An Amphiphilic Molecule‐Regulated Core‐Shell‐Solvation Electrolyte for Li‐Metal Batteries at Ultra‐Low Temperature

Abstract

Lithium metal batteries hold great promise for promoting energy density and operating at low temperatures, yet they still suffer from insufficient Li compatibility and slow kinetic, especially at ultra‐low temperatures. Herein, we rationally design and synthesize a new amphiphilic solvent, 1,1,2,2‐tetrafluoro‐3‐methoxypropane, for use in battery electrolytes. The lithiophilic segment is readily to solvate Li+ to induce self‐assembly of the electrolyte solution to form a peculiar core‐shell‐solvation structure. Such unique solvation structure not only largely improves the ionic conductivity to allow fast Li+ transport and lower the desolvation energy to enable facile desolvation, but also leads to the formation of a highly robust and conductive inorganic SEI. The resulting electrolyte demonstrates high Li efficiency and superior cycling stability from room temperature to −40 °C at high current densities. Meanwhile, anode‐free high‐voltage cell retains 87 % capacity after 100 cycles.

Locally Concentrated Ionic Liquid Electrolytes Enabling Low‐Temperature Lithium Metal Batteries

“…Meanwhile, the peaks of LiF (F 1s), Li 3 N (N 1s), Li 2 S 2 (S 2p), and Li 2 S (S 2p) got more pronounced, demonstrating a larger contribution from the FSI − decomposition going deeper in the SEI layer. These inorganic species with poor electronic transport and high mechanical strength are known to suppress side reactions between LMAs and electrolytes as well as the lithium dendrite growth, yielding high lithium stripping/plating CE [21, 64] …”

“…These inorganic species with poor electronic transport and high mechanical strength are known to suppress side reactions between LMAs and electrolytes as well as the lithium dendrite growth, yielding high lithium stripping/ plating CE. [21,64] The compatibility of the electrolyte towards nickel-rich cathode at À 20 °C was evaluated using Li/NCA coin cells within the 2.8-4.4 V voltage window. In a first step, electro-des with a moderate NCA loading (2.7 mg cm À 2 ) and thick lithium foils (500 μm) were used.…”

Bifunctional Localized High-Concentration Electrolyte for the Fast Kinetics of Lithium Batteries at Low Temperatures

“…Fan et al developed an all-fluorinated electrolyte with a low binding ability with Li + , enabling the Li/NCA cell to work at a wide temperature range (from −95 to 125 °C). Recently, there have been many molecular engineering strategies applied to reduce the binding ability with Li + to improve the cell’s low-temperature performance. − …”

Locally Concentrated Ionic Liquid Electrolytes Enabling Low‐Temperature Lithium Metal Batteries

“…[19,20] It has also become clear that the solvation structure of Li + has significant influence on the low-temperature performance of LMAs. [7,13,21,22] Due to the electrostatic repulsion effect of negatively charged anodes on anions upon lithium plating, the Li + de-solvation process is mainly limited by the interaction between Li + and solvents, i.e., a Li + solvation shell consisting of anions rather than solvent molecules is beneficial for a more facile desolvation process and consequently dendrite-free lithium stripping/plating. [7,13] Despite the progress, it has to be noted that most of the aforementioned electrolytes designed for low-temperature LMAs are highly flammable.…”

“…So far, a few electrolytes based on liquefied gas, [14, 15] ether, [7, 16] carbonate, [17, 18] and/or acetate solvents with low freezing points have been reported for such a purpose [19, 20] . It has also become clear that the solvation structure of Li + has significant influence on the low‐temperature performance of LMAs [7, 13, 21, 22] . Due to the electrostatic repulsion effect of negatively charged anodes on anions upon lithium plating, the Li + de‐solvation process is mainly limited by the interaction between Li + and solvents, i.e., a Li + solvation shell consisting of anions rather than solvent molecules is beneficial for a more facile de‐solvation process and consequently dendrite‐free lithium stripping/plating [7, 13] .…”