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 Art

[0002] Lithium nitride is known as a high-ion conductor showing a lithium ion conductivity of 10 -3 Scm -1 at room temperature, and for example, applications as a solid electrolyte for lithium ion batteries and an electrode material are being studied.

[0003] Since lithium nitride easily decomposes when it comes into contact with moisture, its synthesis method is subject to many restrictions, and usually lithium nitride is produced by the reaction of metallic lithium and nitrogen gas.

[0004] Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-48504) discloses a method for producing lithium nitride, which comprises reacting metallic lithium with nitrogen while maintaining the temperature of lithium and the produced lithium nitride at or below the melting temperature of lithium by cooling in a nitrogen gas atmosphere. Further, Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-3209) discloses a method for producing lithium nitride, which has a step of heating metallic lithium from 50°C to 110°C at a heating rate of 0.4°C / min to 7.0°C / min in a nitrogen atmosphere.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, our investigations have revealed that in the method for producing lithium nitride by the reaction of metallic lithium with nitrogen gas, as disclosed in Patent Documents 1 and 2, the reaction between metallic lithium and nitrogen gas does not occur reproducibly, and the nitriding reaction may not proceed. This invention has been made in view of the above circumstances, and provides a method for producing lithium nitride in which the formation of lithium nitride proceeds rapidly and stable production of lithium nitride is possible. [Means for solving the problem]

[0007] According to the present invention, A method for producing lithium nitride is provided, comprising the steps of (A) preparing a lithium member embedded with inorganic particles, and (B) contacting the lithium member with nitrogen while the inorganic particles are embedded to nitride the lithium member. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing lithium nitride in which the generation of lithium nitride proceeds rapidly and stable production of lithium nitride is possible. [Modes for carrying out the invention]

[0009] Embodiments of the present invention are described below. Unless otherwise specified, the numerical range "A~B" represents A or greater and B or less.

[0010] The method for producing lithium nitride according to this embodiment includes the steps of (A) preparing a lithium member embedded with inorganic particles and (B) contacting the lithium member with nitrogen while the inorganic particles are embedded to nitride the lithium member. According to the lithium nitride manufacturing method of this embodiment, the production of lithium nitride proceeds rapidly, enabling stable production of lithium nitride.

[0011] As mentioned above, our investigations have revealed that in the method for producing lithium nitride by the reaction of metallic lithium with nitrogen gas, as disclosed in Patent Documents 1 and 2, the reaction between metallic lithium and nitrogen gas does not occur reproducibly, and the nitriding reaction may not proceed. Therefore, after diligent research, the inventors discovered that by bringing nitrogen into contact with the lithium material while inorganic particles are embedded in it, the nitriding reaction of the lithium material proceeds rapidly. Generally, commercially available metallic lithium has a thin film on its surface composed of carbon and oxygen. When metallic lithium is processed into foil or other forms, this film prevents it from adhering to itself. The above-mentioned coating, composed of carbon and oxygen, typically has lithium carbonate as its main component, and may also contain lithium oxide. As mentioned above, the above-mentioned coating on the surface of metallic lithium, composed of carbon and oxygen, has the effect of preventing adhesion of lithium foil, while also suppressing the progression of nitriding. Therefore, it is thought that metallic lithium manufactured in an atmosphere with properly controlled oxygen concentration and dew point will not undergo the nitriding reaction even when heated in a nitrogen gas atmosphere. Therefore, after diligent research, the inventors discovered that introducing nitrogen while inorganic particles are embedded in the lithium material rapidly accelerates the nitriding reaction of the lithium component. This is thought to be because embedding inorganic particles in the lithium material causes the lithium material to deform, exposing fresh metallic lithium around the contact points between the lithium material and the inorganic particles. When nitrogen comes into contact with this area, this exposed fresh metallic lithium acts as a nitriding initiation point, allowing the nitriding reaction of the lithium material to proceed rapidly.

[0012] The following provides a detailed explanation of each step.

