WO2011099575A1 - ホウ酸化合物、二次電池用正極、及び二次電池の製造方法 - Google Patents
ホウ酸化合物、二次電池用正極、及び二次電池の製造方法 Download PDFInfo
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Definitions
- the present invention relates to a method for producing a boric acid compound, a positive electrode for a secondary battery, and a method for producing a secondary battery.
- lithium ion secondary batteries have been widely used as power sources for portable electronic devices such as mobile phones and notebook computers, and power tools.
- boric acid compounds having an olivine type crystal structure have been proposed from the viewpoints of resources, safety, cost, stability, etc., and their production methods have been studied. Yes.
- M 2-2x B 2x O 3 (M is one or more metal atoms selected from transition metals, x is 0 ⁇ x ⁇ 1), An electrode active material mainly composed of a crystalline metal complex is described, and a method for producing the amorphous metal complex represented by M 2-2x B 2x O 3 by mechanical milling, M Describes a method of rapidly solidifying a mixture containing a metal oxide having boron as a constituent metal atom and a boron oxide from a molten state. Amorphization of a metal complex requires a lot of energy and is not suitable for mass production.
- Patent Document 1 describes that a lithium compound is further added to a mixture containing a metal oxide and a boron oxide, but this description is only for a system containing V 2 O 5 , such as FeO and the like. No examples are given for systems containing these transition metals.
- Non-Patent Document 1 describes a method for producing LiMBO 3 by a solid-phase reaction represented by the following formula (5).
- Non-Patent Document 2 describes a method for producing LiFeBO 3 by a solid-phase reaction represented by the following formula (6), and structural analysis of the product has been made.
- Non-Patent Document 1 uses expensive oxalate as a compound containing atom M, and has a drawback that the manufacturing cost of LiMBO 3 increases.
- a large amount of gas is generated due to decomposition of the raw material.
- the generation of gas not only includes gas species that require processing, but also inhibits the generation of LiMBO 3 and grain growth, so that two-stage heating, that is, the raw material mixture is first heated to generate gas, then crushed, After carrying out steps such as pulverization and molding, it is necessary to synthesize LiMBO 3 particles by heating again at a high temperature.
- the manufacturing method described in Non-Patent Document 2 is also the same.
- the present inventor follows a method described in Patent Document 1 by heating triiron tetroxide (Fe 3 O 4 ), lithium carbonate (Li 2 CO 3 ), and boron oxide (B 2 O 3 ). Production of LiFeBO x was attempted under atmospheric pressure. However, a uniform melt of triiron tetroxide, lithium carbonate, and boron oxide could not be obtained.
- An object of the present invention is to produce a boric acid compound that enables inexpensive and efficient production of a boric acid compound having excellent battery characteristics and reliability by controlling the composition and particle size of the boric acid compound. It is to provide a method.
- the present invention also provides a positive electrode for a secondary battery excellent in electrical characteristics and reliability and a method for producing the secondary battery.
- a first compound having a composition represented by the following formula (1) and a second compound containing at least one atom A selected from Li, Na, and K are represented by the following formula (2):
- A: M: B a: b: 1 (2)
- a and M represent the same kind of atoms as described above, a is 0 ⁇ a ⁇ 2, and b is 0.8 ⁇ b ⁇ 1.2.
- a a M b BO c (3) (Wherein, A and M have the same kind of atoms and the valence of M is less than or N 1 equal to the N 1, a and b have the same numerical value as the, c is a, b And the number depending on the valence of M.)
- the first compound is selected from at least one selected from M oxide, M oxyhydroxide, and M metal, and boric acid, boron oxide, ammonium borate, and ammonium hydrogen borate.
- M and B have the composition represented by the formula (1) to obtain a raw material mixture, pulverizing the raw material mixture and heating to obtain a melt.
- the manufacturing method of the boric acid compound of [1] including the process of obtaining the 1st compound which has a composition represented by Formula (1).
- the second compound comprises A carbonate (A 2 CO 3 ), A hydrogen carbonate (AHCO 3 ), A hydroxide (AOH), A nitrate (ANO 3 ), A Chloride (ACl), A sulfate (A 2 SO 4 ), A acetate (CH 3 COOA) and A oxalate ((COOA) 2 ) (however, these compounds are hydrated salts, respectively)
- the method for producing a boric acid compound according to [1] to [7] wherein a heating temperature in the step of obtaining the boric acid compound having the composition represented by the formula (3) by heating is 400 to 800 ° C.
- the formulation contains at least one carbon source selected from an organic compound and carbon powder, and the amount of the carbon source is determined according to the formulation and the carbon in the carbon source.
- a boric acid compound having a composition represented by the formula (3) is a particle containing LiFe d Mn 1-d BO 3 (d is 0 ⁇ d ⁇ 1) having an olivine type crystal structure.
- a and M have the same kind of atoms and the valence of M is less than or N 1 equal to the N 1, a and b show the same value as above.
- [14] Obtaining a boric acid compound by the production method of [1] to [13], and then producing a positive electrode for a secondary battery using the boric acid compound as a positive electrode material for a secondary battery.
- a method for producing a positive electrode for a secondary battery comprising: obtaining a positive electrode for a secondary battery by the production method of [14], and then producing a secondary battery using the positive electrode for a secondary battery.
- the production method of the present invention is a method that makes it easy to control the composition and particle size of the boric acid compound. Therefore, a boric acid compound having excellent battery characteristics and reliability can be produced at low cost and efficiently. Moreover, the positive electrode for secondary batteries and secondary battery which are excellent in a battery characteristic and reliability can be manufactured by using the boric-acid compound obtained by this invention.
- FIG. 3 is a diagram showing an X-ray diffraction pattern of the first compound (flaky solidified product) produced in Examples 1 to 6.
- FIG. 4 is a diagram showing an X-ray diffraction pattern of boric acid compound (having an olivine type crystal structure) particles produced in Examples 1 to 3.
- FIG. 4 is a diagram showing an X-ray diffraction pattern of boric acid compound (having an olivine type crystal structure) particles produced in Examples 4 to 6.
- FIG. 4 is a view showing an X-ray diffraction pattern of a first compound (flaky solidified product) produced in Examples 20 to 25.
- FIG. 3 is a diagram showing an X-ray diffraction pattern of boric acid compound (having an olivine type crystal structure) particles produced in Examples 20 to 22.
- FIG. 6 is a view showing an X-ray diffraction pattern of boric acid compound (having an olivine type crystal structure) particles produced in Examples 23 to 25.
- A represents at least one atom selected from Li, Na, and K.
- A represents an atom of the above three alkali metal elements.
- A may consist of a combination of two or more atoms.
- M represents at least one atom selected from Fe, Mn, Co and Ni.
- M represents an atom of the above four transition metal elements.
- M may consist of a combination of two or more atoms.
- chemical formulas, such as Formula (1) and Formula (3) represent an average composition.
- a crystal having an olivine structure is hereinafter referred to as an olivine crystal, and a particle containing the olivine crystal is also referred to as an olivine crystal particle.
- the olivine-type crystal particle may partially include a crystal structure other than the olivine-type crystal structure, or may partially include an amorphous structure. It is preferable that substantially all of the olivine type crystal particles are made of olivine type crystals.
- the boric acid compound having the composition represented by the formula (3) which is an object of the production method of the present invention, is also referred to as a boric acid compound (3).
- step (I), step (II), and step (III) are performed in this order. Other steps may be performed before, between, and after the steps (I) to (III) as long as each step is not affected.
- the compound containing M and the compound containing B are prepared so that M and B may become a composition represented by Formula (1), a raw material mixture is obtained, and this raw material mixture is grind
- the step of producing the first compound is hereinafter referred to as step (IV).
- the first compound is particularly selected from at least one selected from M oxide, M oxyhydroxide and M metal, and boric acid, boron oxide, ammonium borate and ammonium hydrogen borate.
- the boric acid compound produced by the production method of the present invention is a useful compound as a positive electrode material for a secondary battery, and particularly useful as a positive electrode material for a lithium ion secondary battery.
- a boric acid compound having a desired composition could not be obtained.
- a mixture of raw materials prepared by mixing a compound containing M and the like and a compound containing boron so as to have a composition represented by the formula (1) is melted by heating.
- the desired boric acid compound (3) can be obtained.
- the melting means that the carbonate of A, the oxide of M, and boric acid are melted and become a transparent state visually.
- a compound having the composition represented by formula (1) is used as the first compound, and a second compound is blended with the first compound at a predetermined ratio to produce a formulation, and the formulation is heated. By doing so, it becomes possible to obtain a desired boric acid compound (3).
- the method described in Patent Document 1 requires a lot of energy for amorphization of the metal complex and is not suitable for mass production. On the other hand, according to the present invention, the method requires less energy. Since a boric acid compound having a desired composition can be obtained, the production method is advantageous for mass production.
