Lithium nitride manufacturing method

Abstract

To provide a lithium nitride manufacturing method that quickly forms lithium nitride and can stably produce lithium nitride.SOLUTION: The lithium nitride manufacturing method includes a step (A) of preparing a lithium member embedded with inorganic particles, and a step (B) of allowing the lithium member in a state of being embedded with inorganic particles and nitrogen to contact with each other for nitriding the lithium member.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing lithium nitride. [Background technology]

[0002] Lithium nitride has a lithium ion conductivity of 10 at room temperature. -3 Scm -1 For example, its application as a solid electrolyte or electrode material for lithium-ion batteries is being investigated.

[0003] Lithium nitride easily decomposes when it comes into contact with moisture, so its synthesis methods are subject to many restrictions. Lithium nitride is usually produced by reacting metallic lithium with nitrogen gas.

[0004] Patent Document 1 (JP 2001-48504 A) discloses a method for producing lithium nitride, which is characterized by reacting metallic lithium with nitrogen in a nitrogen gas atmosphere while maintaining the temperatures of lithium and the lithium nitride produced below the melting point of lithium by cooling. Furthermore, Patent Document 2 (JP 2002-3209 A) discloses a method for producing lithium nitride, which includes a step of heating metallic lithium to 50° C. to 110° C. at a temperature increase rate of 0.4° C. / min to 7.0° C. / min in a nitrogen atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-48504 A [Patent Document 2] JP 2002-3209 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the investigations of the present inventors, it has become clear that in the methods of producing lithium nitride by reacting metallic lithium with nitrogen gas as disclosed in the above Patent Documents 1 and 2, the reaction between metallic lithium and nitrogen gas does not occur with good reproducibility, and the nitridation reaction may not proceed. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing lithium nitride in which lithium nitride production proceeds quickly and lithium nitride can be produced stably. [Means for solving the problem]

[0007] According to the present invention, There is provided a method for producing lithium nitride, comprising: a step (A) of preparing a lithium component having inorganic particles embedded therein; and a step (B) of contacting the lithium component with nitrogen in a state in which the inorganic particles are embedded, thereby nitriding the lithium component. Effect of the Invention

[0008] According to the present invention, it is possible to provide a method for producing lithium nitride, in which lithium nitride production proceeds quickly and lithium nitride can be produced stably. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. Unless otherwise specified, a numerical range "A to B" indicates A or more and B or less.

[0010] The method for producing lithium nitride according to this embodiment includes a step (A) of preparing a lithium component having inorganic particles embedded therein, and a step (B) of nitriding the lithium component by contacting the lithium component with nitrogen while the inorganic particles are embedded therein. According to the method for producing lithium nitride according to the present embodiment, the production of lithium nitride proceeds quickly, enabling stable production of lithium nitride.

[0011] As described above, according to the investigations of the present inventors, it became clear that in the methods of producing lithium nitride by reacting metallic lithium with nitrogen gas as disclosed in the above Patent Documents 1 and 2, the reaction between metallic lithium and nitrogen gas does not occur with good reproducibility, and the nitriding reaction may not proceed. Therefore, the present inventors conducted extensive research and found that the nitriding reaction of the lithium member proceeds quickly by contacting nitrogen with the lithium member in a state in which inorganic particles are embedded. Generally, commercially available lithium metal has a thin film made of carbon and oxygen on its surface, which prevents lithium metal foils from adhering to each other. The above-mentioned film, which is composed of carbon and oxygen, is usually mainly composed of lithium carbonate and may contain lithium oxide. As described above, the above-mentioned film, which is composed of carbon and oxygen on the surface of metallic lithium, has the effect of preventing adhesion of the lithium foil, while it also has the effect of suppressing the progress of nitridation. Therefore, it is considered that the nitridation reaction does not progress even if metallic lithium produced in an atmosphere in which the oxygen concentration and dew point are appropriately controlled is heated in a nitrogen gas atmosphere. Therefore, the present inventors conducted extensive research and found that the nitriding reaction of the lithium member proceeds quickly by introducing nitrogen into the lithium member while inorganic particles are embedded in the lithium member. This is because embedding inorganic particles in the lithium component causes the lithium component to deform, exposing fresh metallic lithium around the contact area between the lithium component and the inorganic particles. When nitrogen comes into contact with the exposed fresh metallic lithium, it becomes the starting point of nitridation, and the nitridation reaction of the lithium component proceeds quickly.

