JP2001048504A - Production of lithium nitride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a local runaway reaction from occurring, a dense lithium nitride layer from forming on the surface and the reaction from becoming unprogressive by carrying out the reaction of metallic lithium with nitrogen in an atmosphere of nitrogen gas while keeping temperatures of the lithium and the generated lithium nitride at the melting temperature of the lithium or below by cooling. SOLUTION: Metallic lithium is charged into an atmosphere of nitrogen gas such as a glove box without containing water and oxygen and a reaction of the metallic lithium with the nitrogen is started while ventilating nitrogen gas. Nitriding reaction progresses on the surface of the metallic lithium contacting the nitrogen while generating heat of -47 kcal/mol. The reaction velocity increases according to a temperature rise of the lithium by heat of the reaction and a temperature thereof further increases. The reaction is continued under cooling so that the temperatures of the lithium and the generated lithium nitride are preferably 80-120 deg.C when the temperatures thereof reach a certain constant value. The reaction is finally completed when the temperatures thereof become normal temperature. Methods of circulating and cooling the nitrogen gas, using cooled nitrogen and the like are preferred for cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing lithium ion conductive high-purity lithium nitride (Li ₃ N) having high utility as a solid electrolyte for a lithium secondary battery.

[0002]

2. Description of the Related Art As a method for producing lithium ion conductive lithium nitride used as a solid electrolyte for a battery, there is known a method of producing a high purity nitrogen gas which does not contain impurities which easily react with lithium such as moisture or oxygen. Alternatively, a method is generally employed in which metallic lithium is heated and reacted with nitrogen in a high-purity nitrogen gas mixed with an inert gas that does not react with lithium such as argon. When this is divided by the reaction temperature, it is higher than the melting point of lithium and lower than the melting point of lithium nitride (18
(0-845 ° C.) and a method of reacting at a temperature (<180 ° C.) from below the melting point of lithium to room temperature (<180 ° C.).

[0003] The method of reacting with nitrogen gas after melting the metallic lithium by heating has the advantage of increasing the reaction rate and shortening the reaction time, but the lithium nitride in the molten lithium is particularly corrosive. It is necessary to use expensive metals such as tungsten, niobium, ruthenium or tantalum for the reaction vessel, and it is structurally and operationally complicated, such as a method for separating lithium nitride from slurry and a method for sealing lithium nitride mist generated. It is difficult to produce lithium nitride on an industrial scale.

On the other hand, when lithium is reacted with nitrogen gas at a temperature equal to or lower than the melting point, the reaction speed is slower than when lithium is melted. It is very easy in terms of structure and operation, such as simply putting it in a reaction vessel and reacting with nitrogen, and easy removal of lithium nitride after the reaction.
It is considered a suitable method for producing lithium nitride on an industrial scale.

For example, Japanese Patent Application Laid-Open No. 55-47211 discloses a 40 m
The surface of a metal lithium lump of mx 14 mm x 12 mm is gently polished with abrasive paper to give processing strain, and if left in a high-purity nitrogen atmosphere, the reaction is completed in 6 hours, and there is no damage to the container due to heat generation, and heating is performed. No source or temperature control system is required.

However, when producing lithium nitride on an industrial scale of several kg / B or more, the heat of formation of lithium nitride is-
Since the reaction is an exothermic reaction of 47 kcal / mol, the temperature of the reaction surface rises with the progress of the reaction, and the reaction rapidly proceeds locally to cause a runaway reaction, or a dense lithium nitride layer is formed on the surface. On the other hand, a phenomenon such that the reaction does not proceed occurs, and there is a problem that a stable reaction cannot be constantly performed.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an industrial production method of lithium ion conductive lithium nitride which is highly useful as a solid electrolyte. is there.

[0008]

The present invention is characterized in that metallic lithium and nitrogen are reacted in a nitrogen gas atmosphere while maintaining the temperature of lithium and lithium nitride produced by cooling below the melting temperature of lithium. Is a method for producing lithium nitride.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The form of metallic lithium used for producing lithium nitride may be an ingot, tape, ribbon, bead, or any other commercially available form. The grade may be any grade such as industrial grade, catalyst grade and battery grade. When reacting these metallic lithium with nitrogen gas in a nitrogen gas atmosphere, the reaction initiation method is to damage the surface of the lithium with a file or the like, to apply a pressure to the lithium to give a strain, or to locally heat the lithium surface. Any of the reaction initiation methods usually performed without melting lithium may be used.

When metal lithium is placed in a nitrogen gas atmosphere containing no moisture or oxygen, such as a glove box, and the reaction with nitrogen is started by the above-described method while passing the nitrogen gas, the surface of the metal lithium in contact with nitrogen is reduced. -47 kcal /
The nitriding reaction proceeds while generating heat in moles. Part of the heat generated by the reaction is radiated to the outside, but a significant part is transmitted to the metallic lithium, raising the temperature of the lithium itself. As the reaction proceeds, the temperature of the reaction section rises, and the reaction rate also increases with the temperature rise, so that the temperature further rises. When the temperature reaches a certain temperature, the reaction is continued while cooling so that the temperature of lithium and the generated lithium nitride is 80 to 120 ° C. As the reaction proceeds, the temperature of the lithium nitride gradually decreases, and finally reaches room temperature, and the reaction ends. The cooling method is not particularly limited.Since the reaction is a reaction that dislikes moisture and the like, the reaction is performed while circulating and cooling the nitrogen gas, the reaction is performed using cooling nitrogen, and the shelf for loading the raw material of the glove box to be reacted is formed in a box structure. It is preferable to cool by a method such as cooling through cooling oil.

