KR102758576B1 - Method for producing lithium titanium phosphate - Google Patents

Abstract

An industrially advantageous method is provided, which enables obtaining lithium titanium phosphate having a single phase by X-ray diffraction.
The following general formula (1):

A method for producing lithium titanium phosphate having a NASICON structure represented by , characterized by comprising: a first step of preparing a raw material mixture slurry (1) containing at least titanium dioxide, phosphoric acid, a surfactant, and a solvent; a second step of heat-treating the raw material mixture slurry (1) to obtain a raw material heat-treated product slurry (2); a third step of mixing a lithium source into the raw material heat-treated product slurry (2) to obtain a lithium-containing raw material heat-treated product slurry (3); a fourth step of spray-drying the lithium-containing raw material heat-treated product slurry (3) to obtain a reaction precursor containing at least Ti, P, and Li; and a fifth step of calcining the reaction precursor.

Description

Method for producing lithium titanium phosphate

The present invention relates to a method for producing lithium titanium phosphate useful as a solid electrolyte.

As one method to improve the safety of lithium secondary batteries, a method of using an oxide-based solid electrolyte with a wide operating temperature range and stability in the air is being studied.

As oxide-based solid electrolytes, garnet-type oxides, NASICON-type oxides, and perovskite-type oxides are being studied, for example.

Lithium titanium phosphate having a NASICON structure is stable in the air, and in particular, lithium titanium phosphate (LATP), in which some of the titanium in lithium titanium phosphate is replaced with the Al element, is one of the materials that is attracting attention as a solid electrolyte due to its high lithium ion conductivity (see, for example, Patent Documents 1 to 4).

As a method for manufacturing lithium titanium phosphate (LATP), for example, a method including dry mixing TiO ₂ , a lithium salt, a phosphate, and aluminum oxide, and then performing a solid-state reaction by heating (see Patent Document 1, etc.), a method including melting a plurality of oxides to be raw materials for lithium titanium phosphate (LATP) together with Ca(PO ₄ ) ₂ to vitrify, and then heat-treating and acid-treating the glass (see Patent Document 3), a method including mixing a plurality of oxides to be raw materials for lithium titanium phosphate (LATP), heating and dissolving at a temperature higher than the melting point of each raw material, and then naturally cooling to generate a crystal having a NASICON structure, pulverizing the crystal, and then performing calcination (see Patent Document 4), etc. have been proposed.

Japanese Patent Publication No. 2017-216062 Japanese Patent Publication No. 2-162605 Japanese Patent Publication No. 5-139781 International Publication No. 2016/063607 Pamphlet

However, in the above-mentioned solid-state method, it is difficult to obtain a raw material mixture in which titanium and phosphorus are uniformly mixed in an industrially advantageous manner, and therefore, there is a problem in that it is difficult to obtain a single-phase material in terms of X-ray diffraction in an industrially advantageous manner, and furthermore, the method of obtaining it by the vitrification method is not industrially advantageous because the process is complicated.

Accordingly, an object of the present invention is to provide an industrially advantageous method capable of obtaining lithium titanium phosphate which is single-phase in terms of X-ray diffraction.

In consideration of the above circumstances, the present inventors have conducted extensive studies and, as a result, have found that by heat-treating a mixed slurry (1) containing titanium dioxide, phosphoric acid, and a surfactant, a lithium-containing heat-treated slurry (3) is obtained in which adhesion inside a spray drying apparatus is suppressed even after addition of a lithium source due to a synergistic effect of the effect of the heat treatment and the effect of adding a surfactant, and that a reaction precursor containing Ti, P, Li, and further M elements obtained by spray-drying the lithium-containing heat-treated slurry (3) has excellent reactivity and that by calcining the reaction precursor, lithium titanium phosphate having a single phase in X-ray diffraction can be easily obtained, thereby completing the present invention.

That is, the present invention (1) has the following general formula (1):

(Wherein, 0≤x≤1.0, 0≤y≤0.5, and M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co. A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn, and Si.)

A method for manufacturing lithium titanium phosphate having a NASICON structure represented by

A first step of preparing a raw material mixed slurry (1) containing at least titanium dioxide, phosphoric acid, a surfactant and a solvent,

A second process of heat-treating the raw material mixture slurry (1) to obtain a raw material heat-treated slurry (2),

A third process of mixing a lithium source into the raw material heat treatment slurry (2) to obtain a lithium-containing raw material heat treatment slurry (3),

A fourth step of spray drying the lithium-containing raw material heat treatment slurry (3) to obtain a reaction precursor containing at least Ti, P and Li;

Step 5 of calcining the reaction precursor

The present invention provides a method for producing lithium titanium phosphate, characterized by having:

In addition, the present invention (2) provides a method for producing lithium titanium phosphate of (1), characterized in that, in the first process, an M source (M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co) and/or an A source (A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn and Si) is additionally contained in the raw material mixed slurry (1).