[0013] (Process (A)) First, prepare a lithium component embedded with inorganic particles.

[0014] The lithium member according to this embodiment is, for example, metallic lithium having a thin film containing carbon and oxygen as constituent components on its surface, and its shape may be any generally provided shape such as an ingot, foil, wire, rod, etc., and there is no need for a special shape. However, since a shape with a large surface area is preferable for promptly completing the nitriding reaction, a foil is preferable as the shape of the lithium member. That is, the lithium member according to this embodiment is preferably a metallic lithium foil. The thickness of the metallic lithium foil is preferably 3 mm or less, and more preferably 1 mm or less. When the thickness of the metallic lithium foil is below the above upper limit value, an explosive reaction due to the accumulation of reaction heat can be suppressed. The thickness of the metallic lithium foil is not particularly limited, but for example, it may be 0.05 mm or more, or may be 0.1 mm or more.

[0015] The inorganic particles according to this embodiment are not particularly limited, and for example, lithium nitride powder, lithium sulfide powder, phosphorus sulfide powder, solid electrolyte powder, etc. can be used. From the viewpoint of obtaining high-purity lithium nitride and simplifying the removal process of the inorganic particles, lithium nitride powder is preferable as the inorganic particles.

[0016] Also, as the inorganic particles, for example, inorganic particles containing any one or two or more elements 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 preferable. From the viewpoint of obtaining high-purity lithium nitride and simplifying the removal process of the inorganic particles, lithium nitride powder is particularly preferable as the inorganic particles.

[0017] The inorganic particles according to this embodiment are not particularly limited, but the average particle diameter d in the weight-based particle size distribution measured by the laser diffraction scattering method 50 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. The average particle diameter d of the inorganic particles 50By setting it to be not less than the above lower limit value, the handling property of the inorganic particles can be improved. Further, the average particle diameter d of the inorganic particles 50 By setting it to be not more than the above upper limit value, the amount of generation of the nitrogenation starting region described later can be increased, and as a result, the nitrogenation reaction of the lithium member can proceed more rapidly.

[0018] In the lithium member in which inorganic particles are embedded, when the total of the inorganic particles and the lithium member is 100% by mass, the embedding amount of the inorganic particles is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less. When the embedding amount of the inorganic particles is not less than the above lower limit value, the amount of generation of the nitrogenation starting region described later can be increased, and as a result, the nitrogenation reaction of the lithium member can proceed more rapidly. Further, when the embedding amount of the inorganic particles is not more than the above upper limit value, an explosive reaction due to the accumulation of reaction heat can be suppressed, and as a result, the nitrogenation reaction of the lithium member can proceed more safely.

[0019] As a method of embedding inorganic particles in a part of the lithium member, for example, a method of sprinkling inorganic particles on the surface of the lithium member and then pressing the lithium member to which the inorganic particles are attached can be mentioned. The pressing of the lithium member can be carried out, for example, by a hand roller, a roll press, a flat press, etc. Among these, a roll press is preferable. A roll press is preferable because it can continuously press while applying a constant pressing pressure by setting the roll interval and is suitable for mass production.

[0020] (Step (B)) In the method for producing lithium nitride according to the present embodiment, in step (B), the nitrogenation reaction of the lithium member is advanced by bringing nitrogen into contact with the lithium member in a state where inorganic particles are embedded. For example, the lithium member in which inorganic particles are embedded is placed in a nitrogen atmosphere to bring the lithium member into contact with nitrogen. In the initial stages of the nitriding reaction, the reaction occurs around the region where the inorganic particles are embedded, causing that area to turn black. In this embodiment, this blackened region is called the nitriding initiation region. In the initial stages of the nitriding reaction, multiple nitriding initiation regions are generated. Starting from these initiation regions, the nitriding region expands around them over time, and lithium nitride formation progresses. Ultimately, the entire lithium material becomes nitrided.

