Metal fluorides with high redox potential and capacity from strong metal–fluoride bond and conversion reaction make them promising cathodic materials. However, detailed lithium insertion and extraction mechanisms have not yet been clearly understood and explained. Here we report low-temperature synthesis of electrochemically active FeF3/FeF2 nanoparticles by catalytic decomposition of a fluoropolymer [perfluoropolyether (PFPE)] using a hydrated iron oxalate precursor both in air and in inert atmosphere. Freshly synthesized FeF3 nanoparticle delivered specific capacity above 210 mAh/g with decent cycling performance as a Li-ion battery cathode. Both in situ and ex situ characterization techniques were used to investigate the detailed PFPE decomposition and fluorination mechanisms leading to FeF3/FeF2 formation as well as the lithium insertion mechanism in a FeF3 cathode. Specifically, a detailed understanding was investigated using thermogravimetry–mass spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, transmission electron microscopy, scanning electron microscopy/energy dispersive spectroscopy, and X-ray absorption near-edge structure. The novel synthesis route developed not only offers access to electrochemically active metal fluorides but also offers a catalytic approach for decomposing highly inert fluoropolymers for environmental protection.

While futuristic‐all‐electric cars are set to revolutionize the clean energy concept, it is the time to consider the sustainability of the lithium sources. Article number https://doi.org/10.1002/adsu.201700026, by Sung‐Jin Cho and co‐workers, features the lithium deficient ratio, as opposed to the general trend of lithium excess ratio, and provides a new perspective on energy storage sustainability.

The ever‐growing demand for high capacity cathode materials is on the rise since the futuristic applications are knocking on the door. Conventional approach to developing such cathode relies on the lithium‐excess materials to operate the cathode at high voltage and extract more lithium‐ion. Yet, they fail to satiate the needs because of their unresolved issues upon cycling such as, for lithium manganese‐rich layered oxides—their voltage fading, and for as nickel‐based layered oxides—the structural transition. Here, in contrast, lithium‐deficient ratio is demonstrated as a new approach to attain high capacity at high voltage for layered oxide cathodes. Rapid and cost effective lithiation of a porous hydroxide precursor with lithium deficient ratio is acted as a driving force to partially convert the layered material to spinel phase yielding in a multiphase structure (MPS) cathode material. Upon cycling, MPS reveals structural stability at high voltage and high temperature and results in fast lithium‐ion diffusion by providing a distinctive solid electrolyte interface (SEI) chemistry—MPS displays minimum lithium loss in SEI and forms a thinner SEI. MPS thus offers high energy and high power applications and provides a new perspective compared to the conventional layered cathode materials denying the focus for lithium excess material.