxygen, it shifts to a higher energy side. Yes. Specifically, peaks based on C—C bonds, C═C double bonds, and C—H bonds in which carbon is not bonded to oxygen are detected in the vicinity of 284 eV without shifting, and in the case of C—O single bond 286 In the case of C = O double bond, it shifts to about 287.5 eV, and in the case of COO bond, it shifts to about 288.5 eV. Therefore, a signal derived from carbon is detected in a form in which respective peaks around 284 eV, 286.5 eV, 287.5 eV, and 288.5 eV are superimposed. It is possible to calculate the intensity of each peak area by performing peak separation analysis on each component by peak fitting of the superimposed peaks. Signals also appear near 286e and 290.5eV based on the graphite component. This signal is fitted as a component based on CC, C = C and CH bonds. The functionalization rate in the present invention is
Functionalization rate = [(peak area based on C—O single bond) + (C = peak area based on O double bond) + (peak area based on COO bond)] / (C—C, C = C and Peak area based on C—H bond)
It is a numerical value defined by. As an example of peak fitting, FIG. 1 shows an example in which the intermediate particles produced in Example 1 are measured.

[Step 2]
The intermediate particles prepared in Step 1 are mixed with a carbon source in the next step.

  Examples of carbon sources include polymer systems, sugars, and graphenes. As the polymer system, polyvinyl alcohol, polyacrylic acid (salt), polyvinyl butyral, polyvinyl pyrrolidone, or a copolymer thereof is preferably used. Among them, polyvinyl alcohol and polyvinyl pyrrolidone have high carbonization efficiency and easily obtain high conductivity. The saccharide is not particularly limited, and examples thereof include monosaccharides such as glucose, sucrose and fructose having a low molecular weight, polysaccharides such as cellulose, starch and dextrin, and sugar derivatives such as sugar alcohol and sugar ester. In addition, carbon sources with high carbonization efficiency include glycerin compounds such as polyglycerin and polyglycerin esters, organic acids such as citric acid and ascorbic acid, and graphenes such as graphene and graphite oxide. Among these, saccharides and graphenes have particularly high carbonization efficiency, and high conductivity is easily obtained. In the present invention, the polyoxyalkylene compound to be deposited in Step 1 has a low carbonization yield, and therefore, the carbon source is preferably a substance other than the polyoxyalkylene compound.

  These carbon sources are preferably mixed in an amount of 10% to 50% with respect to the intermediate particles before firing, and adjusted so that the carbon weight ratio is 2% to 8% after firing.

  Although there is no restriction | limiting in the method of mixing an intermediate body particle and a carbon source, The method of mixing with a ball mill, a planetary mixer, a mortar etc. is mentioned. In addition, a solvent may be added and mixed at the time of mixing, and then the solvent may be dried. If drying is performed by a technique such as freeze drying or spray drying, it is possible to mix better.

  The carbon weight ratio in the carbon-coated polyanionic positive electrode active material after calcination can be quantified by a carbon-sulfur analyzer in the same manner as the intermediate particles described above.

[Step 3]
The intermediate particles mixed with the carbon source in Step 2 become carbon-coated polyanionic positive electrode active material particles by carbonizing the carbon source. Although there is no restriction | limiting in the method to carbonize, baking is generally used. The firing temperature is preferably 500 ° C. or higher, more preferably 600 ° C. or higher, and further preferably 700 ° C. or higher. The heating time is preferably 3 hours or longer, and more preferably 6 hours or longer.

  In addition, it is necessary to prevent the carbon from disappearing due to oxidation, and it is preferable to fire in an inert atmosphere or a reducing atmosphere.

When the polyanionic positive electrode active material particles are phosphoric acid-based active material particles, the carbon-coated polyanionic positive electrode active material particles produced by the method of the present invention are 950 cm ⁻ based on phosphoric acid when measured by Raman spectroscopy. preferably ¹ near the ratio I _P / Ig of the peak I _P and 1600 cm ^-1 peak intensity I _g based on the carbon of 0.01 or less, still more preferably 0.008 or less. On the other hand, if the coating carbon is too much, the ionic conductivity decreases, so that it is preferably 0.002 or more, and more preferably 0.004 or more.

  The physical property values in the examples were measured by the following methods.