[0012] Each step will be described in detail below.

[0013] (Process (A)) First, a lithium member having inorganic particles embedded therein is prepared.

[0014] The lithium member according to the present embodiment is, for example, metallic lithium having a thin film composed of carbon and oxygen on its surface, and the shape of the lithium member does not need to be a special shape, as long as it is a commonly available shape such as an ingot, foil, wire, rod, etc. However, since a shape with a large surface area is preferable for quickly completing the nitriding reaction, the shape of the lithium member is preferably foil. That is, the lithium member according to the present embodiment is preferably metallic lithium foil. The thickness of the metallic lithium foil is preferably 3 mm or less, more preferably 1 mm or less. When the thickness of the metallic lithium foil is the above upper limit or less, explosive reaction due to accumulation of reaction heat can be suppressed. The thickness of the metallic lithium foil is not particularly limited, but may be, for example, 0.05 mm or more, or 0.1 mm or more.

[0015] The inorganic particles according to the present embodiment are not particularly limited, and may be, for example, lithium nitride powder, lithium sulfide powder, phosphorus sulfide powder, solid electrolyte powder, etc. From the viewpoint of obtaining lithium nitride with high purity and simplifying the process of removing the inorganic particles, lithium nitride powder is preferred as the inorganic particles.

[0016] As the inorganic particles, for example, inorganic particles containing one or more of lithium, phosphorus, sulfur, and nitrogen can be used, and one or more inorganic particles selected from the group consisting of lithium nitride powder, phosphorus sulfide powder, and red phosphorus powder are more preferred. From the viewpoint of obtaining lithium nitride with high purity and from the viewpoint of simplifying the process of removing the inorganic particles, lithium nitride powder is particularly preferred as the inorganic particles.

[0017] The inorganic particles according to the present embodiment are not particularly limited, but may have an average particle diameter d 50 However, it is preferably 0.1 μm or more and 45 μm or less, and more preferably 0.5 μm or more and 20 μm or less. Average particle size of inorganic particles d 50By making the average particle diameter d of the inorganic particles equal to or larger than the above lower limit, the handling properties of the inorganic particles can be improved. 50 By making the amount of nitridation starting regions generated, which will be described later, equal to or less than the upper limit, the nitridation reaction of the lithium member can be made to proceed more quickly.

[0018] In a lithium component having embedded inorganic particles, when the total of the inorganic particles and the lithium component is 100 mass%, the amount of embedded inorganic particles is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and preferably 10 mass% or less, more preferably 5 mass% or less. When the amount of embedded inorganic particles is equal to or greater than the above lower limit, the amount of nitridation starting regions formed, which will be described later, can be increased, and as a result, the nitridation reaction of the lithium component can proceed more quickly. Furthermore, when the amount of embedded inorganic particles is equal to or less than the upper limit, explosive reactions caused by accumulation of reaction heat can be suppressed, and as a result, the nitriding reaction of the lithium component can be carried out more safely.

[0019] An example of a method for embedding inorganic particles in a partial region of the lithium component is to sprinkle inorganic particles on the surface of the lithium component and then press the lithium component with the inorganic particles attached thereto. The pressing of the lithium member can be performed, for example, by a hand roller, a roll press, a flat plate press, etc. Among these, the roll press is preferable. The roll press is preferable because it can continuously press the lithium member while applying a constant pressing pressure by setting the roll interval, and is suitable for mass production.

