WO2018029745A1

WO2018029745A1 - Lithium manganese phosphate nanoparticles and method for producing same, carbon-coated lithium manganese phosphate nanoparticles, carbon-coated lithium manganese phosphate nanoparticle granule, and lithium ion battery

Info

Publication number: WO2018029745A1
Application number: PCT/JP2016/073278
Authority: WO
Inventors: 辻洋悦; 久保田泰生; 川村博昭; 玉木栄一郎; 田林未幸
Original assignee: 東レ株式会社
Priority date: 2016-08-08
Filing date: 2016-08-08
Publication date: 2018-02-15

Abstract

The present invention achieves high capacity when lithium manganese phosphate is used as an active material for lithium ion batteries. The present invention provides lithium manganese phosphate nanoparticles which are characterized by having: a ratio, I₂₀/I₂₉, of a peak intensity at 20º to a peak intensity at 29º obtained by X-ray diffraction of 0.88 to 1.05; and a crystallite size obtained by X-ray diffraction of 10 to 50 nm.

Description

Lithium manganese phosphate nanoparticles and production method thereof, carbon-coated lithium manganese phosphate nanoparticles, carbon-coated manganese manganese phosphate nanoparticle granules, lithium ion battery

The present invention relates to lithium manganese phosphate nanoparticles and a method for producing the same, carbon-coated lithium manganese phosphate nanoparticles, carbon-coated lithium manganese phosphate nanoparticle granules, and a lithium ion battery.

Lithium-ion secondary batteries are widely used in information-related mobile communication electronic devices such as mobile phones and laptop computers as batteries that provide higher voltage and higher energy density than conventional nickel cadmium batteries and nickel metal hydride batteries. ing. In the future, as one means to solve environmental problems, it is expected that the use will be expanded to in-vehicle applications mounted on electric vehicles / hybrid electric vehicles and industrial applications such as electric tools.

In the lithium ion secondary battery, the positive electrode active material and the negative electrode active material play an important role in determining the capacity and output. In conventional lithium ion secondary batteries, lithium cobaltate (LiCoO ₂ ) is often used as the positive electrode active material, and carbon is often used as the negative electrode active material. However, as the use of lithium-ion batteries such as hybrid cars and electric cars has expanded in recent years, not only the capacity of batteries is improved, but also the output of how much capacity can be taken out in a short time will be increasingly required. It is becoming. In order to increase the output of the battery, that is, to efficiently extract a large current from the battery, it is necessary to increase the ionic conductivity of lithium ions as well as the electron conductivity.

On the other hand, search for next-generation active materials has been actively pursued for higher capacity and higher output of lithium ion secondary batteries. In the positive electrode active material, active materials such as olivine-based materials, that is, lithium iron phosphate (LiFePO ₄ ) and lithium manganese phosphate (LiMnPO ₄ ) are attracting attention as next-generation active materials. The capacity of lithium iron phosphate and lithium manganese phosphate is limited to about 20% of that of lithium cobaltate, so the effect on increasing the capacity is limited, but it does not contain cobalt, which is a rare metal, so it can be supplied stably. It has a great merit in terms of Furthermore, since the olivine-based active material is covalently bonded to phosphorus, oxygen is not easily released and has a high safety feature. Among them, lithium manganese phosphate has a high discharge potential when used as a positive electrode active material of a lithium ion secondary battery, and can be expected to contribute to higher output. However, unlike the lithium cobaltate (LiCoO ₂ ) and the like, the olivine-based positive electrode active material has a large change in crystal lattice due to charge / discharge, and has low electron conductivity and low ionic conductivity. That is, there is a problem that it is difficult to extract the theoretical capacity.

Therefore, by reducing the crystallite size of the olivine-based positive electrode material to about 200 nm and further coating the particle surface with carbon, the effect of strain accompanying changes in the crystal lattice size can be reduced, and ion conduction and electron conduction can be improved. It is offended. However, although the theoretical capacity of lithium iron phosphate is almost expressed by this method, it is difficult to achieve high capacity for lithium manganese phosphate alone. Attempts have been reported.

It is well known that the shape of the particles is important for increasing the capacity of lithium manganese phosphate. Lithium manganese phosphate, which has extremely low ionic and electronic conductivity, is required to have a smaller particle size than that of lithium iron phosphate, but it also improves Li ion conductivity. A shape that reduces the influence of strain associated with the charge / discharge reaction is required.