[0021] Nitrogen gas is used in the nitriding reaction of lithium components. Nitrogen gas reacts readily with lithium, is inexpensive, and is non-toxic. A lower oxygen concentration in the nitrogen gas used is preferable. This is because a high oxygen concentration in the nitrogen gas causes significant oxidation and corrosion of metallic lithium, which not only inhibits the formation of lithium nitride but also leads to the contamination of lithium nitride with lithium oxide and lithium hydroxide. 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 lithium nitride manufacturing method according to this embodiment, it is preferable to nitride the lithium member in a nitrogen atmosphere with a dew point of less than -15°C, and it is more preferable to nitride the lithium member by heating it in a nitrogen atmosphere with a dew point of less than -15°C. The dew point is more preferably -18°C or lower, even more preferably -20°C or lower, even more preferably -25°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, and even more preferably -50°C or lower. The lower limit of the dew point is not particularly limited, but for example, it is -90°C or higher. By setting the dew point of the nitrogen atmosphere below the above upper limit, the formation of films containing lithium oxide and lithium hydroxide on the surface of metallic lithium can be suppressed. As a result, the contact area between metallic lithium and nitrogen increases, allowing the nitriding reaction of the lithium material to proceed even more rapidly.

[0023] In step (B), it is preferable to heat the lithium component using a local heating means capable of heating the lithium component locally. That is, rather than heating the entire nitrogen atmosphere, it is preferable to heat the lithium component placed in the nitrogen atmosphere or the lithium component and its surroundings locally. By doing so, the temperature in the nitrogen atmosphere does not rise easily, so it is possible to suppress the evaporation of moisture adhering to moisture adsorbents such as molecular sieves, or to devices and equipment in the nitrogen atmosphere, which would cause the dew point in the nitrogen atmosphere to rise. In other words, by using a local heating means capable of heating the lithium component locally, it is possible to heat the lithium component while maintaining the dew point in the nitrogen atmosphere below the above upper limit.

[0024] Examples of the above-mentioned local heating means include conductive heat transfer heating and radiant heat transfer heating. local The heating method may be used individually or in combination of two or more methods. Conduction heating is a method of heating a lithium component by bringing it into contact with a high-temperature object and allowing heat to conduct. Examples of devices that perform conduction heating include hot plate heaters and heating rolls. Radiant heating is a method of heating by absorbing the energy emitted as electromagnetic waves from a high-temperature object into a lithium-ion component. Examples of devices that perform radiant heating include infrared heaters and infrared lamps.

[0025] In the method for producing lithium nitride according to this embodiment, step (B) local From the viewpoint of further accelerating the formation of lithium nitride, the heating temperature of the heating means is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 45°C or higher. local While there is no particular upper limit to the heating temperature of the heating means, from the viewpoint of suppressing explosive reactions due to the accumulation of reaction heat, it is preferably 120°C or lower, more preferably 100°C or lower, even more preferably 80°C or lower, and even more preferably 60°C or lower. Here, localThe heating temperature of the heating means is local This refers to the set temperature of the heating device, i.e., the temperature of the heating element.

[0026] In the lithium nitride manufacturing method according to this embodiment, the actual temperature of the lithium material 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 further accelerating the formation of lithium nitride. The upper limit of the actual temperature of the lithium material in step (B) is not particularly limited, but from the viewpoint of suppressing explosive reactions due to the 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 actual temperature of the lithium component in process (B) is the surface temperature of the lithium component.

[0027] In the lithium nitride production method according to this embodiment, the atmospheric temperature of the nitrogen atmosphere in step (B) is preferably 20°C or higher, more preferably 23°C or higher, even more preferably 25°C or higher, and even more preferably 28°C or higher, from the viewpoint of further accelerating the formation of lithium nitride. There is no particular upper limit to the atmospheric temperature of the nitrogen atmosphere in step (B), but from the viewpoint of maintaining the dew point under the nitrogen atmosphere in step (B) below the above upper limit, it is preferably 40°C or lower, more preferably 35°C or lower, and even more preferably 30°C or lower. Here, the atmospheric temperature of the nitrogen atmosphere in process (B) is: local This is the temperature of the space at a point 30 cm away from the heating element of the heating device.

