CN116802148A

CN116802148A - Method for producing positive electrode active material for alkali metal ion secondary battery

Info

Publication number: CN116802148A
Application number: CN202280008668.3A
Authority: CN
Inventors: 本间刚; 平塚雅史; 山内英郎; 田中步; 角田启; 山崎良宪
Original assignee: Nippon Electric Glass Co Ltd; Nagaoka University of Technology NUC
Current assignee: Nippon Electric Glass Co Ltd; Nagaoka University of Technology NUC
Priority date: 2021-02-16
Filing date: 2022-02-03
Publication date: 2023-09-22

Abstract

The present invention provides a method for producing a positive electrode active material for an alkali metal ion secondary battery, which has a high transition metal content and can drive the battery. The method for producing a positive electrode active material for an alkali metal ion secondary battery, which contains 34% or more by mole of CrO+FeO+MnO+CoO+NiO, is characterized by comprising: preparing a positive electrode active material precursor containing crystals; and a step of irradiating the positive electrode active material precursor with light to melt the crystal and amorphize at least a part of the crystal.

Description

Method for producing positive electrode active material for alkali metal ion secondary battery

Technical Field

The present invention relates to a method for producing a positive electrode active material used as an electrode material for an alkali metal ion secondary battery such as a sodium ion secondary battery.

Background

In recent years, as for a positive electrode active material of an alkali metal ion secondary battery such as a sodium ion secondary battery, a layered rock salt oxide and the like have been studied in addition to a polyanion-based material (for example, see non-patent document 1). In order to achieve high energy density of a battery, it is important to increase the capacity of the material. For example, sodium ferrophosphorus ore type NaFePO is known ₄ The theoretical capacity of the crystal is relatively high (about 155 mAh/g) because the content of transition metal element in the crystal is relatively high.

Prior art literature

Non-patent literature

Non-patent document 1: prabeer Barpanda et al, solid State Ionics,2014 (DOI: 10.1016/j. Ssi.2014.03.011)

Disclosure of Invention

Problems to be solved by the invention

However, since the sodium ferrophosphorus ore type crystal does not have a diffusion path for Na ions and is inactive in electrochemical properties, it cannot function as a positive electrode active material and cannot drive a battery.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a method for producing a positive electrode active material for an alkali metal ion secondary battery, which has a high transition metal content and can drive a battery.

Means for solving the problems

The method for producing a positive electrode active material for an alkali metal ion secondary battery according to the present invention is characterized by comprising 34% or more by mole of CrO+FeO+MnO+CoO+NiO, and by comprising: preparing a positive electrode active material precursor containing crystals; and a step of irradiating the positive electrode active material precursor with light to melt the crystal and amorphize at least a part of the crystal. By irradiating the positive electrode active material precursor containing the crystals with light in this manner to melt the precursor, the crystal structure is disintegrated, and the interatomic distance in the positive electrode active material can be widened to form a three-dimensional conduction path for alkali metal ions. This can function as a positive electrode active material, and the battery can be driven. It is to be noted that a material containing a large amount of a transition metal element component as described above is hardly vitrified by a conventional melting method using a melting vessel. On the other hand, in the production method of the present invention, since the positive electrode active material precursor containing crystals is used as a raw material and melted by irradiation with light, amorphization can be easily performed even in a material containing a large amount of transition metal element components.

In the present specification, "x+y+ … …" means the total amount of each component. In this formula, each component is not necessarily contained as an essential component, and may be a component not contained (i.e., the content is 0%).

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, the positive electrode active material for an alkali metal ion secondary battery preferably contains 20 to 55% of Li in terms of mole% of the oxide ₂ O+Na ₂ O, 34-70% CrO+FeO+MnO+CoO+NiO, 5-55% P ₂ O ₅ +SiO ₂ +B ₂ O ₃ 。

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, it is preferable that the positive electrode active material for an alkali metal ion secondary battery further contains lif+naf in an amount of 40 to 60% by mol% based on the ratio of the additional components.

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, the crystals are preferably sodium ferrophosphorus crystals. This is because the proportion of transition metal element in the crystals of the sodium ferrophosphorus ore type crystals is high, and it is preferable to obtain a positive electrode active material having a high discharge capacity.

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, the peak wavelength of light is preferably 0.1 to 30 μm. This makes it possible to easily amorphize the positive electrode active material precursor containing crystals.

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, the light source for irradiating light is preferably selected from the group consisting of a near infrared heater, a far infrared heater, a halogen lamp, and CO ₂ Laser, YAG laser, yb:YVO ₄ At least 1 of a laser, a laser diode, and a xenon lamp.

In the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention, a layer containing a positive electrode active material for an alkali metal ion secondary battery may be formed on the solid electrolyte layer by irradiating light to the positive electrode active material precursor in a state where the positive electrode active material precursor is disposed on the solid electrolyte layer.

The method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention may include a step of amorphizing at least a part of a positive electrode active material precursor to obtain an amorphous phase, and then crystallizing at least a part of the amorphous phase by heat treatment.