In order to realize such a shape, plate-like particles oriented in the b-axis direction have been proposed. In lithium manganese phosphate, since lithium ions can move only in the b-axis direction, the movement distance of lithium ions in the particles is made as short as possible, and the surface from which lithium ions are desorbed and inserted is wide. is there. For example, in the production methods disclosed in Patent Document 1 and Non-Patent Document 1, lithium manganese phosphate having a thickness of about 20 to 30 nm oriented in the b-axis in a diethylene glycol aqueous solution is obtained. Patent Document 2 also discloses the effect of lithium manganese phosphate oriented in the b-axis direction.

Japanese Patent No. 5174803 specification JP 2012-204015 A

In the methods of Patent Document 1 and Non-Patent Document 1, lithium manganese phosphate oriented to the b-axis method is obtained, but the obtained b-axis oriented lithium manganese phosphate particles are obtained by a ball mill before use as an active material. Since it is crushed, finally the orientation is not sufficiently maintained. Further, since materials other than the active material, that is, additives such as binders and conductive assistants do not directly contribute to the battery capacity, it is required to reduce the amount added to the electrode as much as possible. However, since 20% by weight of carbon black is added to lithium manganese phosphate at the time of battery formation, there is a problem that the capacity when viewed as the whole electrode is lowered.

Patent Document 2 also produces plate-like particles of lithium manganese phosphate oriented in the b-axis direction, but the discharge capacity that the particles develop is less than half of the theoretical capacity. Therefore, the crystal orientation of the particles disclosed in Patent Document 2 cannot sufficiently exhibit the performance of lithium manganese phosphate.

As described above, in order to increase the capacity of lithium manganese phosphate, it is necessary to optimize the shape and crystallinity of lithium manganese phosphate particles. However, focusing only on the movement of lithium ions and producing particles oriented in the b-axis, it was difficult to express the original high capacity of lithium manganese phosphate.

An object of the present invention is to clarify the orientation of crystals capable of realizing a high capacity for lithium manganese phosphate, and to provide an electrode using lithium manganese phosphate, and further to lithium ion secondary using the electrode. The next battery is to provide.

The inventors of the present invention have made extensive studies on the orientation of primary particles indicated by the peak intensity ratio by powder X-ray diffraction so that lithium manganese phosphate exhibits a high capacity close to the theoretical capacity.

The present invention for solving the above-mentioned problem is that the ratio I ₂₀ / I ₂₉ of the peak intensity at 20 ° and the peak intensity at 29 ° obtained by X-ray diffraction is 0.88 or more and 1.05 or less. Lithium manganese phosphate nanoparticles having a crystallite size determined by diffraction of 10 nm to 50 nm.

According to the present invention, it is possible to increase the capacity by controlling the crystallite size and crystal orientation of the primary particles in lithium manganese phosphate having low electron conductivity and ion conductivity. Moreover, a high capacity | capacitance and a high output lithium ion secondary battery can be provided by using the positive electrode active material of this invention.

2 is a scanning electron micrograph of lithium manganese phosphate nanoparticles obtained in Example 1. FIG.

The lithium manganese phosphate in the present invention is an olivine crystal structure compound represented by the chemical formula LiMnPO ₄ , but may contain a trace amount of other elements as doping elements within the range in which the olivine crystal structure can be maintained. May be slightly increased or decreased. The doping element is added for the purpose of improving the electronic conductivity and ionic conductivity of lithium manganese phosphate and alleviating the change in crystal lattice size. As doping elements, Na, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Cs, Ba, etc. can be used. The doping element content may be up to 10 mol% with respect to the phosphorus element for doping elements other than Fe. Fe can substitute Mn in the olivine crystal structure and can easily maintain the olivine crystal structure, so it may be contained up to 30 mol% with respect to the phosphorus element. As the doping element, Fe is preferable because it can improve the electron conductivity and ion conductivity in the crystal. If the doping amount of Fe is too large, the voltage drops during discharge and the energy density decreases, so that the doping amount is preferably small. The doping amount of Fe is preferably 20 mol% or less, more preferably 15 mol% or less, still more preferably 10 mol% or less, and most preferably 5% or less.

The lithium manganese phosphate nanoparticles in the present invention are lithium manganese phosphate particles having an average primary particle size of 100 nm or less. Here, the average particle diameter is an average value of the particle diameters of 100 particles, and the particle diameter of each particle is a two-dimensional image obtained by observing 10 to 20 particles in one field of view with a field emission scanning electron microscope. From the average of the diameters of the inscribed circle and circumscribed circle obtained from

The crystallite size obtained from the X-ray diffraction peak of lithium manganese phosphate in the present invention is 10 nm or more and 50 nm or less. Since lithium manganese phosphate nanoparticles are generally obtained as a single crystal, the crystallite size directly corresponds to the particle size. Therefore, the crystallite size of 50 nm or less means that the particle size is atomized to about 50 nm or less. Lithium manganese phosphate has a large change in the crystal lattice size during charge and discharge, so it is necessary to reduce the strain generated during charge and discharge by making the particles fine. For this purpose, the crystallite size must be 50 nm or less. When the crystallite size exceeds 50 nm, an excessive voltage is required to desorb lithium ions from lithium manganese phosphate during charging. In addition, the crystallite size of less than 10 nm means that there is almost no crystallinity, and reversible lithium desorption is difficult with such lithium manganese phosphate nanoparticles.