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

[0029] The duration for the nitriding reaction of the lithium material is, for example, 0.5 hours to 24 hours, preferably 0.5 hours to 8 hours, and more preferably 1 hour to 5 hours.

[0030] (Process (C)) If necessary, after step (B), the nitrided lithium material is crushed into a powder. This yields powdered lithium nitride. The method of powdering is not particularly limited and can be carried out by generally known crushing methods.

[0031] The lithium nitride obtained by the manufacturing method according to this embodiment can be suitably used, for example, as a solid electrolyte for lithium-ion batteries, an electrode material for lithium-ion batteries, or an intermediate raw material for chemicals. Because the lithium nitride obtained by the manufacturing method according to this embodiment is of high purity, it can be suitably used as a raw material for solid electrolytes and electrode materials for lithium-ion batteries, where high purity is particularly required.

[0032] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted. [Examples]

[0033] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0034] (Example 1) 80 mg of lithium nitride powder was sprinkled on both sides of a 99.7% pure lithium metallic foil (manufactured by Honjo Metal Co., Ltd., 60 mm x 250 mm x 1 mm, 8 g). Then, using a hand-operated roller, the lithium nitride powder adhering to the lithium metallic foil was embedded into the surface layer of the foil. Next, a hot plate heated to 50°C was placed inside a stainless steel vacuum-purged glove box in a nitrogen atmosphere (dew point: -30°C, temperature: 25°C). The aforementioned lithium metallic foil, with lithium nitride powder embedded on its surface, was then placed on the further heated hot plate to initiate the nitriding reaction of the lithium metallic foil. The temperature inside the glove box was controlled to the ambient temperature (25°C) using a heat exchanger connected to an air-cooled solvent circulation system. Furthermore, moisture in the nitrogen gas inside the glove box was removed by circulating it through a column of moisture adsorbent (Molecular Sieves 3A, manufactured by Wako Pure Chemical Industries, Ltd.), maintaining the dew point inside the glove box at -30°C. The nitrogen gas inside the glove box was also automatically controlled by a pressure switch. When the internal pressure decreased due to the consumption of nitrogen gas in the nitriding reaction with the lithium metallic foil, an equivalent amount of nitrogen gas was introduced into the glove box. Next, the nitridation rate was calculated from the weight change of the metallic lithium foil. As a result, the nitridation rate was 81% after 1 hour of placing the metallic lithium foil on the hot plate, and 100% after 2 hours. Here, a nitridation rate of 100% means that all of the metallic lithium foil (Li) has been converted to lithium nitride (Li3N).

[0035] (Example 2) The nitriding reaction of the metallic lithium foil was carried out in the same manner as in Example 1, except that the metallic lithium foil was not heated (i.e., a hot plate was not used). The nitriding rate was 100% after 5 hours of placing the metallic lithium foil in the glove box.

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

[0037] (Example 4) In a glove box under 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 metallic lithium foil (manufactured by Honjo Metal Co., Ltd., 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, embedding the lithium nitride powder adhering to the metallic lithium foil into the surface layer of the foil. Next, the metallic lithium foil was placed in a stainless steel vacuum-purged glove box under a nitrogen atmosphere (dew point: -30°C, temperature: 25°C), and the nitriding reaction of the metallic lithium foil was started. The temperature inside the glove box was controlled to ambient temperature (25°C) using a heat exchanger connected to an air-cooled solvent circulation system. Furthermore, the nitrogen gas inside the glove box was circulated through a column of moisture adsorbent (Molecular Sieves 3A, manufactured by Wako Pure Chemical Industries, Ltd.) to remove moisture from the nitrogen gas and maintain the dew point inside the glove box at -30°C. The nitrogen gas inside the glove box was also automatically controlled by a pressure switch; when the internal pressure decreased due to the nitrogen gas being consumed in the nitriding reaction with the metallic lithium foil, an equivalent amount of nitrogen gas was introduced into the glove box. Next, the nitridation rate was calculated from the weight change of the metallic lithium foil. As a result, the nitridation rate of the metallic lithium foil 24 hours after being placed in a glove box under a nitrogen atmosphere was 97%.