- Step (I) is a step of obtaining a preparation by preparing the first compound and the second compound so as to have an atomic ratio represented by the formula (2).
- the first compound is preferably prepared after pulverization.
- the pulverization is preferably performed by a dry method or a wet method using a mixer, a ball mill, a jet mill, a planetary mill or the like, and a dry method is preferable because solvent removal is unnecessary.
- M is at least one atom selected from Fe, Mn, Co and Ni.
- M is preferably at least one selected from Fe and Mn from the viewpoint of cost. Fe is particularly preferable because the theoretical capacity of the positive electrode material for a secondary battery is easily developed. From the viewpoint of increasing the operating voltage, at least one selected from Co and Ni is preferable.
- the valence of M is a numerical value that can vary in each step of the production method of the present invention, and is in the range of +2 to +4. Therefore, the valence N 1 of M in the first compound is + 2 ⁇ N 1 ⁇ + 4.
- M is Fe, +2, +8/3, or +3, when Mn is +2, +3, or +4, when Co is +8/3, when Ni is +2 or +4 is preferable.
- X and y in the formula (1) are arbitrary numbers satisfying 0.8 ⁇ x / y ⁇ 1.2.
- the boric acid compound (3) can be obtained by satisfying this formula.
- x and y in Formula (1) it is preferable that x / y is 1.
- M x B y O z is M 2 B 2 O 5
- the valence N 1 of M is +2, easily obtained boric acid compound having an olivine-type crystal structure (3).
- M 2 B 2 O 5 is mixed with an oxide of A as the second compound (eg, A 2 O) and heated, the solid phase reaction represented by the following formula (7) is stoichiometrically Since it proceeds, AMBO 3 is easily obtained.
- the value of z is generally obtained from the formula (x + yN 1 +3) / 2.
- M is Mn, Co, and Ni
- the first compound preferably contains an amorphous substance.
- the next step (II) can be easily performed, and the composition of the boric acid compound can be easily controlled.
- the product can be prevented from becoming agglomerated, and the particle size of the product can be easily controlled.
- the crystallized product becomes a crystal nucleus in step (III), and it is easy to crystallize.
- the amount of the crystallized product in the first compound is preferably 0 to 20% by mass with respect to the total mass of the first compound. If the crystalline portion is 20% by mass or less, the reaction becomes a crystal nucleus in step (III) and promotes the reaction without reducing the ease of crushing the first compound and the reactivity with the second compound. It is preferable because it has the effect of
- the first compound is not limited to only M, boron (B), and oxygen (O), but includes at least one atom X selected from V, Si, P, Al, Mg, and Zn. Also good. By containing X in the first compound, the reactivity between the first compound and the second compound can be improved. In addition, when an amorphous material is used as the first compound, the first compound can be made amorphous.
- the content of X (the total amount when X consists of a plurality of atoms) is the atomic ratio of X to the total amount of boron (B) and X (X / (B + X)) is 0.01 to 0.2. It is preferable to set it as the range.
- the atomic ratio of Y to the total amount of boron (B) and Y (Y / (B + Y)) of the element Y acting as a reducing agent (for example, carbon (C)) is 0.01 to 0.1. It may be included in the range.
- the first compound is preferably flaky or fibrous.
- the average thickness is preferably 200 ⁇ m or less, particularly preferably 100 ⁇ m or less.
- the average diameter of the surface perpendicular to the average thickness in the case of flakes is not particularly limited.
- the average diameter is preferably 50 ⁇ m or less, particularly preferably 30 ⁇ m or less.
- the average thickness and average diameter can be measured with a caliper or a micrometer. The average diameter can also be measured by microscopic observation.
- the second compound is a compound containing at least one atom A selected from Li, Na, and K, as long as it is a compound that is thermally decomposed by heating and changes to A 2 O.
- the second compound is preferably a compound that changes to A 2 O in step (III).
- the boric acid compound (3) can be obtained efficiently.
- the second compound include A carbonate (A 2 CO 3 ), A hydrogen carbonate (AHCO 3 ), A hydroxide (AOH), A nitrate (ANO 3 ), A chloride ( ACl), A sulfate (A 2 SO 4 ), A acetate (CH 3 COOA) and A oxalate ((COOA) 2 ) (however, these compounds each form a hydrated salt).
- At least one selected from the group consisting of At least one selected from A 2 CO 3 , AHCO 3, and AOH is particularly preferable because it is inexpensive and easily available, and easily becomes A 2 O by heating.
- a 2 O is not preferable because it easily reacts with H 2 O and CO 2 and has low chemical stability.
- a constituting the second compound is suitable as a positive electrode material for a secondary battery, it is preferable that Li is essential, and only Li is particularly preferable.
- the boric acid compound containing Li can increase the capacity per unit volume (mass) of the secondary battery.
- the purity of the first compound or the second compound is not particularly limited, and is preferably 99% by mass or more in consideration of reactivity, characteristics of the obtained boric acid compound (3) (for example, characteristics of the positive electrode material), and the like.
- the first compound and the second compound are preferably particles.
- the average particle diameter of the particles is not particularly limited, and any of the average particle diameters is preferably 1 nm to 100 ⁇ m, more preferably 10 nm to 10 ⁇ m, and particularly preferably 10 nm to 1 ⁇ m, in terms of volume median diameter. When the average particle size is in the above range, the reaction between the first compound and the second compound can be promoted.
- the average particle diameter of a 1st compound or a 2nd compound is the said range when it is used as a raw material of process (I). That is, for example, in the case of producing the first compound by the step (IV), even if the average particle size of the obtained first compound is outside the above range, it is pulverized in advance before the preparation in the step (I). It only needs to be adjusted within the above range. In addition, it is not necessary to remove particularly the fine particles generated by the pulverization.
- the particle size can be measured by a sedimentation method or a laser diffraction / scattering particle size measuring device.
- the first compound and the second compound have an atomic ratio represented by the above formula (2), that is, a in formula (2) is 0 ⁇ a ⁇ 2, and b is 0.8. ⁇ B ⁇ 1.2.
- a boric acid compound (3) is obtained by making a and b into the said range.
- the boric acid compound (3) obtained by the present invention is preferably a particle, more preferably a crystalline particle, and particularly preferably an olivine type crystal particle.
- the atomic ratio of oxygen atoms in the preparation (when it is assumed that an oxide is formed, boron (B )
- the value of the atomic ratio of oxygen atoms when the atom is 1 is a value that can be changed in the subsequent step (III), and is a value that becomes c after the step (III).
- the value of the oxygen atomic ratio increases or decreases due to oxidation / reduction or volatilization of the components in the step (III)
- the value of the atomic ratio of oxygen atoms when the boron (B) atom is 1 in the preparation should be 100% or more and 103% or less with respect to the value of c of the target boric acid compound (3). preferable.
- the preparation of the first compound and the second compound may contain at least one carbon source selected from an organic compound and carbon powder described later.
- a carbon source is included in the preparation. Is preferred.
- the carbon source functions as a reducing agent when heated, and further functions as a conductive material after heating.
- the carbon powder contained in the preparation adheres to the surface of the boric acid compound (3) particles and improves the conductivity of the powder, which is an aggregate of the boric acid compound (3) particles.
- organic compounds are also thermally decomposed by, for example, the step (III), and further carbonized to become carbides. 3) The conductivity is improved. Accordingly, it is preferable that the organic compound has a property of undergoing a thermal decomposition reaction in step (III), for example, a hydrogen atom or an oxygen atom is desorbed and carbonized, whereby the reactant in the organic compound step (III) is converted into a conductive material.
- carbon powder When carbon powder is used as the carbon source, it is preferable to use it together with an organic compound in order to increase the binding strength to the boric acid compound (3). That is, it is preferable that the preparation contains an organic compound alone or contains an organic compound and carbon powder.
- the organic compound and carbon powder have a function of promoting the reduction reaction between the first compound and the second compound in the step (III).
- MBO 3 the valence of M is +3
- a 2 O are heated and an organic compound (C m H n ) is included
- AMBO 3 M has a valence of +2
- An organic compound decomposes and carbonizes at a temperature higher than the reaction temperature between the first compound and the second compound (including the generation of crystal nuclei and the grain growth temperature when the first compound is amorphous).
- the organic compound itself functions as a binder for the boric acid compound (3) of the carbon powder, it is preferably used in combination with the carbon powder. Further, it is preferable to use an organic compound having reducibility in order to prevent oxidation of the preparation during pulverization and further promote reduction.
- the organic compound is preferably at least one selected from saccharides, amino acids, peptides, aldehydes and ketones, and saccharides, amino acids and peptides are particularly preferable.
- sugars include monosaccharides such as glucose, fructose and galactose, oligosaccharides such as sucrose, maltose, cellobiose and trehalose, invert sugar, polysaccharides such as dextrin, amylose, amylopectin and cellulose, and similar substances such as ascorbic acid. Is mentioned. Monosaccharides and some oligosaccharides are preferred because of their strong reducing properties.