Effects of the invention

According to the present invention, a positive electrode active material for an alkali metal ion secondary battery which has a high transition metal content and can drive a battery can be produced.

Detailed Description

(Positive electrode active Material for alkali Metal ion Secondary Battery)

First, a positive electrode active material for an alkali metal ion secondary battery (hereinafter also referred to simply as "positive electrode active material") produced by the method of the present invention will be described. In the following description of the content of each component, unless otherwise indicated, "%" means "% by mole".

The positive electrode active material for an alkali metal ion secondary battery produced by the production method of the present invention contains at least 1 selected from CrO, feO, mnO, coO and NiO as an essential component. CrO, feO, mnO, coO and NiO, which are transition metal oxides, have an effect of increasing the oxidation-reduction potential of the positive electrode active material by valence changes during charge and discharge. Among them, mnO and NiO have a higher effect of increasing oxidation-reduction potential. In addition to the above effects, feO has an effect of stabilizing the structure of the positive electrode active material during charge and discharge and improving cycle characteristics. Therefore, the transition metal oxide is preferably selected appropriately according to the target characteristics, and mixed according to circumstances.

The valence of Cr, fe, mn, co and Ni is preferably low, and particularly preferably 2. When alkali metal ions are released from the positive electrode active material with initial charge, oxidation reaction of transition metal ions (e.g., fe ²⁺ →Fe ³⁺ ). The higher the proportion of low-valence (in particular, 2-valence) transition metal ions contributing to such charge compensation, the greater the amount of alkali metal ions released from the positive electrode active material, the more likely it is to exhibit a high charge-discharge capacity.

The content of cro+feo+mno+coo+nio is 34% or more, preferably 35% or more, 40% or more, 45% or more, and particularly preferably 48% or more. When the content of cro+feo+mno+coo+nio is too small, the amount of the transition metal element that causes the oxidation-reduction reaction decreases, and thus alkali metal ions involved in the adsorption, storage and release decrease, and thus the charge-discharge capacity tends to decrease. On the other hand, when the content of cro+feo+mno+coo+nio is too large, amorphous materials are difficult to form, and the discharge capacity tends to decrease. Therefore, the content of cro+feo+mno+coo+nio is preferably 70% or less, 60% or less, 55% or less, and particularly preferably 53% or less. When any 2 or more of CrO, feO, mnO, coO and NiO are contained, the total amount thereof is preferably also in the above range.

The content of each component of CrO, feO, mnO, coO and NiO is preferably 0% or more, 10% or more, 20% or more, 30% or more, 34% or more, 35% or more, 40% or more, 45% or more, particularly preferably 48% or more, preferably 70% or less, 60% or less, 55% or less, particularly preferably 53% or less. In the present invention, a transition metal oxide other than 2 (e.g., cr ₂ O ₃ 、Fe ₂ O ₃ 、MnO ₂ Etc.) is converted to a 2-valent transition metal oxide.

Li ₂ O and Na ₂ O is a supply source of alkali metal ions that move between the positive electrode active material and the negative electrode active material during charge and discharge. Li (Li) ₂ O+Na ₂ The content of O is preferably 20% or more and 23% or more, particularly preferably 25% or more, preferably 55% or less, 40% or less, 32% or less, 29% or less, particularly preferably 27% or less. When Li ₂ O+Na ₂ When the content of O is too small, alkali metal ions involved in the adsorption, storage and release decrease, and thus the charge and discharge capacity tends to decrease. On the other hand, when Li ₂ O+Na ₂ When the content of O is too large, li ₃ PO ₄ 、Na ₃ PO ₄ Such as a heterogeneous crystal which does not participate in charge and discharge is likely to precipitate, and thus the charge and discharge capacity tends to be lowered. When the positive electrode active material for an alkali metal ion secondary battery of the present invention is used as a positive electrode active material for a sodium ion secondary battery, na as an alkali metal oxide ₂ The content of O is preferably in the above range. In addition, when the positive electrode active material for an alkali metal ion secondary battery of the present invention is used as a positive electrode active material for a lithium ion secondary battery, li as an alkali metal oxide ₂ The content of O is preferably in the above range.

P ₂ O ₅ 、SiO ₂ And B ₂ O ₃ Is a positive electrode active material which forms a three-dimensional network structure and is stabilizedThe structural components. By containing these components, an amorphous phase is easily formed, and alkali metal ion conductivity is easily improved. In particular P ₂ O ₅ Is preferable because of excellent alkali metal ion conductivity. P (P) ₂ O ₅ +SiO ₂ +B ₂ O ₃ The content of (2) is preferably 5% or more, 10% or more, 20% or more, particularly preferably 23% or more, preferably 55% or less, 40% or less, 35% or less, 30% or less, particularly preferably 26% or less. P (P) ₂ O ₅ +SiO ₂ +B ₂ O ₃ When the content of (b) is too small, the above effect is hardly achieved. On the other hand, when P ₂ O ₅ +SiO ₂ +B ₂ O ₃ When the content of (B) is too large, P ₂ O ₅ Such as a heterogeneous crystal which does not participate in charge and discharge is likely to precipitate, and thus the charge and discharge capacity tends to be lowered. When containing P ₂ O ₅ 、SiO ₂ And B ₂ O ₃ When the total amount is at least 2 kinds, the total amount is preferably within the above range.

