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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. [ABSTRACT FROM AUTHOR]

Li 2 FeSiO 4 (LFS) has drawn much attention as cathode for high capacity Li-ion batteries. Even though significant volume of study has been devoted to its crystal chemistry and electrochemistry, many questions relating to its Li-ion storage dynamics remain yet to be fully elucidated. In this context, synchrotron-based X-ray diffraction and absorption spectroscopies are employed to characterize the phase stability and charge compensation mechanism in a metastable Li 2 FeSiO 4 nanostructured cathode as a function of state-of-charge (Li 2− x FeSiO 4 , x = 0, 0.25, 0.50, 0.75, 1.0) and cycling at very low current. The results demonstrate (i) no detectable phase transition from monoclinic to orthorhombic phase during the first charge-discharge cycle but rather formation of antisite defects that progressively induce phase transformation after several electrochemical cycles; (ii) characteristics of solid solution Li-ion storage (Li 2− x FeSiO 4 , x = 0–1); and (iii) the charge compensation for the first Li extraction does not come solely from the ferrous to ferric conversion, but interestingly from prominent participation of lattice oxygen as well that appears to destabilize the cycled LFS structure with significant performance implications. [ABSTRACT FROM AUTHOR]

Silicate Nanocrystals: PEDOT Encapsulated and Mechanochemically Engineered Silicate Nanocrystals for High Energy Density Cathodes (Adv. Keywords: interfacial engineering; Li-ion batteries; lithium iron silicate; mechanochemistry; PEDOT; surface modification EN interfacial engineering Li-ion batteries lithium iron silicate mechanochemistry PEDOT surface modification 1 1 1 07/13/20 20200709 NES 200709 In article number 2000226 Majid Rasool, George P. Demopoulos, and co-workers report the fabrication of a robust core-shell lithium iron silicate (Li SB 2 sb FeSiO SB 4 sb , LFS) cathode architecture, where nanocrystal's core is prepared via mechanochemical annealing and shell via PEDOT polymerization. Interfacial engineering, Li-ion batteries, lithium iron silicate, mechanochemistry, PEDOT, surface modification. [Extracted from the article]