- amino acids examples include amino acids such as alanine and glycine.
- Peptides include low molecular weight peptides having a molecular weight of 1,000 or less.
- organic compounds having a reducing functional group such as an aldehyde group or a ketone group are also included.
- the organic compound glucose, sucrose, glucose-fructose invert sugar, caramel, starch, pregelatinized starch, carboxymethyl cellulose and the like are particularly preferable.
- carbon powder carbon black, graphite, acetylene black or the like is preferably used.
- the carbon powder at the time of pulverizing the preparation it is not necessary to separately provide a step of mixing the carbon powder after generating the olivine type particles of the boric acid compound (3) in the step (III).
- the carbon powder together with the organic compound at the time of pulverizing the preparation the distribution of the carbon powder in the boric acid compound (3) powder becomes uniform, and the organic compound or its pyrolyzate (carbide) The contact area increases. This makes it possible to increase the binding force of the carbon powder to the boric acid compound (3).
- the amount of the carbon source is preferably such that the ratio of the carbon equivalent (mass) to the total mass of the preparation and the carbon equivalent (mass) in the carbon source is 0.1 to 20% by mass. An amount of mass% is particularly preferred.
- a commercial item may be used for the 1st compound, and it may manufacture it.
- the 1st compound containing the said atom X and the atom Y it can manufacture by using the compound containing X and the compound containing Y with the compound containing M, and the compound containing B.
- the compound containing M in the raw material mixture includes oxides of M (FeO, Fe 3 O 4 , Fe 2 O 3 , MnO, Mn 2 O 3 , MnO 2 , CoO, Co 3 O 4 , Co 2 O 3 and NiO). And at least one compound selected from M oxyhydroxides (MO (OH)). It is also possible to use M in the metal state instead of the compound containing M. Fe 3 O 4 , Fe 2 O 3 , MnO, Mn 2 O 3 , MnO 2 , Co 3 O 4 and NiO are particularly preferred from the viewpoint of availability and cost.
- Compounds containing B in the raw material mixture include boric acid (H 3 BO 3 ), boron oxide (B 2 O 3 ), ammonium borate (NH 4 B 5 O 8 ), and ammonium hydrogen borate (NH 4 HB 4 O At least one selected from 7 ) is preferred.
- B 2 O 3 and H 3 BO 3 are particularly preferable from the viewpoint of easy availability and handling.
- Preferred combinations of the compound containing M and the compound containing B are Fe 3 O 4 , Fe 2 O 3 , MnO, Mn 2 O 3 , MnO 2 , Co 3 O 4, NiO, and B 2 O in terms of easy availability. 3 and H 3 BO 3 .
- the pulverization of the raw material mixture is preferably performed using a ball mill, a jet mill, a planetary mill or the like.
- the pulverization step is carried out dry or wet, and it is preferable to pulverize in a dry manner in that it is not necessary to remove the dispersion medium.
- pulverization a pulverized product in which raw materials having smaller particle diameters are uniformly and intimately mixed is obtained.
- the pulverized product after the raw material mixture is pulverized may be heated in air, in an inert gas, or in a reducing gas. Melting of the pulverized product in air is preferable in terms of cost. Even if it is a compound manufactured in the air, M which comprises a compound is reduce
- the inert gas refers to a gas containing 99% by volume or more of at least one inert gas selected from nitrogen gas (N 2 ) and rare gases such as helium gas (He) and argon gas (Ar).
- the reducing gas refers to a gas that is substantially free of oxygen by adding a reducing gas to the above-described inert gas.
- the reducing gas include hydrogen gas (H 2 ), carbon monoxide gas (CO), and ammonia gas (NH 3 ).
- the amount of the reducing gas in the inert gas is preferably 0.1% by volume or more, and particularly preferably 1 to 10% by volume of the reducing gas contained in the total gas volume.
- the oxygen content is preferably 1% by volume or less, and particularly preferably 0.1% by volume or less in the gas volume.
- the heating temperature of the pulverized material mixture is preferably 1,000 to 1,500 ° C, particularly preferably 1,200 to 1,400 ° C. When it is at least the lower limit of the above range, melting becomes easy, and when it is at most the upper limit of the above range, the raw material is difficult to volatilize.
- the heating time of the pulverized material mixture is preferably 0.2 to 4 hours, particularly preferably 0.5 to 2 hours. By setting it as the said range, the uniformity of the melt of a raw material mixture becomes sufficient, and a raw material component does not volatilize easily.
- the melt obtained by heating is cooled to obtain a glassy substance.
- a method for producing a sol, a hydrothermal method and a sol-gel method are used.
- a method of producing a glassy substance by cooling a melt obtained by heating is preferable in that an amorphous material can be produced in a large amount at a low cost.
- a method for cooling the melt a method in which the melt is dropped between the twin rollers rotating at high speed and the melt is cooled, a method in which the melt is dropped on the rotating single roller to cool, and a carbon plate on which the melt is cooled.
- a method of cooling by pressing on a metal plate is preferable.
- a cooling method using a twin roller is particularly preferable because the cooling rate is high and a large amount of processing can be performed.
- the double roller it is preferable to use one made of metal, carbon or ceramic.
- a cooling method there is also a method in which the melt is directly poured into water, but this method is difficult to control, it is difficult to obtain an amorphous material, the solidified product becomes a lump, and the disadvantage of requiring a lot of labor for grinding There is.
- a cooling method there is also a method in which a melt is directly added to liquid nitrogen, and the cooling rate can be made faster than in the case of water, but there are problems similar to the method using water, and the cost is high.
- the cooling of the melt is preferably performed in air, in an inert gas, or in a reducing gas because the equipment is simple. According to this cooling method, an amorphous substance can be obtained more easily.
- the cooling rate of the melt is preferably not less than -1 ⁇ 10 3 °C / sec, -1 ⁇ 10 4 °C / sec or more is particularly preferable.
- a temperature change per unit time (ie, cooling rate) in the case of cooling is indicated by a negative value
- a temperature change per unit time in case of heating ie, the heating rate
- the upper limit of the cooling rate is preferably about ⁇ 1 ⁇ 10 10 ° C./second from the viewpoint of manufacturing equipment and mass productivity, and 1 ⁇ 10 8 ° C./second is particularly preferable from the viewpoint of practicality.
- Step (II) is a step of obtaining a pulverized product by mixing and pulverizing the preparation obtained in step (I). Grinding gives a pulverized product of the formulation in which the smaller particle size compounds are uniformly and intimately mixed. Moreover, you may mix the said carbon source in the formulation which does not contain a carbon source at this process instead of using the formulation containing a carbon source. When a carbon source is mixed in this step, the type and amount of the carbon source may be the same as in the case of producing a preparation containing the carbon source.
- the pulverization of the preparation is preferably carried out dry or wet using a ball mill, jet mill, planetary mill or the like.
- a preparation containing a carbon source is used or when a carbon source is mixed in this step, it is preferable to wet pulverize the carbon source evenly on the surface of the pulverized product.
- the carbon source is an organic compound
- wet pulverization using a dispersion medium capable of dissolving the organic compound is preferable.
- the average particle size of the pulverized product at the end of the step (II) is preferably 1 nm to 100 ⁇ m in terms of volume median diameter in order to promote the reaction between the first compound and the second compound, and more preferably 10 nm to 10 ⁇ m. 10 nm to 1 ⁇ m is particularly preferable. When the average particle size is in the above range, the reaction between the first compound and the second compound can be promoted.
- a small particle size of the pulverized product is preferable because the heating temperature and heating time in step (III) can be reduced.
- the step (II) is carried out in a wet manner, it is preferable to carry out the step (III) after removing the dispersion medium by sedimentation, filtration, drying under reduced pressure, heat drying or the like.
- Step (III) is a step of reacting the first compound and the second compound to obtain a boric acid compound (3), preferably crystalline particles thereof, more preferably olivine type crystal particles.
- the step (III) preferably includes a thermal decomposition reaction step of the second compound, a crystal nucleus generation step and a grain growth step in the case where the first compound is an amorphous substance.
- a pulverized product containing a carbon source it is preferable that the carbon source or a thermally decomposed product thereof be bonded to the surface of the generated boric acid compound (3) particles.
- the step (II) is performed by a wet method, the dispersion medium may be removed by heating in the step (III).
- Step (III) is performed in an inert gas or a reducing gas.
- the pressure may be normal pressure, increased pressure (1.1 ⁇ 10 5 Pa or more), and reduced pressure (0.9 ⁇ 10 5 Pa or less).
- the container containing the reducing agent for example, graphite
- the pulverized material is loaded in the heating furnace, reduction of M ions in the pulverized material (for example, change from M 3+ to M 2+ ). Can be promoted.
