A High-Capacity Lithium–Gas Battery Based on Sulfur Fluoride Conversion

Abstract

Identification of novel redox reactions that combine the prospects of high potential and capacity can contribute new opportunities in the development of advanced batteries with significantly higher energy density than today's state of the art, while advancing current understanding of nonaqueous electrochemical transformations and reaction mechanisms. The immense research efforts directed in recent years towards metal-gas, and in particular lithiumoxygen (Li-O 2 ) batteries, have highlighted the role that gas-to-solid conversion reactions can play in future energy technologies; however, efforts have mainly focused on tailoring the anode (alkali metal) in the metal-gas couple to achieve improved reversibility. Here, in a different approach, we introduce and characterize a new gas cathode reaction that capitalizes on the full change in oxidation state (from +6 to -2) available in redox-active sulfur, based on the cathodic reduction of highly fluorinated sulfur hexafluoride (SF 6 ) in a Li metal battery. In glyme-based electrolyte (0.3 M LiClO 4 in TEGDME), we establish, using quantitative gas and 19 F NMR analysis, that discharge predominantly involves an 8-electron reduction of SF 6 , yielding stoichiometric LiF, as well as Li 2 S and modest amounts of higher-order Li polysulfides. This multi-phase conversion reaction yields capacities of ~3600 mAh g C -1 at moderate rates (30 mA g C -1 ) and potentials up to 2.2 V vs. Li/Li + .In a non-glyme electrolyte, 0.3 M LiClO 4 in DMSO, SF 6 reduction also proceeds readily, yielding higher capacities of ~7800 mAh g C -1 at 30 mA g C -1 . Although not at present rechargeable, the demonstration of, and insights gained, from the primary Li-SF 6 system provides a promising first step for design of novel sulfur conversion chemistries with energy densities that exceed those of today's Li primary batteries, while demonstrating a new design space for nonaqueous gas-to-solid electrochemical reactions.

Electrochemical carbon dioxide capture to close the carbon cycle

“…Examples of electrochemical hybrid capture and utilization is the electrochemical seawater battery system [176], the alkali metal-based CO 2 batteries (e.g., lithium-CO 2 batteries [177,178]) and electrochemical CO 2 capture and conversion combinations [25,[179][180][181][182][183]. The absence of pH-swings, and the lack of further development of these proposed electrochemical capture routes, categorizes these concepts beyond the scope of this review.…”

Electrochemical Conversion of Nitrogen Trifluoride as a Gas-to-Solid Cathode in Li Batteries

“…Our own recent efforts have shown that gas cathode reactions need not be limited to common O 2 , CO 2 or SO 2 , but can also involve nominally ‗inert', highly fluorinated gases. 12 The present work explores the viability of a highly-fluorinated gas, nitrogen trifluoride (NF 3 ), as a gas cathode in a Li battery. NF 3 is a colorless, nonflammable gas with routine usage in the microelectronics industry.…”

Fluorinated graphene nanoribbons from unzipped single-walled carbon nanotubes for ultrahigh energy density lithium-fluorinated carbon batteries

“…Among various solid cathode materials, fluorinated carbon (CF x ) has attracted unprecedent attention due to their high theoretical energy density, which is much higher than that of lithium ion batteries (~500 W h kg −1 ) [3]. To fill this short-term technology gap for producing batteries with higher energy densities, several types of nonaqueous metal-gas batteries have been explored to meet growing demands, such as Li-O 2 [4], Na-O 2 [5], K-O 2 [6], Li-CO 2 [7,8], Li-NF 3 [9], and Li-SF 6 [10][11][12]. However, the gas-to-solid conversion reaction involves a solution-mediated electrochemical process that induces complex thermodynamics, kinetics, and transport considerations, and it remains a challenge to achieve the potential energy densities and realize practical applications for these systems.…”