[0020] (Process (B)) In the method for producing lithium nitride according to the present embodiment, in step (B), the lithium component with the inorganic particles embedded therein is brought into contact with nitrogen to promote the nitridation reaction of the lithium component. For example, the lithium component with the inorganic particles embedded therein is placed in a nitrogen atmosphere to bring the lithium component into contact with nitrogen. In the initial stage of the nitriding reaction, the nitriding reaction occurs around the region where the inorganic particles are embedded, and the region turns black. In this embodiment, this blackened region is called a nitriding initiation region. In the initial stage of the nitriding reaction, a plurality of nitriding initiation regions are generated, and from these nitriding initiation regions, nitriding regions expand around them over time, and the generation of lithium nitride progresses. Finally, the entire lithium component is nitrided.

[0021] Nitrogen gas is used for the nitridation reaction of lithium components. Nitrogen gas reacts easily with lithium, is inexpensive, and is non-toxic. The lower the oxygen concentration in the nitrogen gas used, the more preferable it is, because if the oxygen concentration in the nitrogen gas is high, metallic lithium is significantly oxidized and corroded, not only inhibiting the formation of lithium nitride, but also causing lithium oxide and lithium hydroxide to become mixed into the lithium nitride. Specifically, the oxygen concentration in the nitrogen gas is preferably 100 ppm or less, and more preferably 60 ppm or less. Furthermore, the purity of the nitrogen gas is preferably 99.99% or higher.

[0022] In the method for producing lithium nitride according to this embodiment, it is preferable to nitride the lithium material in a nitrogen atmosphere having a dew point of less than -15°C, and it is more preferable to nitride the lithium material by heating the lithium material in a nitrogen atmosphere having a dew point of less than -15°C. The dew point is more preferably -18° C. or less, even more preferably -20° C. or less, even more preferably -25° C. or less, even more preferably -30° C. or less, even more preferably -40° C. or less, even more preferably -50° C. or less. The lower limit of the dew point is not particularly limited, but is, for example, -90° C. or more. By setting the dew point of the nitrogen atmosphere to be less than the upper limit, it is possible to suppress the formation of a film containing lithium oxide or lithium hydroxide on the surface of the metallic lithium, thereby increasing the contact area between the metallic lithium and nitrogen and allowing the nitriding reaction of the lithium material to proceed more rapidly.

[0023] In step (B), it is preferable to heat the lithium component using a local heating means capable of locally heating the lithium component. That is, it is preferable to locally heat the lithium component placed in the nitrogen atmosphere or the lithium component and its periphery, rather than heating the entire nitrogen atmosphere. In this way, the temperature in the nitrogen atmosphere is less likely to rise, so that it is possible to suppress the moisture adsorbent such as molecular sieves, devices, instruments, etc. in the nitrogen atmosphere from evaporating, and the dew point in the nitrogen atmosphere from increasing. That is, by using a local heating means capable of locally heating the lithium component, it is possible to heat the lithium component while maintaining the dew point in the nitrogen atmosphere below the upper limit value.

[0024] Examples of the local heating means include conductive heat transfer heating, radiative heat transfer heating, etc. These heating means may be used alone or in combination of two or more. Conductive heating is a method in which a lithium member is brought into contact with a high-temperature object and heated by thermal conduction. Examples of devices for conducting conductive heating include a hot plate heater and a heating roll. Radiation heat transfer heating is a method of heating a high-temperature object by absorbing energy emitted as electromagnetic waves into a lithium material. Examples of devices that perform radiation heat transfer heating include infrared heaters and infrared lamps.

[0025] In the method for producing lithium nitride according to this embodiment, the heating temperature of the heating means in step (B) is, from the viewpoint of proceeding with the production of lithium nitride more rapidly, preferably 30° C. or more, more preferably 40° C. or more, and even more preferably 45° C. or more. There is no particular upper limit to the heating temperature of the heating means, but, from the viewpoint of suppressing an explosive reaction due to accumulation of reaction heat, it is preferably 120° C. or less, more preferably 100° C. or less, even more preferably 80° C. or less, and even more preferably 60° C. or less. Here, the heating temperature of the heating means is the set temperature of the heating means, that is, the temperature of the heating part.