- the valence N 3 of M in the boric acid compound (3) is equal to the valence N 1 of M in the first compound or M 1 smaller than the valence N 1 of.
- the valence N 3 of M in the boric acid compound (3) is preferably smaller than the valence N 1 of M of the first compound as the raw material (N 3 ⁇ N 1 ) as an average value. It is particularly preferred that substantially all of M in the first compound is reduced (N 3 ⁇ N 1 ⁇ 1) by the step (III). Further, the valence N 3 of M in the boric acid compound (3) is preferably N 1 -1.
- the heating temperature is preferably 400 to 800 ° C, particularly preferably 500 to 700 ° C.
- a compound containing an amorphous part particularly a compound having an amorphous part of 80 to 100% by mass
- it may be heated at a temperature lower than the heating temperature of a normal solid phase reaction. it can.
- the heating temperature is not less than the lower limit of the above range, the reaction is likely to occur. If it is below the upper limit of the above range, the pulverized product will not melt.
- the heating may be held at a constant temperature or may be performed by changing the temperature in multiple stages. As the heating temperature is increased, the diameter of the generated particles tends to increase. Therefore, it is preferable to set the heating temperature according to the desired particle diameter.
- the heating time (holding time depending on the heating temperature) is preferably 2 to 72 hours in consideration of the desired particle size.
- the cooling rate in the cooling is preferably ⁇ 30 ° C./hour to ⁇ 300 ° C./hour.
- the cooling rate is preferably ⁇ 30 ° C./hour to ⁇ 300 ° C./hour.
- the cooling may be left to cool to room temperature. Cooling is preferably performed in an inert gas or a reducing gas.
- the organic compound and carbon powder adhering to the surface of the pulverized product in the step (II) are bonded to the particle surface of the boric acid compound (3) generated in the step (III) and function as a conductive material.
- the organic compound is thermally decomposed in the step (III), and further becomes at least a part of a carbide to function as a conductive material.
- the thermal decomposition of the organic compound is preferably performed at 400 ° C. or lower, and the carbonization is preferably performed at 600 ° C. or lower.
- volume change associated with the pyrolysis reaction can be reduced, so that the carbide and carbon powder are uniformly and firmly bonded to the surface of the boric acid compound (3). it can.
- the boric acid compound (3) obtained by the production method of the present invention is a boric acid compound particularly useful as a positive electrode material for a secondary battery.
- the solid composed of the boric acid compound (3) preferably includes an olivine type crystal structure, and particularly preferably olivine type crystal particles.
- the particles include both primary particles and secondary particles.
- the conductive material based on the organic compound or carbon powder is uniformly and firmly bonded to the surface of the boric acid compound (3) at the same time as the crystalline particles are formed.
- a powder material can be produced. This powder material is suitable for a positive electrode material for a secondary battery.
- the boric acid compound can be produced inexpensively and efficiently.
- olivine-type crystal particles having excellent chemical composition and particle size uniformity and high crystallinity can be obtained.
- Such olivine-type crystal particles of the boric acid compound (3) can improve the characteristics and reliability based on the chemical composition and the uniformity of the particle diameter.
- the obtained olivine type crystal particles have high crystallinity, when applied to a positive electrode material for a secondary battery, it is possible to suppress functional deterioration in repeated use. Therefore, it is possible to provide a positive electrode material for a secondary battery having excellent characteristics and reliability at a low cost.
- the conductive material can be uniformly and firmly bonded to the surface of the boric acid compound (3) particles. For this reason, the electroconductivity of the positive electrode material which consists of powder of a boric-acid compound (3), and its reliability can be improved. That is, a positive electrode material for a secondary battery that is excellent in characteristics including conductivity and reliability can be obtained with good reproducibility. Therefore, while improving the capacity
- the boric acid compound (3) obtained by the production method of the present invention is preferably a boric acid compound having a composition represented by the following formula (4).
- a a M b BO (0.5a + b + 1.5) (4) (In the formula, A and M represent the same kind of atoms as described above, and a and b represent the same numerical values as described above.)
- the boric acid compound (3) is more preferably a boric acid compound having a composition represented by LiMBO 3 , and boric acid having a composition represented by LiFe d Mn 1-d BO 3 (0 ⁇ d ⁇ 1).
- a compound is further preferable, and a boric acid compound having a composition represented by LiFeBO 3 is particularly preferable.
- These boric acid compounds are preferably olivine type crystal particles, and a powder comprising the olivine type crystal particles is suitable as a positive electrode material for a secondary battery.
- the average particle size of the boric acid compound (3) particles of the present invention is preferably from 10 nm to 10 ⁇ m, particularly preferably from 10 nm to 2 ⁇ m, in terms of volume median diameter.
- the average particle diameter can be determined by, for example, observation with an electron microscope or measurement with a laser diffraction particle size distribution meter.
- the specific surface area of the powder consisting of boric acid compound (3) is preferably 0.2 ⁇ 200m 2 / g, 1 ⁇ 200m 2 / g is particularly preferred. By making a specific surface area into this range, the electroconductivity of the powder which consists of a boric acid compound (3) becomes high.
- the specific surface area can be measured by, for example, a specific surface area measuring apparatus using a nitrogen adsorption method.
- the first compound is preferably a compound that easily becomes amorphous.
- M x B y O z using at least one selected from Fe and Mn as M, that is, (Fe e Mn 1-e ) x B y O z (0 ⁇ e ⁇ 1) is exemplified.
- the second compound is preferably Li carbonate or bicarbonate.
- the obtained boric acid compound is preferably a crystalline material.
- Fe f Mn 2-f B 2 O 5 (0 ⁇ f ⁇ 2) is used as the first compound, and Li 2 CO 3 and LiHCO 3 are used as the second compound.
- a method for producing particles containing LiFe d Mn 1-d BO 3 (0 ⁇ d ⁇ 1) having an olivine type crystal structure As a second specific example, Fe g Mn 1-g BO 3 (0 ⁇ g ⁇ 1) is used as the first compound, and at least one selected from Li 2 CO 3 and LiHCO 3 is used as the second compound.
- a method for producing particles containing LiFe d Mn 1-d BO 3 (0 ⁇ d ⁇ 1) having an olivine type crystal structure by using seeds is mentioned.
- a positive electrode for a secondary battery and a secondary battery can be produced using the boric acid compound (3) obtained by the production method of the present invention as a positive electrode material for a secondary battery.
- the secondary battery include a metal lithium secondary battery, a lithium ion secondary battery, and a lithium polymer secondary battery, and a lithium ion secondary battery is preferable.
- the battery shape is not limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately employed.
- the positive electrode for a secondary battery of the present invention can be manufactured according to a known electrode manufacturing method except that the boric acid compound (3) obtained by the manufacturing method of the present invention is used.
- a powder of boric acid compound (3) may be added to a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine if necessary.
- the mixed powder thus obtained may be press-molded on a support made of stainless steel or filled in a metal container.
- the mixed powder is mixed with an organic solvent (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran. Etc.) can also be employed such as applying the slurry obtained by mixing with a metal substrate such as aluminum, nickel, stainless steel, or copper.
- organic solvent N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran. Etc.
- Etc. can also be employed such as applying the slurry obtained by mixing with
- the structure of the secondary battery a structure in a known secondary battery can be adopted except that the positive electrode for a secondary battery obtained by the production method of the present invention is used as an electrode.
- the negative electrode a known negative electrode active material can be used as the active material, and it is preferable to use at least one selected from the group consisting of alkali metal materials and alkaline earth metal materials.
- the electrolytic solution a non-aqueous electrolytic solution is preferable. That is, as the secondary battery obtained by the production method of the present invention, a non-aqueous electrolyte lithium ion secondary battery is preferable.
- Table 1 shows triiron tetroxide (Fe 3 O 4 ), manganese dioxide (MnO 2 ), tricobalt tetroxide (Co 3 O 4 ), nickel oxide (NiO), and boron oxide (B 2 O 3 ).
- the raw material mixture was weighed so as to have the composition of the first compound, and the raw material mixture was pulverized by a dry method. These pulverized products were each filled in a platinum alloy crucible containing 20% by mass of rhodium. Next, the crucible was placed in an electric furnace (manufactured by Motoyama Co., Ltd., apparatus name: NH3045F) equipped with a heating element made of molybdenum silicide. The electric furnace was heated by heating at 1,350 ° C. for 0.5 hours while flowing N 2 gas at a flow rate of 2 L / min. Each melt was obtained after confirming that it became transparent visually.
- the molten material in the crucible is cooled at ⁇ 1 ⁇ 10 5 ° C./second by passing through a stainless steel double roller having a diameter of about 15 cm rotating at 400 revolutions per minute, and the black or brownish flaky solidified product is obtained. Obtained.
- the obtained solidified product was a glassy substance. It was found from the X-ray diffraction pattern that the flaky solidified product obtained in each example was mainly composed of an amorphous part. The ratio of the amorphous part was 90% by mass or more.