In addition, the present invention (3) provides a method for producing lithium titanium phosphate of (1), characterized in that an M source (M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co) and/or an A source (A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn and Si) is additionally mixed into the heat-treated slurry (2) or the lithium-containing heat-treated slurry (3).

In addition, the present invention (4) provides a method for producing lithium titanium phosphate according to any one of (1) to (3), characterized in that the titanium dioxide is in the anatase form.

In addition, the present invention (5) provides a method for producing lithium titanium phosphate according to any one of (1) to (4), characterized in that the surfactant is an anionic surfactant.

In addition, the present invention (6) provides a method for producing lithium titanium phosphate of (5), characterized in that the anionic surfactant is a polycarboxylic acid surfactant.

In addition, the present invention (7) provides a method for producing lithium titanium phosphate according to any one of (1) to (6), characterized in that the heat treatment temperature in the second process is 50 to 120°C.

In addition, the present invention (8) provides a method for producing lithium titanium phosphate according to any one of (1) to (7), characterized in that the reaction precursor exhibits a peak observed at around 975 cm ^-1 in Raman spectrum analysis.

In addition, the present invention (9) provides a method for producing lithium titanium phosphate according to any one of (1) to (8), characterized in that the M source is an Al-containing compound.

In addition, the present invention (10) provides a method for producing lithium titanium phosphate of (9), characterized in that the Al-containing compound is aluminum phosphate.

In addition, the present invention (11) provides a method for producing lithium titanium phosphate according to any one of (1) to (8), characterized in that the M source is a Cr-containing compound.

In addition, the present invention (12) provides a method for producing lithium titanium phosphate of (9), characterized in that the Cr-containing compound is chromium phosphate.

According to the present invention, an industrially advantageous method can be provided for obtaining lithium titanium phosphate which is single-phase in terms of X-ray diffraction.

Figure 1 is an X-ray diffraction diagram of a reaction precursor obtained in the fourth process of Example 1.
Figure 2 is a Raman spectrum of the reaction precursor obtained in the fourth process of Example 1.
Figure 3 is an X-ray diffraction diagram of lithium titanium phosphate obtained in Example 1.
Figure 4 is a SEM photograph of lithium titanium phosphate obtained in Example 1.
Figure 5 is a Raman spectrum of the attachment obtained in Comparative Example 1.
Figure 6 is an X-ray diffraction diagram of lithium titanium phosphate obtained in Example 2.
Figure 7 is a Raman spectrum of the reaction precursor obtained in the fourth process of Example 3.

The method for producing lithium titanium phosphate of the present invention comprises the following general formula (1):

(Wherein, 0≤x≤1.0, 0≤y≤0.5, and M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co. A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn, and Si.)

A method for manufacturing lithium titanium phosphate having a NASICON structure represented by

A first step of preparing a raw material mixed slurry (1) containing at least titanium dioxide, phosphoric acid, a surfactant and a solvent,

A second process of heat-treating the raw material mixture slurry (1) to obtain a raw material heat-treated slurry (2),

A third process of mixing a lithium source into the raw material heat treatment slurry (2) to obtain a lithium-containing raw material heat treatment slurry (3),

A fourth step of spray drying the lithium-containing raw material heat treatment slurry (3) to obtain a reaction precursor containing at least Ti, P and Li;

A method for producing lithium titanium phosphate, characterized by having a fifth process of calcining the reaction precursor.

The lithium titanium phosphate obtained by the method for producing lithium titanium phosphate of the present invention has the following general formula (1):

(Wherein, 0≤x≤1.0, 0≤y≤0.5, and M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co. A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn, and Si.)

It is lithium titanium phosphate having a NASICON structure represented by .

In the general formula (1), x is 0≤x≤1.0, preferably 0≤x≤0.7. y is 0≤y≤0.5, preferably 0≤y≤0.4. M and/or A are metal elements contained as needed for the purpose of improving performance such as, for example, lithium ion conductivity. M is a divalent or trivalent metal element, and represents one or more metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co, and is preferably Al and/or Cr.

A is a tetravalent or pentavalent metal element, and represents one or more metal elements selected from Ge, Zr, V, Nb, Sn, and Si, preferably Zr.

In addition, in the general formula (1), it is preferable that x+y is 0≤x+y≤1.5, preferably 0≤x+y≤1.0, from the viewpoint of improving performance such as lithium ion conductivity.

The first step of the method for producing lithium titanium phosphate of the present invention is a step of mixing titanium dioxide, phosphoric acid and a surfactant in a solvent by adding titanium dioxide, phosphoric acid and a surfactant to the solvent and stirring, thereby preparing a raw material mixed slurry (1) containing titanium dioxide, phosphoric acid and a surfactant.

The titanium dioxide for the first process may be manufactured by a sulfuric acid method, a hydrochloric acid method, a vapor phase method, or any other known method, and the method for manufacturing the titanium dioxide is not particularly limited.