[0026] In the method for producing lithium nitride according to this embodiment, the actual temperature of the lithium component in step (B) is preferably 30° C. or higher, more preferably 40° C. or higher, and even more preferably 50° C. or higher, from the viewpoint of proceeding with the production of lithium nitride more rapidly. There is no particular upper limit to the actual temperature of the lithium component in step (B), but from the viewpoint of suppressing an explosive reaction due to accumulation of reaction heat, it is preferably 120° C. or lower, more preferably 100° C. or lower, and even more preferably 80° C. or lower. Here, the substantial temperature of the lithium component in step (B) is the temperature of the surface of the lithium component.

[0027] In the method for producing lithium nitride according to this embodiment, the temperature of the nitrogen atmosphere in step (B) is, from the viewpoint of proceeding with the production of lithium nitride more rapidly, preferably 20° C. or more, more preferably 23° C. or more, even more preferably 25° C. or more, and even more preferably 28° C. or more. There are no particular limitations on the upper limit of the temperature of the nitrogen atmosphere in step (B), but, from the viewpoint of maintaining the dew point in the nitrogen atmosphere in step (B) below the above upper limit, it is preferably 40° C. or less, more preferably 35° C. or less, and even more preferably 30° C. or less. Here, the atmospheric temperature of the nitrogen atmosphere in step (B) is the temperature of the space at a point 30 cm away from the heating part of the heating means.

[0028] In the method for producing lithium nitride according to this embodiment, from the viewpoint of maintaining the dew point in the nitrogen atmosphere in step (B) below the upper limit, the temperature of the nitrogen atmosphere may be controlled using a heat exchanger. In this way, even if the temperature at which the lithium component placed in the nitrogen atmosphere is heated is increased, the increase in the temperature of the nitrogen atmosphere in step (B) can be suppressed, and as a result, the dew point in the nitrogen atmosphere in step (B) can be effectively maintained below the upper limit.

[0029] The time for carrying out the nitriding reaction of the lithium member is, for example, from 0.5 hours to 24 hours, preferably from 0.5 hours to 8 hours, and more preferably from 1 hour to 5 hours.

[0030] (Process (C)) If necessary, after step (B), the nitrided lithium component is pulverized to obtain powdered lithium nitride. The method for pulverizing the lithium component is not particularly limited, and can be performed by a commonly known pulverizing method.

[0031] The lithium nitride obtained by the manufacturing method according to the present embodiment can be suitably used, for example, as a solid electrolyte for lithium ion batteries, an electrode material for lithium ion batteries, and an intermediate raw material for chemicals. The lithium nitride obtained by the manufacturing method according to the present embodiment has high purity, and therefore can be suitably used as a raw material for solid electrolytes for lithium ion batteries and electrode materials for lithium ion batteries, which require particularly high purity.

[0032] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can also be adopted. EXAMPLES

[0033] EXAMPLES Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these.

[0034] Example 1 80 mg of lithium nitride powder was sprinkled on both sides of a 99.7% pure lithium metal foil (Honjo Metals, 60 mm × 250 mm × 1 mm, 8 g). Next, a hand roller was used to embed the lithium nitride powder attached to the lithium metal foil into the surface layer of the lithium metal foil. Next, a hot plate heated to 50°C was placed in a stainless steel vacuum replacement glove box in a nitrogen atmosphere (dew point: -30°C, temperature: 25°C), and the above-mentioned metallic lithium foil with lithium nitride powder embedded in the surface layer was placed on the heated hot plate to start the nitridation reaction of the metallic lithium foil. Here, the inside of the glove box was controlled to an outside temperature (25°C) using a heat exchanger connected to an air-cooled solvent circulation device. In addition, the nitrogen gas in the glove box was circulated through a column of a moisture adsorbent (Molecular Sieves 3A, manufactured by Wako Pure Chemical Industries, Ltd.) to remove moisture in the nitrogen gas, and the dew point in the glove box was maintained at -30°C. In addition, the nitrogen gas in the glove box was automatically controlled by a pressure switch, and it was set so that when the nitrogen gas was consumed in the nitridation reaction with the metallic lithium foil and the internal pressure decreased, the nitrogen gas equivalent to the consumed amount was introduced into the glove box. The nitriding rate was then calculated from the weight change of the metallic lithium foil. As a result, the nitriding rate was 81% one hour after the metallic lithium foil was placed on the hot plate, and 100% two hours later. Here, a nitridation rate of 100% means that the entire lithium metal foil (Li) has become lithium nitride (Li3N).