- the first compound was produced as described above.
- the X-ray diffraction patterns of the flaky solidified products obtained in Examples 1 to 6 are shown in FIG. FIG.
- a) is an X-ray diffraction pattern of the flaky solidified product obtained in Example 1.
- b) to f) are X-ray diffraction patterns of the flaky solidified product obtained in Examples 2 to 6, respectively. It is.
- the flaky solidified product obtained in each example was pulverized in advance by dry process, and these and lithium carbonate (second compound) were prepared so as to have a molar ratio of 1: 1 based on the oxide, and then the formulation was ethanol.
- Each pulverized product was heated in 3% by volume H 2 —Ar gas at 600 ° C. for 8 hours to obtain boric acid compound particles each having a composition represented by LiMBO 3 .
- each pulverized product was heated at 500 ° C. ⁇ 8 hours in 3% by volume H 2 —Ar gas, and heated at 700 ° C. ⁇ 8 hours, and at any temperature, the above 600 ° C. ⁇ Boric acid compound particles having the same composition represented by LiMBO 3 as in the case of heating for 8 hours were obtained.
- Example 12 The first compound is Fe 2 B 2 O 5 , the second compound is Li 2 CO 3, and the molar ratio of these oxide standards is 1: 0.8 (Example 12) and 1: 1.2 (implemented).
- Example 13) was pulverized in the same manner as in Example 1 and the pulverized product was heated at 600 ° C. for 8 hours in 3% by volume H 2 —Ar gas to thereby obtain Li 0.8 MBO 2. 9 and boric acid compound particles having a composition represented by Li 1.2 MBO 3.1 were obtained.
- the particle size distribution of the boric acid compounds obtained in Examples 1 and 6 was measured with a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., apparatus name: LA-920).
- the median diameters in terms of volume were 0.68 ⁇ m (Example 1) and 0.75 ⁇ m (Example 6), respectively. Furthermore, it was 24 m ⁇ 2 > / g (Example 1) and 22 micrometers (Example 6) when the specific surface area was measured with the specific surface area measuring apparatus (The Shimadzu Corporation Corp. make, apparatus name: ASAP2020).
- Example 14 to 19 The flaky solidified products obtained in Examples 1 to 6 were previously pulverized in a dry manner, and these and lithium carbonate (second compound) were blended so that the molar ratio based on the oxide was 1: 1. In addition, carbon black was added to the formulation so that the mass ratio of the formulation to carbon black was 90:10. These were pulverized wet in the same manner as in Example 1. Each pulverized product was heated in N 2 gas at 600 ° C. for 8 hours to obtain boric acid compound particles each having a composition represented by carbon-containing LiMBO 3 .
- the mineral phase of each particle obtained was identified with an X-ray diffractometer. As a result, diffraction patterns of existing LiFeBO 3 (PDF No. 01-070-8321) and / or LiMnBO 3 (PDF No. 01-053-0371) were all found. A similar diffraction pattern was obtained. Furthermore, when the carbon content of the boric acid compound particles obtained in Examples 14, 16 and 19 was measured with a carbon analyzer, it was 8.5% (Example 14) and 8.2% (implementation) on a C mass basis, respectively. Example 16) and 8.7% (Example 19).
- Example 20 to 25 Triiron tetroxide (Fe 3 O 4 ), manganese dioxide (MnO 2 ), and boron oxide (B 2 O 3 ) are weighed and mixed so as to have the composition of the first compound shown in Table 2, respectively, The mixture was pulverized in the same manner as in Example 1 and then heated at 1,350 ° C. for 0.5 hour. Next, the melt was cooled in the same manner as in Example 1 to produce a flaky solidified product.
- FIGS. 4A to 4F are X-ray diffraction patterns of the flaky solidified products obtained in Examples 20 to 25.
- FIG. 4A to 4F are X-ray diffraction patterns of the flaky solidified products obtained in Examples 20 to 25.
- the flaky solidified product obtained in each example was previously pulverized in a dry manner, and these and lithium carbonate (second compound) were prepared so as to have a molar ratio based on oxide of 1: 1 to obtain a formulation, Furthermore, carbon black and glucose (10% aqueous solution) were added to the formulation so that the mass ratio of the formulation to carbon black and glucose was 90: 5: 5. These were pulverized wet in the same manner as in Example 1. Each pulverized product was heated in 3% by volume H 2 —Ar gas at 600 ° C. for 8 hours to obtain boric acid compound particles each having a composition represented by carbon-containing LiMBO 3 . Also, similar boric acid compound particles were obtained by heating each pulverized product in 3 volume% H 2 —Ar gas at 700 ° C. for 8 hours.
- Example 26 to 29 ⁇ Manufacture of positive electrode for Li ion secondary battery and battery for evaluation> Boric acid compound particles having a composition represented by LiMBO 3 obtained by heating at 600 ° C. for 8 hours in Examples 1, 14, 16 and 19, or a boric acid compound having a composition represented by carbon-containing LiMBO 3
- the particles were active materials.
- the active material powder, polyvinylidene fluoride resin (binder), and acetylene black (conductive material) were weighed so as to have a mass ratio of 85: 5: 10, and then in N-methylpyrrolidone (solvent).
- the slurry was prepared by mixing until uniform. Next, the slurry was applied to an aluminum foil having a thickness of 30 ⁇ m with a bar coater. After these were dried at 120 ° C. in air to remove the solvent, the coating layer was consolidated by a roll press, and then cut into strips having a width of 10 mm and a length of 40 mm.
- the coating layer was peeled off leaving a 10 ⁇ 10 mm tip of strip-shaped aluminum foil, which was used as an electrode.
- the coating thickness of the obtained electrode after roll pressing was 20 ⁇ m.
- the obtained electrode was vacuum-dried at 150 ° C., then carried into a glove box filled with purified argon gas, and opposed to a counter electrode in which lithium foil was pressure-bonded to a nickel mesh with a porous polyethylene film separator, Both sides were fixed with a polyethylene plate.
- This charge / discharge cycle was repeated 10 cycles.
- the discharge capacities of the 10th cycle of the half-cells using the active materials of Examples 1, 14, 16 and 19 were 130 mAh / g (Example 1), 141 mAh / g (Example 14), and 122 mAh / g (implemented), respectively.
- the half battery using the active material of Example 1 was put into a 60 degreeC thermostat, and the same charging / discharging test was done.
- the discharge capacity at the 10th cycle was 165 mAh / g.
- the boric acid compound obtained by the present invention is useful as a positive electrode material used for manufacturing a positive electrode of a secondary battery such as a lithium ion secondary battery. It should be noted that the entire content of the specification, claims, drawings and abstract of Japanese Patent Application 2010-028572 filed on February 12, 2010 is cited herein as the disclosure of the specification of the present invention. Incorporated.