Moreover, the X-ray diffraction peak in the present invention can be measured using an X-ray diffraction apparatus using Cu as an X-ray source. The crystallite size can be obtained by Rietveld analysis of the spectrum of the X-ray diffraction peak. In Rietveld analysis, it is necessary to verify the validity of the analysis, and when a GOF (Goodness-of-fit) value is used as an index, it may be 2.0 or less. For example, D8ADVANCE manufactured by Bruker, Inc. can be used as the X-ray diffractometer, and TOPAS can be used as analysis software for Rietveld analysis.

The lithium manganese phosphate in the present invention has clear peaks around 20 °, 25 °, 29 °, and 35 ° obtained by X-ray diffraction (hereinafter simply referred to as 20 ° peak, 25 ° peak, 29 ° peak, and 35 °). It is called a peak) and has the characteristics described later. When the 20 ° peak, 25 ° peak, 29 ° peak, and 35 ° peak obtained by powder X-ray diffraction are indexed to the (101), (201), (020), and (311) planes, the intensity of each peak Represents the strength of the orientation to the crystal plane. In particular, the 29 ° peak indicates the (020) plane and indicates the intensity of grain growth orientation in the b-axis direction. In this specification, values obtained by dividing the intensity of the 20 ° peak, 25 ° peak, and 35 ° peak by the 29 ° peak intensity are expressed as I ₂₀ / I ₂₉ , I ₂₅ / I ₂₉ , and I ₃₅ / I ₂₉ , respectively. .

The crystallinity and particle shape of lithium manganese phosphate in the present invention are defined by the peak intensity ratios I ₂₀ / I ₂₉ , I ₂₅ / I ₂₉ , and I ₃₅ / I ₂₉ measured by the three X-ray diffractions. According to the study by the present inventors, the crystallinity necessary for the lithium manganese phosphate to exhibit a high capacity is not to be oriented on the b axis but only focusing on the conductivity of lithium ions. Rather, it has become clear that the crystal orientation in a specific direction is reduced as much as possible, and the crystal is preferably grown uniformly. The uniform growth of crystals is close to a sphere as the shape of the nanoparticles, but this is due to the change in the crystal lattice size during the charge / discharge reaction due to the reduction in the surface area of the particles. In addition to the effect of relaxing the strain, it is considered that the strain is not absorbed in a specific direction but absorbed by the whole particle. It is considered that lithium manganese phosphate nanoparticles, which are less susceptible to strain, have reduced energy required for lithium insertion and removal, and as a result, contributed to higher capacity.

The lithium manganese phosphate nanoparticles of the present invention have an I ₂₀ / I ₂₉ of 0.88 to 1.05, preferably 0.90 to 1.05. I ₂₀ / I ₂₉ is the ratio of the b-axis plane (020) to the (101) plane. (020) and (101) are orthogonal to each other, and the value of I ₂₀ / I ₂₉ is 0.88 or more and 1.05 or less, indicating that the lithium manganese phosphate nanoparticles are extremely oriented in the b-axis direction. This means that the shape of the particles is not plate-like but close to a sphere. When the particles approach a spherical shape, it becomes possible to alleviate distortion of the crystal lattice due to lithium ion desorption during charging and discharging, and as a result, it is possible to contribute to an increase in capacity.

The lithium manganese phosphate nanoparticles in the present invention preferably have an I ₂₅ / I ₂₉ of 0.95 or more and 1.15 or less. I ₂₅ / I ₂₉ is the ratio of the b-axis plane (020) to the (201) plane. (020) and (201) are orthogonal to each other. In addition to I ₂₀ / I ₂₉ being 0.88 or more and 1.05 or less, I ₂₅ / I ₂₉ being 0.95 or less and 1.15 or less further reduces the crystal orientation of the particles, It means that the crystal orientation becomes more homogeneous and the particle shape is closer to a sphere. Therefore, the effect of alleviating distortion of the crystal lattice due to lithium ion desorption / insertion during charge / discharge is enhanced, and as a result, it is possible to contribute to the improvement of capacity.

