Powders were synthesized under two different conditions (hydrothermal or mechanochemical activation) using iron(II) phosphate and lithium phosphate as starting materials. The samples were characterized by X-ray diffraction, chemical titration, and their electrochemical performance was investigated in terms of cycling behavior and impedance response. We also report the benefit of introducing an electronic conductor precursor (typically a sucrose) during or after the synthesis to overcome the poor charge transfer associated to the lithium iron phosphate. © 2002 The Electrochemical Society. All rights reserved.

With a specific capacity of 3600 mA h g⁻¹, silicon is a promising anode active material for Li-ion batteries (LIBs). However, because of the huge volume changes undergone by Si particles upon (de)alloying with lithium, Si electrodes suffer from rapid capacity fading. A deep understanding of the associated failure mechanisms is necessary to improve these electrochemical performances. To reach this goal, we investigate here nano-Si based electrodes by several characterization techniques. Thanks to all these techniques, many aspects, such as the behaviour of the active material or the solid electrolyte interphase (SEI) and the lithiation mechanisms, are studied upon cycling. A clear picture of the failure mechanisms of nano-Si based electrodes is provided. In particular, by combining Hg analyses, SEM observations of electrode cross-sections, and EIS measurements, we follow the evolution of the porosity within the electrode. For the first time, our results clearly show a real dynamic of the pore size distribution: the first cycles lead to the formation of a micrometric porosity which is not present initially. During the following cycles, these large pores are progressively filled up with SEI products which form continuously at the Si particle surface. Thus, from the 50th cycle, Li⁺ ion diffusion is dramatically hindered leading to a strongly heterogeneous lithiation of the electrode and a rapid capacity fading.