WO2024084393A1

WO2024084393A1 - Carrageenan based polymer electrolyte

Info

Publication number: WO2024084393A1
Application number: PCT/IB2023/060478
Authority: WO
Inventors: Siziwi BEBE
Original assignee: Selantro
Priority date: 2022-10-21
Filing date: 2023-10-17
Publication date: 2024-04-25

Abstract

Carrageenan is an attractive bio-derived polymer electrolyte due to its low cost, high ionic conductivity, cyclic stability, and its ability to blend/crosslink with other biocompatible polymers, such as Polyvinyl Alcohol (PVA). Described are the physical and chemical characterization of the bio-electrolyte(s): PVA, carrageenan and PVA-carrageenan bio-polymer blend. A lso described is the fabrication method to create a soft-printed, thin film, bio-gel electrolytic double layer capacitor (Bio-EDLC) using a PVA-carrageenan polymer blend.

Description

Carrageenan based Polymer Electrolyte

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to co-pending U.S. Provisional patent applications Ser.

No. 63/418,044 titled "Soft-Assembled, Bio-gel Electrolytic Double Layer Capacitor System for Sustainable Energy Storage", filed on October 21^st, 2022, the disclosure of which is herein incorporated by reference in its entirety.

PATENTS CITED:

[0002] The following documents and references are incorporated by reference in their entirety, Morant et al (WO 2022/189566), Zakaria et al (A review of Carrageenan as a Polymer Electrolyte in Energy Resource Applications, Journal of Polymers and the Environment 31, 4127-4142 (2023).

FIELD OF THE INVENTION

[0003] The invention relates to bio-gel electrolytes, and specifically to the use of Carrageenan and Polyvinyl Alcohol (PVA) in the creation of a polymer blend electrolyte for an electrolytic double layer capacitor (EDLC) and similar electrochemical energy storage systems.

DESCRIPTION OF THE RELATED ART

[0004] The negative environmental effects of battery manufacturing and the emerging shortage of key resources such as lithium have oriented new research into alternative energy storage materials, and to design high-performance electrolytic energy storage devices using such sustainable, low-cost, and environmentally friendly materials. As energy storage devices, electrolytic capacitors serve as a compromise between traditional capacitors (high power but low energy density) and batteries (moderate power but high energy density). One category of these devices is the electrolytic double layer capacitor (EDLC), which is characterized by a relatively high-power density and large capacitance.

[0005] EDLCs are typically configured with two non-reactive porous electrodes that are placed in contact with an electrolytic medium and electrically isolated by a separator. The power density of the EDLC depends on the fast adsorption of electrolyte ions at the electrode/electrolyte interface forming the double layer during the charge-discharge process. The capacitance of an EDLC comes from the pure electrostatic charge accumulated at the electrode/electrolyte interface during the charge-discharge process. Therefore, EDLC charge storage is largely a surface-controlled process which relies strongly on the surface area of the electrode materials that is accessible to the electrolyte ions and the dielectric constant of the electrolyte.

[0006] The accessible surface can be enhanced by the selection of electrode material (e.g., carbon-based electrode materials) and surface roughness at the interface. Previous studies illustrate that the addition of graphene-based materials, such as reduced graphene oxide (rGO), at the interface results in increased surface area and an enhanced overall EDLC performance. Graphene-based materials are attractive for energy storage applications due to their active surface area and high electrical conductivity, which are critical parameters to the device performance.

[0007] Several types of electrolyte materials have been incorporated in traditional EDLCs, most using aqueous electrolytes, solid-state and quasi-solid hydrogels electrolytes. Traditional electrolytes using liquid electrolytes are at a disadvantage of leakage, limited packaging, and inflexibility, making them undesirable for portable and flexible electronic devices. As for hydrogel electrolytes, they are characterized by semi-solid, compactness properties, high degree of flexibility, high ionic conductivity, effective solid-liquid interface, larger electrochemically active surface area, shortened pathways for charge/mass transport and ease of processability. Furthermore, they prevent some problems such as leakage, internal shorting, and the use of corrosive solvent, hence a reduced overall cost. What is needed, is a biopolymer capable of improving the situation.

SUMMARY OF THE INVENTION

[0008] This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention.

[0009] All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art.