The average particle size of titanium dioxide is preferably 20 ㎛ or less, particularly preferably 0.1 to 10 ㎛. When the average particle size of titanium dioxide is within the above range, the reactivity with each raw material increases. In addition, the BET specific surface area of titanium dioxide is preferably 50 m2/g or more, particularly preferably 150 to 400 m2/g. When the BET specific surface area of titanium dioxide is within the above range, the reactivity with each raw material increases.

The crystal structure of titanium dioxide is largely divided into anatase type and rutile type, and either crystal structure can be used in the present invention. Among these, the crystal structure of titanium dioxide in the anatase type is preferable because it improves reactivity.

The phosphoric acid for the first process is not particularly limited as long as it is industrially available. The phosphoric acid may be an aqueous solution.

The surfactant for the first process selectively adsorbs onto the particle surface of titanium dioxide particles, has a function of highly dispersing titanium dioxide in the raw material mixed slurry (1), and, in a state where the titanium dioxide is highly dispersed, can produce titanium phosphate represented by the general formula (2) described later in the heat treatment of the second process. In addition, in the method for producing lithium titanium phosphate of the present invention, the viscosity of the lithium-containing raw material heat treatment slurry (2) is lowered by the synergistic effect of the heat treatment in the second process and the surfactant remaining in the raw material heat treatment slurry (2) and the lithium-containing heat treatment slurry (3). Therefore, in the spray drying treatment of the fourth process, adhesion of the slurry inside the spray drying device is dramatically reduced.

As the surfactant for the first process, any one of anionic surfactant, cationic surfactant, nonionic surfactant and amphoteric surfactant may be used, and anionic surfactant is preferable because the effect of suppressing adhesion of slurry inside the spray drying device is enhanced.

The anionic surfactant is preferably at least one anionic surfactant selected from a carboxylic acid salt, a sulfuric acid ester salt, a sulfonate salt, and a phosphoric acid ester salt, because it has a high effect of lowering the viscosity of the raw material heat-treated slurry (2) and the lithium-containing raw material heat-treated slurry (3), and because a reaction precursor with excellent reactivity is obtained. A polycarboxylic acid surfactant or a polyacrylic acid surfactant is particularly preferable, and a polycarboxylic acid surfactant is more preferable. As the polycarboxylic acid surfactant, an ammonium salt of polycarboxylic acid is preferable.

The surfactant may be a commercially available one. Examples of commercially available polycarboxylic acid type surfactants include SN Dispersant 5020, SN Dispersant 5023, SN Dispersant 5027, SN Dispersant 5468, NOPCOSUS 5600 manufactured by San Nopco, and POISE 532A manufactured by KAO.

The solvent for the first process is a water solvent, or a mixed solvent of water and a hydrophilic organic solvent. The hydrophilic organic solvent is not particularly limited as long as it is inert to the raw material, and examples thereof include alcohols such as ethanol, propanol, and butanol, and methyl ethyl ketone. In the case of a mixed solvent of water and a hydrophilic organic solvent, the mixing ratio of water and the hydrophilic organic solvent is appropriately selected.

The content of titanium dioxide in the raw material mixed slurry (1) is preferably such that the molar ratio of P atoms in phosphoric acid to Ti atoms in titanium dioxide (P/Ti) is 1.50 to 3.00, particularly preferably 1.60 to 2.30. When the content of titanium dioxide in the raw material mixed slurry (1) is within the above range, it becomes easy to obtain single-phase lithium titanium phosphate.

The content of titanium dioxide as a solid content in the raw material mixed slurry (1) is preferably 0.3 to 40 mass%, particularly preferably 0.3 to 35 mass%, and more preferably 5 to 25 mass%, relative to the total amount of the raw material mixed slurry (1). When the content of titanium dioxide as a solid content in the raw material mixed slurry (1) is within the above range, the dispersibility of each raw material component is improved, and the effect of suppressing an increase in the viscosity of the slurry is also improved.

The content of the surfactant in the raw material mixed slurry (1) is preferably 1 to 20 parts by mass, particularly preferably 5 to 15 parts by mass, per 100 parts by mass of titanium dioxide. When the content of the surfactant in the raw material mixed slurry (1) is within the above range, the effect of suppressing an increase in the viscosity of the slurry is enhanced.

Additionally, the order of addition of titanium dioxide, phosphoric acid and surfactant to the solvent in the first process is not particularly limited.

In the first process, it is preferable to prepare the raw material mixed slurry (1) at a temperature at which titanium dioxide and phosphoric acid do not react. The temperature when preparing the raw material mixed slurry (1) is preferably less than 50°C, particularly preferably 40°C or less, and more preferably 10 to 30°C.

The second step of the method for producing lithium titanium phosphate of the present invention is a step of heat-treating the raw material mixed slurry (1) obtained by performing the first step to obtain a raw material heat-treated slurry (2).

