LiF Splitting Catalyzed by Dual Metal Nanodomains for an Efficient Fluoride Conversion Cathode

Abstract

The critical challenges for fluoride conversion cathodes lie in the absence of built-in Li source, poor capacity retention, and rate performance. For lithiated fluorides, the reason to limit their competitiveness is rooted in the facile coarsing of insulating LiF (as built-in Li source) and its insufficient splitting kinetics during charging. Previous efforts on blending LiF nanodomains with reductive metal, metal oxide, or fluoride by ballmilling method still face the problems of large overpotential and low current density. Herein we propose a strategy of dual-metal (Fe−Cu) driven LiF splitting to activate the conversion reaction of fluoride cathode. This lithiated heterostructure (LiF/Fe/Cu) with compact nanodomain contact enables a substantial charge process with considerable capacity release (300 mAh g −1 ) and low charge overpotential. Its reversible capacity is as high as 375−400 mAh g −1 with high energy efficiency (76%), substantial pseudocapacitance contribution (>50%), and satisfactory capacity retention (at least 200 cycles). The addition of Cu nanodomains greatly catalyzes the kinetics of Fe−Cu−F formation and decomposition compared with the redox process of Fe−F, which lead to the energy and power densities exceeding 1000 Wh kg −1 and 1500 W kg −1 , respectively. These results indicate that LiF-driven cathode is promising as long as its intrinsic conductive network is elegantly designed.

Construction of solid-liquid fluorine transport channel to enable highly reversible conversion cathodes

“…From the Ragone plots in Fig. 3F , our Li/FeO x F 2- x cells both show the evident improvement of energy and power densities (based on the weight of active materials), compared with previous reports on (oxy)fluoride cathodes even with the assistance of intentional nanoengineering and extra conductive wiring ( 12 , 16 , 17 , 19 , 21 , 45 ). In particular, they perform the superior energy densities of 1100 Wh/kg for FeO 0.3 F 1.7 and 700 Wh/kg for FeO 0.7 F 1.3 under the power densities of 220 and 4300 W/kg, respectively.…”

“…In the same spectrum, a strong Li 1s peak emerges at 56.0 eV belonging to LiF, and accordingly, the positive displacement of F 1s peak is observed (fig. S26A) ( 45 ). Meanwhile, the Fe─O signal is weakened in O 1s, and a new signal corresponding to Li 2 O generates at 528.5 eV ( 64 ).…”

Carbon electrodes with ionophobic characteristics in organic electrolyte for high-performance electric double-layer capacitors

“…The signal at approximately 686.7 eV corresponds to low-density fluorination, with individual F atoms semi-ionically bonded to C in the basal plane and characterized by a dilated C-F bond. The second signal at approximately 688 eV corresponds to the intense covalent C-F bond, which results in a significant distortion of the carbon lattice [22]. Semi-ionic C-F bond contents progressively decrease, whereas covalent C-F bond contents increase as the plasma treatment time increases.…”

3D Honeycomb Architecture Enables a High‐Rate and Long‐Life Iron (III) Fluoride–Lithium Battery

“…However, the commercial Li‐ion batteries employing Ni‐ and Co‐based intercalation‐type cathodes with limited capacities and energy densities cannot meet the rapidly rising market demands in transportation, telecommunication, aviation, and electronics, which are motivating the development of next‐generation lightweight, compact, and low‐cost rechargeable batteries . Recently, battery materials including FeF 3 , FeF 2 , CuF 2 , and elemental sulfur based on conversion reactions have attracted great attention for both Li and Na batteries because of their much higher theoretical capacities originating from multiple electron transfer per redox center and reversibility . Compared to lithium–sulfur batteries, metal fluoride–lithium batteries with relatively higher operating voltage are more competitive in both gravimetric and volumetric energy densities .…”

“…Recently, battery materials including FeF 3 , FeF 2 , CuF 2 , and elemental sulfur based on conversion reactions have attracted great attention for both Li and Na batteries because of their much higher theoretical capacities originating from multiple electron transfer per redox center and reversibility . Compared to lithium–sulfur batteries, metal fluoride–lithium batteries with relatively higher operating voltage are more competitive in both gravimetric and volumetric energy densities . Compared to Ni and Co, Fe and Cu are low‐cost, more abundant in the Earth's crust, and friendlier to the environment, which are beneficial for future large‐scale applications .…”