Exploring electrochemically driven conversion reactions for the development of novel energy storage materials is an important topic as they can deliver higher energy densities than current Li-ion battery electrodes. Conversion-type fluorides promise particularly high energy densities by involving the light and small fluoride anion, and bond breaking can occur at relatively low Li activity (i.e., high cell voltage). Cells based on such electrodes may become competitors to other envisaged alternatives such as Lisulfur or Li-air systems with their many unsolved thermodynamic and kinetic problems. Relevant conversion reactions are typically multiphase redox reactions characterized by nucleation and growth processes along with pronounced interfacial and mass transport phenomena. Hence significant overpotentials and nonequilibrium reaction pathways are involved. In this review, we summarize recent findings in terms of phase evolution phenomena and mechanistic features of (oxy)fluorides at different redox stages during the conversion process, enabled by advanced characterization technologies and simulation methods. It can be concluded that well-designed nanostructured architectures are helpful in mitigating kinetic problems such as the usually pronounced voltage hysteresis. In this context, doping and open-framework strategies are useful. By these tools, simple materials that are unable to allow for substantial Li nonstoichiometry (e.g., by Li-insertable channels) may be turned into electroactive materials.

Metal ions are important trace elements in the human body, which directly affect the human metabolism and the regeneration of damaged tissues. For instance, the advanced combination of magnesium ions (Mg 2+ ) and bone repair materials make the composite materials have the function of promoting vascular repair and enhancing the adhesion of osteoblasts. Herein, inspired by magnets to attract metals, we utilized the coordination reaction of metal ion ligand to construct a bisphosphonate-functionalized injectable hydrogel microsphere (GelMA-BP-Mg) which could promote cancellous bone reconstruction of osteoporotic bone defect via capturing Mg 2+ . By grafting bisphosphonate (BP) on GelMA microspheres, GelMA-BP microspheres could produce powerful Mg 2+ capture ability and sustained release performance through coordination reaction, while sustained release BP has bonetargeting properties. In the injectable GelMA-BP-Mg microsphere system, the atomic percentage of captured Mg 2+ was 0.6%, and the captured Mg 2+ could be effectively released for 18 days. These proved that the composite microspheres could effectively capture Mg 2+ and provided the basis for the composite microspheres to activate osteoblasts and endothelial cells and inhibit osteoclasts. Both in vivo and in vitro experimental results revealed that the magnet-inspired Mg 2+ -capturing composite microspheres are beneficial to osteogenesis and angiogenesis by stimulating osteoblasts and endothelial cells while restraining osteoclasts, and ultimately effectively promote cancellous bone regeneration. This study could provide some meaningful conceptions for the treatment of osteoporotic bone defects on the basis of metal ions.

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Blending additive with electrolyte is a facile and effective method to suppress anode dendrite growth in Li metal batteries (LMBs), especially when a LiF-rich solid electrolyte interface (SEI) is formed as a consequence of additive decomposition or deposition. However LiF still suffers from poor bulk ion conductivity as well as the difficult access to tailored nanostructure. Exploring new Li fluoride of high Li-ion conductivity as SEI component is still a big challenge in view of the lacking of desired structure prototype or mineral phase. Here, we propose a Li-rich LiAlF derivative from cryolite phase as solid electrolyte additive, which is characterized by textured nanoporous morphology and ionic liquid coating. Its room temperature ion conductivity is as high as ∼10 S/cm with a low activation energy of 0.29 eV, the best level among fluoride-based solid electrolytes. These features guarantee a homogenization of Li fluxing through bulk and grain boundary of LiAlF-rich SEI and reinforce the effect on Li dendrite suppression. LiAlF additive enables a stable cyclability of Li∥Li symmetric cells for at least 100 cycles even under a high areal capacity of 3 mA h/cm and a significant improvement on capacity retention for various LMBs based on LiFePO, FeS, and S cathodes.

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Garnet-type Li–La–Zr–O electrolytes suffer from poor contact with the Li metal anode because of the facile formation of a passivation layer at the interface, thus leading to frustrating interfacial impedance or lithium dendrite penetration. Herein, we introduce a eutectic Na–Li intermediate layer between the Li anode and garnet electrolyte to enable sufficient wettability. The potential mechanism of solid–solid convection between Li and Na domains promotes the prompt extension of the eutectic zone, preservation of the highly soldered interface, and homogenization of Li plating during cycling. The Li–Na/garnet/Na–Li cell exhibits a small interfacial resistance of 18.98 Ω·cm2 at 60 °C and steady cycling for 3500 h (with a small overpotential of 10.8 mV). The first prototype of a solid-state battery combining a conversion-type FeF3 cathode with garnet electrolyte is successfully operated at 60 °C, with a high reversible capacity of 500 mAh·g–1 and ultrastable cycling for 300 cycles at 100 μA·cm–2, as well as high-rate endurance up to 500 μA·cm–2.

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All-solid-state batteries are appealing electrochemical energy storage devices because of their high energy content and safety. However, their practical development is hindered by inadequate cycling performances due to poor reaction reversibility, electrolyte thickening and electrode passivation. Here, to circumvent these issues, we propose a fluorination strategy for the positive electrode and solid polymeric electrolyte. We develop thin laminated all-solid-state Li||FeF3 lab-scale cells capable of delivering an initial specific discharge capacity of about 600 mAh/g at 700 mA/g and a final capacity of about 200 mAh/g after 900 cycles at 60 °C. We demonstrate that the polymer electrolyte containing AlF3 particles enables a Li-ion transference number of 0.67 at 60 °C. The fluorinated polymeric solid electrolyte favours the formation of ionically conductive components in the Li metal electrode’s solid electrolyte interphase, also hindering dendritic growth. Furthermore, the F-rich solid electrolyte facilitates the Li-ion storage reversibility of the FeF3-based positive electrode and decreases the interfacial resistances and polarizations at both electrodes.