N/S Co-doped microporous carbon derived from PSSH-Melamine salt solution as cathode host for Lithium-Selenium batteries

Advanced potassium ion batteries anode enhanced by Fe-doping strategy

KVPO4F (KVPF) is a novel insertion-type anode for potassium ion batteries. For improving its electrochemical performance, the doping strategy was selected and a series of Fe-doped KVPF materials were synthesized by a facile solid-state sintering method to find out the suitable ratio. After comparation, KVPF sample with 5 % Fe-doped ratio (KVPF/Fe-5) delivers the best performance, e.g. rate capacity (94.3 mA h g-1 at 500 mA g-1) and long-term discharge capacity (74.1 mA h g-1 after 1000 cycles at 200 mA g-1, 0.03 % capacity decay ratio per cycle), which is mainly attributed to its larger K+ diffusion rate. The in-situ X-ray diffraction analysis clarify the two-step K+ storage mechanism of KVPF/Fe-5 anode, and the density functional theory calculations verify that Fe-doping can reduce diffusion energy barrier of K+ and increase electronic conductivity of KVPF. When used as cathode, KVPF/Fe-5 delivers 51.8 mA h g-1 at 100 mA g-1 after cycling 200 cycles. In addition, the symmetric cell by employing KVPF/Fe-5 as anode and cathode simultaneously was also assembled successfully, pointing out a new research direction for potassium-ion batteries.

In-situ texturing hollow carbon host anchored with Fe single atoms accelerating solid-phase redox for Li-Se batteries

Se-based cathodes have caught tremendous attention owing to their comparable volumetric capacity and better electronic conductivity to S cathodes. However, its low utilization ratio and sluggish redox kinetics due to the high reaction barrier of solid-phase transformation from Se to Li2Se limit its practical application. Herein, an in-situ texturing hollow carbon host by gas-solid interface reaction anchored with Fe single-atomic catalyst is designed and prepared for advanced Li-Se batteries. This Se host presents high pore volume of 1.49 cm3 g-1, Fe single atom content of 1.53 wt%, and its specific structure protects single-atomic catalyst from the destructive reaction environment, thus balancing catalytic activity and durability. After Se loading by reduction of H2SeO3, this homogenous Se-based cathode delivers a superior rate capacity of 431.3 mA h g-1 at 4C, and great discharge capacity of 301.8 mA h g-1 after 1000 cycles at 10C, with high Li-ion diffusion coefficient and capacitance-contributed ratio. The distribution of relaxation times analysis verifies solid-phase transformation mechanism of this cathode and density functional theory calculations confirm the adsorption and bidirectionally catalysis effect of Fe single-atomic catalyst. This work provides a new strategy to prepare high-efficient Se cathode associated with non-noble metal single atoms for high-performance Li-Se batteries.