P ₂ O ₅ 、SiO ₂ And B ₂ O ₃ The content of each component is preferably 0% or more, 5% or more, 10% or more, 20% or more, particularly preferably 23% or more, preferably 55% or less, 40% or less, 35% or less, 30% or less, particularly preferably 26% or less.

LiF and NaF function as fluxes that promote amorphization, and are sources of alkali metal ions that move between a positive electrode active material and a negative electrode active material during charge and discharge. Since fluoride ions have a smaller ionic radius than oxide ions, the diffusion ability of alkali metal ions in the positive electrode active material can be easily improved by containing these components.

The total amount of LiF and NaF is preferably 40 to 60%, 45 to 55%, and particularly preferably 47.5 to 52.5% by mol% of the additive component ratio (specifically, the additive component ratio relative to the total amount of the oxide components). When the total amount of LiF and NaF is too large, alkali metal ions that do not participate in charge and discharge increase, and thus the charge and discharge capacity tends to decrease. On the other hand, when the total amount of LiF and NaF is too small, the rapid charge-discharge characteristics tend to be lowered. Both LiF and NaF may be contained, or only one of them may be contained.

The content of the amorphous phase in the positive electrode active material is preferably 50% or more, 70% or more, 80% or more, 85% or more, 95% or more, and particularly preferably 100% by mass. When the content of the amorphous phase is too small, alkali metal ion conductivity tends to be low, and charge-discharge characteristics (particularly, high-rate charge-discharge characteristics), cycle characteristics, and the like tend to be low.

The content of the amorphous phase in the positive electrode active material can be obtained by separating peaks into a crystalline diffraction line and an amorphous halo in a diffraction line curve having a2 theta value of 10 to 60 degrees obtained by powder X-ray diffraction measurement using cukα rays. Specifically, based on a total scattering curve obtained by subtracting the background radiation from the diffraction line curve, when the integrated intensity obtained by peak separation with a wide diffraction line (amorphous halation) at 10 to 45 ° is Ia and the integrated intensity obtained by peak separation with a crystalline diffraction line from the crystal detected at 10 to 60 ° is Ic, the content Xg of the amorphous phase is obtained by the following formula.

Xg= [1- { Ic/(ic+Ia) } ]. Times.100 (mass%)

The shape of the positive electrode active material is not particularly limited, but is preferably in the form of powder. When the polymer is in powder form, the sites for absorbing and releasing alkali metal ions increase due to the increase in specific surface area, and thus the charge and discharge capacity can be easily improved. The average particle diameter of the positive electrode active material is preferably 0.1 to 20. Mu.m, 0.3 to 15. Mu.m, 0.5 to 10. Mu.m, particularly preferably 0.6 to 5. Mu.m. The maximum particle diameter is preferably 150 μm or less and 100 μm or less and 75 μm or less, particularly preferably 55 μm or less. When the average particle diameter or the maximum particle diameter is excessively large, since the adsorption and release of alkali metal ions are difficult to proceed during charge and discharge, the charge and discharge capacity tends to be lowered. On the other hand, when the average particle diameter is too small, the dispersion state of the powder after pulping is poor, making it difficult to manufacture a uniform electrode.

In the present invention, the average particle diameter and the maximum particle diameter are values obtained by measuring the median particle diameter of primary particles, respectively, as D50 (50% volume cumulative particle diameter) and D99 (99% volume cumulative particle diameter), by a laser diffraction type particle size distribution measuring apparatus.

(method for producing positive electrode active Material for alkaline Metal ion Secondary Battery)

Next, the method for producing the positive electrode active material for an alkali metal ion secondary battery according to the present invention will be described in detail.

First, a positive electrode active material precursor containing crystals is prepared. For example, a raw material prepared to obtain a positive electrode active material having a desired composition is fired and reacted (solid layer reaction) to obtain a positive electrode active material precursor. The composition of the positive electrode active material precursor is the same as that of the positive electrode active material for the alkali metal ion secondary battery described above, and therefore, the description thereof is omitted. Examples of the crystal contained in the positive electrode active material precursor include sodium ferrophosphorus ore type crystals (NaMPO ₄ The method comprises the steps of carrying out a first treatment on the surface of the M is at least 1 selected from Cr, fe, mn, co and Ni). The sodium ferrophosphorus ore type crystal is preferable because the proportion of the transition metal element in the crystal is high and a positive electrode active material having a high discharge capacity can be obtained.

The positive electrode active material precursor may be composed of only crystals (i.e., the crystal content is 100%), or may contain an amorphous phase in a part thereof. The positive electrode active material precursor may be a bulk or a powder formed by, for example, pulverization.

