A comparative XPS surface study of Li2FeSiO4/C cycled with LiTFSI-and LiPF6-based electrolytes

• Published in: Journal of materials chemistry Vol. 19; no. 1; pp. 82 - 88
• Main Authors: ENSLING, David, STJERNDAHL, Marten, NYTEN, Anton, GUSTAFSSON, Torbjörn, THOMAS, John O
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2009
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Lithium Iron Silicates; Iron oxide; Organic carbonate; Lithium fluoride; Reaction product; Surface chemistry; Ethylene; Laser induced fluorescence; Electrode material; Optimization; Lithium battery; Hydrolysis; Organic solvent; Electrolyte; Silicon oxides; Hafnium; Lithium oxide; Comparative study; X-ray photoelectron spectra
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/b813099j

X-Ray photoelectron spectroscopy (XPS) has been used to characterise the surfaces of carbon-coated Li2FeSiO4 cathodes extracted from Li-ion batteries in both a charged and discharged state. 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6) based electrolytes were used with ethylene carbonate (EC) and diethyl carbonate (DEC) as organic solvents. The LiTFSI-based electrolyte exhibited high salt stability and no significant formation of LiF. However, solvent reaction products from EC were found together with lithium carbonate. A LiPF6-based electrolyte, on the other hand, showed inferior salt stability with LixPFy, LixPOyFz and LiF species formed on the surface. Solvent reaction products together with lithium carbonate were also found. There are also indications that Li2FeSiO4 is degraded by the HF formed in the electrolyte by the hydrolysis of LiPF6. A better understanding of the surface chemistry of carbon-coated Li2FeSiO4 after the first cycles in a Li-ion battery has thus been achieved, thereby facilitating the optimisation of Li-ion batteries based on this potentially cheap and electrochemically most promising cathode material giving excellent capacity retention: < 3% drop over 120 cycles.