The lithium manganese phosphate nanoparticles in the present invention preferably have an I ₃₅ / I ₂₉ of 1.05 or more and 1.20 or less. I ₃₅ / I ₂₉ is the ratio of the (311) plane to the b-axis plane (020). When I ₃₅ / I ₂₉ is 1.05 or more and 1.20 or less, the crystal orientation of the lithium manganese phosphate nanoparticles is further reduced, resulting in a more uniform crystal orientation, and the particle shape is further spherical. It means approaching. Therefore, the effect of alleviating distortion of the crystal lattice due to lithium ion desorption / insertion during charge / discharge is enhanced, and as a result, it is possible to contribute to the improvement of capacity.

The lithium manganese phosphate nanoparticles in the present invention preferably have a crystallinity of 45% or more. The crystallinity in the present invention is a ratio obtained by Rietveld analysis when X-ray diffraction is measured by mixing cerium oxide as a standard substance and the same weight as lithium manganese phosphate. A degree of crystallinity of 45% or more means that the amorphous part in the lithium manganese phosphate nanoparticles is sufficiently small, which enables reversible desorption of lithium ions and contributes to an increase in capacity. Therefore, it is preferable. The measurement of crystallinity in the present invention shall be in accordance with Example A below.

The lithium manganese phosphate nanoparticles of the present invention can also be carbon-coated lithium manganese phosphate nanoparticles that have been subjected to a conductive treatment by coating the particle surface with carbon. In this case, the powder resistance value of the particles is preferably 1 Ω · cm to 10 ⁸ Ω · cm. If it is 10 ⁸ Ω · cm or more, the electron resistance from the current collector to the particle surface when it is used as an electrode increases, which may significantly inhibit the expression of capacity.

In order to sufficiently draw out the capacity of lithium manganese phosphate, such carbon-coated lithium manganese phosphate nanoparticles contain 1% by weight or more and less than 10% by weight of carbon relative to the lithium manganese phosphate nanoparticles. Preferably it is. By containing an appropriate amount of carbon, the electron conductivity in the electrode when used as an electrode is improved, and the lithium manganese phosphate nanoparticles contribute to the development of capacity. On the other hand, when a large amount of carbon is added, carbon tends to inhibit lithium ion conduction and ion conductivity tends to be lowered. Therefore, the amount of carbon contained is more preferably less than 5% by weight.

In order to use the lithium manganese phosphate nanoparticles in the present invention as a positive electrode active material of a lithium ion secondary battery, the form of secondary particles in which carbon-coated lithium manganese phosphate nanoparticles are assembled, that is, carbon-coated lithium manganese phosphate nanoparticles. It is preferable to use a particle granulated body. The carbon-coated lithium manganese phosphate nanoparticle granules are preferably granulated in a spherical shape. Here, the spherical shape refers to the circumscribed circle with respect to the inscribed circle of the granulated body in a two-dimensional image observed with a field emission scanning electron microscope so that 3 to 10 granulated bodies are contained within one field of view. It means that the ratio of diameters is 0.7 or more and 1 or less. In the present invention, if the average ratio of the diameter of the circumscribed circle to the inscribed circle when 100 carbon-coated lithium manganese phosphate nanoparticle granules are observed is 0.7 or more and 1 or less, it is granulated into a spherical shape. It shall be judged that In the present invention, when 100 carbon-coated lithium manganese phosphate nanoparticle granules are observed, it is preferable that 80 or more are spherical.

The average particle diameter of the carbon-coated lithium manganese phosphate nanoparticle granules is preferably 0.1 μm or more and 30 μm or less. When the average particle size is 0.1 μm or less, the solid content of the electrode paste decreases, and the amount of solvent necessary for coating tends to increase. Further, when the average particle size is 30 μm or more, the electrode surface is uneven when the electrode is applied, and the battery reaction tends not to proceed uniformly in the electrode.

The method for producing the lithium manganese phosphate nanoparticles of the present invention is not particularly limited, and is produced by appropriately controlling the solvent species, the moisture content in the solvent, the stirring rate, the synthesis temperature, and the raw material using liquid phase synthesis. It is preferable. Hereinafter, a method for producing the lithium manganese phosphate nanoparticles of the present invention by liquid phase synthesis will be described.

