A porous micron silicon sphere material, preparation method and application thereof

Abstract

The present invention provides a method for preparing porous micron silicon spheres as a negative electrode material, comprising the following steps: subjecting a layered silicate raw material to high-temperature expansion and mechanical ball milling, followed by acid washing and purification to obtain layered silicon dioxide; mixing the layered silicon dioxide with aluminum powder, sodium chloride, and aluminum chloride, charging the mixture into a reaction vessel, and heating to carry out a reduction reaction; washing the reactants with hydrochloric acid and hydrofluoric acid solutions, subsequently filtering them to a neutral state, and vacuum drying to obtain porous micron silicon spheres. The porous micron silicon sphere negative electrode material of the present invention has a simple preparation process, a wide range of raw material sources, a high tap density, and a stable structure. Its application in lithium-ion batteries has advantages such as long-lasting cycling, excellent rate performance, and a low electrode film swelling rate, and has great commercial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a porous micron silicon sphere material, a preparation method and applications thereof. Background Art

[0002] Lithium-ion batteries are important energy storage devices and have been widely used in consumer electronics, electric vehicles, and energy storage. Currently, the theoretical specific capacity of commercial graphite anodes is 372 mAh / g, which cannot meet application requirements. Developing high-capacity anode materials is essential for increasing battery energy density. Silicon, with a theoretical capacity 10 times that of graphite, is an ideal anode material for next-generation high-energy-density batteries. However, the large volume change (>300%) of silicon during lithium insertion and extraction can easily lead to mechanical particle fragmentation, loss of electrical contact between particles, and continued growth of the solid-electrolyte interface (SEI), resulting in rapid capacity decay and deterioration of battery performance.

[0003] In order to mitigate the pulverization problem caused by the volume change of Si during the charge and discharge process and improve the structural stability of the electrode material, researchers have focused their attention on the nano-sizing of Si. Various nanostructures such as nanowires, nanoporous structures, nanotubes and nanosheets have made significant progress in solving the problem of Si particle crushing and improving battery performance. However, the nano-sizing preparation process is complex and the preparation cost is high. In addition, the tap density and first coulomb efficiency of the nanostructure are difficult to meet the requirements of practical applications, which hinders its large-scale process. Micron-scale silicon-based materials have natural advantages in cost, tap density and coulomb efficiency, and are more attractive than nano-scale materials in industrial production.

[0004] Chinese patent CN109694075A discloses a method for preparing nano-silicon powder by low-temperature ball milling. The method involves mixing a silicon source, aluminum or magnesium powder, and a reaction accelerator, followed by grinding. The mixture is then subjected to intermittent ball milling at 95-160°C for 6-8 hours to obtain a nano-silicon powder preform. This preform is then sprayed with deionized water, reacted with hydrochloric acid, and washed with hydrofluoric acid to obtain the nano-silicon powder. This method is complex, resulting in silicon spheres with a particle size of 30-10 nm, a low tap density, and severe sintering.

[0005] Chinese patent CN108666560A discloses a method for preparing nano-silicon materials. The method involves mixing silicon raw material particles, a low-melting-point metal salt, and a strongly reducing metal, followed by ball milling to obtain a nano-silicon material precursor. The precursor is then washed with water, acid-washed, and dried to obtain the nano-silicon material. This method is also cumbersome, and the resulting silicon material has a particle size of 100-650 nm and a low tap density that cannot meet practical application requirements.

[0006] In view of this, the development of a silicon negative electrode material with a simple preparation process, high material tap density, stable structure, long-term cycle, excellent rate performance, and small electrode film swelling rate is of great significance to the development of lithium-ion batteries. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention provides a porous micron silicon sphere negative electrode material, a preparation method and an application thereof. The material has multiple sources, a simple preparation method and low cost. The material can not only achieve the advantages of micron silicon in cost, tap density and Coulomb efficiency, but also retain sufficient space inside to alleviate volume expansion and achieve excellent cycle performance.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing porous micron silicon sphere material comprises the following steps:

[0010] (1) The layered silicate raw material is subjected to high temperature expansion and then mechanically ball milled, and then purified by hydrochloric acid pickling to obtain layered silicon dioxide;

[0011] (2) Mixing layered silica with aluminum powder, sodium chloride, and aluminum chloride into a reaction vessel and heating to perform a reduction reaction;

[0012] (3) The reactant obtained in step (2) is washed with hydrochloric acid and hydrofluoric acid solution, then filtered to neutrality and vacuum dried to obtain a porous micron silicon sphere material.

[0013] In some embodiments of the present invention, the layered silicate in step (1) is selected from one or more of vermiculite, montmorillonite, talc, and kaolin.

[0014] The high temperature expansion in step (1) refers to burning the layered silicate raw material to 500-1500°C and then cooling it naturally; more preferably, the layered silicate raw material is burned to 800-1200°C and then cooling it naturally.

[0015] In step (1), after mechanical ball milling, the size is preferably controlled to be 1-100 μm; more preferably 5-50 μm.

