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Conversion‐reaction metal fluoride cathodes have the advantages of low cost, environmental friendliness, and high energy density. However, their tailored synthesis and structure design under safe, facile, and scalable conditions have always been a puzzle, which limits the popularization of conversion‐type cathodes in lithium metal batteries. To address these challenges, here an iron fluoride heterostructure with FeF2 and FeF3 binary phases is proposed and prepared by deep eutectic solvent method under the assistance of cobalt cation as an oxidization promoter. The compact heterogeneous contact between tetragonal FeF2 and hexagonal tungsten bronze FeF3 phases enables the promotion and stabilization of interface charge transfer and topotactic conversion reaction. The narrower band gap of FeF2, higher theoretical capacity and thermodynamic potential of FeF3 synergistically contribute to the balance between cycling reversibility and capacity. The heterostructure cathode with an optimized molar ratio of FeF2/FeF3 can realize a highly reversible capacity of ≈520 mAh g−1 in the first tens of cycles and 305 mAh g−1 after 200 cycles. The typical two‐stage reaction plateaus are well preserved even under the high current density of 1000 mA g−1. The green synthesis strategy and heterostructure fluoride design open a new horizon for the development of high‐energy‐density metal fluoride batteries. [ABSTRACT FROM AUTHOR]

The garnet‐type solid‐state Li‐metal batteries are promising to develop into the high‐energy‐density system when coupled with the high‐capacity conversion reaction cathodes. However, the high interfacial resistance and poor contact between garnet electrolyte and Li anode are still a challenge. Here, an alloyable viscous fluid strategy is proposed for Li/garnet interface welding to enable highly reversible fluoride conversion solid‐state batteries. The super‐assembled phenide polymer with liquid metal property can serve as "oily" interlayer to in situ construct an ionic/electronic mixed conduction network by thermal and electrochemical lithiation. The resultant healing effect of contact voids between garnet and Li enables a dramatic reduction of interfacial resistance to 6 Ω cm2. The confinement and compaction of conversion products by garnet electrolyte endow the FeF3 based batteries with long‐cycling and high‐rate performance (520 and 330 mAh g−1 at 0.2 and 2 C respectively). This ceramic configuration also endows the CuF2 conversion battery with much better rechargeability (instead as widely known primary battery). [ABSTRACT FROM AUTHOR]

Metastable orthorhombic niobium pentoxide (T‐Nb2O5) is a promising anode to fulfill the requirements for high‐rate Li‐ion batteries (LIBs). Stoichiometric T‐Nb2O5 is plagued by low electric conductivity and particle pulverization after repeated charge/discharge processes. In this work, oxygen vacancies are implanted into T‐Nb2O5 particles via acid immersion of Nb2O5·nH2O with the formation of Lewis acid sites. The multiple characterizations and simulations reveal the lengthening of NbO bonds, and the transformation from NbO7 pentagonal bipyramids and NbO6 tetragonal bipyramids in T‐Nb2O5−x. The enrichment of oxygen vacancies endows T‐Nb2O5−x with higher electric conductivity, better electrochemical kinetics, larger pseudocapacitive contribution. O‐doped graphitic C3N4 is creatively proposed as a trace oxygen pump to repair excessive oxygen vacancies, and it also serves as a sacrifice template for Nb2O5−x growth to construct a porous and monolithic electrode network. Defect‐modulated Nb2O5−x displays extraordinary cycling stability (164 mAh g−1 at 5 C after 1100 cycles), high capacity retention (104 mAh g−1) at an ultrahigh rate (25 C), and large areal capacity (0.74 mAh cm−2) under high mass loading (4 mg cm−2). The practical prospect is proved by Nb2O5−x/LiNi0.8Co0.1Mn0.1O2 full cells with high average platform (2.12 V) and high specific capacity (229 mAh g−1). The oxygen‐defect modulation strategy on oxide anodes provides an alternative solution to fast‐charging and durable LIBs. [ABSTRACT FROM AUTHOR]