AN ELECTROCHEMICAL CELL AND METHOD OF MAKING THE SAME

Abstract

This invention relates to an electrochemical cell comprising an anode structure comprising an element selected from the group consisting of group 1, group 2, group 8, group 12 and group 13 of the Periodic Table of Elements; a cathode structure comprising a catalyst; and a hydrogel located between the anode structure and the cathode structure. In a preferred embodiment, the cell comprises the anode of Zinc, the catalyst of CoOx/C, the hydrogel of free-standing alkaline polyacrylamide hydrogel, wherein said hydrogel was first synthesized via UV-initiated radical polymerization of acrylamides, followed by exchange of water with an alkaline electrolyte of potassium hydroxide (KOH). The invention further relates to a method of manufacturing such an electrochemical cell and the use of a hydrogel in a metal/air battery.

Claims

1-27. (canceled)

28. An electrochemical cell comprising: an anode structure comprising an element selected from the group consisting of group 1, group 2, group 8, group 12 and group 13 of the Periodic Table of Elements; a cathode structure comprising a catalyst; and a hydrogel located between the anode structure and the cathode structure, wherein the hydrogel comprises water and a cross-linked polymer having repeating units of the following formula (I): ##STR00014## wherein A is selected from the group consisting of —NH—, —C(O)O—, —OC(O)—, and —C(O)NR.sup.10C(O)—; R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 and R.sup.10 are independently selected from the group consisting of hydrogen, optionally substituted alkyl, and optionally substituted alkenyl; M is an alkali metal; n is an integer of at least 1; and the wavy line (˜˜˜) indicates the point of attachment to other repeating units of Formula (I), wherein the degree of cross-linking in the cross-linked polymer is in the range of 20 mol % to 80 mol %.

29. The electrochemical cell according to claim 28, wherein the number of repeating units of formula (I) in the cross-linked polymer is in the range of 50 to 50,000.

30. The electrochemical cell according to claim 28, wherein the element in the anode structure is selected from the group consisting of zinc, aluminium, iron, magnesium and lithium.

31. The electrochemical cell according to claim 28, wherein the catalyst is a reductant selected from a group consisting of cobalt oxide-carbon hybrid derived from cobalt acetate and polyacrylonitrile (PAN), cobalt (II) oxide, manganese (II) oxide, binary cobalt-manganese spinel oxides, binary cobalt-nickel spinel oxides, binary nickel-iron spinel oxides, binary cobalt-iron oxides, complex spinel oxides comprising an element selected from the group consisting of cobalt, manganese, iron, nickel, copper and any mixture thereof, perovskite oxides containing lanthanide and first-row transition metals, and perovskite oxides containing lanthanide, rare earth metals and first-row transition metals.

32. The electrochemical cell according to claim 31, wherein the catalyst is a cobalt oxide-carbon hybrid derived from cobalt acetate and polyacrylonitrile (PAN) or CoO.sub.x/C, wherein x is a value between 1 and 1.5.

33. The electrochemical cell according to claim 28, wherein the cathode structure further comprises a current collector or a binder.

34. The electrochemical cell according to claim 33, wherein the current collector comprises a material selected from the group consisting of carbon, copper, stainless steel, titanium, nickel and any mixture thereof or is porous.

35. The electrochemical cell according to claim 33, wherein the binder is selected from the group consisting of a sulfonated tetrafluoroethylene copolymer, polytetrafluoroethylene and polyvinylidene fluoride.

36. The electrochemical cell according to claim 28, wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are all hydrogen or wherein M is selected from the group consisting of sodium, potassium and lithium.

37. The electrochemical cell according to claim 28, wherein the electrochemical cell is a battery.

38. The electrochemical cell according to claim 28, wherein the electrochemical cell is a capacitator.

39. A method for manufacturing an electrochemical cell, the method comprising the operations of: providing a hydrogel comprising water and a cross-linked polymer having repeating units of the following formula (I): ##STR00015## wherein A is selected from the group consisting of —NH—, —C(O)O—, —OC(O)—, and —C(O)NR.sup.10C(O)—; R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 and R.sup.10 are independently selected from the group consisting of hydrogen, optionally substituted alkyl, and optionally substituted alkenyl; M is an alkali metal; n is an integer of at least 1; and the wavy line (˜˜˜) indicates the point of attachment to other repeating units of Formula (I), wherein the degree of cross-linking in the cross-linked polymer is in the range of 20 mol % to 80 mol %, and contacting the hydrogel with an anode structure comprising an element selected from the group consisting of group 1, group 2, group 8, group 12 and group 13 of the Periodic Table of Elements; and a cathode structure comprising a catalyst; wherein the hydrogel is located between the anode structure and the cathode structure.

