Preparation method of ant nest like porous silicon for lithium-ion battery

Abstract

A preparation method of an ant nest like porous silicon for a lithium-ion battery comprises: (1) enabling a magnesium silicide raw material to react for 2-24 h in an ammonia gas or an atmosphere containing an ammonia gas at 600-900° C. to obtain a crude product containing porous silicon; and (2) subjecting the crude product containing porous silicon to an acid pickling treatment to obtain the ant nest like porous silicon. The preparation method has the advantages of simplicity and easiness. A large amount of porous silicon can be obtained by directly heating the magnesium silicide raw material in the ammonia gas or a mixed gas of the ammonia gas and an inert gas with a high yield.

Claims

1. A preparation method of an ant nest like porous silicon for a lithium-ion battery, comprising: (1) conducting a reaction of a magnesium silicide raw material with an ammonia gas or an atmosphere containing ammonia gas for 2-24 h at 600-900° C. to obtain a crude product containing porous silicon and magnesium nitride, wherein the magnesium silicide raw material has a particle size of 0.2-10 μm, wherein the atmosphere containing ammonia gas is a mixed atmosphere of the ammonia gas and a protective gas; and (2) subjecting the crude product obtained in the step (1) to an acid pickling treatment to obtain the ant nest like porous silicon for the lithium-ion battery.

2. The preparation method of claim 1, wherein in the step (1), the reaction has an equation represented by 3Mg.sub.2Si+4NH.sub.3.fwdarw.3Si+2Mg.sub.3N.sub.2+6H.sub.2.

3. The preparation method of claim 1, wherein in the step (1), the magnesium silicide raw material is prepared by a reaction of silicon powder and magnesium powder in an inert atmosphere; the reaction of silicon powder and magnesium powder is carried out at 400-900° C. with a holding time of 1-12 h; and a mass ratio of the silicon powder to the magnesium powder is 1:(1.8-3).

4. The preparation method of claim 1, wherein in the step (1), a volume fraction of the ammonia gas in the atmosphere containing ammonia gas is 5-95%; and the protective gas is an inert gas.

5. The preparation method of claim 1, wherein in the step (1), the magnesium silicide raw material is ball-milled via a ball milling treatment so that the magnesium silicide raw material has the particle size of 0.2-10 μm; and the ball milling treatment is carried out under a protection of an inert gas.

6. The preparation method of claim 1, wherein in the step (2), the acid pickling treatment is carried out by hydrochloric acid pickling to remove magnesium nitride which is a reaction by-product in the crude product obtained in the step (1); the ammonia gas generated in the acid pickling treatment is collected and used for participating in the reaction of the magnesium silicide raw material in the step (1); and magnesium salt generated in the acid pickling treatment is used for preparing magnesium powder.

7. The preparation method of claim 1, wherein the ant nest like porous silicon obtained in the step (2) has a specific surface area of 30-56 m.sup.2/g, a tap density of 0.77-0.85 g/cm.sup.3, and a compacted density of 1.64-1.97 g/cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a XRD spectrum of ant nest like porous silicon prepared in Embodiment 1 of the present invention;

(2) FIGS. 2A and 2B are scanning electron micrographs (SEMs) of the ant nest like porous silicon prepared in Embodiment 1 of the present invention;

(3) FIG. 3 is a transmission electron microscope (TEM) of the ant nest like porous silicon prepared in Embodiment 1 of the present invention;

(4) FIG. 4 is a diagram showing the electrochemical cycling performance of the ant nest like porous silicon prepared in Embodiment 1 of the present invention, in which the first coulombic efficiency (CE) is 78.7%; and

(5) FIGS. 5A and 5B are micrographs of electrode film thicknesses before and after cycling of the ant nest like porous silicon prepared in Embodiment 1 of the present invention, respectively.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) For clear understanding of the objectives, features and advantages of the present invention, detailed description of the present invention will be given below in conjunction with accompanying drawings and specific embodiments. It should be noted that the embodiments described herein are only meant to explain the present invention, and not to limit the scope of the present invention.

(7) According to the present invention, a preparation method of ant nest like porous silicon for a lithium-ion battery comprises: commercially available magnesium silicide (particle size: 1-50 μm) or magnesium silicide (particle size: 1-50 μm) prepared by thermal reaction (2Mg+Si=Mg.sub.2Si) of an uniform mixture of silicon powder and an appropriate amount of magnesium powder in an inert atmosphere is ball-milled under the protection of inert gas to prepare particles with a size of 0.2-10 μm, then ant nest like porous silicon with its by-product (magnesium nitride) is obtained by thermal reaction (3Mg.sub.2Si+4NH.sub.3=3Si+2Mg.sub.3N.sub.2+6H.sub.2) of the prepared particles in ammonia gas or in a gas mixture of a certain volume ratio of ammonia gas (content: 5-95%) and inert gas (e.g., argon) at 600-900° C., and finally the by-product is removed by acid pickling treatment (Mg.sub.3N.sub.2+6HCl=3MgCl.sub.2+2NH.sub.3) to obtain ant nest like porous silicon in high yield.