[0010] It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning— i.e., that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process

[0011] In one aspect, the invention is about is about a bio-gel composition for use in an electrolytic double layer capacitor comprised of: 25% to 45% by weight of carrageenan, under 0.1% by weight of an acid and 4.5% of Polyvinyl Alcohol (PVA) with water representing the remaining balance of said gel by weight %. In another aspect, said acid is one of: acetic acid or hyaluronic acid. In yet another aspect, the amount of carrageenan is from 25% to 40%.

[0012] In one aspect, the invention is about a method for preparing a bio-gel composition for use in an electrolytic double layer capacitor comprised of bio-gel for use in an electrolytic double layer capacitor described above, where said method comprises, mixing the acid, carrageenan and PVA, stirring and heating to at least 90 °C until all elements are fully dissolved, reducing the mix temperature below 70 °C while stirring and continuing stirring until a homogeneous solution is obtained.

[0013] Other features and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings, which are provided for purposes of illustration and not of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows a top view of a proposed Bio-Gel electrolyte energy storage unit, according to an exemplary embodiment of the invention. [0015] FIG. 2 shows an isometric view of a proposed Bio-Gel electrolyte energy storage unit, according to an exemplary embodiment of the invention.

[0016] FIG. 3 shows a side view of a proposed Bio-Gel non-polarized bio-electrolyte capacitor, according to an exemplary embodiment of the invention.

[0017] FIG. 4 shows the impact of carrageenan concentration on the overall specific capacitance of a bio-EDLC as a function of weight.

[0018] The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description and drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0019] To provide an overall understanding of the invention, certain illustrative embodiments and examples will now be described. However, it will be understood by one of ordinary skill in the art that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the disclosure. The compositions, apparatuses, systems and/or methods described herein may be adapted and modified as is appropriate for the application being addressed and that those described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope hereof.

[0020] As used in the specification and claims, the singular forms "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a transaction" may include a plurality of transaction unless the context clearly dictates otherwise. As used in the specification and claims, singular names or types referenced include variations within the family of said name unless the context clearly dictates otherwise.

[0021] Certain terminology is used in the following description for convenience only and is not limiting. The words "lower," "upper," "bottom," "top," "front," "back," "left," "right" and "sides" designate directions in the drawings to which reference is made, but are not limiting with respect to the orientation in which the modules or any assembly of them may be used.

[0022] Biopolymer gel (Bio-gel) electrolytes are naturally occurring gelatinous materials that are environmentally friendly, multi-functional, biodegradable, and can be processed at a relatively low cost. They have shown to be promising components of hybrid materials with suitable electroconductive properties for electrode and electrolyte production. This enables application in energy storage devices as well as in diverse biomedical applications including tissue engineering, drug delivery and in wearable electronics where safety and reliability are crucial.

[0023] Examples of bio-gel electrolytes previously incorporated in an EDLC setup include alginate, chitosan, chondroitin sulphate, starch, hyaluran, poly-hydroxy-alkenoates, cellulose and its derivatives such as carboxymethyl cellulose as well as carrageenan. Carrageenan is a natural biopolymer from different algal sources, with the original source being extracted from red seaweed such as Chondrus Crispus. It is characterized by its gelling, emulsifying and stabilizing abilities. Carrageenan-based compounds have a high surface area, well-balanced micro and mesoporosity, high specific capacitance, good rate capabilities, high ionic conductivity, and cyclic stability. It is also a highly attractive polymer due to its ability to dissolve in water without the need of an organic solvent. [0024] Carrageenan has proven significant advantages in the skin healing process, and many of these advantages go to the fact that the healing process is an ionic process, and its inclusion in composite electrolytes. Composite electrolytes are prepared via the blending of two or more polymers; natural and/or synthetic polymer blends. Polymer blending can result in composite electrolytes with better mechanical and chemical properties. The addition of PVA to hydrogels provides structural integrity and good mechanical properties to the bio-gel electrolyte.

[0025] When we speak of carrageenan, we speak of a blend of carrageenan together with lesser amounts of one or more other constituents. For example, most available carrageenan gelling agents contain a blend of carrageenan and minor amounts of other constituents such as inorganic or organic salts and/or a gum. Preferably, the carrageenan blend used in the gel described below is a 99% k-carrageenan compound(s).

[0026] Referring to FIGS. 1 - 3 we see a proposed Bio-Gel Electrolyte energy storage 200 utilizing the proposed Carrageenan based electrolyte 104. Such a unit is unit comprised of two Ozone activated Cu strips 102 having a cellulose membrane separator 108 with the bio-gel 108 on both sides. The electrode/electrolyte interface 106 is deposited, the assembly resulting in a non-polarized bio-electrolytic capacitor 300.