40. The method according to claim 39, wherein the providing operation comprises the operations of: irradiating a solution of an acrylic monomer, a cross-linking agent and a polymerization initiator to form a film; and contacting said film with an aqueous solution comprising a base having a formula MOH.

41. The method according to claim 40, wherein the irradiating operation comprises the operations of: dissolving said acrylic monomer in water that is substantially free of dissolved gases, to form solution A; dissolving said cross-linking agent and polymerization initiator in water, to form solution B; contacting solution A and solution B to form a mixture C; pouring mixture C onto a surface to form a film; and irradiating the film with ultraviolet radiation, or further comprising the operation of drying the film.

42. The method according to claim 41, wherein the acrylic monomer is present in solution A at a concentration in the range of 5 wt % to 20 wt %.

43. The method according to claim 41, wherein the cross-linking agent is present in solution B at a concentration in the range of 0.02 wt % to 1 wt %, and the polymerization initiator is present in solution B at a concentration in the range of 0.02 wt % to 1 wt %.

44. The method according to claim 40, wherein the acrylic monomer is acrylamide, the cross-linking agent is N,N-methylenebisacrylamide and the polymerization initiator is ammonium persulphate.

45. The method according to claim 40, wherein the irradiating operation is performed for a duration in the range of 30 mins to 60 mins or wherein the drying operation is performed at room temperature.

46. The method according to claim 40, wherein the aqueous solution comprising a base comprises 0.5 wt % to 50 wt % MOH.

47. A method for synthesizing a hydrogel comprising water and a cross-linked polymer having repeating units of the following formula (I): ##STR00016## wherein A is selected from the group consisting of —NH—, —C(O)O—, —OC(O)—, and —C(O)NR.sup.10C(O)—, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 and R.sup.10 are independently selected from the group consisting of hydrogen, optionally substituted alkyl, and optionally substituted alkenyl; M is an alkali metal; n is an integer of at least 1; the wavy line (˜˜˜) indicates the point of attachment to other repeating units of Formula (I); and the degree of cross-linking in the cross-linked polymer is in the range of 20 mol % to 80 mol %, wherein the providing operation comprises the operations of: irradiating a solution of an acrylic monomer, a cross-linking agent and a polymerization initiator to form a film; and contacting said film with an aqueous solution comprising a base having a formula MOH.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0198] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0199] FIG. 1 is a schematic representation of the synthesis of free-standing alkaline polymer gel electrolytes (PGEs). Inset shows a sample of the free-standing alkaline PGE.

[0200] FIG. 2 refers to photographs showing a blank carbon paper disk ((A), pre-punched into a diameter of 12.5 mm) and 3 such disks after uniform loading by drop-casting with catalyst ink (B).

[0201] FIG. 3 shows the components of the CR2032 Zn/air coin battery assembly.

[0202] FIG. 4 refers to graphs showing the performance of Zn-ABs using free-standing PAM PGE films as electrolytes. (A) shows a typical polarization curve and corresponding power density plot of the battery, (B) shows the discharge performance at different currents, (C) shows the full discharge curve at a current of 2 mA and (D) shows the discharge/charge cycling data at a current of 2 mA.

[0203] FIG. 5 is a graph showing a comparison of the discharge volume of Zn-Air CR2032 cells using free standing PAM PGE (blue and black) and common PAA PGE (red), showing comparable performance in terms of the discharge voltage.

[0204] FIG. 6 refers to images of Zn-AB CR2032 cells using (A) PAM PGE and (B) PAA PGE, showing that the PAM PGE being a free-standing film, is able to retain its original geometry and does not displace under operating conditions, whereas PAA tends to “spill out” of the device.

[0205] FIG. 7 refers to images showing a large area Zn-AB cell used to power a small fan, in (A) flat geometry and (B) after bending.

[0206] FIG. 8 refers to a schematic illustration on how to fabricate a compressible/expandable Zn-AB cell. (A) shows the main components of the compressible/expandable Zn-AB cell, (B) shows the assembly of the battery using elastic sealant. (C) shows the assembled Zn-AB cell and (D) shows the side view of the battery at normal, compressed and expanded states.

EXAMPLES

[0207] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Materials

[0208] Polyacrylonitrile, cobalt acetate, dimethylformamide and zinc metal were obtained from Sigma-Aldrich of St. Louis, Mo. of the United States of America and was used without further purification. Carbon paper was obtained from SGL Carbon GmbH, Germany, and the Copper mesh and Nickel foam were obtained from Latech Scientific Supply Pte. Ltd., Singapore.