(8) The invention is described in conjunction with the following embodiments.

Embodiment 1

(9) The embodiment comprises the following steps:

(10) (1) uniformly mixing commercially available silicon particles and magnesium powder in a mass ratio of 1:1.8, and then placing them in a container;

(11) (2) placing the container containing the reactants in a high temperature furnace filled with an inert gas, heating to 400-700° C. at a rate of 5° C./min with a holding time of 6 h so as to obtain magnesium silicide as the product, and taking out the product after being cooled with the furnace to the room temperature;

(12) (3) subjecting the product obtained in the step (2) to ball-milling under the protection of argon and then to screening so as to obtain magnesium silicide particles with a size of 0.2-10 μm;

(13) (4) placing the magnesium silicide particles obtained in the step (3) in a tube furnace in an ammonia gas atmosphere, heating to 600-900° C. with a holding time of 2-24 h, and taking out the product after being cooled with the furnace to the room temperature; and

(14) (5) subjecting the product obtained in the step (4) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(15) It can be seen from the XRD spectrum of the sample subjected to acid pickling in FIG. 1 that the three strong peaks at 28.4°, 47.3°, and 56.1° correspond to three strong peaks of silicon (JCPDS No. 27-1402), and there are substantially no impurity phase; it can be seen from SEMs in FIG. 2 (including FIGS. 2A and 2B) that the product prepared in this embodiment has a micron-sized porous structure; and it can be seen from TEM in FIG. 3 that three-dimensionally penetrated porous silicon composed of nanocells prepared in this embodiment has a rich pore structure. Thus, the resulting product is micron particles with nanoscale pore structure, and has a tap density of 0.83 g/cm.sup.3. FIG. 4 shows the cycling performance of the porous silicon, and after 1000 cycles, the capacity of the porous silicon can reach 1200 mA h/g, showing outstanding cycling stability. FIG. 5 (including FIGS. 5A and 5B) is a comparison diagram of electrode film thicknesses before and after cycling of the ant nest like micron-sized porous silicon prepared in Embodiment 1 of the present invention, and it can be seen that the film thickness does not change much before ((FIG. 5A) and after (FIG. 5B) the cycling, thus greatly reducing battery expansion and improving battery safety. In addition, the product has a specific surface area of 56 m.sup.2/g and a compacted density of 1.96 g/cm.sup.3.

Embodiment 2

(16) The embodiment comprises the following steps:

(17) (1) uniformly mixing commercially available silicon particles and magnesium powder in a mass ratio of 1:1.9, and then placing them in a container;

(18) (2) placing the container containing the reactants in a high temperature furnace filled with an inert gas, heating to 400° C. at a rate of 3° C./min with a holding time of 12 h so as to obtain magnesium silicide as the product, and taking out the product after being cooled with the furnace to the room temperature;

(19) (3) subjecting the product obtained in the step (2) to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 1-8 μm;

(20) (4) placing the magnesium silicide particles obtained in the step (3) in a tube furnace in an ammonia gas atmosphere, heating to 650° C. with a holding time of 4 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(21) (5) subjecting the product obtained in the step (4) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(22) In this way, the obtained ant nest like porous silicon has a specific surface area of 34 m.sup.2/g, a tap density of 0.78 g/cm.sup.3 and a compacted density of 1.78 g/cm.sup.3.

Embodiment 3

(23) The embodiment comprises the following steps:

(24) (1) uniformly mixing commercially available silicon particles and magnesium powder in a mass ratio of 1:2, and then placing them in a container;

(25) (2) placing the container containing the reactants in a high temperature furnace filled with an inert gas, heating to 500° C. at a rate of 10° C./min with a holding time of 10 h so as to obtain magnesium silicide as the product, and taking out the product after being cooled with the furnace to the room temperature;

(26) (3) subjecting the product obtained in the step (2) to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 0.5-4 μm;

(27) (4) placing the magnesium silicide particles obtained in the step (3) in a tube furnace in an ammonia gas atmosphere, heating to 600° C. with a holding time of 6 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(28) (5) subjecting the product obtained in the step (4) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(29) In this way, the obtained ant nest like porous silicon has a specific surface area of 46 m.sup.2/g, a tap density of 0.77 g/cm.sup.3 and a compacted density of 1.81 g/cm.sup.3.