[0016] In some embodiments of the present invention, the mass ratio of layered silica to aluminum powder, sodium chloride, and aluminum chloride in step (2) is 1:0.5-1.5:0.5-10:6.25-18.75; further preferably 1:0.7-1:2-5:8.75-12.5, and most preferably 1:0.8:2.875:10.

[0017] The reduction reaction temperature in step (2) is 200-600°C, more preferably 250-400°C; the reaction time is 6-20h, more preferably 10-14h.

[0018] The present invention heat-reacts layered silica with aluminum powder, sodium chloride, and aluminum chloride in specific ratios. Under high temperature and pressure, AlCl3 forms a liquid phase. Under liquid phase conditions, the spherical surface tension is minimal, so the thin layered silica tends to curl into balls. The addition of molten sodium chloride further reduces the van der Waals forces between the layers, making it easier to curl into balls. If the temperature is too low, the layers cannot curl into balls, while if the temperature is too high, the spheres are destroyed and collapsed. When the ratio of aluminum powder to aluminum chloride is too low, the silica cannot be effectively reduced; when the ratio of sodium chloride is too low, the van der Waals forces between the silica layers cannot be effectively weakened. When the ratio of sodium chloride is too high, the layered silica is completely exfoliated into flakes.

[0019] The porous micron-sized silicon spheres prepared by the present invention range in size from approximately 1 to 30 μm and consist of nano-sized silicon sheets encased in a micron-sized silicon shell. The interior of the material consists of nano-sized or lightly sintered silicon sheets, while the exterior is a shell formed by curled-up two-dimensional silicon sheets. This method utilizes the natural curling of layered silicates into spheres in the liquid phase. This allows for ample "breathing space" between the nanosheets within the micron-sized silicon spheres to mitigate expansion during lithium insertion and removal. The preparation process requires strict control of the size of the layered silicate raw material. If the raw material particle size is too large, the van der Waals forces and bending resistance between the layers will prevent the spheres from curling into spheres during the reduction process. If the raw material particle size is too small, nano-sized silicon spheres will form.

[0020] The present invention also provides the use of the porous micron silicon spheres described above in preparing a negative electrode material for a lithium-ion battery, and a lithium-ion battery comprising the porous micron silicon spheres of the present invention. The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet comprises the porous micron silicon sphere material of the present invention.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The porous micron silicon sphere negative electrode material of the present invention has a simple preparation process, a wide range of raw material sources, a high tap density and a stable structure. Its application in lithium-ion batteries has the advantages of long-term cycle life, excellent rate performance, and a small electrode film swelling rate, and has good commercial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD patterns of micron silicon spheres prepared by aluminothermic reduction at different heating temperatures in Example 1 of the present invention;

[0024] Figure 2 SEM images of micron silicon spheres prepared by aluminothermic reduction at different heating temperatures in Example 1 of the present invention;

[0025] Figure 3TEM image of micron silicon spheres prepared by aluminothermic reduction in Example 1 of the present invention;

[0026] Figure 4 This is a cycle performance diagram of micron silicon spheres prepared by aluminothermic reduction in Example 1 of the present invention;

[0027] Figure 5 This is a rate performance diagram of micron silicon spheres prepared by aluminothermic reduction in Example 1 of the present invention. Implementation Method

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. In addition, it is worth noting that the raw materials involved in the present invention are all common commercially available products unless otherwise specified. Example

[0029] Commercial vermiculite is selected, calcined at a high temperature of 900-1100°C and then naturally cooled. The particle size is controlled to about 5-10 μm by mechanical ball milling and gradient centrifugation, and then purified by pickling with 10% hydrochloric acid to obtain layered silica. The layered silica is mixed with aluminum powder, sodium chloride, and aluminum chloride in a mass ratio of 1:0.8:2.875:10 and charged into a reaction vessel. The reaction vessel is heated at 200-350°C for 12 hours. The reactant obtained in the above steps is washed with hydrochloric acid and hydrofluoric acid solutions, then filtered to neutrality and vacuum dried.

[0030] Experimental results

[0031] Figure 1 Figure 3 is the XRD diagram of micron silicon spheres obtained at different temperatures. When the temperature is low, there is still a SiO2 peak. As the reduction temperature increases, the SiO2 peak gradually weakens and eventually disappears, and the silicon peak gradually strengthens, indicating that the silicon reduction rate gradually increases with increasing temperature.

[0032] Figure 2 The SEM images of micron silicon spheres obtained at different temperatures show that at low temperatures, the surface of the silicon spheres has a porous structure similar to a skeleton. When the temperature is increased, the surface of the micron silicon spheres no longer has obvious holes and the spheres are intact.

[0033] Figure 3 This is a TEM image of the micron silicon sphere. The sphere is complete and it can be clearly seen that the silicon sphere is wrapped with a nanosheet structure. There is enough space between the internal nanosheets to effectively alleviate the volume expansion of the micron silicon sphere during the lithium insertion and extraction process, giving it good cycle performance.

