Method for preparing core-shell silicon nanowire material by using retired photovoltaic cell silicon wafer and application of core-shell silicon nanowire material

Abstract

The invention discloses a method for preparing a core-shell silicon nanowire material by using a decommissioned photovoltaic cell silicon wafer and application of the core-shell silicon nanowire material, and belongs to the technical field of secondary resource utilization. According to the preparation method, a silicon wafer obtained after decommissioning photovoltaic solar cell interlayer separation is used as a raw material, the particle size and the aluminum-silicon proportion of the silicon wafer are controlled through grinding, then ground silicon powder is loaded on a carbon substrate, and the decommissioning photovoltaic cell silicon wafer is regenerated into the core-shell silicon nanowire material in one step by applying voltage and current. The core-shell silicon nanowire material with adjustable diameter, controllable shell thickness and uniform growth can be prepared by using the preparation method, and when the core-shell silicon nanowire material is used for a lithium ion battery negative electrode, high first-circle coulombic efficiency and excellent long-cycle stability are shown; the preparation method is short in process, high in efficiency and low in energy consumption, and is expected to realize low-cost large-scale preparation of the core-shell silicon nanowire material and high-valued circulation of the retired photovoltaic cell silicon wafer.

Description

Technical Field

[0001] The invention relates to a method for preparing core-shell silicon nanowire materials by utilizing retired photovoltaic cell silicon wafers and application thereof, belonging to the technical field of secondary resource utilization. Background Art

[0002] In recent years, photovoltaic solar cells have flourished. By the end of 2022, my country's photovoltaic installed capacity totaled 392.04GW, of which crystalline silicon photovoltaic solar cells accounted for more than 96%. As the service life comes, a large number of retired photovoltaic cell modules will be generated. According to the International Renewable Energy Agency, by 2030, the cumulative amount of photovoltaic module waste in China will reach nearly one million tons, and by 2050 it will surge to 20 million tons. As the basic material of crystalline silicon photovoltaic solar cells, silicon wafers have a huge amount of waste; traditional refining and recycling methods have a long process and can only achieve the downgrading cycle of silicon materials, resulting in a serious waste of high-purity secondary metal resources.

[0003] Silicon materials used for lithium-ion battery anodes have a high theoretical specific capacity (3579mAh / g), which is about ten times that of graphite anodes, and a suitable lithium insertion and extraction potential (~0.4V vs Li / Li + ), good safety performance and other advantages, and is considered to be a candidate material for the next generation of high energy density battery negative electrode. However, silicon will undergo huge volume changes during the lithium insertion and extraction process, resulting in particle pulverization, electrode structure destruction, and a rapid decrease in cycle performance. The structural design and regulation of silicon materials are the key to improving their structural stability. One-dimensional core-shell silicon nanowires have the advantages of excellent electron transport and can effectively alleviate the stress pulverization caused by the charging and discharging process, making them stand out as negative electrode materials for lithium-ion batteries. Therefore, if retired photovoltaic cell silicon wafers can be regenerated into core-shell silicon nanowire materials for high-performance lithium-ion batteries, it will be of great significance to achieve their high-value cycles.

[0004] Compared with pure silicon nanowire materials, when core-shell silicon nanowires are used in lithium-ion batteries, the charge and discharge process can more effectively alleviate the stress problem caused by the volume change process. The shell layer can also effectively reduce the side reactions between the nanowires and the electrolyte, significantly improving the cycle stability and first-cycle coulomb efficiency of the battery. At present, the synthesis steps of core-shell silicon nanowires mainly include multiple steps such as catalytic metal deposition, nanowire growth and shell coating. The prepared core-shell silicon nanowires contain catalyst metals and polluting materials. CN202210409112.7 discloses a core-shell silicon nanowire material, which uses a photolithography process to prepare a dot matrix of photoresist on a silicon wafer, and then uses a wet etching process to prepare a silicon nanowire array, and uses a thermal oxidation method to obtain an insulating layer on the surface of the obtained silicon nanowire array, and then evaporates a magnetic metal layer on the insulating layer, and partially oxidizes the magnetic metal layer by thermal oxidation to obtain a metal oxide as a catalyst layer. The prepared core-shell silicon nanowires are used for high-efficiency micro-nano robots;