In the case where the positive electrode active material contains LiF or NaF, for example, li is given as a positive electrode active material precursor ₂ MPO ₄ F crystallization, na ₂ MPO ₄ F crystallization, and the like. Alternatively, liMPO may be used ₄ Mixtures of crystals with LiP, or NaMPO ₄ A mixture of crystals and NaF was used as a positive electrode active material precursor. In particular, li is used as a positive electrode active material precursor ₂ MPO ₄ F crystallization or Na ₂ MPO ₄ In the case of crystallization of F, it is preferable to easily obtain a homogeneous positive electrode active material. In the above Li ₂ MPO ₄ F crystallization, na ₂ MPO ₄ F crystallization, liMPO ₄ Crystallization and NaMPO ₄ In the crystallization, M is at least 1 selected from Cr, fe, mn, co and Ni.

Then, light is irradiated to the positive electrode active material precursor. Thus, the crystals are melted and then quenched to perform amorphization. As a result, a positive electrode active material for an alkali metal ion secondary battery having an amorphous phase can be obtained. The entire crystal may be amorphized, or a part of the crystal may be amorphized.

The peak wavelength of the irradiated light is preferably 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, particularly preferably 0.9 μm or more, preferably 30 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, particularly preferably 3 μm or less. In this way, the energy density of light can be easily increased, and the positive electrode active material precursor can be amorphized by irradiation for a shorter period of time.

Examples of the light source for irradiating light include a near infrared heater, a far infrared heater, a halogen lamp, and CO ₂ Laser, YAG laser, yb:YVO ₄ Lasers, laser diodes, xenon lamps, and the like. Among them, a halogen lamp capable of irradiating light over a large area is preferably used. Only 1 kind of these light sources may be used, or 2 or more kinds may be used in combination.

The irradiation time of the light may be appropriately selected so that the crystals in the positive electrode active material precursor are sufficiently melted and further amorphized, and is preferably 1 second or more, 3 seconds or more, and particularly preferably 5 seconds or more, for example. The upper limit of the light irradiation time is not particularly limited, but since there is a risk that evaporation of an alkali metal component or the like occurs too long and a positive electrode active material having a desired composition or the like cannot be obtained, it is preferably 1000 seconds or less, 500 seconds or less, 200 seconds or less, particularly preferably 100 seconds or less. In particular, when the light source is a laser, the irradiation portion is preferably irradiated while scanning as needed because the irradiation portion is easily concentrated on a local area.

Preferably, the positive electrode active material precursor is mixed with conductive carbon and irradiated with light. Since the conductive carbon has light absorption properties, amorphization can be efficiently performed in a short time when light is irradiated to the positive electrode active material precursor. Further, since the positive electrode active material composited with conductive carbon is formed in this manner, conductivity can be imparted to the positive electrode active material, and the discharge capacity and high-speed charge-discharge characteristics can be improved. Further, since the conductive carbon has reducibility, oxidation (valence change) of the transition metal element contained in the positive electrode active material precursor can be suppressed during light irradiation, and a positive electrode active material having a high charge-discharge capacity and good cycle characteristics can be easily obtained. As the conductive carbon, high conductivity carbon black such as acetylene black and ketjen black, carbon powder such as graphite, carbon fiber, and the like can be used. Among them, acetylene black having high conductivity is preferable.

Instead of conductive carbon, an organic compound as a conductive carbon source may be mixed with the positive electrode active material precursor, and then light irradiation may be performed. Thus, the organic compound can be carbonized by light irradiation to obtain a positive electrode active material composited with conductive carbon. Any material may be used as the organic compound, and the organic compound remaining as carbon during the light irradiation (heat treatment) is preferably glucose, citric acid, ascorbic acid, phenol resin, a surfactant, or the like. Particularly preferred are surfactants that readily adsorb to the surface of the positive electrode active material. The surfactant may be any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant, and is particularly preferably a nonionic surfactant having excellent adsorptivity to the surface of the positive electrode active material. Examples of the nonionic surfactant include polyethylene oxide nonylphenyl ether and the like.

The ratio of the positive electrode active material to the conductive carbon in the positive electrode active material compounded with the conductive carbon is preferably 80 to 99.5:0.5 to 20, more preferably 85 to 98:2 to 15, in terms of mass ratio. When the content of conductive carbon is too small, the conductivity tends to be poor. On the other hand, when the content of conductive carbon is too large, the content of the positive electrode active material is relatively small, and thus the discharge capacity tends to decrease.

After at least a part of the positive electrode active material precursor is amorphized to obtain an amorphous phase, at least a part of the amorphous phase may be crystallized by heat treatment. The method has a junctionThe composition is effective as a functional composition of the active material after crystallization. As such a crystal composition, na may be mentioned ₄ Ni ₃ (PO ₄ ) ₂ (P ₂ O ₇ )、Na ₄ Ni ₅ (PO ₄ ) ₂ (P ₂ O ₇ ) ₂ Etc. The heat treatment temperature may be appropriately selected from temperatures at or above the temperature at which crystallization begins, and is, for example, preferably 400℃or higher and 450℃or higher, and particularly preferably 500℃or higher. The upper limit of the heat treatment temperature is not particularly limited, but if it is too high, there is a risk that the alkali metal component or the like as the positive electrode active material component is evaporated, resulting in a decrease in discharge capacity, and therefore it is preferably 800 ℃ or less and 700 ℃ or less, particularly preferably 600 ℃ or less.