When lithium changes to lithium nitride, about 3
Although the volume shrinks by 0%, if the cooling is performed properly, countless minute cracks are generated inside the lithium nitride, and the reaction proceeds because nitrogen gas is supplied through this space. Molten Li during small cracks in lithium nitride
It is considered that nitrogen enters and is nitrided, a thin dense lithium nitride layer is formed, and diffusion of nitrogen is suppressed, so that the reaction rate is reduced. In this way, by performing appropriate cooling, there is no need to add an inert gas to adjust the reaction rate, and only by passing high-purity nitrogen gas, the lithium nitride can be industrially produced while controlling the reaction. It can be manufactured.

[0012]

The present invention will be described below with reference to specific examples.

Example 1 A thermocouple tip with a SUS protective tube was inserted into a cylindrical lithium ingot (about 97 g) having a diameter of about 100 mm and a thickness of about 40 mm, and placed in a glove box in a high-purity nitrogen gas atmosphere. Immediately after the surface of the lithium ingot was scratched with a steel file, about 4 L of cylindrical S kept warm.
Quickly placed in US container. A normal-temperature high-purity nitrogen gas was flowed at 30 L / min into the vessel so that the heat of reaction due to nitriding could be removed. The reaction raises the ingot temperature,
After about 1 hour, the temperature rose to about 110 ° C., and fluctuated between 90 ° C. and 110 ° C. after about 9 hours. Thereafter, the temperature gradually decreased, and returned to room temperature after about 15 hours to complete the reaction. The weight was about 162 g, and all the lithium was changed to lithium nitride.

Example 2 The procedure was the same as in Example 1, except that a high-purity nitrogen gas for cooling was supplied at a flow rate of 15 L / min to remove the heat of reaction caused by nitriding. The temperature of the ingot rises due to the reaction, rises to about 110 ° C. after about 30 minutes, and increases to about 9 hours.
Although the temperature fluctuated between 0 and 110 ° C., the temperature gradually decreased thereafter, and returned to room temperature after about 19 hours to complete the reaction.
The weight was about 162 g, and all the lithium was changed to lithium nitride.

Comparative Example 1 A nitriding reaction of the same lithium ingot as in Example 1 was started under the same conditions as in Example 1. After about 1 hour, the heat generated by the reaction and the heat radiation from the surface were balanced and settled at 100 ° C. After 2 hours, the ingot surface was temporarily heated with a blaster until the temperature rose to 160 ° C. The temperature decreased to ８０80 ° C. After 5.5 hours, the surface of the ingot was temporarily heated again with a blaster until the temperature reached 140 ° C. After that, the temperature decreased to 55 to 60 ° C, and returned to the original temperature after the start of the reaction. It took about 23 hours. Weight is about 83g
And all of the lithium had changed to lithium nitride.

Comparative Example 2 The procedure was the same as in Example 1, except that high-purity nitrogen gas for cooling was not passed, and nitrogen for reaction was allowed to freely enter and exit. The temperature of the ingot increased due to the reaction, increased to about 110 ° C. after about 30 minutes, and fluctuated between 90 and 110 ° C. until about 15 hours, but then gradually decreased, and finally after about 26 hours. The temperature returned to room temperature and the reaction was completed. The weight was about 162 g, and all the lithium was changed to lithium nitride.

COMPARATIVE EXAMPLE 3 About 17 g of tape-shaped metallic lithium having a width of 17 mm and a thickness of 0.57 mm was cut in dry air, cut out in a SUS container, and placed in a glove box in a high-purity nitrogen gas atmosphere. . Thereafter, the surface of the lithium tape was scratched with a steel file to start a nitriding reaction. The tape was wound up six times and left as it was, and the temperature progress of the lithium surface was measured with a surface thermometer. The temperature started to rise due to the reaction,
After one minute, the temperature rose to 400 ° C. or higher due to the heat generated by the reaction, and a red-hot reaction occurred, and the reaction was terminated immediately. When the weight was measured after the temperature was lowered, the weight was about 50 g, and all the lithium was changed to lithium nitride. The SUS container was slightly corroded.

[0018]

According to the production method of the present invention, there is no need to add an inert gas to adjust the reaction rate, and the reaction can be carried out in a reaction vessel of a usual material such as SUS. The invention is an industrially superior production method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiichi Hayatsu 950, Fujisawa, Nakago-mura, Nakakubijo-gun, Niigata Japan Inside Nihongi Plant of Soda Co., Ltd. Inside the Takaoka factory

Claims (2)

[Claims] 1. A method for producing lithium nitride, comprising reacting metallic lithium and nitrogen in a nitrogen gas atmosphere while maintaining the temperature of lithium and lithium nitride produced by cooling at or below the melting temperature of lithium. 2. The method according to claim 1, wherein the reaction is carried out while maintaining the temperature at 80 to 120 ° C.