Example 2

Synthesis of the Polyacrylamide Polymer Gel Electrolyte (PAM PGE) Film

[0209] As shown in FIG. 1, briefly, acrylamide (2.5 g) was dissolved in deionised water (10 mL) and bubbled with dry N.sub.2 gas for 15 minutes and this was labeled as Solution 1. N,N-Methylenebisacrylamide (MBAa) (5 mg) and ammonium persulphate (APS) (5 mg) were dissolved in deionised water (5 mL), capped tight and placed under stirring. This solution was labeled as Solution 2. After Solution 1 was bubbled with dry N.sub.2 gas for 15 minutes, it was quickly added to Solution 2 to prevent excess exposure to atmospheric air. After stirring for another 2 minutes, the combined solution was poured onto a glass petri dish and placed under UV illumination for 45 minutes. Once the UV-initiated radical polymerisation was completed, the polyacrylamide (PAM) films were removed from the petri dish and free-standing hydrogel films were obtained. These PAM films were then allowed to dry at room temperature. The dried films were then placed in a closed container containing a fixed amount (6M) of KOH to allow for adsorption of KOH solution into the gel to produce free-standing alkaline PAM polymer gel electrolytes (PGEs).

Example 3

Preparation of a Catalyst Electrode

[0210] To prepare the catalyst electrode, a homogeneous catalyst ink solution was firstly prepared. The catalyst such as CoO.sub.x/C may be synthesized (refer further below for details) or commercially purchased such as Pt/C, but is not limited to the above two. Using the synthesized catalyst of CoO.sub.x/C as an example, 30 mg CoO.sub.x/C was dispersed in 5 mL water solution containing 600 μL Nafion solution (5 wt. % water solution, Sigma Aldrich of St. Louis, Mo., United States of America). After sonication for at least 30 minutes, an appropriate volume of such solution was then carefully dropped onto a current collector (carbon paper disk pre-punched with a diameter of 12.5 mm, as shown in FIG. 2A). A fixed volume of catalyst ink solution was uniformly casted onto the carbon paper disk to ensure equal distribution of catalyst as well as constant amount of catalyst loaded onto each carbon paper disk (FIG. 2B). In such a way, the mass loading of the catalyst was well controlled, for example 1.0 mg cm.sup.−2, so that the catalyst electrodes prepared are identical and comparable.

[0211] CoO.sub.x/C catalyst was synthesised as follows:

[0212] A homogeneous polymer precursor containing 10 wt. % of polyacrylonitrile (PAN) and 2 wt. % of cobalt acetate was prepared in dimethylformamide (DMF). Then the precursor solution was loaded into a syringe with a 22-gauge blunt tip needle which was mounted onto a syringe pump to control the flow rate at 0.3-1.5 mL per minute. The electro-spinning process was conducted by applying a positive voltage of 8-20 kV between the needle and a grounded aluminium foil separated with a distance of 10-20 cm. The as-prepared electrospun fibres collected on the aluminium foil were heated and stabilized at 260° C. in air for 1 hour and consequently carbonized at 900° C. in nitrogen environment for another 1 hour. After being cooled to room temperature, the obtained black fibre materials were re-heated to 200° C. in air for 1.5 hours to obtain the final catalyst of CoO.sub.x/C.

Example 4

Fabricating a Coin-Cell Type Zn-AB

[0213] Zn/air coin cells of the CR2032 type were assembled with the components as shown in FIG. 3, together with the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in the presence of a catalyst.

[0214] The batteries were assembled with customized CR2032 coin cell, the cathode cover was drilled with small holes for air permission. Zn-air battery performance was evaluated on a battery tester of NEWARE BTS-610 (Shenzhen, China). All discharge tests and discharge-charge cycling tests were carried out at ambient air conditions (oxygen supplied only from environment, without additional oxygen).

[0215] The cathode catalysts used were CoO.sub.x/C. The alkaline PAM PGEs were cut into desired disk shape before assembly, and subjected to discharge as well as discharge/charge cycling tests to evaluate battery performance. FIG. 4A shows the polarization and the corresponding power density curves of a typical Zn-AB using PAM PGE. At the discharging voltage of 1V, the battery delivers a current density of ˜22 mA cm.sup.−2. The peak power density of the battery reaches 39 mW cm.sup.−2 as it was discharged at 65.7 mA cm.sup.−2. FIG. 4B demonstrates the ability of the fabricated Zn-AB to discharge smoothly at different currents. The decrease in the discharge voltage plateaus at higher discharge current density is attributed to the conventional polarization; in agreement with the results shown in FIG. 4A.