When the lithium manganese phosphate nanoparticles of the present invention are produced by liquid phase synthesis, manganese sulfate, manganese chloride, manganese nitrate, manganese formate, manganese acetate, and hydrates thereof may be used as the manganese raw material. it can. As the phosphoric acid raw material, phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate and hydrates thereof can be used. Moreover, as a lithium raw material, lithium hydroxide, lithium carbonate, lithium chloride, lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, and hydrates thereof can be used. The lithium manganese phosphate nanoparticles of the present invention can be suitably produced without by-products by using manganese sulfate, phosphoric acid, and lithium hydroxide in a molar ratio of 1: 1: 3.

As the solvent species used in the liquid phase synthesis, a coordinating organic solvent is preferable from the viewpoint of controlling particle growth and crystal orientation, and among the coordinating solvents, alcohol solvents are preferable. Specific examples include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 2-propanol, 1,3-propanediol, and 1,4-butanediol. In addition, polar solvents such as N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, N, N-dimethylformamide, and acetic acid can be used. A plurality of kinds of solvents may be mixed and used as the solvent. In order to control the crystal orientation of lithium manganese phosphate and to produce lithium manganese phosphate nanoparticles of the present invention, the solvent is required to have strong coordination with lithium manganese phosphate. Among these solvents, diethylene glycol, triethylene glycol, and tetraethylene glycol having particularly strong coordination are preferable, and among them, diethylene glycol is preferable.

It is preferable to use an organic solvent as the solvent for the liquid phase synthesis, but in order to uniformly dissolve the lithium raw material, the manganese raw material, and the phosphoric acid raw material and to control the coordination property to the lithium manganese phosphate nanoparticles, Is more preferably a mixture of an organic solvent and water. The proportion of water in the total solvent at the end of the synthesis is preferably 15% by weight or more and 50% by weight or less. When the water content is 15% by weight or less, it is difficult to dissolve all the raw materials. When the water content is 50% by weight or more, the coordination effect of the organic solvent is reduced, and lithium manganese phosphate is a nanoparticle having a crystallite size of 50 nm or less. Difficult to do.

The manganese manganese phosphate nanoparticles of the present invention are prepared by adding a solution of a manganese raw material and a phosphoric acid raw material while stirring the lithium raw material solution at a high speed, and then stirring under normal pressure or a pressure close to normal pressure of 0.13 MPa or less. It can be obtained by heating to the synthesis temperature. By adding phosphoric acid and manganese sulfate while stirring the lithium raw material solution at high speed, a fine precursor dispersion with a weak orientation in a specific crystal direction can be obtained. It becomes possible to obtain lithium manganese phosphate particles having a size. The high-speed stirring in the present invention is stirring at a peripheral speed of 1 m / second or more.

For example, it is manufactured by liquid phase synthesis using manganese sulfate, phosphoric acid, and lithium hydroxide as raw materials and further using a molar ratio of Mn: P: Li = 1: 1: 3. In this case, after dissolving lithium hydroxide in an aqueous solution of diethylene glycol, a precursor solution is prepared by adding an aqueous solution in which phosphoric acid and manganese sulfate are dissolved at a room temperature of about 25 ° C. under high-speed stirring, and then up to the synthesis temperature. It is preferable to heat.

The synthesis temperature is preferably 100 ° C or higher and 150 ° C or lower. In order for the chemical reaction to change the raw material to lithium manganese phosphate proceeds, it is necessary to supply a certain amount of thermal energy, and the production of lithium manganese phosphate nanoparticles is promoted at a high temperature of 100 ° C. or higher. In addition, the size of the generated particles greatly depends on the synthesis temperature, and when synthesized at a temperature higher than 150 ° C., the particles tend to grow coarsely and it is difficult to obtain nanoparticles having a crystallite size of 50 nm or less.

The liquid phase synthesis needs to be carried out under a pressure close to a normal pressure of 0.13 MPa or less, and is preferably 0.12 MPa or less, more preferably 0, in order to weaken the crystal growth orientation. .11 MPa or less, more preferably at normal pressure. In general, particles with high crystallinity can be obtained when synthesized under pressure using an autoclave or the like, but when synthesized under pressure, the crystal orientation in a specific direction tends to be strong.

In order to convert the lithium manganese phosphate nanoparticles of the present invention into carbon-coated lithium manganese phosphate nanoparticles, the lithium manganese phosphate nanoparticles and saccharides such as glucose are mixed and fired at about 700 ° C. in an inert atmosphere. Thus, a method of forming a carbon layer on the particle surface is preferable. The amount of carbon contained in the carbon-coated lithium manganese phosphate nanoparticles is preferably controlled by the amount of sugars to be mixed.

In order to make the carbon-coated lithium manganese phosphate nanoparticles of the present invention into a carbon-coated lithium manganese phosphate nanoparticle granulated body, it is preferable to granulate using spray drying in the process of carbon coating. Specifically, it is preferable that lithium manganese phosphate nanoparticles, saccharides and water are mixed to prepare a dispersion, which is dried and granulated by spray drying and then fired at about 700 ° C. in an inert atmosphere.

