Reversible Multielectron Redox Chemistry in a NASICON-Type Cathode toward High-Energy-Density and Long-Life Sodium-Ion Full Batteries.
basic_science · Level V
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- Also identified by DOI 10.1002/adma.202304428.
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Abstract
Na-superionic-conductor (NASICON)-type cathodes (e.g., Na<sub>3</sub> V<sub>2</sub> (PO<sub>4</sub> )<sub>3</sub> ) have attracted extensive attention due to their open and robust framework, fast Na<sup>+</sup> mobility, and superior thermal stability. To commercialize sodium-ion batteries (SIBs), higher energy density and lower cost requirements are urgently needed for NASICON-type cathodes. Herein, Na<sub>3.5</sub> V<sub>1.5</sub> Fe<sub>0.5</sub> (PO<sub>4</sub> )<sub>3</sub> (NVFP) is designed by an Fe-substitution strategy, which not only reduces the exorbitant cost of vanadium, but also realizes high-voltage multielectron reactions. The NVFP cathode can deliver extraordinary capacity (148.2 mAh g<sup>-1</sup> ), and decent cycling durability up to 84% after 10 000 cycles at 100 C. In situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy characterizations reveal reversible structural evolution and redox processes (Fe<sup>2+</sup> /Fe<sup>3+</sup> , V<sup>3+</sup> /V<sup>4+</sup> , and V<sup>4+</sup> /V<sup>5+</sup> ) during electrochemical reactions. The low ionic-migration energy barrier and ideal Na<sup>+</sup> -diffusion kinetics are elucidated by density functional theory calculations. Combined with electron paramagnetic resonance spectroscopy, Fe with unpaired electrons in the 3d orbital is inseparable from the higher-valence redox activation. More competitively, coupling with a hard carbon (HC) anode, HC//NVFP full cells demonstrate high-rate capability and long-duration cycling lifespan (3000 stable cycles at 50 C), along with material-level energy density up to 304 Wh kg<sup>-1</sup> . The present work can provide new perspectives to accelerate the commercialization of SIBs.