In the heat treatment in the second process, at least phosphoric acid and titanium dioxide or A source added as needed react to form the following general formula (2):

(In the formula, 0≤y≤0.5, A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn and Si, and n represents 0≤n≤1.) is generated. Then, in the second process, by heat-treating the raw material mixed slurry (1), a raw material heat-treated slurry (2) containing the titanium phosphate represented by the general formula (2) is obtained.

A slurry containing titanium dioxide and phosphoric acid, and a slurry obtained by performing a heat treatment on a slurry containing titanium dioxide and phosphoric acid, have a significantly high viscosity of the slurry itself. Therefore, when the slurry is introduced into a spray drying device, the slurry adheres to the inside of the spray drying device, making spray drying impossible. In contrast, the inventors of the present invention found that by heat-treating a raw material mixed slurry (1) containing titanium dioxide and phosphoric acid in the presence of a surfactant, a slurry containing at least titanium phosphate represented by the general formula (2) is obtained, and further, by a synergistic effect of the effect of this heat treatment and the effect of adding the surfactant, a slurry (raw material heat-treated slurry (2), lithium-containing raw material heat-treated product slurry (3)) having lower viscosity than the raw material mixed slurry (1) and which is difficult to adhere to the inside of a spray drying device is obtained, and further, a lithium source is added to the raw material heat-treated slurry (2) to obtain a lithium-containing raw material heat-treated product slurry (3), and then a reaction precursor obtained by spray pyrolysis of the lithium-containing raw material heat-treated product slurry (3) is a reaction precursor having excellent reactivity.

The temperature of the heat treatment in the second step is preferably 50 to 120°C, particularly preferably 70 to 105°C. When the temperature of the heat treatment in the second step is in the above range, the reaction of titanium dioxide and phosphoric acid can be completed in an industrially advantageous manner. The time of the heat treatment in the second step is not critical in the method for producing lithium titanium phosphate of the present invention, but is preferably 2 hours or more, particularly preferably 4 to 24 hours. When the time of the heat treatment in the second step is in the above range, titanium phosphate represented by the general formula (2) is produced, and further, as described later, the reaction is sufficiently carried out until a peak is observed in the vicinity of 975 cm ^-1 in Raman spectrum analysis, so that adhesion of the slurry to the spray drying device is suppressed, and furthermore, it becomes easy to obtain a reaction precursor having excellent reactivity. In addition, in the present invention, the observation of a peak around 975 cm ^-1 in the Raman spectrum analysis means that the maximum value of the detected peak exists around 975 cm ^-1 , and also, around 975 cm ^-1 indicates a range of 975±20 cm ^-1 .

In the second process, it is preferable to perform the heat treatment under stirring in order to efficiently carry out the reaction between titanium dioxide and phosphoric acid. In addition, in the second process, it is preferable to perform the heat treatment under atmospheric pressure.

The third step of the method for producing lithium titanium phosphate of the present invention is a step of mixing a lithium source into a raw material heat treatment slurry (2) to obtain a lithium-containing raw material heat treatment slurry (3).

Lithium sources for the third process include lithium hydroxide, lithium carbonate, lithium oxide, and lithium organic acid. Among these, lithium hydroxide is preferable from the viewpoint of being able to exist in a dissolved state in the slurry and also being easy to obtain industrially.

As for the timing of addition to the slurry (2) of the lithium source heat treatment material, the lithium source may be added to the slurry (2) of the raw material heat treatment material in a heated state after the second process, or the lithium source may be added to the slurry (2) of the raw material heat treatment material that has been cooled to around room temperature, preferably to 30°C or lower, after the second process. In addition, it is preferable to add the lithium source to the slurry (2) of the raw material heat treatment material that has been cooled to around room temperature, preferably to 30°C or lower, after the second process, from the viewpoint of suppressing an increase in the viscosity of the slurry.

The amount of lithium source added is preferably such that the molar ratio (Li/Ti) of Li atoms in the lithium source to Ti atoms in the raw material heat treatment slurry (2) is 0.5 to 2.0, particularly preferably 0.6 to 1.3. When the amount of lithium source added is within the above range, the lithium ion conductivity increases.

In this way, a lithium-containing raw material heat-treated slurry (3) is obtained in the third process. In the method for producing lithium titanium phosphate of the present invention, at any time between the start of the first process and the end of the third process, if necessary, an M source (M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co) and/or an A source (A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn, and Si) can be additionally contained in the slurry (raw material mixed slurry (1), raw material heat-treated slurry (2), lithium-containing raw material heat-treated slurry (3)). That is, in the method for manufacturing lithium titanium phosphate of the present invention, when preparing the raw material mixed slurry (1) in the first step, the M source and/or the A source can be mixed into the solvent, when preparing the raw material heated-processed slurry (2) obtained in the second step, or when mixing the lithium source in the third step, the M source and/or the A source can be mixed into the slurry.