The lithium ion battery of the present invention uses the manganese manganese phosphate nanoparticles, carbon-coated lithium manganese phosphate nanoparticles, or carbon-coated lithium manganese phosphate particle granules of the present invention as the positive electrode material.

Hereinafter, the present invention will be described specifically and in detail with reference to examples. However, the present invention is not limited to these examples. The physical property values in the examples were measured by the following methods. The part in an Example means a weight part unless there is particular description.

A. Calculation of crystallite size and each peak intensity ratio The crystallite size and the powder X-ray diffraction pattern of each sample were measured using D8 ADVANCE manufactured by Bruker ASX. The measurement conditions were 2θ = 5 ° to 70 °, a scan interval of 0.02 °, and a scan speed of 20 seconds / deg. The calculation of the crystallite size was obtained by conducting Rietveld analysis using powder X-ray diffraction analysis software TOPAS manufactured by Bruker ASX. Each peak intensity ratio was calculated by performing background removal (coefficient 1.77) using a powder X-ray diffraction analysis software EVA manufactured by Bruker ASX, and reading the peak intensity. Values obtained by dividing the intensity of the 20 ° peak, 25 ° peak, and 35 ° peak by the intensity of the 29 ° peak were I ₂₀ / I ₂₉ , I ₂₅ / I ₂₉ , and I ₃₅ / I ₂₉ , respectively.

B. Measurement of crystallinity The crystallinity was measured by powder X-ray diffraction using D8 ADVANCE manufactured by Bruker ASX. 50 mg each of lithium manganese phosphate particles and cerium oxide (Sigma Aldrich) were weighed with a balance, and powder X-ray diffraction was performed with a sample mixed in a mortar. Using a powder X-ray diffraction analysis software TOPAS manufactured by Bruker ASX, the ratio of lithium manganese phosphate and cerium oxide was calculated by performing a Rietveld analysis, and the ratio of lithium manganese phosphate was defined as the crystallinity. .

C. Measurement of resistivity The resistivity was measured using Loresta (registered trademark) GP manufactured by Mitsubishi Chemical Analytech. Measurement was performed after putting 100 mg of lithium manganese phosphate particles in a φ13 mm press jig and molding a pellet by applying a pressure of 8 t with a press.

D. Measurement of carbon ratio The weight ratio of carbon contained in the lithium manganese phosphate nanoparticles was measured with a carbon sulfur analyzer EMIA-810W manufactured by HORIBA.

E. Measurement of Particle Size Distribution The average secondary particle diameter of the lithium manganese phosphate nanoparticles after granulation was measured using a laser diffraction / scattering particle size distribution measuring apparatus LA-920 manufactured by HORIBA.

F. Measurement of Charging / Discharging Characteristics Using the obtained lithium manganese phosphate particles, an electrode was produced as follows. 900 parts by weight of lithium manganese phosphate nanoparticles, 50 parts by weight of acetylene black (Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent, 50 parts by weight of polyvinylidene fluoride (Arkema Kynar HSV900) as a binder, As a solvent, 1200 weight of N-methylpyrrolidone was mixed with a planetary mixer to obtain an electrode paste. The electrode paste was applied to an aluminum foil (thickness: 18 μm) using a doctor blade (300 μm) and dried at 80 ° C. for 30 minutes to obtain an electrode plate. Cell guard (registered trademark) # 2400 (manufactured by Celgard Co., Ltd.) obtained by cutting out the produced electrode plate to a diameter of 15.9 mm to make a positive electrode, lithium foil cut to a diameter of 16.1 mm and a thickness of 0.2 mm as a negative electrode, and cutting to a diameter of 20 mm As a separator, a 2032 type coin battery was produced using a solvent of ethylene carbonate: diethyl carbonate = 3: 7 (volume ratio) containing 1 M of LiPF ₆ as an electrolytic solution, and electrochemical evaluation was performed. The measurement was performed at a theoretical capacity of 171 mAh / g, charge / discharge measurement was performed 3 times at a rate of 0.1 C, and then 3 times at 3 C, and the capacity at the third discharge of each rate was defined as the discharge capacity.

