Low temperature sulfur and sodium metal battery for grid-scale energy storage application

Abstract

A re-chargeable battery comprising a non-dendrite forming sodium (Na)/potassium (K) liquid metal alloy anode, a sulfur and polyacrylonitrile (PAN) conductive polymer composite cathode, a polyethyleneoxide (PEO) solid electrolyte, a solid electrolyte interface (SEI) formed on the PEO solid electrolyte; and a cell housing, wherein the anode, cathode, and electrolyte are assembled into the cell housing with the PEO solid electrolyte disposed between the cathode and anode.

Claims

1. A re-chargeable battery comprising: a non-dendrite forming sodium (Na)/potassium (K) liquid metal alloy anode; a sulfur and polyacrylonitrile (PAN) conductive polymer composite cathode; a polyethyleneoxide (PEO) solid electrolyte; a solid electrolyte interface (SEI) directly in contact with the PEO solid electrolyte, wherein the PEO solid electrolyte completely surrounds the sulfur and PAN composite cathode; and a cell housing, wherein the anode, cathode, and electrolyte are assembled into the cell housing.

2. The re-chargeable battery of claim 1, wherein the PEO solid electrolyte comprises a sodium triflate salt and a potassium triflate salt.

3. The re-chargeable battery of claim 1, wherein a potassium concentration in the sodium and potassium alloy is approximately 40% K to 90% K by weight.

4. The re-chargeable battery of claim 2, wherein the sodium and potassium liquid metal alloy is approximately 56% K and 44% Na by weight.

5. The re-chargeable battery of claim 1, wherein the PEO is cross-linked.

6. The re-chargeable battery of claim 5, wherein the PEO is UV cross-linked with a benzophenone initiator.

7. The re-chargeable battery of claim 1, wherein the PEO solid electrolyte is a Na/K ion conducting membrane.

8. The re-chargeable battery of claim 1, wherein the PEO solid electrolyte prevents the anode from contacting the cathode.

9. The re-chargeable battery of claim 1, wherein the PEO oxygen to Na ion ratio is at 20:1 and the PEO oxygen to K ion ratio is at 20:1.

10. The re-chargeable battery of claim 1 wherein the anode comprises a copper Cu current collector.

11. The re-chargeable battery of claim 1, wherein the cathode comprises an aluminum Al current collector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

(2) FIG. 1 illustrates a schematic diagram of low temperature sulfur and sodium re-chargeable metal battery according to an embodiment of the invention.

(3) FIGS. 2 and 3 illustrate the extended cycling performance of the NaK/S cell.

(4) FIGS. 4A and 4B illustrate voltage profiles of a cell during a charge and discharge processes. FIG. 4B is an enlargement of one charge and discharge cycle as shown in FIG. 4A.

DETAILED DESCRIPTION

(5) Various embodiments of the invention describe a re-chargeable battery design that comprises a non-dendrite forming sodium (Na)/potassium (K) liquid metal alloy anode, a sulfur/polyacrylonitrile (PAN) conductive polymer composite cathode, a cross-linked solid polyethyleneoxide (PEO) polymer with a Na and K based salt (e.g. sodium triflate and potassium triflate) electrolyte, and a stable interface (SEI) on the solid PEO polymer electrolyte without any of the previously reported inherent drawbacks associated with prior designs. Various embodiments of the invention will enable the usage of both low cost materials and a low cost production process for sulfur based low cost and safe rechargeable batteries for large scale energy storage applications. Additional advantages of such a design are that all materials are naturally abundant, the large-scale production of these materials is already in place, the design is inherently safe (thermal dynamically prohibit dendrite formation), and a low cost manufacturability is possible.

(6) FIG. 1 illustrates a schematic diagram of a low temperature sulfur cathode and sodium/potassium anode re-chargeable metal battery 100 according to an embodiment of the invention. The re-chargeable metal battery 100 comprises a Cu current collector 102, an aluminum current collector 104, a sodium (Na)/potassium (K) liquid alloy anode 106, an in situ formed stable interface (or solid electrolyte interface SEI) 108, a cross-linked polyethyleneoxide (PEO) 110 solid electrolyte, and a sulfur/polyacrylonitrile (PAN) conductive polymer composite cathode 112.

(7) An embodiment of the invention describes the utilization of a sodium (Na)/potassium (K) liquid alloy anode 106. Within a certain ratio of Na/K, the alloy is liquid. Therefore, metal dendrite formation is completely prohibited. Potassium and sodium are miscible in all portions. The alloy, in concentrations of 40-90 wt. % K, is a liquid at room temperature. The potassium-sodium alloy is not soluble in hydrocarbons or ethers. In one embodiment of the invention the anode 106 composition is described as follows: sodium and potassium alloy at 56% K and 44% Na by weight with an excess of Na/K alloy in the anode 106.

