Fluorinated electrolyte for 4.5 V Li(Ni0.4Mn0.4Co0.2)O2/graphite Li-ion cells

• Published in: Journal of power sources 2016-03, Vol.307, p.340-350
• Main Authors: Xia, Jian, Nie, M., Burns, J.C., Xiao, A., Lamanna, W.M., Dahn, J.R.
• Format: Article
• Language: English
• Subjects: Battery lifetime; Fluorinated electrolytes; Gas generation; High precision coulometry; High voltage Li-ion cells; Impedance growth
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2015.12.132

A fluorinated electrolyte mixture, containing 1 M LiPF6/fluoroethylene carbonate:bis (2,2,2-trifluoroethyl) carbonate (1:1 w:w) with prop-1-ene-1,3-sultone as an electrolyte additive exhibited promising cycling and storage performance in Li(Ni0.4Mn0.4Co0.2)O2/graphite pouch type Li-ion cells tested to 4.5 V. The prop-1-ene-1,3-sultone additive was added to help control gas evolution in the fluorinated electrolyte cells, which was improved but still problematic even with the additive. Cells with the fluorinated electrolyte demonstrated higher impedance in early cycles compared to cells with carbonate solvents and state of the art additives. Symmetric cells were used to show this high impedance originated at the negative electrode/electrolyte interface. Nevertheless, in charge–discharge cycling tests to 4.5 V, cells with the fluorinated electrolyte and 1, 2 or 3% prop-1-ene-1,3-sultone additive, outperformed all non-fluorinated electrolytes with all additives tested. With further work, these, or other fluorinated carbonates, coupled with appropriate additives, may represent a viable path to NMC/graphite cells that can operate to 4.5 V and above. •Fluorinated electrolyte leads to better tolerance of Li-ion cells to high potentials.•Impedance increase at positive electrodes in mitigated using fluorinated electrolyte.•However, fluorinated electrolyte leads to high impedance at the negative electrode.•A wide variety of fluorinated solvents need to be explored with the methods described.