[Example 1]
After dissolving 60 mmol of lithium hydroxide monohydrate in 16 g of pure water, 104 g of diethylene glycol was added to prepare a lithium hydroxide / diethylene glycol aqueous solution. The obtained lithium hydroxide / diethylene glycol aqueous solution was stirred at 2000 rpm using a homodisper (Homodisper 2.5 type manufactured by Primics), and 20 mmol of phosphoric acid (85% aqueous solution) and manganese sulfate monohydrate were added. An aqueous solution obtained by dissolving 20 mmol of the product in 10 g of pure water was added to obtain a lithium manganese phosphate nanoparticle precursor. The obtained precursor solution was heated to 110 ° C. and held for 2 hours to obtain lithium manganese phosphate nanoparticles as a solid content. The obtained nanoparticles were washed by adding pure water and repeating solvent removal with a centrifuge. The obtained lithium manganese phosphate nanoparticles were nanoparticles having a shape close to an elliptical rotating body, as shown in FIG. The synthesis was repeated until the lithium manganese phosphate particles obtained by washing reached 10 g.

To 10 g of the obtained lithium manganese phosphate nanoparticles, 2.5 g of glucose and 40 g of pure water were added and mixed. Using a spray drying device (ADL-311-A manufactured by Yamato Kagaku), the nozzle diameter was 400 μm, the drying temperature was 150 ° C., and atomization. Granulation was performed at a pressure of 0.2 MPa. The obtained granulated particles were fired in a firing furnace at 700 ° C. for 1 hour in a nitrogen atmosphere to obtain carbon-coated lithium manganese phosphate nanoparticle granules.

When the powder X-ray diffraction was measured according to the above A, each peak intensity ratio was I ₂₀ / I ₂₉ = 1.01, I ₂₅ / I ₂₉ = 1.07, I ₃₅ / I ₂₉ = 1.14, The crystallite size was 41.2 nm.

According to the above B, the crystallinity was calculated to be 49%.

According to the above C, the resistivity was measured and found to be 89 kΩ · cm.

When the carbon ratio was measured according to D above, it was 3.5 wt%.

When the particle size distribution was measured according to E above, the average particle size was 9.2 μm.

According to the above F, the discharge capacity was measured under the conditions of an upper limit voltage of 4.4 V and a lower limit voltage of 3.0 V, and it was 142 mAh / g at a rate of 0.1 C and 109 mAh / g at a rate of 3 C.

The results are shown in Table 1. In the table, DEG is diethylene glycol, TriEG is triethylene glycol, and TEG: tetraethylene glycol.

[Example 2]
A carbon-coated lithium manganese phosphate nanoparticle granule was obtained in the same manner as in Example 1 except that the synthesis temperature was 125 ° C. Table 1 shows the results of evaluating the carbon-coated lithium manganese phosphate nanoparticle granules obtained in the same manner as in Example 1.

[Example 3]
A carbon-coated lithium manganese phosphate nanoparticle granulate was obtained in the same manner as in Example 1 except that the synthesis temperature was 140 ° C. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 4] Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that the rotation speed of the homodisper was set to 3000 rpm. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 5]
Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that the rotation speed of the homodisper was 4000 rpm. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 6]
Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that the solvent used in the synthesis was changed from diethylene glycol to triethylene glycol. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 7]
A carbon-coated lithium manganese phosphate nanoparticle granulate was obtained in the same manner as in Example 1 except that the solvent used in the synthesis was changed from 104 g of diethylene glycol to 48 g of tetraethylene glycol. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 8]
A carbon-coated lithium manganese phosphate nanoparticle granulate was obtained in the same manner as in Example 1 except that the solvent used for the synthesis was changed from 104 g of diethylene glycol to 104 g of tetraethylene glycol. Table 1 shows the results of evaluating the obtained lithium manganese phosphate nanoparticles in the same manner as in Example 1.