As M sources, examples thereof include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing the M element. As M sources, examples thereof include Al-containing compounds and Cr-containing compounds. As Al-containing compounds, examples thereof include aluminum phosphate. As Cr-containing compounds, examples thereof include chromium phosphate.

Also, as element A, examples thereof include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing element A.

The content of the M source is such that the molar ratio of the M atoms in the M source to the molar ratio of the sum of the Ti atoms in the titanium dioxide and the M atoms in the M source (M/(M+Ti)) is greater than 0 and not more than 0.50, preferably 0.10 to 0.35, and particularly preferably 0.15 to 0.30. When the molar ratio of the M atoms in the M source to the molar ratio of the sum of the Ti atoms in the titanium dioxide and the M atoms in the M source (M/(M+Ti)) is in the above range, it becomes easy to obtain lithium titanium phosphate which is single-phase in terms of X-ray diffraction. In addition, when adding M source, in terms of increasing lithium ion conductivity, the amount of lithium source added in the third process is preferably such that the molar ratio of Li atoms in the lithium source to the total molar ratio of Ti atoms in the heat-treated slurry (2) and M atoms in the M source (Li/(Ti+M)) is 0.50 to 1.00, and is particularly preferably such that the amount is 0.60 to 0.90.

The content of the A source is such that the molar ratio of the A atoms in the A source to the molar ratio of the sum of the Ti atoms in the titanium dioxide and the A atoms in the A source (A / (A + Ti)) is greater than 0 and 0.50 or less, preferably greater than 0 and 0.40 or less, and particularly preferably 0.02 to 0.25. When the molar ratio of the A atoms in the A source to the molar ratio of the sum of the Ti atoms in the titanium dioxide and the A atoms in the A source (A / (A + Ti)) is within the above range, it becomes easy to obtain lithium titanium phosphate which is single-phase in terms of X-ray diffraction. In addition, when adding A source, in terms of increasing lithium ion conductivity, the amount of lithium source added in the third process is preferably such that the molar ratio of Li atoms in the lithium source to the total molar ratio of Ti atoms in the heat-treated slurry (2) and A atoms in the A source (Li/(Ti+A)) is 0.50 to 1.00, and is particularly preferably such that the amount is 0.60 to 0.90.

In addition, when the M source and the A source are used together, the content of the M source and the A source is such that the molar ratio of the sum of the M atoms in the M source and the A atoms in the A source to the molar ratio of the sum of the Ti atoms in the titanium dioxide, the M atoms in the M source, and the A atoms in the A source ((M+A)/(M+A+Ti)) is greater than 0 and 0.5 or less, preferably 0.1 to 0.35, and particularly preferably 0.15 to 0.30. When the molar ratio of the sum of the M atoms in the M source and the A atoms in the A source to the molar ratio of the Ti atoms in the titanium dioxide, the M atoms in the M source, and the A atoms in the A source ((M+A)/(M+A+Ti)) is in the above range, it becomes easy to obtain lithium titanium phosphate which is single-phase in terms of X-ray diffraction.

The fourth step of the method for producing lithium titanium phosphate of the present invention is a step of spray drying the lithium-containing raw material heat treatment slurry (3) obtained by performing the third step to obtain a reaction precursor.

In the fourth process, since a granulated product in which raw material particles are densely packed is obtained by performing a drying process by spray drying, it becomes easy to obtain lithium titanium phosphate that is single-phase in X-ray diffraction.

In the spray drying in the fourth process, the slurry is atomized by a predetermined means, and the resulting fine droplets are dried to obtain a reaction precursor. For atomizing the slurry, there are methods using a rotating disc and methods using a pressure nozzle, for example. Either method can be used in the fourth process.

In the spray drying in the fourth process, the size of the atomized droplets is not particularly limited, but is preferably 1 to 40 μm, and particularly preferably 5 to 30 μm. It is preferable to determine the supply amount of slurry to the spray drying device by taking this viewpoint into consideration.

In the fourth process, it is preferable to adjust the drying temperature in the spray drying device so that the hot air inlet temperature is 150 to 300°C, preferably 200 to 250°C, and so that the hot air outlet temperature is 80 to 200°C, preferably 100 to 170°C, in order to prevent moisture absorption of the powder and facilitate recovery of the powder.

The reaction precursor obtained by carrying out the fourth process contains titanium phosphate represented by the general formula (2). In addition, the reaction precursor is preferable in that a peak is observed around 975 cm ^-1 in Raman spectrum analysis, which suppresses adhesion of the slurry to the spray drying device and makes it a reaction precursor with excellent reactivity. In addition, the reaction precursor obtained by further adding a lithium source and, if necessary, an M source is a compound other than titanium phosphate represented by the general formula (2), and the added lithium source or M source may be included as a compound containing a Li element and/or a compound containing an M element by reacting in the slurry.

By performing the fourth process in this manner, a reaction precursor for sintering in the fifth process is obtained.

