High-Safety and High-Energy-Density Lithium Metal Batteries in a Novel Ionic-Liquid Electrolyte

Lithium metal batteries with high energy density have attracted much attention, but the stability limits their application and development. People hope to solve the lithium dendrite problem on the lithium metal surface by designing a new type of electrolyte to improve the performance of the lithium metal battery and promote its wide application. Solid electrolytes, polymer electrolytes and ionic liquid electrolytes have been the focus of research in recent years.

Among them  ionic liquid electrolytes have  excellent characteristics such as low volatility, high temperature resistance, non-flammability, large hot melt, and wide electrochemical window.

Recently, Academician Hongjie Dai from Stanford University reported a lithium metal batteries in a novel nonflammable ionic-liquid (IL) electrolyte composed of EMIm cations and FSI anions, with sodium NaTFSI as a key additive are reported.

The ionic liquid electrolyte has excellent performances. Firstly,the Na ion participates in the formation of hybrid passivation interphases and contributes to dendrite free Li deposition and reversible cathode electrochemistry. Then the electrolyte of low viscosity allows practically useful cathode mass loading up to ≈16 mg cm⁻². At the same time,Li anodes paired with lithium cobalt oxide (LiCoO₂) and lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, NCM 811) cathodes exhibit 99.6–99.9% Coulombic efficiencies, high discharge voltages up to 4.4 V, high specific capacity and energy density up to ≈199 mAh g−1 and ≈765 Wh kg⁻¹ respectively, with impressive cycling performances over up to 1200 cycles.

Highly stable passivation interphases formed on both electrodes in the novel IL electrolyte are the key to highly reversible lithium metal batteries, especially for Li–NMC 811 full batteries.

Ionic liquid electrolyte can meet the requirements of "green chemistry", and its special chemical properties can greatly improve the safety performance of lithium batteries. This new type of ionic liquid electrolyte realizes the perfect fusion of high energy density and high safety of lithium metal batteries.

references:

Hao Sun, et al, High-Safety and High-Energy-Density Lithium Metal Batteries in a Novel Ionic-Liquid Electrolyte, Adv. Mater. 2020, DOI: 10.1002 / adma.202001741