The positive electrode active material produced by the method of the present invention can be used for an alkali metal ion secondary battery (sodium ion secondary battery, lithium ion secondary battery) using an electrolyte such as an aqueous solvent, a nonaqueous solvent, or an ionic liquid. In addition, the present invention can also be applied to all-solid alkali metal ion secondary batteries (all-solid sodium ion secondary batteries, all-solid lithium ion secondary batteries) using a solid electrolyte.

As the solid electrolyte, for example, sodium ion conductive oxide can be used. Examples of the sodium ion conductive oxide include compounds containing at least 1 selected from Al, Y, zr, si and P, na, and O. Specific examples thereof include beta-alumina, and sodium super-ion-conductor type (NASICON) crystals. Preferably, the sodium ion conductive oxide is β -alumina or β "-alumina. They will make sodium ion conductivity more optimal.

When the solid electrolyte is β -alumina or β "-alumina, for example, it contains Al in mol% ₂ O ₃ ：65％～98％、Na ₂ O：2％～20％、MgO+Li ₂ O:0.3 to 15 percent of oxide.

The solid electrolyte preferably contains ZrO in addition to the above components ₂ 、Y ₂ O ₃ Etc. ZrO (ZrO) ₂ And Y ₂ O ₃ Preparation of raw materials with firing inhibitionThe effect of abnormal grain growth of beta-alumina and/or beta-alumina and further improving the adhesion of the particles of beta-alumina and/or beta-alumina in the solid electrolyte. ZrO (ZrO) ₂ The content of (2) is preferably 0% to 15%, more preferably 1% to 13%, and even more preferably 2% to 10%. In addition, Y ₂ O ₃ The content of (2) is preferably 0% to 5%, more preferably 0.01% to 4%, and still more preferably 0.02% to 3%. When ZrO (ZrO) ₂ Or Y ₂ O ₃ If the amount of beta-alumina is too large, the amount of beta-alumina produced will be easily reduced, and the sodium ion conductivity will be reduced.

In the case where the solid electrolyte is a sodium super ion conductor crystal, the solid electrolyte contains a compound having the general formula Na _s A1 _t A2 _u O _v (A1 is at least 1 selected from Al, Y, yb, nd, nb, ti, hf and Zr, A2 is at least 1 selected from Si and P, s=1.4 to 5.2, t=1 to 2.9, u=2.8 to 4.1, v=9 to 14). In a preferred embodiment of the above crystal, A1 is at least 1 selected from Y, nb, ti, and Zr, s=2.5 to 3.5, t=1 to 2.5, u=2.8 to 4, and v=9.5 to 12. In this case, crystals having more excellent sodium ion conductivity can be obtained. In particular, when the sodium super-ion conductor type crystal is monoclinic or trigonal, sodium ion conductivity is more excellent, which is preferable.

As the above general formula Na _s A1 _t A2 _u O _v Specific examples of the crystals represented include Na ₃ Zr ₂ Si ₂ PO ₁₂ 、Na _3.2 Zr _1.3 Si _2.2 P _0.8 O _10.5 、Na ₃ Zr _1.6 Ti _0.4 Si ₂ PO ₁₂ 、Na ₃ Hf ₂ Si ₂ PO ₁₂ 、Na _3.4 Zr _0.9 Hf _1.4 Al _0.6 Si _1.2 P _1.8 O ₁₂ 、Na ₃ Zr _1.7 Nb _0.24 Si ₂ PO ₁₂ 、Na _3.6 Ti _0.2 Y _0.8 Si _2.8 O ₉ 、Na ₃ Zr _1.88 Y _0.12 Si ₂ PO ₁₂ 、Na _3.12 Zr _1.88 Y _0.12 Si ₂ PO ₁₂ 、Na _3.6 Zr _0.13 Yb _1.67 Si _0.11 P _2.9 O ₁₂ Etc.

The layer containing the positive electrode active material (positive electrode layer) can be formed on the solid electrolyte layer by irradiating the positive electrode active material precursor with light in a state where the positive electrode active material precursor is disposed on the surface of the solid electrolyte layer. In this way, the positive electrode active material precursor can be amorphized by irradiation with light and fused with the solid electrolyte layer, thereby forming a conductive path for alkali metal ions.

Further, the positive electrode layer containing the positive electrode active material may be formed on the solid electrolyte by irradiation with light, and then heat treatment may be performed to crystallize the positive electrode active material. The heat treatment temperature may be appropriately selected from temperatures at which crystallization is induced, and is, for example, preferably 400℃or higher and 450℃or higher, and particularly preferably 500℃or higher. The upper limit of the heat treatment temperature is not particularly limited, but if it is too high, alkali metal components and the like as positive electrode active material components are evaporated, and there is a risk of decreasing the discharge capacity. In addition, the positive electrode active material reacts with the solid electrolyte, and heterogeneous crystals are precipitated at the interface between the positive electrode active material and the solid electrolyte, so that there is a risk that the internal resistance of the battery increases. Therefore, the heat treatment temperature is preferably 800 ℃ or lower and 700 ℃ or lower, and particularly preferably 600 ℃ or lower.

