Surface Layer and Morphology of Lithium Metal Electrodes

Abstract

The surface morphology of the electrodeposited lithium metal from electrolyte solutions containing electrolyte additives: fluoroethylene carbonate (FEC), vinylene carbonate (VC) and lithium bis(oxalate)borate (LiBOB), were investigated. All the film forming additive improved the surface morphology. The FEC especially shows the most uniform surface morphology compared with the other electrolyte additives and the additive-free electrolyte. The surface analyses of the lithium metal were conducted using X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analytical study revealed that the FEC suppresses the decomposition of the PF 6 − anion, resulting in the formation of a thin stable SEI layer on the lithium metal.

Effect of Anion Species in Early Stage of SEI Formation Process

“…The detected signals are displayed by dotted lines, while the backgrounds, the deconvoluted peaks, and the sums are displayed by solid lines. The peak assignments for the spectra are carried out by referring multiple sources: the spectra we took with reference samples, NIST X-ray Photoelectron Spectroscopy Database, and past reports 16,51,52 and listed in Table I. Relative elemental composition is estimated by integration of peak area and listed in Table II. The XPS spectra and the elemental composition for the LiBH 4 /THF also prove that the LiBH 4 /THF produces a tiny amount of the surface layer.…”

“…14,15 We previously reported that fluoroethylene carbonate (FEC) stabilizes the surface layer, and a solvate ionic liquid delays the dendrite formation. 16,17 However, the dendrite formation still remains as a fundamental challenge on the lithium metal anodes. 13,[18][19][20] In the case of the alloy/intermetallic anodes, the volume expansion and shrinkage of the active material leads pulverization of the particles during the charging and discharging processes.…”

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

“…The result of SEM observation revealed that the improved homogeneity of SEI. Actually, FEC and LiBOB were reported to contribute to the formation of compact and uniform SEI with improved morphology 22–24 . In addition, the improved morphological homogeneity of the SEI surface in the presence of LiBr has also recently reported 25 .…”

Three dimensional porous frameworks for lithium dendrite suppression

“…Based on the above growth mechanisms of Li dendrites, many promising methods have been proposed to suppress the undesired electrochemical behavior, including liquid electrolyte modification [22][23][24][25] , solid-state electrolyte [26][27][28][29] , artificial SEI [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] (including fluorinated SEI [35][36][37][38][39][40] and sulfurized SEI [41][42][43][44][45] ), and nanostructured frameworks [46 , 47] . Liquid electrolyte modification improves significantly the ionic conductivity, but most liquid electrolytes can react with the fresh Li dendrites, leading to low coulombic efficiency [48] .…”