JP2013028843A - Method for producing transition metal sulfide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing at least one of transition metal sulfide selected from Groups 8-10, on an industrial scale in a stable manner.SOLUTION: The method for producing the transition metal sulfide includes a step of arranging two electrodes in at least one of liquid sulfidizing agents to generate a rectangular pulse plasma discharge between the two electrodes. At least one of the electrodes contains at least one of elements selected from transition metal elements of Groups 8-10.

Description

  The present invention relates to a method for producing a transition metal sulfide, and more particularly to a method for producing a transition metal sulfide containing at least one kind of transition metal element selected from Group 8 to Group 10 transition metal elements.

In recent years, as a positive electrode material for a lithium ion secondary battery, a transition metal sulfide capable of reversibly inserting and extracting lithium ions (MS _x , where M is a transition metal, x represents a positive number), Attention has been focused on transition metal sulfides of Group 8 to Group 10 transition metals (for example, iron and nickel) in which the molar ratio of the constituent sulfur to the transition metal exceeds 1.

  For example, as a method for producing iron sulfide, iron and sulfur are mixed at a molar ratio of 1: 2, and iodine is added, and then enclosed in a quartz tube and heated for about 5 days to produce pyrite crystals (non-patented). Reference 1), after adding a sodium hydroxide aqueous solution saturated with hydrogen sulfide to a mixture of ferrous sulfate heptahydrate and orthorhombic sulfur, the system is sealed after passing through the hydrogen sulfide, and in a constant temperature dryer. A method of generating flamboid pyrite by maintaining for about 2 weeks (see Non-Patent Document 2), iron powder and sulfur powder are mixed at a molar ratio of 1: 2, and a tungsten carbide container is placed in a tungsten carbide container with a ball mill ball A method of generating iron sulfide by ball milling for about 110 hours after sealing is known (see Non-Patent Document 3).

  However, the above production method has a drawback that a long reaction time exceeding 100 hours is required to obtain the target iron sulfide.

Known methods for producing nickel sulfide include a mechanical milling method and a liquid phase precipitation reaction method. For example, it is known that NiS can be generated with relatively low energy by a mechanical milling method (see Non-Patent Document 4). In addition, it is known that crystalline Ni ₃ S ₂ , Ni ₃ S _{4, and the} like are generated from an aqueous reaction solution containing nickel chloride and sodium dithionite adjusted for pH by a liquid phase precipitation reaction method ( Non-patent document 5). In these methods, it is difficult to completely remove oxygen in the system, so it is difficult to avoid mixing nickel oxide and hydroxide, and it is difficult to obtain nickel sulfide having a high S / Ni ratio. is there.

Furthermore, a method for producing a transition metal sulfide by spark plasma sintering has been proposed (see Patent Document 1). According to this production method, a metal sulfide having a composition of MS ₂ (where M represents a transition metal) can be obtained relatively easily, but it requires treatment under high temperature and high pressure, and batch reaction. Therefore, it is difficult to implement on an industrial scale.

  Also disclosed is a method of generating a transition metal sulfide by intermittently generating a plasma discharge in sulfur and reacting with a transition metal in a condenser system (see Patent Document 2). In this method, since the current density is not stable, sulfur polymerization proceeds due to the high current density temporarily applied to the reaction field, and there is a problem that a uniform product cannot be obtained and continuous production is not possible. .

  As described above, a method for stably producing a transition metal sulfide, in particular, a transition metal sulfide of Group 8 to Group 10 on an industrial scale has not been established.

International Publication No. 09/028326 USSR No. 860428

Acta Chem. Scand., 1969, 23, p. 2186 Econ. Geol., 1969, 64, p. 383 J. Solid State Chem., 1998, 138, p. 114 J. Alloys Comp., 2003, 349, p. 290-296 Inorg. Chem., 2001, 40, p. 73-77

  An object of the present invention is to provide a method for stably producing a sulfide of at least one transition metal selected from Group 8 to Group 10 on an industrial scale.

According to the present invention, the above object is
[1] A method for producing a transition metal sulfide comprising disposing two electrodes in at least one liquid sulfiding agent and generating a rectangular pulse plasma discharge between the two electrodes, wherein at least one of the electrodes One of them contains at least one transition metal element selected from Group 8 to Group 10 transition metal elements;
[2] The method for producing a transition metal sulfide according to [1], wherein the liquid sulfiding agent is molten sulfur;
[3] The method for producing a transition metal sulfide according to [1] above, wherein the liquid sulfiding agent contains carbon disulfide;
[4] The method for producing a transition metal sulfide according to [3] above, wherein the liquid sulfiding agent is sealed with a water layer;
[5] Composition formula: MS _x (wherein M is at least one transition metal selected from the group consisting of Fe, Co, and Ni, and x is a positive number in the range of 1 <x ≦ 2. And a transition metal sulfide obtained by the production method of any one of the above [1] to [4];
Is achieved by providing

  According to the present invention, at least one transition metal sulfide selected from Group 8 to Group 10 can be stably produced on an industrial scale.

