Description:TECHNICAL FIELD OF THE PRESENT INVENTION
The present invention relates to a method for extracting silicon granules from a photovoltaic cell.
BACKGROUND OF THE PRESENT INVENTION
Lithium-Ion or Li-ion batteries which are generally used in electric vehicles require an anode having a high energy density characteristic. Anodes with the high energy density characteristics enable efficient charging of the Li-ion battery along with efficient discharging of power during operation of the electric vehicle.
Silicon is generally well suited as an anode in the Li-ion batteries. However, silicon is required to be extracted before it can be used as the anode in the Li-ion batteries. One of the ways in which silicon is extracted is by extracting it from used or spent photovoltaic cells.
Many methods are known in the prior art which are employed to extract silicon from photovoltaic cells. One of the methods is known as pyrometallurgical method which involves burning the photovoltaic cells at high temperatures. Due to the high temperatures, an adhesive, such as Ethyl Vinyl Acetate (EVA), which is applied to the photovoltaic cells, begins to burn. However, upon burning, the adhesive emits carcinogens which are known to cause cancer in humans.
Another method for extracting silicon from photovoltaic cells is known as hydrometallurgical method. The hydrometallurgical method includes a process of chemically treating the spent photovoltaic cells for segregating the adhesive from the photovoltaic cells. However, as the photovoltaic cells are chemically treated, it becomes challenging to control various parameters associated with the process of chemically treating the spent photovoltaic cells. Additionally, the process of chemically treating the photovoltaic cells involves extensive reaction time, and hence the hydrometallurgical method is time consuming.
Therefore, in view of the above-mentioned problems, it is advantageous or desirable to provide an improved method for extracting silicon from photovoltaic cells which can overcome the above-mentioned problems and limitations.
SUMMARY OF THE PRESENT INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention nor is it intended for determining the scope of the invention.
To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.
As per an embodiment of the present invention, a method for extracting silicon granules from a photovoltaic cell is disclosed herein. The method includes a step of cutting the photovoltaic cell into a plurality of pieces of a predetermined dimension. A further step of immersing the plurality of pieces in a solvent for changing a state of an adhesive is disclosed. Here, the adhesive is adapted on the plurality of pieces. Additionally, a step of performing heat treatment on the plurality of pieces for segregating the adhesive from the plurality of pieces is disclosed too. Finally, a step of performing a dry-ball milling process on the plurality of pieces through a dry-ball milling machine is disclosed, by which the silicon granules are extracted.
As per an embodiment of the present invention, a step of leaching the silicon granules by acid, which is succeeding to the step of dry-ball milling process is performed, to refine the silicon granules.
As per another embodiment of the present invention, succeeding to the step of leaching the silicon granules, a step wet-ball milling process on the silicon granules in a liquid medium through a wet-ball milling machine to reduce a granular size of the silicon granules and for removing traces of the adhesive, is performed. Here, the liquid medium comprises ethanol.
As per yet another embodiment of the present invention, a step of washing and drying the silicon granules in deionized water is performed, which is succeeding to the wet-ball milling process.
As per yet another embodiment of the present invention, the step of segregating the adhesive includes an intermediate step of scrubbing the plurality of pieces for removing traces of the silicon granules entrapped in the adhesive, and segregating the adhesive. Here, the adhesive is an Ethyl Vinyl Acetate (EVA) binder.
As per still another embodiment of the present invention, the step of leaching the silicon granules includes an intermediate step of removing metallic impurities from the silicon granules. Here, the metallic impurities are aluminum-based impurities.
As per an embodiment of the present invention, the step of immersing the plurality of pieces in a solvent includes immersing in Toluene solution.
As per yet another embodiment of the present invention, the step of heat treating includes exposing the plurality of pieces to a pulsated microwave treatment.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The foregoing and other features of embodiments will become more apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings. In the drawings, like reference numerals refer to like elements.
Figs. 1a, 1b and 1c illustrate flowcharts depicting a method for extracting silicon granules from a photovoltaic cell, as per an embodiment of the present invention.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof.
Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element does not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, “there needs to be one or more…” or “one or more elements is required.”
Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements of the present disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and/or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.
Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.
Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by “comprises... a” does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.
Referring to the accompanying Figs. 1a, 1b and 1c, a method 100 for extracting silicon granules from a photovoltaic cell is disclosed herein. The method 100 includes at step 110, the step of cutting the photovoltaic cell into a plurality of pieces of a predetermined dimension. The predetermined dimension is in a range between 3 x 3 centimeters and 5 x 5 centimeters.
At step 120, the step of immersing the plurality of pieces in a solvent is disclosed. The step 120 is performed for changing a state of an adhesive. Here, the adhesive is adapted on the plurality of pieces, i.e. the adhesive is applied on the plurality of pieces. The step 120 involves use of Toluene solution as the solvent, in a preferred embodiment of the present invention.
At step 130, the step of performing heat treatment on the plurality of pieces is disclosed. The step 130 performing the heat treatment includes exposing the plurality of pieces to a pulsated microwave treatment of power output between 119 Watts and 700 Watts and which is operating at a voltage of 230 Volts and 50 Hertz. The step 130 is performed for segregating or separating the adhesive from the plurality of pieces. Additionally, the adhesive which is segregated or separated can be recycled and reused. The step 130 of performing heat treatment on the plurality of pieces further includes intermediate step 130-A of scrubbing the plurality of pieces for removing traces of the silicon granules entrapped in the adhesive. An additional step 130-B of segregating the adhesive is also disclosed herein. Here, the adhesive in a preferred embodiment of the present invention is an Ethyl Vinyl Acetate (EVA) binder.
At step 140, the step of performing a dry-ball milling process on the plurality of pieces is disclosed. The dry-ball milling process is performed through a dry-ball milling machine for extracting the silicon granules. Hence, at step 140, the silicon granules are extracted in a raw form. However, the silicon granules which are extracted have a size between 1 micron and 2 microns, and still unfit for use as anode in Li-ion batteries. Hence, further refinement and reduction in the size of the silicon granules is required, which is achieved through the succeeding steps 150 through 180.
At step 150, leaching of the silicon granules is performed. The acid used for performing the step 150 is sulphuric acid (H2SO4), hydrochloric acid (HCl), or hydrofluoric acid (HF). In a preferred embodiment of the present invention, sulphuric acid (H2SO4) offers enhanced results in terms of leaching the silicon granules, which is performed at the step 150 of the method 100. A concentration of the acid is maintained in a range between 1 Molar Concentration (M) and 3 Molar Concentration (M), in a preferred embodiment of the present invention. The step 150 helps to refine the silicon granules. The step 150 includes an intermediate step 150-A of removing metallic impurities from the silicon granules. Here, the metallic impurities are aluminum-based impurities in a preferred embodiment of the present invention.
At step 160, the step of performing a wet-ball milling process on the silicon granules is disclosed. The step 160 is performed through a wet-ball milling machine, in a liquid medium such as ethanol in a preferred embodiment of the present invention. The step 160 enables further reduction in the granular size of the silicon granules, which is between 0.3 microns and 0.5 microns. Additionally, traces of the adhesive are also removed from the silicon granules, as zirconia balls which are used for performing the wet-ball milling process in the wet-ball milling machine, offer friction over the silicon granules. Due to the said friction, traces of the adhesive remaining on the silicon granules is let loose, and silicon granules which are free of the adhesive is obtained.
At step 170, the step of washing the silicon granules in deionized water is performed. Thereafter, at step 180, the step of drying the silicon granules is disclosed.
By using the method 100 as disclosed herein, the silicon granules thus obtained can be used as anode in Li-ion batteries. That is, the granular size and refinement of the silicon granules obtained is at a level which is battery-grade. Additionally, owing to implementation of the method 100 disclosed herein, the existing pyrometallurgical method to extract silicon is not required and therefore, limitations associated with such method are avoided. For example, limitation such as burning of the adhesive which takes place during use of the pyrometallurgical method is avoided, thereby eliminating emission of carcinogens. Also, compared to the hydrometallurgical method from the prior art, the method 100 disclosed herein is quite controllable, i.e. various parameters associated with the process of chemically treating the spent photovoltaic cells are controllable and hence the method 100 disclosed herein is time saving.
, Claims:1. A method (100) for extracting silicon granules from a photovoltaic cell, the method (100) comprising steps of:
cutting (110) the photovoltaic cell into a plurality of pieces of a predetermined dimension;
immersing (120) the plurality of pieces in a solvent for changing a state of an adhesive, wherein the adhesive is adapted on the plurality of pieces;
performing (130) heat treatment on the plurality of pieces for segregating the adhesive from the plurality of pieces; and
performing (140) a dry-ball milling process on the plurality of pieces through a dry-ball milling machine for extracting the silicon granules.