[0216] FIG. 4C shows the full discharge curve at a current of 2 mA. The fabricated battery is able to maintain a high and flat discharge voltage plateau at ˜1.2 V for ˜10.5 hours, corresponding to an energy capacity of 21 mAh. In this experiment, the cathode used was ˜1.23 cm.sup.2, hence the specific areal capacity of the battery is estimated to be 17.1 mAh cm.sup.−2 which is about 5 times higher than the highest areal capacity reported to date among all types of foldable energy-storage devices (3 mAh cm.sup.−2) as demonstrated by using Li—S type batteries. The alkaline PAM PGE of the present disclosure is intrinsically free standing and flexible which in principle allows fabrication of bendable or even foldable Zn-ABs with even higher specific areal capacities.

[0217] Besides good discharge capability and high specific areal capacity, the Zn-AB with PAM PGE also illustrates good cycling performance as shown in FIG. 4D, with no obvious voltage changes observed in both discharge and charge states after testing for more than 35 cycles.

Example 5

PAM PGE vs PAA PGE

[0218] Preliminary benchmarking experiments using polyacrylic acid (PAA) instead of polyacrylamide (PAM) were carried out. PAA has been demonstrated to be an alkaline polymer gel electrolyte (PGE) before, but PAA exists in the form of a highly viscous fluid and is not a free-standing film. Zn/Air CR2032 cells with identical components (zinc plate as the anode and Pt/C as the cathode catalyst) were fabricated, where the only component difference was in the PGE used. The weight of the PGE used is kept constant for both PAA and PAM based cells. Discharge tests (FIG. 5) indicated that PAM PGEs derived according to the present disclosure exhibit similar performance to PAA PEGs in terms of voltage stability during discharge. Advantages of using PAM over PAA include the ease of handling and preparation (where it is easier to cut the PAM PGE film into the desired geometry as compared to manipulating the very viscous PAA fluid into the desired geometry) as well as the minimizing of gel protrusion from the cell under operation as indicated in FIG. 6. PAM PGE, being a free-standing film, is able to retain its original geometry and does not displace under operating conditions (FIG. 6A) whereas PAA tends to “spill out” of the device (FIG. 6B).

Example 6

Bendable Zn-AB

[0219] Next, utilising the advantages of free-standing and easy to handle properties of the PAM PGE, a larger PAM PGE film (approximately 2 cm×10 cm) was prepared for fabricating bendable Zn-AB. The battery was simply constructed by using a zinc sheet as the anode, a free standing PAM film as the gel electrolyte, CoO.sub.x/C powder deposited directly on the PAM as the catalyst and a copper mesh was employed as the current collector for forming a cathode (FIG. 7). As demonstrated, a small fan can be powered by a single cell regardless of whether the cell is in a flat state (FIG. 7A) or bent state (FIG. 7B). This cell was in fully solid state, and exhibited the ability to continuously power the small fan even in a bent state.

Example 7

Compressible/Expandable Zn-AB

[0220] In future iterations, compressible/expandable Zn-AB cells will be fabricated according to the diagrams in FIG. 8. FIG. 8A shows the main components of the compressible/expandable Zn-AB cell, FIG. 8B shows the assembly of the battery using elastic sealant. FIG. 8C shows the assembled Zn-AB cell and FIG. 8D shows the side view of the battery at normal, compressed and expanded states.

[0221] Instead of using hard and rigid materials as the housing for Zn-AB cells, rubbery materials such as PDMS or silicone will be used as a defined casing for Zn-AB cells (FIG. 8B). As illustrated in FIG. 8D, the usage of elastic sealants confers compressibility as well as expandability to the Zn-AB cells. Furthermore, coupled with the flexibility of our free-standing alkaline PGE, a truly flexible electrochemical cell will be devised which can be applied to applications such as wearable technologies.

INDUSTRIAL APPLICABILITY

[0222] The disclosed electrochemical cell may be useful in energy storage. The disclosed electrochemical device may be useful as an alternative to existing aqueous electrolytes for use in safer batteries. The disclosed electrochemical cell may have applications in wearable technology, particularly in consumer products such as watches, eye glasses and textiles, in monitoring healthcare equipment, such as in data acquisition and communication, and in medical devices such as drug delivery devices, for example for insulin injection.

[0223] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.