A. Measurement of crystallite size X-ray diffraction using D8 ADVANCE manufactured by Bruker AXS Co., Ltd., an X-ray diffractometer, under the conditions of 2θ = 5 ° to 70 ° with a step angle of 0.040 ° and a step time of 70.4 seconds Measurements were made. Based on the measurement results, the crystallite size was calculated using the Rietveld analysis software TOPAS attached to D8 ADVANCE.

B. Measurement of the mass ratio of carbon For the measurement of the mass ratio of carbon, a carbon / sulfur simultaneous quantitative analyzer (EMIA-920V, manufactured by Horiba, Ltd.) was used.

C. X-ray photoelectron spectroscopy measurement The X-ray photoelectron measurement of each sample was performed using Quantera SXM (manufactured by PHI). Excitation X-rays were monochromatic Al K _α1,2 rays (1486.6 eV), the X-ray diameter was 200 μm, and the photoelectron escape angle was 45 °. The ratio of oxygen atoms to carbon atoms in graphite oxide was determined from the peak area of oxygen atoms in a wide scan and the peak area of carbon atoms.

D. Charge / Discharge Measurement Evaluation Planetary mixer with 700 mg of produced carbon-coated polyanionic positive electrode active material particles, 40 mg of acetylene black as a conductive additive, 60 mg of polyvinylidene fluoride as a binder, and 800 mg of N-methylpyrrolidone as a solvent To obtain an electrode paste. The electrode paste was applied to aluminum foil (thickness: 18 μm) using a doctor blade (300 μm) and dried at 80 ° C. for 30 minutes to obtain an electrode plate.

The produced electrode plate was cut to a diameter of 15.9 mm to be a positive electrode, a lithium foil cut to a diameter of 16.1 mm and a thickness of 0.2 mm was used as a negative electrode, and Celgard # 2400 (manufactured by Cellguard) was cut to a diameter of 17 mm. As a result, a 2042 type coin battery was prepared using a solvent of ethylene carbonate: diethyl carbonate = 7: 3 containing 1 M of LiPF ₆ and subjected to electrochemical evaluation.

In the charge / discharge measurement, when the active material is LiMnPO ₄ , the upper limit voltage is 4.4V, the lower limit voltage is 2.7V, the charge / discharge is performed 3 times at a rate of 0.1C, and then 3 times at 3C. The capacity at the third discharge of each rate was defined as the discharge capacity. When the active material is Li ₂ MnSiO ₄ , the upper limit voltage is 4.5 V, the lower limit voltage is 2.7 V, the charge and discharge is performed three times at a rate of 0.1 C, and then the charge and discharge is performed three times at 0.3 C. The capacity at the third discharge of each rate was defined as the discharge capacity.

E. Raman spectroscopic measurement evaluation The produced carbon-coated polyanionic positive electrode active material particles were evaluated by Raman spectroscopic measurement. Raman measurement was performed using Raman T-64000 (Jobin Yvon / Ehime Bussan). The beam diameter was 100 μm, and the light source was an argon ion laser (wavelength: 514.5 nm). For the active material of the phosphate, and peak I _P around 950 cm ^-1 based on phosphoric acid, since the the 1600 cm ^-1 peak intensity I _g based on carbon is detected, the intensity ratio of these peak intensities I _P / Ig was calculated.

(Synthesis Example 1: Preparation 1 of lithium manganese phosphate particles)
Lithium phosphate (Li ₃ PO ₄ ) and manganous sulfate (MnSO ₄ ) were dissolved in pure water so that the molar ratio was Li: Mn: P = 3: 1: 1 to prepare an aqueous solution. This aqueous solution was put into a pressure vessel and hydrothermal synthesis was performed under conditions of 180 ° C. and 24 hours. After cooling and taking out, washing with pure water was carried out 5 to 6 times, followed by vacuum drying to obtain LiMnPO ₄ powder. When the crystallite size was measured according to Measurement Example 1, it was 42 nm.

(Synthesis Example 2: Production of lithium manganese silicate particles)
Lithium hydroxide (LiOH), manganese chloride tetrahydrate (MnCl ₂ .4H ₂ O), tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ), ethanol / water = 3 at a molar ratio of 4: 1: 1 / 1 in a solvent to obtain a raw material solution. Furthermore, after ascorbic acid was added, it put into the pressure vessel and synthesize | combined on the conditions of 300 degreeC36MPa. After cooling and taking out, it was washed three times with ethanol and pure water, and vacuum dried to obtain Li ₂ MnSiO ₄ powder.