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Abstract
Description
LiBO2+M(COO)2・nH2O
→LiMBO3+CO+CO2+nH2O …(5)
非特許文献2には、下式(6)で表される固相反応でLiFeBO3を製造する方法が記載されており、また生成物の構造解析がなされている。
Li2CO3+2M(COO)2・2H2O+2H3BO3
→2LiMBO3+2CO+4CO2+7H2O …(6)
[1]下式(1)で表される組成を有する第1の化合物と、Li、Na、及びKから選択される少なくとも1種の原子Aを含む第2の化合物とを、下式(2)で表される原子比となるように調合して調合物を得る工程、
前記調合物を混合しつつ粉砕して粉砕物を得る工程、
前記粉砕物を不活性ガス中又は還元ガス中で加熱し、下式(3)で表される組成を有するホウ酸化合物を得る工程、
を含むことを特徴とするホウ酸化合物の製造方法。
MxByOz (1)
(式中、MはFe、Mn、Co及びNiから選択される少なくとも1種の原子であり、かつ、Mの価数N1は+2≦N1≦+4であり、x及びyは0.8≦x/y≦1.2を満足する数であり、zはx、yの数値及びMの価数N1に依存する数である。)
A:M:B=a:b:1 (2)
(式中、A及びMは前記と同じ種類の原子を示し、aは0<a<2、bは0.8<b<1.2である。)
AaMbBOc (3)
(式中、A及びMは前記と同じ種類の原子を示し、Mの価数は前記N1と等しいかN1よりも小さく、a及びbは前記と同じ数値を示し、cはa、bの数値及びMの価数に依存する数である。)
[3]Mの酸化物、Mのオキシ水酸化物及びMの金属から選択される少なくとも1種と、ホウ酸、酸化ホウ素、ホウ酸アンモニウム及びホウ酸水素アンモニウムから選択される少なくとも1種とを、MとBが式(1)で表される組成となるように調合して原料混合物を得、該原料混合物を粉砕し、加熱して溶融物を得た後、該溶融物を冷却して式(1)で表される組成を有する第1の化合物を得る工程を含む、[1]のホウ酸化合物の製造方法。
[4]前記溶融物の冷却速度が、-103℃/秒~-1010℃/秒である、[2]又は[3]のホウ酸化合物の製造方法。
[6]前記第2の化合物が、加熱によりA2Oに変化する化合物である、[1]~[5]のホウ酸化合物の製造方法。
[7]前記第2の化合物が、Aの炭酸塩(A2CO3)、Aの炭酸水素塩(AHCO3)、Aの水酸化物(AOH)、Aの硝酸塩(ANO3)、Aの塩化物(ACl)、Aの硫酸塩(A2SO4)、Aの酢酸塩(CH3COOA)及びAのシュウ酸塩((COOA)2)(ただし、これらの化合物は、それぞれ水和塩を形成していてもよい。)から選択される少なくとも1種である、[1]~[6]のホウ酸化合物の製造方法。
[8]前記加熱して式(3)で表される組成を有するホウ酸化合物を得る工程における加熱温度が、400~800℃である、[1]~[7]のホウ酸化合物の製造方法。
[9]前記粉砕物を得る工程において、前記調合物に、有機化合物及び炭素粉末から選択される少なくとも1種の炭素源を含ませ、該炭素源の量は、調合物と炭素源中の炭素換算量(質量)との合計質量に対する該炭素換算量(質量)の割合が0.1~20質量%となる量である、[1]~[8]のホウ酸化合物の製造方法。
[10]式(3)で表される組成を有するホウ酸化合物が、下式(4)で表される組成を有する結晶粒子である、[1]~[9]のホウ酸化合物の製造方法。
AaMbBO(0.5a+b+1.5) (4)
(式中、A及びMは前記と同じ種類の原子を示し、a及びbは前記と同じ数値を示す。)
[11]式(3)で表される組成を有するホウ酸化合物が、オリビン型結晶構造のLiMBO3を含む粒子である、[1]~[10]のホウ酸化合物の製造方法。
[12]式(3)で表される組成を有するホウ酸化合物が、オリビン型結晶構造のLiFedMn1-dBO3(dは0≦d≦1である)を含む粒子である、[1]~[11]のホウ酸化合物の製造方法。
前記調合物を混合しつつ粉砕して粉砕物を得る工程、
前記粉砕物を不活性ガス中又は還元ガス中で加熱し、下式(4)で表される組成を有するホウ酸化合物を得る工程、
を含むことを特徴とするホウ酸化合物の製造方法。
MxByOz (1)
(式中、MはFe、Mn、Co及びNiから選択される少なくとも1種の原子であり、かつ、Mの価数N1は+2≦N1≦+4であり、x及びyは0.8≦x/y≦1.2を満足する数であり、zはx、yの数値及びMの価数N1に依存する数である。)
AaMbBO(0.5a+b+1.5) (4)
(式中、A及びMは前記と同じ種類の原子を示し、Mの価数は前記N1と等しいかN1よりも小さく、a及びbは前記と同じ数値を示す。)
[15]前記[14]の製造方法で二次電池用正極を得て、次に、該二次電池用正極を用いて二次電池を製造することを特徴とする二次電池の製造方法。
また、オリビン型構造の結晶を以下オリビン型結晶といい、オリビン型結晶を含む粒子を以下オリビン型結晶粒子ともいう。オリビン型結晶粒子は、オリビン型結晶構造以外の結晶構造を部分的に含んでいてもよく、非結晶構造を部分的に含んでいてもよい。オリビン型結晶粒子としては、その実質的にすべてがオリビン型結晶からなっていることが好ましい。
さらに、本発明製造方法の目的物である、式(3)で表される組成を有するホウ酸化合物を、ホウ酸化合物(3)ともいう。
工程(I):前記第1の化合物と前記第2の化合物とを、前記式(2)で表される原子比となるように調合して調合物を得る工程、
工程(II):前記調合物を混合しつつ粉砕して粉砕物を得る工程、
工程(III):前記粉砕物を不活性ガス中又は還元ガス中で加熱し、ホウ酸化合物(3)を得る工程。
第1の化合物としては、特に、Mの酸化物、Mのオキシ水酸化物及びMの金属から選択される少なくとも1種と、ホウ酸、酸化ホウ素、ホウ酸アンモニウム及びホウ酸水素アンモニウムから選択される少なくとも1種とを、MとBが式(1)で表される組成となるように調合して原料混合物を得、該原料混合物を粉砕し、加熱して溶融物を得た後、該溶融物を冷却して得られた化合物であることが好ましい。
本発明の製造方法で製造されるホウ酸化合物は、二次電池用正極材料として有用な化合物であり、特にリチウムイオン二次電池用正極材料として有用である。
また、特許文献1に記載の方法では、金属錯体の非晶質化に多くのエネルギーを要し、また大量生産には向かないという難点があるのに対し、本発明によれば、少ないエネルギーで所望の組成を有するホウ酸化合物を得られることから、大量生産に有利な製造方法である。
工程(I)は、第1の化合物と第2の化合物とを、式(2)で表される原子比となるように調合して調合物を得る工程である。
第1の化合物は予め粉砕してから調合するのが好ましい。粉砕は、ミキサー、ボールミル、ジェットミル、又は遊星ミル等を用いて、乾式又は湿式で行うことが好ましく、溶媒除去が不要なことから乾式が好ましい。
M(II)2B2O5+A2O→2AM(II)BO3 …(7)
また、x/y=1であるMxByOzがMBO3である場合、オリビン型結晶構造のホウ酸化合物(3)を得やすいと共に、空気中等で効率的に製造できるので好ましい。MBO3を、第2の化合物としてのAの酸化物(例えばA2O)と混合して不活性ガス中又は還元ガス中で加熱した場合、下式(8)で表される固相反応が化学量論的に進行するため、AMBO3が得やすい。
2M(III)BO3+A2O→2AM(II)BO3+0.5O2 …(8)
第1の化合物や第2の化合物は粒子であることが好ましい。該粒子の平均粒径は特に限定されず、いずれの平均粒径も体積換算のメディアン径で1nm~100μmが好ましく、10nm~10μmがより好ましく、10nm~1μmが特に好ましい。平均粒径が上記範囲であると、第1の化合物と第2の化合物との反応を促進できる。平均粒径が小さい場合には、還元反応が促進され、工程(III)の加熱温度や時間を低減できるために好ましい。なお、第1の化合物や第2の化合物の平均粒径は、工程(I)の原料として使用される際に上記範囲であるのが好ましい。すなわち、例えば工程(IV)によって第1の化合物を製造する場合、得られた第1の化合物の平均粒径は上記範囲外であっても、工程(I)において調合する前に予め粉砕して上記範囲に調整できていればよい。なお、粉砕によって生じた微粒子等は、特に除去する必要はない。粒径の測定は、沈降法やレーザ回折/散乱式粒子径測定装置で測定できる。
AとMとBを式(2)で表される原子比となるように調合して調合物とする際、調合物における酸素原子の原子比(酸化物となったと仮定した場合、ホウ素(B)原子を1とした場合の酸素原子の原子比)の値は後の工程(III)で変化しうる値であり、工程(III)の後にcとなる値である。例えば、工程(III)で成分の酸化還元、揮発等により酸素原子比の値が増減する場合には、該増減を考慮に入れた値とするのが好ましい。調合物においてホウ素(B)原子を1とした場合の酸素原子の原子比の値は、目的とするホウ酸化合物(3)のcの値に対して、100%以上103%以内とするのが好ましい。