[0038] (Example 5) The nitriding 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 Koshu Chemical Laboratory, 99% purity) was used instead of lithium nitride powder. The nitriding rate after 24 hours of placing the metallic lithium foil in a glove box under a nitrogen atmosphere was 78%.

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

[0040] (Comparative Example 1) The nitriding reaction of metallic lithium foil was carried out in the same manner as in Example 2, except that lithium nitride powder was not used. The nitriding rate was 0% 96 hours after the metallic lithium foil was placed in the glove box.

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

[0042] (Comparative Example 3) The nitriding reaction of metallic lithium foil was carried out in the same manner as in Example 4, except that lithium nitride powder was not used. The nitriding rate was 0% after 24 hours of placing the metallic lithium foil in a glove box under a nitrogen atmosphere.

[0043] This application claims priority based on Japanese Patent Application No. 2019-182299, filed on 2 October 2019, and incorporates all of its disclosures herein.

Claims

1. Step (A) involves preparing a lithium component embedded with inorganic particles, (B) A step in which nitrogen is brought into contact with the lithium member while the inorganic particles are embedded in the lithium member, A method for producing lithium nitride containing [the specified substance].

2. In the method for producing lithium nitride according to claim 1, A 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.

3. In the method for producing lithium nitride according to claim 1 or 2, A method for producing lithium nitride, wherein the inorganic particles are one or more inorganic particles selected from the group consisting of lithium nitride powder, phosphorus sulfide powder, and red phosphorus powder.

4. In the method for producing lithium nitride according to any one of claims 1 to 3, A method for producing lithium nitride, wherein the inorganic particles are lithium nitride powder.

5. In a method for producing lithium nitride according to any one of claims 1 to 4, When the total amount of the inorganic particles and the lithium member is 100% by mass, A method for producing lithium nitride, wherein the amount of inorganic particles embedded is 0.1% by mass or more and 10% by mass or less.

6. In the method for producing lithium nitride according to any one of claims 1 to 5, The method for producing lithium nitride involves nitriding the lithium member in a nitrogen atmosphere with a dew point of less than -15°C, in step (B) above.

7. In the method for producing lithium nitride according to any one of claims 1 to 6, A method for producing lithium nitride, wherein step (B) involves heating the lithium member using a local heating means capable of locally heating the lithium member.

8. In the method for producing lithium nitride according to claim 7, A method for producing lithium nitride, comprising the local heating means, at least one local heating means selected from conductive heat transfer heating and radiant heat transfer heating.

9. In the method for producing lithium nitride according to claim 7 or 8, A method for producing lithium nitride, wherein the heating temperature of the local heating means in step (B) is 30°C or higher.

10. In a method for producing lithium nitride according to any one of claims 1 to 9, A method for producing lithium nitride, wherein the ambient temperature in step (B) is 20°C or higher and 40°C or lower.

11. A method for producing lithium nitride according to any one of claims 1 to 10, A method for producing lithium nitride, in which the ambient temperature in step (B) is controlled using a heat exchanger.

12. In a method for producing lithium nitride according to any one of claims 1 to 11, A method for producing lithium nitride, wherein the actual temperature of the lithium member in step (B) is 30°C or higher.

13. In a method for producing lithium nitride according to any one of claims 1 to 12, A method for producing lithium nitride, wherein the lithium component is metallic lithium foil.

14. In the method for producing lithium nitride according to claim 13, A method for producing lithium nitride, wherein the thickness of the metallic lithium foil is 3 mm or less.

15. A method for producing lithium nitride according to any one of claims 1 to 14, A method for producing lithium nitride, further comprising the step (C) of crushing the nitrided lithium member into a powder after the above step (B).