[0027] In one embodiment, the composite thin film bio-gel electrolytic double layer capacitor (Bio-EDLC) with reduced graphene oxide at the electrode/electrolyte interface. The outcome is a low-cost flexible, thin film bio-EDLC with excellent electrical properties; high specific capacitance of 118F/g, voltage breakdown of 1.1V and charging efficiency reaching 0.78V (79%).

[0028] Carrageenan's ionic nature fits naturally into the Bio-EDCL nature, where it contributes to the ability of the electrons to attach themselves to the non-polar electrodes. Within the electrolyte, the addition of PVA to carrageenan provides structural support and mechanical stability/strength, as confirmed by the hydrogen bonds detected during experimentation and calibration of the various embodiments. Initially dissolving the PVA and Carrageenan in Acetic Acid and/or Halogenic acid improves plasticizing.

[0029] As shown in FIG. 4, the different PVA-carrageenan blends when prepared by dissolving increasing weight percent of carrageenan (10, 15, 20, 25, 30, 35, 40 and 45 wt.%) vis-a-vis the specific capacitance measurements, resulting in the optimal performance range for an electrolyte of between 25 and 40 % of Carrageenan as a percentage of weight of the bio-gel hydrogen solution.

[0030] In one proposed embodiment, to prepare the proposed composite hydrogel, PVA and carrageenan in a 1% acetic acid or hyaluronic acid solution representing under 0.1 % of the total weight, with a variable Carrageenan proportion of between 25 and 45 % carrageenan, with 4.5 % PVA the balance being a complementary percentage (i.e. 70.4 to 54.6 % respectively) of water.. We note that the percentages above are shown before the mix is processed (see Example below), which results in a percentage of the water being evaporated and the gel firmed up.

[0031] In another embodiment, further optimization by the addition of reduced graphene oxide (rGO) at the electrode/electrolyte interface creates surface micro-roughness which results in a bio-EDLC, with superior electrical characteristics. When rGO is deposited at the interface, the energy and power density are low due to the low internal resistance. However, increasing the dielectric strength of electrolyte would increase the internal resistance, the energy and power densities at the expense of the conductivity, which is a desirable compromise. Example 1

[0032] In one embodiment, the above PVA-Carrageenan aqueous solution is heated (while stirring) to at least 90 °C until the PVA and carrageenan are fully dissolved, the temperature is then reduced below 70 °C, and the solution is stirred at a lower stirring speed until a homogeneous solution is obtained. We note that the above times and temperatures may be adjusted in order to allow for the water evaporation to determine the gel firming up. The above results in a final product with slightly higher % by weight of Carrageenan, but with the same original amount of carrageenan in the solution.

CONCLUSION

[0033] In concluding the detailed description, it should be noted that it would be obvious to those skilled in the art that many variations and modifications can be made to the shown embodiments without substantially departing from the principles of the present invention. Also, such variations and modifications are intended to be included herein within the scope of the present invention as set forth in the disclosure.

[0034] It should be emphasized that the above-described embodiments of the present invention, particularly any "exemplary embodiments" are merely possible examples of the implementations, merely set forth for a clear understanding of the principles of the invention. Any variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit of the principles of the invention. All such modifications and variations are intended to be included herein within the scope of the disclosure and present invention. [0035] The present invention has been described in sufficient detail with a certain degree of particularity. The utilities thereof are appreciated by those skilled in the art. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention.

Claims

I Claim:

1. A bio-gel composition for use in an electrolytic double layer capacitor comprised of:

25% to 45% by weight of carrageenan; under 0.1% by weight of an acid; and over 4.5% of Polyvinyl Alcohol (PVA) with water representing the remaining balance of said gel by weight.

2. The gel of claim 1 wherein: said acid is one of: acetic acid or hyaluronic acid.

3. A composition according to claims 1 or 2 in which the amount of carrageenan is from 25% to 45%.

4. A method for preparing a bio-gel composition for use in an electrolytic double layer capacitor comprised of bio-gel for use in an electrolytic double layer capacitor according to any one of the claims 1 to 3, said method comprising: mixing the acid, carrageenan and PVA; stirring and heating to at least 90 °C until all elements are fully dissolved; reducing the mix temperature below 70 °C while stirring; and continuing stirring and allowing water evaporation until the desired homogeneous solution is obtained.