(Synthesis Example 3: Preparation 2 of lithium manganese phosphate particles)
As a positive electrode active material raw material, 0.06 mol of manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O) was dissolved in 30 ml of ion exchange water and further mixed with 200 ml of diethylene glycol. The mixture was heated at 100 ° C. for 1 hour with vigorous stirring. 30 ml of an aqueous 0.2 mol / L lithium hydrogen phosphate (Li ₂ HPO ₄ ) solution was added dropwise to the mixture at a speed of 1 ml / min. The temperature was kept at 100 ° C. for 4 hours. After cooling to room temperature, mixing with ethanol and centrifuging were repeated three times to wash the diethylene glycol on the surface.

(Synthesis Example 4: Production of graphite oxide)
The raw material was 2000-mesh natural graphite powder (Shanghai Ichiho Graphite Co., Ltd.). Put 10 ml of natural graphite powder in an ice bath with 220 ml of 98% concentrated sulfuric acid, 3.5 g of sodium nitrate, 21 g of potassium permanganate, and maintain the temperature of the mixture at 20 ° C. or lower for 1 hour. Stir. This mixed solution was taken out of the ice bath and reacted with stirring in a 35 ° C. water bath for 4 hours. Thereafter, 500 ml of ion-exchanged water was added, and the resulting suspension was further reacted at 90 ° C. for 15 minutes. Finally, 600 ml of ion exchange water and 50 ml of hydrogen peroxide water (concentration 70%) were added and reacted for 5 minutes to obtain a graphite oxide dispersion. This was filtered, the metal ions were washed with a diluted hydrochloric acid solution, the acid was washed with ion-exchanged water, and the washing was repeated until the pH became 7, thereby producing a graphite oxide gel. The graphite oxide powder was obtained by freeze-drying the graphite oxide gel. The element ratio of oxygen atoms to carbon atoms in the obtained graphite oxide powder was measured in Measurement Example 1 and found to be 0.45.

Example 1
1 g of lithium manganese phosphate particles prepared in Synthesis Example 1 was added to a liquid for mixing 9.5 g of pure water and 0.5 g of diethylene glycol (polyoxyalkylene compound), stirred at 80 ° C. for 2 hours, filtered and dried. Thus, intermediate particles were obtained. The carbon weight of the intermediate particles was measured and found to be 0.43%. When the functionalization rate of carbon was measured by X-ray photoelectron spectroscopy, it was 0.55.

  0.8 g of this intermediate particle and 0.2 g of glucose were dispersed in 10 g of pure water, freeze-dried, and calcined at 700 ° C. for 6 hours in a nitrogen atmosphere to obtain carbon-coated lithium manganese phosphate particles. The carbon weight ratio after firing was measured and found to be 2.5%. It was 46 nm when the crystallite size after baking was measured.

  When the carbon-coated lithium manganese phosphate particles after firing were subjected to charge / discharge measurement evaluation, a discharge capacity of 155 mAh / g at a rate of 0.1 C and 140 mAh / g at a rate of 3 C was obtained.

When the Raman measurement of the carbon-coated lithium manganese phosphate particles after firing was performed, the peak intensity ratio I _P / Ig was 0.006.

(Example 2) to (Example 11)
Various evaluations were performed in the same manner as in Example 1 except that the types of the polyanionic positive electrode active material, the polyoxyalkylene compound solution, and the carbon source were changed as shown in Table 1.

(Comparative Example 1)
Various evaluations were performed in the same manner as in Example 1 except that instead of the polyoxyalkylene compound solution, the solvent was not used and only 10 g of diethylene glycol was stirred.

(Comparative Example 2)
Various evaluations were performed in the same manner as in Example 1 except that instead of the polyoxyalkylene compound solution, the solvent was not used and only 10 g of PEG 400 (polyoxyalkylene compound having a weight average molecular weight of 400) was stirred.

(Comparative Example 3)
Various evaluations were performed in the same manner as in Example 1 except that a solution of 5 g of diethylene glycol dissolved in 5 g of pure water was used as the polyoxyalkylene compound solution.

(Comparative Example 4)
When the carbon weight ratio of the lithium manganese phosphate particles synthesized and washed in Synthesis Example 1 was measured without adhering a polyoxyalkylene compound, it was 0.04%. Moreover, it was 0.25 when the functionalization rate of carbon was measured by the X ray photoelectron spectroscopy.

