LiFePO 4 has an interesting spin-polarized electronic structure showing a (3dv) 5 (3dV) 1 electron configuration of the Fe 2+ ion. In this work, we have experimentally evidenced the valence electronic structure of LiFePO 4 and of its delithiated compound FePO 4 by X-ray photoelectron spectroscopy (XPS), which allows a visualization of the occupied densities of states (DOS) in the valence band. XPS valence spectra were compared with the DOS obtained from DFT calculations by considering GGA and GGA + U approaches. Thanks to electrochemical extraction/insertion of Li + ions in LiFePO 4 /FePO 4 , it was possible to display the Fe 3d spindown electron of LiFePO 4 , which is not present in the valence spectrum of FePO 4 . We show that the study of XPS valence spectra is an efficient way to access the lithium insertion rate in Li x FePO 4 positive electrode materials for lithium-ion batteries. Besides the contribution to the Li-ion battery field, this paper is also a rare example of experimental evidence of a spin-resolved electronic structure from in-lab XPS experiments.
We
report an innovative cross-linked composite polymer electrolyte
(CPE) based on the garnet-type ceramic super Li+ ion conductor,
Li7La3Zr2O12 (LLZO),
that is encompassed in a supersoft poly(ethylene oxide)/tetraglyme
matrix. UV-induced, facile and solvent-free cross-linking process
ensures flexible and self-standing CPEs, which are nonflammable and
perfectly shape-retaining under thermal/mechanical stress. The CPEs
exhibit high ionic conductivity, exceeding 0.1 mS cm–1 at 20 °C, suitable for ambient and subambient temperature operation.
Lab-scale lithium metal polymer cells assembled with LiFePO4-based composite cathode and the optimized CPE deliver full capacity
at low current rates and outstanding specific discharge capacity
of 115 mAh g–1 at 1C rate and ambient temperature.
Remarkably, the lithium metal cell can run for hundreds of galvanostatic
cycles (>400) with low overpotential, limited fading, and excellent
Coulombic efficiency (>99%), which postulates the practical application
of the newly developed CPEs as truly solid separating electrolytes
in high-power energy storage technologies, assuring safety and performance
in a wide range of operating conditions.
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