Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous “native” solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF—whether chemical, mechanical, or kinetic in nature—remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric “outer layer,” is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationGao, Haining and Gallant, Betar M. 2020. "Advances in the chemistry and applications of alkali-metal-gas batteries." Nature Reviews Chemistry, 4 (11).

Discovery of new electrochemical redox motifs is essential to expand the design landscape for energy-dense batteries. We report a family of fluorinated reactants based on pentafluorosulfanyl arenes ( R-Ph-SF 5 ) that allow for high electron-transfer numbers (up to 8-e − /reactant) by exploiting multiple coupled redox processes, including extensive S–F bond breaking, yielding capacities of 861 mAh·g reactant −1 and voltages up to ∼2.9 V when used as catholytes in primary Li cells. At a cell level, gravimetric energies of 1,085 Wh·kg −1 are attained at 5 W·kg −1 and moderate temperatures of 50 °C, with 853 Wh·kg −1 delivered at >100 W·kg −1 , exceeding all leading primary batteries based on electrode + electrolyte (substack) mass. Voltage compatibility of R-Ph-SF 5 reactants and carbon monofluoride (CF x ) conversion cathodes further enabled investigation of a hybrid battery containing both fluorinated catholyte and cathode. The hybrid cells reach extraordinarily high cell active mass loading (∼80%) and energy (1,195 Wh·kg −1 ), allowing for significant boosting of substack gravimetric energy of Li−CF x cells by at least 20% while exhibiting good shelf life and safety characteristics.

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).

Macro-scale assembly of graphene quantum dots has great potential in diverse applications.