[0005] CN117361542A discloses a method for preparing boron or phosphorus doped silicon nanowire materials by thermal shock regeneration of waste photovoltaic cell silicon wafers. Compared with the boron or phosphorus doped silicon nanowire materials prepared by this method, the method for preparing core-shell silicon nanowire materials by one step using retired photovoltaic cell silicon wafers proposed in the present invention has different composition and structure from the doped silicon nanowires prepared by the aforementioned invention, and can more effectively improve the battery cycle performance and first-cycle coulomb efficiency when used for the negative electrode of lithium-ion batteries. Furthermore, the current method for preparing core-shell silicon nanowire materials has high silicon source requirements, long process, low efficiency, high cost, and is difficult to prepare on a large scale.

[0006] In summary, the development of a short-range, efficient, low-cost and easy-to-operate method for preparing core-shell silicon nanowires can not only expand the existing preparation process of core-shell silicon nanowires and reduce the preparation cost of silicon nanowires, but also increase the value of recycling retired photovoltaic cell silicon wafers into core-shell silicon nanowires. Summary of the invention

[0007] In order to solve the problems existing in the existing silicon nanowires, one of the purposes of the present invention is to provide a method for preparing core-shell silicon nanowire materials using retired photovoltaic cell silicon wafers, the preparation method comprising the following steps:

[0008] (1) Grind the waste silicon wafers after interlayer separation into silicon powder.

[0009] (2) Add aluminum powder to the silicon powder obtained in step (1) to obtain a silicon-aluminum mixed powder.

[0010] (3) Loading the silicon-aluminum mixed powder prepared in step (2) onto a carbon substrate.

[0011] (4) The carbon substrate loaded with the silicon-aluminum mixed powder in step (3) is mounted on a thermal shock device, and the voltage, current, atmosphere, temperature and time are controlled to prepare a core-shell silicon nanowire material.

[0012] Preferably, the waste silicon wafers described in step (1) are derived from retired photovoltaic crystalline silicon solar cell modules.

[0013] Preferably, the particle size of the silicon powder in step (1) is 0.05 to 200 μm.

[0014] Preferably, the mass percentage of aluminum powder in the silicon-aluminum mixed powder in step (2) is 5% to 60%.

[0015] Preferably, the silicon powder in step (3) is loaded on the carbon substrate by a wet method or a dry method.

[0016] Preferably, the carbon substrate described in step (3) includes any one of carbon cloth, carbon felt, carbon paper, graphite paper, carbon nanofiber paper, graphene film, graphite sheet, graphite crucible, and carbon fiber products, or a combination of at least two thereof.

[0017] Preferably, the voltage in step (4) is 1 to 400 V, the current is 1 to 1000 A, the temperature is 800 to 3000° C., and the time is 0.01 to 60 s.

[0018] Preferably, the atmosphere of the thermal shock process in step (4) is a weakly oxidizing environment, with an oxygen content of 0.001% to 5%, and the rest being any one of the inert gases argon, nitrogen, and carbon dioxide, or a combination of at least two of them.

[0019] Preferably, the diameter of the core-shell silicon nanowires prepared in step (4) is 10 to 1000 nm; the shell thickness of the core-shell silicon nanowires is 1 to 50 nm.

[0020] Another object of the present invention is to provide an application of the prepared core-shell silicon nanowires in preparing negative electrode materials for lithium-ion batteries.

[0021] Beneficial effects of the present invention

[0022] (1) The preparation method of the present invention prepares core-shell silicon nanowire materials. On the one hand, the core of the core-shell silicon nanowire prepared by the preparation method is crystalline silicon and the outer shell is Al2O3; on the other hand, the preparation process is short and efficient. The preparation method is simple to operate and low in cost, and is suitable for large-scale production.

