Structure‐Reactivity Relationships of Methylated Tetrahydrofurans with Lithium

Abstract

Tetrahydrofurans methylated in the α‐position manifest remarkable chemical and electrochemical stability toward Li. While tetrahydrofuran (THF) distilled off benzophenone ketyl and stored with Li at 71°C reacts in two days, 2‐methyltetrahydrofuran (2‐Me‐THF) treated similarly was stable for over 10 months. Electrolytes comprising either 2‐Me‐THF or 2,5‐dimethyltetrahydrofuran (2,5‐di‐Me‐THF) were subjected to cycling studies in half‐cell configurations. Average Li on Li cycling efficiencies exceeded 96% for Q=1 C/cm2 . Unlike the α‐methylated ethers, 3‐methyltetrahydrofuran (3‐Me‐THF) was as reactive towards Li as THF. Thus, the position of the methyl substituent with respect to the cyclic ether's oxygen atom is critically important, and several mechanisms are considered.

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 .…”

“…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 .…”

Electrochemical behaviors of li electrode in organic electrolytes

“…A hump approximately at 0.5 V (vs Li/Li § was always present during galvanostatic deposition of Li on CO2 adsorbed Ni substrates both in LiCIO~ and LiPF, electrolytes. This is probably due to the formation of Li2CO~ as in [12]. …”

High-throughput combinatorial screening of multi-component electrolyte additives to improve the performance of Li metal secondary batteries

“…In these experiments, five different additives were selected from the list of fourteen chemical compounds shown in Table 1, all of which are representative lithium salts and other additives previously described in the literature. Employing a method already described in a prior paper 18 , the coulombic efficiency (CE) of each cell containing five additives was quantitatively evaluated according to the protocol shown in Fig. 2.…”