[Example 9]
10 g of lithium manganese phosphate nanoparticles were synthesized in the same manner as in Example 1 except that the synthesis temperature was 160 ° C. Next, after the obtained particles were crushed by a planetary ball mill, glucose 2.5 and 40 g of pure water were added and spray-dried in the same manner as in Example 1, followed by firing. The planetary ball mill treatment was performed under the conditions of a rotation speed of 300 rpm and a treatment time of 6 hours using a P5 made by Fritsch as the main body of the apparatus, a 45 ml container made of zirconia as the container, and 18 10 mm beads made of zirconia as the beads. Table 1 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 10]
Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that 16 mmol of manganese sulfate monohydrate and 4 mmol of iron sulfate heptahydrate were dissolved. Table 1 shows the results of evaluating the obtained lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Example 11]
Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that 17 mmol of manganese sulfate monohydrate and 3 mmol of iron sulfate heptahydrate were dissolved. Table 1 shows the results of evaluating the obtained lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 1]
A carbon-coated lithium manganese phosphate nanoparticle granule was obtained in the same manner as in Example 1 except that the rotation speed of the homodisper was 500 rpm. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 2]
Carbon-coated lithium manganese phosphate nanoparticle granules were obtained in the same manner as in Example 1 except that the pure water in which lithium hydroxide was dissolved was changed from 16 g to 117 g. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 3]
In Example 1, instead of heating the precursor solution of lithium manganese phosphate nanoparticles to 110 ° C. at normal pressure and holding for 2 hours, the precursor solution was placed in a pressure-resistant sealed container and heated to 110 ° C. A carbon-coated lithium manganese phosphate nanoparticle granulate was obtained in the same manner except that it was held for 4 hours. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 4]
After heating the lithium hydroxide / diethylene glycol aqueous solution to 110 ° C., an aqueous solution obtained by dissolving 20 mmol of phosphoric acid (85% aqueous solution) and 20 mmol of manganese sulfate tetrahydrate in 10 g of pure water was added for 2 hours. A carbon-coated lithium manganese phosphate nanoparticle granulated material was obtained in the same manner as in Example 1 except that it was retained. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 5]
A carbon-coated lithium manganese phosphate nanoparticle granule was obtained in the same manner as in Example 9 except that crushing using a planetary ball mill was not performed. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 6]
20 mmol of manganese acetate tetrahydrate was dissolved in 4.4 g of water, 60 g of diethylene glycol was added, and the mixture was kept at 110 ° C. for 1 hour to obtain a brown suspension. While maintaining the obtained manganese acetate suspension at 110 ° C., an aqueous solution prepared by dissolving 20 mmol of lithium dihydrogen phosphate in 9.17 g of water was dropped into the manganese solution and held for 4 hours to obtain a solid content. Lithium manganese phosphate nanoparticles were obtained. The obtained nanoparticles were washed in the same manner as in Example 1, followed by granulation by spray drying and carbon coating using glucose. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

[Comparative Example 7]
In 190 g of pure water, 40 mmol of trilithium phosphate and 40 mmol of manganese sulfate monohydrate were dissolved and kept at 130 ° C. for 1 hour using a pressure vessel to obtain lithium manganese phosphate nanoparticles as a solid content. The obtained nanoparticles were subjected to the same washing, granulation and carbon coating treatment as in Example 1. Table 2 shows the results of evaluating the obtained carbon-coated lithium manganese phosphate nanoparticle granules in the same manner as in Example 1.

Claims

The ratio I 20 / I 29 of the peak intensity at 20 ° and the peak intensity at 29 ° obtained by X-ray diffraction is 0.88 or more and 1.05 or less, and the crystallite size determined by X-ray diffraction is 10 nm or more and 50 nm or less. Lithium manganese phosphate nanoparticles.
The lithium manganese phosphate nanoparticles according to claim 1, wherein I 20 / I 29 is 0.90 or more and 1.05 or less.
3. The lithium manganese phosphate nanoparticles according to claim 1, wherein the ratio I 25 / I 29 of the peak intensity at 25 ° and the peak intensity at 29 ° obtained by X-ray diffraction is 0.95 or more and 1.15 or less. .
The manganese phosphate according to any one of claims 1 to 3, wherein the ratio I 35 / I 29 of the peak intensity at 35 ° and the peak intensity at 29 ° obtained by X-ray diffraction is 1.05 or more and 1.20 or less. Lithium nanoparticles.
The lithium manganese phosphate nanoparticles according to any one of claims 1 to 4, having a crystallinity of 45% or more.
Carbon-coated lithium manganese phosphate nanoparticles obtained by coating the lithium manganese phosphate nanoparticles according to any one of claims 1 to 5 with carbon.
The carbon-coated lithium manganese phosphate nanoparticles according to claim 6, comprising 1 wt% or more and less than 10 wt% of carbon with respect to the lithium manganese phosphate nanoparticles.
A carbon-coated lithium manganese phosphate nanoparticle granulated product obtained by granulating the carbon-coated lithium manganese phosphate nanoparticles according to claim 6 or 7 to an average particle size of 0.1 µm to 30 µm.
A method for producing lithium manganese phosphate nanoparticles, comprising adding a solution of a manganese raw material and a phosphoric acid raw material while stirring a lithium raw material solution at high speed, and then heating to a synthesis temperature under a pressure of 0.13 MPa or less.
The lithium manganese phosphate particles according to any one of claims 1 to 6, the carbon-coated lithium manganese phosphate nanoparticles according to claim 7, or the carbon-coated lithium manganese phosphate particle granules according to claim 8 Lithium ion battery used for positive electrode material.