[0023] (2) The core-shell silicon nanowire material obtained by the preparation method of the present invention can achieve control of the diameter, shell composition and thickness of the nanowire material by controlling the parameters of the thermal shock process. The lithium ion battery negative electrode prepared using the core-shell silicon nanowire material shows higher first-cycle coulombic efficiency and long-cycle stability than pure silicon nanowires.

[0024] (3) The present invention uses retired crystalline silicon photovoltaic solar cell silicon wafers as raw materials to prepare core-shell silicon nanowire materials, which not only reduces the production cost of core-shell silicon nanowire materials and expands the source of raw materials for preparing silicon nanowire materials, but also realizes the high-value utilization of high-purity secondary metal resources, which can save huge energy and resource consumption.

[0025] (4) The present invention adds aluminum powder to prepare core-shell silicon nanowire materials (the outer shell is aluminum oxide and the inner core is crystalline silicon). This core-shell structure is used as a negative electrode material to help improve the first-cycle coulomb efficiency of the battery and inhibit the volume expansion of silicon to improve long-cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1This is the actual object and scanning electron microscope image of the retired photovoltaic cell silicon wafer raw material in specific embodiment 1 of the present invention.

[0027] Figure 2 It is a scanning electron microscope image of the core-shell silicon nanowire material prepared in specific embodiment 1 of the present invention.

[0028] Figure 3 It is a transmission electron microscope image of the core-shell silicon nanowire material prepared in specific embodiment 1 of the present invention.

[0029] Figure 4 This is a charge and discharge cycle performance diagram of the core-shell silicon nanowire material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0031] Example 1

[0032] This embodiment provides a method and application of preparing core-shell silicon nanowire materials using retired photovoltaic cell silicon wafers. The preparation method comprises the following steps:

[0033] (1) The retired photovoltaic cell silicon wafers obtained after interlayer separation were ground and the amount of aluminum powder added was changed to prepare silicon powder raw materials with a particle size of 5 μm and an aluminum content of 20%.

[0034] (2) The silicon powder raw material prepared in step (1) is loaded on the carbon cloth by wet stirring, and then installed in a thermal shock device for testing, and the oxygen content of the environment during the thermal shock process is controlled to be 0.01%.

[0035] (3) The voltage of the thermal shock process is 40 V, the temperature of the thermal shock process is 1600° C., and the thermal shock process time is about 0.1 s, and a silicon / aluminum oxide core-shell nanowire material with a diameter of 50 nm and a shell thickness of 5 nm is prepared.

[0036] Scanning electron microscope (JSM-7800) and transmission electron microscope (JEM-2100F) were used to test the waste photovoltaic cell silicon wafer raw materials and core-shell silicon nanowire materials under the above conditions. The test results are as follows: Figures 1 to 3 As shown, from Figure 1 It can be seen from the figure that the retired photovoltaic cell silicon wafer is a layered structure, with a silicon layer of about 150μm and an aluminum layer of about 30μm. Figure 2 It can be seen that the prepared core-shell silicon nanowires are uniform. Figure 3 It can be seen that the prepared core-shell silicon nanowires have a diameter of about 50 nm and a shell thickness of about 5 nm.

[0037] The core-shell silicon nanowire material prepared in Example 1 was directly used to prepare the negative electrode material of lithium-ion battery, with metal lithium sheet as the counter electrode, Celgard2325 as the separator, 1 mol / LLiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1:1) as the electrolyte, and CR2032 button battery shell. The button battery was assembled in an argon-protected glove box. The charge and discharge test was performed at 500 mA / g, the voltage charge and discharge range was 0.01 to 3 V, and the charge and discharge cycle performance was as follows. Figure 4 shown.

