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The search for new cathode materials is primordial for alkali-ion battery systems, which are facing a constantly growing demand for high energy density storage devices. In quest of more performing active compounds on the positive side, anhydrous iron(III) fluoride demonstrated to be a good compromise in terms of high capacity, operating voltage, and low cost. However, its reaction toward lithium leads to complicated insertion/conversion reactions, which hinder its performances in Li-ion cells. Cycling this material against larger ions such as sodium and potassium is hard or simply impossible due to the size of the channels of the FeF3framework impeding ions diffusion. Herein, we propose a strategy based on the use of cubic perovskite AFeF3(A = K+, NH4+) as starting materials, allowing the straightforward insertion (after a first disinsertion of the alkali and/or NH4+ion) of lithium within the structure and enabling the cycling toward larger alkali ions such as sodium and potassium. For example, a cubic KFeF3perovskite, produced by a facile synthesis method, shows superior rate capability toward lithium retaining a capacity of up to 132 mA·h·g–1at 5 C or of 120 mA·h·g–1at 5 C toward sodium and enabling cycling toward potassium. Moreover, cubic NH4FeF3perovskite is discussed for the first time as the suitable cathode material for alkali-ion batteries.

To meet the demands of long cycle life under high rate for lithium-ion batteries, the advancement of anode materials with stable structural properties is necessarily demanded. Such promotion needs to design reasonable structure to facilitate the transportation of electron and lithium ions (Li+). Herein, a novel C/Fe3O4sea-sponge-like structure was synthesized by ultrasonic spray pyrolysis following thermal decomposition process. On the basis of sea-sponge carbon (SSC) excellences in electronic conductivity and short Li+diffusion pathway, nano-Fe3O4anchored on stable SSC skeleton can deliver high electrochemical performance with long cycle life under high rate. During electrochemical cycling, well-dispersed nano-Fe3O4in ∼6 nm not only averts excessive pulverization and is enveloped by solid electrolyte interphase film, but also increases Li+diffusion efficiency. The much improved electrochemical properties showed a capacity of around 460 mAh g–1at a high rate of 1.5C with a retention rate of 93%, which is maintained without degradation up to 1000 cycles (1C = 1000 mA g–1).

Niobium pentoxides have received considerable attention and are promising anode materials for lithium-ion batteries (LIBs), due to their fast Li storage kinetics and high capacity. However, their cycling stability and rate performance are still limited owing to their intrinsic insulating properties and structural degradation during charging and discharging. Herein, a series of mesoporous Nb2O5@TiO2core–shell spherical heterostructures have been prepared for the first time by a sol–gel method and investigated as anode materials in LIBs. Mesoporosity can provide numerous open and short pathways for Li+diffusion; meanwhile, heterostructures can simultaneously enhance the electronic conductivity and thus improve the rate capability. The TiO2coating layer shows robust crystalline skeletons during repeated lithium insertion and extraction processes, retaining high structural integrity and, thereby, enhancing cycling stability. The electrochemical behavior is strongly dependent on the thickness of the TiO2layer. After optimization, a mesoporous Nb2O5@TiO2core–shell structure with a ∼13 nm thick TiO2layer delivers a high specific capacity of 136 mA h g–1at 5 A g–1and exceptional cycling stability (88.3% retention over 1000 cycles at 0.5 A g–1). This work provides a facile strategy to obtain mesoporous Nb2O5@TiO2core–shell spherical structures and underlines the importance of structural engineering for improving the performance of battery materials.