Examples

The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

(I) Liquid sodium ion secondary battery

Table 1 shows examples (Nos. 1 to 4) and comparative examples (Nos. 5 and 6) when the method for producing a positive electrode active material for an alkali metal ion secondary battery according to the present invention is applied to a liquid sodium ion secondary battery.

TABLE 1

(1) Preparation of raw materials

The respective oxide raw materials, carbonate raw materials and phosphate raw materials were weighed according to the compositions shown in table 1, and a batch was prepared. The resultant batch was fired in nitrogen at 1200 ℃ to react, thereby producing a positive electrode active material precursor. After the crystal structure of the positive electrode active material precursor was examined by XRD (powder X-ray diffraction apparatus), it was confirmed that No.1 to 3 synthesized sodium ferrophosphorus ore type NaFePO ₄ Crystallization, no.4 synthesizes ferrophosphorus sodium ore type NaMnPO ₄ And (5) crystallizing. The positive electrode active material precursor powder having an average particle diameter of 0.8 μm was obtained by pulverizing and classifying the positive electrode active material precursor.

(2) Preparation of positive electrode active material powder

The positive electrode active material powder of No.1 was prepared as follows. Depositing a positive electrode active material precursor powder on a Si substrate, and continuously oscillating Yb/YVO from above ₄ The laser was irradiated while scanning (output power: 0.35W, laser diameter: 40 μm, peak wavelength: 1080nm, scanning speed: 1 mm/s). Thereby, the positive electrode active material precursor powder is amorphized. The obtained sample was pulverized to obtain a positive electrode active material powder having an average particle diameter of 2.5. Mu.m.

The positive electrode active material powder of No.2 was prepared as follows. To 100 parts by mass of the positive electrode active material precursor powder, 21 parts by mass (12 parts by mass in terms of carbon) of polyethylene oxide nonylphenyl ether (mass average molecular weight 660) and 10 parts by mass of ethanol were sufficiently mixed as nonionic surfactants of a carbon source, and then dried at a temperature of 100℃for about 1 hour. The resultant mixture was irradiated with near infrared light (output 200W, irradiation time 60 seconds) using a halogen lamp under a vacuum atmosphere, whereby carbonization of the nonionic surfactant and amorphization of the positive electrode active material precursor powder were simultaneously performed. The obtained sample was pulverized to obtain a positive electrode active material powder having an average particle diameter of 2.5 μm and a surface covered with carbon.

The positive electrode active material powders of nos. 3 and 4 were prepared as follows. After 1 part by mass of acetylene black and 30 parts by mass of ethanol as a conductive additive were sufficiently mixed into 100 parts by mass of the positive electrode active material precursor powder, the mixture was dried at a temperature of 100℃for about 1 hour. The resultant mixture was irradiated with near infrared light (output 800W, irradiation time 10 seconds) using a halogen lamp under a vacuum atmosphere, whereby the positive electrode active material precursor powder was amorphized. The obtained sample was pulverized to obtain a positive electrode active material powder having an average particle diameter of 2.5 μm and having conductive carbon dispersed therein.

As a result of analyzing each of the obtained positive electrode active material powders by XRD, the peak intensity of the diffraction pattern of the sodium ferrophosphorus ore type crystal was significantly reduced. The inventors believe that this is because amorphization is achieved by melting the crystals by light irradiation and then suppressing recrystallization by quenching. The amorphous content was calculated from the obtained XRD pattern. The results are shown in Table 1.

The positive electrode active material precursor powders obtained in nos. 1 and 4 were directly used as positive electrode active materials in nos. 5 and 6, respectively.

(3) Preparation of the Positive electrode

The positive electrode material was obtained by weighing acetylene black (Super C65 manufactured by Timcal corporation) as a conductive additive and polyvinylidene fluoride as a binder in a ratio of positive electrode active material powder to conductive additive to binder=90:5:5 (mass ratio), dispersing the mixture into N-methylpyrrolidone (NMP), and then sufficiently stirring the mixture with a rotation-revolution stirrer to obtain a slurry.

The positive electrode material obtained was coated with a doctor blade having a gap of 125 μm on an aluminum foil having a thickness of 20 μm as a positive electrode current collector, and vacuum-dried in a dryer at 70℃to obtain an electrode sheet by passing the dried material between a pair of rotating rolls and pressing the material. The electrode plate was punched out to a diameter of 11mm by an electrode punching machine, and dried at 150℃under reduced pressure for 8 hours to obtain a circular positive electrode.

(4) Preparation of test cells

The positive electrode obtained above was placed on the lower cover of a button cell with the aluminum foil facing downward, and a polypropylene porous film having a diameter of 16mm was laminated thereon and dried under reduced pressure at 70℃for 8 hours to obtain a positive electrodeThe resulting separator, metallic sodium as a counter electrode, and an upper cover of a coin cell were fabricated into test cells. As the electrolyte, 1M NaPF was used ₆ Solution/ec:dec=1:1 (ec=ethylene carbonate, dec=diethyl carbonate). And the test cells were assembled in an environment with a dew point temperature of-70 c or less.