It is an XRD chart of the transition metal sulfide obtained in Examples 1-3. 2 is a thermal mass analysis chart of nickel sulfide 1 obtained in Example 1. FIG. 2 is a thermal mass spectrometry chart of nickel sulfide 2 obtained in Example 2. FIG. 2 is a thermal mass spectrometry chart of nickel sulfide 3 obtained in Example 3. FIG.

  The method for producing a metal sulfide according to the present invention generates a rectangular pulse plasma discharge by applying a voltage between two electrodes arranged in a liquid sulfiding agent, and the Group 8 contained in at least one of the electrodes. A transition metal sulfide is produced by a reaction of at least one transition metal element selected from Group 10 transition metal elements and the liquid sulfiding agent.

Examples of the electrode include a transition metal element composed of a transition metal element belonging to Group 8 to Group 10, an alloy containing the transition metal element, and an electrode obtained by coating the transition metal element with another metal by plating or the like. . In the present invention, by using an electrode containing any transition metal element belonging to Group 8 to Group 10 of the Periodic Table of Elements, a transition metal sulfide (MS) corresponding to the contained transition metal element (M) is used. _x ) particles can be generated. The positive electrode and the negative electrode may be the same type of electrodes or different types of electrodes. One of the two electrodes used in the method for producing a transition metal sulfide of the present invention may not contain a transition metal element selected from Group 8 to Group 10. Examples of the electrode material that does not contain a transition metal element selected from Group 8 to Group 10 include various metal simple substances and compounds thereof, and conductive substances such as carbon materials such as graphite. When a carbon material is used as the electrode material not containing the transition metal element, a transition metal sulfide containing carbon is obtained.

  The form of the electrode used in the method for producing a transition metal sulfide of the present invention may be any form such as a rod, wire, or plate. The size of both electrodes may be the same or different.

  In the method for producing a transition metal sulfide of the present invention, at least one liquid sulfiding agent can be used. The liquid sulfiding agent may be an inorganic substance, an organic substance or a combination thereof containing a sulfur element as a constituent element and can maintain a liquid state at the reaction temperature. For example, sulfur alone can be used as a liquid sulfiding agent at a reaction temperature of 120 ° C. to 160 ° C. Further, carbon disulfide or a carbon disulfide solution of sulfur (referred to as “carbon disulfide” in the present specification) can be used as a liquid sulfiding agent at around room temperature. When carbon disulfide or the like is used as a liquid sulfiding agent, the transition metal sulfide is generated together with a carbon material (for example, amorphous carbon).

  Moreover, you may add an additive to these liquid sulfiding agents according to the objective. For example, by adding a salt of a metal that does not belong to Group 8 to Group 10 as an additive, the metal can be incorporated into a transition metal compound that is generated as fine particles. Such metals include copper, zinc, tin and the like.

  In the method for producing a transition metal sulfide of the present invention, the temperature of the liquid sulfiding agent at the time of rectangular pulse plasma discharge is not limited as long as the liquid sulfiding agent is maintained in a liquid state. For example, when sulfur alone is used as the liquid sulfiding agent, a range of 120 ° C. or higher and 160 ° C. or lower is preferable, and 130 ° C. or higher and 150 ° C. or lower is more preferable. When carbon disulfide is used, a temperature of 46 ° C. or lower, which is the boiling point of carbon disulfide, can be selected. When a sulfur carbon disulfide solution is used as the liquid sulfiding agent, it is preferably 20 ° C. or higher and 46 ° C. or lower so that the solubility of sulfur in carbon disulfide is maintained at a good level.

  In the present invention, when the liquid sulfiding agent contains carbon disulfide, it is preferably sealed with a liquid layer immiscible with carbon disulfide in consideration of the volatility and flammability of carbon disulfide. The immiscible liquid used for liquid sealing is preferably non-flammable and immiscible with a liquid sulfiding agent containing carbon disulfide. From the viewpoint of availability, safety, etc. Is preferred. When the liquid sulfiding agent is composed only of carbon disulfide, and the carbon disulfide is sealed with water, the volume ratio of carbon disulfide / water used is usually in the range of 1 / 0.01 to 1/10. Is preferred.