The fifth step of the method for producing lithium titanium phosphate of the present invention is a step of calcining the reaction precursor obtained by performing the fourth step to obtain lithium titanium phosphate that is single-phase in X-ray.

The sintering temperature in the fifth process is preferably 500 to 1100°C, particularly preferably 550 to 1050°C. When the sintering temperature is in the above range, lithium titanium phosphate having a single phase in X-ray is obtained. On the other hand, when the sintering temperature is lower than the above range, the sintering time until it becomes a single phase in X-ray tends to be too long, and it also tends to be difficult to obtain a sharp particle size distribution. In addition, when the sintering temperature exceeds the above range, the sintered body in which the primary particles have grown significantly becomes coarse particles and is therefore not preferable.

The sintering atmosphere in the fifth process is an atmospheric atmosphere or an inert gas atmosphere. Examples of inert gases include argon gas, helium gas, and nitrogen gas, and among these, nitrogen gas is preferable from the viewpoint of being inexpensive and industrially advantageous.

The calcination time in the fifth process is not particularly limited, and is 0.5 hours or more, preferably 2 to 20 hours. In the fifth process, when calcination is performed for 0.5 hours or more, preferably 2 to 20 hours, lithium titanium phosphate having a single phase in X-ray diffraction can be obtained.

In the fifth process, the lithium titanium phosphate obtained by performing calcination once may be calcined multiple times as needed.

The lithium titanium phosphate obtained by performing the fifth process may be subjected to crushing or pulverizing treatment as needed, and may be further classified.

Thus, the lithium titanium phosphate obtained by the method for producing lithium titanium phosphate of the present invention, in addition to being lithium titanium phosphate having a single phase in terms of X-ray diffraction, has an average particle size determined by a laser diffraction scattering method of preferably 10 µm or less, particularly preferably 0.1 to 5 µm, and a BET specific surface area of preferably 1 m2/g or more, particularly preferably 5 to 30 m2/g. In addition, the average particle size determined by a laser diffraction scattering method refers to a particle size of an integrated 50% (D50) determined by a volume frequency particle size distribution measurement measured by a laser diffraction scattering method.

The lithium titanium phosphate obtained by carrying out the method for producing lithium titanium phosphate of the present invention is suitably used as a solid electrolyte or a positive electrode or negative electrode material of a secondary battery.

Example

Hereinafter, the present invention will be described by examples, but the present invention is not limited to these.

<Evaluation Device>

ㆍX-ray diffraction: Rigakusa UltimaIV was used.

Cu-Kα was used as a source. The measurement conditions were tube voltage 40 kV, tube current 40 mA, and scan speed 0.1°/sec.

ㆍRaman spectrometer: Nicolet Almega XR from Thermo Fisher Scientific was used. The measurement conditions were a laser wavelength of 532 nm.

(Example 1)

<Process 1>

While stirring at room temperature (25°C) using a three-one motor stirrer in 4.6 L of pure water, 600 g of anatase-type titanium dioxide (average particle size of 4 μm, BET surface area of 323 m2/g, anatase content of 99.9 mass%) with a purity of 89.9%, 52.2 g of anionic surfactant (ammonium polycarboxylate, SN Dispersant 5468 manufactured by San Nopco), and 962.9 g of 85 mass% phosphoric acid (moisture content of 15 mass%) were added in that order to prepare a raw material mixing slurry (1).

<2nd Process>

Next, the raw material mixture slurry (1) was heated to 90°C at 30°C/h under stirring, maintained at 90°C for 8 hours, and then cooled to room temperature (25°C) to obtain a raw material heat treatment slurry (2).

<Process 3>

Next, 715 g of a 50 mass% aluminum bisulfite aqueous solution and then 216.7 g of lithium hydroxide monohydrate dissolved in 870 ml of pure water were added to the raw material heat-treated material slurry (2) under stirring over 20 minutes to obtain a lithium-containing raw material heat-treated material slurry (3).

<Fourth Process>

Next, a slurry of lithium-containing raw material heat treatment material (3) was supplied at a supply rate of 2.4 L/h to a spray dryer set to 220°C, and a dried product was obtained. As a result of visually observing the inside of the spray dryer, the internal attachment was small, and the recovery rate was 95% on a solids basis. As a result of X-ray diffraction analysis of the obtained dried product, α-Ti(HPO ₄ ) ₂ (H ₂ O) was observed, and in addition, Li(H ₂ PO ₄ ), Al(PO ₄ ), Al(PO ₄ )(H ₂ O), and Al(H ₂ PO ₄ )(HPO ₄ ) were also detected (Fig. 1). In addition, a peak at 975 cm ^-1 was confirmed as a result of Raman spectrum analysis (Fig. 2).

<Process 5>

Next, the obtained reaction precursor was calcined at 700°C in the air for 4 hours to obtain a calcined product. Next, the calcined product was pulverized using an airflow pulverizer to obtain a pulverized product.