(5) Charge and discharge test

The test battery prepared as described above was subjected to CC (constant current) charging from an open-loop voltage to 4V at a temperature of 30 ℃ and then to CC discharging from 4V to 2V, and the amount of electricity discharged per unit mass of the positive electrode active material (initial discharge capacity) was determined. The C magnification was set to 0.1C. The results are shown in Table 1.

As shown in Table 1, in the examples No.1 to 4, the discharge capacity was 48 to 102mAh/g. On the other hand, in nos. 5 and 6 as comparative examples, the battery was not operated.

(II) all-solid sodium ion secondary battery (all-solid sodium ion secondary battery containing FeO as a composition of positive electrode active material)

Table 2 shows examples (No. 7) and comparative examples (No. 8) when the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention is applied to an all-solid sodium ion secondary battery.

TABLE 2

(1) Preparation of raw materials

As a raw material, naH was weighed according to the composition shown in Table 2 ₂ PO ₄ (NACALAAI TESQUE Co., ltd.), feO (high purity chemical Co., ltd.), and NaF (pure chemical Co., ltd.) were prepared as a batch. The resulting batch was wet mixed in ethanol at 700rpm for 2 hours using a planetary ball mill. After drying, in H ₂ /N ₂ The positive electrode active material precursor was prepared by firing at 600℃under ambient conditions. After the crystal structure of the positive electrode active material precursor was examined by XRD, it was confirmed that Na was synthesized ₂ FePO ₄ F junctionAnd (5) crystal. Next, the positive electrode active material precursor was pulverized and classified to obtain a positive electrode active material precursor powder having an average particle diameter of 0.8 μm.

(2) Preparation of the Positive electrode

The positive electrode active material precursor powder obtained above was pulverized by a ball mill and air-classified to obtain a sodium super ion conductor crystalline solid electrolyte powder (Na ₃ Zr ₂ PSi ₂ O ₁₂ Average particle diameter of 2 μm) and acetylene black as a conductive additive to obtain a positive electrode composite material. The polypropylene carbonate as a binder was added so that the content of the additive was 10 mass% relative to the obtained positive electrode composite material, and the N-methylpyrrolidone as a solvent was added so that the solid content concentration was 60 mass%. The obtained mixture was kneaded using a rotation-revolution mixer, thereby preparing a positive electrode paste.

After crystallization from sodium super ion conductor (Na ₃ Zr ₂ PSi ₂ O ₁₂ ) The positive electrode composite paste was coated on the solid electrolyte substrate to a thickness of 150 μm, and vacuum-dried at 300 ℃. No.7 was prepared by subjecting Yb/YVO to continuous oscillation ₄ The laser irradiates the positive electrode composite layer while scanning (output power 0.35W, laser diameter 90 μm, peak wavelength 1080nm, scanning speed 1 mm/s). Thus, the positive electrode active material precursor powder in the positive electrode composite material is amorphized, and becomes a positive electrode active material. And at this time, the positive electrode composite layers and the solid electrolyte substrate are fusion-bonded to each other. On the other hand, in the case of No.8, instead of laser irradiation, the laser irradiation is performed on N ₂ Firing was performed at 550℃for 1 hour in the ambient.

As a result of XRD analysis of each of the obtained positive electrode composite layers, na of No.7 was obtained ₂ FePO ₄ The peak intensity of the diffraction pattern of the F crystal decreases. The inventors considered that this is because the crystallization was melted by light irradiation, and then the recrystallization was suppressed by quenching, thereby making a part amorphous. The amorphous content was calculated from the obtained XRD pattern. The results are shown inTable 2.

(3) Preparation of test cells

A metal aluminum thin film as a current collector was formed on the surface of the positive electrode composite layer by sputtering. A CR2032 type coin cell was fabricated by bonding sodium metal to the surface of the solid electrolyte layer opposite to the surface on which the positive electrode composite layer was formed, and housing the sodium metal in the coin cell.

(4) Charge and discharge test

The obtained test battery was charged with CC (constant current) from the open-loop voltage to 5V at a temperature of 80 ℃, and then with CC discharge from 5V to 2V, to obtain the amount of electricity discharged per unit mass of the positive electrode active material (initial discharge capacity). The C magnification was set to 0.02C.

As shown in Table 2, in No.7 as an example, the discharge capacity was 96mAh/g. On the other hand, in No.8 as a comparative example, the battery was not operated.

(III) all-solid sodium ion Secondary Battery (all-solid sodium ion Secondary Battery comprising NiO as the composition of the Positive electrode active Material)

Table 3 shows examples (Nos. 9 to 13) and comparative examples (No. 14) when the method for producing a positive electrode active material for an alkali metal ion secondary battery of the present invention is applied to an all-solid sodium ion secondary battery.