(8) By tuning the Na and K ratio in the alloy, the melting point of the mixture can be controlled. An embodiment of the invention describes the control of the melting point of the alloy below the operational temperature of the re-chargeable battery 100 so that the metal alloy anode 106 will be a liquid to prohibit dendrite growth. In one embodiment, a KNa alloy eutectic mixture at 78 wt. % K and 22 wt. % Na has a melting point of 12.6 C.

(9) An embodiment of the invention describes the use of the cross-linked PEO and Na and K based salt solid polymer electrolyte 110. The Na and K salt dissolved in PEO polymer forms a good solid polymer electrolyte 110 for conducting Na and K ion for this re-chargeable battery system 100. The PEO will be UV cross-linked with a benzophenone initiator. For a further discussion on cross-linking PEO with a benzophenone initiator, see Barbara Rupp, Martin Schmuck, Andrea Balducci, Martin Winter, Wolfgang Kern, Polymer electrolyte for lithium batteries based on photochemically cross-linked poly(ethylene oxide) and ionic liquid. European Polymer Journal 44 (2008) 2986-2990, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

(10) This is a solid electrolyte 110 and a Na/K ion conducting membrane that also serves to block the Na/K alloy metal anode 104 from contacting the sulfur cathode 112. On the surface of the solid polymer electrolyte 110, a protective layer (SEI) 108 can form to stabilize the solid polymer electrolyte 110 and the Na/K liquid alloy electrode/anode 106.

(11) In one embodiment, the solid polymer electrolyte 110 comprises the polyethyleneoxide (PEO), and sodium triflate and potassium triflate, and 5 wt. % of benzophenone. The PEO oxygen to Na ion ratio is at 20:1 and the PEO oxygen to K ion ratio is at 20:1. The solid polymer electrolyte 110 will be cast as a membrane and UV cross-linked to form a stable ion-conducting separator. The solid polymer electrolyte 110 can also be used both as a cathode binder (sulfur/conductive polymer composite) and an electrolyte 110 in the cathode composition. In one embodiment, this solid polymer electrolyte 110 will ideally operate between 60-80 C. The separator/solid PEO electrolyte/membrane 110 composition is described as follows: PEO (0.5 g), Sodium triflate (0.12 g) and potassium triflate (0.16 g) salts. An estimated thickness is approximately 80-250 m.

(12) An embodiment of the invention describes the use of a stable interface (SEI) 108 on the solid PEO electrolyte/membrane 110. This is a new and enabling concept. In most of the Li metal based systems, the stable interface (SEI) is on a metal surface. An embodiment of the invention forms a stable interface (SEI) 108 at the PEO solid polymer electrolyte membrane 110 surface.

(13) An embodiment of the invention describes the use of a sulfur and polyacrylonitrile (PAN) conductive polymer cathode 112. The cathode 112 composition is described as follows: PEO(0.5 g); Sodium triflate(0.12 g); Potassium triflate(0.16 g); Sulfur-PAN composite(0.4 g); AB(0.15 g). Active material sulfur in cathode:0.062 mg. Cathode area: 1.6 cm.sup.2. For a further discussion on sulfur composite cathode materials, see Jiulin Wang, Jun Yang, Yanna Nuli, Rudolf Holze. Room temperature Na/S batteries with sulfur composite cathode materials. ScienceDirect Electrochmistry Communications 9 (2007) 31-34, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

(14) Preparation of the sulfur and polyacrylonitrile (PAN) conductive polymer is described as follows: typically, sublimed sulfur (with purity of 99.99%) is thoroughly mixed with polyacrylonitrile (PAN). Ethanol is used as dispersant to improve the mixing of sulfur and PAN. After drying, the mixture is heated to 300 C. and dwelled for 6 hours under argon gas. A black, powdery material was obtained.

RESULTS

(15) FIGS. 2 and 3 illustrate the extended cycling performance of a NaK/S cell. A theoretical capacity of 568 mAh/g is calculated for a sulfur cathode. A theoretical capacity for Na.sub.2S is 680 mAh/g and K.sub.2S is 480 mAh/g. A theoretical capacity of the cathode is estimated based on the assumption that the formation of both salts based on the weight ratio of Na and K in the alloy.

(16) FIGS. 4A and 4B illustrate voltage profiles of the cell during charge and discharge processes. FIG. 4B is an enlargement of one charge and discharge cycle as shown in FIG. 4A.