Abstract The development of new solvents is imperative in lithium metal batteries due to the incompatibility of conventional carbonate and narrow electrochemical windows of ether-based electrolytes. Whereas the fluorinated ethers showed improved electrochemical stabilities, they can hardly solvate lithium ions. Thus, the challenge in electrolyte chemistry is to combine the high voltage stability of fluorinated ethers with high lithium ion solvation ability of ethers in a single molecule. Herein, we report a new solvent, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDL), combining a cyclic fluorinated ether with a linear ether segment to simultaneously achieve high voltage stability and tune lithium ion solvation ability and structure. High oxidation stability up to 5.5 V, large lithium ion transference number of 0.75 and stable Coulombic efficiency of 99.2% after 500 cycles proved the potential of DTDL in high-voltage lithium metal batteries. Furthermore, 20 μm thick lithium paired LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell incorporating 2 M LiFSI-DTDL electrolyte retained 84% of the original capacity after 200 cycles at 0.5 C. 

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Fluorinated ether electrolyte with controlled solvation structure for high voltage lithium metal batteries

The solid-electrolyte interphase (SEI) is known to dictate the performance of a Li metal anode, where its inorganic compositions are primarily responsible for Li+ conduction, electron insulation, a...

Tailoring Electrolyte Solvation Chemistry toward an Inorganic-Rich Solid-Electrolyte Interphase at a Li Metal Anode

Current knowledge on Na metal anode has been limited on its room-temperature or high-temperature (molten Na-S system) performances. However, the properties related to its low-temperature and fast-charging performances are rarely covered. Herein, we show that, using a conventional carbonate-based electrolyte, needle-like Na deposits sprout at −20 °C with a spiking impedance of ∼2.8 × 104 Ω observed in symmetric cell configuration, making an early failure of the battery within tens of hours. By knocking down the kinetic barriers of Na+ ion de-solvation and its subsequent diffusion through the solid electrolyte interphase (SEI), we enable flat and spherical Na deposits at −20 °C with a massively reduced interfacial impedance. This has been realized by using (i) a weakly solvated electrolyte that shows a low solvation energy towards Na+ ions, and (ii) a Na15Sn4/NaF biphasic artificial SEI for promoting unhindered Na+ ion transfer at the Na metal/electrolyte interface. Ultimately, a high-voltage Na/Na3V2(PO4)2O2F battery is developed to stand low temperatures down to −30 °C and fast charging up to 30C. The design strategy provided herein underlines the simultaneous de-solvation and SEI control for achieving low-temperature and fast-charging sodium metal batteries and presents as a prototype of how the kinetic barriers can be overcome under extreme conditions.

Knocking down the kinetic barriers towards fast-charging and low-temperature sodium metal batteries

The lifespan of high-energy-density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3-) is proposed and validated to improve the homogeneity of SEI in practical LMBs. NO3- is connected to an ether-based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3- and improve the reducibility. The decomposition of non-resonant -NO3 in ISDN enriches SEI with abundant LiNxOy and induces uniform lithium deposition. Lithium-sulfur batteries with ISDN additives deliver a capacity retention of 83.7% for 100 cycles compared with rapid decay with LiNO3 after 55 cycles. Moreover, lithium-sulfur pouch cells with ISDN additives perform a specific energy of 319 Wh kg-1 and undergo 20 cycles. This work provides a realistic reference in designing additives to modify SEI for stabilizing LMBs.

Fengyuan Min

Papers

Critical effects of electrolyte recipes for Li and Na metal batteries