【introduction】

Lithium-air batteries, more precisely, lithium-oxygen batteries, have received wide attention due to their high specific energy density. In the past period of time, researchers have focused on the positive electrode and less on the stability of the lithium metal negative electrode in the special environment of lithium-oxygen battery. In a lithium-oxygen battery, oxygen molecules dissolved in the electrolyte may pass from the positive electrode to the negative electrode, thereby aggravating the instability of the metallic lithium negative electrode. Therefore, how to improve the stability of the lithium metal anode in the oxygen atmosphere is a big challenge for the lithium oxygen battery, and in a broad sense, it is also a new topic for lithium metal anode research. This push will introduce a new way to address this challenge through the design of lithium salts.

Advanced Materials recently published a collaborative study from the Peng Zhangquan research group of the Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences and the Zhou Zhibin team of Huazhong University of Science and Technology, entitled "The Salt Matters: Enhanced Reversibility of Li-O2 Batteries with a Li[(CF3SO2)(n-C4F9SO2)N]-ba sed Electrolyte". In this paper, a novel sulfonimide lithium salt {Li[(CF3SO2)(n-C4F9SO2)N], LiTNFSI} was used, and tetraethylene glycol dimethyl ether (TEGDME) was used as a solvent to prepare an electrolyte. Through a series of advanced characterization methods, the paper found that this new electrolyte leads to the formation of a dense, polyfluorinated, oxygen-depleted solid electrolyte interface (SEI) film in situ on the surface of the lithium metal anode, which significantly enhances the lithium metal in oxygen. Stability in the atmosphere. In contrast to the commercial lithium salt {Li[(CF3SO2)2], LiTFSI}, the application of this new lithium salt can double the life of a lithium-oxygen battery.

Professor Peng Zhangquan and Professor Zhou Zhibin are the co-authors of the paper. The 2015 Ph.D. student of Huazhong University of Science and Technology is the first author of the thesis. Associate Professor Huang Jun of Central South University is the second author of the thesis.

[Graphic introduction]

Figure 1 Conductive lithium salt structure

Figure 2 Lithium metal anode stability under O2 atmosphere

a) Li|1.0 M LiTNFSI TEGDME|Li0.5FePO4

b) Li|1.0 M LiTFSI TEGDME|Li0.5FePO4

Lithium metal maintains good stability in 1.0 M LiTNFSI TEGDME under oxygen atmosphere.

Figure 3 Li|Li battery cycle performance under Ar (or O2) conditions

a) 1.0 M LiTFSI TEGDME Ar

b) 1.0 M LiTFSI TEGDME O2

c) 1.0 M LiTNFSI TEGDME Ar

d) 1.0 M LiTNFSI TEGDME O2

The Li|Li battery cycle shows that lithium metal maintains good cycle stability in 1.0 M LiTNFSI TEGDME, both in oxygen and argon.

Figure 4 Li-Li battery appearance after 100 weeks of Li|Li battery cycle in O2 atmosphere

a, b, c) fresh lithium metal

d, e, f) 1.0 M LiTNFSI TEGDME

g, h, i) 1.0 M LiTFSI TEGDME

In the 1.0 M LiTNFSI TEGDME system, the surface of the metallic lithium maintained good flatness, and the side reaction was effectively suppressed.

Figure 5 Li-O2 battery cycle curve and DEMS test results

a,b,c) 1.0 M LiTNFSI TEGDME

d,e,f) 1.0 M LiTFSI TEGDME

The cycle performance and reversibility of lithium-oxygen battery based on 1.0 M LiTNFSI TEGDME electrolyte were significantly improved.

【summary】

This work improves the interface of the lithium metal and improves its stability under O2 conditions by adjusting the lithium salt structure (LiTNFSI vs LiTFSI). It was found that LiTNFSI preferentially reduced on the surface of metallic lithium, and a dense, polyfluorinated SEI film was formed. The SEI film significantly improved the stability of the metallic lithium interface in the O2 atmosphere and enhanced the cycle performance of the Li-O2 battery. This research work provides a new solution to improve the stability of the metal lithium interface.