2M(III)BO3+A2O+CmHn
→2AM(II)BO3+mCO2+n/2H2O …(9)
第1の化合物は、市販品を使用してもよいし、製造してもよい。製造する場合には、前記工程(IV)で製造することが好ましい。すなわち、まずMを含む化合物及びBを含む化合物を、MとBが式(1)で表される組成となるように調合して原料混合物を得、該原料混合物を粉砕し、該粉砕物を加熱して溶融物を得た後、該溶融物を冷却して第1の化合物を製造するのが好ましい。また、前記原子Xや原子Yを含む第1の化合物を製造する場合には、Xを含む化合物やYを含む化合物をMを含む化合物及びBを含む化合物とともに使用することにより、製造できる。
原料混合物におけるBを含む化合物としては、ホウ酸(H3BO3)、酸化ホウ素(B2O3)、ホウ酸アンモニウム(NH4B5O8)及びホウ酸水素アンモニウム(NH4HB4O7)から選択される少なくとも1種が好ましい。入手のし易さや取扱い易さの点から、B2O3及びH3BO3が特に好ましい。
Mを含む化合物とBを含む化合物の好ましい組み合わせは、入手容易な点からFe3O4、Fe2O3、MnO、Mn2O3、MnO2、Co3O4及びNiOと、B2O3及びH3BO3とである。
不活性ガスとは、窒素ガス(N2)、及びヘリウムガス(He)及びアルゴンガス(Ar)等の希ガスから選択される少なくとも1種の不活性ガスを99体積%以上含む気体をいう。還元ガスとは、上記した不活性ガスに、還元性を有するガスを添加し、実質的に酸素を含まない気体をいう。還元性を有するガスとしては、水素ガス(H2)、一酸化炭素ガス(CO)及びアンモニアガス(NH3)等が挙げられる。不活性ガス中の還元性を有するガスの量は、全気体体積中に含まれる還元性を有するガスの量が0.1体積%以上であるのが好ましく、1~10体積%が特に好ましい。酸素の含有量は、該気体体積中に1体積%以下が好ましく、0.1体積%以下が特に好ましい。
また、原料混合物の粉砕物の加熱時間は0.2~4時間が好ましく、0.5~2時間が特に好ましい。上記範囲とすることにより原料混合物の溶融物の均一性が充分になり、また原料成分が揮発しにくい。
溶融物の冷却方法としては、高速で回転する双ローラの間に溶融物を滴下して冷却する方法、回転する単ローラに溶融物を滴下して冷却する方法、及び溶融物を冷却したカーボン板や金属板にプレスして冷却する方法が好ましい。中でも、双ローラを用いた冷却方法が、冷却速度が速く、大量に処理できるので特に好ましい。双ローラとしては、金属製、カーボン製、セラミックス製のものを用いることが好ましい。
なお、冷却方法としては、溶融物を水に直接投入する方法もあるが、該方法は制御が難しく、非晶質物を得るのが難しく、固化物が塊状となり、粉砕に多くの労力を要する欠点がある。冷却方法としては、液体窒素に溶融物を直接投入する方法もあり、水の場合よりも冷却速度を速くできるが、水を使用する方法と同様な問題があり、高コストである。
溶融物の冷却速度は-1×103℃/秒以上が好ましく、-1×104℃/秒以上が特に好ましい。本明細書では、冷却する場合の単位時間当たりの温度変化(すなわち冷却速度)を負の値で示し、加熱する場合の単位時間当たりの温度変化(すなわち加熱速度)を正の値で示す。冷却速度を該値以上にすると非晶質物が得られやすい。冷却速度の上限値は製造設備や大量生産性の点から-1×1010℃/秒程度が好ましく、実用性の点からは1×108℃/秒が特に好ましい。
工程(II)は、工程(I)で得た調合物を混合しつつ粉砕して粉砕物を得る工程である。粉砕により、より小さな粒径の化合物が均一にかつ密に混合した、調合物の粉砕物が得られる。また、炭素源を含む調合物を使用する代わりに、この工程で炭素源を含まない調合物に前記炭素源を混入してもよい。この工程で炭素源を混入する場合、炭素源の種類や量などは前記炭素源を含む調合物を製造する場合と同じでよい。調合物の粉砕はボールミル、ジェットミル、遊星ミル等を用いて、乾式又は湿式で行うことが好ましい。炭素源を含む調合物を用いた場合やこの工程で炭素源を混入する場合には、炭素源を粉砕物の表面に均一に分散させる上で、湿式で粉砕することが好ましい。特に炭素源が有機化合物の場合、該有機化合物を溶解しうる分散媒を使用した湿式粉砕が好ましい。
工程(III)は、第1の化合物と第2の化合物とを反応させて、ホウ酸化合物(3)、好ましくはその結晶質粒子、さらに好ましくはオリビン型結晶粒子を得る工程である。工程(III)は、第2の化合物の熱分解反応工程や、第1の化合物が非晶質物である場合の結晶核生成工程及び粒成長工程を含むことが好ましい。さらに、炭素源を含む粉砕物を使用した場合には、生成するホウ酸化合物(3)の粒子の表面に炭素源やその熱分解物を結合させる工程であることが好ましい。工程(II)を湿式で行った場合には、工程(III)における加熱により分散媒の除去を行ってもよい。
圧力は、常圧、加圧(1.1×105Pa以上)、減圧(0.9×105Pa以下)のいずれでもよい。また、還元剤(例えばグラファイト)と粉砕物とを入れた容器を加熱炉内に装填して実施した場合には、粉砕物中のMイオンの還元(例えばM3+からM2+への変化)を促進することができる。
加熱は一定温度で保持しても、多段階に温度を変化させて行ってもよい。加熱温度を高くするほど、生成する粒子の径が大きくなる傾向があるため、所望の粒子径に応じて加熱温度を設定することが好ましい。
また、加熱時間(加熱温度による保持時間)は所望の粒子径を考慮して2~72時間が好ましい。
本発明の製造方法により得られるホウ酸化合物(3)は、特に二次電池用正極材料として有用なホウ酸化合物である。該ホウ酸化合物(3)からなる固体はオリビン型結晶構造を含むことが好ましく、特にオリビン型結晶粒子であることが好ましい。該粒子としては、一次粒子及び二次粒子の双方を含む。また、調合物に炭素源を含ませた場合には、ホウ酸化合物(3)の結晶質粒子の生成と同時に、その表面に有機化合物や炭素粉末に基づく導電材が均一にかつ強固に結合した粉末材料を製造することができる。この粉末材料は二次電池用正極材料に好適である。得られたホウ酸化合物(3)の粒子やそれを含む粉末材料中に二次粒子が存在する場合、一次粒子が破壊されない程度の範囲で解砕及び粉砕してもよい。
AaMbBO(0.5a+b+1.5) (4)
(式中、A及びMは前記と同じ種類の原子を示し、a及びbは前記と同じ数値を示す。)
特に、AとしてLiを使用すると共に、MとしてFe及びMnから選択される少なくとも1種を使用した組成を有することが好ましい。
ホウ酸化合物(3)はLiMBO3で表される組成を有するホウ酸化合物であることがより好ましく、LiFedMn1-dBO3(0≦d≦1)で表される組成を有するホウ酸化合物がさらに好ましく、LiFeBO3で表される組成を有するホウ酸化合物が特に好ましい。これらのホウ酸化合物はオリビン型結晶粒子であることが好ましく、該オリビン型結晶粒子からなる粉末は二次電池用正極材料として好適である。
第2の具体例としては、第1の化合物としてFegMn1-gBO3(0≦g≦1)を用いると共に、第2の化合物としてLi2CO3及びLiHCO3から選択される少なくとも1種を用いて、オリビン型結晶構造のLiFedMn1-dBO3(0≦d≦1)を含む粒子を製造する方法が挙げられる。
本発明の製造方法により得られたホウ酸化合物(3)を、二次電池用正極材料として用いて、二次電池用正極及び二次電池を製造できる。二次電池としては、金属リチウム二次電池、リチウムイオン二次電池、リチウムポリマー二次電池等が挙げられるが、リチウムイオン二次電池が好ましい。電池形状は制限されることはなく、例えば円筒状、角型、コイン型等の種々の形状及びサイズを適宜採用できる。
四酸化三鉄(Fe3O4)、二酸化マンガン(MnO2)、四酸化三コバルト(Co3O4)、酸化ニッケル(NiO)及び酸化ホウ素(B2O3)を、それぞれ表1に示す第1の化合物の組成となるように秤量して原料混合物を得、該原料混合物を乾式で粉砕した。これらの粉砕物を、ロジウムを20質量%含む白金合金製のるつぼにそれぞれ充填した。次に、該るつぼをケイ化モリブデン製の発熱体を備える電気炉(株式会社モトヤマ社製、装置名:NH3045F)の中に入れた。該電気炉を、流量2L/分でN2ガスを流通しつつ、1,350℃で0.5時間加熱し加熱した。目視で透明になったことを確認して、それぞれの溶融物を得た。
第1の化合物をFe2B2O5、第2の化合物をLi2CO3とし、これらの酸化物基準のモル比で1:0.8(実施例12)及び1:1.2(実施例13)となるように実施例1と同様にして粉砕し、粉砕物を3体積%H2-Arガス中にて、600℃で8時間加熱することによって、それぞれLi0.8MBO2.9及びLi1.2MBO3.1で表される組成を有するホウ酸化合物粒子を得た。
上記X線回折パターンは、いずれの粒子もオリビン型結晶粒子であることを示している。