The obtained pulverized product was subjected to X-ray diffraction analysis, and the sintered product was found to be a single-phase Li _1.2 Al _0.2 Ti _1.8 (PO ₄ ) ₃ having a NASICON structure (Fig. 3). This was used as a lithium titanium phosphate sample. In addition, an SEM image of the obtained lithium titanium phosphate sample is shown in Fig. 4.

(Comparative Example 1)

At room temperature (25℃), using a Three-One motor stirrer, 600 g of anatase-type titanium dioxide having a purity of 89.9% (average particle size of 4 ㎛, BET surface area of 323 m2/g, anatase content of 99.9 mass%), 52.2 g of anionic surfactant (ammonium polycarboxylate, SN Dispersant 5468 manufactured by San Nopco), and 962.9 g of 85 mass% phosphoric acid (moisture content of 15 mass%) were added in that order to 4.6 L of pure water, and stirred for 8 hours to obtain a raw material mixed slurry (1).

Next, 715 g of a 50 mass% aluminum bicarbonate aqueous solution and then 216.7 g of lithium hydroxide monohydrate dissolved in 870 ml of pure water were added to the raw material mixed slurry (1) under stirring over 20 minutes to obtain a lithium-containing slurry.

Next, lithium-containing slurry was supplied to a spray dryer set at 220°C at a supply rate of 2.4 L/h, but almost all of the slurry was attached to the inside of the spray dryer. When the attachment was analyzed by Raman spectrum, no peak around 975 cm ^-1 was confirmed (Fig. 5).

(Comparative Example 2)

At room temperature (25°C), using a three-one motor stirrer, 600 g of anatase-type titanium dioxide (average particle size of 4 μm, BET surface area of 323 m2/g, anatase content of 99.9 mass%) with a purity of 89.9% and 962.9 g of 85 mass% phosphoric acid (moisture content of 15 mass%) were sequentially added to 4.6 L of pure water, and stirred for 8 hours to obtain a mixed slurry (1).

Subsequently, the slurry was heated to 90°C at 30°C/h under stirring, whereupon it gelled and became impossible to stir. When the gelled cake was analyzed by Raman spectrum, a peak near 975 cm ^-1 was confirmed.

(1) <Property Evaluation>

For the lithium titanium phosphate sample obtained in the example, the average particle diameter and BET specific surface area were measured. In addition, the average particle diameter was obtained by laser diffraction scattering method.

(2) <Evaluation of lithium ion conductivity>

<Production of a molded body 1>

In the example, 0.5 g of the lithium titanium phosphate sample and 0.05 g of a binder (Spectro Blend (registered trademark), 4.4 μm Powder) were mixed in a mortar for 5 minutes, completely filled into a φ10 mm mold, and formed into a pellet shape using a hand press at a pressure of 300 kg to produce a powder molded body. The obtained powder molded body was fired in an electric furnace at 850°C for 4 hours in the air to obtain a ceramic molded body.

<Measurement of lithium ion conductivity>

After forming electrodes on both sides of the ceramic molded body by Pt deposition, AC impedance was measured, and fitting was performed from the obtained Cole-Cole plot to obtain the lithium ion conductivity at room temperature (25°C).

(Example 2)

<Process 1>

While stirring at room temperature (25°C) using a Three-Won motor stirrer in 4.6 L of pure water, 540 g of anatase-type titanium dioxide having a purity of 89.9% (average particle size of 4 μm, BET specific surface area of 323 m2/g, anatase content of 99.9 mass%), 295.0 g of zirconium hydroxide having a purity of 28.2% in terms of ZrO ₂ , 52.2 g of anionic surfactant (ammonium polycarboxylate, SN Dispersant 5468 manufactured by San Nopco), and 962.9 g of 85 mass% phosphoric acid (moisture content of 15 mass%) were added in that order to prepare a raw material mixing slurry (1).

<Process 2 to 4>

Next, the second to fourth processes were performed in the same manner as in Example 1 to obtain a reaction precursor. When the reaction precursor obtained in the fourth process was analyzed by Raman spectrum, a peak was confirmed at 975 cm ^-1 . In addition, when the reaction precursor was analyzed by X-ray diffraction, in addition to titanium phosphate containing Zr in a molar ratio (Zr/Ti) of 0.1 in α-(Ti)(HPO ₄ ) ₂ (H ₂ O), Li(H ₂ PO ₄ ), Al(PO ₄ ), Al(PO ₄ )(H ₂ O), and Al(H ₂ PO ₄ )(HPO ₄ ) were also detected.

In addition, in the fourth process, as in Example 1, when the inside of the spray dryer was visually observed after spray drying, the amount of internal attachment was small and the recovery rate was 94%.

<Process 5>

Next, the fifth process was performed on the obtained reaction precursor in the same manner as in Example 1 to obtain a calcined product.

