PEDOT Encapsulated and Mechanochemically Engineered Silicate Nanocrystals for High Energy Density Cathodes

Abstract Lithium iron silicate (LFS) attracts a lot of attention due to its 330 mAh g⁻¹ theoretical capacity (2 Li⁺ per formula unit). However, inherently it exhibits poor Li‐ion intercalation kinetics, interfacial reactivity, and complex phase transitions resulting in lower than one Li⁺ capacity and poor retention. In this work, a core–shell architecture is devised largely overcoming these obstacles. At first, the nanostructure of Pmn2₁ LFS is annealed via mechanochemical processing enabling the activation of Li‐ion diffusion. Subsequently, the LFS nanocrystals are coated via in situ poly(3,4‐ethylenedioxythiophene) (PEDOT) polymerization involving partial chemical de‐lithiation/re‐lithiation, the latter catalyzed with FeCl₃. As a result of the devised mechanochemical/interphasial engineering of the LFS@PEDOT nanocrystals, their Li‐ion storage capacity is augmented to > 1 Li, namely 200 mAh g⁻¹ after 50 cycles or 1.2 Li⁺ units—the highest capacity reported for the Pmn2₁ LFS cathode. A key attribute of the new PEDOT coating technique is the generation of a Fe³⁺‐rich subsurface layer that contributes to structure stabilization via accelerated phase transition to inverse Pmn2₁ phase, in addition to rendering the nanocrystals electronically conductive and protected against reaction with electrolyte. Such core–shell engineered nanocrystals provide a powerful paradigm in developing viable high energy density cathodes for next‐generation Li‐ion batteries.