[0038] Example 2

[0039] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. The preparation method comprises the following steps:

[0040] (1) The retired photovoltaic cell silicon wafers obtained after interlayer separation are ground and the aluminum content is adjusted to prepare a silicon powder raw material with a particle size of 0.05 μm and an aluminum content of 5%.

[0041] (2) The silicon powder raw material prepared in step (1) is loaded on the carbon cloth by wet stirring, and then installed in a thermal shock device for testing, and the oxygen content of the environment during the thermal shock process is controlled to be 0.001%.

[0042] (3) The voltage of the thermal shock process is 30 V, the temperature of the thermal shock process is 1500° C., and the time of the thermal shock process is about 0.01 s. Silicon / aluminum oxide core-shell nanowire materials with a diameter of 20 nm and a shell thickness of 5 nm are prepared.

[0043] Example 3

[0044] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. The preparation method comprises the following steps:

[0045] (1) The retired photovoltaic cell silicon wafers obtained after interlayer separation are ground and the aluminum content is adjusted to prepare a silicon powder raw material with a particle size of 20 μm and an aluminum content of 50%.

[0046] (2) The silicon powder raw material prepared in step (1) is loaded on the carbon cloth by wet stirring, and then installed in a thermal shock device for testing, and the oxygen content of the environment during the thermal shock process is controlled to be 0.1%.

[0047] (3) The voltage of the thermal shock process is 60 V, the temperature of the thermal shock process is 1800° C., and the time of the thermal shock process is about 0.1 s. Silicon / aluminum oxide core-shell nanowire materials with a diameter of 120 nm and a shell thickness of 30 nm are prepared.

[0048] Comparative Example 1

[0049] As a comparison, the only difference between this comparative example and Example 1 is that the aluminum content is not adjusted. The specific steps are as follows:

[0050] (1) The retired photovoltaic cell silicon wafers obtained after interlayer separation are ground to prepare silicon powder raw materials with a particle size of 5 μm.

[0051] (2) The silicon powder raw material prepared in step (1) is loaded on the carbon cloth by wet stirring, and then installed in a thermal shock device for testing, and the oxygen content of the environment during the thermal shock process is controlled to be 0.01%.

[0052] (3) The voltage of the thermal shock process is 40 V, the temperature of the thermal shock process is 1600°C, and the time of the thermal shock process is about 0.1 s. The prepared core-shell silicon nanowire material is small in amount and has an uneven morphology and a larger diameter, with a diameter of 50 to 100 nm and a shell thickness of about 3 nm.

[0053] After testing, the performance of the core-shell silicon nanowire material prepared in this comparative example in terms of the first coulombic efficiency and long-cycle stability is not as good as that in Example 1. The reason is that the core-shell silicon nanowires have an uneven morphology, a larger diameter, and a thinner shell thickness. During the charge and discharge process, it is difficult to inhibit the volume expansion of silicon and prevent side reactions from occurring, resulting in a decrease in the first cycle coulombic efficiency and cycle stability.

[0054] Comparative Example 2

[0055] This comparative example provides a method for preparing a silicon nanowire material, and the specific steps are as follows:

[0056] (1) The retired photovoltaic cell silicon wafers obtained after interlayer separation are subjected to acid washing to remove the silver and aluminum adhering to the surface of the silicon wafers, and then a silicon powder raw material with a particle size of 5 μm is prepared.

[0057] (2) The silicon powder raw material prepared in step (1) is loaded on the carbon cloth by wet stirring, and then installed in a thermal shock device for testing, and the oxygen content of the environment during the thermal shock process is controlled to be 0.01%.

[0058] (3) The voltage of the thermal shock process is 40 V, the temperature of the thermal shock process is 1600° C., and the time of the thermal shock process is about 0.1 s. Silicon nanowire materials with a diameter of 50 nm and a shell thickness of 5 nm are prepared.

