The performance of Li-ion battery electrodes is dependent upon the crystal structure of the intercalation material and its evolution during cycling. Methodology for structural studies under realistic operating conditions has been developed using synchrotron radiation for in-situ x-ray diffraction in coin cells. Neutron diffraction has the advantage of being sensitive to Li, which is transparent to x-rays; additionally, vanadium is practically transparent under neutron diffraction, allowing independent refinement of V-O and Li-O lattices in lithium vanadium oxides (LiaVOx) using complementary diffraction techniques, as illustrated below (note 1.81, 2.66, and 2.79 �-1).The limiting factor in in-situ neutron diffraction is incoherent scattering from hydrogenous components, which reduces signal and increases background intensity. Deuteration and fluorination of hydrogenous components reduces incoherent scattering, e.g. replacing polyvinylidene difluoride with polytetrafluoroethylene as the electrode binder. The major source of hydrogenous material in a typical Li-ion cell is the carbonate-based electrolyte. Unfortunately, deuteration and fluorination of these carbonates is not feasible due to cost and reactivity, respectively. Other advanced electrolyte systems, such as ionic liquids, do not mitigate these issues, necessitating the development of novel electrolyte systems specifically for in-situ neutron diffraction.This presentation will discuss in-situ neutron diffraction in Li-ion electrode materials in the context of LiaVOx. Focus will be placed on the neutron scattering properties and electrochemical performance of deuterated perfluorocarboxylate esters as electrolyte solvents, e.g. d3-methyl-heptafluorobutyrate (CF3CF2CF2COOCD3).

<i>In-situ</i> neutron diffraction of lithium vanadium oxide cathodes

247th National Meeting (2014)

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In-situ neutron diffraction of lithium vanadium oxide cathodes