[0035] Example 2 Except for not heating the metallic lithium foil (i.e., not using a hot plate), the nitridation reaction of the metallic lithium foil was carried out in the same manner as in Example 1. The nitridation rate was 100% 5 hours after the metallic lithium foil was placed in the glove box.

[0036] Example 3 Instead of lithium nitride powder, sulfide-based solid electrolyte material (Li 10 P3S 12 A nitridation reaction of a metallic lithium foil was carried out in the same manner as in Example 1, except that a nitridation reaction was carried out using the same lithium foil as in Example 1. The nitridation rate was 77% 3 hours after the metallic lithium foil was placed on the hot plate, and the nitridation rate was 100% 48 hours after the foil was placed on the hot plate.

[0037] Example 4 In a glove box with an argon atmosphere (dew point: -76°C, temperature 25°C), 4 mg of lithium nitride powder was sprinkled on both sides of a 99.7% pure lithium metal foil (manufactured by Honjo Metals, φ14 mm, t=0.1 mm, 9 mg).Then, using a hydraulic hand press, the foil was pressed at approximately 20 MPa for 10 seconds, and the lithium nitride powder attached to the lithium metal foil was embedded in the surface layer of the lithium metal foil. Next, the metallic lithium foil was placed in a stainless steel vacuum replacement glove box in a nitrogen atmosphere (dew point: -30°C, temperature: 25°C), and the nitridation reaction of the metallic lithium foil was started. Here, the inside of the glove box was controlled to an outside temperature (25°C) using a heat exchanger connected to an air-cooled solvent circulation device. In addition, the nitrogen gas in the glove box was circulated through a column of moisture adsorbent (Molecular Sieves 3A, manufactured by Wako Pure Chemical Industries, Ltd.) to remove moisture in the nitrogen gas, and the dew point in the glove box was maintained at -30°C. In addition, the nitrogen gas in the glove box was automatically controlled by a pressure switch, and it was set so that when the nitrogen gas was consumed in the nitridation reaction with the metallic lithium foil and the internal pressure decreased, the nitrogen gas equivalent to the consumed amount was introduced into the glove box. The nitriding rate was then calculated from the weight change of the lithium metal foil. As a result, the nitriding rate was 97% 24 hours after the lithium metal foil was placed in the glove box with a nitrogen atmosphere.

[0038] Example 5 A nitridation reaction of metallic lithium foil was carried out in the same manner as in Example 1, except that 4 mg of red phosphorus (manufactured by Kojundo Chemical Laboratory, purity 99%) was used instead of the lithium nitride powder. The nitridation rate of metallic lithium foil was 78% 24 hours after the foil was placed in a glove box with a nitrogen atmosphere.

[0039] Example 6 A nitridation reaction of a metallic lithium foil was carried out in the same manner as in Example 1, except that 4 mg of P2S5 (manufactured by Perimeter Solutions, product name: Normal / S) was used instead of the lithium nitride powder. The nitridation rate was 68% 24 hours after the metallic lithium foil was placed in a glove box with a nitrogen atmosphere.

[0040] Comparative Example 1 Except for not using the lithium nitride powder, the nitridation reaction of the metallic lithium foil was carried out in the same manner as in Example 2. The nitridation rate of the metallic lithium foil was 0% 96 hours after it was placed in the glove box.

