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Fluorides show great application prospects as conversion electrodes for lithium-ion batteries due to their high theoretical capacity. However, their use is limited by low electronic conductivity and slow reaction kinetics. In addition, fluorides usually contain crystal water in their structure, and the effect of this water on their performance is unclear. In view of this, the team of Professor Wang Huanlei from Ocean University of China achieved fast, high lithium-ion storage capacity and ultra-long cycling stability by eliminating the crystal water in hydrated iron fluoride. The relevant research results were published in the journal "Chemical Engineering Journal" (IF 13.3) under the title "Eliminating the crystal water in hydrated iron fluoride towards fast and high Li-ion storage capacity with ultralong cycling stability".
1. This study used a simple electrospinning and fluorination process to create FeF3@CNF nanofibers as potential anodes for lithium-ion batteries.
2. These nanofibers embed FeF3 nanoparticles (∼50 nm) into carbon, providing an efficient pathway for lithium-ion transport.
3. The rapid storage of Li+ in the FeF3@CNF anode is due to the reversible transformation mechanism and particle refinement during cycling. The FeF3@CNF anode shows kinetic advantages that are perfectly matched with the activated carbon cathode, resulting in excellent cycling stability.
This work highlights the key role of crystallization water removal in optimizing fluoride-based electrodes and provides new insights into the development of high-performance fluoride-based anodes for lithium-ion capacitors.
1. High specific capacity: FeF3@CNF nanofibers exhibit significantly higher specific capacity than hydrated iron fluoride. Removal of crystal water enhances electrochemical performance, resulting in stronger lithium ion storage capacity.
2. Improved reaction kinetics: The structure of FeF3@CNF promotes efficient channels for lithium ion transport, leading to faster reaction kinetics.
3. Enhanced cycle stability: FeF3@CNF anode exhibits excellent cycle stability, maintaining high capacity over multiple cycles. Removal of crystal water alleviates volume expansion and reduces mechanical stress during cycling, which contributes to the durability of the anode material.
4. Structural integrity: The unique nanofiber structure of FeF3@CNF is maintained even after long-term cycling, indicating its good structural stability.
5.Kinetic advantage: FeF3@CNF anode exhibits kinetic advantages that match those of activated carbon cathode, resulting in high energy density and good capacity retention over multiple cycles.
1. Hindered ion movement: Crystal water occupies interstitial space in the fluoride lattice, which may hinder the movement of lithium ions. This hindrance reduces the overall ionic conductivity, making it more difficult for the material to promote lithium ion transport during charge and discharge cycles.
2. Electrolyte decomposition: The presence of crystal water may cause adverse side reactions with the electrolyte, resulting in electrolyte decomposition.
3.Structural degradation: Hydrated fluorides (such as FeF3·3H2O) are more susceptible to structural degradation during long-term cycles. The volume changes accompanying lithium insertion and extraction may exacerbate mechanical stress, leading to capacity decay and reduced cycle stability.
Reduced conductivity: The presence of crystal water has been shown to increase the band gap of the material, thereby reducing its conductivity. For example, the calculated band gap of FeF3·3H2O is higher than that of anhydrous FeF3, indicating that removing crystal water can enhance conductivity and overall electrochemical performance.
Electrospinning Nanofibers Article Source:
https://www.sciencedirect.com/science/article/pii/S1385894724096700?via%3Dihub