2. The method as claimed in claim 1, further comprising:
leaching (150), succeeding to the dry-ball milling process, the silicon granules, by acid, to refine the silicon granules.

3. The method as claimed in claim 1, further comprising:
performing (160), succeeding to the step of leaching the silicon granules, a wet-ball milling process on the silicon granules in a liquid medium through a wet-ball milling machine to reduce a granular size of the silicon granules and for removing traces of the adhesive, wherein the liquid medium comprises ethanol.

4. The method as claimed in claim 2 further comprising:
washing (170), succeeding to the wet-ball milling process, the silicon granules in deionized water; and
drying (180) the silicon granules.

5. The method as claimed in claim 1, wherein the step of performing (130) heat treatment on the plurality of pieces for segregating the adhesive comprises an intermediate step of:
scrubbing (130-A) the plurality of pieces for removing traces of the silicon granules entrapped in the adhesive; and
segregating (130-B) the adhesive, wherein the adhesive is an Ethyl Vinyl Acetate (EVA) binder.

6. The method as claimed in claim 2, wherein the step of leaching (150) the silicon granules comprises an intermediate step of removing (150-A) metallic impurities from the silicon granules, wherein the metallic impurities are aluminum-based impurities.

7. The method as claimed in claim 1, wherein the step of immersing (120) the plurality of pieces in a solvent comprises immersing in Toluene solution.

8. The method as claimed in claim 1, wherein the step of performing heat treatment (130) comprises exposing the plurality of pieces to a pulsated microwave treatment.