Specular Lithium Deposits from Lithium Hexafluoroarsenate/Diethyl Ether Electrolytes

Abstract

JANUARY 1982 ABSTRACTA new class of aprotic organic electrolytes in which to cycle the lithium electrode has been developed. Blends of diethyl ether (DEE) and tetrahydrofuran (THF) incorporating LiAsF6 have been found to afford Li electrode cycling efficiencies in excess of 98%. In addition, specular deposits of up to 10 C/cm 2 may be plated from these systems. The kinetic stability of these blended electrolytes toward Li is thought to be due to the formation of a protective lithium ethoxide film.Our ongoing search for electrolytes suitable for use in ambient temperature secondary Li batteries has led us to investigate solutions of LiAsF6 in propylene carbonate (PC) (1), tetrahydrofuran (THF) (2), and 2-methyltetrahydrofuran (2-Me-THF) (3). Average cycling efficiencies for the Li electrode in these media are 84, 88, and 96%, respectively (1C Li/cm 2 at 5 mA/ cm2). In this paper, we elaborate on the discovery of a class of diethyl ether (DEE)-based electrolytes which afford cycling efficiencies in excess of 98% (4,5). Moreover, Li plate morphologies are so regular and dendrite free that they may be deemed specular in appearance.Electrolytes comprising DEE have found use in ambient temperature Li primary batteries (6). More recently, Higgens reported on the stability of purified DEE toward Li and found that 1M LiAsF6/DEE was stable for over one month at 71~ (7). To our knowledge, however, no reports of DEE-based electrolytes employed in secondary Li batteries have surfaced in the open literature.While a variety of cosolvents have been found to improve the conductivity of LiAsF6/DEE electrolyte without degrading Li cycling performance (5), the best electrolyte to date comprises a 90:10 v/v mixture of DEE and THF, 2.5M in LiAsF6. We refer to this mixture as . This paper also explores the variation of Li half-cell cycling efficiencies with LiAsF6 concentration and with the addition of asymmetric ether cosolvents. ExperimentalGeneral.--All purification procedures subsequent to distillation and the electrochemical experiments were conducted at ambient temperature under Ar atmosphere in a Vacuum-Atmospheres Corporation dry box equipped with a Model He-493 Dri-Train.

RETRACTED ARTICLE: Polymer electrolytes: characteristics and peculiarities

“…On average, lithium cycling efficiencies could reach >95% in these systems, [52,54,58], although long-term cycling in these electrolytes still promoted the growth of lithium dendrites [59] very similar to the case of LiClO 4 , an SEI formed from LiAsF 6 -based electrolytes, either on a lithium or carbonaceous anode, which mainly consists of alkyl carbonates or Li 2 CO 3 rather than LiF, as one would expect from the behavior of its close structural brothers LiPF 6 or LiBF 4 [33,47]. This can be attributed to the much less labile As-F bond that is resistive to hydrolysis [60].…”

“…In the late 1970s, lithium hexafluoroarsenate (LiAsF 6 ) was found to be superior to LiClO 4 salt as an electrolyte solute for lithium batteries [52]. For a long period, the combination of LiAsF 6 with various ethers became the most popular system under investigation [53][54][55][56][57].…”

Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes

“…While modest improvement (CE = 83.6%, 1977) was subsequently achievable using additives 11 , carbonate solvents are particularly unstable at Li potentials due to their strongly polar carbon-oxygen bonds and inability to form a protective SEI 12 . Thus, replacing carbonates with weakly polar, more cathodically stable ethers led to more substantial increases in CE [13][14][15][16][17][18][19][20] . This era also saw growing use of LiAsF 6 due to its improved safety over LiClO 4 and ability to passivate Al current collectors at cathode potentials 6 .…”

“…For example, 1 M LiAsF 6 in tetrahydrofuran (THF) achieved a CE of 89.4% (1978) 13 , motivating use of more-stable 2-methyl-tetrahydrofuran (with 1-1.5 M LiAsF 6 salt), which reached a CE of 97.4% in the following year 15,17 . Later, ether-based blends were introduced, such as LiAsF 6 in diethyl ether (DEE)/THF (CE = 97.6%, 1982) 16 or ether/carbonate cosolvents having ethers as the primary constituent (for example, 1 M LiAsF 6 in 12% PC or 30-35% EC in 1,3-dioxolane (DOL), CE ≈ 98%, 1992) 20 . Following these gains, remarkably, subsequent CE improvements appear to have largely stagnated for over two decades while greater strides were being achieved with Li-ion batteries, which were undergoing commercialization throughout the 1990s; Li-ion batteries employ a graphite anode with an SEI that is sufficiently stable in carbonate electrolytes.…”

Charge–discharge reaction mechanism of manganese molybdenum vanadium oxide as a high capacity anode material for Li secondary battery

“…5 In the field of anode materials, graphite provides a favorable low potential of Li insertion/removal and a long life cycle. However, its capacity is limited to about 370 A h kg 21 , which is substantially smaller than that of metallic lithium, 6 and its rate property is not always sufficient if it is to be considered as the anode for large-scale batteries in the near future.…”