実施例1~6で得たフレーク状固化物を予め乾式で粉砕し、これらと炭酸リチウム(第2の化合物)とを酸化物基準のモル比で1:1となるように調合して調合物を得、さらに該調合物に対してカーボンブラックを、該調合物とカーボンブラックとの質量比が90:10となるように添加した。これらを実施例1と同様に湿式で粉砕した。各粉砕物をN2ガス中にて600℃で8時間加熱することによって、それぞれ炭素含有のLiMBO3で表される組成を有するホウ酸化合物粒子を得た。
四酸化三鉄(Fe3O4)、二酸化マンガン(MnO2)及び酸化ホウ素(B2O3)を、それぞれ表2に示す第1の化合物の組成となるように秤量して混合し、該混合物を実施例1と同様に乾式で粉砕した後、1,350℃で0.5時間加熱した。次いで、実施例1と同様にして溶融物を冷却して、フレーク状固化物を製造した。実施例20~25で得たフレーク状固化物のX線回折パターンを図4に示す。図4のa)~f)は実施例20~25で得たフレーク状固化物のX線回折パターンである。
炭酸リチウム(Li2CO3)、四酸化三鉄(Fe3O4)、及び酸化ホウ素(B2O3)を、LiFeBO3で表される組成となるように秤量して混合し、混合物を実施例1と同様に乾式で粉砕した後、1,400℃で加熱したが、完全に溶融させることはできなかった。すなわち、第1の化合物を予め製造しておかなかったので、完全に溶融させることはできなかった。
<Liイオン二次電池用正極及び評価用電池の製造>
実施例1、14、16及び19にて600℃で8時間加熱して得たLiMBO3で表される組成を有するホウ酸化合物粒子又は炭素含有のLiMBO3で表される組成を有するホウ酸化合物粒子を活物質とした。該活物質の粉末とポリフッ化ビニリデン樹脂(結着剤)とアセチレンブラック(導電材)とを、質量比で85:5:10の比率となるように秤量し、N-メチルピロリドン(溶媒)中で均一になるまで混合してスラリーを調製した。次いで、該スラリーをバーコーターで厚さ30μmのアルミニウム箔に塗布した。これらを空気中にて120℃で乾燥させて溶媒を除去した後、ロールプレスで塗工層を圧密化した後、幅10mm×長さ40mmの短冊状に切り出した。
得られた半電池を25℃の恒温槽に入れ、定電流充放電試験機(北斗電工社製、装置名:HJ201B)に接続して充放電試験を行った。電流密度は電極活物質の質量(導電材と結着剤とを除いた質量)当たりの電流値を85mA/gとして充放電を行った。充電終止電位はLi対極基準で4.2Vとし、終止電圧に到達後即座に放電を開始した。放電終止電圧はLi対極基準で2.0Vとした。この充放電サイクルを10サイクル繰り返した。実施例1、14、16及び19の活物質を用いた半電池の10サイクル目の放電容量は、それぞれ130mAh/g(実施例1)、141mAh/g(実施例14)、122mAh/g(実施例16)、78mAh/g(実施例19)であった。さらに、実施例1の活物質を用いた半電池を60℃の恒温槽に入れ同様の充放電試験を行った。この10サイクル目の放電容量は、165mAh/gであった。
なお、2010年2月12日に出願された日本特許出願2010-028572号の明細書、特許請求の範囲、図面及び要約書の全内容をここに引用し、本発明の明細書の開示として、取り入れるものである。
Claims (15)
- 下式(1)で表される組成を有する第1の化合物と、Li、Na、及びKから選択される少なくとも1種の原子Aを含む第2の化合物とを、下式(2)で表される原子比となるように調合して調合物を得る工程、
前記調合物を混合しつつ粉砕して粉砕物を得る工程、
前記粉砕物を不活性ガス中又は還元ガス中で加熱し、下式(3)で表される組成を有するホウ酸化合物を得る工程、
を含むことを特徴とするホウ酸化合物の製造方法。
MxByOz (1)
(式中、MはFe、Mn、Co及びNiから選択される少なくとも1種の原子であり、かつ、Mの価数N1は+2≦N1≦+4であり、x及びyは0.8≦x/y≦1.2を満足する数であり、zはx、yの数値及びMの価数N1に依存する数である。)
A:M:B=a:b:1 (2)
(式中、A及びMは前記と同じ種類の原子を示し、aは0<a<2、bは0.8<b<1.2である。)
AaMbBOc (3)
(式中、A及びMは前記と同じ種類の原子を示し、Mの価数は前記N1と等しいかN1よりも小さく、a及びbは前記と同じ数値を示し、cはa、bの数値及びMの価数に依存する数である。) - 前記第1の化合物が、
Mの酸化物、Mのオキシ水酸化物及びMの金属から選択される少なくとも1種と、ホウ酸、酸化ホウ素、ホウ酸アンモニウム及びホウ酸水素アンモニウムから選択される少なくとも1種とを、MとBが式(1)で表される組成となるように調合して原料混合物を得、該原料混合物を粉砕し、加熱して溶融物を得た後、該溶融物を冷却して得られた化合物である、請求項1に記載のホウ酸化合物の製造方法。 - Mの酸化物、Mのオキシ水酸化物及びMの金属から選択される少なくとも1種と、ホウ酸、酸化ホウ素、ホウ酸アンモニウム及びホウ酸水素アンモニウムから選択される少なくとも1種とを、MとBが式(1)で表される組成となるように調合して原料混合物を得、該原料混合物を粉砕し、加熱して溶融物を得た後、該溶融物を冷却して式(1)で表される組成を有する第1の化合物を得る工程を含む、請求項1に記載のホウ酸化合物の製造方法。
- 前記溶融物の冷却速度が、-103℃/秒~-1010℃/秒である、請求項2又は3に記載のホウ酸化合物の製造方法。
- 前記第1の化合物が、非晶質部分を含む固体状化合物である、請求項1~4のいずれか一項記載のホウ酸化合物の製造方法。
- 前記第2の化合物が、加熱によりA2Oに変化する化合物である、請求項1~5のいずれか一項記載のホウ酸化合物の製造方法。
- 前記第2の化合物が、Aの炭酸塩(A2CO3)、Aの炭酸水素塩(AHCO3)、Aの水酸化物(AOH)、Aの硝酸塩(ANO3)、Aの塩化物(ACl)、Aの硫酸塩(A2SO4)、Aの酢酸塩(CH3COOA)及びAのシュウ酸塩((COOA)2)(ただし、これらの化合物は、それぞれ水和塩を形成していてもよい。)から選択される少なくとも1種である、請求項1~6のいずれか一項記載のホウ酸化合物の製造方法。
- 前記加熱して式(3)で表される組成を有するホウ酸化合物を得る工程における加熱温度が、400~800℃である、請求項1~7のいずれか一項記載のホウ酸化合物の製造方法。
- 前記粉砕物を得る工程において、前記調合物に、有機化合物及び炭素粉末から選択される少なくとも1種の炭素源を含ませ、該炭素源の量は、調合物と炭素源中の炭素換算量(質量)との合計質量に対する該炭素換算量(質量)の割合が0.1~20質量%となる量である、請求項1~8のいずれか一項記載のホウ酸化合物の製造方法。
- 式(3)で表される組成を有するホウ酸化合物が、下式(4)で表される組成を有する結晶粒子である、請求項1~9のいずれか一項記載のホウ酸化合物の製造方法。
AaMbBO(0.5a+b+1.5) (4)
(式中、A及びMは前記と同じ種類の原子を示し、a及びbは前記と同じ数値を示す。) - 式(3)で表される組成を有するホウ酸化合物が、オリビン型結晶構造のLiMBO3を含む粒子である、請求項1~10のいずれか一項記載のホウ酸化合物の製造方法。
- 式(3)で表される組成を有するホウ酸化合物が、オリビン型結晶構造のLiFedMn1-dBO3(dは0≦d≦1である)を含む粒子である、請求項1~11のいずれか一項記載のホウ酸化合物の製造方法。
- 下式(1)で表される組成を有する第1の化合物と、A2CO3、AHCO3及びAOH(式中、AはLi、Na、及びKから選択される少なくとも1種の原子である。いずれもそれぞれの水和塩を含む。)から選択される第2の化合物とを、調合して調合物を得る工程、
前記調合物を混合しつつ粉砕して粉砕物を得る工程、
前記粉砕物を不活性ガス中又は還元ガス中で加熱し、下式(4)で表される組成を有するホウ酸化合物を得る工程、
を含むことを特徴とするホウ酸化合物の製造方法。
MxByOz (1)
(式中、MはFe、Mn、Co及びNiから選択される少なくとも1種の原子であり、かつ、Mの価数N1は+2≦N1≦+4であり、x及びyは0.8≦x/y≦1.2を満足する数であり、zはx、yの数値及びMの価数N1に依存する数である。)
AaMbBO(0.5a+b+1.5) (4)
(式中、A及びMは前記と同じ種類の原子を示し、Mの価数は前記N1と等しいかN1よりも小さく、a及びbは前記と同じ数値を示す。) - 請求項1~13のいずれか一項記載の製造方法によってホウ酸化合物を得て、次に、該ホウ酸化合物を二次電池用正極材料として用いて、二次電池用正極を製造することを特徴とする二次電池用正極の製造方法。
- 請求項14記載の製造方法で二次電池用正極を得て、次に、該二次電池用正極を用いて二次電池を製造することを特徴とする二次電池の製造方法。
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