[0059] The performance comparison of the material prepared in this comparative example and the material prepared in the example is shown in Table 1. It can be seen from Table 1 that the pure silicon nanowire material prepared in the absence of aluminum has a first-cycle coulomb efficiency of 80.7%, and a capacity retention rate of less than 69.3% after 100 cycles, which are significantly lower than the core-shell silicon nanowire material prepared in Example 1. This is mainly because the outer shell layer of the core-shell silicon nanowire material is aluminum oxide, which helps to reduce the consumption of irreversible lithium sources and improve the first-cycle coulomb efficiency; on the other hand, the aluminum oxide shell, as a rigid shell layer, can suppress the volume expansion problem of the silicon material during the lithium insertion process and improve the long-cycle stability of the battery; in addition, the aluminum oxide shell layer will form a fast lithium ion conductor LiAlO2 layer during the lithiation process, which promotes the diffusion of lithium ions in the material.

[0060] Table 1 Comparison of material properties prepared in Comparative Example 1 and Example 1

[0061]

[0062] Example 7

[0063] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. Except that the particle size of the silicon powder raw material in step (1) is 200 μm, other conditions are exactly the same as those in Example 1.

[0064] Example 8

[0065] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. The preparation method is exactly the same as that of embodiment 1 except that the oxygen content in the thermal shock process environment in step (2) is 5%.

[0066] Example 9

[0067] This embodiment provides a method and application for preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. Except that the voltage of the thermal shock process in step (3) is 400V, other conditions of the preparation method are exactly the same as those of Example 1.

[0068] Example 10

[0069] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. Except that the temperature of the thermal shock process in step (3) is 3000° C., other conditions of the preparation method are exactly the same as those of Example 1.

[0070] Embodiment 11

[0071] This embodiment provides a method and application of preparing core-shell silicon nanowire materials in one step using retired photovoltaic cell silicon wafers. Except that the thermal shock process time in step (3) is 60 seconds, other conditions of the preparation method are exactly the same as those of Example 1.

Claims

1. A method for preparing core-shell silicon nanowire materials using retired photovoltaic cell silicon wafers, characterized in that: The preparation method comprises the following steps: (1) Grinding the waste silicon wafers after interlayer separation into silicon powder; (2) adding aluminum powder to the silicon powder obtained in step (1) to obtain a silicon-aluminum mixed powder; (3) loading the silicon-aluminum mixed powder prepared in step (2) onto a carbon substrate; (4) The carbon substrate loaded with the silicon-aluminum mixed powder in step (3) is mounted on a thermal shock device, and the voltage, current, atmosphere, temperature and time are controlled to prepare a core-shell silicon nanowire material.

2. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The waste silicon wafers described in step (1) are derived from retired photovoltaic crystalline silicon solar cell modules.

3. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The particle size of the silicon powder in step (1) is 0.05 to 200 μm.

4. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The mass percentage of aluminum powder in the silicon-aluminum mixed powder in step (2) is 5% to 60%.

5. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The silicon powder described in step (3) is loaded on the carbon substrate by a wet method or a dry method.

6. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The carbon substrate described in step (3) includes any one of carbon cloth, carbon felt, carbon paper, graphite paper, carbon nanofiber paper, graphene film, graphite sheet, graphite crucible, and carbon fiber products, or a combination of at least two thereof.

7. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The voltage in step (4) is 1-400V, the current is 1-1000A, the temperature is 800-3000°C, and the time is 0.01-60s.

8. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The atmosphere of the thermal shock process in step (4) is a weakly oxidizing environment, with an oxygen content of 0.001% to 5%, and the rest is any one of the inert gases argon, nitrogen, and carbon dioxide, or a combination of at least two of them.

9. The method for preparing core-shell silicon nanowire material using retired photovoltaic cell silicon wafers according to claim 1, characterized in that: The core-shell silicon nanowires prepared in step (4) have a diameter of 10 to 1000 nm; and a shell thickness of 1 to 50 nm.

10. Use of the core-shell silicon nanowires prepared by the method according to any one of claims 1 to 9 in preparing negative electrode materials for lithium-ion batteries.

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