  The current for rectangular pulse plasma discharge may be either direct current or alternating current, but direct current is preferred from the viewpoint of temperature control of the reaction and the stability of the produced transition metal sulfide. The voltage for generating the rectangular pulse plasma discharge may be in the range of 50 to 500V, but in view of safety and the necessity of a special device, the voltage is preferably in the range of 60 to 400V. A value in the range of 80 to 300V is more preferable.

The current for rectangular pulse plasma discharge is preferably in the range of 0.1 to 100 A, and more preferably in the range of 0.2 to 30 A in consideration of energy efficiency.
The pause time in the rectangular pulse plasma discharge is preferably 2 microseconds or more from the viewpoint of the stability of the produced transition metal sulfide, and more preferably 20 milliseconds or less from the viewpoint of production efficiency.

  The duration per rectangular pulse plasma discharge may be in the range of 1 to 8000 microseconds, but is preferably in the range of 2 to 500 microseconds.

In the manufacturing method of the present invention, it is possible to apply vibration to one or both electrodes. By applying vibration to the electrodes, the retention of the transition metal sulfide (MS _x ) generated between the electrodes is eliminated, and the effect that the reaction is efficiently promoted can be obtained. The vibration may be applied to the electrode continuously or intermittently.

  The reaction system for carrying out the present invention may be in any state of reduced pressure, increased pressure, and normal pressure. The atmosphere of the reaction system is preferably an inert gas atmosphere such as nitrogen or argon in consideration of safety and operability.

  Since the produced transition metal sulfide is dispersed or deposited in the liquid sulfiding agent, the transition metal sulfide can be separated and recovered by a conventional solid-liquid separation method (for example, filtration, simple distillation, vacuum distillation, etc.).

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.
In each example, a nickel electrode manufactured by Niraco Co., Ltd. was used. In addition, an actuator (WaveMaker SL-0105 manufactured by Asahi Seisakusho) was used as a vibration generator for vibrating the nickel electrode during plasma discharge.
For XRD measurement, a powder X-ray diffractometer (MiniFlex II manufactured by Rigaku Corporation) was used.
The composition of the obtained positive electrode material for a non-aqueous secondary battery and the value of _x in the composition formula NiS _x were calculated by organic carbon analysis and thermal mass spectrometry. The organic carbon analysis was conducted with Perkin Elmer 2400CHNS. Thermal mass spectrometry was performed using a thermal mass spectrometer (TG / DTA6300 EXSTAR6000 manufactured by SII) while heating to 1000 ° C. at 10 ° C./min in the air.

[Example 1] (When the electrode / liquid sulfide / electrode combination is Ni / S / Ni)
In a 100 ml beaker, 100 g of sulfur was taken and heated to 140 ° C. to melt. As a positive electrode and a negative electrode, two cylindrical nickel electrodes (purity 99% or more) having a diameter of 5 mm and a length of 100 mm were immersed in a sulfur melt, and the distance between the electrodes was set to 1 mm. Vibration (about 100 vibrations per second) was applied to both electrodes with an electric vibration generator (actuator) to prevent reaction products from being deposited on the surface of the nickel electrode. The positive and negative electrodes are connected to a power source, and a rectangular pulse plasma discharge is performed for 30 minutes by applying a voltage with a direct current so that the duration of one round pulse plasma discharge is 200 microseconds at 200 V and 60 A, and the rest time is 10 milliseconds. Continued. After the rectangular pulse plasma discharge, the mass decrease of the positive electrode was 0.55 g, and the mass decrease of the negative electrode was 0.52 g. Sulfur was removed from the molten sulfur containing the reaction product by distillation under reduced pressure to obtain 1.71 g of nickel sulfide (referred to as nickel sulfide 1) as a powder. The measurement result of XRD is shown in FIG.
Moreover, the result of the thermal mass measurement of the nickel sulfide 1 is shown in FIG. It is estimated that the 8% mass reduction observed over 250 ° C. is based on volatile components such as water, and the 26% mass reduction observed over 250 ° C. to 900 ° C. is the sulfur content associated with oxidation of nickel sulfide. Estimated to be based on volatilization. The value of x in the composition formula NiS _x calculated from the thermal mass spectrometry was 1.4.