Embodiment 4

(30) The embodiment comprises the following steps:

(31) (1) uniformly mixing commercially available silicon particles and magnesium powder in a mass ratio of 1:2.2, and then placing them in a container;

(32) (2) placing the container containing the reactants in a high temperature furnace filled with an inert gas, heating to 600° C. at a rate of 1° C./min with a holding time of 12 h so as to obtain magnesium silicide as the product, and taking out the product after being cooled with the furnace to the room temperature;

(33) (3) subjecting the product obtained in the step (2) to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 1-5 μm;

(34) (4) placing the magnesium silicide particles obtained in the step (3) in a tube furnace in an ammonia gas atmosphere, heating to 700° C. with a holding time of 12 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(35) (5) subjecting the product obtained in the step (4) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(36) In this way, the obtained ant nest like porous silicon has a specific surface area of 49 m.sup.2/g, a tap density of 0.80 g/cm.sup.3 and a compacted density of 1.77 g/cm.sup.3.

Embodiment 5

(37) The embodiment comprises the following steps:

(38) (1) uniformly mixing commercially available silicon particles and magnesium powder in a mass ratio of 1:1.9, and then placing them in a container;

(39) (2) placing the container containing the reactants in a high temperature furnace filled with an inert gas, heating to 700° C. at a rate of 5° C./min with a holding time of 6 h so as to obtain magnesium silicide as the product, and taking out the product after being cooled with the furnace to the room temperature;

(40) (3) subjecting the product obtained in the step (2) to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 0.2-3 μm;

(41) (4) placing the magnesium silicide particles obtained in the step (3) in a tube furnace in an ammonia gas atmosphere, heating to 800° C. with a holding time of 4 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(42) (5) subjecting the product obtained in the step (4) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(43) In this way, the obtained ant nest like porous silicon has a specific surface area of 51 m.sup.2/g, a tap density of 0.81 g/cm.sup.3 and a compacted density of 1.92 g/cm.sup.3.

Embodiment 6

(44) The embodiment comprises the following steps:

(45) (1) subjecting commercially available magnesium silicide to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 1-3 μm;

(46) (2) placing the magnesium silicide particles obtained in the step (1) in a tube furnace in an ammonia gas atmosphere, heating to 750° C. with a holding time of 6 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(47) (3) subjecting the product obtained in the step (2) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(48) In this way, the obtained ant nest like porous silicon has a specific surface area of 56 m.sup.2/g, a tap density of 0.84 g/cm.sup.3 and a compacted density of 1.94 g/cm.sup.3.

Embodiment 7

(49) The embodiment comprises the following steps:

(50) (1) subjecting commercially available magnesium silicide to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 3-5 μm;

(51) (2) placing the magnesium silicide particles obtained in the step (1) in a tube furnace in a mixed atmosphere of ammonia gas and argon gas (volume fraction of ammonia gas: 50%), heating to 780° C. with a holding time of 6 h, and then taking out the product after being cooled with the furnace to the room temperature; and

(52) (3) subjecting the product obtained in the step (2) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(53) In this way, the obtained ant nest like porous silicon has a specific surface area of 56 m.sup.2/g, a tap density of 0.85 g/cm.sup.3 and a compacted density of 1.97 g/cm.sup.3.

Embodiment 8

(54) The embodiment comprises the following steps:

(55) (1) subjecting commercially available magnesium silicide to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 5-8 μm;

(56) (2) placing the magnesium silicide particles obtained in the step (1) in a tube furnace in a mixed atmosphere of ammonia gas and argon gas (volume fraction of ammonia gas: 90%), heating to 850° C. with a holding time of 6 h, and then taking out the product after being cooled with the furnace to the room temperature;

(57) (3) subjecting the product obtained in the step (2) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(58) In this way, the obtained ant nest like porous silicon has a specific surface area of 30 m.sup.2/g, a tap density of 0.79 g/cm.sup.3 and a compacted density of 1.7 g/cm.sup.3.

Embodiment 9

(59) The embodiment comprises the following steps:

(60) (1) subjecting commercially available magnesium silicide to ball-milling in a an argon-protected ball mill and then to screening so as to obtain magnesium silicide particles with a size of 0.2-1 μm;

(61) (2) placing the magnesium silicide particles obtained in the step (1) in a tube furnace in a mixed atmosphere of ammonia gas and argon gas (volume fraction of ammonia gas: 70%), heating to 780° C. with a holding time of 6 h, and then taking out the product after being cooled with the furnace to the room temperature;

(62) (3) subjecting the product obtained in the step (2) to hydrochloric acid pickling so as to remove magnesium nitride, and then to cleaning, filtration and drying so as to obtain ant nest like porous silicon.

(63) In this way, the obtained ant nest like porous silicon has a specific surface area of 51 m.sup.2/g, a tap density of 0.73 g/cm.sup.3 and a compacted density of 1.64 g/cm.sup.3.

(64) In the present invention, the commercially available magnesium silicide raw material has a main component of magnesium silicide and may also contain a certain amount of magnesium impurities. In the case of using thermal reaction of silicon powder and magnesium powder to prepare magnesium silicide, the mass ratio of the magnesium raw material may be greater than the corresponding ratio in the ideal reaction equation. For example, the mass ratio of the silicon powder and the magnesium powder may be 1: (1.8-3), so that there is a certain amount of surplus magnesium.

(65) While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the spirit and scope of the present invention.