The obtained sintered product was analyzed by X-ray diffraction, and no abnormalities were observed. The sintered product was a single-phase lithium titanium phosphate having a NASICON structure of Li _1.2 Al _0.2 Ti _1.8 (PO ₄ ) ₃ and containing Zr in a molar ratio (Zr/Ti) of 0.1 (Fig. 6). This was used as a lithium titanium phosphate sample.

(Example 3)

The first and second processes were performed in the same manner as in Example 1, except that the amount of phosphoric acid added was 1033 g, to obtain a slurry (2) of a raw material heat treatment product.

<Process 3>

Next, 1808 g of a 2M 30.6 mass% chromium phosphate solution (manufactured by Nippon Chemical Industry, Cr( _H1.5PO4 ) ₂ ) and then 283.4 g of lithium hydroxide monohydrate dissolved in 1140 ml of pure water were added to the raw material heat-treated material slurry ( ₂ ) with stirring over 20 minutes to obtain a lithium-containing raw material heat-treated material slurry (3).

<Fourth Process>

Next, a slurry of lithium-containing raw material heat treatment material (3) was supplied at a supply rate of 2.4 L/h to a spray dryer set at 220°C, and a dried product was obtained. As a result of visually observing the inside of the spray dryer, the internal attachment was small, and the recovery rate was 96% on a _solids basis. When the obtained dried product was subjected to X-ray diffraction analysis, α-Ti( _HPO4 ) ₂ ( _H2O ) and _CrHP2O7 were detected. In addition, a peak at 975 cm ^-1 was confirmed in Raman spectrum analysis (Fig. 7).

<Process 5>

Next, the obtained reaction precursor was calcined in the air at 1000°C for 4 hours to obtain a calcined product. Next, the calcined product was pulverized using an airflow pulverizer to obtain a pulverized product.

The obtained pulverized product was analyzed by X-ray diffraction and found to be a single-phase Li _1.5 Cr _0.5 Ti _1.5 (PO ₄ ) ₃ having a NASICON structure. This was used as a lithium titanium phosphate sample.

Note) “x” and “y” in the table represent the values of x and y in the general formula (1).

(1) <Property Evaluation>

For the lithium titanium phosphate samples obtained in Examples 2 and 3, the average particle size and BET specific surface area were measured in the same manner as in Example 1.

(2) <Evaluation of lithium ion conductivity>

<Making a mold 2>

Using the lithium titanium phosphate sample obtained in Example 3, a powder molded body was obtained in the same manner as in Manufacturing of a molded body 1. Then, the powder molded body was fired in an electric furnace at 1100°C for 4 hours in the air to obtain a ceramic molded body.

<Measurement of lithium ion conductivity>

For the ceramic molded body obtained above, the lithium ion conductivity at room temperature (25°C) was obtained in the same manner as in Example 1.

Note) “-” in the table indicates unmeasured.

Claims (12)

The following general formula (1):

(Wherein, 0≤x≤1.0, 0≤y≤0.5, and M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In, and Co. A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn, and Si.)
A method for manufacturing lithium titanium phosphate having a NASICON structure represented by
A first step of preparing a raw material mixed slurry (1) containing at least titanium dioxide, phosphoric acid, a polycarboxylic acid surfactant and a solvent,
A second process of heat-treating the raw material mixture slurry (1) at 50 to 105°C to obtain a raw material heat-treated slurry (2);
A third process of mixing a lithium source into the raw material heat treatment slurry (2) to obtain a lithium-containing raw material heat treatment slurry (3),
A fourth step of spray drying the lithium-containing raw material heat treatment slurry (3) to obtain a reaction precursor containing at least Ti, P and Li;
Step 5 of calcining the reaction precursor
A method for producing lithium titanium phosphate, characterized by having: A method for producing lithium titanium phosphate, characterized in that in the first paragraph, in the first process, an M source (M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co) and/or an A source (A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn and Si) is additionally contained in the raw material mixed slurry (1). A method for producing lithium titanium phosphate, characterized in that in claim 1, an M source (M represents one or more divalent or trivalent metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co) and/or an A source (A represents one or more tetravalent or pentavalent metal elements selected from Ge, Zr, V, Nb, Sn and Si) are additionally mixed in the heat-treated material slurry (2) or the lithium-containing raw material heat-treated material slurry (3). A method for producing lithium titanium phosphate, characterized in that the titanium dioxide according to any one of claims 1 to 3 is of the anatase type. A method for producing lithium titanium phosphate according to any one of claims 1 to 3, characterized in that the reaction precursor has a peak observed at around 975 cm ^-1 in Raman spectrum analysis. A method for producing lithium titanium phosphate, characterized in that the M source in claim 2 or 3 is an Al-containing compound. A method for producing lithium titanium phosphate, characterized in that in claim 6, the Al-containing compound is aluminum biphosphate. A method for producing lithium titanium phosphate, characterized in that the M source in claim 2 or 3 is a Cr-containing compound. A method for producing lithium titanium phosphate, characterized in that in claim 8, the Cr-containing compound is chromium phosphate. delete delete delete