[Example 2] (When the electrode / liquid sulfiding agent / electrode combination is Ni / CS ₂ / Ni)
The rectangular pulse plasma discharge was continued for 30 minutes under the same conditions as in Example 1 except that 100 g of carbon disulfide at 20 ° C. was used instead of sulfur at 140 ° C. After the rectangular pulse plasma discharge, the mass reduction of the positive electrode was 0.25 g, and the mass reduction of the negative electrode was 0.19 g. Carbon disulfide was removed from the carbon disulfide containing the reaction product by simple distillation to obtain 0.81 g of nickel sulfide (referred to as nickel sulfide 2) as a powder. The measurement result of XRD is shown in FIG.
Further, when the obtained nickel sulfide 2 was subjected to organic carbon analysis, the carbon content was 7% by mass. These carbons are presumed to be contained in nickel sulfide as amorphous carbon. Moreover, the result of the thermal mass measurement of the nickel sulfide 2 is shown in FIG. The 9% mass loss observed over 250 ° C. is estimated to be based on the reduction of volatiles such as water, and the 23% mass reduction observed over 250 ° C. to 900 ° C. is due to volatilization associated with carbon oxidation and It is estimated to be based on the volatilization of the sulfur content accompanying the oxidation of nickel sulfide. The value of x of NiS _x calculated from the measurement results of organic carbon analysis and thermal mass spectrometry was 1.1.

[Example 3] (When electrode / liquid sulfiding agent / electrode combination is Ni / (S + CS ₂ ) / Ni)
A rectangular pulse plasma discharge was continued for 30 minutes under the same conditions as in Example 1 except that 100 g of a 10% by mass sulfur carbon disulfide solution at 20 ° C. was used instead of 140 ° C. sulfur. After the rectangular pulse plasma discharge, the mass reduction of the positive electrode was 0.23 g, and the mass reduction of the negative electrode was 0.18 g. Carbon disulfide was removed by simple distillation, and then sulfur was removed by vacuum distillation to obtain 0.69 g of nickel sulfide (referred to as nickel sulfide 3) as a powder. The measurement result of XRD is shown in FIG.
Further, FIG. 3 shows the result of thermogravimetric analysis performed while raising the reaction product to 900 ° C. at a temperature rising rate of 10 ° C./min in the air atmosphere. It is considered that it is a mixture of amorphous carbon and nickel sulfide.
Further, when the obtained nickel sulfide 3 was subjected to organic carbon analysis, the carbon content was 3% by mass. These carbons are presumed to be contained in nickel sulfide as amorphous carbon. Moreover, the result of the thermal mass measurement of the nickel sulfide 3 is shown in FIG. The 10% mass loss observed over 250 ° C. is estimated to be based on volatiles such as water, and the 32% mass reduction observed over 250 ° C. to 900 ° C. is due to volatilization due to oxidation of carbon and nickel sulfide. It is estimated to be based on the volatilization of the sulfur content accompanying oxidation of The value of x of NiS _x calculated from the measurement results of organic carbon analysis and thermal mass spectrometry was 1.7.

[Example 4] (When electrode / liquid sulfiding agent / electrode combination is Ni / CS ₂ + water / Ni)
Instead of 100 g of carbon disulfide at 20 ° C., rectangular pulse plasma discharge was continued for 30 minutes under the same conditions as in Example 2 except that 50 g of ion-exchanged water was added to 100 g of carbon disulfide at 20 ° C. After the rectangular pulse plasma discharge, the mass reduction of the positive electrode was 0.25 g, and the mass reduction of the negative electrode was 0.19 g. The mass of the solid powder obtained by removing carbon disulfide by simple distillation was 0.81 g of nickel sulfide (referred to as nickel sulfide 4).
Further, when the obtained nickel sulfide 4 was subjected to organic carbon analysis, the carbon content was 7% by mass. These carbons are presumed to be contained in nickel sulfide as amorphous carbon. Moreover, the thermal mass measurement of the nickel sulfide 4 was performed, and the value of x of NiS _x calculated together with the measurement result of the organic carbon analysis was 1.1.

  The present invention provides a method capable of stably producing a transition metal sulfide containing any of the transition metal elements of Groups 8, 9, and 10 of the Periodic Table of Elements on an industrial scale. The obtained transition metal sulfide is useful for production and development of a high-capacity lithium ion secondary battery as a transition metal sulfide-based positive electrode material.

Claims (5)

  A method for producing a transition metal sulfide comprising disposing two electrodes in at least one liquid sulfiding agent and generating a rectangular pulse plasma discharge between the two electrodes, wherein at least one of the electrodes comprises: A method for producing a transition metal sulfide, comprising at least one transition metal element selected from Group 8 to Group 10 transition metal elements.   The method for producing a transition metal sulfide according to claim 1, wherein the liquid sulfiding agent is molten sulfur.   The method for producing a transition metal sulfide according to claim 1, wherein the liquid sulfiding agent contains carbon disulfide.   The method for producing a transition metal sulfide according to claim 3, wherein the liquid sulfiding agent is sealed with a water layer. Composition formula: MS _x (wherein M is at least one transition metal selected from the group consisting of Fe, Co, and Ni, and x is a positive number in the range of 1 <x ≦ 2) The transition metal sulfide obtained by the manufacturing method according to any one of claims 1 to 4.