TABLE 3

(1) Preparation of raw materials

As a raw material, naH was weighed according to the composition of Table 3 ₂ PO ₄ NiO, and is prepared into batch materials. The resulting batch was mixed with a planetary ball mill at 700rpm for 2 hours. Then, firing was performed at a temperature of 800 ℃ to prepare a positive electrode active material precursor. The crystal structure of the positive electrode active material precursor was examined by XRD, and as a result, it was confirmed that the crystals shown in table 3 were synthesized. Next, the positive electrode active material precursor was pulverized and classified to obtain a positive electrode active material precursor powder having an average particle diameter of 2 μm.

(2) Preparation of the Positive electrode

The positive electrode active material precursor powder obtained above, and beta "-alumina crystalline solid electrolyte powder (Na _1.6 Li _0.34 Al _10.66 O ₁₇ Average particle diameter of 2 μm) and acetylene black as a conductive additive to obtain a positive electrode composite material. The polypropylene carbonate as a binder was added so that the content of the additive was 10 mass% relative to the obtained positive electrode composite material, and the N-methylpyrrolidone as a solvent was added so that the solid content concentration was 60 mass%. The obtained mixture was kneaded using a rotation-revolution mixer, thereby preparing a positive electrode paste.

In the composition type Na _1.6 Li _0.34 Al _10.66 O ₁₇ The positive electrode composite paste was applied on a substrate of 100 μm thick β -alumina solid electrolyte to a thickness of 150 μm, and vacuum-dried at 300 ℃. With regard to Nos. 9 to 13, yb/YVO of continuous oscillation type was used ₄ The laser irradiates the positive electrode composite layer while scanning (output power 0.9W, peak wavelength 1080nm, scanning speed 5 mm/s). Thus, the positive electrode active material precursor powder in the positive electrode composite material is amorphized, and becomes a positive electrode active material. At this time, the positive electrode composite materials are fusion-bonded to each other and the positive electrode composite material layer (positive electrode layer) and the solid electrolyte substrate.

Further, regarding Nos. 12 and 13, after irradiation with laser light, the laser light was irradiated at N at the temperature shown in Table 3 ₂ The positive electrode active material was crystallized by heat treatment for 30 minutes in the atmosphere. As a result of examining the crystal structure of the positive electrode active material by XRD, it was confirmed that the same crystal as that of the positive electrode active material precursor was precipitated.

In addition, in place of laser irradiation, in the case of No.14, N ₂ The heat treatment was performed at 600℃for 30 minutes in an air atmosphere.

(3) Preparation of test cells

(4) Charge and discharge test

The obtained test battery was charged with CC (constant current) from the open-loop voltage to 5.5V at a temperature of 80 ℃, and then with CC discharge from 5.5V to 2V, to obtain the amount of electricity discharged per unit mass of the positive electrode active material (initial discharge capacity). The C magnification was set to 0.05C.

As shown in Table 3, in examples No.9 to 13, the discharge capacity was 63mAh/g. On the other hand, in No.14 as a comparative example, the battery was not operated.

Industrial applicability

The positive electrode active material for an alkali metal ion secondary battery produced according to the present invention is suitable as a constituent material of a secondary battery used in, for example, a main power source of a mobile communication device, a portable electronic device, an electric bicycle, an electric motorcycle, an electric automobile, or the like.

Claims

1. A method for producing a positive electrode active material for an alkali metal ion secondary battery, the positive electrode active material containing 34% or more by mole of cro+feo+mno+coo+nio, the method comprising:

preparing a positive electrode active material precursor containing crystals; and

and a step of irradiating the positive electrode active material precursor with light to melt the crystal and amorphize at least a part of the crystal.

2. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to claim 1, wherein:

the positive electrode active material for an alkali metal ion secondary battery contains 20 to 55% of Li in terms of mole% of oxide ₂ O+Na ₂ O, 34-70% CrO+FeO+MnO+CoO+NiO, 5-55% P ₂ O ₅ +SiO ₂ +B ₂ O ₃ 。

3. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to claim 1 or 2, characterized by:

the positive electrode active material for an alkali metal ion secondary battery further contains lif+naf in an amount of 40 to 60% by mole based on the ratio of the additional components.

4. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to any one of claims 1 to 3, wherein:

the crystal is a sodium ferrophosphorus ore type crystal.

5. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to any one of claims 1 to 4, wherein:

the peak wavelength of the light is 0.1-30 mu m.

6. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to any one of claims 1 to 5, wherein:

the light source for irradiating the light is selected from near infrared heater, far infrared heater, halogen lamp, CO ₂ Laser, YAG laser, yb:YVO ₄ At least 1 of a laser, a laser diode, and a xenon lamp.

7. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to any one of claims 1 to 6, wherein:

in a state where the positive electrode active material precursor is disposed on the solid electrolyte layer, a layer containing a positive electrode active material for an alkali metal ion secondary battery is formed on the solid electrolyte layer by irradiating light to the positive electrode active material precursor.

8. The method for producing a positive electrode active material for an alkali metal ion secondary battery according to any one of claims 1 to 7, wherein:

the method comprises a step of crystallizing at least a part of the positive electrode active material precursor by heat treatment after amorphizing at least a part of the positive electrode active material precursor to obtain an amorphous phase.