[0034] Figure 4This is the cycling performance diagram of the micron silicon spheres. The first three cycles were activated with a small current of 0.1 Ag-1, and then charged and discharged with 2 Ag-1 for 200 cycles. The results show that the micron silicon spheres can still maintain a high reversible capacity of 1400 mAhg-1 after 200 cycles, and the coulombic efficiency after activation is close to 100%, indicating that the micron silicon spheres have excellent cycling performance.

[0035] Figure 5 This is the rate performance diagram of the micron silicon spheres. At a current density of 0.1 Ag-1, the micron silicon spheres have a high reversible capacity of 2435 mAhg-1. When the current density is increased to 1 Ag-1, the reversible capacity is still 1673 mAhg-1, with a capacity retention rate of 68.7%. At a higher current of 5 Ag-1, the high reversible capacity of 824 mAhg-1 is still maintained.

[0036] Comparative Example 1

[0037] Commercial vermiculite is selected and, without high-temperature firing and mechanical ball milling, is pickled and purified with 10% hydrochloric acid to obtain layered silica. The layered silica is mixed with aluminum powder, sodium chloride, and aluminum chloride in a mass ratio of 1:0.8:2.875:10 and loaded into a reaction vessel. The reaction vessel is heated at 200-350° C. for 12 hours. The reactant obtained in the above steps is washed with hydrochloric acid and hydrofluoric acid solutions, then filtered to neutrality and vacuum dried.

[0038] In this comparative example, the micron silicon prepared by using vermiculite that has not been subjected to high-temperature expansion and ball milling treatment is in block form, and micron silicon balls cannot be obtained.

[0039] Comparative Example 2

[0040] Commercial vermiculite is mechanically ball-milled and then gradient centrifuged to control the particle size to about 5-10 μm, and then purified by pickling with 10% hydrochloric acid to obtain layered silica. The layered silica is mixed with aluminum powder, sodium chloride, and aluminum chloride in a mass ratio of 1:0.8:2.875:10 and loaded into a reaction vessel. The reactor is heated at 200-350°C for 12 hours. The reactant obtained in the above steps is washed with hydrochloric acid and hydrofluoric acid solutions, then filtered to neutrality and vacuum dried.

[0041] The micron silicon obtained in this comparative example is in block form, indicating that micron silicon balls cannot be prepared from vermiculite that has not been subjected to high-temperature expansion but only to ball milling.

[0042] Comparative Example 3

[0043] Commercial vermiculite is calcined at a high temperature of 900-1100°C and then naturally cooled. Layered silica is obtained by pickling with 10% hydrochloric acid for purification. The layered silica is mixed with aluminum powder, sodium chloride, and aluminum chloride in a mass ratio of 1:0.8:2.875:10 and loaded into a reaction vessel. The reactor is heated at 200-350°C for 12 hours. The reactants obtained in the above steps are washed with hydrochloric acid and hydrofluoric acid solutions, then filtered to neutrality and vacuum dried.

[0044] The micron silicon obtained in this comparative example is in block form, indicating that micron silicon balls cannot be prepared from vermiculite that has only been subjected to high-temperature expansion without ball milling.

[0045] Comparative Example 4

[0046] Commercial expanded vermiculite is selected, calcined at a high temperature of 900-1100°C and then naturally cooled. The particle size is controlled to about 5-10 μm by mechanical ball milling and gradient centrifugation, and then purified by pickling with 10% hydrochloric acid to obtain layered silica. The layered silica is mixed with aluminum powder and aluminum chloride in a mass ratio of 1:0.8:10 and charged into a reaction vessel. The reactor is heated at 200-350°C for 12 hours. The reactants obtained in the above steps are washed with hydrochloric acid and hydrofluoric acid solutions, then filtered to neutrality and vacuum dried.

[0047] The micron silicon obtained in this comparative example is in block form, indicating that without adding molten salt sodium chloride, the van der Waals forces between the layered silicon dioxide layers cannot be further weakened, and micron silicon spheres cannot be obtained.

[0048] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing porous micron silicon sphere material, comprising the following steps: (1) The layered silicate raw material is subjected to high-temperature expansion and mechanical ball milling, and then purified by hydrochloric acid pickling to obtain layered silicon dioxide; (2) Mixing layered silica with aluminum powder, sodium chloride, and aluminum chloride into a container and heating to perform a reduction reaction; (3) washing the reactant obtained in step (2) with hydrochloric acid and hydrofluoric acid solutions, then filtering to neutrality, and vacuum drying to obtain a porous micron silicon sphere material; In step (1), the layered silicate raw material is selected from vermiculite; the high temperature expansion temperature is 800-1200°C; and the size is controlled to be 5-50 μm after mechanical ball milling; In step (2), the mass ratio of layered silica to aluminum powder, sodium chloride, and aluminum chloride is 1:0.8:2.875:10; the reduction reaction temperature is 250-400°C; and the reaction time is 10-14h.

2. A porous micron silicon sphere material, characterized in that: Prepared according to the method of claim 1.

3. The use of the porous micron silicon sphere material according to claim 2, characterized in that: Used in lithium-ion battery negative electrode materials.

4. A negative electrode material for a lithium ion battery, characterized in that: The invention comprises the porous micron silicon sphere material according to claim 2, a conductive agent and a binder.

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