  0.8 g of this lithium manganese phosphate particles and 0.2 g of glucose were dispersed in 10 g of pure water, freeze-dried, and calcined at 700 ° C. for 6 hours in nitrogen to obtain carbon-coated lithium manganese phosphate particles. The carbon weight after firing was measured and found to be 1.1%. The crystallite size after firing was measured and found to be 94 nm.

(Comparative Example 5)
When the carbon weight ratio of the lithium manganese phosphate particles synthesized and washed in Synthesis Example 3 was measured without adhering a polyoxyalkylene compound, it was 0.05%. The carbon functionalization rate measured by X-ray photoelectron spectroscopy was 0.26.

  0.8 g of this lithium manganese phosphate particles and 0.2 g of glucose were dispersed in 10 g of pure water, freeze-dried, and calcined at 700 ° C. for 6 hours in nitrogen to obtain carbon-coated lithium manganese phosphate particles. The carbon weight after firing was measured and found to be 1.2%. The crystallite size after firing was measured and found to be 150 nm.

(Comparative Example 6)
The carbon weight ratio of the lithium manganese silicate particles synthesized and washed in Synthesis Example 2 measured without adhering a polyoxyalkylene compound was 0.04%. The carbon functionalization rate measured by X-ray photoelectron spectroscopy was 0.21.

  0.8 g of this lithium manganese silicate particles and 0.2 g of glucose were dispersed in 10 g of pure water, freeze-dried, and calcined at 700 ° C. for 6 hours in nitrogen to obtain carbon-coated lithium manganese phosphate particles. The carbon weight after firing was measured and found to be 1.0%. The crystallite size after firing was measured and found to be 62 nm.

  Table 1 shows various measurement results of the carbon-coated polyanionic positive electrode active material particles prepared in each Example and Comparative Example.

Claims (10)

Step 1: Polyanionic positive electrode active material particles (intermediate particles) to which a polyoxyalkylene compound represented by the following general formula (1) is attached so that the carbon weight ratio is 0.1% to 1.0% Preparing the step;

[In General Formula (1), R represents a hydrogen atom or a methyl group, and each structural unit may be the same or different. X and Y represent a hydrogen atom or an arbitrary substituent. n represents an integer of 2 or more. ]
Step 2: mixing the intermediate particles with a carbon source;
Step 3: Carbonizing the carbon source;
A method for producing carbon-coated polyanionic positive electrode active material particles having the above in this order. The method for producing carbon-coated polyanionic positive electrode active material particles according to claim 1, wherein a polyoxyalkylene compound having a weight average molecular weight of 1000 or less is used. The method for producing carbon-coated polyanionic positive electrode active material particles according to claim 1 or 2, wherein both the polyoxyalkylene compound having a weight average molecular weight of 300 or more and a weight average molecular weight of 200 or less are used. The carbon-coated polyanionic positive electrode active material according to any one of claims 1 to 3, wherein the intermediate particles have a carbon functionalization rate of 0.4 to 0.7 as measured by X-ray photoelectron spectroscopy. Particle production method. The said process 1 is a process of removing the solvent of this polyoxyalkylene compound solution, after making the polyanion type positive electrode active material particle contact with the solution of a polyoxyalkylene compound. Of producing carbon-coated polyanionic positive electrode active material particles. Wherein said polyanion-based positive active material particles are phosphate-based positive electrode active material particle, and when measured by Raman spectroscopy, the ratio of the peak intensity I _g based on the peak intensity I _P and a carbon-based phosphate I _p / The method for producing carbon-coated polyanionic positive electrode active material particles according to any one of claims 1 to 5, wherein _Ig is 0.01 or less. Intermediate particles for producing carbon-coated polyanionic positive electrode active material particles to which a polyoxyalkylene compound is adhered such that the carbon weight ratio is 0.1% or more and 1.0% or less. The intermediate particles for producing carbon-coated polyanionic positive electrode active material particles according to claim 7, wherein the polyoxyalkylene compound has a weight average molecular weight of 1000 or less. The intermediate particle for the production of carbon-coated polyanionic positive electrode active material particles according to claim 7 or 8, wherein the functionalization rate of carbon is 0.4 or more and 0.7 or less in X-ray photoelectron spectroscopy. Intermediate particles for producing carbon-coated polyanionic positive electrode active material particles according to any one of claims 7 to 9, wherein manganese chemically bonded to a phosphate ester is present on the surface.

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