Rechargeable Solid-State Copper Sulfide Cathodes for Alkaline Batteries: Importance of the Copper Valence State. Issue 4 (1st January 2019)

• Record Type: Journal Article
• Authors: Duay, Jonathon; Lambert, Timothy N.; Kelly, Maria; Pineda-Dominguez, Ivan
• Is Part Of: Journal of the Electrochemical Society. Volume 166:Issue 4(2019)
• Page Start: A687
• Page End: A694
• Publication Date: 2019-01-01
• Subjects: Batteries -- Batteries - aqueous -- Energy Storage -- Alkaline -- Battery -- Energy storage; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0261904jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Batteries for grid storage applications must be inexpensive, safe, reliable, as well as have a high energy density. Here, we utilize the high capacity of sulfur (S) (1675 mAh g −1, based on the idealized redox couple of S 2− /S) in order to demonstrate for the first time, a reversible high capacity solid-state S-based cathode for alkaline batteries. To maintain S in the solid-state, it is bound to copper (Cu), initially in its fully reduced state as the sulfide. Upon charging, the sulfide is oxidized to a polysulfide species which is captured and maintained in the solid-state by the Cu ions. This solid-state sulfide/polysulfide cathode was analyzed versus a zinc (Zn) anode which gives a nominal >1.2 V cell voltage based on the sulfide/polysulfide redox cathode chemistry. It was found that in order for the S cathode to have the best cycle life in the solid-state it must not only be bound to Cu ions but bound to Cu ions in the +1 valence state, forming Cu2 S as a discharge product. Zn/Cu2 S batteries cycled between 1.45 V and 0.4 V vs. Zn displayed capacities of ∼1500 mAh g −1 (based on mass of S) or ∼300 mAh g −1 (based on mass of Cu2 S) and high areal (>23 mAh cm −2 ) and energy densities (>135 Wh L −1 ), but suffered from moderate cycle lifes (<250 cycles). The failure mechanism of this electrode was found to be disproportionation of the charged S species into irreversible sulfite releasing the bound Cu ions. The Cu ions become free to perform Cu specific redox reactions which slowly changes the battery redox chemistry from that of S to that of Cu with a S additive. Batteries utilizing the Cu2 S cathode and a 50% depth of charge (DOC) cathode cycling protocol, with 5 wt% Na2 S added to the electrolyte, retained a cathode capacity of 838 mAh g −1 (based on the mass of S) or 169 mA h g −1 (based on mass of Cu2 S) after 450 cycles with >99.7% coulombic efficiency. These Zn/Cu2 S batteries provided a grid storage relevant energy density of >42 W h L −1 (at 65 wt% Cu2 S loading), despite only using a 3% depth of discharge (DOD) for the Zn anode. This work opens the way to a new class of energy dense grid storage batteries based on high capacity solid-state S-based cathodes.