Understanding the influence of electrolyte additives on the electrochemical performance and morphology evolution of silicon nanowire based lithium-ion battery anodes

• Published in: Journal of power sources Vol. 359; pp. 601 - 610
• Main Authors: Kennedy, Tadhg, Brandon, Michael, Laffir, Fathima, Ryan, Kevin M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2017
• Subjects: Electrolyte additive; Lithium-ion battery; Nanowire; Silicon anode; Solid electrolyte interface layer; X-ray photoelectron spectroscopy; Nanowire; Lithium-ion battery; Solid electrolyte interface layer; Electrolyte additive; Silicon anode; X-ray photoelectron spectroscopy
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2017.05.093

Here we report new insights into the effect various electrolyte additives have on the cycling stability and rate capability of Si nanowire (NW) Li-ion battery anodes. The additives tested were vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate and lithium bis(oxalato)borate. All four significantly improve the capacity retention of the electrodes over 250 cycles compared to the additive-free electrolyte, with vinylene carbonate being the outstanding performer. The results provide a new understanding of the cycling behaviour of Si in the presence of electrolyte additives, revealing that not only is the stability of the SEI layer affected but that this consequently has a profound influence on the morphology evolution and chemical composition of the Si active material. Ex-situ characterisation of the electrodes post-cycling demonstrates that the improvement in cycling stability arises as the additives minimise irreversible decomposition reactions at the surface and facilitate a transformation from a NW morphology into a porous sponge-like network. This transformation process does not occur in the absence of any stable SEI forming additives as instability in the passivating layer leads to the continuous and irreversible consumption of Si to form Li silicates. [Display omitted] •VC, FEC, LiBOB and VEC all significantly improve the capacity retention of Si NWs.•Li silicates are a major decomposition product of the Si active material.•A more stable SEI layer facilitates the formation of a porous morphology of Si.•The rate capability of Si NWs is considerably affected by SEI layer composition.