Controlling Fluoride‐Forming Reactions for Improved Rate Capability in Lithium‐Perfluorinated Gas Conversion Batteries

Abstract

Nonaqueous metal-gas batteries based on halogenated reactants exhibit strong potential for future high-energy electrochemical systems. The lithium-sulfur hexafluoride (Li-SF 6) primary battery, which utilizes a safe, noncombustible, energy-dense gas as cathode, demonstrates attractive eight-electron transfer reduction during discharge and high attainable capacities (> 3000 mAh/g carbon) at voltages above 2.2 V Li. However, improved rate capability is needed for practical applications. Here, we report two viable strategies to achieve this by targeting the solubility of the passivating discharge product, lithium fluoride (LiF). Operating at moderately elevated temperatures, e.g. 50 °C, in DMSO dramatically improves LiF solubility and promotes sparser and larger LiF nuclei on gas diffusion layer (GDL) electrodes, leading to capacity improvements of ~10x at 120 µA cm-2. More aggressive chemical modification of the electrolyte by including a tris(pentafluorophenyl)borane (TPFPB) anion receptor further promotes LiF solubilization; capacity increased even at room temperature by a factor of 25 at 120 μA cm-2 , with attainable capacities up to 3 mAh cm-2. This work shows that bulk fluoride-forming conversion reactions can be strongly This article is protected by copyright. All rights reserved. 2 manipulated by tuning the electrolyte environment to be solvating towards F-, and that significantly improved rates can be achieved, leading a step closer to application. Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff)) Significant improvement of rate capability of Li-SF 6 cells is achieved by controlling the formation of LiF. Two viable strategies, moderately elevating temperature to 50 °C or using an anion receptor (TPFPB) as additive in electrolyte, can increase attainable capacity by a factor of 10 or 25, respectively, at high current density (120 μA cm-2).

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.…”

A nitroaromatic cathode with an ultrahigh energy density based on six-electron reaction per nitro group for lithium batteries

“…Nevertheless, CF x must be synthesized in harsh conditions with precise control, leading to high cost and hindering the wide application ( 20 ). Some liquid and gas cathodes, such as SO 2 , SOCl 2 , and SF 6 ( 24 – 27 ), can also offer high energy densities, but they tend to be volatile and induce severe safety hazards, especially on the occasion of thermal runaway. Therefore, it is highly desired to develop feasible and reliable battery systems with high energy density.…”

Enhancing the Reduction Kinetics of LiSF6 Batteries by Dispersed Cobalt Phthalocyanines on Porous Carbon

“…[7] Further, a high areal capacity of about 25 mAh cm −2 with an initial voltage plateau of ≈2.74 V can be obtained at the current density of 0.1 mA cm −2 (Figure 7c, the weight loading of CoPc/NCNC is about 0.6 mg cm −2 ), which is much superior to that reported in previous reports (Figure 7d). [6,7,16] Moreover, the obtained capacity is comparable to the LiS cell with a sulfur loading of over 20 mg cm −2 , [17] indicating the promising prospect of the LiSF 6 battery as a high-energy-density system.…”

“…c) Full discharge profiles of the LiSF 6 cells with CoPc/NCNC gas electrode at 0.1 mA cm −2 . d) Performance comparison of LiSF 6 cells between this work and published works [6,7,16] in terms of areal capacity with voltage. VC is vulcan carbon.…”