[0041] Comparative Example 2 The nitridation reaction of the lithium metal foil was carried out in the same manner as in Example 2, except that the lithium nitride powder was not embedded in the lithium metal foil using a hand roller (i.e., the lithium nitride powder was in a state of being attached to the surface of the lithium metal foil). The nitridation rate of the lithium metal foil was 0% 96 hours after the lithium metal foil was placed in the glove box.

[0042] Comparative Example 3 Except for not using the lithium nitride powder, the nitridation reaction of the metallic lithium foil was carried out in the same manner as in Example 4. The nitridation rate of the metallic lithium foil was 0% 24 hours after it was placed in a glove box filled with nitrogen.

[0043] This application claims priority based on Japanese Patent Application No. 2019-182299, filed on October 2, 2019, the disclosure of which is incorporated herein in its entirety.

Claims

1. (A) preparing a lithium component having inorganic particles embedded therein; a step (B) of contacting the lithium component with nitrogen in a state in which the inorganic particles are embedded, to nitride the lithium component; A method for producing lithium nitride comprising the steps of:

2. The method for producing lithium nitride according to claim 1, In the step (B), the periphery of the region in which the inorganic particles are embedded is nitrided to generate a nitridation origin region, and the nitridation region is expanded from the nitridation origin region to its periphery, and finally the entire lithium component is nitrided.

3. The method for producing lithium nitride according to claim 1 or 2, The method for producing lithium nitride, wherein the inorganic particles are inorganic particles containing one or more elements selected from the group consisting of lithium, phosphorus, sulfur, and nitrogen.

4. The method for producing lithium nitride according to any one of claims 1 to 3, The method for producing lithium nitride, wherein the inorganic particles are one or more types of inorganic particles selected from the group consisting of lithium nitride powder, phosphorus sulfide powder, and red phosphorus powder.

5. The method for producing lithium nitride according to any one of claims 1 to 4, The method for producing lithium nitride, wherein the inorganic particles are lithium nitride powder.

6. The method for producing lithium nitride according to any one of claims 1 to 5, When the total amount of the inorganic particles and the lithium component is 100 mass%, The method for producing lithium nitride, wherein the embedded amount of the inorganic particles is 0.1% by mass or more and 10% by mass or less.

7. The method for producing lithium nitride according to any one of claims 1 to 6, In the step (B), the lithium component is nitrided in a nitrogen atmosphere having a dew point of less than −15° C.

8. The method for producing lithium nitride according to any one of claims 1 to 7, In the step (B), the lithium component is heated using a local heating means capable of locally heating the lithium component.

9. The method for producing lithium nitride according to claim 8, The method for producing lithium nitride, wherein the local heating means includes at least one heating means selected from conductive heat transfer heating and radiative heat transfer heating.

10. The method for producing lithium nitride according to claim 8 or 9, The method for producing lithium nitride, wherein the heating temperature of the heating means in the step (B) is 30° C. or higher.

11. The method for producing lithium nitride according to any one of claims 1 to 10, The method for producing lithium nitride, wherein the atmospheric temperature in the step (B) is 20° C. or higher and 40° C. or lower.

12. The method for producing lithium nitride according to any one of claims 1 to 11, A method for producing lithium nitride, comprising controlling the atmospheric temperature in the step (B) using a heat exchanger.

13. The method for producing lithium nitride according to any one of claims 1 to 12, The method for producing lithium nitride, wherein the actual temperature of the lithium component in the step (B) is 30° C. or higher.

14. The method for producing lithium nitride according to any one of claims 1 to 13, The method for producing lithium nitride, wherein the lithium component is a metallic lithium foil.

15. The method for producing lithium nitride according to claim 14, The method for producing lithium nitride, wherein the lithium metal foil has a thickness of 3 mm or less.

16. The method for producing lithium nitride according to any one of claims 1 to 15, The method for producing lithium nitride further comprises, after the step (B), a step (C) of pulverizing the nitrided lithium component into a powder form.